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Sample records for mg ca zn

  1. Microstructure, In Vitro Corrosion Behavior and Cytotoxicity of Biodegradable Mg-Ca-Zn and Mg-Ca-Zn-Bi Alloys

    NASA Astrophysics Data System (ADS)

    Bakhsheshi-Rad, H. R.; Hamzah, E.; Tok, H. Y.; Kasiri-Asgarani, M.; Jabbarzare, S.; Medraj, M.

    2017-02-01

    The effects of bismuth (Bi) addition on the microstructure and corrosion behavior of the Mg-Ca-Zn-Bi alloys were evaluated using electron microscopy, electrochemical test and electrochemical impedance spectroscopy. Microstructural observations showed that Mg-1.2Ca-1Zn- xBi ( x = 0.5, 1.5, 3 wt.%) are composed of Mg2Ca, Ca2Mg6Zn3 and Mg3Bi2 phases while a new phase Mg2Bi2Ca appeared after the addition of 5 and 12 wt.% Bi to the Mg-1.2Ca-1Zn alloy. Furthermore, the additions of 0.5 wt.% Bi to the Mg-1.2Ca-1Zn alloy slightly improved the corrosion behavior of the alloy, while further increase in Bi amount from 1.5 to 12 wt.% has a deleterious effect on the corrosion behavior of the ternary Mg-1.2Ca-1Zn alloy which is driven by galvanic coupling effect. Cytotoxicity tests indicate that the Mg-1.2Ca-1Zn presents higher cell viability compared to Mg-1.2Ca-1Zn-0.5Bi alloy. In addition, the cell viability of both alloys increased with increasing incubation time while diluting the extracts to 50% and 10% improved the cell viabilities. The present results suggest that the Mg-1.2Ca-1Zn-0.5Bi can be interesting candidate for the development of degradable biomaterials and it is worthwhile for further investigation in an in vivo environment.

  2. Microstructure, In Vitro Corrosion Behavior and Cytotoxicity of Biodegradable Mg-Ca-Zn and Mg-Ca-Zn-Bi Alloys

    NASA Astrophysics Data System (ADS)

    Bakhsheshi-Rad, H. R.; Hamzah, E.; Tok, H. Y.; Kasiri-Asgarani, M.; Jabbarzare, S.; Medraj, M.

    2017-01-01

    The effects of bismuth (Bi) addition on the microstructure and corrosion behavior of the Mg-Ca-Zn-Bi alloys were evaluated using electron microscopy, electrochemical test and electrochemical impedance spectroscopy. Microstructural observations showed that Mg-1.2Ca-1Zn-xBi (x = 0.5, 1.5, 3 wt.%) are composed of Mg2Ca, Ca2Mg6Zn3 and Mg3Bi2 phases while a new phase Mg2Bi2Ca appeared after the addition of 5 and 12 wt.% Bi to the Mg-1.2Ca-1Zn alloy. Furthermore, the additions of 0.5 wt.% Bi to the Mg-1.2Ca-1Zn alloy slightly improved the corrosion behavior of the alloy, while further increase in Bi amount from 1.5 to 12 wt.% has a deleterious effect on the corrosion behavior of the ternary Mg-1.2Ca-1Zn alloy which is driven by galvanic coupling effect. Cytotoxicity tests indicate that the Mg-1.2Ca-1Zn presents higher cell viability compared to Mg-1.2Ca-1Zn-0.5Bi alloy. In addition, the cell viability of both alloys increased with increasing incubation time while diluting the extracts to 50% and 10% improved the cell viabilities. The present results suggest that the Mg-1.2Ca-1Zn-0.5Bi can be interesting candidate for the development of degradable biomaterials and it is worthwhile for further investigation in an in vivo environment.

  3. Structure of Ca-Mg-Zn Metallic Glasses (Preprint)

    DTIC Science & Technology

    2011-07-01

    can be described as a mixture of Mg- and Zn- centered clusters, with Ca dominating in the first coordination shell of these clusters. The coordination...simulation. The amorphous structure can be described as a mixture of Mg- and Zn- centered clusters, with Ca dominating in the first coordination...in mm). The presence of the ternary eutectic reaction provides a strong liquidus temperature gradient in the selected composition area, which leads

  4. Microstructures, mechanical properties and corrosion resistances of extruded Mg-Zn-Ca-xCe/La alloys.

    PubMed

    Tong, L B; Zhang, Q X; Jiang, Z H; Zhang, J B; Meng, J; Cheng, L R; Zhang, H J

    2016-09-01

    Magnesium alloys are considered as good candidates for biomedical applications, the influence of Ce/La microalloying on the microstructure, mechanical property and corrosion performance of extruded Mg-5.3Zn-0.6Ca (wt%) alloy has been investigated in the current study. After Ce/La addition, the conventional Ca2Mg6Zn3 phases are gradually replaced by new Mg-Zn-Ce/La-(Ca) phases (T1'), which can effectively divide the Ca2Mg6Zn3 phase. The Ca2Mg6Zn3/T1' structure in Mg-Zn-Ca-0.5Ce/La alloy is favorably broken into small particles during the extrusion, resulting in an obvious refinement of secondary phase. The dynamic recrystallized grain size is dramatically decreased after 0.5Ce/La addition, and the tensile yield strength is improved, while further addition reverses the effect, due to the grain coarsening. However, the corrosion resistance of extruded Mg-Zn-Ca alloy deteriorates after Ce/La addition, because the diameter of secondary phase particle is remarkably decreased, which increases the amount of cathodic sites and accelerates the galvanic corrosion process.

  5. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr

    PubMed Central

    Li, H. F.; Xie, X. H.; Zheng, Y. F.; Cong, Y.; Zhou, F. Y.; Qiu, K. J.; Wang, X.; Chen, S. H.; Huang, L.; Tian, L.; Qin, L.

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  6. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-05-29

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals.

  7. Microstructure and mechanical properties of the as-cast Mg-Zn-Mn-Ca alloys

    NASA Astrophysics Data System (ADS)

    Fu, Junjian; Liu, Ke; Du, Wenbo; Wang, Zhaohui; Li, Shubo; Du, Xian

    2017-03-01

    As-cast Mg-Zn-Mn-Ca alloys are the candidates for medical implants. The microstructure and mechanical properties of the as-cast Mg-Zn-Mn-Ca alloys were investigated by using optical microscope (OM), X-ray diffraction (XRD) and scanning electron microscope (SEM). The results suggested that the addition of Zn significantly refined the grain size of the as-cast magnesium alloys, and hence improved the mechanical properties of the alloys. Meanwhile, the secondary phase mainly distributed in the grain boundaries and the solution treatment made parts of secondary phases dissolved into the matrix, resulting in enhancement of the plasticity of the as-cast Mg-Zn-Mn-Ca alloy.

  8. The Influence of Zn Content on the Corrosion and Wear Performance of Mg-Zn-Ca Alloy in Simulated Body Fluid

    NASA Astrophysics Data System (ADS)

    Li, Hua; Liu, Debao; Zhao, Yue; Jin, Feng; Chen, Minfang

    2016-09-01

    Mg-Zn-Ca alloy has been attracting increasing attention as a potential biodegradable implant material. In this paper, Mg-3Zn-0.2Ca and Mg-4Zn-0.2Ca alloys were prepared by means of vacuum melting and subsequent hot extrusion process. The influences of Zn content on the microstructure, mechanical properties, and corrosion and wear behavior of Mg-Zn-Ca alloys in simulated body fluid (SBF) were studied. The results show that with increased Zn content, the grain size and corrosion resistance were decreased, while the mechanical strength and wear resistance were increased, under both dry sliding and SBF-lubricated conditions. For the same Mg-Zn-Ca alloy, the wear loss rate under SBF lubrication was higher than dry sliding condition, indicating a strong corrosion-assisted wear effect of SBF to the Mg-Zn-Ca alloy.

  9. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    PubMed Central

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-01-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis. PMID:26907515

  10. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn.

    PubMed

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-02-24

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis.

  11. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    NASA Astrophysics Data System (ADS)

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-02-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis.

  12. Exploring Mg-Zn-Ca-Based Bulk Metallic Glasses for Biomedical Applications Based on Thermodynamic Approach

    NASA Astrophysics Data System (ADS)

    Ramya, M.; Sarwat, Syed Ghazi; Udhayabanu, V.; Raj, Baldev; Ravi, K. R.

    2015-12-01

    Magnesium (Mg)-based metallic glasses are considered as possible candidates in orthopedic implant applications. This paper aims to theoretically predict the glass-forming ability (GFA) in Mg-Zn-Ca alloy using a newly proposed thermodynamic model ( P HHS), and the consistency of this model is verified through experimental analysis. P HHS is based on thermodynamic parameters such as enthalpy of chemical mixing, elastic enthalpy, and configurational entropy, thus incorporating the pivotal effects, i.e., electron transfer effects, effect of atomic size mismatch, and effect of randomness, which aid to high GFA. In essence, P HHS can be visualized as the energy barrier that exists between the transformations of random atomic structure of glass to ordered crystalline structure. When the P HHS value is more negative, the energy barrier will be high, supporting easy glass formation. Various Mg-Zn-Ca metallic glass compositions displayed almost an expected and supporting trend, where the critical diameter of the metallic glass rod increased with a more negative P HHS value. Among the predicted Mg-Zn-Ca systems, the Mg60Zn35Ca5 composition shows deviation from the expected trend. This discrepancy has been clearly elucidated using a eutectic phase diagram. In addition to the consistency of the P HHS parameter to verifying the GFA of various compositions, the unique ability of this model is to predict unexplored Mg-Zn-Ca glass-forming compositions using contour development. Thus, proving P HHS parameter to be used as an efficient tool in predicting new glass-forming compositions.

  13. Local Atomic Structure of Ca-Mg-Zn Metallic Glasses (Postprint)

    DTIC Science & Technology

    2010-09-16

    cluster packing ECP model of amor - phous structure,20 the Ca-Mg-Zn ternary glasses are repre- sented as 10,9 efficient cluster packing structures...diffraction data as the basis on which to model the amor - phous structure of a series of ternary Ca60MgXZn40−X X =10,15,20,25 at. % metallic glasses using...Reverse Monte Carlo RMC methods. The effect of alloy composition on the structure and GFA is examined and the average amor - phous structure identified

  14. Effect of Ca and Zn additions on the mechanical properties of Mg produced by powder metallurgy

    NASA Astrophysics Data System (ADS)

    Guleryuz, L. F.; Ipek, R.; Arıtman, I.; Karaoglu, S.

    2017-02-01

    Magnesium and its alloys are among important research topics in view of their excellent biocompatibility.In this study mechanical and microstructure properties of hot sintered Mg-Zn-Ca alloys were studied.The effects of the addition of different amounts Ca and Zn were added to the base material has been processed by powder metallurgy method.resulting microstructures densities and compression test behaviors of the Mg-based alloys were studied.Visual inspection using SEM (Scanning Electron Microscope) analyses indicates that the microstructure of the composite is also greatly effected by these parameters. In addition, EDS (Energy Dispersive X-Ray Spectroscopy) analyses were performed for reliable determination of the chemical composition.

  15. Concentrations of morphologically normal, motile spermatozoa: Mg, Ca and Zn in the semen of infertile men.

    PubMed

    Pandy, V K; Parmeshwaran, M; Soman, S D; Dacosta, J C

    1983-03-01

    Semen from infertile men (n = 23) has been compared with that of control subjects (n = 25). Whereas the concentrations of morphologically normal, motile sperms, Mg, Ca and Zn fell within the acceptable limits for all the control subjects, only two infertile men qualified by all five parameters. Of the patient group, seven were abnormal on all counts; sperm motility, Mg and Zn were low in 16, Ca in 19 and abnormal morphology was encountered in 12. Since there was no linear correlation between any two parameters, it is possible that each factor may singly or jointly influence the physiological integrity of the spermatozoa. The results are discussed from a consideration of pathological manifestations known to occur in deficiency of these trace elements à propos their role in determining the fertility index of the semen.

  16. Antioxidant response and carboxylate metabolism in Brassica rapa exposed to different external Zn, Ca, and Mg supply.

    PubMed

    Blasco, Begoña; Graham, Neil S; Broadley, Martin R

    2015-03-15

    Zinc (Zn), calcium (Ca), and magnesium (Mg) malnutrition are common deficiencies in many developed and developing countries, resulting in a widespread health problem. Biofortification of food crops is an agricultural strategy that can be used to increase the levels of these elements in the edible portions of crops. Deficiency or toxicity of these cations in soils reduces plant growth, crop yield, and the quality of plant foodstuff. The aim of this study was to investigate the effect of external Zn, Ca, and Mg supply on accumulation and distribution of this elements as well as antioxidant response and organic acid composition of Brassica rapa ssp. trilocularis line R-o-18. Plants were grown at low Zn (0.05 μM Zn) and high Zn (500 μM Zn), low Ca (0.4 mM) and high Ca (40 mM), and low Mg (0.2 mM), and high Mg (20 mM) to simulate deficiency and toxicity conditions. Larger shoot biomass reductions were observed under high Zn, Ca and Mg treatments, and superoxide dismutase (SOD), ascorbate peroxidase (APX), H2O2, malondialdehyde (MDA), and total ascorbate (AA) showed a marked increase in these treatments. Therefore, Brassica plants might be more sensitive to excess of these elements in the nutrient solution. The translocation factor (TF) and distribution coefficient (DC) values of Zn, Ca, and Mg indicated higher translocation and accumulation in deficient conditions. High biosynthesis and citrate content in Brassica plants may be associated mainly with a high-nutrient solution extraction ability of these plants. These results provide background data, which will be used to characterize TILLING mutants to study the effects of mutations in genes involved in regulating Zn, Ca, and Mg distribution and accumulation in plants.

  17. Microstructure, mechanical properties and bio-corrosion properties of Mg-Si(-Ca, Zn) alloy for biomedical application.

    PubMed

    Zhang, Erlin; Yang, Lei; Xu, Jianwei; Chen, Haiyan

    2010-05-01

    Mg-Si alloy was investigated for biomedical application due to the biological function of Si in the human body. However, Mg-Si alloy showed a low ductility due to the presence of coarse Mg(2)Si. Ca and Zn elements were used to refine and modify the morphology of Mg(2)Si in order to improve the corrosion resistance and the mechanical properties. The cell toxicity of Mg, Zn and Ca metals was assessed by an MTT test. The test results indicated that increasing the concentrations of Mg, Zn and Ca ions did not cause cell toxicity, which showed that the release of these three elements would not lead to cell toxicity. Then, microstructure, mechanical properties and bio-corrosion properties of as-cast Mg-Si(-Ca, Zn) alloys were investigated by optical microscopy, scanning electronic microscopy, mechanical properties testing and electrochemical measurement. Ca element can slightly refine the grain size and the morphology Mg(2)Si phase in Mg-Si alloy. The bio-corrosion resistance of Mg-Si alloys was improved by the addition of Ca due to the reduction and refinement of Mg(2)Si phase; however, no improvement was observed in the strength and elongation. The addition of 1.6% Zn to Mg-0.6Si can modify obviously the morphology of Mg(2)Si phase from course eutectic structure to a small dot or short bar shape. As a result, tensile strength, elongation and bio-corrosion resistance were all improved significantly; especially, the elongation improved by 115.7%. It was concluded that Zn element was one of the best alloying elements of Mg-Si alloy for biomedical application.

  18. Understanding corrosion behavior of Mg-Zn-Ca alloys from subcutaneous mouse model: effect of Zn element concentration and plasma electrolytic oxidation.

    PubMed

    Jang, Yongseok; Tan, Zongqing; Jurey, Chris; Xu, Zhigang; Dong, Zhongyun; Collins, Boyce; Yun, Yeoheung; Sankar, Jagannathan

    2015-03-01

    Mg-Zn-Ca alloys are considered as suitable biodegradable metallic implants because of their biocompatibility and proper physical properties. In this study, we investigated the effect of Zn concentration of Mg-xZn-0.3Ca (x=1, 3 and 5wt.%) alloys and surface modification by plasma electrolytic oxidation (PEO) on corrosion behavior in in vivo environment in terms of microstructure, corrosion rate, types of corrosion, and corrosion product formation. Microstructure analysis of alloys and morphological characterization of corrosion products were conducted using x-ray computed tomography (micro-CT) and scanning electron microscopy (SEM). Elemental composition and crystal structure of corrosion products were determined using x-ray diffraction (XRD) and electron dispersive x-ray spectroscopy (EDX). The results show that 1) as-cast Mg-xZn-0.3Ca alloys are composed of Mg matrix and a secondary phase of Ca2Mg6Zn3 formed along grain boundaries, 2) the corrosion rate of Mg-xZn-0.3Ca alloys increases with increasing concentration of Zn in the alloy, 3) corrosion rates of alloys treated by PEO sample are decreased in in vivo environment, and 4) the corrosion products of these alloys after in vivo tests are identified as brucite (Mg(OH)2), hydroxyapatite (Ca10(PO4)6(OH)2), and magnesite (MgCO3·3H2O).

  19. Microstructure, mechanical and bio-corrosion properties of Mn-doped Mg-Zn-Ca bulk metallic glass composites.

    PubMed

    Wang, Jingfeng; Huang, Song; Li, Yang; Wei, Yiyun; Xi, Xingfeng; Cai, Kaiyong

    2013-10-01

    The effects of Mn substitution for Mg on the microstructure, mechanical properties, and corrosion behavior of Mg69-xZn27Ca4Mnx (x=0, 0.5 and 1at.%) alloys were investigated using X-ray diffraction, compressive tests, electrochemical treatments, and immersion tests, respectively. Microstructural observations showed that the Mg69Zn27Ca4 alloy was mainly amorphous. The addition of Mn decreases the glass-forming ability, which results in a decreased strength from 545 MPa to 364 MPa. However, this strength is still suitable for implant application. Polarization and immersion tests in the simulated body fluid at 37 °C revealed that the Mn-doped Mg-Zn-Ca alloys have significantly higher corrosion resistance than traditional ZK60 and pure Mg alloys. Cytotoxicity test showed that cell viabilities of osteoblasts cultured with Mn-doped Mg-Zn-Ca alloys extracts were higher than that of pure Mg. Mg68.5Zn27Ca4Mn0.5 exhibits the highest bio-corrosion resistance, biocompatibility and has desirable mechanical properties, which could suggest to be used as biomedical materials in the future.

  20. Bio-corrosion characterization of Mg-Zn-X (X = Ca, Mn, Si) alloys for biomedical applications.

    PubMed

    Rosalbino, F; De Negri, S; Saccone, A; Angelini, E; Delfino, S

    2010-04-01

    The successful applications of magnesium-based alloys as biodegradable orthopedic implants are mainly inhibited due to their high degradation rates in physiological environment. This study examines the bio-corrosion behaviour of Mg-2Zn-0.2X (X = Ca, Mn, Si) alloys in Ringer's physiological solution that simulates bodily fluids, and compares it with that of AZ91 magnesium alloy. Potentiodynamic polarization and electrochemical impedance spectroscopy results showed a better corrosion behaviour of AZ91 alloy with respect to Mg-2Zn-0.2Ca and Mg-2Zn-0.2Si alloys. On the contrary, enhanced corrosion resistance was observed for Mg-2Zn-0.2Mn alloy compared to the AZ91 one: Mg-2Zn-0.2Mn alloy exhibited a four-fold increase in the polarization resistance than AZ91 alloy after 168 h exposure to the Ringer's physiological solution. The improved corrosion behaviour of the Mg-2Zn-0.2Mn alloy with respect to the AZ91 one can be ascribed to enhanced protective properties of the Mg(OH)(2) surface layer. The present study suggests the Mg-2Zn-0.2Mn alloy as a promising candidate for its applications in degradable orthopedic implants, and is worthwhile to further investigate the in vivo corrosion behaviour as well as assessed the mechanical properties of this alloy.

  1. In vitro degradation and mechanical integrity of Mg-Zn-Ca alloy coated with Ca-deficient hydroxyapatite by the pulse electrodeposition process.

    PubMed

    Wang, H X; Guan, S K; Wang, X; Ren, C X; Wang, L G

    2010-05-01

    The key to manufacturing magnesium-based alloys that are suitable as biodegradable orthopaedic implants is how to adjust their degradation rates and mechanical integrity in the physiological environment. In this study, to solve this challenge, a soluble Ca-deficient hydroxyapatite (Ca-def HA) coating was deposited on an Mg-Zn-Ca alloy substrate by pulse eletrodeposition. This deposition can be demonstrated by X-ray diffractometry and energy dispersion spectroscopy analyses, and the Ca/P atomic ratio of as-deposited coating is about 1.33 (within the range from 1.33 to 1.65). By regulating the appropriate pulse amplitude and width, the Ca-def HA coating shows better adhesion to Mg-Zn-Ca alloy, whose lap shear strength is increased to 41.8+/-2.7 MPa. Potentiodynamic polarization results in Kokubo's simulated body fluid (SBF) indicate that the corrosion potential of Mg alloy increases from -1645 to -1414 mV, while the corrosion current density decreases from 110 to 25 microA/cm(2), which illustrates that the Ca-def HA coating improves the substrate corrosion resistance significantly. Since orthopaedic implants generally serve under conditions of stress corrosion, the mechanical integrity of the Mg-Zn-Ca alloy was measured using the slow strain rate tensile (SSRT) testing technique in SBF. The SSRT results show that the ultimate tensile strength and time of fracture for the coated Mg-Zn-Ca alloy are higher than those of the uncoated one, which is beneficial in supporting fractured bone for a longer time. Thus Mg-Zn-Ca alloy coated with Ca-def HA is be a promising candidate for biodegradable orthopaedic implants, and is worthwhile to further investigate the in vivo degradation behavior.

  2. Introducing Mg-4Zn-3Gd-1Ca/ZnO nanocomposite with compressive strengths matching/exceeding that of mild steel

    PubMed Central

    Chen, Y.; Tekumalla, S.; Guo, Y. B.; Gupta, M.

    2016-01-01

    This work introduces Mg-4Zn-3Gd-1Ca/2ZnO (wt.%) nanocomposite fabricated using the technique of disintegrated melt deposition and extrusion. Addition of ZnO nanoparticles enhanced the compressive strengths of alloy by ~100 MPa. Nanocomposite samples display high strength and good ductility: 0.2% compressive yield stress of 355 MPa, ultimate compressive stress of 703 MPa, and compressive failure strain of 10.6%. The significant enhancement of compressive yield stress is mainly attributed to the grain refinement by adding nanoparticles. The strength levels exceed that of commercial magnesium alloys (i.e. WE43, WE54, ZK60, and ME21) and mild steels (i.e. S275 and S355), making Mg-4Zn-3Gd-1Ca/2ZnO a very promising material for multiple engineering and biomedical applications. PMID:27572903

  3. Introducing Mg-4Zn-3Gd-1Ca/ZnO nanocomposite with compressive strengths matching/exceeding that of mild steel

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Tekumalla, S.; Guo, Y. B.; Gupta, M.

    2016-08-01

    This work introduces Mg-4Zn-3Gd-1Ca/2ZnO (wt.%) nanocomposite fabricated using the technique of disintegrated melt deposition and extrusion. Addition of ZnO nanoparticles enhanced the compressive strengths of alloy by ~100 MPa. Nanocomposite samples display high strength and good ductility: 0.2% compressive yield stress of 355 MPa, ultimate compressive stress of 703 MPa, and compressive failure strain of 10.6%. The significant enhancement of compressive yield stress is mainly attributed to the grain refinement by adding nanoparticles. The strength levels exceed that of commercial magnesium alloys (i.e. WE43, WE54, ZK60, and ME21) and mild steels (i.e. S275 and S355), making Mg-4Zn-3Gd-1Ca/2ZnO a very promising material for multiple engineering and biomedical applications.

  4. In vitro bioaccessibility of β-carotene, Ca, Mg and Zn in landrace carrots (Daucus carota, L.).

    PubMed

    Zaccari, Fernanda; Cabrera, María Cristina; Ramos, Ana; Saadoun, Ali

    2015-01-01

    Four landrace carrots ("Becaria", "CRS", "González" and "Rodríguez") and two marketable cultivars (Kuroda and Brasilia), raw and steamed, were characterised by the total content of β-carotene Ca, Mg and Zn, in vitro bioaccessibility and by colour and were evaluated to determine the effect of particle size in nutrient bioaccessibility. Steaming increased the content of β-carotene extracted from "CRS" and Brasilia (29% and 75%) and decreased the content of β-carotene extracted from "CRS" by 23% in "Rodríguez." In addition, steaming caused a loss of Ca (21%) but did not change the amount of Mg and Zn. The bioaccessibility of β-carotene in raw and pulped carrots was very low (<0.5%). Furthermore, steaming and a smaller particle size increased the bioaccessibility of β-carotene by 3-16 times. Additionally, cooking increased the in vitro bioaccessibility of Ca and Zn but had no effect on Mg. Moreover, homogenisation increased the bioaccessibility by 20% in Ca, 17% in Mg, and 10% in Zn compared to pulping.

  5. In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass.

    PubMed

    Li, H F; Xie, X H; Zhao, K; Wang, Y B; Zheng, Y F; Wang, W H; Qin, L

    2013-11-01

    In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4 weeks of implantation, and they can promote osteogenesis and new bone formation after 2 weeks of implantation. The improved mechanical properties and corrosion behavior can be attributed to the different chemical composition as well as the formation of a unique high-entropy atomic structure with a maximum degree of disorder.

  6. Influence of solid-solution treatment on microstructure, mechanical property and corrosion behavior of biodegradable Mg-Zn-Ca alloy

    NASA Astrophysics Data System (ADS)

    Ly, Xuan Nam; Yang, S.; Qin, Y.

    2017-03-01

    The influence of solid-solution treatment on microstructure, mechanical property and corrosion behavior of Mg-Zn-Ca alloy was studied in the present investigation by SEM, tensile test, electrochemical and immersion test. The results show that the microstructure of Mg alloys after solid solution treatment significantly changed, a large number of the second phase (Ca2Mg6Zn3, Mg2Ca) dissolved into the α-Mg matrix reaching a supersaturated state, and the grains size was bigger than before solid solution treatment; the mechanical properties were obviously improved. In particular the tensile strength of 0.5wt.% Ca of Mg alloy reached 220MPa and the ductility reached 16.6%. Compared with the as-cast Mg alloys, the corrosion potential after solid-solution treatment slightly shifted negative, but the corrosion current density significantly decreased. After solid solution treatment, the surface corrosion was not serious and the result of weight gain was lower compared with those of the as-cast Mg alloys.

  7. Analysis of Relations Between the Level of Mg, Zn, Ca, Cu, and Fe and Depressiveness in Postmenopausal Women.

    PubMed

    Szkup, Małgorzata; Jurczak, Anna; Brodowska, Aleksandra; Brodowska, Agnieszka; Noceń, Iwona; Chlubek, Dariusz; Laszczyńska, Maria; Karakiewicz, Beata; Grochans, Elżbieta

    2017-03-01

    Numerous observations suggest a possible connection between the levels of Mg, Zn, Fe, and Zn and the incidence of depressive symptoms. Depression is two to three times more common in women than in men. The menopausal period is extremely conducive to depressive disorders. The aim of this study was to assess the severity of depressive symptoms in postmenopausal women depending on the levels of Mg, Zn, Ca, Cu, and Fe. The study included 198 healthy postmenopausal women at the average age of 56.26 ± 5.55 years. In the first part of the study, standardized research tools were used, namely the Primary Care Evaluation of Mental Disorders (PRIME-MD) and the Beck Depression Inventory (BDI). The second part involved biochemical analysis of Mg, Zn, Ca, Cu, and Fe levels in blood serum. The lowest Cu levels were observed in women without depressive symptoms (1.07 ± 0.22 mg/l) and the highest in those with severe depressive symptoms (1.19 ± 0.17 mg/l), (p ≤ 0.05). The lowest Mg levels were observed in women with depressive symptoms (14.28 ± 2.13 mg/l), and the highest in women without depressive symptoms (16.30 ± 3.51 mg/l), (p ≤ 0.05). The average serum Mg levels (15.75 ± 3.23 mg/l) decreased compared to the reference values (18.77-24 mg/l). What is striking is a potential relation between the levels of Mg and Cu and depressiveness. Our results indicate to a higher vulnerability to depression in a group of women with lower levels of Mg and higher levels of Cu.

  8. Improved mechanical performance and delayed corrosion phenomena in biodegradable Mg-Zn-Ca alloys through Pd-alloying.

    PubMed

    González, S; Pellicer, E; Fornell, J; Blanquer, A; Barrios, L; Ibáñez, E; Solsona, P; Suriñach, S; Baró, M D; Nogués, C; Sort, J

    2012-02-01

    The influence of partial substitution of Mg by Pd on the microstructure, mechanical properties and corrosion behaviour of Mg(72-x)Zn(23)Ca(5)Pd(x) (x=0, 2 and 6 at.%) alloys, synthesized by copper mould casting, is investigated. While the Mg(72)Zn(23)Ca(5) alloy is mainly amorphous, the addition of Pd decreases the glass-forming ability, thus favouring the formation of crystalline phases. From a mechanical viewpoint, the hardness increases with the addition of Pd, from 2.71 GPa for x=0 to 3.9 GPa for x=6, mainly due to the formation of high-strength phases. In turn, the wear resistance is maximized for an intermediate Pd content (i.e., Mg(70)Zn(23)Ca(5)Pd(2)). Corrosion tests in a simulated body fluid (Hank's solution) indicate that Pd causes a shift in the corrosion potential towards more positive values, thus delaying the biodegradability of this alloy. Moreover, since the cytotoxic studies with mouse preosteoblasts do not show dead cells after culturing for 27 h, these alloys are potential candidates to be used as biomaterials.

  9. Effect of Ca addition on the damping capacity of Mg-Al-Zn casting alloys

    NASA Astrophysics Data System (ADS)

    Jun, Joong-Hwan; Moon, Jung-Hyun

    2015-07-01

    The influences of Ca addition on the microstructures and damping capacities of AZ91-(0˜2)%Ca casting alloys were investigated, on the basis of the results of X-ray diffractometry, optical microscopy, scanning electron microscopy and vibration tests in a single cantilever mode. The amount of intermetallic compounds decreased with increasing Ca content up to 0.5%, above which it increased; the average cell size showed the opposite tendency. All alloys exhibited similar damping levels in the strain-amplitude independent region. Considering the very low solubility of Ca in the matrix, and that most of the Ca elements are consumed by the formation of the Al2Ca phase and incorporation into the Mg17Al12 phase, this would be ascribed to the almost identical concentrations of Ca solutes distributed in the matrix. In the strain-amplitude dependent region, however, the AZ91-0.5%Ca alloy possessed the maximum damping capacity. From the viewpoint of microstructural evolution with Ca addition, the number density of compound particles is considered to be the principal factor affecting the damping behavior in the strain-amplitude dependent region.

  10. Composition-dependent structural and electronic properties of Mg(95-x)Zn(x)Ca5 metallic glasses: an ab initio molecular dynamics study.

    PubMed

    Li, S N; Liu, J B; Li, J H; Wang, J; Liu, B X

    2015-02-26

    Recent progress in the synthesis of Mg-based metallic glasses (MGs) has allowed them to be considered as potential candidates for biodegradable and bioabsorbable implant materials. In this work, we use the Mg-Zn-Ca system as a representative to investigate the effect of composition on the atomic-level structure and local chemical environment in Mg-based MGs from ab initio molecular dynamics simulations. The results suggest that the short-range order of Mg(95-x)Zn(x)Ca5 (x = 21, 25, 29, and 33) MGs is characterized by Zn-centered icosahedral and icosahedral-like clusters, which show an increasing number and a rising tendency to interpenetrate each other with the enrichment of Zn constituents. A considerable degree of charge transfer between Zn and the surrounding Mg/Ca atoms is observed through electronic structure and bonding character analysis. At Zn-rich compositions, a percolated Zn-Zn network extended throughout the entire sample is formed, upon which the accumulated charges around Zn atoms are associated into a continuous conductivity path. Such results may shed light on the improved corrosion resistance of the Zn-rich Mg-Zn-Ca MGs.

  11. Microstructure and Fatigue Behavior of Friction Stir-welded Noncombustive Mg-9Al-Zn-Ca Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Zhou, L.; Li, Z. Y.; Nakata, K.; Feng, J. C.; Huang, Y. X.; Liao, J. S.

    2016-06-01

    Microstructure and fatigue behavior of friction stir-welded noncombustive Mg-9Al-Zn-Ca magnesium alloy were investigated. The as-received hot-extruded material consisted of equiaxed α-Mg grains with β-Mg17Al12 and Al2Ca compounds distributed along the grain boundaries. Friction stir welding produced much refined α-Mg grains accompanied by the dissolution of the eutectic β-Mg17Al12 phase, while Al2Ca phase was dispersed homogenously into the Mg matrix. Friction stir welding produced slightly increased hardness and tensile strength in the defect-free welds compared with the base material due to microstructural refinement and uniform distribution of intermetallic compounds. The load-controlled uniaxial tensile high-cycle fatigue tests indicated that fatigue strength of 90 MPa was obtained for the friction stir-welded joint with fatigue crack initiated basically near the specimen's surface and at the retreating side of the joint. Crack propagation was characterized by cleavage and fatigue striations.

  12. Pt–Mg, Pt–Ca, and Pt–Zn lantern complexes and metal-only donor–acceptor interactions [Pt-Mg Pt-Ca and Pt-Zn compounds with metal-only donor-acceptor interactions

    DOE PAGES

    Baddour, Frederick G.; Hyre, Ariel S.; Guillet, Jesse L.; ...

    2016-12-12

    Here, Pt-based heterobimetallic lantern complexes of the form [PtM(SOCR)4(L)] have been shown previously to form intermolecular metallophilic interactions and engage in antiferromagnetic coupling between lanterns having M atoms with open shell configurations. In order to understand better the influence of the carboxylate bridge and terminal ligand on the electronic structure, as well as the metal–metal interactions within each lantern unit, a series of diamagnetic lantern complexes, [PtMg(SAc)4(OH2)] (1), [PtMg(tba)4(OH2)] (2), [PtCa(tba)4(OH2)] (3), [PtZn(tba)4(OH2)] (4), and a mononuclear control (Ph4P)2[Pt(SAc)4] (5) have been synthesized. Crystallographic data show close Pt–M contacts enforced by the lantern structure in each dinuclear case. 195Pt-NMR spectroscopymore » of 1–4, (Ph4P)2[Pt(SAc)4] (5), and several previously reported lanterns revealed a strong chemical shift dependence on the identity of the second metal (M), mild influence by the thiocarboxylate ligand (SOCR; R = CH3 (thioacetate, SAc), C6H5 (thiobenzoate, tba)), and modest influence from the terminal ligand (L). Fluorescence spectroscopy has provided evidence for a Pt···Zn metallophilic interaction in [PtZn(SAc)4(OH2)], and computational studies demonstrate significant dative character. In all of 1–4, the short Pt–M distances suggest that metal-only Lewis donor (Pt)–Lewis acceptor (M) interactions could be present. DFT and NBO calculations, however, show that only the Zn examples have appreciable covalent character, whereas the Mg and Ca complexes are much more ionic.« less

  13. Ca:Mg:Zn:CO3 and Ca:Mg:CO3-tri- and bi-elemental carbonate microparticles for novel injectable self-gelling hydrogel-microparticle composites for tissue regeneration.

    PubMed

    Douglas, Timothy E L; Sobczyk, Katarzyna; Łapa, Agata; Włodarczyk, Katarzyna; Brackman, Gilles; Vidiasheva, Irina; Reczyńska, Katarzyna; Pietryga, Krzysztof; Schaubroeck, David; Bliznuk, Vitaliy; Voort, Pascal Van Der; Declercq, Heidi A; Bulcke, Jan Van den; Samal, Sangram Keshari; Khalenkow, Dmitry; Parakhonskiy, Bogdan V; Van Acker, Joris; Coenye, Tom; Lewandowska-Szumieł, Małgorzata; Pamuła, Elżbieta; Skirtach, Andre G

    2017-03-24

    Injectable composites for tissue regeneration can be developed by dispersion of inorganic microparticles and cells in a hydrogel phase. In this study, multifunctional carbonate microparticles containing different amounts of calcium, magnesium and zinc were mixed with solutions of gellan gum (GG), an anionic polysaccharide, to form injectable hydrogel-microparticle composites, containing Zn, Ca and Mg. Zn and Ca were incorporated into microparticle preparations to a greater extent than Mg. Microparticle groups were heterogeneous and contained microparticles of differing shape and elemental composition. Zn-rich microparticles were 'star shaped' and appeared to consist of small crystallites, while Zn-poor, Ca- and Mg-rich microparticles were irregular in shape and appeared to contain lager crystallites. Zn-free microparticle groups exhibited the best cytocompatibility and, unexpectedly, Zn-free composites showed the highest antibacterial activity towards methicilin-resistant Staphylococcus aureus. Composites containing Zn-free microparticles were cytocompatible and therefore appear most suitable for applications as an injectable biomaterial. This study proves the principle of creating bi- and tri-elemental microparticles to induce the gelation of GG to create injectable hydrogel-microparticle composites.

  14. Acidity and metal (Mg2+, Ca2+, Zn2+) affinity of L-γ-carboxyglutamic acid and its peptide analog

    NASA Astrophysics Data System (ADS)

    Remko, Milan; Broer, Ria; Remková, Anna; Van Duijnen, Piet Th.

    2014-10-01

    Density functional theory methods with the B3LYP and B97D functionals with triple-zeta 6-311++G(d,p) basis set have been used to study the acidity, basicity and metal affinity of L-γ-carboxyglutamic acid (GLA) and its peptide derivative [2-acetylamino-3-(methylamino)-3-oxopropyl]malonic acid (AMD-GLA). The Gibbs interaction energies of the GLA2-…M2+ and AMD-GLA2-…M2+ (M = Mg, Ca, Zn) complexes show an increasing binding affinity in the order Ca2+ < Mg2+ < Zn2+ The transition metal Zn2+ is most effectively recognized by the dianions of GLA and AMD-GLA. Of the dianions studied the AMD-GLA dianion is the strongest Lewis base. Computations that include the effect of solvation showed that in water the relative stability of GLA2-…M2+ and AMD-GLA2-…M2+ ionic bonds is rapidly diminished. The computed interaction Gibbs energy in water is small and negative.

  15. Pt-Mg, Pt-Ca, and Pt-Zn Lantern Complexes and Metal-Only Donor-Acceptor Interactions.

    PubMed

    Baddour, Frederick G; Hyre, Ariel S; Guillet, Jesse L; Pascual, David; Lopez-de-Luzuriaga, José Maria; Alam, Todd M; Bacon, Jeffrey W; Doerrer, Linda H

    2017-01-03

    Pt-based heterobimetallic lantern complexes of the form [PtM(SOCR)4(L)] have been shown previously to form intermolecular metallophilic interactions and engage in antiferromagnetic coupling between lanterns having M atoms with open shell configurations. In order to understand better the influence of the carboxylate bridge and terminal ligand on the electronic structure, as well as the metal-metal interactions within each lantern unit, a series of diamagnetic lantern complexes, [PtMg(SAc)4(OH2)] (1), [PtMg(tba)4(OH2)] (2), [PtCa(tba)4(OH2)] (3), [PtZn(tba)4(OH2)] (4), and a mononuclear control (Ph4P)2[Pt(SAc)4] (5) have been synthesized. Crystallographic data show close Pt-M contacts enforced by the lantern structure in each dinuclear case. (195)Pt-NMR spectroscopy of 1-4, (Ph4P)2[Pt(SAc)4] (5), and several previously reported lanterns revealed a strong chemical shift dependence on the identity of the second metal (M), mild influence by the thiocarboxylate ligand (SOCR; R = CH3 (thioacetate, SAc), C6H5 (thiobenzoate, tba)), and modest influence from the terminal ligand (L). Fluorescence spectroscopy has provided evidence for a Pt···Zn metallophilic interaction in [PtZn(SAc)4(OH2)], and computational studies demonstrate significant dative character. In all of 1-4, the short Pt-M distances suggest that metal-only Lewis donor (Pt)-Lewis acceptor (M) interactions could be present. DFT and NBO calculations, however, show that only the Zn examples have appreciable covalent character, whereas the Mg and Ca complexes are much more ionic.

  16. Effects of secondary phase and grain size on the corrosion of biodegradable Mg-Zn-Ca alloys.

    PubMed

    Lu, Y; Bradshaw, A R; Chiu, Y L; Jones, I P

    2015-03-01

    The bio-corrosion behaviour of Mg-3Zn-0.3Ca (wt.%) alloy in simulated body fluid (SBF) at 37°C has been investigated using immersion testing and electrochemical measurements. Heat treatment has been used to alter the grain size and secondary phase volume fraction; the effects of these on the bio-corrosion behaviour of the alloy were then determined. The as-cast sample has the highest bio-corrosion rate due to micro-galvanic corrosion between the eutectic product (Mg+Ca2Mg6Zn3) and the surrounding magnesium matrix. The bio-corrosion resistance of the alloy can be improved by heat treatment. The volume fraction of secondary phases and grain size are both key factors controlling the bio-corrosion rate of the alloy. The bio-corrosion rate increases with volume fraction of secondary phase. When this is lower than 0.8%, the dependence of bio-corrosion rate becomes noticeable: large grains corrode more quickly.

  17. Ab Initio Molecular Dynamics Simulation of the Amorphous Structure of Ca-Mg-Cu and Ca-Mg-Zn Alloys (Preprint)

    DTIC Science & Technology

    2012-08-01

    believed to depend on the type of short range order (SRO) and medium range order ( MRO ) of alloying elements in the amorphous structure. It is...which allowed calculation of local structural features (SRO and MRO ) such as total and partial CN, type and distribution of characteristic...indicate the presence of MRO in these alloys [32,33], as well as the fluctuation in the atomic scattering cross-sections: The solutes, Cu, Zn and Mg

  18. Pt–Mg, Pt–Ca, and Pt–Zn lantern complexes and metal-only donor–acceptor interactions [Pt-Mg Pt-Ca and Pt-Zn compounds with metal-only donor-acceptor interactions

    SciTech Connect

    Baddour, Frederick G.; Hyre, Ariel S.; Guillet, Jesse L.; Pascual, David; Lopez-de-Luzuriaga, Jose Maria; Alam, Todd M.; Bacon, Jeffrey W.; Doerrer, Linda H.

    2016-12-12

    Here, Pt-based heterobimetallic lantern complexes of the form [PtM(SOCR)4(L)] have been shown previously to form intermolecular metallophilic interactions and engage in antiferromagnetic coupling between lanterns having M atoms with open shell configurations. In order to understand better the influence of the carboxylate bridge and terminal ligand on the electronic structure, as well as the metal–metal interactions within each lantern unit, a series of diamagnetic lantern complexes, [PtMg(SAc)4(OH2)] (1), [PtMg(tba)4(OH2)] (2), [PtCa(tba)4(OH2)] (3), [PtZn(tba)4(OH2)] (4), and a mononuclear control (Ph4P)2[Pt(SAc)4] (5) have been synthesized. Crystallographic data show close Pt–M contacts enforced by the lantern structure in each dinuclear case. 195Pt-NMR spectroscopy of 1–4, (Ph4P)2[Pt(SAc)4] (5), and several previously reported lanterns revealed a strong chemical shift dependence on the identity of the second metal (M), mild influence by the thiocarboxylate ligand (SOCR; R = CH3 (thioacetate, SAc), C6H5 (thiobenzoate, tba)), and modest influence from the terminal ligand (L). Fluorescence spectroscopy has provided evidence for a Pt···Zn metallophilic interaction in [PtZn(SAc)4(OH2)], and computational studies demonstrate significant dative character. In all of 1–4, the short Pt–M distances suggest that metal-only Lewis donor (Pt)–Lewis acceptor (M) interactions could be present. DFT and NBO calculations, however, show that only the Zn examples have appreciable covalent character, whereas the Mg and Ca complexes are much more ionic.

  19. Effect of Mg(2+), Ca(2+), Sr(2+) and Ba(2+) metal ions on the antifungal activity of ZnO nanoparticles tested against Candida albicans.

    PubMed

    Haja Hameed, Abdulrahman Syedahamed; Karthikeyan, Chandrasekaran; Senthil Kumar, Venugopal; Kumaresan, Subramanian; Sasikumar, Seemaisamy

    2015-01-01

    The antifungal ability of pure and alkaline metal ion (Mg(2+), Ca(2+), Sr(2+) and Ba(2+)) doped ZnO nanoparticles (NPs) prepared by the co-precipitation method was tested against the pathogenic yeast, Candida albicans (C. albicans), and the results showed that the Mg-doped ZnO NPs possessed greater effect than the other alkaline metal ion doped ZnO NPs. The impact of the concentration of Mg doped ZnO sample on the growth of C. albicans was also studied. The Minimal Fungicidal Concentration (MFC) of the Mg doped ZnO NPs was found to be 2000 μg/ml for which the growth of C. albicans was completely inhibited. The ZnO:Mg sample (1.5mg/ml) with various concentrations of histidine reduced the fungicidal effect of the nanoparticles against C. albicans, which was deliberately explained by the role of ROS. The ZnO:Mg sample added with 5mM of histidine scavenged the ample amount of generated ROS effectively. The binding of the NPs with fungi was observed by their FESEM images and their electrostatic attraction is confirmed by the zeta potential measurement.

  20. Fabrication and characterization of a biodegradable Mg-2Zn-0.5Ca/1β-TCP composite.

    PubMed

    Huang, Yan; Liu, Debao; Anguilano, Lorna; You, Chen; Chen, Minfang

    2015-09-01

    A biodegradable magnesium matrix and beta-tricalcium phosphate (β-TCP) particles reinforced composite Mg-2Zn-0.5Ca/1beta-TCP (wt.%) was fabricated for biomedical applications by the novel route of combined high shear solidification (HSS) and equal channel angular extrusion (ECAE). The as-cast composite obtained by HSS showed a fine and equiaxed grain structure with globally uniformly distributed β-TCP particles in aggregates of 2-25 μm in size. The ECAE processing at 300 °C resulted in further microstructural refinement and the improvement of β-TCP particle distribution. During ECAE, the β-TCP aggregates were broken into smaller ones or individual particles, forming a dispersion in the matrix. Such fabricated composite exhibited enhanced hardness and in vitro corrosion resistance. The enhanced hardness was attributed to both the addition of β-TCP particles and grain refinement while the development of a Ca-P rich surface layer from β-TCP during corrosion was responsible for the improvement in corrosion resistance. The composite was characterized in terms of microstructural evolution during fabrication, mechanical properties and electrochemical performance during polarization and immersion tests in a simulated body fluid. Discussions are made on the benefits of both HSS and ECAE and the mechanisms responsible for the enhanced corrosion resistance.

  1. Levels of Se, Zn, Mg and Ca in commercial goat and cow milk fermented products: Relationship with their chemical composition and probiotic starter culture.

    PubMed

    Navarro-Alarcón, Miguel; Cabrera-Vique, Carmen; Ruiz-López, Ma Dolores; Olalla, Manuel; Artacho, Reyes; Giménez, Rafael; Quintana, Verónica; Bergillos, Triana

    2011-12-01

    We determined Se, Zn, Mg and Ca levels in 42 samples of goat and cow fermented milks which are widely consumed in Spain were determined. Atomic absorption spectrometry (hydride generation for Se and flame atomisation for remaining elements) was used as an analytical technique. Reliability of the procedure was checked. Only Mg levels in goat fermented milks were significantly higher to those found in cow fermented milks (p<0.022). Important similarities in concentrations and behaviours for Mg and Ca have been observed. Mg contents were significantly correlated with Zn (r=0.590; p<0.001) and Ca (r=0.344; p<0.028) concentrations, Zn, Mg and Ca levels with protein content (r=0.554, r=0.479, r=0.388, respectively), Mg levels with fats (r=0.403; p=0.011) and Se levels with carbohydrates (r=-0.379; p=0.031). Mineral and macronutrient levels in yogurts with traditional probiotic starter cultures were not significantly different to those found in fermented milks with additional probiotic microorganisms (p>0.05). It was concluded that goat fermented milks are a better source for Mg than cow samples.

  2. Influence of trace impurities on the in vitro and in vivo degradation of biodegradable Mg-5Zn-0.3Ca alloys.

    PubMed

    Hofstetter, J; Martinelli, E; Pogatscher, S; Schmutz, P; Povoden-Karadeniz, E; Weinberg, A M; Uggowitzer, P J; Löffler, J F

    2015-09-01

    The hydrogen evolution method and animal experiments were deployed to investigate the effect of trace impurity elements on the degradation behavior of high-strength Mg alloys of type ZX50 (Mg-5Zn-0.3Ca). It is shown that trace impurity elements increase the degradation rate, predominantly in the initial period of the tests, and also increase the material's susceptibility to localized corrosion attack. These effects are explained on the basis of the corrosion potential of the intermetallic phases present in the alloys. The Zn-rich phases present in ZX50 are nobler than the Mg matrix, and thus act as cathodic sites. The impurity elements Fe and Mn in the alloy of conventional purity are incorporated in these Zn-rich intermetallic phases and therefore increase their cathodic efficiency. A design rule for circumventing the formation of noble intermetallic particles and thus avoiding galvanically accelerated dissolution of the Mg matrix is proposed.

  3. Metallic elements (Ca, Hg, Fe, K, Mg, Mn, Na, Zn) in the fruiting bodies of Boletus badius.

    PubMed

    Kojta, Anna K; Falandysz, Jerzy

    2016-06-01

    The aim of this study was to investigate and compare the levels of eight metallic elements in the fruiting bodies of Bay Bolete (Boletus badius; current name Imleria badia) collected from ten sites in Poland to understand better the value of this popular mushroom as an organic food. Bay Bolete fruiting bodies were collected from the forest area near the towns and villages of Kętrzyn, Poniatowa, Bydgoszcz, Pelplin, Włocławek, Żuromin, Chełmno, Ełk and Wilków communities, as well as in the Augustów Primeval Forest. Elements such as Ca, Fe, K, Mg, Mn, Na and Zn were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-OES), and mercury by cold vapor atomic absorption spectrometry (CV-AAS). This made it possible to assess the nutritional value of the mushroom, as well as possible toxicological risks associated with its consumption. The results were subjected to statistical analysis (Kruskal-Wallis test, cluster analysis, principal component analysis).

  4. Influence of Applied Voltage and Film-Formation Time on Microstructure and Corrosion Resistance of Coatings Formed on Mg-Zn-Zr-Ca Bio-magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Yandong, Yu; Shuzhen, Kuang; Jie, Li

    2015-09-01

    The influence of applied voltage and film-formation time on the microstructure and corrosion resistance of coatings formed on a Mg-Zn-Zr-Ca novel bio-magnesium alloy has been investigated by micro-arc oxidation (MAO) treatment. Phase composition and microstructure of as-coated samples were analyzed by the x-ray diffraction, energy dispersive x-ray spectroscopy and scanning electron microscopy. And the porosity and average of micro-pore aperture of the surface on ceramic coatings were analyzed by general image software. Corrosion microstructure of as-coated samples was caught by a microscope digital camera. The long-term corrosion resistance of as-coated samples was tested in simulated body fluid for 30 days. The results showed that the milky white smooth ceramic coating formed on the Mg-Zn-Zr-Ca novel bio-magnesium alloy was a compound of MgO, Mg2SiO4 and MgSiO3, and its corrosion resistance was significantly improved compared with that of the magnesium substrate. In addition, when the MAO applied voltage were 450 V and 500 V and film-formation time were 9 min and 11 min, the surface micro-morphology and the corrosion resistance of as-coated samples were relatively improved. The results provided a theoretical foundation for the application of the Mg-Zn-Zr-Ca novel bio-magnesium alloy in biomedicine.

  5. Terahertz Spectroscopy of CaH (X^{2}Σ^{+}), MgH (X^{2}Σ^{+}), and ZnH (X^{2}Σ^{+}) : Extreme Hydride Synthesis

    NASA Astrophysics Data System (ADS)

    Bucchino, Matthew P.; Ziurys, Lucy M.

    2013-06-01

    Sub-millimeter spectra of CaH (X^{2}Σ^{+}), MgH (X^{2}Σ^{+}), and ZnH (X^{2}Σ^{+}) have been measured in the sub-mm{/}THz regime (500{-805} GHz) using direct{-absorption} methods. All species were produced by the reaction of metal vapor with H_{2} under DC discharge in a Broida-type oven. Because of efficient molecule production, spectra of ^{26}MgH, ^{66}ZnH, ^{68}ZnH and ^{70}ZnH could be recorded in their natural abundance as well, with high signal-to-noise. Additionally, the N = 0 {→} 1 and N = 1 {→} 2 transitions of ^{25}MgH and ^{67}ZnH were measured. Fermi contact, dipolar, and quadrupole constants for the ^{25}Mg and ^{67}Zn nuclei have been accurately determined for the first time in the gas phase, and are in good agreement with previous ESR studies. The hyperfine constants suggest a substantial amount of covalent character is present in metal hydrides.

  6. In vitro metal ion release and biocompatibility of amorphous Mg67Zn28Ca5 alloy with/without gelatin coating.

    PubMed

    Chan, W Y; Chian, K S; Tan, M J

    2013-12-01

    Amorphous zinc-rich Mg-Zn-Ca alloys have exhibited good tissue compatibility and low hydrogen evolution in vivo. However, suboptimal cell-surface interaction on magnesium alloy surface observed in vitro could lead to reduced integration with host tissue for regenerative purpose. This study aims to improve cell-surface interaction of amorphous Mg67Zn28Ca5 alloy by coating a gelatin layer by electrospinning. Coated/uncoated alloys were immersed and extracted for 3 days under different CO2. The immersion results showed that pH and metal ion release in the alloy extracts were affected by gelatin coating and CO2, suggesting their roles in alloy biocorrosion and a mechanism has been proposed for the alloy-CO2 system with/without coating. Cytotoxicity results are evident that gelatin-coated alloy with 2-day crosslinking not only exhibited no indirect cytotoxicity, but also supported attachment of L929 and MG63 cell lines around/on the alloy with high viability. Therefore, amorphous Mg67Zn28Ca5 alloy coated with gelatin by electrospinning technique provides a useful method to improve alloy biocompatibility.

  7. Biological and mechanical properties of an experimental glass-ionomer cement modified by partial replacement of CaO with MgO or ZnO.

    PubMed

    Kim, Dong-Ae; Abo-Mosallam, Hany; Lee, Hye-Young; Lee, Jung-Hwan; Kim, Hae-Won; Lee, Hae-Hyoung

    2015-01-01

    Some weaknesses of conventional glass ionomer cement (GIC) as dental materials, for instance the lack of bioactive potential and poor mechanical properties, remain unsolved.Objective The purpose of this study was to investigate the effects of the partial replacement of CaO with MgO or ZnO on the mechanical and biological properties of the experimental glass ionomer cements.Material and Methods Calcium fluoro-alumino-silicate glass was prepared for an experimental glass ionomer cement by melt quenching technique. The glass composition was modified by partial replacement (10 mol%) of CaO with MgO or ZnO. Net setting time, compressive and flexural properties, and in vitrorat dental pulp stem cells (rDPSCs) viability were examined for the prepared GICs and compared to a commercial GIC.Results The experimental GICs set more slowly than the commercial product, but their extended setting times are still within the maximum limit (8 min) specified in ISO 9917-1. Compressive strength of the experimental GIC was not increased by the partial substitution of CaO with either MgO or ZnO, but was comparable to the commercial control. For flexural properties, although there was no significance between the base and the modified glass, all prepared GICs marked a statistically higher flexural strength (p<0.05) and comparable modulus to control. The modified cements showed increased cell viability for rDPSCs.Conclusions The experimental GICs modified with MgO or ZnO can be considered bioactive dental materials.

  8. Biological and mechanical properties of an experimental glass-ionomer cement modified by partial replacement of CaO with MgO or ZnO

    PubMed Central

    Dong-Ae, KIM; Hany, ABO-MOSALLAM; Hye-Young, LEE; Jung-Hwan, LEE; Hae-Won, KIM; Hae-Hyoung, LEE

    2015-01-01

    Some weaknesses of conventional glass ionomer cement (GIC) as dental materials, for instance the lack of bioactive potential and poor mechanical properties, remain unsolved. Objective The purpose of this study was to investigate the effects of the partial replacement of CaO with MgO or ZnO on the mechanical and biological properties of the experimental glass ionomer cements. Material and Methods Calcium fluoro-alumino-silicate glass was prepared for an experimental glass ionomer cement by melt quenching technique. The glass composition was modified by partial replacement (10 mol%) of CaO with MgO or ZnO. Net setting time, compressive and flexural properties, and in vitro rat dental pulp stem cells (rDPSCs) viability were examined for the prepared GICs and compared to a commercial GIC. Results The experimental GICs set more slowly than the commercial product, but their extended setting times are still within the maximum limit (8 min) specified in ISO 9917-1. Compressive strength of the experimental GIC was not increased by the partial substitution of CaO with either MgO or ZnO, but was comparable to the commercial control. For flexural properties, although there was no significance between the base and the modified glass, all prepared GICs marked a statistically higher flexural strength (p<0.05) and comparable modulus to control. The modified cements showed increased cell viability for rDPSCs. Conclusions The experimental GICs modified with MgO or ZnO can be considered bioactive dental materials. PMID:26398508

  9. Estimated equilibrated dietary intakes for nine minerals (Na, K, Ca, Mg, P, Fe, Zn, Cu, and Mn) adjusted by mineral balance medians in young Japanese females.

    PubMed

    Nishimuta, Mamoru; Kodama, Naoko; Shimada, Mieko; Yoshitake, Yutaka; Matsuzaki, Nobue; Morikuni, Eiko

    2012-01-01

    The present study sought to determine estimated equilibrated dietary intakes (EEDIs) for nine essential minerals: sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn), using data from 17 human mineral balance studies conducted from 1986 to 2007 (subjects=178). Among these studies, two used male subjects, two subjected some or all subjects to sodium restriction, and one study utilized a low protein diet; these subjects were not included in the present analysis. Consequently, data from 13 studies of young female subjects (n=131) consuming a standard diet were selected. Balance distribution medians for six of the minerals (Na, K, Mg, Fe, Zn and Cu) were positive, so the data were adjusted to set the medians of the balances to zero. Medians for the other minerals (Ca, P and Mn) were close to zero and were not adjusted. Intake and balance for each mineral were divided by body weight (BW), lean body mass (LBM), and standard body weight (SBW), which was calculated using height and standard body mass index (BMI=22), and EEDIs were calculated as the intercept of a simple regression equation. When relationships between intake and balance of a mineral were not significant in the regression equation, a significant regression equation comparing intake and balance of another mineral was used to calculate the intercept. Significant simple regression equations were not obtained from any of the three parameters of Na or Zn, or for two of the parameters of P; thus, K, Fe and Ca balances were used to determine the intercepts for Na, Zn and P, respectively. EEDIs for the minerals were: Na (67.9, 89.0, 62.5), K (39.5, 53.5, 37.4), Ca (11.0, 14.4, 10.1), Mg (4.18, 5.51, 3.86), P (18.7, 24.6, 17.3) (mg/kg BW/d, mg/kg LBM/d, mg/kg SBW/d), Fe (180, 237, 165), Zn (181, 241, 166), [corrected] Cu (32.3, 42.6, 29.7), [corrected] Mn (55.1, 72.1, 50.7) (µg/kg BW/d, µg/kg LBM/d, µg/kg SBW/d), respectively. These values

  10. Ultrafiltration of skimmed goat milk increases its nutritional value by concentrating nonfat solids such as proteins, Ca, P, Mg, and Zn.

    PubMed

    Moreno-Montoro, Miriam; Olalla, Manuel; Giménez-Martínez, Rafael; Bergillos-Meca, Triana; Ruiz-López, María Dolores; Cabrera-Vique, Carmen; Artacho, Reyes; Navarro-Alarcón, Miguel

    2015-11-01

    Goat milk has been reported to possess good nutritional and health-promoting properties. Usually, it must be concentrated before fermented products can be obtained. The aim of this study was to compare physicochemical and nutritional variables among raw (RM), skimmed (SM), and ultrafiltration-concentrated skimmed (UFM) goat milk. The density, acidity, ash, protein, casein, whey protein, Ca, P, Mg, and Zn values were significantly higher in UFM than in RM or SM. Dry extract and fat levels were significantly higher in UFM than in SM, and Mg content was significantly higher in UFM than in RM. Ultrafiltration also increased the solubility of Ca and Mg, changing their distribution in the milk. The higher concentrations of minerals and proteins, especially caseins, increase the nutritional value of UFM, which may therefore be more appropriate for goat milk yogurt manufacturing in comparison to RM or SM.

  11. Microstructure and mechanical properties of spray-deposited Mg-12.55Al-3.33Zn-0.58Ca-1Nd alloy

    SciTech Connect

    Bai Pucun; Dong Taishang; Hou Xiaohu; Zhao Chunwang; Xing Yongming

    2010-07-15

    A Mg-Al-Zn-Ca-Nd magnesium alloy was prepared by spray forming technology, and the spray-deposited alloy was subsequently hot-extruded with a reduction rate of 16:1 at 623 K. The mechanical properties of the extruded alloy were investigated, and the result shows that the spray-formed Mg alloy offers superior tensile strength with poor ductility. The morphologies, fracture characteristic and chemical compositions of the extruded alloy were then explored by scanning electron microscopy with energy dispersive spectrometer. Furthermore, microstructure of the extruded alloy was examined by X-ray diffractometry and transmission electron microscopy. The results indicate that the microstructure of the spray-deposited magnesium alloy consists of {alpha}-Mg and Al{sub 2}Ca phases, and the Al{sub 2}Ca compound is distributed along the grain boundaries of the primary {alpha}-Mg. Moreover, twin substructure is found to exist in microstructure of the Al{sub 2}Ca phase, rare earth Nd in the Al{sub 2}Ca phase in the form of solid solution.

  12. [Mineral composition of different types of Canarian gofio; factors affecting the presence of Na, K, Mg, Ca, Mn, Fe, Cn and Zn].

    PubMed

    Caballero, J M; Tejera, R L; Caballero A, A; Rubio, C; González-Weller, D; Gutiérrez, A J; Hardisson, A

    2014-03-01

    The contents of Na, K, Mg, Ca, Mn, Fe, Cu and Zn were analyzed and evaluated in 181 samples of various types of gofio produced from different roasted cereal grains. Samples were analyzed by ICP-OES. Based on a daily gofio intake of 30 g/day for adults and 15 g/day for children, the daily intake of each metal, and its percentage contribution to the RDAs established for the Spanish population, were estimated. The metal with the highest concentration was K (2189 ± 766 mg/kg). The lowest concentration was observed for Cu in corn gofio samples (2.05 ± 0.36 mg/kg). With respect to daily intake, it is noteworthy that gofio contributes significantly to the recommended allowance of copper (53.77%-71.45% of the RDI), depending on the population group considered and on the type of gofio.

  13. Evaluation of sewage sludge, septic waste and sludge compost applications to corn and forage: Ca, Mg, S, Fe, Mn, Cu, Zn and B content of crops and soils.

    PubMed

    Warman, P R; Termeer, W C

    2005-06-01

    This is the second of two papers presenting the data from an experiment on the application of aerobically-digested sewage sludge (AES), anaerobic lagoon septic wastes (ANS), sewage sludge compost and fertilizer to soils for grass forage and feed corn production at two different sites in Nova Scotia. Crop yields, plant tissue and Mehlich-1 extractable soil nutrients were evaluated; 15 elements were analyzed in the plant tissue and 9 elements in the soil extracts. This paper describes the Ca, Mg, S, Fe, Mn, Cu, Zn and B content of the crops and the Mehlich-1 extractable content of the soils. The response to the amendments was not consistent at the two sites with the two different crops. We found that the septic sludge (ANS) produced the highest forage Fe, Cu and Zn levels and was equal to compost in elevating corn stover and forage S and the forage B content. The compost produced the highest forage Ca and corn Zn, the AES produced the highest corn Mn, and fertilizer produced the highest forage Mn. None of the amendments produced excessive levels of the above nutrients; rather, the amendments improved the feed quality of the forage and corn stover. Lastly, it was noted that the Mehlich-1 extract only had a significantly positive correlation with forage Cu content.

  14. Determination of Ca, Mg, Na, Cd, Cu, Fe, K, Li and Zn in acid mine and reference water samples by inductively coupled plasma atomic fluorescence spectrometry

    USGS Publications Warehouse

    Sanzolone, R.F.; Meier, A.L.

    1986-01-01

    An inductively coupled plasma atomic fluorescence spectrometric (ICP-AFS) method was used for the determination of nine elements in natural water. Reference and acid mine water samples were analysed by this method to demonstrate its usefulness for hydrogeochemical exploration. The elements were determined in two groups based on the compatibility of operating conditions and consideration of element abundance levels in natural water. Ca, Mg and Na were determined as a group using one set of instrumental conditions and a 1 + 99 dilution of the sample, and Cd, Cu, Fe, K, Li and Zn were determined using another set of conditions and the undiluted sample. The detection limits for the elements are as follows: Ca, 1.4; Mg, 1.7; Na, 2.0; Cd, 1.8; Cu, 6.2; Fe, 15.8; K, 3.5; Li, 0.3; and Zn, 1.2 ng m1-1. Each element has a linear range spanning about four orders of magnitude. The method has good precision and accuracy, as shown by statistics on replicate analyses and by the agreement between values obtained and those recommended for the reference water samples, and also those obtained by atomic absorption spectrometry for the acid mine water samples.

  15. Stress corrosion cracking and corrosion fatigue characterisation of MgZn1Ca0.3 (ZX10) in a simulated physiological environment.

    PubMed

    Jafari, Sajjad; Raman, R K Singh; Davies, Chris H J; Hofstetter, Joelle; Uggowitzer, Peter J; Löffler, Jörg F

    2017-01-01

    Magnesium (Mg) alloys have attracted great attention as potential materials for biodegradable implants. It is essential that an implant material possesses adequate resistance to cracking/fracture under the simultaneous actions of corrosion and mechanical stresses, i.e., stress corrosion cracking (SCC) and/or corrosion fatigue (CF). This study investigates the deformation behaviour of a newly developed high-strength low-alloy Mg alloy, MgZn1Ca0.3 (ZX10), processed at two different extrusion temperatures of 325 and 400°C (named E325 and E400, respectively), under slow strain tensile and cyclic tension-compression loadings in air and modified simulated body fluid (m-SBF). Extrusion resulted in a bimodal grain size distribution with recrystallised grain sizes of 1.2 μm ± 0.8 μm and 7 ± 5 μm for E325 and E400, respectively. E325 possessed superior tensile and fatigue properties to E400 when tested in air. This is mainly attributed to a grain-boundary strengthening mechanism. However, both E325 and E400 were found to be susceptible to SCC at a strain rate of 3.1×10(-7)s(-1) in m-SBF. Moreover, both E325 and E400 showed similar fatigue strength when tested in m-SBF. This is explained on the basis of crack initiation from localised corrosion following tests in m-SBF.

  16. Tululite, Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36: a new Ca zincate-aluminate from combustion metamorphic marbles, central Jordan

    NASA Astrophysics Data System (ADS)

    Khoury, Hani N.; Sokol, Ella V.; Kokh, Svetlana N.; Seryotkin, Yurii V.; Nigmatulina, Elena N.; Goryainov, Sergei V.; Belogub, Elena V.; Clark, Ian D.

    2016-02-01

    Tululite (Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36 (the hypothetical end-member formula Ca14{Fe3+O6}[SiO4][Zn5Al9]O26) (IMA2014-065) is a new natural Ca zincate-aluminate, identified in medium-temperature (800-850 °C) combustion metamorphic (CM) spurrite-fluorellestadite marbles from central Jordan. The type locality (Tulul Al Hammam area) is situated in the northern part of the Siwaqa complex, the largest area of the "Mottled Zone" Formation in the Dead Sea region. The marbles originated from bitumen-rich chalky marine sediments of the Maastrichtian-Paleogene Muwaqqar Chalk Marl Formation, which have low clay content (and, consequently, low Al) and high Zn, Cd, and U enrichments. The bulk CM rocks derived from the low-Al protolith have unusually high (Zn + Cd)/Al ratios ( 0.2) and, as a result, a mineralogy with negligibly small percentages of Ca aluminates having low Ca:Al molar ratios (minerals of mayenite supergroup, Ca:Al = 6:7) common to most of calcareous CM rocks in the Mottled Zone. Instead, the mineral assemblage of the Zn-rich marbles contains tululite, with high Ca:Al = 2.55 molar ratios and Zn substituting for a large portion of Al (Zn:Al = 1.1). Tululite occurs in thin clusters as irregular grains with indented outlines (20-100 μm in size), having typical open-work textures associated with rock-forming calcite, fluorellestadite, spurrite, and accessory Zn-rich periclase, lime-monteponite solid solutions, calcium uranates, and zincite. Marbles also bear brownmillerite, dorrite, fluormayenite, high-fluorine Ca aluminate, and lakargiite. Secondary phases are brucite, gel-like calcium silicate hydrates and calcium silicate aluminate hydrates, including Zn- and U-bearing and Cd-rich compounds, Si-bearing hydrated compounds after calcium uranates, and basic Cd chlorides. The empirical formula of the holotype tululite (a mean of 32 analyses) is (Ca13.29Cd0.75)Σ14.04(Al5.46Zn5.20Fe3+ 2.23Si0.95Mn3+ 1.01Mg0.78P0.41)Σ16.04O36. Tululite is cubic, space

  17. Improvement of the mechanical properties and corrosion resistance of biodegradable β-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy: the adding β-Ca3(PO4)2, hot extrusion and aging treatment.

    PubMed

    Yan, Yang; Kang, Yijun; Li, Ding; Yu, Kun; Xiao, Tao; Deng, Youwen; Dai, Han; Dai, Yilong; Xiong, Hanqing; Fang, Hongjie

    2017-05-01

    In this study, 10%β-Ca3(PO4)2/Mg-6%Zn (wt.%) composites with Mg-6%Zn alloy as control were prepared by powder metallurgy. After hot extrusion, the as-extruded composites were aged for 72h at 150°C. The effects of the adding β-Ca3(PO4)2, hot extrusion and aging treatment on their microstructure, mechanical properties and corrosion resistance were investigated. The XRD results identified α-Mg, MgZn phase and β-Ca3(PO4)2 phase in these composites. After hot extrusion, grains were significantly refined, and the larger-sized β-Ca3(PO4)2 particles and coarse MgZn phases were broken into linear-distributed β-Ca3(PO4)2 and MgZn phases along the extrusion direction. After aging treatment, the elements of Zn, Ca, P and O presented a more homogeneous distribution. The compressive strengths of the β-Ca3(PO4)2/Mg-Zn composites were approximately double those of natural bone, and their densities and elastic moduli matched those of natural bone. The immersion tests and electrochemical tests revealed that the adding β-Ca3(PO4)2, hot extrusion and aging treatment could promote the formation of protective corrosion product layer on the sample surface in Ringer's solution, which improved corrosion resistance of the β-Ca3(PO4)2/Mg-Zn composites. The XRD results indicated that the corrosion product layer contained Mg(OH)2, β-Ca3(PO4)2 and hydroxyapatite (HA). The cytotoxicity assessments showed the as-extruded β-Ca3(PO4)2/Mg-Zn composite aged for 72h was harmless to L-929 cells. These results suggested that the β-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy were promising to be used for bone tissue engineering.

  18. Synthesis of layered double hydroxides containing Mg2+, Zn2+, Ca2+ and Al3+ layer cations by co-precipitation methods-A review

    NASA Astrophysics Data System (ADS)

    Theiss, Frederick L.; Ayoko, Godwin A.; Frost, Ray L.

    2016-10-01

    Co-precipitation is a common method for the preparation of layered double hydroxides (LDHs) and related materials. This review article is aimed at providing newcomers to the field with some examples of the types of co-precipitation reactions that have been reported previously and to briefly investigate some of the properties of the products of these reactions. Due to the sheer volume of literature on the subject, the authors have had to limit this article to the synthesis of Mg/Al, Zn/Al and Ca/Al LDHs by co-precipitation and directly related methods. LDHs have been synthesised from various reagents including metal salts, oxides and hydroxides. Co-precipitation is also useful for the direct synthesis of LDHs with a wide range of interlayer anions and various bases have been successfully employed to prepare LDHs. Examples of other synthesis techniques including the urea method, hydrothermal synthesis and various mechanochemical methods that are undoubtedly related to co-precipitation have also been included in this review. The effect of post synthesis hydrothermal has also been summarised.

  19. MALDI time-of-flight mass spectrometry and thermogravimetric analysis of Mg(II), Ca(II), Cu(II), Zn(II) and Pt(II) adducts with monomethoxypolyethylene glycol 5000

    NASA Astrophysics Data System (ADS)

    Mwelase, S. R.; Bariyanga, J.

    2002-05-01

    We have prepared and isolated complexes of Mg(II), Ca(II), Cu(II), Zn(II) and Pt(II) with monomethoxypolyethylene glycol 5000 in a pH 7 buffer at 40 °C in order to study the interaction of this polymer carrier with the ions likely to be found in the human body. Their characterization was done by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, Fourier transform infrared, UV-Vis spectrophotometry, thermogravimetry and elemental analysis. The mass spectra allowed us to determine not only the molecular weights but also the nature of the complexes and the findings were in agreement with the elementary analysis data. The calcium ion was found not directly linked to polyethylene glycol but through water molecules. The overall results indicated strong bonding for Cu(II) and Zn(II) complexes and weak interactions for Mg(II), Ca(II) and Pt(II).

  20. Spontaneous polarization driven Mg concentration profile reconstruction in MgZnO/ZnO heterostructures

    SciTech Connect

    Imasaka, K.; Falson, J.; Kozuka, Y. Kawasaki, M.; Tsukazaki, A.

    2014-06-16

    Atomic reconstruction at the interface of MgZnO and ZnO in molecular beam epitaxy grown heterostructures is investigated. Using secondary ion mass spectroscopy, we experimentally find that Mg atomic reconstruction depends on the polarity of the interface; it is not observed in n-type interfaces (MgZnO on Zn-polar ZnO) owing to electron accumulation, while in p-type interfaces (ZnO on Zn-polar MgZnO), Mg drastically redistributes into the ZnO layer. Combined with self-consistent calculation of band profiles and carrier distributions, we reveal that the observed Mg reconstruction is not due to thermal diffusion but consequences in order to avoid hole accumulation. This tendency implies inherent significant asymmetry of energy scales of atomic and electronic reconstructions between n-type and p-type interfaces.

  1. High Resolution Structures of p-Aminobenzamidine- and Benzamidine- VIIa/Soluble Tissue Factor: Unpredicted Conformation of the 192-193 Peptide Bond and Mapping of Ca2+, Mg2+, Na+ an Zn2+ Sites in Facto VIIa

    SciTech Connect

    Bajaj,S.; Schmidt, A.; Agah, S.; Bajaj, M.; Padmanabhan, K.

    2006-01-01

    Factor VIIa (FVIIa) consists of a {gamma}-carboxyglutamic acid (Gla) domain, two epidermal growth factor-like domains, and a protease domain. FVIIa binds seven Ca{sup 2+} ions in the Gla, one in the EGF1, and one in the protease domain. However, blood contains both Ca{sup 2+} and Mg{sup 2+}, and the Ca{sup 2+} sites in FVIIa that could be specifically occupied by Mg{sup 2+} are unknown. Furthermore, FVIIa contains a Na{sup +} and two Zn{sup 2+} sites, but ligands for these cations are undefined. We obtained p-aminobenzamidine-VIIa/soluble tissue factor (sTF) crystals under conditions containing Ca{sup 2+}, Mg{sup 2+}, Na{sup +}, and Zn{sup 2+}. The crystal diffracted to 1.8{angstrom} resolution, and the final structure has an R-factor of 19.8%. In this structure, the Gla domain has four Ca{sup 2+} and three bound Mg{sup 2+}. The EGF1 domain contains one Ca{sup 2+} site, and the protease domain contains one Ca{sup 2+}, one Na{sup +}, and two Zn{sup 2+} sites. {sup 45}Ca{sup 2+} binding in the presence/absence of Mg{sup 2+} to FVIIa, Gla-domainless FVIIa, and prothrombin fragment 1 supports the crystal data. Furthermore, unlike in other serine proteases, the amide N of Gly{sup 193} in FVIIa points away from the oxyanion hole in this structure. Importantly, the oxyanion hole is also absent in the benzamidine-FVIIa/sTF structure at 1.87{angstrom} resolution. However, soaking benzamidine-FVIIa/sTF crystals with D-Phe-Pro-Arg-chloromethyl ketone results in benzamidine displacement, D-Phe-Pro-Arg incorporation, and oxyanion hole formation by a flip of the 192-193 peptide bond in FVIIa. Thus, it is the substrate and not the TF binding that induces oxyanion hole formation and functional active site geometry in FVIIa. Absence of oxyanion hole is unusual and has biologic implications for FVIIa macromolecular substrate specificity and catalysis.

  2. Chemical stability and dielectric properties of RO-La{sub 2}O{sub 3}-B{sub 2}O{sub 3} (R = Ca, Mg, Zn)-based ceramics

    SciTech Connect

    Jo, Yeon Hwa; Kang, Min Soo; Chung, Kyung Won; Cho, Yong Soo

    2008-02-05

    New lanthanum borate (La{sub 2}O{sub 3}-B{sub 2}O{sub 3}) glasses modified with divalent oxides, such as CaO, MgO and ZnO were investigated as potential low temperature dielectrics by understanding compositional dependence of dielectric properties and chemical leaching resistance. Firing behavior, such as densification and crystallization, depended strongly on the glass composition and is found to influence the resultant dielectric performance. Specifically, the dielectric composition of 20ZnO-20La{sub 2}O{sub 3}-60B{sub 2}O{sub 3} glass with 40 wt% Al{sub 2}O{sub 3} as a filler showed distinct enhancements of dielectric properties, i.e., k {approx} 8.3 and Q {approx} 1091 at the resonant frequency of 17.1 GHz, as a result of 850 deg. C firing. The result was believed related to earlier densification and unexpected evolvements of ZnAl{sub 2}O{sub 4} and La(BO{sub 2}){sub 3} phases during firing. The Mg-containing glass sample was most stable in strong acid solutions and did not show any significant changes in microstructure even after 300 min exposure. The Ca-containing glass sample was not regarded as a promising candidate for low temperature dielectrics from the observed low quality factor and weak chemical durability.

  3. Effects of the Oral Administration of K2Cr2O7 and Na2SeO3 on Ca, Mg, Mn, Fe, Cu, and Zn Contents in the Heart, Liver, Spleen, and Kidney of Chickens.

    PubMed

    Chen, Peng; Zhu, Yiran; Wan, Huiyu; Wang, Yang; Hao, Pan; Cheng, Ziqiang; Liu, Yongxia; Liu, Jianzhu

    2017-03-28

    This study aimed to investigate the effects of selenium on the ion profiles in the heart, liver, spleen, and kidney through the oral administration of hexavalent chromium. Approximately 22.14 mg/kg b.w. K2Cr2O7 was added to water to establish a chronic poisoning model. Different selenium levels (0.00, 0.31, 0.63, 1.25, 2.50, and 5.00 mg Na2SeO3/kg b.w.) around the safe dose were administered to the experimental group model. Ca, Mg, Mn, Fe, Cu, and Zn were detected in the organs through flame atomic absorption spectrometry after these organs were exposed to K2Cr2O7 and Na2SeO3 for 14, 28, and 42 days. Results showed that these elements exhibited various changes. Ca contents declined in the heart, liver, and spleen. Ca contents also decreased on the 28th day and increased on the 42nd day in the kidney. Mn contents declined in the heart and spleen but increased in the kidney. Mn contents also decreased on the 28th day and increased on the 42nd day in the liver. Cu contents declined in the heart and spleen. Cu contents increased on the 28th day and decreased on the 42nd day in the liver and kidney. Zn contents declined in the heart and spleen. Zn contents increased on the 28th day and decreased on the 42nd day in the liver and kidney. Fe contents decreased in the heart and liver. Fe contents increased on the 28th day and decreased on the 42nd day in the spleen and kidney. Mg contents did not significantly change in these organs. Appropriate selenium contents enhanced Mn and Zn contents, which were declined by chromium. Conversely, appropriate selenium contents reduced Ca, Fe, and Cu contents, which were increased by chromium. In conclusion, the exposure of chickens to K2Cr2O7 induced changes in different trace elements, and Na2SeO3 supplementation could alleviate this condition.

  4. Diffusion of Ca and Mg in Calcite

    SciTech Connect

    Cygan, R.T.; Fisler, D.K.

    1999-02-10

    The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

  5. Mg/Ca of Continental Ostracode Shells

    NASA Astrophysics Data System (ADS)

    Ito, E.; Forester, R. M.; Marco-Barba, J.; Mezquita, F.

    2007-12-01

    Marine ionic chemistry is thought to remain constant. This, together with the belief that marine calcifiers partition Mg/Ca in a systematic manner as functions of temperature (and Mg/Ca) of water forms the basis of the Mg/Ca thermometer. In continental settings both of these assumptions are usually not true. Continental waters contain a wide variety of solutes in absolute and relative ion concentrations. Hence, waters with identical Mg/Ca may have very different concentrations of Mg and Ca and very different anions. Here we use two examples to focus on the effects of ion chemistry on Mg/Ca partitioning in continental ostracode shells and we ignore the complexities of solute evolution, which can change Mg/Ca over timescales of minutes to millennia. Palacios-Fest and Dettman (2001) conducted a monthly study of ,Cypridopsis vidua at El Yeso Lake in Sonora, Mexico. They established a relation between temperature and average shell Mg/Ca using regression analyses on averaged data. When their Mg/Ca-temperature relation is applied to monthly ,C. vidua data from Page Pond near Cleveland, Ohio, water temperatures of -8 to -1°C are obtained. The observed Mg/Ca ranges for El Yeso Lake (0.31 to 0.46) and Page Pond (0.33 to 0.46) are similar, as are their specific conductivities (700 to 850μS for El Yeso Lake; 400 to 600μS for Page Pond). However, [Ca] is 140-260 mg/L for El Yeso, but only 70-90 mg/L for Page Pond. Page Pond data, in fact, shows a good temperature shell Mg/Ca relation for .C. vidua, but the relation is different from that at El Yeso. Hence, shell Mg/Ca is a multi-valued, family of curves function of temperature and Mg/Ca of water that depends on the [Mg] and [Ca] values in water and perhaps other factors. Our second example comes from sites near Valencia, Spain and involves shell data for ,Cyprideis torosa, an estuarine ostracode that is tolerant of a wide range of salinity and can live in continental waters as long as the carbonate alkalinity to Ca ratio is

  6. An electrochemical study of Ni/2+/, Co/2+/, and Zn/2+/ ions in melts of composition CaMgSi2O6

    NASA Technical Reports Server (NTRS)

    Semkow, K. W.; Haskin, L. A.; Lindstrom, D. J.; Rizzo, R. A.

    1982-01-01

    Results are reported for a study of the behavior of Ni(2+), Co(2+), and Zn(2+) in molten diopside, determined by cyclic voltametry, as a first step in adapting electrochemical methods for use in experimental geochemistry. The techniques used are described, the theory is briefly discussed, and it is demonstrated that Ni(2+), Co(2+), and Zn(2+) can be reduced, then reoxidized in an uncomplicated case of reversible charge transfer at the Pt electrode. This implies that the neutral metal atoms remain undissolved in the melt. The kinetics of the reduction process, the effects of concentration, the standard reduction potentials, and the diffusion coefficients are discussed in detail. The observations are consistent with the mechanism of Ni(2+) diffusion by transport from site to site. As the proportion of SiO2 in the melt increases, a higher activation energy is required for Ni(2+) to move, and the rate of diffusion is lowered.

  7. Structural relationships among MgZn2 and Mg4Zn7 phases and transition structures in Mg-Zn-Y alloys

    NASA Astrophysics Data System (ADS)

    Rosalie, Julian M.; Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji

    2010-08-01

    Isothermal ageing of plastically deformed Mg-Zn-Y alloys resulted in precipitation along ? twin boundaries. The bulky precipitates so formed had structures similar to those recently reported for the rod-like ? precipitates, but afforded a more detailed study by high-resolution TEM due to their larger size. The core of the precipitates often had the structure of the monoclinic Mg4Zn7 phase, and had the orientation ? ; ? with either the matrix or the twin. On this Mg4Zn7 phase, the hexagonal MgZn2 phase grew in two orientations, both with ? . One of these orientations formed a known orientation relationship ? ; ? with the matrix. The part of the precipitate with the MgZn2 structure was usually in direct contact with the twin boundary. Both the Mg4Zn7 and MgZn2 phases have layered structures that can be described with similar building blocks of icosahedrally coordinated atoms. The atomic positions of zinc atoms comprise the vertices of these icosahedra and form 'thick' rhombic tiles. The orientations of these rhombuses remain unchanged across the interfaces between the two phases. Near the interface with MgZn2, transition structures formed in the Mg4Zn7 phase, with the Zn:Mg atom ratio between those of the Mg4Zn7 and MgZn2 phases. In these transition structures, the unit cell of the Mg4Zn7 phase is extended along [100] or [001] by half a unit cell length by continuation of the rhombic tiling. Structures of these extended unit cells are proposed.

  8. Electrochemical formation of Mg-Li-Ca alloys by codeposition of Mg, Li and Ca from LiCl-KCl-MgCl2-CaCl2 melts.

    PubMed

    Yan, Yong De; Zhang, Mi Lin; Xue, Yun; Han, Wei; Cao, Dian Xue; Jing, Xiao Yan; He, Li Yi; Yuan, Yi

    2009-08-07

    This work presents electrochemical formation of Mg-Li-Ca alloys via codeposition of Mg, Li and Ca on a molybdenum electrode in KCl-LiCl-MgCl(2)-CaCl(2) melts at 943 K. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of calcium on pre-deposited magnesium leads to the formation of a liquid Mg-Ca alloy, and the succeeding underpotential deposition of lithium on pre-deposited Mg-Ca alloy leads to the formation of a liquid Mg-Li-Ca solution. Chronopotentiometric measurements indicated that the codepositon of Mg, Li and Ca occurs at current densities more negative than -0.31 A cm(-2) in LiCl-KCl-MgCl(2) (5 wt%) melts containing 1 wt% CaCl(2). Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Ca is -2.200 V, and the codeposition of Mg, Li and Ca is formed when the applied potentials are more negative than -2.200 V. X-Ray diffraction (XRD) indicated that Mg-Li-Ca alloys with different phases were formed via galvanostatic electrolysis. The microstructures of typical alpha and beta phases of Mg-Li-Ca alloys were characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the element Ca mainly distributes along grain boundary in Mg-Li-Ca alloys. The results of inductively coupled plasma analysis determined that the chemical compositions of Mg-Li-Ca alloys correspond with the phase structures of XRD patterns, and the lithium and calcium contents of Mg-Li-Ca alloys depend on the concentrations of MgCl(2) and CaCl(2).

  9. Structural and optical properties of ZnMgO nanostructures formed by Mg in-diffused ZnO nanowires

    SciTech Connect

    Pan, C.-J.; Hsu, H.-C.; Cheng, H.-M.; Wu, C.-Y.; Hsieh, W.-F.

    2007-04-15

    ZnMgO nanostructures with wurtzite phase were prepared by thermal diffusion of Mg into the ZnO nanowires. As ZnO light-emitting devices have been operated by using ZnMgO layers as energy barrier layers to confine the carriers, it is essential to realize the characterization of ZnMgO particularly. In this work, the Mg content in Zn{sub 1} {sub -x} Mg {sub x} O alloy determined by X-ray diffraction (XRD) and photoluminescence (PL) shows a good coincidence. The variation of lattice constant and the blueshift of near-band-edge emission indicate that Zn{sup 2+} ions are successfully substituted by Mg{sup 2+} ions in the ZnO lattice. In Raman-scattering studies, the change of E {sub 2}(high) phonon line shape in ZnO:Mg nanostructures reveals the microscopic substitutional disorder. In addition to the host phonons of ZnO, two additional bands around 383 and 510 cm{sup -1} are presumably attributed to the Mg-related vibrational modes. - Graphical abstract: We reported the synthesis of the ZnMgO nanostructures prepared by a simple vapor transport method. Magnesium-related anomalous modes are observed by Raman spectra for the first time in ZnMgO system.

  10. ZnO/(ZnMg)O single quantum wells with high Mg content graded barriers

    SciTech Connect

    Laumer, Bernhard; Schuster, Fabian; Wassner, Thomas A.; Stutzmann, Martin; Rohnke, Marcus; Schoermann, Joerg; Eickhoff, Martin

    2012-06-01

    ZnO/Zn{sub 1-x}Mg{sub x}O single quantum wells (SQWs) were grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Compositional grading allows the application of optimized growth conditions for the fabrication of Zn{sub 1-x}Mg{sub x}O barriers with high crystalline quality and a maximum Mg content of x = 0.23. High resolution x-ray diffraction reveals partial relaxation of the graded barriers. Due to exciton localization, the SQW emission is found to consist of contributions from donor-bound and free excitons. While for narrow SQWs with well width d{sub W}{<=}2.5nm, the observed increase of the exciton binding energy is caused by quantum confinement, the drop of the photoluminescence emission below the ZnO bulk value found for wide SQWs is attributed to the quantum-confined Stark effect. For a Mg content of x = 0.23, a built-in electric field of 630 kV/cm is extracted, giving rise to a decrease of the exciton binding energy and rapid thermal quenching of the SQW emission characterized by an activation energy of (24 {+-} 4) meV for d{sub W} = 8.3 nm.

  11. Diffusion Couple Investigation of the Mg-Zn System

    SciTech Connect

    Brennan, Sarah; Bermudez, Katrina; Sohn, Yong Ho; Kulkarni, Nagraj S

    2012-01-01

    Phase layer growth and interdiffusion in the binary Mg-Zn system was investigated utilizing solid-to-solid diffusion couples annealed at 295 , 315 and 325 C for 21, 7 and 5 days, respectively. The diffusion microstructure was examined by scanning electron microscopy and concentration profiles were determined using X-ray energy dispersive spectroscopy and electron microprobe analysis. The Mg solid solution, Mg2Zn11, MgZn2 and Mg2Zn3 in all three couples were observed in addition to the high temperature, Mg51Zn20 phase at 325 C. The MgZn2 phase was observed to grow the thickest layer, followed by the Mg2Zn3 and the Mg2Zn11 phases. Activation energies for the parabolic growth were calculated to be 105 kJ/mol and 207 kJ/mol for the Mg2Zn3 and MgZn2, respectively. Relevant interdiffusion coefficients were calculated for the phases present by analyses of concentration profiles. This study was sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program (DE-AC05-00OR22725).

  12. Effect of ambient Mg/Ca ratio on Mg fractionation in calcareous marine invertebrates: A record of the oceanic Mg/Ca ratio over the Phanerozoic

    NASA Astrophysics Data System (ADS)

    Ries, Justin B.

    2004-11-01

    The Mg/Ca ratio of seawater has changed significantly over the Phanerozoic, primarily as a function of the rate of ocean-crust production. Echinoids, crabs, shrimps, and calcareous serpulid worms grown in artificial seawaters encompassing the range of Mg/Ca ratios that existed throughout the Phanerozoic exhibit a direct nonlinear relationship between skeletal and ambient Mg/Ca. Specimens grown in seawater with the lowest Mg/Ca (˜1) changed their mineralogy to low-Mg calcite (<4 mol% MgCO3), suggesting that these high-Mg calcareous organisms would have produced low-Mg calcite in the Cretaceous, when oceanic Mg/Ca was lowest (˜1). These results support the empirical evidence that the skeletal chemistry of calcareous organisms has varied significantly over the Phanerozoic as a function of the Mg/Ca of seawater, and that the Mg/Ca of unaltered fossils of such organisms may be a record of oceanic Mg/Ca throughout the Phanerozoic. Mg fractionation algorithms, which relate skeletal Mg/Ca, seawater Mg/Ca, and temperature, were derived from these and other experiments. They can be used to estimate paleoceanic Mg/ Ca ratios and temperatures from fossil skeletal Mg/Ca of the organisms evaluated. Pale oceanic Mg/Ca ratios, recalculated by using the echinoderm Mg fractionation algorithm from published fossil echinoid Mg/Ca, crinoid Mg/Ca, and paleotemperature data, are consistent with other estimates and models of oceanic Mg/Ca over the Phanerozoic.

  13. Mg-Ca Alloys Produced by Reduction of CaO: Understanding of ECO-Mg Alloy Production

    NASA Astrophysics Data System (ADS)

    Jung, In-Ho; Lee, Jin Kyu; Kim, Shae K.

    2017-04-01

    There have been long debates about the environment conscious (ECO) Mg technology which utilizes CaO to produce Ca-containing Mg alloys. Two key process technologies of the ECO-Mg process are the chemical reduction of CaO by liquid Mg and the maintenance of melt cleanliness during the alloying of Ca. Thermodynamic calculations using FactSage software were performed to explain these two key issues. In addition, an experimental study was performed to compare the melt cleanliness of the Ca-containing Mg alloys produced by the conventional route with metallic Ca and the ECO-Mg route with CaO.

  14. Mg-Ca Alloys Produced by Reduction of CaO: Understanding of ECO-Mg Alloy Production

    NASA Astrophysics Data System (ADS)

    Jung, In-Ho; Lee, Jin Kyu; Kim, Shae K.

    2016-12-01

    There have been long debates about the environment conscious (ECO) Mg technology which utilizes CaO to produce Ca-containing Mg alloys. Two key process technologies of the ECO-Mg process are the chemical reduction of CaO by liquid Mg and the maintenance of melt cleanliness during the alloying of Ca. Thermodynamic calculations using FactSage software were performed to explain these two key issues. In addition, an experimental study was performed to compare the melt cleanliness of the Ca-containing Mg alloys produced by the conventional route with metallic Ca and the ECO-Mg route with CaO.

  15. Study on the compounds of Mg12La and (Mg,Zn)11.5La

    NASA Astrophysics Data System (ADS)

    Huang, M. L.; Si, Z. Y.; Li, H. X.

    2017-01-01

    The composition, crystal structure and phase relationship of the main intermetallics of the Mg-Zn-La system on the low La side have been studied. The results show that there exists a binary solid solutions of Mg12La as (Mg,Zn)La12 and a linear ternary compound (Mg,Zn)11.5La. Though the composition formula of the two phases are similar, but the composition of Zn in them are different. The maximum Zn content of (Mg,Zn)12La is 7.2at% and the minimum Zn content of (Mg,Zn)11.5La is 8.5at%. What’s more, the crystal structures of (Mg,Zn)12La and (Mg,Zn)11.5La phase are also totally different. (Mg,Zn)La12 have the body centered tetragonal lattice structure, but the crystal structure of (Mg,Zn)11.5La is C-centered orthorhombic lattice structure.

  16. Mixture designs to assess composition-structure-property relationships in SiO₂-CaO-ZnO-La₂O₃-TiO₂-MgO-SrO-Na₂O glasses: potential materials for embolization.

    PubMed

    Kehoe, Sharon; Langman, Maxine; Werner-Zwanziger, Ulli; Abraham, Robert J; Boyd, Daniel

    2013-09-01

    Embolization with micron-sized particulates is widely applied to treat uterine fibroids. The objective of this work was to develop mixture designs to predict materials composition-structure-property relationships for the SiO₂-CaO-ZnO-La₂O₃-TiO₂-MgO-SrO-Na₂O glass system and compare its fundamental materials properties (density and cytocompatibility), against a state-of-the-art embolic agent (contour polyvinyl alcohol) to assess the potential of these materials for embolization therapies. The glass structures were evaluated using ²⁹Si MAS NMR to identify chemical shift and line width; the particulate densities were determined using helium pycnometry and the cell viabilities were assessed via MTT assay. ²⁹Si MAS NMR results indicated peak maxima for each glass in the range of -82.3 ppm to -89.9 ppm; associated with Q² to Q³ units in silicate glasses. All experimental embolic compositions showed enhanced in vitro compatibility in comparison to Contour PVA with the exceptions of ORP9 and ORP11 (containing no TiO₂). In this study, optimal compositions for cell viability were obtained for the following compositional ranges: 0.095-0.188 mole fraction ZnO; 0.068-0.159 mole fraction La₂O₃; 0.545-0.562 mole fraction SiO₂ and 0.042-0.050 mole fraction TiO₂. To ensure ease of producibility in obtaining good melts, a maximum loading of 0.068 mole fraction La₂O₃ is required. This is confirmed by the desirability approach, for which the only experimental composition (ORP5) of the materials evaluated was presented as an optimum composition; combining high cell viability with ease of production (0.188 mole fraction ZnO; 0.068 mole fraction La₂O₃; 0.562 mole fraction SiO₂ and 0.042 mole fraction TiO₂).

  17. Ab initio simulation of elastic and mechanical properties of Zn- and Mg-doped hydroxyapatite (HAP).

    PubMed

    Aryal, Sitaram; Matsunaga, Katsuyuki; Ching, Wai-Yim

    2015-07-01

    Hydroxyapatite (HAP) is an important bioceramic which constitutes the mineral components of bones and hard tissues in mammals. It is bioactive and used as bioceramic coatings for metallic implants and bone fillers. HAP readily absorbs a large amount of impurities. Knowledge on the elastic and mechanical properties of impurity-doped HAP is a subject of great importance to its potential for biomedical applications. Zn and Mg are the most common divalent cations HAP absorbs. Using density function theory based ab initio methods, we have carried out a large number of ab initio calculations to obtain the bulk elastic and mechanical properties of HAP with Zn or Mg doped in different concentration at the Ca1 and Ca2 sites using large 352-atom supercells. Detailed information on their dependece on the concetraion of the substitued impurity is obtained. Our results show that Mg enhances overall elastic and bulk mechanical properties whereas Zn tends to degrade except at low concentrations. At a higher concentration, the mechanical properties of Zn and Mg doped HAP also depend significantly on impurity distribution between the Ca1 and Ca2 sites. There is a strong evidence that Zn prefers Ca2 site for substituion whereas Mg has no such preference. These results imply that proper control of dopant concentration and their site preference must carefully considered in using doped HAP for specific biomedical applications.

  18. A DFT study on the complex formation between desferrithiocin and metal ions (Mg(2+), Al(3+), Ca(2+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+)).

    PubMed

    Kaviani, Sadegh; Izadyar, Mohammad; Housaindokht, Mohammad Reza

    2017-04-01

    In recent years, Metal-chelating compounds, namely siderphores have been considered very much because of their crucial role in various fields of the environmental researches. Their importance lies in the fact that they are able to be bonded to a variety of metals in addition to iron. A theoretical study on the structures of desferrithiocin siderphore coordinated to Mg(2+), Al(3+), Ca(2+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+) and Zn(2+) metal ions was carried out, using the CAM-B3LYP/6-31G(d) level of the theory in the water. In order to understand the factors which control the stability, reactivity and the strength of toxic metals excretion as well as microbial uptake of the metal-siderphore complexes, we examined the stability and binding energies of the desferrithiocin and various metal ions with different spin states. The binding affinity of desferrithiocin to Fe(3+) (log β2=23.88) showed that the desferrithiocin can scavenge the excess iron(III) from the labile sources. Also, the binding energy values were well described by addition of the dispersion-corrected D3 functional. Because of the importance of the charge transfer in the complex formation, donor-acceptor interaction energies were evaluated. Based on this analysis, an increase in the effective nuclear charge increases E(2) values. Vibrational analysis showed that the critical bonds (CO stretching and CH bending) are in the range of 1300-1800cm(-1). Finally, some probable correlations between the complexation behavior and quantum chemistry descriptors have been analyzed.

  19. Transport characteristics of a ZnMgO/ZnO hetero junction and the effect of temperature and Mg content

    NASA Astrophysics Data System (ADS)

    Uslu, Salih; Yarar, Zeki

    2017-02-01

    The Ensemble Monte Carlo method is used to calculate the transport characteristics of two dimensional electron gas (2DEG) at a ZnMgO/ZnO hetero structure. The spontaneous and piezoelectric polarizations are considered and there is no intentional doping in either material. Numerical Schrödinger and Poisson equations are solved self consistently to obtain the scattering rates of various scattering mechanisms. The density of carriers, each energy sub bands, potential profile and corresponding wave functions are obtained from the self consistent calculations. The self consistent sub band wave functions of acoustic and optic phonon scattering and interface roughness scattering are used in Monte Carlo method to obtain transport characteristics at ZnMgO/ZnO junction. Two dimensional electron gas confined to ZnMgO/ZnO hetero structure is studied and the effect of temperature and Mg content are investigated.

  20. Selective antibacterial effects of mixed ZnMgO nanoparticles

    NASA Astrophysics Data System (ADS)

    Vidic, Jasmina; Stankic, Slavica; Haque, Francia; Ciric, Danica; Le Goffic, Ronan; Vidy, Aurore; Jupille, Jacques; Delmas, Bernard

    2013-05-01

    Antibiotic resistance has impelled the research for new agents that can inhibit bacterial growth without showing cytotoxic effects on humans and other species. We describe the synthesis and physicochemical characterization of nanostructured ZnMgO whose antibacterial activity was compared to its pure nano-ZnO and nano-MgO counterparts. Among the three oxides, ZnO nanocrystals—with the length of tetrapod legs about 100 nm and the diameter about 10 nm—were found to be the most effective antibacterial agents since both Gram-positive ( B. subtilis) and Gram-negative ( E. coli) bacteria were completely eradicated at concentration of 1 mg/mL. MgO nanocubes (the mean cube size 50 nm) only partially inhibited bacterial growth, whereas ZnMgO nanoparticles (sizes corresponding to pure particles) revealed high specific antibacterial activity to Gram-positive bacteria at this concentration. Transmission electron microscopy analysis showed that B. subtilis cells were damaged after contact with nano-ZnMgO, causing cell contents to leak out. Our preliminary toxicological study pointed out that nano-ZnO is toxic when applied to human HeLa cells, while nano-MgO and the mixed oxide did not induce any cell damage. Overall, our results suggested that nanostructured ZnMgO, may reconcile efficient antibacterial efficiency while being a safe new therapeutic for bacterial infections.

  1. Distribution of calcium (Ca) and magnesium (Mg) in the leaves of Brassica rapa under varying exogenous Ca and Mg supply

    PubMed Central

    Rios, Juan Jose; Ó Lochlainn, Seosamh; Devonshire, Jean; Graham, Neil S.; Hammond, John P.; King, Graham J.; White, Philip J.; Kurup, Smita; Broadley, Martin R.

    2012-01-01

    Background and Aims Leafy vegetable Brassica crops are an important source of dietary calcium (Ca) and magnesium (Mg) and represent potential targets for increasing leaf Ca and Mg concentrations through agronomy or breeding. Although the internal distribution of Ca and Mg within leaves affects the accumulation of these elements, such data are not available for Brassica. The aim of this study was to characterize the internal distribution of Ca and Mg in the leaves of a vegetable Brassica and to determine the effects of altered exogenous Ca and Mg supply on this distribution. Methods Brassica rapa ssp. trilocularis ‘R-o-18’ was grown at four different Ca:Mg treatments for 21 d in a controlled environment. Concentrations of Ca and Mg were determined in fully expanded leaves using inductively coupled plasma-mass spectrometry (ICP-MS). Internal distributions of Ca and Mg were determined in transverse leaf sections at the base and apex of leaves using energy-dispersive X-ray spectroscopy (EDS) with cryo-scanning electron microscopy (cryo-SEM). Key Results Leaf Ca and Mg concentrations were greatest in palisade and spongy mesophyll cells, respectively, although this was dependent on exogenous supply. Calcium accumulation in palisade mesophyll cells was enhanced slightly under high Mg supply; in contrast, Mg accumulation in spongy mesophyll cells was not affected by Ca supply. Conclusions The results are consistent with Arabidopsis thaliana and other Brassicaceae, providing phenotypic evidence that conserved mechanisms regulate leaf Ca and Mg distribution at a cellular scale. The future study of Arabidopsis gene orthologues in mutants of this reference B. rapa genotype will improve our understanding of Ca and Mg homeostasis in plants and may provide a model-to-crop translation pathway for targeted breeding. PMID:22362665

  2. Thermal Parameters and Microstructural Development in Directionally Solidified Zn-Rich Zn-Mg Alloys

    NASA Astrophysics Data System (ADS)

    Vida, Talita A.; Freitas, Emmanuelle S.; Brito, Crystopher; Cheung, Noé; Arenas, Maria A.; Conde, Ana; De Damborenea, Juan; Garcia, Amauri

    2016-06-01

    Transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn11Mg2 and Zn-Zn2Mg). For 0.3 wt-pct Mg and 0.5 wt-pct Mg alloys, the Zn-rich matrix is shown to be characterized by high-cooling rates plate-like cells (cooling rates >9.5 and 24 K/s, respectively), followed by a granular-dendritic morphological transition for lower cooling rates. In contrast, a directionally solidified Zn1.2 wt-pct Mg alloy casting is shown to have the Zn-rich matrix formed only by dendritic equiaxed grains. Experimental growth laws are proposed relating the plate-like cellular interphase, the secondary dendritic arm spacing, and the eutectic interphase spacings to solidification thermal parameters, i.e., cooling rate and growth rate. The experimental law for the growth of secondary dendritic spacings under unsteady-state solidifications is also shown to encompass results of hypoeutectic Zn-Mg alloys subjected to steady-state Bridgman growth.

  3. ZnCdMgSe-Based Semiconductors for Intersubband Devices

    SciTech Connect

    Tamargo, Maria C.

    2008-11-13

    This paper presents a review of recent results on the application of ZnCdMgSe-based wide bandgap II-VI compounds to intersubband devices such as quantum cascade lasers and quantum well infrared photodetectors operating in the mid-infrared region. The conduction band offset of ZnCdSe/ZnCdMgSe quantum well structures was determined from contactless electroreflectance measurements to be as high as 1.12 eV. FT-IR was used to measure intersubband absorption in multi-quantum well structures in the mid-IR range. Electroluminescence at 4.8 {mu}m was observed from a quantum cascade emitter structure made from these materials. Preliminary results are also presented on self assembled quantum dots of CdSe on ZnCdMgSe, and novel quantum well structures with metastable binary MgSe barriers.

  4. Distribution of P, K, Ca, Mg, Cd, Cu, Fe, Mn, Pb and Zn in wood and bark age classes of willows and poplars used for phytoextraction on soils contaminated by risk elements.

    PubMed

    Zárubová, Pavla; Hejcman, Michal; Vondráčková, Stanislava; Mrnka, Libor; Száková, Jiřina; Tlustoš, Pavel

    2015-12-01

    Fast-growing clones of Salix and Populus have been studied for remediation of soils contaminated by risk elements (RE) using short-rotation coppice plantations. Our aim was to assess biomass yield and distributions of elements in wood and bark of highly productive willow (S1--[Salix schwerinii × Salix viminalis] × S. viminalis, S2--Salix × smithiana clone S-218) and poplar (P1--Populus maximowiczii × Populus nigra, P2--P. nigra) clones with respect to aging. The field experiment was established in April 2008 on moderately Cd-, Pb- and Zn- contaminated soil. Shoots were harvested after four seasons (February 2012) and separated into annual classes of wood and bark. All tested clones grew on contaminated soils, with highest biomass production and lowest mortality exhibited by P1 and S2. Concentrations of elements, with exception of Ca and Pb, decreased with age and were higher in bark than in wood. The Salix clones were characterised by higher removal of Cd, Mn and Zn compared to the Populus clones. Despite generally higher RE content in young shoots, partly due to lower wood/bark ratios and higher RE concentrations in bark, the overall removal of RE was higher in older wood classes due to higher biomass yield. Thus, longer rotations seem to be more effective when phytoextraction strategy is considered. Of the four selected clones, S1 exhibited the best removal of Cd and Zn and is a good candidate for phytoextraction.

  5. Application of calcite Mg partitioning functions to the reconstruction of paleocean Mg/Ca

    NASA Astrophysics Data System (ADS)

    Hasiuk, Franciszek J.; Lohmann, Kyger C.

    2010-12-01

    Calcite Mg/Ca is usually assumed to vary linearly with solution Mg/Ca, that a constant partition coefficient describes the relationship between these two ratios. Numerous published empirical datasets suggests that this relationship is better described by a power function. We provide a compilation of these literature data for biotic and abiotic calcite in the form of Calcite Mg/Ca = F(Solution Mg/Ca) H, where F and H are empirically determined fitting parameters describing the slope and deviation from linearity, respectively, of the function. This is equivalent to Freundlich sorption behavior controlling Mg incorporation in calcite. Using a power function, instead of a partition coefficient, lowers Phanerozoic seawater Mg/Ca estimates based on echinoderm skeletal material by, on average, 0.5 mol/mol from previous estimates. These functions can also be used to model the primary skeletal calcite Mg/Ca of numerous calcite phases through geologic time. Such modeling suggests that the Mg/Ca of all calcite precipitated from seawater has varied through the Phanerozoic in response to changing seawater Mg/Ca and that the overall range in Mg/Ca measured among various calcite phases would be greatest when seawater Mg/Ca was also high (e.g., "aragonite seas") and lowest when seawater Mg/Ca was low (e.g., "calcite seas"). It follows that, during times of "calcite seas" when the seawater Mg/Ca is presumed to have been lower, deposition of calcite with low Mg contents would have resulted in a depressed drive for diagenetic stabilization of shelfal carbonate and, in turn, lead to greater preservation of crystal and skeletal microfabrics and primary chemistries in biotic and abiotic calcites.

  6. [Determination of Mg and Zn contents of Naruto "wakame" (Undaria pinnatifida)].

    PubMed

    Ito, S; Miyoshi, T

    1990-08-01

    The contents of Mg and Zn in the sea-weed "wakame" were determined and compared at different growth stages, in different parts, for different root cultivation intervals, and in processed foods. The results obtained were as follows: 1. Mg (2.09-2.60 g/100 g) and Zn (8.00-10.76 mg/100 g) contents were independent of growth stage with the exception of Zn (29.00-35.78 mg/100 g) in the natural young "wakame". 2. The mineral contents of leaves, stipes, fruiting bodies and rhizoids of "wakame" at different growth stages were determined. The contents of Mg (1.00-2.36 g/100 g) and Zn (3.93-12.01 mg/100 g) were richer in leaves and stipes than in fruiting bodies and rhizoids. 3. Densely cultured "wakame" showed higher contents of Zn (6.73 mg/100 g) than thinly cultured plants (5.99 mg/100 g), and Mg content was not affected by changes in environmental conditions. 4. The Mg/Ca ratios reached a maximum in the stipe (3.3) and at fruiting bodies (2.9) in the middle stage, and in the base of the stipe of the mature plant (3.5). 5. Contents of the minerals in processed foods were determined. "Suboshi" was rich in Mg (1.07 +/- 0.42 g/100 g), and "Haiboshi" was rich in Zn (10.90 +/- 1.20 mg/100 g). The mineral contents in "Enzo" were small.

  7. In Vitro Degradation Behavior of Ternary Mg-Zn-Se and Mg-Zn-Cu Alloys as Biomaterials

    PubMed Central

    Persaud-Sharma, Dharam; Budiansky, Noah

    2013-01-01

    In this study, the corrosion behavior of Mg-Zn-Se and Mg-Zn-Cu alloys was investigated to evaluate their corrosion behavior related to use as implantable biomaterials. The corrosion behavior of these alloys and a commercially available Mg-Zn alloy were examined using static solution electrochemical testing, dynamic solution gravimetric testing, ion leaching testing, and microscopic evaluation. Fluctuations in the pH of the Dulbecco’s Modified Eagles Medium (DMEM) used for the gravimetric and ion leaching immersion testing were also recorded over the 30-day duration to assess whether the media conditions induced by the alloy degradation would permit for cellular survival. Weight loss experimentation and electrochemical tests revealed the Mg-Zn-Cu alloy to have the greatest corrosion rate. PMID:24465245

  8. Nanoscale order in ZnSe:(Mg, O)

    SciTech Connect

    Elyukhin, Vyacheslav A.

    2014-02-21

    Self-assembling of 1O4Mg identical tetrahedral clusters resulting in the nanoscale order in ZnSe:(Mg, O) is presented. Co-doping transforms ZnSe into Mg{sub x}Zn{sub 1−x}O{sub y}Se{sub 1−y} alloy of MgO, MgSe, ZnO and ZnSe. The decrease of a sum of the enthalpies of the constituent compounds and diminution of the strain energy are the causes of this phenomenon. The self-assembling conditions are obtained from the free energy minimum when magnesium and oxygen are in the dilute and ultra dilute limits, correspondingly. The occurrence of 1O4Mg clusters and completion of self-assembling when all oxygen atoms are in clusters are results of the continuous phase transitions. The self-assembling occurrence temperature does not depend on the oxygen content and it is a function of magnesium concentration. Mg{sub x}Zn{sub 1−x}O{sub y}Se{sub 1−y} with all oxygen atoms in clusters can be obtained in temperature ranges from T = 206 °C (x = 0.001, y = 1×10{sup −4}) to T = 456 °C (x = 0.01, y = 1×10{sup −4}) and from T = 237 °C (x = 0.001, y = 1×10{sup −6}) to T = 462 °C (x = 0.01, y = 1×10{sup −6})

  9. Blood compatibility of zinc-calcium phosphate conversion coating on Mg-1.33Li-0.6Ca alloy

    NASA Astrophysics Data System (ADS)

    Zou, Yu-Hong; Zeng, Rong-Chang; Wang, Qing-Zhao; Liu, Li-Jun; Xu, Qian-Qian; Wang, Chuang; Liu, Zhi-Wei

    2016-09-01

    Magnesium alloys as a new class of biomaterials possess biodegradability and biocompatibility in comparison with currently used metal implants. However, their rapid corrosion rates are necessary to be manipulated by appropriate coatings. In this paper, a new attempt was used to develop a zinc-calcium phosphate (Zn-Ca-P) conversion coating on Mg-1.33Li-0.6Ca alloys to increase the biocompatibility and improve the corrosion resistance. In vitro blood biocompatibility of the alloy with and without the Zn-Ca-P coating was investigated to determine its suitability as a degradable medical biomaterial. Blood biocompatibility was assessed from the hemolysis test, the dynamic cruor time test, blood cell count and SEM observation of the platelet adhesion to membrane surface. The results showed that the Zn-Ca-P coating on Mg-1.33Li-0.6Ca alloys had good blood compatibility, which is in accordance with the requirements for medical biomaterials.

  10. A comparison of Zn2+- and Ca2+- triggered depolarization of liver mitochondria reveals no evidence of Zn2+-induced permeability transition

    PubMed Central

    Devinney, Michael J.; Malaiyandi, Latha M.; Vergun, Olga; DeFranco, Donald B.; Hastings, Teresa G.; Dineley, Kirk E.

    2013-01-01

    Intracellular Zn2+ toxicity is associated with mitochondrial dysfunction. Zn2+ depolarizes mitochondria in assays using isolated organelles as well as cultured cells. Some reports suggest that Zn2+-induced depolarization results from the opening of the mitochondrial permeability transition pore (mPTP). For a more detailed analysis of this relationship, we compared Zn2+-induced depolarization with the effects of Ca2+ in single isolated rat liver mitochondria monitored with the potentiometric probe Rhodamine123. Consistent with previous work, we found that relatively low levels of Ca2+ caused rapid, complete and irreversible loss of mitochondrial membrane potential, an effect that was diminished by classic inhibitors of mPT, including high Mg2+, ADP and cyclosporine A. Zn2+ also depolarized mitochondria, but only at relatively high concentrations. Furthermore Zn2+-induced depolarization was slower, partial and sometimes reversible, and was not affected by inhibitors of mPT. We also compared the effects of Ca2+ and Zn2+ in a calcein-retention assay. Consistent with the well-documented ability of Ca2+ to induce mPT, we found that it caused rapid and substantial loss of matrix calcein. In contrast, calcein remained in Zn2+-treated mitochondria. Considered together, our results suggest that Ca2+ and Zn2+ depolarize mitochondria by considerably different mechanisms, that opening of the mPTP is not a direct consequence of Zn2+-induced depolarization, and that Zn2+ is not a particularly potent mitochondrial inhibitor. PMID:19349076

  11. ZnO and MgZnO Nanocrystalline Flexible Films: Optical and Material Properties

    DOE PAGES

    Huso, Jesse; Morrison, John L.; Che, Hui; ...

    2011-01-01

    An emore » merging material for flexible UV applications is Mg x Zn 1 − x O which is capable of tunable bandgap and luminescence in the UV range of ~3.4 eV–7.4 eV depending on the composition x . Studies on the optical and material characteristics of ZnO and Mg 0.3 Zn 0.7 O nanocrystalline flexible films are presented. The analysis indicates that the ZnO and Mg 0.3 Zn 0.7 O have bandgaps of 3.34 eV and 4.02 eV, respectively. The photoluminescence (PL) of the ZnO film was found to exhibit a structural defect-related emission at ~3.316 eV inherent to the nanocrystalline morphology. The PL of the Mg 0.3 Zn 0.7 O film exhibits two broad peaks at 3.38 eV and at 3.95 eV that are discussed in terms of the solubility limit of the ZnO-MgO alloy system. Additionally, external deformation of the film did not have a significant impact on its properties as indicated by the Raman LO-mode behavior, making these films attractive for UV flexible applications.« less

  12. Biodegradable Mg-Zn-Y alloys with long-period stacking ordered structure: optimization for mechanical properties.

    PubMed

    Zhao, Xu; Shi, Ling-ling; Xu, Jian

    2013-02-01

    To optimize the mechanical properties for biodegradable orthopedic implant, microstructures and tensile properties of Mg-Zn-Y alloys containing long period stacking ordered (LPSO) phase were investigated. For the as-cast Mg(100-3x)(Zn(1)Y(2))(x) (1 ≤ x ≤ 3) alloys, volume fraction of 18R LPSO phase increases with increasing the contents of Zn and Y. Mg(97)Zn(1)Y(2) alloy exhibits the optimal combination of strength and plasticity. Substitution of bioactive element Ca for Y in the Mg(97)Zn(1)Y(2) does not favor the formation of LPSO phase, but involving the formation of Mg(2)Ca phase. By micro-alloying with Zr as grain refinement agent, morphology of α-Mg in the Mg(96.83)Zn(1)Y(2)Zr(0.17) alloy is changed into the equiaxial shape, together with a significant refinement in grain size to 30 μm. It brings about an improvement not only in strength but also in plasticity, in contrast to the Zr-free alloy. In comparison with the as-cast state, warm-extruded alloys manifest significantly improved properties not only in strength but also in plasticity due to the refinement of α-Mg grain by dynamic recrystallization and the alignment of LPSO phase along extrusion direction.

  13. The suitability of the simplified method of the analysis of coffee infusions on the content of Ca, Cu, Fe, Mg, Mn and Zn and the study of the effect of preparation conditions on the leachability of elements into the coffee brew.

    PubMed

    Stelmach, Ewelina; Pohl, Pawel; Szymczycha-Madeja, Anna

    2013-12-01

    A fast and straightforward method of the analysis of coffee infusions was developed for measurements of total concentrations of Ca, Cu, Fe, Mg, Mn and Zn by flame atomic absorption spectrometry. Its validity was proved by the analysis of spiked samples; recoveries of added metals were found to be within 98-104% while the precision was better than 4%. The method devised was used for the analysis of re-distilled water infusions of six popular ground coffees available in the Polish market. Using the mud coffee preparation it was established that percentages of metals leached in these conditions varied a lot among analysed coffees, especially for Ca (14-42%), Mg (6-25%) and Zn (1-24%). For remaining metals, the highest extractabilities were assessed for Mn (30-52%) while the lowest for Fe (4-16%) and Cu (2-12%). In addition, it was found that the water type and the coffee brewing preparation method influence the concentration of studied metals in coffee infusions the most.

  14. Purification and characteristics of Ca2+,Mg2+- and Ca2+,Mn2+-dependent and acid DNases from spermatozoa of the sea urchin Strongylocentrotus intermedius.

    PubMed

    Shastina, V V; Menzorova, N I; Sibirtsev, Yu T; Rasskazov, V A

    2003-05-01

    Ca2+,Mg2+- and Ca2+,Mn2+-dependent and acid DNases were isolated from spermatozoa of the sea urchin Strongylocentrotus intermedius. The enzymes have been purified by successive chromatography on DEAE-cellulose, phenyl-Sepharose, Source 15Q, and by gel filtration, and the principal physicochemical and enzymatic properties of the purified enzymes were determined. Ca2+,Mg2+-dependent DNase (Ca,Mg-DNase) is a nuclear protein with molecular mass of 63 kD as the native form and its activity optimum is at pH 7.5. The enzyme activity in the presence of bivalent metal ions decreases in the series (Ca2+ + Mg2+) > Mn2+ = (Ca2+ + Mn2+) > (Mg2+ + EGTA) > Ca2+. Ca,Mg-DNase retains its maximal activity in sea water and is not inhibited by G-actin and N-ethylmaleimide, whereas Zn(2+) inhibits the enzyme. The endogenous Ca,Mg-DNase is responsible for the internucleosomal cleavage of chromosomal DNA of spermatozoa. Ca2+,Mn2+-dependent DNase (Ca,Mn-DNase) has molecular mass of 25 kD as the native form and the activity optimum at pH 8.5. The enzyme activity in the presence of bivalent metal ions decreases in the series (Ca2+ + Mn2+) > (Ca2+ + Mg2+) > Mn2+ > (Mg2+ + EGTA). In seawater the enzyme is inactive. Zinc ions inhibit Ca,Mn-DNase. Acid DNase of spermatozoa (A-DNase) is not a nuclear protein, it has molecular mass of 37 kD as a native form and the activity optimum at pH 5.5, it is not activated by bivalent metal ions, and it is inhibited by N-ethylmaleimide and iodoacetic acid. Mechanisms of the endonuclease cleavage of double-stranded DNA have been established for the three enzymes. The possible involvement of DNases from sea urchin spermatozoa in programmed cell death is discussed.

  15. Thermal variation of MgZn nanoferrites for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Kim, Sam Jin; Hyun, Sung Wook; Kim, Chul Sung; Kim, Hyung Joon

    2014-08-01

    Mg1- x Zn x Fe2O4 (x = 0.2, 0.4, 0.5, 0.6, 0.8) nanoparticles were prepared for the characterization of the crystallographic and magnetic properties. The Rietveld refinement for x-ray diffraction was used to confirm that the Zn ion occupied on B-site for dopings over 0.5 doping. The lattice constant ( a 0) was increased from 8.3969 to 8.4100 ± 0.0001 Å with increasing Zn concentration. Mössbauer spectra of all samples were taken at room temperature and showed Fe3+ and Fe2+ valence states. The thermal properties of all samples were measured at 50 kHz and 25 mT. The heating temperature was increased up to 124 °C until 0.5 doping of Zn ions, however it was decreased down to 69 °C over 0.5 doping of Zn ions. These results can be explained by the fact that the saturation magnetization was increased by Fe2+ ion, but, the heating temperature was decreased due to occupation of Zn ions on B-site for dopings above 0.5.

  16. The solar chromospheric Ca and Mg indices from Aura OMI

    NASA Astrophysics Data System (ADS)

    Deland, Matthew; Marchenko, Sergey

    2013-04-01

    Direct observations of long-term variations in solar UV irradiance from satellites, although important for monitoring the energetic forcing of the Earth's atmosphere, is challenging because of the difficulty of accurately tracking instrument response changes. Proxy indexes based on core-to-wing ratios of solar Fraunhofer lines, such as the Mg II feature at 280 nm, can minimize the impact of both time- and wavelength-dependent instrument changes to better monitor solar UV activity. Here we present new data sets from the Ozone Monitoring Instrument (OMI) on the Aura satellite, which began operations in late 2004. The high quality of OMI irradiance measurements allows us to construct daily indexes for the Mg II, Ca II K (393.4 nm), Ca II H (396.8 nm), and Mg I (285.2 nm) lines. The OMI Ca II K index is well correlated with the Mg II index measured by multiple instruments, as well as the ground-based National Solar Observatory (NSO) Ca II K 1.0 Å index data derived from Integrated Sunlight Spectrometer measurements. OMI Ca II K data can be used to evaluate anomalous short-term features in the NSO data set. The OMI solar data products represent a valuable addition to current data sets.

  17. The electrochemical behaviors of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn in sodium chloride solution

    NASA Astrophysics Data System (ADS)

    Lv, Yanzhuo; Liu, Min; Xu, Yan; Cao, Dianxue; Feng, Jing

    2013-03-01

    The electrochemical oxidation behaviors of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn electrodes in 0.7 mol L-1 NaCl solution are investigated by methods of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance spectroscopy and scanning electron microscopy. The phase composition of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn alloys is analyzed conducted by X-ray diffraction. The performances of Mg-8Li-3Al-0.5Zn and Mg-8Li-3Al-1.0Zn as the anode of Mg-H2O2 semi fuel cells are determined. The effect of Zn content on the corrosion resistant of these Mg-Li-based alloys is studied. It is found that the Mg-8Li-3Al-0.5Zn electrode has higher discharge activity and less corrosion resistance than that of Mg-8Li-3Al-1.0Zn electrode in 0.7 mol L-1 NaCl solution. The Mg-H2O2 semi fuel cell with Mg-8Li-3Al-0.5Zn anode presents a maximum power density of 100 mW cm-2 at room temperature, which is higher than that of Mg-8Li-3Al-1.0Zn anode (80 mW cm-2). The performance of semi fuel cell with the Mg-8Li-3Al-0.5Zn electrode is better than that with Mg-8Li-3Al-1.0Zn electrode, especially at higher current density (>30 mA cm-2).

  18. Hall field-induced resistance oscillations in MgZnO/ZnO heterostructures

    NASA Astrophysics Data System (ADS)

    Shi, Q.; Zudov, M. A.; Falson, J.; Kozuka, Y.; Tsukazaki, A.; Kawasaki, M.; von Klitzing, K.; Smet, J.

    2017-01-01

    We report on nonlinear magnetotransport in a two-dimensional electron gas hosted in a MgZnO/ZnO heterostructure. Upon application of a direct current, we observe pronounced Hall field-induced resistance oscillations (HIRO), which are well known from experiments on high-mobility GaAs/AlGaAs quantum wells. The unique sensitivity of HIRO to the short-range component of the disorder potential allows us to unambiguously establish that the mobility of our MgZnO/ZnO heterostructure is limited by impurities residing within or near the two-dimensional (2D) channel. This demonstration that HIRO can be realized in a system with a much lower mobility, much higher density, and much larger effective mass than in previously studied systems highlights the remarkable universality of the phenomenon and its great promise for use in studies of a wide variety of emerging 2D materials.

  19. Estrogen enhancement of Ca-, Mg-, and Ca-Mg-stimulated adenosine triphosphatase activity in the chick shell gland.

    PubMed

    Qin, X; Klandorf, H; Porter, D W; Holt, S B; Martin, W G

    1993-01-01

    The effect of 17 beta-estradiol (E2) on Ca-, Mg-, and Ca-Mg-ATPase activity was investigated in the shell gland of 6-week-old chicks. In the first study, each of 42 birds was implanted with three E2 (Compudose-200) pellets. An additional 6 sham-implanted birds served as controls for measurements of body weight and concentrations of E2 and Ca in plasma. The activities of Mg-, Ca-, and Ca-Mg-ATPase peaked coincident with maximum plasma E2 concentrations 8 days after implantation and then progressively declined in concert with the decline in plasma E2. By 29 days after implantation, the ATPase activities were similar to those measured in birds whose E2 pellets had been removed for 11 days. Concentrations of plasma E2 dropped from peak values of 1676 +/- 317 at Day 8 to 611 +/- 180 pg/ml at Day 29. When birds whose E2 pellets had been removed were reimplanted with three pellets per bird, plasma E2 again increased to 1637 +/- 227 pg/ml. ATPase activity in these reimplanted birds also was greater (P < 0.05) than activities measured in E2-removed or E2-maintained birds. In a second study the Ca-ATPase Km and Vmax were determined in E2-implanted chicks (three pellets per bird) and compared to E2-withdrawn chicks. Five days after reimplantation of chicks with E2, there was a significant increase in both Vmax (3.38 +/- 0.21 vs 2.37 +/- 0.28 micrograms Pi/mg protein/min; P < 0.05) and Km (0.31 +/- 0.02 vs 0.25 +/- 0.01 mM Ca; P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

  20. Near ultraviolet light emitting diodes using ZnMgO:N/ZnO hetero-junction grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Fujita, Yasuhisa; Yanase, Shogo; Nishikori, Hirokazu; Hiragino, Yuto; Furubayashi, Yutaka; Lin, Jie; Yoshida, Toshiyuki

    2017-04-01

    A ZnMgO:N/ZnO/ZnO:Ga single hetero-junction light emitting diode structure on Al2O3 (11 2 ̅0) substrate was fabricated by metalorganic vapor phase epitaxy. By using ZnMgO:N as a substitute for a ZnO:N top layer of a homojunction LED, improved rectifying current-voltage characteristics were obtained. Although the device had a heating problem and the luminescent area was partly in the ZnMgO:N layer, a sharp ultraviolet electroluminescence emission at 3.17 eV was successfully observed at room temperature.

  1. MgCaO Dry Etching on GaN

    NASA Astrophysics Data System (ADS)

    Hlad, M.; Ren, F.

    2005-11-01

    MgCaO films grown by rf plasma-assisted Molecular Beam Epitaxy and capped with Sc2O3 are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs) respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively Coupled Plasmas of CH4/H2/Ar produced etch rates only in the range 20-70 å/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (˜100 å/min) were obtained with Cl2/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH4/H2/Ar plasma chemistry produced a selectivity of around 2 or etching the MgCaO with respect to GaN.

  2. Synthesis and Characterization of Mg-doped ZnO Nanorods for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Gemar, H.; Das, N. C.; Wanekaya, A.; Delong, R.; Ghosh, K.

    2013-03-01

    Nanomaterials research has become a major attraction in the field of advanced materials research in the area of Physics, Chemistry, and Materials Science. Bio-compatible and chemically stable metal nanoparticles have biomedical applications that includes drug delivery, cell and DNA separation, gene cloning, magnetic resonance imaging (MRI). This research is aimed at the fabrication and characterization of Mg-doped ZnO nanorods. Hydrothermal synthesis of undoped ZnO and Mg-doped ZnO nanorods is carried out using aqueous solutions of Zn(NO3)2 .6H2O, MgSO4, and using NH4OH as hydrolytic catalyst. Nanomaterials of different sizes and shapes were synthesized by varying the process parameters such as molarity (0.15M, 0.3M, 0.5M) and pH (8-11) of the precursors, growth temperature (130°C), and annealing time during the hydrothermal Process. Structural, morphological, and optical properties are studied using various techniques such as XRD, SEM, UV-vis and PL spectroscopy. Detailed structural, and optical properties will be discussed in this presentation. This work is partially supported by National Cancer Institute (1 R15 CA139390-01).

  3. Fabrication of biodegradable Zn-Al-Mg alloy: Mechanical properties, corrosion behavior, cytotoxicity and antibacterial activities.

    PubMed

    Bakhsheshi-Rad, H R; Hamzah, E; Low, H T; Kasiri-Asgarani, M; Farahany, S; Akbari, E; Cho, M H

    2017-04-01

    In this work, binary Zn-0.5Al and ternary Zn-0.5Al-xMg alloys with various Mg contents were investigated as biodegradable materials for implant applications. Compared with Zn-0.5Al (single phase), Zn-0.5Al-xMg alloys consisted of the α-Zn and Mg2(Zn, Al)11 with a fine lamellar structure. The results also revealed that ternary Zn-Al-Mg alloys presented higher micro-hardness value, tensile strength and corrosion resistance compared to the binary Zn-Al alloy. In addition, the tensile strength and corrosion resistance increased with increasing the Mg content in ternary alloys. The immersion tests also indicated that the corrosion rates in the following order Zn-0.5Al-0.5Mg-0.5Al-0.3Mg-0.5Al-0.1Mg-0.5Al. The cytotoxicity tests exhibited that the Zn-0.5Al-0.5Mg alloy presents higher viability of MC3T3-E1 cell compared to the Zn-0.5Al alloy, which suggested good biocompatibility. The antibacterial activity result of both Zn-0.5Al and Zn-0.5Al-Mg alloys against Escherichia coli presented some antibacterial activity, while the Zn-0.5Al-0.5Mg significantly prohibited the growth of Escherichia coli. Thus, Zn-0.5Al-0.5Mg alloy with appropriate mechanical properties, low corrosion rate, good biocompatibility and antibacterial activities was believed to be a good candidate as a biodegradable implant material.

  4. Growth rate effects on Mg/Ca and Sr/Ca ratios constrained by belemnite calcite

    NASA Astrophysics Data System (ADS)

    Vinzenz Ullmann, Clemens

    2016-04-01

    Multiple temperature proxies from single species are important to achieve robust palaeotemperature estimates. Besides the commonly employed oxygen isotope thermometer, also Mg/Ca and Sr/Ca ratios perform well as proxies for calcification temperature in the shells of some species. While salinity changes affect the ratios of earth alkaline elements much less than the δ18O thermometer, metabolic effects may exert a strong control on the expression of element ratios. Such effects are hard to study because biomineralization experiments have to overcome large intraspecific variability and can hardly ever isolate the controls of a single parameter on shell geochemistry. The unique geometry of the belemnite rostrum constitutes an exception to this rule. Its shape, large size, and the visibility of growth increments as bands enable the analysis of multiple, correlatable, high resolution geochemical profiles in a single fossil. The effects of the growth rate variability amongst these profiles on Mg/Ca and Sr/Ca ratios has been tested here. Within a specimen of Passaloteuthis bisulcata (Early Toarcian, Cleveland Basin, UK), Mg/Ca and Sr/Ca data were obtained from four profiles. With respect to growth rate in the first profile, which was taken as a reference, the relative growth rates in the remaining three profiles varied by a factor of 0.9 to 2.7. Results suggest that relative growth rate is linearly correlated with Mg/Ca and Sr/Ca, with a decrease of Mg/Ca by 8 % and increase of Sr/Ca by 6 % per 100 % increase in relative growth rate. The observed trends are consistent with abiogenic precipitation experiments and suggest that crystal precipitation rate exerts a significant, predictable control on the element distribution in biogenic calcite.

  5. A Bayesian, multivariate calibration for Globigerinoides ruber Mg/Ca

    NASA Astrophysics Data System (ADS)

    Khider, D.; Huerta, G.; Jackson, C.; Stott, L. D.; Emile-Geay, J.

    2015-09-01

    The use of Mg/Ca in marine carbonates as a paleothermometer has been challenged by observations that implicate salinity as a contributing influence on Mg incorporation into biotic calcite and that dissolution at the sea-floor alters the original Mg/Ca. Yet, these factors have not yet been incorporated into a single calibration model. We introduce a new Bayesian calibration for Globigerinoides ruber Mg/Ca based on 186 globally distributed core top samples, which explicitly takes into account the effect of temperature, salinity, and dissolution on this proxy. Our reported temperature, salinity, and dissolution (here expressed as deep-water ΔCO32-) sensitivities are (±2σ) 8.7±0.9%/°C, 3.9±1.2%/psu, and 3.3±1.3%/μmol.kg-1 below a critical threshold of 21 μmol/kg in good agreement with previous culturing and core-top studies. We then perform a sensitivity experiment on a published record from the western tropical Pacific to investigate the bias introduced by these secondary influences on the interpretation of past temperature variability. This experiment highlights the potential for misinterpretations of past oceanographic changes when the secondary influences of salinity and dissolution are not accounted for. Multiproxy approaches could potentially help deconvolve the contributing influences but this awaits better characterization of the spatio-temporal relationship between salinity and δ18Osw over millennial and orbital timescales.

  6. Ca2+, Mg2+-dependent endonuclease and ADP-ribosylation.

    PubMed

    Yoshihara, K; Tanaka, Y; Kamiya, T

    1983-01-01

    The molecular mechanism of the inhibition of Ca2+, Mg2+-dependent endonuclease by ADP-ribosylation was studied by using purified bull seminal plasma Ca2+, Mg2+-dependent endonuclease, endonuclease-stimulating proteins, and poly-(ADP-ribose) polymerase. The activity of an essentially homogeneous preparation of the endonuclease was markedly suppressed by its preincubation with NAD+, poly-(ADP-ribose) polymerase, DNA, and Mg2+. These four components of the incubation mixture were all essential for the suppression of the activity. Analyses of the initial and the chased reaction product by Sephadex G-100 column chromatography and sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis revealed that Ca2+, Mg2+-dependent endonuclease was ADP-ribosylated during the incubation and its activity was markedly inhibited by the elongation of the ADP-ribose polymer covalently attached to the endonuclease. When the suppressed enzymes were mildly treated with an alkaline pH of 10.0, the activity was restored almost to the level of the unmodified control sample. These facts indicate that the linkage between the enzyme and poly(ADP-ribose) is hydrolyzed at this pH, and that the liberated polymer itself does not appreciably affect the endonuclease activity. These results also suggest that an electric repulsion between negative charges on DNA and poly(ADP-ribose) attached to Ca2+, Mg2+-dependent endonuclease is the basis for the observed suppression of the enzyme by ADP-ribosylation. Though histone H2B and H1 are shown to be as good endonuclease-stimulators (1) as they are good acceptors of ADP-ribose in poly(ADP-ribose) polymerase reaction (2), ADP-ribosylation of these two proteins did not affect their endonuclease-stimulating ability appreciably, at least under the conditions used.

  7. K -shell double photoionization of Be, Mg, and Ca

    NASA Astrophysics Data System (ADS)

    Kheifets, A. S.; Bray, Igor; Hoszowska, J.

    2009-04-01

    We perform convergent close-coupling calculations of double photoionization (DPI) of the K -shell of alkaline-earth metal atoms (Be, Mg, and Ca) from the threshold to the nonrelativistic limit of infinite photon energy. Theoretical double-to-single photoionization cross-section ratios for Mg and Ca are compared with experimental values derived from high-resolution x-ray spectra following the radiative decay of the K -shell double vacancy. We investigate the role of many-electron correlations in the ground and doubly-ionized final states played in the DPI process. Universal scaling of DPI cross section with an effective nuclear charge is examined in neutral atoms in comparison with corresponding heliumlike ions.

  8. Liquation Cracking in Arc and Friction-Stir Welding of Mg-Zn Alloys

    NASA Astrophysics Data System (ADS)

    Wagner, Dustin C.; Chai, Xiao; Tang, Xin; Kou, Sindo

    2015-01-01

    As compared to Al alloys, which are known to be susceptible to liquation ( i.e., liquid formation) and liquation-induced cracking, most Mg alloys have a lower eutectic temperature and thus are likely to be even more susceptible. The present study was conducted to study liquation and liquation cracking in Mg alloys during arc welding and friction-stir welding (FSW). Binary Mg-Zn alloys were selected as a model material in view of their very low eutectic temperature of 613 K (340 °C). Mg-Zn alloys with 2, 4, and 6 wt pct of Zn were cast and welded in the as-cast condition by both gas-tungsten arc welding (GTAW) and FSW. A simple test for liquation cracking was developed, which avoided interference by solidification cracking in the nearby fusion zone. Liquation and liquation cracking in GTAW were found to be in the decreasing order of Mg-6Zn, Mg-4Zn, and Mg-2Zn. Liquation cracking occurred in FSW of Mg-6Zn but not Mg-4Zn or Mg-2Zn. Instead of a continuous ribbon-like flash connected to the weld edge, small chips, and powder covered the weld surface of Mg-6Zn. The results from GTAW and FSW were discussed in light of the binary Mg-Zn phase diagram and the curves of temperature vs fraction solid during solidification.

  9. Studies on ZnS-MgS Nano Composites

    NASA Astrophysics Data System (ADS)

    Rajkumar, M.; Raj, S. Alfred Cecil

    2011-10-01

    ZnS-MgS nanocomposites was successfully prepared by the microwave assisted solvothermal method using a domestic microwave oven. The prepared sample was annealed at 100 °C for 1 hr to improve the ordering. Grain sizes and lattice parameters were determined by carrying out X-ray powder diffraction measurements. Scanning electron microscopy (SEM) shows the morphology. AC electrical measurements were carried out on pelletised samples at various temperatures ranging from 40-150 °C. Results of the present study reveal that the space charge contribution plays a significant role in the charge transport process and polarizability.

  10. Characterization of (Mg, La) Substituted Ni-Zn Spinel Ferrite

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Wei, S. C.; Wang, Y. J.; Tian, H. L.; Tong, H.; Xu, B. S.

    Spinel structure of (Mg, La) substituted spinel Ni-Zn ferrite has been synthesized by sol-gel auto combustion method. The ferrite exhibits a single-spinel structure. The ferrite is studied as a microwave absorbing material. The microwave measurements are carried out by a vector network analyzer. The reflection loss of the ferrite is calculated as a single-layer absorber. The results indicate that the ferrite annealed at 850°C has great potential for application in electromagnetic wave attenuation.

  11. Ostracode Mg/Ca Paleothermometry: Applications and Complications

    NASA Astrophysics Data System (ADS)

    Cronin, T. M.; Dwyer, G. S.

    2007-12-01

    Ostracode (bivalved Crustacea) shell Mg/Ca paleothermometry has wide applicability in Cenozoic paleoclimatology over 101 to 107 year timescales because they are commonly fossilized, live in freshwater, shallow- and deep-marine habitats, and grow by molting, which minimizes Mg/Ca variability due to ontogenetic variability. Two empirically derived Mg/Ca-temperature calibrations based on core top and culturing include one for the shallow marine, estuarine genus Loxoconcha (5 to 30°C) and another for deep-sea genus Krithe (<1 to 14°C). The former produced a temperature history for Chesapeake Bay for the last millennium, which has been intensively analyzed in the context of the hockey stick temperature curve. The latter produced evidence for decreased deep-sea temperature during glacial intervals and the first Atlantic-wide reconstruction of deep-sea temperature during the warm mid-Pliocene. In addition to temperature, however, factors such as host-water magnesium concentrations, salinity, intra-shell, intra-population, and interspecific variabilility, seasonality, biological factors (shell secretion rate), and post-mortem dissolution can contribute to scatter in calibration datasets and uncertainty in paleotemperature estimates. We will review these processes, present a new 2000 year Chesapeake temperature record, and discuss its relation to twentieth century climate change.

  12. Biocompatibility Assessment of Novel Bioresorbable Alloys Mg-Zn-Se and Mg-Zn-Cu for Endovascular Applications: In- Vitro Studies.

    PubMed

    Persaud-Sharma, Dharam; Budiansky, Noah; McGoron, Anthony J

    2013-01-01

    Previous studies have shown that using biodegradable magnesium alloys such as Mg-Zn and Mg-Zn-Al possess the appropriate mechanical properties and biocompatibility to serve in a multitude of biological applications ranging from endovascular to orthopedic and fixation devices. The objective of this study was to evaluate the biocompatibility of novel as-cast magnesium alloys Mg-1Zn-1Cu wt.% and Mg-1Zn-1Se wt.% as potential implantable biomedical materials, and compare their biologically effective properties to a binary Mg-Zn alloy. The cytotoxicity of these experimental alloys was evaluated using a tetrazolium based- MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and a lactate dehydrogenase membrane integrity assay (LDH). The MTS assay was performed on extract solutions obtained from a 30-day period of alloy immersion and agitation in simulated body fluid to evaluate the major degradation products eluted from the alloy materials. Human foreskin fibroblast cell growth on the experimental magnesium alloys was evaluated for a 72 hour period, and cell death was quantified by measuring lactate dehydrogenase concentrations. Both Mg-Zn-Se and Mg-Zn-Cu alloys exhibit low cytotoxicity levels which are suitable for biomaterial applications. The Mg-Zn-Cu alloy was found to completely degrade within 72 hours, resulting in lower human foreskin fibroblast cell viability. The Mg-Zn-Se alloy was shown to be less cytotoxic than both the Mg-Zn-Cu and Mg-Zn alloys.

  13. Biocompatibility Assessment of Novel Bioresorbable Alloys Mg-Zn-Se and Mg-Zn-Cu for Endovascular Applications: In- Vitro Studies

    PubMed Central

    Budiansky, Noah; McGoron, Anthony J.

    2013-01-01

    Previous studies have shown that using biodegradable magnesium alloys such as Mg-Zn and Mg-Zn-Al possess the appropriate mechanical properties and biocompatibility to serve in a multitude of biological applications ranging from endovascular to orthopedic and fixation devices. The objective of this study was to evaluate the biocompatibility of novel as-cast magnesium alloys Mg-1Zn-1Cu wt.% and Mg-1Zn-1Se wt.% as potential implantable biomedical materials, and compare their biologically effective properties to a binary Mg-Zn alloy. The cytotoxicity of these experimental alloys was evaluated using a tetrazolium based- MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and a lactate dehydrogenase membrane integrity assay (LDH). The MTS assay was performed on extract solutions obtained from a 30-day period of alloy immersion and agitation in simulated body fluid to evaluate the major degradation products eluted from the alloy materials. Human foreskin fibroblast cell growth on the experimental magnesium alloys was evaluated for a 72 hour period, and cell death was quantified by measuring lactate dehydrogenase concentrations. Both Mg-Zn-Se and Mg-Zn-Cu alloys exhibit low cytotoxicity levels which are suitable for biomaterial applications. The Mg-Zn-Cu alloy was found to completely degrade within 72 hours, resulting in lower human foreskin fibroblast cell viability. The Mg-Zn-Se alloy was shown to be less cytotoxic than both the Mg-Zn-Cu and Mg-Zn alloys. PMID:24058329

  14. Optical probing of MgZnO/ZnO heterointerface confinement potential energy levels

    SciTech Connect

    Solovyev, V. V.; Van'kov, A. B.; Kukushkin, I. V.; Falson, J.; Kozuka, Y.; Zhang, D.; Smet, J. H.; Maryenko, D.; Tsukazaki, A.; Kawasaki, M.

    2015-02-23

    Low-temperature photoluminescence and reflectance measurements were employed to study the optical transitions present in two-dimensional electron systems confined at Mg{sub x}Zn{sub 1–x}O/ZnO heterojunctions. Transitions involving A- and B-holes and electrons from the two lowest subbands formed within the confinement potential are detected. In the studied density range of 2.0–6.5 × 10{sup 11 }cm{sup −2}, the inter-subband splitting is measured and the first excited electron subband is shown to be empty of electrons.

  15. In vitro degradation of ZnO flowered coated Zn-Mg alloys in simulated physiological conditions.

    PubMed

    Alves, Marta M; Prosek, Tomas; Santos, Catarina F; Montemor, Maria F

    2017-01-01

    Flowered coatings composed by ZnO crystals were successfully electrodeposited on Zn-Mg alloys. The distinct coatings morphologies were found to be dependent upon the solid interfaces distribution, with the smaller number of bigger flowers (ø 46μm) obtained on Zn-Mg alloy containing 1wt.% Mg (Zn-1Mg) contrasting with the higher number of smaller flowers (ø 38μm) achieved on Zn-Mg alloy with 2wt.% Mg (Zn-2Mg). To assess the in vitro behaviour of these novel resorbable materials, a detailed evaluation of the degradation behaviour, in simulated physiological conditions, was performed by electrochemical impedance spectroscopy (EIS). The opposite behaviours observed in the corrosion resistances resulted in the build-up of distinct corrosion layers. The products forming these layers, preferentially detected at the flowers, were identified and their spatial distribution disclosed by EDS and Raman spectroscopy techniques. The presence of smithsonite, simonkolleite, hydrozincite, skorpionite and hydroxyapatite were assigned to both corrosion layers. However the distinct spatial distributions depicted may impact the biocompatibility of these resorbable materials, with the bone analogue compounds (hydroxyapatite and skorpionite) depicted in-between the ZnO crystals and on the top corrosion layer of Zn-1Mg flowers clearly contrasting with the hindered layer formed at the interface of the substrate with the flowers on Zn-2Mg.

  16. Infrared spectroscopic method for analysis of Mg 2Ca(SO 4) 3 in mixtures with MgSO 4 and/or CaSO 4

    NASA Astrophysics Data System (ADS)

    Smith, Duane H.; Seshadri, Kal S.

    1999-04-01

    Mg 2Ca(SO 4) 3 is prepared from, and may be found in, mixtures with MgSO 4 and CaSO 4. Such mixtures frequently occur in the ash produced by various types of coal combustion, especially in filter cakes from pressurized fluidized bed combustion with dolomite as a SO x sorbent. Previously, qualitative analyses could be performed for Mg 2Ca(SO 4) 3 in these mixtures, but no quantitative analytical method was available. An infrared spectroscopic method has been developed that provides reasonably quantitative results for Mg 2Ca(SO 4) 3, MgSO 4,and CaSO 4 in their mixtures.

  17. Thermoluminescence of K-Mg-Al-Zn fluorophosphate glass

    NASA Astrophysics Data System (ADS)

    Thomas, Sunil; Chithambo, M. L.

    2017-02-01

    The thermoluminescence of beta irradiated K-Mg-Al-Zn fluorophosphate glass is reported. A glow-curve corresponding to 10 Gy measured at 1 °C/s shows two peaks, a weaker-intensity one at 70 °C and a more prominent one at 235 °C, the subject of this report. The main peak was observed to fade with delay between irradiation and measurement and specifically, by 11% in 15 h. Its dose response is superlinear in the dose range 1-190 Gy although the change was linear for the initial 10 Gy. Regarding kinetic analysis, the activation energy of the higher temperature peak was evaluated as 1.31 eV and that of the lower temperature peak was found as 0.47 eV. It was also noted that the main peak is affected by thermal quenching with an activation energy for thermal quenching equal to 1.37 eV. It is proposed that the mechanism associated with the thermoluminescence in K-Mg-Al-Zn fluorophosphate glass is that electrons trapped by the metal cations are released during heating and then recombine with holes at oxygen sites.

  18. Formation of Zn Ca phyllomanganate nanoparticles in grass roots

    NASA Astrophysics Data System (ADS)

    Lanson, Bruno; Marcus, Matthew A.; Fakra, Sirine; Panfili, Frédéric; Geoffroy, Nicolas; Manceau, Alain

    2008-05-01

    It is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33 Å in the ab plane and contain only 1.2 layers (∼8.6 Å) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn-Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere.

  19. Influence of valence electron concentration on Laves phases: Structures and phase stability of pseudo-binary MgZn2-xPdx

    DOE PAGES

    Thimmaiah, Srinivasa; Miller, Gordon J.

    2015-06-03

    A series of pseudo-binary compounds MgZn2-xPdx (0.15 ≤ x ≤ 1.0) were synthesized and structurally characterized to understand the role of valence electron concentration (vec) on the prototype Laves phase MgZn2 with Pd-substitution. Three distinctive phase regions were observed with respect to Pd content, all exhibiting fundamental Laves phase structures: 0.1 ≤ x ≤ 0.3 (MgNi2-type, hP24; MgZn1.80Pd0.20(2)), 0.4 ≤ x ≤ 0.6 (MgCu2-type, cF24; MgZn1.59Pd0.41(2)), and 0.62 ≤ x ≤ 0.8 (MgZn2-type, hP12: MgZn1.37Pd0.63(2)). Refinements from single-crystal X-ray diffraction indicated nearly statistical distributions of Pd and Zn atoms among the majority atom sites in these structures. Interestingly, the MgZn2-typemore » structure re-emerges in MgZn2–xPdx at x ≈ 0.7 with the refined composition MgZn1.37(2)Pd0.63 and a c/a ratio of 1.59 compared to 1.64 for binary MgZn2. Electronic structure calculations on a model “MgZn1.25Pd0.75” yielded a density of states (DOS) curve showing enhancement of a pseudogap at the Fermi level as a result of electronic stabilization due to the Pd addition. Moreover, integrated crystal orbital Hamilton population values show significant increases of orbital interactions for (Zn,Pd)–(Zn,Pd) atom pairs within the majority atom substructure, i.e., within the Kagomé nets as well as between a Kagomé net and an apical site, from binary MgZn2 to the ternary “MgZn1.25Pd0.75”. Multi-centered bonding is evident from electron localization function plots for “MgZn1.25Pd0.75”, an outcome which is in accordance with analysis of other Laves phases.« less

  20. First-principles calculations of Zn-K XANES in Ca-deficient hydroxyapatite.

    PubMed

    Murata, Hidenobu; Shitara, Kazuki; Tanaka, Isao; Nakahira, Atsushi; Mizoguchi, Teruyasu; Matsunaga, Katsuyuki

    2010-09-29

    The local environment of substitutional Zn(2+) in Ca-deficient hydroxyapatite (HAp) was investigated using experimental and theoretical analyses of the x-ray absorption near edge structure (XANES). For Zn-K XANES calculations, two situations of Zn(2+) were considered. One was Zn(2+) substituted for Ca sites in perfect HAp, and the other was a Ca-deficient HAp model of substitutional Zn(2+) associated with a Ca(2+) vacancy charge compensated by two protons. The model of Zn(2+) in perfect HAp did not reproduce the experimental Zn-K XANES spectrum. In contrast, the Ca-deficient HAp model agreed well with the experimental spectrum. This indicates that substitutional Zn(2+) in Ca-deficient HAp is associated with the Ca(2+) vacancy complex in HAp.

  1. Evaluation of an Al, La Modified MgZn2Y2 Alloy

    DTIC Science & Technology

    2014-02-01

    of yttrium (Y) and zinc (Zn) atoms arranged in alternating layers of Mg and an intermetallic phase. For the MgZn1Y2 alloys, the LPSO phase has been...scanning electron microscope Tb terbium Y yttrium Zn zinc NO. OF COPIES ORGANIZATION 20 1 DEFENSE TECHNICAL (PDF) INFORMATION CTR

  2. Structural and optical properties of MgO doped ZnO

    SciTech Connect

    Verma, Kavita; Shukla, S.; Varshney, Dinesh; Varshney, M.; Asthana, A.

    2014-04-24

    Samples of ZnO, Zn{sub 0.5}Mg{sub 0.5}O and MgO were prepared by co-precipitation method. X-ray diffraction (XRD) pattern infers that the sample of ZnO is in single-phase wurtzite structure (hexagonal phase, space group P6{sub 3}mc), MgO crystallizes in cubic Fd3m space group and Zn{sub 0.5}Mg{sub 0.5}O represents mixed nature of ZnO and MgO lattices. Similar features were observed from Raman spectroscopy. The energy band gaps estimated from UV-Vis spectroscopy are found to be 4.21 and 3.42 eV for ZnO and Zn{sub 0.5}Mg{sub 0.5}O samples respectively.

  3. The ZnO p-n homojunctions modulated by ZnMgO barriers

    SciTech Connect

    Yang, Jing-Jing; Fang, Qing-Qing Wang, Dan-Dan; Du, Wen-Han

    2015-04-15

    In this paper, we fabricated the ultrathin ZnO p-n homojunctions, which modulated by ZnMgO asymmetrical double barriers (ADB). The ADB p-n homojunctions displays step-like curve in the absorption spectrums, this is the first time that quantum confinement effect has been observed in the absorption spectrums at room temperature (RT). The Hall-effect data confirm there is 2-dimensional electron gas in the interface of the ZnMgO ADB p-n junctions. The quantum confinement effect enhances the hall-mobility μ to 10{sup 3} cm{sup 2}V {sup −1}s{sup −1} based on the polarity of the films. There was no rectification property in the ZnO homojunctions with thickness of 250nm, however, when the ADB was added in the n-type layer of the homojunctions, it displays a typical Zener diode rectification property in the I-V curve.

  4. Self-compensation induced high-resistivity in MgZnO

    NASA Astrophysics Data System (ADS)

    Liu, Lishu; Mei, Zengxia; Tang, Aihua; Liang, Huili; Du, Xiaolong

    2017-02-01

    The degradation of conductivity with increased Mg content for Mg x Zn1-x O wide bandgap materials has always been a fundamental application-motivated research issue. Herein, the study of self-compensating defects in Mg x Zn1-x O:F (0  ⩽  x  ⩽  0.29) thin films was performed to reveal their influence on increased resistivity. Our observations solidly evidence that the degradation of conductivity is mainly owing to the increased concentration of Zn vacancy (V Zn)-related compensating defects in Mg x Zn1-x O alloys. The formation enthalpy of intrinsic V Zn defects decreases as Mg content (x) increases. Thus, the compensation ratio increases from 0.23 at x  =  0 to 0.47 at x  =  0.29, resulting in deteriorated conductivity in Mg x Zn1-x O alloys. Cathodoluminescence (CL) spectra further confirm higher V Zn concentrations with increased Mg content. The electron transport is demonstrated to be dominated by an ionized scattering mechanism. Formation of F\\text{O}+ -V\\text{Zn}2- complexes could reduce the concentration of ionized scattering centers and thus increase mobility. These results clarify the reason of increasingly high resistivity in Mg x Zn1-x O, which is a long-sought-after physics problem in this area, and provide crucial information on controlling the conductivity of Mg x Zn1-x O alloys.

  5. Eocene sea temperatures for the mid-latitude southwest Pacific from Mg/Ca ratios in planktonic and benthic foraminifera

    NASA Astrophysics Data System (ADS)

    Creech, John B.; Baker, Joel A.; Hollis, Christopher J.; Morgans, Hugh E. G.; Smith, Euan G. C.

    2010-11-01

    We have used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to measure elemental (Mg/Ca, Al/Ca, Mn/Ca, Zn/Ca, Sr/Ca, and Ba/Ca) ratios of 13 species of variably preserved early to middle Eocene planktonic and benthic foraminifera from New Zealand. The foraminifera were obtained from Ashley Mudstone, mid-Waipara River, South Island, which was deposited at bathyal depth ( ca. 1000 m) on the northern margin of the east-facing Canterbury Basin at a paleo-latitude of ca. 55°S. LA-ICP-MS data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings, mineralisation and detrital sediment. Screened Mg/Ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late Early to early Middle Eocene ( ca. 51 to 46.5 Ma), a time interval that spans the termination of the Early Eocene Climatic Optimum (EECO). During this time, sea surface temperatures (SST) varied from 30 to 24 °C, and bottom water temperatures (BWT) from 21 to 14 °C. Comparison of Mg/Ca sea temperatures with published δ 18O and TEX 86 temperature data from the same samples (Hollis et al., 2009) shows close correspondence, indicating that LA-ICP-MS can provide reliable Mg/Ca sea temperatures even where foraminiferal test preservation is variable. Agreement between the three proxies also implies that Mg/Ca-temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to Eocene species, although some species (e.g., V. marshalli) show significant calibration differences. The Mg/Ca ratio of the Eocene ocean is constrained by our data to be 35-50% lower than the modern ocean depending on which TEX 86 - temperature calibration (Kim et al., 2008; Liu et al., 2009) - is used to compare with the Mg/Ca sea temperatures. Sea temperatures derived from δ 18O analysis of foraminifera from Waipara show

  6. In vitro biodegradation behavior, mechanical properties, and cytotoxicity of biodegradable Zn-Mg alloy.

    PubMed

    Gong, Haibo; Wang, Kun; Strich, Randy; Zhou, Jack G

    2015-11-01

    Zinc-Magnesium (Zn-Mg) alloy as a novel biodegradable metal holds great potential in biodegradable implant applications as it is more corrosion resistant than Magnesium (Mg). However, the mechanical properties, biodegradation uniformity, and cytotoxicity of Zn-Mg alloy remained as concerns. In this study, hot extrusion process was applied to Zn-1 wt % Mg (Zn-1Mg) to refine its microstructure. Effects of hot extrusion on biodegradation behavior and mechanical properties of Zn-1Mg were investigated in comparison with Mg rare earth element alloy WE43. Metallurgical analysis revealed significant grain size reduction, and immersion test found that corrosion rates of WE43 and Zn-1Mg were reduced by 35% and 57%, respectively after extrusion. Moreover, hot extrusion resulted in a much more uniform biodegradation in extruded Zn-1Mg alloy and WE43. In vitro cytotoxicity test results indicated that Zn-1Mg alloy was biocompatible. Therefore, hot extruded Zn-1Mg with homogenous microstructure, uniform as well as slow degradation, improved mechanical properties, and good biocompatibility was believed to be an excellent candidate material for load-bearing biodegradable implant application.

  7. Dual-color ultraviolet photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction

    NASA Astrophysics Data System (ADS)

    Xie, X. H.; Zhang, Z. Z.; Shan, C. X.; Chen, H. Y.; Shen, D. Z.

    2012-08-01

    We report a dual-color ultraviolet (UV) photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction. The device exhibits distinct dominant responses at solar blind (250 nm) and visible blind (around 330 nm) UV regions under different reverse biases. By using the energy band diagram of the structure, it is found that the bias-tunable two-color detection is originated from different valence band offset between cubic MgZnO/MgO and hexagonal MgZnO/MgO. Meanwhile, due to the large conduction band offset at the Si/MgO interface, the visible-light photoresponse from Si substrate is suppressed.

  8. Electrical properties of Mg x Zn1- x O thin films deposited by using RF magnetron co-sputtering with ZnO and Mg0.3Zn0.7O targets

    NASA Astrophysics Data System (ADS)

    Yue, Li Li; Yang, Yi Da; Kim, Hong Seung; Jang, Nak Won; Yun, Young

    2016-03-01

    We successfully deposited hexagonal wurtzite Mg x Zn1- x O (0 ≤ x ≤ 0.18) films on Si substrates by using RF magnetron co-sputtering with ZnO and Mg0.3Zn0.7O targets. The Mg content was varied by controlling the RF power of the Mg0.3Zn0.7O target while the RF power of the ZnO target was fixed at 100 W. The electrical properties of the Mg x Zn1- x O films were investigated by using a transmission line model (TLM) with Ti/Au electrode and Hall effect measurements. The X-ray diffraction (XRD) results demonstrate that some Zn atoms can be replaced by Mg atoms in the Mg x Zn1- x O films. As the Mg content was increased from 0 at.% to 18 at.%, the resistivity of Mg x Zn1- x O films increased and the carrier concentration decreased from 1.17 × 1019 cm-3 to 1.17 × 1017 cm-3, which indicates a decrease in the number of oxygen vacancies. Meanwhile, the Hall mobility increased to 15.3 cm2/Vs. The electrical properties of Mg x Zn1- x O films were tuned by using the Mg content.

  9. Schottky Diodes Prepared with Ag, Au, or Pd Contacts on a MgZnO/ZnO Heterostructure

    NASA Astrophysics Data System (ADS)

    Lee, Jong Hoon; Kim, Chang Hoi; Kim, Ah Ra; Kim, Hong Seung; Jang, Nak Won; Yun, Young; Kim, Jin-Gyu; Pin, Min Wook; Lee, Won Jae

    2012-09-01

    We successfully fabricated lateral Schottky diodes with a thin MgZnO layer inserted between the ZnO and Schottky contact metal layers. The MgZnO/ZnO heterostructure was deposited onto a c-sapphire substrate by pulsed laser deposition using Mg0.3Zn0.7O and ZnO targets. Ti/Au was used to achieve ohmic contact with the Mg0.3Zn0.7O thin film layer, whereas Schottky contacts were prepared using silver (Ag), gold (Au), and palladium (Pd). The Ag Schottky diode devices exhibited rectification ratios as high as ˜103 at a bias voltage of ±1 V, with an ideality factor of 2.37 and a work function of 0.73 eV. The possibility of preparing Schottky contacts with a high carrier concentration on the ZnO layer is discussed as a function of the presence or absence of a MgZnO thin layer and in terms of the measured current-voltage properties.

  10. On the synthesis, structural, optical and magnetic properties of nano-size Zn-MgO

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Dwivedi, Sonam

    2015-09-01

    Chemical co-precipitation method is employed to synthesize ZnO, MgO and Zn0.5Mg0.5O nanoparticles. X-ray diffraction (XRD) pattern infers that the sample of ZnO is in single-phase wurtzite structure (hexagonal phase, P63mc), MgO crystallizes in cubic Fd3m space group and Zn0.5Mg0.5O represents mixed nature of ZnO and MgO lattices. MgO nanocrystals band around 1078 cm-1 is ascribed to the TO-LO surface phonon modes in MgO lattice. In case of Zn0.5Mg0.5O lattice illustrating two bands at 436 and 1087 cm-1. FTIR spectra clearly show the broad band within 450-600 cm-1 is associated with the special vibration of magnesium oxide. FT-IR spectrum of Zn0.5Mg0.5O represents the combined bands of both ZnO-MgO oxides. Further the optical study obtained value of MgO (4.08 eV) is much lower than the corresponding bulk value (7.08 eV). All samples show diamagnetic nature at room temperature.

  11. Spin-Selective Electron Quantum Transport in Nonmagnetic MgZnO/ZnO Heterostructures.

    PubMed

    Maryenko, D; Falson, J; Bahramy, M S; Dmitriev, I A; Kozuka, Y; Tsukazaki, A; Kawasaki, M

    2015-11-06

    We report magnetotransport measurements on a high-mobility two-dimensional electron system at the nonmagnetic MgZnO/ZnO heterointerface showing distinct behavior for electrons with spin-up and spin-down orientations. The low-field Shubnikov-de Haas oscillations manifest alternating resistance peak heights which can be attributed to distinct scattering rates for different spin orientations. The tilt-field measurements at a half-integer filling factor reveal that the majority spins show usual diffusive behavior, i.e., peaks with the magnitude proportional to the index of the Landau level at the Fermi energy. By contrast, the minority spins develop "plateaus" with the magnitude of dissipative resistivity that is fairly independent of the Landau level index and is of the order of the zero-field resistivity.

  12. Spin-Selective Electron Quantum Transport in Nonmagnetic MgZnO /ZnO Heterostructures

    NASA Astrophysics Data System (ADS)

    Maryenko, D.; Falson, J.; Bahramy, M. S.; Dmitriev, I. A.; Kozuka, Y.; Tsukazaki, A.; Kawasaki, M.

    2015-11-01

    We report magnetotransport measurements on a high-mobility two-dimensional electron system at the nonmagnetic MgZnO /ZnO heterointerface showing distinct behavior for electrons with spin-up and spin-down orientations. The low-field Shubnikov-de Haas oscillations manifest alternating resistance peak heights which can be attributed to distinct scattering rates for different spin orientations. The tilt-field measurements at a half-integer filling factor reveal that the majority spins show usual diffusive behavior, i.e., peaks with the magnitude proportional to the index of the Landau level at the Fermi energy. By contrast, the minority spins develop "plateaus" with the magnitude of dissipative resistivity that is fairly independent of the Landau level index and is of the order of the zero-field resistivity.

  13. Air-gap gating of MgZnO/ZnO heterostructures

    SciTech Connect

    Tambo, T.; Falson, J. Kozuka, Y.; Maryenko, D.; Tsukazaki, A.; Kawasaki, M.

    2014-08-28

    The adaptation of “air-gap” dielectric based field-effect transistor technology to controlling the MgZnO/ZnO heterointerface confined two-dimensional electron system (2DES) is reported. We find it possible to tune the charge density of the 2DES via a gate electrode spatially separated from the heterostructure surface by a distance of 5 μm. Under static gating, the observation of the quantum Hall effect suggests that the charge carrier density remains homogeneous, with the 2DES in the 3 mm square sample the sole conductor. The availability of this technology enables the exploration of the charge carrier density degree of freedom in the pristine sample limit.

  14. Exciton dynamics in individual semimagnetic (Zn,Mn)Te/(Zn,Mg)Te nanowires

    SciTech Connect

    Gałkowski, K.; Papierska, J.; Sawicki, K.; Kossacki, P.; Suffczyński, J.; Wojnar, P.; Janik, E.

    2015-09-07

    Dynamics and mechanisms of photocreated carriers decay in individual core/shell (Zn,Mn)Te/(Zn,Mg)Te semimagnetic nanowires are studied with a high temporal resolution. Exciton lifetime determined to 44 ± 5 ps is found to increase to 78 ± 5 ps upon application of magnetic field of up to 10 T. A quantitative modeling attributes the effects observed in time-resolved and time-integrated micro-photoluminescence to the magnetic field induced quenching of exchange Auger type, non-radiative carrier recombination related to Mn{sup 2+} ions. The reported properties of the semimagnetic nanowires are promising for their implementation in high-speed devices exploiting light-induced conductivity.

  15. Growth of high Mg content wurtzite MgZnO epitaxial films via pulsed metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Ledyaev, Oleg; Miller, Ross; Beletsky, Valeria; Osinsky, Andrei; Schoenfeld, Winston V.

    2016-02-01

    We report on the growth of high Mg content, high quality, wurtzite MgxZn1-xO (MgZnO) epitaxial films using a pulsed metal organic chemical vapor deposition (PMOCVD) method. Series of MgZnO films with variable Mg concentration were deposited on bare and AlN coated sapphire substrates. The band gap of the films estimated using UV-visible transmission spectra ranges from 3.24 eV to 4.49 eV, corresponding to fraction of Mg between x=0.0 and x=0.51, as determined by Rutherford backscattering spectroscopy. The cathodoluminescence (CL) measurement has shown a blue-shift in the peak position of MgZnO with an increasing Mg content. No multi-absorption edges and CL band splitting were observed, suggesting the absence of phase segregation in the as grown films. The crystal structure and phase purity of the films were also confirmed by XRD analysis. Hall effect measurement in van der Pauw configuration was employed to evaluate the electrical properties of the films. With a rise in Mg incorporation into the ZnO lattice, the films became very resistive, consistent with the widening of the band gap. The AFM measurement on the films has shown a decreasing surface roughness with an Mg content. To the best of our knowledge, the current result shows the highest Mg content (x=0.51), high quality, wurtzite MgZnO epitaxial film ever grown by MOCVD. The high Mg incorporation without phase separation is believed to be due to the non-equilibrium behavior of the PMOCVD in which the kinetic processes dominate the thermodynamic one.

  16. In vitro degradation and cytotoxicity of Mg/Ca composites produced by powder metallurgy.

    PubMed

    Zheng, Y F; Gu, X N; Xi, Y L; Chai, D L

    2010-05-01

    Mg/Ca (1 wt.%, 5 wt.%, 10 wt.% Ca) composites were prepared from pure magnesium and calcium powders using the powder metallurgy method, aiming to enlarge the addition of Ca content without the formation of Mg(2)Ca. The microstructures, mechanical properties and cytotoxicities of Mg/Ca composite samples were investigated. The corrosion of Mg/Ca composites in Dulbecco's modified Eagle's medium (DMEM) for various immersion intervals was studied by electrochemical impedance spectroscopy measurements and environmental scanning electron microscope, with the concentrations of released Mg and Ca ions in DMEM for various immersion time intervals being measured. It was shown that the main constitutional phases were Mg and Ca, which were uniformly distributed in the Mg matrix. The ultimate tensile strength (UTS) and elongation of experimental composites decreased with increasing Ca content, and the UTS of Mg/1Ca composite was comparable with that of as-extruded Mg-1Ca alloy. The corrosion potential increased with increasing Ca content, whereas the current density and the impedance decreased. It was found that the protective surface film formed quickly at the initial immersion stage. With increasing immersion time, the surface film became compact, and the corrosion rate of Mg/Ca composites slowed down. The surface film consisted mainly of CaCO(3), MgCO(3)x3H(2)O, HA and Mg(OH)(2) after 72 h immersion in DMEM. Mg/1Ca and Mg/5Ca composite extracts had no significant toxicity (p>0.05) to L-929 cells, whereas Mg/10Ca composite extract induced approximately 40% reduced cell viability.

  17. Mechanical Properties and Tensile Failure Analysis of Novel Bio-absorbable Mg-Zn-Cu and Mg-Zn-Se Alloys for Endovascular Applications

    PubMed Central

    Persaud-Sharma, Dharam; Budiansky, Noah; McGoron, Anthony J.

    2013-01-01

    In this paper, the mechanical properties and tensile failure mechanism of two novel bio-absorbable as-cast Mg-Zn-Se and Mg-Zn-Cu alloys for endovascular medical applications are characterized. Alloys were manufactured using an ARC melting process and tested as-cast with compositions of Mg-Zn-Se and Mg-Zn-Cu, being 98/1/1 wt.% respectively. Nanoindentation testing conducted at room temperature was used to characterize the elastic modulus (E) and surface hardness (H) for both the bare alloys and the air formed oxide layer. As compared to currently available shape memory alloys and degradable as-cast alloys, these experimental alloys possess superior as-cast mechanical properties that can increase their biocompatibility, degradation kinetics, and the potential for medical device creation. PMID:23543822

  18. Enhanced Mechanical Properties and Corrosion Behavior of Biodegradable Mg-Zn/HA Composite

    NASA Astrophysics Data System (ADS)

    Salleh, Emee Marina; Zuhailawati, Hussain; Ramakrishnan, Sivakumar; Dhindaw, Brij Kumar

    2017-03-01

    Magnesium (Mg) and its alloys have shown potential for use in the biomedical industry due to their excellent biological performance and biodegradability in the bioenvironment. Thus, the aim of the present study was to develop a reliable biodegradable hard tissue substituent. Biodegradable and bioactive Mg-Zinc (Zn) reinforced by hydroxyapatite (HA) composite was prepared using mechanically alloyed Mg-6.5 wt pct Zn and pure HA powders as starting materials. Various HA contents (i.e., 5, 10, 15, and 20 wt pct) were introduced in forming the Mg-Zn/HA composite. The effect of bioactive HA incorporation in biodegradable Mg-6.5 wt pct Zn alloy matrix on mechanical and biodegradation properties as well as microstructural observation was investigated. As measured by the Williamson-Hall formula, the Mg crystallite size of the sintered composites containing 5, 10, 15, and 20 wt pct HA were 36.76, 29.08, 27.93, and 27.31 nm, respectively. According to X-ray diffraction (XRD) analysis, there was no new crystalline phase formed during milling, indicating that no mechanochemical reactions between Mg-Zn alloy and HA occurred. The -1.70 V shifted significantly toward the passive position of the plain Mg-6.5 wt pct Zn alloy and Mg-Zn/10 wt pct HA composite, which were -1.50 and -1.46 V, respectively, indicating that the Mg-Zn/10 wt pct HA composite was least susceptible to corrosion in the bioenvironment.

  19. Understanding the light soaking effect of ZnMgO buffer in CIGS solar cells.

    PubMed

    Kim, Suncheul; Lee, Chang-Soo; Kim, Seungtae; Chalapathy, R B V; Al-Ammar, Essam A; Ahn, Byung Tae

    2015-07-15

    This study investigated the mechanism underlying the light soaking effect of a ZnMgO buffer in Cu(In,Ga)Se2 (CIGS) solar cells, where the cell efficiency increased with an increase of light soaking time. The ZnMgO buffer layer was deposited by an atomic layer deposition method. With light soaking, the cell efficiency of ZnMgO/CIGS cells increased mainly by the increase of the fill factor and partly by the increase of the open-circuit voltage. With light soaking, the electron carrier concentration of the ZnMgO layer increased and the XPS intensity of the hydroxyl bond in the ZnMgO layer decreased. Based on the above results and the comparison of other buffers in literature, we assumed that the hydrogen atoms broken away from the hydroxyl bond by photon irradiation occupied the interstitial sites of the ZnMgO layer as a donor atom and also passivated the defects at the ZnMgO/CIGS interface. The increase of the fill factor and open circuit voltage was explained based on H doping in the ZnMgO layer and H passivation at the ZnO/CIGS interface.

  20. Microstructures and Thermal Properties of Mg-Sn-Ca Alloys: Casts and Extrusions

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Han; Choi, Jeong-Won; Kim, Yong-Ho; Yoo, Hyo-Sang; Woo, Kee-Do; Lee, Seong-Hee; Son, Hyeon-Taek

    2015-11-01

    Microstructure and thermal properties of Mg-(3 mass% or 5 mass%) Sn-2 mass% Ca alloys as casts and extrusions have been investigated with different ram speeds and extrusion temperatures. Mg-(3 mass% or 5 mass%) Sn-2 mass% Ca alloys are composed of \\upalpha -Mg, MgSnCa, and {Mg}2{Ca} phases. By adding Sn content from 3 mass% to 5 mass%, the MgSnCa phase is increased and the {Mg}2{Ca} phase is decreased. During hot extrusion, the average grain sizes are increased with increasing ram speed and temperature. The ultimate tensile strength ( UTS) and elongation for the Mg-5Sn-2Ca alloy at 2.3 {mm}{\\cdot }{s}^{-1} are 227.73 MPa and 18.43 %, respectively. With increasing extrusion ram speed, the UTS and elongation for the Mg-5Sn-2Ca alloy are remarkably decreased to 215.95 MPa, 206.33 MPa, and 14.74 %, 6.88 %, respectively. The thermal conductivity for the Mg-3Sn-2Ca alloy is dramatically improved, compared to commercialized Mg alloys such as AZ31 and AZ91 due to formation of MgSnCa and {Mg}2{Ca} phases.

  1. Microstructure evolution and mechanical properties of biomedical Mg-Zn-Gd alloy wires

    NASA Astrophysics Data System (ADS)

    Chunlei, Gan; Xiaohui, Li; Deng, Nong; Xiang, Zhang; Kaihong, Zheng; Zhenghua, Huang

    2017-03-01

    In order to manufacture the Mg-Zn-Gd alloy fine wires for the development of new biomedical Mg alloy implant devices, a hot extrusion and cold drawing process which is used to develop the Mg-Zn-Gd alloy fine wires were investigated. The results demonstrate that the Mg-Zn-Gd alloy has good formability. The microstructure and properties of the Mg-Zn-Gd alloy wires were studied by the observations of optical microscopy and scanning electron microscopy. The results show that the process is successfully developed to manufacture the high-quality wires with 3.00 mm diameter. The achievement of the high-quality Mg-Zn-Gd alloy wires is ascribed to the refined microstructure due to dynamic recrystallization during hot extrusion. Additionally, the grain morphology can play an important role in affecting the subsequent cold drawing performance.

  2. Preparation and structural properties of pure and codoped (Mg, Ag) ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Reddy, B. Sankara; Reddy, S. Venkatramana; Reddy, N. Koteeswara

    2013-06-01

    Pure and co-doped (Mg, Ag) ZnO nanoparticles (Zn0.90Mg0.05Ag0.05O) are synthesized by chemical co-precipitation method in the presence of capping agent Polyethylene glycol 600 (PEG 600) and annealed at 500°C in air ambient for 1h. The XRD measurements reveals that the pure and co-doped ZnO samples have hexagonal structure without any change and the size of ZnO nanoparicles were decreased from 17 nm to 13 nm. FESEM images indicates that they are flake like structures of the ZnO and co-doped ZnO samples and ED AX spectra reveals that the successful doping concentration of Mg and Ag. From the TEM results, the size of the ZnO nanoparticles which are in good agreement with the XRD results.

  3. Luminescence properties of MgxZn1-xSe prepared by Mg diffusion

    NASA Astrophysics Data System (ADS)

    Łożykowski, H. J.; Holtz, P. O.; Monemar, B.

    1983-07-01

    The photoluminescence of ZnSe doped with the isoelectronic substituent Mg with a simple diffusion procedure has been studied. It was found that Mg easily enters substitutionally on Zn-site to form MgxZn1-xSe. The diffused samples therefore show a graded bandgap due to a composition gradient in the surface region. In contrast to ZnSe the photoluminescence spectrum of MgxZn1-xSe is dominated by a near bandgap emission at all temperatures between 1.5 and 300 K. The bandgap shift compared with “pure” ZnSe is estimated from photoluminescence excitation spectra. The luminous efficiency of MgxZn1-xSe makes the material promising for future applications as light emitting diodes with a well defined narrow emission band at a wavelength determined by the Mg content x.

  4. Study of ZnO and Mg doped ZnO nanoparticles by sol-gel process

    SciTech Connect

    Ansari, Mohd Meenhaz Arshad, Mohd; Tripathi, Pushpendra

    2015-06-24

    Nano-crystalline undoped and Mg doped ZnO (Mg-ZnO) nanoparticles with compositional formula Mg{sub x}Zn{sub 1-x}O (x=0,1,3,5,7,10 and 12 %) were synthesized using sol-gel process. The XRD diffraction peaks match with the pattern of the standard hexagonal structure of ZnO that reveals the formation of hexagonal wurtzite structure in all samples. SEM images demonstrates clearly the formation of spherical ZnO nanoparticles, and change of the morphology of the nanoparticles with the concentration of the magnesium, which is in close agreement with that estimated by Scherer formula based on the XRD pattern. To investigate the doping effect on optical properties, the UV–VIS absorption spectra was obtained and the band gap of the samples calculated.

  5. Study of p-type ZnO and MgZnO Thin Films for Solid State Lighting

    SciTech Connect

    Liu, Jianlin

    2015-07-31

    This project on study of p-type ZnO and MgZnO thin films for solid state lighting was carried out by research group of Prof. Jianlin Liu of UCR during the four-year period between August 2011 and July 2015. Tremendous progress has been made on the proposed research. This final report summarizes the important findings.

  6. Effect of reaction time and (Ca+Mg)/Al molar ratios on crystallinity of Ca-Mg-Al layered double Hydroxide

    NASA Astrophysics Data System (ADS)

    Heraldy, E.; Nugrahaningtyas, K. D.; Sanjaya, F. B.; Darojat, A. A.; Handayani, D. S.; Hidayat, Y.

    2016-02-01

    Ca-Mg-Al Layered Double Hydroxides (Ca-Mg-Al-LDH) compounds were successfully synthesized from brine water and AlCl3.6H2O as the starting materials by coprecipitation method. The product result was characterized by X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR). The effects of the reaction time and the molar ratios of the raw material on the crystallinity of Ca-Mg-Al-LDH were examining. Results show that increasing reaction time (30; 60 and 90 min.) could improve the crystallinity and monodispersity of layered double hydroxide compounds particles. The well-defined Ca-Mg- Al-LDH could be prepared with (Ca+Mg)/Al molar ratios 0.5.

  7. Damage accumulation and annealing behavior in high fluence implanted MgZnO

    NASA Astrophysics Data System (ADS)

    Azarov, A. Yu.; Hallén, A.; Svensson, B. G.; Du, X. L.; Kuznetsov, A. Yu.

    2012-02-01

    Molecular beam epitaxy grown Mg xZn 1-xO ( x ⩽ 0.3) layers were implanted at room temperature with 150 keV 166Er + ions in a fluence range of 5 × 10 15-3 × 10 16 cm -2. Evolution of ion-induced damage and structural changes were studied by a combination of Rutherford backscattering spectrometry, nuclear reaction analysis and time-of-flight elastic recoil detection analysis. Results show that damage production enhances in both Zn- and O-sublattices with increasing the Mg content in the MgZnO. However, MgZnO as well as pure ZnO exhibits a high degree of dynamic annealing and MgZnO can not be amorphized even at the highest ion fluence used. Annealing of heavily damaged ZnO leads to a strong surface erosion and thinning of the film. Increasing the Mg content suppresses the surface evaporation in high fluence implanted MgZnO but leads to a strong surface decomposition accompanied with a Mg-rich surface layer formation during post-implantation annealing.

  8. Phosphorus recovery from biogas fermentation liquid by Ca-Mg loaded biochar.

    PubMed

    Fang, Ci; Zhang, Tao; Li, Ping; Jiang, Rongfeng; Wu, Shubiao; Nie, Haiyu; Wang, Yingcai

    2015-03-01

    Shortage in phosphorus (P) resources and P wastewater pollution is considered as a serious problem worldwide. The application of modified biochar for P recovery from wastewater and reuse of recovered P as agricultural fertilizer is a preferred process. This work aims to develop a calcium and magnesium loaded biochar (Ca-Mg/biochar) application for P recovery from biogas fermentation liquid. The physico-chemical characterization, adsorption efficiency, adsorption selectivity, and postsorption availability of Ca-Mg/biochar were investigated. The synthesized Ca-Mg/biochar was rich in organic functional groups and in CaO and MgO nanoparticles. With the increase in synthesis temperature, the yield decreased, C content increased, H content decreased, N content remained the same basically, and BET surface area increased. The P adsorption of Ca-Mg/biochar could be accelerated by nano-CaO and nano-MgO particles and reached equilibrium after 360min. The process was endothermic, spontaneous, and showed an increase in the disorder of the solid-liquid interface. Moreover, it could be fitted by the Freundlich model. The maximum P adsorption amounts were 294.22, 315.33, and 326.63mg/g. The P adsorption selectivity of Ca-Mg/biochar could not be significantly influenced by the typical pH level of biogas fermentation liquid. The nano-CaO and nano-MgO particles of Ca-Mg/biochar could reduce the negative interaction effects of coexisting ions. The P releasing amounts of postsorption Ca-Mg/biochar were in the order of Ca-Mg/B600>Ca-Mg/B450>Ca-Mg/B300. Results revealed that postsorption Ca-Mg/biochar can continually release P and is more suitable for an acid environment.

  9. Fossil Echinoderms As Monitor of the Mg/Ca Ratio of Phanerozoic Oceans

    NASA Astrophysics Data System (ADS)

    Dickson, J. A. D.

    2002-11-01

    Opinion has long been divided as to whether the Mg/Ca ratio of seawater remained constant during the Phanerozoic or underwent substantial secular change. Existing empirical evidence for the Mg/Ca of ancient seawater provides a poorly resolved and often controversial signal. Echinoderm fossils that have retained their bulk original chemistry, despite micrometer-scale changes, preserve a record of seawater Mg/Ca and confirm that major changes in Mg/Ca occurred during the Phanerozoic. Echinoderms from the Cambrian and from the Carboniferous to the Triassic indicate a seawater Mg/Ca of ~3.3, whereas echinoderms from the Jurassic to the Cretaceous indicate a Mg/Ca of ~1.4. The present seawater Mg/Ca is ~5.

  10. Auger recombination rates in ZnMgO from first principles

    NASA Astrophysics Data System (ADS)

    Heinemann, Markus; Heiliger, Christian

    2011-10-01

    We investigate direct electron-electron-hole interband Auger recombination for wurtzite Zn1-xMgxO alloys in the range 0 ≤ x ≤ 1. Recombination rates are computed by interpolating the band structure and transition matrix elements from ab initio calculations of bulk ZnO, Zn0.5Mgn0.5O, and MgO primitive cells. We find that interband Auger recombination is most probable for Mg concentrations around 50%, where ZnMgO does not exist in a stable wurtzite phase. Since, for low Mg concentrations, the calculated Auger coefficients are far below 10-32 cm6/s, we do not expect significant nonradiative loss through direct interband recombination in wurtzite ZnMgO.

  11. Synthesis, Structure, and Properties of Ca2ZnN2

    DTIC Science & Technology

    1990-04-30

    ternary nitride CaiZnN9, prepared by the reaction of Ca3N2 and Zn in NT gas at 680-. The structure, determined by x-ray powder diffraction and...ZnN 2, prepared by the reaction of Ca 3N2 and Zn in N2 gas at 680 0 C. The structure, determined by x-ray powder diffraction and refined by Rietveld...properties of Ca2ZnN2. Experimental Synthesis All manipulations were carried out in an argon-filled glove box. Calcium nitride was first prepared by

  12. Structural and electronic properties of wurtzite MgZnO and BeMgZnO alloys and their thermodynamic stability

    NASA Astrophysics Data System (ADS)

    Gorczyca, I.; Teisseyre, H.; Suski, T.; Christensen, N. E.; Svane, A.

    2016-12-01

    Structural and electronic properties of MgZnO and BeMgZnO alloys are studied by the ab-initio Density Functional Theory method. Large band gap bowings are found for both kinds of alloys. The total energies as functions of the lattice constants are calculated and used to determine the ranges of composition in which the alloys are stable in the wurtzite structure. It is shown that the addition of 6% of Be can already help in stabilization of the MgZnO alloy in the wurtzite structure. The band gap can reach 7 eV for the wurtzite BexMg0.5Zn0.5-xO alloys with x approaching 0.5 and about 5.0 eV for Be0.125MgxZn0.875-xO type alloys for x approaching 0.6. Varying the alloy composition according to the presented stabilization diagram showing ranges of the x, y, for which BexMgyZn1-x-yO is stable in the wurtzite phase, one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.

  13. Sr/Ca and Mg/Ca in Aragonitic Bivalves: Do They Record Temperature?

    NASA Astrophysics Data System (ADS)

    Gillikin, D. P.; Ulens, H.; Dehairs, F.; Baeyens, W.; Navez, J.; Andre, L.; Keppens, E.; Calmars Group,.

    2003-12-01

    The chemical or isotopic composition of calcareous skeletons have long been recognized as archives of past and present environmental conditions. Oxygen isotopes (d18O) of biogenic carbonates are a powerful proxy of SST, however, although usually dominated by SST, salinity (SSS) also significantly effects the oxygen isotopic signal recorded in the carbonate. This has led researchers to explore new proxies, which are independent of SSS. Generally, Sr/Ca and Mg/Ca of seawater remains unchanged above salinities of 10 and marine animals will commonly live in habitats that do not fluctuate below this salinity. To solve the issue of SSS complicating paleotemperature records, these "new" proxies must be at least as reliable as d18O. If an environmental control is dominant, the proxies should be reproducible between specimens growing under the same field conditions. Both Sr and Mg have been used as paleotemperature proxies in corals and foraminifera, whereas a fewer attempts have been made to use these proxies in bivalves. Some report a clear seasonal periodicity in Sr/Ca profiles of bivalves, which covaries with d18O (i.e., temperature), whereas others have found no clear periodicity. We test the robustness of these proxies by analyzing the shell material from three species of aragonitic clams from around the world using a LA-ICP-MS. Three individuals of M. mercenaria from North Carolina, USA, three individuals of Saxidomus giganteus from Washington, USA and one Arctica islandica from Norway have been analyzed. As expected, there is excellent reproducibility of d18O between specimens (both M. mercenaria and S. giganteus) indicating external environmental conditions control this proxy (i.e. SST and SSS). Preliminary data analysis show that Sr and Mg are not reproducible between specimens from the same site nor do they exhibit a clear seasonal cyclicity, indicating individual metabolic effects (i.e., vital effects) dominate the incorporation of these elements. A. islandica

  14. The Crystal Structures of Mg 3N 2and Zn 3N 2

    NASA Astrophysics Data System (ADS)

    Partin, D. E.; Williams, D. J.; O'Keeffe, M.

    1997-08-01

    The structures of Mg3N2and Zn3N2have been refined from neutron time-of-flight powder diffraction data. These compounds have the antibixbyite structure and are the first such to be fully refined. The space group isIaoverline3,a=9.9528(1) Å (Mg3N2) and 9.7691(1) Å (Zn3N2). A revised bond valence parameter for Mg-N bonds is suggested.

  15. Thermodynamic analysis and experimental study on the oxidation of the Zn-Al-Mg coating baths

    NASA Astrophysics Data System (ADS)

    Su, Xuping; Zhou, Jie; Wang, Jianhua; Wu, Changjun; Liu, Ya; Tu, Hao; Peng, Haoping

    2017-02-01

    Surface oxidation of molten Zn-6Al baths containing 0.0, 3.0 and 6.0 wt. % Mg were analyzed using X-ray photoelectron spectroscopy. γ-Al2O3 is formed on the surface of the Zn-6Al bath, while MgAl2O4 and MgO occur at 460 °C in the Zn-6Al-3Mg and Zn-6Al-6Mg baths, respectively. Thermodynamic analysis on the oxidation of the Zn-Al-Mg baths was performed. Calculated phase diagrams at 460 °C and 560 °C show good agreements with the experimental results. MgO or MgAl2O4 exists in almost the entire composition range of the calculated oxidation diagrams. According to the calculation, oxidation products depend on the composition and temperature of the baths. The primary and secondary oxidation products of the Zn-Al-Mg baths can be reasonably explained by oxidation phase diagrams. Utilizing these results, the favorable practical bath melts and operating conditions can be designed.

  16. Zn- and Mg- Containing Tricalcium Phosphates-Based Adjuvants for Cancer Immunotherapy

    NASA Astrophysics Data System (ADS)

    Wang, Xiupeng; Li, Xia; Onuma, Kazuo; Sogo, Yu; Ohno, Tadao; Ito, Atsuo

    2013-07-01

    Zn-, and Mg-containing tricalcium phosphates (TCPs) loaded with a hydrothermal extract of a human tubercle bacillus (HTB) were prepared by immersing Zn-TCP and Mg-TCP in HTB-containing supersaturated calcium phosphate solutions. The in vitro and in vivo immunogenic activities of the HTB-loaded Zn-, and Mg-TCPs (Zn-Ap-HTB and Mg-Ap-HTB, respectively) were evaluated as potential immunopotentiating adjuvants for cancer immunotherapy. The Zn-Ap-HTB and Mg-Ap-HTB adjuvants showed no obvious cytotoxicity and more effectively stimulated granulocyte-macrophage colony-stimulating factor (GM-CSF) secretion by macrophage-like cells than unprocessed HTB or HTB-loaded TCP (T-Ap-HTB) in vitro. Zn-Ap-HTB and Mg-Ap-HTB mixed with liquid-nitrogen-treated tumor tissue markedly inhibited the in vivo development of rechallenged Lewis lung carcinoma (LLC) cells compared with T-Ap-HTB and the unprocessed HTB mixed liquid-nitrogen-treated tumor tissue. Zn-Ap-HTB and Mg-Ap-HTB contributed to eliciting potent systemic antitumor immunity in vivo.

  17. AC conductivity and structural properties of Mg-doped ZnO ceramic

    NASA Astrophysics Data System (ADS)

    Othman, Zayani Jaafar; Hafef, Olfa; Matoussi, Adel; Rossi, Francesca; Salviati, Giancarlo

    2015-11-01

    Undoped ZnO and Zn1- x Mg x O ceramic pellets were synthesized by the standard sintering method at the temperature of 1200 °C. The influence of Mg doping on the morphological, structural and electrical properties was studied. The scanning electron microscopy images revealed rough surface textured by grain boundaries and compacted grains having different shapes and sizes. Indeed, the X-ray diffraction reveals the alloying of hexagonal ZnMgO phase and the segregation of cubic MgO phase. The crystallite size, strain and stress were studied using Williamson-Hall (W-H) method. The results of mean particle size of Zn1- x Mg x O composites showed an inter-correlation with W-H analysis and Sherrer method. The electrical conductivity of the films was measured from 173 to 373 K in the frequency range of 0.1 Hz-1 MHz to identify the dominant conductivity mechanism. The DC conductivity is thermally activated by electron traps having activation energy of about 0.09 to 0.8 eV. The mechanisms of AC conductivity are controlled by the correlated barrier hopping model for the ZnO sample and the small polaron tunneling (SPT) model for Zn0.64Mg0.36O and Zn0.60Mg0.40O composites.

  18. In vitro and in vivo corrosion measurements of Mg-6Zn alloys in the bile.

    PubMed

    Chen, Yigang; Yan, Jun; Wang, Zhigang; Yu, Song; Wang, Xiaohu; Yuan, Ziming; Zhang, Xiaonong; Zhao, Changli; Zheng, Qi

    2014-09-01

    Mg-6Zn alloy was studied as candidate biodegradable metallic implants for the common bile duct (CBD) in terms of its in vitro corrosion and in vivo corrosion. Electrochemical measurements, immersion tests and hydrogen evolution were performed in the bile and Hanks' solution to evaluate the in vitro degradation behavior of Mg-6Zn alloy. The results showed that the degradation rate and hydrogen evolution were higher when Mg-6Zn alloy immersed in the bile than in the Hanks' solution. The polarization resistance of the samples in the Hanks' solution was about 1.5 times to that in the bile. In the in vivo experiment, Mg-6Zn alloy stents were inserted in CBD of 42 rabbits, and CT scans, the value of total bilirubin (TB) and in vivo corrosion rate were determined. From the results of CT images and the fluctuations of TB values, it can be seen that the stent was degraded gradually in CBD. After 1 week post-implantation, the majority of the Mg-6Zn alloy sample remained in the CBD. Usually the required support time for CBD stent was approximately 7-10 days, thus the Mg-6Zn alloy stent was very close to the clinical requirement for CBD support materials. After three weeks, the residual weight of the Mg-6Zn alloy was only 9% of the original weight. The in vivo corrosion rate of Mg-6Zn alloy was ~0.107 mm·year(-1), which was much lower than that calculated in vitro (~0.72 mm·year(-1) by electrochemical test). Based on our research, there is promising for the Mg-6Zn alloy in CBD applications.

  19. Room temperature ferromagnetism in Mg-doped ZnO nanoparticles

    SciTech Connect

    Singh, Jaspal Vashihth, A.; Gill, Pritampal Singh; Verma, N. K.

    2015-06-24

    Zn{sub 1-x}Mg{sub x}O (x = 0, 0,10) nanoparticles were successfully synthesized using sol-gel method. X-ray diffraction (XRD) confirms that the synthesized nanoparticles possess wurtzite phase having hexagonal structure. Morphological analysis was carried out using transmission electron microscopy (TEM) which depicts the spherical morphology of ZnO nanoparticles. Energy dispersive spectroscopy (EDS) showed the presence of Mg in ZnO nanoparticles. Electron spin resonance (ESR) signal was found to be decreasing with increasing of Mg-doping concentration. The room temperature ferromagnetism was observed in undoped and Mg-doped ZnO nanoparticles. The increase of Mg-doping concentration resulted in decrease of saturation magnetization value which could be attributed to decrease of oxygen vacancies present in host nanoparticles.

  20. Determination of the spontaneous polarization of wurtzite (Mg,Zn)O

    SciTech Connect

    Stölzel, Marko Müller, Alexander; Benndorf, Gabriele; Lorenz, Michael; Grundmann, Marius; Patzig, Christian; Höche, Thomas

    2014-05-12

    We report on the experimental determination of the spontaneous polarization of wurtzite-(Mg,Zn)O by examination of the recombination dynamics of polar ZnO/(Mg,Zn)O quantum wells (QWs). The thickness-dependent decay time of the unscreened single-exciton states inside the QWs was modeled by a self-consistent solution of Schrödinger- and Poisson-equation to deduce the total polarization across the QW for different Mg-contents inside the barriers. By the separation of the piezoelectric components of the polarization, a linear increase in spontaneous polarization with increasing Mg-content x of P/x = (0.151 ± 0.015) C/m{sup 2} was determined for Mg{sub x} Zn{sub 1−x} O.

  1. Segregation of Mg in Zn1-xMgxO single crystals grown from the melt

    NASA Astrophysics Data System (ADS)

    Schulz, Detlev; Bertram, Rainer; Klimm, Detlef; Schulz, Tobias; Thiede, Elvira

    2011-11-01

    Solid solutions between zinc oxide and magnesium oxide containing up to 4 at.% Mg were grown from the melt using a modified Bridgman technique. Chemical analysis (ICP-OES) and photoluminescence (PL) measurements revealed that the Mg concentration in the melt is larger compared with the starting material. This observation contradicts the commonly accepted assumption, that the ZnO-MgO phase diagram is of eutectic type. Peritectic melting of Zn-rich Zn1-xMgxO can explain the new experimental results, and a new ZnO-MgO phase diagram is proposed. Furthermore a distribution coefficient for Mg of keff=1.32…1.4 has been determined.

  2. Excellent capability in degrading azo dyes by MgZn-based metallic glass powders.

    PubMed

    Wang, Jun-Qiang; Liu, Yan-Hui; Chen, Ming-Wei; Louzguine-Luzgin, Dmitri V; Inoue, Akihisa; Perepezko, John H

    2012-01-01

    The lack of new functional applications for metallic glasses hampers further development of these fascinating materials. In this letter, we report for the first time that the MgZn-based metallic glass powders have excellent functional ability in degrading azo dyes which are typical organic water pollutants. Their azo dye degradation efficiency is about 1000 times higher than that of commercial crystalline Fe powders, and 20 times higher than the Mg-Zn alloy crystalline counterparts. The high Zn content in the amorphous Mg-based alloy enables a greater corrosion resistance in water and higher reaction efficiency with azo dye compared to crystalline Mg. Even under complex environmental conditions, the MgZn-based metallic glass powders retain high reaction efficiency. Our work opens up a new opportunity for functional applications of metallic glasses.

  3. Room temperature fabrication of dielectric Bragg reflectors composed of a CaF2/ZnS multilayered coating.

    PubMed

    Muallem, Merav; Palatnik, Alex; Nessim, Gilbert D; Tischler, Yaakov R

    2015-01-14

    We describe the design, fabrication, and characterization of mechanically stable, reproducible, and highly reflecting distributed Bragg reflectors (DBR) composed of thermally evaporated thin films of calcium fluoride (CaF2) and zinc sulfide (ZnS). CaF2 and ZnS were chosen as the low and high refractive index components of the multilayer DBR structures, with n = 1.43 and n = 2.38 respectively, because neither material requires substrate heating during the deposition process in order to produce optical quality thin films. DBRs consisting of seven pairs of CaF2 and ZnS layers, were fabricated with thicknesses of 96 and 58 nm, respectively, as characterized by high-resolution scanning electron microscopy (HR-SEM), and exhibited a center wavelength of λc = 550 nm and peak reflectance exceeding 99%. The layers showed good adhesion to each other and to the glass substrate, resulting in mechanically stable DBR coatings. Complete optical microcavities consisting of two such DBR coatings and a CaF2 spacer layer between them could be fabricated in a single deposition run. Optically, these structures exhibited a resonator quality factor of Q > 160. When a CaF2/ZnS DBR was grown, without heating the substrate during deposition, on top of a thin film containing the fluorescent dye Rhodamine 6G, the fluorescence intensity showed no degradation compared to an uncoated film, in contrast to a MgF2/ZnS DBR coating grown with substrate heating which showed a 92% reduction in signal. The ability to fabricate optical quality CaF2/ZnS DBRs without substrate heating, as introduced here, can therefore enable formation of low-loss high-reflectivity coatings on top of more delicate heat-sensitive materials such as organics and other nanostructured emitters, and hence facilitate the development of nanoemitter-based microcavity device applications.

  4. Thermally stimulated luminescence of Mg-doped ZnO Nanophosphors

    NASA Astrophysics Data System (ADS)

    Cruz-Vázquez, C.; Borbón-Nuñez, H. A.; Bernal, R.; Gaspar-Armenta, J. A.; Castaño, V. M.

    2014-05-01

    Nanosized ZnO:Mg phosphors were synthesized through a controlled chemical reaction. X-ray diffraction patterns confirmed that Mg entered in a substitutive way in Zn sites. To investigate their thermoluminescence (TL) properties, some samples were exposed to beta-particle irradiation. The results reported here show that Mg doping improves ZnO TL features that are important for TL dosimetry applications, such as the shape of the glow curve, the temperature at which the maximum TL intensity is observed, and the TL fading and reproducibility. No saturation clues of the TL response as a function of the dose is observed for doses below 1600 Gy.

  5. Reconstructing past seawater Mg/Ca and Sr/Ca from mid-ocean ridge flank calcium carbonate veins.

    PubMed

    Coggon, Rosalind M; Teagle, Damon A H; Smith-Duque, Christopher E; Alt, Jeffrey C; Cooper, Matthew J

    2010-02-26

    Proxies for past seawater chemistry, such as Mg/Ca and Sr/Ca ratios, provide a record of the dynamic exchanges of elements between the solid Earth, the atmosphere, and the hydrosphere and the evolving influence of life. We estimated past oceanic Mg/Ca and Sr/Ca ratios from suites of 1.6- to 170-million-year-old calcium carbonate veins that had precipitated from seawater-derived fluids in ocean ridge flank basalts. Our data indicate that before the Neogene, oceanic Mg/Ca and Sr/Ca ratios were lower than in the modern ocean. Decreased ocean spreading since the Cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early Tertiary may explain the recent rise in these ratios.

  6. Multi-terminal Two-color ZnCdSe/ZnCdMgSe Based Quantum-well Infrared Photodetector

    NASA Astrophysics Data System (ADS)

    Kaya, Yasin; Ravikumar, Arvind; Chen, Guopeng; Tamargo, Maria C.; Shen, Aidong; Gmachl, Claire

    Target recognition and identification applications benefits from two-color infrared (IR) detectors in the mid and long-wavelength IR regions. Currently, InGaAs/AlGaAs and GaAs/AlGaAs multiple quantum wells (QWs) grown on GaAs substrate are the most commonly used two-color QW IR photodetectors (QWIPs). However, the lattice-mismatch and the buildup of strain limit the number of QWs that can be grown, in turn increasing the dark current noise, and limiting the device detectivity.In this work, we report on two-color QWIPs based on the large conduction band offset (~1.12ev) ZnCdSe/ZnCdMgSe material system lattice matched to InP. QWIPs were designed based on a bound to quasi-bound transition, centered at 4 μm and 7 μm and each QW is repeated 50 times to eliminate the high dark current and a contact layer is inserted between the two stacks of QWs for independent electrical contacts. Wafers are processed into two step rectangular mesas by lithography and wet etching. Experiments showed absorption spectra centered at 4.9 μm and 7.6 μm at 80 K and the full width at half maximums were Δλ / λ = 21 % and Δλ / λ = 23 % , respectively. Current work studies the Johnson and the background noise limited detectivities of these QWIPs. Current address: School of Earth, Energy and Environmental Sciences, Stanford, CA 94305, USA.

  7. Impact of strain on electronic defects in (Mg,Zn)O thin films

    SciTech Connect

    Schmidt, Florian Müller, Stefan; Wenckstern, Holger von; Benndorf, Gabriele; Pickenhain, Rainer; Grundmann, Marius

    2014-09-14

    We have investigated the impact of strain on the incorporation and the properties of extended and point defects in (Mg,Zn)O thin films by means of photoluminescence, X-ray diffraction, deep-level transient spectroscopy (DLTS), and deep-level optical spectroscopy. The recombination line Y₂, previously detected in ZnO thin films grown on an Al-doped ZnO buffer layer and attributed to tensile strain, was exclusively found in (Mg,Zn)O samples being under tensile strain and is absent in relaxed or compressively strained thin films. Furthermore a structural defect E3´ can be detected via DLTS measurements and is only incorporated in tensile strained samples. Finally it is shown that the omnipresent deep-level E3 in ZnO can only be optically recharged in relaxed ZnO samples.

  8. Growth of new ternary intermetallic phases from Ca/Zn eutectic flux

    SciTech Connect

    Stojanovic, Milorad Latturner, Susan E.

    2007-03-15

    The eutectic 7.3:2.7 molar ratio mixture of calcium and zinc metal melts at 394 deg. C and was explored as a solvent for the growth of new intermetallic phases for potential use as hydrogen storage materials. The reaction of nickel in this molten mixture produces two new phases-the CaCu{sub 5}-related structure CaNi{sub 2}Zn{sub 3} (P6/mmm, a=8.9814(5) A, c=4.0665(5) A) and a new cubic structure Ca{sub 21}Ni{sub 2}Zn{sub 36} (Fd-3m, a=21.5051(4) A). Palladium-containing reactions produced CaPd{sub 0.85}Zn{sub 1.15} with the orthorhombic TiNiSi structure type (Pnma, a=7.1728(9) A, b=4.3949(5) A, c=7.7430(9) A). Reactions of platinum in the Ca/Zn mixture produce Ca{sub 6}Pt{sub 3}Zn{sub 5}, with an orthorhombic structure related to that of W{sub 3}CoB{sub 3} (Pmmn, a=13.7339(9) A, b=4.3907(3) A, c=10.7894(7) A). - Graphical abstract: The calcium/zinc eutectic is a useful synthesis medium for the growth of new intermetallic phases. Addition of group 10 transition metals to this flux produces ternary phases CaNi{sub 2}Zn{sub 3}, Ca{sub 21}Ni{sub 2}Zn{sub 36}, CaPd{sub 0.85}Zn{sub 1.15}, and Ca{sub 6}Pt{sub 3}Zn{sub 5}. The nickel-centered zinc icosahedron surrounded by a pentagonal dodecahedron of calcium atoms is found in Ca{sub 21}Ni{sub 2}Zn{sub 36}.

  9. Superconducting tunnel junctions on MgB2 using MgO and CaF2 as a barrier

    NASA Astrophysics Data System (ADS)

    Sakoda, Masahito; Aibara, Masato; Mede, Kazuya; Kikuchi, Motoyuki; Naito, Michio

    2016-11-01

    We report the fabrication of superconducting tunnel junctions, both of superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS), on MgB2 using MgO and CaF2 as a barrier. The SIN junctions fabricated using an MgO barrier showed excellent quasi-particle characteristics, including a large superconducting gap (Δ) of 2.5-3 meV and a low zero-bias conductance. We have also fabricated SIS junctions with an MgO barrier, but the quasi-particle characteristics of the SIS junctions are not as good as those of the SIN junctions, namely a reduced superconducting gap and a high zero-bias conductance. It appears that top MgB2 electrodes do not grow well on an MgO barrier, which is also suggested from in-situ RHEED observation. The SIN junctions fabricated using a CaF2 barrier showed less sharp quasi-particle characteristics than using an MgO barrier. However, the SIS junctions using a CaF2 barrier showed a fairly large IcRN value at 4.2 K over 1 mV and also exhibited finite Josephson current up to almost the film's Tc (∼30 K). The RHEED observation revealed that top MgB2 electrodes grow well on a CaF2 barrier.

  10. Interdiffusion and impurity diffusion in polycrystalline Mg solid solution with Al or Zn

    SciTech Connect

    Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Sohn, Yong Ho

    2014-01-01

    Interdiffusion and impurity diffusion in Mg binary solid solutions, Mg(Al) and Mg(Zn) were investigated at temperatures ranging from 623 to 723 K. Interdiffusion coef cients were determined via the Boltzmann Matano Method using solid-to-solid diffusion couples assembled with polycrystalline Mg and Mg(Al) or Mg(Zn) solid solutions. In addition, the Hall method was employed to extrapolate the impurity diffusion coef cients of Al and Zn in pure polycrystalline Mg. For all diffusion couples, electron micro-probe analysis was utilized for the measurement of concentration pro les. The interdiffusion coef cient in Mg(Zn) was higher than that of Mg(Al) by an order of magnitude. Additionally, the interdiffusion coef cient increased signi cantly as a function of Al content in Mg(Al) solid solution, but very little with Zn content in Mg(Zn) solid solution. The activation energy and pre-exponential factor for the average effective interdiffusion coef cient in Mg(Al) solid solution were determined to be 186.8 ( 0.9) kJ/mol and 7.69 x 10-1 ( 1.80 x 10-1) m2/s, respectively, while those determined for Mg(Zn) solid solution were 139.5 ( 4.0) kJ/mol and 1.48 x 10-3 ( 1.13 x 10-3) m2/s. In Mg, the Zn impurity diffusion coef cient was an order of magnitude higher than the Al impurity diffusion coef cient. The activation energy and pre-exponential factor for diffusion of Al impurity in Mg were determined to be 139.3 ( 14.8) kJ/mol and 6.25 x 10-5 ( 5.37 x 10-4) m2/s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 ( 6.3) kJ/mol and 2.90 x 10-5 ( 4.41 x 10-5) m2/s.

  11. The in vitro biocompatibility and macrophage phagocytosis of Mg17Al12 phase in Mg-Al-Zn alloys.

    PubMed

    Liu, Chen; He, Peng; Wan, Peng; Li, Mei; Wang, Kehong; Tan, Lili; Zhang, Yu; Yang, Ke

    2015-07-01

    Mg alloys are gaining interest for applications as biodegradable medical implant, including Mg-Al-Zn series alloys with good combination of mechanical properties and reasonable corrosion resistance. However, whether the existence of second phase particles in the alloys exerts influence on the biocompatibility is still not clear. A deeper understanding of how the particles regulate specific biological responses is becoming a crucial requirement for their subsequent biomedical application. In this work, the in vitro biocompatibility of Mg17Al12 as a common second phase in biodegradable Mg-Al-Zn alloys was investigated via hemolysis, cytotoxicity, cell proliferation, and cell adhesion tests. Moreover, osteogenic differentiation was evaluated by the extracellular matrix mineralization assay. The Mg17Al12 particles were also prepared to simulate the real situation of second phase in the in vivo environment in order to estimate the cellular response in macrophages to the Mg17Al12 particles. The experimental results indicated that no hemolysis was found and an excellent cytocompatibility was also proved for the Mg17Al12 second phase when co-cultured with L929 cells, MC3T3-E1 cells and BMSCs. Macrophage phagocytosis co-culture test revealed that Mg17Al12 particles exerted no harmful effect on RAW264.7 macrophages and could be phagocytized by the RAW264.7 cells. Furthermore, the possible inflammatory reaction and metabolic way for Mg17Al12 phase were also discussed in detail.

  12. Adsorption and desorption of Zn(II) and Cu(II) on Ca- alginate immobilized activated rice bran

    NASA Astrophysics Data System (ADS)

    Suratman, A.; Kamalia, N. Z.; Kusumawati, W. A.

    2016-02-01

    Ca-alginate immobilized activated rice bran has been used for adsorption of Zn(II) and Cu(II) from aqueous solution. The effect of the pH, kinetics model, adsorption isotherm and desorption on the adsorption performance was investigated. Activated rice bran was immobilized by the entrapment in alginate beads. The adsorption strength of Ca-alginate immobilized activated rice bran was compared to Ca-alginate and non-immobilized activated rice bran. The concentrations of adsorbed ions were analyzed using Atomic Absorption Spectrophotometer (AAS). The result showed that pH of 4.0 and the contact time of 120 min are the optimum condition for adsorption of Zn(II) and Cu(II). The adsorption kinetic of Zn(II) and Cu(II) followed the pseudo-second-order model with adsorption rate constant 4.9 x 10-2 and 3.14 g.mg-1.min-1, respectively. The both adsorption processes obeyed Langmuir isotherm with adsorption capacity of 2.03 and 2.42 mg.g-1 of adsorbent, respectively. The strength of Zn adsorption on Ca-alginate immobilized activated rice bran (86.63%) was more effective compared to Ca-alginate beads (60.96%) and activated rice bran (43.85%). The strength of Cu adsorption was 80.00%, 61.50% and 22.10%, respectively. The desorption of Zn(II) and Cu(II) showed that recovery percentage of the adsorption was 76.56% and 57.80% with the condition of using HCl 0.1 M as desorption agent for 1 hour.

  13. Surface and cut-edge corrosion behavior of Zn-Mg-Al alloy-coated steel sheets as a function of the alloy coating microstructure

    NASA Astrophysics Data System (ADS)

    Oh, Min-Suk; Kim, Sang-Heon; Kim, Jong-Sang; Lee, Jae-Won; Shon, Je-Ha; Jin, Young-Sool

    2016-01-01

    The effects of Mg and Al content on the microstructure and corrosion resistance of hot-dip Zn-Mg-Al alloycoated steel sheets were investigated. Pure Zn and Zn-based alloy coatings containing Mg (0-5 wt%) and Al (0.2-55 wt%) were produced by a hot-dip galvanizing method. Mg and Al addition induced formation of intermetallic microstructures, like primary Zn, Zn/MgZn2 binary eutectic, dendric Zn/Al eutectoid, and Zn/Al/MgZn2/ternary eutectic structures in the coating layer. MgZn2-related structures (Zn/MgZn2, Zn/Al/MgZn2, MgZn2) played an important role in increasing the corrosion resistance of Zn-Mg-Al alloy-coated steel sheets. Zn-3%Mg-2.5%Al coating layer containing a large volume of lamellar-shaped Zn/MgZn2 binary eutectic structures showed the best cut-edge corrosion resistance. The analysis indicated that Mg dissolved from MgZn2 in the early stage of corrosion and migrated to the cathodic region of steel-exposed cut-edge area to form dense and ordered protective corrosion products, leading to prolonged cathodic protection of Zn-Mg-Al alloy-coated steel sheets.

  14. Effect of secular variation in oceanic Mg/Ca on calcareous biomineralization

    NASA Astrophysics Data System (ADS)

    Ries, J. B.; Stanley, S. M.

    2006-12-01

    The polymorph mineralogy of simple, hypercalcifying marine organisms has generally varied in synchroneity with the polymorph mineralogy of abiotic CaCO3 precipitates (ooids, marine cements) throughout the Phanerozoic Eon. This synchroneity is caused by secular variation in the Mg/Ca ratio of seawater (SW; mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = calcite), determined primarily by the mixing rate of mid-ocean-ridge/large-igneous-province hydrothermal brines and river water, driven by the global rate of ocean crust production. Here, we present experiments evaluating the effect of seawater Mg/Ca on the biomineralization and growth of extant representatives of hypercalcifying taxa that have been subjected to fluctuations in oceanic Mg/Ca in the past. Codiacean algae (arag), scleractinian corals (arag), coccolithophores (low-high Mg-calc), coralline algae (high Mg-calc), various reef-dwelling animals (echinoids, crabs, shrimp, calcareous serpulid worms; high Mg- calc), and calcifying microbial mats (arag + high-Mg calc) were grown in artificial SW formulated over the range of mMg/Ca (1.0 to 5.2) that occurred throughout each taxon's history. Codiacean algae and scleractinian corals exhibited higher rates of calcification and growth in artificial SW favoring their aragonite mineralogy and, significantly, produced a portion of their CaCO3 as calcite in the artificial calcite SW. Coccolithophores (low-high Mg calc.) showed higher calcification and growth rates and produced low-Mg calcite in the calcite SW. Likewise, coralline algae and the reef-dwelling animals (high-Mg calc) varied skeletal Mg/Ca with seawater Mg/Ca. The calcifying microbial mats grew equally well in the calcite and aragonite SW and varied their mineral polymorph commensurate with the SW (mMg/Ca<2 = low- Mg calc; mMg/Ca>2 = arag + high-Mg calc), suggesting a nearly abiotic mode of calcification. The precipitation of low-Mg calcite + aragonite by codiacean algae and scleractinian corals (arag

  15. Corrosion Behavior and Surface Modification of Mg-Zn Implant Alloys

    NASA Astrophysics Data System (ADS)

    Ghayad, I. M.; Maamoun, M. A.; Metwally, W. A.; El-Baradie, Z. M.; Abdel-Azim, A. N.

    2016-10-01

    In this study, Mg-Zn alloys (1-4 wt.% Zn) were fabricated with high-purity raw materials using a clean melting process (fluxless method) and a protective atmosphere of CO2 + 0.4 SF6. The as-cast microstructures of the investigated alloys were characterized by optical and scanning electron microscopes, EDS and XRD. Corrosion properties of the prepared alloys were examined in simulated body fluid by electrochemical techniques and immersion test (hydrogen evolution method). Surface modification of the prepared alloys was performed using micro-arc oxidation (MAO) treatment and hydroxyapatite (HA) coating. Microstructure observation revealed that Zn was completely dissolved in the α-Mg matrix up to 2 wt.%. Higher Zn content led to a reduction in the grain size and the development of a second phase (MgZn2). Corrosion testing results revealed that Mg-1,2,3 wt.% Zn have almost the same degradation rate, whereas Mg-4Zn has the highest degradation rate. HA coating on MAO-treated magnesium alloys formed a dense and compact layer on the alloy surface, which had largely improved surface properties and enhanced corrosion resistance of the prepared alloys.

  16. Review: the effects of secular variation in seawater Mg/Ca on marine biocalcification

    NASA Astrophysics Data System (ADS)

    Ries, J. B.

    2009-07-01

    Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time is believed to have been caused by tectonically-induced variations in seawater molar Mg/Ca (>2="aragonite seas"; <2="calcite seas"). Here, I review a series of experiments in which extant calcifying taxa were reared in experimental seawater formulated over the range of mMg/Ca ratios (1.0 to 5.2) that occurred throughout their geologic history. Aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibited higher rates of calcification and growth in the experimental seawaters that favored their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification in mineralogically-favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within autotrophs through the liberation of CO2. The Mg/Ca ratio of calcite secreted by the coccolithophores, coralline algae and reef-dwelling animals (crustacea, urchins, calcareous tube worms) declined with reductions in seawater Mg/Ca. Calcifying microbial biofilms varied their mineral polymorph with seawater Mg/Ca (mMg/Ca<2=low Mg calc; mMg/Ca>2=arag+high Mg calc), suggesting a nearly abiotic mode of calcification. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggests that modern high Mg calcite organisms probably secreted low Mg calcite in calcite seas of the past. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in seawater Mg/Ca, a probable consequence of them inducing a less controlled

  17. Identification and characteristics of ZnO/MgO core-shell nanowires

    SciTech Connect

    Yang, S. Wang, L.; Wang, Y.; Li, L.; Wang, T.; Jiang, Z.

    2015-03-15

    In this paper, ZnO/MgO core-shell nanowires are synthesized based on a one-step chemical vapor deposition (CVD) method. The scanning electron microscopy (SEM) images of core-shell nanowires indicate that Mg addition has little influence on the morphology of the synthesizing products. High crystalline quality ZnO/MgO core-shell nanowires instead of ZnMgO ternary compounds are identified by X-ray diffraction (XRD) patterns, transmission electron microscopy (TEM) images, selected area electron diffraction (SAED) pattern and photoluminescence (PL) spectra. The experimental results show that the ultraviolet (UV) emission of these samples with MgO shell is 12 times higher than that of the corresponding bare ZnO nanowires, and the suppression of the green emission is only 1/45 of the bare ZnO nanowires. It is also found that PL properties are proportional to Mg ratio. The UV emission enhancement and green emission suppression are due to the passivation of surface defects and the improvement of ZnO crystalline quality. The results are very useful for the development of optical devices based on nanowires.

  18. Structural and photoluminescence properties of Mg substituted ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Mallika, A. N.; Ramachandra Reddy, A.; Sowri Babu, K.; Sujatha, Ch.; Venugopal Reddy, K.

    2014-03-01

    This paper reports on structural and optical properties of Mg doped ZnO nanoparticles prepared through sol-gel method using polyvinyl alcohol as chelating agent. X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FE-SEM), UV-Vis (UV-Vis), Fourier Transform Infrared (FTIR) and Photoluminescence (PL) spectrophotometers were employed to study the structural and optical properties. XRD and FE-SEM results demonstrated that particle size of ZnO decreased with increase in Mg concentrations. It was observed that the absorption spectrum of ZnO blue shifted as the Mg concentration enhanced from 1 mol.% to 5 mol.%, presumably due to reduction in particle size. It was found that MgO secondary phase was not formed even above the solid solubility limit of Mg in ZnO. ZnO nanoparticles exhibited an intense and strong UV emission peak at 396 nm and this peak is attributed to the electron transition from the localized level slightly below conduction band to the valence band. The position of this emission peak remained same for all concentrations of Mg in ZnO.

  19. High Strength, Nano-Structured Mg-Al-Zn Alloy

    DTIC Science & Technology

    2011-01-01

    nanocrystalline (nc) Mg AZ80 alloy, synthesized via a cryomilling and spark plasma sintering (SPS) approach are reported and discussed. The effects of...nanocrystalline (nc) Mg AZ80 alloy, synthesized via a cryomilling and spark plasma sintering (SPS) approach are reported and discussed. The effects of...forging capability [23,24]. Therefore, the Mg AZ80 alloy system was selected and processed using a cryomilling and spark plasma sintering (SPS

  20. The (Ca2+ + Mg2+)-stimulated ATPase of the rat parotid endoplasmic reticulum.

    PubMed Central

    Thiyagarajah, P; Lim, S C

    1986-01-01

    A membrane fraction enriched in endoplasmic reticulum was prepared from rat parotid glands by using sucrose-gradient centrifugation. The fraction showed a 10-fold increase in specific activity of NADPH: cytochrome c reductase activity over that of tissue homogenates and minimal contamination with plasma membranes or mitochondria. The endoplasmic reticulum fraction possessed both Mg2+ -stimulated ATPase as well as Ca2+, Mg2+-ATPase [( Ca2+ + Mg2+)-stimulated ATPase]activity. The Ca2+, Mg2+-ATPase required 2-5 mM-Mg2+ for optimal activity and was stimulated by submicromolar concentrations of free Ca2+. The Km for free Ca2+ was 0.55 microM and the average Vmax. was 60 nmol/min per mg of protein. The Km for ATP was 0.11 mM. Other nucleotides, such as GTP, CTP or ADP, could not substitute for ATP in supporting the Ca2+-activated nucleotidase activity. Increasing the K+ concentration from 0 to 100 mM caused a 2-fold activation of the Ca2+, Mg2+-ATPase. Trifluoperazine, W7 [N-(6-aminohexyl)-5-chloronaphthalene-1-sulphonamide] and vanadate inhibited the enzyme. The concentration of trifluoperazine and vanadate required for 50% inhibition of the ATPase were 52 microM and 28 microM respectively. Calmodulin, cyclic AMP, cyclic AMP-dependent protein kinase and inositol 1,4,5-trisphosphate had no effect on the ATPase. The properties of the Ca2+, Mg2+ -ATPase were distinct from those of the Mg2+-ATPase, but comparable with those reported for the parotid endoplasmic-reticulum Ca2+-transport system [Kanagasuntheram & Teo (1982) Biochem. J. 208, 789-794]. The results suggest that the Ca2+, Mg2+-ATPase is responsible for driving the ATP-dependent Ca2+ accumulation by this membrane. PMID:2943271

  1. Synthesis, characterization and antibacterial property of ZnO:Mg nanoparticles

    NASA Astrophysics Data System (ADS)

    Kompany, A.; Madahi, P.; Shahtahmasbi, N.; Mashreghi, M.

    2012-09-01

    Sol-gel method was successfully used for the synthesis of ZnO nanoparticles (NPs) doped with different concentrations of Mg and the structural, optical and antibacterial properties of the nanoparticles were studied. The synthesized ZnO:Mg powders were characterized using x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformation Infrared (FTIR) and UV-Vis spectroscopy. It was revealed that the samples have hexagonal Wurtzite structure, and the phase segregation takes place for 15% Mg content. TEM images show that the average size of the particles is about 50 nm. Also, the antibacterial activities of the nanoparticles were tested against Escherichia coli (Gram negative) cultures. ZnO:Mg nanofluid showed good antibacterial activity which increases with the increase of NPs concentration, and decreases slightly with the amount of Mg.

  2. Controls on shell Mg/Ca and Sr/Ca in cultured planktonic foraminiferan, Globigerinoides ruber (white)

    NASA Astrophysics Data System (ADS)

    Kısakürek, B.; Eisenhauer, A.; Böhm, F.; Garbe-Schönberg, D.; Erez, J.

    2008-09-01

    Mg/Ca and Sr/Ca ratios were determined on a single species of planktonic foraminiferan, Globigerinoides ruber (white), collected from the Gulf of Eilat and cultured in seawater at five different salinities (32 to 44), five temperatures (18 to 30 °C) and four pH values (7.9 to 8.4). The Mg/Ca-temperature calibration of cultured G. ruber (with an exponential slope of 8 ± 3%/°C) agrees well with previously published calibrations from core-tops and sediment traps. However, the dependence of Mg/Ca on salinity (with an exponential slope of 5 ± 3%/psu) is also significant and should be included in the calibration equation. With this purpose, we calculated a calibration equation for G. ruber dependent on both temperature and salinity within the 95% confidence limits: Mg/Ca(mmol/mol)=exp[0.06(±0.02)∗S(psu)+0.08(±0.02)∗T(°C)-2.8(±1.0)],R=0.95 The influence of pH on Mg/Ca ratios is negligible at ambient seawater pH (8.1 to 8.3). However, we observe a dominating pH control on shell Mg/Ca when the pH of seawater is lower than 8.0. Sr/Ca in G. ruber shows a significant positive correlation with average growth rate. Presumably, part of the variability in shell Sr/Ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions.

  3. Luminescence and electrical properties of single ZnO/MgO core/shell nanowires

    SciTech Connect

    Grinblat, Gustavo; Comedi, David; Bern, Francis; Barzola-Quiquia, José; Esquinazi, Pablo; Tirado, Mónica

    2014-03-10

    To neutralise the influence of the surface of ZnO nanowires for photonics and optoelectronic applications, we have covered them with insulating MgO film and individually contacted them for electrical characterisation. We show that such a metal-insulator-semiconductor-type nanodevice exhibits a high diode ideality factor of 3.4 below 1 V. MgO shell passivates ZnO surface states and provides confining barriers to electrons and holes within the ZnO core, favouring excitonic ultraviolet radiative recombination, while suppressing defect-related luminescence in the visible and improving electrical conductivity. The results indicate the potential use of ZnO/MgO nanowires as a convenient building block for nano-optoelectronic devices.

  4. Lubrication performance and mechanisms of Mg/Al-, Zn/Al-, and Zn/Mg/Al-layered double hydroxide nanoparticles as lubricant additives

    NASA Astrophysics Data System (ADS)

    Li, Shuo; Bhushan, Bharat

    2016-08-01

    Solid lubricant particles are commonly used as oil additives for low friction and wear. Mg/Al-, Zn/Al-, and Zn/Mg/Al-layered double hydroxides (LDH) were synthesized by coprecipitation method. The benefits of LDH nanoparticles are that they can be synthesized using chemical methods where size and shape can be controlled, and can be modified organically to allow dispersal in fluids. The LDH nanoparticles were characterized by X-ray diffraction, scanning electron microscope, thermogravimetry, and differential scanning calorimetry. A pin-on-disk friction and wear tester was used for evaluating the friction and wear properties of LDH nanoparticles as lubricant additives. LDH nanoparticles have friction-reducing and anti-wear properties compared to oil without LDHs. Mg/Al-LDH has the best lubrication, possibly due to better thermal stability in severe conditions.

  5. Effect of co substitution of Mg and Zn on electromagnetic properties of NiCuZn ferrites

    NASA Astrophysics Data System (ADS)

    Sujatha, Ch.; Reddy, K. Venugopal; Babu, K. Sowri; Reddy, A. Rama Chandra; Suresh, M. Buchi; Rao, K. H.

    2013-07-01

    Ni0.5-2xMgxCu0.05Zn0.45+xFe2O4 (x=0, 0.04, 0.08, 0.12, and 0.16) ferrite samples were prepared through sol-gel method using polyvinyl alcohol as a chelating agent. Structural, magnetic, dielectric and electrical properties of the sintered samples were investigated using the characterisation techniques such as X-ray Diffractometer, Vibration sample magnetometer and impedance analyser respectively. X-ray diffraction patterns confirmed the formation of single phase cubic spinel structure of the samples. FTIR spectra showed two prominent bands (400 cm-1 and 600 cm-1) corresponding to characteristic of ferrites. Substitution of Mg and Zn for Ni showed gradual decrease of both magnetisation and coercivity. Magnetic permeability showed increasing trend with composition due to low anisotropy constant of Mg and Zn compared to Ni. Dielectric properties of the samples showed that both the dielectric constant as well as the dielectric loss factor was decreased with the composition. Cole-Cole plots consist of distorted semicircle with increasing diameter as a function of composition indicating improved resistance of the samples. The effect of substitution of Mg and Zn for Ni in NiCuZn ferrite system resulted in improved permeability with high cut off frequency, reduced dielectric losses and enhanced resistance of the samples.

  6. Experimental 25Mg and 13C NMR and Computational Modeling Studies of Amorphous Mg-Ca Carbonates

    NASA Astrophysics Data System (ADS)

    Singer, J. W.; Yazaydin, A. O.; Kirkpatrick, R. J.; Saharay, M.; Bowers, G. M.

    2012-12-01

    Nuclear magnetic resonance (NMR) spectroscopy of synthetic Mg-Ca amorphous carbonates (AMC-ACC) provides direct, element specific structural information about these complicated phases. The 13C, 25Mg, and 43Ca resonances are typically broad and span the chemical shift ranges of all the crystalline polymorphs in the Ca-Mg-CO3-H2O system. In a fashion similar to our previous analysis of 43Ca NMR results for ACC,1 here we integrate new experimental 13C and 25Mg spectra obtained at 20T for samples with Mg/(Ca+Mg) ratios from x=0 to x=1 with quantum chemical calculations of the NMR parameters of the crystalline phases using CASTEP calculations, simulations of the spectra using the SIMPSON software, and classical molecular dynamics calculations. XRD and 13C NMR results are in general agreement with the one-phase/two-phase model of ACC-AMC derived from thermochemical work by others.2 13C-NMR spectra of amorphous materials having intermediate compositions can not be completely fit by mechanical mixing of ACC and AMC end members—requiring a degree of Ca/Mg solid solution. Amorphous samples in two-phase region crystallize to assemblages of dolomite-like (x~0.5) and hydromagnesite-like (x~1) defective structures, but we also observe aragonite co-nucleation in the presence of excess water, indicative of a more complex evolution. While 43Ca NMR of X-ray amorphous materials shows featureless, symmetric, Gaussian line shapes, the large quadrupole moment of 25Mg gives rise to superposition of several quadrupolar line shapes representing different local structural environments. Singularities of static Mg spectra are best explained by local environments similar to nequehonite, hydromagnesite, and landsfordite. The spectra can not exclude minor contributions from anhydrous phases dolomite, huntite, and magnesite. Additional sites having very large quadrupolar coupling and/or site asymmetry are not explained by any known reference phases. CITATIONS (1) Singer, J. W.; Yazaydin, A. O

  7. A Mg2+-independent Ca2+-stimulated ATPase activity in the tegument of Schistosoma mansoni.

    PubMed

    Cunha, V M; Noël, F

    1988-01-01

    A tegumental fraction was prepared from Schistosoma mansoni. This fraction exhibited ATPase activity stimulated by Ca2+ in the absence of Mg2+. The Mg2+ independency was assessed by lowering contaminant Mg2+ using CDTA. The peak of activity was 220 mumol Pi mg-1 protein h-1 and the K0.5 for CaATP was 0.32 mM; the same K0.5 was obtained using MgATP as substrate, in the absence of Ca2+. Both activities may be promoted by the same enzyme since the addition of Ca2+ did not increase the ATPase activity measured in the presence of a saturating MgATP concentration.

  8. Chamber formation leads to Mg/Ca banding in the planktonic foraminifer Neogloboquadrina pachyderma

    NASA Astrophysics Data System (ADS)

    Jonkers, Lukas; Buse, Ben; Brummer, Geert-Jan A.; Hall, Ian R.

    2016-10-01

    Many species of planktonic foraminifera show distinct banding in the intratest distribution of Mg/Ca. This heterogeneity appears biologically controlled and thus poses a challenge to Mg/Ca paleothermometry. The cause of this banding and its relation with chamber formation are poorly constrained and most of what we know about intratest Mg/Ca variability stems from culture studies of tropical, symbiont-bearing foraminifera. Here we present data on the non-spinose, symbiont-barren Neogloboquadrina pachyderma from the subpolar North Atlantic where wintertime mixing removes vertical gradients in temperature and salinity. This allows investigation of biologically controlled Mg/Ca intratest variability under natural conditions. We find that intratest Mg/Ca varies between <0.1 and 7 mmol/mol, even in winter specimens. High Mg/Ca bands occur at the outer edge of the laminae, indicating reduced Mg removal at the end of chamber formation. Our data thus provide new constraints on the timing of the formation of such bands and indicate that their presence is intrinsic to the chamber formation process. Additionally, all specimens are covered with an outer crust consisting of large euhedral crystals. The composition of the crust is similar to the low Mg/Ca bands in the laminar calcite in winter and summer specimens, indicating a tight biological control on crust formation and composition. Nevertheless, despite high intratest variability, the median Mg/Ca of summertime tests is higher than that of wintertime tests. This provides support for Mg/Ca paleothermometry, but to improve the accuracy of paleotemperature estimates biological effects on Mg incorporation need to be better accounted for.

  9. Thermoluminescence studies of γ-irradiated ZnO:Mg2+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Pushpa, N.; Kokila, M. K.; Nagabhushana, K. R.

    2016-07-01

    Pure and Mg2+ doped ZnO nanoparticles are synthesized by solution combustion method. X-ray diffraction studies of the samples confirm hexagonal phase. Crystallite size is calculated using Scherer formula and found to be ∼30 nm for undoped ZnO and 34-38 nm for Mg2+ doped ZnO. A broad PL emission in the range 400-600 nm with peaks at 400, 450, 468, 483, 492, 517, 553 nm are observed in both pure and Mg2+ doped nanoparticles. Near band edge emission of ZnO is observed at 400 nm. The broad band emissions are due to surface defects. PL emission intensity is found to increase with Mg2+ concentration up to 1.5 mol% and then decreases due to concentration quenching. Samples are irradiated with γ-rays in a dose range 0.05-8 kGy. Gamma irradiation doesn't affect PL properties. Undoped samples exhibit unstructured low intense TL glow with peak at 720 K. Whereas Mg2+ doped samples exhibit well structured TL glow curves with peak at ∼618 K. TL glow peak intensity of Mg2+ doped samples increases with Mg2+ concentration up to 2 mol%, thereafter decreases. TL curves of Mg2+ (2 mol%) doped ZnO exhibit two glows, a high intense peak at 618 K and a weak one with peak at ∼485 K. TL intensity of Mg2+ (2 mol%) doped ZnO samples increases with gamma dose up to 1 kGy and then decreases. Kinetic parameters of TL glows are calculated by deconvolution technique. Activation energy and frequency factor are found to be 1.5 eV and 3.38 × 1011 s-1 respectively.

  10. In vitro degradation and cell viability assessment of Zn-3Mg alloy for biodegradable bone implants.

    PubMed

    Dambatta, M S; Murni, N S; Izman, S; Kurniawan, D; Froemming, G R A; Hermawan, H

    2015-05-01

    This article reports the in vitro degradation and cytotoxicity assessment of Zn-3Mg alloy developed for biodegradable bone implants. The alloy was prepared using casting, and its microstructure was composed of Mg2Zn11 intermetallic phase distributed within a Zn-rich matrix. The degradation assessment was done using potentiodynamic polarization and electrochemical impedance spectrometry. The cell viability and the function of normal human osteoblast cells were assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and alkaline phosphatase extracellular enzyme activity assays. The results showed that the degradation rate of the alloy was slower than those of pure Zn and pure Mg due to the formation of a high polarization resistance oxide film. The alloy was cytocompatible with the normal human osteoblast cells at low concentrations (<0.5 mg/mL), and its alkaline phosphatase activity was superior to pure Mg. This assessment suggests that Zn-3Mg alloy has the potential to be developed as a material for biodegradable bone implants, but the toxicity limit must be carefully observed.

  11. Foram Farming in the Mid-Continent: Culturing Low-Mg Benthic Foraminifera to Calibrate the Mg/Ca Paleothermometer

    NASA Astrophysics Data System (ADS)

    Jennings, D.; Hasiuk, F.; Thomas, E.; Varekamp, J. C.

    2014-12-01

    The initiation of Cenozoic continental ice sheets and the history of their growth/decay is difficult to reconstruct because of the mixed effects of polar ice volume and temperature on benthic foraminiferal oxygen isotope values. Coupled measurements of foraminiferal δ18O and Mg/Ca are a promising tool to unlock the history of past continental glaciation by calculating the oxygen isotopic composition of paleo-seawater. This method has been applied on Quaternary timescales with success, but uncertainty about secular changes in seawater Mg/Ca and potential changes in carbonate saturation have produced varying results with deeper time data. Currently, no experimentally-calibrated model explains how the Mg/Ca of low-Mg calcite, such as secreted by benthic foraminifera, responds to variations in seawater temperature and Mg/Ca. Our "Foram Farm" is a culture system for low-Mg calcite benthic foraminifera, composed of a colony and an experimental line. Currently, the colony hosts several species of rotaliids, miliolids, and buliminids obtained from Qatar, the Dominican Republic, Scotland, and Long Island Sound, USA. In addition, two tanks contain "live sand," a mixture of sandy material and seawater obtained from tropical reefs, and commonly used to condition hobbyist saltwater aquaria. This sand contains foraminifera and numerous other microorganisms. "Live sand" could be a source for cheap and easy to obtain test subjects. The foram farm gives access to a constant supply and variety of test subjects for the experimental line, which consists of several analytical refrigerators with varying temperatures. Each refrigerator houses petri dishes where forams are grown in water with varying Mg/Ca compositions. Elphidium excavatum, a well-researched, eurytopic taxon, will be the first to be cultured in the experimental line. After growing under experimental conditions, specimens will be analyzed using LA-ICP-MS, in order to model effects of seawater T and Mg/Ca on foram Mg/Ca

  12. Phosphorescence quenching by mechanical stimulus in CaZnOS:Cu

    SciTech Connect

    Tu, Dong; Kamimura, Sunao; Xu, Chao-Nan; Fujio, Yuki; Sakata, Yoshitaro; Ueno, Naohiro

    2014-07-07

    We have found that phosphorescence intensity of CaZnOS:Cu decreased visibly under an applied load. This mechanical quenching (MQ) of phosphorescence in CaZnOS:Cu corresponded to the mechanical stimuli. We have thus demonstrated that the MQ of CaZnOS:Cu could be used for visualizing stress distributions in practical applications. We propose that MQ arises from non-radiative recombination due to electron-transfer from trap levels to non-radiative centers as a result of the mechanical load.

  13. Rapid and High-Efficiency Laser-Alloying Formation of ZnMgO Nanocrystals

    PubMed Central

    Liu, Peisheng; Wang, Hao; Chen, Jun; Li, Xiaoming; Zeng, Haibo

    2016-01-01

    Applications of ZnMgO nanocrystals (NCs), especially in photoelectric detectors, have significant limitations because of the unresolved phase separation in the synthesis process. Here, we propose a rapid and highly efficient ZnMgO NC alloying method based on pulsed laser ablation in liquid. The limit value of homogeneous magnesium (Mg) is pushed from 37% to 62%, and the optical band gap is increased to 3.7 eV with high doping efficiency (>100%). Further investigations on the lattice geometry of ZnMgO NCs indicate that all ZnMgO NCs are hexagonal wurtzite structures, and the (002) and (100) peaks shift to higher diffraction angles with the increase in Mg doping content. The calculated results of the lattice constants a and c slightly decrease based on Bragg’s law and lattice geometry equations. Furthermore, the relationship between annealing temperature and the limit value of homogeneous Mg is examined, and the results reveal that the latter decreases with the former because of the phase separation of MgO. A probable mechanism of zinc magnesium alloy is introduced to expound on the details of the laser-alloying process. PMID:27324296

  14. Biological responses of human bone marrow mesenchymal stem cells to Sr-M-Si (M = Zn, Mg) silicate bioceramics.

    PubMed

    Zhang, Meili; Wu, Chengtie; Lin, Kaili; Fan, Wei; Chen, Lei; Xiao, Yin; Chang, Jiang

    2012-11-01

    Strontium (Sr), Zinc (Zn), magnesium (Mg), and silicon (Si) are reported to be essential trace elements for the growth and mineralization of bone. We speculated that the combination of these bioactive elements in bioceramics may be effective to regulate the osteogenic property of bone-forming cells. In this study, two Sr-containing silicate bioceramics, Sr(2)ZnSi(2)O(7) (SZS) and Sr(2)MgSi(2)O(7) (SMS), were prepared. The biological response of human bone marrow mesenchymal stem cells (BMSCs) to the two bioceramics (in the forms of powders and dense ceramic bulks) was systematically studied. In powder form, the effect of powder extracts on the viability and alkaline phosphatase (ALP) activity of BMSCs was investigated. In ceramic disc form, both direct and indirect coculture of BMSCs with ceramic discs were used to investigate their biological response, including attachment, proliferation, ALP activity, and bone-related genes expression. Beta-tricalcium phosphate (β-TCP) and akermanite (Ca(2)MgSi(2)O(7), CMS) were used as control materials. The results showed that the Sr, Zn, and Si (or Sr, Mg, and Si)-containing ionic products from SZS and SMS powders enhanced ALP activity of BMSCs, compared to those from β-TCP. Both SZS and SMS ceramic discs supported the growth of BMSCs, and most importantly, significantly enhanced the ALP activity and bone-related genes expression of BMSCs as compared to β-TCP. The results suggest that the specific combination of bioactive ions (Sr, Zn, Si, e.g.) in bioceramics is a viable way to improve the biological performance of biomaterials, and the form of materials and surface properties were nonnegligible factors to influence cell response.

  15. Influence of ZnO on the crystallization kinetics and properties of diopside-Ca-Tschermak based glasses and glass-ceramics

    SciTech Connect

    Goel, Ashutosh; Ferreira, Jose M. F.; Tulyaganov, Dilshat U.; Shaaban, Essam R.; Basu, Rajendra N.

    2008-08-15

    We report on the influence of ZnO on the structural, thermal, and crystallization behavior of the diopside-Ca-Tschermak based glasses, and on the processing, microstructure, and the properties of the sintered glass ceramics. Four glasses with nominal compositions of CaMg{sub 0.8}Al{sub 0.4}Si{sub 1.8}O{sub 6}, CaMg{sub 0.75}Zn{sub 0.05}Al{sub 0.4}Si{sub 1.8}O{sub 6}, CaMg{sub 0.70}Zn{sub 0.10}Al{sub 0.4}Si{sub 1.8}O{sub 6}, and CaMg{sub 0.60}Zn{sub 0.20}Al{sub 0.4}Si{sub 1.8}O{sub 6} were obtained by melting at 1580 deg. C for 1 h. Structural and thermal behavior of the glasses was investigated by Fourier-transform infrared spectroscopy, density measurements, dilatometry, and differential thermal analysis. Nonisothermal crystallization kinetics has been employed to study the crystallization mechanism in the glasses. Sintering, crystallization, microstructure, and properties of the glass ceramics were investigated under nonisothermal heating conditions in the temperature range of 850-1000 deg. C.

  16. Structure and optical properties of ternary alloy BeZnO and quaternary alloy BeMgZnO films growth by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Su, Longxing; Zhu, Yuan; Zhang, Quanlin; Chen, Mingming; Wu, Tianzhun; Gui, Xuchun; Pan, Bicai; Xiang, Rong; Tang, Zikang

    2013-06-01

    Ternary alloy BeZnO and quaternary alloy BeMgZnO films were prepared on sapphire (0 0 1) substrate by radio-frequency plasma-assisted molecular beam epitaxy (RF-PAMBE). Based on X-ray diffraction (XRD) analysis, no phase segregation is observed for all the alloys. However, BexZn1-xO alloys exhibit a constantly worse crystal quality than BexMgyZn1-x-yO alloys at the similar incorporation contents (i.e. x in BeZnO approximately equals to x + y in BeMgZnO). Optical transmittance spectra were recorded to determine the energy band gap of the films. BeMgZnO was revealed more effective in widening the band gap. Finally, BeZnO and BeMgZnO based MSM structure UV detectors were fabricated. BeMgZnO alloys with better crystal quality showed a favorable optical response and the cutoff wavelength shifted continuously to deep ultraviolet range, while BeZnO based detectors were found no response. This is the first report on BeMgZnO based UV detector, which is a meaningful step forward to the real application.

  17. Direct determination of the band alignment at the (Zn,Mg)O/CISSe interface

    SciTech Connect

    Erfurth, F.; Reinert, F.; Weinhardt, L.; Grimm, A.; Palm, J.; Niesen, T. P.; Umbach, E.

    2011-04-04

    The electronic and chemical properties of the (Zn{sub 1-x},Mg{sub x})O/CuIn(S,Se){sub 2} interface, prepared by sputtering of thin (Zn,Mg)O layers, were investigated with direct and inverse photoelectron spectroscopy on in situ prepared samples. With the combination of both techniques we have determined the band alignment at this interface as a function of Mg-content in the range 0{<=}x{<=}0.30. We find that the band alignment at the interface can be tailored between a ''cliff'' (downward step) in the conduction band for pure ZnO and a 'spike' (upward step) for high Mg-contents. A direct influence of the band alignment modifications on the solar cell parameters is found.

  18. High response solar-blind MgZnO photodetectors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schoenfeld, Winston V.; Wei, Ming; Boutwell, R. Casey; Liu, Huiyong

    2014-03-01

    High quality w-MgxZn1-xO thin films were grown epitaxially on c-plane sapphire substrates by plasma-assisted Molecular Beam Epitaxy. ZnO thin films with high crystalline quality, low defect and dislocation densities, and subnanometer surface roughness were achieved by applying a low temperature nucleation layer. By tuning Mg/Zn flux ratio, wurtzite MgxZn1-xO thin films with Mg composition as high as x=0.46 were obtained without phase segregation. Metal- Semiconductor-Metal (MSM) photoconductive and Schottky barrier devices with interdigitated electrode geometry and active surface area of 1 mm2 were fabricated and characterized. Resultant devices showed ~100 A/W peak responsivity at wavelength of ~260nm. We also report on cubic rock salt c-MgxZn1-xO thin films, following a non-traditional approach on MgO substrates, to demonstrate solar-blind photoresponse in MSM photodetectors, realizing a peak responsivity of 460 A/W (@ 250 nm) and 12.6 mA/W (@ 240nm) for mixed phase and single crystal films, respectively. A specific focus of the work is on identifying the impact of various growth parameters on the performance of the c- MgZnO detectors.

  19. Synthesis and optical properties of MgO-doped ZnO microtubes using microwave heating

    NASA Astrophysics Data System (ADS)

    Al-Naser, Qusay A. H.; Zhou, Jian; Wang, Han; Liu, Guizhen; Wang, Lin

    2015-08-01

    The Zn1-xMgxO (x = 0%, 2% and 5%) microtubes have been successfully synthesized via a microwave heating method. The as synthesized microtubes were carefully investigated. Field emission scanning electron microscope (FE-SEM) showed that all the microtubes exhibit an exact hexagonal hollow structure with smooth surfaces and straight characteristics throughout their whole lengths. UV-Vis measurement indicates that the absorption peak for ZnO microtube was shifted from 378.88 nm (3.27 eV) to 369.91 nm (3.35 eV) for Zn0.95Mg0.05O microtube. Room temperature photoluminescence (PL) spectra showed that the intensity of UV emission peak decreased with increase of MgO concentration and the visible emission band showed a blue shift from 538.06812 nm for ZnO microtube to 529.54114 nm for Zn0.95Mg0.05O microtube. Energy-dispersive spectrometer (EDS) analysis revealed the presence of Zn and O as the only elementary components with the absence of MgO as a doping material.

  20. Ammonia sensing properties of V-doped ZnO:Ca nanopowders prepared by sol–gel synthesis

    SciTech Connect

    Fazio, E.; Hjiri, M.; Dhahri, R.; El Mir, L.; Sabatino, G.; Barreca, F.; Neri, F.; Leonardi, S.G.; Pistone, A.; Neri, G.

    2015-03-15

    V-doped ZnO:Ca nanopowders with different V loading were prepared by sol–gel synthesis and successive drying in ethanol under supercritical conditions. Characterization data of nanopowders annealed at 700 °C in air, revealed that they have the wurtzite structure. Raman features of V-doped ZnO:Ca samples were found to be substantially modified with respect to pure ZnO or binary ZnO:Ca samples, which indicate the substitution of vanadium ions in the ZnO lattice. The ammonia sensing properties of V-doped ZnO:Ca thick films were also investigated. The results obtained demonstrate the possibility of a fine tuning of the sensing characteristics of ZnO-based sensors by Ca and V doping. In particular, their combined effect has brought to an enhanced response towards NH{sub 3} compared to bare ZnO and binary V-ZnO and Ca-ZnO samples. Raman investigation suggested that the presence of Ca play a key role in enhancing the sensor response in these ternary composite nanomaterials. - Graphical abstract: V-doped ZnO:Ca nanopowders prepared by sol–gel synthesis possess enhanced sensing characteristics towards NH{sub 3} compared to bare ZnO. - Highlights: • V-doped ZnO:Ca nanopowders with different V loading were prepared by sol–gel synthesis. • Raman features of V-doped ZnO:Ca samples indicate the substitution of V ions in the ZnO lattice. • Combined effects of dopants have brought to an enhanced response to NH{sub 3} compared to ZnO. • Ca play a key role in enhancing the sensor response of ternary V-doped ZnO:Ca composites.

  1. Effect of Ca2+ and Zn2+ on UO2 dissolution rates.

    PubMed

    Cerrato, José M; Barrows, Charles J; Blue, Lisa Y; Lezama-Pacheco, Juan S; Bargar, John R; Giammar, Daniel E

    2012-03-06

    The dissolution of UO(2) in a continuously stirred tank reactor (CSTR) in the presence of Ca(2+) and Zn(2+) was investigated under experimental conditions relevant to contaminated groundwater systems. Complementary experiments were performed to investigate the effect of adsorption and precipitation reactions on UO(2) dissolution. The experiments were performed under anoxic and oxic conditions. Zn(2+) had a much greater inhibitory effect on UO(2) dissolution than did Ca(2+). This inhibition was most substantial under oxic conditions, where the experimental rate of UO(2) dissolution was 7 times lower in the presence of Ca(2+) and 1450 times lower in the presence of Zn(2+) than in water free of divalent cations. EXAFS and solution chemistry analyses of UO(2) solids recovered from a Ca experiment suggest that a Ca-U(VI) phase precipitated. The Zn carbonate hydrozincite [Zn(5)(CO(3))(2)(OH)(6)] or a structurally similar phase precipitated on the UO(2) solids recovered from experiments performed in the presence of Zn. These precipitated Ca and Zn phases can coat the UO(2) surface, inhibiting the oxidative dissolution of UO(2). Interactions with divalent groundwater cations have implications for the longevity of UO(2) and the mobilization of U(VI) from these solids in remediated subsurface environments, waste disposal sites, and natural uranium ores.

  2. The formation of FHA coating on biodegradable Mg-Zn-Zr alloy using a two-step chemical treatment method

    NASA Astrophysics Data System (ADS)

    Jiang, S. T.; Zhang, J.; Shun, S. Z.; Chen, M. F.

    2016-12-01

    To improve the corrosion resistance of the biomedical magnesium alloy, a two-step chemical treatment method has been employed to prepare an FHA coating on the alloy surface. Prior to forming an FHA layer, the samples of Mg-3 wt% Zn-0.5 wt% Zr alloy were soaked in HF with concentration of 20% (v/v) at 37 °C temperature for 2 h, and were then placed into an aqueous solution with 0.1 mol/L Ca(NO3).4H2O and 0.06 mol/L NH4H2PO4 at 90 °C to prepare the Ca-P coating. The concentrations of Mg2+, F- ions, and pH variation with immersing time in the solution were investigated to explore the growth mechanism of FHA. The surface morphologies and compositions of the coatings were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results showed that the alloy surface treated with acid formed a layer of MgF2 nanoparticles with a thickness of 0.7 μm. The corrosion resistance of coatings in SBF solution was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results showed that the substrate with FHA coating had good corrosion resistance. After immersing into the calcium phosphate solution, some small spherical particles were first formed on the surface; these then cover the surface completely after 20 min. Some clusters consisting of needle-like crystal were observed in the spherical particles covering the surface, and the Ca/P ratio of the needle-like crystal was 1.46, clearly growing along the c axis preferred orientation growth. After immersion for 60 min, the FHA coating with completely uniform growth was obtained on the Mg-Zn-Zr alloy surface with its thickness reaching about 120 μm.

  3. P- T- X controls on Ca and Na distribution between Mg-Al tourmaline and fluid

    NASA Astrophysics Data System (ADS)

    Berryman, Eleanor J.; Wunder, Bernd; Rhede, Dieter; Schettler, Georg; Franz, Gerhard; Heinrich, Wilhelm

    2016-04-01

    Ca-Na partitioning between tourmaline and a coexisting fluid is investigated in the system CaO-Na2O-B2O3-Al2O3-MgO-SiO2-H2O-Cl between 0.2-4.0 GPa and 500-700 °C. The synthesis experiments produced a mineral assemblage of tourmaline, coesite/quartz, and in some cases additional phases, typically comprising <1 wt% of the solid product. The synthesized tourmalines are solid solutions of dravite [NaMg3Al6Si6O18(BO3)3(OH)3(OH)], "oxy-uvite" (i.e. "Ca-Mg-O root name") [CaMg3Al6Si6O18(BO3)3(OH)3O], and magnesio-foitite [☐(Mg2Al)Al6Si6O18(BO3)3(OH)3(OH)]. Starting materials comprised a fluid of constant ionic strength (2.00 m) and an oxide mixture with a constant Mg/Al ratio. As a result, the number of vacancies at the X site and the Mg/Al ratio of tourmaline crystals synthesized at the same temperature vary only slightly. The major solid solution is Ca-Na exchange at the X site via the exchange vector X Ca W O[ X Na W (OH)]-1, with the exchange vector X (Ca☐)[ X Na2]-1 serving as a secondary Ca-incorporation mechanism. Tourmaline's X-site composition reflects the fluid composition, whereby the Ca (or Na) concentration in the fluid corresponds with the Ca (or Na) content in tourmaline at each pressure and temperature. At 0.2 GPa, 700 °C, Ca preferentially partitions into tourmaline, producing the most Ca-rich tourmaline crystals synthesized here. At pressures >1.0 GPa, Ca partitions preferentially into the fluid, resulting in Na-dominant tourmaline compositions. Temperature has a secondary effect on Ca-Na partitioning, with higher temperatures correlating with increased Ca incorporation in tourmaline. Based on the experimental findings, tourmaline is expected to have Ca-rich compositions when it forms in low pressure, high-temperature Ca-rich rocks, consistent with the current record of tourmaline occurrence. The bulk Mg/Al ratio and the pH of the tourmaline-forming system may also affect Ca incorporation in tourmaline, but remain to be investigated experimentally.

  4. Using benthic foraminiferal B/Ca to constrain the effect of dissolution on key Pliocene Mg/Ca temperature records

    NASA Astrophysics Data System (ADS)

    White, S. M.; Ravelo, A. C.

    2015-12-01

    The state of the Pliocene tropical Pacific is currently the subject of heated debate. The debate hinges on the veracity of planktic foraminiferal Mg/Ca temperatures from the west Pacific warm pool (WPWP) and the eastern equatorial Pacific (EEP) that show Pliocene WPWP temperatures similar to today but a warmer Pliocene EEP, resulting in a much reduced east-west gradient [Wara et al., 2005]. These findings form the basis of the "permanent El Niño-like state" paradigm of Pliocene climate. However, recent studies using organic biomarker proxies produce temperature records that indicate a WPWP cooling trend since the Pliocene that differs markedly from Mg/Ca-temperature records [O'Brien et al., 2014; Zhang et al., 2014]. Though much of the debate has focused on changes in seawater Mg/Ca, spatial variations in proxy agreement point to dissolution as a key factor. Dissolution, which imparts a cool bias to Mg/Ca temperatures, varies across ocean basins depending on Δ[CO32-], the difference from the carbonate ion concentration needed for calcite saturation. By necessity, dissolution corrections use the modern value of Δ[CO32-] for the entire record, so it is possible that Pliocene proxy discrepancies could stem from varying Δ[CO32-] over time. Here we present benthic foraminiferal B/Ca data (a proxy for Δ[CO32-]) from the EEP and WEP spanning the past 5 Myr, to constrain the effect of dissolution on Pliocene Mg/Ca records. To account for possible changes in seawater B/Ca, we present paired epifaunal-infaunal B/Ca data. Infaunal species are much less sensitive to Δ[CO32-] than epifaunal species, but would still record long-term changes in seawater B/Ca. The true Δ[CO32-] can thus be calculated from the epifaunal-infaunal B/Ca difference [Brown et al., 2011]. Our study is the first to apply this approach downcore; by accounting for long-term changes in seawater, it greatly expands use of the B/Ca proxy and enables a first attempt at correcting for time

  5. Timing and mechanism for intratest Mg/Ca variability in a living planktic foraminifer

    NASA Astrophysics Data System (ADS)

    Spero, Howard J.; Eggins, Stephen M.; Russell, Ann D.; Vetter, Lael; Kilburn, Matt R.; Hönisch, Bärbel

    2015-01-01

    Geochemical observations indicate that planktic foraminifer test Mg/Ca is heterogeneous in many species, thereby challenging its use as a paleotemperature proxy for paleoceanographic reconstructions. We present Mg/Ca and Ba/Ca data collected by laser ablation ICP-MS from the shells of Orbulina universa cultured in controlled laboratory experiments. Test calcite was labeled with Ba-spiked seawater for 12 h day or night calcification periods to quantify the timing of intratest Mg-banding across multiple diurnal cycles. Results demonstrate that high Mg bands are precipitated during the night whereas low Mg bands are precipitated during the day. Data obtained from specimens growing at 20 °C and 25 °C show that Mg/Ca ratios in both high and low Mg bands increase with temperature, and average test Mg/Ca ratios are in excellent agreement with previously published empirical calibrations based on bulk solution ICP-MS analyses. In general, Mg band concentrations decrease with increasing pH and/or [CO2-3] but this effect decreases as experimental temperatures increase from 20 °C to 25 °C. We suggest that mitochondrial uptake of Mg2+ from the thin calcifying fluid beneath streaming rhizopodial filaments may provide the primary locus for Mg2+ removal during test calcification, and that diurnal variations in either mitochondrial density or activity produce Mg banding. These results demonstrate that Mg banding is an inherent component of test biomineralization in O. universa and show that the Mg/Ca paleothermometer remains a fundamental tool for reconstructing past ocean temperatures from fossil foraminifers.

  6. Ostracode Mg/Ca Ratios from Quaternary Sediments of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Dwyer, G. S.; Caverly, E. K.; Cronin, T. M.; Polyak, L. V.; DeNinno, L.; Rodriguez-Lazaro, J.

    2013-12-01

    We analyzed magnesium/calcium (Mg/Ca) ratios from adult, calcitic shells of the deep-sea ostracode Krithe from the Northwind and Mendeleev Ridges, Arctic Ocean, to reconstruct orbital-scale Quaternary bottom-water temperature history. Results show an early Pleistocene (~1.5 Ma to 500 ka) Mg/CaKrithe pattern with low-amplitude, possibly orbitally controlled, oscillations between 10.5 and 12.5 mmol/mol followed by a progressive trend towards higher ratios (> 17 mmol/mol) during the last 500 ka. This shift coincides with the mid-Pleistocene Transition and mid-Brunhes Event (~ 300-500 ka) recognized in microfaunal proxy records in the Arctic Ocean. Analyses of Mg/CaKrithe from intervals representing marine isotope stage 11 (MIS 11) in 5 cores from water depths from 700 to 1470 m show Mg/Ca ratios ranging from 10.5 to 14 mmol/mol. A 2 mmol/mol excursion in Mg/CaKrithe within MIS 11 seen in all cores likely corresponds to a brief stadial event recognized also in planktic and benthic microfaunas. We will discuss the implications of Mg/Ca paleothermometry for deep Arctic Ocean circulation and the evolution of Arctic sea ice during major Quaternary climatic transitions as well as possible factors other than water temperature that may influence Mg/Ca ratios in Krithe shells from Quaternary sediments from the Arctic Ocean.

  7. High-pressure modifications of CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends

    SciTech Connect

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

    2008-11-15

    High-pressure forms of intermetallic compounds with the composition CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (CaZn{sub 2}), and electron microscopy (SrZn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.

  8. The role of ionic sizes in inducing the cubic to tetragonal distortion in AV2O4 and ACr2O4 (A = Zn, Mg and Cd) compounds

    NASA Astrophysics Data System (ADS)

    Lal, Sohan; Pandey, Sudhir K.

    2016-11-01

    Cubic to tetragonal distortion in AV2O4 and ACr2O4 (A = Zn, Mg and Cd) compounds have been a contentious issue for last two decades. Different groups have proposed different mechanisms to understand such a distortion in these spinels, which are: (i) spin lattice coupling mechanism known as the spin driven Jahn-Teller (JT) effect, (ii) the strong relativistic spin-orbit coupling, a moderate JT distortion and weak V-V interactions and (iii) the JT effect. Now, in order to know the possible cause for such a distortion, we have avoided these complexities (various interactions among spin, electronic, orbital and lattice degrees of freedom) by carrying out spin unpolarized calculations. The calculated values of bulk moduli for ZnV2O4 (ZnCr2O4), MgV2O4 (MgCr2O4) and CdV2O4 (CdCr2O4) are found to be ˜289 (˜254), ˜244 (˜243) and ˜230 (˜233) GPa, respectively which suggest that CdV2O4 (among vanadates) and CdCr2O4 (among chromates) are more compressible. For vanadates and chromates, the order of calculated values of lattice parameter a are found to CdV2O4 > MgV2O4 > ZnV2O4 and CdCr2O4 > MgCr2O4 > ZnCr2O4, respectively and are consistent with the experimental results. The calculated values of cubic to tetragonal distortion (c/a), with c/a < 1 for ZnV2O4 (ZnCr2O4), MgV2O4 (MgCr2O4) and CdV2O4 (CdCr2O4) are ˜0.996 (˜0.997), ˜0.995 (˜0.994) and ˜0.997 (˜0.998), respectively. These values are in good agreement with the experimental data for ZnV2O4, MgV2O4, ZnCr2O4 and MgCr2O4 compounds. The present study clearly shows the role of ionic sizes in inducing the cubic to tetragonal distortion in these spinels. However, the discrepancies between the calculated and experimental data for CdV2O4 and CdCr2O4 are expected to improve by considering the above mentioned mechanisms. These mechanisms also appear to be responsible for deciding the other physical properties of these compounds.

  9. Effect of Mn on microstructure and corrosion properties of extruded Mg-1%Zn alloy

    NASA Astrophysics Data System (ADS)

    Zhang, Z. M.; Ma, Y.; Xi, Z. Z.; Xu, C. J.; Lv, Z. L.

    2017-03-01

    The microstructure of the extruded Mg-1Zn alloy doped with different content of manganese was analyzed by optical microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffractometry. The mass-loss immersion method and electrochemical test were used to evaluate the corrosion properties. The results show that the microstructure of the extruded Mg-1%Zn-x%Mn (mass fraction, x=0.4, 0.8, 1.2) alloys consists of α-Mg and α-Mn, the grain size of α-Mg decreases with increasing Mn content. Electrochemical corrosion behavior of the alloys is similar. Mn has considerable effect on the corrosion rate, the corrosion process is exacerbated by the galvanic corrosion occurred at interface between α-Mg and α-Mn. The corrosion rate increases as the Mn content increases. Mg-1%Zn-0.4% Mn alloy exhibits the best corrosion resistance between the Mg-1%Zn-x%Mn alloys

  10. Compositional tuning of atomic layer deposited MgZnO for thin film transistors

    NASA Astrophysics Data System (ADS)

    Wrench, J. S.; Brunell, I. F.; Chalker, P. R.; Jin, J. D.; Shaw, A.; Mitrovic, I. Z.; Hall, S.

    2014-11-01

    Thin film transistors (TFTs) have been fabricated using magnesium zinc oxide (MgZnO) layers deposited by atomic layer deposition at 200 °C. The composition of the MgZnO is systematically modified by varying the ratio of MgO and ZnO deposition cycles. A blue-shift of the near band-edge photoluminescence after post-deposition annealing at 300 °C indicates significant activation of the Mg dopant. A 7:1 ratio of ZnO:MgO deposition cycles was used to fabricate a device with a TFT channel width of 2000 μm and a channel length of 60 μm. This transistor yielded an effective saturation mobility of 4 cm2/V s and a threshold voltage of 7.1 V, respectively. The on/off ratio was 1.6 × 10 6 and the maximum interface state density at the ZnO/SiO2 interface is ˜ 6.5 × 10 12 cm-2.

  11. Investigations on structural, vibrational and dielectric properties of nanosized Cu doped Mg-Zn ferrites

    NASA Astrophysics Data System (ADS)

    Yadav, Anand; Rajpoot, Rambabu; Dar, M. A.; Varshney, Dinesh

    2016-05-01

    Transition metal Cu2+ doped Mg-Zn ferrite [Mg0.5Zn0.5-xCuxFe2O4 (0.0 ≤ x ≤ 0.5)] were prepared by sol gel auto combustion (SGAC) method to probe the structural, vibrational and electrical properties. X-ray diffraction (XRD) pattern reveals a single-phase cubic spinel structure without the presence of any secondary phase corresponding to other structure. The average particle size of the parent Mg0.5Zn0.5Fe2O4 is found to be ~29.8 nm and is found to increase with Cu2+ doping. Progressive reduction in lattice parameter of Mg0.5Zn0.5Fe2O4 has been observed due to difference in ionic radii of cations with improved Cu doping. Spinel cubic structure is further confirmed by Raman spectroscopy. Small shift in Raman modes towards higher wave number has been observed in doped Mg-Zn ferrites. The permittivity and dielectric loss decreases at lower doping and increases at higher order doping of Cu2+.

  12. Synthesis and luminescence of ZnMgS:Mn2+ nanoparticles.

    PubMed

    Zhang, Jun; Su, Fuhai; Chen, Wei; Sammynaiken, Ramaswami; Westcott, Sarah L; McCready, David E; Li, Guohua; Joly, Alan G

    2005-09-01

    Efficient green emission from ZnMgS:Mn2+ nanoparticles prepared by co-doping Mg2+ and Mn2+ ions into ZnS lattices has been observed. The synthesis is carried out in aqueous solution, followed by a post-annealing process, thus showing the features of less complexity, low cost, and easy incorporation of dopants. In comparison with the emission of ZnS:Mn2+ nanoparticles, which is located generally around 590 nm, the photoluminescence of ZnMgS:Mn2+ nanoparticles is blue-shifted by 14 nm in wavelength, leading to the enhanced green emission. The X-ray diffraction, electron spin resonance, and pressure dependent photoluminescence measurements suggest that the change of the crystal field caused by Mg2+ ionic doping and the lower symmetry in the nanoparticles may account for the blue-shift of the photoluminescence. The ZnMgS:Mn2+ nanoparticles with 1% Mn2+ doping exhibit the strongest luminescence, which could potentially meet the requirements for the construction of green light emitting diodes.

  13. Compositional tuning of atomic layer deposited MgZnO for thin film transistors

    SciTech Connect

    Wrench, J. S.; Brunell, I. F.; Chalker, P. R.; Jin, J. D.; Shaw, A.; Mitrovic, I. Z.; Hall, S.

    2014-11-17

    Thin film transistors (TFTs) have been fabricated using magnesium zinc oxide (MgZnO) layers deposited by atomic layer deposition at 200 °C. The composition of the MgZnO is systematically modified by varying the ratio of MgO and ZnO deposition cycles. A blue-shift of the near band-edge photoluminescence after post-deposition annealing at 300 °C indicates significant activation of the Mg dopant. A 7:1 ratio of ZnO:MgO deposition cycles was used to fabricate a device with a TFT channel width of 2000 μm and a channel length of 60 μm. This transistor yielded an effective saturation mobility of 4 cm{sup 2}/V s and a threshold voltage of 7.1 V, respectively. The on/off ratio was 1.6×10{sup 6} and the maximum interface state density at the ZnO/SiO{sub 2} interface is ∼6.5×10{sup 12} cm{sup −2}.

  14. The effects of shell characteristics on the UV photoresponse behaviors of photoconductivity based on ZnO/ZnMgO core-shell nanowire arrays

    NASA Astrophysics Data System (ADS)

    Fang, F.; Wang, X. J.; Fang, X.; Li, T.; Wei, Zhipeng; Li, Jinhua; Chu, Xueying

    2015-07-01

    Through a facile hydrothermal process and atomic layer deposition (ALD) technology, we obtained a kind of ZnO/ZnMgO core-shell nanowire array. The x-ray diffraction (XRD) results show a dominant (002) peak appears in as-grown ZnO, while the strongest peak is assigned an intensity of (100) in ZnO/ZnMgO core-shell structure. After ZnMgO shell coating, the main ultraviolet emission peak in room photoluminescence (PL) spectrum splits into two peaks, which locate at 364 nm and 378 nm. Furthermore, significant enhancement (one order of magnitude) in photoconductivity has been demonstrated. It is possible that the ZnMgO layer acts as an interfacial carrier transport layer, reducing the probability of carrier recombination.

  15. The Dissolution Kinetics of MgO into CaO-MgO-Fe2O3 Slag

    NASA Astrophysics Data System (ADS)

    Wei, Ruirui; Lv, Xuewei; Yue, Zhiwen; Xiang, Shenglin

    2017-02-01

    Calcium ferrite is the main binding phase for high-basicity sinter. The production and structure of calcium ferrite greatly influence the quality of the sinter. With the change in gangue composition, MgO becomes an important factor in the generation of calcium ferrite. In this study, the rotating cylinder method was used to study the dissolution kinetics of MgO into CaO-MgO-Fe2O3 melt. The experimental variables included the temperature, the initial composition of the melt, the Fe2O3/CaO mass ratio, the rotation time, and the rotation speed. The results indicate that the dissolution rate increases with increasing dissolution time, temperature, and rotation speed but decreases with increasing MgO content and Fe2O3/CaO mass ratio in the initial slag. The dissolution rate was observed to increase and then decrease with the addition of SiO2 in the initial slag. The activation energy and diffusion coefficient for MgO dissolution were found to range from 117.31 to 234.24 kJ mol-1 and from 1.03 × 10-6 to 1.18 × 10-5 cm2 s-1, respectively. The concentration difference between the solid and liquid phases is the main driving force for dissolution, but the viscosity and magnesium ion diffusivity of the melt also affect the process.

  16. Ca2+, Mg2+-dependent DNase involvement in apoptotic effects in spermatozoa of sea urchin Strongylocentrotus intermedius induced by two-headed sphingolipid rhizochalin.

    PubMed

    Sibirtsev, Juriy T; Shastina, Valeria V; Menzorova, Natalia I; Makarieva, Tatyana N; Rasskazov, Valeriy A

    2011-06-01

    Previously, we have purified three distinct DNases from spermatozoa of sea urchin Strongylocentrotus intermedius and we suppose the role of Ca(2+), Mg(2+)-dependent DNase (Ca, Mg-DNase) in apoptosis of spermatozoa. Two-headed sphingolipid rhizochalin (Rhz) induced characteristic apoptotic nuclear chromatin changes, internucleosomal DNA cleavage, and activation of caspase-9, caspase-8, and caspase-3 in spermatozoa as was shown by fluorescence Hoechst 33342/PI/FDA analysis, DNA fragmentation assay, and fluorescence caspase inhibitors FAM-LEHD-fmk, FAM-IETD-fmk, and FAM-DEVD-fmk, respectively. Inhibitor of caspase-3 z-DEVD-fmk subdued Rhz-induced internucleosomal ladder formation, which confirmed the major role of caspase-3 in apoptotic DNA cleavage probably through Ca, Mg-DNase activation. Participation of sea urchin Ca, Mg-DNase in apoptosis of spermatozoa was demonstrated by ions Zn(2+) blocking of Rhz-induced DNA fragmentation due to direct inhibition of the Ca, Mg-DNase and internucleosomal cleavage of HeLa S and Vero E6 cell nuclei chromatin by highly purified Ca, Mg-DNase.

  17. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    SciTech Connect

    Ingram, B.L.; De Deckker, P.; Chivas, A.R.; Conrad, M.E.; Byrne, A.R.

    2004-10-19

    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} between 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.

  18. Novel Approach for the Reduction of ZnO and MgO Using a Direct Diode-Laser

    NASA Astrophysics Data System (ADS)

    Mahmoud, M. S.; Yabe, T.; Iida, E.

    2017-02-01

    In this work, we present the results of using the diode laser with an energy density of 6.6 × 1011 W/m3 for reducing ZnO to Zn in vacuum as a first step. Subsequently, we use the diode laser for the reduction of MgO using Zn as the reducing agent. Although Zn is one of the candidates proposed for the renewable energy cycle, it is more auspicious to use it as a recyclable reducing agent. Herein, the reduction efficiency was measured in terms of moles of Zn or Mg obtained per moles of ZnO or MgO ablated. The energy efficiency is measured in terms of mass of Zn or Mg produced per energy consumed by diode laser. For the first part, the largest reduction rate was 15.8 mg/s, corresponding to reduction and energy efficiencies of 76.6 pct and 16.14 mg/kJ, respectively. The yield for the process was 8.8 pct of the theoretically calculated one, which is only better than the solar ZnO reduction process. For the second part, the reduction of MgO with Zn was attainable by diode laser, the resultant Mg was associated with Zn traces, and the electron probe micro analysis results showed that the MgO reduction efficiency fluctuates between 14.4 and 26.6 pct. Different scenarios were suggested for the mechanism of the reaction.

  19. [Adsorption of perchlorate by calcined Mg/Zn/Al layered double hydroxides].

    PubMed

    Wang, Hong-Yu; Liu, Yan

    2014-07-01

    The adsorption capacity of perchlorate by Mg/Zn/Al layered double hydroxides was investigated. The samples were characterized by X-ray diffraction (XRD) and the adsorption isothermal model and dynamic model were discussed. The effect of calcination temperature, Mg/Zn/Al molar ratio, pH value of solution, adsorption time and dosage on the adsorption capacity of samples were studied. The experiment results showed that the removal ratio and adsorption capacity reached the highest and the pH value had good applicability when the molar ratio was Mg/Zn/Al = 2: 1 : 1. The adsorption of perchlorate basically conformed to the pseudo-second kinetics and Langmuir, Freundlich isotherm model.

  20. The ternary system K2SO4MgSO4CaSO4

    USGS Publications Warehouse

    Rowe, J.J.; Morey, G.W.; Silber, C.C.

    1967-01-01

    Melting and subsolidus relations in the system K2SO4MgSO4CaSO4 were studied using heating-cooling curves, differential thermal analysis, optics, X-ray diffraction at room and high temperatures and by quenching techniques. Previous investigators were unable to study the binary MgSO4CaSO4 system and the adjacent area in the ternary system because of the decomposition of MgSO4 and CaSO4 at high temperatures. This problem was partly overcome by a novel sealed-tube quenching method, by hydrothermal synthesis, and by long-time heating in the solidus. As a result of this study, we found: (1) a new compound, CaSO4??3MgSO4 (m.p. 1201??C) with a field extending into the ternary system; (2) a high temperature form of MgSO4 with a sluggishly reversible inversion. An X-ray diffraction pattern for this polymorphic form is given; (3) the inversion of ??-CaSO4 (anhydrite) to ??-CaSO4 at 1195??C, in agreement with grahmann; (1) (4) the melting point of MgSO4 is 1136??C and that of CaSO4 is 1462??C (using sealed tube methods to prevent decomposition of the sulphates); (5) calcium langbeinite (K2SO4??2CaSO4) is the only compound in the K2SO4CaSO4 binary system. This resolved discrepancies in the results of previous investigators; (6) a continuous solid solution series between congruently melting K2SOP4??2MgSO4 (langbeinite) and incongruently melting K2SO4??2CaSO4 (calcium langbeinite); (7) the liquidus in the ternary system consists of primary phase fields of K2SO4, MgSO4, CaSO4, langbeinite-calcium langbeinite solid solution, and CaSO4??3MgSO4. The CaSO4 field extends over a large portion of the system. Previously reported fields for the compounds (K2SO4??MgSO4??nCaSO4), K2SO4??3CaSO4 and K2SO4??CaSO4 were not found; (8) a minimum in the ternary system at: 740??C, 25% MgSO4, 6% CaSO4, 69% K2SO4; and ternary eutectics at 882??C, 49% MgSO4, 19% CaSO4, 32% K2SO4; and 880??, 67??5% MgSO4, 5% CaSO4, 27??5% K2SO4. ?? 1967.

  1. Microstructural analysis of biodegradable Mg-0.9Ca-1.2Zr alloy

    NASA Astrophysics Data System (ADS)

    Istrate, B.; Munteanu, C.; Geanta, V.; Baltatu, S.; Focsaneanu, S.; Earar, K.

    2016-08-01

    Magnesium alloys have applications in aerospace and medical applications as biodegradable orthopedic implants. Alloying with biocompatible elements, such as calcium or zirconium contribute to refining the the microstructure and improves corrosion resistance with the formation of an eutectic compound - Mg2Ca at boundary alpha-Mg grains. The purpose of this paper is to present the microstructure throw optical and scanning electron methods and phase and constituents identification with X-ray analysis. The results showed the presence of alpha-Mg grains with formation of a mechanical compound - Mg2Ca and appearance of alpha- Zr phase relatively uniformly distributed in nests.

  2. Effect of sertraline on [Ca2+](i) and viability of human MG63 osteosarcoma cells.

    PubMed

    Lin, Ko-Long; Chi, Chao-Chuan; Lu, Ti; Tseng, Li-Ling; Wang, Jue-Long; Lu, Yi-Chau; Jan, Chung-Ren

    2013-04-01

    The antidepressant, sertraline, has been shown to have diverse in vitro effects. This study examined whether sertraline altered [Ca(2+)](i) in MG63 human osteosarcoma cells by using fura-2 as a Ca(2+)-sensitive fluorescent dye. At 50-200 µM, sertraline induced a [Ca(2+)](i) rise in a concentration-dependent manner. Ca(2+) response was decreased by removing extracellular Ca(2+), suggesting that Ca(2+) entry and release contributed to the [Ca(2+)](i) signal. Sertraline-induced Ca(2+) entry was inhibited by nifedipine, La(3+), Gd(3+), and SK&F96365. When extracellular Ca(2+) was removed, pretreatment with the endoplasmic reticulum (ER) Ca(2+) pump inhibitor, thapsigargin, or 2,5-di-tert-butylhydroquinone (BHQ) abolished the sertraline-evoked [Ca(2+)](i) rise. Incubation with sertraline also abolished the thapsigargin or BHQ-induced [Ca(2+)](i) rise. Inhibition of phospholipase C (PLC) with U73122 abolished the sertraline-induced [Ca(2+)](i) rise. At 20-30 µM, overnight treatment with sertraline killed cells in a concentration-dependent manner. The cytotoxic effect of sertraline was not reversed by chelating cytosolic Ca(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Annexin V/propidium iodide staining data demonstrate that sertraline (30 µM) evoked apoptosis. Sertraline (20 and 30 µM) also increased levels of reactive oxygen species. Together, in human osteosarcoma cells, sertraline evoked a [Ca(2+)](i) rise by inducing PLC-dependent Ca(2+) release from the ER and Ca(2+) entry by L-type Ca(2+) channels and store-operated Ca(2+) channels. Sertraline induced cell death that may involve apoptosis by mitochondrial pathways.

  3. Effect of surface mechanical attrition treatment on biodegradable Mg-1Ca alloy.

    PubMed

    Li, N; Li, Y D; Li, Y X; Wu, Y H; Zheng, Y F; Han, Y

    2014-02-01

    Surface mechanical attrition treatment (SMAT) is considered to be an effective approach to obtain a nanostructured layer in the treated surface of metals. In this study, we evaluated the effect of SMAT on the microstructure, mechanical properties and corrosion properties of biodegradable Mg-1Ca alloy, with pure Mg as control. Grain refinement layers with grain size at the nanometer scale in the topmost surface were successfully prepared on Mg-1Ca alloy using SMAT technique, similar to pure Mg. The SMAT not only refined the surface layer of Mg-1Ca alloy, but also promoted the re-dissolution of the Mg2Ca phase into the matrix. As a result, the microhardness of the SMATed samples in the near-surface region was considerably enhanced, and the surface roughness and wettability of the SMATed samples were increased. However, the SMAT led to high density of crystalline defects such as grain boundaries (subgrain boundaries) and dislocations, which severely weakened the corrosion resistance of Mg-1Ca alloy, same as pure Mg.

  4. Scleractinian corals cultured in low Mg/Ca seawater form aragonite skeleton

    NASA Astrophysics Data System (ADS)

    Stolarski, Jaroslaw; Reynaud, Stéphanie; Ferrier-Pages, Christine; Janiszewska, Katarzyna; Domart-Coulon, Isabelle; Beraud, Eric; Marrocchi, Yves; Mazur, Maciej; Szlachetko, Jakub; Meibom, Anders

    2010-05-01

    Scleractinian corals represent a testing ground for ideas regarding biologically vs. environmentally controlled calcification. The morphology of skeletal micro-structural units (arrangement of the skeletal fibers) and their biogeochemical composition have, for a long time, been interpreted from two opposite view points: (1) as a purely physico-chemical process involving simple supersaturation of a fluid close in composition to seawater, hypothesized to exist at the interface between the skeleton and the calicoblastic cell-layer, or (2) a complete physiological control of calcification by the organism by means of a presumed amorphous precursor phase and precisely utilized organic macromolecules that control mineralogy, crystal orientation etc. Paleontological data originally supported the second interpretation because the aragonitic skeletal mineralogy appeared to be stable through geological time despite of changes in seawater chemistry (e.g., the late Mesozoic decrease of Mg/Ca ratio), which was believed to promote inorganic precipitation of calcite. However, Ries et al. (Geology 2006, 34: 525-528) argued that scleractinians are so-called 'hyper-calcifiers' and limited in their mineralogical control. Accordingly, in modern seawater (Mg/Ca molar ratio = 5.2) such organisms form aragonite simply because the Mg/Ca ratio favors this mineralogy. However, if the Mg/Ca ratio drops below 3.5, the mineralogy of such 'hyper-calcifiers' are supposed to become calcitic. In low-Mg/Ca experiments, Ries et al. detected calcite by X-ray diffraction of the bulk skeleton of Acropora, Montipora, and Porites and also indicated, by electron microprobe analyses, the presence of calcite in the uppermost portion of coral skeleton, though the exact position of the mapped areas were not indicated. We have cultured Acropora, Porites, Pavona and Galaxea in low Mg/Ca (compared with normal seawater) artificial seawater (ASW). A low Mg/Ca ratio can be obtained either by lowering the Mg

  5. Refining Globigerinoides ruber Mg/Ca paleothermometry in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Hertzberg, Jennifer E.; Schmidt, Matthew W.

    2013-12-01

    The Mg/Ca ratio of the planktonic foraminifera Globigerinoides ruber (white) has become a widely used proxy for reconstructing sea surface temperature (SST), as numerous studies have shown that temperature is the primary control on Mg/Ca ratios in foraminiferal calcite. However, a recent study of core-top sediments across an Atlantic meridional transect suggests that salinity might have a stronger control on foraminiferal Mg/Ca ratios than previously thought. By analyzing Mg/Ca ratios and δO18 values in G. ruber (white), Arbuszewski et al. (2010) found a 27% increase in G. ruber Mg/Ca ratios per 1 salinity unit increase for seawater salinities above 35.5. Here, we use shell weight analyses and SEM images from a subset of the core-tops used in the Arbuszewski et al. (2010) study across a narrow depth range (3197-3733 m) to show that G. ruber shells from the equatorial region are highly dissolved compared to those from the subtropical North and South Atlantic gyres, significantly impacting their Mg/Ca-SSTs. Shell weights from the higher-productivity equatorial region of the Atlantic are on average 20% and 15% lower than those from the oligotrophic North and South Atlantic gyres, respectively. Given the large preservation gradient along the transect studied by Arbuszewski et al. (2010), application of a single dissolution-corrected Mg/Ca:SST calibration equation (Dekens et al., 2002) on cores from the subtropical gyres and the equatorial region is not appropriate. When regional differences in preservation are considered, as well as realistic habitat depths and calcification seasons for G. ruber in temperate latitudes, we find a strong correlation between observational SSTs and calculated G. ruber Mg/Ca-SSTs in core-top samples spanning 43°N to 25°S in the Atlantic. In addition, our re-calibrated Mg/Ca-SSTs are more strongly correlated with isotopic calcification temperatures across the transect than originally reported by Arbuszewski et al. (2010). This study

  6. Isotopic fractionation of Mg 2+(aq), Ca 2+(aq), and Fe 2+(aq) with carbonate minerals

    NASA Astrophysics Data System (ADS)

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.

    2010-11-01

    Density-functional electronic structure calculations are used to compute the equilibrium constants for 26Mg/ 24Mg and 44Ca/ 40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 10 3ln ( K) at 25 °C, of -5.3, -1.1, and +1.2 for 26Mg/ 24Mg exchange between calcite (CaCO 3), magnesite (MgCO 3), and dolomite (Ca 0.5Mg 0.5CO 3), respectively, and Mg 2+(aq), with positive values indicating enrichment of the heavy isotope in the mineral phase. For 44Ca/ 40Ca exchange between calcite and Ca 2+(aq) at 25 °C, the calculations predict values of +1.5 for Ca 2+(aq) in 6-fold coordination and +4.1 for Ca 2+(aq) in 7-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO)610- and M(HO)62+ embedded in a set of fixed atoms representing the second-shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe 3+-hematite and Fe 2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe 3+(aq) and Fe 2+(aq) species.

  7. Isotopic Fractionation of Mg2+(aq), Ca2+(aq), and Fe2+(aq) with Carbonate Minerals

    SciTech Connect

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.

    2010-11-15

    Density functional electronic structure calculations are used to compute the equilibrium constant (the isotope fractionation factor) for 26Mg/24Mg and 44Ca/40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 103ln(K) at 25 °C, of -5.3, -1.1, and +1.1 for 26Mg/24Mg exchange between calcite (CaCO3), magnesite (MgCO3), and dolomite (Ca0.5Mg0.5CO3), respectively, and Mg2+(aq), with positive values indicating enrichment in the mineral phase. For 44Ca/40Ca exchange between calcite and Ca2+(aq), the calculations predict values of +1.5 for Ca2+(aq) in six-fold coordination and +4.1 for Ca2+(aq) in seven-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO3)610- and M2+(H2O)6 embedded in a set of fixed atoms representing the 2nd shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using 2 the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe3+-hematite and Fe2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe3+(aq) and Fe2+(aq) species.

  8. A Ca2+-stimulated, Mg2+-dependent ATPase activity in subcellular fractions from Schistosoma mansoni.

    PubMed

    Cunha, V M; de Souza, W; Noël, F

    1988-12-05

    A Ca2+-stimulated, Mg2+-dependent ATPase activity was found in subcellular fractions from Schistosoma mansoni. Its specific and relative activities were higher in the heterogeneous cuticle fraction and in the microsomal fraction. The K0.5 for ATPase activation by free Ca2+ was 0.2-0.5 microM. This is the first description of an ATPase activity stimulated by Ca2+ in the micromolar range in S. mansoni.

  9. Seawater Mg/Ca controls polymorph mineralogy of microbial CaCO3: a potential proxy for calcite-aragonite seas in Precambrian time.

    PubMed

    Ries, J B; Anderson, M A; Hill, R T

    2008-03-01

    A previously published hydrothermal brine-river water mixing model driven by ocean crust production suggests that the molar Mg/Ca ratio of seawater (mMg/Ca(sw)) has varied significantly (approximately 1.0-5.2) over Precambrian time, resulting in six intervals of aragonite-favouring seas (mMg/Ca(sw) > 2) and five intervals of calcite-favouring seas (mMg/Ca(sw) < 2) since the Late Archaean. To evaluate the viability of microbial carbonates as mineralogical proxy for Precambrian calcite-aragonite seas, calcifying microbial marine biofilms were cultured in experimental seawaters formulated over the range of Mg/Ca ratios believed to have characterized Precambrian seawater. Biofilms cultured in experimental aragonite seawater (mMg/Ca(sw) = 5.2) precipitated primarily aragonite with lesser amounts of high-Mg calcite (mMg/Ca(calcite) = 0.16), while biofilms cultured in experimental calcite seawater (mMg/Ca(sw) = 1.5) precipitated exclusively lower magnesian calcite (mMg/Ca(calcite) = 0.06). Furthermore, Mg/Ca(calcite )varied proportionally with Mg/Ca(sw). This nearly abiotic mineralogical response of the biofilm CaCO3 to altered Mg/Ca(sw) is consistent with the assertion that biofilm calcification proceeds more through the elevation of , via metabolic removal of CO2 and/or H+, than through the elevation of Ca2+, which would alter the Mg/Ca ratio of the biofilm's calcifying fluid causing its pattern of CaCO3 polymorph precipitation (aragonite vs. calcite; Mg-incorporation in calcite) to deviate from that of abiotic calcification. If previous assertions are correct that the physicochemical properties of Precambrian seawater were such that Mg/Ca(sw) was the primary variable influencing CaCO3 polymorph mineralogy, then the observed response of the biofilms' CaCO3 polymorph mineralogy to variations in Mg/Ca(sw), combined with the ubiquity of such microbial carbonates in Precambrian strata, suggests that the original polymorph mineralogy and Mg/Ca(calcite )of well

  10. Effects of Mg doping content and annealing temperature on the structural properties of Zn1- x Mg x O thin films prepared by radio-frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Du, Wen-han; Yang, Jing-jing; Zhao, Yu; Xiong, Chao

    2017-01-01

    The doping content of Mg plays an important role in the crystalline structure and morphology properties of Zn1- x Mg x O thin films. Here, using radio-frequency magnetron sputtering method, we prepared Zn1- x Mg x O thin films on single crystalline Si(100) substrates with a series of x values. By means of X-ray diffraction (XRD) and scanning electron microscope (SEM), the crystalline structure and morphology of Zn1- x Mg x O thin films with different x values are investigated. The crystalline structure of Zn1- x Mg x O thin film is single phase with x<0.3, while there is phase separation phenomenon with x>0.3, and hexagonal and cubic structures will coexist in Zn1- x Mg x O thin films with higher x values. Especially with lower x values, a shoulder peak of 35.1° appearing in the XRD pattern indicates a double-crystalline structure of Zn1- x Mg x O thin film. The crystalline quality has been improved and the inner stress has been released, after the Zn1- x Mg x O thin films were annealed at 600 °C in vacuum condition.

  11. Testing the cation-hydration effect on the crystallization of Ca-Mg-CO3 systems.

    PubMed

    Xu, Jie; Yan, Chao; Zhang, Fangfu; Konishi, Hiromi; Xu, Huifang; Teng, H Henry

    2013-10-29

    Dolomite and magnesite are simple anhydrous calcium and/or magnesium carbonate minerals occurring mostly at Earth surfaces. However, laboratory synthesis of neither species at ambient temperature and pressure conditions has been proven practically possible, and the lack of success was assumed to be related to the strong solvation shells of magnesium ions in aqueous media. Here, we report the synthesis of MgCO3 and MgxCa(1-x)CO3 (0 < x < 1) solid phases at ambient conditions in the absence of water. Experiments were carried out in dry organic solvent, and the results showed that, although anhydrous phases were readily precipitated in the water-free environment, the precipitates' crystallinity was highly dependent on the Mg molar percentage content in the solution. In specific, magnesian calcite dominated in low [Mg(2+)]/[Ca(2+)] solutions but gave way to exclusive formation of amorphous MgxCa(1-x)CO3 and MgCO3 in high-[Mg(2+)]/[Ca(2+)] and pure-Mg solutions. At conditions of [Mg(2+)]/[Ca(2+)] = 1, both nanocrystals of Ca-rich protodolomite and amorphous phase of Mg-rich MgxCa(1-x)CO3 were formed. These findings exposed a previously unrecognized intrinsic barrier for Mg(2+) and CO3(2-) to develop long-range orders at ambient conditions and suggested that the long-held belief of cation-hydration inhibition on dolomite and magnesite mineralization needed to be reevaluated. Our study provides significant insight into the long-standing "dolomite problem" in geochemistry and mineralogy and may promote a better understanding of the fundamental chemistry in biomineralization and mineral-carbonation processes.

  12. Fabrication of stable, wide-bandgap thin films of Mg, Zn and O

    DOEpatents

    Katiyar, Ram S.; Bhattacharya, Pijush; Das, Rasmi R.

    2006-07-25

    A stable, wide-bandgap (approximately 6 eV) ZnO/MgO multilayer thin film is fabricated using pulsed-laser deposition on c-plane Al2O3 substrates. Layers of ZnO alternate with layers of MgO. The thickness of MgO is a constant of approximately 1 nm; the thicknesses of ZnO layers vary from approximately 0.75 to 2.5 nm. Abrupt structural transitions from hexagonal to cubic phase follow a decrease in the thickness of ZnO sublayers within this range. The band gap of the thin films is also influenced by the crystalline structure of multilayer stacks. Thin films with hexagonal and cubic structure have band-gap values of 3.5 and 6 eV, respectively. In the hexagonal phase, Mg content of the films is approximately 40%; in the cubic phase Mg content is approximately 60%. The thin films are stable and their structural and optical properties are unaffected by annealing at 750.degree. C.

  13. Diffuse Scattering and Phason Fluctuations in the Zn-Mg-Sc Icosahedral Quasicrystal and Its Zn-Sc Periodic Approximant

    SciTech Connect

    Boissieu, M. de; Francoual, S.; Kaneko, Y.; Ishimasa, T.

    2005-09-02

    We report on the absolute scale measurement of the x-ray diffuse scattering in the ZnMgSc icosahedral quasicrystal and its periodic approximant. Whereas the diffuse scattering in the approximant is purely accounted for by thermal diffuse scattering, an additional signal is observed in the quasicrystal. It is related to phason fluctuations as indicated by its Q{sub per}{sup 2} dependence. Moreover, when compared to previous measurements carried out on the i-AlPdMn phase, we find that the amount of diffuse scattering is smaller in the i-ZnMgSc phase, in agreement with larger phason elastic constants in this phase. This is confirmed by the observation of a large number of weak Bragg peaks having a high Q{sub per} reciprocal space component.

  14. Diffuse scattering and phason fluctuations in the Zn-Mg-Sc icosahedral quasicrystal and its Zn-Sc periodic approximant.

    PubMed

    de Boissieu, M; Francoual, S; Kaneko, Y; Ishimasa, T

    2005-09-02

    We report on the absolute scale measurement of the x-ray diffuse scattering in the ZnMgSc icosahedral quasicrystal and its periodic approximant. Whereas the diffuse scattering in the approximant is purely accounted for by thermal diffuse scattering, an additional signal is observed in the quasicrystal. It is related to phason fluctuations as indicated by its Q(2)(per) dependence. Moreover, when compared to previous measurements carried out on the i-AlPdMn phase, we find that the amount of diffuse scattering is smaller in the i-ZnMgSc phase, in agreement with larger phason elastic constants in this phase. This is confirmed by the observation of a large number of weak Bragg peaks having a high Q(per) reciprocal space component.

  15. Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy

    NASA Astrophysics Data System (ADS)

    Cai, Yuan-hua; Wang, Cong; Zhang, Ji-shan

    2013-07-01

    Al-Mg-Si-Cu alloys with and without Zn addition were fabricated by conventional ingot metallurgy method. The microstructures and properties were investigated using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), tensile test, hardness test, and electrical conductivity measurement. It is found that the as-cast Al-Mg-Si-Cu-Zn alloy is composed of coarse dendritic grains, long needle-like β/δ-AlFeSi white intermetallics, and Chinese script-like α-AlFeSi compounds. During high temperature homogenization treatment, only harmful needle-like β-AlFeSi phase undergoes fragmentation and spheroidizing at its tips, and the destructive needle-like δ-phase does not show any morphological and size changes. Phase transitions from β-AlFeSi to α-AlFeSi and from δ-AlFeSi to β-AlFeSi are also not found. Zn addition improves the aging hardening response during the former aging stage and postpones the peak-aged hardness to a long aging time. In T4 condition, Zn addition does not obviously increase the yield strength and decrease the elongation, but it markedly improves paint-bake hardening response during paint-bake cycle. The addition of 0.5wt% Zn can lead to an increment of 99 MPa in yield strength compared with the value of 69 MPa for the alloy without Zn after paint-bake cycle.

  16. Impurity Diffusion Coefficients of Al and Zn in Mg Determined from Solid-to-Solid Diffusion Couples

    SciTech Connect

    Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Perry, Kelly A; Belova, Irina; Murch, Prof. Graeme; Sohn, Yong Ho

    2013-08-01

    Increasing use and development of lightweight Mgalloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As property enhancing components, Al and Zn are two of the most important and common alloying elements for Mg-alloys. We have investigated the concentration dependent interdiffusion of Al and Zn in Mg using diffusion couples of pure polycrystalline Mg mated to Mg solid solutions containing either <9 at.% Al or <3 at.% Zn. Concentration profiles were determined by electron micro-probe microanalysis of the diffusion zone. The interdiffusion coefficients were determined by the classical Boltzmann-Matano method within the Mg solid solution. As the concentration of Al or Zn approaches the dilute ends, we employ an analytical approach based on the Hall method to estimate the impurity diffusion coefficients. Results of Al and Zn impurity diffusion in Mg are reported and compared to published impurity diffusion coefficients typically determined by thin film techniques.

  17. Inter-species and Seasonal Variability in Mg / Ca in Larger Benthic Foraminifera: Implications for Paleo-proxy

    NASA Astrophysics Data System (ADS)

    Singh, A.; Saraswati, P. K.; Pande, K.; Sanyal, P.

    2015-12-01

    The reports of inter-species variability to intra-test heterogeneity in Mg/Ca in several species of foraminifera have raised question about its use in estimation of seawater temperatures and necessitate field and culture studies to verify it for species from different habitats. In this study, we attempt to investigate if Mg/Ca in larger benthic foraminifera (LBF) could be a potential proxy of seawater temperatures for shallow marine carbonates. The samples were collected in different seasons from coral reef at Akajima (Okinawa, Japan). The Ca and Mg of 13 species of LBF and small benthic foraminifera from the same season were determined to examine variation in Mg/Ca among the species calcified under presumably the same temperature and salinity conditions. We also analyzed Amphistegina lessoni from different seasons for Ca, Mg and δ18O to determine variation in Mg/Ca with temperature and see how the two proxies of temperatures, Mg/Ca and δ18O, correlate in the same species. The species cluster about two distinctly separated Mg/Ca values. The first group comprising species of Amphistegina, Gypsina, Ammonia and Elphidium have relatively lower Mg/Ca, varying from 30 to 45 mmol/mol. The second group, having average Mg/Ca ranging from ~110 to 170 mmol/mol, includes species of Schlumbergerella, Baculogypsinoides, Baculogypsina, Heterostegina, Operculina, Calcarina, Amphisorus, Alveolinella and Poroeponides. The result suggests large interspecies variability implying vital effect in foraminiferal Mg/Ca. There is no distinct difference in Mg/Ca values between porcelaneous and hyaline types or symbiont-bearing and symbiont-free types. In Amphistegina lessoni the variation in Mg/Ca between individuals of the same season is as large as variation across the seasons. There is no correlation between Mg/Ca and seawater temperature. Lack of correlation between Mg/Ca and δ18O further suggests that Mg/Ca in the species is not primarily controlled by temperature.

  18. The effect of Mg/2+/ and Ca/2+/ on urea-catalyzed phosphorylation reactions

    NASA Technical Reports Server (NTRS)

    Handschuk, G. J.; Lohrmann, R.; Orgel, L. E.

    1973-01-01

    The effect of Mg(2+) and Ca(2+) on phosphorylation reactions catalyzed by urea is investigated, showing that Mg(2+) improves markedly the yield of products containing pyrophosphate bonds. Yields of up to 25% of uridine diphosphate can be obtained with struvite at temperatures as low as 65 C.

  19. Influence of ZnO/MgO substitution on sintering, crystallisation, and bio-activity of alkali-free glass-ceramics.

    PubMed

    Kapoor, Saurabh; Goel, Ashutosh; Correia, Ana Filipa; Pascual, Maria J; Lee, Hye-Young; Kim, Hae-Won; Ferreira, José M F

    2015-08-01

    The present study reports on the influence of partial replacement of MgO by ZnO on the structure, crystallisation behaviour and bioactivity of alkali-free bioactive glass-ceramics (GCs). A series of glass compositions (mol%): 36.07 CaO-(19.24-x) MgO-x ZnO-5.61 P2O5-38.49 SiO2-0.59 CaF2 (x=2-10) have been synthesised by melt-quench technique. The structural changes were investigated by solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray diffraction and differential thermal analysis. The sintering and crystallisation behaviours of glass powders were studied by hot-stage microscopy and differential thermal analysis, respectively. All the glass compositions exhibited good densification ability resulting in well sintered and mechanically strong GCs. The crystallisation and mechanical behaviour were studied under non-isothermal heating conditions at 850 °C for 1h. Diopside was the primary crystalline phase in all the GCs followed by fluorapatite and rankinite as secondary phases. Another phase named petedunnite was identified in GCs with ZnO content >4 mol. The proliferation of mesenchymal stem cells (MSCs) and their alkaline phosphatase activity (ALP) on GCs was revealed to be Zn-dose dependent with the highest performance being observed for 4 mol% ZnO.

  20. Reversible Hydrogen Storage Characteristics of Catalytically Enhanced Ca(Li)-nMg-B-N-H System

    NASA Astrophysics Data System (ADS)

    Srinivasan, Sesha; Emre Demircak, Dervis; Sharma, Prakash; Yogi, Goswami; Stefanakos, Elias

    2013-04-01

    The aim of the present investigation is to study the synergistic effects of multi-walled carbon nanotubes, Nb2O5 and other catalysts for reversible hydrogen storage characteristics of Ca(Li)-nMg-B-N-H systems. Multinary hydride using light weight, high capacity hydride compounds such as Ca(BH4)2, LiBH4, LiNH2, nanoMgH2 in 3:1:8:4 composition was synthesized using high energy planetary milling under Ar/H2 ambient. Various nano additives and bi-metallic catalysts were added in a very small concentration with the host hydride (Ca)Li-nMg-B-N-H. The TGA and DSC results demonstrated that the catalytically enhanced Ca(Li)-nMg-B-N-H with hydrogen release at lower temperatures when compared to the pristine systems such as either Ca-Li-B-H or Ca-Li-Mg-B-H. Analyses of metrological characterization using XRD, SEM and have revealed the effectiveness and the role of the catalytic nanoparticles and their enhanced reversible hydrogen storage behavior on the host hydride matrix. The mass spectrometric investigations employing RGA on these nanocrystalline, multi-component hydride systems exhibit the release of hydrogen in major proportion (˜80-90%) as compared to previously attributed ammonia.

  1. Deep-sea ostracode shell chemistry (Mg:Ca ratios) and late Quaternary Arctic Ocean history

    USGS Publications Warehouse

    Cronin, T. M.; Dwyer, G.S.; Baker, P.A.; Rodriguez-Lazaro, J.; Briggs, W.M.; ,

    1996-01-01

    The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus Krithe obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for paleoceanographic study. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation (r2=0.59) between Mg:Ca ratios and bottom-water temperature in Krithe shells from water depths <900 m.

  2. Electron microprobe analyses of Ca, S, Mg and P distribution in incisors of Spacelab-3 rats

    NASA Technical Reports Server (NTRS)

    Rosenberg, G. D.; Simmons, D. J.

    1985-01-01

    The distribution of Ca, S, Mg and P was mapped within the incisors of Spacelab-3 rats using an electron microprobe. The data indicate that Flight rats maintained in orbit for 7 days have significantly higher Ca/Mg ratios in dentin due to both higher Ca and lower Mg content than in dentin of ground-based Controls. There is no statistical difference in distribution of either P or S within Fligth animals and Controls, but there is clear indication that, for P at least, the reason is the greater variability of the Control data. These results are consistent with those obtained on a previous NASA/COSMOS flight of 18.5 days duration, although they are not pronounced. The results further suggest that continuously growing rat incisors provide useful records of the effects of weightlessness on Ca metabolism.

  3. Combinatorial sputtering of Ga-doped (Zn,Mg)O for contact applications in solar cells

    SciTech Connect

    Rajbhandari, Pravakar P.; Bikowski, André; Perkins, John D.; Dhakal, Tara P.; Zakutayev, Andriy

    2017-01-01

    Development of tunable contact materials based on environmentally friendly chemical elements using scalable deposition approaches is necessary for existing and emerging solar energy conversion technologies. In this paper, the properties of ZnO alloyed with magnesium (Mg), and doped with gallium (Ga) are studied using combinatorial thin film experiments. As a result of these studies, the optical band gap of the sputtered Zn1-xMgxO thin films was determined to vary from 3.3 to 3.6 eV for a compositional spread of Mg content in the 0.04 < x < 0.17 range. Depending on whether or not Ga dopants were added, the electron concentrations were on the order of 1017 cm-3 or 1020 cm-3, respectively. Based on these results and on the Kelvin Probe work function measurements, a band diagram was derived using basic semiconductor physics equations. The quantitative determination of how the energy levels of Ga-doped (Zn, Mg)O thin films change as a function of Mg composition presented here, will facilitate their use as optimized contact layers for both Cu2ZnSnS4 (CZTS), Cu(In, Ga)Se2 (CIGS) and other solar cell absorbers.

  4. Bandwidth enhancement of MgZnO-based MSM photodetectors by inductive gain peaking

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Guo, Xinlu; Guo, Lixin; He, Jingfang; Yang, Yintang; Zhang, Zhiyong

    2016-08-01

    For high-speed optical communication applications, the bandwidth of photodetector would be a key limitation. In this work, the bandwidth property of MgZnO-based Metal-Semiconductor-Metal (MSM) photodetector considering RC and transit limitations is investigated on the basis of the series and enhanced gain peaked photodetector circuits proposed by us with different finger widths. To ensure the accuracy of parameters, the high-filed transportation characteristics of MgZnO are investigated by a three-valley ensemble Monte Carlo simulation combined with first principle calculations. The results show that the gain peaking technique, especially the enhanced gain peaking, can improve the bandwidth of MgZnO MSM photodetector to a maximum value of 61.28 GHz, corresponding to a bandwidth enhancement of 49% without undesired effects. Three-dimensional electromagnetic computation is further performed to design and simulate the on-chip-inductor. The value of the simulated inductor is approximately 0.0529 nH, which is in good agreement with the designed value of 0.0569 nH. This work benefits the development of high speed MgZnO MSM photodetector.

  5. Shape and Site Dependent in Vivo Degradation of Mg-Zn Pins in Rabbit Femoral Condyle

    PubMed Central

    Han, Pei; Tan, Moyan; Zhang, Shaoxiang; Ji, Weiping; Li, Jianan; Zhang, Xiaonong; Zhao, Changli; Zheng, Yufeng; Chai, Yimin

    2014-01-01

    A type of specially designed pin model of Mg-Zn alloy was implanted into the full thickness of lesions of New Zealand rabbits’ femoral condyles. The recovery progress, outer surface healing and in vivo degradation were characterized by various methods including radiographs, Micro-CT scan with surface rendering, SEM (scanning electron microscope) with EDX (Energy Dispersive X-ray analysis) and so on. The in vivo results suggested that a few but not sufficient bridges for holding force were formed between the bone and the implant if there was a preexisting gap between them. The rapid degradation of the implantation in the condyle would result in the appearance of cavities. Morphological evaluation of the specially designed pins indicated that the cusp was the most vulnerable part during degradation. Furthermore, different implantation sites with distinct components and biological functions can lead to different degradation rates of Mg-Zn alloy. The rate of Mg-Zn alloy decreases in the following order: implantation into soft tissue, less trabecular bone, more trabecular bone, and cortical bone. Because of the complexities of in vivo degradation, it is necessary for the design of biomedical Mg-Zn devices to take into consideration the implantation sites used in clinics. PMID:24566138

  6. Novel ZnO/MgO/Fe2O3 composite optomagnetic nanoparticles.

    PubMed

    Kamińska, I; Sikora, B; Fronc, K; Dziawa, P; Sobczak, K; Minikayev, R; Paszkowicz, W; Elbaum, D

    2013-05-15

    A facile sol-gel synthesis of novel ZnO/MgO/Fe2O3 nanoparticles (NPs) is reported and their performance is compared to that of ZnO/MgO. Powder x-ray diffraction (XRD) patterns reveal the crystal structure of the prepared samples. The average particle size of the sample was found to be 4.8 nm. The optical properties were determined by UV-vis absorption and fluorescence measurements. The NPs are stable in biologically relevant solutions (phosphate buffered saline (PBS), 20 mM, pH = 7.0) contrary to ZnO/MgO NPs which degrade in the presence of inorganic phosphate. Superparamagnetic properties were determined with a superconducting quantum interference device (SQUID). Biocompatible and stable in PBS ZnO/MgO/Fe2O3 core/shell composite nanocrystals show luminescent and magnetic properties confined to a single NP at room temperature (19-24 ° C), which may render the material to be potentially useful for biomedical applications.

  7. Structural and optoelectronic properties of Mg substituted ZTe (Z=Zn, Cd and Hg)

    NASA Astrophysics Data System (ADS)

    Khan, Imad; Subhan, Fazle; Ahmad, Iftikhar; Ali, Zahid

    2015-08-01

    Wide band gap semiconductor alloys, MgxZ1-xTe (Z=Zn, Cd and Hg), are investigated over a full range of Mg compositions (0≤x≤1) using density functional theory (DFT). The variation in the lattice constant of MgxZ1-xTe is linear with the composition x, and all these alloys obey Vegrd's law. The CdTe (6.50 Å) and MgTe (6.44 Å) are lattice matched compounds, therefore the lattice constant of MgCdTe decreases slightly with the concentration x, whereas the lattice constant also decreases for MgHgTe but increases for MgZnTe. It is due to the fact that Mg has larger size than Zn and smaller size than Cd and Hg. The band gap of these compounds are calculated using the modified Becke-Johnson (mBJ) exchange potential as LDA and GGA are not effective in producing the experimental band gap of a strongly correlated electron system. The calculated band gaps of these compounds cover the range 0-3.5 eV and are consistent with the experimental band gaps. The band gaps exhibit nonlinear behavior or bowing effect with the change in concentration. The frequency dependent optical properties like dielectric functions, and indices of refraction of these ternary systems are also calculated and discussed.

  8. Mechanical properties and corrosion behavior of Mg-Gd-Ca-Zr alloys for medical applications.

    PubMed

    Shi, Ling-Ling; Huang, Yuanding; Yang, Lei; Feyerabend, Frank; Mendis, Chamini; Willumeit, Regine; Ulrich Kainer, Karl; Hort, Norbert

    2015-07-01

    Magnesium alloys are promising candidates for biomedical applications. In this work, influences of composition and heat treatment on the microstructure, the mechanical properties and the corrosion behavior of Mg-Gd-Ca-Zr alloys as potential biomedical implant candidates were investigated. Mg5Gd phase was observed at the grain boundaries of Mg-10Gd-xCa-0.5Zr (x=0, 0.3, 1.2wt%) alloys. Increase in the Ca content led to the formation of additional Mg2Ca phase. The Ca additions increased both the compressive and the tensile yield strengths, but reduced the ductility and the corrosion resistance in cell culture medium. After solution heat treatment, the Mg5Gd particles dissolved in the Mg matrix. The compressive strength decreased, while the corrosion resistance improved in the solution treated alloys. After ageing at 200°C, metastable β' phase formed on prismatic planes and a new type of basal precipitates have been observed, which improved the compressive and tensile ultimate strength, but decreased the ductility.

  9. Effects of Mg II and Ca II ionization on ab-initio solar chromosphere models

    NASA Technical Reports Server (NTRS)

    Rammacher, W.; Cuntz, M.

    1991-01-01

    Acoustically heated solar chromosphere models are computed considering radiation damping by (non-LTE) emission from H(-) and by Mg II and Ca II emission lines. The radiative transfer equations for the Mg II k and Ca II K emission lines are solved using the core-saturation method with complete redistribution. The Mg II k and Ca II K cooling rates are compared with the VAL model C. Several substantial improvements over the work of Ulmschneider et al. (1987) are included. It is found that the rapid temperature rises caused by the ionization of Mg II are not formed in the middle chromosphere, but occur at larger atmospheric heights. These models represent the temperature structure of the 'real' solar chromosphere much better. This result is a major precondition for the study of ab-initio models for solar flux tubes based on MHD wave propagation and also for ab-initio models for the solar transition layer.

  10. The effects of diagenesis and dolomitization on Ca and Mg isotopes in marine platform carbonates: Implications for the geochemical cycles of Ca and Mg

    NASA Astrophysics Data System (ADS)

    Fantle, Matthew S.; Higgins, John

    2014-10-01

    The Ca, Mg, O, and C isotopic and trace elemental compositions of marine limestones and dolostones from ODP Site 1196A, which range in depth (∼58 to 627 mbsf) and in depositional age (∼5 and 23 Ma), are presented. The objectives of the study are to explore the potential for non-traditional isotope systems to fingerprint diagenesis, to quantify the extent to which geochemical proxies are altered during diagenesis, and to investigate the importance of diagenesis within the global Ca and Mg geochemical cycles. The data suggest that Ca, which has a relatively high solid to fluid mass ratio, can be isotopically altered during diagenesis. In addition, the alteration of Ca correlates with the alteration of Mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks. Bulk carbonate δ44Ca values vary between 0.60 and 1.31‰ (SRM-915a scale); the average limestone δ44Ca is 0.97 ± 0.24‰ (1SD), identical within error to the average dolostone (1.03 ± 0.15 1SD ‰). Magnesium isotopic compositions (δ26Mg, DSM-3 scale) range between -2.59‰ and -3.91‰, and limestones (-3.60 ± 0.25‰) and dolostones (-2.68 ± 0.07‰) are isotopically distinct. Carbon isotopic compositions (δ13C, PDB scale) vary between 0.86‰ and 2.47‰, with average limestone (1.96 ± 0.31‰) marginally offset relative to average dolostone (1.68 ± 0.57‰). The oxygen isotopic compositions (δ18O, PDB scale) of limestones (-1.22 ± 0.94‰) are substantially lower than the dolostones measured (2.72 ± 1.07‰). The isotopic data from 1196A suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories. Numerical modeling supports the contention that such trends can be interpreted as diagenetic, and suggests that the appropriate distribution coefficient (KMg) associated with limestone diagenesis is ∼1 to 5 × 10-3, distinctly lower than those values (>0.015) reported in laboratory

  11. Synthesis, Characterization and Photocatalytic Activity of Mg-Impregnated ZnO-SnO2 Coupled Nanoparticles.

    PubMed

    Behnajady, Mohammad A; Tohidi, Yasamin

    2014-01-01

    ZnO-SnO2 nanoparticles were prepared by coprecipitation method; then Mg, with different molar ratios and calcination temperatures, was loaded on the coupled nanoparticles by impregnation method. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) techniques. Based on XRD results, the ZnO-SnO2 and Mg/ZnO-SnO2 nanoparticles were made of ZnO and SnO2 nanocrystallites. According to DRS spectra, the band gap energy value of 3.13 and 3.18 eV were obtained for ZnO-SnO2 and Mg/ZnO-SnO2 nanoparticles, respectively. BET analysis revealed a Type III isotherm with a microporous structure and surface area of 32.051 and 49.065 m(2)  g(-1) for ZnO-SnO2 and Mg/ZnO-SnO2 , respectively. Also, the spherical shape of nanocrystallites was deduced from TEM and FESEM images. The photocatalytic performance of pure ZnO-SnO2 and Mg/ZnO-SnO2 was analyzed in the photocatalytic removal of methyl orange (MO). The results indicated that Mg/ZnO-SnO2 exhibited superior photocatalytic activity to bare ZnO-SnO2 photocatalyst due to high surface area, increased MO adsorption and larger band gap energy. Maximum photocatalytic activity of Mg/ZnO-SnO2 nanoparticles was obtained with 0.8 mol% Mg and calcination temperature of 350°C.

  12. Effect of Mg/Ca ratios on microbially induced carbonate precipitation

    NASA Astrophysics Data System (ADS)

    Balci, Nurgul; Demirel, Cansu; Seref Sonmez, M.; Kurt, M. Ali

    2016-04-01

    Influence of Mg/Ca ratios on microbially induced carbonate mineralogy were investigated by series of experiments carried out under various environmental conditions (Mg/Ca ratio, temperature and salinity). Halophilic bacterial cultures used for biomineralization experiments were isolated from hypersaline Lake Acıgöl (Denizli, SW Turkey), displaying extreme water chemistry with an average pH around 8.6 (Balci eta l.,2015). Enriched bacterial culture used in the experiments consisted of Halomonas saccharevitans strain AJ275, Halomonas alimentaria strain L7B; Idiomarina sp. TBZ29, 98% Idiomarina seosensis strain CL-SP19. Biomineralization experiments were set up using above enriched culture with Mg/Ca ratios of 0.05, 1, 4 and 15 and salinity of 8% and 15% experiments at 30oC and 10oC. Additionally, long-term biomineralization experiments were set up to last for a year, for Mg/Ca=4 and Mg/Ca=15 experiments at 30oC. For each experimental condition abiotic experiments were also conducted. Solution chemistry throughout incubation was monitored for Na, K, Mg, Ca, bicarbonate, carbonate, ammonium and phosphate for a month. At the end of the experiments, precipitates were collected and morphology and mineralogy of the biominerals were investigated and results were evaluated using the software DIFFRAC.SUITE EVA. Overall the preliminary results showed chemical precipitation of calcite, halite, hydromagnesite and sylvite. Results obtained from biological experiments indicate that, low Mg/Ca ratios (0.05 and 1) favor chlorapatite precipitation, whereas higher Mg/Ca ratios favor struvite precipitation. Biomineralization of dolomite, huntite and magnesite is favorable at high Mg/Ca ratios (4 and 15), in the presence of halophilic bacteria. Moreover, results indicate that supersaturation with respect to Mg (Mg/Ca=15) combined with NaCl (15%) inhibits biomineralization and forms chemical precipitates. 15% salinity is shown to favor chemical precipitation of mineral phases more than

  13. Mg/Ca composition of benthic foraminifera Miliolacea as a new tool of paleoceanography

    NASA Astrophysics Data System (ADS)

    Sadekov, Aleksey Yu.; Bush, Flora; Kerr, Joanna; Ganeshram, Raja; Elderfield, Henry

    2014-10-01

    The Mg/Ca compositions of benthic foraminifera from the superfamily Miliolacea have been studied to explore the use of these high-Mg foraminifera as a proxy for deep ocean conditions. Taxonomic analyses, relative abundance, and depth distributions of different Miliolacea species were carried out on a collection of core top samples, covering a depth range of 131 m to 2530 m, along the Australian coast of the Timor Sea. Pyrgo sp., composed of Pyrgo sarsi and Pyrgo murrhina, was found to be the most suitable for proxy studies. Mg/Ca values of this group of foraminifera show a strong correlation with bottom water temperatures and carbonate ion saturation described by the linear relationship: Mg/Ca = 2.53(±0.22) × BWT + 0.129(±0.023) × Δ[CO32-] + 4.63(±0.53), within the -1°C to 8°C temperature range. Absolute Mg/Ca values of Pyrgo sp. calcite and their temperature sensitivity are similar to those observed for inorganic calcite, suggesting that Mg composition of Pyrgo sp. calcite is mainly controlled by inorganic processes. The Mg/Ca composition of Pyrgo sp. calcite provides a new tool for reconstructing both water temperature and carbonate ion saturation when combined with other proxies for one of these parameters. A down core record from the Eastern Equatorial Pacific has been generated to illustrate how Mg/Ca values can be used for paleoclimate studies. This down core record shows large changes in Pacific bottom waters [CO32-] across glacial-interglacial transition, implying an increase in [CO32-] during the glacial period.

  14. Mechanochemical synthesis of MgF2 - MF2 composite systems (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Scholz, G.; Breitfeld, S.; Krahl, T.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2015-12-01

    The capability of mechanochemical synthesis for the formation of MgF2-MF2 (M: Ca, Sr, Ba) composites, solid solutions or well-defined compounds was tested applying a fluorination of different fluorine-free metal sources with NH4F directly at milling. No evidence was found for a substitution of Mg2+ with Ca2+ (Sr2+, Ba2+) ions, or vice versa, in rutile or fluorite structure. However, an equimolar ratio of Mg2+ to the second cation allows the mechanochemical synthesis of tetrafluoromagnesates, MMgF4, which is more and more hampered the smaller the radius of the cation M2+ is. BaMgF4 is formed even phase pure from the acetates, SrMgF4 can only be observed in a mixture accompanied by the binary fluorides. In addition, 19F MAS NMR spectra along with calculations of 19F isotropic chemical shift values according to the superposition model point to the formation of a metastable phase of CaMgF4, which disappears at thermal treatment and decomposes into the binary fluorides CaF2 and MgF2.

  15. Characteristic chemical shifts of quasicrystalline Zn-Mg-Zr alloys studied by EELS and SXES

    NASA Astrophysics Data System (ADS)

    Koshiya, S.; Terauchi, M.; Ohhashi, S.; Tsai, A. P.

    2013-06-01

    Chemical shifts of the constituent atoms of primitive icosahedral quasicrystal (P-QC), face-centred icosahedral quasicrystal (F-QC) and 1/1-approximant (1/1-AP) of F-QC Zn-Mg-Zr alloys were investigated for the first time using high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Zn M-shell and Mg L-shell excitation EELS spectra of P-QC, F-QC and 1/1-AP alloys, only the quasicrystalline alloys showed a chemical shift towards the larger binding energy side. In Zn-L and Zr-L emission SXES spectra, the P-QC and F-QC alloys showed a chemical shift towards larger binding energy side. The magnitudes of the shifts in the Zn-L emission spectra of the quasicrystalline alloys were almost the same as for ZnO. These results strongly suggest a decrease in valence charge in quasicrystalline states. Therefore, it should be concluded that bonding in quasicrystalline states involves a characteristic increase in covalency compared with bonding in corresponding approximant and standard metal crystals.

  16. Effects in Mg-Zn-based alloys strengthened by quasicrystalline phase

    NASA Astrophysics Data System (ADS)

    Vlček, M.; Čížek, J.; Lukáč, F.; Melikhova, O.; Hruška, P.; Procházka, I.; Vlach, M.; Stulíková, I.; Smola, B.; Jäger, A.

    2016-01-01

    Magnesium Mg-based alloys are promising lightweight structural materials for automotive, aerospace and biomedical applications. Recently Mg-Zn-Y system attracted a great attention due to a stable icosahedral phase (I-phase) with quasicrystalline structure which is formed in these alloys. Positron lifetime spectroscopy and in situ synchrotron X-ray diffraction were used to study thermal stability of I-phase and precipitation effects in Mg-Zn-Y and Mg- Zn-Al alloys. All alloys containing quasicrystalline I-phase exhibit misfit defects characterized by positron lifetime of ∼ 300 ps. These defects are associated with the interfaces between I- phase particles and Mg matrix. The quasicrystalline I-phase particles were found to be stable up to temperatures as high as ∼ 370°C. The W-phase is more stable and melts at ∼ 420°C. Concentration of defects associated with I-phase decreases after annealing at temperatures above ∼ 300°C.

  17. Enhanced antibacterial properties, biocompatibility, and corrosion resistance of degradable Mg-Nd-Zn-Zr alloy.

    PubMed

    Qin, Hui; Zhao, Yaochao; An, Zhiquan; Cheng, Mengqi; Wang, Qi; Cheng, Tao; Wang, Qiaojie; Wang, Jiaxing; Jiang, Yao; Zhang, Xianlong; Yuan, Guangyin

    2015-06-01

    Magnesium (Mg), a potential biodegradable material, has recently received increasing attention due to its unique antibacterial property. However, rapid corrosion in the physiological environment and potential toxicity limit clinical applications. In order to improve the corrosion resistance meanwhile not compromise the antibacterial activity, a novel Mg alloy, Mg-Nd-Zn-Zr (Hereafter, denoted as JDBM), is fabricated by alloying with neodymium (Nd), zinc (Zn), zirconium (Zr). pH value, Mg ion concentration, corrosion rate and electrochemical test show that the corrosion resistance of JDBM is enhanced. A systematic investigation of the in vitro and in vivo antibacterial capability of JDBM is performed. The results of microbiological counting, CLSM, SEM in vitro, and microbiological cultures, histopathology in vivo consistently show JDBM enhanced the antibacterial activity. In addition, the significantly improved cytocompatibility is observed from JDBM. The results suggest that JDBM effectively enhances the corrosion resistance, biocompatibility and antimicrobial properties of Mg by alloying with the proper amount of Zn, Zr and Nd.

  18. Reinvestigating the "salinity effect" on Atlantic Globigerinoides ruber Mg/Ca ratios

    NASA Astrophysics Data System (ADS)

    Hertzberg, J. E.; Schmidt, M. W.

    2012-12-01

    Numerous culturing, core-top, and sediment trap studies show that temperature is the primary control on Mg/Ca ratios in foraminiferal calcite, and calibrations of this relationship have been applied successfully to the paleo-record to reconstruct ocean temperatures across a wide range of time periods. In addition, paired Mg/Ca temperatures and δ18Ocalcite measurements on surface dwelling foraminifera are often used to reconstruct past δ18Osw variability, a robust proxy for sea surface salinity. However, a recent study of core-top sediments across an Atlantic meridional transect suggests that salinity might have a stronger control on foraminiferal Mg/Ca ratios than previously thought. By analyzing Mg/Ca ratios and δ18O on the planktonic foraminifera Globigerinoides ruber (white), Arbuszewski et al. [2010] found a 27% increase in G. ruber Mg/Ca ratios per 1 salinity unit increase for seawater salinities above 35. In this study, we use shell weight analyses and SEM images from a subset of the core-tops used in the Arbuszewski et al. [2010] study across a narrow depth range (3197 - 3559 m) to show that G. ruber shells from the equatorial region are highly dissolved compared to those from the gyres, significantly impacting their Mg/Ca-SSTs. Shell weights from the higher-productivity equatorial regions of the Atlantic are on average 20% and 15% lower than those from the oligotrophic North and South Atlantic gyres, respectively. Given the large preservation gradient along the Mid Atlantic Ridge, Arbuszewski et al.'s [2010] application of a single depth-corrected Mg/Ca:SST equation [Dekens et al., 2002] on cores from the subtropical gyres and the equatorial region is not appropriate. When regional differences in preservation are considered, as well as realistic calcification seasons for G. ruber in temperate latitudes, we find a strong correlation between SST and G. ruber Mg/Ca ratios in core-top samples spanning 43°N to 25°S in the Atlantic. When we also consider

  19. Influence of Zn Interlayer on Interfacial Microstructure and Mechanical Properties of TIG Lap-Welded Mg/Al Joints

    NASA Astrophysics Data System (ADS)

    Gao, Qiong; Wang, Kehong

    2016-03-01

    This study explored 6061 Al alloy and AZ31B Mg alloy joined by TIG lap welding with Zn foils of varying thicknesses, with the additional Zn element being imported into the fusion zone to alloy the weld seam. The microstructures and chemical composition in the fusion zone near the Mg substrate were examined by SEM and EDS, and tensile shear strength tests were conducted to investigate the mechanical properties of the Al/Mg joints, as well as the fracture surfaces, and phase compositions. The results revealed that the introduction of an appropriate amount of Zn transition layer improves the microstructure of Mg/Al joints and effectively reduces the formation of Mg-Al intermetallic compounds (IMCs). The most common IMCs in the fusion zone near the Mg substrate were Mg-Zn and Mg-Al-Zn IMCs. The type and distribution of IMCs generated in the weld zone differed according to Zn additions; Zn interlayer thickness of 0.4 mm improved the sample's mechanical properties considerably compared to thicknesses of less than 0.4 mm; however, any further increase in Zn interlayer thickness of above 0.4 mm caused mechanical properties to deteriorate.

  20. Mechanical, thermal, and physical properties of Mg-Ca compounds in the framework of the modified embedded-atom method.

    PubMed

    Groh, Sébastien

    2015-02-01

    Interatomic potentials for pure Ca and the Mg-Ca binary have been developed in the framework of the second nearest-neighbors modified embedded-atom method (MEAM). The validity and the transferability of the Ca MEAM potential was performed by calculating physical, mechanical, and thermal properties. These properties were compared to experimental data and numerical data obtained from existing Ca potentials, and a good agreement was found. In addition, the dissociation of the edge dislocation into two Shockley partials aligns with the linear elasticity solution. Furthermore, the velocity of an edge dislocation under static and dynamics loading conditions predicted in Ca using the MEAM formalism reproduces the expected behavior of an edge dislocation in fcc crystal structures. The Ca MEAM potential was then coupled to an existing Mg MEAM potential to describe the properties of the Mg-Ca alloys. Heat of formation, structural energy difference, and elastic constants were calculated for several ordered Mg-Ca compounds containing different concentrations of Ca. As expected from first-principle calculations based on DFT, Mg2Ca with the Laves phase C14 was found to be the most stable structure with the lowest heat of formation compared to compounds with other Ca concentrations (Mg3Ca, MgCa, and MgCa3). Moreover, the mechanical stability was recovered for the different tested compounds and is in agreement with first-principle data.

  1. Influence of Zn Coating on Interfacial Reactions and Mechanical Properties During Laser Welding-Brazing of Mg to Steel

    NASA Astrophysics Data System (ADS)

    Li, Liqun; Tan, Caiwang; Chen, Yanbin; Guo, Wei; Hu, Xinbin

    2012-12-01

    To investigate the influence of Zn coating on the joining of magnesium alloy AZ31 to Zn-coated steel, dissimilar metal joining both with and without Zn coating was performed by the laser welding-brazing (LWB) process. Welding characteristics including joint appearance, identification of interfacial reaction layers, and mechanical properties were comparatively studied. The results indicated that the presence of Zn coating promoted the wetting of liquid filler wire on the steel substrate. Heterogeneous interfacial reaction layers formed along the interface between the Mg alloy and Zn-coated steel, whereas no distinct reaction layer and increased concentration of Al were identified at the interface between the Mg alloy and noncoated steel. The maximum tensile-shear strength of Mg/steel lap joint with Zn coating reached 180 N/mm, which was slightly higher than that achieved without Zn coating (160 N/mm). Failure of joint in both cases occurred at the interface; however, the fracture mode was found to differ. For Zn-coated steel, the crack propagated along the Mg-Zn reaction layer and Fe-Al phase, with little Mg-Zn reaction phases remaining on the steel side. As for noncoated steel, some remnants of the seam adhered to the steel substrate.

  2. Influence of surface pre-treatment on the cytocompatibility of a novel biodegradable ZnMg alloy.

    PubMed

    Jablonská, Eva; Vojtěch, Dalibor; Fousová, Michaela; Kubásek, Jiří; Lipov, Jan; Fojt, Jaroslav; Ruml, Tomáš

    2016-11-01

    Degradable zinc-based alloys with an appropriate corrosion rate are promising materials for the preparation of temporary orthopaedic implants. Previously, we prepared and characterised a novel Zn1.5Mg alloy. This paper is focused on the characterisation of this alloy after a surface pre-treatment, which should mimic processes occurring in vivo. The samples of the Zn1.5Mg alloy were immersed in a simulated body fluid (SBF) at 37°C for 14days in order to form a protective layer of corrosion products. Thereafter, these samples were used for the corrosion rate determination, an indirect in vitro cytotoxicity test, as well as for a direct contact test and were compared with the non-treated samples. The protective layer was characterized by SEM and its chemical composition was determined by EDS and XPS analysis. The corrosion rate was significantly decreased after the pre-incubation. The protective layer of corrosion products was rich in Ca and P. The pre-incubated samples exhibited increased cytocompatibility in the indirect test (metabolic activity of L929 cells was above 70%) and we also observed osteoblast-like cell growth directly on the samples during the contact tests. Thus, the pre-incubation in SBF leading to improved cytocompatibility could represent more appropriate model to in vivo testing.

  3. MgZnO/ZnO heterostructures with electron mobility exceeding 1 × 106 cm2/Vs

    PubMed Central

    Falson, Joseph; Kozuka, Yusuke; Uchida, Masaki; Smet, Jurgen H.; Arima, Taka-hisa; Tsukazaki, Atsushi; Kawasaki, Masashi

    2016-01-01

    The inherently complex chemical and crystallographic nature of oxide materials has suppressed the purities achievable in laboratory environments, obscuring the rich physical degrees of freedom these systems host. In this manuscript we provide a systematic approach to defect identification and management in oxide molecular beam epitaxy grown MgZnO/ZnO heterostructures which host two-dimensional electron systems. We achieve samples displaying electron mobilities in excess of 1 × 106 cm2/Vs. This data set for the MgZnO/ZnO system firmly establishes that the crystalline quality has become comparable to traditional semiconductor materials. PMID:27229479

  4. Ca2+ and Zn2+ are transported by the electrogenic 2Na+/1H+ antiporter in echinoderm gastrointestinal epithelium

    PubMed

    Zhuang; Duerr; Ahearn

    1995-01-01

    45Ca2+ uptake by purified brush-border membrane vesicles of starfish (Pycnopodia helianthoides) pyloric ceca was stimulated by an outwardly directed H+ gradient and this stimulation was enhanced by the simultaneous presence of an induced membrane potential (inside negative; K+/valinomycin). External amiloride (competitive inhibitor; Ki=660 µmol l-1) and a monoclonal antibody raised against proteins associated with the lobster (Homarus americanus) electrogenic 2Na+/1H+ antiporter both inhibited approximately half of the proton-gradient-stimulated 45Ca2+ uptake. These results suggested that Ca2+ might be transported by the electrogenic antiporter and that the crustacean antibody was inhibitory to the exchange function in echinoderms, as was recently shown in crustacean epithelial brush-border membrane vesicles. Carrier-mediated 45Ca2+ influx by amiloride-sensitive and amiloride-insensitive systems displayed the following kinetic constants: (amiloride-sensitive) Kt=66±2 µmol l-1; Jmax=0.173±0.002 pmol µg-1 protein 8 s-1; (amiloride-insensitive) Kt=18±0.3 µmol l-1; Jmax=0.100±0.001 pmol µg-1 protein 8 s-1. Zn2+ was a mixed inhibitor of 45Ca2+ influx by carrier-mediated transport, displaying a Ki of 920 µmol l-1. Mn2+, Cu2+, Fe2+ and Mg2+ also inhibited 45Ca2+ uptake, but the mechanism(s) of inhibition by these other cations was not disclosed. An equilibrium shift experiment showed that both Na+ and Zn2+ were able to exchange with equilibrated 45Ca2+ in these vesicles, suggesting that both monovalent and divalent cations were able to enter pyloric cecal cells through a common carrier-mediated transport system. In addition, the echinoderm electrogenic system appeared to exhibit a molecular component recognized by the crustacean antibody that may imply a similar epitope in the two animals.

  5. Microstructure Evolution and Mechanical and Corrosion Behavior of Accumulative Roll Bonded Mg-2%Zn/Al-7075 Multilayered Composite

    NASA Astrophysics Data System (ADS)

    Anne, Gajanan; Ramesh, M. R.; Shivananda Nayaka, H.; Arya, Shashi Bhushan; Sahu, Sandeep

    2017-02-01

    Multilayered composite of Mg-2%Zn/Al-7075 was developed by accumulative roll bonding (ARB) of wrought Mg-2%Zn and aluminum 7075 alloy. The Mg-2%Zn/Al-7075 multilayered composite exhibited density of 2295 kg/m3 and an average grain size of 1 and 1.3 μm in Mg-2%Zn and Al-7075 layers, respectively. A thorough microstructural characterization was performed on the composites by scanning electron microscope, electron backscatter diffraction (EBSD), transmission electron microscope and phase analysis by x-ray diffraction. In addition, mechanical properties were evaluated by microhardness and tensile tests. Corrosion behavior of the multilayered composite was examined using electrochemical polarization test. EBSD analysis showed the presence of ultrafine grains with high-angle grain boundaries. The composite exhibited a significant improvement in ultimate tensile strength ( 1.82 times) and elongation ( 1.5 times) as compared with Mg-2%Zn alloy, after four-pass ARB process.

  6. Ca and Mg Incorporation in Siderite at Low Temperatures (< 50° C): Results from Laboratory Experiments

    NASA Astrophysics Data System (ADS)

    Sanchez-Roman, M.; Romanek, C. S.; Xu, H.; Coleman, M.

    2008-12-01

    Siderite (FeCO3) is a common mineral found in modern environments and in ancient rocks produce usually by microbia mediation [1,2]. It usually forms concretions with strongly varying chemical compositions which are governed by both pore-water origin and by microbial influence. In addition, siderite has also been identified in extraterrestrial material such as meteorites and dust particles [3,4]. The geochemical information stored in siderite provides valuable insights into the environmental conditions of mineral formation and the processes by which it is modified over time [5]. To unerstand the inorganic constraints on precipitation relative to natural compositions we undertook free drift experiments under anaerobic conditions at 25, 35 and 45°C with variable concentrations of Fe, Ca and Mg in solution. Samples of solution and solid were withdrawn at different time intervals (15, 21 and 30 days) during time course experiments to determine the composition of the solution and mineral precipitates, and the morphology and mineralogy of the precipitates. After 15 days of incubation a metastable phase was formed, whereas after 21 and 30 days of incubation siderite, Ca-siderite, Mg-siderite Ca-Mg siderite and/or Fe-pokrovskite (a hydrated magnesium hydroxy carbonate) were formed depending on the aqueous Fe, Ca and Mg concentrations in the solution. The Mg and Ca contents in the siderite increased with increasing Mg and Ca concentrations in the medium and with increasing temperature. Siderite precipitates ranged from 1.5 to 50.81 mol percent CaCO3 and from 0.54 to 41.38 mol percent MgCO3. Pokrovskite precipitates ranged from 48.8 to 57.7 mol percent MgCO3 and from 42.34 to 51.17 mol percent FeCO3. The Fe content in the pokrovskite increased with increasing temperature. These inorganic experiments will help to understand the mechanism of Ca-Mg-Fe carbonate formation in natural systems and they are of fundamental importance not only for understanding modern and

  7. The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

    NASA Astrophysics Data System (ADS)

    Chen, S. S.; Pan, X. H.; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

    2014-09-01

    We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1-xO/BexMgyZn1-x-yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1-xO and BexMgyZn1-x-yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( Δ E V) of Mg0.15Zn0.85O ( E g = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( E g = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1-xO is lower by 0.03 eV with the enlargement of E g from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E g of the alloy is 3.73 eV. The Δ E V of Mg0.11Zn0.89O ( E g = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( E g = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the E g of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1-xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

  8. Lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.

    PubMed

    Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M

    2014-02-05

    A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and computational study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare these to the lattice dynamics of the cubic 1/1-approximant Zn6Sc. The two phases, quasicrystal and approximant, are built up from the same atomic clusters, which are packed either quasiperiodically or on a body centered cubic lattice, respectively. Using inelastic neutron scattering and atomic scale simulations, we show that the vibrational spectra of these three systems are very similar, however, they contain a clear signature of the increasing structural complexity from approximant to quasicrystal.

  9. Effects of Mg2+ on Ca2+ handling by the sarcoplasmic reticulum in skinned skeletal and cardiac muscle fibres.

    PubMed

    Kabbara, A A; Stephenson, D G

    1994-10-01

    The influence of myoplasmic Mg2+ (0.05-10 mM) on Ca2+ accumulation (net Ca2+ flux) and Ca2+ uptake (pump-driven Ca2+ influx) by the intact sarcoplasmic reticulum (SR) was studied in skinned fibres from the toad iliofibularis muscle (twitch portion), rat extensor digitorum longus (EDL) muscle (fast twitch), rat soleus muscle (slow twitch) and rat cardiac trabeculae. Ca2+ accumulation was optimal between 1 and 3 mM Mg2+ in toad fibres and reached a plateau between 1 and 10 mM Mg2+ in the rat EDL fibres and between 3 and 10 mM Mg2+ in the rat cardiac fibres. In soleus fibres, optimal Ca2+ accumulation occurred at 10 mM Mg2+. The same trend was obtained with all preparations at 0.3 and 1 microM Ca2+. Experiments with 2,5-di-(tert-butyl)-1,4-benzohydroquinone, a specific inhibitor of the Ca2+ pump, revealed a marked Ca2+ efflux from the SR of toad iliofibularis fibres in the presence of 0.2 microM Ca2+ and 1 mM Mg2+. Further experiments indicated that the SR Ca2+ leak could be blocked by 10 microM ruthenium red without affecting the SR Ca2+ pump and this allowed separation between SR Ca2+ uptake and SR Ca2+ accumulation. At 0.3 microM Ca2+, Ca2+ uptake was optimal with 1 mM Mg2+ in the toad iliofibularis and rat EDL fibres and between 1 and 10 mM Mg2+ in the rat soleus and trabeculae preparations. At higher [Ca2+] (1 microM), Ca2+ uptake was optimal with 1 mM Mg2+ in the iliofibularis fibres and between 1 and 3 mM Mg2+ in the EDL fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

  10. Liquidus (Ca+Mg)-rich exsolution phases in low-sulfur fly ash

    SciTech Connect

    O'Connor, J.T.; Meeker, G.M.

    1999-07-01

    Ca- and Mg-rich fly ash samples from an electric power plant burning low-sulfur Powder River Coal were analyzed using optical petrographic microscope (OPM), scanning electron microscope (SEM), electron microprobe analyzer (EMPA), and Gandolfi and bulk-powder X-ray diffraction (XRD) techniques. Abundant Ca and Mg in the fly ash, probably originating from dispersed authigenic and residual minerals in the coal feed stock, flux the molten fly ash, effectively allowing many crystalline phases to achieve ordering, to separate from each other, and to grow to appreciable size (>10{micro}m) in the brief time (<20 sec) they spend at high temperature. Phases identified from the (Ca+Mg)-rich fly ash are listed in a table and shown in figures.

  11. H2O2: a Ca(2+) or Mg(2+)-sensing function in statin passive diffusion.

    PubMed

    Guillaume, Yves Claude; Lethier, Lydie; André, Claire

    2015-09-01

    In a previous paper Guillaume's group demonstrated that magnesium (Mg(2+) concentration range 0.00-2.60 mm) increased the passive diffusion of statins and thus played a role in their potential toxicity. In order to confirm an increase in this passive diffusion by divalent salt cations, the role of calcium chloride (CaCl2) on the statin-immobilized artificial membrane (IAM) association was studied. It was demonstrated that calcium supplementation (Ca(2+) concentration range 0.00-3.25 mm) increases the statin passive diffusion. In addition, it was shown that the Ca(2+) effect on the statin-IAM association is higher than that of Mg(2+). These results show that Ca(2+) enhances the passive diffusion of drugs into biological membranes and thus their potential toxicity. Also, addition of H2O2 to the medium showed a hyperbolic response for the statin passive diffusion and this effect was enhanced for the highest Ca(2+) or Mg(2+) concentrations in the medium. H2O2 is likely to interact with the polar head groups of the IAM through dipole-dipole interactions. The conformational changes in H2O2-IAM result in a higher degree of exposure of hydrophobic areas, thus explaining why the binding of pravastatin, which showed the lowest logP value, was less affected by H2O2. This result shows the significant contribution of H2O2 and thus the oxidative stress on the statin passive diffusion. Much of the sensitivity derives from the action of Ca(2+) or Mg(2+), in turn supported the idea that H2O2 may serve a Ca(2+) or Mg(2+) sensing function in statin passive diffusion.

  12. Comparison between Mg II k and Ca II H images recorded by SUNRISE/SuFI

    SciTech Connect

    Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Berkefeld, T.; Schmidt, W.; Knölker, M.; Rodríguez, J. Blanco; Iniesta, J. C. Del Toro

    2014-03-20

    We present a comparison of high-resolution images of the solar surface taken in the Mg II k and Ca II H channels of the Filter Imager on the balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled with 0.48 nm and 0.11 nm wide filters, respectively. The two channels show remarkable qualitative and quantitative similarities in the quiet Sun, in an active region plage and during a small flare. However, the Mg filtergrams display 1.4-1.7 times higher intensity contrast and appear more smeared and smoothed in the quiet Sun. In addition, the fibrils in a plage are wider. Although the exposure time is 100 times longer for Mg images, the evidence suggests that these differences cannot be explained only with instrumental effects or the evolution of the solar scene. The differences at least partially arise because of different line-formation heights, the stronger response of Mg k emission peaks to the higher temperatures, and the larger height range sampled by the broad Mg filter used here. This is evidently manifested during the flare when a surge in Mg evolves differently than in Ca.

  13. Local structures of polar wurtzites Zn1-xMgxO studied by raman and 67Zn/25Mg NMR spectroscopies and by total neutron scattering

    SciTech Connect

    Proffen, Thomas E; Kim, Yiung- Il; Cadars, Sylvian; Shayib, Ramzy; Feigerle, Charles S; Chmelka, Bradley F; Seshadri, Ram

    2008-01-01

    Research in the area of polar semiconductor heterostructures has been growing rapidly, driven in large part by interest in two-dimensional electron gas (2DEG) systems. 2DEGs are known to form at heterojunction interfaces that bear polarization gradients. They can display extremely high electron mobilities, especially at low temperatures, owing to spatial confinement of carrier motions. Recent reports of 2DEG behaviors in Ga{sub 1-x}Al{sub x}N/GaN and Zn{sub 1-x}Mg{sub x}O/ZnO heterostructures have great significance for the development of quantum Hall devices and novel high-electron-mobility transistors (HEMTs). 2DEG structures are usually designed by interfacing a polar semiconductor with its less or more polar alloys in an epitaxial manner. Since the quality of the 2DEG depends critically on interface perfection, as well as the polarization gradient at the heterojunction, understanding compositional and structural details of the parent and alloy semiconductors is an important component in 2DEG design and fabrication. Zn{sub 1-x}Mg{sub x}O/ZnO is one of the most promising heterostructure types for studies of 2DEGs, due to the large polarization of ZnO, the relatively small lattice mismatch, and the large conduction band offsets in the Zn{sub 1-x}Mg{sub x}O/ZnO heterointerface. Although 2DEG formation in Zn{sub 1-x}Mg{sub x}O/ZnO heterostructures have been researched for some time, a clear understanding of the alloy structure of Zn{sub 1-x}Mg{sub x}O is currently lacking. Here, we conduct a detailed and more precise study of the local structure of Zn{sub 1-x}Mg{sub x}O alloys using Raman and solid-state nuclear magnetic resonance (NMR), in conjunction with neutron diffraction techniques.

  14. DC electrical and thermoelectric power measurement studies of Ni-Mg-Zn-Co ferrites

    NASA Astrophysics Data System (ADS)

    Patil, S. B.; Patil, R. P.; Chougule, B. K.

    2013-06-01

    Ni-Mg-Zn-Co ferrites having general formula, Ni0.5-xMgx-0.01Zn0.5-yCoy+0.01Fe2O4 (where x=0.1-0.4 and y=0.1-0.4) were prepared by a ceramic method. X-ray diffraction reveals formation of single-phase cubic spinel structures. The lattice parameter is found to increase linearly with increase in Zn content. The variation of the electrical resistivity vs. temperature is linear with a transition near the Curie temperature. The thermoelectric power was measured from room temperature to 500 °C by maintaining a temperature difference of 20 °C between the hot and cold ends. All samples show a negative Seebeck coefficient. This indicates n-type charge carriers in the samples.

  15. Mg/Ca and δ18O in the calcite of benthic foraminifera: does size matter?

    NASA Astrophysics Data System (ADS)

    de Nooijer, Lennart; Bijma, Jelle; -Jan Reichart, Gert; Hathorne, Ed

    2010-05-01

    Mg/Ca and del-18O are popular proxies for past sea water temperatures, ice volume and, together, salinity. The biological control that foraminifera have over calcification results in precipitation of calcium carbonate that has an isotope and element composition that is very different from those of inorganically precipitated calcium carbonates. Indications for an effect of ontogeny (i.e. size of a specimen) on the fractionation of oxygen isotopes are contradictory, while for the incorporation of most (trace) elements, data are lacking. The causes of size-based variability in element incorporation and isotope fractionation need to be understood and quantified in order to reliably use them as paleoproxies. In this study, we present Mg/Ca and oxygen isotope data from cultured specimens of the benthic foraminifer Ammonia tepida. When asexual reproduction takes place in this species, 50-300 genetically identical juveniles (i.e. clones) are produced. These juveniles are cultured at constant temperature, carbonate chemistry, salinity, etc to determine inter- and intra-specimen variability in Mg/Ca, Ba/Ca and Sr/Ca. From the same groups of clones, del-18O was determined from specimens with different sizes. Results show that the variability differs greatly between the analysed elements (e.g. relatively constant for Sr and Ba, variable for Mg) and isotopes, underscoring the need for a biological understanding of foraminiferal calcification pathways.

  16. Automated cleaning of foraminifera shells before Mg/Ca analysis using a pipette robot

    NASA Astrophysics Data System (ADS)

    Johnstone, Heather J. H.; Steinke, Stephan; Kuhnert, Henning; Bickert, Torsten; Pälike, Heiko; Mohtadi, Mahyar

    2016-08-01

    The molar ratio of magnesium to calcium (Mg/Ca) in foraminiferal calcite is a widely used proxy for reconstructing past seawater temperatures. Thorough cleaning of tests is required before analysis to remove contaminant phases such as clay and organic matter. We have adapted a commercial pipette robot to automate an established cleaning procedure, the "Mg-cleaning" protocol of Barker et al. (2003). Efficiency of the automated nine-step method was assessed through monitoring Al/Ca of trial samples (GeoB4420-2 core catcher). Planktonic foraminifera Globigerinoides ruber, Globigerinoides sacculifer, and Neogloboquadrina dutertrei from this sample gave Mg/Ca consistent with the habitat range of the three species, and 40-60% sample recovery after cleaning. Comparison between manually cleaned and robot-cleaned samples of G. ruber (white) from a sediment core (GeoB16602) showed good correspondence between the two methods for Mg/Ca (r = 0.93, p < 0001, n = 27). Average Al/Ca in robot-cleaned samples was 0.05 mmol/mol, showing that the samples are cleaned effectively by the robot. The robot offers increased sample throughput as batch sizes of up to 88 samples/blanks can be processed in ˜7 h with little intervention.

  17. Persistent luminescence of CaMgSi2O6:Eu(2+),Dy(3+) and CaMgSi2O6:Eu(2+),Ce(3+) phosphors prepared using the solid-state reaction method.

    PubMed

    Chandrakar, P; Baghel, R N; Bisen, D P; Chandra, B P

    2016-02-01

    CaMgSi2O6:Eu(2+),Dy(3+) and CaMgSi2O6:Eu(2+),Ce(3+) phosphors were synthesized using the solid-state reaction method. X-Ray diffraction (XRD) and photoluminescence (PL) analyses were used to characterize the phosphors. The XRD results revealed that the synthesized CaMgSi2O6:Eu(2+),Dy(3+) and CaMgSi2O6:Eu(2+),Ce(3+) phosphors were crystalline and are assigned to the monoclinic structure with a space group C2/c. The calculated crystal sizes of CaMgSi2O6:Eu(2+),Dy(3+) and CaMgSi2O6:Eu(2+),Ce(3+) phosphors with a main (221) diffraction peak were 44.87 and 53.51 nm, respectively. Energy-dispersive X-ray spectroscopy (EDX) confirmed the proper preparation of the sample. The PL emission spectra of CaMgSi2O6:Eu(2+),Dy(3+) and CaMgSi2O6:Eu(2+),Ce(3+) phosphors have a broad band peak at 444.5 and 466 nm, respectively, which is due to electronic transition from 4f(6) 5d(1) to 4f(7). The afterglow results indicate that the CaMgSi2O6:Eu(2+),Dy(3+) phosphor has better persistence luminescence than the CaMgSi2O6:Eu(2+),Ce(3+) phosphor.

  18. Multifunctions of dual Zn/Mg ion co-implanted titanium on osteogenesis, angiogenesis and bacteria inhibition for dental implants.

    PubMed

    Yu, Yiqiang; Jin, Guodong; Xue, Yang; Wang, Donghui; Liu, Xuanyong; Sun, Jiao

    2017-02-01

    In order to improve the osseointegration and long-term survival of dental implants, it is urgent to develop a multifunctional titanium surface which would simultaneously have osteogeneic, angiogeneic and antibacterial properties. In this study, a potential dental implant material-dual Zn/Mg ion co-implanted titanium (Zn/Mg-PIII) was developed via plasma immersion ion implantation (PIII). The Zn/Mg-PIII surfaces were found to promote initial adhesion and spreading of rat bone marrow mesenchymal stem cells (rBMSCs) via the upregulation of the gene expression of integrin α1 and integrin β1. More importantly, it was revealed that Zn/Mg-PIII could increase Zn(2+) and Mg(2+) concentrations in rBMSCs by promoting the influx of Zn(2+) and Mg(2+) and inhibiting the outflow of Zn(2+), and then could enhance the transcription of Runx2 and the expression of ALP and OCN. Meanwhile, Mg(2+) ions from Zn/Mg-PIII increased Mg(2+) influx by upregulating the expression of MagT1 transporter in human umbilical vein endothelial cells (HUVECs), and then stimulated the transcription of VEGF and KDR via activation of hypoxia inducing factor (HIF)-1α, thus inducing angiogenesis. In addition to this, it was discovered that zinc in Zn/Mg-PIII had certain inhibitory effects on oral anaerobic bacteria (Pg, Fn and Sm). Finally, the Zn/Mg-PIII implants were implanted in rabbit femurs for 4 and 12weeks with Zn-PIII, Mg-PIII and pure titanium as controls. Micro-CT evaluation, sequential fluorescent labeling, histological analysis and push-out test consistently demonstrated that Zn/Mg-PIII implants exhibit superior capacities for enhancing bone formation, angiogenesis and osseointegration, while consequently increasing the bonding strength at bone-implant interfaces. All these results suggest that due to the multiple functions co-produced by zinc and magnesium, rapid osseointegration and sustained biomechanical stability are enhanced by the novel Zn/Mg-PIII implants, which have the potential

  19. Mg and Ca isotope signatures of authigenic dolomite in siliceous deep-sea sediments

    NASA Astrophysics Data System (ADS)

    Blättler, Clara L.; Miller, Nathaniel R.; Higgins, John A.

    2015-06-01

    Authigenic carbonates in marine sediments frequently have carbon isotope ratios that reflect local organic carbon processing rather than the δ13C of the global DIC (dissolved inorganic carbon) reservoir, but their contributions to ancient sedimentary sections are difficult to assess. In this study of authigenic dolomite from the Miocene-age Monterey Formation of offshore California, Mg and Ca isotopes are shown to vary with stratigraphic depth as a result of early diagenetic processes. The dolomite is a pre-compaction authigenic phase that occurs as beds and nodules with δ13C ranging from -16 to + 9 ‰. Light δ13C values were likely acquired from the sedimentary zone of microbial sulfate reduction, while heavy δ13C values were acquired from the zone of methanogenesis. Mg and Ca isotopes are roughly anti-correlated, with intervals of negative δ13C associated with low δ26Mg and higher δ 44/40Ca values. The variability is observed over a wide range of length-scales, from 10-2 meters within individual authigenic beds/nodules, to 102 meters over the entire stratigraphic column, and can be understood as the consequence of dolomite precipitation in pore fluids where Mg supply is limited by diffusive transport. The relationship of δ26Mg and δ 44/40Ca to the more common stable isotope measurements of δ13C and δ18O represents a new, diagenetically robust, geochemical fingerprint for identifying synsedimentary authigenic carbonates in the geological record.

  20. The in vitro biological properties of Mg-Zn-Sr alloy and superiority for preparation of biodegradable intestinal anastomosis rings

    PubMed Central

    Liu, Ling; Li, Nianfeng; Lei, Ting; Li, Kaimo; Zhang, Yangde

    2014-01-01

    Background Magnesium (Mg) alloy is a metal-based biodegradable material that has received increasing attention in the field of clinical surgery, but it is currently seldom used in intestinal anastomosis. This study was conducted to comprehensively assess a ternary magnesium (Mg)-zinc (Zn)-strontium (Sr) alloy’s biological superiorities as a preparation material for intestinal anastomosis ring. Material/Methods Mouse L-929 fibroblasts were cultured with Mg-Zn-Sr alloy extract and compared with both positive (0.64% phenol) and negative (original broth culture) controls. The cell morphology of different groups was examined using microscopy, and a cytotoxicity assessment was performed. Fresh anticoagulated human blood was mixed with Mg-Zn-Sr alloy extract and compared with both positive (distilled water) and negative (normal saline) controls. The absorbance of each sample at 570 nm was used to calculate the Mg-Zn-Sr alloy hemolysis ratio in order to test the Mg alloy’s blood compatibility. Bacterial cultures of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were added to Mg-Zn-Sr alloy block samples and compared with positive (Ceftazidime), negative (316LSS stainless steel), and blank controls. The broth cultures were sampled to compare their bacterial colony counts so as to evaluate the antibacterial properties of the Mg-Zn-Sr alloy. The Mg-Zn-Sr alloy was surface-coated with a layer of poly(lactic-co-glycolic acid) carrying everolimus. The surface morphology and degradability of the coating were examined so as to demonstrate feasibility of coating, which can release the drug evenly. Results The experiments proved that Mg-Zn-Sr alloy has good biocompatible, antibacterial, and drug-loaded coating performances, which are lacking in existing intestinal anastomosis devices/materials. Conclusions The Mg-Zn-Sr alloy increases biocompatibility, and yields a safer and better therapeutic effect; therefore, it is a novel biomaterial that is feasible for

  1. Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films

    PubMed Central

    Li, D. L.; Ma, Q. L.; Wang, S. G.; Ward, R. C. C.; Hesjedal, T.; Zhang, X.-G.; Kohn, A.; Amsellem, E.; Yang, G.; Liu, J. L.; Jiang, J.; Wei, H. X.; Han, X. F.

    2014-01-01

    Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. Here, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. In this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices. PMID:25451163

  2. Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films

    DOE PAGES

    Li, D. L.; Ma, Q. L.; Wang, S. G.; ...

    2014-12-02

    Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. In this paper, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1more » spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. Finally, in this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices.« less

  3. Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films

    SciTech Connect

    Li, D. L.; Ma, Q. L.; Wang, S. G.; Ward, R. C. C.; Hesjedal, T.; Zhang, X. -G.; Kohn, A.; Amsellem, E.; Yang, G.; Liu, J. L.; Jiang, J.; Wei, H. X.; Han, X. F.

    2014-12-02

    Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. In this paper, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. Finally, in this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices.

  4. Ultraviolet random lasing from asymmetrically contacted MgZnO metal-semiconductor-metal device

    SciTech Connect

    Morshed, Muhammad M.; Suja, Mohammad; Zuo, Zheng; Liu, Jianlin

    2014-11-24

    Nitrogen-doped Mg{sub 0.12}Zn{sub 0.88}O nanocrystalline thin film was grown on c-plane sapphire substrate. Asymmetric Ni/Au and Ti/Au Schottky contacts and symmetric Ni/Au contacts were deposited on the thin film to form metal-semiconductor-metal (MSM) laser devices. Current-voltage, photocurrent, and electroluminescence characterizations were performed. Evident random lasing with a threshold current of ∼36 mA is demonstrated only from the asymmetric MSM device. Random lasing peaks are mostly distributed between 340 and 360 nm and an output power of 15 nW is measured at 43 mA injection current. The electron affinity difference between the contact metal and Mg{sub 0.12}Zn{sub 0.88}O:N layer plays an important role for electron and hole injection and subsequent stimulated random lasing.

  5. Friction Stir Welding of a Thick Al-Zn-Mg Alloy Plate

    NASA Astrophysics Data System (ADS)

    Buchibabu, V.; Reddy, G. M.; Kulkarni, D.; De, A.

    2016-03-01

    Al-Zn-Mg alloys are widely used as structural materials due to high strength-to-weight ratio and impact toughness. As fusion welds in these alloys commonly face hot cracking and macro porosity, friction stir welding is increasingly becoming the preferred recourse. We report here a detailed experimental study on friction stir welding of a specific Al-Zn-Mg alloy with its chemical compositions close to AA7039. The effect of tool rotational speed and welding speed on the weld profile, joint microstructure, and mechanical properties is studied extensively. The results show sound weld profiles and joint properties within the selected range of process conditions. Within the selected range of welding conditions, the welds made at a tool rotational speed of 350 rpm and welding speed of 3 mm/s have showed joint structure, tensile, and impact toughness properties fairly close to that of the base material.

  6. Removal of K+, Na+, Ca2+, and Mg2+ from saline-alkaline water using the microalga Scenedesmus obliquus

    NASA Astrophysics Data System (ADS)

    Yao, Zongli; Ying, Chengqi; Lu, Jianxue; Lai, Qifang; Zhou, Kai; Wang, Hui; Chen, Ling

    2013-11-01

    The capability of Scenedesmus obliquus to remove cations (K+, Na+, Ca2+, Mg2+) from saline-alkaline water was investigated at different salinities (0, 5, 10, 15, 20, 25) and carbonate alkalinities (0, 5, 10, 15, 20, 25, 30, 35 mmol/L). K+, Na+, Ca2+, and Mg2+ in saline-alkaline water were efficiently removed by S. obliquus. The maximum removal of the cations (29.37 mg for K+, 185.85 mg for Na+, 23.07 mg for Ca2+, 66.14 mg for Mg2+) occurred at salinity 25. The maximum removal of K+ (2.28 mg), Na+ (6.62 mg), Ca2+ (1.01 mg), and Mg2+ (0.62 mg) occurred at carbonate alkalinities of 25 mmol/L for K+, 35 mmol/L for Na+, 20 mmol/L for Ca2+, and 25 mmol/L for Mg2+, respectively. Under a salinity stress, the concentration of Na+ in S. obliquus increased significantly, while that of K+ decreased significantly. The concentrations of Ca2+ and Mg2+ decreased as well. The ratios of K+/Na+, Ca2+/Na+, and Mg2+/Na+ were significantly lower in all salinity treatments than those of the control. Under alkaline stress, the concentrations of Na+ and K+ in S. obliquus decreased significantly and the ratios of K+/Na+, Ca2+/Na+, and Mg2+/Na+ were significantly higher in all treatments than in the control. Moreover, the concentrations of Ca2+ and Mg2+ in S. obliquus at alkalinities of 5-10 mmol/L were significantly higher than those of the other treatments. The removal of Na+ by S. obliquus mainly occurs through biosorption, and Mg2+ and Ca2+ were removed through both biosorption and bioaccumulation.

  7. Mechanical properties and phase composition of potential biodegradable Mg-Zn-Mn-base alloys with addition of rare earth elements

    SciTech Connect

    Stulikova, Ivana; Smola, Bohumil

    2010-10-15

    Mechanical properties and creep resistance of the MgY4Zn1Mn1 alloy in the as cast as well as in the T5 condition were compared to those of the MgCe4Zn1Mn1 alloy in the same conditions. Yield tensile stress and ultimate tensile strength of the MgY4Zn1Mn1 alloy are slightly better in the temperature range 20 deg. C-400 deg. C than these of the MgCe4Zn1Mn1 alloy. Better thermal stability of ultimate tensile strength was observed in the T5 treated MgCe4Zn1Mn1 alloy than in this material in the as cast condition. An outstanding creep resistance at 225 deg. C-350 deg. C found in the MgY4Zn1Mn1 alloy is due to the existence of the 18R long period stacking structure persisting in this alloy even a long heat treatment of 500 deg. C/32 h. No similar stacking effects happen when Ce substitutes Y in approximately the same concentration. The creep resistance deteriorates considerably in the MgCe4Zn1Mn1 alloy. Rectangular particles of the equilibrium Mg{sub 12}Ce phase dominate in the microstructure of as cast as well as of high temperature heat-treated MgCe4Zn1Mn1 alloy. A population of small oval particles containing Mg and Zn develops additionally during annealing of this alloy. These particles pin effectively dislocations and can be responsible for the better thermal stability of the T5 treated material.

  8. Orientation Dependence of Cracking in Hot-Dip Zn-Al-Mg Alloy Coatings on a Sheet Steel

    NASA Astrophysics Data System (ADS)

    Park, Y. B.; Kim, I. G.; Kim, S. G.; Kim, W. T.; Kim, T. C.; Oh, M. S.; Kim, J. S.

    2017-01-01

    The present study was aimed at investigating a basic cause of cracking in hot-dip Zn-Al-Mg alloy coatings on an extra deep drawing quality sheet steel. The electron backscattering diffraction technique was employed to examine the crystallographic planes of the cracks generated before and after bending deformation of the coated steel sheets. It was clarified that the occurrence of cracking in the Zn-Al-Mg alloy coatings absolutely depends on the orientation of the primary Zn and eutectic Zn alloy phases. Finally, a cracking mechanism was proposed on the basis of the anisotropy of thermal expansion and the Young's modulus in the phases constituting the coatings.

  9. Orientation Dependence of Cracking in Hot-Dip Zn-Al-Mg Alloy Coatings on a Sheet Steel

    NASA Astrophysics Data System (ADS)

    Park, Y. B.; Kim, I. G.; Kim, S. G.; Kim, W. T.; Kim, T. C.; Oh, M. S.; Kim, J. S.

    2017-03-01

    The present study was aimed at investigating a basic cause of cracking in hot-dip Zn-Al-Mg alloy coatings on an extra deep drawing quality sheet steel. The electron backscattering diffraction technique was employed to examine the crystallographic planes of the cracks generated before and after bending deformation of the coated steel sheets. It was clarified that the occurrence of cracking in the Zn-Al-Mg alloy coatings absolutely depends on the orientation of the primary Zn and eutectic Zn alloy phases. Finally, a cracking mechanism was proposed on the basis of the anisotropy of thermal expansion and the Young's modulus in the phases constituting the coatings.

  10. Microstructure evolution and tensile mechanical properties of thixoformed high performance Al-Zn-Mg-Cu alloy

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Chen, Qiang; Wang, Bo; Du, Zhi-ming

    2015-09-01

    Al-Zn-Mg-Cu alloys are the strongest aluminum alloys which have been widely used for aerospace applications. They are usually machined from the wrought state usually with a high waste percentage. To reduce waste, it is important to thixoform these alloys in near net shape. In this work, the thixoformability of a commercial high performance Al-Zn-Mg-Cu alloy 7075 was studied. A novel multistep reheating regime was developed in recrystallization and partial melting (RAP) route to obtain spheroidal semi-solid microstructures. The as-extruded 7075 alloy was fully recrystallized for a short holding time using the multistep reheating regime. Semi-solid microstructures with fine and spherical solid grains with a grain size of 40-50 μm embedded in liquid matrix were obtained. The advantage of the multistep reheating regimes over those conventional routes was also discussed. Some wheel-shaped components were thixoformed from the as-received 7075 alloy. The ultimate tensile strength, yield strength and elongation to fracture of the thixoformed component based on multistep reheating regime, are 510 MPa, 446 MPa and 17.5% respectively. These values are superior to those of the products manufactured with the conventional RAP route. As the results indicated, thixoforming could be conducted based on commercial extruded Al-Zn-Mg-Cu alloys, which has important practical significance.

  11. Ultrafast intramolecular relaxation dynamics of Mg- and Zn-bacteriochlorophyll a

    NASA Astrophysics Data System (ADS)

    Kosumi, Daisuke; Nakagawa, Katsunori; Sakai, Shunsuke; Nagaoka, Yuya; Maruta, Satoshi; Sugisaki, Mitsuru; Dewa, Takehisa; Nango, Mamoru; Hashimoto, Hideki

    2013-07-01

    Ultrafast excited-state dynamics of the photosynthetic pigment (Mg-)bacteriochlorophyll a and its Zn-substituted form were investigated by steady-state absorption/fluorescence and femtosecond pump-probe spectroscopic measurements. The obtained steady-state absorption and fluorescence spectra of bacteriochlorophyll a in solution showed that the central metal compound significantly affects the energy of the Qx state, but has almost no effect on the Qy state. Photo-induced absorption spectra were recorded upon excitation of Mg- and Zn-bacteriochlorophyll a into either their Qx or Qy state. By comparing the kinetic traces of transient absorption, ground-state beaching, and stimulated emission after excitation to the Qx or Qy state, we showed that the Qx state was substantially incorporated in the ultrafast excited-state dynamics of bacteriochlorophyll a. Based on these observations, the lifetime of the Qx state was determined to be 50 and 70 fs for Mg- and Zn-bacteriochlorophyll a, respectively, indicating that the lifetime was influenced by the central metal atom due to the change of the energy gap between the Qx and Qy states.

  12. Adsorption of methyl orange from aqueous solutions by calcined ZnMgAl hydrotalcite

    NASA Astrophysics Data System (ADS)

    Yuan, Dong; Zhou, Liangqin; Fu, Dayou

    2017-02-01

    The calcined ZnMgAl hydrotalcite was used for degration of methyl orange (MO). The adsorbent was characterized by XRD, SEM, and FT-IR. The results reveal that the ZnMgAl layered structures were disappeared after calcining for 5 h at 500 °C, then were recovered to layer hydrotalcite structure after adsorbing MO anions. The several important affecting factors of adsorption behavior, including the initial pH value of solution, adsorbent dosage, and the initial concentration of solution, were also discussed. The adsorption kinetic processes were fitted with the equations of pseudo-first-order, pseudo-second-order, and intraparticle diffusion, respectively, in which the pseudo-second-order equation fitting results was the better. The equilibrium isotherm of MO was described by both Langmuir and Freundlich model, but better complys with the Langmuir model ( R 2 > 0.98). The possible adsorption mechanism has been presumed. The adsorption experiments indicated that the ZnMgAl hydrotalcite had good adsorption ability to methyl orange in wastewater.

  13. Factors Affecting the Hydrogen Environment Assisted Cracking Resistance of an AL-Zn-Mg-(Cu) Alloy

    SciTech Connect

    Young, G A; Scully, J R

    2002-04-09

    Precipitation hardenable Al-Zn-Mg alloys are susceptible to hydrogen environment assisted cracking (HEAC) when exposed to aqueous environments. In Al-Zn-Mg-Cu alloys, overaged tempers are used to increase HEAC resistance at the expense of strength but overaging has little benefit in low copper alloys. However, the mechanism or mechanisms by which overaging imparts HEAC resistance is poorly understood. The present research investigated hydrogen uptake, diffusion, and crack growth rate in 90% relative humidity (RH) air for both a commercial copper bearing Al-Zn-Mg-Cu alloy (AA 7050) and a low copper variant of this alloy in order to better understand the factors which affect HEAC resistance. Experimental methods used to evaluate hydrogen concentrations local to a surface and near a crack tip include nuclear reaction analysis (NRA), focused ion beam, secondary ion mass spectroscopy (FIB/SIMS) and thermal desorption spectroscopy (TDS). Results show that overaging the copper bearing alloys both inhibits hydrogen ingress from oxide covered surfaces and decreases the apparent hydrogen diffusion rates in the metal.

  14. Optical properties of NbCl5 and ZnMg intercalated graphite compounds

    NASA Astrophysics Data System (ADS)

    Jung, Eilho; Lee, Seokbae; Roh, Seulki; Meng, Xiuqing; Tongay, Sefaattin; Kang, Jihoon; Park, Tuson; Hwang, Jungseek

    2014-12-01

    We studied NbCl5 and ZnMg alloy intercalated graphite compounds using an optical spectroscopy technique. These intercalated metallic graphite samples were quite challenging to obtain optical reflectance spectra since they were not flat and quite thin. By using both a new method and an in situ gold evaporation technique we were able to obtain reliable reflectance spectra of our samples in the far and mid infrared range (80-7000 cm-1). We extracted the optical constants including the optical conductivity and the dielectric function from the measured reflectance spectra using a Kramers-Kronig analysis. We also extracted the dc conductivity and the plasma frequencies from the optical conductivity and dielectric functions. NbCl5 intercalated graphite samples show similar optical conductivity spectra as bare highly oriented pyrolytic graphite even though there are some differences in detail. ZnMg intercalated samples show significantly different optical conductivity spectra from the bare graphite. Optical spectroscopy is one of the most reliable experimental techniques to obtain the electronic band structures of materials. The obtained optical conductivities support the recent theoretically calculated electronic band structures of NbCl5 and ZnMg intercalated graphite compounds. Our results also provide important information of electronic structures and charge carrier properties of these two new intercalated materials for applications.

  15. Ultrafast intramolecular relaxation dynamics of Mg- and Zn-bacteriochlorophyll a

    SciTech Connect

    Kosumi, Daisuke; Nagaoka, Yuya; Maruta, Satoshi; Sugisaki, Mitsuru; Dewa, Takehisa; Hashimoto, Hideki

    2013-07-21

    Ultrafast excited-state dynamics of the photosynthetic pigment (Mg-)bacteriochlorophyll a and its Zn-substituted form were investigated by steady-state absorption/fluorescence and femtosecond pump-probe spectroscopic measurements. The obtained steady-state absorption and fluorescence spectra of bacteriochlorophyll a in solution showed that the central metal compound significantly affects the energy of the Q{sub x} state, but has almost no effect on the Q{sub y} state. Photo-induced absorption spectra were recorded upon excitation of Mg- and Zn-bacteriochlorophyll a into either their Q{sub x} or Q{sub y} state. By comparing the kinetic traces of transient absorption, ground-state beaching, and stimulated emission after excitation to the Q{sub x} or Q{sub y} state, we showed that the Q{sub x} state was substantially incorporated in the ultrafast excited-state dynamics of bacteriochlorophyll a. Based on these observations, the lifetime of the Q{sub x} state was determined to be 50 and 70 fs for Mg- and Zn-bacteriochlorophyll a, respectively, indicating that the lifetime was influenced by the central metal atom due to the change of the energy gap between the Q{sub x} and Q{sub y} states.

  16. Band gap engineering of ZnO by doping with Mg

    NASA Astrophysics Data System (ADS)

    Rana, N.; Chand, Subhash; Gathania, Arvind K.

    2015-08-01

    Mg-doped zinc oxide (MgxZn1-xO (0 ≤ x ≤ 0.20)) samples were synthesized by polymeric precursor method. The structural and optical properties were investigated by x-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), UV-visible spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopy. XRD patterns reveal that synthesized samples have a wurtzite structure. Lattice parameters, the degree of distortion of the samples were calculated from the XRD. SEM images show that the synthesized samples contain the elongated spherical shaped grains. The Raman scattering investigation and FTIR spectra authenticate the presence of Mg in the system and also show phase segregation at the higher Mg doping concentration. Optical band gap energy is determined from the Tauc relation. It is interesting to know that optical band energy exhibits blue shift with the increase of Mg doping concentration up to 16 mole %.

  17. Characterization and luminescence properties of CaMgSi2O6:Eu2+ blue phosphor.

    PubMed

    Chandrakar, P; Baghel, R N; Bisen, D P; Chandra, B P

    2015-11-01

    A blue CaMgSi2O6:Eu(2+) phosphor was prepared by the solid-state reaction method and the phosphor characterized in terms of crystal structure, particle size, photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) properties using X-ray diffraction (XRD), transmission electron microscopy (TEM), PL spectroscopy, TLD reader and ML impact technique. The XRD result shows that phosphor is formed in a single phase and has a monoclinic structure with the space group C2/c. Furthermore, the PL excitation spectra of Eu(2+) -doped CaMgSi2 O6 phosphor showed a strong band peak at 356 nm and the PL emission spectrum has a peak at 450 nm. The depths and frequency factors of trap centers were calculated using the TL glow curve by deconvolution method in which the trap depths were found to be 0.48 and 0.61 eV. The formation of CaMgSi2O6:Eu(2+) phosphor was confirmed by Fourier transform infrared spectroscopy. The ML intensity increased linearly with the impact velocity of the piston used to deform the phosphor. It was shown that the local piezoelectricity-induced electron bombardment model is responsible for the ML emission. Finally, the optical properties of CaMgSi2O6:Eu(2+) phosphors are discussed.

  18. Dry etching of MgCaO gate dielectric and passivation layers on GaN

    NASA Astrophysics Data System (ADS)

    Hlad, M.; Voss, L.; Gila, B. P.; Abernathy, C. R.; Pearton, S. J.; Ren, F.

    2006-09-01

    MgCaO films grown by rf plasma-assisted molecular beam epitaxy and capped with Sc 2O 3 are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs), respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively coupled plasmas of CH 4/H 2/Ar produced etch rates only in the range 20-70 Å/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (˜100 Å/min) were obtained with Cl 2/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH 4/H 2/Ar plasma chemistry produced a selectivity of around 2 for etching the MgCaO with respect to GaN.

  19. A DFT study of hydrogen adsorption on Be, Mg and Ca frameworks in erionite zeolite

    NASA Astrophysics Data System (ADS)

    Fellah, Mehmet Ferdi

    2017-02-01

    The molecular hydrogen adsorption was investigated on additional frameworks with earth alkaline metal atoms (Be, Mg and Ca) in 24T ERI zeolite cluster model by means of Density Functional Theory study. HOMO and LUMO energy values, chemical potential, chemical hardness, electronegativity, adsorption energy and adsorption enthalpy values have been calculated in this study. Mg-ERI and Ca-ERI clusters have much lower chemical potentials with much lower adsorption energy values when compared to the value of Be-ERI cluster. Additionally, they are softer than Be-ERI cluster with respect to their lower chemical hardness values. Hydrogen adsorption enthalpy values were computed as -3.6 and -3.9 kJ/mol on Mg-ERI and Ca-ERI clusters, respectively. These adsorption enthalpy values are significantly larger than the enthalpy value of liquefaction for hydrogen molecule. This consequently specifies that Mg-ERI and Ca-ERI zeolite structures which have higher chemical reactivity appear to be a promising candidate cryoadsorbent for hydrogen storage.

  20. Polymorph transformation kinetics of Ca3SiO5 with MgO

    NASA Astrophysics Data System (ADS)

    Ma, Suhua; Zhou, Weiqiang; Wang, Shaopeng; Li, Weifeng; Shen, Xiaodong

    2015-09-01

    Tricalcium silicate (Ca3SiO5 (C3S)) is the primary cement phase in Portland cement. An understanding of its transformation kinetics is important to make use of its polymorphism. In this study, X-ray diffractometry and Rietveld refinement were used to qualitatively and quantitatively analyze the phase compositions of C3S with 2.0% MgO. The results show that C3S with 2.0% MgO is a monoclinic polymorph, M3. Heat treatment changes this monoclinic polymorph to a triclinic polymorph via the precipitation of MgO. The transformation kinetics follows the first-order exponential decay function ?.

  1. VizieR Online Data Catalog: NLTE corrections for Mg and Ca lines (Merle+ 2011)

    NASA Astrophysics Data System (ADS)

    Merle, T.; Thevenin, F.; Pichon, B.; Bigot, L.

    2012-05-01

    Non-LTE corrections for Mg and Ca lines in the stellar parameter range Teff=[3500,5250]K, log(g)=[0.5, 2.0], [Fe/H]=[-4.0,0.5] and [α/Fe]=[0.0,0.4]. The W/W* ratio can be applied to the measured equivalent widths to determine NLTE abundance with classical LTE radiative transfer codes. 45 files for 45 lines of MgI, CaI and CaII are given. In each file, 453 rows at max for a grid of 453 model atmospheres. Only models with W>=1mÅ are given. Only models with 0.0

  2. The content of Ca, Cu, Fe, Mg and Mn and antioxidant activity of green coffee brews.

    PubMed

    Stelmach, Ewelina; Pohl, Pawel; Szymczycha-Madeja, Anna

    2015-09-01

    A simple and fast method of the analysis of green coffee infusions was developed to measure total concentrations of Ca, Cu, Fe, Mg and Mn by high resolution-continuum source flame atomic absorption spectrometry. The precision of the method was within 1-8%, while the accuracy was within -1% to 2%. The method was used to the analysis of infusions of twelve green coffees of different geographical origin. It was found that Ca and Mg were leached the easiest, i.e., on average 75% and 70%, respectively. As compared to the mug coffee preparation, the rate of the extraction of elements was increased when infusions were prepared using dripper or Turkish coffee preparation methods. Additionally, it was established that the antioxidant activity of green coffee infusions prepared using the mug coffee preparation was high, 75% on average, and positively correlated with the total content of phenolic compounds and the concentration of Ca in the brew.

  3. Evaluation of foraminiferal trace element cleaning methods on the Mg/Ca of marine ostracoda Krithe

    NASA Astrophysics Data System (ADS)

    Gray, W. R.; Holmes, J. A.; Shevenell, A.

    2012-12-01

    Mg/Ca of marine ostracod Krithe calcite is a potentially important tool for reconstructing oceanic bottom water (150-4000m) temperatures, as core top studies show ostracod Mg uptake is unaffected by carbonate ion saturation. Rigorous cleaning procedures, routinely used to remove clays, organic matter and Fe-Mn-oxides in trace element studies of foraminifera are not regularly applied to marine ostracods. Here we assess the possibility of reducing the analytical uncertainty in Krithe Mg/Ca analyses by employing foraminiferal trace element cleaning procedures and determining the effects of these cleaning procedures on valve chemistry. Using coretop samples of adult and juvenile male Krithe pernoides valves from boxcore OCE205-50BC (26.23oN, 77.7oW, 817m water depth), we apply methanol sonication, hydrogen peroxide oxidation, and hydrazine reduction to single ostracod valves, and sequentially assess the impact of each cleaning step. We compare the results from each cleaning step to valves cleaned using the traditional ethanol/DI rinse method. Significant correlation between Al/Fe and Mn/Fe respectively indicate that clays and Fe-Mn-oxides are detectable in traditionally cleaned samples. Mn and Al covary with Mg in juvenile but not in adult valves, indicating that clays and Fe-Mn-oxides exert a significant control on the Mg/Ca of low valve weight juveniles. Results of our Krithe cleaning experiments confirm that the removal of clays by sonication in methanol results in a decrease in average Fe, Al and Mn values, as well as a reduction in Mg/Ca by 1 mmol/mol in juveniles and 0.5 mmol/mol in adults. Following hydrogen peroxide oxidation samples show a reduction in Fe, Al and Mn concentrations with no significant change in valve Mg/Ca (±0.15 mmol/mol). After reductive cleaning we observe a significant decrease in valve Mg (>1 mmol/mol in juveniles), however there is little effect on Mn and Fe. Examination of adult and juvenile Krithe valves using scanning electron

  4. Tropical Pacific Mg/Ca paleo-thermometry: A contribution to the core top calibration

    NASA Astrophysics Data System (ADS)

    Clark, S.; Mekik, F.; Kienast, M.; Groeneveld, J.

    2009-12-01

    The magnesium to calcium ratio in foraminifera is widely used as a proxy to estimate ocean temperatures in Earth’s past. However, studies have shown that both dissolution within the sediments and seawater salinity influence the Mg/Ca in the shells of tropical foraminifera and skew paleo-temperature estimates. We measured Mg/Ca and d18O in shells of mixed layer-dwelling species (Globigernoides ruber sensu stricto, Globigernoides ruber sensu lato, and Globigerinoides sacculifer) from a series of core tops in the eastern equatorial Pacific. We specifically chose these three taxa because they are most commonly used for sea surface temperature estimates, particularly in down core work. We compared our results with global core top data from which paleo-temperature equations have already been derived and published (e.g. Brown and Elderfield, 1996; Lea et al., 2000; Dekens et al., 2002). We find that at the same surface ocean temperature, Mg/Ca values can range as much as 1.5 mmol/mol, and we find no influence of salinity on outliers from the expected exponential relationship between Mg/Ca and temperature. Nor do we see dissolution as the cause of this variation. Most samples used for core top calibration work are well above the calcite saturation horizon and show no evidence of dissolution. We demonstrate this both with carbonate dissolution proxies, like data using the Globorotalia menardii Fragmentation Index (MFI) (Mekik et al., 2002) from our same core tops, and with estimates of bottom water carbonate ion concentration. Potential other influences which cause these variations could include seasonality, differences in analytical methods, and potential differences among morphotypes of G. ruber. Brown S. and H. Elderfield, 1996. Variations in Mg/Ca in Sr/Ca ratios of planktonic foraminifera caused by postdepositional dissolution: Evidence of shallow Mg-dependant dissolution, Paleoceanography, 11,5,543-551. Dekens P., D. Lea, D. Pak, and H. Spero, 2002. Core top

  5. Effect of alloying elements Al and Ca on corrosion resistance of plasma anodized Mg alloys

    NASA Astrophysics Data System (ADS)

    Anawati, Asoh, Hidetaka; Ono, Sachiko

    2016-04-01

    Plasma anodizing is a surface treatment used to form a ceramic-type oxide film on Mg alloys by the application of a high anodic voltage to create intense plasma near the metal surface. With proper selection of the process parameters, the technique can produce high quality oxide with superior adhesion, corrosion resistance, micro-hardness, wear resistance and strength. The effect of alloying element Al on plasma anodizing process of Mg alloys was studied by comparing the anodizing curves of pure Mg, AZ31, and AZ61 alloys while the effect of Ca were studied on AZ61 alloys containing 0, 1, and 2 wt% Ca. Anodizing was performed in 0.5 M Na3PO4 solution at a constant current density of 200 Am-2 at 25°C. Anodic oxide films with lava-like structure having mix composition of amorphous and crystal were formed on all of the alloys. The main crystal form of the oxide was Mg3(PO4)2 as analyzed by XRD. Alloying elements Al and Ca played role in modifying the plasma lifetime during anodization. Al tended to extend the strong plasma lifetime and therefore accelerated the film thickening. The effect of Ca on anodizing process was still unclear. The anodic film thickness and chemical composition were altered by the presence of Ca in the alloys. Electrochemical corrosion test in 0.9% NaCl solution showed that the corrosion behavior of the anodized specimens depend on the behavior of the substrate. Increasing Al and Ca content in the alloys tended to increase the corrosion resistance of the specimens. The corrosion resistance of the anodized specimens improved significantly about two orders of magnitude relative to the bare substrate.

  6. SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} - two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    SciTech Connect

    Stegmaier, Saskia; Faessler, Thomas F.

    2012-08-15

    SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn{sub 2}Sn{sub 2} comprises (anti-)PbO-like {l_brace}ZnSn{sub 4/4}{r_brace} and {l_brace}SnZn{sub 4/4}{r_brace} layers. Ca{sub 2}Zn{sub 3}Sn{sub 6} shows similar {l_brace}ZnSn{sub 4/4}{r_brace} layers and {l_brace}Sn{sub 4}Zn{r_brace} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn{sub 2}Sn{sub 2} adopts the SrPd{sub 2}Bi{sub 2} structure type, and Ca{sub 2}Zn{sub 3}Sn{sub 6} is isotypic to the R{sub 2}Zn{sub 3}Ge{sub 6} compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {l_brace}Sn{sub 4}Zn{r_brace} layers of Ca{sub 2}Zn{sub 3}Sn{sub 6}. - Graphical abstract: Crystal structures of the new Ae-Zn-Sn polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Highlights: Black-Right-Pointing-Pointer New polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Black-Right-Pointing-Pointer Obtained by high temperature reactions of the elements. Black-Right-Pointing-Pointer Single crystal XRD structure determination and DFT electronic structure calculations. Black-Right-Pointing-Pointer Closely related crystal and electronic structures. Black-Right-Pointing-Pointer Metallic conductivity coexisting with lone pairs and covalent bonding

  7. Stabilization calculations of the low-lying temporary anions states of Be, Mg, and Ca

    NASA Astrophysics Data System (ADS)

    Falcetta, Michael F.; Reilly, Nathan D.; Jordan, Kenneth D.

    2017-01-01

    The stabilization method is used in conjunction with the equation-of-motion electron-attachment coupled-cluster method to calculate the complex energies of the 2P temporary anion states of Be and Mg as well as of the 2D temporary anions states of Mg and Ca. The calculated resonance parameters for the 2P state of Mg- and 2D state of Ca- agree well with experiment. Experimental results are not available for the 2P anion of Be, but we note that our calculated resonance parameters of 2P Be-, while in good agreement with the CI results of McNutt and McCurdy (1983), differ significantly from the results of two other recent theoretical studies.

  8. What do we know about the evolution of Mg to Ca ratios in seawater?

    NASA Astrophysics Data System (ADS)

    Broecker, Wally; Yu, Jimin

    2011-09-01

    Although most reconstructions of the evolution of the Mg to Ca ratio in seawater conclude that it has increased during the course of the Cenozoic, they disagree widely regarding the magnitude of this change. On the basis of fluid inclusion and CaCO3 mineralogy observations, the increase was at least threefold. On the basis of Mg content of foraminifera shells it was only a factor of 1.7. A recently published reconstruction based on the Mg content of calcite fillings of voids in ridge flank basalts lends support to the conclusion that the change was severalfold. But as it is very difficult to come up with a plausible geologic scenario which could account for such a large change, we lean toward the smaller estimate based on the magnesium content of foraminifera shells.

  9. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    NASA Astrophysics Data System (ADS)

    Mark, J. Abraham Hudson; Peter, A. John

    2014-04-01

    Third order susceptibility of third order harmonic generation is investigated in a Zn0.1Mg0.9Se/Zn0.8Mg0.2Se/Zn0.1Mg0.9Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.

  10. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    SciTech Connect

    Mark, J. Abraham Hudson Peter, A. John

    2014-04-24

    Third order susceptibility of third order harmonic generation is investigated in a Zn{sub 0.1}Mg{sub 0.9}Se/Zn{sub 0.8}Mg{sub 0.2}Se/Zn{sub 0.1}Mg{sub 0.9}Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.

  11. X-ray Diffraction Analysis on Post Treatment of Ca-Mg-Al-Layered Double Hydroxide Slurry

    NASA Astrophysics Data System (ADS)

    Heraldy, E.; Nugrahaningtyas, K. D.; Heriyanto

    2017-02-01

    This research objectives to study post treatment on Ca-Mg-Al-Layered Double Hydroxide (Ca-Mg-Al-LDH) slurry which was prepared from brine water by cooling treatment. The cooling rate was varied from 1 to 3 °C/min by using stirring and without stirring, and the cooling time was done at 0, 30 minutes and 24 hours. The quantitative X-ray diffraction (QXRD) was employed on Ca-Mg-Al-LDH using Le Bail refinement method. The refinement results found another Mg-Al-LDH and Ca-Al-LDH phases, such as Mg(OH)2, Al(OH)3 and CaCO3. The highest phase composition on material Ca-Mg-Al-LDH using Le Bail refinement was showed by Al(OH)3.

  12. Atomic structure of biodegradable Mg-based bulk metallic glass.

    PubMed

    Christie, J K

    2015-05-21

    We have used highly accurate first-principles molecular dynamics simulations to elucidate the structure of Mg60Zn35Ca5 and Mg72Zn23Ca5 bulk metallic glasses, which are candidate materials for biomedical implants; these two compositions exhibit different behaviours when implanted. The environments of each species are different, and average coordination numbers are ∼13 for Mg, ∼11 for Zn and ∼18-19 for Ca. A wide range of local environments were found and icosahedral motifs, often seen in bulk metallic glasses, were among the most common for both Mg and Zn. Through the computation of a chemical short-range order parameter, a moderate avoidance of Zn-Zn bonding over Zn-Mg or Zn-Ca was observed. No statistically significant difference in structure was observed between the two compositions.

  13. Novel structure, morphology, and optical property of Mg-doped ZnO nanostructures fabricated by PCVD method

    NASA Astrophysics Data System (ADS)

    Wang, Y. L.; Wei, X. Q.; Guo, N.; Xu, X. J.

    2017-02-01

    Mg -doped ZnO nanostructures with different growth temperature and Mg contents have been successfully fabricated on Si (111) substrates via physical chemical vapor deposition (PCVD) method. The influences of the growth temperature and Mg contents on the nanostructure, morphologies, and crystallinities were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The SEM results show that it is beneficial to grow regular ZnMgO nanorods with the growth temperature of 750 °C and Zn/Mg molar ratio of 50:1, respectively. XRD results indicate that the nanorods possess the preferential orientation along the c-axis with the best crystals. The nanorod arrays, dendritic, and like-caltrop nanostructure were achieved at various growth temperature and Mg contents, respectively. The photoluminescence (PL) spectra show that the UV emissions present the obvious blueshift owing to the increasing growth temperature and Mg contents.

  14. Photoluminescence performance enhancement of ZnO/MgO heterostructured nanowires and their applications in ultraviolet laser diodes.

    PubMed

    Shi, Zhi-Feng; Zhang, Yuan-Tao; Cui, Xi-Jun; Zhuang, Shi-Wei; Wu, Bin; Chu, Xian-Wei; Dong, Xin; Zhang, Bao-Lin; Du, Guo-Tong

    2015-06-07

    Vertically aligned ZnO/MgO coaxial nanowire (NW) arrays were prepared on sapphire substrates by metal-organic chemical vapor deposition combined with a sputtering system. We present a comparative investigation of the morphological and optical properties of the produced heterostructures with different MgO layer thicknesses. Photoluminescence measurements showed that the optical performances of ZnO/MgO coaxial NWs were strongly dependent on the MgO layer thickness. The intensity of deep-level emission (DLE) decreased monotonously with the increase of MgO thickness, while the enhancement of ultraviolet (UV) emission showed a critical thickness of 15 nm, achieving a maximum intensity ratio (∼226) of IUV/IDLE at the same time. The significantly improved exciton emission efficiency of the coaxial NW structures allows us to study the surface passivation effect, photogenerated carrier confinement and transfer in terms of energy band theory. More importantly, we achieved an ultralow threshold (4.5 mA, 0.58 A cm(-2)) electrically driven UV lasing action based on the ZnO/MgO NW structures by constructing an Au/MgO/ZnO metal/insulator/semiconductor diode, and the continuous-current-driven diode shows a good temperature tolerance. The results obtained on the unique optical properties of ZnO/MgO coaxial NWs shed light on the design and development of ZnO-based UV laser diodes assembled with nanoscale building blocks.

  15. Application of benthic foraminiferal Mg/Ca ratios to questions of Cenozoic climate change

    NASA Astrophysics Data System (ADS)

    Billups, K.; Schrag, D. P.

    2003-04-01

    We investigate the evolution of Cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater (δ 18O sw) derived from benthic foraminiferal Mg/Ca ratios to constrain the temperature effect contained in foraminiferal δ 18O values. We have constructed two benthic foraminiferal Mg/Ca records from intermediate water depth sites (Ocean Drilling Program sites 757 and 689 from the subtropical Indian Ocean and the Weddell Sea, respectively). Together with the previously published composite record of Lear et al. [Science 287 (2002) 269-272] and the Neogene record from the Southern Ocean of Billups and Schrag [Paleoceanography 17 (2002) 10.1029/2000PA000567], we obtain three, almost complete representations of the δ 18O sw for the past 52 Myr. We discuss the sensitivity of early Cenozoic Mg/Ca-derived paleotemperatures (and hence the δ 18O sw) to assumptions about seawater Mg/Ca ratios. We find that during the middle Eocene (˜49-40 Ma), modern seawater ratios yield Mg/Ca-derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice-free conditions. Intermediate waters cooled during the middle Eocene reaching minimum temperatures by 40 Ma. The corresponding δ 18O sw reconstructions support ice growth on Antarctica beginning by at least 40 Ma. At the Eocene/Oligocene boundary, Mg/Ca ratios (and hence temperatures) from Weddell Sea site 689 display a well-defined maximum. We caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of Mg in benthic foraminifera may be sensitive to factors other than temperature. Throughout the remainder of the Cenozoic, the temporal variability among δ 18O sw records is similar and similar to longer-term trends in the benthic foraminiferal δ 18O record. An exception occurs during the Pliocene when δ 18O sw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal

  16. Ca and Mg isotope constraints on the origin of Earth's deepest δ13 C excursion

    NASA Astrophysics Data System (ADS)

    Husson, Jon M.; Higgins, John A.; Maloof, Adam C.; Schoene, Blair

    2015-07-01

    Understanding the extreme carbon isotope excursions found in carbonate rocks of the Ediacaran Period (635-541 Ma), where δ13 C of marine carbonates (δ13 Ccarb) reach their minimum (- 12 ‰) for Earth history, is one of the most vexing problems in Precambrian geology. Known colloquially as the 'Shuram' excursion, the event has been interpreted by many as a product of a profoundly different Ediacaran carbon cycle. More recently, diagenetic processes have been invoked, with the very negative δ13 C values of Ediacaran carbonates explained via meteoric alteration, late-stage burial diagenesis or growth of authigenic carbonates in the sediment column, thus challenging models which rely upon a dramatically changing redox state of the Ediacaran oceans. Here we present 257 δ 44 / 40 Ca and 131 δ26 Mg measurements, along with [Mg], [Mn] and [Sr] data, from carbonates of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia to bring new isotope systems to bear on understanding the 'Shuram' excursion. Data from four measured sections spanning the basin reveal stratigraphically coherent trends, with variability of ∼1.5‰ in δ26 Mg and ∼1.2‰ in δ 44 / 40 Ca. This Ca isotope variability dwarfs the 0.2-0.3 ‰ change seen coeval with the Permian-Triassic mass extinction, the largest recorded in the rock record, and is on par with putative changes in the δ 44 / 40 Ca value of seawater seen over the Phanerozoic Eon. Changes in both isotopic systems are too large to explain with changes in the isotopic composition of Ca and Mg in global seawater given modern budgets and residence times, and thus must be products of alternative processes. Relationships between δ 44 / 40 Ca and [Sr] and δ26 Mg and [Mg] are consistent with mineralogical control (e.g., aragonite vs. calcite, limestone vs. dolostone) on calcium and magnesium isotope variability. The most pristine samples in the Wonoka dataset, preserving Sr concentrations (in the 1000s of ppm range) and δ 44 / 40

  17. Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene-Pleistocene seawater Mg/Ca, temperature and sea level change

    NASA Astrophysics Data System (ADS)

    Evans, David; Brierley, Chris; Raymo, Maureen E.; Erez, Jonathan; Müller, Wolfgang

    2016-03-01

    Foraminifera Mg/Ca paleothermometry forms the basis of a substantial portion of ocean temperature reconstruction over the last 5 Ma. Furthermore, coupled Mg/Ca-oxygen isotope (δ18O) measurements of benthic foraminifera can constrain eustatic sea level (ESL) independent of paleo-shoreline derived approaches. However, this technique suffers from uncertainty regarding the secular variation of the Mg/Ca seawater ratio (Mg/Casw) on timescales of millions of years. Here we present coupled seawater-test Mg/Ca-temperature laboratory calibrations of Globigerinoides ruber in order to test the widely held assumptions that (1) seawater-test Mg/Ca co-vary linearly, and (2) the Mg/Ca-temperature sensitivity remains constant with changing Mg/Casw. We find a nonlinear Mg/Catest-Mg/Casw relationship and a lowering of the Mg/Ca-temperature sensitivity at lower than modern Mg/Casw from 9.0% °C-1 at Mg/Casw = 5.2 mol mol-1 to 7.5 ± 0.9% °C-1 at 3.4 mol mol-1. Using our calibrations to more accurately calculate the offset between Mg/Ca and biomarker-derived paleotemperatures for four sites, we derive a Pliocene Mg/Casw ratio of ∼4.3 mol mol-1. This Mg/Casw implies Pliocene ocean temperature 0.9-1.9 °C higher than previously reported and, by extension, ESL ∼30 m lower compared to when one assumes that Pliocene Mg/Casw is the same as at present. Correcting existing benthic foraminifera datasets for Mg/Casw indicates that deep water source composition must have changed through time, therefore seawater oxygen isotope reconstructions relative to present day cannot be used to directly reconstruct Pliocene ESL.

  18. Long phase coherence length and anisotropic magnetoresistance in MgZnO thin film

    SciTech Connect

    Lv, Meng; Xu, Yonggang; Yu, Guolin Lin, Tie; Hu, Gujin; Chu, Junhao; Wang, Hao; Zhang, Huahan; Dai, Ning

    2015-04-21

    We comprehensively investigate magnetotransport properties of MgZnO thin film grown on ZnO substrate by molecular-beam epitaxy. We measure the weak localization effect and extract the electron phase coherence length by fitting to a three-dimensional weak localization theory and by analyzing the different changing rate of the magnetoresistance, results of which are in good agreement with each other. The phase coherence length ranges from 38.4±1    nm at 50 K to 99.8±3.6 nm at 1.4  K, almost the same as that of ZnO nanoplates and In-doped ZnO nanowires, and its temperature dependence is found to scale as T{sup −3/4}. Meanwhile, we study the anisotropic magnetoresistance resulting from the geometric effect as well as the Lorentz force induced path-length effect, which will be enhanced in higher magnetic fields.

  19. Molecular-beam-epitaxy-grown ZnMgS ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Sou, I. K.; Wu, Marcus C. W.; Sun, T.; Wong, K. S.; Wong, G. K. L.

    2001-03-01

    Epitaxial growth of Zn1-xMgxS alloy thin films on GaP(100) substrates was carried out using the molecular-beam-epitaxy technique. In situ reflection high-energy electron diffraction studies show that the alloys can be grown with a stable zinc-blende structure up to x around 30%. For x>30%, a structural transition will occur at a critical thickness which is sensitively dependent on the x composition. A near-band-edge peak with a full width at half maximum of about 10 nm was observed in room-temperature photoluminescence measurements made on as-grown alloy thin films. Several Zn1-xMgxS-based Schottky barrier photodetectors were fabricated. Room-temperature photoresponse measurements were performed on these detectors and abrupt long-wavelength cutoffs covering 325, 305, 295, and 270 nm were achieved for devices with Mg composition of 16%, 44%, 57%, and 75%, respectively. The response curve of the Zn0.43Mg0.57S device offers a close match to the erythemal action spectrum that describes human skin sensitivity to UV radiation.

  20. Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments

    NASA Astrophysics Data System (ADS)

    Holroyd, N. J. Henry; Scamans, G. M.

    2013-03-01

    Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack ("pop-in" vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies ( E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (<0.2 wt pct) are typically ranging from

  1. Temperature calibration of Mg/Ca ratios in the intermediate water benthic foraminifer Hyalinea balthica

    NASA Astrophysics Data System (ADS)

    Rosenthal, Yair; Morley, Audrey; Barras, Christine; Katz, Miriam E.; Jorissen, Frans; Reichart, Gert-Jan; Oppo, Delia W.; Linsley, Braddock K.

    2011-04-01

    Core top samples from Indonesian and northeast Atlantic depth transects were used to calibrate Mg/Ca and δ18O in tests of the calcitic benthic foraminifer Hyalinea balthica to bottom water temperature between 4°C and 13°C. This shallow infaunal species is primarily abundant in neritic to upper bathyal sediments (<600 m). Both linear and exponential calibrations suggest a temperature sensitivity of ˜12% per °C that is ˜4 times higher than observed in other species of deep-sea benthic foraminifera. Culture experiments support the core top calibration. We find no discernible effect of salinity and saturation on Mg/Ca. Comparison between the measured benthic foraminiferal δ18O and predicted equilibrium values suggests that on average H. balthica δ18O is 0.64‰ ± 0.13‰ lower than predicted from the equilibrium composition. To test the reliability of using paired H. balthica Mg/Ca and δ18O measurements for reconstructing seawater δ18Osw and salinity, we apply this calibration to another depth transect from Cape Ghir off NW Africa, which was not included in the calibration. Based on error analysis of the calibration data and this validation test, we show that the uncertainty of reconstructing bottom water temperature and salinity from paired Mg/Ca and δ18O measurements of H. balthica is better than ±0.7°C and ±0.69 practical salinity scale, respectively. The small uncertainties allow for the reconstruction of seawater density to better than 0.3σθ units, which is precise enough for the identification of specific water masses and reconstruction of changes in their properties. We propose that the relatively high Mg content and temperature sensitivity of H. balthica might be due to minor, biologically mediated contribution of high-Mg calcite to the primarily low Mg calcite test, which is influenced by the ambient temperature. This hypothesis, if correct, suggests that benthic species with relatively high Mg/Ca may be better suited for deepwater temperature

  2. Is ryanodine receptor a calcium or magnesium channel? Roles of K+ and Mg2+ during Ca2+ release.

    PubMed

    Gillespie, Dirk; Chen, Haiyan; Fill, Michael

    2012-06-01

    The ryanodine receptor (RyR) is a poorly selective channel that mediates Ca(2+) release from intracellular Ca(2+) stores. How RyR's selectivity between the physiological cations K(+), Mg(2+), and Ca(2+) affects single-channel Ca(2+) current amplitude is examined using a recent model of RyR permeation. It is found that K(+) provides the vast majority of the countercurrent (through RyR itself) that is needed to prevent the sarcoplasmic reticulum (SR) membrane potential from changing and stopping Ca(2+) release. Moreover, intra-pore competition between Ca(2+) and Mg(2+) defines single RyR Ca(2+) current amplitude. Since both [Mg(2+)] and [Ca(2+)](SR) can change during pathophysiological conditions, the RyR unitary Ca(2+) current amplitude during Ca(2+) release may change significantly due to this Ca(2+)/Mg(2+) competition. Compared to the classic action of Mg(2+) on RyR open probability, these Ca(2+) current amplitude changes have as large or larger effects on overall RyR Ca(2+) mobilization. A new aspect of RyR divalent versus monovalent selectivity is also identified where this kind of selectivity decreases as divalent concentration increases.

  3. High-performance solar-blind ultraviolet photodetector based on mixed-phase ZnMgO thin film

    SciTech Connect

    Fan, M. M.; Liu, K. W. E-mail: shendz@ciomp.ac.cn; Zhang, Z. Z.; Li, B. H.; Chen, X.; Zhao, D. X.; Shan, C. X.; Shen, D. Z. E-mail: shendz@ciomp.ac.cn

    2014-07-07

    High Mg content mixed-phase Zn{sub 0.38}Mg{sub 0.62}O was deposited on a-face sapphire by plasma-assisted molecular beam epitaxy, based on which a metal-semiconductor-metal solar-blind ultraviolet (UV) photodetector was fabricated. The dark current is only 0.25 pA at 5 V, which is much lower than that of the reported mixed-phase ZnMgO photodetectors. More interestingly, different from the other mixed-phase ZnMgO photodetectors containing two photoresponse bands, this device shows only one response peak and its −3 dB cut-off wavelength is around 275 nm. At 10 V, the peak responsivity is as high as 1.664 A/W at 260 nm, corresponding to an internal gain of ∼8. The internal gain is mainly ascribed to the interface states at the grain boundaries acting as trapping centers of photogenerated holes. In view of the advantages of mixed-phase ZnMgO photodetectors over single-phase ZnMgO photodetectors, including easy fabrication, high responsivity, and low dark current, our findings are anticipated to pave a new way for the development of ZnMgO solar-blind UV photodetectors.

  4. Coupled gating of skeletal muscle ryanodine receptors is modulated by Ca2+, Mg2+, and ATP

    PubMed Central

    Porta, Maura; Diaz-Sylvester, Paula L.; Neumann, Jake T.; Escobar, Ariel L.; Fleischer, Sidney

    2012-01-01

    Coupled gating (synchronous openings and closures) of groups of skeletal muscle ryanodine receptors (RyR1), which mimics RyR1-mediated Ca2+ release underlying Ca2+ sparks, was first described by Marx et al. (Marx SO, Ondrias K, Marks AR. Science 281: 818–821, 1998). The nature of the RyR1-RyR1 interactions for coupled gating still needs to be characterized. Consequently, we defined planar lipid bilayer conditions where ∼25% of multichannel reconstitutions contain mixtures of coupled and independently gating RyR1. In ∼10% of the cases, all RyRs (2–10 channels; most frequently 3–4) gated in coupled fashion, allowing for quantification. Our results indicated that coupling required cytosolic solutions containing ATP/Mg2+ and high (50 mM) luminal Ca2+ (Calum) or Sr2+ solutions. Bursts of coupled activity (events) started and ended abruptly, with all channels activating/deactivating within ∼300 μs. Coupled RyR1 were heterogeneous, where highly active RyR1 (“drivers”) seemed open during the entire coupled event (Po = 1), while other RyR1s (“followers”) displayed abundant flickering and smaller amplitude. Drivers mean open time increased with cytosolic Ca2+ (Cacyt) or caffeine, whereas followers flicker frequency was Cacyt independent and more sensitive to inhibition by cytosolic Mg2+. Coupled events were insensitive to varying lumen-to-cytosol Ca2+ fluxes from ∼1 to 8 pA, which does not corroborate coupling of neighboring RyR1 by local Ca2+-induced Ca2+ release. However, coupling requires specific Calum sites, as it was lost when Calum was replaced by luminal Ba2+ or Mg2+. In summary, coupled events reveal complex interactions among heterogeneous RyR1, differentially modulated by cytosolic ATP/Mg2+, Cacyt, and Calum, which under cell-like ionic conditions may parallel synchronous RyR1 gating during Ca2+ sparks. PMID:22785120

  5. Mechanical and corrosion properties of biodegradable Mg-1.5Mn-1Ca-xSr alloys

    NASA Astrophysics Data System (ADS)

    Sun, X.; Sun, S. Y.; Ning, Y. H.; Ning, Y. T.

    2017-03-01

    The mechanical properties and corrosion mechanism of both as-cast and solution-naturally age (T4) treated Mg-1.5Mn-1Ca-xSr alloys were investigated. The results showed that Sr is helpful to decrease grain size and increase the strength. The corrosion process of alloys was mainly determined by the quantity and distribution of second phases. Mg17Sr2, α-Mn and Ca-Sr phases acted as cathodes accelerated the corrosion of Mg2Ca anodic phase and α-Mg matrix. However, continuous distributed Mg17Sr2 was beneficial to resist the happening of localized corrosion because of its barrier effect. T4 treatment could significantly improve the mechanical properties and corrosion resistance of Mg alloys because of the dissolution of Mg2Ca phase and the dispersive distribution of Mg17Sr2 and α-Mn phases.

  6. Microstructural evolution in Mg-Zn alloys during solidification: An experimental and simulation study

    NASA Astrophysics Data System (ADS)

    Paliwal, Manas; Jung, In-Ho

    2014-05-01

    A comprehensive microstructural evolution of Mg-1.5, 4.0 and 5.5 wt% Zn alloys with respect to the solidification parameters such as thermal gradient (G), solidification velocity (V), cooling rate (GV) and solute (Zn) content were investigated in the present study. Solidification techniques such as directional solidification and wedge casting were employed in order to obtain cooling rates between 0.05 and 250 K/s. Microstructural features such as secondary dendrite arm spacing (SDAS), primary dendrite arm spacing (PDAS), microsegregration along the secondary dendrites and secondary phase fractions were experimentally determined. A solidification model that incorporates solute back diffusion, secondary arm coarsening, dendrite tip undercooling and dynamically linked with accurate thermodynamic databases is used to explain the experimental results.

  7. Temperature and [CO3 ] Effects on Mg/Ca and Sr/Ca in the Benthic Foraminifera Species of Hoeglundina Elegans and Cibicidoides

    NASA Astrophysics Data System (ADS)

    Lear, C. H.; Rosenthal, Y.; Oppo, D. W.; Linsley, B. K.

    2005-12-01

    Current core-top calibrations suggest that the temperature sensitivity of Mg/Ca in Cibicidoides sp. tests is essentially identical with the 10% increase in Mg/Ca per 1°C observed in many planktonic species. However, there is also evidence suggesting that non temperature-related effects may exert additional control on Mg/Ca in foraminiferal calcite. Here we use core-top samples from Atlantic (Little Bahama Banks, LBB; Arctic) and Pacific (Hawaii, and Indonesia) depth transects to assess the influence of bottom water temperature (BWT) and carbonate saturation levels on metal/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans and calcitic Cibicidoides sp. We find that in situ CO3 ion concentrations play an important role in determining the Mg/Ca ratios in Cibicidoides sp. and Mg/Ca and Sr/Ca in H. elegans. The CO3 ion effect is limited, however, only to relatively low saturation levels, whereas at over-saturated levels, temperature exert the dominant effect on these metal ratios. Because we find no significant difference between results obtained on ``live'' and ``dead'' specimens, we propose that these differences are due to primary effects on metal uptake during test formations and not because of dissolution. Based on the new results we reappraise the Mg/Ca-temperature relationship of Cibicidoides sp. and propose a new calibration. We also propose that Sr/Ca and Mg/Ca in H. elegans tests can be used to reconstruct thermocline temperatures. Sr/Ca-thermometry in H. elegans may be especially useful in cases where the use of Mg/Ca thermometry in calcitic foraminfera has been compromised by contamination issues. In both cases, temperature estimates in low carbonate saturation levels may be grossly inaccurate.

  8. The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

    SciTech Connect

    Chen, S. S.; Pan, X. H. E-mail: yezz@zju.edu.cn; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z. E-mail: yezz@zju.edu.cn

    2014-09-22

    We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of Mg{sub x}Zn{sub 1−x}O/Be{sub x}Mg{sub y}Zn{sub 1−x−y}O heterojunctions using X-ray photoelectron spectroscopy measurements. Mg{sub x}Zn{sub 1−x}O and Be{sub x}Mg{sub y}Zn{sub 1−x−y}O films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset (ΔE{sub V}) of Mg{sub 0.15}Zn{sub 0.85}O (E{sub g} = 3.62 eV)/Be{sub 0.005}Mg{sub 0.19}Zn{sub 0.805}O (E{sub g} = 3.73 eV) heterojunction is 0.01 eV and Be{sub 0.005}Mg{sub 0.19}Zn{sub 0.805}O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of Mg{sub x}Zn{sub 1−x}O is lower by 0.03 eV with the enlargement of E{sub g} from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E{sub g} of the alloy is 3.73 eV. The ΔE{sub V} of Mg{sub 0.11}Zn{sub 0.89}O (E{sub g} = 3.56 eV)/Be{sub 0.007}Mg{sub 0.12}Zn{sub 0.873}O (E{sub g} = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be{sub 0.007}Mg{sub 0.12}Zn{sub 0.873}O has a higher VBM than Mg{sub 0.11}Zn{sub 0.89}O, which means that a little amount Be lifts the VBM by 0.03 eV when the E{sub g} of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in Mg{sub x}Zn{sub 1−x}O alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

  9. Effect of Inner Electrode on Reliability of (Zn,Mg)TiO3-Based Multilayer Ceramic Capacitor

    NASA Astrophysics Data System (ADS)

    Lee, Wen‑His; Su, Chi‑Yi; Lee, Ying Chieh; Yang, Jackey; Yang, Tong; PinLin, Shih

    2006-07-01

    In this study, different proportions of silver-palladium alloy acting as the inner electrode were adopted to a (Zn,Mg)TiO3-based multilayer ceramic capacitor (MLCC) sintered at 925 °C for 2 h to evaluate the effect of the inner electrode on reliability. The main results show that the lifetime is inversely proportional to Ag content in the Pd/Ag inner electrode. Ag+1 diffusion into the (Zn,Mg)TiO3-based MLCC during cofiring at 925 °C for 2 h and Ag+1 migration at 140 °C against 200 V are both responsible for the short lifetime of the (Zn,Mg)TiO3-based MLCC, particularly the latter factor. A (Zn,Mg)TiO3-based MLCC with high Ag content in the inner electrode Ag/Pd=99/01 exhibits the shortest lifetime (13 h), and the effect of Ag+1 migration is markedly enhanced when the activation energy of the (Zn,Mg)TiO3 dielectric is greatly lowered due to the excessive formation of oxygen vacancies and the semiconducting Zn2TiO4 phase when Ag+ substitutes for Zn+2 during co-firing.

  10. Structure and physical properties of the polar oxysulfide CaZnOS.

    PubMed

    Sambrook, Timothy; Smura, Catherine F; Clarke, Simon J; Ok, Kang Min; Halasyamani, P Shiv

    2007-04-02

    The synthesis, structure, and electrical properties of the oxysulfide CaZnOS are reported. The white compound has a band gap of 3.7(1) eV and crystallizes in hexagonal space group P6(3)mc (No. 186) with a = 3.75726(3) A, c = 11.4013(1) A, and Z = 2. The noncentrosymmetric structure, which has few analogues, is composed of isotypic puckered hexagonal ZnS and CaO layers arranged so that ZnS3O tetrahedra are all aligned parallel, resulting in a polar structure. The compound shows type 1 non-phase-matchable second harmonic generation, determined using 1064 nm radiation, with an efficiency approximately 100 times that of alpha-SiO2 and a piezoelectric coefficient of 38 pm V-1. Although polar, CaZnOS is not ferroelectric and the pyroelectric coefficient is very small, approximately 0.0 microC m-2 K-1 between room temperature and 100 degrees C.

  11. A novel biodegradable nicotinic acid/calcium phosphate composite coating on Mg-3Zn alloy.

    PubMed

    Song, Yingwei; Shan, Dayong; Han, En-Hou

    2013-01-01

    A novel biodegradable composite coating is prepared to reduce the biodegradation rate of Mg-3Zn alloy. The Mg-3Zn substrate is first immersed into 0.02 mol L(-1) nicotinic acid (NA) solution, named as vitamin B3, to obtain a pretreatment film, and then the electrodeposition of calcium phosphate coating with ultrasonic agitation is carried out on the NA pretreatment film to obtain a NA/calcium phosphate composite coating. Surface morphology is observed by scanning electron microscopy (SEM). Chemical composition is determined by X-ray diffraction (XRD) and EDX. Protection property of the coatings is evaluated by electrochemical tests. The biodegradable behavior is investigated by immersion tests. The results indicate that a thin but compact bottom layer can be obtained by NA pretreatment. The electrodeposition calcium phosphate coating consists of many flake particles and ultrasonic agitation can greatly improve the compactness of the coating. The composite coating is biodegradable and can reduce the biodegradation rate of Mg alloys in stimulated body fluid (SBF) for twenty times. The biodegradation process of the composite coating can be attributed to the gradual dissolution of the flake particles into chippings.

  12. Effects of gas produced by degradation of Mg-Zn-Zr Alloy on cancellous bone tissue.

    PubMed

    Wang, Jingbo; Jiang, Hongfeng; Bi, Yanze; Sun, Jin e; Chen, Minfang; Liu, Debao

    2015-10-01

    Mg-Zn-Zr alloy cylinders were implanted into the femoral condyles of Japanese big-ear white rabbits. X-ray showed that by 12 weeks following implantation the implant became obscure, around which the low-density area appeared and enlarged. By 24 weeks, the implant was more obscure and the density of the surrounding cancellous bone increased. Scanning electron microscopy examination showed bone tissue on the surface of the alloy attached by living fibers at 12 weeks. Micro-CT confirmed that new bone tissue on the surface of the residual alloy implant increased from 12 weeks to 24 weeks. By 12 weeks, many cavities in the cancellous bone tissue around the implant were noted with a CT value, similar to gas value, and increasing by 24 weeks (P<0.01). Histological examination of hard tissue slices showed that bone tissue was visibly attached to the alloy in the femoral condyle at 12 weeks. The trabecular bone tissues became more intact and dense, and the cavities were filled with soft tissue at 24 weeks. In general, gas produced by the degradation of the Mg-Zn-Zr alloy can cause cavitation within cancellous bone, which does not affect osteogenesis of Mg alloy.

  13. Lattice parameters and electronic structure of BeMgZnO quaternary solid solutions: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Toporkov, M.; Demchenko, D. O.; Zolnai, Z.; Volk, J.; Avrutin, V.; Morkoç, H.; Özgür, Ü.

    2016-03-01

    BexMgyZn1-x-yO semiconductor solid solutions are attractive for UV optoelectronics and electronic devices owing to their wide bandgap and capability of lattice-matching to ZnO. In this work, a combined experimental and theoretical study of lattice parameters, bandgaps, and underlying electronic properties, such as changes in band edge wavefunctions in BexMgyZn1-x-yO thin films, is carried out. Theoretical ab initio calculations predicting structural and electronic properties for the whole compositional range of materials are compared with experimental measurements from samples grown by plasma assisted molecular beam epitaxy on (0001) sapphire substrates. The measured a and c lattice parameters for the quaternary alloys BexMgyZn1-x with x = 0-0.19 and y = 0-0.52 are within 1%-2% of those calculated using generalized gradient approximation to the density functional theory. Additionally, composition independent ternary BeZnO and MgZnO bowing parameters were determined for a and c lattice parameters and the bandgap. The electronic properties were calculated using exchange tuned Heyd-Scuseria-Ernzerhof hybrid functional. The measured optical bandgaps of the quaternary alloys are in good agreement with those predicted by the theory. Strong localization of band edge wavefunctions near oxygen atoms for BeMgZnO alloy in comparison to the bulk ZnO is consistent with large Be-related bandgap bowing of BeZnO and BeMgZnO (6.94 eV). The results in aggregate show that precise control over lattice parameters by tuning the quaternary composition would allow strain control in BexMgyZn1-x-yO/ZnO heterostructures with possibility to achieve both compressive and tensile strain, where the latter supports formation of two-dimensional electron gas at the interface.

  14. Phase controlled synthesis of (Mg, Ca, Ba)-ferrite magnetic nanoparticles with high uniformity

    NASA Astrophysics Data System (ADS)

    Wang, S. F.; Li, Q.; Zu, X. T.; Xiang, X.; Liu, W.; Li, S.

    2016-12-01

    (Mg, Ca, Ba)-ferrite magnetic nanoparticles were successfully synthesized through modifying the atomic ratio of polysaccharide and chelating agent at an optimal sintering temperature. In the process, the polysaccharide plays an important role in drastically shrinking the precursor during the gel drying process. In the metal-complex structure, M2+ ion active sites were coordinated by -OH of the water molecules except for EDTA anions. The MFe2O4 magnetic nanoparticles exhibited enhanced magnetic properties when compared with nano-MFe2O4 of similar particle size synthesized by other synthesis route reported in the literature. In particular, the sintering temperature improves the crystallinity and increases the hysteresis loop squareness ratio of (Mg, Ca, Ba)-ferrite nanoparticles significantly.

  15. The structure of coatings obtained in the Zn-31Al-3Mg bath by the batch hot dip method

    NASA Astrophysics Data System (ADS)

    Kania, H.

    2012-05-01

    Zn-Al dip coatings provide effective protection of steel surface against corrosion - better than traditional zinc coatings. Corrosion resistance can be further increased by adding Mg to the bath. Coatings obtained in Zn-Al-Mg baths are produced on metal plates by applying the continuous method. In this paper the author presents the results of tests on obtaining Zn-Al-Mg coatings on products with limited shape by use of the batch hot dip method. The growth kinetics of coatings obtained in the Zn-31Al-3Mg bath on steel with low silicon contents has been defined. The structure has been developed and the chemical composition of particular structural components of the coating has be established. It has been determined that the structure of coatings obtained in the Zn-31Al-3Mg bath is continuous. The course of reaction between the tested steel and liquid Zn-31Al-3Mg alloy is very abrupt, which leads to the formation of coatings with excess and non-uniform thickness.

  16. Gas-source molecular beam epitaxy of MgZnSSe for fabricating blue/green laser diodes

    NASA Astrophysics Data System (ADS)

    Imaizumi, Masayuki; Endoh, Yasuyuki; Suita, Muneyoshi; Sugimoto, Hiroshi; Ohtsuka, Ken-ichi; Isu, Toshiro; Ozeki, Tatsuo

    1996-11-01

    MgZnSSe layers were successfully grown by gas-source molecular beam epitaxy using hydride group VI sources. Employing n-type dopant Ga, Mg xZn 1- xS 0.12Se 0.88 layers (0 ≤ x ≤ 0.12) with electron concentrations in the 10 17 cm -3 range were obtained. The electron mobility was around 200 cm 2/V · s. with an increase in the Mg composition, the Ga donor ionization energy increased markedly. Active nitrogen was doped into the MgZnSSe layers for p-type control. Net acceptor concentrations of the p-Mg xZn 1- xS 0.15Se 0.85 layers were 4.5 × 10 17 cm -3 for x = 0 and 1.8 × 10 17 cm -3 for x = 0.10, which were comparable to the highest values ever reported. ZnCdSeMgZnSSe SCH-SQW LDs have been fabricated. Lasing was observed up to 203 K. The threshold current density was 420 A/cm 2 at 77 K and 1.8 kA/cm 2 at 203 K.

  17. Structure, mechanical characteristics and in vitro degradation, cytotoxicity, genotoxicity and mutagenicity of novel biodegradable Zn-Mg alloys.

    PubMed

    Kubásek, J; Vojtěch, D; Jablonská, E; Pospíšilová, I; Lipov, J; Ruml, T

    2016-01-01

    Zn-(0-1.6)Mg (in wt.%) alloys were prepared by hot extrusion at 300 °C. The structure, mechanical properties and in vitro biocompatibility of the alloys were investigated. The hot-extruded magnesium-based WE43 alloy was used as a control. Mechanical properties were evaluated by hardness, compressive and tensile testing. The cytotoxicity, genotoxicity (comet assay) and mutagenicity (Ames test) of the alloy extracts and ZnCl2 solutions were evaluated with the use of murine fibroblasts L929 and human osteosarcoma cell line U-2 OS. The microstructure of the Zn alloys consisted of recrystallized Zn grains of 12 μm in size and fine Mg2Zn11 particles arranged parallel to the hot extrusion direction. Mechanical tests revealed that the hardness and strength increased with increasing Mg concentration. The Zn-0.8 Mg alloys showed the best combination of tensile mechanical properties (tensile yield strength of 203 MPa, ultimate tensile strength of 301 MPa and elongation of 15%). At higher Mg concentrations the plasticity of Zn-Mg alloys was deteriorated. Cytotoxicity tests with alloy extracts and ZnCl2 solutions proved the maximum safe Zn(2+) concentrations of 120 μM and 80 μM for the U-2 OS and L929 cell lines, respectively. Ames test with extracts of alloys indicated that the extracts were not mutagenic. The comet assay demonstrated that 1-day extracts of alloys were not genotoxic for U-2 OS and L929 cell lines after 1-day incubation.

  18. Benthic foraminiferal growth seasons implied from Mg/Ca-temperature correlations for three Arctic species

    NASA Astrophysics Data System (ADS)

    Skirbekk, Kari; Hald, Morten; Marchitto, Thomas M.; Junttila, Juho; Klitgaard Kristensen, Dorthe; Aagaard Sørensen, Steffen

    2016-11-01

    Core-top sediment samples from Kongsfjorden, Svalbard, and adjacent fjord and shelf areas were collected in order to investigate a potential relationship between Mg/Ca-ratios of Arctic benthic foraminifera and the ambient bottom water temperatures (BWT). The area is influenced by large seasonal variation in factors such as light and temperature, which is further strengthened by oceanographic shifts, including inflow of relatively warm Atlantic water. Four hydrological seasons have been defined. The studied samples were collected during the years 2005-2010 and comprise data from three hydrological seasons: spring, summer, and autumn. Five common species of cold-water benthic foraminifera were investigated: Islandiella helenae/norcrossi, Buccella frigida, Nonionellina labradorica, Elphidium clavatum, and Cassidulina reniforme. For E. clavatum and C. reniforme, the investigations failed. For the remaining three species, the Mg/Ca-temperature correlations initially appeared stochastic holding correlation coefficients between 0.01 and 0.15. However, grouping the data based on seasons gave stronger Mg/Ca-temperature correlations, indicating specific growing seasons for the three species. The equations represent a starting point for a discussion on seasonality rather than robust, "ready-to-use" equations. I. helenae/norcrossi seems to reproduce and grow during summer (July/August) in outer Kongsfjorden. For B. frigida, a Mg/Ca-temperature correlation is seen both in summer (July/August) and autumn (October/November) samples, indicative of a continuous reproduction/growth-season lasting from July to November. N. labradorica appears to reproduce and grow during autumn (October/November). The results indicate that temperature reconstructions based on these benthic foraminifera reproduce seasonal temperatures rather than annual average temperatures.

  19. Mg/Ca ratios in freshwater microbial carbonates: Thermodynamic, kinetic and vital effects

    NASA Astrophysics Data System (ADS)

    Saunders, P.; Rogerson, M.; Wadhawan, J. D.; Greenway, G.; Pedley, H. M.

    2014-12-01

    The ratio of magnesium to calcium (Mg/Ca) in carbonate minerals in an abiotic setting is conventionally assumed to be predominantly controlled by (Mg/Ca)solution and a temperature dependant partition coefficient. This temperature dependence suggests that both marine (e.g. foraminiferal calcite and corals) and freshwater (e.g. speleothems and surface freshwater deposits, “tufas”) carbonate deposits may be important archives of palaeotemperature data. However, there is considerable uncertainty in all these settings. In surface freshwater deposits this uncertainty is focussed on the influence of microbial biofilms. Biogenic or “vital” effects may arise from microbial metabolic activity and/or the presence of extracellular polymeric substances (EPS). This study addresses this key question for the first time, via a series of unique through-flow microcosm and agitated flask experiments where freshwater calcite was precipitated under controlled conditions. These experiments reveal there is no strong relationship between (Mg/Ca)calcite and temperature, so the assumption of thermodynamic fractionation is not viable. However, there is a pronounced influence on (Mg/Ca)calcite from precipitation rate, so that rapidly forming precipitates develop with very low magnesium content indicating kinetic control on fractionation. Calcite precipitation rate in these experiments (where the solution is only moderately supersaturated) is controlled by biofilm growth rate, but occurs even when light is excluded indicating that photosynthetic influences are not critical. Our results thus suggest the apparent kinetic fractionation arises from the electrochemical activity of EPS molecules, and are therefore likely to occur wherever these molecules occur, including stromatolites, soil and lake carbonates and (via colloidal EPS) speleothems.

  20. Nonlinear absorption coefficient of pulsed laser deposited MgZnO thin film

    SciTech Connect

    Agrawal, Arpana Dar, Tanveer A.; Solanki, Ravi; Sen, Pratima; Phase, D. M.

    2015-06-24

    We report the imaginary part of 3{sup rd} order nonlinear susceptibility and the nonlinear absorption coefficient of Mg doped ZnO thin film using standard Z-scan technique. The origin of nonlinear absorption is attributed to the two photon absorption followed by the free carrier absorption because of the presence of oxygen vacancy defects. We have also confirmed the experimental results with the theoretical results obtained by considering the steady state response of a two level atom with the monochromatic field models.

  1. Dynamic Recrystallization Behavior of a Coarse-Grained Mg-2Zn-2Nd Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Wang, Tong; Jonas, John J.; Yue, Stephen

    2017-02-01

    Compression tests were performed on samples of Mg-2Zn-2Nd at 673 K (400 °C) and at three different strain rates. At 0.1/s, three mechanisms of dynamic recrystallization (DRX) were observed to operate: discontinuous DRX (DDRX), twinning DRX (TDRX), and continuous DRX (CDRX). At 0.01/s, DDRX took place as a result of grain boundary bulging, followed by CDRX on further straining. At 0.001/s, only CDRX was observed. At a strain of 0.3, the activation of multiple DRX mechanisms in the 0.1/s samples produced the weakest deformation textures.

  2. Impact of Zn, Mg, Ni and Co elements on glass alteration: Additive effects

    NASA Astrophysics Data System (ADS)

    Aréna, H.; Godon, N.; Rébiscoul, D.; Podor, R.; Garcès, E.; Cabie, M.; Mestre, J.-P.

    2016-03-01

    The minor elements present in the nuclear glass composition or coming from the groundwater of the future repository may impact glass alteration. In this study, the effects of Zn, Mg, Ni and Co on the International Simple Glass (ISG) alteration were studied throughout 511 days of aqueous leaching experiments. The aim was to determine their additive or competitive effect on glass alteration and the nature of the alteration products. The four elements were introduced separately or altogether in solution as XCl2 chloride salts (X = Zn, Mg, Ni or Co) with monthly additions to compensate for their consumption. The alteration kinetics were determined by leachate analyses (ICP-AES) and alteration products were characterized in terms of composition, morphology and microstructure (SEM, TEM-EDX, ToF-SIMS and XRD). Results indicate that when they are introduced separately, Zn, Mg, Ni and Co have the same qualitative and quantitative effect on glass alteration kinetics and on pH: they form secondary phases leading to a pH decrease and a significant increase in glass alteration. The secondary phases were identified as silicates of the added X element: trioctahedral smectites with a stoichiometry of[(Si(4-a) Ala) (X(3-b) Alb) O10 (OH)2](a+b)- [Xc Nad Cae] (2c+d+2e) + with a = 0.11 to 0.45, b = 0.00 to 0.29, c = 0, d = 0.19 to 0.74 and e = 0.10 to 0.14. . It was shown that as pH stabilizes at a minimum value, X-silicates no longer precipitate, thus leading to a significant drop in the glass alteration rate. This pH value depends on X and it has been identified as being 8 for Mg-silicates, probably around 7.3 for Ni and Co-silicates and less than 6.2 for Zn-silicates. When tested together, the effects of these four elements on glass alteration are additive and lead to the formation of a mix of X-silicates that precipitate as long as their constitutive elements are available and the pH is above their respective minimum value. This study brings new quantitative information about the

  3. Improvement of physico-mechanical properties of Mg-Zn nanoferrites via Cr3+ doping

    NASA Astrophysics Data System (ADS)

    Mansour, S. F.; Abdo, M. A.; El-Dek, S. I.

    2017-01-01

    A series of Mg0.8Zn0.2CrxFe2-xO4 (0≤x≤0.025) nanoferrites were prepared by citrate-nitrate auto-combustion method. X-ray diffraction assured the formation of the ferrites in nanoscale and in single phase spinel structure. The magnetic and mechanical properties were investigated. All the elastic moduli values increase slowly and steadily with increasing Cr3+ content reaching the critical composition x=0.02. The magnetic parameters increased up to x=0.02 and then decreased with further Cr doping. Versatile applications were recommended owing to the porous nature of the nanoferrites.

  4. Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.

    PubMed

    Euchner, H; Yamada, T; Rols, S; Ishimasa, T; Kaneko, Y; Ollivier, J; Schober, H; Mihalkovic, M; de Boissieu, M

    2013-03-20

    A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn(6)Sc. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T(c) = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.

  5. Phase diagram, crystal chemistry and thermoelectric properties of compounds in the Ca-Co-Zn-O system

    SciTech Connect

    Wong-Ng, W; Luo, T; Xie, W; Tang, W H; Kaduk, J A; Huang, Q; Yan, Y; Chattopadhyay, S; Tang, X; Tritt, T

    2011-11-17

    In the Ca-Co-Zn-O system, we have determined the tie-line relationships and the thermoelectric properties, solid solution limits, and structures of two low-dimensional cobaltite series, Ca3(Co, Zn)4O9-z and Ca3(Co,Zn)2O6-z at 885 ºC in air. In Ca3(Co,Zn)4O9-z, which has a misfit layered structure, Zn was found to substitute in the Co site to a limit of Ca3(Co3.8Zn0.2)O9-z. The compound Ca3(Co,Zn)2O6-z (n=1 member of the homologous series, Can+2(Co,Zn)n(Co,Zn)'O3n+3-z) consists of one-dimensional parallel (Co,Zn)2O66- chains that are built from successive alternating face-sharing (Co,Zn)O6 trigonal prisms and 'n' units of (Co,Zn)O6 octahedra along the hexagonal c-axis. Zn substitutes in the Co site of Ca3Co2O6 to a small amount of approximately Ca3(Co1.95Zn0.05)O6-z. In the ZnO-CoOz system, Zn substitutes in the tetrahedral Co site of Co3O4 to the maximum amount of (Co2.49Zn0.51)O4-z and Co substitutes in the Zn site of ZnO to (Zn0.94Co0.06)O. The crystal structures of (Co2.7Zn0.3)O4-z, (Zn0.94Co0.06)O, and Ca3(Co1.95 Zn0.05)O6-z are described. Despite the Ca3(Co, Zn)2O6-z series having reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical resistivity values of its members are too high to achieve high figure of merit, ZT.

  6. Evidence that the platelet plasma membrane does not contain a (Ca2+ + Mg2+)-dependent ATPase.

    PubMed

    Steiner, B; Lüscher, E F

    1985-09-10

    The present study was designed to determine the subcellular distribution of the platelet (Ca2+ + Mg2+)-ATPase. Human platelets were surface labeled by the periodate-boro[3H]hydride method. Plasma membrane vesicles were then isolated to a purity of approx. 90% by a procedure utilizing wheat germ agglutinin affinity chromatography. These membranes were found to be 2.6-fold enriched in surface glycoproteins compared to an unfractionated vesicle fraction and almost 7-fold enriched compared to intact platelets. In contrast, the isolated plasma membranes showed a decreased specific activity of the (Ca2+ + Mg2+)-ATPase compared to the unfractionated vesicle fraction. This decrease in specific activity was found to be similar to that of an endoplasmic reticulum marker, glucose-6-phosphatase, and to that of a platelet inner membrane marker, phospholipase A2. We conclude, therefore, that the (Ca2+ + Mg2+)-ATPase is not located in the platelet plasma membrane but is restricted to membranes of intracellular origin.

  7. Microwave plasma atomic emission spectrometric determination of Ca, K and Mg in various cheese varieties.

    PubMed

    Ozbek, Nil; Akman, Suleyman

    2016-02-01

    Microwave plasma-atomic emission spectrometry (MP-AES) was used to determine calcium, magnesium and potassium in various Turkish cheese samples. Cheese samples were dried at 100 °C for 2 days and then digested in a mixture of nitric acid/hydrogen peroxide (3:1). Good linearities (R(2) > 0.999) were obtained up to 10 μg mL(-1) of Ca, Mg and K at 445.478 nm, 285.213 nm and 766.491 nm, respectively. The analytes in a certified reference milk powder sample were determined within the uncertainty limits. Moreover, the analytes added to the cheese samples were recovered quantitatively (>90%). All determinations were performed using aqueous standards for calibration. The LOD values for Ca, Mg and K were 0.036 μg mL(-1), 0.012 μg mL(-1) and 0.190 μg mL(-1), respectively. Concentrations of Ca, K and Mg in various types of cheese samples produced in different regions of Turkey were found between 1.03-3.70, 0.242-0.784 and 0.081-0.303 g kg(-1), respectively.

  8. Chemistry of soluble β-diketiminatoalkaline-earth metal complexes with M-X bonds (M=Mg, Ca, Sr; X=OH, Halides, H).

    PubMed

    Sarish, Sankaranarayana Pillai; Nembenna, Sharanappa; Nagendran, Selvarajan; Roesky, Herbert W

    2011-03-15

    Victor Grignard's Nobel Prize-winning preparation of organomagnesium halides (Grignard reagents) marked the formal beginning of organometallic chemistry with alkaline earth metals. Further development of this invaluable synthetic route, RX+Mg→RMgX, with the heavier alkaline earth metals (Ca and Sr) was hampered by limitations in synthetic methodologies. Moreover, the lack of suitable ligands for stabilizing the reactive target molecules, particularly with the more electropositive Ca and Sr, was another obstacle. The absence in the literature, until just recently, of fundamental alkaline earth metal complexes with M-H, M-F, and M-OH (where M is the Group 2 metal Mg, Ca, or Sr) bonds amenable for organometallic reactions is remarkable. The progress in isolating various unstable compounds of p-block elements with β-diketiminate ligands was recently applied to Group 2 chemistry. The monoanionic β-diketiminate ligands are versatile tools for addressing synthetic challenges, as amply demonstrated with alkaline earth complexes: the synthesis and structural characterization of soluble β-diketiminatocalcium hydroxide, β-diketiminatostrontium hydroxide, and β-diketiminatocalcium fluoride are just a few examples of our contribution to this area of research. To advance the chemistry beyond synthesis, we have investigated the reactivity and potential for applications of these species, for example, through the demonstration of dip coating surfaces with CaCO(3) and CaF(2) with solutions of the calcium hydroxide and calcium fluoride complexes, respectively. In this Account, we summarize some recent developments in alkaline earth metal complex chemistry, particularly of Mg, Ca, and Sr, through the utilization of β-diketiminate ligands. We focus on results generated in our laboratory but give due mention to work from other groups as well. We also highlight the closely related chemistry of the Group 12 element Zn, as well as the important chemistry developed by other groups

  9. Microstructure and mechanical properties of Zn-Mg alloys as implant materials manufactured by powder metallurgy method

    NASA Astrophysics Data System (ADS)

    Guleryuz, L. F.; Ipek, R.; Arıtman, I.; Karaoglu, S.

    2017-02-01

    Currently some biomaterials, especially Zn and Mg alloys and related manufacturing methods are among important research topics due to their suitable biocompatibility, mechanical and corrosion properties. Zn Mg alloy has been processed by Mechanical Alloying method. Hot sintering was conducted at 410°C under argon atmosphere. Resulting microstructures densities and hardness test behaviors of the Zn-based alloys were studied.Visual inspection using SEM (Scanning Electron Microscope) analyses indicates that the microstructure of the composite is also greatly effected by these parameters. In addition, EDS (Energy Dispersive X-Ray Spectroscopy analyses were performed for reliable determination of the chemical composition.

  10. Exposing the hidden complexity of stoichiometric and catalytic metathesis reactions by elucidation of Mg-Zn hybrids

    PubMed Central

    Hevia, Eva; Chua, Jonathan Z.; García-Álvarez, Pablo; Kennedy, Alan R.; McCall, Matthew D.

    2010-01-01

    Studying seemingly simple metathesis reactions between ZnCl2 and tBuMgCl has, surprisingly, revealed a much more complex chemistry involving mixed magnesium-zinc compounds that could be regarded as Mg-Zn hybrids. Thus, the reaction of equimolar amounts of ZnCl2 and tBuMgCl reveals the formation of the unprecedented mixed Mg-Zn complex [(THF)4Mg(μ-Cl)2Zn(tBu)(Cl)] (1), as a result of the co-complexation of the two anticipated exchange products of the metathesis. This magnesium zincate adopts a contacted ion-pair structure, closely related to Knochel’s pioneering “Turbo” Grignard reagents. Furthermore, a second coproduct identified in this reaction is the solvent-separated mixed magnesium-zinc chloride complex [{Mg(THF)6}2+{Zn2Cl6}2-] (3) that critically diminishes the amount of ZnCl2 available for the intended metathesis reaction to take place. In another surprising result, when the reaction is carried out by using an excess of 3 M equivalents of the Grignard reagent (closer to the catalytic conditions employed by synthetic chemists), solvent-separated magnesium trialkyl zincate [{Mg2Cl3(THF)6}+{Zn(tBu)3}-] (4) is obtained that can be viewed as a model for the active species involved in the increasingly important organic transformations of Grignard reagents catalysed by ZnCl2. Furthermore, preliminary reactivity studies reveal that complex 4 can be used as an effective new reagent for direct Zn-I exchange reactions that allow the preparation and structural identification of the magnesium tris(aryl) zincate [{Mg2Cl3(THF)6}+{Zn(p-Tol)3}-] (5) that represents the first example of complete 3-fold activation of a zincate in a Zn-I exchange reaction which, in turn, can efficiently be used as a precursor for Negishi cross-coupling reactions. PMID:20212145

  11. Li/Ca, B/Ca, and Mg/Ca content in sea urchin spines cultured at different temperatures and pCO2

    NASA Astrophysics Data System (ADS)

    Nguyen, T.; Eagle, R.; Courtney, T.; Ries, J. B.; Brillo, V.; Rollion-Bard, C.; Gabitov, R. I.; Tripati, A. K.

    2012-12-01

    Element/calcium ratios within biogenic calcium carbonate minerals have been used as tools to reconstruct seawater temperature and pH. Most recent studies have focused on examining systematics governing elemental incorporation in coral, foraminifera, and otoliths [1-3, etc.]. In this study we focus on examining Li/Ca, B/Ca, and Mg/Ca ratios in sea urchins cultured at different temperatures and pCO2. We conducted in situ secondary ion mass spectrometry (SIMS) analyses on two different species of sea urchins. A temperate species of sea urchin (Arbacia punctulata) was cultured at variable pCO2 (400, 600, 900, 2850 ppmv) and at a constant temperature (25°C) [4]. We also investigated a tropical species of sea urchins (Echinometra viridis) that was cultured at variable pCO2 (400 and 1000 ppmv) and variable temperature (20°C and 30°C). The highly porous spines were embedded in epoxy and polished with 3 μm diamond suspension. SIMS analyses were performed with an oxygen primary beam and a lateral spatial resolution of about 40 μm. The standard deviation for SIMS spot analysis of Li in the reference synthetic calcite, CAL-HTP, was 3.5 % (1σ). The standard deviation of SIMS spots analyses of coral reference material M93-TB-FC-1 was 9.5 % (1σ). The bulk B content in this reference coral was determined by LA-ICP-MS as 39.3 ppm [6]. The standard deviation for the SIMS spot analysis of Mg in the reference synthetic calcite, UCI, was 1% (1σ). For the temperate species, B/Ca ratios decrease from ~0.39 to 0.29 mmol/mol as pCO2 increase from 400 to 2850 ppmv. This suggests that B/Ca ratios in this species may be a viable proxy for paleo-seawater pH. Other elements such as Li/Ca showed an increase from .047 to .052 mmol/mol as pCO2 increased. However, Mg/Ca did not show any significant trend as pCO2 increased. The tropical species showed a general increase in Li/Ca, B/Ca, Mg/Ca with increasing temperature. When temperature was held constant, there was no significant effect of

  12. Investigating the effects of abyssal peridotite alteration on Si, Mg and Zn isotopes

    NASA Astrophysics Data System (ADS)

    Savage, P. S.; Wimpenny, J.; Harvey, J.; Yin, Q.; Moynier, F.

    2013-12-01

    Around 1/3 of Earth's divergent ridge system is now classified as "slow" spreading [1], exposing ultramafic rocks (abyssal peridotites) at the seafloor. Such material is often highly altered by serpentinisation and steatisation (talc formation). It is crucial to understand such processes in order to access the original composition of the mantle, and to quantify any impact on ocean composition. Here we examine the effect of both serpentinisation and steatisation on Si, Mg and Zn isotopes. Hydrothermal alteration and seafloor weathering are both sources of oceanic Si [2] and weathering of abyssal peridotites is a source of oceanic Mg [3]; hence isotopic fractionation as a result of seafloor alteration could affect oceanic Si and Mg isotope composition. Zinc isotopes can provide complimentary information; the magnitude and direction of fractionation is highly dependent on complexing ligand [4] and can provide compositional information on the fluids driving metasomatism. For this study, two cores from the well-characterised abyssal peridotites recovered on ODP Leg 209 were examined [5]. Hole 1274a peridotites exhibit variable serpentinisation at ~200°C, whereas samples from Hole 1268a have been comprehensively serpentinised and then subsequently steatised to talc facies at ~350°C, by a low Mg/Si, low pH fluid. The Si, Mg and Zn isotope compositions of 1274a samples are extremely homogeneous, identical to that of pristine mantle rocks (BSE) i.e., serpentinisation at this locality was predominantly isochemical [5]. In contrast, samples from 1268a show greater isotopic variability. In all samples, Mg is enriched in the heavier isotopes relative to BSE, consistent with formation of isotopically heavy secondary phases [6]. For Si, serpentinised samples are slightly enriched in the lighter isotopes compared to BSE, again consistent with the behaviour of Si during formation of secondary phases [7]. Within the steatised samples, some exhibit enrichments in the lighter Si

  13. Robust room temperature ferromagnetism and band gap tuning in nonmagnetic Mg doped ZnO films

    NASA Astrophysics Data System (ADS)

    Quan, Zhiyong; Liu, Xia; Qi, Yan; Song, Zhilin; Qi, Shifei; Zhou, Guowei; Xu, Xiaohong

    2017-03-01

    Mg doped ZnO films with hexagonal wurtzite structure were deposited on c-cut sapphire Al2O3 substrates by pulsed laser deposition. Both room temperature ferromagnetism and band gap of the films simultaneously tuned by the concentration of oxygen vacancies were performed. Our results further reveal that the singly occupied oxygen vacancies should be responsible for the room temperature ferromagnetism and band gap narrowing. Singly occupied oxygen vacancies having the localized magnetic moments form bound magnetic polarons, which results in a long-range ferromagnetic ordering due to Mg doping. Moreover, band gap narrowing of the films is probably due to the formation of impurity band in the vicinity of valence band, originating from singly occupied oxygen vacancies. These results may build a bridge to understand the relationship between the magnetic and optical properties in oxide semiconductor, and are promising to integrate multiple functions in one system.

  14. Determination of the Bond Lengths in MgCCH, CaCCH and SrCCH

    NASA Astrophysics Data System (ADS)

    Forthomme, D.; Tokaryk, D. W.; Linton, C.; Adam, A. G.

    2011-06-01

    %High resolution spectra have been analyzed for the tilde{A}2E-tilde{X}2A_1 transition of M-12C12CH, M-12C12CD and M-13C13CH, where M refers to Mg, Ca and Sr. All the molecules except CaCCH have been recorded and analyzed in our laboratory in a laser ablation molecular jet source. The rotational constants extracted from the fits allowed us to calculate accurate bond lengths in MgCCH, CaCCH and SrCCH. This study is of particular interest since it shows how the structure of the molecules evolves as we substitute the alkaline earth atom by another one from the same family. The results showed clear trends in how the molecules account for changes in the mass of the metal atom and how the bond lengths in the ligand CCH are significantly different from the bond lengths in HCCH. Surprisingly, the triple bond between the two carbon atoms happens to be the one that experiences the greatest change. To determine the three bond lengths in a linear four atom molecule, one requires spectral data from three isotopologues of that molecule. By combining information from previously published analyses with new high resolution isotopically substituted spectra, we have determined the bond lengths for MgCCH, CaCCH and SrCCH. In each case, the tilde{A}2Π-tilde{X}2Σ^+ spectra of the M-12C12CH, M-12C12CD and M-13C13CH isotopologues were considered, where M refers to Mg, Ca and Sr. This study is of particular interest since it shows how the structure of this family of molecules evolves as we change the alkaline earth atom attached to the CCH ligand. In MgCCH, the structure of the CCH ligand is nearly the same as it is in acetylene, HCCH. Surprisingly, the bonding in the ligand is quite different from that of acetylene for the two heavier acetylide molecules, with the triple bond between the two carbon atoms experiencing the greatest change. M. Li and J. A. Coxon, J. Mol. Spectrosc. 176 (1996) 206-210 M. J. Dick, P. M. Sheridan, J. -G. Wang and P. F. Bernath, J. Mol. Spectrosc. 233 (2005

  15. Corrosion Behavior of Mg-6Al-1Zn+XRE Magnesium Alloy with Minor Addition of Yttrium

    NASA Astrophysics Data System (ADS)

    Manivannan, S.; Babu, S. P. Kumaresh; Sundarrajan, Srinivasan

    2015-04-01

    The effect of yttrium addition on the microstructure of Mg-6Al-1Zn alloy was investigated by optical microscopy, x-ray diffraction analysis, and scanning electron microscopy. The experimental alloys were prepared by melting high-purity Mg, Al, Zn, and Y, respectively. Melting was carried out in a Inconel 718 crucible under SF6 and ultra pure Ar (99.999%) gas mixture environment using electric arc furnace. The corrosion behavior of Mg-6Al-1Zn+ xYttrium ( x = 0.5, 1.0 and 1.5 wt.% Y) magnesium alloy with different levels of yttrium additions was studied in 3.5 wt.% NaCl solution. Microstructure of yttrium-added alloy shows that higher grainrefinement is obtained in Mg-6Al-1Zn+0.5wt.%Y. Increasing yttrium content reduces the size of α-grain and alters the distribution of the β-phase (Mg17Al12) from continuous network morphology to small and dispersive distribution. It forms secondary intermetallic phase Al2Y which has high melting point along the grain boundary. The corrosion resistance of Mg-6Al-1Zn magnesium alloy improved with addition of Yttrium. It was confirmed by the results of electrochemical polarization test. Based on the polarization curves, it is seen that fine precipitates of Al-Y intermetallic phase in Mg-6Al-1Zn alloy decrease the corrosion current density, thereby improving the corrosion resistance of the Mg-6Al-1Zn magnesium alloy.

  16. Ca(2+)-loading modulates potencies of cyclosporin A, Mg2+ and ADP to recouple permeabilized rat liver mitochondria.

    PubMed

    Andreyev AYu; Mikhaylova, L M; Starkov, A A; Kushnareva YuE

    1994-09-01

    We studied the relative potencies of cyclosporin A and endogenous effectors (Mg2+ and ADP) to recouple rat liver mitochondria permeabilized by different Ca(2+)-loading in a P(i)-containing medium. Recoupling efficiency of cyclosporin A dramatically decreased at high Ca(2+)-loading (approx. 100 nM of Ca2+/mg protein and more). Mitochondria permeabilized by high Ca2+ were recoupled with approximately equal efficiency by higher cyclosporin A concentrations or by adding 1-5 mM Mg2+ together with low concentrations of cyclosporin A while potentiating effect of ADP on the cyclosporin A recoupling potency was insignificant. Mg2+ ions at concentrations of 3 mM and higher also prevented the carboxyatractylate-induced reversion of cyclosporin A recoupling effect. The data point to competitive relationships between cyclosporin A and/or Mg2+ ions and Ca2+ ions for the site(s) regulating permeability state of the pore.

  17. MgCaCO3 Versus CaCO3 in Peritoneal Dialysis Patients – A Cross-Over Pilot Trial

    PubMed Central

    Evsanaa, Baigalmaa; Liu, Irene; Aliazardeh, Babak; Mahdavi, Sara; Bajwa, Gursarn; Gula, Jerry; Tam, Michelle; Sze, Elena; Roscoe, Janet M.; Tam, Paul Y.; Sikaneta, Tabo

    2015-01-01

    ♦ Background: Despite adverse effects such as constipation, vascular calcification, and hypercalcemia, calcium-based salts are relatively affordable and effective phosphate binders that remain in widespread use in the dialysis population. We conducted a pilot study examining whether the use of a combined magnesium/calcium-based binder was as effective as calcium carbonate at lowering serum phosphate levels in peritoneal dialysis (PD) patients. ♦ Methods: This was a cross-over, investigator-masked pilot study in which prevalent PD patients received calcium carbonate alone (200 mg calcium per tablet) or calcium magnesium carbonate (100 mg calcium, 85 mg magnesium per tablet). Primary outcome was serum phosphate level at 3 months. Analysis was as per protocol. ♦ Results: Twenty patients were recruited, 17 completed the study. Mean starting dose was 11.35 ± 7.04 pills per day of MgCaCO3 and 9.00 ± 4.97 pills per day of CaCO3. Mean phosphate levels fell from 2.13 mmol/L to 2.01 mmol/L (95% confidence interval (CI): 1.76 – 2.30, p = 0.361) in the MgCaCO3 group, and 1.81 mmol/L (95% CI: 1.56 – 2.0, p = 0.026) in the CaCO3 alone group. Six (35%) patients taking MgCaCO3 and 9 (54%) taking CaCO3 alone achieved Kidney Disease Outcomes Quality Initiative (KDOQI) serum phosphate targets at 3 months. Diarrhea developed in 9 patients taking MgCaCO3 and 3 taking CaCO3. Serum magnesium exceeded 1.4 mmol/L in 5 patients taking MgCaCO3 while serum calcium exceeded 2.65 mmol/L in 3 patients receiving CaCO3. When compared to the initial dose, the prescribed dose at 3 months was reduced by 44% (to 6.41 tablets/day) in the MgCaCO3 group and by 8% (to 8.24 pills per day) in the CaCO3 alone group. ♦ Conclusion: Compared with CaCO3 alone, the preparation and dose of MgCaCO3 used in this pilot study was no better at lowering serum phosphate levels in PD patients, and was associated with more dose-limiting side effects. PMID:24584605

  18. Structural and magnetic properties of Mg-Zn ferrites (Mg1-xZnxFe2O4) prepared by sol-gel method

    NASA Astrophysics Data System (ADS)

    Reyes-Rodríguez, Pamela Yajaira; Cortés-Hernández, Dora Alicia; Escobedo-Bocardo, José Concepción; Almanza-Robles, José Manuel; Sánchez-Fuentes, Héctor Javier; Jasso-Terán, Argentina; De León-Prado, Laura Elena; Méndez-Nonell, Juan; Hurtado-López, Gilberto Francisco

    2017-04-01

    In this study, the Mg1-xZnxFe2O4 nanoparticles (x=0-0.9) were prepared by sol-gel method. These ferrites exhibit an inverse spinel structure and the lattice parameter increases as the substitution of Zn2+ ions is increased. At lower Zn content (0.1≤x≤0.5), saturation magnetization (Ms) increases, while it decreases at higher Zn content (x≥6). The remnant magnetization (0.17-2.0 emu/g) and coercive field (6.0-60 Oe) indicate a ferrimagnetic behavior. The average core diameter of selected ferrites is around 15 nm and the nanoparticles morphology is quasi spherical. The heating ability of some Mg0.9Zn0.1Fe2O4 and Mg0.7Zn0.3Fe2O4 aqueous suspensions indicates that the magnetic nanoparticles can increase the medium temperature up to 42 °C in a time less than 10 min

  19. Temperature and carbonate ion effects on Mg/Ca and Sr/Ca ratios in benthic foraminifera: Aragonitic species Hoeglundina elegans

    NASA Astrophysics Data System (ADS)

    Rosenthal, Yair; Lear, Caroline H.; Oppo, Delia W.; Linsley, Braddock K.

    2006-03-01

    Core top samples from Atlantic (Little Bahama Banks (LBB)) and Pacific (Hawaii and Indonesia) depth transects have been analyzed in order to assess the influence of bottom water temperature (BWT) and aragonite saturation levels on Mg/Ca and Sr/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans. Both the Mg/Ca and Sr/Ca ratios in H. elegans tests show a general decrease with increasing water depth. Although at each site the decreasing trends are consistent with the in situ temperature profile, Mg/Ca and Sr/Ca ratios in LBB are substantially higher than in Indonesia and Hawaii at comparable water depths with a greater difference observed with increasing water depth. Because we find no significant difference between results obtained on "live" and "dead" specimens, we propose that these differences are due to primary effects on the metal uptake during test formation. Evaluation of the water column properties at each site suggests that in situ CO3 ion concentrations play an important role in determining the H. elegans Mg/Ca and Sr/Ca ratios. The CO3 ion effect is limited, however, only to aragonite saturation levels ([ΔCO3]aragonite) below 15 μmol kg-1. Above this level, temperature exerts a dominant effect. Accordingly, we propose that Mg/Ca and Sr/Ca in H. elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships: Mg/Ca = (0.034 ± 0.002)BWT + (0.96 ± 0.03) and Sr/Ca = (0.060 ± 0.002)BWT + (1.53 ± 0.03) (for [ΔCO3]aragonite > 15 μmol kg-1). The standard error associated with these equations is about ±1.1°C. Reconstruction of deeper water temperatures is complicated because in undersaturated waters, changes in Mg/Ca and Sr/Ca ratios reflect a combination of changes in [CO3] and BWT. Overall, we find that Sr/Ca, rather than Mg/Ca, in H. elegans may be a more accurate proxy for reconstructing paleotemperatures.

  20. Cytotoxicity evaluation of biodegradable Zn-3Mg alloy toward normal human osteoblast cells.

    PubMed

    Murni, N S; Dambatta, M S; Yeap, S K; Froemming, G R A; Hermawan, H

    2015-04-01

    The recent proposal of using Zn-based alloys for biodegradable implants was not supported with sufficient toxicity data. This work, for the first time, presents a thorough cytotoxicity evaluation of Zn-3Mg alloy for biodegradable bone implants. Normal human osteoblast cells were exposed to the alloy's extract and three main cell-material interaction parameters: cell health, functionality and inflammatory response, were evaluated. Results showed that at the concentration of 0.75mg/ml alloy extract, cell viability was reduced by ~50% through an induction of apoptosis at day 1; however, cells were able to recover at days 3 and 7. Cytoskeletal changes were observed but without any significant DNA damage. The downregulation of alkaline phosphatase protein levels did not significantly affect the mineralization process of the cells. Significant differences of cyclooxygenase-2 and prostaglandin E2 inflammatory biomarkers were noticed, but not interleukin 1-beta, indicating that the cells underwent a healing process after exposure to the alloy. Detailed analysis on the cell-material interaction is further discussed in this paper.

  1. Optical properties of MgZnO alloys: Excitons and exciton-phonon complexes

    SciTech Connect

    Neumann, M. D.; Cobet, C.; Esser, N.; Laumer, B.; Wassner, T. A.; Eickhoff, M.; Feneberg, M.; Goldhahn, R.

    2011-07-01

    The characteristics of the excitonic absorption and emission around the fundamental bandgap of wurtzite Mg{sub x}Zn{sub 1-x}O grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy with Mg contents between x = 0 and x = 0.23 are studied using spectroscopic ellipsometry and photoluminescence (PL) measurements. The ellipsometric data were analyzed using a multilayer model yielding the dielectric function (DF). The imaginary part of the DF for the alloys exhibits a pronounced feature which is attributed to exciton-phonon coupling (EPC) similar to the previously reported results for ZnO. Thus, in order to determine reliable transition energies, the spectral dependence is analyzed by a model which includes free excitonic lines, the exciton continuum, and the enhanced absorption due to EPC. A line shape analysis of the temperature-dependent PL spectra yielded in particular the emission-related free excitonic transition energies, which are compared to the results from the DF line-shape analysis. The PL linewidth is discussed within the framework of an alloy disorder model.

  2. Electrical modulus and dielectric behavior of Cr3+ substituted Mg-Zn nanoferrites

    NASA Astrophysics Data System (ADS)

    Mansour, S. F.; Abdo, M. A.

    2017-04-01

    The dielectric parameters and ac electrical conductivity of Mg0.8Zn0.2CrxFe2-xO4; (0≤x≤0.025) nanoferrites synthesized citrate-nitrate auto-combustion method were studied using the complex impedance technique in the frequency and temperature ranges 4 Hz-5 MHz and 303-873 K respectively. Hopping of charge carriers plus interfacial polarization could interpret the behaviors of dielectric constant (ε‧), dielectric loss tangent (tanδ) and ac electrical conductivity (σac) with frequency, temperatures and composition. The up-normal behavior observed in tanδ trend with temperatures confirms the presence of relaxation loss (dipoles losses). Correlated barrier hopping (CBH) of electron is the conduction mechanism of the investigated nanoferrites. Cole-Cole plots at different temperatures emphasize the main role of grain and grain boundaries in the properties of the investigated nanoferrites. Cr3+ substitution can control the dielectric parameters and ac electrical conductivity of Mg-Zn nanoferrites making it candidates for versatile applications.

  3. Pure and Zn-doped Pt Clusters go Flat and Upright on MgO(100)

    SciTech Connect

    Shen, Lu; Dadras, Mostafa J.; Alexandrova, Anastassia N.

    2014-12-28

    Pure and doped sub-nanoclusters can exhibit superb catalytic activity, which, however, strongly depends on their size, shape, composition, and the nature of the support. This work is about surface-deposited sub-nano Pt-based clusters, which are promising catalysts for the reactions of dehydrogenation. Using density functional theory and ab initio calculations, and an ab initio genetic algorithm for finding the global minima of clusters, we found a peculiar effect that Pt₅ and Pt₄Zn clusters exhibit upon deposition on MgO(100). Both of them change shapes from the gas phase 3-D form to a planar form, and they stand upright on the support. Several reasons are responsible for this behaviour. In part, clusters go flat due to the electron transfer from the support. Indeed, the anionic Pt₅- and Pt₄Zn- species are flat also in the gas phase. Charging induces the second-order Jahn–Teller effect (or partial covalency) facilitated by the recruitment of the higher-energy 6p atomic orbitals on Pt into the valence manifold, and that is the reason for the planarization of the anions. Secondly, clusters maximize interactions with the surface O atoms (resulting in further favouring of 2-D structures over 3-D), and avoid contacts with surface Mg atoms (resulting in upright morphologies).

  4. Crop residue effects on Ca, Mg, K and Na concentrations and loads in runoff water

    NASA Astrophysics Data System (ADS)

    Miras-Avalos, J. M.; Sande-Fouz, P.; Bertol, I.; Paz-Gonzalez, A.

    2009-04-01

    Soil organic matter constitutes and important source of macro and micronutrients for plants and microorganisms while improving some physical and chemical properties of the soil. In Galicia (NW Spain), cultivated soils developed on schists from the Ordenes series show a relatively high susceptibility to surface degradation, which tends to be increased when soil organic content decreases. Therefore, management systems providing a high protection to the soil and increasing its organic matter content should also improve its quality. However, tillage practices may reduce the organic matter content in soil surface horizons, causing crust formation. Degraded soil surface conditions favor surface runoff, thus enhancing nutrient losses. This study examined the effect of applying crop residues to the soil surface on main nutrient (Ca, Mg, K and Na) losses by runoff from a tilled soil with a relatively low organic matter content. Runoff and sediment yield were made over 1 m2 plots using a rainfall simulator with constant 65 mmh-1 intensity. Four successive rainfall applications were performed, the first three ones 25 mm each and the last one 65 mm. Added corn straw varied between 0 and 4 tha-1 in the five studied treatments. Total and dissolved concentrations of the studied elements showed a trend to decrease due to the effect of corn straw on soil losses. After 140 mm cumulative rainfall, total nutrient losses were as follows: Ca from 12.32 to 28.94 mg L-1, Mg from 20.81 to 148.90 mg L-1, K from 14.20 to 35.17 mg L-1 and Na from 14.99 to 23.41 mg L-1. The relative contribution of the dissolved fraction to the total nutrient content loss was highly variable, being up to 90% in the case of Na. The obtained results confirmed that corn residues applied to a degraded soil, with low structural stability, prevented macronutrient losses.

  5. The Raman spectrum of Ca-Mg-Fe carbonates; Applications in geobiology

    NASA Astrophysics Data System (ADS)

    van Zuilen, M. A.; Rividi, N.; Ménez, B.; Philippot, P.

    2012-04-01

    Carbonates form a very important mineral group in geobiological studies. They are a common mineral matrix for putative carbonaceous microfossils in Archean greenstone belts, form an important chemical deposit in seafloor hydrothermal systems, and are a common product in biomineralization processes. In many geobiological studies there is a specific need for simple characterization of carbonate composition while avoiding complex sample preparation or sample destruction. Raman spectroscopy is a highly versatile non-destructive technique enabling in-situ characterization of minerals and carbonaceous materials. It can be combined with confocal microscopy enabling high-resolution Raman mapping of entire rock thin sections, or can be integrated in submersibles and potentially Mars-rovers for direct field-based mineral identification. It is thus important that well-established spectral databases exist which enable unambiguous identification of a wide variety of carbonate minerals. The most common carbonates in the Ca-Mg-Fe system include the CaCO3 polymorphs calcite, aragonite, and vaterite, as well as the solid solutions CaMg(CO3)2-CaFe(CO3)2 (dolomite-ankerite) and MgCO3-FeCO3 (magnesite-siderite). Although various carbonate end-members have been studied exhaustively by Raman spectroscopy, a simple protocol for rapid distinction of various carbonate solid solutions is still lacking. Here we present a detailed study of Raman shifts in various carbonate standards of known composition in the Ca-Mg-Fe system. Carbonates with rhombohedral symmetry display a Raman spectrum with six characteristic vibrational modes - four of these represent vibrations within the (CO3)2- unit and two represent external vibrations of the crystal lattice. We show that Raman band shifts of internal mode 2ν2 (range 1725-1765 cm-1), and external modes T (range 170-215 cm-1) and L (range 285-330 cm-1) for siderite-magnesite and ankerite-dolomite solid solutions display distinct and well defined

  6. Measurement of Ca, Zn and Sr in enamel of human teeth by XRF

    SciTech Connect

    Wielopolski, L.; Featherstone, J.D.B.; Cohn, S.H.

    1984-01-01

    Energy dispersive x-ray fluorescence (EDXRF) has been employed to measure Ca, Zn, and Sr in enamel of human teeth. The calibration of the EDXRF system was performed by comparing Sr/Ca ratios with values obtained by atomic absorption analysis of acid etched biopsies of the enamel surface. Two calibration lines were obtained, one line for untreated teeth and the second line for teeth immersed (treated) in solutions containing Sr. A simple analytical model demonstrated that the two calibration lines were the result of the difference in the depth of the enamel sampled by EDXRF and by the acid-etched biopsy. The multi-elemental, non-destructive and quantitative aspects of EDXRF permit the sequential monitoring of the effects of Sr and Zn ions on the mineralization and demineralization processes in human enamel. The portability of the system and adaptability to non-invasive measurements makes it suitable for field studies. 26 references, 4 figures.

  7. How strong are Ca2+-heparin and Zn2+-heparin interactions?

    NASA Astrophysics Data System (ADS)

    Remko, Milan; Broer, Ria; Remková, Anna; Van Duijnen, Piet Th.

    2015-02-01

    The formation of the calcium and zinc salts from CaCl2, ZnCl2 and six monomeric structural units of heparin (1-OMe ΔUA-2S, 1-OMe GlcN-S6S, 1,4-DiOMe GlcA, 1,4-DiOMe GlcN-S3S6S, 1,4-DiOMe IdoA-2S, and 1,4-DiOMe GlcN-S6S) have been studied in gas phase and aqueous solution as model reactions for formation of heparin-Ca2+ and heparin-Zn2+ complexes. Gibbs reaction energies computed at the B3LYP/6-311++G(d,p) level of theory for the reactions studied in aqueous solution are positive and range from 20 to 250 kJ/mol.

  8. Effect of spark plasma sintering on plasma electrolytic oxidation coatings on gas-atomized Mg-Zn-Y alloy containing nano-sized powders.

    PubMed

    Lee, Du Hyung; Kim, Bo Sik; Song, Yo-seung; Kim, Sung Ho; Lee, Chan Bok; Chang, Si Young

    2010-01-01

    Mg-1.0wt%Zn-2.0wt%Y alloy powders were produced by gas atomization, and subsequently sintered by spark plasma sintering (SPS). The SPSed Mg-1.0wt%Zn-2.0wt%Y alloy, which showed a microstructure of well-bonded grains containing nano-sized powders of approximately 100 nm in diameter, was coated by a plasma electrolytic oxidation (PEO) method. Microstructure, mechanical properties and corrosion properties of PEO coatings were investigated and compared to those of normally sintered Mg-1.0wt%Zn-2.0wt%Y and cast Mg-1.0wt%Zn alloys. All coatings consisted of MgO and Mg2SiO4. The micro-hardness and friction coefficient of coatings on the SPSed Mg-1.0wt%Zn-2.0wt%Y alloy were higher than those on normally sintered Mg-1.0wt%Zn-2.0wt%Y and cast Mg-l.0wt%Zn alloys. However, the corrosion resistance in 3.5% NaCl solution for the SPSed Mg-1.0wt%Zn-2.0wt%Y alloy was between that for normally sintered Mg-1.0wt%Zn-2.0wt%Y alloy and cast Mg-1.0wt%Zn alloy.

  9. Influx of extracellular Zn(2+) into the hippocampal CA1 neurons is required for cognitive performance via long-term potentiation.

    PubMed

    Takeda, A; Suzuki, M; Tempaku, M; Ohashi, K; Tamano, H

    2015-09-24

    Physiological significance of synaptic Zn(2+) signaling was examined in the CA1 of young rats. In vivo CA1 long-term potentiation (LTP) was induced using a recording electrode attached to a microdialysis probe and the recording region was locally perfused with artificial cerebrospinal fluid (ACSF) via the microdialysis probe. In vivo CA1 LTP was inhibited under perfusion with CaEDTA and ZnAF-2DA, extracellular and intracellular Zn(2+) chelators, respectively, suggesting that the influx of extracellular Zn(2+) is required for in vivo CA1 LTP induction. The increase in intracellular Zn(2+) was chelated with intracellular ZnAF-2 in the CA1 1h after local injection of ZnAF-2DA into the CA1, suggesting that intracellular Zn(2+) signaling induced during learning is blocked with intracellular ZnAF-2 when the learning was performed 1h after ZnAF-2DA injection. Object recognition was affected when training of object recognition test was performed 1h after ZnAF-2DA injection. These data suggest that intracellular Zn(2+) signaling in the CA1 is required for object recognition memory via LTP. Surprisingly, in vivo CA1 LTP was affected under perfusion with 0.1-1μM ZnCl2, unlike the previous data that in vitro CA1 LTP was enhanced in the presence of 1-5μM ZnCl2. The influx of extracellular Zn(2+) into CA1 pyramidal cells has bidirectional action in CA1 LTP. The present study indicates that the degree of extracellular Zn(2+) influx into CA1 neurons is critical for LTP and cognitive performance.

  10. Heat capacities and entropies at 298.15 K of MgTiO3 (geikielite), ZnO (zincite), and ZnCO3 (smithsonite)

    USGS Publications Warehouse

    Robie, R.A.; Haselton, H.T.; Hemingway, B.S.

    1989-01-01

    Heat capacities of synthetic MgTiO3 (geikielite), ZnO (zincite), and natural crystals of smithsonite (ZnCO3) were measured between 9 and 366 K using an automatic adiabatically shielded calorimeter. At 298.15 K the standard molar entropies Smo of MgTiO3, ZnO, and ZnCO3 are (74.64 ?? 0.15), (43.16 ?? 0.09), and (81.19 ?? 0.16) J??K-1??mol-1, respectively. Debye temperatures for MgTiO3 and ZnO calculated from our Cp, mo values below 20 K are (900 ?? 20) K and (440 ?? 25) K respectively. Heat capacities for MgTiO3 and ZnO were combined with enthalpy increments from the literature to derive heat-capacity equations for these phases from 260 to about 1800 K. The heat capacities of MgTiO3 between 260 and 1720 K were fitted with an average deviation of 0.3 per cent by the equation: C??p,m/(J??K-1??mol-1) = 222.5-0.05274(T/K)-6.092x105(T/K)-1-1874.6(T/K) -1/2+1.878x10-5(T/K)2 and for ZnO the equation: C??p,m/(J??K-1??mol-1) = 53.999+7.851x10-4(T/K)-5.868x105(T/K)-2 -127.50(T/K)-:1/2+1.9376x10-6(T/K)2 fits the heat capacities in the temperature interval of 250 to 1800 K with an average deviation of 0.7 per cent. ?? 1989.

  11. Investigation of phase formation of (Zn, Mg)0.5Co0.5Fe2O4 nanoferrites

    NASA Astrophysics Data System (ADS)

    Msomi, J. Z.; Dlamini, W. B.; Moyo, T.; Ezekiel, P.

    2015-01-01

    Zn0.5Co0.5Fe2O4 and Mg0.5Co0.5Fe2O4 nanoparticles have been prepared through high energy ball milling of single phase mixtures of ZnFe2O4 and CoFe2O4 or MgFe2O4 and CoFe2O4 nanosized oxides. The Mössbauer spectra of the milled products ZnFe2O4/CoFe2O4 and MgFe2O4/CoFe2O4 reveal the presence of Zn0.5Co0.5Fe2O4 and Mg0.5Co0.5Fe2O4, respectively. In an alternative route, Zn0.5Co0.5Fe2O4 and Mg0.5Co0.5Fe2O4 compounds were prepared directly from metal chloride solutions through glycol-thermal reaction. The coercive fields of the Zn0.5Co0.5Fe2O4 and Mg0.5Co0.5Fe2O4 oxides produced by glycol-thermal reaction were found to be about 100 Oe and 161 Oe, respectively. Larger coercive fields of about 184 Oe and 255 Oe have been observed for the milled ZnFe2O4/CoFe2O4 and MgFe2O4/CoFe2O4 oxides.

  12. Rhombohedral ilmenite group nickel titanates with Zn, Mg, and Mn: synthesis and crystal structures

    NASA Astrophysics Data System (ADS)

    Liferovich, Ruslan P.; Mitchell, Roger H.

    2005-09-01

    Binary, ternary, and quaternary rhombohedral ordered titanates, Ni1/2Mn1/2TiO3, Ni1/2Mg1/2TiO3, Ni1/3Zn1/3Mg1/3TiO3, and Ni1/4Zn1/4Mg1/4Mn1/4TiO3, were obtained by solid-state synthesis at 1095°C at ambient pressure in a nitrogen atmosphere. All of the compounds adopt ATiO3 ( A = Ni, Mn, Zn, and Mg) stoichiometry. Crystal structures were refined by the Rietveld method from powder X-ray diffraction data. Unit cell parameters and unit cell volumes decrease with decreasing average radius of the vi A 2+ cation. All the synthetic titanates adopt the space group Rbar 3 and the ilmenite structure consisting of distorted AO6 and TiO6 octahedra. The divalent cations and Ti4+ are distributed in layers of octahedra alternating along c with no evidence for disorder. In common with pyrophanite, NiTiO3, and ilmenite sensu stricto, the distortion of the AO6 octahedra is less than that of the TiO6 octahedra. The Ti4+ and A-site cations in the titanates are off-centred within the coordination polyhedra. Deviation of the z positional parameters from their theoretical values for the A and Ti atoms indicate that in the titanates with the larger A 2+ cations and Goldschmidt tolerance factors, t ≥ 0.745, the AO6 octahedral layer is more “puckered” above and below planes parallel to (001) than that of the TiO6 octahedra, and vice versa in the titanates with smaller R{/A 2+} for which t≤0.745. Data are given for the volumes and distortion indices of all the coordination polyhedra. This study confirms the existence and stability of complex solid solutions between ordered rhombohedral titanates of Ni and first-row transition metals at ambient conditions over a range of t from 0.786 to 0.737. These experimental data suggest that the formation of ilmenite-type titanates enriched in Ni is possible in exotic mineral-forming systems at low pressure and/or in extraterrestrial rocks.

  13. Effects of electron interference on temperature dependent transport properties of two dimensional electron gas at MgZnO/ZnO interfaces

    SciTech Connect

    Das, Amit K. Misra, P.; Ajimsha, R. S.; Joshi, M. P.; Kukreja, L. M.

    2015-09-07

    We report the effects of electron interference on temperature dependent transport properties of two dimensional electron gas (2DEG) confined at the interface in polycrystalline MgZnO/ZnO heterostructures grown by pulsed laser deposition on c-alumina substrates. On increasing Mg concentration in the MgZnO layer, the sheet electron concentration was found to increase and the sheet resistance was found to decrease. In addition, the electron concentration and mobility were almost temperature independent in the range from 4.2 to 300 K, indicating the formation of 2DEG at the interface. The temperature dependent resistivity measurements showed a negative temperature coefficient of resistivity at low temperatures together with negative magnetoresistance. These were found to be caused by electron interference effects, and the experimental data could be explained using the models of quantum corrections to conductivity.

  14. Structural, magnetic, DC-AC electrical conductivities and thermo electric studies of MgCuZn Ferrites for microinductor applications.

    PubMed

    Varalaxmi, N; Sivakumar, K V

    2013-01-01

    Multilayer chip inductors (MLCIs) have been rapidly developed for electromagnetic applications. NiCuZn ferrites are the most preferred ferrite materials to produce MLCIs. MgCuZn ferrites have similar properties to those of NiCuZn ferrites. MgCuZn ferrites owing to their superior properties like low magnetostriction, environmental stability, low stress sensitivity, high resistivity and low cost can replace NiCuZn ferrites, which have a wide range of electronic applications. In view of this, a series of polycrystalline MgCuZn ferrites with generic formula MgxCu0.5Zn0.5-xFe2O4 (X=0.0 0.1, 0.2, 0.3, 0.4 and 0.5) are successfully synthesized by conventional double sintering technique. The samples were then characterized by the X-ray diffraction patterns (XRD) microstructural studies and the grain size was estimated using SEM micrographs. The sintered ferrites have been investigated in their magnetic, electrical and thermoelectric effect studies, which were carried out in the temperature range from 30 °C to 490 °C. The investigated ferrites are found to exhibit excellent properties that are suitable for the core materials in multilayer chip inductors, and the results are discussed.

  15. In vivo behavior of biodegradable Mg-Nd-Y-Zr-Ca alloy.

    PubMed

    Aghion, E; Levy, G; Ovadia, S

    2012-03-01

    The aim of the this study is to evaluate the in vivo behavior of Mg-1.5%Nd-0.5%Y-0.5%Zr implants with and without 0.4%Ca in comparison with inert Ti-6Al-4V reference implants. This was carried out by implanting cylindrical disks at the back midline of Wister male rats within the subcutaneous layer of the skin for up to 12 weeks. The degradation of magnesium-based implants in terms of hydrogen gas bubble formation was evaluated by radiography assessment; corrosion rate was analyzed by visual examination and weight loss measurements. The physiological response of the rats post-implantation was obtained by evaluating their wellbeing behavior and blood biochemical analysis including serum Mg, blood urea nitrogen, and serum creatinine. In addition, histological analyses of the soft tissue around the implants were carried out to assess local lesions relating to the implants such as inflammation, tissue necrosis, granulation, mineralization, and tumor development. The results obtained clearly indicate that apart from the normal degradation characteristics and subsequent formation of hydrogen gas bubbles, the in vivo behavior of Mg implants was adequate and comparable to that of Ti-6Al-4V reference alloy. In addition, it was evident that the corrosion degradation of the magnesium alloys was strongly related to the location of the implant within the animal's body. The addition of 0.4%Ca improves the biodegradation corrosion resistance of the tested magnesium implants.

  16. Determination of the Mg/Mn ratio in foraminiferal coatings: An approach to correct Mg/Ca temperatures for Mn-rich contaminant phases

    NASA Astrophysics Data System (ADS)

    Hasenfratz, Adam P.; Martínez-García, Alfredo; Jaccard, Samuel L.; Vance, Derek; Wälle, Markus; Greaves, Mervyn; Haug, Gerald H.

    2017-01-01

    The occurrence of manganese-rich coatings on foraminifera can have a significant effect on their bulk Mg/Ca ratios thereby biasing seawater temperature reconstructions. The removal of this Mn phase requires a reductive cleaning step, but this has been suggested to preferentially dissolve Mg-rich biogenic carbonate, potentially introducing an analytical bias in paleotemperature estimates. In this study, the geochemical composition of foraminifera tests from Mn-rich sediments from the Antarctic Southern Ocean (ODP Site 1094) was investigated using solution-based and laser ablation ICP-MS in order to determine the amount of Mg incorporated into the coatings. The analysis of planktonic and benthic foraminifera revealed a nearly constant Mg/Mn ratio in the Mn coating of ∼0.2 mol/mol. Consequently, the coating Mg/Mn ratio can be used to correct for the Mg incorporated into the Mn phase by using the down core Mn/Ca values of samples that have not been reductively cleaned. The consistency of the coating Mg/Mn ratio obtained in this study, as well as that found in samples from the Panama Basin, suggests that spatial variation of Mg/Mn in foraminiferal Mn overgrowths may be smaller than expected from Mn nodules and Mn-Ca carbonates. However, a site-specific assessment of the Mg/Mn ratio in foraminiferal coatings is recommended to improve the accuracy of the correction.

  17. Role of Mg(2+) in Ca(2+)-induced Ca(2+) release through ryanodine receptors of frog skeletal muscle: modulations by adenine nucleotides and caffeine.

    PubMed Central

    Murayama, T; Kurebayashi, N; Ogawa, Y

    2000-01-01

    Mg(2+) serves as a competitive antagonist against Ca(2+) in the high-affinity Ca(2+) activation site (A-site) and as an agonist of Ca(2+) in the low-affinity Ca(2+) inactivation site (I-site) of the ryanodine receptor (RyR), which mediates Ca(2+)-induced Ca(2+) release (CICR). This paper presents the quantitative determination of the affinities for Ca(2+) and Mg(2+) of A- and I-sites of RyR in frog skeletal muscles by measuring [(3)H]ryanodine binding to purified alpha- and beta-RyRs and CICR activity in skinned fibers. There was only a minor difference in affinity at most between alpha- and beta-RyRs. The A-site favored Ca(2+) 20- to 30-fold over Mg(2+), whereas the I-site was nonselective between the two cations. The RyR in situ showed fivefold higher affinities for Ca(2+) and Mg(2+) of both sites than the purified alpha- and beta-RyRs with unchanged cation selectivity. Adenine nucleotides, whose stimulating effect was found to be indistinguishable between free and complexed forms, did not alter the affinities for cations in either site, except for the increased maximum activity of RyR. Caffeine increased not only the affinity of the A-site for Ca(2+) alone, but also the maximum activity of RyR with otherwise minor changes. The results presented here suggest that the rate of CICR in frog skeletal muscles appears to be too low to explain the physiological Ca(2+) release, even though Mg(2+) inhibition disappears. PMID:10733962

  18. The effect of shell secretion rate on Mg / Ca and Sr / Ca ratios in biogenic calcite as observed in a belemnite rostrum

    NASA Astrophysics Data System (ADS)

    Vinzenz Ullmann, Clemens; Pogge von Strandmann, Philip A. E.

    2017-01-01

    Isotopic ratios and concentrations of the alkaline earth metals Mg and Sr in biogenic calcite are of great importance as proxies for environmental parameters. In particular, the Mg / Ca ratio as a temperature proxy has had considerable success. It is often hard to determine, however, which parameter ultimately controls the concentration of these elements in calcite. Here, multiple Mg / Ca and Sr / Ca transects through a belemnite rostrum of Passaloteuthis bisulcata (Blainville, 1827) are used to isolate the effect of calcite secretion rate on incorporation of Mg and Sr into the calcite. With increasing calcite secretion rate Mg / Ca ratios decrease and Sr / Ca ratios in the rostrum increase. In the studied specimen this effect is found to be linear for both element ratios over a calcite secretion rate increase of ca. 150 %. Mg / Ca ratios and Sr / Ca ratios show a linear co-variation with increasing relative growth rate, where a 100 % increase in growth rate leads to a (8.1 ± 0.9) % depletion in Mg and a (5.9 ± 0.7) % enrichment in Sr. The magnitude of the calcite secretion rate effect on Mg is (37 ± 4) % greater than that on Sr. These findings are qualitatively confirmed by a geochemical transect through a second rostrum of Passaloteuthis sp. Growth rate effects are well defined in rostra of Passaloteuthis, but only account for a minor part of chemical heterogeneity. Biasing effects on palaeoenvironmental studies can be minimized by informed sampling, whereby the apex and apical line of the rostrum are avoided.

  19. Abnormal alterations in the Ca2+/CaV1.2/calmodulin/caMKII signaling pathway in a tremor rat model and in cultured hippocampal neurons exposed to Mg2+-free solution

    PubMed Central

    LV, XINTONG; GUO, FENG; XU, XIAOXUE; CHEN, ZAIXING; SUN, XUEFEI; MIN, DONGYU; CAO, YONGGANG; SHI, XIANBAO; WANG, LEI; CHEN, TIANBAO; SHAW, CHRIS; GAO, HUILING; HAO, LIYING; CAI, JIQUN

    2015-01-01

    Voltage-dependent calcium channels (VDCCs) are key elements in epileptogenesis. There are several binding-sites linked to calmodulin (CaM) and several potential CaM-dependent protein kinase II (CaMKII)-mediated phosphorylation sites in CaV1.2. The tremor rat model (TRM) exhibits absence-like seizures from 8 weeks of age. The present study was performed to detect changes in the Ca2+/CaV1.2/CaM/CaMKII pathway in TRMs and in cultured hippocampal neurons exposed to Mg2+-free solution. The expression levels of CaV1.2, CaM and phosphorylated CaMKII (p-CaMKII; Thr-286) in these two models were examined using immunofluorescence and western blotting. Compared with Wistar rats, the expression levels of CaV1.2 and CaM were increased, and the expression of p-CaMKII was decreased in the TRM hippocampus. However, the expression of the targeted proteins was reversed in the TRM temporal cortex. A significant increase in the expression of CaM and decrease in the expression of CaV1.2 were observed in the TRM cerebellum. In the cultured neuron model, p-CaMKII and CaV1.2 were markedly decreased. In addition, neurons exhibiting co-localized expression of CaV1.2 and CaM immunoreactivities were detected. Furthermore, intracellular calcium concentrations were increased in these two models. For the first time, o the best of our knowledge, the data of the present study suggested that abnormal alterations in the Ca2+/CaV1.2/CaM/CaMKII pathway may be involved in epileptogenesis and in the phenotypes of TRMs and cultured hippocampal neurons exposed to Mg2+-free solution. PMID:26299765

  20. Ultrafiltration behavior of major ions (Na, Ca, Mg, F, Cl, and SO4) in natural waters.

    PubMed

    Guo, L; Hunt, B J; Santschi, P H

    2001-04-01

    Aquatic colloids, including macromolecules and microparticles, with sizes ranging between 1 nm to 1 micron, play important roles in the mobility and bioavailability of heavy metals and other contaminants in natural waters. Cross-flow ultrafiltration has become one of the most commonly used techniques for isolating aquatic colloids. However, the ultrafiltration behavior of chemical species remains poorly understood. We report here the permeation behavior of major ions (Na, Ca, Mg, F, Cl, and SO4) in natural waters during ultrafiltration using an Amicon 1 kDa ultrafiltration membrane (S10N1). Water samples across a salinity gradient of 0-20@1000 were collected from the Trinity River and Galveston Bay. The permeation behavior of major ions was well predicted by a permeation model, resulting in a constant permeation coefficient for each ion. The value of the model-derived permeation coefficient (Pc) was 0.99 for Na, 0.97 for Cl, and 0.95 for F, respectively, in Trinity River waters. Values of Pc close to 1 indicate that retention of Na, Cl, and F by the 1 kDa membrane during ultrafiltration was indeed minimal (< 1-5%). In contrast, significant (14-36%) retention was observed for SO4, Ca, and Mg in Trinity River waters, with a Pc value of 0.64, 0.82, and 0.86 for SO4, Ca and Mg, respectively. However, these retained major ions can further permeate through the 1 kDa membrane during diafiltration with ultrapure water. The selective retention of major ions during ultrafiltration may have important implications for the measurement of chemical and physical speciation of trace elements when using cross-flow ultrafiltration membranes to separate colloidal species from natural waters. Our results also demonstrate that the percent retention of major ions during ultrafiltration decreases with increasing salinity or ionic strength. This retention is largely attributed to electrostatic repulsion by the negatively charged cartridge membrane.

  1. Measuring past changes in ENSO variance using Mg/Ca measurements on individual planktic foraminifera

    NASA Astrophysics Data System (ADS)

    Marchitto, T. M.; Grist, H. R.; van Geen, A.

    2013-12-01

    Previous work in Soledad Basin, located off Baja California Sur in the eastern subtropical Pacific, supports a La Niña-like mean-state response to enhanced radiative forcing at both orbital and millennial (solar) timescales during the Holocene. Mg/Ca measurements on the planktic foraminifer Globigerina bulloides indicate cooling when insolation is higher, consistent with an ';ocean dynamical thermostat' response that shoals the thermocline and cools the surface in the eastern tropical Pacific. Some, but not all, numerical models simulate reduced ENSO variance (less frequent and/or less intense events) when the Pacific is driven into a La Niña-like mean state by radiative forcing. Hypothetically the question of ENSO variance can be examined by measuring individual planktic foraminiferal tests from within a sample interval. Koutavas et al. (2006) used d18O on single specimens of Globigerinoides ruber from the eastern equatorial Pacific to demonstrate a 50% reduction in variance at ~6 ka compared to ~2 ka, consistent with the sense of the model predictions at the orbital scale. Here we adapt this approach to Mg/Ca and apply it to the millennial-scale question. We present Mg/Ca measured on single specimens of G. bulloides (cold season) and G. ruber (warm season) from three time slices in Soledad Basin: the 20th century, the warm interval (and solar low) at 9.3 ka, and the cold interval (and solar high) at 9.8 ka. Each interval is uniformly sampled over a ~100-yr (~10-cm or more) window to ensure that our variance estimate is not biased by decadal-scale stochastic variability. Theoretically we can distinguish between changing ENSO variability and changing seasonality: a reduction in ENSO variance would result in narrowing of both the G. bulloides and G. ruber temperature distributions without necessarily changing the distance between their two medians; while a reduction in seasonality would cause the two species' distributions to move closer together.

  2. Microstructure evolution of Al/Mg butt joints welded by gas tungsten arc with Zn filler metal

    SciTech Connect

    Liu Fei; Zhang Zhaodong; Liu Liming

    2012-07-15

    Based on the idea of alloying welding seam, Gas tungsten arc welding method with pure Zn filler metal was chosen to join Mg alloy and Al alloy. The microstructures, phases, element distribution and fracture morphology of welding seams were examined. The results indicate that there was a transitional zone in the width of 80-100 {mu}m between the Mg alloy substrate and fusion zone. The fusion zone was mainly composed of MgZn{sub 2}, Zn-based solid solution and Al-based solid solution. The welding seam presented distinct morphology in different location owning to the quite high cooling rate of the molten pool. The addition of Zn metal could prevent the formation of Mg-Al intermetallics and form the alloyed welding seam during welding. Therefore, the tensile strengths of joints have been significantly improved compared with those of gas tungsten arc welded joints without Zn metal added. Highlights: Black-Right-Pointing-Pointer Mg alloy AZ31B and Al alloy 6061 are welded successfully. Black-Right-Pointing-Pointer Zinc wire is employed as a filler metal to form the alloyed welding seam. Black-Right-Pointing-Pointer An alloyed welding seam is benefit for improving of the joint tensile strength.

  3. Photocatalytic decomposition of Congo red under visible light irradiation using MgZnCr-TiO2 layered double hydroxide.

    PubMed

    Ma, Chi; Wang, Fenghua; Zhang, Chang; Yu, Zhigang; Wei, Jingjing; Yang, Zhongzhu; Li, Yongqiu; Li, Zihao; Zhu, Mengying; Shen, Liuqing; Zeng, Guangming

    2017-02-01

    The new nanophotocatalyst MgZnCr-TiO2 was prepared by co-precipitation under different molar ratio of metals (Zn:Cr) and the loaded amount of TiO2. And it was characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy et al. Langmuir model fitted well the adsorption isotherm with the value of R(2) 0.9765, the maximum adsorption capacity was 526.32 mg g(-1), the adsorption followed pseudo second order kinetic by MgZnCr-TiO2 (1:1:2-0.05). The photocatalytic oxidation of Congo red was used to determine the photocatalytic performance of MgZnCr-TiO2 (1:1:2-0.05) under visible light irradiation, and the removal rate reached 98% after reaction for 40 min. The degradation mechanism of Congo red also was proposed, and the MgZnCr-TiO2 (1:1:2-0.05) was stable after five cycles. Compared to the adsorption, Congo red was removed fundamentally by photocatalysis and it is expected to be an effective way to eliminate Congo red.

  4. Linear-Source Ultrasonic Spray Chemical Vapor Deposition Method for Fabrication of ZnMgO Films and Ultraviolet Photodetectors

    NASA Astrophysics Data System (ADS)

    Kamada, Yudai; Kawaharamura, Toshiyuki; Nishinaka, Hiroyuki; Fujita, Shizuo

    2006-08-01

    A linear-source ultrasonic spray chemical vapor deposition method has been developed and applied to fabricate ZnMgO ternary alloy thin films on glass substrates. A water solution of zinc acetate and magnesium acetate was ultrasonically atomized to form aerosol particles of water containing the sources, and then they were supplied onto the heated substrate by a nitrogen carrier gas through a nozzle with a linear aperture to form ZnMgO films. The source concentration ratios in the water solution successfully controlled the solid composition and hence raised the band gap of ZnMgO up to 3.75 eV, keeping the optical transmission higher than 90% for the visible-light region. An UV photodetector fabricated using the ZnMgO film showed the photoresponsivity to be as high as a few A/W, suggesting that this simple and cost-effective technique is promising for fabricating ZnMgO films for various applications.

  5. Epitaxial wurtzite-MgZnO barrier based magnetic tunnel junctions deposited on a metallic ferromagnetic electrode

    SciTech Connect

    Belmoubarik, M. Al-Mahdawi, M.; Sato, H.; Nozaki, T.; Sahashi, M.

    2015-06-22

    An epitaxial wurtzite (WZ) Mg{sub 0.23}Zn{sub 0.77}O barrier based magnetic tunnel junction (MTJ), with electrode-barrier structure of Co{sub 0.30}Pt{sub 0.70} (111)/Mg{sub 0.23}Zn{sub 0.77}O (0001)/Co (0001), was fabricated. The good crystallinity and tunneling properties were experimentally confirmed. Electrical and magnetic investigations demonstrated its high resistance-area product of 1.05 MΩ μm{sup 2}, a maximum tunneling magneto-resistance (TMR) of 35.5%, and the existence of localized states within the tunneling barrier producing TMR rapid decrease and oscillation when increasing the applied bias voltage. The TMR value almost vanished at 200 K, which was attributed to the induced moment and strong spin-orbit coupling in Pt atoms at the Co{sub 0.30}Pt{sub 0.70}/Mg{sub 0.23}Zn{sub 0.77}O interface. Owing to the ferroelectric behavior in WZ-MgZnO materials, the fabrication of WZ-MgZnO barrier based MTJs deposited on a metallic ferromagnetic electrode will open routes for electrically controllable non-volatile devices that are compatible with CMOS technology.

  6. Factors Affecting the Hydrogen Environment Assisted Cracking Resistance of an Al-Zn-Mg-(Cu) Alloy

    SciTech Connect

    G.A. Young; J.R. Scully

    2001-09-12

    It is well established that Al-Zn-Mg-(Cu) aluminum alloys are susceptible to hydrogen environment assisted cracking (HEAC) when exposed to aqueous environments. In Al-Zn-Mg-Cu alloys, overaged tempers are commonly used to increase HEAC resistance at the expense of strength. Overaging has little benefit in low copper alloys. However, the mechanism or mechanisms by which overaging imparts HEAC resistance is poorly understood. The present research investigated hydrogen uptake, diffusion, and crack growth rate in 90% relative humidity (RH) air for both a commercial copper bearing Al-Zn-Mg-Cu alloy (AA 7050) and a low copper variant of this alloy in order to better understand the factors which affect HEAC resistance. Experimental methods used to evaluate hydrogen concentrations local to a surface and near a crack tip include nuclear reaction analysis (NRA), focused ion beam, secondary ion mass spectroscopy (FIB/SIMS) and thermal desorption spectroscopy (TDS). When freshly bared coupons of AA 7050 are exposed to 90 C, 90% RH air, hydrogen ingress follows inverse-logarithmic-type kinetics and is equivalent for underaged (HEAC susceptible) and overaged (HEAC resistant) tempers. However, when the native oxide is allowed to form (24 hrs in 25 C, 40% RH lab air) prior to exposure to 90 C, 90% RH air, underaged alloy shows significantly greater hydrogen ingress than the overaged alloy. Humid air is a very aggressive environment producing local ({approx}1{micro}m) hydrogen concentrations in excess of 10,000 wt. ppm at 90 C. In the copper bearing alloy, overaging also effects the apparent diffusivity of hydrogen. As AA 7050 is aged from underaged {yields} peak aged {yields} overaged, the activation energy for hydrogen diffusion increases and the apparent diffusivity for hydrogen decreases, In the low copper alloy, overaging has little effect on hydrogen diffusion. Comparison of the apparent activation energies for hydrogen diffusion and for K independent (stage II) crack growth

  7. Growth of rocksalt-structured Mg x Zn1- x O (x > 0.5) films on MgO substrates and their deep-ultraviolet luminescence

    NASA Astrophysics Data System (ADS)

    Kaneko, Kentaro; Onuma, Takeyoshi; Tsumura, Keiichi; Uchida, Takayuki; Jinno, Riena; Yamaguchi, Tomohiro; Honda, Tohru; Fujita, Shizuo

    2016-11-01

    Single-phase rocksalt-structured Mg x Zn1- x O (x > 0.5) alloy films were grown on MgO substrates using the mist chemical vapor deposition method. A specular surface with a step and terrace structure was obtained. The bandgap was tuned from 5.9 to 7.8 eV as x varied from 0.5 to 1. Deep ultraviolet cathodoluminescence, stemming from near band edge transitions, was observed for Mg0.57Zn0.43O in the 4.8-5.5 eV range, peaking at ˜5.1 eV (˜240 nm) in the 12-100 K range.

  8. Impact of Mg content on native point defects in Mg{sub x}Zn{sub 1−x}O (0 ≤ x ≤ 0.56)

    SciTech Connect

    Perkins, J.; Foster, G. M.; Myer, M.; Mehra, S.; Chauveau, J. M.; Hierro, A.; Windl, W.; Brillson, L. J.

    2015-06-01

    We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar Mg{sub x}Zn{sub 1−x}O alloys over a wide (0 ≤ x ≤ 0.56) range. Within this wide range, both defect types exhibit strong Mg content-dependent surface segregation and pronounced bulk density minima corresponding to unit cell volume minima, which can inhibit defect formation due to electrostatic repulsion. Mg in ZnO significantly reduces native defect densities and their non-polar surface segregation, both major factors in carrier transport and doping of these oxide semiconductors.

  9. Effect of Ca content percentage and sintering temperature on corrosion rate in Mg-Ca composite fabricated using powder metallurgy technique

    NASA Astrophysics Data System (ADS)

    Syaza Nabilla, M. S.; Zuraidawani, C. D.; Nazree, D. M.

    2016-07-01

    Magnesium (Mg) is a good element with high potential to be used in various field of work. It has the benefit of lightweight and low density its application is limited for Mg is relatively low in term of strength. Hence, calcium (Ca) is chosen to be mixed with Mg as additional element for it is lightweight and non-toxic. In this research, Mg is prepared with different weight percentage (0, 0.5, 1, 1.5 and 2 wt. %) of Cavia powder metallurgy (PM) method. The samples were sintered at 500 and 550°Cin argon atmosphere and electrochemically using SBF solution as the electrolyte medium. The effect of Ca content on corrosion rateis investigated by focusing on the microstructure and properties of sintered sample. Increase of Ca content causes reduction in grain structure due to increase Mg2Ca phase at grain boundaries. Subsequently, reduce corrosion resistance. Hence, the amount of Ca content and sintering temperature of Mg-Ca composite is controlled to acquire optimum corrosion rate.

  10. Diagenesis of echinoderm skeletons: Constraints on paleoseawater Mg/Ca reconstructions

    NASA Astrophysics Data System (ADS)

    Gorzelak, Przemysław; Krzykawski, Tomasz; Stolarski, Jarosław

    2016-09-01

    One of the most profound environmental changes thought to be reflected in chemical composition of numerous geological archives is Mg/Ca ratio of the seawater, which has varied dramatically throughout the Phanerozoic. Echinoderms that today typically form high magnesium calcite skeletons are increasingly being utilized as a proxy for interpreting secular changes in seawater chemistry. However, accurate characterization of the diagenetic changes of their metastable high magnesium calcite skeletons is a prerequisite for assessing their original, major-element geochemical composition. Here we expand the existing models of diagenesis of echinoderm skeleton by integration of various analytical methods that up to now rarely have been used to assess the diagenetic changes of fossil echinoderms. We validated the preservation of a suite of differently preserved echinoderm ossicles, mostly crinoids, ranging in age from the Cambrian through Recent. In 13 of 99 fossil echinoderm ossicles we found well-preserved porous microstructure (stereom), non-luminescent behaviour or blotchy dark color in cathodoluminescence, and distinct nanostructural features (layered and nanocomposite structure). Moreover, in representatives of such preserved samples, distribution of sulphates associated with organic matter is identical to those in Recent echinoderms. Only such ossicles, despite of local micrometer-scale diagenetic changes, were herein considered well-preserved, retaining their original major-element skeletal composition. By contrast, majority of samples show transformation to the stable low magnesium calcite that leads to obliteration of the primary geochemical and micro/nanostructural features and is accompanied with increase in cathodoluminescence emission intensity. Using only well-preserved fossil echinoderm samples, we found purely random variation in Mg/Ca in echinoderm skeletons through the observed time series; any periodicities in echinoderm skeletal Mg/Ca ratio which might

  11. Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications for and modeling of speleothem paleoclimate records

    USGS Publications Warehouse

    Wong, C.I.; Banner, J.L.; Musgrove, M.

    2011-01-01

    A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO2 concentrations. These results are consistent with lower cave-air CO2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of caves

  12. Removal of Ca2+ and Zn2+ from aqueous solutions by zeolites NaP and KP.

    PubMed

    Yusof, Alias Mohd; Malek, Nik Ahmad Nizam Nik; Kamaruzaman, Nurul Asyikin; Adil, Muhammad

    2010-01-01

    Zeolites P in sodium (NaP) and potassium (KP) forms were used as adsorbents for the removal of calcium (Ca2+) and zinc (Zn2+) cations from aqueous solutions. Zeolite KP was prepared by ion exchange of K+ with Na+ which neutralizes the negative charge of the zeolite P framework structure. The ion exchange capacity of K+ on zeolite NaP was determined through the Freundlich isotherm equilibrium study. Characterization of zeolite KP was determined using infrared spectroscopy and X-ray diffraction (XRD) techniques. From the characterization, the structure of zeolite KP was found to remain stable after the ion exchange process. Zeolites KP and NaP were used for the removal of Ca and Zn from solution. The amount of Ca2+ and Zn2+ in aqueous solution before and after the adsorption by zeolites was analysed using the flame atomic absorption spectroscopy method. The removal of Ca2+ and Zn2+ followed the Freundlich isotherm rather than the Langmuir isotherm model. This result also revealed that zeolite KP adsorbs Ca2+ and Zn2+ more than zeolite NaP and proved that modification of zeolite NaP with potassium leads to an increase in the adsorption efficiency of the zeolite. Therefore, the zeolites NaP and KP can be used for water softening (Ca removal) and reducing water pollution/toxicity (Zn removal).

  13. Experimental Determination of the Liquidus Surface of the Cu-O-ZnO-CaO System in Equilibrium with Air

    NASA Astrophysics Data System (ADS)

    Xia, Longgong; Liu, Zhihong; Taskinen, Pekka

    2016-12-01

    Phase relationships of the Cu-O-ZnO-CaO system in equilibrium with air ( p tot = 1 atm, p_{{{{O}}2 }} = 0.21 {{atm}} ) have been studied using the equilibration and quenching technique within the temperature range from 1273 K to 1773 K (1000 °C to 1500 °C). The chemical compositions of the molten oxide and solid phases in equilibrium were analyzed by EPMA. The eutectic point in the Cu-O-ZnO-CaO system was found to be 1293 K ± 2 K (1020 °C ± 2 °C) and 0.6785 mole fraction tenorite (`CuO'), 0.1793 mole fraction halite (CaO), and 0.1422 mole fraction wurtzite (ZnO). The results from the present study have been used in constructing the liquidus surface of the Cu-O-ZnO-CaO system. The liquidus surface expands dramatically along with increasing temperature, and it moves simultaneously toward the primary phase fields of wurtzite (ZnO) and halite (CaO). The constructed liquidus surfaces have been compared with the isothermal sections (`Cu2O'-ZnO-CaO) calculated by MTDATA 5.10 software and its Mtox 8.1 database. Deviations between the thermodynamically assessed diagrams and the experimental results are significant. Thus, the system requires a reassessment.

  14. A Combined MG II/CA II Survey of Stellar Magnetic Activity in the Solar Neighborhood

    NASA Technical Reports Server (NTRS)

    Wicklund, B. M.; Donahue, R. A.; Dobson, A. K.; Baliunas, Sallie L.

    1997-01-01

    We use nearly contemporaneus low-resolution IUE observations of Mg II h + k emission and Mount Wilson Observatory Ca II H + K S indices for 33 pairs of observations of lower main sequence stars to formulate a relationship that will permit accurate predictions of S values as a function of (B - V) color and Mg II h + k flux. The resulting relationship is useful because it will extend the set of solar neighborhood stars for which a uniform estimate of chromospheric activity is available to include stars that are not observable from Mount Wilson as well as providing additional estimates of activity levels for stars that are on the Mount Wilson HK Project observing list.

  15. Mineralogy and geochemistry of Zn-rich mine-drainage precipitates from an MgO passive treatment system by synchrotron-based X-ray analysis.

    PubMed

    Pérez-López, Rafael; Macías, Francisco; Caraballo, Manuel A; Nieto, José Miguel; Román-Ross, Gabriela; Tucoulou, Rémi; Ayora, Carlos

    2011-09-15

    Synchrotron radiation-induced micro-X-ray analysis were applied to characterize the newly formed phases that precipitate in a passive treatment system using magnesium oxide to remove high concentrations of zinc (ca. 440 mg/L) and other minor metals from neutral pretreated waters in the Iberian Pyrite Belt (SW Iberian Peninsula). Micro-X-ray fluorescence (μ-XRF) maps of polished samples were used to find spatial correlations among metals, pinpointing zones of interest where micro-X-ray diffraction (μ-XRD) data were exploited to identify the mineral phases responsible for metal retention. This coupled technique identified hydrozincite (Zn(5)(CO(3))(2)(OH)(6)) and minor loseyite ((Mn,Zn)(7)(CO(3))(2)(OH)(10)) as the mineral sinks for Zn and also other potentially toxic elements such as Co and Ni. Although hydrozincite retains traces of Mn, this metal is mainly retained by precipitation of loseyite. The precipitation of zinc hydroxy-carbonates and their ability to uptake other metals (Mn, Co, and Ni) is hence of potential interest not only for the treatment of contaminated waters but also for the generation of a solid waste that could be exploited as a new Zn economic resource.

  16. Microstructure and mechanical properties of the micrograined hypoeutectic Zn-Mg alloy

    NASA Astrophysics Data System (ADS)

    Kubásek, J.; Vojtěch, D.; Pospíšilová, I.; Michalcová, A.; Maixner, J.

    2016-10-01

    A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples' mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness (Hv = 122 MPa), compressive yield strength (382 MPa), tensile yield strength (332 MPa), ultimate tensile strength (370 MPa), and elongation (9%). This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.

  17. Structure and mechanical characterization of Mg-Nd-Zn alloys prepared by different processes

    NASA Astrophysics Data System (ADS)

    Dvorský, D.; Kubásek, J.; Vojtěch, D.; Voňavková, I.; Veselý, M.; Čavojský, M.

    2017-02-01

    Magnesium alloys containing about 3 wt. % of Nd and 0.5 wt. % of Zn are considered as promising materials for application in transport and medical industry. Properly treated materials can reach ultimate tensile strength (UTS) higher than 300 MPa. Also the corrosion resistance of these alloys is superior to many other magnesium-based materials. Present work is focused on the preparation of Mg-3Nd-0.5Zn magnesium alloy by classical casting and subsequent thermal treatment. As-cast material was extruded at 400 °C, with extrusion ratio equal to 16 and velocity of 0.2 mm/s. The effect of thermal treatment and also strong plastic deformation during extrusion on final structure conditions and mechanical properties is specified. Present results confirm significant improvement of tensile yield strength (TYS) and UTS after extrusion process as a consequence of fine-grained structure combined with precipitation strengthening. Beside, texture strengthening in the direction parallel to the extrusion has been observed too.

  18. Post-Mesozoic Rapid Increase of Seawater Mg/Ca due to Enhanced Mantle-Seawater Interaction

    PubMed Central

    Ligi, Marco; Bonatti, Enrico; Cuffaro, Marco; Brunelli, Daniele

    2013-01-01

    The seawater Mg/Ca ratio increased significantly from ~ 80 Ma to present, as suggested by studies of carbonate veins in oceanic basalts and of fluid inclusions in halite. We show here that reactions of mantle-derived peridotites with seawater along slow spreading mid-ocean ridges contributed to the post-Cretaceous Mg/Ca increase. These reactions can release to modern seawater up to 20% of the yearly Mg river input. However, no significant peridotite-seawater interaction and Mg-release to the ocean occur in fast spreading, East Pacific Rise-type ridges. The Mesozoic Pangean superocean implies a hot fast spreading ridge system. This prevented peridotite-seawater interaction and Mg release to the Mesozoic ocean, but favored hydrothermal Mg capture and Ca release by the basaltic crust, resulting in a low seawater Mg/Ca ratio. Continent dispersal and development of slow spreading ridges allowed Mg release to the ocean by peridotite-seawater reactions, contributing to the increase of the Mg/Ca ratio of post-Mesozoic seawater. PMID:24067442

  19. Post-mesozoic rapid increase of seawater Mg/Ca due to enhanced mantle-seawater interaction.

    PubMed

    Ligi, Marco; Bonatti, Enrico; Cuffaro, Marco; Brunelli, Daniele

    2013-09-25

    The seawater Mg/Ca ratio increased significantly from ~ 80 Ma to present, as suggested by studies of carbonate veins in oceanic basalts and of fluid inclusions in halite. We show here that reactions of mantle-derived peridotites with seawater along slow spreading mid-ocean ridges contributed to the post-Cretaceous Mg/Ca increase. These reactions can release to modern seawater up to 20% of the yearly Mg river input. However, no significant peridotite-seawater interaction and Mg-release to the ocean occur in fast spreading, East Pacific Rise-type ridges. The Mesozoic Pangean superocean implies a hot fast spreading ridge system. This prevented peridotite-seawater interaction and Mg release to the Mesozoic ocean, but favored hydrothermal Mg capture and Ca release by the basaltic crust, resulting in a low seawater Mg/Ca ratio. Continent dispersal and development of slow spreading ridges allowed Mg release to the ocean by peridotite-seawater reactions, contributing to the increase of the Mg/Ca ratio of post-Mesozoic seawater.

  20. Effect of heat treatment on microwave absorption properties of Ni-Zn-Mg-La ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Wei, Shicheng; Xu, Binshi; Wang, Yujiang; Tian, Haoliang; Tong, Hui

    2014-01-01

    Spinel structure Ni-Zn-Mg-La ferrites have been prepared by the sol-gel route and investigated as a radar absorbing material (RAM) in a frequency range of 1-18 GHz. The structure and morphological studies on the nanoparticles of the ferrites have been carried out using X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The complex permeability and complex permittivity are measured by a network analyzer. The electromagnetic wave loss and microwave absorbing property are studied as a function of frequency, annealing temperature and thickness of the absorber. The results indicate that electromagnetic wave loss of the ferrite only annealed at 850 °C shows two peaks. The reflection loss varies with the change of the annealing temperature. The absorber annealed at 850 °C exhibits the best microwave absorbing properties, which is suitable for microwave absorption materials.

  1. Enhanced field emission from ZnO nanowire arrays utilizing MgO buffer between seed layer and silicon substrate

    NASA Astrophysics Data System (ADS)

    Chen, Si; Chen, Jiangtao; Liu, Jianlin; Qi, Jing; Wang, Yuhua

    2016-11-01

    Field emitters based on ZnO nanowires and other nanomaterials are promising high-brightness electron sources for field emission display, microscopy and other applications. The performance of a ZnO nanowire field emitter is linked to the quality, conductivity and alignment of the nanowires on a substrate, therefore requiring ways to improve these parameters. Here, ZnO nanowire arrays were grown on ZnO seed layer on silicon substrate with MgO buffer between the seed layer and Si. The turn-on field and enhancement factor of these nanowire arrays are 3.79 V/μm and 3754, respectively. These properties are improved greatly compared to those of ZnO nanowire arrays grown on ZnO seed layer without MgO buffer, which are 5.06 V/μm and 1697, respectively. The enhanced field emission properties can be attributed to better electron transport in seed layer, and better nanowire alignment because of MgO buffer.

  2. Resistivity Changes Due to Precipitation Effects in Fibre Reinforced Mg-Al-Zn-Mn Alloy

    NASA Astrophysics Data System (ADS)

    Kiehn, J.; Kainer, K. U.; Vostrý, P.; Stulíková, I.

    1997-05-01

    The change of electrical properties of alumina short fibre reinforced Mg-Al-Zn-Mn alloy AZ91D during isochronal annealing up to 300 °C is discussed. The Saffil® fibres were incorporated into the magnesium alloy by direct squeeze casting. The fibre distribution is random planar parallel to the flat faces of the dc four-point resistivity specimens machined from the solution treated castings. A sharp drop of resistivity between 140 and 260 °C is explained by the formation of incoherent -phase particles. Some practical recommendations concerning the use of alumina short fibre reinforced AZ91 alloy are made on the basis of the results obtained. Es werden die Änderungen der elektrischen Eigenschaften der aluminiumoxid-kurzfaserverstärkten Mg-Al-Zn-Mn Legierung AZ91D während isochroner Wärmebehandlungen bis 300 °C diskutiert. Das direkte Preßgießverfahren diente zur Herstellung der Saffil®-Faser Magnesium Verbundwerkstoffe. Die Proben zur Widerstandsmessung nach der Vier-Punkt Methode wurden durch spanende Bearbeitung aus den lösungsgeglühten Preßgußstücken herausgearbeitet, so daß sie regellose Faserverteilung in den Ebenen parallel zu den flachen Probenseiten aufwiesen. Ein starker Abfall des elektrischen Widerstands im Temperaturbereich zwischen 140 und 260 °C wird durch die Bildung inkohärenter β-Phase erklärt. Auf Grundlage der Ergebnisse werden einige Empfehlungen zur Anwendung der kurzfaserverstärkten Legierung AZ91 gegeben.

  3. Mg-Zn based composites reinforced with bioactive glass (45S5) fabricated via powder metallurgy

    NASA Astrophysics Data System (ADS)

    Ab llah, N.; Jamaludin, S. B.; Daud, Z. C.; Zaludin, M. A. F.

    2016-07-01

    Metallic implants are shifting from bio-inert to bioactive and biodegradable materials. These changes are made in order to improve the stress shielding effect and bio-compatibility and also avoid the second surgery procedure. Second surgery procedure is required if the patient experienced infection and implant loosening. An implant is predicted to be well for 15 to 20 years inside patient body. Currently, magnesium alloys are found to be the new biomaterials because of their properties close to the human bones and also able to degrade in the human body. In this work, magnesium-zinc based composites reinforced with different content (5, 15, 20 wt. %) of bioactive glass (45S5) were fabricated through powder metallurgy technique. The composites were sintered at 450˚C. Density and porosity of the composites were determined using the gas pycnometer. Microstructure of the composites was observed using an optical microscope. In-vitro bioactivity behavior was evaluated in the simulated body fluid (SBF) for 7 days. Fourier Transform Infrared (FTIR) was used to characterize the apatite forming on the samples surface. The microstructure of the composite showed that the pore segregated near the grain boundaries and bioglass clustering was observed with increasing content of bioglass. The true density of the composites increased with the increasing content of bioglass and the highest value of porosity was indicated by the Mg-Zn reinforced with 20 wt.% of bioglass. The addition of bio-glass to the Mg-Zn has also induced the formation of apatite layer after soaking in SBF solution.

  4. Microstructure and Mechanical Properties of Mg-6Zn-2Sn-1Al Alloy Designed by Numerical Analysis with Extrusion Process

    NASA Astrophysics Data System (ADS)

    Lee, K. W.; Lee, B. D.; Baek, U. H.; Kwon, E. H.; Han, J. W.

    2015-03-01

    In the extrusion process, the temperature of the workpiece results in non-uniformity of dimensions, microstructure, and mechanical properties of the product. Although many researchers are expected to participate in the extrusion behavior of Mg alloys, no specific information is available yet to clarify their roles in extrusion process of Mg alloys because of a wide variety of compositions. In this study, a good understanding the role of die in the extrusion process is expected to contribute to the improvement of processing efficiency for Mg-6Zn-2Sn-1Al alloy. To design Mg-6Zn-2Sn-1Al alloy, the parameters, such as temperature and angle of the designed materials, were determined using the commercial software DEFORM 3D. With this simulation model, the real-time extrusion temperature and angle of the die were adjusted according to the simulation results. Using the optimal extrusion process predicted by finite element method analysis, the Mg-6Zn-2Sn-1Al alloy was manufactured. Also, the extruded Mg-6Zn-2Sn-1Al alloys were evaluated on the microstructure and mechanical properties.

  5. Characterization of Porous Mg-Zn Alloy Using X-Ray Tomography and its Drug-Loading Behavior

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Li, Kaikai; Zhang, Yuhong; Yan, Biao; Lu, Wei

    2013-07-01

    Porous Mg alloys will be promising orthopedic implants materials. In this study, porous Mg-Zn alloy with a porosity of 30% was prepared by powder metallurgy process. XRD was used to examine the composition of the sample and synchrotron radiation-based X-ray micro-computed tomography (SR-μCT) was used to investigate the pore properties of the sample. The results showed that the sample comprised a single Mg phase and a Mg2Zn11 phase. The SR-μCT results showed that the porosity of the sample is about 30% which is approximate to the theoretical porosity. The pore morphology was irregular and the largest pore was about 200 μm in diameter. And a large pore cluster was identified meaning that most of the pores in the sample were interconnected with each other. This is beneficial for the materials transformation after the implantation of the sample in human body, which will boost the bone regeneration. Drug-loading experiment showed that Ibuprofen can be successfully loaded in porous Mg-Zn alloy, which means that porous Mg-Zn alloy could be an orthopedic drug delivery system (DDS).

  6. Determination of Ca, K, Mg and Fe in four fish species by FAAS

    NASA Astrophysics Data System (ADS)

    Cui, Xiaoli; Wang, Yijun; She, Xilin

    2010-09-01

    A method for determining calcium (Ca), potassium (K), magnesium (Mg) and iron (Fe) in four fish species was optimized and validated. It included microwave mineralization of the samples and subsequent quantification by flame atomic absorption spectroscopy (FAAS) with Zeeman-effect background correction. Using HNO3 (65%) and H2O2 (33%) as extraction solutions, the optimal conditions of extraction were established as follows: 0.5 g of sample mass; microwave time program of 300 W/5 min and 600 W/5 min. The method was free of matrix interferences. The linear correlation coefficients were ⩾0.9991, the recovery percentage of analytes was from 99.31% to 103.70% and the RSD (relative standard deviation) was lower than 2.06%. The detection limits obtained were 32.3, 43.2, 14.0 and 68.6 ng mL-1 for Ca, K, Mg and Fe in FAAS respectively. It is shown that the method is rapid, simple, sensitive and accurate. The method was applied to the studies of digestibility and measurement of these nutrients in samples of fish collected from Norway, Japan and China.

  7. Intrinsic Proton NMR Studies of Mg(OH)2 and Ca(OH)2

    NASA Astrophysics Data System (ADS)

    Itoh, Yutaka; Isobe, Masahiko

    2016-09-01

    We studied the short proton free induction decay signals and the broad 1H NMR spectra of Mg(OH)2 and Ca(OH)2 powders at 77-355 K and 42 MHz using pulsed NMR techniques. Using a Gaussian-type back extrapolation procedure for the obscured data of the proton free induction decay signals, we obtained more precise values of the second moments of the Fourier-transformed broad NMR spectra than those in a previous report [Y. Itoh and M. Isobe, http://doi.org/10.7566/JPSJ.84.113601, J. Phys. Soc. Jpn. 84, 113601 (2015)] and compared with the theoretical second moments. The decrease in the second moment could not account for the large decrease in the magnitude of the intrinsic proton spin-lattice relaxation rate 1/T1 from Mg(OH)2 to Ca(OH)2. The analysis of 1/T1 ∝ exp(-Eg/kBT) with Eg ˜ 0.01 eV points to a local hopping mechanism, and that of 1/T1 ∝ Tn with n ˜ 0.5 points to an anharmonic rattling mechanism.

  8. Glass-ceramic coated Mg-Ca alloys for biomedical implant applications.

    PubMed

    Rau, J V; Antoniac, I; Fosca, M; De Bonis, A; Blajan, A I; Cotrut, C; Graziani, V; Curcio, M; Cricenti, A; Niculescu, M; Ortenzi, M; Teghil, R

    2016-07-01

    Biodegradable metals and alloys are promising candidates for biomedical bone implant applications. However, due to the high rate of their biodegradation in human body environment, they should be coated with less reactive materials, such, for example, as bioactive glasses or glass-ceramics. Fort this scope, RKKP composition glass-ceramic coatings have been deposited on Mg-Ca(1.4wt%) alloy substrates by Pulsed Laser Deposition method, and their properties have been characterized by a number of techniques. The prepared coatings consist of hydroxyapatite and wollastonite phases, having composition close to that of the bulk target material used for depositions. The 100μm thick films are characterized by dense, compact and rough morphology. They are composed of a glassy matrix with various size (from micro- to nano-) granular inclusions. The average surface roughness is about 295±30nm due to the contribution of micrometric aggregates, while the roughness of the fine-texture particulates is approximately 47±4nm. The results of the electrochemical corrosion evaluation tests evidence that the RKKP coating improves the corrosion resistance of the Mg-Ca (1.4wt%) alloy in Simulated Body Fluid.

  9. The effect of light on intrashell trace metal variability (Mg/Ca and Sr/Ca) in the planktic foraminifer Orbulina universa

    NASA Astrophysics Data System (ADS)

    Fehrenbacher, J. S.; Spero, H. J.; Russell, A. D.; Gagnon, A. C.; Vetter, L.; Snyder, J.; Naumann, E.; Grimm, B. L.; Holland, K.

    2012-12-01

    The shell walls of many planktic foraminifers contain alternating bands of high and low Mg/Ca calcite. These bands have been attributed to chamber formation, light-modulated (circadian-like) biological effects, and light (e.g. pH change in the calcifying environment driven by the photosynthesis/respiration of photosynthetic symbionts). Previous experiments on the living planktic foraminifer Orbulina universa confirm a diurnal nature in the banding of O. universa: a wide band of low-Mg calcite forms during the day (12-hour light) and a narrower band of high Mg calcite forms at night (12-hour dark) (Spero et al., in prep). During the summer of 2011, we explored the response of Mg banding to light by culturing foraminifera at constant temperature, salinity, and ambient seawater pH, but with different light schedules: reverse light cycles (day/night cycle shifted by 12 hours), constant (24-hour) light, and constant (24-hour) dark conditions. We used an artificial Ba spike to mark 12-hour intervals of growth, regardless of the imposed light regime. In specimens grown with a reversed day/night light/dark cycle, we observe an immediate shift in the timing of Mg/Ca banding. The timing of high and low Mg/Ca bands in these specimens is indistinguishable from specimens grown under a normal day/night light/dark cycle. Mg/Ca bands are present in some of the specimens cultured in constant light and in all specimens grown in constant dark conditions. Banding in the constant light and constant dark specimens is not paced by a diurnal cycle. The amplitude of the banding in these specimens is diminished and the average Mg/Ca ratios are 30% lower in comparison to those kept on a 12-hour light/dark cycle. Additionally, we find the Sr/Ca ratios are similar in both the constant light and reverse light/dark specimens, but are statistically significantly lower in the constant dark specimens (8% lower, p-value << 0.05). These results indicate that changes in microenvironment pH due to

  10. Microstructures, mechanical and corrosion properties and biocompatibility of as extruded Mg-Mn-Zn-Nd alloys for biomedical applications.

    PubMed

    Zhou, Ying-Long; Li, Yuncang; Luo, Dong-Mei; Ding, Yunfei; Hodgson, Peter

    2015-04-01

    Extruded Mg-1Mn-2Zn-xNd alloys (x=0.5, 1.0, 1.5 mass %) have been developed for their potential use as biomaterials. The extrusion on the alloys was performed at temperature of 623K with an extrusion ratio of 14.7 under an average extrusion speed of 4mm/s. The microstructure, mechanical property, corrosion behavior and biocompatibility of the extruded Mg-Mn-Zn-Nd alloys have been investigated in this study. The microstructure was examined using X-ray diffraction analysis and optical microscopy. The mechanical properties were determined from uniaxial tensile and compressive tests. The corrosion behavior was investigated using electrochemical measurement. The biocompatibility was evaluated using osteoblast-like SaOS2 cells. The experimental results indicate that all extruded Mg-1Mn-2Zn-xNd alloys are composed of both α phase of Mg and a compound of Mg7Zn3 with very fine microstructures, and show good ductility and much higher mechanical strength than that of cast pure Mg and natural bone. The tensile strength and elongation of the extruded alloys increase with an increase in neodymium content. Their compressive strength does not change significantly with an increase in neodymium content. The extruded alloys show good biocompatibility and much higher corrosion resistance than that of cast pure Mg. The extruded Mg-1Mn-2Zn-1.0Nd alloy shows a great potential for biomedical applications due to the combination of enhanced mechanical properties, high corrosion resistance and good biocompatibility.

  11. Differential Vulnerability of CA1 versus CA3 Pyramidal Neurons After Ischemia: Possible Relationship to Sources of Zn2+ Accumulation and Its Entry into and Prolonged Effects on Mitochondria.

    PubMed

    Medvedeva, Yuliya V; Ji, Sung G; Yin, Hong Z; Weiss, John H

    2017-01-18

    Excitotoxic mechanisms contribute to the degeneration of hippocampal pyramidal neurons after recurrent seizures and brain ischemia. However, susceptibility differs, with CA1 neurons degenerating preferentially after global ischemia and CA3 neurons after limbic seizures. Whereas most studies address contributions of excitotoxic Ca(2+) entry, it is apparent that Zn(2+) also contributes, reflecting accumulation in neurons either after synaptic release and entry through postsynaptic channels or upon mobilization from intracellular Zn(2+)-binding proteins such as metallothionein-III (MT-III). Using mouse hippocampal slices to study acute oxygen glucose deprivation (OGD)-triggered neurodegeneration, we found evidence for early contributions of excitotoxic Ca(2+) and Zn(2+) accumulation in both CA1 and CA3, as indicated by the ability of Zn(2+) chelators or Ca(2+) entry blockers to delay pyramidal neuronal death in both regions. However, using knock-out animals (of MT-III and vesicular Zn(2+) transporter, ZnT3) and channel blockers revealed substantial differences in relevant Zn(2+) sources, with critical contributions of presynaptic release and its permeation through Ca(2+)- (and Zn(2+))-permeable AMPA channels in CA3 and Zn(2+) mobilization from MT-III predominating in CA1. To assess the consequences of the intracellular Zn(2+) accumulation, we used OGD exposures slightly shorter than those causing acute neuronal death; under these conditions, cytosolic Zn(2+) rises persisted for 10-30 min after OGD, followed by recovery over ∼40-60 min. Furthermore, the recovery appeared to be accompanied by mitochondrial Zn(2+) accumulation (via the mitochondrial Ca(2+) uniporter MCU) in CA1 but not in CA3 neurons and was markedly diminished in MT-III knock-outs, suggesting that it depended upon Zn(2+) mobilization from this protein.

  12. Hyperpolarizabilities of alkaline-earth metal ions Be+, Mg+, and Ca+

    NASA Astrophysics Data System (ADS)

    Yin, Dong; Zhang, Yong-Hui; Li, Cheng-Bin; Gao, Ke-Lin; Shi, Ting-Yun

    2016-09-01

    The knowledge of the hyperpolarizabilities of atoms and ions is helpful for the analysis of the high order effects of the frequency shifts in precision spectroscopy experiments. Liu et al. [Phys. Rev. Lett. 114, 223001 (2015)] proposed to establish all-optical trapped ion clocks using laser at the magic wavelength for clock transition. To evaluate the high-order frequency shifts in this new scheme of optical clocks, hyperpolarizabilities are needed, but absent. Using the finite field method based on the B-spline basis set and model potentials, we calculated the electric-field-dependent energy shifts of the ground and low-lying excited states in Be+, Mg+, and Ca+ in the field strength range of 0.0-6×10-5 a.u.. The scalar and tensor polarizabilities ( α 0, α 2) and hyperpolarizabilities ( γ 0, γ 2, γ 4) were deduced. The results of the hyperpolarizabilities for Be+ showed good agreement with the values in literature, implying that the present method can be applied for the effective estimation of the atomic hyperpolarizabilities, which are rarely reported but needed in experiments. The feasibility of optical trapping of Ca+ is discussed, and the contributions of hyperpolarizabilities to the transition frequency shift for Ca+ in the optical dipole trap are estimated using quasi-electrostatic approximation.

  13. Retina specific GCAPs in zebrafish acquire functional selectivity in Ca2+-sensing by myristoylation and Mg2+-binding

    PubMed Central

    Sulmann, Stefan; Vocke, Farina; Scholten, Alexander; Koch, Karl-Wilhelm

    2015-01-01

    Zebrafish photoreceptor cells express six guanylate cyclase-activating proteins (zGCAPs) that share a high degree of amino acid sequence homology, but differ in Ca2+-binding properties, Ca2+-sensitive target regulation and spatial-temporal expression profiles. We here study a general problem in cellular Ca2+-sensing, namely how similar Ca2+-binding proteins achieve functional selectivity to control finely adjusted cellular responses. We investigated two parameters of critical importance for the trigger and switch function of guanylate cyclase-activating proteins: the myristoylation status and the occupation of Ca2+-binding sites with Mg2+. All zGCAPs can be myristoylated in living cells using click chemistry. Myristoylation does not facilitate membrane binding of zGCAPs, but it significantly modified the regulatory properties of zGCAP2 and zGCAP5. We further determined for all zGCAPs at least two binding sites exhibiting high affinities for Ca2+ with KD values in the submicromolar range, whereas for other zGCAPs (except zGCAP3) the affinity of the third binding site was in the micromolar range. Mg2+ either occupied the low affinity Ca2+-binding site or it shifted the affinities for Ca2+-binding. Hydrodynamic properties of zGCAPs are more influenced by Ca2+ than by Mg2+, although to a different extent for each zGCAP. Posttranslational modification and competing ion-binding can tailor the properties of similar Ca2+-sensors. PMID:26061947

  14. Study on biodegradation of the second phase Mg17Al12 in Mg-Al-Zn alloys: in vitro experiment and thermodynamic calculation.

    PubMed

    Liu, Chen; Yang, Huazhe; Wan, Peng; Wang, Kehong; Tan, Lili; Yang, Ke

    2014-02-01

    The in vitro biodegradation behavior of Mg17Al12 as a second phase in Mg-Al-Zn alloys was investigated via electrochemical measurement and immersion test. The Hank's solutions with neutral and acidic pH values were adopted as electrolytes to simulate the in vivo environment during normal and inflammatory response process. Furthermore, the local orbital density functional theory approach was employed to study the thermodynamical stability of Mg17Al12 phase. All the results proved the occurrence of pitting corrosion process with crackings for Mg17Al12 phase in Hank's solution, but with a much lower degradation rate compared with both AZ31 alloy and pure magnesium. Furthermore, a preliminary explanation on the biodegradation behaviors of Mg17Al12 phase was proposed.

  15. Wavefunction Engineering of Spintronic devices in ZnO/MgO and GaN/AlN Quantum Structures Doped with Transition Metal Ions

    DTIC Science & Technology

    2006-08-01

    modeling terahertz lasers in the wurtzite materials such as ZnO/MgZnO (or even in GaN /AlGaN quantum well structures) when we ’L. R. Ram-Mohan, "Finite...06 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Wavefunction Engineering of Spintronic Devices in ZnO/MgO & GaN /AIN Quantum Structures Doped with...wurtzite heterostructures of ZnO/MgZnO and GaN /AlGaN systems grown on R-plane sapphire. The FEM approach gives wavefunctions and allows device modeling

  16. Static mechanical properties for Ca48Mg27Cu25 bulk metallic glass by ultrasonic velocity measurement

    NASA Astrophysics Data System (ADS)

    Okai, D.; Inoue, M.; Mori, T.; Fukami, T.; Kobayashi, E.; Yamasaki, T.; Kimura, H. M.; Inoue, A.

    2009-01-01

    The static mechanical properties of a Ca48Mg27Cu25 bulk metallic glass were investigated using a technique of ultrasonic measurement and compressive test. The Young's modulus (E), Poisson's ratio (v), shear modulus (G) and bulk modulus (B) for the Ca48Mg27Cu25 alloy at room temperature are significantly smaller than those for Zr- and Pd- based bulk metallic glasses. The values of E, v, G and B for the Ca48Mg27Cu25 alloy are 29.8GPa, 0.230, 12.1GPa and 18.4GPa, respectively. The results of compression test for the Ca48Mg27Cu25 alloy have been also described.

  17. Effects of phosphates on microstructure and bioactivity of micro-arc oxidized calcium phosphate coatings on Mg-Zn-Zr magnesium alloy.

    PubMed

    Pan, Y K; Chen, C Z; Wang, D G; Zhao, T G

    2013-09-01

    Calcium phosphate (CaP) coatings were prepared on Mg-Zn-Zr magnesium alloy by micro-arc oxidation (MAO) in electrolyte containing calcium acetate monohydrate (CH3COO)2Ca·H2O) and different phosphates (i.e. disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), sodium phosphate (Na3PO4·H2O) and sodium hexametaphosphate((NaPO3)6)). Scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray diffractometer (XRD) were employed to characterize the microstructure, elemental distribution and phase composition of the CaP coatings. Simulated body fluid (SBF) immersion test was used to evaluate the coating bioactivity and degradability. Systemic toxicity test was used to evaluate the coating biocompatibility. Fluoride ion selective electrode (ISE) was used to measure F(-) ions concentration during 30 days SBF immersion. The CaP coatings effectively reduced the corrosion rate and the surfaces of CaP coatings were covered by a new layer formed of numerous needle-like and scale-like apatites. The formation of these calcium phosphate apatites indicates that the coatings have excellent bioactivity. The coatings formed in (NaPO3)6-containging electrolyte exhibit thicker thickness, higher adhesive strength, slower degradation rate, better apatite-inducing ability and biocompatibility.

  18. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    SciTech Connect

    Guer, Emre; Tabares, G.; Hierro, A.; Chauveau, J. M.

    2012-12-15

    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  19. Does a calmodulin-dependent Ca2+-regulated Mg2+-dependent ATPase contribute to hepatic microsomal calcium uptake?

    PubMed Central

    Schütze, S; Söling, H D

    1987-01-01

    Solubilization of microsomal proteins followed by calmodulin affinity chromatography resulted in the separation of two distinct Ca2+-Mg2+-ATPases (Ca2+-regulated Mg2+-dependent ATPases), one being insensitive to calmodulin (ATPase-1), the other being stimulated about 5-fold by calmodulin (ATPase-2). ATPase-2 accounts for only 8% of total microsomal Ca2+-Mg2+-ATPase-activity. ATPase-1 and -2 can also be distinguished by different pH optima, different sensitivity towards inhibition by vanadate and LaCl3, and different apparent Mr values of the phosphoenzyme intermediates (115,000 and 150,000 for ATPase-1 and ATPase-2 respectively). ATPase-1 from liver co-migrated with Ca2+-Mg2+-ATPase from rat skeletal-muscle sarcoplasmic reticulum, whereas ATPase-2 from liver co-migrated with calmodulin-dependent Ca2+-Mg2+-ATPase derived from rat skeletal-muscle sarcolemma. After separation of parenchymal and nonparenchymal liver cells, a calmodulin-dependent Ca2+-Mg2+-ATPase of Mr 150,000 was found only in the non-parenchymal cells. The kinetic parameters of ATPase-2 and the similarity of the apparent Mr of its phosphoenzyme intermediate to that of skeletal-muscle sarcolemma Ca2+-Mg2+-ATPase makes it likely that the calmodulin-sensitive Ca2+-Mg2+-ATPase found in rat liver microsomal fractions reflects a contamination with plasma membranes (possibly from non-parenchymal cells) rather than a true location in the endoplasmic reticulum of parenchymal liver cells. Images Fig. 5. Fig. 6. PMID:2959269

  20. Variation of the matter densities of nuclei from /sup 40/Ca to /sup 68/Zn

    SciTech Connect

    Papanicolas, C N; Sumner, W Q; Blair, J S; Bernstein, A M

    1981-01-01

    Analysis is made of elastic scattering of 42 MeV ..cap alpha..-particles from 19 nuclei from /sup 40/Ca to /sup 68/Zn in terms of a folding model, allowing determination of matter densities in the nuclear surface region relative to that of /sup 40/Ca. Specifically, values are deduced for the radii at which the matter density equals 0.016 nucleon/fm/sup 3/ as well as matter RMS radii. The relative sizes vary more slowly than A/sup 1/3/ between /sup 40/Ca and /sup 54/Fe and more rapidly than A/sup 1/3/ between /sup 54/Fe and /sup 68/Zn. The overall trend gives an increase with A/sup 1/3/ but with a bowing effect. The near equality of proton and matter RMS radii indicates that the neutron-proton radii are approximately equal to within the errors of the present analysis. The results are in reasonable agreement with those obtained with other hadronic probes and with calculated Hartree-Fock Bogolyubov densities.

  1. Zn, Ca and Na levels in the prostatic secretion of patients with prostatic adenoma.

    PubMed

    Romics, I; Bach, D

    1991-01-01

    Zinc, calcium and sodium levels of the prostatic secretions in patients with prostatic adenoma were studied. In a control group of 20 patients, two samples of the secretion, taken on the first and the seventh day, were compared and found to show no difference. In the treated group of 20 patients, where a 7-day therapy of ERU (extractum radix urticae) followed upon the first sampling, the 7th-day specimen presented a significant drop in the Zn level. Correlation was found to exist between the Zn and Ca levels. From literary data the inference was drawn that ERU is producing a derangement in the zinc-testosterone metabolism and diminishes the zinc secretion in adenomatous tissue.

  2. Microwave sintering studies on low loss (Zn, Mg)TiO3 dielectric resonator materials.

    PubMed

    Sirugudu, Roopas Kiran; Vemuri, Rama Krishna Murthy; Murty, B S

    2013-01-01

    Low dielectric loss Zn07Mg0.3TiO3 and MgTiO3 microwave dielectric resonators were prepared by the conventional solid state reaction method. The microwave interaction with these materials has been studied using both single-mode and multimode microwave furnaces operating at a frequency of 2.45 GHz. Microwave sintering could be achieved using a multimode microwave furnace only, whereas, interaction with a single-mode furnace showed plasma generation. Phase formation was observed by X-ray diffraction. Microwave dielectric characteristics such as dielectric constant (epsilon'), quality factor (Q x f) and temperature coefficient of resonant frequency (tauf) of microwave sintered samples were measured using a vector network analyzer and compared with conventional sintered ones. Microstructure of all the conventional and microwave sintered samples was observed using high resolution scanning electron microscope. Although epsilon' and tauf of the conventional and microwave sintered samples are found to be comparable, the quality factor (the vital characteristic of dielectric resonators) of microwave sintered samples are observed to be much lower than those obtained by conventional sintering. The difference in these values is discussed with respect to the grain size.

  3. Preparation and Characterization of Mg Substituted NiCuZn Nano Ferrites for Multilayer Chip Inductors

    NASA Astrophysics Data System (ADS)

    Ch, Sujatha; Reddy K, Venugopal; Babu K, Sowri; Reddy A, R. C.; K, H. Rao

    2012-02-01

    The present paper examines the effect of magnesium substitution on structural and magnetic properties of NiCuZn nano ferrites synthesized by sol - gel method. Formation of single phase spinel structure was confirmed both from XRD and FTIR. The initial permeability shows decreasing trend with increasing Mg concentration due to reduced magnetization, grain size and increased magneto - crystalline anisotropy constant. At the same time, the cut off frequency increases with increasing Mg content. This is attributed to domain wall pinning arising due to the presence of non magnetic magnesium ions. Also the permeability is observed to be constant up to 10MHz frequency range showing compositional stability and quality of the material. The magnetic loss factor shows very low values at higher frequencies. It is concluded that even though both zinc and magnesium are non magnetic ions, substitution of one cation by another prone to influence the magnetic properties due to their change in dimension and cation distribution among the two available sites of a spinel system. These samples have advantages of low sintering temperature find applications in multilayer chip inductors due to their high and constant permeability even at higher frequencies.

  4. Exciting transition metal doped dilute magnetic thin films: MgO:Er and ZnO:Er

    NASA Astrophysics Data System (ADS)

    Ćakıcı, T.; Sarıtaş, S.; Muǧlu, G. Merhan; Yıldırım, M.

    2017-02-01

    Erbium doped MgO and doped ZnO thin films have reasonably important properties applications in spintronic devices. These films were synthesized on glass substrates by Chemical Spray Pyrolysis (CSP) method. In the literature there has been almost no report on preparation of MgO:Er dilute magnetic thin films by means of CSP. Because doped thin films show different magnetic behaviors, depending upon the type of magnetic material ions, concentration of them, synthesis route and experimental conditions, synthesized MgO:Er and ZnO:Er films were compared to thin film properties. Optical analyses of the synthesized thin films were examined spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. Structural analysis of the thin films was examined by using XRD, Raman Analysis, FE-SEM, EDX and AFM techniques. Also, magnetic properties of the MgO:Er and ZnO:Er films were investigated by vibrating sample magnetometer (VSM) which show that diamagnetic behavior of the MgO:Er thin film and ferromagnetic (FM) behavior of the ZnO:Er film were is formed.

  5. Using Mg/Ca on oyster shells as paleoclimatic proxy, example from the Paleogene of Central Asia.

    NASA Astrophysics Data System (ADS)

    Bougeois, Laurie; de Rafélis, Marc; Reichart, Gert-Jan; de Nooijer, Lennart; Dupont-Nivet, Guillaume

    2015-04-01

    Due to their large occurrence in sedimentary records from Triassic to Quaternary, their strong resistance to post-mortem alteration, and the incremental nature of their shell growth, oysters are recognized to be a highly powerful tool to infer infra-annual paleoclimate variations. However, the common use of δ18O in biomineralisation to infer paleotemperatures is hindered by the difficulties in valuating δ18O of sea water (δ18Osw). If the δ18Osw values can be fairly well estimated when orking at the million-year time scale, the estimation of the infra-annual variation of the δ18Osw constitutes a considerable barrier for high-resolution paleo-reconstitutions. This issue can be resolved using the Mg/Ca ratio as a suitable and valuable independent high-resolution paleothermometer in oyster shells. However, if numerous studies provided new paleothermometer using Mg/Ca ratio in calcitic bivalve shells, their application to paleo-studies remains to be established. In this study, we combine incremental δ18O analyses with Mg/Ca ratio on Paleogene oyster shells from the Proto-Paratethys (Central Asia) that is characterized by high seasonal variability. We analysed various species growing in different depositional environments throughout late Paleocene to late Eocene times. Results from both proxies show consistent values from oysters of the same age and of the same species, attesting for the consistent Mg incorporation into shells. However, the Mg/Ca-T calibrations tested in this study reveals the importance of specie-specific effect for the incorporation of Mg, as well as the environment. This enables discarding results inappropriate for existing Mg/Ca calibrations and identifying those yielding meaningful paleo-temperatures. In particular, the consistency of the Mg/Ca temperature proxies yielded by the species Ostrea (T.) strictiplicata and Sokolowia buhsii shows that, with careful data selection, Mg/Ca provides a reliable infra-annual paleotemperature proxy.

  6. Improvement of CaFe/sub 2/O/sub 4/ photocathode by doping with Na and Mg

    SciTech Connect

    Matsumoto, Y.; Sugiyama, K.; Sato, E.

    1988-05-01

    The low conductivity of CaFe/sub 2/O/sub 4/ and the nonohmic contact in the CaFe/sub 2/O/sub 4//metal interface, which lead to only a small photocurrent, were improved by doping with Na and Mg. The oxides of the Ca/sub 1-x/Na/sub x/Fe/sub 2-y/Mg/sub y/O/sub 4/ system gave the high conductivity and the ohmic contact of the oxide/Pt-Pd interface, but very small photocurrent. It was judged from the measurement of the Seebeck coefficient that the hopping mechanism is dominant for the conduction of the oxides containing Na. The hopping level is presumed to bring about the ohmic contact and the very small photocurrent because of the small band bending. The CaFe/sub 2/O/sub 4//Na,Mg electrode, where one side of the surfaces was doped with Na and Mg and the interface of CaFe/sub 2/O/sub 4//Na,Mg/Pt-Pd was ohmic contact, gave a large photocurrent. Photoelectrochemical dissolution was observed for the CaFe/sub 2/O/sub 4//Na,Mg electrode in acidic solution but not in neutral solution. The mechanism of the dissolution is also discussed.

  7. Interaction of 28Mg with Ca and K in the smooth muscle of guinea-pig taenia coli

    PubMed Central

    Sparrow, M. P.

    1969-01-01

    1. The uptake of 28Mg, and the total tissue content of Mg, Ca, Na and K have been determined in the smooth muscle of the guinea-pig taenia coli. The Mg content was 6·56 m-mole/kg fresh wt. immediately after dissection, falling slowly to 5·11 after 6 hr immersion in Krebs solution at 37° C. 2. The Mg content rose to 15·4 m-mole/kg fresh wt. during immersion in isotonic sucrose containing only MgCl2. It was independent of the Mg2+ concentration in this solution, but was depressed when K+ or Ca2+ ions were added. 3. 28Mg uptake showed three separate phases, extracellular, intermediate and slow. The size of the extracellular phase was proportional to the Mg2+ concentration in the solution, but the size of the slow phase was constant. The size of the intermediate phase, exchanging with a half-time of a few minutes, was depressed when K+ or Ca2+ ions were added. 4. The results are compatible with a competition between Mg in the intermediate phase of tracer exchange, and K+ or Ca2+ ions for fixed anionic sites in the tissue. PMID:5347717

  8. Effects of vanadium complexes supplementation on V, Cu, Mn, K, Fe, Zn, and Ca concentration in STZ diabetic rats pancreas.

    PubMed

    Krośniak, Mirosław; Kowalska, Joanna; Francik, Renata; Gryboś, Ryszard; Kwiatek, Wojciech M

    2014-01-01

    The objective of the study was to assess the effects of Na[V(V)O(O2)2(2,2'-bpy)] x 8 H2O (complex 1), Na[V(V)O(O2)2(1,10'-phen)] x 5 H2O (complex 2), Na[V(V)O(O2)2(4,4'-Me-2,2'-bpy)] x 8 H2O (complex 3), [V(V)O(SO,)(1,10'-phen)] x 2 H2O, (complex 4), [V(IV)O(SO4)(2,2'-bpy)] x H2O (complex 5), where: 2,2'-bpy = 2,2'-bipyridine, 1.10'-phen = 1,10'-phenanthroline, 4,4'-Me-2,2'-bpy = 4,4'-dimethyl-2,2'-bipyridine and a small insulin injection on V, Cu, Mn, K, Fe, Zn, and Ca concentration in the STZ (streptozotocin) diabetic rats pancreas during a 5-week treatment with the tested complexes. In all groups of animals metal concentration in the pancreas was investigated by means of Proton Induced X-ray Emission (PIXE) method. Maximum concentration of vanadium was observed in the pancreas for complex 5 (1.69 +/- 0.09 mg/kg dry weight), lower for complex 3 (1.51 +/- 0.10 mg/kg dry weight), and the lowest for complex 1 (1.21 +/- 0.27 mg/kg dry weight) supplementation. The influence of vanadium administration on other metals' concentration in the rats' pancreas was also investigated. All vanadium-tested complexes showed an increase of zinc concentration in the examined pancreas in comparison to the diabetic animals not treated with vanadium. The results were the highest for complex 1 and the lowest for complex 5. The concentration of Fe, Cu, Mn, K and Ca in the pancreas is not evidently influenced by administration of the vanadium complexes.

  9. Enhanced photocatalytic activity of TiO2-impregnated with MgZnAl mixed oxides obtained from layered double hydroxides for phenol degradation

    NASA Astrophysics Data System (ADS)

    de Almeida, Marciano Fabiano; Bellato, Carlos Roberto; Mounteer, Ann Honor; Ferreira, Sukarno Olavo; Milagres, Jaderson Lopes; Miranda, Liany Divina Lima

    2015-12-01

    A series of TiO2/MgZnAl photocatalysts were successfully synthesized from ternary (Mg, Zn and Al) layered double hydroxides impregnated with TiO2 nanoparticles by the co-precipitation method at variable pH with different Zn2+/Mg2+ molar ratios. The composite photocatalysts were calcined at 500 °C resulting in the incorporation of oxide zinc, in the calcined MgZnAl LDH structure. Synergistic effect between ZnO and TiO2 lead to significant enhancement of TiO2/MgZnAl photocatalytic activity. Composite photocatalysts were characterized by ICP-MS, N2 adsorption-desorption, XRD, SEM, EDS, IR and UV-vis DRS. Phenol in aqueous solution (50 mg/L) was used as a model compound for evaluation of UV-vis (filter cut-off for λ > 300 nm) photocatalytic activity. The most efficient photocatalyst composite was obtained at a 5% Zn2+/Mg2+ molar ratio, in the catalyst identified as TiO2/MgZnAl-5. This composite catalyst had high photocatalytic activity, completely destroying phenol and removing 80% of total organic carbon in solution after 360 min. The TiO2/MgZnAl-5 catalyst remained relatively stable, presenting a 15% decrease in phenol degradation efficiency after five consecutive photocatalytic cycles.

  10. Deep traps and photo-electric properties of p-Si/MgO/n-Zn{sub 1−x}Mg{sub x}O heterojunction

    SciTech Connect

    Placzek-Popko, E. Paradowska, K. M.; Gumienny, Z.; Biegański, P.; Pietrzyk, M. A.; Kozanecki, A.

    2015-08-21

    In the paper, the photoluminescence (PL) measurements, current–voltage–temperature (I-V-T) measurements, space charge techniques (C-V and deep level transient spectroscopy (DLTS)), and photocurrent spectral characteristics have been applied to investigate defects in p-Si/MgO/ n-Zn{sub 1−x}Mg{sub x}O heterojunction (HJ). The HJ structure was grown on p-type Si (111) substrate with resistivity equal to 0.1 Ω cm by the plasma-assisted molecular beam epitaxy technique. A radio-frequency cell was used for the generation of oxygen plasma. PL spectrum let us determine the Mg content ∼10%. Besides the excitonic Zn{sub 0.9}Mg{sub 0.1}O line, the PL spectrum also contains green and yellow emission bands indicating the presence of defect states in the investigated structures. I-V measurements reveal the rectifying properties of the HJ and the current thermally activated with a trap with the activation energy equal to 0.42 eV. DLTS studies yield the majority trap of the activation energy 0.42 eV, confirming the result obtained from the I-V measurements. It was found that the defects related to this trap have a point like behaviour. A spectral characteristic of the photocurrent shows that the p-Si/MgO/n-Zn{sub 1−x}Mg{sub x}O HJ may be applied as a photodiode operating within the wavelength range of 300 nm-1100 nm. The dark current transport and photocurrent spectrum were explained using the Anderson model of a HJ.

  11. Enhanced bioactivity of Mg-Nd-Zn-Zr alloy achieved with nanoscale MgF2 surface for vascular stent application.

    PubMed

    Mao, Lin; Shen, Li; Chen, Jiahui; Wu, Yu; Kwak, Minsuk; Lu, Yao; Xue, Qiong; Pei, Jia; Zhang, Lei; Yuan, Guangyin; Fan, Rong; Ge, Junbo; Ding, Wenjiang

    2015-03-11

    Magnesium (Mg) alloys have revolutionized the application of temporary load-bearing implants as they meet both engineering and medical requirements. However, rapid degradation of Mg alloys under physiological conditions remains the major obstacle hindering the wider use of Mg-based implants. Here we developed a simple method of preparing a nanoscale MgF2 film on Mg-Nd-Zn-Zr (denoted as JDBM) alloy, aiming to reduce the corrosion rate as well as improve the biological response. The corrosion rate of JDBM alloy exposed to artificial plasma is reduced by ∼20% from 0.337 ± 0.021 to 0.269 ± 0.043 mm·y(-1) due to the protective effect of the MgF2 film with a uniform and dense physical structure. The in vitro cytocompatibility test of MgF2-coated JDBM using human umbilical vein endothelial cells indicates enhanced viability, growth, and proliferation as compared to the naked substrate, and the MgF2 film with a nanoscale flakelike feature of ∼200-300 nm presents a much more favorable environment for endothelial cell adhesion, proliferation, and alignment. Furthermore, the animal experiment via implantation of MgF2-coated JDBM stent to rabbit abdominal aorta confirms excellent tissue compatibility of the well re-endothelialized stent with no sign of thrombogenesis and restenosis in the stented vessel.

  12. EFFECT OF Sn AND Pb ADDITIONS ON MICROSTRUCTURE OF Mg-6Al-1Zn AS-CAST MAGNESIUM ALLOYS

    NASA Astrophysics Data System (ADS)

    Hou, Haibo; Zhu, Tianping; Wang, Yuxin; Gao, Wei

    2013-07-01

    Much attention has been paid to Mg alloys given that Mg alloys are the most promising lightweight metallic material. They have found applications in automobile and other fields where weight saving is of great significance. Mg-Al-Zn alloy system (AZ series), including AZ91 and AZ61 Mg alloys, is widely used in industry. We have studied the enhancement of mechanical properties by adding alloying elements Sn and Pb. This paper reports our study on the microstructure and element distribution of the alloys with small amounts of tin (Sn) and lead (Pb) additions.

  13. Structural and thermal characterization of CaO-MgO-SiO2-P2O5-CaF2 glasses

    SciTech Connect

    Kansal, Ishu; Goel, Ashutosh; Tulyaganov, Dilshat U.; Rajagopal, Raghu R.; Ferreira, Jose M.

    2012-08-01

    The paper presents the influence of varying CaO/MgO ratio on the structure and thermal properties of CaO-MgO-SiO2-P2O5-CaF2 glasses. A series of eight glass compositions in the glass forming region of diopside (CaMgSi2O6) - fluorapatite [Ca5(PO4)3F] - wollastonite (CaSiO3) ternary system have been designed and synthesized by varying diopside/wollastonite ratio in glasses. The as prepared melt-quenched glasses have been characterized for their structure by infrared spectroscopy (FTIR) and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) spectroscopy. Silicon is predominantly present as Q2 (Si) species, while phosphorus tends to coordinate in orthophosphate environment in all the investigated glasses. The change in CaO/MgO ratio had an insignificant affect on the structure of glasses. The thermal sintering and crystallization parameters for the studied glasses have been obtained from differential thermal analysis (DTA) while crystalline phase fractions in the sintered glass-ceramics have been analyzed by X-ray diffraction adjoined with Rietveld refinement. Diopside, fluorapatite, wollastonite and pseudowollastonite have crystallized as the main crystalline phases in all the glass-ceramics with their content varying with respect to variation in CaO/MgO ratio in glasses. Scanning electron microscopy (SEM) has been used to shed light on the microstructure of glass-ceramics. The possible implications of structure and sintering behaviour of glasses on their bioactivity have been discussed.

  14. Enhanced corrosion resistance and biocompatibility of AZ31 Mg alloy using PCL/ZnO NPs via electrospinning

    NASA Astrophysics Data System (ADS)

    Kim, Jinwoo; Mousa, Hamouda M.; Park, Chan Hee; Kim, Cheol Sang

    2017-02-01

    In the efforts to improve corrosion resistance and biocompatibility of magnesium alloys, polycarprolactone (PCL) and zinc oxide nanoparticles (ZnO NPs) composite coatings were applied onto AZ31 Mg alloys via electrospinning technique in this study. The PCL/ZnO composite coatings on Mg alloys were characterized by using FE-SEM, EDX, XPS, and FT-IR. Moreover, coating adhesion test, electrochemical corrosion test, and biocompatibility test in vitro were performed to measure coating performance. Our results revealed that the increase in the content of ZnO NPs in the composite coatings not only improved the coating adhesion of composite coatings on Mg alloys, but also increased the corrosion resistance. Furthermore, the biocompatibility of MC3T3-E1 osteoblasts of the PCL/ZnO composite coated samples was superior to the biocompatibility of the bare samples. Such data suggest that applying PCL/ZnO composite coating to the magnesium alloys has suitable potential in biomedical applications.

  15. In-situ grown MgO-ZnO ceramic coating with high thermal emittance on Mg alloy by plasma electrolytic oxidation

    NASA Astrophysics Data System (ADS)

    Li, Hang; Lu, Songtao; Qin, Wei; Wu, Xiaohong

    2017-07-01

    Intense solar radiation and internal heat generation determine the equilibrium temperature of an in-orbit spacecraft. Thermal control coatings with low solar absorptance and high thermal emittance effectively maintain the thermal equilibrium within safe operating limits for exposed, miniaturized and highly integrated components. A novel ceramic coating with high thermal emittance and good adhesion was directly prepared on the Mg substrate using an economical process of controlled plasma electrolytic oxidation (PEO) in the electrolyte containing ZnSO4. XRD and XPS results showed that this coating was mainly composed of the MgO phase as well as an unusual ZnO crystalline phase. The adhesive strength between the coating and substrate determined by a pull-off test revealed an excellent adhesion. Thermal and optical properties test revealed that the coating exhibited a high infrared emittance of 0.88 (2-16 μm) and low solar absorptance of 0.35 (200-2500 nm). The result indicated that the formation of ZnO during the PEO process played an important role in the improvement of the coating emittance. The process developed provides a simple surface method for improving the thermal emittance of Mg alloy, which presents a promising application prospect in the thermal management of the spacecraft.

  16. Effect of Ca:Mg ratio on precipitated P species identified using 31P solid state NMR

    NASA Astrophysics Data System (ADS)

    Manimel Wadu, M.

    2009-04-01

    M.C.W. Manimel Wadu1, O.O Akinremi1, S. Kroeker2 1Department of Soil Science, University of Manitoba, Winnipeg, R3T 2N2, Canada 2Department of Chemistry, University of Manitoba, Winnipeg, R3T 2N2, Canada Agronomic efficiency of added P fertilizer is reduced by the precipitation reactions with the exchangeable Ca and Mg in calcareous soils. We hypothesized that the ratio of Ca to Mg on the soil exchange complex will affect the species of P that is precipitated and its solubility in the soil. A laboratory experiment was conducted using a model calcareous soil system which was composed of resin (Amberlite IRP69) and sand coated with CaCO3 packed into a column. The resin was pre saturated with Ca and Mg in order to achieve five different saturation ratios of Ca:Mg approximately as 100:0, 70:30, 50:50, 30:70 and 0:100. Monoammonium Phosphate was applied to the soil surface to simulate one-dimensional diffusive transport. The column was then incubated for 2 weeks. Chemical analysis for water and acid soluble P, pH, NH4, Ca and Mg was performed on 2mm sections of the soil to a depth of 10 cm. This paper will present and discuss the distribution of P along the soil column. Unlike similar studies that have speculated on the precipitation of P, this study will identify and quantify the P species that is formed using 31P solid state NMR technique. Such knowledge will be helpful in understanding the effect of Ca and Mg on P availability in calcareous system and the role of each cation on P precipitation. Key words: P fertilizers, Ca, Mg, model system, solid state NMR

  17. Exciton confinement in homo- and heteroepitaxial ZnO/Zn{sub 1-x}Mg{sub x}O quantum wells with x < 0.1

    SciTech Connect

    Laumer, Bernhard; Wassner, Thomas A.; Schuster, Fabian; Stutzmann, Martin; Schoermann, Joerg; Eickhoff, Martin; Rohnke, Marcus; Chernikov, Alexej; Bornwasser, Verena; Koch, Martin; Chatterjee, Sangam

    2011-11-01

    ZnO/Zn{sub 1-x}Mg{sub x}O single quantum well (SQW) structures with well widths d{sub W} between 1.1 nm and 10.4 nm were grown by plasma-assisted molecular beam epitaxy both heteroepitaxially on c-plane sapphire and homoepitaxially on (0001)-oriented bulk ZnO. A significantly reduced Mg incorporation in the top barrier related to the generation of stacking faults is observed for heteroepitaxial samples. Exciton localization is observed for both types of samples, while an enhancement of the exciton binding energy compared to bulk ZnO is only found for homoepitaxial SQWs for 2 nm {<=} d{sub W} {<=} 4 nm. Consistently, for homoepitaxial samples, the carrier dynamics are mainly governed by radiative recombination and carrier cooling processes at temperatures below 170 K, whereas thermally activated non-radiative recombination dominates in heteroepitaxial samples. The effects of polarization-induced electric fields are concealed for Mg concentrations x < 0.1 due to the reduction of the exciton binding energy, the screening by residual carriers as well as the asymmetric barrier structure in heteroepitaxial wells.

  18. Mg/Ca in the Benthic Foraminifera Elphidium Williamsoni: Evaluating pH and Calcification Rate Effects

    NASA Astrophysics Data System (ADS)

    Allison, N.; Austin, W.; Paterson, D.; Austin, H.

    2008-12-01

    We cultured the benthic foraminifera, Elphidium williamsoni, in a physicochemically stable, large volume (400 l) recirculating seawater system over a range of pH (7.6, 8.1 and 8.3) for a period of 8 weeks. We used calcein staining to identify the foraminifera chambers deposited in the experimental system. The foraminifera typically deposited 1-3 new chambers during the culturing period which were analysed by electron probe. Mg/Ca varied significantly within single chambers. Mean Mg/Ca varied significantly (by as much as x 2) between individuals of similar size and calcification rate (numbers of chambers deposited over the experimental period), cultured under the same conditions. E. williamsoni is an epibenthic species and individuals were visible on the silica substrate surface during culturing. Mg/Ca variations between specimens do not reflect changes in ambient water chemistry but must reflect biological variability between individual foraminifera e.g. dependent on genotype or phenotype. Variations in test chemistry may reflect variability in the composition of the calcifying fluid used for test construction or variations in the relative proportions of high and low Mg calcites incorporated in each test. Within each of the pH treatments we observed no relationship between calcification rate and test Mg/Ca, within each culture pH. Foraminifera cultured at low pH produced less dense chamber walls but we observed no relationship between culture pH and test Mg/Ca. Our study indicates that any effect of pH or calcification rate on test Mg/Ca is effectively swamped by chemistry differences between individual specimens. Foraminifera test Mg/Ca is a commonly used paleothermometer. Our study shows that variations in the relative proportions of individual foraminifera, of different geochemistry, that make up a sample for chemical analysis may affect bulk determinations of test chemistry and subsequent estimates of past climate.

  19. Ultraviolet photodetector based on Mg{sub x}Zn{sub 1-x}O films using plasma-enhanced atomic layer deposition

    SciTech Connect

    Lin, Yu-Chang; Lee, Hsin-Ying; Lee, Ching-Ting

    2016-01-15

    A plasma-enhanced atomic layer deposition (PE-ALD) system was used to deposit magnesium zinc oxide (Mg{sub x}Zn{sub 1−x}O) films with various Mg content (x). The Mg{sub x}Zn{sub 1-x}O films were applied to metal–semiconductor–metal ultraviolet (UV) photodetectors (MSM-UPDs) as an active layer. The Mg content in the Mg{sub x}Zn{sub 1-x}O films was modulated by adjusting the ZnO–MgO cycle ratios to 15:1, 12:1, and 9:1. Correspondingly, the Mg content in the Mg{sub x}Zn{sub 1-x}O films characterized using an energy dispersive spectrometer was 0.10, 0.13, and 0.16, respectively. The optical bandgap of the Mg{sub x}Zn{sub 1-x}O films increased from 3.56 to 3.66 eV with an increase in Mg content from 0.10 to 0.16. The peak position of photoresponsivity for the Mg{sub x}Zn{sub 1-x}O MSM-UPDs was also shifted from 350 to 340 nm. The UV-visible rejection ratios of the Mg{sub x}Zn{sub 1-x}O MSM-UPDs were higher than 3 orders of magnitude. In addition, excellent detectivity and noise equivalent power for the Mg{sub x}Zn{sub 1-x}O MSM-UPDs were observed at a bias voltage of 5 V. The high performance of the Mg{sub x}Zn{sub 1-x}O MSM-UPDs was achieved by PE-ALD at a low temperature.

  20. Broad range tuning of structural and optical properties of Zn x Mg1-x O nanostructures grown by vapor transport method

    NASA Astrophysics Data System (ADS)

    Vanjaria, Jignesh V.; Azhar, Ebraheem Ali; Yu, Hongbin

    2016-11-01

    One-dimensional (1D) Zn x Mg1-x O nanomaterials have drawn global attention due to their remarkable chemical and physical properties, and their diverse current and future technological applications. In this work, 1D ZnMgO nanostructures with different magnesium concentrations and different morphologies were grown directly on zinc oxide-coated silicon substrates by thermal evaporation of zinc oxide, magnesium boride and graphite powders. Highly well-defined Mg-rich ZnMgO nanorods with a rock salt structure and Zn-rich ZnMgO nanostructures with a wurtzite structure have been deposited individually by careful optimization of the source mixture and process parameters. Structural and optical properties of the deposited products were studied by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and Raman spectroscopy. Cathodoluminescence measurements demonstrate strong dominant peaks at 3.3 eV in Mg poor ZnMgO nanostructures and 4.8 eV in Mg rich nanostructures implying that the ZnMgO nanostructures can be used for the fabrication of deep UV optoelectronic devices. A mechanism for the formation and achieved diverse morphology of the ZnMgO nanostructures was proposed based on the characterization results.

  1. Simultaneous observations of Ca II K and Mg II k in T Tauri stars

    NASA Technical Reports Server (NTRS)

    Calvet, N.; Basri, G.; Imhoff, C. L.; Giampapa, M. S.

    1985-01-01

    The first simultaneous, calibrated observations of the Ca II K and Mg II k resonance lines in T Tauri stars are presented. It is found that for T Tauri stars with mass greater than 1.5 solar mass, which have radiative cores and tend to be fast rotators, the k line seems to arise in an extended region (probably also responsible for the H-alpha emission), whereas the K line apparently originates closer to the highly inhomogeneous stellar surface. The lower mass stars, which are fully convective and tend to be slow rotators, are more easily described by a largely chromospheric model, consistent with main-sequence activity structures but at greater values of the nonradiative flux. The strongest emission-line stars in the low-mass group, however, are also likely to have extended k line regions.

  2. Excitons in Mg(OH)2 and Ca(OH)2 from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Pishtshev, A.; Karazhanov, S. Zh.; Klopov, M.

    2014-09-01

    By using ab initio calculations with the HSE06 hybrid functional and GW approximation combined with numerical solution of the Bethe Salpeter equation (GW-BSE) we predict the existence of diverse number of excitonic states in multifunctional hydroxides X(OH)2 (X=Mg and Ca) that were not previously reported experimentally or theoretically. The imaginary part of the dielectric function and the reflectivity spectra show very strong peaks corresponding to the electron-hole pair states of large binding energy. The origin of the excitons is attributed to strong localization of the hole and the electron associated with oxygen 2px,2py occupied states as well as to oxygen and earth metal s empty states, respectively. The results have important implications for different applications of the materials in optoelectronic devices.

  3. Bioactive diopside (CaMgSi(2)O(6)) as a drug delivery carrier - a review.

    PubMed

    Saravanan, C; Sasikumar, S

    2012-11-01

    The bone infections are the most divesting complications confronted by the physicians and patients. The antibiotic loaded bone cements, such as synthetic ceramics and natural ceramics were accepted for bone infections. The currently available bone cements were not accepted due to the lack of mechanical strength, porosity and quick degradation rate etc. The major aim of this review is to discuss about several different synthetic methods used to prepare the bioactive diopside (CaMgSi(2)O(6)) and its applications in ceramic drug delivery systems for controlled and targeted delivery. It has been reported from various research articles, diopside was mainly used for bone tissue regeneration, dentistry, orthopedics and enzyme delivery matrices with different formulations. Compared to other bioceramics diopside is preferable due to its biocompatibility and high mechanical strength.

  4. Conformational changes in the (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum detected using phosphorescence polarization.

    PubMed

    Restall, C J; Coke, M; Murray, E K; Chapman, D

    1985-02-28

    The technique of time-averaged phosphorescence has been used to study the interaction of calcium ions and ATP with the (Ca2+ + Mg2+)-ATPase in sarcoplasmic reticulum vesicles. The presence of excess calcium ions was found to cause a 20% decrease in the phosphorescence emission anisotropy. This is interpreted as being due to a conformational change in the protein and is supported by data from time-resolved phosphorescence measurements which also show a lowering of the anisotropy. This change in the decay of the emission anisotropy is associated with only minor changes in the rotational relaxation time of the protein and is again suggestive of a conformational change in the protein. In some cases ATP was also observed to lower the time-averaged phosphorescence anisotropy possibly via an interaction with the low-affinity regulatory site of the protein.

  5. Effect of multiaxial forging on microstructure and mechanical properties of Mg-o.8Ca alloy

    NASA Astrophysics Data System (ADS)

    Yurchenko, N. Yu; Stepanov, N. D.; Salishchev, G. A.; Rokhlin, L. L.; Dobatkin, S. V.

    2014-08-01

    It was shown that multiaxial forging with continuous decrease of temperature from 450°C to 250°C turns coarse structure of the Mg-0.8Ca alloy in homogenized state with grain size of several hundreeds gm into fine structure with average grain size of about 2.1 gm. Refinement of structure is accompanied by drastic increase of mechanical properties: tensile yield strength increases from 50 MPa to 193 MPa, ultimate tensile strength increases from 78 to 308 MPa and elongation to fracture increases from 3.0% to 7.2%. The microstructural evolution during multiaxial forging is studied using optical microscopy, scanning electron microscopy and EBSD analysis. The mechanisms responsible for refinement of microstructure are discussed

  6. Fast and accurate approximate quasiparticle band structure calculations of ZnO, CdO, and MgO polymorphs

    NASA Astrophysics Data System (ADS)

    Ataide, C. A.; Pelá, R. R.; Marques, M.; Teles, L. K.; Furthmüller, J.; Bechstedt, F.

    2017-01-01

    We investigate ZnO, CdO, and MgO oxides crystallizing in rocksalt, wurtzite, and zincblende structures. Whereas in MgO calculations, the conventional LDA-1/2 method is employed through a self-energy potential (VS), the shallow d bands in ZnO and CdO are treated through an increased amplitude (A ) of VS to modulate the self-energy of the d states to place them in the quasiparticle position. The LDA+A -1/2 scheme is applied to calculate band structures and electronic density of states of ZnO and CdO. We compare the results with those of more sophisticated quasiparticle calculations and experiments. We demonstrate that this new LDA+A -1/2 method reaches accuracy comparable to state-of-the-art methods, opening a door to study more complex systems containing shallow core electrons to the prize of LDA studies.

  7. Ascorbate protects against tert-butyl hydroperoxide inhibition of erythrocyte membrane Ca2+ + Mg2(+)-ATPase.

    PubMed

    Moore, R B; Bamberg, A D; Wilson, L C; Jenkins, L D; Mankad, V N

    1990-05-01

    The incubation of erythrocyte suspensions or isolated membranes containing a residual amount of hemoglobin (0.04% of original cellular hemoglobin) with tert-butyl hydroperoxide (tBHP, 0.5 mM) caused significant inhibition of basal and calmodulin-stimulated Ca2+ + Mg2(+)-ATPase activities and the formation of thiobarbituric acid reactive products measured as malondialdehyde. In contrast, the treatment of white ghosts (membranes not containing hemoglobin) with tBHP (0.5 mM) did not lead to appreciable enzyme inhibition within the first 20 min and did not result in malondialdehyde (MDA) formation. However, the addition of either 10 microM hemin or 100 microM ferrous chloride + 1 mM ADP to white ghosts produced hydroperoxide effects similar to those in pink ghosts (membranes with 0.04% hemoglobin). The concentrations of hemin and ferrous chloride which caused half-maximal inhibition of Ca2+ + Mg2(+)-ATPase activity at 10 min were 0.5 and 30 microM, respectively. The effects of several antioxidants (mannitol, thiourea, hydroxyurea, butylated hydroxytoluene, and ascorbate) were investigated for their protective effects against oxidative changes resulting from tBHP treatment. Over a 30-min incubation period only ascorbate significantly reduced the enzyme inhibition, MDA formation, and protein polymerization. Thiourea and hydroxyurea decreased MDA formation and protein polymerization but failed to protect against the enzyme inhibition. Butylated hydroxytoluene was similar to thiourea and hydroxyurea but with better protection at 10 min. Mannitol, under these conditions, was an ineffective antioxidant for all parameters tested.

  8. TRPM2 channel deficiency prevents delayed cytosolic Zn2+ accumulation and CA1 pyramidal neuronal death after transient global ischemia

    PubMed Central

    Ye, M; Yang, W; Ainscough, J F; Hu, X-P; Li, X; Sedo, A; Zhang, X-H; Zhang, X; Chen, Z; Li, X-M; Beech, D J; Sivaprasadarao, A; Luo, J-H; Jiang, L-H

    2014-01-01

    Transient ischemia is a leading cause of cognitive dysfunction. Postischemic ROS generation and an increase in the cytosolic Zn2+ level ([Zn2+]c) are critical in delayed CA1 pyramidal neuronal death, but the underlying mechanisms are not fully understood. Here we investigated the role of ROS-sensitive TRPM2 (transient receptor potential melastatin-related 2) channel. Using in vivo and in vitro models of ischemia–reperfusion, we showed that genetic knockout of TRPM2 strongly prohibited the delayed increase in the [Zn2+]c, ROS generation, CA1 pyramidal neuronal death and postischemic memory impairment. Time-lapse imaging revealed that TRPM2 deficiency had no effect on the ischemia-induced increase in the [Zn2+]c but abolished the cytosolic Zn2+ accumulation during reperfusion as well as ROS-elicited increases in the [Zn2+]c. These results provide the first evidence to show a critical role for TRPM2 channel activation during reperfusion in the delayed increase in the [Zn2+]c and CA1 pyramidal neuronal death and identify TRPM2 as a key molecule signaling ROS generation to postischemic brain injury. PMID:25429618

  9. Enhanced Osteogenic Activity of TiO2 Nanorod Films with Microscaled Distribution of Zn-CaP.

    PubMed

    He, Meng; Chen, Xiaoyi; Cheng, Kui; Weng, Wenjian; Wang, Huiming

    2016-03-23

    The topography at the micro-/nanoscale level and bioactive composition of material surfaces have been thought to play vital roles in their interactions with cells. However, it is still a challenge to further modify special topography with biodegradable composition or vice versa. In this study, TiO2 nanorod films covered with microscale-distributed Zn-containing calcium phosphate (Zn-CaP) were prepared, trying to create a micro-/nanoscale topography and Zn(2+) release capability. MC3T3-E1 cells cultured on TiO2 nanorod film with sparsely distributed Zn-CaP (TiO2/S-ZCP) had significantly higher biological responses than those on the films with densely distributed Zn-CaP (TiO2/D-ZCP) and fully covered Zn-CaP (F-ZCP). TiO2/S-ZCP film was demonstrated to facilitate osteogenic differentiation much more strongly than F-ZCP and TiO2/D-ZCP films based on evaluations of ALP, related gene expressions, and extracellular matrix mineralization. The higher osteogenic differentiation on TiO2/S-ZCP film is ascribed to the micro-/nanoscale topography from Zn-CaP coverage promoting cell adhesion and filopodia extension, and inducing differentiation-orientation in the initial stage. And consequently Zn(2+) release results in enhancement of differentiation. Therefore, we believe that better organization of the micro-/nanotopography and bioactive ion release on the surface would be a promising way to enhance osteogenic activity for orthopedic and dental implants.

  10. Calmodulin antagonists have differential effects on Ca/sup 2 +/ uptake, (Ca/sup 2 +/ + Mg/sup 2 +/)-ATPase and Ca/sup 2 +/ release in hepatic endoplasmic reticulum

    SciTech Connect

    Delfert, D.M.; Koepnick, S.; McDonald, J.M.; Chan, K.M.

    1986-05-01

    The effect of calmodulin (CaM) antagonists on Ca/sup 2 +/ handling by hepatic endoplasmic reticulum (ER) was studied. Ca/sup 2 +/ uptake by saponin-permeabilized hepatocytes or isolated ER was measured using /sup 45/Ca/sup 2 +/ in a filtration assay in the presence of 0.09 ..mu..M free (Ca/sup 2 +/) and inhibitors of mitochondrial Ca/sup 2 +/ transport. Each CaM-antagonist (chlorpromazine, CPZ; trifluoperazine, TFP; calmidazolium, W7 and 48/80) showed a dose-dependent inhibition of Ca/sup 2 +/ accumulation in permeabilized hepatocytes. Both the initial rate and steady state values for Ca/sup 2 +/ uptake were reduced by 50% with 40 ..mu..M calmidazolium, 100 ..mu..M TFP, 150..mu..M W7, 150 ..mu..M CPZ and 300 ..mu..M 48/80. Using isolated ER both calmidazolium (20 ..mu..M) and W7 (150 ..mu..M) inhibited the initial rate and steady state level of Ca/sup 2 +/ accumulation. At this concentration calmidazolium inhibited the initial rate of (Ca/sup 2 +/ + Mg/sup 2 +/)-ATPase activity, and enhanced Ca/sup 2 +/ release. In contrast, W7 had no effect on these parameters. These results suggest that the reduced level of Ca/sup 2 +/ uptake into ER vesicles in the presence of calmidazolium may result from inhibition of the (Ca/sup 2 +/ + Mg/sup 2 +/)-ATPase as well as induction of Ca/sup 2 +/ release, while W7 may act to uncouple Ca/sup 2 +/ transport from its (Ca/sup 2 +/ + Mg/sup 2 +/)-ATPase counterpart.

  11. Photoluminescence properties and energy levels of RE (RE = Pr, Sm, Er, Tm) in layered-CaZnOS oxysulfide

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi-Jun; Feng, Ang; Chen, Xiang-Yang; Zhao, Jing-Tai

    2013-12-01

    RE3+ (RE = Pr, Sm, Er, Tm)-activated CaZnOS samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. Doping with RE3+ (RE = Pr, Sm, Er, Tm) into layered-CaZnOS resulted in typical RE3+ (RE = Pr, Sm, Er, Tm) f-f line absorptions and emissions, as well as the charge transfer band of Sm3+ at about 3.3 eV. The energy level scheme containing the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions with respect to the valence and conduction bands of CaZnOS has been constructed based on the new data presented in this work, together with the data from literature on Ce3+ and Eu2+ doping in CaZnOS. The detailed energy level scheme provides a platform for interpreting the optical spectra and could be used to comment on the valence stability of the lanthanide ions in CaZnOS.

  12. Mg/Ca, Sr/Ca, and stable isotopes in modern and Holocene Protothaca staminea shells from a northern California coastal upwelling region

    USGS Publications Warehouse

    Takesue, R.K.; VanGeen, A.

    2004-01-01

    This study explores the potential of intertidal Protothaca staminea shells as high-resolution geochemical archives of environmental change in a coastal upwelling region. Mg/Ca and Sr/Ca ratios were analyzed by excimer laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) at sub-weekly temporal resolution in shells growing ???1 mm per month. Growth patterns of a modern P. staminea shell from Humboldt Bay, California, collected in December 1999 made it possible to infer a lifespan from 1993 to 1998. Growth hiatuses in the shell may have excluded records of extreme events. Mg/Ca ratios appeared to be partly controlled by water temperature; the correlation coefficient between temperature and Mg/Ca was r = 0.71 in one of four growth increments. Significant year-to-year differences in the sensitivity of Mg/Ca to temperature in P. staminea could not be explained, however. Sr/Ca ratios appeared to be more closely related to shell growth rate. Oxygen isotopes, measured at 2-week temporal resolution in the same shell, did not show a clear relation to local temperature in summer, possibly because temperatures were higher and less variable at the King Salmon mudflat, where the shell was collected, than in the main channel of Humboldt Bay, where water properties were monitored. Negative shell ??13C values (<-0.5???) marked spring and summer coastal upwelling events. The Mg contents of P. staminea midden shells dated to ???3 ka and ???9 ka were significantly lower than in the modern shell. This may have resulted from degradation of a Mg-rich shell organic matrix and precluded quantitative interpretation of the older high-resolution records. Elevated ??13C values in the ???3 ka shell suggested that the individual grew in highly productive or stratified environment, such as a shallow coastal embayment or lagoon. Copyright ?? 2004 Elsevier Ltd.

  13. Growth and stability of rocksalt Zn1-xMgxO epilayers and ZnO/MgO superlattice on MgO (100) substrate by molecular beam epitaxy.

    PubMed

    Lu, C-Y James; Tu, Y-T; Yan, T; Trampert, A; Chang, L; Ploog, K H

    2016-06-07

    Zn1-xMgxO films with x = 0.04-0.50 grown on MgO (100) substrates by molecular beam epitaxy retain the rocksalt (rs) crystal structure and grow epitaxially for x ≥ 0.17. In addition, the rs-ZnO epilayer is observed to be stable up to a thickness of 5 nm and also in a ZnO/MgO superlattice sample. However, a portion of the superlattice has transformed to wurtzite (wz)-structure islands in a self-accommodated manner during growth. The transformation is a combination of a Bain distortion, an in-plane rotation of 14.5°, and a Peierls distortion, resulting in an orientation relationship of (100)rs//(101̄0)wz and 〈011〉rs ∼//〈1̄21̄3〉wz. In such a manner, the volume expansion is only necessary along the growth direction and the in-plane strains can be minimized. A negative pressure generated during the transformation of ZnO stabilizes the MgO into a wurtzite structure.

  14. Surface compositions of atomic layer deposited Zn{sub 1−x}Mg{sub x}O thin films studied using Auger electron spectroscopy

    SciTech Connect

    Xie, Ting; Romero, Danilo; Gomez, Romel D.

    2015-09-15

    In this paper, the authors present Auger electron spectroscopy (AES) studies of Zn{sub 1−x}Mg{sub x}O (ZMO) films grown via interrupted atomic-layer deposition (ALD) techniques. The ZMO films were fabricated by alternating ALD deposition of ZnO and MgO layers up to 1000 cycles. Zn{sub 1−x}Mg{sub x}O films with progressively decreasing Mg/Zn ratios (Mg/Zn = 1/1, 1/2, 1/3, 1/4, 1/5, 1/6, 1/9, and 2/8, 3/12, 4/16, and 5/20) were fabricated for this study. The AES results exhibit an abrupt drop of Mg composition on the ZMO surface when the Mg/Zn < 1/3. Additionally, the surface composition ratios of O to Mg, O to Zn, and Mg to Zn were estimated with known Auger sensitivity factors. The results indicate that Mg ions diffuse into the bulk, forming Zn{sub 1−x}Mg{sub x}O alloys.

  15. The Giant Pacific Oyster (Crassostrea gigas) as a modern analog for fossil ostreoids: Isotopic (Ca, O, C) and elemental (Mg/Ca, Sr/Ca, Mn/Ca) proxies

    NASA Astrophysics Data System (ADS)

    Ullmann, Clemens V.; Böhm, Florian; Rickaby, Rosalind E. M.; Wiechert, Uwe; Korte, Christoph

    2013-10-01

    Modern analogs are an essential part of palaeoclimate studies, because they provide the basis for the understanding of geochemical signatures of fossils. Ostreoids are common in many sedimentary sequences and because of their fast growth, high temporal resolution sampling of past seasonal variability is possible. Here, two shell structures of modern Giant Pacific Oysters (Crassostrea gigas), the chalky substance and foliate layers, have been sampled for trace element distributions (Mg, Sr, Mn) and stable isotope variability (C, O, Ca). Oxygen isotopes exhibit a clear seasonal signature. Mean carbon isotope values of different oysters agree within 0.1‰, but ontogenic variability is complicated by shell growth patterns and potential small vital effects. The calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of δ44/40Ca = 0.68 ± 0.16‰ (2 sd) SRM-915a which is consistent with other bivalve species. Calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios. Element/Ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high Sr/Ca and Mn/Ca ratios are observed for the first growth season of the oysters. Mg/Ca ratios in the chalky substance show a negative correlation with δ18O values, compatible with a temperature dependence, whereas this correlation is absent in the foliate layers. Seasonal changes of Sr/Ca are controlled by metabolic processes, whereas for Mn/Ca an additional environmental control is evident.

  16. Modeling regulation of cardiac KATP and L-type Ca2+ currents by ATP, ADP, and Mg2+

    NASA Technical Reports Server (NTRS)

    Michailova, Anushka; Saucerman, Jeffrey; Belik, Mary Ellen; McCulloch, Andrew D.

    2005-01-01

    Changes in cytosolic free Mg(2+) and adenosine nucleotide phosphates affect cardiac excitability and contractility. To investigate how modulation by Mg(2+), ATP, and ADP of K(ATP) and L-type Ca(2+) channels influences excitation-contraction coupling, we incorporated equations for intracellular ATP and MgADP regulation of the K(ATP) current and MgATP regulation of the L-type Ca(2+) current in an ionic-metabolic model of the canine ventricular myocyte. The new model: 1), quantitatively reproduces a dose-response relationship for the effects of changes in ATP on K(ATP) current, 2), simulates effects of ADP in modulating ATP sensitivity of K(ATP) channel, 3), predicts activation of Ca(2+) current during rapid increase in MgATP, and 4), demonstrates that decreased ATP/ADP ratio with normal total Mg(2+) or increased free Mg(2+) with normal ATP and ADP activate K(ATP) current, shorten action potential, and alter ionic currents and intracellular Ca(2+) signals. The model predictions are in agreement with experimental data measured under normal and a variety of pathological conditions.

  17. Effects of acidity and alkalinity on corrosion behaviour of Al-Zn-Mg based anode alloy

    NASA Astrophysics Data System (ADS)

    Ma, Jingling; Wen, Jiuba; Li, Quanan; Zhang, Qin

    2013-03-01

    Effects of 1 M HCl, 0.6 M NaCl with different pH values and 4 M NaOH solutions on the corrosion behaviour of Al-5Zn-1Mg-0.02In-0.05Ti-0.5Mn (wt%) alloy have been investigated using measurements of self-corrosion, potentiodynamic polarization, cyclic polarization experiment combined with open circuit potential technique and scanning electron microscopy. The corrosion behaviour of the alloy was found to be dependant on the Cl-, OH- ions and pH value. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion which was traced back to the dissolution of the resistive oxidation film on the surface of the alloy. Experience revealed that the alloy was susceptible to pitting corrosion in all chloride solution. The alloy undergoes two types of localized corrosion process, leading to the formation of hemispherical and crystallographic pits. Polarization resistance measurements which are in good agreement with those of self-corrosion, show that the corrosion kinetic is minimized in slightly neutral solutions (pH = 7).

  18. Softening Behavior of a New Al-Zn-Mg-Cu Alloy Due to TIG Welding

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Li, Xiaoyan; Nie, Zuoren; Huang, Hui; Sun, Jiantong

    2016-05-01

    A new Al-Zn-Mg-Cu alloy with T6 temper was welded by TIG welding, and the softening behavior of the joint was evaluated. Results show that the ultimate tensile strength of the joint is 436.2 ± 26.4 MPa which is about 64.5% of that of the base metal (BM). Fusion zone (FZ) is the weakest region even though its microhardness increases from 107.6 to 131.3 HV within 90 days after welding. Microhardness of the heat-affected zone (HAZ) adjacent to FZ increases from 125.2 to 162.3 HV within 90 days. However, a valley value of microhardness appears in the rest of the HAZ that increases from 112.1 to 128.1 HV within 90 days. The variation of grain size and precipitates is regarded as the main cause of softening in both FZ and HAZ. The grain size of FZ is about 33.9 μm, whereas 8.7 and 8.4 μm for HAZ and BM, respectively. A large number of η' phases distribute dispersively in BM, whereas precipitates in FZ identified as GPI zones are finer and fewer. Besides, precipitates in HAZ adjacent to FZ are also GPI zones. Precipitates in HAZ far away from FZ are coarser and fewer than those in BM and η phases begin to emerge.

  19. Aging kinetics of a silicon carbide reinforced Al-Zn-Mg-Cu alloy

    SciTech Connect

    Davies, C.H.J.; Raghunathan, N.; Sheppard, T.

    1994-01-01

    The aging kinetics of a composite of an Al-Zn-Mg-Cu powder (CW67) combined with a varied volume fraction of a particulate silicon carbide were investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). DSC revealed that the maximum rate of precipitation of the metastable {eta}{prime} phase was substantially lower for CW67/SiC/20p than for the unreinforced alloy or CW67/SiC/10p. TEM of isothermally aged material revealed differences between the unreinforced alloy and composites in respect of precipitate size and morphology. The authors conclude that SiC additions, by dint of additional dislocations generated during quenching, can affect the aging of CW67 either by accelerating the nucleation of precipitates or by accelerating precipitate growth. The aging rate of CW67/SiC/20p was increased by accelerating both the nucleation of precipitates and growth, whereas the aging in CW67/SiC10p was enhanced by accelerating precipitate growth only.

  20. Selective UV radiation detection on the basis of low-dimensional ZnCdS/ZnMgS/GaP and ZnCdS/ZnS/GaP heterostructures

    SciTech Connect

    Averin, S. V. Kuznetzov, P. I.; Zhitov, V. A.; Zakharov, L. Yu.; Kotov, V. M.; Alkeev, N. V.; Gladisheva, N. B.

    2015-11-15

    The detecting properties of periodic heterostructures with ZnCdS quantum wells separated by ZnMgS or ZnS barrier layers are studied. Heterostructures are grown on semi-insulating GaP substrates by metal organic vapor-phase epitaxy (MOVPE). On their basis, metal–semiconductor–metal (MSM) diodes with interdigital Schottky contacts 3 μm, distances between them of 3 μm, and a total detector area of 100 × 100 μm are fabricated. The detectors have low dark currents (10{sup –12} A); at low bias voltages, they provide a narrow- band response (full-width at half-maximum of FWHM = 18 nm at a wavelength of 350 nm) which is controlled by the ZnCdS quantum-well composition. As bias is increased to 70 V, the maximum detector sensitivity shifts by a wavelength of 450 nm, which is caused by penetration of the external-bias electric field into the semi-insulating GaP substrate. In this case, the narrow-band response of the detector at a wavelength of 350 nm is retained, i.e., the two-color detection of light is provided.

  1. Effects of Mg on the electrical characteristics and thermal stability of MgxZn1-xO thin film transistors

    NASA Astrophysics Data System (ADS)

    Ku, Chieh-Jen; Duan, Ziqing; Reyes, Pavel I.; Lu, Yicheng; Xu, Yi; Hsueh, Chien-Lan; Garfunkel, Eric

    2011-03-01

    The effects of the Mg composition (x=0, 0.06, and 0.10) on the electrical characteristics and thermal stability of MgxZn1-xO thin film transistors (TFTs) are investigated. The Mg0.06Zn0.94O TFT shows the smallest subthreshold slope and highest field effect mobility. The O1s spectra of x-ray photoelectron spectroscopy measurements indicate that the oxygen vacancies are reduced in Mg0.06Zn0.94O relative to a pure ZnO channel device. Mg0.06Zn0.94O TFTs also show higher thermal stability compared to the pure ZnO TFTs, which is mainly attributed to the suppression of oxygen vacancies in the channel.

  2. Effect of Aging Treatment on the Damping Capacity and Mechanical Properties of Mg-6Al-1Zn Alloy

    PubMed Central

    El-Morsy, Abdel-Wahab; Farahat, Ahmed I. Z.

    2015-01-01

    The damping capacity and mechanical properties of Mg-6Al-1Zn alloy after heat treatment were investigated. The damping characteristics of un-heat-treated, solution treated, and aged Mg-6Al-1Zn specimens were determined by measuring the damping ratio and the logarithmic decrement of free vibrations of a bending beam clamped at one side. The microstructural evaluations confirmed that the β-Mg17Al12 phase was reprecipitated after aging and increased with an increase in aging time. The peak level of damping ratio and logarithmic decrement was obtained after 34 hr of aging time, over which the damping capacity declined according to increasing amount of strong pining points. PMID:25918738

  3. Mg2+ ions reduce microglial and THP-1 cell neurotoxicity by inhibiting Ca2+ entry through purinergic channels.

    PubMed

    Lee, Moonhee; Jantaratnotai, Nattinee; McGeer, Edith; McLarnon, James G; McGeer, Patrick L

    2011-01-19

    Mg(2+) is a known antagonist of some Ca(2+) ion channels. It may therefore be able to counteract the toxic consequences of excessive Ca(2+) entry into immune-type cells. Here we examined the effects of Mg(2+) on inflammation induced by Ca(2+) influx into microglia and THP-1 cells following activation of purinergic receptors. Using tissue culture, an inflammatory response was induced by treatment with either the P2X7 purinergic receptor agonist 2',3'-[benzoyl-4-benzoyl]-ATP (BzATP) or the P2Y2,4 receptor agonist uridine 5'-triphosphate (UTP). Both microglia and THP-1 cells expressed the mRNAs for these receptors. Treatment produced a rapid rise in intracellular Ca(2+) which was significantly reduced by Mg(2+) or the calcium chelator BAPTA-AM. Purinergic receptor stimulation activated the intracellular inflammatory pathway P38 MAP kinase and NFκB. This caused release of TNFα, IL-6, nitrite ions and other materials that are neurotoxic to SH-SY5Y cells. These effects were all ameliorated by Mg(2+). They were also partly ameliorated by the P2X7R antagonists, oxATP and KN-62, the P2YR antagonist MRS2179, and the store operated Ca(2+) channel blocker, SK96365. These results indicate that elevated Mg(2+) is a broad spectrum inhibitor of Ca(2+) entry into microglia or THP-1 cells. Mg(2+) administration may be a strategy for reducing the damaging consequences Ca(2+) induced neuroinflammation in degenerative neurological disorders such as Alzheimer disease and Parkinson disease.

  4. Chemistry of BDI*M2+ complexes (M = Mg, Zn) and their role in lactide polymerization where BDI* is the anion derived from methylenebis(C-(t)Bu, N-2,6-diisopropylphenyl)imine BDI*H.

    PubMed

    Ayala, Carla N; Chisholm, Malcolm H; Gallucci, Judith C; Krempner, Clemens

    2009-11-14

    The bulky diimine CH(2){C((t)Bu)N-2,6-Pr(i)(2)C(6)H(3)}(2), BDI*H, is shown to exist in two isomers trans-trans, 1a and cis-trans, 1b that interconvert slowly on the NMR time-scale. Treatment of the diimine with (n)BuLi in hexane proceeds slowly to give the lithium beta-diketoiminate LiBDI*, 2, which upon hydrolysis yields the eneimine tautomer of BDI*H which has been characterized by X-ray studies in three rotamers, 3a, 3b and 3c. Dialkylmetal compounds (M = Mg, R = Bu; M = Zn, R = Et) react with either 1 or 3 in hydrocarbon and ether solvents to give BDI*Mg((n)Bu)THF, 4, and BDI*ZnEt, 5, which have been structurally characterized. M(N(SiMe(3))(2))(2) compounds where M = Mg, Zn or Ca failed to react with either 1 or 3 in hydrocarbon solvents. The reactions between ZnCl(2) and 2 yield BDI*ZnCl, 6, and a further reaction with LiNMe(2) yields BDI*ZnNMe(2), 7. The compounds 5 and 6 are shown to contain trigonal planar, M(2+) ions. Compounds 4, and 7 initiate ring-opening polymerization, ROP, of rac-lactide to give atactic polylactide, PLA. The rate of ROP depends on the metal M = Mg > Zn and is slower than that observed for the related beta-diketoiminate complexes where the bulky-(t)Bu group is replaced by Me.

  5. Competition between (001) and (111) MgO thin film growth on Al-doped ZnO by oxygen plasma assisted pulsed laser deposition

    SciTech Connect

    Xiao, Bo; Yang, Qiguang; Walker, Brandon; Gonder, Casey A.; Romain, Gari C.; Mundle, Rajeh; Bahoura, Messaoud; Pradhan, A. K.

    2013-06-07

    We report on the study of epitaxial MgO thin films on (0001) Al-doped ZnO (Al: ZnO) underlayers, grown by oxygen plasma assisted pulsed laser deposition technique. A systematic investigation of the MgO thin films was performed by X-ray diffraction and atomic force microscopy, along with the current-voltage characteristics. A distinguished behavior was observed that the preferred MgO orientation changes from (111) to (001) in the films as the growth temperature increases. Two completely different in-plane epitaxial relationships were also determined from X-ray diffraction as: [110]MgO//[1120]Al: ZnO and [110]MgO//[1100]Al: ZnO for (001) MgO with 60 Degree-Sign rotated triplet domains, and [110]MgO//[1120]Al: ZnO for (111) MgO with 180 Degree-Sign rotated twin. The pronounced temperature dependence indicates a reconciliation of the nucleation driving forces among surface, interfacial, and strain energy for heteroepitaxy of cubic MgO on hexagonal Al: ZnO. The related interfacial atomic registry is considered to be important to the formation of unusual (001) MgO on hexagonal crystals.