Reduction Mechanisms of Cu2+-Doped Na2O-Al2O3-SiO2 Glasses during Heating in H2 Gas.

PubMed

Nogami, Masayuki; Quang, Vu Xuan; Ohki, Shinobu; Deguchi, Kenzo; Shimizu, Tadashi

2018-01-25

Controlling valence state of metal ions that are doped in materials has been widely applied for turning optical properties. Even though hydrogen has been proven effective to reduce metal ions because of its strong reducing capability, few comprehensive studies focus on practical applications because of the low diffusion rate of hydrogen in solids and the limited reaction near sample surfaces. Here, we investigated the reactions of hydrogen with Cu 2+ -doped Na 2 O-Al 2 O 3 -SiO 2 glass and found that a completely different reduction from results reported so far occurs, which is dominated by the Al/Na concentration ratio. For Al/Na < 1, Cu 2+ ions were reduced via hydrogen to metallic Cu, distributing in glass body. For Al/Na > 1, on the other hand, the reduction of Cu 2+ ions occurred simultaneously with the formation of OH bonds, whereas the reduced Cu metal moved outward and formed a metallic film on glass surface. The NMR and Fourier transform infrared results indicated that the Cu 2+ ions were surrounded by Al 3+ ions that formed AlO 4 , distorted AlO 4 , and AlO 5 units. The diffused H 2 gas reacted with the Al-O - ···Cu + units, forming Al-OH and metallic Cu, the latter of which moved freely toward glass surface and in return enhanced H 2 diffusion.

Optical properties of BaO added bioactive Na2O-CaO-P2O5 glasses

NASA Astrophysics Data System (ADS)

Edathazhe, Akhila B.; Shashikala, H. D.

2018-04-01

This paper deals with the effect of BaO addition on the optical properties of bioactive Na2O-CaO-P2O5 glasses for biomedical optics applications. The phosphate glasses with composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x = 0, 5, 10, 15 mol%) have been prepared by melt-quenching technique at 1100°C. The refractive index of glasses increased with BaO content. The optical band gap and Urbach energy of synthesized glasses were derived from the optical absorption spectra by using UV-Visible spectrometer. The addition of 5 mol% of BaO increased the band gap energy of glasses due to the formation of ionic cross-links in the glass structure. The defect and interstitial bonds formation in theglasses decreased with BaO additions as indicated by reductions in the Urbach energy values. No such variations in the band gap and Urbach energy values of glasses were observed with BaO content from 5 to 15 mol%. The molar and oxide ion polarizability values were calculated from the band gap and molar volume of glasses. The increase in the calculated optical basicity and metallization criteria of glasses supported the rise in band gap energy values with BaO additions. As the melting temperature of glasses decreased from 1200 to 1100°C, the refractive index increased as supported by the measured density values. The band gap energy is not changed with melting temperature. The Urbach energy decreased with decrease in melting temperature in case of BaO-free Na2O-CaO-P2O5 glasses, whereas it increased in case of BaO added glasses due to the role of BaO as modifying oxide.

On the existence of a high-temperature polymorph of Na2Ca6Si4O15—implications for the phase equilibria in the system Na2O-CaO-SiO2

NASA Astrophysics Data System (ADS)

Kahlenberg, Volker; Maier, Matthias

2016-12-01

Singe crystals of a new high-temperature polymorph of Na2Ca6Si4O15 have been obtained from solid state reactions performed at 1300 °C. The basic crystallographic data of this so-called β-phase at ambient conditions are as follows: space group P1 c1, a = 9.0112(5) Å, b = 7.3171(5) Å, c = 10.9723(6) Å, β = 107.720(14)°, V = 689.14(7) Å3, Z = 2. The crystals showed twinning by reticular merohedry (mimicking an orthorhombic C-centred unit cell) which was accounted for during data processing and structure solution. Structure determination was accomplished by direct methods. Least-squares refinements resulted in a residual of R(|F|) = 0.043 for 5811 observed reflections with I > 2σ(I). From a structural point of view β-Na2Ca6Si4O15 can be attributed to the group of mixed-anion silicates containing [Si2O7]-dimers as well as isolated [SiO4]-tetrahedra in the ratio 1:2, i.e. more precisely the formula can be written as Na2Ca6[SiO4]2[Si2O7]. The tetrahedral groups are arranged in layers parallel to (100). Sodium and calcium cations are located between the silicate anions for charge compensation and are coordinated by six to eight nearest oxygen ligands. Alternatively, the structure can be described as a mixed tetrahedral-octahedral framework based on kröhnkite-type [Ca(SiO4)2O2]-chains in which the CaO6-octahedra are corner-linked to bridging SiO4-tetrahedra. The infinite chains are running parallel to [001] and are concentrated in layers parallel to (010). Adjacent layers are shifted relative to each other by an amount of +δ or -δ along a*. Consequently, a …ABABAB… stacking sequence is created. A detailed comparison with related structures such as α-Na2Ca6Si4O15 and other A2B6Si4O15 representatives including topological as well as group theoretical aspects is presented. There are strong indications that monoclinic Na2Ca3Si2O8 mentioned in earlier studies is actually misinterpreted β-Na2Ca6Si4O15. In addition to the detailed crystallographic analysis of

Investigating the solubility and cytocompatibility of CaO-Na2 O-SiO2 /TiO2 bioactive glasses.

PubMed

Wren, Anthony W; Coughlan, Aisling; Smith, Courtney M; Hudson, Sarah P; Laffir, Fathima R; Towler, Mark R

2015-02-01

This study aims to investigate the solubility of a series of titanium (TiO2 )-containing bioactive glasses and their subsequent effect on cell viability. Five glasses were synthesized in the composition range SiO2 -Na2 O-CaO with 5 mol % of increments TiO2 substituted for SiO2 . Glass solubility was investigated with respect to (1) exposed surface area, (2) particle size, (3) incubation time, and (4) compositional effects. Ion release profiles showed that sodium (Na(+) ) presented high release rates after 1 day and were unchanged between 7 and 14 days. Calcium (Ca(2+) ) release presented a significant change at each time period and was also composition dependent, where a reduction in Ca(2+) release is observed with an increase in TiO2 concentration. Silica (Si(4+) ) release did not present any clear trends while no titanium (Ti(4+) ) was released. Cell numbers were found to increase up to 44%, compared to the growing control population, with a reduction in particle size and with the inclusion of TiO2 in the glass composition. © 2014 Wiley Periodicals, Inc.

Effects of Al2O3, B2O3, Li2O, Na2O, and SiO2 on Nepheline Crystallization in Hanford High Level Waste Glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroll, Jared O.; Vienna, John D.; Schweiger, Michael J.

2016-09-15

Nepheline (nominally NaAlSiO4) formation during slow cooling of high-alumina (25.4 - 34.5 mass% Al2O3) Hanford high level waste glasses may significantly reduce product durability. To investigate the effects of composition on nepheline crystallization, 29 compositions were formulated by adjusting Al2O3, B2O3, Li2O, Na2O, and SiO2 around a baseline glass that precipitated 12 mass% nepheline. Thirteen of these compositions were generated by adjusting one-component-at-a-time, while two or three components were adjusted to produce the other 16 (with all remaining components staying in the same relative proportions). Quantitative X-ray diffraction was used to determine nepheline concentration in each sample. Twenty two glassesmore » precipitated nepheline, two of which also precipitated eucryptite (nominally LiAlSiO4), and one glass formed only eucryptite upon slow cooling. Increasing Na2O and Li2O had the strongest effect in promoting nepheline formation. Increasing B2O3 inhibited nepheline formation. SiO2 and Al2O3 showed non-linear behavior related to nepheline formation. The composition effects on nepheline formation in these glasses are reported.« less

Phase Equilibria Study in the TeO2-Na2O-SiO2 System in Air Between 723 K (500 °C) and 1473 K (1200 °C)

NASA Astrophysics Data System (ADS)

Santoso, Imam; Taskinen, Pekka

2016-08-01

Knowledge of phase equilibria in the TeO2-Na2O-SiO2 system at elevated temperatures is important for ceramic and glass industries and for improving the operation of the smelting process of tellurium-containing materials. A review of previous investigations has indicated, however, that there are omissions in the available datasets on the liquidus temperatures of the molten TeO2-Na2O-SiO2 mixtures. The employed experimental method included equilibration of mixtures made from high purity oxides, rapid quenching of the equilibrated samples in water and followed by compositional analysis of the phases using an electron probe X-ray microanalyzer. The liquidus and phase equilibria in the TeO2-SiO2, TeO2-Na2O, and SiO2-TeO2-Na2O systems have been studied for a wide range of compositions between 723 K (500 °C) and 1473 K (1200 °C) at TeO2, SiO2, and Na2SiO3 saturations. New data have been generated in the SiO2-TeO2-Na2O system at SiO2 saturation. The liquidus compositions in the TeO2-Na2O system at TeO2 saturation have been compared with the previous data and an assessed phase diagram.

First investigations on the quaternary system Na2O-K2O-CaO-SiO2: synthesis and crystal structure of the mixed alkali calcium silicate K1.08Na0.92Ca6Si4O15

NASA Astrophysics Data System (ADS)

Kahlenberg, Volker; Mayerl, Michael Jean-Philippe; Schmidmair, Daniela; Krüger, Hannes; Tribus, Martina

2018-04-01

In the course of an exploratory study on the quaternary system Na2O-K2O-CaO-SiO2 single crystals of the first anhydrous sodium potassium calcium silicate have been obtained from slow cooling of a melt in the range between 1250 and 1050 °C. Electron probe micro analysis suggested the following idealized molar ratios of the oxides for the novel compound: K2O:Na2O:CaO:SiO2 = 1:1:12:8 (or KNaCa6Si4O15). Single-crystal diffraction measurements on a crystal with chemical composition K1.08Na0.92Ca6Si4O15 resulted in the following basic crystallographic data: monoclinic symmetry, space group P 21/ c, a = 8.9618(9) Å, b = 7.3594(6) Å, c = 11.2453(11) Å, β= 107.54(1)°, V = 707.2(1) Å3, Z = 2. Structure solution was performed using direct methods. The final least-squares refinement converged at a residual of R(|F|) = 0.0346 for 1288 independent reflections and 125 parameters. From a structural point of view, K1.08Na0.92Ca6Si4O15 belongs to the group of mixed-anion silicates containing [Si2O7]- and [SiO4]-units in the ratio 1:2. The mono- and divalent cations occupy a total of four crystallographically independent positions located in voids between the tetrahedra. Three of these sites are exclusively occupied by calcium. The fourth site is occupied by 54(1)% K and 46%(1) Na, respectively. Alternatively, the structure can be described as a heteropolyhedral framework based on corner-sharing silicate tetrahedra and [CaO6]-octahedra. The network can build up from kröhnkite-like [Ca(SiO4)2O2]-chains running along [001]. A detailed comparison with other A2B6Si4O15-compounds including topological and group-theoretical aspects is presented.

Experimental and first-principles study of photoluminescent and optical properties of Na-doped CuAlO2: the role of the NaAl-2Na i complex

NASA Astrophysics Data System (ADS)

Liu, Ruijian; Li, Yongfeng; Yao, Bin; Ding, Zhanhui; Deng, Rui; Zhang, Ligong; Zhao, Haifeng; Liu, Lei

2015-08-01

We report that a band-tail emission at 3.08 eV, lower than near-band-edge energy, is observed in photoluminescence measurements of bulk Na-doped CuAlO2. The band-tail emission is attributed to Na-related defects. Electronic structure calculations based on the first-principles method demonstrate that the donor-acceptor compensated complex of NaAl-2Na i in Na-doped CuAlO2 plays a key role in leading to the band-tail emission and bandgap narrowing. Furthermore, Hall effect measurements indicates that the hole concentration in CuAlO2 is independent on Na doping, which is well understood by the donor-acceptor compensation effect of NaAl-2Na i complex.

Structure and properties of α-NaFeO{sub 2}-type ternary sodium iridates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baroudi, Kristen, E-mail: kbaroudi@princeton.edu; Yim, Cindi; Wu, Hui

2014-02-15

The synthesis, structure, and elementary magnetic and electronic properties are reported for layered compounds of the type Na{sub 3−x}MIr{sub 2}O{sub 6} and Na{sub 3−x}M{sub 2}IrO{sub 6}, where M is a transition metal from the 3d series (M=Zn, Cu, Ni, Co, Fe and Mn). The rhombohedral structures, in space group R−3m, were determined by refinement of neutron and synchrotron powder diffraction data. No clear evidence for long range 2:1 or 1:2 honeycomb-like M/Ir ordering was found in the neutron powder diffraction patterns except in the case of M=Zn, and thus in general the compounds are best designated as sodium deficient α-NaFeO{submore » 2}-type phases with formulas Na{sub 1−x}M{sub 1/3}Ir{sub 2/3}O{sub 2} or Na{sub 1−x}M{sub 2/3}Ir{sub 1/3}O{sub 2}. Synchrotron powder diffraction patterns indicate that several of the compounds likely have honeycomb in-plane metal–iridium ordering with disordered stacking of the layers. All the compounds are sodium deficient under our synthetic conditions and are black and insulating. Weiss constants derived from magnetic susceptibility measurements indicate that Na{sub 0.62}Mn{sub 0.61}Ir{sub 0.39}O{sub 2}, Na{sub 0.80}Fe{sub 2/3}Ir{sub 1/3}O{sub 2}, Na{sub 0.92}Ni{sub 1/3}Ir{sub 2/3}O{sub 2}, Na{sub 0.86}Cu{sub 1/3}Ir{sub 2/3}O{sub 2}, and Na{sub 0.89}Zn{sub 1/3}Ir{sub 2/3}O{sub 2} display dominant antiferromagnetic interactions. For Na{sub 0.90}Co{sub 1/3}Ir{sub 2/3}O{sub 2} the dominant magnetic interactions at low temperature are ferromagnetic while at high temperatures they are antiferromagnetic; there is also a change in the effective moment. Low temperature specific heat measurements (to 2 K) on Na{sub 0.92}Ni{sub 1/3}Ir{sub 2/3}O{sub 2} indicate the presence of a broad magnetic ordering transition. X-ray absorption spectroscopy shows that iridium is at or close to the 4+ oxidation state in all compounds. {sup 23}Na nuclear magnetic resonance measurements comparing Na{sub 2}IrO{sub 3} to Na{sub 0.92}Ni{sub 1

Effect of increasing concentration of Na2O on structural, elastic and optical properties of (90  -  x)GeO2-xNa2O-10PbO glass system in the germanate anomaly region

NASA Astrophysics Data System (ADS)

Zainudin, C. N.; Hisam, R.; Yusof, M. I. M.; Yahya, A. K.; Halimah, M. K.

2017-10-01

Ternary germanate glasses (90  -  x)GeO2-xNa2O-10PbO (x  =  10-30 mol%) have been prepared by the melt-quenching method. Density, ρ increased with Na2O content up to maxima at 20 mol% while molar volume, V a showed an opposite trend to the density, with a minima at 20 mol% of Na2O content indicating the presence of the germanate anomaly. Ultrasonic velocity measurements showed both longitudinal, v l and shear, v s velocities increased up to 20 mol% before decreasing with further addition of Na2O. Independent longitudinal, L and shear, G moduli along with Young’s modulus, Y, mean sound velocity, v m, Debye temperature, θ D, and hardness, H recorded maximum values at 20 mol% of Na2O content which were suggested to be related to the germanate anomaly. Structural modification occurring due to conversion of six-membered GeO4 rings to three-membered rings of GeO4 changed bond density and compactness of the glass systems and caused the increase in rigidity and stiffness of the glasses. Beyond 20 mol% of Na2O, the decrease in the elastic moduli was due to depolymerization of the glass network. Meanwhile, optical energy gap, E opt exhibited a minima at 20 mol% whereas Urbach energy, E U and refractive index, n showed a maxima at the same concentration, thereby indicating variation in polarizability due to changes in concentration of bridging and non-bridging oxygen.

Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2O.

PubMed

Tan, S Y; Jiang, J; Ye, Z R; Niu, X H; Song, Y; Zhang, C L; Dai, P C; Xie, B P; Lai, X C; Feng, D L

2015-04-30

The electronic structure of Na2Ti2Sb2O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na2Ti2Sb2O in the non-magnetic state, which indicates that there is no magnetic order in Na2Ti2Sb2O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na2Ti2Sb2O. Photon energy dependent ARPES results suggest that the electronic structure of Na2Ti2Sb2O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV at 7 K, indicating that Na2Ti2Sb2O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime.

Effects of Na2MoO4 and Na2WO4 on molybdenum and tungsten electrodes for the alkali metal thermoelectric converter (AMTEC)

NASA Technical Reports Server (NTRS)

Williams, R. M.; Wheeler, B. L.; Jeffries-Nakamura, B.; Loveland, M. E.; Bankston, C. P.

1988-01-01

The effects of adding Na2MoO4 and Na2WO4 to porous Mo and W electrodes, respectively, on the performance and impedance characteristics of the electrodes in an alkali metal thermoelectric converter (AMTEC) were investigated. It was found that corrosion of the porous electrode by Na2MoO4 or Na2WO4 to form Na2MO3O6 and WO2, respectively, and recrystallization of the Mo or W as the salt evaporates, result in major morphological changes including a loss of columnar structure and a significant increase in porosity. This effect is more pronounced in Na2MoO4/Mo electrodes, due to the lower stability of Na2MoO4.

Controlled phase stability of highly Na-active triclinic structure in nanoscale high-voltage Na2-2xCo1+xP2O7 cathode for Na-ion batteries

NASA Astrophysics Data System (ADS)

Song, Hee Jo; Kim, Jae-Chan; Dar, Mushtaq Ahmad; Kim, Dong-Wan

2018-02-01

With the increasing demand for high energy density in energy-storage systems, a high-voltage cathode is essential in rechargeable Li-ion and Na-ion batteries. The operating voltage of a triclinic-polymorph Na2CoP2O7, also known as the rose form, is above 4.0 V (vs. Na/Na+), which is relatively high compared to that of other cathode materials. Thus, it can be employed as a potential high-voltage cathode material in Na-ion batteries. However, it is difficult to synthesize a pure rose phase because of its low phase stability, thus limiting its use in high-voltage applications. Herein, compositional-engineered, rose-phase Na2-2xCo1+xP2O7/C (x = 0, 0.1 and 0.2) nanopowder are prepared using a wet-chemical method. The Na2-2xCo1+xP2O7/C cathode shows high electrochemical reactivity with Na ions at 4.0 V, delivering high capacity and high energy density.

Mineral-solution equilibria—III. The system Na 2OAl 2O 3SiO 2H 2OHCl

NASA Astrophysics Data System (ADS)

Popp, Robert K.; Frantz, John D.

1980-07-01

Chemical equilibrium between sodium-aluminum silicate minerals and chloride bearing fluid has been experimentally determined in the range 500-700°C at 1 kbar, using rapid-quench hydrothermal methods and two modifications of the Ag + AgCl acid buffer technique. The temperature dependence of the thermodynamic equilibrium constant ( K) for the reaction NaAlSi 3O 8 + HCl o = NaCl o + 1/2Al 2SiO 5, + 5/2SiO 2 + 1/2H 2O Albite Andalusite Qtz. K = (a NaCl o) /(a H 2O ) 1/2/(a HCl o) can be described by the following equation: log k = -4.437 + 5205.6/ T( K) The data from this study are consistent with experimental results reported by MONTOYA and HEMLEY (1975) for lower temperature equilibria defined by the assemblages albite + paragonite + quartz + fluid and paragonite + andalusite + quartz + fluid. Values of the equilibrium constants for the above reactions were used to estimate the difference in Gibbs free energy of formation between NaCl o and HCl o in the range 400-700°C and 1-2 kbar. Similar calculations using data from phase equilibrium studies reported in the literature were made to determine the difference in Gibbs free energy of formation between KCl o and HCl o. These data permit modelling of the chemical interaction between muscovite + kspar + paragonite + albite + quartz assemblages and chloride-bearing hydrothermal fluids.

K0.78Na0.22MoO2AsO4

PubMed Central

Jouini, Raja; Bouzidi, Chahira; Zid, Mohamed Faouzi; Driss, Ahmed

2013-01-01

The title compound, potassium sodium dioxidomolybden­um(VI) arsenate, K0.78Na0.22MoO2AsO4, was synthesized by a solid-state reaction route. The structure is built up from corner-sharing MoO6 octa­hedra and AsO4 tetra­hedra, creating infinite [MoAsO8]∞ chains running along the b-axis direction. As, Mo and all but one O atom are on special positions (4c) with m symmetry and K (occupancy 0.78) is on a position (4a) of -1 in the tunnels. The possible motion of the alkali cations has been investigated by means of the bond-valance sum (BVS) model. The simulation shows that the Na+ motion appears to be easier mainly along the b-axis direction. Structural relationships between the different compounds of the AMoO2AsO4 (A = Ag, Li, Na, K, Rb) series and MXO8 (M = V; X = P, As) chains are discussed. PMID:24109253

Na2Ti6O13@TiO2 core-shell nanorods with controllable mesoporous shells and their enhanced photocatalytic performance

NASA Astrophysics Data System (ADS)

Zhou, Xuefan; Zhong, Donglin; Luo, Hang; Pan, Jun; Zhang, Dou

2018-01-01

In this study, dispersive and free-standing Na2Ti6O13 nanorods with diameter of about 500 nm and length of about 10 μm were synthesized by the molten salt method. The Na2Ti6O13@TiO2 (denoted as TTO) core-shell nanorods were fabricated by a versatile kinetics controlled coating method. The TiO2 shells were uniform and mesoporous with exposed {101} facets. The thickness of TiO2 shells can be well controlled by the content of Ti(OC4H9)4, ranging from 0 nm, 15 nm, 60 nm to 70 nm corresponding to Na2Ti6O13, 0.25-TTO, 0.50-TTO and 0.75-TTO nanorods respectively. The crystalline phases, microstructure, porosity, photoabsorption and photocatalytic performance of all the samples were investigated systematically. The nanoscale heterojunction structure between Na2Ti6O13 and TiO2, reductive TiO2 {101} facets and high aspect ratio Na2Ti6O13 nanorods resulted in the enhanced photocatalytic performance of TTO nanorods. The optimized thickness of TiO2 shells were about 60 nm for 0.50-TTO nanorods, which possessed superior BET surface area, optical absorption and photocatalytic performance.

Thermodynamic and kinetic analyses of the CO2 chemisorption mechanism on Na2TiO3: Experimental and theoretical evidences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Yuhua

2014-01-01

ABSTRACT: Sodium metatitanate (Na2TiO3) was successfully synthesized via a solid-state reaction. The Na2TiO3 structure and microstructure were characterized using X-ray diffraction, scanning and transmission electron microscopy, and N2 adsorption. Then, the CO2 chemisorption mechanism on Na2TiO3 was systematically analyzed to determine the influence of temperature. The CO2 chemisorption capacity of Na2TiO3 was evaluated both dynamically and isothermally, and the products were reanalyzed to elucidate the Na2TiO3-CO2 reaction mechanism. Different chemical species (Na2CO3, Na2O, and Na4Ti5O12 or Na16Ti10O28) were identified during the CO2 capture process in Na2TiO3. In addition, some CO2 chemisorption kinetic parameters were determined. The ΔH‡ was found tomore » be 140.9 kJ/mol, to the Na2TiO3-CO2 system, between 600 and 780 °C. Results evidenced that CO2 chemisorption on Na2TiO3 highly depends on the reaction temperature. Furthermore, the experiments were theoretically supported by different thermodynamic calculations. The calculated thermodynamic properties of CO2 capture reactions by (Na2TiO3, Na4Ti5O12, and Na16Ti10O28) sodium titanates were fully investigated.« less

Self induced gratings in ternary SiO2:SnO2:Na2O bulk glasses by UV light seeding.

PubMed

Lancry, M; Douay, M; Niay, P; Beclin, F; Menke, Y; Milanese, D; Ferraris, M; Poumellec, B

2005-09-05

The diffraction efficiency of gratings written in ternary SnO2:SiO2:Na2O bulk glasses rises dramatically with time after the occultation of the cw 244nm light used to write the thick hologram. This self-induced behavior lasts for several hours and ultimately leads to refractive index changes as high as 3 10-3.

Synthesis of Nanoscale CaO-Al2O3-SiO2-H2O and Na2O-Al2O3-SiO2-H2O Using the Hydrothermal Method and Their Characterization

PubMed Central

Yang, Jingbin; Li, Dongxu; Fang, Yuan

2017-01-01

C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O) have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O)/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH)2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH)2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali-activated materials. PMID

Phase and Physicochemical Properties Diagrams of Quaternary System Li2B4O7 + Na2B4O7 + Mg2B6O11 + H2O

NASA Astrophysics Data System (ADS)

Wang, Shi-qiang; Du, Xue-min; Jing, Yan; Guo, Ya-fei; Deng, Tian-long

2017-12-01

The phase and physicochemical properties diagrams of the quaternary system (Li2B4O7 + Na2B4O7 + Mg2B6O11) at 288.15 K and 0.1 MPa were constructed using the solubilities, densities, and refractive indices measured. In the phase diagrams of the system there are one invariant point, three univariant isothermic dissolution curves, and three crystallization regions corresponding to Li2B4O7 · 3H2O, Na2B4O7 · 10H2O, and Mg2B6O11 · 15H2O, respectively. The solution density, refractive index of the quaternary system changes regularly with the increasing of Li2B4O7 concentration. The calculated values of density and refractive index using empirical equations of the quaternary system are in good agreement with the experimental values.

High performance sodium-ion hybrid capacitor based on Na2Ti2O4(OH)2 nanostructures

NASA Astrophysics Data System (ADS)

Babu, Binson; Shaijumon, M. M.

2017-06-01

Hybrid Na-ion capacitors bridge the performance gap between Na-ion batteries and supercapacitors and offer excellent energy and power characteristics. However, designing efficient anode and cathode materials with improved kinetics and long cycle life is essential for practical implementation of this technology. Herein, layered sodium titanium oxide hydroxide, Na2Ti2O4(OH)2, synthesized through hydrothermal technique, is studied as efficient anode material for hybrid Na-ion capacitor. Half-cell electrochemical studies vs. Na/Na+ showed excellent performance for Na2Ti2O4(OH)2 electrode, with ∼57.2% of the total capacity (323.3 C g-1 at 1.0 mV s-1) dominated by capacitive behavior and the remaining due to Na-intercalation. The obtained values are in good agreement with Trasatti plots indicating the potential of this material as efficient anode for hybrid Na-ion capacitor. Further, a full cell Na-ion capacitor is fabricated with Na2Ti2O4(OH)2 as anode and chemically activated Rice Husk Derived Porous Carbon (RHDPC-KOH) as cathode by using organic electrolyte. The hybrid device, operated at a maximum cell voltage of 4 V, exhibits stable electrochemical performance with a maximum energy density of ∼65 Wh kg-1 (at 500 W kg-1, 0.20 A g-1) and with more than ∼ 93% capacitive retention after 3000 cycles.

Evaluation to the effect of B2O3-La2O3-SrO-Na2O-Al2O3 bonding agent on Ti6Al4V-porcelain bonding.

PubMed

Zhao, C Q; Wu, S Q; Lu, Y J; Gan, Y L; Guo, S; Lin, J J; Huang, T T; Lin, J X

2016-10-01

Low-fusing bonding agents have been widely applied in Ti-ceramics restorations. As an important category, borate bonding agents have great potentials in increasing Ti-porcelain bonding. The purpose of this study is to evaluate the effect of borate bonding agent with addition of Na2O and Al2O3 on Ti6Al4V-porcelain bonding. The thermal properties of borate bonding agent, such as glass transition temperature (Tg) and crystallization peak temperature (Tp), were investigated to establish the sintering process. And the coefficient of thermal expansion (CTE) was to evaluate the matching effect of porcelain to Ti6Al4V. The bond strength was analyzed by the three point bending test. The microscopic morphology of the borate bonding agent surface after sintering, the interface of Ti-borate bonding agent-porcelain, and the fracture mode after porcelains fracture, were studied to assess the influence of borate bonding agent on Ti6Al4V-ceramics. With the addition of Na2O and Al2O3, the porcelain residues were observed increased indication on the Ti6Al4V surface after porcelain fracture and the bond strength was acquired the maximum (49.45MPa) in the bonding agent composition of 75.70B2O3-5.92La2O3-11.84SrO-4.67Na2O-1.87Al2O3. Those results suggest that borate bonding agent is an effective way to improve the Ti6Al4V-ceramics bond strength. And the addition of Na2O and Al2O3 strengthen this effect. Copyright © 2016 Elsevier Ltd. All rights reserved.

On the temperature dependence of Na migration in thin SiO 2 films during ToF-SIMS O 2+ depth profiling

NASA Astrophysics Data System (ADS)

Krivec, Stefan; Detzel, Thomas; Buchmayr, Michael; Hutter, Herbert

2010-10-01

The detection of Na in insulating samples by means of time of flight-secondary ion mass spectrometry (ToF-SIMS) depth profiling has always been a challenge. In particular the use of O 2+ as sputter species causes a severe artifact in the Na depth distribution due to Na migration under the influence of an internal electrical filed. In this paper we address the influence of the sample temperature on this artifact. It is shown that the transport of Na is a dynamic process in concordance with the proceeding sputter front. Low temperatures mitigated the migration process by reducing the Na mobility in the target. In the course of this work two sample types have been investigated: (i) A Na doped PMMA layer, deposited on a thin SiO 2 film. Here, the incorporation behavior of Na into SiO 2 during depth profiling is demonstrated. (ii) Na implanted into a thin SiO 2 film. By this sample type the migration behavior could be examined when defects, originating from the implantation process, are present in the SiO 2 target. In addition, we propose an approach for the evaluation of an implanted Na profile, which is unaffected by the migration process.

Asymmetric supercapacitors with high energy density based on helical hierarchical porous Na x MnO2 and MoO2.

PubMed

Lu, Xue-Feng; Huang, Zhi-Xiang; Tong, Ye-Xiang; Li, Gao-Ren

2016-01-01

Helical hierarchical porous Na x MnO 2 /CC and MoO 2 /CC, which are assembled from nanosheets and nanoparticles, respectively, are fabricated using a simple electrodeposition method. These unique helical porous structures enable electrodes to have a high capacitance and an outstanding cycling performance. Based on the helical Na x MnO 2 /CC as the positive electrodes and helical MoO 2 /CC as the negative electrodes, high performance Na x MnO 2 /CC//MoO 2 /CC asymmetric supercapacitors (ASCs) are successfully assembled, and they achieve a maximum volume C sp of 2.04 F cm -3 and a maximum energy density of 0.92 mW h cm -3 for the whole device and an excellent cycling stability with 97.22% C sp retention after 6000 cycles.

Fabrication of Na0.7MnO2/C composite cathode material by simple heat treatment for high-power na-ion batteries

NASA Astrophysics Data System (ADS)

Sohn, DongRak; Lim, Sung-Jin; Nam, Do-Hwan; Hong, Kyung-Sik; Kim, Tae-Hee; Oh, SeKwon; Eom, Ji-Yong; Cho, EunAe; Kwon, HyukSang

2018-01-01

A Na0.7MnO2/C composite cathode material is synthesized by simple and costeffective two-step heat treatment for an improvement in the rate capability of Na0.7MnO2. The first heat treatment is to synthesize Na0.7MnO2, and the second one is a low temperature annealing at 350 °C for 1 h in air, which is necessary to suppress an interfacial reaction between the Na0.7MnO2 and C in the synthesis process of Na0.7MnO2/C composite. Structural analyses by XRD and XPS reveal that the Na0.7MnO2/C shows the same structural properties as that of the pristine Na0.7MnO2, and hence they exhibit the same initial discharge capacity of 175 mAh g-1 at 20 mA g-1. At a current density of 400 mA g-1, the discharge capacity of Na0.7MnO2 reduces to 50 mAh g-1 (28% of the initial discharge capacity), whereas that of Na0.7MnO2/C reduces to 108 mAh g-1 (61% of the initial discharge capacity). The enhanced rate capability of the Na0.7MnO2/C is attributed to the conductive carbon layer formed on the surface of Na0.7MnO2 particles, enabling the facile transport of electrons from the current collector to the surface of the Na0.7MnO2 particles. [Figure not available: see fulltext.

Layered-to-Rock-Salt Transformation in Desodiated Na xCrO 2 ( x 0.4)

DOE PAGES

Bo, Shou-Hang; Li, Xin; Toumar, Alexandra J.; ...

2016-02-01

O3 layered sodium transition metal oxides (i.e., NaMO 2, M = Ti, V, Cr, Mn, Fe, Co, Ni) are a promising class of cathode materials for Na-ion battery applications. These materials, however, all suffer from severe capacity decay when the extraction of Na exceeds certain capacity limits. Understanding the causes of this capacity decay is critical to unlocking the potential of these materials for battery applications. In this work, we investigate the structural origins of capacity decay for one of the compounds in this class, NaCrO 2. The (de)sodiation processes of NaCrO 2 were studied both in situ and exmore » situ through X-ray and electron diffraction measurements. We demonstrate that Na xCrO 2 (0 < x < 1) remains in the layered structural framework without Cr migration up to a composition of Na 0.4CrO 2. Further removal of Na beyond this composition triggers a layered-to-rock-salt transformation, which converts P'3-Na 0.4CrO 2 into the rock-salt CrO 2 phase. This structural transformation proceeds via the formation of an intermediate O3 Na δCrO 2 phase that contains Cr in both Na and Cr slabs and shares very similar lattice dimensions with those of rock-salt CrO 2. It is intriguing to note that intercalation of alkaline ions (i.e., Na + and Li + ) into the rock-salt CrO 2 and O3 Na δCrO 2 structures is actually possible, albeit in a limited amount (~0.2 per formula unit). When these results were analyzed under the context of electrochemistry data, it was apparent that preventing the layered-to-rock-salt transformation is crucial to improve the cyclability of NaCrO 2. Possible strategies for mitigating this detrimental phase transition are proposed.« less

An isopiestic study of aqueous NaBr and KBr at 50 °C: Chemical equilibrium model of solution behavior and solubility in the NaBr-H 2O, KBr-H 2O and Na-K-Br-H 2O systems to high concentration and temperature

NASA Astrophysics Data System (ADS)

Christov, Christomir

2007-07-01

The isopiestic method has been used to determine the osmotic coefficients of the binary solutions NaBr-H 2O (from 0.745 to 5.953 mol kg -1) and KBr-H 2O (from 0.741 to 5.683 mol kg -1) at the temperature t = 50 °C. Sodium chloride solutions have been used as isopiestic reference standards. The isopiestic results obtained have been combined with all other experimental thermodynamic quantities available in literature (osmotic coefficients, water activities, bromide mineral's solubilities) to construct a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the NaBr-H 2O, KBr-H 2O and Na-K-Br-H 2O systems from dilute to high solution concentration within the 0-300 °C temperature range. The Harvie and Weare [Harvie C., and Weare J. (1980) The prediction of mineral solubilities in naturalwaters: the Na-K-Mg-Ca-Cl-SO 4-H 2O system from zero to high concentration at 25 °C. Geochim. Cosmochim. Acta44, 981-997] solubility modeling approach, incorporating their implementation of the concentration-dependent specific interaction equations of Pitzer [Pitzer K. (1973) Thermodynamics of electrolytes. I. Theoretical basis and general equations. J. Phys. Chem.77, 268-277] is employed. The model for binary systems is validated by comparing activity coefficient predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solutions model due to data insufficiencies are discussed. This model expands the variable temperature sodium-potassium model of Greenberg and Moller [Greenberg J., and Moller N. (1989) The prediction of mineral solubilities in natural waters: a chemical equilibrium model for the Na-K-Ca-Cl-SO 4-H 2O system to high concentration from 0 to 250 °C. Geochim. Cosmochim. Acta53, 2503-2518] by evaluating Br - pure electrolyte and mixing solution parameters and the chemical potentials of three bromide solid phases: NaBr-2H 2O (cr), NaBr (cr) and KBr (cr).

Fluorine sites in glasses and transparent glass-ceramics of the system Na{sub 2}O/K{sub 2}O/Al{sub 2}O{sub 3}/SiO{sub 2}/BaF{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bocker, Christian, E-mail: christian.bocker@uni-jena.d; Munoz, Francisco; Duran, Alicia

2011-02-15

The transparent glass-ceramics obtained in the silicate system Na{sub 2}O/K{sub 2}O/SiO{sub 2}/BaF{sub 2} show homogeneously dispersed BaF{sub 2} nano crystals with a narrow size distribution. The X-ray diffraction and the nuclear magnetic resonance spectroscopy were applied to glasses and the respective glass-ceramics in order to clarify the crystallization mechanism and the role of fluorine during crystallization. With an increasing annealing time, the concentration and also the number of crystals remain approximately constant. With an increasing annealing temperature, the crystalline fraction increases until a saturation limit is reached, while the number of crystals decreases and the size of the crystals increases.more » Fluoride in the glassy network occurs as Al-F-Ba, Al-F-Na and also as Ba-F structures. The latter are transformed into crystalline BaF{sub 2} and fluoride is removed from the Al-F-Ba/Na bonds. However, some fluorine is still present in the glassy phase after the crystallization. -- Graphical abstract: The X-ray diffraction and the nuclear magnetic resonance spectroscopy were applied to glasses in the silicate system Na{sub 2}O/K{sub 2}O/SiO{sub 2}/BaF{sub 2} and the respective glass-ceramics with BaF{sub 2} nano crystals in order to clarify the crystallization mechanism and the role of fluorine during crystallization. Display Omitted Research highlights: {yields} BaF{sub 2} nano crystals are precipitated from a silicate glass system. {yields} Ostwald ripening during the late stage of crystallization does not occur. {yields} Fluorine in the glass is coordinated with Ba as well as Al together with Ba or Na.{yields} In the glass-ceramics, the residual fluorine is coordinated as Al-F-Ba/Na.« less

Cesium and strontium ion exchange on the framework titanium silicate M2Ti2O3SiO4.nH2O (M = H, Na).

PubMed

Solbrå, S; Allison, N; Waite, S; Mikhalovsky, S V; Bortun, A I; Bortun, L N; Clearfield, A

2001-02-01

The ion exchange properties of the titanium silicate, M2Ti2O3SiO4.nH2O (M = H, Na), toward stable and radioactive 137Cs+ and 89Sr2+, have been examined. By studying the cesium and strontium uptake in the presence of NaNO3, CaCl2, NaOH, and HNO3 (in the range of 0.01-6 M) the sodium titanium silicate was found to be an efficient Cs+ ion exchanger in acid, neutral, and alkaline media and an efficient Sr2+ ion exchanger in neutral and alkaline media, which makes it promising for treatment of contaminated environmental media and biological systems.

Characteristics of NaNO3-Promoted CdO as a Midtemperature CO2 Absorbent.

PubMed

Kim, Kang-Yeong; Kwak, Jin-Su; An, Young-In; Oh, Kyung-Ryul; Kwon, Young-Uk

2017-06-28

In this study, we explored the reaction system CdO(s) + CO 2 (g) ⇄ CdCO 3 (s) as a model system for CO 2 capture agent in the intermediate temperature range of 300-400 °C. While pure CdO does not react with CO 2 at all up to 500 °C, CdO mixed with an appropriate amount of NaNO 3 (optimal molar ratio NaNO 3 /CdO = 0.14) greatly enhances the conversion of CdO into CdCO 3 up to ∼80% (5.68 mmol/g). These NaNO 3 -promoted CdO absorbents can undergo many cycles of absorption and desorption by temperature swing between 300 and 370 °C under a 100% CO 2 condition. Details of how NaNO 3 promotes the CO 2 absorption of CdO have been delineated through various techniques using thermogravimetry, coupled with X-ray diffraction and electron microscopy. On the basis of the observed data, we propose a mechanism of CO 2 absorption and desorption of NaNO 3 -promoted CdO. The absorption proceeds through a sequence of events of CO 2 adsorption on the CdO surface covered by NaNO 3 , dissolution of so-formed CdCO 3 , and precipitation of CdCO 3 particles in the NaNO 3 medium. The desorption occurs through the decomposition of CdCO 3 in the dissolved state in the NaNO 3 medium where CdO nanoparticles are formed dispersed in the NaNO 3 medium. The CdO nanoparticles are aggregated into micrometer-large particles with smooth surfaces and regular shapes.

Calculation of the vapor-saturated liquidus for the NaCl-CO2-H2O system

USGS Publications Warehouse

Barton, P.B.; I-Ming, C.

1993-01-01

The polybaric liquidus surface for the H2O-rich corner of the NaCl-CO2-H2O ternary is calculated, relying heavily on 1. (1) a Henry's law equation for CO2 in brines (modified from Drummond, 1981), 2. (2) the assumption that the contributions of dissolved NaCl and CO2 in lowering the activity of H2O are additive, and 3. (3) data on the CO2 clathrate solid solution (nominally CO2 ?? 7.3H2O, but ranging from 5.75 to 8 or 9 H2O) from Bozzo et al. (1975). The variation with composition of the activity of CO2??7.3H2O, or any other composition within the clathrate field, is small, thereby simplifying the calculations appreciably. Ternary invariant points are 1. (1) ternary eutectic at -21.5??C, with ice + clathrate + hydrohalite NaCl-??H2O + brine mNaCl = 5.15, mco2 = 0.22 + vapor Ptotal ??? Pco2 = 5.7 atm; 2. (2) peritectic at -9.6??C, with clathrate + hydrohalite + liquid CO2 + brine mNaCl = 5.18, mco2 = 0.55 + vapor (Ptotal ??? Pco2 = 26.47 atm); and 3. (3) peritectic slightly below +0.1 ??C, with halite + hydrohalite + liquid CO2 + brine (mNaCl ??? 5.5, mco2 ??? 0.64) + vapor (Ptotal ??? Pco2 ??? 34 atm). CO2 isobars have been contoured on the ternary liquidus and also on the 25??C isotherm. An important caveat regarding the application of this information to the interpretation of the freezing-thawing behavior of fluid inclusions is that metastable behavior is a common characteristic of the clathrate. ?? 1993.

Preparation and Characterization of PbO-SrO-Na2O-Nb2O5-SiO2 Glass Ceramics Thin Film for High-Energy Storage Application

NASA Astrophysics Data System (ADS)

Tan, Feihu; Zhang, Qingmeng; Zhao, Hongbin; Wei, Feng; Du, Jun

2018-03-01

PbO-SrO-Na2O-Nb2O5-SiO2 (PSNNS) glass ceramic thin films were prepared by pulsed laser deposition technology on heavily doped silicon substrates. The influence of annealing temperatures on microstructures, dielectric properties and energy storage performances of the as-prepared films were investigated in detail. X-ray diffraction studies indicate that Pb2Nb2O7 crystallizes at 800°C and disappears at 900°C, while NaNbO3 and PbNb2O6 are formed at the higher temperature of 900°C. The dielectric properties of the glass ceramics thin films have a strong dependence on the phase assemblages that are developed during heat treatment. The maximum dielectric constant value of 171 was obtained for the film annealed at 800°C, owing to the high electric breakdown field strength, The energy storage densities of the PSNNS films annealed at 800°C were as large as 36.9 J/cm3, These results suggest that PSNNS thin films are promising for energy storage applications.

Glass transition temperature and conductivity in Li2O and Na2O doped borophosphate glasses

NASA Astrophysics Data System (ADS)

Ashwajeet, J. S.; Sankarappa, T.; Ramanna, R.; Sujatha, T.; Awasthi, A. M.

2015-08-01

Two alkali doped Borophosphate glasses in the composition, (B2O3)0.2. (P2O5)0.3. (Na2O)(0.5-x). (Li2O)x, where x = 0.05 to 0.50 were prepared by standard melt quenching method at 1200K. Non-crystalline nature was confirmed by XRD studies. Room temperature density was measured by Archimedes principle. DC conductivity in the temperature range from 300K to 575K has been measured. Samples were DSC studied in the temperature range from 423K to 673K and glass transition temperature was determined. Glass transition temperature passed through minima for Li2O con.2centration between 0.25 and 0.30 mole fractions. Activation energy of conduction has been determined by analyzing temperature variation of conductivity determining Arrhenius law. Conductivity passed through minimum and activation passed through maximum for Li2O content from 0.25 to 0.30 mole fractions. Glass transition temperature passed through minimum for the same range of Li2O content. These results revealed mixed alkali effect taking place in these glasses. It is for the first time borophosphate glasses doped with Li2O and Na2O have been studied for density and dc conductivity and, the mixed alkali effect (MAE) has been observed.

Threshold oxygen levels in Na(I) for the formation of NaCrO 2(s) on 18-8 stainless steels from accurate thermodynamic measurements

NASA Astrophysics Data System (ADS)

Sreedharan, O. M.; Madan, B. S.; Gnanamoorthy, J. B.

1983-12-01

The compound NaCrO 2(s) is an important corrosion product in sodium-cooled LMFBRs. The standard Gibbs energy of formation of NaCrO 2(s) is required for the computation of threshold oxygen levels in Na(1) for the formation of NaCrO 2(s) on 18-8 stainless steels. For this purpose the emf of the galvanic cell: Pt, NaCrO 2, Cr 2O 3, Na 2CrO 4/15 YSZ/O 2 ( P O 2 = 0.21 atm, air), Pt was measured over 784-1012 K to be: (E±4.4)(mV) = 483.67-0.34155 T(K). From this, the standard Gibbs energy of formation of NaCrO 2(s) from the elements ( ΔG f,T0) and from the oxides ( ΔG f,OX,T0) was calculated to be: [ΔG f,T0(NaCrO 2, s)±1.86] (kJ/mol) =-869.98 + 0.18575 T(K) , [ΔG f,OX,T0(NaCr0 2, s)±4.8] (kJ/mol) = -104.25-0.00856 T(K) . The molar heat capacity, C P0, of NaCrO 2(s) was measured by DSC to be (350-600 K): C P0(NaCrO 2, s) (J/K mol) = 27.15 + 0.1247 T (K) , From these data, values of -99.3 kJ/mol and 91.6 J/K mol were computed for ΔH f,2980 and S 2980 of NaCrO 2(s). The internal consistency was checked with the use of enthalpy data on Na 2CrO 4(s). From the standard Gibbs energy of formation of NaCrO 2(s) the equation logC 0(wppm) = 3.9905-3147.6 T(K) was derived, where C 0 is the threshold oxygen level for the formation of NaCrO 2(s) on 18-8 stainless steels.

Structure and temperature-dependent phase transitions of lead-free Bi 1/2Na 1/2TiO 3-Bi 1/2K 1/2TiO 3-K 0.5Na 0.5NbO 3 piezoceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anton, Eva-Maria; Schmitt, Ljubomira Ana; Hinterstein, Manuel

2014-05-28

Structure and phase transitions of (1-y)((1-x)Bi 1/2Na 1/2TiO 3-xBi 1/2K 1/2TiO 3)-yK 0.5Na 0.5NbO 3 (x; y) piezoceramics (0.1 ≤ x ≤ 0.4; 0 ≤ y ≤ 0.05) were investigated by transmission electron microscopy, neutron diffraction, temperature-dependent x-ray diffraction, and Raman spectroscopy. The local crystallographic structure at room temperature (RT) does not change by adding K 0.5Na 0.5NbO 3 to Bi 1/2Na 1/2TiO 3-xBi 1/2K 1/2TiO 3 for x = 0.2 and 0.4. The average crystal structure and microstructure on the other hand develop from mainly long-range polar order with ferroelectric domains to short-range order with polar nanoregions displaying amore » more pronounced relaxor character. The (0.1; 0) and (0.1; 0.02) compositions exhibit monoclinic Cc space group symmetry, which transform into Cc + P4bm at 185 and 130 °C, respectively. This high temperature phase is stable at RT for the morphotropic phase boundary compositions of (0.1; 0.05) and all compositions with x = 0.2. For the compositions of (0.1; 0) and (0.1; 0.02), local structural changes on heating are evidenced by Raman; for all other compositions, changes in the long-range average crystal structure were observed.« less

Effect of Na poisoning catalyst (V2O5-WO3/TiO2) on denitration process and SO3 formation

NASA Astrophysics Data System (ADS)

Xiao, Haiping; Chen, Yu; Qi, Cong; Ru, Yu

2018-03-01

This paper aims to study the effect of alkali metal sodium (Na) poisoning on the performance of the Selective Catalytic Reduction (SCR) catalyst. The result showed that Na2SO4 poisoning leads to a reduced denitration rate of the SCR catalyst and an increase in the SO3 generation rate. Na2O poisoning leads to a significant reduction in the denitration rate of the SCR catalyst and marginally improves the formation of SO3. The maximum of the SO3 generation rate for a Na2SO4-poisoned catalyst reached 1.35%, whereas it was only 0.85% for the SCR catalyst. When the SO2 was contained in flue gas, the denitration rate for the Na2O-poisoned catalyst clearly increased by more than 28%. However, the effect of SO2 on the Na2SO4-poisoned catalyst was very slight. The denitration rate of the SCR catalyst decreased with an increase in the Na content. The BET and XRD results showed that Na poisoning of the catalyst decreased the number of acid sites, the reducibility of the catalyst, the surface area, and pore volume. The H2-TPR and NH3-TPD results show that Na decreases the number of acid sites and the reducibility of the catalyst. The FT-IR and XPS results showed that Na2O poisoning led to the decrease of V5+dbnd O bonds and the consumptions of oxygen atoms. Na2SO4 poisoning can improve surface adsorbed oxygen, which was beneficial for the SO2-SO3 conversion reaction.

Influence of pH and ionic strength (NaCl/Na2SO4) on the reaction HO Cl/ClO- + NO2-

NASA Astrophysics Data System (ADS)

Marcellos da Rosa, M.; Zetzsch, C.

2003-04-01

Equilibria such as HOCl + NO_2^- leftrightarrow ClNO_2 + OH^- and ClNO_2 + H_2O leftrightarrow NO_3^- + 2H^+ + Cl^- play an important role in halogen activation in the troposphere. We studied the oxidation of NO_2^- by HOCl/ClO^- in aqueous phase by stopped-flow measurements at different ionic strengths (bidestilled water, 0.1M NaCl, 1.0M NaCl and 1.0M Na_2SO^4) at various pH values (4.0, 5.5, 6.2 and 10.0) at 293K. The experiments were performed using a SX.18MV Applied Photophysics spectrophotometer, observing the exponential decay of HOCl/ClO^- at λ = 290nm between 10ms and 100s. HOCl (pK_a= 7.50) was obtained by bubbling N_2 with 1% Cl_2 through bidestilled water. The pH of the aqueous solutions of HOCl was determined by a pH meter (CG820, Schott) with a glass electrode N6180 (calibrated with standard buffer solutions at pH = 3.0, 4.0, 7.0 and 10.0), and the pH values were adjusted by dropwise addition of HClO_4 or NaOH. The concentrations of HOCl (ɛHOCl (230nm) = 100M-1cm-1) ([HOCl] = 1.3mM - 10mM) and ClO- (ɛClO- (292nm) = 350 M-1cm-1) ([ClO^-] = 1.3mM - 5mM) were determined by UV spectrometry (Kontron UVIKON 860) at a resolution of 2 nm in 1 cm cells at various pH values. The concentration range of NO_2^- was between 5mM and 50mM. The following second-order rate constant kII were obtained at 293K at various pH values (in units of M-1s-1) in H_2O: pH 4.0, (5.6±0.3)\\cdot 10^3; pH 5.5, (5.0±0.4)\\cdot 10^3; pH 10.0, 3.9±0.4; in 0.1M NaCl: pH 5.5, (4.3±0.4)\\cdot 10^3; pH 10.0, 2.6±0.4; in 1.0M NaCl: pH 5.5, (4.0±0.3); pH 10.0, 0.7±0.2 and in 1.0M Na_2SO_4: pH 5.5, (3.0±0.3)\\cdot 10^3; pH 10.0, 1.9±0.4. There is a strong effect of the pH on the reaction HOCl/ClO^- + NO_2^-, as reflected in the ratio kII_a(pH 5.5, HOCl)/kII_b(pH 10.0, ClO^-): in H_2O (kII_a ˜ 1200 \\cdot kII_b), in 0.1M NaCl (kII_a ˜ 1900 \\cdot kII_b), in 1.0M NaCl (kII_a ˜ 5700 \\cdot kII_b) and in 1.0 M Na_2SO_4 (kII_a ˜ 1500 \\cdot kII_b). A mechanism for the oxidation of NO

Enhanced enzymatic saccharification of sugarcane bagasse pretreated by combining O2 and NaOH.

PubMed

Bi, Shuaizhu; Peng, Lincai; Chen, Keli; Zhu, Zhengliang

2016-08-01

Sugarcane bagasse pretreated by combining O2 and NaOH with different variables was conducted to improve its enzymatic digestibility and sugar recovery, and the results were compared with sole NaOH pretreatment. Lignin removal for O2-NaOH pretreatment was around 10% higher than that for sole NaOH pretreatment under the same conditions, and O2-NaOH pretreatment resulted in higher glucan recovery in the solid remain. Subsequently, O2-NaOH pretreated sugarcane bagasse presented more efficient enzymatic digestibility than sole NaOH pretreatment. Under the moderate pretreatment conditions of combining 1% NaOH and 0.5MPa O2 at 80°C for 120min, a high glucan conversion of 95% was achieved after 48h enzymatic hydrolysis. Coupled with the operations of pretreatment and enzymatic hydrolysis, an admirable total sugar recovery of 89% (glucose recovery of 93% and xylose recovery of 84%) was obtained. The susceptibility of the substrates to enzymatic digestibility was explained by their physical and chemical characteristics. Copyright © 2016 Elsevier Ltd. All rights reserved.

Na Diffusion in Quasi One-Dimensional Ion Conductor NaMn2O4 Observed by μ+SR

NASA Astrophysics Data System (ADS)

Umegaki, Izumi; Nozaki, Hiroshi; Harada, Masashi; Månsson, Martin; Sakurai, Hiroya; Kawasaki, Ikuto; Watanabe, Isao; Sugiyama, Jun

A quasi one-dimensional (1D) compound, NaMn2O4, in which Mn2O4 zigzag chains form a 1D channel along the b-axis and Na ions locate at the center of the channel, is thought to be a good Na ionic conductor. In order to study Na-ion diffusion, we have measured μ+SR spectra using a powder sample in the temperature range between 100 and 500 K. A diffusive behavior was clearly observed above 325 K. Assuming a thermal activate process for jump diffusion of Na-ion between two nearest neighboring sites, a self diffusion coefficient of Na ion (DNa) and its activation energy (Ea) were estimated as DNa = (3.1 ± 0.2) × 10 - 11 cm2/s at 350 K and Ea = 180(9) meV.

Bioactivity of Y2O3 and CeO2 doped SiO2-SrO-Na2O glass-ceramics.

PubMed

Placek, L M; Keenan, T J; Wren, A W

2016-08-01

The bioactivity of yttrium and cerium are investigated when substituted for Sodium (Na) in a 0.52SiO2-0.24SrO-0.24-xNa2O-xMO glass-ceramics (where x = 0.08 and MO = Y2O3 or CeO2). Bioactivity is monitored through pH and inductively coupled plasma-optical emission spectrometry where pH of simulated body fluid ranged from 7.5 to 7.6 and increased between 8.2 and 10.0 after 14-day incubation with the glass-ceramic disks. Calcium (Ca) and phosphorus (P) levels in simulated body fluid after incubation with yttrium and cerium containing disks show a continual decline over the 14-day period. In contrast, Con disks (not containing yttrium or cerium) caused the elimination of Ca in solution after 1 day and throughout the incubation period, and initially showed a decline in P levels followed by an increase at 14 days. Scanning electron microscopy and energy dispersive spectroscopy confirmed the presence of Ca and P on the surface of the simulated body fluid-incubated disks and showed precipitates on Con and HCe (8 mol% cerium) samples. Cell viability of MC3T3 osteoblasts was not significantly affected at a 9% extract concentration. Optical microscopy after 24 h cell incubation with disks showed that Con samples do not support osteoblast or Schwann cell growth, while all yttrium and cerium containing disks have direct contact with osteoblasts spread across the wells. Schwann cells attached in all wells, but only showed spreading with the HY-S (8 mol% yttrium, heated to sintering temperature) and YCe (4 mol% yttrium and cerium) disks. Scanning electron microscopy of the compatible disks shows osteoblast and sNF96.2 Schwann cells attachment and spreading directly on the disk surfaces. © The Author(s) 2016.

Frustration by competing interactions in the highly-distorted double perovskites La2NaRuO6 and La2NaOsO6

NASA Astrophysics Data System (ADS)

Aczel, A. A.; Bugaris, D. E.; Li, L.; Yan, J.-Q.; de La Cruz, C.; Zur Loye, H.-C.; Nagler, S. E.

2013-03-01

The usual classical behavior of S = 3/2, B-site ordered double perovskites results in simple, commensurate magnetic ground states. In contrast, heat capacity and neutron powder diffraction measurements for the S = 3/2 systems La2NaB'O6 (B' = Ru, Os) reveal an incommensurate magnetic ground state for La2NaRuO6 and a drastically suppressed ordered moment for La2NaOsO6. This behavior is attributed to the large monoclinic structural distortions of these double perovskites. The distortions have the effect of weakening the nearest neighbor superexchange interactions, presumably to an energy scale that is comparable to the next nearest neighbor superexchange. The exotic ground states in these materials can then arise from a competition between these two types of antiferromagnetic interactions, providing a novel mechanism for achieving frustration in the double perovskite family. Work at ORNL is supported by the Division of Scientific User Facilities and the Materials Science and Engineering Division, DOE Basic Energy Sciences. Work at the University of South Carolina is supported by the Heterogeneous Functional Materials Research Center, funded by DOE under award number de-sc0001061.

Thermochemical generation of hydrogen and oxygen from water. [NaMnO/sub 2/ and TiO/sub 2/

DOEpatents

Robinson, P.R.; Bamberger, C.E.

1980-02-08

A thermochemical cyclic process for the production of hydrogen exploits the reaction between sodium manganate (NaMnO/sub 2/) and titanium dioxide (TiO/sub 2/) to form sodium titanate (Na/sub 2/TiO/sub 3/), manganese (II) titanate (MnTiO/sub 3/) and oxygen. The titanate mixture is treated with sodium hydroxide, in the presence of steam, to form sodium titanate, sodium manganate (III), water and hydrogen. The sodium titanate-manganate (III) mixture is treated with water to form sodium manganate (III), titanium dioxide and sodium hydroxide. Sodium manganate (III) and titanium dioxide are recycled following dissolution of sodium hydroxide in water.

A study of Na(x)Pt3O4 as an O2 electrode bifunctional electrocatalyst

NASA Technical Reports Server (NTRS)

Fielder, William L.; Singer, Joseph

1991-01-01

The present study suggests that polytetrafluoroethylene (PTFE) bonded Na(X)Pt3O4 gas porous diffusion electrodes may be a viable candidate for bifunctional O2 reduction and evolution activity. The electrodes exhibited Tafel slopes of about 0.06 V/decade for both O2 reduction an evolution. For O2 reduction, the 0.06 slope doubled to 0.12 V/decade at larger current densities. Preliminary stability testing at 24 C suggest that the Na(x)Pt3O4 electrodes were relatively stable at reducing and oxidizing potentials typically encountered at the O2 electrodes in a regenerative fuel cell.

Heat treatment of Na2O-CaO-P2O5-SiO2 bioactive glasses: densification processes and postsintering bioactivity.

PubMed

Sola, A; Bellucci, D; Raucci, M G; Zeppetelli, S; Ambrosio, L; Cannillo, V

2012-02-01

Because of their excellent bioactivity, bioactive glasses are increasingly diffused to produce biomedical devices for bone prostheses, to face the dysfunctions that may be caused by traumatic events, diseases, or even natural aging. However, several processing routes, such as the production of scaffolds or the deposition of coatings, include a thermal treatment to apply or sinter the glass. The exposure to high temperature may induce a devetrification phenomenon, altering the properties and, in particular, the bioactivity of the glass. The present contribution offers an overview of the thermal behavior and properties of two glasses belonging to the Na2O-CaO-P2O5-SiO2 system, to be compared to the standard 45S5 Bioglass(®). The basic goal is to understand the effect of both the original composition and the thermal treatment on the performance of the sintered glasses. The new glasses, the one (BG_Na) with a high content of Na2O, the other (BG_Ca) with a high content of CaO, were fully characterized and sintering tests were performed to define the most interesting firing cycles. The sintered samples, treated at 880°C and 800°C respectively, were investigated from a microstructural point of view and their mechanical properties were compared to those of the bulk (not sintered) glass counterparts. The effect of sintering was especially striking on the BG_Ca material, whose Vickers hardness increased from 598.9 ± 46.7 HV to 1053.4 ± 35.0 HV. The in vitro tests confirmed the ability of the glasses, both in bulk and sintered form, of generating a hydroxyapatite surface layer when immersed in a simulated body fluid. More accurate biological tests performed on the sintered glasses proved the high bioactivity of the CaO-rich composition even after a heat treatment. Copyright © 2011 Wiley Periodicals, Inc.

Structure, microstructure and infrared studies of Ba{sub 0.06}(Na{sub 1/2}Bi{sub 1/2}){sub 0.94}TiO{sub 3}-NaNbO{sub 3} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roy, Sumit K., E-mail: sumit.sxc13@gmail.com; Singh, S. N., E-mail: snsphyru@gmail.com; Prasad, K., E-mail: k.prasad65@gmail.com

2016-05-06

Lead-free solid solutions (1-x)Ba{sub 0.06}(Na{sub 1/2}Bi{sub 1/2}){sub 0.94}TiO{sub 3}-xNaNbO{sub 3} (0 ≤ x ≤ 1.0) were prepared by conventional ceramic fabrication technique. X-ray diffraction and Rietveld refinement analyses of these ceramics were carried out using X’Pert HighScore Plus software to determine the crystal symmetry, space group and unit cell dimensions. Rietveld refinement revealed that NaNbO{sub 3} with orthorhombic structure was completely diffused into Ba{sub 0.06}(Na{sub 1/2}Bi{sub 1/2}){sub 0.94}TiO{sub 3} lattice having the rhombohedral-tetragonal symmetry. EDS and SEM studies were carried out in order to evaluate the quality and purity of the compounds. SEM images showed a change in grain shapemore » with the increase of NaNbO{sub 3} content. FTIR spectra confirmed the formation of solid solution.« less

Crystallization Behavior and Heat Transfer of Fluorine-Free Mold Fluxes with Different Na2O Concentration

NASA Astrophysics Data System (ADS)

Yang, Jian; Zhang, Jianqiang; Sasaki, Yasushi; Ostrovski, Oleg; Zhang, Chen; Cai, Dexiang; Kashiwaya, Yoshiaki

2016-08-01

In this study, the crystallization behavior and heat transfer of CaO-SiO2-Na2O-B2O3-TiO2-Al2O3-MgO-Li2O fluorine-free mold fluxes with different Na2O contents (5 to 11 mass pct) were studied using single/double hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. Continuous cooling transformation (CCT) and time-temperature transformation (TTT) diagrams constructed using SHTT showed that crystallization temperature increased and incubation time shortened with the increase of Na2O concentration, indicating an enhanced crystallization tendency. The crystallization process of mold fluxes in the temperature field simulating the casting condition was also investigated using DHTT. X-ray diffraction (XRD) analysis of the quenched mold fluxes showed that the dominant phase changed from CaSiO3 to Ca11Si4B2O22 with the increasing concentration of Na2O. The heat transfer examined by IET showed that the increase of Na2O concentration reduced the responding heat flux when Na2O was lower than 9 mass pct but the further increase of Na2O to 11 mass pct enhanced the heat flux. The correlation between crystallinity and heat transfer was discussed in terms of crystallization tendency and crystal morphology.

Formation of hydroxyapatite onto glasses of the CaO-MgO-SiO2 system with B2O3, Na2O, CaF2 and P2O5 additives.

PubMed

Agathopoulos, S; Tulyaganov, D U; Ventura, J M G; Kannan, S; Karakassides, M A; Ferreira, J M F

2006-03-01

New bioactive glasses with compositions based on the CaO-MgO-SiO(2) system and additives of B(2)O(3), P(2)O(5), Na(2)O, and CaF(2) were prepared. The in vitro mineralization behaviour was tested by immersion of powders or bulk glasses in simulated body fluid (SBF). Monitoring of ionic concentrations in SBF and scanning electron microscopy (SEM) observations at the surface of the glasses were conducted over immersion time. Raman and infrared (IR) spectroscopy shed light on the structural evolution occurring at the surface of the glasses that leads to formation of hydroxyapatite.

Highly Durable Na2V6O16·1.63H2O Nanowire Cathode for Aqueous Zinc-Ion Battery.

PubMed

Hu, Ping; Zhu, Ting; Wang, Xuanpeng; Wei, Xiujuan; Yan, Mengyu; Li, Jiantao; Luo, Wen; Yang, Wei; Zhang, Wencui; Zhou, Liang; Zhou, Zhiqiang; Mai, Liqiang

2018-03-14

Rechargeable aqueous zinc-ion batteries are highly desirable for grid-scale applications due to their low cost and high safety; however, the poor cycling stability hinders their widespread application. Herein, a highly durable zinc-ion battery system with a Na 2 V 6 O 16 ·1.63H 2 O nanowire cathode and an aqueous Zn(CF 3 SO 3 ) 2 electrolyte has been developed. The Na 2 V 6 O 16 ·1.63H 2 O nanowires deliver a high specific capacity of 352 mAh g -1 at 50 mA g -1 and exhibit a capacity retention of 90% over 6000 cycles at 5000 mA g -1 , which represents the best cycling performance compared with all previous reports. In contrast, the NaV 3 O 8 nanowires maintain only 17% of the initial capacity after 4000 cycles at 5000 mA g -1 . A single-nanowire-based zinc-ion battery is assembled, which reveals the intrinsic Zn 2+ storage mechanism at nanoscale. The remarkable electrochemical performance especially the long-term cycling stability makes Na 2 V 6 O 16 ·1.63H 2 O a promising cathode for a low-cost and safe aqueous zinc-ion battery.

Electrochemical properties and structures of the mixed-valence lithium cuprates Li 3Cu 2O 4 and Li 2NaCu 2O 4

NASA Astrophysics Data System (ADS)

Raekelboom, E. A.; Hector, A. L.; Weller, M. T.; Owen, J. R.

The electrochemical performances of Li 3Cu 2O 4 and Li 2NaCu 2O 4 as cathode materials in lithium coin type batteries have been studied. In Li 3Cu 2O 4, the copper was oxidised to the III level when cycling. The replacement of the lithium by the sodium ions in the octahedral sites in Li 2NaCu 2O 4 might have an effect on the pathway of the lithium ions during the (de)intercalations.

Effect of Na2O on Crystallisation Behaviour and Heat Transfer of Fluorine-Free Mould Fluxes

NASA Astrophysics Data System (ADS)

Yang, Jian; Zhang, Jianqiang; Sasaki, Yasushi; Ostrovski, Oleg; Zhang, Chen; Cai, Dexiang; Kashiwaya, Yoshiaki

Most of the commercial mould fluxes contain fluorides which bring about serious environmental problems. The major challenge in the application of fluorine-free mould fluxes is to control the heat transfer from the strand to copper mould which is closely related to crystallisation behaviour. In this study, the effects of Na2O on the crystallisation behaviour and heat transfer of CaO-SiO2-Na2O-B2O3-TiO2-Al2O3-MgO-Li2O mould fluxes were investigated using single /double hot thermocouple technique (SHTT/DHTT) and infrared emitter technique (IET), respectively. Continuous cooling transformation (CCT) and time-temperature transformation (TTT) diagrams constructed using SHTT showed that the increase of Na2O concentration led to higher critical cooling rate and shorter incubation time. The crystallisation behaviour in a thermal gradient was examined using DHTT. The heat flux measured by IET showed that the increase of Na2O concentration decreased the heat flux when Na2O was lower than 9 mass% but the further increase of Na2O raised the heat flux. The relationship between flux crystallisation and heat transfer was also discussed.

A new sol-gel process for producing Na(2)O-containing bioactive glass ceramics.

PubMed

Chen, Qi-Zhi; Li, Yuan; Jin, Li-Yu; Quinn, Julian M W; Komesaroff, Paul A

2010-10-01

The sol-gel process of producing SiO(2)-CaO bioactive glasses is well established, but problems remain with the poor mechanical properties of the amorphous form and the bioinertness of its crystalline counterpart. These properties may be improved by incorporating Na(2)O into bioactive glasses, which can result in the formation of a hard yet biodegradable crystalline phase from bioactive glasses when sintered. However, production of Na(2)O-containing bioactive glasses by sol-gel methods has proved to be difficult. This work reports a new sol-gel process for the production of Na(2)O-containing bioactive glass ceramics, potentially enabling their use as medical implantation materials. Fine powders of 45S5 (a Na(2)O-containing composition) glass ceramic have for the first time been successfully synthesized using the sol-gel technique in aqueous solution under ambient conditions, with the mean particle size being approximately 5 microm. A comparative study of sol-gel derived S70C30 (a Na(2)O-free composition) and 45S5 glass ceramic materials revealed that the latter possesses a number of features desirable in biomaterials used for bone tissue engineering, including (i) the crystalline phase Na(2)Ca(2)Si(3)O(9) that couples good mechanical strength with satisfactory biodegradability, (ii) formation of hydroxyapatite, which may promote good bone bonding and (iii) cytocompatibility. In contrast, the sol-gel derived S70C30 glass ceramic consisted of a virtually inert crystalline phase CaSiO(3). Moreover, amorphous S70C30 largely transited to CaCO(3) with minor hydroxyapatite when immersed in simulated body fluid under standard tissue culture conditions. In conclusion, sol-gel derived Na(2)O-containing glass ceramics have significant advantages over related Na(2)O-free materials, having a greatly improved combination of mechanical capability and biological absorbability. 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

X-ray diffraction and infrared spectroscopy studies of Ba(Fe1/2Nb1/2)O3-(Na1/2Bi1/2)TiO3 ceramics

NASA Astrophysics Data System (ADS)

Chandra, K. P.; Yadav, Anjana; Prasad, K.

2018-05-01

Ceramics (1-x)Ba(Fe1/2Nb1/2)O3-x(Na1/2Bi1/2)TiO3; 0≤x≤1.0 were prepared by conventional ceramic synthesis technique. Rietveld refinements of X-ray diffraction data of these ceramics were carried out using FullProf software and determined their crystal symmetry, space group and unit cell dimensions. Rietveld refinement revealed that Ba(Fe1/2Nb1/2)O3 has cubic structure with space group Pm 3 ¯ m and Na1/2Bi1/2)TiO3 has rhombohedral structure with space group R3c. Addition of (Na1/2Bi1/2)TiO3 to Ba(Fe1/2Nb1/2)O3 resulted in the change of unit cell structure from cubic to tetragonal (P4/mmm) for x = 0.75 and the X-Ray diffraction peaks slightly shift towards higher Bragg's angle, suggesting slight decrease in unit cell volume. SEM studies were carried out in order to access the quality of the prepared ceramics which showed a change in grain shapes with the increase of (Na1/2Bi1/2)TiO3 content. FTIR spectra confirmed the formation of perovskite type solid solutions.

Dithallium(III)-Containing 30-Tungsto-4-phosphate, [Tl2Na2(H2O)2(P2W15O56)2]16-: Synthesis, Structural Characterization, and Biological Studies.

PubMed

Ayass, Wassim W; Fodor, Tamás; Farkas, Edit; Lin, Zhengguo; Qasim, Hafiz M; Bhattacharya, Saurav; Mougharbel, Ali S; Abdallah, Khaled; Ullrich, Matthias S; Zaib, Sumera; Iqbal, Jamshed; Harangi, Sándor; Szalontai, Gábor; Bányai, István; Zékány, László; Tóth, Imre; Kortz, Ulrich

2018-06-18

Here we report on the synthesis and structural characterization of the dithallium(III)-containing 30-tungsto -4-phosphate [Tl 2 Na 2 (H 2 O) 2 {P 2 W 15 O 56 } 2 ] 16- (1) by a multitude of solid-state and solution techniques. Polyanion 1 comprises two octahedrally coordinated Tl 3+ ions sandwiched between two trilacunary {P 2 W 15 } Wells-Dawson fragments and represents only the second structurally characterized, discrete thallium-containing polyoxometalate to date. The two outer positions of the central rhombus are occupied by sodium ions. The title polyanion is solution-stable as shown by 31 P and 203/205 Tl NMR. This was also supported by Tl NMR spectra simulations including several spin systems of isotopologues with half-spin nuclei ( 203 Tl, 205 Tl, 31 P, 183 W). 23 Na NMR showed a time-averaged signal of the Na + counter cations and the structurally bonded Na + ions. 203/205 Tl NMR spectra also showed a minor signal tentatively attributed to the trithallium-containing derivative [Tl 3 Na(H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 14- , which could also be identified in the solid state by single-crystal X-ray diffraction. The bioactivity of polyanion 1 was also tested against bacteria and Leishmania.

Oxidation of MnO(100) and NaMnO2 formation: Characterization of Mn2+ and Mn3+ surfaces via XPS and water TPD

NASA Astrophysics Data System (ADS)

Feng, Xu; Cox, David F.

2018-09-01

The oxidation of clean and Na precovered MnO(100) has been investigated by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD) of adsorbed water. XPS results indicate that Mn3O4-like and Mn2O3-like surfaces can be formed by various oxidation treatments of clean and nearly-stoichiometric MnO(100), while a NaMnO2-like surface can be produced by the oxidation of MnO(100) pre-covered with multilayers of metallic Na. Water TPD results indicate that water adsorption/desorption is sensitive to the available oxidation states of surface Mn cations, and can be used to distinguish between surfaces exposing Mn2+and Mn3+ cations, or a combination of these oxidation states. Carbon dioxide and water TPD results from the NaMnO2-like surface indicate that pre-adsorbed water blocks the uptake of CO2, while water displaces pre-adsorbed CO2. No indication of a strong reactive interaction is observed between CO2, water and the NaMnO2-like surface under the conditions of our study.

Critical behavior of dilute NaCl in H2O

USGS Publications Warehouse

Pitzer, Kenneth S.; Bischoff, J.L.; Rosenbauer, R.J.

1987-01-01

The compositions of the saturated vapor and liquid phases are measured for the system NaCl-H2O at 380??C, which is close to the critical point of pure water. The shape of the phase equilibrium curve is classical, which confirms a conclusion reached earlier on the basis of less accurate data. This implies that the long-range forces introduced by the NaCl suppress the non-classical effects present in pure H2O. An empirical equation of a classical type fits these data. ?? 1987.

Probing the local structure of crystalline NaBiO3·XH2O and its acidified derivatives

NASA Astrophysics Data System (ADS)

Kozma, Karoly; Surta, T. Wesley; Molina, Pedro I.; Lyubinetsky, Igor; Stoxen, Wynn; Byrne, Nicole M.; Dolgos, Michelle; Nyman, May

2018-07-01

Sodium bismuthate is a commercially available, inexpensive, non-toxic and very potent inorganic oxidant and photocatalyst. It is one of the important reagents for oxidative separation of Am3+ from the chemically similar lanthanide ions, for its recovery or safe disposal from reprocessed nuclear fuel. While the structure of NaBiO3 has been described from powder and neutron diffraction; the structure of NaBiO3·XH2O, the manufactured form of sodium bismuthate, is currently unknown. Herein, we describe the structure of NaBiO3·XH2O (X = 3) using pair distribution function (PDF) analysis of X-ray total scattering data. In our proposed structure model, NaBiO3·3H2O is similar to NaBiO3, but with turbostratic disorder in the stacking direction of the alternating Bi-O and Na-O layers. We propose locations for the lattice water, and its role in creating turbostratic disorder. We also used PDF to describe the structural evolution of sodium bismuthate upon exposure to nitric acid, the conditions employed in for nuclear fuel reprocessing. We supported the proposed model for pristine NaBiO3·3H2O and its acidified derivatives by a variety of techniques including thermogravimetry, powder X-ray diffraction (PXRD), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). By employing both surface and bulk techniques, we hypothesize that the bismuth reduced to Bi3+ upon aqueous acid exposure remains in the lattice, rather than completely dissolving and/or depositing on the surface, as prior suggested. Using pretreated acidified sodium bismuthate samples, we delineated the effects of acid strength vs. bismuthate structure/composition on Ce3+ to Ce4+ oxidation efficacy.

Selective photocatalytic reduction of CO2 to methanol in CuO-loaded NaTaO3 nanocubes in isopropanol

PubMed Central

Xiang, Tianyu; Chen, Jingshuai; Wang, Yuwen; Yin, Xiaohong; Shao, Xiao

2016-01-01

Summary A series of NaTaO3 photocatalysts were prepared with Ta2O5 and NaOH via a hydrothermal method. CuO was loaded onto the surface of NaTaO3 as a cocatalyst by successive impregnation and calcination. The obtained photocatalysts were characterized by XRD, SEM, UV–vis, EDS and XPS and used to photocatalytically reduce CO2 in isopropanol. This worked to both absorb CO2 and as a sacrificial reagent to harvest CO2 and donate electrons. Methanol and acetone were generated as the reduction product of CO2 and the oxidation product of isopropanol, respectively. NaTaO3 nanocubes loaded with 2 wt % CuO and synthesized in 2 mol/L NaOH solution showed the best activity. The methanol and acetone yields were 137.48 μmol/(g·h) and 335.93 μmol/(g·h), respectively, after 6 h of irradiation. Such high activity could be attributed to the good crystallinity, morphology and proper amount of CuO loading, which functioned as reductive sites for selective formation of methanol. The reaction mechanism was also proposed and explained by band theory. PMID:27335766

Fluor-ferro-leakeite, NaNa2(FC2+2Fe3+2Li)Si8O22F2, a new alkali amphibole from the Canada Pinabete pluton, Questa, New Mexico, U.S.A.

USGS Publications Warehouse

Hawthorne, F.C.; Oberti, R.; Ungaretti, L.; Ottolini, L.; Grice, Joel D.; Czamanske, G.K.

1996-01-01

Fluor-ferro-leakeite is a new amphibole species from the Canada Pinabete pluton, Questa, New Mexico, U.S.A.; it occurs in association with quartz, alkali feldspar, acmite, ilmenite, and zircon. It forms as anhedral bluish black crystals elongated along c and up to 1 mm long. It is brittle, H = 6, Dmeas = 3.37 g/cm3, Dcalc = 3.34 g/cm3. In plane-polarized light, it is strongly pleochroic, X = very dark indigo blue, Y = gray blue, Z = yellow green; X ??? c = 10?? (in ??obtuse), Y = b, Z ??? a = 4?? (in ?? obtuse), with absorption X > Y > Z. Fluor-ferro-leakeite is biaxial positive, ?? = 1.675(2), ??= 1.683(2), ?? = 1.694(1); 2V = 87(2)??; dispersion is not visible because of the strong absorption. Fluor-ferro-leakeite is monoclinic, space group C2/m, a = 9.792(1), b = 17.938(1), c = 5.3133(4) A??, ??= 103.87(7)??, V = 906.0(1) A??3, Z = 2. The ten strongest X-ray diffraction lines in the powder pattern are [d(I,hkl)]: 2.710(100,151), 2.536(92,202), 3.404(57,131), 4.481(54,040), 8.426(45,110), 2.985(38,241), 2.585(38,061), 3.122(29,310), 2.165(26,261), and 1.586(25,403). Analysis by a combination of electron microprobe, ion microprobe, and crystal-structure refinement (Hawthorne et al. 1993) gives SiO2 51.12, Al2O3 1.13, TiO2 0.68, Fe2O3 16.73, FeO 8.87, MgO 2.02, MnO 4.51, ZnO 0.57, CaO 0.15, Na2O 9.22, K2O 1.19, Li2O 0.99, F 2.87, H2Ocalc 0.60, sum 99.44 wt%. The formula unit, calculated on the basis of 23 O atoms, is (K0.23Na0.76)(Na1.97Ca0.03)(Mg 0.46Fe2+1.4Mn2+0.59Zn0.07Fe3+1.93-Ti 0.08Al0.02Li0.61])(Si7.81Al 0.19)O22(F1.39OH0.61). A previous crystal-structure refinement (Hawthorne et al. 1993) shows Li to be completely ordered at the M3 site. Fluor-ferro-leakeite, ideally NaNa2(Fe2+2Fe3+2Li)Si8O22F2, is related to leakeite, NaNa2(Mg2Fe3+3Li)Si 8O22(OH)2, by the substitutions Fe2+ ??? Mg and F ??? OH.

Optical and Luminescence Properties of β-NaFeO2 Nanoparticles

NASA Astrophysics Data System (ADS)

Singh, Sarbjit; Tangra, Ankush Kumar; Lotey, Gurmeet Singh

2018-05-01

β-NaFeO2 nanoparticles have been synthesized by sol-gel method and their morphological, structural and optical properties investigated. Transmission electron microscope study reveals that the size of the synthesis nanoparticles is 37 nm and they are possessing spherical symmetry. X-ray diffraction pattern shows the orthorhombic crystal structure of nanoparticles with space group Pn21 a. UV-visible spectra of β-NaFeO2 divulges that these nanoparticles have direct band gap 2.35 eV. The observed Fourier transform infrared spectroscopy spectra confirms the presence of Fe-Na bonding at 1074 cm-1. The photoluminescence study of these nanoparticles shows that these nanoparticles possesses various transition in the visible spectrum.

Hydrothermal synthesis and structural characterization of an organic–inorganic hybrid sandwich-type tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu(en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yingjie; College of Medicine, Henan University, Kaifeng, Henan 475004; Cao, Jing

An organic–inorganic hybrid sandwich-type tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu(en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O (1) has been synthesized by reaction of Sb{sub 2}O{sub 3}, Na{sub 2}WO{sub 4}·2H{sub 2}O, CuCl{sub 2}·2H{sub 2}O with en (en=ethanediamine) under hydrothermal conditions and structurally characterized by elemental analysis, inductively coupled plasma atomic emission spectrometry, IR spectrum and single-crystal X-ray diffraction. 1 displays a centric dimeric structure formed by two equivalent trivacant Keggin [α-SbW{sub 9}O{sub 33}]{sup 9−} subunits sandwiching a hexagonal (Cu{sub 2}Na{sub 4}) cluster. Moreover, those related hexagonal hexa-metal cluster sandwiched tungstoantimonates have been also summarized and compared. The variable-temperature magneticmore » measurements of 1 exhibit the weak ferromagnetic exchange interactions within the hexagonal (Cu{sub 2}Na{sub 4}) cluster mediated by the oxygen bridges. - Graphical abstract: An organic–inorganic hybrid (Cu{sub 2}Na{sub 4}) sandwiched tungstoantimonate [Cu(en){sub 2}(H{sub 2}O)]{sub 4}[Cu (en){sub 2}(H{sub 2}O){sub 2}][Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]·6H{sub 2}O was synthesized and magnetic properties was investigated. Display Omitted - Highlights: • Organic–inorganic hybrid sandwich-type tungstoantimonate. • (Cu{sub 2}Na{sub 4} sandwiched) tungstoantimonate [Cu{sub 2}Na{sub 4}(α-SbW{sub 9}O{sub 33}){sub 2}]{sup 10−}. • Ferromagnetic tungstoantimonate.« less

Influence of O-Co-O layer thickness on the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4} studied by positron annihilation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, H. Q.; Zhao, B.; Zhang, T.

2015-07-21

Nominal stoichiometric Na{sub x}Co{sub 2}O{sub 4} (x = 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0) polycrystals were synthesized by a solid-state reaction method. They were further pressed into pellets by the spark plasma sintering. The crystal structure and morphology of Na{sub x}Co{sub 2}O{sub 4} samples were characterized by X-ray diffraction and scanning electron microscopy measurements. Good crystallinity and layered structures were observed for all the samples. Positron annihilation measurements were performed for Na{sub x}Co{sub 2}O{sub 4} as a function of Na content. Two lifetime components are resolved. τ{sub 1} is attributed mainly to positron annihilation in the O-Co-O layers and shifts tomore » Na layers only in the H3 phase. The second lifetime τ{sub 2} is due to positron annihilation in vacancy clusters which may exist in the Na layers or grain boundary region. The size of vacancy clusters grow larger but their concentration decreases with increasing Na content in the range of 1.0 < x < 1.8. The thickness of O-Co-O layer also shows continuous increase with increasing Na content, which is reflected by the increase of τ{sub 1}. The thermal conductivity κ, on the other hand, shows systematic decrease with increasing Na content. This suggests that the increasing spacing of O-Co-O layer could effectively reduce the thermal conductivity of Na{sub x}Co{sub 2}O{sub 4}.« less

Structural variability in neptunium(V) oxalate compounds: synthesis and structural characterization of Na2NpO2(C2O4)OH.H2O.

PubMed

Bean, Amanda C; Garcia, Eduardo; Scott, Brian L; Runde, Wolfgang

2004-10-04

Reaction of a (237)Np(V) stock solution in the presence of oxalic acid, calcium chloride, and sodium hydroxide under hydrothermal conditions produces single crystals of a neptunium(V) oxalate, Na(2)NpO(2)(C(2)O(4))OH.H(2)O. The structure consists of one-dimensional chains running down the a axis and is the first example of a neptunium(V) oxalate compound containing hydroxide anions.

Triosephosphate isomerase tyrosine nitration induced by heme-NaNO2 -H2 O2 or peroxynitrite: Effects of different natural phenolic compounds.

PubMed

Gao, Wanxia; Zhao, Jie; Li, Hailing; Gao, Zhonghong

2017-06-01

Peroxynitrite and heme peroxidases (or heme)-H 2 O 2 -NaNO 2 system are the two common ways to cause protein tyrosine nitration in vitro, but the effects of antioxidants on reducing these two pathways-induced protein nitration and oxidation are controversial. Both nitrating systems can dose-dependently induce triosephosphate isomerase (TIM) nitration, however, heme-H 2 O 2 -NaNO 2 was less destructive to protein secondary structures and led to more nitrated tyrosine residue than 3-morpholinosydnonimine hydrochloride (SIN-1, a peroxynitrite donor). Both of desferrioxamine and catechin could inhibit TIM nitration induced by heme-H 2 O 2 -NaNO 2 and SIN-1 and protein oxidation induced by SIN-1, but promoted heme-H 2 O 2 -NaNO 2 -induced protein oxidation. Moreover, the antagonism of natural phenolic compounds on SIN-1-induced tyrosine nitration was consistent with their radical scavenging ability, but no similar consensus was found in heme-H 2 O 2 -NaNO 2 -induced nitration. Our results indicated that peroxynitrite and heme-H 2 O 2 -NaNO 2 -induced protein nitration was different, and the later one could be a better model for anti-nitration compounds screening. © 2017 Wiley Periodicals, Inc.

Phase Diagram of Quaternary System NaBr-KBr-CaBr2-H2O at 323 K

NASA Astrophysics Data System (ADS)

Cui, Rui-Zhi; Wang, Wei; Yang, Lei; Sang, Shi-Hua

2018-03-01

The phase equilibria in the system NaBr-KBr-CaBr2-H2O at 323 K were studied using the isothermal dissolution equilibrium method. Using the experimental solubilities of salts data, phase diagram was constructed. The phase diagram have two invariant points, five univariant curves, and four crystallization fields. The equilibrium solid phases in the system are NaBr, NaBr · 2H2O, KBr, and CaBr2 · 4H2O. The solubilities of salts in the system at 323 K were calculated by Pitzer's equation. There is shown that the calculated solubilities agree well with experimental data.

Polaronic and ionic conduction in NaMnO2: influence of native point defects

NASA Astrophysics Data System (ADS)

Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

Layered NaMnO2 has promising applications as a cathode material for sodium ion batteries. We will discuss strategies to improve the electrical performance of NaMnO2, including how to optimize the conditions of synthesis and how impurity doping affects the performance. Using hybrid density functional theory, we explored the structural, electronic, and defect properties of bulk NaMnO2. It is antiferromagnetic in the ground state with a band gap of 3.75 eV. Small hole and electron polarons can form in the bulk either through self-trapping or adjacent to point defects. We find that both Na and Mn vacancies are shallow acceptors with the induced holes trapped as small polarons, while O vacancies are deep defect centers. Cation antisites, especially MnNa, are found to have low formation energies. As a result, we expect that MnNa exists in as-grown NaMnO2 in moderate concentrations, rather than forming only at a later stage of the charging process, at which point it causes undesirable structural phase transitions. Both electronic conduction, via polaron hopping, and ionic conduction, through VNa migration, are significantly affected by the presence of point defects. This work was supported by DOE.

Nanostructured Na2Ti9O19 for Hybrid Sodium-Ion Capacitors with Excellent Rate Capability.

PubMed

Bhat, Swetha S M; Babu, Binson; Feygenson, Mikhail; Neuefeind, Joerg C; Shaijumon, M M

2018-01-10

Herein, we report a new Na-insertion electrode material, Na 2 Ti 9 O 19 , as a potential candidate for Na-ion hybrid capacitors. We study the structural properties of nanostructured Na 2 Ti 9 O 19 , synthesized by a hydrothermal technique, upon electrochemical cycling vs Na. Average and local structures of Na 2 Ti 9 O 19 are elucidated from neutron Rietveld refinement and pair distribution function (PDF), respectively, to investigate the initial discharge and charge events. Rietveld refinement reveals electrochemical cycling of Na 2 Ti 9 O 19 is driven by single-phase solid solution reaction during (de)sodiation without any major structural deterioration, keeping the average structure intact. Unit cell volume and lattice evolution on discharge process is inherently related to TiO 6 distortion and Na ion perturbations, while the PDF reveals the deviation in the local structure after sodiation. Raman spectroscopy and X-ray photoelectron spectroscopy studies further corroborate the average and local structural behavior derived from neutron diffraction measurements. Also, Na 2 Ti 9 O 19 shows excellent Na-ion kinetics with a capacitve nature of 86% at 1.0 mV s -1 , indicating that the material is a good anode candidate for a sodium-ion hybrid capacitor. A full cell hybrid Na-ion capacitor is fabricated by using Na 2 Ti 9 O 19 as anode and activated porous carbon as cathode, which exhibits excellent electrochemical properties, with a maximum energy density of 54 Wh kg -1 and a maximum power density of 5 kW kg -1 . Both structural insights and electrochemical investigation suggest that Na 2 Ti 9 O 19 is a promising negative electrode for sodium-ion batteries and hybrid capacitors.

Optical properties of Na2O-TiO2-SiO2 glass films prepared by the sol-gel method

NASA Astrophysics Data System (ADS)

Barton, Ivo; Matejec, Vlastimil; Mrazek, Jan; Predoana, Luminita; Zaharescu, Maria

2017-12-01

Layers based on TiO2-SiO2 systems fabricated by sol-gel method have been investigated for the preparation of planar waveguides, antireflective coatings, Bragg mirrors, etc. However, at high titania contents such materials exhibit high viscosities and tendency to phase separation. In this paper we present optical properties of films containing TiO2 which are prepared via a novel approach sol-gel on the basis of ternary Na2O-TiO2-SiO2 glasses and which can exhibit lower viscosities. Films of Na2O-TiO2-SiO2 systems were prepared from input sols mixed of silica, titania and sodium oxide sols. The silica sol was prepared from tetraethyl orthosilicate (TEOS), ethanol, hydrochloric acid and water, with a TEOS c= 2 mol/l and water/alkoxide ratio 1.75. The titania sol was mixed from titanium tetraisopropoxide (TiPr), propan-2-ol, nitric acid and water, c= 0.5 mol/l, RW= 0.42. The sodium oxide sols with c= 0.474 mol/l were prepared from sodium ethoxide and ethanol. Input sols were prepared by mixing the silica and titania sols first and then the sodium sol was added. The input sols were aged for one hour. Stable input sols were obtained. The input sols were deposited on glass and silica slides by dip-coating technique at a withdrawing speeds of 200 mm/min. Applied gel layers were thermally treated at temperatures of 450 and 900°C. Layers containing sodium oxide and titania in concentration ranges of 0-20 mol.% and 0-30 mol.% respectively have been fabricated. Optical properties of layers were determined by UV-VIS-NIR transmission and reflection spectrophotometry. Refractive indices of layers were determined by spectral ellipsometry and from transmission spectra. Optical properties were correlated with results of XRD spectroscopy, optical microscopy, and atomic force microscopy. Transparent homogenous films with a maximum refractive index of 1.61 at a wavelength of 600 nm have been obtained.

Rational Design of Na(Li1/3 Mn2/3 )O2 Operated by Anionic Redox Reactions for Advanced Sodium-Ion Batteries.

PubMed

Kim, Duho; Cho, Maenghyo; Cho, Kyeongjae

2017-09-01

In an effort to develop high-energy-density cathodes for sodium-ion batteries (SIBs), low-cost, high capacity Na(Li 1/3 Mn 2/3 )O 2 is discovered, which utilizes the labile O 2p-electron for charge compensation during the intercalation process, inspired by Li 2 MnO 3 redox reactions. Na(Li 1/3 Mn 2/3 )O 2 is systematically designed by first-principles calculations considering the Li/Na mixing enthalpy based on the site preference of Na in the Li sites of Li 2 MnO 3 . Using the anionic redox reaction (O 2- /O - ), this Mn-oxide is predicted to show high redox potentials (≈4.2 V vs Na/Na + ) with high charge capacity (190 mAh g -1 ). Predicted cathode performance is validated by experimental synthesis, characterization, and cyclic performance studies. Through a fundamental understanding of the redox reaction mechanism in Li 2 MnO 3 , Na(Li 1/3 Mn 2/3 )O 2 is designed as an example of a new class of promising cathode materials, Na(Li 1/3 M 2/3 )O 2 (M: transition metals featuring stabilized M 4+ ), for further advances in SIBs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The influence of excess K2O on the electrical properties of (K,Na)1/2Bi1/2TiO3 ceramics

NASA Astrophysics Data System (ADS)

Li, Linhao; Li, Ming; Sinclair, Derek C.

2018-04-01

The solid solution (KxNa0.50-x)Bi0.50TiO3 (KNBT) between Na1/2Bi1/2TiO3 and K1/2Bi1/2TiO3 (KBT) has been extensively researched as a candidate lead-free piezoelectric material because of its relatively high Curie temperature and good piezoelectric properties, especially near the morphotropic phase boundary (MPB) at x ˜ 0.10 (20 mol. % KBT). Here, we show that low levels of excess K2O in the starting compositions, i.e., (Ky+0.03Na0.50-y)Bi0.50TiO3.015 (y-series), can significantly change the conduction mechanism and electrical properties compared to a nominally stoichiometric KNBT series (KxNa0.50-x)Bi0.50TiO3 (x-series). Impedance spectroscopy measurements reveal significantly higher bulk conductivity (σb) values for y ≥ 0.10 samples [activation energy (Ea) ≤ 0.95 eV] compared to the corresponding x-series samples which possess bandgap type electronic conduction (Ea ˜ 1.26-1.85 eV). The largest difference in electrical properties occurs close to the MPB composition (20 mol. % KBT) where y = 0.10 ceramics possess σb (at 300 °C) that is 4 orders of magnitude higher than that of x = 0.10 and the oxide-ion transport number in the former is ˜0.70-0.75 compared to <0.05 in the latter (between 600 and 800 °C). The effect of excess K2O can be rationalised on the basis of the (K + Na):Bi ratio in the starting composition prior to ceramic processing. This demonstrates the electrical properties of KNBT to be sensitive to low levels of A-site nonstoichiometry and indicates that excess K2O in KNBT starting compositions to compensate for volatilisation can lead to undesirable high dielectric loss and leakage currents at elevated temperatures.

The electronic structure and optical properties of ABP 2O 7 ( A = Na, Li) double phosphates

NASA Astrophysics Data System (ADS)

Hizhnyi, Yu. A.; Oliynyk, A.; Gomenyuk, O.; Nedilko, S. G.; Nagornyi, P.; Bojko, R.; Bojko, V.

2008-01-01

Partial densities of states and reflection spectra of NaAlP 2O 7, KAlP 2O 7 and LiInP 2O 7 double phosphate crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. Experimental reflection spectra of KAlP 2O 7, CsAlP 2O 7 and NaInP 2O 7 are measured in the 4-20 eV energy range. The values of band gaps, Eg, are found from a comparison of experiment and calculations to be 6.0 eV for NaAlP 2O 7 and KAlP 2O 7, and 4.6 eV for LiInP 2O 7.

Floating zone growth of α-Na 0.90MnO 2 single crystals

DOE PAGES

Dally, Rebecca; Clement, Raphaele J.; Chisnell, Robin; ...

2016-12-03

Here, single crystal growth of α-Na xMnO 2 (x=0.90) is reported via the floating zone technique. The conditions required for stable growth and intergrowth-free crystals are described along with the results of trials under alternate growth atmospheres. Chemical and structural characterizations of the resulting α-Na 0.90MnO 2 crystals are performed using ICP-AES NMR, XANES, XPS, and neutron diffraction measurements. As a layered transition metal oxide with large ionic mobility and strong correlation effects, α-Na xMnO 2 is of interest to many communities, and the implications of large volume, high purity, single crystal growth are discussed.

Novel synthesis approach for stable sodium superoxide (NaO2) nanoparticles for LPG sensing application

NASA Astrophysics Data System (ADS)

Nemade, Kailash; Waghuley, Sandeep

2017-05-01

The synthesis of stable superoxide is still great challenge for the researchers working in the field of materials science. Through this letter, we report the novel and simple synthesis approach for the preparation of stable sodium superoxide (NaO2) nanoparticles. NaO2 nanoparticles were prepared by a spray pyrolysis technique, under oxygen rich environment for gas sensing application. The texture characterizations show that as-obtained NaO2 nanoparticles have high structural purity. Most importantly, NaO2 nanoparticles exhibits higher sensing response, shorter response time and recovery time, low operating temperature and good stability during sensing of liquefied petroleum gas (LPG). The main accomplishment of present work is that as-fabricated sensor has low operating temperature (423 K), which is below auto-ignition temperature of LPG. The gas sensing mechanism of NaO2 nanoparticles was discussed without the conventional oxygen bridging mechanism. Through this short communication, LPG sensing application of stable sodium superoxide nanoparticle is explored.

Preparation and structure of Na2Ag5Fe3(P2O7)4 -Ag metal composite: Insights on electrochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yiman; Marschilok, Amy C.; Takeuchi, Esther S.

ABSTRACT Ag 7Fe 3(P 2O 7) 4is a 3D structured material which has been recently studied as a possible cathode material for lithium batteries. Notably, Na 7Fe 3(P 2O 7) 4is reported to be a fast-ion conductor, yet poor electrical conductor. Here, partial replacement of Na +for Ag +yielded Na 2Ag 5Fe 3(P 2O 7) 4pyrophosphate framework where the formation of Ag metal is proposed to increase the intrinsic low electrical conductivity of this polyanion electrode. Specifically, the Ag 5Na 2Fe 3(P 2O 7) 4-Ag composite is synthesized via chemical reduction of Ag 7Fe 3(P 2O 7) 4using NaBH 4.more » The occupancy of Ag +and Na +in each site was determined via Rietveld analysis of the diffraction pattern. Electrochemistry of the Ag 5Na 2Fe 3(P 2O 7) 4-Ag metal composite was explored with voltammetry and galvanostatic charge/discharge cycling. The Ag 5Na 2Fe 3(P 2O 7) 4-Ag metal composite electrodes displayed good rate capability assisted by the presence of Ag metal from the chemical reduction and in-situ electrochemical formation of a Ag conductive network.« less

A Structural Molar Volume Model for Oxide Melts Part I: Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-Al2O3-SiO2 Melts—Binary Systems

NASA Astrophysics Data System (ADS)

Thibodeau, Eric; Gheribi, Aimen E.; Jung, In-Ho

2016-04-01

A structural molar volume model was developed to accurately reproduce the molar volume of molten oxides. As the non-linearity of molar volume is related to the change in structure of molten oxides, the silicate tetrahedral Q-species, calculated from the modified quasichemical model with an optimized thermodynamic database, were used as basic structural units in the present model. Experimental molar volume data for unary and binary melts in the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-Al2O3-SiO2 system were critically evaluated. The molar volumes of unary oxide components and binary Q-species, which are model parameters of the present structural model, were determined to accurately reproduce the experimental data across the entire binary composition in a wide range of temperatures. The non-linear behavior of molar volume and thermal expansivity of binary melt depending on SiO2 content are well reproduced by the present model.

Compositional dependence of bioactivity of glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2.

PubMed

Brink, M; Turunen, T; Happonen, R P; Yli-Urpo, A

1997-10-01

The bioactivity, i.e., bone-bonding ability, of 26 glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2 was studied in vivo. This investigation of bioactivity was performed to establish the compositional dependence of bioactivity, and enabled a model to be developed that describes the relation between reactions in vivo and glass composition. Reactions in vivo were investigated by inserting glass implants into rabbit tibia for 8 weeks. The glasses and the surrounding tissue were examined using scanning electron microscopy (SEM), light microscopy, and energy-dispersive X-ray analysis (EDXA). For most of the glasses containing < 59 mol % SiO2, SEM and EDXA showed two distinct layers at the glass surface after implantation, one silica-rich and another containing calcium phosphate. The build-up of these layers in vivo was taken as a sign of bioactivity. The in vivo experiments showed that glasses in the investigated system are bioactive when they contain 14-30 mol % alkali oxides, 14-30 mol % alkaline earth oxides, and < 59 mol % SiO2. Glasses containing potassium and magnesium bonded to bone in a similar way as bioactive glasses developed so far.

Structural studies on a high-pressure polymorph of NaYSi 2O 6

NASA Astrophysics Data System (ADS)

Kahlenberg, Volker; Konzett, Jürgen; Kaindl, Reinhard

2007-06-01

High-pressure synthesis experiments in the system Na 2O-Y 2O 3-SiO 2 revealed the existence of a previously unknown polymorph of NaYSi 2O 6 or Na 3Y 3[Si 3O 9] 2 which was quenched from 3.0 GPa and 1000 °C. Structural investigations on this modification have been performed using single-crystal X-ray diffraction data collected at ambient conditions. Furthermore, unpolarized micro-Raman spectra have been obtained from single-crystal material. The high-P modification of NaYSi 2O 6 crystallizes in the centrosymmetric space group C2/ c with 12 formula units per cell ( a=8.2131(9) Å, b=10.3983(14) Å, c=17.6542(21) Å, β=100.804(9)°, V=1481.0(3) Å 3, R(| F|)=0.033 for 1142 independent observed reflections) and belongs to the group of cyclo-silicates. Basic building units are isolated three-membered [Si 3O 9] rings located in layers parallel to (010). Within a single layer the rings are concentrated in strings parallel to [100]. The sequence of directedness of up ( U) or down ( D) pointing tetrahedra of a single ring is UUU or DDD, respectively. Stacking of the layers parallel to b results in the formation of a three-dimensional structure in which yttrium and sodium cations are incorporated for charge compensation. In more detail, four non-tetrahedral cation positions can be differentiated which are coordinated by 6 and 8 oxygen ligands. Refinements of the site occupancies did not reveal any indication for mixed Na-Y populations on these positions. Finally, several geometrical parameters of rings occurring in cyclo-trisilicate structures have been compiled and are discussed.

Confined NaAlH4 nanoparticles inside CeO2 hollow nanotubes towards enhanced hydrogen storage.

PubMed

Gao, Qili; Xia, Guanglin; Yu, Xuebin

2017-10-05

NaAlH 4 has been widely regarded as a potential hydrogen storage material due to its favorable thermodynamics and high energy density. The high activation energy barrier and high dehydrogenation temperature, however, significantly hinder its practical application. In this paper, CeO 2 hollow nanotubes (HNTs) prepared by a simple electrospinning technique are adopted as functional scaffolds to support NaAlH 4 nanoparticles (NPs) towards advanced hydrogen storage performance. The nanoconfined NaAlH 4 inside CeO 2 HNTs, synthesized via the infiltration of molten NaAlH 4 into the CeO 2 HNTs under high hydrogen pressure, exhibited significantly improved dehydrogenation properties compared with both bulk and ball-milled CeO 2 HNTs-catalyzed NaAlH 4 . The onset dehydrogenation temperature of the NaAlH 4 @CeO 2 composite was reduced to below 100 °C, with only one main dehydrogenation peak appearing at 130 °C, which is 120 °C and 50 °C lower than for its bulk counterpart and for the ball-milled CeO 2 HNTs-catalyzed NaAlH 4 , respectively. Moreover, ∼5.09 wt% hydrogen could be released within 30 min at 180 °C, while only 1.6 wt% hydrogen was desorbed from the ball-milled NaAlH 4 under the same conditions. This significant improvement is mainly attributed to the synergistic effects contributed by the CeO 2 HNTs, which could act as not only a structural scaffold to fabricate and confine the NaAlH 4 NPs, but also as an effective catalyst to enhance the hydrogen storage performance of NaAlH 4 .

Preparation and photoelectrocatalytic performance of N-doped TiO2/NaY zeolite membrane composite electrode material.

PubMed

Cheng, Zhi-Lin; Han, Shuai

2016-01-01

A novel composite electrode material based on a N-doped TiO2-loaded NaY zeolite membrane (N-doped TiO2/NaY zeolite membrane) for photoelectrocatalysis was presented. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible (UV-vis) and X-ray photoelectron spectroscopy (XPS) characterization techniques were used to analyze the structure of the N-doped TiO2/NaY zeolite membrane. The XRD and SEM results verified that the N-doped TiO2 nanoparticles with the size of ca. 20 nm have been successfully loaded on the porous stainless steel-supported NaY zeolite membrane. The UV-vis result showed that the N-doped TiO2/NaY zeolite membrane exhibited a more obvious red-shift than that of N-TiO2 nanoparticles. The XPS characterization revealed that the doping of N element into TiO2 was successfully achieved. The photoelectrocatalysis performance of the N-doped TiO2/NaY zeolite membrane composite electrode material was evaluated by phenol removal and also the effects of reaction conditions on the catalytic performance were investigated. Owing to exhibiting an excellent catalytic activity and good recycling stability, the N-doped TiO2/NaY zeolite membrane composite electrode material was of promising application for photoelectrocatalysis in wastewater treatment.

Gels and gel-derived glasses in the system Na2O-B2O3-SiO2

NASA Technical Reports Server (NTRS)

Mukherjee, S. P.

1983-01-01

The containerless melting of high-purity multicomponent homogeneous gels and gel monoliths offers a unique approach to making ultrapure multicomponent optical glasses in the reduced gravity environment of space. Procedures for preparing and characterizing gels and gel-derived glasses in the system Na2O-B2O3-SiO2 are described. Preparation is based on the polymerization reactions of alkoxysilane with trimethyl borate or boric acid and a suitable sodium compound. The chemistry of the gelling process is discussed in terms of process parameters and the gel compositions. The physicochemical nature of gels prepared by three different procedures was found to be significantly different. Infrared absorption spectra indicate finite differences in the molecular structures of the different gels. The melting of the gel powders and the transformation of porous gel monoliths to transparent 'glass' without melting are described.

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics.

PubMed

Peitl, Oscar; Zanotto, Edgar D; Serbena, Francisco C; Hench, Larry L

2012-01-01

Bioactive glasses having chemical compositions between 1Na(2)O-2CaO-3SiO(2) (1N2C3S) and 1.5Na(2)O-1.5CaO-3SiO(2) (1N1C2S) containing 0, 4 and 6 wt.% P(2)O(5) were crystallized through two stage thermal treatments. By carefully controlling these treatments we separately studied the effects on the mechanical properties of two important microstructural features not studied before, crystallized volume fraction and crystal size. Fracture strength, elastic modulus and indentation fracture toughness were measured as a function of crystallized volume fraction for a constant crystal size. Glass-ceramics with a crystalline volume fraction between 34% and 60% exhibited a three-fold improvement in fracture strength and an increase of 40% in indentation fracture toughness compared with the parent glass. For the optimal crystalline concentration (34% and 60%) these mechanical properties were then measured for different grain sizes, from 5 to 21 μm. The glass-ceramic with the highest fracture strength and indentation fracture toughness was that with 34% crystallized volume fracture and 13 μm crystals. Compared with the parent glass, the average fracture strength of this glass-ceramic was increased from 80 to 210 MPa, and the fracture toughness from 0.60 to 0.95 MPa.m(1/2). The increase in indentation fracture toughness was analyzed using different theoretical models, which demonstrated that it is due to crack deflection. Fortunately, the elastic modulus E increased only slightly; from 60 to 70 GPa (the elastic modulus of biomaterials should be as close as possible to that of cortical bone). In summary, the flexural strength of our best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus. These results thus provide a relevant guide for the design of bioactive glass-ceramics with improved microstructure. Copyright © 2011 Acta

Mechanism of corrosion of Ni base superalloys by molten Na2MoO4 at elevated temperatures

NASA Technical Reports Server (NTRS)

Misra, A. K.; Stearns, C. A.

1983-01-01

The corrosion of nickel base superalloy, U-700, by molten Na2MoO4 was studied in the temperature range of 750 deg to 950 deg C. After an induction period, the rate of corrosion is linear and catastrophic corrosion is observed. It is shown that the induction period is associated with the attainment of a minimum MoO3 activity in the melt, which corresponds to the equilibrium MoO3 activity for the reaction, 2MoO3(l) + Mo = 3MoO2(s). A mechanism is proposed to describe the catastrophic nature of corrosion, which involves transport of Ni++ through the melt resulting in formulation of NiO at the melt gas interface and basic fluxing of Cr2O3. The effect of the amount of Na2MoO4 on the corrosion kinetics was also studied. It is found that evaporation and the thermodynamic calculations for the Na2MoO4 - MoO3 system the activity of MoO3 is reduced considerably when dissolved in Na2MoO4, which causes a sharp decrease in the rate of evaporation of MoO3 from a Na2MoO4 - MoO3 melt.

TiO2 Nanostructures as Anode Materials for Li/Na-ion Batteries.

PubMed

Vazquez-Santos, Maria B; Tartaj, Pedro; Morales, Enrique; Amarilla, Jose Manuel

2018-03-14

Here we summarize some results on the use of TiO 2 nanostructures as anode materials for more efficient Li-ion (LIBs) and Na-ion (NIBs) batteries. LIBs are the leader to power portable electronic devices, and represent in the short-term the most adequate technology to power electrical vehicles, while NIBs hold promise for large storage of energy generated from renewable sources. Specifically, TiO 2 an abundant, low cost, chemically stable and environmentally safe oxide represents in LIBs an alternative to graphite for applications in which safety is mandatory. For NIBs, TiO 2 anodes (or more precisely negative electrodes) work at low voltage, assuring acceptable energy density values. Finally, assembling different TiO 2 polymorphs in the form of nanostructures decreases diffusion distances, increases the number of contacts and offering additional sites for Na + storage, helping to improve power efficiency. More specifically, in this contribution we highlighted our work on TiO 2 anatase mesocrystals of colloidal size. These sophisticate materials; showing excellent textural properties, have remarkable electrochemical performance as anodes for Li/Na-ion batteries, with conventional alkyl carbonates electrolytes and safe electrolytes based on ionic liquids. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Siudaite, Na8(Mn2+ 2Na)Ca6Fe3+ 3Zr3NbSi25O74(OH)2Cl·5H2O: a new eudialyte-group mineral from the Khibiny alkaline massif, Kola Peninsula

NASA Astrophysics Data System (ADS)

Chukanov, Nikita V.; Rastsvetaeva, Ramiza K.; Kruszewski, Łukasz; Aksenov, Sergey M.; Rusakov, Vyacheslav S.; Britvin, Sergey N.; Vozchikova, Svetlana A.

2018-03-01

The new eudialyte-group mineral siudaite, ideally Na8(Mn2+ 2Na)Ca6Fe3+ 3Zr3NbSi25O74(OH)2Cl·5H2O, was discovered in a peralkaline pegmatite situated at the Eveslogchorr Mt., Khibiny alkaline massif, Kola Peninsula, Russia. The associated minerals are aegirine, albite, microcline, nepheline, astrophyllite, and loparite-(Ce). Siudaite forms yellow to brownish-yellow equant anhedral grains up to 1.5 cm across. Its lustre is vitreous, and the streak is white. Cleavage is none observed. The Mohs' hardness is 4½. Density measured by hydrostatic weighing is 2.96(1) g/cm3. Density calculated using the empirical formula is equal to 2.973 g/cm3. Siudaite is nonpleochroic, optically uniaxial, negative, with ω = 1.635(1) and ɛ = 1.626(1) (λ = 589 nm). The IR spectrum is given. The chemical composition of siudaite is (wt%; electron microprobe, H2O determined by HCN analysis): Na2O 8.40, K2O 0.62, CaO 9.81, La2O3 1.03, Ce2O3 1.62, Pr2O3 0.21, Nd2O3 0.29, MnO 6.45, Fe2O3 4.51. TiO2 0.54, ZrO2 11.67, HfO2 0.29, Nb2O5 2.76, SiO2 47.20, Cl 0.54, H2O 3.5, -O = Cl - 0.12, total 99.32. According to Mössbauer spectroscopy data, all iron is trivalent. The empirical formula (based on 24.5 Si atoms pfu, in accordance with structural data) is [Na7.57(H2O)1.43]Σ9(Mn1.11Na0.88Ce0.31La0.20Nd0.05Pr0.04K0.41)Σ3(H2O)1.8(Ca5.46Mn0.54)Σ6(Fe3+ 1.76Mn2+ 1.19)Σ2.95Nb0.65(Ti0.20Si0.50)Σ0.71(Zr2.95Hf0.04Ti0.01)Σ3Si24.00Cl0.47O70(OH)2Cl0.47·1.82H2O. The crystal structure was determined using single-crystal X-ray diffraction data. The new mineral is trigonal, space group R3m, with a = 14.1885(26) Å, c = 29.831(7) Å, V = 5200.8(23) Å3 and Z = 3. Siudaite is chemically related to georgbarsanovite and is its analogue with Fe3+-dominant M2 site. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 6.38 (60) (-114), 4.29 (55) (-225), 3.389 (47) (131), 3.191 (63) (-228). 2.963 (100) (4-15), 2.843 (99) (-444), 2.577 (49) (3-39). Siudaite is named after the Polish

Room-temperature NaI/H2O compression icing: solute-solute interactions.

PubMed

Zeng, Qingxin; Yao, Chuang; Wang, Kai; Sun, Chang Q; Zou, Bo

2017-10-11

In situ Raman spectroscopy revealed that transiting the concentrated NaI/H 2 O solutions to an ice VI phase and then into an ice VII phase at 298 K proceeds in a way different from that activated by the solute type. Unlike the solute type that raises both the critical pressures P C1 and P C2 , for the liquid-VI, the VI-VII transition simultaneously occurs in the Hofmeister series order: I > Br > Cl > F ∼ 0; concentration increase raises the P C1 faster than the P C2 that remains almost constant at higher NaI/H 2 O molecular number ratios. Concentration increase moves the P C1 along the liquid-VI phase boundary and it finally merges with P C2 at the triple-phase junction featured at 350 K and 3.05 GPa. The highly-deformed H-O bond is less sensitive to the concentration because of the involvement of anion-anion repulsion that weakens the electric field in the hydration shells. Observations confirm that the salt solvation lengthens the O:H nonbond and softens its phonon but relaxes the H-O bond contrastingly. Compression, however, has the opposite effect from that of salt solvation. Therefore, compression recovers the polarization-deformed O:H-O bond first and then proceeds to the phase transitions. The anion-anion interaction discriminates the effect of NaI/H 2 O concentration from that of the solute type at an identical concentration on the phase transitions.

Fabrication of NIR-responsive NaYF4:Yb,Tm/anatase TiO2 composite aerogel

NASA Astrophysics Data System (ADS)

Li, Fu-Chih; Kitamoto, Yoshitaka

2018-01-01

3-dimensional interconnected network structure of TiO2 aerogel has attracted considerable attention to solve environmental issues due to an advanced oxidation process which uses abundant sunlight for the complete minimization of toxic pollutants. The TiO2 aerogel with high specific surface area, large pores, and low density has a potential to be used as photocatalyst for air and water purification. Nonetheless, due to the larger band gap, TiO2 semiconductor photocatalysts possess high oxidizing properties under UV light only which occupies 5% of solar energy. To expand the absorption spectrum of TiO2 aerogel under solar irradiation, the NaYF4:Yb,Tm nanoparticles (NPs) are introduced into the TiO2 aerogel matrix structure. The morphology and crystal structure of the composite aerogel are investigated by transmission electron microscopy and X-ray diffraction, respectively. The particle size of NaYF4:Yb,Tm NPs is approximately 40 nm and the crystallite size of TiO2 is around 10 nm. In addition, the NaYF4:Yb,Tm NPs are enclosed by anatase phase of TiO2 aerogel. The NaYF4:Yb,Tm NPs which exist in the TiO2 aerogel has a capability of transferring NIR light to UV region.

Optical spectroscopy of Sm(3+) doped Na2O-ZnO-La2O3-TeO2 glasses.

PubMed

Sobczyk, Marcin

2015-10-05

Telluride glasses with the composition xSm2O3-(7-x)La2O3-3Na2O-25ZnO-65TeO2 (where x=0.1, 1, 2, 5 and 7 mol%) were obtained by the melt quenching technique. Electronic absorption and fluorescence spectra as well as fluorescence dynamics of the Sm(3+)-doped title glasses are presented and analysed in detail. A Judd-Ofelt intensity analysis of the absorption spectrum at 300 K has been applied for determination of Ωλ parameters (Ω2=3.10, Ω4=3.80, Ω6=1.61×10(-20) cm(2)) which in turn have been used for calculations of the radiative transition probabilities (AT), the natural (radiative) lifetimes (τR) of the (4)G5/2 level of Sm(3+), the fluorescence branching ratios (β) and the emission cross-sections (σem). The τR value of the (4)G5/2 level amount to 1546 μs and is slightly higher than the measured decay time of 1306 μs. With the increasing of Sm2O3 concentration from 0.1 to 7.0 mol% the experimental lifetime of the fluorescent level decreases from 1306 to 41 μs. An analysis of the non-radiative decay was based on the cross-relaxation mechanisms. The optical achieved results indicate that the investigated glasses are potentially applicable as an orange and/or red laser host. Copyright © 2015 Elsevier B.V. All rights reserved.

First Measurements of Time-Dependent Nucleation as a Function of Composition in Na2O.2CaO.3SiO2 Glasses

NASA Technical Reports Server (NTRS)

Kelton, K. F.; Narayan, K. Lakshmi

1996-01-01

The first measurements in any system of the composition dependence of the time-dependent nucleation rate are presented Nucleation rates of the stoichiometric crystalline phase, Na2O.2CaO.3SiO2, from quenched glasses made with different SiO2 concentrations were determined as a function of temperature and glass composition. A strong compositional dependence of the nucleation rates and a weak dependence for the induction times are observed. Using measured values of the liquidus temperatures and growth velocities as a function of glass composition, these data are shown to be consistent with predictions from the classical theory of nucleation, assuming a composition-dependent interfacial energy.

Vapor-liquid phase equilibria of potassium chloride-water mixtures: Equation-of-state representation for KCl-H2O and NaCl-H2O

USGS Publications Warehouse

Hovey, J.K.; Pitzer, Kenneth S.; Tanger, J.C.; Bischoff, J.L.; Rosenbauer, R.J.

1990-01-01

Measurements of isothermal vapor-liquid compositions for KCl-H2O as a function of pressure are reported. An equation of state, which was originally proposed by Pitzer and was improved and used by Tanger and Pitzer to fit the vapor-liquid coexistence surface for NaCl-H2O, has been used for representation of the KCl-H2O system from 300 to 410??C. Improved parameters are also reported for NaCl-H2O from 300 to 500??C. ?? 1990 American Chemical Society.

High-pressure versus isoelectronic doping effect on the honeycomb iridate Na2IrO3

NASA Astrophysics Data System (ADS)

Hermann, V.; Ebad-Allah, J.; Freund, F.; Pietsch, I. M.; Jesche, A.; Tsirlin, A. A.; Deisenhofer, J.; Hanfland, M.; Gegenwart, P.; Kuntscher, C. A.

2017-11-01

We study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate Na2IrO3 by combining optical spectroscopy with synchrotron x-ray diffraction measurements on single crystals. The obtained optical conductivity of Na2IrO3 is discussed in terms of a Mott-insulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev interactions. With increasing Li content x , (Na1 -xLix )2IrO3 moves deeper into the Mott-insulating regime, and there are indications that up to a doping level of 24% the compound comes closer to the Kitaev limit. The optical conductivity spectrum of single-crystalline α -Li2IrO3 does not follow the trends observed for the series up to x =0.24 . There are strong indications that α -Li2IrO3 is not as close to the Kitaev limit as Na2IrO3 and lies closer to the quasimolecular orbital picture instead. Except for the pressure-induced hardening of the phonon modes, the optical properties of Na2IrO3 seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between x =0.24 and x =1 are given by comparing the pressure-induced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.

Dimerization in honeycomb Na2RuO3 under pressure: a DFT study

NASA Astrophysics Data System (ADS)

Gazizova, D. D.; Ushakov, A. V.; Streltsov, S. V.

2018-04-01

The structural properties of Na2RuO3 under pressure are studied using density functional theory within the nonmagnetic generalized gradient approximation (GGA). We found that one may expect a structural transition at ˜3 GPa. This structure at the high-pressure phase is exactly the same as the low-temperature structure of Li2RuO3 (at ambient pressure) and is characterized by the P21/m space group. Ru ions form dimers in this phase and one may expect strong modification of the electronic and magnetic properties in Na2RuO3 at pressure higher than 3 GPa.

Structural and electrochemical properties of Fe-doped Na2Mn3-xFex(P2O7)2 cathode material for sodium ion batteries

NASA Astrophysics Data System (ADS)

Liu, Huatao; Zhao, Yanming; Zhang, Hui; Lian, Xin; Dong, Youzhong; Kuang, Quan

2017-12-01

A series of Fe-doped Na2Mn3-xFex(P2O7)2 (x = 0.0, 0.5, 1.0, 1.5 and 2.0) compounds have been successfully prepared by using sol-gel method. Rietveld refinement results indicate that single phase Na2Mn3-xFex(P2O7)2 with triclinic structure can be obtained within 0 ≤ x ≤ 2 although no Na2Fe3(P2O7)2 existing under our experimental conditions, and the cell parameters (including a, b, c and V) are decreasing with the increasing of x. Our results reveal that Na2Mn3(P2O7)2 exhibits an electrochemical activity in the voltage range of 1.5 V-4.5 V vs. Na+/Na when using as the cathode material for SIBs although it gives a limited rate capability and poor capacity retention. However, the electrochemical performance of Fe-doped Na2Mn3-xFex(P2O7)2 (0 ≤ x ≤ 2) can be improved significantly where cycle performance and rate capability can be improved significantly than that of the pristine one. Sodium ion diffusion coefficient can be increased by about two orders of magnitude with the Fe-doping content higher than x = 0.5.

The different Li/Na ion storage mechanisms of nano Sb2O3 anchored on graphene

NASA Astrophysics Data System (ADS)

Li, Hai; Qian, Kun; Qin, Xianying; Liu, Dongqing; Shi, Ruiying; Ran, Aihua; Han, Cuiping; He, Yan-Bing; Kang, Feiyu; Li, Baohua

2018-05-01

The antimony oxide/reduced graphene oxide (Sb2O3/rGO) nanocomposites are used as anode of Li-ion and Na-ion batteries (LIBs and NIBs). However, it is unclear about Li-ion and Na-ion storage mechanism in Sb2O3/rGO nanocomposites. Herein, the conversion-alloying mechanisms of Sb2O3/rGO anodes for Na-ion and Li-ion storage are comparatively studied with a combined in-situ XRD and quasi in-situ XPS method. The distinct behaviours are monitored during (de)lithiation and (de)sodiation with respect to crystal structure and chemical composition evolution. It is evidenced that the Na-ion can be easily transported to the inner part of the Sb2O3, where the Li-ion almost cannot reach, leading to a fully transformation during sodiation. In addition, the conversion reaction product of amorphous Na2O display their better chemical stability than amorphous Li2O during electrochemical cycles, which contribute to a stable and long cycling life of NIBs. This work gain insight into the high-capacity anodes with conversation-alloying mechanism for NIBs.

Evaluation of EA-934NA with 2.5 percent Cab-O-Sil

NASA Technical Reports Server (NTRS)

Caldwell, Gordon A.

1990-01-01

Currently, Hysol adhesive EA-934NA is used to bond the Field Joint Protection System on the Shuttle rocket motors at Kennedy Space Center. However, due to processing problems, an adhesive with a higher viscosity is needed to alleviate these difficulties. One possible solution is to add Cab-O-Sil to the current adhesive. The adhesive strength and bond strengths that can be obtained when 2.5 percent Cab-O-Sil is added to adhesive EA-934NA are examined and tested over a range of test temperatures from -20 to 300 F. Tensile adhesion button and lap shear specimens were bonded to D6AC steel and uniaxial tensile specimens (testing for strength, initial tangent modulus, elongation and Poisson's ratio) were prepared using Hysol adhesive EA-934NA with 2.5 percent Cab-O-Sil added. These specimens were tested at -20, 20, 75, 100, 125, 150, 200, 250, and 300 F, respectively. Additional tensile adhesion button specimens bonding Rust-Oleum primed and painted D6AC steel to itself and to cork using adhesive EA-934NA with 2.5 percent Cab-O-Sil added were tested at 20, 75, 125, 200, and 300 F, respectively. Results generally show decreasing strength values with increasing test temperatures. The bond strengths obtained using cork as a substrate were totally dependent on the cohesive strength of the cork.

Spectroscopic properties of Sm3+ and V4+ ions in Na2O-SiO2-ZrO2 glasses

NASA Astrophysics Data System (ADS)

Neeraja, K.; Rao, T. G. V. M.; Kumar, A. Rupesh; Uma Lakshmi, V.; Veeraiah, N.; Rami Reddy, M.

2013-12-01

Na2O-SiO2-ZrO2 glasses of Sm3+ ions with and without V2O5 are characterized by spectroscopic and optical properties. The XRD and EDS spectra of the glass samples reveal an amorphous nature with different compositions within the glass matrix. The Infrared and Raman spectral studies are carried out and the existence of conventional structural units are analyzed in the glass network. The ESR spectra of the glass samples have indicating that a considerable proportion of vanadium ion exists in V4+ state. The optical absorption spectra of these glasses are recorded at room temperature, from the measured intensities of various absorption bands the Judd-Ofelt parameters Ω2, Ω4 and Ω6 are calculated. The photo-luminescence spectra recorded with excited wavelength 400 nm, five emission bands are observed; in this the energy transfer probability takes place between Sm3+ and V4+ ions.

Enhancing Catalyzed Decomposition of Na2CO3 with Co2MnO x Nanowire-Decorated Carbon Fibers for Advanced Na-CO2 Batteries.

PubMed

Fang, Cong; Luo, Jianmin; Jin, Chengbin; Yuan, Huadong; Sheng, Ouwei; Huang, Hui; Gan, Yongping; Xia, Yang; Liang, Chu; Zhang, Jun; Zhang, Wenkui; Tao, Xinyong

2018-05-23

The metal-CO 2 batteries, especially Na-CO 2 , batteries come into sight owing to their high energy density, ability for CO 2 capture, and the abundance of sodium resource. Besides the sluggish electrochemical reactions at the gas cathodes and the instability of the electrolyte at a high voltage, the final discharge product Na 2 CO 3 is a solid and poor conductor of electricity, which may cause the high overpotential and poor cycle performance for the Na-CO 2 batteries. The promotion of decomposition of Na 2 CO 3 should be an efficient strategy to enhance the electrochemical performance. Here, we design a facile Na 2 CO 3 activation experiment to screen the efficient cathode catalyst for the Na-CO 2 batteries. It is found that the Co 2 MnO x nanowire-decorated carbon fibers (CMO@CF) can promote the Na 2 CO 3 decomposition at the lowest voltage among all these metal oxide-decorated carbon fiber structures. After assembling the Na-CO 2 batteries, the electrodes based on CMO@CF show lower overpotential and better cycling performance compared with the electrodes based on pristine carbon fibers and other metal oxide-modified carbon fibers. We believe this catalyst screening method and the freestanding structure of the CMO@CF electrode may provide an important reference for the development of advanced Na-CO 2 batteries.

Removing polysaccharides-and saccharides-related coloring impurities in alkyl polyglycosides by bleaching with the H2O2/TAED/NaHCO3 system.

PubMed

Yanmei, Liu; Jinliang, Tao; Jiao, Sun; Wenyi, Chen

2014-11-04

The effect of H2O2/TAED/NaHCO3 system, namely NaHCO3 as alkaline agent with the (tetra acetyl ethylene diamine (TAED)) TAED-activated peroxide system, bleaching of alkyl polyglycosides solution was studied by spectrophotometry. The results showed that the optimal bleaching conditions about H2O2/TAED/NaHCO3 system bleaching of alkyl polyglycosides solution were as follows: molar ratio of TAED to H2O2 was 0.06, addition of H2O2 was 8.6%, addition of NaHCO3 was 3.2%, bleaching temperature of 50-65 °C, addition of MgO was 0.13%, and bleaching time was 8h. If too much amount of NaHCO3 was added to the system and maintained alkaline pH, the bleaching effect would be greatly reduced. Fixing molar ratio of TAED to H2O2 and increasing the amount of H2O2 were beneficial to improve the whiteness of alkyl polyglycosides, but adding too much amount of H2O2 would reduce the transparency. In the TAED-activated peroxide system, NaHCO3 as alkaline agent and buffer agent, could overcome the disadvantage of producing black precipitates when NaOH as alkaline agent. Copyright © 2014 Elsevier Ltd. All rights reserved.

The influence of Na + and Ca 2+ ions on the SiO 2-AlPO 4 materials structure — IR and Raman studies

NASA Astrophysics Data System (ADS)

Rokita, M.; Mozgawa, W.; Handke, M.

2001-09-01

The series of samples containing 0-20 mol% of NaCaPO4 and 20-0 mol% of AlPO4, respectively, with the constant amount of SiO2 (80 mol%) have been selected. The materials were prepared using both sol-gel as well as aerosil pseudo-aqua solution method. The AlPO4·SiO2 and NaCaPO4·SiO2 (80 mol% of SiO2) samples have been prepared. IR and Raman spectra of these samples are presented. The spectra of materials from NaCaPO4-AlPO4-SiO2 system are compared to those of NaCaPO4·SiO2 and AlPO4·SiO2 sample (samples without Al3+ or Na+ and Ca2+ cations, respectively). The studies have enabled us to identify the bands arising from the internal and lattice vibrations. The slight differences between the spectra of sol-gel and aerosil pseudo-aqua solution materials are pointed out and discussed. The influence of Na+ and Ca2+ ions on the AlPO4-SiO2 materials structure is analysed.

Na7Cr4(P2O7)4PO4

PubMed Central

Bourguiba Fakhar, Noura; Zid, Mohamed Faouzi; Driss, Ahmed

2013-01-01

The title compound, hepta­sodium tetra­chromium(III) tetra­kis­(diphosphate) orthophosphate, was synthesized by solid-state reaction. Its structure is isotypic with that of Na7 M 4(P2O7)4PO4 (M = In, Al) compounds and is made up from a three-dimensional [(CrP2O7)4PO4]7− framework with channels running along [001]. The three Na+ cations are located in the voids of the framework. One of the cations is situated on a general position, one is equally disordered around a twofold rotation axis and one is on a fourfold rotoinversion axis. The isolated PO4 tetra­hedron of the anionic framework is also situated on the -4 axis. Structural relationships between the title compound and different diphosphates containing MP2O11 units (M = Mo, V) are discussed. PMID:23723751

Synthesis, bioactivity and preliminary biocompatibility studies of glasses in the system CaO-MgO-SiO2-Na2O-P2O5-CaF2.

PubMed

Tulyaganov, D U; Agathopoulos, S; Valerio, P; Balamurugan, A; Saranti, A; Karakassides, M A; Ferreira, J M F

2011-02-01

New compositions of bioactive glasses are proposed in the CaO-MgO-SiO(2)-Na(2)O-P(2)O(5)-CaF(2) system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO(4)) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts' cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).

Luminescent properties of Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} and its potential application in white light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhijun, E-mail: wangzhijunmail@yahoo.com.cn; Li, Panlai; Li, Ting

2013-06-01

Graphical abstract: Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} phosphor can be effectively excited by an ultraviolet and near-ultraviolet light, and produce a bright blue emission centered at 436 nm. The CIE chromaticity coordinations (x, y) of Na{sub 2}CaSiO{sub 4}:Eu{sup 2+}(NSCE)/Li{sub 2}SrSiO{sub 4}:Eu{sup 2+}(LSSE) vary with the molar ratio of the two constituents. When NSCE/LSSE is 1:3, the CIE chromaticity coordination is (0.332, 0.346), which is close to that of the natural sunlight (0.33, 0.33). The results indicate that Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} may be a promising blue phosphor for UV chip-based multi-phosphor converted white light emitting diodes. Highlights: ► Na{sub 2}CaSiO{sub 4}:Eu{supmore » 2+} shows the blue emission with a peak at 436 nm and broad excitation band in the UV/n-UV range. ► White light with CIE coordinates (0.332, 0.346) is generated by mixing the blue phosphor with the Li{sub 2}SrSiO{sub 4}:Eu{sup 2+} yellow phosphor. ► Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} would be a promising blue phosphor candidate for UV chip-based multi-phosphor converted white LEDs. - Abstract: A novel blue phosphor Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} is synthesized by a high temperature solid-state reaction, and its luminescent properties are systematically studied. Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} can be effectively excited by the 354 nm radiation, and create blue emission (436 nm). The emission intensity of Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} is influenced by the Eu{sup 2+} doping content, and the optimal doping content is 1.5%, and the concentration quenching mechanism of Eu{sup 2+} in Na{sub 2}CaSiO{sub 4} can be attributed to the multipolar interaction. The white light with CIE coordinates (0.332, 0.346) is generated by mixing the blue phosphor Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} with the yellow phosphor Li{sub 2}SrSiO{sub 4}:Eu{sup 2+}. The results indicate that Na{sub 2}CaSiO{sub 4}:Eu{sup 2+} may be a potential blue emitting phosphor for UV chip-based multi

Theoretical prediction of morphotropic compositions in Na1/2Bi1/2TiO3-based solid solutions from transition pressures

NASA Astrophysics Data System (ADS)

Gröting, Melanie; Albe, Karsten

2014-02-01

In this article we present a method based on ab initio calculations to predict compositions at morphotropic phase boundaries in lead-free perovskite solid solutions. This method utilizes the concept of flat free energy surfaces and involves the monitoring of pressure-induced phase transitions as a function of composition. As model systems, solid solutions of Na1/2Bi1/2TiO3 with the alkali substituted Li1/2Bi1/2TiO3 and K1/2Bi1/2TiO3 and the alkaline earth substituted CaTiO3 and BaTiO3 are chosen. The morphotropic compositions are identified by determining the composition at which the phase transition pressure equals zero. In addition, we discuss the different effects of hydrostatic pressure (compression and tension) and chemical substitution on the antiphase tilts about the [111] axis (a-a-a-) present in pure Na1/2Bi1/2TiO3 and how they develop in the two solid solutions Na1/2Bi1/2TiO3-CaTiO3 and Na1/2Bi1/2TiO3-BaTiO3. Finally, we discuss the advantages and shortcomings of this simple computational approach.

Na2Ti6O13: a potential anode for grid-storage sodium-ion batteries.

PubMed

Rudola, Ashish; Saravanan, Kuppan; Devaraj, Sappani; Gong, Hao; Balaya, Palani

2013-08-28

The ultra-fast (30C or 2 min) rate capability and impressive long cycle life (>5000 cycles) of Na2Ti6O13 are reported. A stable 2.5 V sodium-ion battery full cell is demonstrated. In addition, the sodium storage mechanism and thermal stability of Na2Ti6O13 are discussed.

A Novel Coordination Polymer Constructed by Hetero-Metal Ions and 2,3-Pyridine Dicarboxylic Acid: Synthesis and Structure of [NiNa2(PDC)2(μ-H2O)(H2O)2] n

NASA Astrophysics Data System (ADS)

Dou, Ming-Yu; Lu, Jing

2017-12-01

A novel coordination polymer containing hetero-metal ions, [NiNa2(PDC)2(μ-H2O)(H2O)2] n , where PDC is 2,3-pyridine dicarboxylate ion, has been synthesized. In the structure, the PDC ligand chelates and bridges two Ni(II) and two Na(I) centers. Two kinds of metal centers are connected by μ4-PDC and μ2-H2O to form 2D coordination layers. Hydrogen bonds between coordination water molecules and carboxylate oxygen atoms further link these 2D coordination layers to form 3D supramolecular network.

NMR study of the paramagnetic state of low-dimensional magnets LiCu{sub 2}O{sub 2} and NaCu{sub 2}O{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadykov, A. F., E-mail: sadykov@imp.uran.ru; Piskunov, Yu. V.; Gerashchenko, A. P.

A comprehensive NMR study of the magnetic properties of single crystal LiCu{sub 2}O{sub 2} (LCO) and NaCu{sub 2}O{sub 2} (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for {sup 63,65}Cu, {sup 7}Li, and {sup 23}Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.

β-Li0.37Na0.63Fe(MoO4)2

PubMed Central

Souilem, Amira; Zid, Mohamed Faouzi; Driss, Ahmed

2014-01-01

The title compound, lithium/sodium iron(III) bis­[ortho­molyb­date(VI)], was obtained by a solid-state reaction. The main structure units are an FeO6 octa­hedron, a distorted MoO6 octa­hedron and an MoO4 tetra­hedron sharing corners. The crystal structure is composed of infinite double MoFeO11 chains along the b-axis direction linked by corner-sharing to MoO4 tetra­hedra so as to form Fe2Mo3O19 ribbons. The cohesion between ribbons via mixed Mo—O—Fe bridges leads to layers arranged parallel to the bc plane. Adjacent layers are linked by corners shared between MoO4 tetra­hedra of one layer and FeO6 octa­hedra of the other layer. The Na+ and Li+ ions partially occupy the same general position, with a site-occupancy ratio of 0.631 (9):0.369 (1). A comparison is made with AFe(MoO4)2 (A = Li, Na, K and Cs) structures. PMID:24764805

Structural Stability and Electronic Properties of Na2C6O6 for a Rechargeable Sodium-ion Battery

NASA Astrophysics Data System (ADS)

Yamashita, Tomoki; Fujii, Akihiro; Momida, Hiroyoshi; Oguchi, Tamio

2014-03-01

Sodium-ion batteries have been explored as a promising alternative to lithium-ion batteries owing to a significant advantage of a natural abundance of sodium. Recently, it has been reported that disodium rhodizonate, Na2C6O6, exhibit good electrochemical properties and cycle performance as a minor-metal free organic cathode for sodium-ion batteries. However, its crystal structures during discharge/charge cycle still remain unclear. In this work, we theoretically propose feasible crystal structures of Na2+xC6O6 using first principles calculations. A structural phase transition has been found: Na4C6O6 has a different C6O6 packing arrangement from Na2C6O6. Electronic structures of Na2+xC6O6 during discharge/charge cycle are also discussed. Our predictions could be the key to understanding the discharge/charge process of Na2C6O6. Supported by MEXT program ``Elements Strategy Initiative to Form Core Rersearch Center'' (since 2012), MEXT; Ministry of Education Culture, Sports, Science and Technology, Japan.

Layered P2-Na 2/3 Co 1/2 Ti 1/2 O 2 as a high-performance cathode material for sodium-ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabi, Noha; Doubaji, Siham; Hashimoto, Kazuki

Layered oxides are regarded as promising cathode materials for sodium-ion batteries. We present Na2/3Co1/2Ti1/2O2 as a potential new cathode material for sodium-ion batteries. The crystal features and morphology of the pristine powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The cathode material is evaluated in galvanostatic charge-discharge and galvanostatic intermittent titration tests, as well as ex-situ X-ray diffraction analysis. Synthesized by a high-temperature solid state reaction, Na2/3Co1/2Ti1/2O2 crystallizes in P2-type structure with P6(3)/mmc space group. The material presents reversible electrochemical behavior and delivers a specific discharge capacity of 100 mAh g(-1) when tested in Na halfmore » cells between 2.0 and 4.2 V (vs. Na+/Na), with capacity retention of 98% after 50 cycles. Furthermore, the electrochemical cycling of this titanium-containing material evidenced a reduction of the potential jumps recorded in the NaxCoO2 parent phase, revealing a positive impact of Ti substitution for Co. The ex-situ XRD measurements confirmed the reversibility and stability of the material. No structural changes were observed in the XRD patterns, and the P2-type structure was stable during the charge/discharge process between 2.0 and 4.2 V vs. Na+/Na. These outcomes will contribute to the progress of developing low cost electrode materials for sodium-ion batteries. (C) 2017 Elsevier B.V. All rights reserved.« less

In vitro evaluation of bioactivity of SiO2-CaO-P2O5-Na2O-CaF2-ZnO glass-ceramics

NASA Astrophysics Data System (ADS)

Riaz, Madeeha; Zia, Rehana; Saleemi, Farhat; Bashir, Farooq; Hossain, Tousif; Kayani, Zohra

2014-09-01

Zinc is an essential trace element that stimulates bone formation but it is also known as an inhibitor of apatite crystal growth. In this work addition of ZnO to SiO2-CaO-P2O5-Na2O-CaF2 glass-ceramic system was made by conventional melt-quenching technique. DSC curves showed that the addition of ZnO moved the endothermic and exothermic peaks to lower temperatures. X-ray diffraction analysis did not reveal any additional phase caused by ZnO addition and showed the presence of wollastonite and hydroxyapatite crystalline phases only in all the glass-ceramic samples. As bio-implant apatite forming ability is an essential condition, the surface reactivity of the prepared glass-ceramic specimens was studied in vitro in Kokubo's simulated body fluid (SBF) [1] with ion concentration nearly equal to human blood plasma for 30 days at 37 °C under static condition. Atomic absorption spectroscopy (AAS) was used to study the changes in element concentrations in soaking solutions and XRD, FT-IR and SEM were used to elucidate surface properties of prepared glass-ceramics, which confirmed the formation of HCAp on the surface of all glass-ceramics. It was found that the addition of ZnO had a positive effect on bioactivity of glass-ceramics and made it a potential candidate for restoration of damaged bones.

In Situ Imaging the Oxygen Reduction Reactions of Solid State Na-O2 Batteries with CuO Nanowires as the Air Cathode.

PubMed

Liu, Qiunan; Yang, Tingting; Du, Congcong; Tang, Yongfu; Sun, Yong; Jia, Peng; Chen, Jingzhao; Ye, Hongjun; Shen, Tongde; Peng, Qiuming; Zhang, Liqiang; Huang, Jianyu

2018-06-13

We report real time imaging of the oxygen reduction reactions (ORRs) in all solid state sodium oxygen batteries (SOBs) with CuO nanowires (NWs) as the air cathode in an aberration-corrected environmental transmission electron microscope under an oxygen environment. The ORR occurred in a distinct two-step reaction, namely, a first conversion reaction followed by a second multiple ORR. In the former, CuO was first converted to Cu 2 O and then to Cu; in the latter, NaO 2 formed first, followed by its disproportionation to Na 2 O 2 and O 2 . Concurrent with the two distinct electrochemical reactions, the CuO NWs experienced multiple consecutive large volume expansions. It is evident that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter one-electron-transfer ORR, leading to the formation of NaO 2 . Remarkably, no carbonate formation was detected in the oxygen cathode after cycling due to the absence of carbon source in the whole battery setup. These results provide fundamental understanding into the oxygen chemistry in the carbonless air cathode in all solid state Na-O 2 batteries.

Thermodynamic Study of Solid-Liquid Equilibrium in NaCl-NaBr-H2O System at 288.15 K

NASA Astrophysics Data System (ADS)

Li, Dan; Meng, Ling-zong; Deng, Tian-long; Guo, Ya-fei; Fu, Qing-Tao

2018-06-01

The solubility data, composition of the solid solution and refractive indices of the NaCl-NaBr-H2O system at 288.15 K were studied with the isothermal equilibrium dissolution method. The solubility diagram and refractive index diagram of this system were plotted at 288.15 K. The solubility diagram consists of two crystallization zones for solid solution Na(Cl,Br) · 2H2O and Na(Cl,Br), one invariant points cosaturated with two solid solution and two univariant solubility isothermal curves. On the basis of Pitzer and Harvie-Weare (HW) chemical models, the composition equations and solubility equilibrium constant equations of the solid solutions at 288.15 K were acquired using the solubility data, the composition of solid solutions, and binary Pitzer parameters. The solubilities calculated using the new method combining the equations are in good agreement with the experimental data.

New Defective Brannerite-Type Vanadates. I. Synthesis and Study of Mn 1- x- yφ xNa yV 2-2 x-yMo 2 x+yO 6 Solid Solutions

NASA Astrophysics Data System (ADS)

Masłowska, Bogna; Ziółkowski, Jacek

1994-05-01

MnV 2O 6 of the brannerite-type structure (below 540°C) doped with MoO 3 and Na 2O forms isomorphous solid solutions MnNaφ = Mn 1- x-yφ xNa yV 2-2 x-yMo 2 x+ yO 6 (φ cation vacancy in the original Mn position), belonging to the pseudoternary MnV 2O 6-NaVMoO 6-MoO 3 system. Particular cases are MnNa = Mn 1- yNa y V 2- yMo yO 6 ( x = 0), Mnφ = Mn 1- xφ xV 2-2 xMo 2 xO 6 ( y = 0), and Naφ = Na 1- xφ xV 1- xMo 1+ xO 6 ( x + y = 1). MnV 2O 6 and NaVMoO 6 show miscibility in the entire composition range (MnNa). The opposite boundary of MnNaφ passes through the (100 x, 100 y) points (45, 0), (33, 30), and (30, 70). The phase diagram of the pseudobinary MnV 2O 6-NaVMoO 6 system (determined with DTA) shows (i) a narrow double-lens-type solidus-liquidus gap at high values of y , (ii) two peritectic meltings at lower y (yielding the high temperature β-MnNa and Mn 2V 2O 7), and (iii) little area of β-MnNa. Lattice parameters of MnNa (determined with X-ray diffraction) reveal small deviations from Vegard's law. As the ionic radii of both dopants (Na + and Mo 6+) are, respectively, larger than those of mother ions (Mn 2+ and V 5+), the unit cell increases in all directions with rising y along the MnNa series of solid solutions. However, due to the anisotropy of the structure, parameter c is strongly sensitive to Na/Mn substitution, b is ruled by Mo/V, and a is weakly influenced by Mo/V. Close analogy to the behavior of the previously studied MnV 2O 6-LiVMoO 6-MoO 6 system is discussed.

Structure-electrochemical evolution of a Mn-rich P2 Na 2/3Fe 0.2Mn 0.8O 2 Na-ion battery cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dose, Wesley M.; Sharma, Neeraj; Pramudita, James C.

The structural evolution of electrode materials directly influences the performance of sodium-ion batteries. In this work, in situ synchrotron X-ray diffraction is used to investigate the evolution of the crystal structure of a Mn-rich P2-phase Na 2/3Fe 0.2Mn 0.8O 2 cathode. A single-phase reaction takes place for the majority of the discharge–charge cycle at ~C/10, with only a short, subtle hexagonal P2 to hexagonal P2 two-phase region early in the first charge. Thus, a higher fraction of Mn compared to previous studies is demonstrated to stabilize the P2 structure at high and low potentials, with neither “Z”/OP4 phases in themore » charged state nor significant quantities of the P'2 phase in the discharged state between 1.5 and 4.2 V. Notably, sodium ions inserted during discharge are located on both available crystallographic sites, albeit with a preference for the site sharing edges with the MO 6 octahedral unit. The composition Na ~0.70Fe 0.2Mn 0.8O 2 prompts a reversible single-phase sodium redistribution between the two sites. Sodium ions vacate the site sharing faces (Naf), favoring the site sharing edges (Nae) to give a Nae/Naf site occupation of 4:1 in the discharged state. This site preference could be an intermediate state prior to the formation of the P'2 phase. Furthermore, this work shows how the Mn-rich Na 2/3Fe 0.2Mn 0.8O 2 composition and its sodium-ion distribution can minimize phase transitions during battery function, especially in the discharged state.« less

Structure-electrochemical evolution of a Mn-rich P2 Na 2/3Fe 0.2Mn 0.8O 2 Na-ion battery cathode

DOE PAGES

Dose, Wesley M.; Sharma, Neeraj; Pramudita, James C.; ...

2017-08-04

The structural evolution of electrode materials directly influences the performance of sodium-ion batteries. In this work, in situ synchrotron X-ray diffraction is used to investigate the evolution of the crystal structure of a Mn-rich P2-phase Na 2/3Fe 0.2Mn 0.8O 2 cathode. A single-phase reaction takes place for the majority of the discharge–charge cycle at ~C/10, with only a short, subtle hexagonal P2 to hexagonal P2 two-phase region early in the first charge. Thus, a higher fraction of Mn compared to previous studies is demonstrated to stabilize the P2 structure at high and low potentials, with neither “Z”/OP4 phases in themore » charged state nor significant quantities of the P'2 phase in the discharged state between 1.5 and 4.2 V. Notably, sodium ions inserted during discharge are located on both available crystallographic sites, albeit with a preference for the site sharing edges with the MO 6 octahedral unit. The composition Na ~0.70Fe 0.2Mn 0.8O 2 prompts a reversible single-phase sodium redistribution between the two sites. Sodium ions vacate the site sharing faces (Naf), favoring the site sharing edges (Nae) to give a Nae/Naf site occupation of 4:1 in the discharged state. This site preference could be an intermediate state prior to the formation of the P'2 phase. Furthermore, this work shows how the Mn-rich Na 2/3Fe 0.2Mn 0.8O 2 composition and its sodium-ion distribution can minimize phase transitions during battery function, especially in the discharged state.« less

Magnetic properties of superparamagnetic β-NaFeO2 nanoparticles

NASA Astrophysics Data System (ADS)

Singh, Sarbjit; Tovstolytkin, Alexandr; Lotey, Gurmeet Singh

2018-07-01

Superparamagnetic β-NaFeO2 nanoparticles of particle size 37 nm with orthorhombic crystal structure and space group Pn21a have been prepared by sol-gel method. Temperature dependent magnetic study has been performed. Its systematic analysis has been done to calculate the Curie and blocking temperatures along with its magnetic susceptibility. The Langevin fitting of the magnetic data has been carried out. It has been shown that the synthesized nanoparticles exhibit superparamagnetic behavior. The Neel's relaxation time has been calculated to further support its superparamagnetic nature. The synthesized β-NaFeO2 nanoparticles behave like ferromagnets below 80 K; they are superparamagnetic above 80 K-340 K and thereafter as paramagnetic. The possible mechanism of superparamagnetism has been discussed. It has been concluded that these nanoparticles can find wide applications in the area of biomedical sciences.

Effect of Substituted Ca on the Thermoelectric and Optoelectronic Properties of NaRh2O4 Under Pressure

NASA Astrophysics Data System (ADS)

Rahnamaye Aliabad, H. A.; Hosseini, N.

2018-03-01

In this paper, we have used the first principle calculations for investigation of the structural, optoelectronic and thermoelectric properties of NaRh2O4 compound and substituted with Ca onto the Na sites under pressure. The results show that there are two direct band gaps for the NaRh2O4 compound and three indirect band gaps for the CaRh2O4 compound at the top of the Fermi level. The size of the band gaps increases almost linearly with the increase of the pressure up to 37 GPa. The calculated density of states for the CaRh2O4 compound show that the Ca-3 p state plays a key role for enhancement of the thermoelectric figure of merit ( ZT). We found that the static dielectric function value decreases along the x, y and z directions for the CaRh2O4 compound with the increase of the pressure while it is constant along the x and y directions for the NaRh2O4 compound. The birefringence properties with metallic nature are achieved from the optical spectra. The thermoelectric results show that the maximum peak of the ZT shifts towards the higher value of temperature for the NaRh2O4 compound. The Ca substitution onto the Na sites in the NaRh2O4 compound enhances the ZT value of 0.79 at 250 K.

A mixed iron-manganese based pyrophosphate cathode, Na2Fe0.5Mn0.5P2O7, for rechargeable sodium ion batteries.

PubMed

Shakoor, Rana A; Park, Chan Sun; Raja, Arsalan A; Shin, Jaeho; Kahraman, Ramazan

2016-02-07

The development of secondary batteries based on abundant and cheap elements is vital. Among various alternatives to conventional lithium-ion batteries, sodium-ion batteries (SIBs) are promising due to the abundant resources and low cost of sodium. While there are many challenges associated with the SIB system, cathode is an important factor in determining the electrochemical performance of this battery system. Accordingly, ongoing research in the field of SIBs is inclined towards the development of safe, cost effective cathode materials having improved performance. In particular, pyrophosphate cathodes have recently demonstrated decent electrochemical performance and thermal stability. Herein, we report the synthesis, electrochemical properties, and thermal behavior of a novel Na2Fe0.5Mn0.5P2O7 cathode for SIBs. The material was synthesized through a solid state process. The structural analysis reveals that the mixed substitution of manganese and iron has resulted in a triclinic crystal structure (P1[combining macron] space group). Galvanostatic charge/discharge measurements indicate that Na2Fe0.5Mn0.5P2O7 is electrochemically active with a reversible capacity of ∼80 mA h g(-1) at a C/20 rate with an average redox potential of 3.2 V. (vs. Na/Na(+)). It is noticed that 84% of initial capacity is preserved over 90 cycles showing promising cyclability. It is also noticed that the rate capability of Na2Fe0.5Mn0.5P2O7 is better than Na2MnP2O7. Ex situ and CV analyses indicate that Na2Fe0.5Mn0.5P2O7 undergoes a single phase reaction rather than a biphasic reaction due to different Na coordination environment and different Na site occupancy when compared to other pyrophosphate materials (Na2FeP2O7 and Na2MnP2O7). Thermogravimetric analysis (25-550 °C) confirms good thermal stability of Na2Fe0.5Mn0.5P2O7 with only 2% weight loss. Owing to promising electrochemical properties and decent thermal stability, Na2Fe0.5Mn0.5P2O7, can be an attractive cathode for SIBs.

Heterogeneous reactions of HNO3(g) + NaCl(s) yields HCl(g) + NaNO3(s) and N2O5(g) + NaCl(s) yields ClNO2(g) + NaNO3(s)

NASA Technical Reports Server (NTRS)

Leu, Ming-Taun; Timonen, Raimo S.; Keyser, Leon F.; Yung, Yuk L.

1995-01-01

The heterogeneous reactions of HNO3(g) + NaCl(s) yields HCl(g) + NaNO3(s) (eq 1) and N2O5(g) + NaCl(s) yields ClNO2(g) + NaNO3(S) (eq 2) were investigated over the temperature range 223-296 K in a flow-tube reactor coupled to a quadrupole mass spectrometer. Either a chemical ionization mass spectrometer (CIMS) or an electron-impact ionization mass spectrometer (EIMS) was used to provide suitable detection sensitivity and selectivity. In order to mimic atmospheric conditions, partial pressures of HNO3 and N2O5 in the range 6 x 10(exp -8) - 2 x 10(exp -6) Torr were used. Granule sizes and surface roughness of the solid NaCl substrates were determined by using a scanning electron microscope. For dry NaCl substrates, decay rates of HNO3 were used to obtain gamma(1) = 0.013 +/- 0.004 (1sigma) at 296 K and > 0.008 at 223 K, respectively. The error quoted is the statistical error. After all corrections were made, the overall error, including systematic error, was estimated to be about a factor of 2. HCl was found to be the sole gas-phase product of reaction 1. The mechanism changed from heterogeneous reaction to predominantly physical adsorption when the reactor was cooled from 296 to 223 K. For reaction 2 using dry salts, gamma(2) was found to be less than 1.0 x 10(exp -4) at both 223 and 296 K. The gas-phase reaction product was identified as ClNO2 in previous studies using an infrared spectrometer. An enhancement in reaction probability was observed if water was not completely removed from salt surfaces, probably due to the reaction of N2O5(g) + H2O(s) yields 2HNO3(g). Our results are compared with previous literature values obtained using different experimental techniques and conditions. The implications of the present results for the enhancement of the hydrogen chloride column density in the lower stratosphere after the El Chichon volcanic eruption and for the chemistry of HCl and HNO3 in the marine troposphere are discussed.

New Insights into the Instability of Discharge Products in Na-O2 Batteries.

PubMed

Landa-Medrano, Imanol; Pinedo, Ricardo; Bi, Xuanxuan; Ruiz de Larramendi, Idoia; Lezama, Luis; Janek, Jürgen; Amine, Khalil; Lu, Jun; Rojo, Teófilo

2016-08-10

Sodium-oxygen batteries currently stimulate extensive research due to their high theoretical energy density and improved operational stability when compared to lithium-oxygen batteries. Cell stability, however, needs to be demonstrated also under resting conditions before future implementation of these batteries. In this work we analyze the effect of resting periods on the stability of the sodium superoxide (NaO2) discharge product. The instability of NaO2 in the cell environment is demonstrated leading to the evolution of oxygen during the resting period and the decrease of the cell efficiency. In addition, migration of the superoxide anion (O2(-)) in the electrolyte is observed and demonstrated to be an important factor affecting Coulombic efficiency.

Enhanced near-infrared photocatalysis of NaYF4:Yb, Tm/CdS/TiO2 composites.

PubMed

Guo, Xingyuan; Di, Weihua; Chen, Changfeng; Liu, Chunxu; Wang, Xue; Qin, Weiping

2014-01-21

The previous works by our group (Chem. Commun., 2010, 46, 2304-2306; ACS Catal., 2013, 3, 405-412; Phys. Chem. Chem. Phys., 2013, 15, 14681-14688) have reported the near-infrared-driven photocatalysis of broadband semiconductor TiO2 or ZnO that was combined with upconverting luminescence particles to form a core-shell structure. However, the photocatalytic efficiency is low for this new type of photocatalysts. In this work, NaYF4:Yb,Tm/CdS/TiO2 composites for NIR photocatalysis were prepared by linking CdS and TiO2 nanocrystals on the NaYF4:Yb,Tm microcrystal surfaces. CdS and TiO2 were well interacted to form a heterojunction structure. The energy transfer between NaYF4:Yb,Tm and the semiconductors CdS and TiO2 was investigated by steady-state and dynamic fluorescence spectroscopy. The photocatalytic activities of the as-prepared composites were evaluated by the degradation of methylene blue in aqueous solution upon NIR irradiation. Significantly, it was found that the united adhesions of CdS and TiO2 on the NaYF4:Yb,Tm particle surfaces showed much higher catalytic activities than the individual adhesion of CdS or TiO2 on the NaYF4:Yb,Tm surfaces. This was attributed mainly to the effective separation of the photogenerated electron-hole pairs due to the charge transfer across the CdS-TiO2 interface driven by the band potential difference between them. The presented composite structure of upconverting luminescence materials coupled with narrow/wide semiconductor heterojunctions provides a new model for improved NIR photocatalysis.

Interaction of Corundum, Wollastonite and Quartz With H2O-NaCl Solutions at 800 C and 10 Kbar

NASA Astrophysics Data System (ADS)

Newton, R. C.; Manning, C. E.

2005-12-01

Aqueous fluids are potentially important transport agents in subduction zones and other high-P metamorphic environments. Recent studies indicate that at high P and T, the solubilities of major rock-forming elements are strongly enhanced by the formation of metal-chloride complexes, metal-hydroxide complexes and polynuclear metal-hydroxide clusters. However, the relative abundances of these species and the energetics of their interactions in high-pressure environments remains largely unknown. We measured the solubilities of corundum (Al2O3) and wollastonite (CaSiO3) at 800 °C and 10 kbar in H2O-NaCl solutions to halite saturation (XNaCl = 0.6) . Both minerals show marked enhancement of solubility with increasing salinity. Al2O3 mol fraction rises rapidly to XNaCl = 0.1, and then declines slowly towards halite saturation. Quenched experimental fluids have neutral pH. Modeling based on ideal solution of ions and molecules leads to a simple dissolution reaction and corresponding molality (m=mol/kg H2O) expression: Al2O3(cor) + Na+ + 3H2O = NaAl(OH)4 + Al(OH)2+ and mAl2O3 = [0.0232(aNaCl)1/4(aH2O)3/2+0.00123][1+2XNaCl/(1-XNaCl)] where H2O and NaCl activities are given by aH2O = (2-XNaCl)/(2+XNaCl) and aNaCl = 4(XNaCl)2/(1 + XNaCl)2. Wollastonite solubility in NaCl solutions is accurately described by: mCaSiO3 = 0.6734XNaCl + 0.1183(XNaCl)1/2 + 0.0204. There is a roughly 50-fold enhancement of dissolved wollastonite at halite saturation. Quenched experimental fluids are strongly basic (pH=11). A consistent dissolution reaction must therefore be similar to: CaSiO3(wo) + Na+ + Cl- = CaCl+ + OH- + HNaSiO3 Quartz solubility declines monotonically from mSiO2 = 1.248 in pure H2O to 0.20 at halite saturation. Quenched fluids are neutral, indicating that quartz does not react with solvent NaCl. The only salinity control on solubility is decrease of H2O activity. The simple dissolution behaviors to be deduced from measurements on these minerals suggest that fluid

Thermal expansion of the nuclear fuel-sodium reaction product Na3(U0.84(2),Na0.16(2))O4 - Structural mechanism and comparison with related sodium-metal ternary oxides

NASA Astrophysics Data System (ADS)

Illy, Marie-Claire; Smith, Anna L.; Wallez, Gilles; Raison, Philippe E.; Caciuffo, Roberto; Konings, Rudy J. M.

2017-07-01

Na3.16(2)UV,VI0.84(2)O4 is obtained from the reaction of sodium with uranium dioxide under oxygen potential conditions typical of a sodium-cooled fast nuclear reactor. In the event of a breach of the steel cladding, it would be the dominant reaction product forming at the rim of the mixed (U,Pu)O2 fuel pellets. High-temperature X-ray diffraction measurements show that a distortion of the uranium environment in Na3.16(2)UV,VI0.84(2)O4 results in a strongly anisotropic thermal expansion. A comparison with several related sodium metallates Nan-2Mn+On-1 - including Na3SbO4 and Na3TaO4, whose crystal structures are reported for the first time - has allowed us to assess the role played in the lattice expansion by the Mn+ cation radius and the Na/M ratio. On this basis, the thermomechanical behavior of the title compound is discussed, along with those of several related double oxides of sodium and actinide elements, surrogate elements, or fission products.

Effect of Solids-To-Liquids, Na2SiO3-To-NaOH and Curing Temperature on the Palm Oil Boiler Ash (Si + Ca) Geopolymerisation System

PubMed Central

Yahya, Zarina; Abdullah, Mohd Mustafa Al Bakri; Hussin, Kamarudin; Ismail, Khairul Nizar; Abd Razak, Rafiza; Sandu, Andrei Victor

2015-01-01

This paper investigates the effect of the solids-to-liquids (S/L) and Na2SiO3/NaOH ratios on the production of palm oil boiler ash (POBA) based geopolymer. Sodium silicate and sodium hydroxide (NaOH) solution were used as alkaline activator with a NaOH concentration of 14 M. The geopolymer samples were prepared with different S/L ratios (0.5, 1.0, 1.25, 1.5, and 1.75) and Na2SiO3/NaOH ratios (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0). The main evaluation techniques in this study were compressive strength, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscope (SEM). The results showed that the maximum compressive strength (11.9 MPa) was obtained at a S/L ratio and Na2SiO3/NaOH ratio of 1.5 and 2.5 at seven days of testing.

Fragile magnetic order in the honeycomb lattice Iridate Na2IrO3 revealed by magnetic impurity doping

NASA Astrophysics Data System (ADS)

Mehlawat, Kavita; Sharma, G.; Singh, Yogesh

2015-10-01

We report the structure, magnetic, and thermal property measurements on single-crystalline and polycrystalline samples of the Ru-substituted honeycomb lattice iridate Na2Ir1 -xRuxO3 (x =0 ,0.05 ,0.1 ,0.15 ,0.2 ,0.3 ,0.5 ) . The evolution of magnetism in Na2Ir1 -xRuxO3 has been studied using dc and ac magnetic susceptibilities and heat-capacity measurements. The parent compound Na2IrO3 is a spin-orbit-driven Mott insulator with magnetic order of reduced moments below TN=15 K . In the Ru-substituted samples the antiferromagnetic long-range state is replaced by a spin-glass-like state even for the smallest substitution suggesting that the magnetic order in Na2IrO3 is extremely fragile. We argue that these behaviors indicate the importance of nearest-neighbor magnetic exchange in the parent Na2IrO3 . Additionally, all samples show insulating electrical transport.

Intense 2.7 µm emission and structural origin in Er3+-doped bismuthate (Bi2O3-GeO2-Ga2O3-Na2O) glass.

PubMed

Guo, Yanyan; Li, Ming; Hu, Lili; Zhang, Junjie

2012-01-15

The 2.7 μm emission properties in Er3+-doped bismuthate (Bi2O3-GeO2-Ga2O3-Na2O) glass were investigated in the present Letter. An intense 2.7 μm emission in Er3+-doped bismuthate glass was observed. It is found that Er3+-doped bismuthate glass possesses high spontaneous transition probability A (65.26 s(-1)) and large 2.7 μm emission cross section σ(em) (9.53×10(-21) cm2) corresponding to the stimulated emission of Er3+:4I11/2→4I13/2 transition. The emission characteristic and energy transfer process upon excitation of a conventional 980 nm laser diode in bismuthate glass were analyzed. Additionally, the structure of bismuthate glass was analyzed by the Raman spectrum. The advantageous spectroscopic characteristics of Er3+ single-doped bismuthate glass together with the prominent thermal property indicate that bismuthate glass might become an attractive host for developing solid-state lasers around 2.7 μm.

UV-visible light photocatalytic properties of NaYF4:(Gd, Si)/TiO2 composites

NASA Astrophysics Data System (ADS)

Mavengere, Shielah; Kim, Jung-Sik

2018-06-01

In this study, a new novel composite photocatalyst of NaYF4:(Gd, Si)/TiO2 phosphor has been synthesized by two step method of solution combustion and sol-gel. The photocatalyst powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV-vis spectroscopy and photoluminescence (PL) spectroscopy. Raman spectroscopy confirmed the anatase TiO2 phase which remarkably increased with existence of yttrium silicate compounds between 800 cm-1 and 900 cm-1. Double-addition of Gd3+-Si4+ ions in NaYF4 host introduced sub-energy band levels with intense absorption in the ultraviolet (UV) light region. Photocatalytic activity was examined by exposing methylene blue (MB) solutions mixed with photocatalyst powders to 254 nm UV-C fluorescent lamp and 200 W visible lights. The UV and visible photocatalytic reactivity of the NaYF4:(Gd, 1% Si)/TiO2 phosphor composites showed enhanced MB degradation efficiency. The coating of NaYF4:(Gd, 1% Si) phosphor with TiO2 nanoparticles creates energy band bending at the phosphor/TiO2 interfaces. Thus, these composites exhibited enhanced absorption of UV/visible light and the separation of electron and hole pairs for efficient photocatalysis.

Combustion of Na 2B 4O 7 + Mg + C to synthesis B 4C powders

NASA Astrophysics Data System (ADS)

Guojian, Jiang; Jiayue, Xu; Hanrui, Zhuang; Wenlan, Li

2009-09-01

Boron carbide powder was fabricated by combustion synthesis (CS) method directly from mixed powders of borax (Na 2B 4O 7), magnesium (Mg) and carbon. The adiabatic temperature of the combustion reaction of Na 2B 4O 7 + 6 Mg + C was calculated. The control of the reactions was achieved by selecting reactant composition, relative density of powder compact and gas pressure in CS reactor. The effects of these different influential factors on the composition and morphologies of combustion products were investigated. The results show that, it is advantageous for more Mg/Na 2B 4O 7 than stoichiometric ratio in Na 2B 4O 7 + Mg + C system and high atmosphere pressure in the CS reactor to increase the conversion degree of reactants to end product. The final product with the minimal impurities' content could be fabricated at appropriate relative density of powder compact. At last, boron carbide without impurities could be obtained after the acid enrichment and distilled water washing.

The study for the incipient solvation process of NaCl in water: the observation of the NaCl-(H2O)n (n = 1, 2, and 3) complexes using Fourier-transform microwave spectroscopy.

PubMed

Mizoguchi, Asao; Ohshima, Yasuhiro; Endo, Yasuki

2011-08-14

Pure rotational spectra of the sodium chloride-water complexes, NaCl-(H(2)O)(n) (n = 1, 2, and 3), in the vibronic ground state have been observed by a Fourier- transform microwave spectrometer coupled with a laser ablation source. The (37)Cl-isotopic species and a few deuterated species have also been observed. From the analyses of the spectra, the rotational constants, the centrifugal distortion constants, and the nuclear quadrupole coupling constants of the Na and Cl nuclei were determined precisely for all the species. The molecular structures of NaCl-(H(2)O)(n) were determined using the rotational constants and the molecular symmetry. The charge distributions around Na and Cl nuclei in NaCl are dramatically changed by the complex formation with H(2)O. Prominent dependences of the bond lengths r(Na-Cl) on the number of H(2)O were also observed. By a comparison with results of theoretical studies, it is shown that the structure of NaCl-(H(2)O)(3) is approaching to that of the contact ion-pair, which is considered to be an intermediate species in the incipient solvation process.

Investigation of gamma ray shielding, structural and dissolution rate properties of Bi2O3-BaO-B2O3-Na2O glass system

NASA Astrophysics Data System (ADS)

Dogra, Mridula; Singh, K. J.; Kaur, Kulwinder; Anand, Vikas; Kaur, Parminder; Singh, Prabhjot; Bajwa, B. S.

2018-03-01

In the present study, quaternary system of the composition (0.45 + x) Bi2O3-(0.25 - x) BaO-0.15 B2O3-0.15 Na2O (where 0 ≤ x ≤ 0.2 mol fraction) has been prepared by using melt-quenching technique for investigation of gamma ray shielding properties. Mass attenuation coefficients and half value layer parameters have been determined experimentally at 662 keV by using 137Cs source. It has been found that experimental results of these parameters hold good agreement with theoretical values. The density, molar volume, XRD, FTIR, Raman and UV-visible studies have been used to determine structural properties of the prepared glass samples. Dissolution rate of the samples has also been measured to check their utility as long term durable glasses.

Magnetic ground state of the layered honeycomb compound Na2Co2TeO6

NASA Astrophysics Data System (ADS)

Bera, A. K.; Yusuf, S. M.

2018-04-01

The magnetic correlations in the 2D layered honeycomb compound Na2Co2TeO6 has been investigated. The temperature dependent susceptibility curve reveals a transition to the magnetically ordered state at TN ˜ 25 K. The temperature dependent neutron diffraction study confirms an antiferromagnetic ordering below TN. The magnetic ground state is determined to be a zigzag antiferromagnet that appears due to competing exchange interactions beyond nearest neighbors. The moments align along the crystallographic b axis with reduced ordered magnetic moment values of 2.72(2) μB/Co2+ and 2.52(3) μB/Co2+ for two Co sites, respectively. In comparison to the theoretical phase diagram the determined zigzag antiferromagnetic ground state suggests that the compound Na2Co2TeO6 is situated in the proximity to the quantum spin liquid state in the phase diagram.

A study of low threshold and high gain Nd3+ ions doped SiO2-B2O3-Na2CO3-NaF-CaF2 glasses for NIR laser applications

NASA Astrophysics Data System (ADS)

Megala, Rajesh; Gowthami, T.; John Sushma, N.; Kamala, S.; Deva Prasad Raju, B.

2018-05-01

Fluoroborosilicate glasses of composition 35SiO2-25B2O3-10Na2CO3-15NaF-15CaF2-xNd2O3 (where x = 0.1, 0.5. 1.0, 2.0 mol%) were prepared by melt quenching technique and various physical properties have been calculated. From the absorption spectra J-O Intensity parameters Ωλ (λ = 2, 4, 6) and radiative properties are evaluated by using J-O theory. The high values of Ω2 = 4.213 × 10-20 cm2, Ω4 = 5.345 × 10-20 cm2, Ω6 = 5.526 × 10-20 cm2 suggest that among the prepared glasses 0.5 mol% Nd glass is more asymmetric, more covalent and rigid in nature. The emission spectra were recorded with 808 nm laser as excitation source. The strong NIR emissions were observed at 876 nm, 1056 nm, 1328 nm corresponding to the transitions 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, 4F3/2 → 4I13/2 respectively. Stimulated emission cross -section (σemi) and Gain bandwidth (σemi × Δλeff) were calculated. For 0.5 mol% Nd these values are found to be 3.30 × 10-20 cm2, 11 × 10-26 cm2. From the decay curve analysis the lifetime values for 4F3/2 level have been determined and these values are decreased with increase in Nd3+ ions concentration. These results may suggest that the prepared SBNCNd05 (Nd = 0.5 mol%) glass could be useful for 1056 nm laser applications.

Effect of RE (Nd3+, Sm3+) oxide on structural, optical properties of Na2O-Li2O-ZnO-B2O3 glass system

NASA Astrophysics Data System (ADS)

Hivrekar, Mahesh M.; Bhoyar, D. N.; Mande, V. K.; Dhole, V. V.; Solunke, M. B.; Jadhav, K. M.

2018-05-01

Zinc borate glass activated with rare earth oxide (Nd2O3, Sm2O3) of Na2O-Li2O-ZnO-B2O3 quaternary system has been prepared successfully by melt quenching method. The nucleation and growth of RE oxide were controlled temperature range 950-1000° C and rapid cooling at room temperature. The physical, structural and optical properties were characterized by using X-ray diffraction (XRD), SEM, Ultraviolet-visible spectroscopy (UV-Vis). XRD and SEM studies confirmed the amorphous nature, surface morphology of prepared zinc borate glass. The physical parameters like density, molar volume, molar mass of Nd3+, Sm3+ doped borate glass are summarized in the present article. The optical absorption spectra along with tauc's plot are presented. The optical energy band gap increases due to the addition of rare earth oxide confirming the role of network modifier.

Ionic liquid-assisted hydrothermal synthesis of dendrite-like NaY(MoO4)2:Tb3+ phosphor

NASA Astrophysics Data System (ADS)

Tian, Yue; Chen, Baojiu; Tian, Bining; Sun, Jiashi; Li, Xiangping; Zhang, Jinsu; Cheng, Lihong; Zhong, Haiyang; Zhong, Hua; Meng, Qingyu; Hua, Ruinian

2012-07-01

Micro-sized NaY(MoO4)2:Tb3+ phosphors with dendritic morphology was synthesized by a ionic liquid-assisted hydrothermal process. X-ray diffraction (XRD) indicated that the as-prepared product is pure tetragonal phase of NaY(MoO4)2. Field emission scanning electron microscopy (FE-SEM) images showed that the as-prepared NaY(MoO4)2:Tb3+ phosphors have dendritic morphology. The photoluminescent (PL) spectra displayed that the as-prepared NaY(MoO4)2:Tb3+ phosphors show a stronger green emission with main emission wavelength 545 nm corresponding to the 5D4→7F5 transition of Tb3+ ion, and the optimal Tb3+ doping concentration for obtaining maximum emission intensity was confirmed to be 10 mol%. Based on Van Uitert's and Dexter's models the electric dipole-dipole (D-D) interaction was confirmed to be responsible for the concentration quenching of 5D4 fluorescence of Tb3+ in the NaY(MoO4)2:Tb3+ phosphors. The intrinsic radiative transition lifetime of 5D4 level is found to be 0.703 ms.

Effect of neutron-irradiation on optical properties of SiO2-Na2O-MgO-Al2O3 glasses

NASA Astrophysics Data System (ADS)

Sandhu, Amanpreet Kaur; Singh, Surinder; Pandey, Om Prakash

2009-07-01

Silica based glasses are used as nuclear shielding materials. The effect of radiation on these glasses varies as per the constituents used in these glasses. Glasses of different composition of SiO2-Na2OMgO-Al2O3 were made by melt casting techniques. These glasses were irradiated with neutrons of different fluences. Optical absorption measurements of neutron-irradiated silica based glasses were performed at room temperature (RT) to detect and characterize the induced radiation damage in these materials. The absorption band found for neutron-irradiated glasses are induced by hole type color centers related to non-bridging oxygen ions (NBO) located in different surroundings of glass matrix. Decrease in the transmittance indicates the formation of color-center defects. Values for band gap energy and the width of the energy tail above the mobility gap have been measured before and after irradiation. The band gap energy has been found to decrease with increasing fluence while the Urbach energy shows an increase. The effects of the composition of the glasses on these parameters have been discussed in detail in this paper.

Crystal structure of [NaZn(BTC)(H2O)4]·1.5H2O (BTC = benzene-1,3,5-tri-carb-oxy-l-ate): a heterometallic coordination compound.

PubMed

Ni, Min; Li, Quanle; Chen, Hao; Li, Shengqing

2015-07-01

The title coordination polymer, poly[[μ-aqua-tri-aqua-(μ3-benzene-1,3,5-tri-carboxyl-ato)sodiumzinc] sesquihydrate], {[NaZn(C9H3O6)(H2O)4]·1.5H2O} n , was obtained in ionic liquid microemulsion at room temperture by the reaction of benzene-1,3,5-tri-carb-oxy-lic acid (H3BTC) with Zn(NO3)2·6H2O in the presence of NaOH. The asymmetric unit comprises two Na(+) ions (each located on an inversion centre), one Zn(2+) ion, one BTC ligand, four coordinating water mol-ecules and two solvent water molecules, one of which is disordered about an inversion centre and shows half-occupation. The Zn(2+) cation is five-coordinated by two carboxyl-ate O atoms from two different BTC ligands and three coordinating H2O mol-ecules; the Zn-O bond lengths are in the range 1.975 (2)-2.058 (3) Å. The Na(+) cations are six-coordinated but have different arrangements of the ligands: one is bound to two carboxyl-ate O atoms of two BTC ligands and four O atoms from four coordinating H2O mol-ecules while the other is bound by four carboxyl-ate O atoms from four BTC linkers and two O atoms of coordinating H2O mol-ecules. The completely deprotonated BTC ligand acts as a bridging ligand binding the Zn(2+) atom and Na(+) ions, forming a layered structure extending parallel to (100). An intricate network of O-H⋯O hydrogen bonds is present within and between the layers.

Cooperative down-conversion of UV light in disordered scheelitelike Yb-doped NaGd(MoO4)2 and NaLa(MoO4)2 crystals

NASA Astrophysics Data System (ADS)

Subbotin, K. A.; Osipova, Yu. N.; Lis, D. A.; Smirnov, V. A.; Zharikov, E. V.; Shcherbakov, I. A.

2017-07-01

Concentration series of disordered scheelitelike Yb:NaGd(MoO4)2 and Yb:NaLa(MoO4)2 single crystals are grown by the Czochralski method. The actual concentrations of Yb3+ ions in the crystals are determined by optical-absorption spectroscopy. The luminescence of Yb3+ ions in these crystals in the region of 1 μm is studied under UV and IR excitation. In the case of UV excitation, this luminescence appears as a result of nonradiative excited state energy transfer from donor centers of unknown nature to ytterbium. The character of the concentration dependence of Yb3+ luminescence indicates that the energy transfer at high Yb concentrations occurs with active participation of a cooperative mechanism, according to which the excitation energy of one donor center is transferred simultaneously to two Yb3+ ions. In other words, the quantum yield of this transfer exceeds unity, which can be used to increase the efficiency of crystalline silicon (c-Si) solar cells.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

NASA Astrophysics Data System (ADS)

Gao, Qiang; Min, Yi; Jiang, Maofa

2018-06-01

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

The Temperature and Structure Dependence of Surface Tension of CaO-SiO2-Na2O-CaF2 Mold Fluxes

NASA Astrophysics Data System (ADS)

Gao, Qiang; Min, Yi; Jiang, Maofa

2018-02-01

The surface tension of mold flux is one of the most important properties and varies with the temperature from the top to the bottom of the mold, which influences the adhesion and lubrication between the liquid mold flux and the solidified shell, further influencing the quality of the continuous billet. In the present paper, the effect of temperature on the surface tension of CaO-SiO2-Na2O-CaF2 mold-flux melts with different CaO/SiO2 mass ratios was investigated using the maximum-pull method. Furthermore, the microstructure of mold fluxes was analyzed using FT-IR and Raman spectra to discuss the change mechanism of surface tension. The results indicated that the temperature dependence of surface tension was different with different CaO/SiO2 mass ratios, and agreed with the modification of melt structure. When the CaO/SiO2 mass ratio was 0.67 and 0.85, the change of surface tension with temperature was relatively stable, and the influence of temperature on the structure was small. When the CaO/SiO2 mass ratio was 1.03 and 1.16, with an increase of temperature, the surface tension decreased linearly and the changing amplitude was large; the degree of polymerization of melts and average radii of silicon-oxygen anions also decreased, which intensified the molecular thermal motion and weakened the intermolecular interaction, resulting in a decrease of surface tension of melts.

Structure of H2Ti3O7 and its evolution during sodium insertion as anode for Na ion batteries.

PubMed

Eguía-Barrio, Aitor; Castillo-Martínez, Elizabeth; Zarrabeitia, Maider; Muñoz-Márquez, Miguel A; Casas-Cabanas, Montse; Rojo, Teófilo

2015-03-14

H2Ti3O7 was prepared as a single phase material by ionic exchange from Na2Ti3O7. The complete ionic exchange was confirmed by (1)H and (23)Na solid state Nuclear Magnetic Resonance (NMR). The atomic positions of H2Ti3O7 were obtained from the Rietveld refinement of powder X-ray diffraction (PXRD) and neutron diffraction experimental data, the latter collected at two different wavelengths to precisely determine the hydrogen atomic positions in the structure. All H(+) cations are hydrogen bonded to two adjacent [Ti3O7](2-) layers leading to the gliding of the layers and lattice centring with respect to the parent Na2Ti3O7. In contrast with a previous report where protons were located in two different positions of H2Ti3O7, 3 types of proton positions were found. Two of the three types of proton are bonded to the only oxygen linked to a single titanium atom forming an H-O-H angle close to that of the water molecule. H2Ti3O7 is able to electrochemically insert Na(+). The electrochemical insertion of sodium into H2Ti3O7 starts with a solid solution regime of the C-centred phase. Then, between 0.6 and 1.2 inserted Na(+) the reaction proceeds through a two phase reaction and a plateau at 1.3 V vs. Na(+)/Na is observed in the voltage-composition curve. The second phase resembles the primitive Na2Ti3O7 cell as detected by in situ PXRD. Upon oxidation, from 0.9 to 2.2 V, the PXRD pattern remains mostly unchanged probably due to H(+) removal instead of Na(+), with the capacity quickly fading upon cycling. Conditioning H2Ti3O7 for two cycles at 0.9-2.2 V before cycling in the 0.05-1.6 V range yields similar specific capacity and better retention than the original Na2Ti3O7 in the same voltage range.

Local atomic arrangement and scintillation properties of Eu- and Ce-doped NaYP{sub 2}O{sub 7}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novais, S.M.V., E-mail: suellen.mvn@gmail.com; Macedo, Z.S.

2016-01-15

Direct determination of rare earth location and local environment in NaYP{sub 2}O{sub 7} are presented. Undoped and Ln-doped NaYP{sub 2}O{sub 7} (Ln=Eu, Ce) were produced via PVA-assisted sol–gel method. Lattice parameters were determined from Rietveld refinement, showing monoclinic structure. XAS results suggested Eu{sup 3+} and Ce{sup 3+} are incorporated into NaYP{sub 2}O{sub 7} host in substitution to Y{sup 3+} site, with first coordination shell formed by six oxygen ions. Measurements at Eu edge showed a single peak in R space for Eu–O distribution. In this case, uniform interatomic distances implied to absence of significant disorder. Analysis at Ce edge presentedmore » different behavior, with Ce–O distribution characterized by a split peak in R space. Nearest neighborhood was found to be distributed with Ce occupying an off-center position in Y site. Under X-ray excitation, {sup 5}D{sub 0}→{sup 7}F{sub J} emission lines of Eu{sup 3+} were identified for NaYP{sub 2}O{sub 7}:Eu. NaYP{sub 2}O{sub 7}:Ce presented a broad emission formed by 5d→{sup 2}F{sub J} transitions of Ce{sup 3+}, with the superposition attributed to the effect of distorted oxygen octahedra around the dopant ions. - Graphical abstract: EuO{sub 6} and CeO{sub 6} octahedral arrangement relative to Y site in NaYP{sub 2}O{sub 7} host, and XEOL emission of corresponding doped samples. - Highlights: • Lattice parameters of NaYP{sub 2}O{sub 7} undoped sample confirmed monoclinic structure. • Dopants Eu and Ce are incorporated in the trivalent state. • Local order of Eu{sup 3+} and Ce{sup 3+} dopants substituting Y{sup 3+} consist of octahedral symmetry. • Off-center displacement in the case of Ce{sup 3+} position was discussed. • Luminescent properties under X-ray excitation may allow practical applications.« less

Effect of (Li,Ce) doping in Aurivillius phase material Na0.25K0.25Bi2.5Nb2O9

NASA Astrophysics Data System (ADS)

Gai, Zhi-Gang; Wang, Jin-Feng; Wang, Chun-Ming

2007-01-01

The effect of (Li,Ce) substitution for A site on the properties of Na0.25K0.25Bi2.5Nb2O9-based ceramics was investigated. The piezoelectric activity of Na0.25K0.25Bi2.5Nb2O9-based ceramics is significantly improved by the modification of lithium and cerium. The Curie temperature (TC) gradually increases from 668to684°C with increasing the (Li,Ce) modification. The piezoelectric coefficient d33 of the [(Na0.5K0.5)Bi]0.44(LiCe)0.03[]0.03Bi2Nb2O9 ceramic was found to be 28pC/N, the highest value among the Na0.25K0.25Bi2.5Nb2O9-based ceramics and also almost 50% higher than the reported d33 values of other bismuth layer-structured ferroelectric systems (˜5-19pC/N). The planar coupling factors kp and kt were found to be 8.0% and 23.0%, together with the high TC (˜670°C) and stable piezoelectric properties, demonstrating that the (Li,Ce) modified Na0.25K0.25Bi2.5Nb2O9-based material a promising candidate for high temperature applications.

Combined effects Na and SO2 in flue gas on Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO by NH3 simulated by Na2SO4 doping

NASA Astrophysics Data System (ADS)

Zhou, Aiyi; Yu, Danqing; Yang, Liu; Sheng, Zhongyi

2016-08-01

A series of Mn-Ce/TiO2 catalysts were synthesized through an impregnation method and used for low temperature selective catalytic reduction (SCR) of NOx with ammonia (NH3). Na2SO4 was added into the catalyst to simulate the combined effects of alkali metal and SO2 in the flue gas. Experimental results showed that Na2SO4 had strong and fluctuant influence on the activity of Mn-Ce/TiO2, because the effect of Na2SO4 included pore occlusion and sulfation effect simultaneously. When Na2SO4 loading content increased from 0 to 1 wt.%, the SCR activities of Na2SO4-doped catalysts decreased greatly. With further increasing amount of Na2SO4, however, the catalytic activity increased gradually. XRD results showed that Na2SO4 doping could induce the crystallization of MnOx phases, which were also confirmed by TEM and SEM results. BET results showed that the surface areas decreased and a new bimodal mesoporous structure formed gradually with the increasing amount of Na2SO4. XPS results indicated that part of Ce4+ and Mn3+ were transferred to Ce3+ and Mn4+ due to the sulfation after Na2SO4 deposition on the surface of the catalysts. When the doped amounts of Na2SO4 increased, NH3-TPD results showed that the Lewis acid sites decreased and the Brønsted acid sites of Mn-Ce/TiO2 increased quickly, which could be considered as another reason for the observed changes in the catalytic activity. The decreased Mn and Ce atomic concentration, the changes of their oxidative states, and the variation in acidic properties on the surface of Na2SO4-doped catalysts could be the reasons for the fluctuant changes of the catalytic activity.

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2.

PubMed

Maitra, Urmimala; House, Robert A; Somerville, James W; Tapia-Ruiz, Nuria; Lozano, Juan G; Guerrini, Niccoló; Hao, Rong; Luo, Kun; Jin, Liyu; Pérez-Osorio, Miguel A; Massel, Felix; Pickup, David M; Ramos, Silvia; Lu, Xingye; McNally, Daniel E; Chadwick, Alan V; Giustino, Feliciano; Schmitt, Thorsten; Duda, Laurent C; Roberts, Matthew R; Bruce, Peter G

2018-03-01

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li + -O(2p)-Li + interactions). Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg 2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg 2+ remains in Na 2/3 [Mg 0.28 Mn 0.72 ]O 2 , which stabilizes oxygen.

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2

NASA Astrophysics Data System (ADS)

Maitra, Urmimala; House, Robert A.; Somerville, James W.; Tapia-Ruiz, Nuria; Lozano, Juan G.; Guerrini, Niccoló; Hao, Rong; Luo, Kun; Jin, Liyu; Pérez-Osorio, Miguel A.; Massel, Felix; Pickup, David M.; Ramos, Silvia; Lu, Xingye; McNally, Daniel E.; Chadwick, Alan V.; Giustino, Feliciano; Schmitt, Thorsten; Duda, Laurent C.; Roberts, Matthew R.; Bruce, Peter G.

2018-03-01

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li+-O(2p)-Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2, which stabilizes oxygen.

Silver-Containing α-MnO 2 Nanorods: Electrochemistry in Na-Based Battery Systems

DOE PAGES

Huang, Jianping; Poyraz, Altug S.; Lee, Seung-Yong; ...

2016-09-01

Manganese oxides are considered attractive cathode materials for rechargeable batteries due to the high abundance and environmental friendliness of manganese. In particular, cryptomelane and hollandite are desirable due to their ability to host cations within their octahedral molecular sieve (OMS-2) Alpha-MnO 2 structure. In this work, we investigate silver containing Alpha-MnO 2 structured materials (Ag xMn 8O 16, x = 1.22, L-Ag-OMS-2 or 1.66, H-Ag-OMS-2) as host materials for Li ion and Na ion insertion/de-insertion. The results indicate a significant difference in the lithiation versus sodiation process the OMS-2 materials. Initial reduction of Ag 1.22Mn 8O 16 to 1.0 Vmore » delivered ~370 mAh/g. Cycling of Ag1.22Mn8O16 between voltage ranges of 3.8 - 1.7 V and 3.8 - 1.3 V in a Na battery delivered initial capacities of 113 and 247 mAh/g, respectively. In contrast, Ag1.66Mn8O16 delivered only 15 mAh/g, ~0.5 electron equivalents, to 1.7 and 1.3 volts. Study of the system by electrochemical impedance spectroscopy (EIS) showed a significant decrease in charge transfer resistance from 2029 Omega to 594 Omega after 1.5 electron equivalents per Ag 1.22Mn 8O 16 formula unit of Na ion insertion. In contrast, both Ag 1.22Mn 8O 16 and Ag 1.66Mn 8O 16 exhibited gradual impedance increases during lithiation. The formation of silver metal could be detected only in the sodiated material by X-ray diffraction (XRD). Thus, the impedance of Ag-OMS-2 decreases upon sodiation coincident with the formation of silver metal during the discharge process, consistent with the more favorable formation of silver metal during the sodiation process relative to the lithation process.« less

High-Performance 2.6 V Aqueous Asymmetric Supercapacitors based on In Situ Formed Na0.5 MnO2 Nanosheet Assembled Nanowall Arrays.

PubMed

Jabeen, Nawishta; Hussain, Ahmad; Xia, Qiuying; Sun, Shuo; Zhu, Junwu; Xia, Hui

2017-08-01

The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na 0.5 MnO 2 nanosheet assembled nanowall arrays are in situ formed on carbon cloth via electrochemical oxidation. It is interesting to find that the electrode potential window for Na 0.5 MnO 2 nanowall arrays can be extended to 0-1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g -1 . The extended potential window for the Na 0.5 MnO 2 electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe 3 O 4 nanorod arrays are synthesized as the anode and can stably work in a negative potential window of -1.3 to 0 V (vs Ag/AgCl). For the first time, a 2.6 V aqueous asymmetric supercapacitor is demonstrated by using Na 0.5 MnO 2 nanowall arrays as the cathode and carbon-coated Fe 3 O 4 nanorod arrays as the anode. In particular, the 2.6 V Na 0.5 MnO 2 //Fe 3 O 4 @C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg -1 as well as excellent rate capability and cycle performance, outperforming previously reported MnO 2 -based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Studies on solid solutions based on layered honeycomb-ordered phases P2-Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berthelot, Romain; Schmidt, Whitney; Sleight, A.W.

2012-12-15

Three complete solid solutions between the layered phases P2-Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn) have been prepared by conventional solid state method and investigated through X-ray diffraction, magnetism and optical measurements. All compositions are characterized by a M{sup 2+}/X{sup 6+} honeycomb ordering within the slabs and crystallize in a hexagonal unit cell. However, a structural transition based on a different stacking is observed as nickel (space group P6{sub 3}/mcm) is substituted by zinc or cobalt (space group P6{sub 3}22). All compositions exhibit a paramagnetic Curie-Weiss behavior at high temperatures; and the magnetic moment values confirm the presence of Ni{supmore » 2+} and/or Co{sup 2+} cations. The low-temperature antiferromagnetic order of Na{sub 2}Ni{sub 2}TeO{sub 6} and Na{sub 2}Co{sub 2}TeO{sub 6} is suppressed by zinc substitution. The color of the obtained compositions varies from pink, to light green and white when M=Co, Ni, Zn, respectively. - Graphical abstract: The comparison between the structure of Na{sub 2}Ni{sub 2}TeO{sub 6} (left) and Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Zn) (right) evidences the stacking difference with distinct atom sequences along the hexagonal c-axis. Highlights: Black-Right-Pointing-Pointer Solid solutions between lamellar phases Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn) are investigated. Black-Right-Pointing-Pointer A M{sup 2+}/X{sup 6+} honeycomb ordering characterized all the compositions. Black-Right-Pointing-Pointer A structural transition is shown when Ni is replaced by Co or Zn. Black-Right-Pointing-Pointer The low-temperature AFM ordering of Na{sub 2}Ni{sub 2}TeO{sub 6} and Na{sub 2}Co{sub 2}TeO{sub 6} is suppressed by zinc substitution. Black-Right-Pointing-Pointer Color changes from pink to light green and white when M=Co, Ni, Zn, respectively.« less

H2O activity in concentrated NaCl solutions at high pressures and temperatures measured by the brucite-periclase equilibrium

NASA Astrophysics Data System (ADS)

Aranovich, L. Y.; Newton, R. C.

1996-10-01

H2O activities in concentrated NaCl solutions were measured in the ranges 600° 900° C and 2 15 kbar and at NaCl concentrations up to halite saturation by depression of the brucite (Mg(OH)2) periclase (MgO) dehydration equilibrium. Experiments were made in internally heated Ar pressure apparatus at 2 and 4.2 kbar and in 1.91-cm-diameter piston-cylinder apparatus with NaCl pressure medium at 4.2, 7, 10 and 15 kbar. Fluid compositions in equilibrium with brucite and periclase were reversed to closures of less than 2 mol% by measuring weight changes after drying of punctured Pt capsules. Brucite-periclase equilibrium in the binary system was redetermined using coarsely crystalline synthetic brucite and periclase to inhibit back-reaction in quenching. These data lead to a linear expression for the standard Gibbs free energy of the brucite dehydration reaction in the experimental temperature range: ΔG° (±120J)=73418 134.95 T(K). Using this function as a baseline, the experimental dehydration points in the system MgO-H2O-NaCl lead to a simple systematic relationship of high-temperature H2O activity in NaCl solution. At low pressure and low fluid densities near 2 kbar the H2O activity is closely approximated by its mole fraction. At pressures of 10 kbar and greater, with fluid densities approaching those of condensed H2O, the H2O activity becomes nearly equal to the square of its mole fraction. Isobaric halite saturation points terminating the univariant brucite-periclase curves were determined at each experimental pressure. The five temperature-composition points in the system NaCl-H2O are in close agreement with the halite saturation curves (liquidus curves) given by existing data from differential thermal analysis to 6 kbar. Solubility of MgO in the vapor phase near halite saturation is much less than one mole percent and could not have influenced our determinations. Activity concentration relations in the experimental P-T range may be retrieved for the binary

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties.

PubMed

Li, Anming; Xu, Dekang; Lin, Hao; Yang, Shenghong; Shao, Yuanzhi; Zhang, Yueli

2016-08-10

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu(3+) nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu(3+) are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb(3+)/Er(3+), Yb(3+)/Tm(3+) nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb(3+)/Er(3+) nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K(-1) at 285 K.

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

PubMed Central

Li, Anming; Xu, Dekang; Lin, Hao; Yang, Shenghong; Shao, Yuanzhi; Zhang, Yueli

2016-01-01

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu3+ nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb3+/Er3+ and Yb3+/Tm3+ nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu3+ are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb3+/Er3+, Yb3+/Tm3+ nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb3+/Er3+ nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K−1 at 285 K. PMID:27506629

A vibrational spectroscopic study of the silicate mineral lomonosovite Na5Ti2(Si2O7)(PO4)O2

NASA Astrophysics Data System (ADS)

Frost, Ray L.; López, Andrés; Theiss, Frederick L.; Graça, Leonardo M.; Scholz, Ricardo

2015-01-01

The mineral lomonosovite has been studied using a combination of scanning electron microscopy with energy dispersive X-ray analysis and vibrational spectroscopy. Qualitative chemical analysis gave Si, P, Na and Ti as the as major elements with small amounts of Mn, Ca, Fe and Al. The mineral lomonosovite has a formula Na5Ti2(Si2O7)(PO4)O2. Raman bands observed at 909, 925 and 939 cm-1 are associated with phosphate units. Raman bands found at 975, 999, 1070, 1080 and 1084 cm-1 are attributed to siloxane stretching vibrations. The observation of multiple bands in both the phosphate stretching and bending regions supports the concept that the symmetry of the phosphate anion in the structure of lomonosovite is significantly reduced. Infrared spectroscopy identifies bands in the water stretching and bending regions, thus suggesting that water is involved with the structure of lomonosovite either through adsorption on the surface or by bonding to the phosphate units.

Gels and gel-derived glasses in the Na2O-B2O3-SiO2 system. [containerless melting in space

NASA Technical Reports Server (NTRS)

Mukherjee, S. P.

1982-01-01

The containerless melting of high-purity multicomponent homogeneous gels and gel-monoliths offers a unique approach to making ultrapure multicomponent optical glasses in the reduced gravity environment of space. Procedures for preparing and characterizing gels and gel-derived glasses in the Na2O-B2O3-SiO2 system are described. Preparation is based on the polymerization reactions of alkoxysilane with trimethyl borate or boric acid and a suitable sodium compound. The chemistry of the gelling process is discussed in terms of process parameters and the gel compositions. The physicochemical nature of gels prepared by three different procedures were found to be significantly different. IR absorption spectra indicate finite differences in the molecular structures of the different gels. The melting of the gel powders and the transformation of porous gel-monoliths to transparent 'glass' without melting are described.

Growth and characterization of Na2Mo2O7 crystal scintillators for rare event searches

NASA Astrophysics Data System (ADS)

Pandey, Indra Raj; Kim, H. J.; Kim, Y. D.

2017-12-01

Disodium dimolybdate (Na2Mo2O7) crystals were grown using the Czochralski technique. The thermal characteristics of the compound were analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements. The crystal structure of the grown sample was confirmed using X-ray diffraction (XRD). Luminescence properties were measured at room and low temperatures, using a light emitting diode (LED) source. Very weak luminescence was observed at room temperature; however, the luminescence intensity was enhanced at low temperatures. The crystal's transmittance spectrum was measured for estimating its optical quality and energy band gap. The grown crystal exhibited a luminescence light yield of 55% compared with CaMoO4 crystals at 10 K, when excited by a 280-nm-wavelength LED source, but does not have the drawbacks of radioactive Ca isotopes. These results suggest that at cryogenic temperatures, Na2Mo2O7 crystal scintillators are promising for the detection of dark matter and neutrinoless double beta decay of 100Mo.

Water activities of NaClO4, Ca(ClO4)2, and Mg(ClO4)2 brines from experimental heat capacities: Water activity >0.6 below 200 K

NASA Astrophysics Data System (ADS)

Toner, J. D.; Catling, D. C.

2016-05-01

Perchlorate salts found on Mars are extremely hygroscopic and form low eutectic temperature aqueous solutions, which could allow liquid water to exist on Mars despite cold and dry conditions. The formation, dynamics, and potential habitability of perchlorate salt solutions can be broadly understood in terms of water activity. Water activity controls condensation and evaporation of water vapor in brines, deliquescence and efflorescence of crystalline salts, and ice formation during freezing. Furthermore, water activity is a basic parameter defining the habitability of aqueous solutions. Despite the importance of water activity, its value in perchlorate solutions has only been measured at 298.15 K and at the freezing point of water. To address this lack of data, we have determined water activities in NaClO4, Ca(ClO4)2, and Mg(ClO4)2 solutions using experimental heat capacities measured by Differential Scanning Calorimetry. Our results include concentrations up to near-saturation and temperatures ranging from 298.15 to 178 K. We find that water activities in NaClO4 solutions increase with decreasing temperature, by as much as 0.25 aw from 298.15 to 178 K. Consequently, aw reaches ∼0.6-0.7 even for concentrations up to 15 molal NaClO4 below 200 K. In contrast, water activities in Ca(ClO4)2 and Mg(ClO4)2 solutions generally decrease with decreasing temperature. The temperature dependence of water activity indicates that low-temperature NaClO4 solutions will evaporate and deliquesce at higher relative humidity, crystallize ice at higher temperature, and potentially be more habitable for life (at least in terms of water activity) compared to solutions at 298.15 K. The opposite effects occur in Ca(ClO4)2 and Mg(ClO4)2 solutions.

Optimization of NaOH Molarity, LUSI Mud/Alkaline Activator, and Na2SiO3/NaOH Ratio to Produce Lightweight Aggregate-Based Geopolymer

PubMed Central

Abdul Razak, Rafiza; Abdullah, Mohd Mustafa Al Bakri; Hussin, Kamarudin; Ismail, Khairul Nizar; Hardjito, Djwantoro; Yahya, Zarina

2015-01-01

This paper presents the mechanical function and characterization of an artificial lightweight geopolymer aggregate (ALGA) using LUSI (Sidoarjo mud) and alkaline activator as source materials. LUSI stands for LU-Lumpur and SI-Sidoarjo, meaning mud from Sidoarjo which erupted near the Banjarpanji-1 exploration well in Sidoarjo, East Java, Indonesia on 27 May 2006. The effect of NaOH molarity, LUSI mud/Alkaline activator (LM/AA) ratio, and Na2SiO3/NaOH ratio to the ALGA are investigated at a sintering temperature of 950 °C. The results show that the optimum NaOH molarity found in this study is 12 M due to the highest strength (lowest AIV value) of 15.79% with lower water absorption and specific gravity. The optimum LUSI mud/Alkaline activator (LM/AA) ratio of 1.7 and the Na2SiO3/NaOH ratio of 0.4 gives the highest strength with AIV value of 15.42% with specific gravity of 1.10 g/cm3 and water absorption of 4.7%. The major synthesized crystalline phases were identified as sodalite, quartz and albite. Scanning Electron Microscope (SEM) image showed more complete geopolymer matrix which contributes to highest strength of ALGA produced. PMID:26006238

Electrical Conductivity of Cancrinite-Type Na8 - 2 x Ca x [Al6Si6O24][CO3] · 2H2O ( x ≤ 0.03) Crystals

NASA Astrophysics Data System (ADS)

Sorokin, N. I.

2018-05-01

The electrical conductivity of crystals of artificial cancrinite Na8 - 2 x Ca x [Al6Si6O24][CO3] · 2H2O ( x ≤ 0.03) has been studied in the temperature range of 498-604 K. These crystals were grown by hydrothermal synthesis on a seed in the Na2O-Al2O3-SiO2-H2O system ( t = 380-420°C, P = 3 × 107-9 × 107 Pa). The ionic conductivity of a single-crystal sample (sp. gr. P63), measured along the crystallographic axis c, is low: σ = 8 × 10-7 S/cm at 300°C. The electric transport activation energy is E a = 0.81 ± 0.05 eV. The relationship between the ionic conductivity and specific features of the atomic structure of cancrinites is discussed.

Flower-like Na2O nanotip synthesis via femtosecond laser ablation of glass

PubMed Central

2012-01-01

The current state-of-the-art in nanotip synthesis relies on techniques that utilize elaborate precursor chemicals, catalysts, or vacuum conditions, and any combination thereof. To realize their ultimate potential, synthesized nanotips require simpler fabrication techniques that allow for control over their final nano-morphology. We present a unique, dry, catalyst-free, and ambient condition method for creating densely clustered, flower-like, sodium oxide (Na2O) nanotips with controllable tip widths. Femtosecond laser ablation of a soda-lime glass substrate at a megahertz repetition rate, with nitrogen flow, was employed to generate nanotips with base and head widths as small as 100 and 20 nm respectively, and lengths as long as 10 μm. Control of the nanotip widths was demonstrated via laser dwell time with longer dwell times producing denser clusters of thinner nanotips. Energy dispersive X-ray analysis reveals that nanotip composition is Na2O. A new formation mechanism is proposed, involving an electrostatic effect between ionized nitrogen and polar Na2O. The synthesized nanotips may potentially be used in antibacterial and hydrogen storage applications. PMID:22809176

One-dimensional magnetic fluctuations in the spin-2 triangular lattice alpha-NaMnO2.

PubMed

Stock, C; Chapon, L C; Adamopoulos, O; Lappas, A; Giot, M; Taylor, J W; Green, M A; Brown, C M; Radaelli, P G

2009-08-14

The S=2 anisotropic triangular lattice alpha-NaMnO2 is studied by neutron inelastic scattering. Antiferromagnetic order occurs at T< or =45 K with opening of a spin gap. The spectral weight of the magnetic dynamics above the gap (Delta approximately equal to 7.5 meV) has been analyzed by the single-mode approximation. Excellent agreement with the experiment is achieved when a dominant exchange interaction (|J|/k(B) approximately 73 K), along the monoclinic b axis and a sizable easy-axis magnetic anisotropy (|D|/k(B) approximately 3 K) are considered. Despite earlier suggestions for two-dimensional spin interactions, the dynamics illustrate strongly coupled antiferromagnetic S=2 chains and cancellation of the interchain exchange due to the lattice topology. alpha-NaMnO2 therefore represents a model system where the geometric frustration is resolved through the lowering of the dimensionality of the spin interactions.

Effect of Na2SiO3/NaOH on mechanical properties and microstructure of geopolymer mortar using fly ash and rice husk ash as precursor

NASA Astrophysics Data System (ADS)

Saloma, Hanafiah, Elysandi, Debby Orjina; Meykan, Della Garnesia

2017-11-01

Geopolymer concrete is an eco-friendly concrete that can reduce carbon emissions on the earth surface because it used industrial waste material such as fly ash, rice husk ash, bagasse ash, and palm oil fuel. Geopolymer is semi-crystalline amorphous materials which has irregular chemical bonds structure. The material is produced by geosynthesis of aluminosilicates and alkali-silicates which produce the Si-O-Al polymer structure. This research used the ratio of fly ash and rice husk ash as precursors e.g. 100:0, 75:25, 50:50, and 25:75. NaOH solutions of 14 M and Na2SiO3 solutions with the variation e.g. 2.5, 2.75, 3.00, and 3.25 were used as activators on mortar geopolymer mixture. The tests of fresh mortar were slump flow and setting time. The optimum compressive strength is 68.36 MPa for 28 days resulted from mixture using 100% fly ash and Na2SiO3 and NaOH with ratio 2.75. The largest value of slump flow test resulted from mixture using Na2SiO3 and NaOH with ratio 2.50 is 17.25 cm. Based on SEM test results, mortar geopolymer microstructure with mixture RHA 0% has less pores and denser CSH structure.

Growth mechanism and magnetic and electrochemical properties of Na{sub 0.44}MnO{sub 2} nanorods as cathode material for Na-ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demirel, S.; Oz, E.; Altin, E.

Nanorods of Na{sub 0.44}MnO{sub 2} are a promising cathode material for Na-ion batteries due to their large surface area and single crystalline structure. We report the growth mechanism of Na{sub 0.44}MnO{sub 2} nanorods via solid state synthesis and their physical properties. The structure and the morphology of the Na{sub 0.44}MnO{sub 2} nanorods are investigated by X-ray diffraction (XRD), scanning and tunneling electron microscopy (SEM and TEM), and energy-dispersive X-ray (EDX) techniques. The growth mechanism of the rods is investigated and the effects of vapor pressure and partial melting of Na-rich regions are discussed. The magnetic measurements show an antiferromagnetic phasemore » transition at 25 K and the μ{sub eff} is determined as 3.41 and 3.24 μ{sub B} from the χ–T curve and theoretical calculation, respectively. The electronic configuration and spin state of Mn{sup 3+} and Mn{sup 4+} are discussed in detail. The electrochemical properties of the cell fabricated using the nanorods are investigated and the peaks in the voltammogram are attributed to the diffusion of Na ions from different sites. Na intercalation process is explained by one and two Margules and van Laar models. - Highlights: • We synthesized Na{sub 0.44}MnO{sub 2} nanorods via a simple solid state reaction technique. • Our studies show that excess Na plays a crucial role in the nanorod formation. • Magnetization measurements show that Mn{sup 3+} ions are in LS and HS states. • The electrochemical properties of the cell fabricated using the nanorods are investigated. • Na intercalation process is explained by one and two Margules and van Laar models.« less

Fluoride gastrointestinal absorption from Na2FPO3/CaCO3- and NaF/SiO2-based toothpastes.

PubMed

Falcão, A; Tenuta, L M A; Cury, J A

2013-01-01

Depending on toothpaste formulation, part of the fluoride is insoluble and would not be totally absorbable in the gastrointestinal tract, thus changing dental fluorosis risk estimation. This hypothesis was tested with formulations with either all fluoride in a soluble form (NaF/SiO2-based toothpaste, 1,100 µg F/g as labeled, 1,129.7 ± 49.4 µg F/g soluble fluoride as analyzed) or with around 20% of insoluble fluoride (Na2FPO3/CaCO3-based toothpaste, 1,450 µg F/g as labeled, 1,122.4 ± 76.4 µg F/g soluble fluoride as analyzed). Toothpastes were evaluated either fresh or after accelerated aging, which increased insoluble fluoride to 40% in the Na2FPO3/CaCO3-based toothpaste. In a blind, crossover clinical trial conducted in five legs, 20 adult volunteers ingested 49.5 µg of total fluoride/kg body weight from each formulation or purified water (control). Whole saliva and urine were collected as bioavailability indicators, and pharmacokinetics parameters calculated showed significantly (p < 0.05) lower fluoride bioavailability for Na2FPO3/CaCO3 toothpaste, which was reduced further after aging. A significant correlation between the amount of soluble fluoride ingested, but not total fluoride, and fluoride bioavailability was found (r = 0.57, p < 0.0001). The findings suggest that the estimated fluorosis risk as a result of ingestion of Na2FPO3/CaCO3-based toothpastes should be calculated based on the toothpaste's soluble rather than total fluoride concentration. Copyright © 2012 S. Karger AG, Basel.

Structural and optical properties of Bi2O3-B2O3-CdO-Na2O glass system for gamma ray shielding applications

NASA Astrophysics Data System (ADS)

Dogra, Mridula; Singh, K. J.; Kaur, Kulwinder

2018-05-01

Quaternary system of the composition (0.15+x) Bi2O3-(0.55-x) B2O3-0.15CdO-0.15Na2O (where x=0, 0.1, 0.3 and 0.5 mole fraction) has been synthesized using melt-quenching technique. Gamma ray shielding properties are measured in terms of mass attenuation coefficient and half value layer at photon energies 662, 1173 and 1332 keV. These parameters are compared with standard nuclear radiation shielding `barite and ferrite' concretes. The results reflect better radiation shielding properties as compared to barite and ferrite concretes. Effective atomic number is calculated at photon energies 662 and 1173 keV. Density, molar volume and XRD studies are analyzed to know physical and structural properties of the glass system. Optical band gap, refractive index and molar refraction are calculated from UV-Visible measurements. Decrease in optical band gap and increase in molar refraction have been observed indicating the increase of non-bridging oxygens in the structure.

High-Capacity Sodium Peroxide Based NaO 2 Batteries with Low Charge Overpotential via a Nanostructured Catalytic Cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Lu; Zhang, Dongzhou; Lei, Yu

The superoxide based Na-O-2 battery has circumvented the issue of large charge overpotential in Li-O-2 batteries; however, the one-electron process leads to limited capacity. Herein, a sodium peroxide based low-overpotential (similar to 0.5 V) Na-O-2 battery with a capacity as high as 7.5 mAh/cm(2) is developed with Pd nanoparticles as catalysts on the cathode.

Ilyukhinite (H3O,Na)14Ca6Mn2Zr3Si26O72(OH)2 • 3H2O, a New Mineral of the Eudialyte Group

NASA Astrophysics Data System (ADS)

Chukanov, N. V.; Rastsvetaeva, R. K.; Rozenberg, K. A.; Aksenov, S. M.; Pekov, I. V.; Belakovsky, D. I.; Kristiansen, R.; Van, K. V.

2017-12-01

A new eudialyte-group mineral, ilyukhinite, ideally (H3O,Na)14Ca6Mn2Zr3Si26O72(OH)2 · 3H2O, has been found in peralkaline pegmatite at Mt. Kukisvumchorr, Khibiny alkaline pluton, Kola Peninsula, Russia. It occurs as brownish orange, with vitreous luster anhedral grains up to 1 mm across in hydrothermally altered peralkaline rock, in association with aegirine, murmanite, albite, microcline, rhabdophane-(Ce), fluorite, sphalerite and molybdenite. The Mohs hardness is 5; cleavage is not observed. D meas 2.67(2), D calc 2.703 g/cm3. Ilyukhinite is optically uniaxial (-): ω = 1.585(2), ɛ = 1.584(2). The IR spectrum is given. The average chemical composition of ilyukhinite (wt %; electron microprobe, ranges given in parentheses; H2O determined by gas chromatography) is as follows: 3.07 (3.63-4.43) Na2O, 0.32 (0.28-0.52) K2O, 10.63 (10.26-10.90) CaO, 3.06 (2.74-3.22) MnO, 1.15 (0.93-1.37) FeO, 0.79 (0.51-0.89) La2O3, 1.21 (0.97-1.44) Ce2O3, 0.41 (0.30-0.56) Nd2O3, 0.90 (0.77-1.12) TiO2, 10.94 (10.15-11.21) ZrO2, 1.40 (0.76-1.68) Nb2O5, 51.24 (49.98-52.28) SiO2, 1.14 (0.89-1.37) SO3, 0.27 (0.19—0.38) Cl, 10.9(5 )H2O,-0.06-O = C1, total is 98.27. The empirical formula is H36.04(Na3.82K0.20)(Ca5.65Ce0.22La0.14Nd0.07)(Mn1.285Fe0.48)(Zr2.645Ti0.34)Nb0.31Si25.41S0.42Cl0.23O86.82. The crystal structure has been solved ( R = 0.046). Ilyukhinite is trigonal, R3 m; a = 14.1695(6) Å, b = 31.026(1) Å, V = 5394.7(7) Å3, Z = 3. The strongest XRD reflections [ d, Å (I, %) ( hkl)] are 11.44 (82) (101), 7.09 (70) (110), 6.02 (44) (021), 4.371 (89) 205), 3.805 (47) (303, 033), 3.376 (41) (131), 2.985 (100) (315, 128), 2.852 (92) (404). Ilyukhinite was named in memory of Vladimir V. Ilyukhin (1934-1982), an outstanding Soviet crystallographer. The type specimen of ilyukhinite has been deposited in the collection of the Natural History Museum, University of Oslo, Norway.

Laser-diode-excited blue upconversion in Tm3+/Yb3+ -codoped TeO2-Ga2O3-R2O (R=Li, Na, K) glasses.

PubMed

Zhao, Chun; Zhang, Qinyuan; Yang, Gangfeng; Jiang, Zhonghong

2008-01-01

This paper reports on intense blue upconversion in Tm(3+)/Yb(3+) codoped TeO(2)-Ga(2)O(3)-R(2)O(R=Li, Na, K) glasses upon excitation with commercial available laser diode (LD). Effects of alkali ions on the Raman spectra, thermal stability and spectroscopic properties of the tellurite-gallium glasses have also been investigated. Energy transfer and the involved upconversion mechanisms have been discussed. Intense blue upconversion emission centered at 476 nm along with a weak red emission at 650 nm has been observed upon excitation of 977 nm LD, assigned to the transitions of 1G4-->3H6, and 1G4-->3H4 and/or 3F(2,3)-->3H6 of Tm(3+), respectively. The blue upconversion intensity has a cubelike dependence on incident pump laser power, indicating a three-photon process. However, a quadratic dependence of the 476 nm upconversion intensity on the incident pump laser power has been observed when samples under excitation of 808 nm LD due to a two-photon absorption process. Enhanced upconversion luminescence have been observed with replacing K(+) for Na(+) and Li(+).

On the entropy of glaucophane Na2Mg3Al2Si8O22(OH)2

USGS Publications Warehouse

Robie, R.A.; Hemingway, B.S.; Gillet, P.; Reynard, B.

1991-01-01

The heat capacity of glaucophane from the Sesia-Lanza region of Italy having the approximate composition (Na1.93Ca0.05Fe0.02) (Mg2.60Fe0.41) (Al1.83Fe0.15Cr0.01) (Si7.92Al0.08)O22(OH)2 was measured by adiabatic calorimetry between 4.6 and 359.4 K. After correcting the Cp0data to values for ideal glaucophane, Na2Mg3Al2Si8O22(OH)2 the third-law entropy S2980-S00was calculated to be 541.2??3.0 J??mol-1??K-1. Our value for S2980-S00is 12.0 J??mol-1??K-1 (2.2%) smaller than the value of Likhoydov et al. (1982), 553.2??3.0, is within 6.2 J??mol-1??K-1 of the value estimated by Holland (1988), and agrees remarkably well with the value calculated by Gillet et al. (1989) from spectroscopic data, 539 J??mol-1??K-1. ?? 1991 Springer-Verlag.

β-Na2TeO4: Phase Transition from an Orthorhombic to a Monoclinic Form. Reversible CO2 Capture.

PubMed

Galven, Cyrille; Pagnier, Thierry; Rosman, Noël; Le Berre, Françoise; Crosnier-Lopez, Marie-Pierre

2018-06-18

The present work concerns the tellurate Na 2 TeO 4 which has a 1D structure and could then present a CO 2 capture ability. It has been synthesized in a powder form via a solid-state reaction and structurally characterized by thermal X-ray diffraction experiments, Raman spectroscopy, and differential scanning calorimetry. The room temperature structure corresponds to the β-Na 2 TeO 4 orthorhombic form, and we show that it undergoes a reversible structural transition near 420 °C toward a monoclinic system. Ab initio computations were also performed on the room temperature structure, the Raman vibration modes calculated, and a normal mode attribution proposed. In agreement with our expectations, this sodium oxide is able to trap CO 2 by a two-step mechanism: Na + /H + exchange and carbonation of the released sodium as NaHCO 3 . This capture is reversible since CO 2 can be released upon heating by recombination of the mother phase.

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2 O-(30-x)K2 O-70B2 O3 (5 ≤ x ≤ 25 mol%) glasses.

PubMed

Zhang, Zhen-Ya; Wu, Shao-Yi; Zhang, Fu; Zhang, Cheng-Xi; Qin, Rui-Jie; Gao, Han

2018-03-01

The local distortions and electron paramagnetic resonance parameters for Cu 2+ in the mixed alkali borate glasses xNa 2 O-(30-x)K 2 O-70B 2 O 3 (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na 2 O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO 6 ] 10- clusters show significant tetragonal elongation ratios p ~19% along the C 4 axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu 2+ with the variation of the composition of Na 2 O. Copyright © 2017 John Wiley & Sons, Ltd.

Synthesis, structure, and polymorphism of A{sub 3}LnSi{sub 2}O{sub 7} (A=Na, K; Ln=Sm, Ho, Yb)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Latshaw, Allison M.; Yeon, Jeongho; Smith, Mark D.

2016-03-15

Four new members of the A{sub 3}LnSi{sub 2}O{sub 7} family, K{sub 3}SmSi{sub 2}O{sub 7}, Na{sub 3}HoSi{sub 2}O{sub 7}, and two polymorphs of Na{sub 3}YbSi{sub 2}O{sub 7}, are reported. K{sub 3}SmSi{sub 2}O{sub 7} crystallizes in the hexagonal space group P6{sub 3}/mcm, Na{sub 3}HoSi{sub 2}O{sub 7} and Na{sub 3}YbSi{sub 2}O{sub 7} crystallize in the hexagonal space group P6{sub 3}/m, and Na{sub 3}YbSi{sub 2}O{sub 7} crystallizes in the trigonal space group P31c. The Na{sub 3}YbSi{sub 2}O{sub 7} composition that crystallizes in P31c is a new structure type. The magnetic properties for the Ho and Yb analogs are reported. - Graphical abstract: The differentmore » structure types and polymorphs of the A{sub 3}LnSi{sub 2}O{sub 7} family reported. - Highlights: • Four new members of the A{sub 3}LnSi{sub 2}O{sub 7} family are presented. • Na{sub 3}YbSi{sub 2}O{sub 7} is reported as two polymorphs, one is a new structure type. • Crystals synthesized out of molten fluoride fluxes.« less

Variable dimensionality and framework found in a series of quaternary zinc selenites, A{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4}·xH{sub 2}O (A = Na, Rb, and Cs; 0≤x≤1) and Cs{sub 2}Zn{sub 2}(SeO{sub 3}){sub 3}·2H{sub 2}O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lü, Minfeng; Jo, Hongil; Oh, Seung-Jin

Five new alkali metal zinc selenites, A{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4}·xH{sub 2}O (A = Na, Rb, and Cs; 0≤x≤1) and Cs{sub 2}Zn{sub 2}(SeO{sub 3}){sub 3}·2H{sub 2}O have been synthesized by heating a mixture of ZnO, SeO{sub 2} and A{sub 2}CO{sub 3} (A = Na, Rb, and Cs), and characterized by X-ray diffraction (XRD) and spectroscopic analyses techniques. All of the reported materials revealed a rich structural chemistry with different frameworks and connection modes of Zn{sup 2+}. While Rb{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4} and Cs{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4}·H{sub 2}O revealed three-dimensional frameworks consisting of isolated ZnO{sub 4} tetrahedra and SeO{submore » 3} polyhedra, Na{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4}, Cs{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4}, and Cs{sub 2}Zn{sub 2}(SeO{sub 3}){sub 3}·2H{sub 2}O contained two-dimensional [Zn{sub 3}(SeO{sub 3}){sub 4}]{sup 2-} layers. Specifically, whereas isolated ZnO{sub 4} tetrahedra and SeO{sub 3} polyhedra are arranged into two-dimensional [Zn{sub 3}(SeO{sub 3}){sub 4}]{sup 2-} layers in two cesium compounds, circular [Zn{sub 3}O{sub 10}]{sup 14-} chains and SeO{sub 3} linkers are formed in two-dimensional [Zn{sub 3}(SeO{sub 3}){sub 4}]{sup 2-} layers in Na{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4}. Close structural examinations suggest that the size of alkali metal is significant in determining the framework geometry as well as connection modes of transition metal cations. - Graphical abstract: Variable dimensions and frameworks were found in a series of quaternary zinc selenites, A{sub 2}Zn{sub 3}(SeO{sub 3}){sub 4} (A = Na, Rb and Cs). - Highlights: • Five novel quaternary zinc selenites are synthesized. • All the selenites with different structures contain polarizable d{sup 10} and lone pair cations. • The size of alkali metal cations is significant in determining the framework geometry.« less

Studies on influence of aluminium ions on the bioactivity of B2O3-SiO2-P2O5-Na2O-CaO glass system by means of spectroscopic studies

NASA Astrophysics Data System (ADS)

Mohini, G. Jagan; Krishnamacharyulu, N.; Sahaya Baskaran, G.; Rao, P. Venkateswara; Veeraiah, N.

2013-12-01

Bioactive multi component glasses of the composition of 27.4 B2O3-6.4 SiO2-2.5 P2O5-25.5 Na2O-(38.2 - x) CaO: x Al2O3 (x between 0 and 3.2) were synthesized, by melt quenching technique and their bioactivity was investigated as a function of Al2O3 concentration. Initially, optical absorption and infrared spectra were recorded and analyzed in order to have some pre-understanding over structural aspects of the glasses. For understanding the bioactivity, the samples were immersed in simulated body fluid (SBF) solution for prolonged times (∼30 days) and the weight loss measurements were carried out. The spectroscopic studies were repeated on the post immersed samples. From the comparison of the analysis of the spectroscopic data of both pre-immersed and post-immersed samples together with the information on variation of pH value of residual solution as a function of immersion time, it is concluded that the participation of aluminium ions in tetrahedral positions is hindrance for the formation of HA layer and for the bioactivity of the samples.

Bulk and grain-boundary ionic conductivity in sodium zirconophosphosilicate Na3Zr2(SiO4)2PO4 (NASICON)

NASA Astrophysics Data System (ADS)

Lunghammer, S.; Ma, Q.; Rettenwander, D.; Hanzu, I.; Tietz, F.; Wilkening, H. M. R.

2018-06-01

Sodium zirconophosphosilicates (Na1+x Zr2(P1-x SixO4)3 (0 < x < 3)) currently experience a kind of renaissance as promising ceramic electrolytes for safe all-solid-state Na batteries. Such energy storage systems are an emerging option for next-generation technologies with attractive cost due to the use of abundant elements as sodium. To identify the right candidates their ion transport properties need to be precisely studied. In many cases less is known about the contributions of blocking grain boundaries to the overall charge carrier transport. Here, we took advantage of broadband impedance and conductivity spectroscopy carried out at sufficiently low temperature to make visible these two contributions for polycrystalline Na3Zr2(SiO4)2PO4. It turned out that ion transport across the grain boundaries of a sintered pellet do not greatly hinder long-range ion dynamics. While bulk ion dynamics in Na3Zr2(SiO4)2PO4 is characterized by 1.0 mS cm-1, the grain boundary ionic conductivity is only slightly lower viz. 0.7 mS cm-1. The latter value is of large practical interest as it allows the realization of all-solid-state Na batteries without strong interfering resistances from grain boundaries.

Pressure effect on the Raman and photoluminescence spectra of Eu3+-doped Na2Ti6O13 nanorods

NASA Astrophysics Data System (ADS)

Zeng, Q. G.; Yang, G. T.; Chen, F.; Luo, J. Y.; Zhang, Z. M.; Leung, C. W.; Ding, Z. J.; Sheng, Y. Q.

2013-12-01

Eu3+-doped Na2Ti6O13 (Na2Ti6O13:Eu) nanorods with diameters of 30 nm and lengths 400 nm were synthesized by hydrothermal and heat treatment methods. Raman spectra at ambient conditions indicated a pure monoclinic phase (space group C2/m) of the nanorods. The relations between structural and optical properties of Na2Ti6O13:Eu nanorods under high pressures were obtained by photoluminescence and Raman spectra. Two structural transition points at 1.39 and 15.48 GPa were observed when the samples were pressurized. The first transition point was attributed to the crystalline structural distortion. The later transition point was the result of pressure-induced amorphization, and the high-density amorphous (HDA) phase formed after 15.48 GPa was structurally related to the monoclinic baddeleyite structured TiO2 (P21/c). However, the site symmetry of the local environment around the Eu3+ ions in Na2Ti6O13 increased with the rising pressure. These above results indicate the occurrence of short-range order for the local asymmetry around the Eu3+ ions and long-range disorder for the crystalline structure of Na2Ti6O13:Eu nanorods by applying pressure. After releasing the pressure from 22.74 GPa, the HDA phase is transformed to low-density amorphous form, which is attributed to be structurally related to the α-PbO2-type TiO2.

Assessment of role of iron ions on the physical and spectroscopic properties of multi-component Na2O-PbO-Bi2O3-SiO2 glass ceramics

NASA Astrophysics Data System (ADS)

Rao, M. V. Sambasiva; Kumar, A. Suneel; Ram, G. Chinna; Tirupataiah, Ch.; Rao, D. Krishna

2018-01-01

Multi-component glass ceramics composition Na2O-PbO-Bi2O3-SiO2 doped with different concentrations of Fe2O3 as nucleating agent were characterised by XRD, SEM (scanning electron microscope) and DTA (differential thermal analysis) techniques. Optical absorption, EPR, FTIR and Raman studies are also carried out on these glass ceramics. Absorption bands observed at about 457, 489, 678 and 820 nm are the characteristics of Fe3+ ions whereas the band observed at about 964 nm is due to Fe2+ ions. EPR studies suggested that Fe3+ ions entered in the lattice as tetragonally distorted octahedral symmetry or rhombic sites at low concentration of Fe2O3, whereas at higher concentration of Fe2O3 (beyond 1 mol%), the super exchange type of interactions between multivalency iron ions begin to dominate. FTIR and Raman spectra have revealed the behaviour of various structural units in the glass ceramic matrix. The analysis of these spectroscopic studies indicates that iron ions do exist in Fe3+ and Fe2+ state.

Synthesis, structure and properties of blödite-type solid solutions, Na2Co1-x Cu x (SO4)2·4H2O (0 < x ≤ 0.18), and crystal structure of synthetic kröhnkite, Na2Cu(SO4)2·2H2O

NASA Astrophysics Data System (ADS)

Marinova, Delyana; Wildner, Manfred; Bancheva, Tsvetelina; Stoyanova, Radostina; Georgiev, Mitko; Stoilova, Donka G.

2018-03-01

Based on different experimental methods—crystallization processes in aqueous solutions, infrared spectroscopy, single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) and TG-DTA-DSC measurements—it has been established that copper ions are included in sodium cobalt sulfate up to about 18 mol%, thus forming limited solid solutions Na2Co1-x Cu x (SO4)2·4H2O (0 < x ≤ 0.18) with a blödite-type structure. In contrast, cobalt ions are not able to accept the coordination environment of the copper ions in the strongly distorted Cu(H2O)2O4 octahedra, thus resulting in the crystallization of Co-free kröhnkite. The solid solutions were characterized by vibrational and EPR spectroscopy. DSC measurements reveal that the copper concentration increase leads to increasing values of the enthalpy of dehydration (ΔH deh) and decreasing values of the enthalpy of formation (ΔH f). The crystal structures of synthetic kröhnkite, Na2Cu(SO4)2·2H2O, as well as of three Cu2+-bearing mixed crystals of Co-blödite, Na2Co1-x Cu x (SO4)2·4H2O with x (Cu) ranging from 0.03 to 0.15, have been investigated from single-crystal X-ray diffraction data. The new data for the structure of synthetic kröhnkite facilitated to clarify structural discrepancies found in the literature for natural kröhnkite samples, traced back to a mix-up of lattice parameters. The crystal structures of Co-dominant Na2Co1-x Cu x (SO4)2·4H2O solid solutions reveal a comparatively weak influence of the Jahn-Teller-affected Cu2+ guest cations up to the maximum content of x (Cu) = 0.15. The response of the MO2(H2O)4 octahedral shape by increased bond-length distortion with Cu content is clear cut (but limited), mainly concerning the M-OH2 bond lengths, whereas other structural units are hardly affected. However, the specific type of imposed distortion seems to play an important role impeding higher Cu/Co replacement ratios.

Thermodynamic Model of the Na-Al-Si-O-F Melts

NASA Astrophysics Data System (ADS)

Dolejs, D.; Baker, D. R.

2004-05-01

Fluorine is a common volatile element in magmatic-hydrothermal systems, but its solution mechanisms in highly polymerized silicate melts are poorly known. We have developed a thermodynamic model for fluorosilicate liquids which links experimentally determined phase equilibria and spectroscopic information on melt structure. The model is applicable to crystallization of fluoride minerals or fluoride-silicate immiscibility in natural felsic melts. Configurational properties of the liquid are defined by mixing of alkali fluoride, polyhedral aluminofluoride and silicofluoride species and non-bridging terminations of the silicate network. Abundances of individual structural species are described by a homogeneous equilibrium, representing melt depolymerization: F- (free) + O0 (bridging) = F0 (terminal) + O- (non-bridging), which is a replacement of one oxygen bridge, Si-O-Si, by two terminations, Si-F | Na-O-Si. In cryolite-bearing systems, the self-dissociation of octahedral aluminofluoride complexes: Na3[AlF6] = Na[AlF4] + 2 NaF, and the short-range order between (O,F)-corners and (Si,NaAl)-centers of tetrahedra: Si-O-Si + 2 [NaAl]-F = [NaAl]-O-[NaAl] + 2 Si-F, represent two additional interaction mechanisms. Portrayal of these equilibria in ternary Thompson reaction space allows to decrease the number of interaction mechanisms by linearly combining melt depolymerization with tetrahedral short-range order. In this formulation, the interaction parameters are incorporated directly in configurational properties, thus the complete melt speciation can be calculated, and the activities of any macroscopic species are readily derived. The model has been applied to subsystems of the Na2O-NaAlO2-SiO2-F2O-1 compositional space. Activity-composition relationships in the villiaumite-sodium silicate binaries require clustering of silicate tetrahedra in fluoride solvent. Phase-equilibria in cryolite-nepheline and cryolite-albite systems illustrate an overall increase of Na3AlF6 self

Solid-state synthesis in the system Na 0.8Nb yW 1-yO 3 with 0⩽ y⩽0.4: A new phase, Na 0.5NbO 2.75, with perovskite-type structure

NASA Astrophysics Data System (ADS)

Debnath, Tapas; Rüscher, Claus H.; Gesing, Thorsten M.; Koepke, Jürgen; Hussain, Altaf

2008-04-01

Series of compounds in the system Na xNb yW 1-yO 3 were prepared according to the appropriate molar ratio of Na 2WO 4, WO 3, WO 2 and Nb 2O 5 with x=0.80 and 0.0⩽ y⩽0.4 at 600 °C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition Na xWO 3 with slightly decreasing x (i.e. 0.8-0.72) with increasing nominal y, (ii) bluish solid solution of composition Na xNb yW 1-yO 3 and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na 0.5NbO 2.75.

Doping Li and K into Na2ZrO3 Sorbent to Improve Its CO2 Capture Capability

NASA Astrophysics Data System (ADS)

Duan, Yuhua

Carbon dioxide is one of the major combustion products which once released into the air can contribute to global climate change. Solid sorbents have been reported in several previous studies to be promising candidates for CO2 sorbent applications due to their high CO2 absorption capacities at moderate working temperatures. However, at a given CO2 pressure, the turnover temperature (Tt) of an individual solid capture CO2 reaction is fixed and may be outside the operating temperature range (ΔTo) for a particularly capture technology. In order to shift such Tt for a solid into the range of ΔTo, its corresponding thermodynamic property must be changed by changing its structure by reacting (mixing) with other materials or doping with other elements. As an example, by combining thermodynamic database searching with ab initio thermodynamics calculations, in this work, we explored the Li- and K-doping effects on the Tt shifts of Na2ZrO3 at different doping levels. The obtained results showed that compared to pure Na2ZrO3, the Li- and K-doped mixtures Na2-αMαZrO3 (M =Li, K) have lower Tt and higher CO2 capture capacities.

Electronic Structure, Phonon Dynamical Properties, and CO 2 Capture Capability of Na 2 - x M x Zr O 3 ( M = Li ,K): Density-Functional Calculations and Experimental Validations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Yuhua; Lekse, Jonathan; Wang, Xianfeng

2015-04-22

The electronic structural and phonon properties of Na 2-αM αZrO 3 (M ¼ Li,K, α = ¼ 0.0,0.5,1.0,1.5,2.0) are investigated by first-principles density-functional theory and phonon dynamics. The thermodynamic properties of CO 2 absorption and desorption in these materials are also analyzed. With increasing doping level α, the binding energies of Na 2-αLi αZrO 3 are increased while the binding energies of Na 2-α K αZrO 3 are decreased to destabilize the structures. The calculated band structures and density of states also show that, at the same doping level, the doping sites play a significant role in the electronic properties.more » The phonon dispersion results show that few soft modes are found in several doped configurations, which indicates that these structures are less stable than other configurations with different doping levels. From the calculated relationships among the chemical-potential change, the CO 2 pressure, and the temperature of the CO 2 capture reactions by Na 2-αM αZrO 3, and from thermogravimetric-analysis experimental measurements, the Li- and K-doped mixtures Na 2-αM αZrO 3 have lower turnover temperatures (T t) and higher CO 2 capture capacities, compared to pure Na 2ZrO 3. The Li-doped systems have a larger T t decrease than the K-doped systems. When increasing the Li-doping level α, the T t of the corresponding mixture Na 2-αLi αZrO 3 decreases further to a low-temperature range. However, in the case of K-doped systems Na 2-αK αZrO 3, although doping K into Na 2ZrO 3 initially shifts its T t to lower temperatures, further increases of the K-doping level α causes T t to increase. Therefore, doping Li into Na 2ZrO 3 has a larger influence on its CO 2 capture performance than the K-doped Na 2ZrO 3. Compared with pure solidsM 2ZrO 3, after doping with other elements, these doped systems’ CO 2 capture performances are improved.« less

Effect of NiO and Light Intensity on Dielectric Constant of SiO2-B2O3-Bi2O3-Na2CO3 Glass Based on Silica Gel of Natural Sands

NASA Astrophysics Data System (ADS)

Diantoro, M.; Muniroh, Z.; Zaini, B.; Mustikasari, A. A.; Nasikhudin; Hidayat, A.; Taufiq, A.; Sunaryono; Mufti, N.

2017-05-01

The use of silica in various fields is significantly increasing. One common application is silica based functional glass which has naturally show specific dielectric, optical, and magnetic properties. Many studies have been performing to explore the influence of dopant, composition, and other processing parameters as well as employing various characterization. In the previous work, we report the use of silica from silica sands. To reduce the melting temperature, we used silica sol-gel beside the utilization of some oxides such as B2O3, Na2CO3, and Bi3O3. We also used NiO as dopant explore the glass properties. We have prepared a series of sample with the composition of 50SiO2-25B2O3-(6.5-x) Bi3O3-18.5 Na2CO3-xNiO (x = 0, 1, 2, 3 and 4 wt%). After weighting process, the composition was blended, then heated to 450 °C for 120 minutes and then raised at 950 °C for 60 minutes in the crucible. Then samples of glass separated from the crucible and in the characterization of the structure using the DTA, XRD, SEM-EDAX and FTIR and measuring dielectric constant using a capacitance meter. The increase of NiO dopant resulted in increasing the dielectric constant of glass. On the other hand, the dielectric constant gradually decreases with the increase of light intensity. One can be noted that the applied intensity give rise to the step-like decrease of the dielectric constant. Whereas, the increasing magnetic field indicate the increase of dielectric constant.

Understanding the magnetic behavior of heat treated CaO-P2O5-Na2O-Fe2O3-SiO2 bioactive glass using electron paramagnetic resonance studies

NASA Astrophysics Data System (ADS)

Shankhwar, Nisha; Kothiyal, G. P.; Srinivasan, A.

2014-09-01

Bioactive glass of composition 41CaO-44SiO2-4P2O5-8Fe2O3-3Na2O has been heat treated in the temperature (TA) range of 750-1150 °C for time periods (tA) ranging from 1 h to 3 h to yield magnetic bioactive glass ceramics (MBCs). X-ray diffraction studies indicate the presence of bone mineral (hydroxyapatite and wollastonite) and magnetic (magnetite and α-hematite) phases in nanocrystalline form in the MBCs. Electron paramagnetic resonance (EPR) study was carried out to understand the variation in saturation magnetization and coercivity of the MBCs with TA and tA. These studies reveal the nature and amount of iron ions present in the MBCs and their interaction in the glassy oxide matrix as a function of annealing parameters. The deterioration in the magnetic properties of the glass heat treated above 1050 °C is attributed to the crystallization of the non-magnetic α-hematite phase. These results are expected to be useful in the application of these MBCs as thermoseeds in hyperthermia treatment of cancer.

Orientational disorder in sodium cadmium trifluoride trihydrate, NaCdF{sub 3}.3H{sub 2}O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Robert W.; Mar, Arthur; Liu Jianjun

2006-03-09

Attempts to synthesize the hypothetical anhydrous fluoroperovskite NaCdF{sub 3}, which has been predicted to be stable, resulted instead in a hydrated fluoride of nominal composition NaCdF{sub 3}.3H{sub 2}O. It decomposes to sodium fluoride, cadmium fluoride, and water at 60deg. C. Its structure has been determined by single-crystal X-ray diffraction. Na{sub 0.92(2)}Cd{sub 1.08}F{sub 3.08}.2.92H{sub 2}O crystallizes in the cubic space group Fm3-bar m with a=8.2369(4)A and Z=4. The structure is based on the NaSbF{sub 6}-type (an ordered variant of the ReO{sub 3}-type) and features tilted sodium- and cadmium-centred octahedra that are linked by shared vertices to form a three-dimensional network. Substitutionalmore » disorder occurs on the nonmetal site, which is occupied by both F and O atoms, and on one of the metal sites, which is occupied by 92% Na and 8% Cd. A four-fold orientational disorder of the tilted octahedra is manifested as partial occupancy (25%) of the nonmetal site. A scheme to synthesize the anhydrous fluoride is presented.« less

Na0.44MnO2 nanorods as a cathode material for Na-ion batteries

NASA Astrophysics Data System (ADS)

Avci, Sevda; Oz, Erdinc; Demirel, Serkan; Altin, Emine; Altin, Serdar; Bayri, Ali; Yakinci, Eyyuphan

2014-03-01

Lithium-ion batteries have dominated the rechargeable battery market because of their high energy and power capability. On the other hand, sodium is one of the more abundant elements on Earth unlike Li. Moreover, Na has similar chemical properties to Li, indicating that Na-ion batteries can be an alternative to Li counterparts. With that respect, we have synthesized Na0.44MnO2 nanorods as cathode materials for Na-ion batteries. We have investigated the effects of structural, electrical, and magnetic properties on battery performance. We report the synthesis conditions and growth mechanism of the nanorods. The structure and the morphology of the materials were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM) techniques. Temperature dependent structural changes were determined via in situ X-ray diffraction and TG-DTA measurements showing structural changes above room temperature. This work is funded by The Scientific and Technological Research Council of Turkey with Grant No:112M487.

Solubility of SC2O3 in NA3ALF6-K3ALF6-ALF3 Melts

NASA Astrophysics Data System (ADS)

Tian, Zhongliang; Hu, Xun; Lai, Yanqing; Yang, Shu; Ye, Shaolong; Li, Jie

The electrolyte with high solubility for Sc2O3 is very important to realize the preparation of Al-Sc master alloy by the molten salt electrolysis. The solubility of Sc2O3 in K3AlF6-Na3AlF6-AlF3 melts is determined with an isothermal saturation method. The effects of KR (ratio of K3AlF6 to K3AlF6+Na3AlF6), the concentration of Al2O3 and the temperature on the solubility of Sc2O3 are also investigated. The results indicate that the solubility of Sc2O3 in K3AlF6-Na3AlF6-AlF3 melts increases and then decreases with KR increasing. The solubility of Sc2O3 is 8.698 wt.% in (K3AlF6-Na3AlF6)(KR25%)-18 wt.%AlF3 melts at 940°C. The effect of temperature on the solubility is little, and the values are 8.575 wt.% and 8.762 wt.% respectively when the temperatures are 930°C and 960°C. The solubility decreases from 8.809 wt.% to 7.058 wt.% as the concentration of Al2O3 increases from 1.5 wt.% to 5.0 wt.% at 950°C.

Nanowire Na0.35MnO2 from a hydrothermal method as a cathode material for aqueous asymmetric supercapacitors

NASA Astrophysics Data System (ADS)

Zhang, B. H.; Liu, Y.; Chang, Z.; Yang, Y. Q.; Wen, Z. B.; Wu, Y. P.; Holze, R.

2014-05-01

Nanowire Na0.35MnO2 was prepared by a simple and low energy consumption hydrothermal method; its electrochemical performance as a cathode material for aqueous asymmetric supercapacitors in Na2SO4 solution was investigated. Due to the nanowire structure its capacitance (157 F g-1) is much higher than that of the rod-like Na0.95MnO2 (92 F g-1) from solid phase reaction although its sodium content is lower. When it is assembled into an asymmetric aqueous supercapacitor using activated carbon as the counter electrode and aqueous 0.5 mol L-1 Na2SO4 electrolyte solution, the nanowire Na0.35MnO2 shows an energy density of 42.6 Wh kg-1 at a power density of 129.8 W kg-1 based on the total weight of the two electrode material, higher than those for the rod-like Na0.95MnO2, with an energy density of 27.3 Wh kg-1 at a power density of 74.8 W kg-1, and that of LiMn2O4. The new material presents excellent cycling behavior even when dissolved oxygen is not removed from the electrolyte solution. The results hold great promise for practical applications of this cathode material since sodium is much cheaper than lithium and its natural resources are rich.

Preparation by Poly(Acrylic Acid) Sol-Gel Method and Thermoelectric Properties of γ-Na x CoO2 Bulk Materials

NASA Astrophysics Data System (ADS)

Li, Xiaoyu; Zhang, Li; Tang, Xinfeng

2017-11-01

γ-Na x CoO2 single-phase powders have been synthesized by a poly(acrylic acid) (PAA) sol-gel (SG) method, and γ-Na x CoO2 bulk ceramic fabricated using spark plasma sintering. The effects of the PAA concentration on the sample phase composition and morphology were investigated. The thermoelectric properties of the γ-Na x CoO2 bulk ceramic were also studied. The results show that the PAA concentration did not significantly affect the crystalline phase of the product. However, agglomeration of γ-Na x CoO2 crystals was suppressed by the steric effect of PAA. The Na x CoO2 bulk ceramic obtained using the PAA SG method had higher crystallographic anisotropy, better chemical homogeneity, and higher density than the sample obtained by solid-state reaction (SSR), leading to improved thermoelectric performance. The PAA SG sample had power factor (in-plane PF = σS 2) of 0.61 mW m-1 K-2 and dimensionless figure of merit ( ZT) along the in-plane direction of 0.19 at 900 K, higher than for the SSR sample (in-plane PF = 0.51 mW m-1 K-2, in-plane ZT = 0.17). These results demonstrate that a simple and feasible PAA SG method can be used for synthesis of Na x CoO2 ceramics with improved thermoelectric properties.

Structural study of Al2O3-Na2O-CaO-P2O5 bioactive glasses as a function of aluminium content.

PubMed

Smith, J M; King, S P; Barney, E R; Hanna, J V; Newport, R J; Pickup, D M

2013-01-21

Calcium phosphate based biomaterials are extensively used in the context of tissue engineering: small changes in composition can lead to significant changes in properties allowing their use in a wide range of applications. Samples of composition (Al(2)O(3))(x)(Na(2)O)(0.11-x)(CaO)(0.445)(P(2)O(5))(0.445), where x = 0, 0.03, 0.05, and 0.08, were prepared by melt quenching. The atomic-scale structure has been studied using neutron diffraction and solid state (27)Al MAS NMR, and these data have been rationalised with the determined density of the final glass product. With increasing aluminium concentration the density increases initially, but beyond about 3 mol. % Al(2)O(3) the density starts to decrease. Neutron diffraction data show a concomitant change in the aluminium speciation, which is confirmed by (27)Al MAS NMR studies. The NMR data reveal that aluminium is present in 4, 5, and 6-fold coordination and that the relative concentrations of these environments change with increasing aluminium concentration. Materials containing aluminium in 6-fold coordination tend to have higher densities than analogous materials with the aluminium found in 4-fold coordination. Thus, the density changes may readily be explained in terms of an increase in the relative concentration of 4-coordinated aluminium at the expense of 6-fold aluminium as the Al(2)O(3) content is increased beyond 3 mol. %.

The TAED/H2O2/NaHCO3 system as an approach to low-temperature and near-neutral pH bleaching of cotton.

PubMed

Long, Xiaoxia; Xu, Changhai; Du, Jinmei; Fu, Shaohai

2013-06-05

A low-temperature and near-neutral pH bleaching system was conceived for cotton by incorporating TAED, H2O2 and NaHCO3. The TAED/H2O2/NaHCO3 system was investigated and optimized for bleaching of cotton using a central composite design (CCD) combined with response surface methodology (RSM). CCD experimental data were fitted to create a response surface quadratic model (RSQM) describing the degree of whiteness of bleached cotton fabric. Analysis of variance for the RSQM revealed that temperature was the most significant variable, followed by [TAED] and time, while [NaHCO3] was insignificant. An effective system was conducted by adding 5.75 g L(-1) TAED together with H2O2 and NaHCO3 at a molar ratio of 1:2.4:2.8 and applied to bleaching of cotton at 70 °C for 40 min. Compared to a commercial bleaching method, the TAED/H2O2/NaHCO3 system provided cotton with comparable degree of whiteness, slightly inferior water absorbency and acceptable dyeability, but had competitive advantage in protecting cotton from severe chemical damage in bleaching. Copyright © 2013 Elsevier Ltd. All rights reserved.

Investigation of the Magnetic Properties of Na0.7CoO2 Prepared by Electrochemical Reaction

NASA Astrophysics Data System (ADS)

Sassa, Y.; Umegaki, I.; Nozaki, H.; Forslund, O. K.; Delmas, C.; Orain, J.-C.; Amato, A.; Andreica, D.; Månsson, M.; Sugiyama, J.

We report a muon spin rotation and relaxation (μ+SR) study on Na0.7CoO2 powder samples, where the sodium (Na) has been intercalated via an electrochemical reaction inside a Na-ion battery. The zero field μ+SR measurement at T = 2 K shows a paramagnetic state for the as-grown sample whereas an antiferromagnetic (AF) ordered state is seen for the electrochemically cycled one. Furthermore, the temperature dependence of the muon-spin precession frequencies reveals a Néel transition temperature of TN = 22 K. The results demonstrate the importance of having high-quality homogenous samples, and put the existing NaxCoO2 magnetic phase diagram under debate.

Spin orientations of the spin-half Ir 4+ ions in Sr 3NiIrO 6, Sr 2IrO 4 and Na 2IrO 3: Density functional, perturbation theory and Madelung potential analyses

DOE PAGES

Gordon, Elijah E.; Xiang, Hongjun; Koehler, Jurgen; ...

2016-03-01

The spins of the low-spin Ir 4+ (S = 1/2, d 5) ions at the octahedral sites of the oxides Sr 3NiIrO 6, Sr 2IrO 4 and Na 2IrO 3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of DFT calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr 3NiIrO 6 and Sr 2IrO 4 are correctly predicted by DFT calculations, and are accounted formore » by the perturbation theory analysis. As for the spin orientation of Na 2IrO 3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir 4+ spin orientation of Na 2IrO 3 should have nonzero components along the c- and a-axes directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir 4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na 2IrO 3 are less strongly localized compared with those of Sr 3NiIrO 6 and Sr 2IrO 4. This implication was confirmed by showing that the Madelung potentials of the Ir 4+ ions are less negative in Na 2IrO 3 than in Sr 3NiIrO 6, Sr 2IrO 4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian because this model Hamiltonian lacks the orbital degree of freedom, thereby leading to the spin-half syndrome. As a result, the spin-orbital entanglement for the 5d spin-half ions Ir 4+ is not as strong as has been assumed lately.« less

Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4, and Na2IrO3: Density functional, perturbation theory, and Madelung potential analyses

NASA Astrophysics Data System (ADS)

Gordon, Elijah E.; Xiang, Hongjun; Köhler, Jürgen; Whangbo, Myung-Hwan

2016-03-01

The spins of the low-spin Ir4+ (S = 1/2, d5) ions at the octahedral sites of the oxides Sr3NiIrO6, Sr2IrO4, and Na2IrO3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of density functional theory (DFT) calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr3NiIrO6 and Sr2IrO4 are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na2IrO3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir4+ spin orientation of Na2IrO3 should have nonzero components along the c- and a-axis directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na2IrO3 are less strongly localized compared with those of Sr3NiIrO6 and Sr2IrO4. This implication was confirmed by showing that the Madelung potentials of the Ir4+ ions are less negative in Na2IrO3 than in Sr3NiIrO6 and Sr2IrO4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian because this model Hamiltonian lacks the orbital degree of freedom, thereby leading to the spin-half syndrome. The spin-orbital entanglement for the 5d spin-half ions Ir4+ is not as strong as has been assumed.

Removal kinetics for gaseous NO and SO2 by an aqueous NaClO2 solution mist in a wet electrostatic precipitator.

PubMed

Park, Hyun-Woo; Park, Dong-Wha

2017-04-01

Removal kinetics for NO and SO 2 by NaClO 2 solution mist were investigated in a wet electrostatic precipitator. By varying the molar concentrations of NO, SO 2 , and NaClO 2 , the removal rates of NO and SO 2 confirmed to range from 34.8 to 72.9 mmol/m 3  s and 36.6 to 84.7 mmol/m 3  s, respectively, at a fixed gas residence time of 0.25 s. The rate coefficients of NO and SO 2 were calculated to be 0.679 (mmol/m 3 ) -0.33  s -1 and 1.401 (mmol/m 3 ) -0.1  s -1 based on the rates of the individual removal of NO and SO 2 . Simultaneous removal of NO and SO 2 investigated after the evaluation of removal rates for their individual treatment was performed. At a short gas residence time, SO 2 gas removed more quickly by a mist of NaClO 2 solution than NO gas in simultaneous removal experiments. This is because SO 2 gas, which has a relatively high solubility in solution, was absorbed more rapidly at the gas-liquid interface than NO gas. NO and SO 2 gases were absorbed as nitrite [Formula: see text] and sulfite [Formula: see text] ions, respectively, by the NaClO 2 solution mist at the gas-liquid interface. Then, [Formula: see text] and [Formula: see text] were oxidized to nitrate [Formula: see text] and sulfate [Formula: see text], respectively, by reactions with [Formula: see text], ClO 2 , HClO, and ClO in the liquid phase.

Ultrafine Nanocrystalline CeO2@C-Containing NaAlH4 with Fast Kinetics and Good Reversibility for Hydrogen Storage.

PubMed

Zhang, Xin; Liu, Yongfeng; Wang, Ke; Li, You; Gao, Mingxia; Pan, Hongge

2015-12-21

A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-Pressure Polymorph of NaBiO3.