Fabrication of thermoelectric modules with Mg2Si and SrRuO3 by the spark plasma sintering method

NASA Astrophysics Data System (ADS)

Nishio, Keishi; Sawada, Yukie; Arai, Koya; Sakamoto, Tatsuya; Kogo, Yasuo; Iida, Tsutomu

2012-06-01

Thermoelectric (TE) modules with a π structure were fabricated by the spark plasma sintering method. The modules were composed of SrRuO3 for the p-type semiconductor, Mg2Si for the n-type semiconductor, and Ni for the electrodes. The SrRuO3 powder was synthesized using the metal-citric-acid complex decomposition method. Mg2Si bulk prepared by meltquenching was ground into powder and sieved to a particle size of 75 μm or less. To obtain the sintered body of SrRuO3, the powder was sintered using spark plasma sintering (SPS). For SPS, the precursor powder was placed in a graphite die and kept at that temperature under a uni-axial pressure of 50 MPa and in vacuum conditions (less than 7 Pa). After sintering by SPS, the ceramic sample was annealed at 1573K in air because the SrRuO3 was slightly reduced during the SPS process in the graphite die. These TE sintered bodies were cut and polished. The dimensions of the samples used for fabrication of the p-type parts of the TE modules were 4.50×9.50×7.45 mm3 and those for the n-type parts were 5.50×11.45×7.45 mm3. Pressed Ni powder was put between these TE materials and the Ni electrodes in order to connect them together, and electrical power was passed through the electrodes from the SPS equipment. The output power under temperature differences ΔT ranging from 100 to 500 K was measured. The open-circuit voltage, maximum output current and maximum output power increased with increasing temperature difference ΔT. The open-circuit voltage of the single module was 91.0 mV, and the maximum output current and maximum output power were 5000 mA and 110 mW at ΔT=500 K, respectively.

Flash (Ultra-Rapid) Spark-Plasma Sintering of Silicon Carbide

PubMed Central

Olevsky, Eugene A.; Rolfing, Stephen M.; Maximenko, Andrey L.

2016-01-01

A new ultra-rapid process of flash spark plasma sintering is developed. The idea of flash spark plasma sintering (or flash hot pressing - FHP) stems from the conducted theoretical analysis of the role of thermal runaway phenomena for material processing by flash sintering. The major purpose of the present study is to theoretically analyze the thermal runaway nature of flash sintering and to experimentally address the challenge of uncontrollable thermal conditions by the stabilization of the flash sintering process through the application of the external pressure. The effectiveness of the developed FHP technique is demonstrated by the few seconds–long consolidation of SiC powder in an industrial spark plasma sintering device. Specially designed sacrificial dies heat the pre-compacted SiC powder specimens to a critical temperature before applying any voltage to the powder volume and allowing the electrode-punches of the SPS device setup to contact the specimens and pass electric current through them under elevated temperatures. The experimental results demonstrate that flash sintering phenomena can be realized using conventional SPS devices. The usage of hybrid heating SPS devices is pointed out as the mainstream direction for the future studies and utilization of the new flash hot pressing (ultra-rapid spark plasma sintering) technique. PMID:27624641

Flash (Ultra-Rapid) Spark-Plasma Sintering of Silicon Carbide

DOE PAGES

Olevsky, Eugene A.; Rolfing, Stephen M.; Maximenko, Andrey L.

2016-09-14

A new ultra-rapid process of flash spark plasma sintering is developed. The idea of flash spark plasma sintering (or flash hot pressing - FHP) stems from the conducted theoretical analysis of the role of thermal runaway phenomena for material processing by flash sintering. The major purpose of the present study is to theoretically analyze the thermal runaway nature of flash sintering and to experimentally address the challenge of uncontrollable thermal conditions by the stabilization of the flash sintering process through the application of the external pressure. The effectiveness of the developed FHP technique is demonstrated by the few seconds–long consolidationmore » of SiC powder in an industrial spark plasma sintering device. Specially designed sacrificial dies heat the pre-compacted SiC powder specimens to a critical temperature before applying any voltage to the powder volume and allowing the electrode-punches of the SPS device setup to contact the specimens and pass electric current through them under elevated temperatures. The experimental results demonstrate that flash sintering phenomena can be realized using conventional SPS devices. The usage of hybrid heating SPS devices is pointed out as the mainstream direction for the future studies and utilization of the new flash hot pressing (ultra-rapid spark plasma sintering) technique.« less

Densification kinetics of nanocrystalline zirconia powder using microwave and spark plasma sintering--a comparative study.

PubMed

Vasylkiv, Oleg; Demirskyi, Dmytro; Sakka, Yoshio; Ragulya, Andrey; Borodianska, Hanna

2012-06-01

Two-stage densification process of nanosized 3 mol% yttria-stabilized zirconia (3Y-SZ) polycrystalline compacts during consolidation via microwave and spark-plasma sintering have been observed. The values of activation energies obtained for microwave and spark-plasma sintering 260-275 kJ x mol(-1) are quite similar to that of conventional sintering of zirconia, suggesting that densification during initial stage is controlled by the grain-boundary diffusion mechanism. The sintering behavior during microwave sintering was significantly affected by preliminary pressing conditions, as the surface diffusion mechanism (230 kJ x mol(-1)) is active in case of cold-isostatic pressing procedure was applied.

Fabrication Processes and Mechanical Behavior of CNT/Metal Nanocomposites

DTIC Science & Technology

2013-12-01

process, were investigated and applied for fabrication of CNT/Cu and CNT/Ni nanocomposite powders. The spark plasma sintering process was applied... spark plasma sintering process to fabricate CNT/NiTi and CNT/Al-Cu nanocomposites. It is confirmed that the CNTs were homogeneously dispersed in NiTi...can be seen in Figure 1-1. The CNT/NiTi composite powders were consolidated by spark plasma sintering (SPS, Dr. Sinter Lab., Sumitomo). The CNT/NiTi

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process

NASA Astrophysics Data System (ADS)

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-01

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Formation of Equiaxed Alpha and Titanium Nitride Precipitates in Spark Plasma Sintered TiB/Ti-6Al-4V Composites (Preprint)

DTIC Science & Technology

2012-08-01

AFRL-RX-WP-TP-2012-0372 FORMATION OF EQUIAXED ALPHA AND TITANIUM NITRIDE PRECIPITATES IN SPARK PLASMA SINTERED TiB/Ti-6Al-4V COMPOSITES...ALPHA AND TITANIUM NITRIDE PRECIPITATES IN SPARK PLASMA SINTERED TiB/Ti-6Al-4V COMPOSITES (PREPRINT) 5a. CONTRACT NUMBER FA8650-08-C-5226 5b...distribution of TiN precipitates, as revealed by TEM studies. 15. SUBJECT TERMS Ti-6Al-4V; TiB; TiN; Spark Plasma Sintering ; Composite; α/β phase

The investigation of order–disorder transition process of ZSM-5 induced by spark plasma sintering

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

Wang, Liang; Wang, Lianjun, E-mail: wanglj@dhu.edu.cn; Jiang, Wan

2014-04-01

Based on the amorphization of zeolites, an order–disorder transition method was used to prepare silica glass via Spark Plasma Sintering (SPS). In order to get a better understanding about the mechanism of amorphization induced by SPS, the intermediate products in this process were prepared and characterized by different characterization techniques. X-ray diffraction and High-energy synchrotron X-ray scattering show a gradual transformation from ordered crystal to glass. Local structural changes in glass network including Si–O bond length, O–Si–O bond angle, size of rings, coordination were detected by Infrared spectroscopy and {sup 29}Si magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Topologically ordered,more » amorphous material with a different intermediate-range structure can be obtained by precise control of intermediate process which can be expected to optimize and design material. - Graphical abstract: Low-density, ordered zeolites collapse to the rigid amorphous glass through spark plasma sintering. The intermediate-range structure formed in the process of order–disorder transition may give rise to specific property. - Highlights: • Order–disorder transition process of ZSM-5 induced by spark plasma sintering was investigated using several methods including XRD, High-energy synchrotron X-ray scattering, SAXS, IR, NMR, ect. • Order–disorder transition induced by SPS was compared with TIA and PIA. • Three stages has been divided during the whole process. • The collapse temperature range which may give rise to intermediate-range structure has been located.« less

Enhanced thermal diffusivity of copperbased composites using copper-RGO sheets

NASA Astrophysics Data System (ADS)

Kim, Sangwoo; Kwon, Hyouk-Chon; Lee, Dohyung; Lee, Hyo-Soo

2017-11-01

The synthesis of copper-reduced graphene oxide (RGO) sheets was investigated in order to control the agglutination of interfaces and develop a manufacturing process for copper-based composite materials based on spark plasma sintering. To this end, copper-GO (graphene oxide) composites were synthesized using a hydrothermal method, while the copper-reduced graphene oxide composites were made by hydrogen reduction. Graphene oxide-copper oxide was hydrothermally synthesized at 80 °C for 5 h, and then annealed at 800 °C for 5 h in argon and hydrazine rate 9:1 to obtain copper-RGO flakes. The morphology and structure of these copper-RGO sheets were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. After vibratory mixing of the synthesized copper-RGO composites (0-2 wt%) with copper powder, they were sintered at 600 °C for 5 min under100 MPa of pressure by spark plasma sintering process. The thermal diffusivity of the resulting sintered composite was characterized by the laser flash method at 150 °C.

Synthesis and characterization of aluminium–alumina micro- and nano-composites by spark plasma sintering

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

Dash, K., E-mail: khushbudash@gmail.com; Chaira, D.; Ray, B.C.

Graphical abstract: The evolution of microstructure by varying the particle size of reinforcement in the matrix employing spark plasma sintering has been demonstrated here in Al–Al{sub 2}O{sub 3} system. An emphasis has been laid on varying the reinforcement particle size and evaluating the microstructural morphologies and their implications on mechanical performance of the composites. Nanocomposites of 0.5, 1, 3, 5, 7 volume % alumina (average size < 50 nm) reinforced in aluminium matrix were fabricated by powder metallurgy route using spark plasma sintering technique technique at a temperature of 773 K and pressure of 50 MPa. Another set of specimensmore » having composition 1, 5, 20 vol.% of alumina (average size ∼ 10 μm) had been fabricated to compare the physical as well as mechanical attributes of the microcomposite as well as the nanocomposites. These micro- and nano-composites have been characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy followed by density, microhardness and nanoindentation measurements. The alumina nanoparticles revealed an interface showing appreciable physical intimacy with the aluminium matrix compared to that of the alumina microparticles. The interfacial integrity in case of nanocomposites is better than in the microcomposite which has been studied using microscopic techniques. Spark plasma sintering imparts enhanced densification as well as matrix-reinforcement proximity which has been corroborated with the experimental results. - Highlights: • The Al–Al{sub 2}O{sub 3} micro- and nano-composites fabricated by spark plasma sintering. • Better matrix-reinforcement integrity in nanocomposites than microcomposites. • Spark plasma sintering method results in higher density and hardness values. • High density and hardness values of nanocomposites than microcomposites. • High dislocation density in spark plasma sintered Al–Al{sub 2}O{sub 3} composites. - Abstract: In the present study, an emphasis has been laid on evaluation of the microstructural morphologies and their implications on mechanical performance of the composites by varying the reinforcement particle size. Nanocomposites of 0.5, 1, 3, 5, 7 volume % alumina (average size < 50 nm) and microcomposites of 1, 5, 20 volume % of alumina (average size ∼ 10 μm) reinforced in aluminium matrix were fabricated by spark plasma sintering technique at a temperature of 773 K and pressure of 50 MPa. These micro- and nano-composites have been characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy followed by density, microhardness and nanoindentation hardness measurements. The alumina nanoparticles revealed appreciable physical intimacy with the aluminium matrix than that of alumina microparticles. The highest nanohardness recorded 0.85 GPa and 99% densification for 7 and 1 vol.% Al–Al{sub 2}O{sub 3} nancomposites respectively. Spark plasma sintering imparts enhanced densification and matrix-reinforcement proximity which have been corroborated with the experimental results.« less

Effect of heat wave at the initial stage in spark plasma sintering.

PubMed

Zhang, Long; Zhang, Xiaomin; Chu, Zhongxiang; Peng, Song; Yan, Zimin; Liang, Yuan

2016-01-01

Thermal effects are important considerations at the initial stage in spark plasma sintering of non-conductive Al2O3 powders. The generalized thermo-elastic theory is introduced to describe the influence of the heat transport and thermal focusing caused by thermal wave propagation within a constrained space and transient time. Simulations show that low sintering temperature can realize high local temperature because of the superposition effect of heat waves. Thus, vacancy concentration differences between the sink and the cross section of the particles increase relative to that observed during pressure-less and hot-pressure sintering. Results show that vacancy concentration differences are significantly improved during spark plasma sintering, thereby decreasing the time required for sintering.

A strategy to optimize the thermoelectric performance in a spark plasma sintering process

PubMed Central

Chiu, Wan-Ting; Chen, Cheng-Lung; Chen, Yang-Yuan

2016-01-01

Spark plasma sintering (SPS) is currently widely applied to existing alloys as a means of further enhancing the alloys’ figure of merit. However, the determination of the optimal sintering condition is challenging in the SPS process. This report demonstrates a systematic way to independently optimize the Seebeck coefficient S and the ratio of electrical to thermal conductivity (σ/κ) and thus achieve the maximum figure of merit zT = S2(σ/κ)T. Sb2−xInxTe3 (x = 0–0.2) were chosen as examples to validate the method. Although high sintering temperature and pressure are helpful in enhancing the compactness and electrical conductivity of pressed samples, the resultant deteriorated Seebeck coefficient and increasing thermal conductivity eventually offset the benefit. We found that the optimal sintering temperature coincides with temperatures at which the maximum Seebeck coefficient begins to degrade, whereas the optimal sintering pressure coincided with the pressure at which the σ/κ ratio reaches a maximum. Based on this principle, the optimized sintering conditions were determined, and the zT of Sb1.9In0.1Te3 is raised to 0.92 at 600 K, showing an approximately 84% enhancement. This work develops a facile strategy for selecting the optimal SPS sintering condition to further enhance the zT of bulk specimens. PMID:26975209

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process.

PubMed

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-25

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Preparation Of Sources For Plasma Vapor Deposition

NASA Technical Reports Server (NTRS)

Waters, William J.; Sliney, Hal; Kowalski, D.

1993-01-01

Multicomponent metal targets serving as sources of vapor for plasma vapor deposition made in modified pressureless-sintering process. By use of targets made in modified process, one coats components with materials previously plasma-sprayed or sintered but not plasma-vapor-deposited.

Enhanced Multiferroic Properties of YMnO3 Ceramics Fabricated by Spark Plasma Sintering Along with Low-Temperature Solid-State Reaction

PubMed Central

Wang, Meng; Wang, Ting; Song, Shenhua; Ravi, Muchakayala; Liu, Renchen; Ji, Shishan

2017-01-01

Based on precursor powders with a size of 200–300 nm prepared by the low-temperature solid-state reaction method, phase-pure YMnO3 ceramics are fabricated using spark plasma sintering (SPS). X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that the high-purity YMnO3 ceramics can be prepared by SPS at 1000 °C for 5 minutes with annealing at 800 °C for 2 h. The relative density of the sample is as high as 97%, which is much higher than those of the samples sintered by other methods. The present dielectric and magnetic properties are much better than those of the samples fabricated by conventional methods and SPS with ball-milling precursors, and the ferroelectric loops at room temperature can be detected. These findings indicate that the YMnO3 ceramics prepared by the low temperature solid reaction method and SPS possess excellent dielectric lossy ferroelectric properties at room temperature, and magnetic properties at low temperature (10 K), making them suitable for potential multiferroic applications. PMID:28772832

Development of High-Strength Nanostructured Magnesium Alloys for Light-Weight Weapon Systems and Vehicles

DTIC Science & Technology

2014-01-13

strength nanocrystalline Mg-alloys via cryomilling and spark - plasma - sintering , 2) demonstrate the unveil evidence of nanotwins in nanocrystalline...Christopher Melnyk, Wei H. Kao, Jenn-Ming Yang. Cryomilling and spark plasma sintering of nanocrystalline magnesium-based alloy, Journal of Materials...accomplished several important milestones: 1) manufacture of high strength nanocrystalline Mg-alloys via cryomilling and spark plasma sintering (SPS

Ultra-high Strength Nanostructured Mg

DTIC Science & Technology

2014-03-31

27709-2211 Nanostructured Mg and Mg alloys, Mg metallic glass, Cryomilling, Powder consolidation, Spark plasma sintering , Deformation mechanisms REPORT...mechanically milled powder and high pressure on spark plasma sintering of Mg-Cu-Gd metallic glasses; (9) microstructure and mechanical behavior of Mg-10Li-3Al...pressure on spark plasma sintering of Mg– Cu–Gd metallic glasses, Acta Materialia , (07 2013): 4414. doi: Baolong Zheng, Ying Li, Weizong Xu

Recent Trends in Newly Developed Plasma-Sprayed and Sintered Coatings for Implant Applications

NASA Astrophysics Data System (ADS)

Bsat, Suzan; Speirs, Andrew; Huang, Xiao

2016-08-01

The current paper aims to review recent trends (2011 to 2015) in newly developed plasma-sprayed and sintered coatings for implant applications. Recent developments in plasma-sprayed and sintered coatings have focused on improving biological performance, bacterial growth resistance, and mechanical properties, predominantly of HA and glass ceramics. The majority of these improvements are attributed to the addition of dopants. To improve biological performance, trace elements, such as Zn and Mg, both of which are found in bone, were added to replicate the functions they provide for the skeletal system. Though bacterial growth resistance is traditionally improved by Ag dopant, the addition of new dopants such as CeO2 and Zn were explored as well. Great effort has also been made to improve coating adherence and reduce stresses by minimizing coefficient of thermal expansion mismatch between the coating and substrate through the addition of elements such as Zn and Mg or the inclusion of a buffer layer. For sintering process in particular, there was an emphasis on reducing sintering temperature through modification of 45S5 Bioglass. New plasma spray and sintering technologies aimed at reducing high-temperature exposure are briefly introduced as well. These include microplasma spray and spark plasma sintering.

High density, uniformly distributed W/UO2 for use in Nuclear Thermal Propulsion

NASA Astrophysics Data System (ADS)

Tucker, Dennis S.; Barnes, Marvin W.; Hone, Lance; Cook, Steven

2017-04-01

An inexpensive, quick method has been developed to obtain uniform distributions of UO2 particles in a tungsten matrix utilizing 0.5 wt percent low density polyethylene. Powders were sintered in a Spark Plasma Sintering (SPS) furnace at 1600 °C, 1700 °C, 1750 °C, 1800 °C and 1850 °C using a modified sintering profile. This resulted in a uniform distribution of UO2 particles in a tungsten matrix with high densities, reaching 99.46% of theoretical for the sample sintered at 1850 °C. The powder process is described and the results of this study are given below.

Tensile Properties and Fracture Characteristics of Nanostructured Copper and Cu-SiC Nanocomposite Produced by Mechanical Milling and Spark Plasma Sintering Process

NASA Astrophysics Data System (ADS)

Akbarpour, M. R.

2018-03-01

The presence of large grains within nanometric and ultrafine grain matrix is an effective method in order to enhance strength while keeping the high ductility of metals. For this purpose, in this research, spark plasma sintering (SPS) was used to consolidate milled Cu and Cu-SiC powders. In SPS process, local sparks with high temperature between particles take place and locally lead to intense grain growth, and therefore, this method has the ability to produce bimodal grain structures in copper and copper-based composites. Microstructural and mechanical studies showed ≈ 185 and ≈ 437 nm matrix grain sizes, high tensile yield strength values of ≈ 188.4 and ≈ 296.9 MPa, and fracture strain values of 15.1 and 6.7% for sintered Cu and Cu-4 vol.% SiC nanocomposite materials, respectively. The presence of nanoparticles promoted the occurrence of static recrystallization and decreased the fraction of coarse grains in microstructure. The high tensile properties of the produced materials are attributed to fine grain size, homogenous dispersion of nanoparticles and retarded grain boundary migration during sintering.

Influence of spark plasma sintering parameters on magnetic properties of FeCo alloy

NASA Astrophysics Data System (ADS)

Albaaji, Amar J.; Castle, Elinor G.; Reece, Mike J.; Hall, Jeremy P.; Evans, Sam L.

2018-04-01

Equiatomic FeCo alloys with average particle size of 24 μm were sintered using spark plasma sintering (SPS) system at sintering temperatures of 1100, 800, and 850 °C for heating rates 50, 100, 300 °C/min by applying pressure of 50 MPa instantly at room temperature for sintering time of 5 and 15 minutes. The highest saturation induction was achieved at SPS conditions of 50 MPa, 50 °C/min, 1100 °C, without dwelling, of value 2.39 T. The saturation induction was improved with extending sintering time, the coercivity was higher in samples sintered at a fast heating rate in comparison to the slowest heating rate.

Structure and characteristics of functional powder composite materials obtained by spark plasma sintering

NASA Astrophysics Data System (ADS)

Oglezneva, S. A.; Kachenyuk, M. N.; Kulmeteva, V. B.; Ogleznev, N. B.

2017-07-01

The article describes the results of spark plasma sintering of ceramic materials based on titanium carbide, titanium carbosilicide, ceramic composite materials based on zirconium oxide, strengthened by carbon nanostructures and composite materials of electrotechnical purpose based on copper with addition of carbon structures and titanium carbosilicide. The research shows that the spark plasma sintering can achieve relative density of the material up to 98%. The effect of sintering temperature on the phase composition, density and porosity of the final product has been studied. It was found that with addition of carbon nanostructures the relative density and hardness decrease, but the fracture strength of ZrO2 increases up to times 2. The relative erosion resistance of the electrodes made of composite copper-based powder materials, obtained by spark plasma sintering during electroerosion treatment of tool steel exceeds that parameter of pure copper up to times 15.

Synthesis of Ti-6Al-4V alloy with nano-TiN microstructure via spark plasma sintering technique

NASA Astrophysics Data System (ADS)

E Falodun, O.; Obadele, B. A.; Oke, S. R.; E Maja, M.; Olubambi, P. A.

2017-12-01

The effect of nano-TiN dispersion strengthened Ti-6Al-4V via spark plasma sintering method has been investigated. Ti-6Al-4V with 4 vol. percent of nano-TiN were mixed in a Turbula shaker mixer for 8 h at a speed of 49 rpm and the admixed powders were sintered at sintering temperature range of 1000 - 1100 °C, holding time of 10-30 mins, heating rate of 100 °C/min under an applied pressure of 50 MPa. The morphology of the as-received and sintered compacts was examined by scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and phase analysis was done by X-ray diffractometry (XRD). The sintered compacts without nano-TiN reveal lamellar structure while reinforced Ti-6Al-4V with nano-TiN shows a bimodal structure and titanium nitride has a great influence on a grain growth at high temperature. Furthermore, the microstructural formation mechanism was investigated. With the addition of the content of Ti-6Al-4V with 4 vol.% of nano-TiN, the micro-hardness also improved and this was due to homogenous distribution of TiN in Ti-6Al-4V matrix.

Application of spark plasma sintering for fabricating Nd-Fe-B composite

NASA Astrophysics Data System (ADS)

Sivkov, A. A.; Ivashutenko, A. S.; Lomakina, A. A.

2015-10-01

Constant magnets are applied in such fields as electric equipment and electric generators with fixed rotor. Rare earth metal neodymium is well known as promising material. Production of magnets by sintering three elements (neodymium, iron and boron) is one the most promising methods. But there are difficulties in choosing the right temperature for sintering and further processing. Structure and properties of the product, consisted of rare earth metals, was analyzed. X-ray analysis of the resulting product and the finished constant magnet was performed. Vickers microhardness was obtained.

Rapid sintering of anisotropic, nanograined Nd-Fe-B by flash-spark plasma sintering

NASA Astrophysics Data System (ADS)

Castle, Elinor; Sheridan, Richard; Grasso, Salvatore; Walton, Allan; Reece, Mike

2016-11-01

A Spark Plasma Sintering (SPS) furnace was used to Flash-Sinter (FS) Nd-Fe-Dy-Co-B-Ga melt spun permanent magnetic material. During the 10 s "Flash" process (heating rate 2660 K min-1), sample sintering (to theoretical density) and deformation (54% height reduction) occurred. This produced texturing and significant magnetic anisotropy, comparable to conventional die-upset magnets; yet with much greater coercivities (>1600 kA m-1) due to the nanoscale characteristics of the plate-like sintered grains. These preliminary results suggest that Flash-SPS could provide a new processing route for the mass production of highly anisotropic, nanocrystalline magnetic materials with high coercivity.

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics

PubMed Central

Malič, Barbara; Koruza, Jurij; Hreščak, Jitka; Bernard, Janez; Wang, Ke; Fisher, John G.; Benčan, Andreja

2015-01-01

The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT). PMID:28793702

Comparative microstructural and corrosion development of VCrNiCoFeCu equiatomic multicomponent alloy produced by induction melting and spark plasma sintering

NASA Astrophysics Data System (ADS)

Fazakas, É.; Heczel, A.; Molnár, D.; Varga, B.; Zadorozhnyy, V.; Vida, Á.

2018-03-01

The present study focuses on the corrosion behavior of a single-phase FCC high entropy alloy (VCrNiCoFeCu) casted by two different methods: induction melting and spark plasma sintering. The corrosion resistance has been evaluated using immersion tests in 3.5% NaCl solution, the potentiodynamic polarization measurements and the results are compared how is dependent the corrosion rate as a function of the production methods. Our results show that induction melted sample is stable in salty environment. On the other hand, based on the changes of polarization curves, there must be an evolution of oxide films on the SPSed sample until reaching the stable oxide layer.

Processing of non-oxide ceramics from sol-gel methods

DOEpatents

Landingham, Richard; Reibold, Robert A.; Satcher, Joe

2014-12-12

A general procedure applied to a variety of sol-gel precursors and solvent systems for preparing and controlling homogeneous dispersions of very small particles within each other. Fine homogenous dispersions processed at elevated temperatures and controlled atmospheres make a ceramic powder to be consolidated into a component by standard commercial means: sinter, hot press, hot isostatic pressing (HIP), hot/cold extrusion, spark plasma sinter (SPS), etc.

Spark plasma sintering and porosity studies of uranium nitride

NASA Astrophysics Data System (ADS)

Johnson, Kyle D.; Wallenius, Janne; Jolkkonen, Mikael; Claisse, Antoine

2016-05-01

In this study, a number of samples of UN sintered by the SPS method have been fabricated, and highly pure samples ranging in density from 68% to 99.8%TD - corresponding to an absolute density of 14.25 g/cm3 out of a theoretical density of 14.28 g/cm3 - have been fabricated. By careful adjustment of the sintering parameters of temperature and applied pressure, the production of pellets of specific porosity may now be achieved between these ranges. The pore closure behaviour of the material has also been documented and compared to previous studies of similar materials, which demonstrates that full pore closure using these methods occurs near 97.5% of relative density.

Mechanical and microstructural characterization of W–Cu FGM fabricated by one-step sintering method through PM route

NASA Astrophysics Data System (ADS)

Gupta, Rajat; Kumar, Rohit; Chaubey, A. K.; Kanpara, Shailesh; Khirwadkar, S. S.

2018-03-01

Five layer W-Cu functionally graded material (FGM) for components in nuclear fusion application was fabricated by a one-step resistance sintering process, known as spark plasma sintering (SPS). In this study effect of sintering temperature (Ts) on physical, mechanical and surface property was investigated. Detailed microstructural study revealed that the graded structure of the composite layers with varying composition from 0 to 100 wt% W and Cu in opposite directions could be well densified after the SPS process. It also indicates that the fine microstructure within functionally graded layers can be maintained because of short sintering time. The sample sintered at 1050°C shows more than 90% theoretical density, hardness greater than 239±5 Hv and excellent surface scratch resistance. The result demonstrates that SPS is promising and more suitable process for fabrication of W-Cu FGM.

Preparation of Ti3Al intermetallic compound by spark plasma sintering

NASA Astrophysics Data System (ADS)

Ito, Tsutomu; Fukui, Takahiro

2018-04-01

Sintered compacts of single phase Ti3Al intermetallic compound, which have excellent potential as refractory materials, were prepared by spark plasma sintering (SPS). A raw powder of Ti3Al intermetallic compound with an average powder diameter of 176 ± 56 μm was used in this study; this large powder diameter is disadvantageous for sintering because of the small surface area. The samples were prepared at sintering temperatures (Ts) of 1088, 1203, and 1323 K, sintering stresses (σs) of 16, 32, and 48 MPa, and a sintering time (ts) of 10 min. The calculated relative densities based on the apparent density of Ti3Al provided by the supplier were approximately 100% under all sintering conditions. From the experimental results, it was evident that SPS is an effective technique for dense sintering of Ti3Al intermetallic compounds in a short time interval. In this report, the sintering characteristics of Ti3Al intermetallic compacts are briefly discussed and compared with those of pure titanium compacts.

Al2O3-TiC Composite Prepared by Spark Plasma Sintering Process: Evaluation of Mechanical and Tribological Properties

NASA Astrophysics Data System (ADS)

Kumar, Rohit; Chaubey, A. K.; Bathula, Sivaiah; Prashanth, K. G.; Dhar, Ajay

2018-03-01

Al2O3-10TiC composites were synthesized by spark plasma sintering (SPS) process. Microstructural and mechanical properties of the composite reveal homogeneous distribution of the fine TiC particles in the matrix. The samples were produced with different sintering temperature, and it shows that the hardness and density gradually increases with increasing sintering temperature. Abrasion wear test result reveals that the composite sintered at 1500 °C shows high abrasion resistance (wt. loss 0.016 g) and the lowest abrasion resistance was observed for the composite sample sintered at 1100 °C (wt. loss 1.459 g). The profilometry surface roughness study shows that sample sintered at 1100 °C shows maximum roughness ( R a = 6.53 µm) compared to the sample sintered at 1500 °C ( R a = 0.66 µm) corroborating the abrasion wear test results.

Modeling the mechanical behavior of ceramic and heterophase structures manufactured using selective laser sintering and spark plasma sintering

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir A.; Skripnyak, Evgeniya G.; Skripnyak, Vladimir V.; Vaganova, Irina K.

A model for predicting mechanical properties of ultra-high temperature ceramics and composites manufactured by selective laser sintering (SLS) and spark plasma sintering (SPS) under shock loading is presented. The model takes into account the porous structure, the specific volume and average sizes of phases, and the temperature of sintering. Residual stresses in ceramic composites reinforced with particles of refractory borides, carbides and nitrides after SLS or SPS were calculated. It is shown that the spall strength of diboride-zirconium matrix composites can be increased by the decreasing of porosity and the introduction of inclusions of specially selected refractory strengthening phases.

Large-Scale Surfactant-Free Synthesis of p-Type SnTe Nanoparticles for Thermoelectric Applications

PubMed Central

Han, Guang; Zhang, Ruizhi; Popuri, Srinivas R.; Greer, Heather F.; Reece, Michael J.; Bos, Jan-Willem G.; Zhou, Wuzong; Knox, Andrew R.; Gregory, Duncan H.

2017-01-01

A facile one-pot aqueous solution method has been developed for the fast and straightforward synthesis of SnTe nanoparticles in more than ten gram quantities per batch. The synthesis involves boiling an alkaline Na2SnO2 solution and a NaHTe solution for short time scales, in which the NaOH concentration and reaction duration play vital roles in controlling the phase purity and particle size, respectively. Spark plasma sintering of the SnTe nanoparticles produces nanostructured compacts that have a comparable thermoelectric performance to bulk counterparts synthesised by more time- and energy-intensive methods. This approach, combining an energy-efficient, surfactant-free solution synthesis with spark plasma sintering, provides a simple, rapid, and inexpensive route to p-type SnTe nanostructured materials. PMID:28772593

Taguchi Analysis on the Effect of Process Parameters on Densification During Spark Plasma Sintering of HfB2-20SiC (Preprint)

DTIC Science & Technology

2011-11-01

30 kN pressure and heating rate of 100 K/min. Introduction Boride , carbides and nitrides of the group IVB and VB transition metals are considered...10. Sciti D., Silvestroni L., Nygren M. Spark plasma sintering of Zr- and Hf- borides with decreasing amounts of MoSi2 as sintering aid Journal of

Mechanisms of Superplastic Deformation of Nanocrystalline Silicon Carbide Ceramics

DTIC Science & Technology

2012-08-01

These included the following: standard hot isostatic pressing (HIP), spark plasma sintering , ultra-high pressure HIP, and a multianvil pressure...96.8 2270 Multianvil apparatus 1200 3000 94.8 1130 Note: SPS = spark plasma sintering . 2 Figure 1. Ultra-high pressure HIP; 1600 °C, 980...strain rate sensitivity and flow stress. 15. SUBJECT TERMS silicon carbide, nanostructure, sintering , hot isostatic pressing, hardness 16. SECURITY

Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr0.95Gd0.05)TiO3 ceramics

NASA Astrophysics Data System (ADS)

Li, Liang-Liang; Qin, Xiao-Ying; Liu, Yong-Fei; Liu, Quan-Zhen

2015-06-01

(Sr0.95Gd0.05)TiO3 (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol-gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ˜ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ˜ 0.24 is achieved at ˜ 1000 K for the samples sintered at 1648 K and 1748 K, which was ˜ 71% larger than that (0.14 at ˜ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174292, 51101150, and 11374306).

Spark plasma sintering of pure and doped tungsten as plasma facing material

NASA Astrophysics Data System (ADS)

Autissier, E.; Richou, M.; Minier, L.; Naimi, F.; Pintsuk, G.; Bernard, F.

2014-04-01

In the current water cooled divertor concept, tungsten is an armour material and CuCrZr is a structural material. In this work, a fabrication route via a powder metallurgy process such as spark plasma sintering is proposed to fully control the microstructure of W and W composites. The effect of chemical composition (additives) and the powder grain size was investigated. To reduce the sintering temperature, W powders doped with a nano-oxide dispersion of Y2O3 are used. Consequently, the sintering temperature for W-oxide dispersed strengthened (1800 °C) is lower than for pure W powder. Edge localized mode tests were performed on pure W and compared to other preparation techniques and showed promising results.

Degradation resistance of 3Y-TZP ceramics sintered using spark plasma sintering

NASA Astrophysics Data System (ADS)

Chintapalli, R.; Marro, F. G.; Valle, J. A.; Yan, H.; Reece, M. J.; Anglada, M.

2009-09-01

Commercially available tetragonal zirconia powder doped with 3 mol% of yttria has been sintered using spark plasma sintering (SPS) and has been investigated for its resistance to hydrothermal degradation. Samples were sintered at 1100, 1150, 1175 and 1600 °C at constant pressure of 100 MPa and soaking for 5 minutes, and the grain sizes obtained were 65, 90, 120 and 800 nm, respectively. Samples sintered conventionally with a grain size of 300 nm were also compared with samples sintered using SPS. Finely polished samples were subjected to artificial degradation at 131 °C for 60 hours in vapour in auto clave under a pressure of 2 bars. The XRD studies show no phase transformation in samples with low density and small grain size (<200 nm), but significant phase transformation is seen in dense samples with larger grain size (>300 nm). Results are discussed in terms of present theories of hydrothermal degradation.

Bio-Inspired Ceramic/Carbon Composites

DTIC Science & Technology

2013-05-01

the links between CNTs and the ceramic when the CNT is previously synthesized. Spark Plasma Sintering of SiC/CNTs composites Composites containing...5% of CVD MWCNTs and 95% of SiC nanoparticles (size  100nm) were prepared by Spark Plasma Sintering under different conditions. Table I shows the...additives when necessary (additives were added to help to improve the sintering increasing the density values), and the mixture continuously stirred until

Flash sintering of ceramic materials

NASA Astrophysics Data System (ADS)

Dancer, C. E. J.

2016-10-01

During flash sintering, ceramic materials can sinter to high density in a matter of seconds while subjected to electric field and elevated temperature. This process, which occurs at lower furnace temperatures and in shorter times than both conventional ceramic sintering and field-assisted methods such as spark plasma sintering, has the potential to radically reduce the power consumption required for the densification of ceramic materials. This paper reviews the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sintering. The flash sintering process is described for oxides of zirconium, yttrium, aluminium, tin, zinc, and titanium; silicon and boron carbide, zirconium diboride, materials for solid oxide fuel applications, ferroelectric materials, and composite materials. While experimental observations have been made on a wide range of materials, understanding of the underlying mechanisms responsible for the onset and latter stages of flash sintering is still elusive. Elements of the proposed theories to explain the observed behaviour include extensive Joule heating throughout the material causing thermal runaway, arrested by the current limitation in the power supply, and the formation of defect avalanches which rapidly and dramatically increase the sample conductivity. Undoubtedly, the flash sintering process is affected by the electric field strength, furnace temperature and current density limit, but also by microstructural features such as the presence of second phase particles or dopants and the particle size in the starting material. While further experimental work and modelling is still required to attain a full understanding capable of predicting the success of the flash sintering process in different materials, the technique non-etheless holds great potential for exceptional control of the ceramic sintering process.

Influence of Sintering Temperature on Hardness and Wear Properties of TiN Nano Reinforced SAF 2205

NASA Astrophysics Data System (ADS)

Oke, S. R.; Ige, O. O.; E Falodun, O.; Obadele, B. A.; Mphalele, M. R.; Olubambi, P. A.

2017-12-01

Conventional duplex stainless steel degrade in wear and mechanical properties at high temperature. Attempts have been made by researchers to solve this problems leading to the dispersion of second phase particles into duplex matrix. Powder metallurgy methods have been used to fabricate dispersion strengthened steels with a challenge of obtaining fully dense composite and grain growth. This could be resolved by appropriate selection of sintering parameters especially temperature. In this research, spark plasma sintering was utilized to fabricate nanostructured duplex stainless steel grade SAF 2205 with 5 wt.% nano TiN addition at different temperatures ranging from 1000 °C to 1200 °C. The effect of sintering temperature on the microstructure, density, hardness and wear of the samples was investigated. The results showed that the densities and grain sizes of the sintered nanocomposites increased with increasing the sintering temperature. The microstructures reveal ferrite and austenite grains with fine precipitates within the ferrite grains. The study of the hardness and wear behaviors, of the samples indicated that the optimum properties were obtained for the sintering temperature of 1150 °C.

Data on the influence of cold isostatic pre-compaction on mechanical properties of polycrystalline nickel sintered using Spark Plasma Sintering.

PubMed

Dutel, Guy-Daniel; Langlois, Patrick; Tingaud, David; Vrel, Dominique; Dirras, Guy

2017-04-01

Data regarding bulk polycrystalline nickel samples obtained by powder metallurgy using Spark Plasma Sintering (SPS) are presented, with a special emphasis on the influence of a cold isostatic pre-compaction on the resulting morphologies and subsequent mechanical properties. Three types of initial powders are used, nanometric powders, micrometric powders and a mixture of the formers. For each type of powder, the SPS cycle has been optimized for the powders without pre-compaction and the same cycle has been used to also sinter pre-compacted powders.

Comparison of Reactive and Non-Reactive Spark Plasma Sintering Routes for the Fabrication of Monolithic and Composite Ultra High Temperature Ceramics (UHTC) Materials

PubMed Central

Orrù, Roberto; Cao, Giacomo

2013-01-01

A wider utilization of ultra high temperature ceramics (UHTC) materials strongly depends on the availability of efficient techniques for their fabrication as dense bodies. Based on recent results reported in the literature, it is possible to state that Spark Plasma Sintering (SPS) technology offers a useful contribution in this direction. Along these lines, the use of two different SPS-based processing routes for the preparation of massive UHTCs is examined in this work. One method, the so-called reactive SPS (R-SPS), consists of the synthesis and densification of the material in a single step. Alternatively, the ceramic powders are first synthesized by Self-propagating High-temperature Synthesis (SHS) and then sintered by SPS. The obtained results evidenced that R-SPS method is preferable for the preparation of dense monolithic products, while the sintering of SHS powders requires relatively milder conditions when considering binary composites. The different kinetic mechanisms involved during R-SPS of the monolithic and composite systems, i.e., combustion-like or gradual solid-diffusion, respectively, provides a possible explanation. An important role is also played by the SHS process, particularly for the preparation of composite powders, since stronger interfaces are established between the ceramic constituents formed in situ, thus favoring diffusion processes during the subsequent SPS step. PMID:28809229

Microstructures and Hardness of the High Chromium Oxide Dispersion Strengthened Alloy Fe-25Cr-Y2O3Sintered by the Arc Plasma Sintering (APS)

NASA Astrophysics Data System (ADS)

Bandriyana; Dimyati, Arbi; Sujatno, Agus; Salam, Rohmad; Sumaryo; Untoro, Pudji; Suharno, Bambang

2018-03-01

High chromium ODS alloy has been developed for application as structural material in high temperature nuclear reactor. In the present study, Fe-25Cr-Y2O3 with dispersed 0.5 wt.% Ytria (Y2O3) were synthesized and characterized by means of various techniques as a function of milling time 1, 2 and 3 hours. The alloy synthesis was carried out by the Mechanical Alloying (MA) process and subsequent sintering by means the new plasma technique using the APS apparatus. Scaning Electron Microscopy (SEM) and X-ray diffraction (XRD) were conducted for morphology and phase analysis. Evaluation of the mechanical properties was studied based on the Vickers hardness measurement. SEM examination revealed that the sample after sintering by APS method at different milling duration exhibited some particle aglomeration and homogenized oxide dispersion that obviously strengthened the alloy. The XRD test, however, proved the formation of the main phase Fe-Cr. The alloy showed exceptionally high hardness of 193 VHR which is mainly due to the grain refining that increase by the increasing of the milling time.

Enhanced thermal conductivity of uranium dioxide-silicon carbide composite fuel pellets prepared by Spark Plasma Sintering (SPS)

NASA Astrophysics Data System (ADS)

Yeo, S.; Mckenna, E.; Baney, R.; Subhash, G.; Tulenko, J.

2013-02-01

Uranium dioxide (UO2)-10 vol% silicon carbide (SiC) composite fuel pellets were produced by oxidative sintering and Spark Plasma Sintering (SPS) at a range of temperatures from 1400 to 1600 °C. Both SiC whiskers and SiC powder particles were utilized. Oxidative sintering was employed over 4 h and the SPS sintering was employed only for 5 min at the highest hold temperature. It was noted that composite pellets sintered by SPS process revealed smaller grain size, reduced formation of chemical products, higher density, and enhanced interfacial contact compared to the pellets made by oxidative sintering. For given volume of SiC, the pellets with powder particles yielded a smaller grain size than pellets with SiC whiskers. Finally thermal conductivity measurements at 100 °C, 500 °C, and 900 °C revealed that SPS sintered UO2-SiC composites exhibited an increase of up to 62% in thermal conductivity compared to UO2 pellets, while the oxidative sintered composite pellets revealed significantly inferior thermal conductivity values. The current study points to the improved processing capabilities of SPS compared to oxidative sintering of UO2-SiC composites.

Processing of uranium dioxide nuclear fuel pellets using spark plasma sintering

NASA Astrophysics Data System (ADS)

Ge, Lihao

Uranium dioxide (UO2), one of the most common nuclear fuels, has been applied in most of the nuclear plant these days for electricity generation. The main objective of this research is to introduce a novel method for UO 2 processing using spark plasma sintering technique (SPS). Firstly, an investigation into the influence of processing parameters on densification of UO2 powder during SPS is presented. A broad range of sintering temperatures, hold time and heating rates have been systematically varied to investigate their influence on the sintered pellet densification process. The results revealed that up to 96% theoretical density (TD) pellets can be obtained at a sintering temperature of 1050 °C for 30s hold time and a total run time of only 10 minutes. A systematic study is performed by varying the sintering temperature between 750°C to 1450°C and hold time between 0.5 min to 20 min to obtain UO2 pellets with a range of densities and grain sizes. The microstructure development in terms of grain size, density and porosity distribution is investigated. The Oxygen/Uranium (O/U) ratio of the resulting pellets is found to decrease after SPS. The mechanical and thermal properties of UO2 are evaluated. For comparable density and grain size, Vickers hardness and Young's modulus are in agreement with the literature value. The thermal conductivity of UO2 increases with the density but the grain size in the investigated range has no significant influence. Overall, the mechanical and thermal properties of UO2 are comparable with the one made using conventional sintering methods. Lastly, the influence of chromium dioxide (Cr2O3) and zirconium diboride (ZrB2) on the grain size of doped UO 2 fuel pellet is performed to investigate the feasibility of producing large-grain-size nuclear fuel using SPS. The benefits of using SPS over the conventional sintering of UO2 are summarized. The future work of designing macro-porous UO2 pellet and thorium dioxide (ThO 2) cored UO2 pellet is also proposed.

Phenomenological analysis of densification mechanism during spark plasma sintering of MgAl2O4

NASA Astrophysics Data System (ADS)

Bernard-Granger, Guillaume; Benameur, Nassira; Addad, Ahmed; Nygren, Mats; Guizard, Christian; Deville, Sylvain

2009-05-01

Spark plasma sintering (SPS) of MgAl2O4 powder was investigated at temperatures between 1200 and 1300{\\deg}C. A significant grain growth was observed during densification. The densification rate always exhibits at least one strong minimum, and resumes after an incubation period. Transmission electron microscopy investigations performed on sintered samples never revealed extensive dislocation activity in the elemental grains. The densification mechanism involved during SPS was determined by anisothermal (investigation of the heating stage of a SPS run) and isothermal methods (investigation at given soak temperatures). Grain-boundary sliding, accommodated by an in-series {interface-reaction/lattice diffusion of the O$^2$-anions} mechanism controlled by the interface-reaction step, governs densification. The zero-densification-rate period, detected for all soak temperatures, arise from the difficulty of annealing vacancies, necessary for the densification to proceed. The detection of atomic ledges at grain boundaries and the modification of the stoichiometry of spinel during SPS could be related to the difficulty to anneal vacancies at temperature soaks.

The Development of a Ti-6Al-4V Alloy via Oxygen Solid Solution Strengthening for Aerospace and Defense Applications

DTIC Science & Technology

2013-03-01

latter strategy. Mixtures of titanium powders and TiO2 particles were employed as starting materials and consolidated by spark - plasma sintering and...were consolidated in a carbon container installed in the spark - plasma sintering (SPS) equipment under vacuum condition (ɞ Pa) at a temperature of...evaluation of tensile properties of the wrought pure titanium materials consolidated by sintering and hot extrusion process, a theoretical approach using

Utilizing Interfaces for Nano- and Micro-scale Control of Thermal Conductivity

DTIC Science & Technology

2015-08-17

performance of these promising materials by 50%. Ballmilling and spark plasma sintering (SPS) processes were investigated to try to lower the thermal...samples fabricated through the spark plasma sintering ”, Mater Renew Sustain Energy, 3, 31-1 31-6 (2014). DOI: 10.1007/s40243-014-0031-8 9. O. Sologub...for doping of foreign elements (therefore no migration problems) is very striking. In further development, addition of Al as a sintering element was

Development of a TiAl Alloy by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Couret, Alain; Voisin, Thomas; Thomas, Marc; Monchoux, Jean-Philippe

2017-12-01

Spark plasma sintering (SPS) is a consolidated powder metallurgy process for which the powder sintering is achieved through an applied electric current. The present article aims to describe the method we employed to develop a TiAl-based alloy adjusted for this SPS process. Owing to its enhanced mechanical properties, this alloy was found to fully match the industrial specifications for the aeronautic and automotive industries, which require a high strength at high temperature and a reasonably good ductility at room temperature. A step-by-step method was followed for this alloy development. Starting from a basic study on the as-SPSed GE alloy (Ti-48Al-2Cr-2Nb) in which the influence of the microstructure was studied, the microstructure-alloy composition relationships were then investigated to increase the mechanical properties. As a result of this study, we concluded that tungsten had to be the major alloying element to improve the resistance at high temperature and a careful addition of boron would serve the properties at room temperature. Thus, we developed the IRIS alloy (Ti-48Al-2W-0.08B). Its microstructure and mechanical properties are described here.

Mechanical Testing of Ultra-High Temperature Ceramics at 1500 C in Air - Development of an Experimental Facility and Test Method

DTIC Science & Technology

2015-03-26

SiC. TEM micrograph courtesy of R. S . Hay (AFRL/RXCC). ...................33 Fig. 5. Schematic of HfB2-based UHTC test specimen...the early work performed by the U. S . Air force and NASA was the identification of hafnium diboride (HfB2) and zirconium diboride (ZrB2) as good high...sintering, reactive routes, and spark plasma sintering. ~ 14 ~ Because diborides exhibit strong covalent bonding and low self-diffusion, high

Sintering behavior of Lanthana-bearing nanostructured ferritic steel consolidated via spark plasma sintering

DOE PAGES

Pasebani, Somayeh; Charit, Indrajit; Butt, Darryl P.; ...

2015-08-03

Elemental powder mixture of Fe–14Cr–1Ti–0.3Mo–0.5La 2O 3 (wt%) composition is mechanically alloyed for different milling durations (5, 10 and 20 h) and subsequently consolidated via spark plasma sintering under vacuum at 950 °C for 7 min. The effects of milling time on the densification behavior and density/microhardness are studied. The sintering activation energy is found to be close to that of grain boundary diffusion. The bimodal grain structure created in the milled and sintered material is found to be a result of milling and not of sintering alone. The oxide particle diameter varies between 2 and 70 nm. As amore » result, faceted precipitates smaller than 10 nm in diameter are found to be mostly La–Ti–Cr-enriched complex oxides that restrict further recrystallization and related phenomena.« less

Welding of titanium and nickel alloy by combination of explosive welding and spark plasma sintering technologies

NASA Astrophysics Data System (ADS)

Malyutina, Yu. N.; Bataev, A. A.; Mali, V. I.; Anisimov, A. G.; Shevtsova, L. I.

2015-10-01

A possibility of titanium and nickel-based alloys composite materials formation using combination of explosive welding and spark plasma sintering technologies was demonstrated in the current research. An employment of interlayer consisting of copper and tantalum thin plates makes possible to eliminate a contact between metallurgical incompatible titanium and nickel that are susceptible to intermetallic compounds formation during their interaction. By the following spark plasma sintering process the bonding has been received between titanium and titanium alloy VT20 through the thin powder layer of pure titanium that is distinguished by low defectiveness and fine dispersive structure.

Welding of titanium and nickel alloy by combination of explosive welding and spark plasma sintering technologies

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

Malyutina, Yu. N., E-mail: iuliiamaliutina@gmail.com; Bataev, A. A., E-mail: bataev@adm.nstu.ru; Shevtsova, L. I., E-mail: edeliya2010@mail.ru

A possibility of titanium and nickel-based alloys composite materials formation using combination of explosive welding and spark plasma sintering technologies was demonstrated in the current research. An employment of interlayer consisting of copper and tantalum thin plates makes possible to eliminate a contact between metallurgical incompatible titanium and nickel that are susceptible to intermetallic compounds formation during their interaction. By the following spark plasma sintering process the bonding has been received between titanium and titanium alloy VT20 through the thin powder layer of pure titanium that is distinguished by low defectiveness and fine dispersive structure.

Effect of heat treatment on the optical properties of perovskite BaZr0.5Ce0.3Y0.2O3-δ ceramic prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Xing, Bohang; Cheng, Zhi; Wang, Cao; Zhao, Zhe

2017-09-01

The effect of heat treatment on the in-line transmittance of BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) ceramics prepared by spark plasma sintering method was investigated. The loss of Ba in transparent BZCY532 ceramics is the key reason for the loss of transmittance during the annealing process. This problem can be effectively alleviated by using a powder bed of BZCY532. Heat treatment atmospheres, wet air and dry air, were also found to be critical for obtaining high quality transparent ceramics. A highly transparent BZCY532 ceramic with the in-line transmittance (Tin) of 71.4% at 2000 nm can be obtained by using SPS method followed by an annealing in powder bed at 1500 °C in wet air.

Matrix Structure Evolution and Nanoreinforcement Distribution in Mechanically Milled and Spark Plasma Sintered Al-SiC Nanocomposites.

PubMed

Saheb, Nouari; Aliyu, Ismaila Kayode; Hassan, Syed Fida; Al-Aqeeli, Nasser

2014-09-19

Development of homogenous metal matrix nanocomposites with uniform distribution of nanoreinforcement, preserved matrix nanostructure features, and improved properties, was possible by means of innovative processing techniques. In this work, Al-SiC nanocomposites were synthesized by mechanical milling and consolidated through spark plasma sintering. Field Emission Scanning Electron Microscope (FE-SEM) with Energy Dispersive X-ray Spectroscopy (EDS) facility was used for the characterization of the extent of SiC particles' distribution in the mechanically milled powders and spark plasma sintered samples. The change of the matrix crystallite size and lattice strain during milling and sintering was followed through X-ray diffraction (XRD). The density and hardness of the developed materials were evaluated as function of SiC content at fixed sintering conditions using a densimeter and a digital microhardness tester, respectively. It was found that milling for 24 h led to uniform distribution of SiC nanoreinforcement, reduced particle size and crystallite size of the aluminum matrix, and increased lattice strain. The presence and amount of SiC reinforcement enhanced the milling effect. The uniform distribution of SiC achieved by mechanical milling was maintained in sintered samples. Sintering led to the increase in the crystallite size of the aluminum matrix; however, it remained less than 100 nm in the composite containing 10 wt.% SiC. Density and hardness of sintered nanocomposites were reported and compared with those published in the literature.

Monoclinic β-Li2TiO3 nanocrystalline particles employing novel urea assisted solid state route: Synthesis, characterization and sintering behavior

NASA Astrophysics Data System (ADS)

Tripathi, Biranchi M.; Mohanty, Trupti; Prakash, Deep; Tyagi, A. K.; Sinha, P. K.

2017-07-01

Pure phase monoclinic nano-crystalline Li2TiO3 powder was synthesized by a novel urea assisted solid state synthesis method using readily available and economical precursors. A single phase and well crystalline Li2TiO3 powder has been obtained at slightly lower temperature (600-700 °C) and shorter duration (2 h) as compared to the conventional solid state method. The proposed method has significant advantages in comparison to other viable methods mainly in terms of phase purity, powder properties and sinterability. Analysis of chemical composition using inductively coupled plasma atomic emission spectroscopy (ICP-AES) shows no loss of lithium from Li2TiO3 in the proposed method. The emergence of monoclinic Li2TiO3 phase was confirmed by X-ray diffraction (XRD) pattern of as-synthesized powder. The crystallite size of Li2TiO3 powder was calculated to be in the range of 15-80 nm, which varied as a function of urea composition and temperature. The morphology of as-prepared Li2TiO3 powders was examined by scanning electron microscope (SEM). The effect of urea composition on phase and morphology was investigated so as to delineate the role of urea. Upon sintering at < 1000 °C temperature, the Li2TiO3 powder compact attained about 98% of the theoretical density with fine grained (grain size: 2-3 μm) microstructure. It indicates excellent sinter-ability of Li2TiO3 powder synthesized by the proposed method. The fine grained structure is desirable for better tritium breeding performance of Li2TiO3. Electrochemical impedance spectroscopy at variable temperature showed good electrical properties of Li2TiO3. The proposed method is simple, anticipated to be cost effective and convenient to realise for large scale production of phase pure nanocrystalline and having significantly enhanced sinter-ability Li2TiO3 powder.

Sintering Behavior of Nanocrystalline Silicon Carbide Using a Plasma Pressure Compaction System: Master Sintering Curve Analysis

NASA Astrophysics Data System (ADS)

Bothara, Manish G.; Atre, Sundar V.; Park, Seong-Jin; German, Randall M.; Sudarshan, T. S.; Radhakrishnan, R.

2010-12-01

Nanostructured ceramics offer significant improvements in properties over corresponding materials with larger grain sizes on the order of tens to hundreds of micrometers. Silicon carbide (SiC) samples with grain sizes on the order of 100 nm can result in improved strength, chemical resistance, thermal stability, and tailored electrical resistivity. In this study, nanocrystalline SiC was processed in a plasma pressure compaction (P2C) system at a temperature of 1973 K (1700 °C) that was much lower than the temperatures reported for other sintering techniques. Microstructure of the resulting samples was studied and the hardness and the fracture toughness were measured. The grain sizes were on the order of 700 nm, the hardness between 22 and 24 GPa, and the toughness between 5 and 6.5 MPa·m1/2. The master sintering curve (MSC) analysis was used to model the densification behavior of SiC powder sintered by the P2C method. The apparent activation energies for three different pressures of 10, 30, and 50 MPa were obtained to be 1666, 1034, and 1162 kJ/mol, respectively. Although densification occurs via diffusion, the activation energies were higher than those associated with self-diffusion in SiC (between 570 and 920 kJ/mol). A validation study of the MSC was also conducted and the variation in observed density from the density predicted by the MSC was found to range from 1 to 10 pct.

Vanadium dioxide-based materials for potential thermal switching applications

NASA Astrophysics Data System (ADS)

Jeong, Minyoung

One of the materials able to exhibit a transition from insulators to metals (IMT materials) is vanadium dioxide (VO2). Through IMT, VO2 shows a drop of resistivity of five orders of magnitude at a picosecond timescale. In this work, the feasibility of using VO2 as an efficient thermal switching device is discussed. Several synthesis methods (sol-gel, hot press and spark plasma sintering) were attempted to obtain VO2 sample in pellet form. From the X-ray diffraction results, it was found that spark plasma sintering (SPS) yielded the highest phase purity. Several sintering parameters such as temperature or sintering time were tested to determine the optimal sintering conditions. For better thermal switching behavior, high-energy ball milling was used to reduce lattice thermal conductivity (klat.) in the insulator phase. Ball-milling time was varied from 30 minutes to 2 hours. It was found that with increasing milling time, the k lat. was reduced. Thus, it was demonstrated that thermal switching behavior was most efficient with 2 hour-milling. To improve electronic thermal conductivity ( kelec.) in the metallic state, nano-sized copper particles were added to the VO2 system with a subtle amount variation ranging from 3at % to 5 at%. Results show that a composite with 5 at% Cu (copper) addition exhibited the largest increase in thermal conductivity ( k) in the metallic state. In addition to this, a basic mechanism behind IMT and some of the exemplary IMT-based applications were introduced.

Effect of Synthesis Procedure on Thermoelectric Property of SiGe Alloy

NASA Astrophysics Data System (ADS)

Li, Jing; Han, Jun; Jiang, Tao; Luo, Lili; Xiang, Yongchun

2018-05-01

SiGe thermoelectric material has been synthesized by ball milling combined with hot pressing (HP) or spark plasma sintering (SPS). Effects of ball milling time, powder to ball weight ratio and sintering method on microstructure and thermoelectric properties of SiGe are studied. The results show that longer ball milling time leads to decreased density and worse electrical properties. In the sintering process, SPS results in much larger density and better electrical properties than HP. The Si0.795Ge0.2B0.005 sample prepared by 2 h ball milling combined with SPS obtains a maximum power factor of 3.0 mW m-1 K-2 at 860 K and ZT of 0.95 at 1000 K.

Nanocrystalline Iron-Cobalt Alloys for High Saturation Indutance

DTIC Science & Technology

2016-02-24

toroid. Before fully embarking on the problem of creating the toroid’s from particles sintered by a process known as sparked plasma sintering which...allows the particles to be rapidly sintered without compromising the nano crystalline particle size, it was deemed necessary to anticipate the

Anisotropy of the ferromagnetic L10 phase in the Mn-Al-C alloys induced by high-pressure spark plasma sintering

NASA Astrophysics Data System (ADS)

Tyrman, Muriel; Ahmim, Smail; Pasko, Alexandre; Etgens, Victor; Mazaleyrat, Frédéric; Quetel-Weben, Simon; Perrière, Loïc; Guillot, Ivan

2018-05-01

The metastable τ-phase of MnAl equi-atomic compound belongs to a family of ferromagnetic alloys with L10 crystal structure. Stabilization of the phase by adding 2 at. % using manganese carbide (Mn23C6) enhances the magnetization in relation with the increase in lattice volume. It is thus a promising candidate for rare-earth-free permanent magnets. Coercivity of Mn-Al-C alloys being still weak, there is an interest to see to which extend sintering/transformation of the ɛ-phase by Spark Plasma Sintering (SPS) can increase the coercivity and the anisotropy. The structural and the magnetic properties were studied for samples sintered at 550 °C under uniaxial pressure of 100, 200, 300 and 400 MPa. Coercivity, remanence and anistotropy appears with the sintering pressure. The high pressure applied while sintering produces preferential orientation of the flake-shaped grains which influences the remanence.

Magnetic properties of ball-milled SrFe12O19 particles consolidated by Spark-Plasma Sintering

PubMed Central

Stingaciu, Marian; Topole, Martin; McGuiness, Paul; Christensen, Mogens

2015-01-01

The room-temperature magnetic properties of ball-milled strontium hexaferrite particles consolidated by spark-plasma sintering are strongly influenced by the milling time. Scanning electron microscopy revealed the ball-milled SrFe12O19 particles to have sizes varying over several hundred nanometers. X-Ray powder-diffraction studies performed on the ball-milled particles before sintering clearly demonstrate the occurrence of a pronounced amorphization process. During sintering at 950 oC, re-crystallization takes place, even for short sintering times of only 2 minutes and transformation of the amorphous phase into a secondary phase is unavoidable. The concentration of this secondary phase increases with increasing ball-milling time. The remanence and maximum magnetization values at 1T are weakly influenced, while the coercivity drops dramatically from 2340 Oe to 1100 Oe for the consolidated sample containing the largest amount of secondary phase. PMID:26369360

The Effects of Spark-Plasma Sintering (SPS) on the Microstructure and Mechanical Properties of BaTiO3/3Y-TZP Composites

PubMed Central

Li, Jing; Cui, Bencang; Wang, Huining; Lin, Yuanhua; Deng, Xuliang; Li, Ming; Nan, Cewen

2016-01-01

Composite ceramics BaTiO3/3Y-TZP containing 0 mol %, 3 mol %, 5 mol %, 7 mol %, and 10 mol % BaTiO3 have been prepared by conventional sintering and spark-plasma sintering (SPS), respectively. Analysis of the XRD patterns and Raman spectra reveal that the phase composition of t-ZrO2, m-ZrO2, and BaTiO3 has been obtained. Our results indicate that SPS can be effective for the decrease in grain size and porosity compared with conventional sintering, which results in a lower concentration of m-ZrO2 and residual stress. Therefore, the fracture toughness is enhanced by the BaTiO3 phase through the SPS technique, while the behavior was impaired by the piezoelectric second phase through conventional sintering. PMID:28773445

Spark plasma sintering of ceramic matrix composite based on alumina, reinforced by carbon nanotubes

NASA Astrophysics Data System (ADS)

Leonov, A. A.; Khasanov, A. O.; Danchenko, V. A.; Khasanov, O. L.

2017-12-01

Alumina composites reinforced with 3 vol.% multi-walled carbon nanotubes (MWCNTs) were prepared by spark plasma sintering (SPS). The influence of sintering temperature (1400-1600 °C) on the composites microstructure and mechanical properties was investigated. Microstructure observations of the composite shows that some CNTs site along alumina grains boundary, while others embed into the alumina grains and shows that CNTs bonded strongly with the alumina matrix contributing to fracture toughness and microhardness increase. MWCNTs reinforcing mechanisms including CNT pull-out and crack deflection were directly observed by scanning electron microscope (SEM). For Al2O3/CNT composite sintered at 1600 °C, fracture toughness and microhardness are 4.93 MPa·m1/2 and 23.26 GPa respectively.

Tribological Properties of Aluminium Alloy Composites Reinforced with Multi-Layer Graphene—The Influence of Spark Plasma Texturing Process

PubMed Central

Kostecki, Marek; Woźniak, Jarosław; Cygan, Tomasz; Petrus, Mateusz; Olszyna, Andrzej

2017-01-01

Self-lubricating composites are designed to obtain materials that reduce energy consumption, improve heat dissipation between moving bodies, and eliminate the need for external lubricants. The use of a solid lubricant in bulk composite material always involves a significant reduction in its mechanical properties, which is usually not an optimal solution. The growing interest in multilayer graphene (MLG), characterised by interesting properties as a component of composites, encouraged the authors to use it as an alternative solid lubricant in aluminium matrix composites instead of graphite. Aluminium alloy 6061 matrix composite reinforced with 2–15 vol % of MLG were synthesised by the spark plasma sintering process (SPS) and its modification, spark plasma texturing (SPT), involving deformation of the pre-sintered body in a larger diameter matrix. It was found that the application of the SPT method improves the density and hardness of the composites, resulting in improved tribological properties, particularly in the higher load regime. PMID:28796172

Tailored Net-Shape Powder Composites by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Khaleghi, Evan Aryan

This dissertation investigates the ability to produce net-shape and tailored composites in spark plasma sintering (SPS), with an analysis of how grain growth, densification, and mechanical properties are affected. Using alumina and four progressively anisotropic dies, we studied the impact of specimen shape on densification. We found specimen shape had an impact on overall densification, but no impact on localized properties. We expected areas of the specimen to densify differently, or have higher grain growth, based on current anisotropy in the specimen during sintering, and preliminary results indicated this, but further investigation showed this did not occur. Overall average grain size and porosity decreased as shape complexity increased. In Fe-V-C steel, we mechanical alloyed two rapidly solidified powders, and used spark sintering to retain the properties imparted during the rapid solidification. We noticed VC grains being produced during densification, which improved the final properties. We conducted spark plasma extrusion (SPE) of aluminum to understand the effect on microstructure. We found, through an analysis of the grain structure, that SPE did have a grain deformation potential, and grain size was severely decreased compared to conventional sintering. Dynamic recrystallization did not occur, due to the reduced temperatures we were able to extrude with SPS. Finally, we examined whether there were particular sintering conditions for SPS that reduced the complexity of the grain growth and porosity relationship to one similar to conventional sintering, of the form G = k G0 ε -1/. We found that although a reasonable case could be made for free sintering, as found in the literature, for hot-pressing and SPS the conditions required go against the common knowledge in grain growth and densification kinetics. We were able to fit our data very well to the model, but the correlated results do not make physical sense.

Uranium migration in spark plasma sintered W/UO2 CERMETS

NASA Astrophysics Data System (ADS)

Tucker, Dennis S.; Wu, Yaqiao; Burns, Jatuporn

2018-03-01

W/UO2 CERMET samples were sintered in a Spark Plasma Sintering (SPS) furnace at various temperature under vacuum and pressure. High Resolution Transmission Electron Microscopy (HRTEM) with Energy Dispersive Spectroscopy (EDS) was performed on the samples to determine interface structures and uranium diffusion from the UO2 particles into the tungsten matrix. Local Electrode Atom Probe (LEAP) was also performed to determine stoichiometry of the UO2 particles. It was seen that uranium diffused approximately 10-15 nm into the tungsten matrix. This is explained in terms of production of oxygen vacancies and Fick's law of diffusion.

Synthesis and characterization of a model dual-phase system using the spark plasma sintering technique

NASA Astrophysics Data System (ADS)

Teimouri, M.; Godfrey, A.

2017-07-01

Samples of a model dual-phase system, consisting of copper and AISI-420 martensitic steel have been synthesized using spark plasma sintering, with the objective of developing a microstructural analogue for dual-phase steels, in which the volume fraction and size of each phase can be controlled independently. Microstructural investigation of the samples, including fractography of samples deformed in tension until failure, show that densification is strongly temperature dependent. Samples sintered at temperatures of 900 °C or above at a pressure of 60 MPa show a density of more than 98%. The best mechanical properties, in terms of ultimate tensile strength and ductility is found in samples sintered at a temperature of 1000 °C, where a density of nearly 99% is achieved.

Effect of low-melting point phases on the microstructure and properties of spark plasma sintered and hot deformed Nd-Fe-B alloys

NASA Astrophysics Data System (ADS)

Zhang, Li; Wang, Meiyu; Yan, Xueliang; Lin, Ye; Shield, Jeffrey

2018-04-01

The effect of adding a low melting point Pr-Cu-Al alloy during spark plasma sintering of melt-spun Nd-Fe-B ribbons is investigated. Regions of coarse grains were reduced and overall grain refinement was observed after the addition of Pr68Cu25Al7, leading to an enhancement of coercivity from 12.7 kOe to 20.4 kOe. Hot deformation of the samples in the spark plasma sintering system resulted in the formation of platelet-like grains, producing crystallographic alignment and magnetic anisotropy. The hot deformation process improved the remanence and energy product but reduced the coercivity. The decrease of coercivity resulted from grain growth and aggregation of Pr and Nd elements at triple-junction phases.

Method of fabricating thin-walled articles of tungsten-nickel-iron alloy

DOEpatents

Hovis, Jr., Victor M.; Northcutt, Jr., Walter G.

1982-01-01

The present invention relates to a method for fabricating thin-walled high-density structures oftungsten-nickel-iron alloys. A powdered blend of the selected alloy constituents is plasma sprayed onto a mandrel having the desired article configuration. The sprayed deposit is removed from the mandrel and subjected to liquid phase sintering to provide the alloyed structure. The formation of the thin-walled structure by plasma spraying significantly reduces shrinkage, and cracking while increasing physical properties of the structure over that obtainable by employing previously known powder metallurgical procedures.

Method of fabricating thin-walled articles of tungsten-nickel-iron alloy

DOEpatents

Hovis, V.M. Jr.; Northcutt, W.G. Jr.

The present invention relates to a method for fabricating thin-walled high-density structures of tungsten-nickel-iron alloys. A powdered blend of the selected alloy constituents is plasma sprayed onto a mandrel having the desired article configuration. The sprayed deposit is removed from the mandrel and subjected to liquid phase sintering to provide the alloyed structure. The formation of the thin-walled structure by plasma spraying significantly reduces shrinkage, and cracking while increasing physical properties of the structure over that obtainable by employing previously known powder metallurgical procedures.

Photothermally Activated Motion and Ignition Using Aluminum Nanoparticles

DTIC Science & Technology

2013-01-17

In comparison with alternative sources such as spark ignition,19 laser igni- tion,20 plasma ignition,21 plasma -assisted combustion,22 and combustion...energy-dispersive X-ray spectroscopy measurements of motion-only and afterignition products confirm significant Al oxidation occurs through sintering ...significant Al oxidation occurs through sintering and bursting after the flash exposure. Simulations suggest local heat generation is enhanced by LSPR. The

A novel in situ synthesis of SiBCN-Zr composites prepared by a sol-gel process and spark plasma sintering.

PubMed

Miao, Yang; Yang, Zhihua; Liang, Bin; Li, Quan; Chen, Qingqing; Jia, Dechang; Cheng, Yi-Bing; Zhou, Yu

2016-08-09

In the work reported here, SiBCN amorphous powders were first prepared by a mechanical alloying technique, employing cubic silicon, graphite and hexagonal boron nitride powders as raw materials. Zirconia was then introduced via sol-gel methods. The resulting powder composite was then consolidated via SPS sintering. The SPS sintering sample was evaluated using XRD, SEM and TEM. XRD reveals a chemical transformation wherein amorphous BN(C) and ZrO2 form the primary ZrC and ZrB2 phases after SPS processing along with SiC and BN(C). Thereafter ZrC reacts with BN(C) completely to form ZrB2. The reaction starts at the temperature of 1500 °C and is complete at the temperature of 1900 °C. The fracture toughness of the sintered composites reaches 4.9 ± 0.2 MPa m(1/2) due to the presence of the laminated structure of the BN(C) phase.

Microstructural and Mechanical Characterization of Ti-12Mo-6Zr Biomaterials Fabricated by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Daoush, Walid Mohamed Rashad Mohamed; Park, Hee Sup; Inam, Fawad; Lim, Byung Kyu; Hong, Soon Hyung

2015-03-01

Ti-12Mo-6Zr/Al2O3 (titanium biomaterial) was prepared by a powder metallurgy route using Spark Plasma Sintering (SPS). Ti, Mo, and Zr powders were mixed by wet milling with different content of alumina nanoparticles (up to 5 wt pct) as an oxide dispersion strengthening phase. Composite powder mixtures were SPSed at 1273 K (1000 °C) followed by heat treatment and quenching. Composite powders, sintered materials, and heat-treated materials were examined using optical and high-resolution electronic microscopy (scanning and transmission) and X-ray diffraction to characterize particle size, surface morphology, and phase identifications for each composition. All sintered materials were evaluated by measuring density, Vickers hardness, and tensile properties. Fully dense sintered materials were produced by SPS and mechanical properties were found to be improved by subsequent heat treatment. The tensile properties as well as the hardness were increased by increasing the content of Al2O3 nanoparticles in the Ti-12Mo-6Zr matrix.

Effect of Spark-Plasma-Sintering Conditions on Tensile Properties of Aluminum Matrix Composites Reinforced with Multiwalled Carbon Nanotubes (MWCNTs)

NASA Astrophysics Data System (ADS)

Chen, B.; Imai, H.; Umeda, J.; Takahashi, M.; Kondoh, K.

2017-04-01

In this study, aluminum (Al) matrix composites containing 2 wt.% multiwalled carbon nanotubes (CNTs) were fabricated by powder metallurgy using high-energy ball milling (HEBM), spark plasma sintering (SPS), and subsequent hot extrusion. The effect of SPS conditions on the tensile properties of CNT/Al composites was investigated. The results showed that composites with well-dispersed CNTs and nearly full-density CNT/Al can be obtained. During HEBM, CNTs were shortened, inserted into welded Al powder particles, bonded to Al, and still stable without CNT-Al reaction. After consolidation, Al4C3 phases formed in composites under different sintering conditions. With the increase of sintering temperature and holding time, the strength decreased. Conversely, the ductility and toughness noticeably increased. As a result, a good balance between strength (367 MPa in ultimate tensile strength) and ductility (13% in elongation) was achieved in the as-extruded CNT/Al composite sintered at 630°C with a holding time of 300 min.

Metal-Intermetallic Laminate Ti-Al3Ti Composites Produced by Spark Plasma Sintering of Titanium and Aluminum Foils Enclosed in Titanium Shells

NASA Astrophysics Data System (ADS)

Lazurenko, Daria V.; Mali, Vyacheslav I.; Bataev, Ivan A.; Thoemmes, Alexander; Bataev, Anatoly A.; Popelukh, Albert I.; Anisimov, Alexander G.; Belousova, Natalia S.

2015-09-01

Metal-intermetallic laminate composites are considered as promising materials for application in the aerospace industry. In this study, Ti-Al3Ti composites enclosed in titanium cases were produced by reactive spark plasma sintering. Sintering was carried out at 1103 K and 1323 K (830 °C and 1050 °C) for 10 minutes. In both cases, high-quality Ti-Al3Ti composites containing thin transition layers at the interfaces were obtained. Al2Ti, AlTi, and AlTi3 intermetallic phases and a solid solution of aluminum in titanium were observed in the transition layers by scanning and transmission electron microscopy. The material sintered at 1323 K (1050 °C) had higher strength in comparison with the composite obtained at 1103 K (830 °C). However, the hardness of the intermetallic component in the sample sintered at higher temperature decreased due to the grain growth. The impact toughness values of both materials were approximately identical.

SPS-RS technique for solid-phase “in situ” synthesis of biocompatible ZrO2 porous ceramics

NASA Astrophysics Data System (ADS)

Shichalin, O. O.; Medkov, M. A.; Grishchenko, D. N.; Mayorov, V. Yu; Fedorets, A. N.; Belov, A. A.; Golub, A. V.; Gridasova, E. A.; Papynov, E. K.

2018-02-01

The prospective method of spark plasma sintering-reaction synthesis (SPS-RS) for fabrication of ceramics based on ZrO2 and biocompatible with living tissue is presented. Nanostructured ceramics has high mechanical strength (more than 400 MPa) and controlled porosity depending on specified sintering conditions. Biocompatible phases Ca10(PO4)6(OH)2 are formed “in situ” during SPS sintering of ZrO2 powder due to chemical interaction of phosphate precursors preliminary introduced into the mixture. The effective method to improve (to develop) porous structure of bioceramics obtained by SPS or SPS-RS techniques using poreforming agent (carbon black) is proposed. Suggested original SPS-RS “in situ” technique provides fabrication of new ZrO2 ceramics containing biocompatible phosphate components and possessing unique structural and mechanical characteristics. Such ceramics is indispensable for bone-ceramic implants that are able to activate processes of osteogenesis during bone tissue recovery.

The effect of lanthanum on the fabrication of ZrB{sub 2}-ZrC composites by spark plasma sintering

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

Kim, Kyoung Hun; Shim, Kwang Bo

2003-01-15

The effect of the addition of the rare earth element, lanthanum, on the sintering characteristics of ZrB{sub 2}-ZrC composites has been analyzed during a spark plasma sintering (SPS) process. Microscopic observation confirmed that lanthanum accelerated mass transport by the formation of the liquid phase between the particles induced by the spark plasma in the initial stage of the SPS process, and then these were recrystallized to form a lanthanum-containing secondary phase at the grain boundaries and at the grain boundary triple junctions. In spite of the strong covalent bonding characteristics of the ZrB{sub 2}-ZrC composite there are many well-developed dislocationmore » structures observed. The fracture toughness of the lanthanum-containing ZrB{sub 2}-ZrC is about 2.56 MPa m{sup 1/2}, which is comparable to that of the pure composite. Therefore, it is concluded that lanthanum is very effective as a sintering aid for the ZrB{sub 2}-ZrC composite without any degradation of the mechanical properties.« less

Method for preparing thin-walled ceramic articles of configuration

DOEpatents

Holcombe, C.E.; Powell, G.L.

1975-11-01

A method for preparing a hollow thin-walled ceramic product is described. Ceramic powder is plasma-sprayed onto a concave surface of a substrate having a coefficient of thermal expansion less than that of the ceramic. The coated substrate is heated to sinter the ceramic and then cooled to effect a separation of the ceramic product from the substrate. (auth)

Surface martensitization of Carbon steel using Arc Plasma Sintering

NASA Astrophysics Data System (ADS)

Wahyudi, Haris; Dimyati, Arbi; Sebayang, Darwin

2018-03-01

In this paper new technology of surface structure modification of steel by short plasma exposure in Arc Plasma Sintering (APS) device is presented. APS is an apparatus working based on plasma generated by DC pulsed current originally used for synthesizing materials via sintering and melting. Plasma exposure in APS was applied into the specimens for 1 and 3 seconds which generate temperature approximately about 1300-1500°C. The SUP9, pearlitic carbon steel samples were used. The hardness, hardening depth and microstructure of the specimens have been investigated by Vickers micro hardness test and Scanning Electron Microscopy (SEM) supported by Energy Dispersive X-Ray Spectroscopy (EDX). The results have showed that the mechanical property was significantly improved due to the formation of single martensitic structures as identified by SEM. The hardness of treated surface evaluated by Vickers hardness test showed significant improvement nearly three time from 190 VHN before to 524 VHN after treatment. Furthermore, EDX confirmed that the formation of martensite layer occurred without altering its composition. The APS also produced uniform hardened layer up to 250 μm. The experiment has demonstrated that arc plasma process was successfully improved the mechanical properties of steel in relatively very short time.

Interface structure and properties of CNTs/Cu composites fabricated by electroless deposition and spark plasma sintering

NASA Astrophysics Data System (ADS)

Wang, Hu; Zhang, Zhao-Hui; Hu, Zheng-Yang; Song, Qi; Yin, Shi-Pan

2018-01-01

In this paper, we fabricated a novel copper matrix composites reinforced by carbon nanotubes (CNTs) using electroless deposition (ED) and spark plasma sintering technique. Microstructure, mechanical, electric conductivity, and thermal properties of the CNTs/Cu composites were investigated. The results show that a favorable interface containing C-O and O-Cu bond was formed between CNTs and matrix when the CNTs were coated with nano-Cu by ED method. Thus, we accomplished the uniformly dispersed CNTs in the CNTs/Cu powders and compacted composites, which eventually leads to the enhancement of the mechanical properties of the CNTs/Cu composites in the macro-scale environment. However, the interface structure can hinder the movement of carriers and free electrons and increase the interface thermal resistance, which leads to modest decrease of electrical and thermal conductivity of the CNTs/Cu composites.

Thermoelectric and mechanical properties of spark plasma sintered Cu3SbSe3 and Cu3SbSe4: Promising thermoelectric materials

NASA Astrophysics Data System (ADS)

Tyagi, Kriti; Gahtori, Bhasker; Bathula, Sivaiah; Toutam, Vijaykumar; Sharma, Sakshi; Singh, Niraj Kumar; Dhar, Ajay

2014-12-01

We report the synthesis of thermoelectric compounds, Cu3SbSe3 and Cu3SbSe4, employing the conventional fusion method followed by spark plasma sintering. Their thermoelectric properties indicated that despite its higher thermal conductivity, Cu3SbSe4 exhibited a much larger value of thermoelectric figure-of-merit as compared to Cu3SbSe3, which is primarily due to its higher electrical conductivity. The thermoelectric compatibility factor of Cu3SbSe4 was found to be ˜1.2 as compared to 0.2 V-1 for Cu3SbSe3 at 550 K. The results of the mechanical properties of these two compounds indicated that their microhardness and fracture toughness values were far superior to the other competing state-of-the-art thermoelectric materials.

Spark plasma sintering of highly dense fine-grained mineral aggregates

NASA Astrophysics Data System (ADS)

Koizumi, S.; Suzuki, T. S.; Sakka, Y.; Hiraga, T.

2017-12-01

To obtain highly dense and fine-grained mineral aggregates, which are suitable for laboratory measurements of their physical and chemical properties, we applied spark plasma sintering (SPS) to synthetic mineral powders and powders originated from naturally derived crystals. SPS is an emerging consolidation technique which has been applied to various metals and ceramics and rarely to geomaterials (e.g., Guignard et al., 2011). The technique uses spark plasma created by a pulse direct current during heat treatment of powders in a graphite die. It has been found that the technique provides better densification with little grain growth during sintering compared to a conventional sintering technique in many materials. To obtain ideal highly dense fine-grained materials, it is essential to prepare starting powders suitable for the sintering and also to find appropriate sintering conditions of applied uniaxial pressures, pulsed current patterns and heating rates. We prepared synthetic mineral powers through solid state reaction of source powders at high temperature well developed by our group (Koizumi et al. 2010). We also used jet milling at wet condition and subsequent elutriation to prepare olivine powders with sub-micron particle size and equiaxed particle shape. At heating rate of ≦10°C/min and an achievement of highest temperature of 1150°C, Fe-free olivine aggregate with average grain size of 200 nm with porosity of 0.003% was obtained. We also could obtain olivine aggregate, which was sintered from powders of Horoman peridotite, with average grain size of 500 nm and porosity of 0.2%. We will show results of other minerals including major rock forming minerals of the Earth's crust.

Toward Better Personal Ballistic Protection

DTIC Science & Technology

2014-03-04

nanotube-reinforced zirconia-toughened alumina composites prepared by spark plasma sintering , Carbon, Vol 50, Iss 2 (2012), 706-717. [4] Bolduc M...attempt to optimize mechanical properties. The processing approaches investigated were pressureless sintering , hot pressing and hot isostatic...pressing (CIP) and pressureless sintering (PS). Test samples were made with high purity commercially available ceramic powder (over 99.5% for Al2O3). For

On the Role of the Electrical Field in Spark Plasma Sintering of UO2+x

PubMed Central

Tyrpekl, Vaclav; Naji, Mohamed; Holzhäuser, Michael; Freis, Daniel; Prieur, Damien; Martin, Philippe; Cremer, Bert; Murray-Farthing, Mairead; Cologna, Marco

2017-01-01

The electric field has a large effect on the stoichiometry and grain growth of UO2+x during Spark Plasma Sintering. UO2+x is gradually reduced to UO2.00 as a function of sintering temperature and time. A gradient in the oxidation state within the pellets is observed in intermediate conditions. The shape of the gradient depends unequivocally on the direction of the electrical field. The positive surface of the pellet shows a higher oxidation state compared to the negative one. An area with larger grain size is found close to the positive electrode, but not in contact with it. We interpret these findings with the redistribution of defects under an electric field, which affect the stoichiometry of UO2+x and thus the cation diffusivity. The results bear implications for understanding the electric field assisted sintering of UO2 and non-stoichiometric oxides in general. PMID:28422164

On the Role of the Electrical Field in Spark Plasma Sintering of UO2+x

NASA Astrophysics Data System (ADS)

Tyrpekl, Vaclav; Naji, Mohamed; Holzhäuser, Michael; Freis, Daniel; Prieur, Damien; Martin, Philippe; Cremer, Bert; Murray-Farthing, Mairead; Cologna, Marco

2017-04-01

The electric field has a large effect on the stoichiometry and grain growth of UO2+x during Spark Plasma Sintering. UO2+x is gradually reduced to UO2.00 as a function of sintering temperature and time. A gradient in the oxidation state within the pellets is observed in intermediate conditions. The shape of the gradient depends unequivocally on the direction of the electrical field. The positive surface of the pellet shows a higher oxidation state compared to the negative one. An area with larger grain size is found close to the positive electrode, but not in contact with it. We interpret these findings with the redistribution of defects under an electric field, which affect the stoichiometry of UO2+x and thus the cation diffusivity. The results bear implications for understanding the electric field assisted sintering of UO2 and non-stoichiometric oxides in general.

Thermoelectric properties of a doped LaNiO3 perovskite system prepared using a spark-plasma sintering process

NASA Astrophysics Data System (ADS)

Tak, Jang-Yeul; Choi, Soon-Mok; Seo, Won-Seon; Cho, Hyung Koun

2013-07-01

Both perovskites LaNiO3 and LaCuO3 have a limitation associated with phase transitions for high-temperature thermoelectric applications. The optimized conditions were investigated to obtain the LaNi1- x Cu x O3- δ perovskite single phase showing a Cu-doping effect into Ni sites against unintended deoxidized phases. Three advantages of synergetic effects due to the simultaneous presence of nickel and copper were investigated: a low melting temperature of CuO as compared to that of NiO, the absence of intermediated deoxidized phases in the LaCuO3 system, and the Cu doping effect, which suppresses the formation of intermediate secondary phases. A solid solution was also fabricated using a spark-plasma sintering (SPS) process for the purpose of sintering LaNi1- x Cu x O3- δ compositions at a low sintering temperature.

Effects of loading modes on densification efficiency of spark plasma sintering: sample study of zirconium carbide consolidation

NASA Astrophysics Data System (ADS)

Wei, Xialu; Maximenko, Andrey L.; Back, Christina; Izhvanov, Oleg; Olevsky, Eugene A.

2017-07-01

Theoretical studies on the densification kinetics of the new spark plasma sinter-forging (SPS-forging) consolidation technique and of the regular SPS have been carried out based on the continuum theory of sintering. Both modelling and verifying experimental results indicate that the loading modes play important roles in the densification efficiency of SPS of porous ZrC specimens. Compared to regular SPS, SPS-forging is shown to be able to enhance the densification more significantly during later sintering stages. The derived analytical constitutive equations are utilised to evaluate the high-temperature creep parameters of ZrC under SPS conditions. SPS-forging and regular SPS setups are combined to form a new SPS hybrid loading mode with the purpose of reducing shape irregularity in the SPS-forged specimens. Loading control is imposed to secure the geometry as well as the densification of ZrC specimens during hybrid SPS process.

Report on in-situ studies of flash sintering of uranium dioxide

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

Raftery, Alicia Marie

Flash sintering is a novel type of field assisted sintering that uses an electric field and current to provide densification of materials on very short time scales. The potential for field assisted sintering techniques to be used in producing nuclear fuel is gaining recognition due to the potential economic benefits and improvements in material properties. The flash sintering behavior has so far been linked to applied and material parameters, but the underlying mechanisms active during flash sintering have yet to be identified. This report summarizes the efforts to investigate flash sintering of uranium dioxide using dilatometer studies at Los Alamosmore » National Laboratory and two separate sets of in-situ studies at Brookhaven National Laboratory’s NSLS-II XPD-1 beamline. The purpose of the dilatometer studies was to understand individual parameter (applied and material) effects on the flash behavior and the purpose of the in-situ studies was to better understand the mechanisms active during flash sintering. As far as applied parameters, it was found that stoichiometry, or oxygen-to-metal ratio, has a significant effect on the flash behavior (time to flash and speed of flash). Composite systems were found to have degraded sintering behavior relative to pure UO 2. The critical field studies are complete for UO 2.00 and will be analyzed against an existing model for comparison. The in-situ studies showed that the strength of the field and current are directly related to the sample temperature, with temperature-driven phase changes occurring at high values. The existence of an ‘incubation time’ has been questioned, due to a continuous change in lattice parameter values from the moment that the field is applied. Some results from the in-situ experiments, which should provide evidence regarding ion migration, are still being analyzed. Some preliminary conclusions can be made from these results with regard to using field assisted sintering to fabricate nuclear fuel. First, the pure UO 2-based system shows promising behavior with flash sintering, but composite systems are likely to show better sintering behavior with spark plasma sintering. Efforts to develop these methods should therefore be tailored towards the likelihood of success. Additionally, modeling is a rapidly developing aspect of current flash sintering research and should be used in parallel with experiments. Ultimately, ongoing flash sintering studies on various materials, like those summarized in this report, are rapidly contributing to the feasibility of controlling this method for use in the future.« less

Method for fabricating beryllium structures

DOEpatents

Hovis, Jr., Victor M.; Northcutt, Jr., Walter G.

1977-01-01

Thin-walled beryllium structures are prepared by plasma spraying a mixture of beryllium powder and about 2500 to 4000 ppm silicon powder onto a suitable substrate, removing the plasma-sprayed body from the substrate and placing it in a sizing die having a coefficient of thermal expansion similar to that of the beryllium, exposing the plasma-sprayed body to a moist atmosphere, outgassing the plasma-sprayed body, and then sintering the plasma-sprayed body in an inert atmosphere to form a dense, low-porosity beryllium structure of the desired thin-wall configuration. The addition of the silicon and the exposure of the plasma-sprayed body to the moist atmosphere greatly facilitate the preparation of the beryllium structure while minimizing the heretofore deleterious problems due to grain growth and grain orientation.

SnO2/CNT nanocomposite supercapacitors fabricated using scanning atmospheric-pressure plasma jets

NASA Astrophysics Data System (ADS)

Xu, Chang-Han; Chiu, Yi-Fan; Yeh, Po-Wei; Chen, Jian-Zhang

2016-08-01

SnO2/CNT electrodes for supercapacitors are fabricated by first screen-printing pastes containing SnO2 nanoparticles and CNTs on carbon cloth, following which nitrogen atmospheric pressure plasma jet (APPJ) sintering is performed at various APPJ scan rates. The APPJ scan rates change the time intervals for which the reactive plasma species and the heat of the nitrogen APPJs influence the designated sintering spot on the carbon cloth, resulting in APPJ-sintered SnO2/CNT nanocomposites with different properties. The water contact angle decreases with the APPJ scan rate. The improved wettability can facilitate the penetration of the electrolyte into the nanopores of the SnO2/CNT nanocomposites, thereby improving the charge storage and specific capacitance of the supercapacitors. Among the three tested APPJ scan rates, 1.5, 3, and 6 mm s-1, the SnO2/CNT supercapacitor sintered by APPJ under the lowest APPJ scan rate of 1.5 mm s-1 shows the best specific capacitance of ˜90 F g-1 as evaluated by cyclic voltammetry under a potential scan rate of 2 mV s-1. A high APPJ scan rate may result in low degree of materials activation and sintering, leading to poorer performance of SnO2/CNT supercapacitors. The results suggest the feasibility of an APPJ roll-to-roll process for the fabrication of SnO2/CNT nanocomposite supercapacitors.

High hardness BaCb-(BxOy/BN) composites with 3D mesh-like fine grain-boundary structure by reactive spark plasma sintering.

PubMed

Vasylkiv, Oleg; Borodianska, Hanna; Badica, Petre; Grasso, Salvatore; Sakka, Yoshio; Tok, Alfred; Su, Liap Tat; Bosman, Michael; Ma, Jan

2012-02-01

Boron carbide B4C powders were subject to reactive spark plasma sintering (also known as field assisted sintering, pulsed current sintering or plasma assisted sintering) under nitrogen atmosphere. For an optimum hexagonal BN (h-BN) content estimated from X-ray diffraction measurements at approximately 0.4 wt%, the as-prepared BaCb-(BxOy/BN) ceramic shows values of Berkovich and Vickers hardness of 56.7 +/- 3.1 GPa and 39.3 +/- 7.6 GPa, respectively. These values are higher than for the vacuum SPS processed B4C pristine sample and the h-BN -mechanically-added samples. XRD and electronic microscopy data suggest that in the samples produced by reactive SPS in N2 atmosphere, and containing an estimated amount of 0.3-1.5% h-BN, the crystallite size of the boron carbide grains is decreasing with the increasing amount of N2, while for the newly formed lamellar h-BN the crystallite size is almost constant (approximately 30-50 nm). BN is located at the grain boundaries between the boron carbide grains and it is wrapped and intercalated by a thin layer of boron oxide. BxOy/BN forms a fine and continuous 3D mesh-like structure that is a possible reason for good mechanical properties.

Numerical study of the process parameters in spark plasma sintering (sps)

NASA Astrophysics Data System (ADS)

Chowdhury, Redwan Jahid

Spark plasma sintering (SPS) is one of the most widely used sintering techniques that utilizes pulsed direct current together with uniaxial pressure to consolidate a wide variety of materials. The unique mechanisms of SPS enable it to sinter powder compacts at a lower temperature and in a shorter time than the conventional hot pressing, hot isostatic pressing and vacuum sintering process. One of the limitations of SPS is the presence of temperature gradients inside the sample, which could result in non-uniform physical and microstructural properties. Detailed study of the temperature and current distributions inside the sintered sample is necessary to minimize the temperature gradients and achieve desired properties. In the present study, a coupled thermal-electric model was developed using finite element codes in ABAQUS software to investigate the temperature and current distributions inside the conductive and non-conductive samples. An integrated experimental-numerical methodology was implemented to determine the system contact resistances accurately. The developed sintering model was validated by a series of experiments, which showed good agreements with simulation results. The temperature distribution inside the sample depends on some process parameters such as sample and tool geometry, punch and die position, applied current and thermal insulation around the die. The role of these parameters on sample temperature distribution was systematically analyzed. The findings of this research could prove very useful for the reliable production of large size sintered samples with controlled and tailored properties.

Spark plasma sintering of titanium aluminide intermetallics and its composites

NASA Astrophysics Data System (ADS)

Aldoshan, Abdelhakim Ahmed

Titanium aluminide intermetallics are a distinct class of engineering materials having unique properties over conventional titanium alloys. gamma-TiAl compound possesses competitive physical and mechanical properties at elevated temperature applications compared to Ni-based superalloys. gamma-TiAl composite materials exhibit high melting point, low density, high strength and excellent corrosion resistance. Spark plasma sintering (SPS) is one of the powder metallurgy techniques where powder mixture undergoes simultaneous application of uniaxial pressure and pulsed direct current. Unlike other sintering techniques such as hot iso-static pressing and hot pressing, SPS compacts the materials in shorter time (< 10 min) with a lower temperature and leads to highly dense products. Reactive synthesis of titanium aluminide intermetallics is carried out using SPS. Reactive sintering takes place between liquid aluminum and solid titanium. In this work, reactive sintering through SPS was used to fabricate fully densified gamma-TiAl and titanium aluminide composites starting from elemental powders at different sintering temperatures. It was observed that sintering temperature played significant role in the densification of titanium aluminide composites. gamma-TiAl was the predominate phase at different temperatures. The effect of increasing sintering temperature on microhardness, microstructure, yield strength and wear behavior of titanium aluminide was studied. Addition of graphene nanoplatelets to titanium aluminide matrix resulted in change in microhardness. In Ti-Al-graphene composites, a noticeable decrease in coefficient of friction was observed due to the influence of self-lubrication caused by graphene.

Porous Nb-Ti based alloy produced from plasma spheroidized powder

NASA Astrophysics Data System (ADS)

Li, Qijun; Zhang, Lin; Wei, Dongbin; Ren, Shubin; Qu, Xuanhui

Spherical Nb-Ti based alloy powder was prepared by the combination of plasma spheroidization and mechanical alloying. Phase constituents, microstructure and surface state of the powder, and pore characteristics of the resulting porous alloy were investigated. The results show that the undissolved W and V in the mechanically alloyed powder is fully alloyed after spheroidization, and single β phase is achieved. Particle size of the spheroidized powder is in the range of 20-110 μm. With the decrease of particle size, a transformation from typical dendrite solidification structure to fine cell microstructure occurs. The surface of the spheroidized powder is coated by a layer of oxides consisting mainly of TiO2 and Nb2O5. Probabilities of sinter-neck formation and particle coalescence increases with increasing sintering temperature. Porous skeleton with relatively homogeneous pore distribution and open pore channel is formed after vacuum sintering at 1700 °C, and the porosity is 32%. The sintering kinetic analysis indicates that grain boundary diffusion is the primary mass transport mechanism during sintering process.

Vacuum Compatibility of Laser-Sintered Metals

NASA Astrophysics Data System (ADS)

Rivera, W. F.; Romero-Talamas, C. A.; Bates, E. M.; Birmingham, W. J.; Quinley, M.; Woodruff, S.; Stuber, J. E.; Sieck, P. E.; Melnik, P. A.

2016-10-01

We present the design and results of a mass spectrometry system used to assess vacuum compatibility of selective laser-sintered parts. The parts are disks with a thickness of 0.20 cm and a diameter of 8.25 cm, and are made of aluminum, stainless steel, inconel, and titanium. From preliminary results, titanium had the lowest partial pressure for hydrogen. Outgassing from laser-sintered parts is compared against parts with similar surface area that are manufactured with traditional methods. Outgassing is also measured while the part is heated, emulating the conditions at the edge of high temperature plasma confinement chambers. Each part is placed on a heated container that can vary in temperature inside the mass spectrometer's vacuum chamber. The partial pressures of elements up to 200 atomic mass units are analyzed to obtain outgassing data from each sample. This work supported under DOE SBIR Grant DE SC0011858.

Development of a Cr-Based Hard Composite Processed by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

García-Junceda, A.; Sáez, I.; Deng, X. X.; Torralba, J. M.

2018-04-01

This investigation analyzes the feasibility of processing a composite material comprising WC particles randomly dispersed in a matrix in which Cr is the main metallic binder. Thus, a new composite material is processed using a commercial, economic, and easily available Cr-based alloy, assuming that there is a certain Cr solubility in the WC particles acting as reinforcement. The processing route followed includes mechanical milling of the powders and consolidation by spark plasma sintering.

Stability of Nanocrystalline Spark Plasma Sintered 3Y-TZP

PubMed Central

Chintapalli, Ravikiran; Mestra, Alvaro; García Marro, Fernando; Yan, Haixue; Reece, Michael; Anglada, Marc

2010-01-01

Spark plasma sintered 3Y-TZP has been investigated with respect to hydrothermal ageing and grinding. The sintering was performed between the temperatures of 1,100 and 1,600 °C for a soaking time of 5 minutes and the resulting materials were obtained with grain sizes between 65 to 800 nm and relative densities between 88.5 to 98.8%. Experiments on hydrothermal ageing in water vapour at 131 °C, 2 bars during 60 hours shows that phase stability is retained, elastic modulus and hardness of near surface region measured by nanoindentation does not change in fine grain (<200 nm) materials, in spite of porosity. In ground specimens, very small amount of transformation was found for all grain sizes studied.

Preparation and characterization of copper-graphite composites by electrical explosion of wire in liquid.

PubMed

Bien, T N; Gul, W H; Bac, L H; Kim, J C

2014-11-01

Copper-graphite nanocomposites containing 5 vol.% graphite were prepared by a powder metallurgy route using an electrical wire explosion (EEW) in liquid method and spark plasma sintering (SPS) process. Graphite rods with a 0.3 mm diameter and copper wire with a 0.2 mm diameter were used as raw materials for EEWin liquid. To compare, a pure copper and copper-graphite mixture was also prepared. The fabricated graphite was in the form of a nanosheet, onto which copper particles were coated. Sintering was performed at 900 degrees C at a heating rate of 30 degrees C/min for 10 min and under a pressure of 70 MPa. The density of the sintered composite samples was measured by the Archimedes method. A wear test was performed by a ball-on-disc tribometer under dry conditions at room temperature in air. The presence of graphite effectively reduced the wear of composites. The copper-graphite nanocomposites prepared by EEW had lower wear rates than pure copper material and simple mixed copper-graphite.

An evaluation of UO2-CNT composites made by SPS as an accident tolerant nuclear fuel pellet and the feasibility of SPS as an economical fabrication process for the nuclear fuel cycle

NASA Astrophysics Data System (ADS)

Cartas, Andrew R.

The innovative and advanced purpose of this study is to understand and establish proper sintering procedures for Spark Plasma Sintering process in order to fabricate high density, high thermal conductivity UO2 -CNT pellets. Mixing quality and chemical reactions have been investigated by field emission scanning electron microscopy (FESEM), wavelength dispersive spectroscopy (WDS), and X-ray diffraction (XRD). The effect of various types of CNTs on the mixing and sintering quality of UO2-CNT pellets with SPS processing have been examined. The Archimedes Immersion Method, laser flash method, and FE-SEM will be used to investigate the density, thermal conductivity, grain size, pinning effects, and CNT dispersion of fabricated UO2-CNT pellets. Pre-fabricated CNT's were added to UO 2 powder and dispersed via sonication and/or ball milling and then made into composite nuclear pellets. An investigation of the economic impact of SPS on the nuclear fuel cycle for producing pure and composite UO2 fuels was conducted.

Mechanism analysis on finishing of reaction-sintered silicon carbide by combination of water vapor plasma oxidation and ceria slurry polishing

NASA Astrophysics Data System (ADS)

Shen, Xinmin; Tu, Qunzhang; Deng, Hui; Jiang, Guoliang; Yamamura, Kazuya

2015-05-01

Reaction-sintered silicon carbide (RS-SiC), which is considered as a promising mirror material for space telescope systems, requires a high surface property. An ultrasmooth surface with a Ra surface roughness of 0.480 nm was obtained after water vapor plasma oxidation for 90 min followed by ceria slurry polishing for 40 min. The oxidation process of RS-SiC by water vapor plasma was analyzed based on the Deal-Grove model, and the theoretical calculation results are consistent with the measured data obtained by scanning white light interferometer (SWLI), scanning electron microscopy/energy-dispersive x-ray, and atomic force microscope. The polishing process of oxidized RS-SiC by ceria slurry was investigated according to the Preston equation, which would theoretically forecast the evolutions of RS-SiC surfaces along with the increasing of polishing time, and it was experimentally verified by comparing the surface roughnesses obtained by SWLI and the surface morphologies obtained by SEM. The mechanism analysis on the finishing of RS-SiC would be effective for the optimization of water vapor plasma oxidation parameters and ceria slurry polishing parameters, which will promote the application of RS-SiC substrates by improving the surface property obtained by the oxidation-assisted polishing method.

Rapidly sintering of interconnected porous Ti-HA biocomposite with high strength and enhanced bioactivity.

PubMed

Zhang, L; He, Z Y; Zhang, Y Q; Jiang, Y H; Zhou, R

2016-10-01

In this work, interconnected porous Ti-HA biocomposites with enhanced bioactivity, high porosity and compressive strength were prepared by spark plasma sintering (SPS) and space holder method. Pore characteristics, mechanical properties, corrosion behaviors and in vitro bioactivity of the porous Ti-HA were investigated. Results showed that porous Ti-HA with 5-30wt% HA contents possessed not only low elastic modulus of 8.2-15.8GPa (close to that of human bone) but also high compressive strength (86-388MPa). Although the HA partially decomposed and formed secondary phases, the sintered porous Ti-HA can still be good bioactivity. The homogeneity and the thickness of apatite layer increased significantly with the increase of HA. But with the thickness of apatite layer increased, micro-cracks appeared on the surface of porous Ti-30%HA. A model was built to discuss the current distribution and sintering mechanism of HA on Ti matrix during SPS process. It indicated that the excessive addition of HA would deteriorate the sintering quality, thus decreasing the mechanical properties and corrosion resistance. However, the combination of interconnected pore characteristics, low elastic modulus, high compressive strength and enhanced bioactivity might make porous Ti-HA biocomposites prepared by SPS a promising candidate for hard tissue implants. Copyright © 2016 Elsevier B.V. All rights reserved.

Spark Plasma Co-Sintering of Mechanically Milled Tool Steel and High Speed Steel Powders

PubMed Central

Pellizzari, Massimo; Fedrizzi, Anna; Zadra, Mario

2016-01-01

Hot work tool steel (AISI H13) and high speed steel (AISI M3:2) powders were successfully co-sintered to produce hybrid tool steels that have properties and microstructures that can be modulated for specific applications. To promote co-sintering, which is made difficult by the various densification kinetics of the two steels, the particle sizes and structures were refined by mechanical milling (MM). Near full density samples (>99.5%) showing very fine and homogeneous microstructure were obtained using spark plasma sintering (SPS). The density of the blends (20, 40, 60, 80 wt % H13) was in agreement with the linear rule of mixtures. Their hardness showed a positive deviation, which could be ascribed to the strengthening effect of the secondary particles altering the stress distribution during indentation. A toughening of the M3:2-rich blends could be explained in view of the crack deviation and crack arrest exerted by the H13 particles. PMID:28773603

Spark Plasma Co-Sintering of Mechanically Milled Tool Steel and High Speed Steel Powders.

PubMed

Pellizzari, Massimo; Fedrizzi, Anna; Zadra, Mario

2016-06-16

Hot work tool steel (AISI H13) and high speed steel (AISI M3:2) powders were successfully co-sintered to produce hybrid tool steels that have properties and microstructures that can be modulated for specific applications. To promote co-sintering, which is made difficult by the various densification kinetics of the two steels, the particle sizes and structures were refined by mechanical milling (MM). Near full density samples (>99.5%) showing very fine and homogeneous microstructure were obtained using spark plasma sintering (SPS). The density of the blends (20, 40, 60, 80 wt % H13) was in agreement with the linear rule of mixtures. Their hardness showed a positive deviation, which could be ascribed to the strengthening effect of the secondary particles altering the stress distribution during indentation. A toughening of the M3:2-rich blends could be explained in view of the crack deviation and crack arrest exerted by the H13 particles.

Characterization of Multiwalled Carbon Nanotube-Reinforced Hydroxyapatite Composites Consolidated by Spark Plasma Sintering

PubMed Central

Kim, Duk-Yeon; Han, Young-Hwan; Lee, Jun Hee; Kang, Inn-Kyu; Jang, Byung-Koog; Kim, Sukyoung

2014-01-01

Pure HA and 1, 3, 5, and 10 vol% multiwalled carbon nanotube- (MWNT-) reinforced hydroxyapatite (HA) were consolidated using a spark plasma sintering (SPS) technique. The relative density of pure HA increased with increasing sintering temperature, but that of the MWNT/HA composite reached almost full density at 900°C, and then decreased with further increases in sintering temperature. The relative density of the MWNT/HA composites increased with increasing MWNT content due to the excellent thermal conductivity of MWNTs. The grain size of MWNT/HA composites decreased with increasing MWNT content and increased with increasing sintering temperature. Pull-out toughening of the MWNTs of the MWNT/HA composites was observed in the fractured surface, which can be used to predict the improvement of the mechanical properties. On the other hand, the existence of undispersed or agglomerate MWNTs in the MWNT/HA composites accompanied large pores. The formation of large pores increased with increasing sintering temperature and MWNT content. The addition of MWNT in HA increased the hardness and fracture toughness by approximately 3~4 times, despite the presence of large pores produced by un-dispersed MWNTs. This provides strong evidence as to why the MWNTs are good candidates as reinforcements for strengthening the ceramic matrix. The MWNT/HA composites did not decompose during SPS sintering. The MWNT-reinforced HA composites were non-toxic and showed a good cell affinity and morphology in vitro for 1 day. PMID:24724100

Particle morphology influence on mechanical and biocompatibility properties of injection molded Ti alloy powder.

PubMed

Gülsoy, H Özkan; Gülsoy, Nagihan; Calışıcı, Rahmi

2014-01-01

Titanium and Titanium alloys exhibits properties that are excellent for various bio-applications. Metal injection molding is a processing route that offers reduction in costs, with the added advantage of near net-shape components. Different physical properties of Titanium alloy powders, shaped and processed via injection molding can achieve high complexity of part geometry with mechanical and bioactivity properties, similar or superior to wrought material. This study describes that the effect of particle morphology on the microstructural, mechanical and biocompatibility properties of injection molded Ti-6Al-4V (Ti64) alloy powder for biomaterials applications. Ti64 powders irregular and spherical in shape were injection molded with wax based binder. Binder debinding was performed in solvent and thermal method. After debinding the samples were sintered under high vacuum. Metallographic studies were determined to densification and the corresponding microstructural changes. Sintered samples were immersed in a simulated body fluid (SBF) with elemental concentrations that were comparable to those of human blood plasma for a total period of 15 days. Both materials were implanted in fibroblast culture for biocompatibility evaluations were carried out. The results show that spherical and irregular powder could be sintered to a maximum theoretical density. Maximum tensile strength was obtained for spherical shape powder sintered. The tensile strength of the irregular shape powder sintered at the same temperature was lower due to higher porosity. Finally, mechanical tests show that the irregular shape powder has lower mechanical properties than spherical shape powder. The sintered irregular Ti64 powder exhibited better biocompatibility than sintered spherical Ti64 powder. Results of study showed that sintered spherical and irregular Ti64 powders exhibited high mechanical properties and good biocompatibility properties.

Fabrication of lanthanum-doped thorium dioxide by high-energy ball milling and spark plasma sintering

NASA Astrophysics Data System (ADS)

Scott, Spencer M.; Yao, Tiankai; Lu, Fengyuan; Xin, Guoqing; Zhu, Weiguang; Lian, Jie

2017-03-01

High-energy ball milling was used to synthesize Th1-xLaxO2-0.5x (x = 0.09, 0.23) solid solutions, as well as improve the sinterability of ThO2 powders. Dense La-doped ThO2 pellets with theoretical density above 94% were consolidated by spark plasma sintering at temperatures above 1400 °C for 20 min, and the densification behavior and the non-equilibrium effects on phase and structure were investigated. A lattice contraction of the SPS-densified pellets occurred with increasing ball milling duration, and a secondary phase with increased La-content was observed in La-doped pellets. A dependence on the La-content and sintering duration for the onset of localized phase segregation has been proposed. The effects of high-energy ball milling, La-content, and phase formation on the thermal diffusivity were also studied for La-doped ThO2 pellets by laser flash measurement. Increasing La-content and high energy ball milling time decreases thermal diffusivity; while the sintering peak temperature and holding time beyond 1600 °C dramatically altered the temperature dependence of the thermal diffusivity beyond 600 °C.

Thermoelectric and mechanical properties of spark plasma sintered Cu{sub 3}SbSe{sub 3} and Cu{sub 3}SbSe{sub 4}: Promising thermoelectric materials

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

Tyagi, Kriti; Gahtori, Bhasker; Bathula, Sivaiah

2014-12-29

We report the synthesis of thermoelectric compounds, Cu{sub 3}SbSe{sub 3} and Cu{sub 3}SbSe{sub 4}, employing the conventional fusion method followed by spark plasma sintering. Their thermoelectric properties indicated that despite its higher thermal conductivity, Cu{sub 3}SbSe{sub 4} exhibited a much larger value of thermoelectric figure-of-merit as compared to Cu{sub 3}SbSe{sub 3}, which is primarily due to its higher electrical conductivity. The thermoelectric compatibility factor of Cu{sub 3}SbSe{sub 4} was found to be ∼1.2 as compared to 0.2 V{sup −1} for Cu{sub 3}SbSe{sub 3} at 550 K. The results of the mechanical properties of these two compounds indicated that their microhardness and fracturemore » toughness values were far superior to the other competing state-of-the-art thermoelectric materials.« less

Synthesis of dense yttrium-stabilised hafnia pellets for nuclear applications by spark plasma sintering

NASA Astrophysics Data System (ADS)

Tyrpekl, Vaclav; Holzhäuser, Michael; Hein, Herwin; Vigier, Jean-Francois; Somers, Joseph; Svora, Petr

2014-11-01

Dense yttrium-stabilised hafnia pellets (91.35 wt.% HfO2 and 8.65 wt.% Y2O3) were prepared by spark plasma sintering consolidation of micro-beads synthesised by the "external gelation" sol-gel technique. This technique allows a preparation of HfO2-Y2O3 beads with homogenous yttria-hafnia solid solution. A sintering time of 5 min at 1600 °C was sufficient to produce high density pellets (over 90% of the theoretical density) with significant reproducibility. The pellets have been machined in a lathe to the correct dimensions for use as neutron absorbers in an experimental test irradiation in the High Flux Reactor (HFR) in Petten, Holland, in order to investigate the safety of americium based nuclear fuels.

Effect of starting powders on the sintering of nanostructured ZrO2 ceramics by colloidal processing

NASA Astrophysics Data System (ADS)

Suárez, Gustavo; Sakka, Yoshio; Suzuki, Tohru S.; Uchikoshi, Tetsuo; Zhu, Xinwen; Aglietti, Esteban F.

2009-04-01

The effect of starting powders on the sintering of nanostructured tetragonal zirconia was evaluated. Suspensions were prepared with a concentration of 10 vol.% by mixing a bicomponent mixture of commercial powders (97 mol.% monoclinic zirconia with 3 mol.% yttria) and by dispersing commercially available tetragonal zirconia (3YTZ, Tosoh). The preparation of the slurry by bead-milling was optimized. Colloidal processing using 50 μm zirconia beads at 4000 rpm generated a fully deagglomerated suspension leading to the formation of high-density consolidated compacts (62% of the theoretical density (TD) for the bicomponent suspension). Optimum colloidal processing of the bicomponent suspension followed by the sintering of yttria and zirconia allowed us to obtain nanostructured tetragonal zirconia. Three different sintering techniques were investigated: normal sintering, two-step sintering and spark plasma sintering. The inhibition of grain growth in the bicomponent mixed powders in comparison with 3YTZ was demonstrated. The inhibition of the grain growth may have been caused by inter-diffusion of cations during the sintering.

Improved microstructure and thermoelectric properties of iodine doped indium selenide as a function of sintering temperature

NASA Astrophysics Data System (ADS)

Dhama, Pallavi; Kumar, Aparabal; Banerji, P.

2018-04-01

In this paper, we explored the effect of sintering temperature on the microstructure, thermal and electrical properties of iodine doped indium selenide in the temperature range 300 - 700 K. Samples were prepared by a collaborative process of vacuum melting, ball milling and spark plasma sintering at 570 K, 630 K and 690 K. Single phase samples were obtained at higher sintering temperature as InSe is stable only at lower temperature. With increasing sintering temperature, densities of the samples were found to improve with larger grain size formation. Negative values of Seebeck coefficient were observed which indicates n-type carrier transport. Seebeck coefficient increases with sintering temperature and found to be the highest for the sample sintered at 690 K. Thermal conductivity found to be lower in the samples sintered at lower temperatures. The maximum thermoelectric figure of merit found to be ˜ 1 at 700 K due to the enhanced power factor as a result of improved microstructure.

Corrosion resistance assessment of Co-Cr alloy frameworks fabricated by CAD/CAM milling, laser sintering, and casting methods.

PubMed

Tuna, Süleyman Hakan; Özçiçek Pekmez, Nuran; Kürkçüoğlu, Işin

2015-11-01

The effects of fabrication methods on the corrosion resistance of frameworks produced with Co-Cr alloys are not clear. The purpose of this in vitro study was to evaluate the electrochemical corrosion resistance of Co-Cr alloy specimens that were fabricated by conventional casting, milling, and laser sintering. The specimens fabricated with 3 different methods were investigated by potentiodynamic tests and electrochemical impedance spectroscopy in an artificial saliva. Ions released into the artificial saliva were estimated with inductively coupled plasma-mass spectrometry, and the results were statistically analyzed. The specimen surfaces were investigated with scanning electron microscopy before and after the tests. In terms of corrosion current and Rct properties, statistically significant differences were found both among the means of the methods and among the means of the material groups (P<.05). With regard to ions released, a statistically significant difference was found among the material groups (P<.05); however, no difference was found among the methods. Scanning electron microscopic imaging revealed that the specimens produced by conventional casting were affected to a greater extent by etching and electrochemical corrosion than those produced by milling and laser sintering. The corrosion resistance of a Co-Cr alloy specimens fabricated by milling or laser sintering was greater than that of the conventionally cast alloy specimens. The Co-Cr specimens produced by the same method also differed from one another in terms of corrosion resistance. These differences may be related to the variations in the alloy compositions. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Sintering and Creep Behavior of Plasma-Sprayed Zirconia and Hafnia Based Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Miller, Robert A.

1998-01-01

The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2-8wt%y2O3, ZrO2-25wt%CeO2-2.5wt%Y2O3, ZrO2-6w%NiO- 9wt%Y2O3, ZrO2-6wt%Sc2O3-2wt%y2O3 and HfO2-27wt%y2O3 coating materials were investigated using dilatometry. It was found that the HfO2-Y2O3 and baseline ZrO2-Y2O3 exhibited the best sintering resistance, while the NiO-doped ZrO2-Y2O3 showed the highest shrinkage strain rates during the tests. Higher shrinkage strain rates of the coating materials were also observed when the specimens were tested in Ar+5%H2 as compared to in air. This phenomenon was attributed to an enhanced metal cation interstitial diffusion mechanism under the reducing conditions. It is proposed that increased chemical stability of coating materials will improve the material sintering resistance.

Mechanical Properties and Plasma Erosion Resistance of ZrO2p(3Y)/BN-SiO2 Ceramic Composites under Different Sintering Temperature

NASA Astrophysics Data System (ADS)

Zhou, Yu; Duan1, Xiaoming; Jia, Dechang; Yang, Zhihua; Meng, Qingchang; Yu, Yang; Yu, Daren; Ding, Yongjie

2011-10-01

ZrO2p(3Y)/BN-SiO2 ceramic composites were hot pressed under different sintering temperature. The ceramic composites were composed by BN, m-ZrO2, t-ZrO2 and SiO2. The relative density, bending strength, elastic modulus and fracture toughness increase with the sintering temperature increasing, the maximum value of which at the sintering temperature of 1800°C are 97.5%, 229.9MPa, 60.8GPa and 3.55MPam1/2, respectively. The erosion resistance ability of ZrO2p(3Y)/BN-SiO2 ceramic composites rise gradually with the sintering temperature increasing, and the erosion rate of the ceramic composite sintered at 1800°C is 8.03×10-3mm/h.

Surprising synthesis of nanodiamond from single-walled carbon nanotubes by the spark plasma sintering process

NASA Astrophysics Data System (ADS)

Mirzaei, Ali; Ham, Heon; Na, Han Gil; Kwon, Yong Jung; Kang, Sung Yong; Choi, Myung Sik; Bang, Jae Hoon; Park, No-Hyung; Kang, Inpil; Kim, Hyoun Woo

2016-10-01

Nanodiamond (ND) was successfully synthesized using single-walled carbon nanotubes (SWCNTs) as a pure solid carbon source by means of a spark plasma sintering process. Raman spectra and X-ray diffraction patterns revealed the generation of the cubic diamond phase by means of the SPS process. Lattice-resolved TEM images confirmed that diamond nanoparticles with a diameter of about ˜10 nm existed in the products. The NDs were generated mainly through the gas-phase nucleation of carbon atoms evaporated from the SWCNTs. [Figure not available: see fulltext.

Structural and magnetic properties of spark plasma sintered Co-Mg-Zn substituted Ba-Sr hexagonal ferrite magnets

NASA Astrophysics Data System (ADS)

Harikrishnan, V.; Vizhi, R. Ezhil; Rajan Babu, D.; Saravanan, P.

2018-02-01

The effect of conventional and spark plasma sintering processes on the structural and magnetic properties of Ba0.5Sr0.5Fe12-2xCox(MgZn)x/2O19 (x = 0.2, 0.4 and 0.6) was investigated in this study. XRD patterns of both conventionally sintered (CS) and spark plasma sintered (SPS) samples with x = 0.2 and 0.4 showed the crystallization of Ba0.5Sr0.5Fe12O19-phase with space group of P63/mmc. However, in the case of SPS sample with x = 0.4, a secondary peak of α-Fe2O3 was observed. SEM analysis on the SPS samples revealed dense morphology with low porosity; while the CS samples showed the presence of aggregated particles with spherical shapes. Maximum values of saturation magnetization, MS (58 emu/g) and coercivity, HC (3.5 kOe) were obtained for the CS samples with x = 0.4; while their SPS counterparts revealed increased MS (65 emu/g) and HC (3.9 kOe) values. The observed magnetization reversal behaviour for both sintering conditions were not smooth in the case of x = 0.2, which indicated the existence of two-phase behavior. The temperature dependent magnetization studies for x = 0.2 and 0.4 were performed in order to analyze the variation in Curie temperature against Co-Mg-Zn substitution and the obtained results are discussed on the basis of crystallization of hexaferrite-phase.

Densification behavior, nanocrystallization, and mechanical properties of spark plasma sintered Fe-based bulk amorphous alloys

NASA Astrophysics Data System (ADS)

Singh, Ashish Kumar

Fe-based amorphous alloys are gaining increasing attention due to their exceptional wear and corrosion resistance for potential structural applications. Two major challenges that are hindering the commercialization of these amorphous alloys are difficulty in processing of bulk shapes (diameter > 10 mm) and lack of ductility. Spark plasma sintering (SPS) is evolving as a promising technique for processing bulk shapes of amorphous and nanocrystalline materials. The objective of this work is to investigate densification behavior, nanocrystallization, and mechanical properties of SPS sintered Fe-based amorphous alloys of composition Fe48Cr15Mo14Y2C15B6. SPS processing was performed in three distinct temperature ranges of amorphous alloys: (a) below glass transition temperature (Tg), (b) between Tg and crystallization temperature (Tx), and (c) above Tx. Punch displacement data obtained during SPS sintering was correlated with the SPS processing parameters such as temperature, pressure, and sintering time. Powder rearrangement, plastic deformation below T g, and viscous flow of the material between Tg and Tx were observed as the main densification stages during SPS sintering. Micro-scale temperature distributions at the point of contact and macro-scale temperature distribution throughout the sample during SPS of amorphous alloys were modeled. The bulk amorphous alloys are expected to undergo structural relaxation and nanocrystallization during SPS sintering. X-ray diffraction (XRD), small angle neutron scattering (SANS), and transmission electron microscopy (TEM) was performed to investigate the evolution of nanocrystallites in SPS sintered Fe-based bulk amorphous alloys. The SANS analysis showed significant scattering for the samples sintered in the supercooled region indicating local structural and compositional changes with the profuse nucleation of nano-clusters (~4 nm). Compression tests and microhardness were performed on the samples sintered at different temperatures ranging from 570 °C to 800 °C. Maximum compression strength (1.1+/-0.2 MPa) was obtained for the samples sintered in the supercooled region. Effects of crystallization on tribological behavior of sintered samples were also investigated where crystallization resulted in increase in wear resistance. Laser surface hardening of SPS sintered amorphous samples were performed. Depending on the processing parameters, the laser surface irradiation causes structural relaxation and nanocrystallization, resulting in surface hardening.

Plasma Synthesis and Sintering of Advanced Ceramics

DTIC Science & Technology

1990-09-15

CONTENTS Page LIST OF TABLES iv OBJECTIVES 1 COLLOIDAL PLASMA PROCESSING: CONCEPTS 1 BACKGROUND 2 Ultrafine Particles 2 Colloidal Plasma 3 Particle...colloidal plasma processing of ceramics. COLLOIDAL PLASMA PROCESSING: CONCEPTS It is well known that ultrafine particles prepared in gas plasmas agglomerate...BACKGROUND Ultrafine Particles . There are well recognized advantages to using small particles in ceramic processing. The instantaneous densification

Effects of CaO on the compaction and sintering by plasma of Powder-metallurgical iron

NASA Astrophysics Data System (ADS)

Ariza Suarez, H. G.; Sarmiento Santos, A.; Ortiz Otálora, C. A.

2017-12-01

This work the effect of the addition of Calcium Oxide (CaO) in the compaction and sintering of powder metallurgical iron Ancoor Steel 1000® is studied. Iron samples were made with proportions of: 0.5%, 1%, 1.5% and 2% by weight of CaO. The samples were sintered in a luminescent discharge furnace, in an atmosphere of H2+Ar at a temperature of 1150°C. XRD analysis was used to determine the formation of compounds, this analysis evidenced the formation of: hematite and magnetite, which were found both on the surface and in the volume. A characterization of the ability to protect against corrosive effects was carried out using the EIS electrochemical impedance spectroscopy method on the samples, in a solution of 1000ppm of chloride, with this procedure it was found that at a concentration of 0.5% and 1% CaO, the electrochemical impedance value is increased with values of 11.7MΩ, 2.2MΩ respectively.

Microstructure and phase analysis of Zirconia-ODS (Oxide Dispersion Strengthen) alloy sintered by APS with milling time variation

NASA Astrophysics Data System (ADS)

Sugeng, Bambang; Bandriyana, B.; Sugeng, Bambang; Salam, Rohmad; Sumariyo; Sujatno, Agus; Dimyati, Arbi

2018-03-01

Investigation on the relationship between the process conditions of milling time and the microstructure on the synthesis of the zirconia-ODS steel alloy has been performed. The elemental composition of the alloy was determined on 20 wt% Cr and zirconia dispersoid of 0.50 wt%. The synthesis was carried out by powder metallurgy method with milling time of 3, 5 and 7 hours, static compression of 20 Ton and sintering process for 4 minutes using the APS (Arc Plasma Sintering) equipment. SEM-EDX and XRD test was carried out to characterize the phase and morphology of the alloy and the effect to the mechanical properties was evaluated by the Vickers Hardness testing. The synthesis produced sample of ODS steel with good dense and very little porous with the Fe-Cr phase that clearly observed in the XRD peak pattern. In addition milling time increased the homogeneously of Fe-Cr phase formulation, enhanced the grain refinement of the structure and increase the hardness of the alloy.

DEVELOPMENT OF PLUTONIUM-BEARING FUEL MATERIALS. Progress Report, October 1-December 31, 1961

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

None

1962-10-31

Continued effort is reported on preparation and characterization of PuO/ sub 2/ and UO/sub 2/-- PuO/sub 2/ mixtures. Sintering and characterization of pellets for irradiation tests was emphasized, and efforts were also devoted to plasma torch production of spherical PuO /sub 2/ and coating of oxide materials. PuO/sub 2/ produced by the oxalate process from low concentration feed contains agglomerates which are not readily broken down, while that produced from normal feed contains larger agglomerates which are easily dispersed ultrasonically, and are more easily calcined. The water filtration method for determining total porosity of powders was adapted for use withmore » PuO/sub 2/. Moisture pickup studies show that the problems encountered with PuO/sub 2/ are similar to those found in handling ceramic-grade UO/. Reproducibility tests carried out on UO/sub 2/--PuO/ sub 2/ mixtures indicate that production methods are satisfactory. Lab-scale experiments on production of PuO/sub 2/-- UO/sub 2/feed for the plasma torch indicate that further work is worthwhile. Adaptation of a potentiometric filtration for Pu is reported. A twophase microstructure found in PuO/ after sintering in N6% H atmosphere was identified as PuO/sub 2/ and cubic Pu/sub 2/O/ sub 3/. Spherical particles were produced in the plasma torch using crushed or preformed high-fired particles. Spherical particles of PuO/sub 2/ were also produced by a multi-step process of drying, pressing, granulation, sizing, shaping, and sintering. Reactor physics studies were continued to determine the effect of cross section assumptions on the calculated behavior of Pu-fueled near- thermal reactor systems. It was concluded that relatively long core life (reactivity limiting) is attainable with these systems. (J.R.D.)« less

The influence of sintering temperature on microstructure and mechanical properties of Ni-Al intermetallics fabricated by SPS

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

Thömmes, A., E-mail: thoemmes.alexander@gmail.com; Shevtsova, L. I., E-mail: edeliya2010@mail.ru; Laptev, I. S., E-mail: ilya-laptev-nstu@mail.ru

2015-10-27

In the present study PN85Yu15 was used as elemental powder to produce a sintered compound with Ni3Al as main phase. The Spark Plasma Sintering (SPS) technique is used to compact the powders. The powder was sintered in a temperature range between 1000°C and 1150°C to observe the influence of the sintering temperature on the microstructure and the mechanical properties. The microstructure was observed with optical microscope (OM), the phase composition was characterized by X-ray diffraction (XRD) technique. Density and microhardness were observed and compared the values with the results of other researchers. The compressive-, density- and microhardness tests show asmore » clear result that with increasing the sintering temperature nearly all properties become better and also the microstructure studies show that porous places become less.« less

Fast synthesis and consolidation of porous FeAl by pressureless Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Dudina, D. V.; Brester, A. E.; Anisimov, A. G.; Bokhonov, B. B.; Legan, M. A.; Novoselov, A. N.; Skovorodin, I. N.; Uvarov, N. F.

2017-07-01

We report one-step fast synthesis and consolidation of iron aluminide FeAl of high open porosity by pressureless reactive Spark Plasma Sintering (SPS). The starting material of the Fe-40at.%Al composition was a mixture of an iron powder with an average particle diameter of 4 μm and an aluminum powder with an average particle diameter of 6 μm. The rationale behind the choice of the SPS as a processing technique and fine and comparable sizes of the two reactants for the synthesis of high-open porosity FeAl was realization of fast full chemical conversion of Fe and Al into single-phase FeAl reducing the time available for the compact shrinkage. According to the XRD phase analysis, single-phase FeAl compacts formed after SPS at 800 and 900°C. These compacts had open porosities of 41 and 46%, respectively. The transverse rupture strength of the compacts sintered at 700-900°C was found to change little with the sintering temperature in the selected range.

Fabrication and characterization of powder metallurgy tantalum components prepared by high compaction pressure technique

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

Kim, Youngmoo; Agency for Defense Development, Yuseong, P.O. Box 35, Yuseong-gu, Daejeon 34186, Republic of Korea.; Lee, Dongju

2016-04-15

The present study has investigated the consolidation behaviors of tantalum powders during compaction and sintering, and the characteristics of sintered components. For die compaction, the densification behaviors of the powders are simulated by finite element analyses based on the yield function proposed by Shima and Oyane. Accordingly, the green density distribution for coarser particles is predicted to be more uniform because they exhibits higher initial relative tap density owing to lower interparticle friction. It is also found that cold isostatic pressing is capable of producing higher dense compacts compared to the die pressing. However, unlike the compaction behavior, the sinteredmore » density of smaller particles is found to be higher than those of coarser ones owing to their higher specific surface area. The maximum sintered density was found to be 0.96 of theoretical density where smaller particles were pressed isostatically at 400 MPa followed by sintering at 2000 °C. Moreover, the effects of processing conditions on grain size and texture were also investigated. The average grain size of the sintered specimen is 30.29 μm and its texture is less than 2 times random intensity. Consequently, it is concluded that the higher pressure compaction technique is beneficial to produce high dense and texture-free tantalum components compared to hot pressing and spark plasma sintering. - Highlights: • Higher Ta density is obtained from higher pressure and sintering temperature. • High compaction method enables P/M Ta to achieve the density of 16.00 g·cm{sup −3}. • A P/M Ta component with fine microstructure and random orientation is developed.« less

Phase Evolution and Mechanical Properties of AlCoCrFeNiSi x High-Entropy Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Kumar, Anil; Swarnakar, Akhilesh Kumar; Chopkar, Manoj

2018-05-01

In the current investigation, AlCoCrFeNiSi x (x = 0, 0.3, 0.6 and 0.9 in atomic ratio) high-entropy alloy systems are prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The microstructural and mechanical properties were analyzed to understand the effect of Si addition in AlCoCrFeNi alloy. The x-ray diffraction analysis reveals the supersaturated solid solution of the body-centered cubic structure after 20 h of ball milling. However, the consolidation promotes the transformation of body-centered phases partially into the face-centered cubic structure and sigma phases. A recently proposed geometric model based on the atomic stress theory has been extended for the first time to classify single phase and multi-phases on the high-entropy alloys prepared by mechanical alloying and spark plasma sintering process. Improved microhardness and better wear resistance were achieved as the Si content increased from 0 to 0.9 in the present high-entropy alloy.

[Effect of two-step sintering method on properties of zirconia ceramic].

PubMed

Huang, Hui; Wei, Bin; Zhang, Fu-Qiang; Sun, Jing; Gao, Lian

2008-04-01

To study the influence of two-step sintering method on the sintering property, mechanical properties and microstructure of zirconia ceramic. The nano-size zirconia powder were compacted and divided into two groups, one group for one-step sintering method, another group for two-step sintering method. All samples sintered at different temperature. The relative density, three-bend strength, HV hardness, fracture toughness and microstructure of sintered block were investigated. Two-step sintering method influenced the sintering property and mechanical properties of zirconia ceramic. The maximal relative density was 98.49% at 900 degrees C/1,450 degrees C sintering temperature. There were significant difference of mechanical properties between one-step sintering and two-step sintering, the three-bend strength and fracture toughness declined, hardness increased at two-step sintering. The three-bend strength, HV hardness and fracture toughness reached to maximum value as 1,059.08 MPa +/- 75.24 MPa, 1,377.00 MPa +/- 16.37 MPa and 5.92 MPa x m1/2 +/- 0.37 MPa x m1/2 at 900 degrees C/1,450 degrees C sintering temperature respectively. Microscopy revealed the relationship between the porosity and shapes of grains was correlated to strength of the zirconia ceramics. Despite of the two-step sintering method influences the properties of zirconia, it also is a promising esthetic all-ceramic dental material.

Production of coloured glass-ceramics from incinerator ash using thermal plasma technology.

PubMed

Cheng, T W; Huang, M Z; Tzeng, C C; Cheng, K B; Ueng, T H

2007-08-01

Incineration is a major treatment process for municipal solid waste in Taiwan. It is estimated that over 1.5 Mt of incinerator ash are produced annually. This study proposes using thermal plasma technology to treat incinerator ash. Sintered glass-ceramics were produced using quenched vitrified slag with colouring agents added. The experimental results showed that the major crystalline phases developed in the sintered glass-ceramics were gehlenite and wollastonite, but many other secondary phases also appeared depending on the colouring agents added. The physical/mechanical properties, chemical resistance and toxicity characteristic leaching procedure of the coloured glass-ceramics were satisfactory. The glass-ceramic products obtained from incinerator ash treated with thermal plasma technology have great potential for building applications.

Processing and Characterization of Fe-Mn-Cu-Sn-C Alloys Prepared by Ball Milling and Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Bączek, Elżbieta; Konstanty, Janusz; Romański, Andrzej; Podsiadło, Marcin; Cyboroń, Jolanta

2018-03-01

In this work, Fe-Mn-Cu-Sn-C alloys were prepared by means of powder metallurgy (PM). Powder mixtures were ball-milled for 8, 30 and 120 h and densified to < 1% porosity using spark plasma sintering (SPS) at 900 °C and 35 MPa. After consolidation, all samples of the Fe alloys were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), hardness and flexural strength tests. Resistance to abrasive wear was evaluated in both three-body abrasion and two-body abrasion tests. The SEM observations revealed an evident dependence of grain size and microstructural homogeneity on milling time. The XRD analysis showed a marked increase in austenite content in the as-sintered specimens with milling time. Although the proportion of deformation-induced martensite was small, the strengthening effect of abrasion on the subsurface layer of the investigated alloys was clearly indicated by Knoop hardness measurements.

High strength nanostructured Al-based alloys through optimized processing of rapidly quenched amorphous precursors.

PubMed

Kim, Song-Yi; Lee, Gwang-Yeob; Park, Gyu-Hyeon; Kim, Hyeon-Ah; Lee, A-Young; Scudino, Sergio; Prashanth, Konda Gokuldoss; Kim, Do-Hyang; Eckert, Jürgen; Lee, Min-Ha

2018-01-18

We report the methods increasing both strength and ductility of aluminum alloys transformed from amorphous precursor. The mechanical properties of bulk samples produced by spark-plasma sintering (SPS) of amorphous Al-Ni-Co-Dy powders at temperatures above 673 K are significantly enhanced by in-situ crystallization of nano-scale intermetallic compounds during the SPS process. The spark plasma sintered Al 84 Ni 7 Co 3 Dy 6 bulk specimens exhibit 1433 MPa compressive yield strength and 1773 MPa maximum strength together with 5.6% plastic strain, respectively. The addition of Dy enhances the thermal stability of primary fcc Al in the amorphous Al-TM -RE alloy. The precipitation of intermetallic phases by crystallization of the remaining amorphous matrix plays important role to restrict the growth of the fcc Al phase and contributes to the improvement of the mechanical properties. Such fully crystalline nano- or ultrafine-scale Al-Ni-Co-Dy systems are considered promising for industrial application because their superior mechanical properties in terms of a combination of very high room temperature strength combined with good ductility.

Structural evolution of plasma-sprayed nanoscale 3 mol% and 5 mol% yttria-stabilized zirconia coatings during sintering

NASA Astrophysics Data System (ADS)

Zhao, Yan; Gao, Yang

2017-12-01

The microstructure of plasma-sprayed nanostructured yttria-stabilized zirconia (YSZ) coatings may change during high-temperature exposure, which would influence the coating performance and service lifetime. In this study, the phase structure and the microstructural evolution of 3YSZ (zirconia-3 mol% yttria) and 5YSZ (zirconia-5 mol% yttria) nanostructured coatings were investigated by means of sintering at 1400 °C for 50-100 h. The microhardness, elastic moduli, and thermal shock cycles of the 3YSZ and 5YSZ nanostructured coatings were also investigated. The results showed that the redistribution of yttrium ions at 1400 °C caused the continuous increase of monoclinic-phase zirconia, but no obvious inter-splat cracking formed at the cross-sections, even after 100 h. Large voids appeared around the nanoporous zone because of the sintering of nanoscale granules upon high-temperature exposure. The microhardness and elastic moduli of the nanostructured coatings first increased and then decreased with increasing sintering times. The growth rate of the nanograins in the 3YSZ coating was lower than that in 5YSZ, which slowed the changes in 3YSZ coating porosity during sintering. Although the 3YSZ coating was prone to monoclinic phase transition, the experimental results showed that the thermal shock resistance of the 3YSZ coating was better than that of the 5YSZ coating.

Lanthana-bearing nanostructured ferritic steels via spark plasma sintering

NASA Astrophysics Data System (ADS)

Pasebani, Somayeh; Charit, Indrajit; Wu, Yaqiao; Burns, Jatuporn; Allahar, Kerry N.; Butt, Darryl P.; Cole, James I.; Alsagabi, Sultan F.

2016-03-01

A lanthana-containing nanostructured ferritic steel (NFS) was processed via mechanical alloying (MA) of Fe-14Cr-1Ti-0.3Mo-0.5La2O3 (wt.%) and consolidated via spark plasma sintering (SPS). In order to study the consolidation behavior via SPS, sintering temperature and dwell time were correlated with microstructure, density, microhardness and shear yield strength of the sintered specimens. A bimodal grain size distribution including both micron-sized and nano-sized grains was observed in the microstructure of specimens sintered at 850, 950 and1050 °C for 45 min. Significant densification occurred at temperatures greater than 950 °C with a relative density higher than 98%. A variety of nanoparticles, some enriched in Fe and Cr oxides and copious nanoparticles smaller than 10 nm with faceted morphology and enriched in La and Ti oxides were observed. After SPS at 950 °C, the number density of Cr-Ti-La-O-enriched nanoclusters with an average radius of 1.5 nm was estimated to be 1.2 × 1024 m-3. The La + Ti:O ratio was close to 1 after SPS at 950 and 1050 °C; however, the number density of nanoclusters decreased at 1050 °C. With SPS above 950 °C, the density improved but the microhardness and shear yield strength decreased due to partial coarsening of the grains and nanoparticles.

Microstructure, Hardness, and Corrosion Behavior of TiC-Duplex Stainless Steel Composites Fabricated by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Han, Ying; Zhang, Wei; Sun, Shicheng; Chen, Hua; Ran, Xu

2017-08-01

Duplex stainless steel composites with various weight fractions of TiC particles are prepared by spark plasma sintering. Ferritic 434L and austenitic 316L stainless steel powders are premixed in a 50:50 weight ratio and added with 3-9 wt.% TiC. The compacts are sintered in the solid state under vacuum conditions at 1223 K for 5 min. The effects of TiC content on the microstructure, hardness, and corrosion resistance of duplex stainless steel composites fabricated by powder metallurgy are evaluated. The results indicate that the TiC particulates as reinforcements can be distributed homogeneously in the steel matrix. Densification of sintered composites decreases with increasing TiC content. M23C6 carbide precipitates along grain boundary, and its neighboring Cr-Mo-depleted region is formed in the sintered microstructure, which can be eliminated subsequently with appropriate heat treatment. With the addition of TiC, the hardness of duplex stainless steel fabricated by powder metallurgy can be markedly enhanced despite increased porosity in the composites. However, TiC particles increase the corrosion rate and degrade the passivation capability, particularly for the composite with TiC content higher than 6 wt.%. Weakened metallurgical bonding in the composite with high TiC content provides the preferred sites for pitting nucleation and/or dissolution.

Unfolding grain size effects in barium titanate ferroelectric ceramics

PubMed Central

Tan, Yongqiang; Zhang, Jialiang; Wu, Yanqing; Wang, Chunlei; Koval, Vladimir; Shi, Baogui; Ye, Haitao; McKinnon, Ruth; Viola, Giuseppe; Yan, Haixue

2015-01-01

Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1 μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size. PMID:25951408

Density, Microstructure, Strength and Fractography of Spark Plasma and Conventionally Sintered Mn Steels

NASA Astrophysics Data System (ADS)

Tenerowicz-Zaba, M.; Kupkova, M.; Kabatova, M.; Dudrova, E.; Dzupon, M.; Sulowski, M.

2017-12-01

The aim of the study was to investigate Spark Plasma Sintering (SPS) of 1-3%Mn steels and compare the resultant microstructures, strengths and failure mechanisms with those of conventionally sintered materials. SPS was performed in a vacuum of 5 Pa at 1000°C for 15min under a uniaxial pressure of 20 MPa. The heating rate of 100°C/min was applied. For conventional processing, mixtures of powders were prepared in a Turbula mixer for 30 minutes. Samples were single pressed at 660 MPa, according to PN-EN ISO 2740 standard. Sintering of compacts was carried out in a laboratory tube furnace at 1120°C and 1250°C for 60 minutes in a mixture of 95%N2-5%H2. Heating and cooling rates were 75C°/min and 60°C/min, respectively. The density of SPS samples was higher (up to 7.37 g/cm3) than those after conventional sintering (up to 6.7 g/cm3). Yield strengths of SPS samples were in the range 920-1220 MPa, compared to the maximum of 602 MPa for conventionally sintered Fe-3%Mn-0.8%C. Transverse rupture strengths were the same for this alloy, 1234 MPa, but reached 1473 MPa for SPS 2Mn variant. Interfaces in SPS samples were significantly less contaminated with oxides, which is the result of a more favorable microclimate and pressure acting during SPS. These preliminary results indicate that further research on the SPS of Mn steels is warranted.

Fabrication of low thermal expansion SiC/ZrW2O8 porous ceramics

NASA Astrophysics Data System (ADS)

Poowancum, A.; Matsumaru, K.; Juárez-Ramírez, I.; Torres-Martínez, L. M.; Fu, Z. Y.; Lee, S. W.; Ishizaki, K.

2011-03-01

Low or zero thermal expansion porous ceramics are required for several applications. In this work near zero thermal expansion porous ceramics were fabricated by using SiC and ZrW2O8 as positive and negative thermal expansion materials, respectively, bonded by soda lime glass. The mixture of SiC, ZrW2O8 and soda lime glass was sintered by Pulsed Electric Current Sintering (PECS, or sometimes called Spark Plasma Sintering, SPS) at 700 °C. Sintered samples with ZrW2O8 particle size smaller than 25 μm have high thermal expansion coefficient, because ZrW2O8 has the reaction with soda lime glass to form Na2ZrW3O12 during sintering process. The reaction between soda lime glass and ZrW2O8 is reduced by increasing particle size of ZrW2O8. Sintered sample with ZrW2O8 particle size 45-90 μm shows near zero thermal expansion.

Development and Investigation of Tungsten Copper Sintered Parts for Using in Medium and High Voltage Switching Devices

NASA Astrophysics Data System (ADS)

Lungu, M. V.; Lucaci, M.; Tsakiris, V.; Brătulescu, A.; Cîrstea, C. D.; Marin, M.; Pătroi, D.; Mitrea, S.; Marinescu, V.; Grigore, F.; Tălpeanu, D.; Stancu, N.; Godeanu, P.; Melnic, C.

2017-06-01

Abstract Tungsten-copper (W-Cu) sintered parts with 75 wt.% W, 24 wt.% Cu and 1 wt.% Ni for using as arcing contacts in medium and high voltage switching devices were developed successfully by powder metallurgy (PM) techniques. Sintered parts with diameter of 50±0.5 mm and height of 6±0.5 mm were manufactured by pressing-sintering-infiltration (P-S-I) and spark plasma sintering (SPS) at sintering temperature of 1150°C, and 1050°C, respectively. Physical, chemical, electrical, thermal and mechanical properties of the samples were investigated. Microstructure was analyzed by optical microscopy and scanning electron microscopy. Material properties were influenced by the consolidation processes. The best results were achieved by SPS process. The relative density was more than 95 %, Vickers hardness HV1/15 was over 227, elastic modulus was over 143 GPa, and homogeneous microstructure was revealed. These good properties can contribute to higher lifetime of arcing contacts under severe working conditions.

High Thermoelectric Performance in Copper Telluride

DOE PAGES

He, Ying; Zhang, Tiansong; Shi, Xun; ...

2015-06-21

Recently, Cu 2-δ S and Cu 2-δ Se were reported to have an ultralow thermal conductivity and high thermoelectric figure of merit zT. Thus, as a member of the copper chalcogenide group, Cu 2-δ Te is expected to possess superior zTs because Te is less ionic and heavy. However, the zT value is low in the Cu 2Te sintered using spark plasma sintering, which is typically used to fabricate high-density bulk samples. In addition, the extra sintering processes may change the samples’ compositions as well as their physical properties, especially for Cu 2Te, which has many stable andmore » meta-stable phases as well as weaker ionic bonding between Cu and Te as compared with Cu 2S and Cu 2Se. In this study, high-density Cu 2Te samples were obtained using direct annealing without a sintering process. In the absence of sintering processes, the samples’ compositions could be well controlled, leading to substantially reduced carrier concentrations that are close to the optimal value. The electrical transports were optimized, and the thermal conductivity was considerably reduced. The zT values were significantly improved—to 1.1 at 1000 K—which is nearly 100% improvement. Furthermore, this method saves substantial time and cost during the sample’s growth. The study demonstrates that Cu 2-δ X (X=S, Se and Te) is the only existing system to show high zTs in the series of compounds composed of three sequential primary group elements.« less

Preparation of Functionally Graded Materials (FGMs) Using Coal Fly Ash and NiCr-Based Alloy Powder by Spark Plasma Sintering (SPS)

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

Kaneko, Gen-yo; Kitagawa, Hiroyuki; Hasezaki, Kazuhiro

2008-02-15

Functionally Graded Materials (FGMs) were prepared by spark plasma sintering (SPS) using coal fly ash and NiCr alloy powder. The coal fly ash was produced by the Misumi Coal Thermal Power Station (Chugoku Electric Power Co., Inc.), with 80 wt% nickel and 20 wt% chromium (Fukuda Metal Foil and Powder Co., Ltd.) used as source materials. The sintering temperature in the graphite die was 1000 deg. C. X-ray diffraction patterns of the sintered coal fly ash materials indicated that mullite (3Al{sub 2}O{sub 3}{center_dot}2SiO{sub 2}) and silica (SiO{sub 2}) phases were predominant. Direct joining of coal fly ash and NiCr causesmore » fracture at the interface. This is due to the mismatch in the thermal expansion coefficients (CTE). A crack in the FGM was observed between the two layers with a CTE difference of over 4.86x10{sup -6} K{sup -1}, while a crack in the FGM was difficult to detect when the CTE difference was less than 2.77x10{sup -6} K{sup -1}.« less

Production of a Powder Metallurgical Hot Work Tool Steel with Harmonic Structure by Mechanical Milling and Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Deirmina, Faraz; Pellizzari, Massimo; Federici, Matteo

2017-04-01

Commercial AISI-H13 gas atomized powders (AT) were mechanically milled (MM) to refine both the particle size and the microstructure. Different volume fractions of coarser grained (CG) AT powders were mixed with the ultra-fine grained (UFG) MM and consolidated by spark plasma sintering to obtain bulks showing a harmonic structure ( i.e. a 3D interconnected network of UFG areas surrounding the CG atomized particles). The low sintering temperature, 1373.15 K (1100 °C) and the short sintering time (30 minutes) made it possible to obtain near full density samples while preserving the refined microstructure induced by MM. A combination of high hardness and significantly improved fracture toughness is achieved by the samples containing 50 to 80 vol pct MM, essentially showing harmonic structure. The design allows to easily achieve specific application oriented properties by varying the MM volume fraction in the initial mixture. Hardness is governed by the fine-grained MM matrix and improved toughening is due to (1) deviatory effect of AT particles and (2) energy dissipation as a result of the decohesion in MM regions or AT and MM interface.

Possible observation of Griffith phase over large temperature range in plasma sintered La0.67Ca0.33MnO3

NASA Astrophysics Data System (ADS)

Mishra, D. K.; Roul, B. K.; Singh, S. K.; Srinivasu, V. V.

2018-02-01

We report on the possible observation of Griffith phase in a wide range of temperature (>272-378 K) in the 2.5 min plasma sintered La0.67Ca0.33MnO3 (LCMO) as deduced from careful electron spin resonance studies. This is 106 K higher than the paramagnetic to ferromagnetic transition (Curie transition ∼272 K) temperature. The indication of Griffith phase in such a wide range is not reported earlier by any group. We purposefully prepared LCMO samples by plasma sintering technique so as to create a disordered structure by rapid quenching which we believe, is the prime reason for the observation of Griffith Phase above the Curie transition temperature. The inverse susceptibility curve represents the existence of ferromagnetic cluster in paramagnetic region. The large resonance peak width (40-60 mT) within the temperature range 330-378 K confirms the sample magnetically inhomogeneity which is also established from our electron probe microstructure analysis (EPMA). EPMA establishes the presence of higher percentage of Mn3+ cluster in comparison to Mn4+. This is the reason for which Griffith state is enhanced largely to a higher range of temperature.

Formation of Fine B2/ β + O Structure and Enhancement of Hardness in the Aged Ti2AlNb-Based Alloys Prepared by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Li, Mengchen; Cai, Qi; Liu, Yongchang; Ma, Zongqing; Wang, Zumin; Huang, Yuan; Li, Huijun

2017-09-01

Ti2AlNb-based alloys synthesized at 1223 K (950 °C) by spark plasma sintering were aged at 973 K, 1023 K, 1073 K, and 1123 K (700 °C, 750 °C, 800 °C, and 850 °C), respectively. Phase composition, microstructure, and microhardness of the aged alloys were investigated in this study. Equiaxed O grains and Widmanstätten B2/ β + O laths were formed in the aged alloys, and the microhardness was improved in contrast with the spark plasma-sintered alloy without aging. The microhardness relies largely on the O-phase content, as well as the length and width of the O laths. In particular, complete Widmanstätten B2/ β + O laths, with locally finely dispersed β precipitates, were obtained in the alloy aged at 1073 K (800 °C), and the alloy exhibited the best microhardness performance. Such fine structure is due to the temperature-dependent transformations Oequiaxed→Oprimary + B2/ β primary, Oprimary→Osecondary + B2/ β secondary, and B2/ β primary→O.

Nanoclay/Polymer Composite Powders for Use in Laser Sintering Applications: Effects of Nanoclay Plasma Treatment

NASA Astrophysics Data System (ADS)

Almansoori, Alaa; Majewski, Candice; Rodenburg, Cornelia

2017-11-01

Plasma-etched nanoclay-reinforced Polyamide 12 (PA12) powder is prepared with its intended use in selective laser sintering (LS) applications. To replicate the LS process we present a downward heat sintering (DHS) process, carried out in a hot press, to fabricate tensile test specimens from the composite powders. The DHS parameters are optimized through hot stage microscopy, which reveal that the etched clay (EC)-based PA12 (EC/PA12) nanocomposite powder melts at a temperature 2°C higher than that of neat PA12, and 1-3°C lower than that of the nonetched clay-based nanocompsite (NEC/PA12 composite). We show that these temperature differences are critical to successful LS. The distribution of EC and NEC onto PA12 is investigated by scanning electron microscopy (SEM). SEM images show clearly that the plasma treatment prevents the micron-scale aggregation of the nanoclay, resulting in an improved elastic modulus of EC/PA12 when compared with neat PA12 and NEC/PA12. Moreover, the reduction in elongation at break for EC/PA12 is less pronounced than for NEC/PA12.

Non-Catalytic Reforming with Applications to Portable Power

DTIC Science & Technology

2013-10-01

and J.J. Beaman, Jr., “Freeform Fabrication of Non-Metallic Objects by Selective Laser Sintering and Infiltration”, Materials Science Forum, 561-565...for syngas production from jet fuel using various methods including catalysts [4, 47-54] and plasmas [55]. Investigations of noncatalytic reforming...Combustion of n-butanol in a spark -ignition IC engine. Fuel. 89(7): p. 1573-1582. 32. Behrens, D.A., I.C. Lee, and C.M. Waits, Catalytic combustion of

Can the use of pulsed direct current induce oscillation in the applied pressure during spark plasma sintering?

PubMed Central

Salamon, David; Eriksson, Mirva; Nygren, Mats; Shen, Zhijian

2012-01-01

The spark plasma sintering (SPS) process is known for its rapid densification of metals and ceramics. The mechanism behind this rapid densification has been discussed during the last few decades and is yet uncertain. During our SPS experiments we noticed oscillations in the applied pressure, related to a change in electric current. In this study, we investigated the effect of pulsed electrical current on the applied mechanical pressure and related changes in temperature. We eliminated the effect of sample shrinkage in the SPS setup and used a transparent quartz die allowing direct observation of the sample. We found that the use of pulsed direct electric current in our apparatus induces pressure oscillations with the amplitude depending on the current density. While sintering Ti samples we observed temperature oscillations resulting from pressure oscillations, which we attribute to magnetic forces generated within the SPS apparatus. The described current–pressure–temperature relations might increase understanding of the SPS process. PMID:27877472

Spark-plasma-sintering magnetic field assisted compaction of Co{sub 80}Ni{sub 20} nanowires for anisotropic ferromagnetic bulk materials

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

Ouar, Nassima; Schoenstein, Frédéric; Mercone, Silvana

We developed a two-step process showing the way for sintering anisotropic nanostructured bulk ferromagnetic materials. A new reactor has been optimized allowing the synthesis of several grams per batch of nanopowders via a polyol soft chemistry route. The feasibility of the scale-up has been successfully demonstrated for Co{sub 80}Ni{sub 20} nanowires and a massic yield of ∼97% was obtained. The thus obtained nanowires show an average diameter of ∼6 nm and a length of ∼270 nm. A new bottom-up strategy allowed us to compact the powder into a bulk nanostructured system. We used a spark-plasma-sintering technique under uniaxial compression andmore » low temperature assisted by a permanent magnetic field of 1 T. A macroscopic pellet of partially aligned nanowire arrays has been easily obtained. This showed optimized coercive properties along the direction of the magnetic field applied during compaction (i.e., the nanowires' direction)« less

Microstructure and Electrical Properties of AZO/Graphene Nanosheets Fabricated by Spark Plasma Sintering

PubMed Central

Yang, Shuang; Chen, Fei; Shen, Qiang; Lavernia, Enrique J.; Zhang, Lianmeng

2016-01-01

In this study we report on the sintering behavior, microstructure and electrical properties of Al-doped ZnO ceramics containing 0–0.2 wt. % graphene sheets (AZO-GNSs) and processed using spark plasma sintering (SPS). Our results show that the addition of <0.25 wt. % GNSs enhances both the relative density and the electrical resistivity of AZO ceramics. In terms of the microstructure, the GNSs are distributed at grain boundaries. In addition, the GNSs are also present between ZnO and secondary phases (e.g., ZnAl2O4) and likely contribute to the measured enhancement of Hall mobility (up to 105.1 cm2·V−1·s−1) in these AZO ceramics. The minimum resistivity of the AZO-GNS composite ceramics is 3.1 × 10−4 Ω·cm which compares favorably to the value of AZO ceramics which typically have a resistivity of 1.7 × 10−3 Ω·cm. PMID:28773759

Effects of intergranular phase on the coercivity for MnBi magnets prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Cao, J.; Huang, Y. L.; Hou, Y. H.; Zhang, G. Q.; Shi, Z. Q.; Zhong, Z. C.; Liu, Z. W.

2018-05-01

MnBi magnets with a high content of low temperature phase (LTP) and excellent magnetic properties were prepared by spark plasma sintering (SPS) using ball milling powders as precursors without magnetic purification. A complicated intergranular phase, which contains Mn phase, Bi phase, MnO phase, and even amorphous phase in MnBi magnets, was characterized and reported systematically. It was found that the formation of intergranular phase which was contributed by ball milling precursors and sintering mechanism, jointly, had important influence on the magnetic properties. The appropriate content of intergranular phase was beneficial in improving the coercivity due to the strong magnetic isolation effects. The optimum magnetic properties with Mr=26.0 emu/g, Hci= 7.11 kOe and (BH)max=1.53 MGOe at room temperature, and a maximum value Hci= 25.37 kOe at 550 K can be obtained. Strongly favorable magnetic properties make SPSed MnBi magnets an attractive candidate material for small permanent magnets used in high-temperature applications.

Spark Plasma Sintering of Commercial Zirconium Carbide Powders: Densification Behavior and Mechanical Properties

PubMed Central

Wei, Xialu; Back, Christina; Izhvanov, Oleg; Khasanov, Oleg L.; Haines, Christopher D.; Olevsky, Eugene A.

2015-01-01

Commercial zirconium carbide (ZrC) powder is consolidated by Spark Plasma Sintering (SPS). Processing temperatures range from 1650 to 2100 °C. Specimens with various density levels are obtained when performing single-die SPS at different temperatures. Besides the single-die tooling setup, a double-die tooling setup is employed to largely increase the actual applied pressure to achieve higher densification in a shorter processing time. In order to describe the densification mechanism of ZrC powder under SPS conditions, a power-law creep constitutive equation is utilized, whose coefficients are determined by the inverse regression of the obtained experimental data. The densification of the selected ZrC powder is shown to be likely associated with grain boundary sliding and dislocation glide controlled creep. Transverse rupture strength and microhardness of sintered specimens are measured to be up to 380 MPa and 24 GPa, respectively. Mechanical properties are correlated with specimens’ average grain size and relative density to elucidate the co-factor dependencies. PMID:28793550

The effect of spark plasma sintering on lithium disilicate glass-ceramics.

PubMed

Al Mansour, Fatima; Karpukhina, Natalia; Grasso, Salvatore; Wilson, Rory M; Reece, Mike J; Cattell, Michael J

2015-10-01

To evaluate the effects of spark plasma sintering (SPS) on the microstructure of lithium disilicate glass-ceramics. IPS e.max CAD glass-ceramic samples were processed using spark plasma sintering (SPS) and conventionally sintered (CS) as a comparison. Specimens were sintered at varying temperatures (T1: 840°C, T2: 820°C, T3: 800°C), heating rates (HR1: 150°C/min, HR2: 300°C/min, HR3: 500°C/min) and pressures (P1: 15MPa, P2: 50MPa, P3: 70MPa). IPS e.max Press glass powder samples were densified at 750 and 800°C (50 or 200MPa pressure). Samples were characterized using XRD, HTXRD, and SEM and quantitative image analysis. There was a significant increase in median crystal size (MCS) between the CS and the SPS T1 groups. A statistical difference (p>0.05) in MCS between SPS T1 and SPS T2 groups was observed. The SPS HR3 sample produced a smaller MCS than the CS, SPS HR1 and HR2 groups (p<0.05). The SPS P3 sample had a reduction in MCS compared with the CS group (p<0.05). XRD of the SPS samples revealed major lithium disilicate/lithium metasilicate phases and minor lithium orthophosphate and cristobalite/quartz phases. Densified IPS e.max Press glass samples resulted in fine fibrils or graduated lithium disilicate crystals. The effects of SPS were used to refine the microstructure of IPS e.max CAD lithium disilicate glass-ceramics. Densification by SPS of IPS e.max Press glass resulted in textured and fine nano-crystalline microstructures. SPS generated glass-ceramic microstructures may have unique properties and could be useful in the production of CAD/CAM materials for dentistry. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Study of distribution of Carbon nanotube in Al-CNT nanocomposite synthesized via Spark-Plasma sintering

NASA Astrophysics Data System (ADS)

Maiti, A.; Laha, T.

2018-03-01

In the present study, first ever attempt has been made to develop physically functionalized multiwalled carbon nanotube (MWCNT) reinforced Al-11 5Si alloy nanocomposites synthesized via novel consolidation technique viz spark plasma sintering (SPS). There is a recent trend in employing carbon nanotubes (CNTs), an allotrope of carbon, as reinforcement for high strength structural metallic composite materials, as these cylindrical nano-fibers poses extremely unique mechanical properties such as very high elastic modulus (~ 300 GPa to 1.5 TPa) as well as tensile strength (~150 GPa). However, it has remained as an ever-existing problem to achieve a porosity-free nanocrystalline matrix with homogenously dispersed CNTs, owing to the very high coagulation tendency of CNTs. The gas-atomized, spherical Al-11.5Si alloy powders (1-8 μm) were subjected to high energy ball milling for the purpose of achieving nanocrystallinity in the powders. The improvement in MWCNT dispersion was effort by treating the MWCNTs with a physical surfactant, sodium dodecyl sulfate (SDS). The nano-grained ball-milled Al-Si powders with varying MWCNT content (0.5 and 1 wt%) were consolidated via spark plasma sintering in order to retain the nano-sized grains in the Al-Si matrix, attributed to the faster and highly effective sintering kinetics of the sintering techniques. FESEM study shows problem of MWCNT agglomeration persists by addition of non-SDS treated as pristine MWCNT in the composite. After treated with SDS, MWCNTs are well separated out from each other and as a result of that good morphological and mechanical property such as high hardness value obtained after analysis. Detailed TEM study of the 0.5wt% MWCNT reinforced SPS nanocomposite revealed that the distribution of CNTs in the matrix. Mechanical analysis study of the nanocomposite attributes higher hardness in case of SDS treated CNT reinforced nanocomposite owing to less agglomeration problem of the CNT in the matrix. Nano-tribological data attributed variation of surface roughness after consolidated by SPS.

Sintering and microstructure of silicon carbide ceramic with Y3Al5O12 added by sol-gel method*

PubMed Central

Guo, Xing-zhong; Yang, Hui

2005-01-01

Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’. PMID:15682507

77 FR 51046 - Certain Sintered Rare Earth Magnets, Methods of Making Same and Products Containing Same; Notice...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-23

... INTERNATIONAL TRADE COMMISSION [Docket No. 2908] Certain Sintered Rare Earth Magnets, Methods of... Certain Sintered Rare Earth Magnets, Methods of Making Same and Products Containing Same, DN 2908; the... importation, and the sale within the United States after importation of certain sintered rare earth magnets...

77 FR 58578 - Certain Sintered Rare Earth Magnets, Methods of Making Same and Products Containing Same...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-09-21

... INTERNATIONAL TRADE COMMISSION [Investigation No. 337-TA-855] Certain Sintered Rare Earth Magnets... importation of certain sintered rare earth magnets, methods of making same and products containing same by... importation of certain sintered rare earth magnets, methods of making same and products containing same that...

Consolidation of metallic hollow spheres by electric sintering

NASA Astrophysics Data System (ADS)

Mironov, V.; Tatarinov, A.; Lapkovsky, V.

2017-07-01

This paper considers peculiarities of the technology of production of structures from metallic hollow spheres (MHS) using magnetic fields and electric sintering. In these studies, the raw material was MHS obtained by burning of polystyrene balls coated by carbon steel. MHS had an outer diameter of 3-5 mm and a steel wall thickness of 70-120 microns. Pulsed current generators were used for electric sintering of MHS to obtain different spatial structures. Since MHS have small strength, the compressive pressure during sintering should be minimal. To improve the adhesion strength and reduce the required energy for sintering, hollow spheres were coated with copper by ion-plasma sputtering in vacuum. The coating thickness was 10-15 microns. The ferromagnetic properties of MHS allowed using of magnet fields for orientation of the spheres in the structures, as well as using of perforated tapes acting as orienting magnetic cores. Ultrasonic testing of MHS structures has been tried using through propagation of ultrasound in low kilohertz frequency range. Sensitivity of the propagation parameters to water filling of inter-spheres space and sintering temperature was demonstrated.

Recent progress on RE2O3-Mo/W emission materials.

PubMed

Wang, Jinshu; Zhang, Xizhu; Liu, Wei; Cui, Yuntao; Wang, Yiman; Zhou, Meiling

2012-08-01

RE2O3-Mo/W cathodes were prepared by powder metallurgy method. La2O3-Y2O3-Mo cermet cathodes prepared by traditional sintering method and spark plasma sintering (SPS) exhibit different secondary emission properties. The La2O3-Y2O3-Mo cermet cathode prepared by SPS method has smaller grain size and exhibits better secondary emission performance. Monte carlo calculation results indicate that the secondary electron emission way of the cathode correlates with the grain size. Decreasing the grain size can decrease the positive charging effect of RE2O3 and thus is favorable for the escaping of secondary electrons to vacuum. The Scandia doped tungsten matrix dispenser cathode with a sub-micrometer microstructure of matrix with uniformly distributed nanometer-particles of Scandia has good thermionic emission property. Over 100 A/cm2 full space charge limited current density can be obtained at 950Cb. The cathode surface is covered by a Ba-Sc-O active surface layer with nano-particles distributing mainly on growth steps of W grains, leads to the conspicuous emission property of the cathode.

Localized Overheating Phenomena and Optimization of Spark-Plasma Sintering Tooling Design

PubMed Central

Giuntini, Diletta; Olevsky, Eugene A.; Garcia-Cardona, Cristina; Maximenko, Andrey L.; Yurlova, Maria S.; Haines, Christopher D.; Martin, Darold G.; Kapoor, Deepak

2013-01-01

The present paper shows the application of a three-dimensional coupled electrical, thermal, mechanical finite element macro-scale modeling framework of Spark Plasma Sintering (SPS) to an actual problem of SPS tooling overheating, encountered during SPS experimentation. The overheating phenomenon is analyzed by varying the geometry of the tooling that exhibits the problem, namely by modeling various tooling configurations involving sequences of disk-shape spacers with step-wise increasing radii. The analysis is conducted by means of finite element simulations, intended to obtain temperature spatial distributions in the graphite press-forms, including punches, dies, and spacers; to identify the temperature peaks and their respective timing, and to propose a more suitable SPS tooling configuration with the avoidance of the overheating as a final aim. Electric currents-based Joule heating, heat transfer, mechanical conditions, and densification are imbedded in the model, utilizing the finite-element software COMSOL™, which possesses a distinguishing ability of coupling multiple physics. Thereby the implementation of a finite element method applicable to a broad range of SPS procedures is carried out, together with the more specific optimization of the SPS tooling design when dealing with excessive heating phenomena. PMID:28811398

Corrosion Behavior and Strength of Dissimilar Bonding Material between Ti and Mg Alloys Fabricated by Spark Plasma Sintering

PubMed Central

Pripanapong, Patchara; Kariya, Shota; Luangvaranunt, Tachai; Umeda, Junko; Tsutsumi, Seiichiro; Takahashi, Makoto; Kondoh, Katsuyoshi

2016-01-01

Ti and solution treated Mg alloys such as AZ31B (ST), AZ61 (ST), AZ80 (ST) and AZ91 (ST) were successfully bonded at 475 °C by spark plasma sintering, which is a promising new method in welding field. The formation of Ti3Al intermetallic compound was found to be an important factor in controlling the bonding strength and galvanic corrosion resistance of dissimilar materials. The maximum bonding strength and bonding efficiency at 193 MPa and 96% were obtained from Ti/AZ91 (ST), in which a thick and uniform nano-level Ti3Al layer was observed. This sample also shows the highest galvanic corrosion resistance with a measured galvanic width and depth of 281 and 19 µm, respectively. The corrosion resistance of the matrix on Mg alloy side was controlled by its Al content. AZ91 (ST) exhibited the highest corrosion resistance considered from its corrode surface after corrosion test in Kroll’s etchant. The effect of Al content in Mg alloy on bonding strength and corrosion behavior of Ti/Mg alloy (ST) dissimilar materials is discussed in this work. PMID:28773788

Methods of flash sintering

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

Raj, Rishi; Cologna, Marco; Francis, John S.

2016-05-10

This disclosure provides methods of flash sintering and compositions created by these methods. Methods for sintering multilayered bodies are provided in which a sintered body is produced in less than one minute. In one aspect, each layer is of a different composition, and may be constituted wholly from a ceramic or from a combination of ceramic and metallic particles. When the body includes a layer of an anode composition, a layer of an electrolyte composition and a layer of a cathode composition, the sintered body can be used to produce a solid oxide fuel cell.

Hydroxyapatite moldable formulation using natural rubber latex as binder.

PubMed

Sailaja, G S; Ramesh, P; Varma, H K

2007-07-01

A simple but efficient processing method for shaping intricate bioceramic green bodies has been developed by using natural rubber latex as binder. Different shapes of hydroxyapatite Ca10(PO4)6(OH)2 (HAP) were molded from a composite formulation containing wet precipitated HAP, natural rubber latex (NRL), and a stabilizer. On controlled heat treatment followed by sintering, dense shapes of HAP contours were obtained. The thermal degradation profile of HAP-NRL composites shows that NRL degrades slowly without any abrupt exotherm. The results of energy dispersive X-ray analysis together with inductively coupled plasma (ICP) analysis indicate that the inorganic residue of NRL does not contain any heavy element. The sintered density of the samples increased with increased HAP content in the formulation and percentage shrinkage reduced accordingly. On varying the HAP content in the formulation from 35 to 95 wt %, the compositions with 85, 90, 92, and 95 wt % HAP showed better flexural strength in the range 40-54 MPa and a flexural modulus value in the range 36-50 GPa. The fracture morphology, as observed by the scanning electron microscope confirms that with increased HAP content in the formulation the sample microstructure attains higher uniformity. The Vickers microhardness for the samples sintered at two different temperatures (1150 and 1250 degrees C) showed that hardness increases with increase in the sintering temperature with a maximum for the highest HAP loaded formulation. Copyright 2006 Wiley Periodicals, Inc.

Multiphase-Multifunctional Ceramic Coatings

DTIC Science & Technology

2013-06-30

were conducted at 1200-1600° C from 10-24 h. Densification of powders in the pyrochlore-fuorite system was also performed by Spark Plasma Sintering ...capability with emphasis on improving toughness and phase stability. The primary goal was clearly accomplished by developing an instrumented air plasma ...composition. Coating compositions were synthesized by atmospheric plasma spray (APS) at CINVESTAV facilities, and dense monolithic counterparts were

Pressureless sintering of whisker-toughened ceramic composites

DOEpatents

Tiegs, T.N.

1993-05-04

A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

Pressureless sintering of whiskered-toughened ceramic composites

DOEpatents

Tiegs, Terry N.

1994-01-01

A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

Pressureless sintering of whisker-toughened ceramic composites

DOEpatents

Tiegs, Terry N.

1993-01-01

A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

Effect of SiC Nanowhisker on the Microstructure and Mechanical Properties of WC-Ni Cemented Carbide Prepared by Spark Plasma Sintering

PubMed Central

Fu, Zhiqiang; Wang, Chengbiao

2014-01-01

Ultrafine tungsten carbide-nickel (WC-Ni) cemented carbides with varied fractions of silicon carbide (SiC) nanowhisker (0–3.75 wt.%) were fabricated by spark plasma sintering at 1350°C under a uniaxial pressure of 50 MPa with the assistance of vanadium carbide (VC) and tantalum carbide (TaC) as WC grain growth inhibitors. The effects of SiC nanowhisker on the microstructure and mechanical properties of the as-prepared WC-Ni cemented carbides were investigated. X-ray diffraction analysis revealed that during spark plasma sintering (SPS) Ni may react with the applied SiC nanowhisker, forming Ni2Si and graphite. Scanning electron microscopy examination indicated that, with the addition of SiC nanowhisker, the average WC grain size decreased from 400 to 350 nm. However, with the additional fractions of SiC nanowhisker, more and more Si-rich aggregates appeared. With the increase in the added fraction of SiC nanowhisker, the Vickers hardness of the samples initially increased and then decreased, reaching its maximum of about 24.9 GPa when 0.75 wt.% SiC nanowhisker was added. However, the flexural strength of the sample gradually decreased with increasing addition fraction of SiC nanowhisker. PMID:25003143

Microstructural evolution and sliding wear studies of copper-alumina micro- and nano-composites fabricated by spark plasma sintering

NASA Astrophysics Data System (ADS)

Dash, Khushbu; Chaira, Debasis; Ray, Bankim Chandra

2015-05-01

Copper-alumina nanocomposites of 0.5, 1, 3, 5, 7 vol.% alumina (average size <50 nm) reinforced in copper matrix were fabricated using spark plasma sintering (SPS) technique. Another set of microcomposites containing 1, 5, 20 vol.% of alumina (average size ˜10 μm) had been fabricated to compare the physical as well as mechanical attributes of composites with variation of reinforcement particle size. These micro- and nano-composites have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) followed by microhardness, nanoindentation hardness, and wear measurements. It has been found that hardness values are higher for nanocomposites as compared to microcomposites. It is also found that wear resistance increases with increasing alumina content. The microcomposites show better wear resistance than nanocomposites for the same composition. The interaction of copper and alumina results in the formation of CuAlO2 which manifests differential interfacial phenomenon. We have obtained 95.82% densification and 93.17 HV hardness for spark plasma sintered Cu-20 vol.% Al2O3 microcomposite. The wear rate is appreciably low, that is, 0.86×10-4 mm3N-1m-1 for 20 vol.% alumina reinforced copper microcomposite.

Electric field-assisted sintering of nanocrystalline hydroxyapatite for biomedical applications

NASA Astrophysics Data System (ADS)

Tran, Tien Bich

As the main inorganic component of bone, hydroxyapatite (HA, Ca 10(PO4)6(OH)2) should be an ideal candidate in biomaterials selection. When grain sizes are in the nanometric regime, protein adsorption and cell adhesion are enhanced, while strength, hardness, and wear resistance are improved. Unfortunately, low phase stability, poor sinterability, and a tendency towards exaggerated grain coarsening challenge full densification of nanocrystalline hydroxyapatite by conventional sintering methods. The field-assisted sintering technique (FAST) has successfully consolidated a variety of nanocrystalline metals and ceramics in dramatically reduced times. The sintering enhancements observed during FAST can be attributed to thermal and athermal effects. The rapid heating rates (up to ˜1000ºC/min) afforded by FAST contribute a significant thermal effect. Since fast heating rates reduce powder exposure to sub-sintering temperatures, non-densifying surface diffusion is limited. The athermal effects of FAST are less well understood and can include plasma generation, dielectric breakdown, particle surface cleaning, grain boundary pinning, and space charge effects. Applying the field-assisted sintering technique to nanocrystalline hydroxyapatite yielded surprising results. Deviations from conventional densification behavior were observed, with dehydroxylation identified as the most deleterious process to densification as well as mechanical and biological performance. Since hydroxyapatite is not a stable phase at high temperatures and low water partial pressure atmospheres, desintering due to dehydroxylation-related pore formation became apparent during Stage III sintering. In fact, the degree of desintering and pore formation increased with the extent of Stage III sintering and grain growth. The atomic rearrangements taking place during grain boundary migration are believed to favor the formation of more-stable oxyapatite through hydroxyapatite dehydroxylation. This behavior was consistent during varied heating rate (50--400ºC/min) and varied pressure application (25--90 MPa) studies. While in vitro cytocompatibility studies using MG63 osteoblast-like cells demonstrated the biocompatibility of the FAST-processed specimens, bioactivity was sensitive to processing parameters. Since extensive dehydroxylation reduces the surface charge of the sintered materials, apatite deposition during simulated body fluid immersion only occurred when dehydroxylation was mild---i.e., on specimens sintered at low temperatures (800--900ºC) or for short periods. Microstructural investigations revealed that HA sintered at temperatures above 900ºC under an applied electric field contained nanometric residual pores in grain interiors, as well as micron-sized dehydroxylation-related pores at grain boundaries and grain boundary junctions. These larger pores were responsible for the increasing embrittlement of specimens sintered at higher temperatures. Although grain size dependence could not be found in the 60--100 nm grain size range, fracture toughness (KIC = 1.92 MPa√m, maximum) increased with decreasing sintering temperature. Results from the suite of investigations conducted demonstrate that biocompatible and bioactive nanocrystalline hydroxyapatite with enhanced mechanical properties can be efficiently manufactured by field-assisted sintering under controlled processing conditions.

Parallel Large-Scale Molecular Dynamics Simulation Opens New Perspective to Clarify the Effect of a Porous Structure on the Sintering Process of Ni/YSZ Multiparticles.

PubMed

Xu, Jingxiang; Higuchi, Yuji; Ozawa, Nobuki; Sato, Kazuhisa; Hashida, Toshiyuki; Kubo, Momoji

2017-09-20

Ni sintering in the Ni/YSZ porous anode of a solid oxide fuel cell changes the porous structure, leading to degradation. Preventing sintering and degradation during operation is a great challenge. Usually, a sintering molecular dynamics (MD) simulation model consisting of two particles on a substrate is used; however, the model cannot reflect the porous structure effect on sintering. In our previous study, a multi-nanoparticle sintering modeling method with tens of thousands of atoms revealed the effect of the particle framework and porosity on sintering. However, the method cannot reveal the effect of the particle size on sintering and the effect of sintering on the change in the porous structure. In the present study, we report a strategy to reveal them in the porous structure by using our multi-nanoparticle modeling method and a parallel large-scale multimillion-atom MD simulator. We used this method to investigate the effect of YSZ particle size and tortuosity on sintering and degradation in the Ni/YSZ anodes. Our parallel large-scale MD simulation showed that the sintering degree decreased as the YSZ particle size decreased. The gas fuel diffusion path, which reflects the overpotential, was blocked by pore coalescence during sintering. The degradation of gas diffusion performance increased as the YSZ particle size increased. Furthermore, the gas diffusion performance was quantified by a tortuosity parameter and an optimal YSZ particle size, which is equal to that of Ni, was found for good diffusion after sintering. These findings cannot be obtained by previous MD sintering studies with tens of thousands of atoms. The present parallel large-scale multimillion-atom MD simulation makes it possible to clarify the effects of the particle size and tortuosity on sintering and degradation.

Pressureless sintering of whiskered-toughened ceramic composites

DOEpatents

Tiegs, T.N.

1994-12-27

A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method. 6 figures.

An application of powder metallurgy to dentistry.

PubMed

Oda, Y; Ueno, S; Kudoh, Y

1995-11-01

Generally, the dental casting method is used to fabricate dental prostheses made with metal. The method of fabricating dental prostheses from sintered titanium alloy has certain advantages: the elimination of casting defects, a sintering temperature that is lower than the melting point, and a shorter processing time. By examining (1) the properties of green, sintered compacts of titanium powder, (2) the effects of adding aluminum powder on the properties of green, sintered compacts of Ti-Al compound, and (3) the effects of adding copper powder on the properties of green, sintered compacts of Ti-Al-Cu compound, the authors developed a sintered titanium alloy on a trial basis. Because the properties satisfied the requirements of dental restorations, a powder metallurgical method of making dental restorations from this sintered titanium alloy was devised. Applications of such sintered titanium alloys for the metal coping of metal-ceramic crowns and denture base plates were discussed.

SinterHab

NASA Astrophysics Data System (ADS)

Rousek, Tomáš; Eriksson, Katarina; Doule, Ondřej

2012-05-01

This project describes a design study for a core module on a Lunar South Pole outpost, constructed by 3D printing technology with the use of in-situ resources and equipped with a bio-regenerative life support system. The module would be a hybrid of deployable (CLASS II) and in-situ built (CLASS III) structures. It would combine deployable membrane structures and pre-integrated rigid elements with a sintered regolith shell for enhanced radiation and micrometeorite shielding. The closed loop ecological system would support a sustainable presence on the Moon with particular focus on research activities. The core module accommodates from four to eight people, and provides laboratories as a test bed for development of new lunar technologies directly in the environment where they will be used. SinterHab also includes an experimental garden for development of new bio-regenerative life support system elements. The project explores these various concepts from an architectural point-of-view particularly, as they constitute the building, construction and interior elements. The construction method for SinterHab is based on 3D printing by sintering of the lunar regolith. Sinterator robotics 3D printing technology proposed by NASA JPL enables construction of future generations of large lunar settlements with little imported material and the use of solar energy. The regolith is processed, placed and sintered by the Sinterator robotics system which combines the NASA ATHLETE and the Chariot remotely controlled rovers. Microwave sintering creates a rigid structure in the form of walls, vaults and other architectural elements. The interior is coated with a layer of inflatable membranes inspired by the TransHab project. The life-support system is mainly bio-regenerative and several parts of the system are intrinsically multifunctional and serve more than one purpose. The plants for food production are also an efficient part of atmosphere revitalization and water treatment. Moreover, the plants will be used as a "winter garden" for psychological and recreational purposes. The water in the revitalization system has a multifunctional use, as radiation shielding in the safe-haven habitat core. The garden module creates an artificial outdoor environment mitigating the notion of confinement on the lunar surface. Fiber optics systems and plasma lamps are used for transmission of natural and artificial light into the interior.

Highly Enhanced Thermoelectric Properties of Bi/Bi2S3 Nanocomposites.

PubMed

Ge, Zhen-Hua; Qin, Peng; He, DongSheng; Chong, Xiaoyu; Feng, Dan; Ji, Yi-Hong; Feng, Jing; He, Jiaqing

2017-02-08

Bismuth sulfide (Bi 2 S 3 ) has been of high interest for thermoelectric applications due to the high abundance of sulfur on Earth. However, the low electrical conductivity of pristine Bi 2 S 3 results in a low figure of merit (ZT). In this work, Bi 2 S 3 @Bi core-shell nanowires with different Bi shell thicknesses were prepared by a hydrothermal method. The core-shell nanowires were densified to Bi/Bi 2 S 3 nanocomposite by spark plasma sintering (SPS), and the structure of the nanowire was maintained as the nanocomposite due to rapid SPS processing and low sintering temperature. The thermoelectric properties of bulk samples were investigated. The electrical conductivity of a bulk sample after sintering at 673 K for 5 min using Bi 2 S 3 @Bi nanowire powders prepared by treating Bi 2 S 3 nanowires in a hydrazine solution for 3 h is 3 orders of magnitude greater than that of a pristine Bi 2 S 3 sample. The nanocomposite possessed the highest ZT value of 0.36 at 623 K. This represents a new strategy for densifying core-shell powders to enhance their thermoelectric properties.

'Beautiful' unconventional synthesis and processing technologies of superconductors and some other materials.

PubMed

Badica, Petre; Crisan, Adrian; Aldica, Gheorghe; Endo, Kazuhiro; Borodianska, Hanna; Togano, Kazumasa; Awaji, Satoshi; Watanabe, Kazuo; Sakka, Yoshio; Vasylkiv, Oleg

2011-02-01

Superconducting materials have contributed significantly to the development of modern materials science and engineering. Specific technological solutions for their synthesis and processing helped in understanding the principles and approaches to the design, fabrication and application of many other materials. In this review, we explore the bidirectional relationship between the general and particular synthesis concepts. The analysis is mostly based on our studies where some unconventional technologies were applied to different superconductors and some other materials. These technologies include spray-frozen freeze-drying, fast pyrolysis, field-assisted sintering (or spark plasma sintering), nanoblasting, processing in high magnetic fields, methods of control of supersaturation and migration during film growth, and mechanical treatments of composite wires. The analysis provides future research directions and some key elements to define the concept of 'beautiful' technology in materials science. It also reconfirms the key position and importance of superconductors in the development of new materials and unconventional synthesis approaches.

Fabrication of Carbon Nanotube - Chromium Carbide Composite Through Laser Sintering

NASA Astrophysics Data System (ADS)

Liu, Ze; Gao, Yibo; Liang, Fei; Wu, Benxin; Gou, Jihua; Detrois, Martin; Tin, Sammy; Yin, Ming; Nash, Philip; Tang, Xiaoduan; Wang, Xinwei

2016-03-01

Ceramics often have high hardness and strength, and good wear and corrosion resistance, and hence have many important applications, which, however, are often limited by their poor fracture toughness. Carbon nanotubes (CNTs) may enhance ceramic fracture toughness, but hot pressing (which is one typical approach of fabricating CNT-ceramic composites) is difficult to apply for applications that require localized heat input, such as fabricating composites as surface coatings. Laser beam may realize localized material sintering with little thermal effect on the surrounding regions. However, for the typical ceramics for hard coating applications (as listed in Ref.[1]), previous work on laser sintering of CNT-ceramic composites with mechanical property characterizations has been very limited. In this paper, research work has been reported on the fabrication and characterization of CNT-ceramic composites through laser sintering of mixtures of CNTs and chromium carbide powders. Under the studied conditions, it has been found that laser-sintered composites have a much higher hardness than that for plasma-sprayed composites reported in the literature. It has also been found that the composites obtained by laser sintering of CNTs and chromium carbide powder mixtures have a fracture toughness that is ~23 % higher than the material obtained by laser sintering of chromium carbide powders without CNTs.

Effect of reinforcement phase on the mechanical property of tungsten nanocomposite synthesized by spark plasma sintering

DOE PAGES

Lee, Jin -Kyu; Kim, Song -Yi; Ott, Ryan T.; ...

2015-07-15

Nanostructured tungsten composites were fabricated by spark plasma sintering of nanostructured composite powders. The composite powders, which were synthesized by mechanical milling of tungsten and Ni-based alloy powders, are comprised of alternating layers of tungsten and metallic glass several hundred nanometers in size. The mechanical behavior of the nanostructured W composite is similar to pure tungsten, however, in contrast to monolithic pure tungsten, some macroscopic compressive plasticity accompanies the enhanced maximum strength up to 2.4 GPa by introducing reinforcement. As a result, we have found that the mechanical properties of the composites strongly depend on the uniformity of the nano-grainedmore » tungsten matrix and reinforcement phase distribution.« less

Fabrication of Titanium-Niobium-Zirconium-Tantalium Alloy (TNZT) Bioimplant Components with Controllable Porosity by Spark Plasma Sintering

PubMed Central

Rechtin, Jack; Torresani, Elisa; Ivanov, Eugene; Olevsky, Eugene

2018-01-01

Spark Plasma Sintering (SPS) is used to fabricate Titanium-Niobium-Zirconium-Tantalum alloy (TNZT) powder—based bioimplant components with controllable porosity. The developed densification maps show the effects of final SPS temperature, pressure, holding time, and initial particle size on final sample relative density. Correlations between the final sample density and mechanical properties of the fabricated TNZT components are also investigated and microstructural analysis of the processed material is conducted. A densification model is proposed and used to calculate the TNZT alloy creep activation energy. The obtained experimental data can be utilized for the optimized fabrication of TNZT components with specific microstructural and mechanical properties suitable for biomedical applications. PMID:29364165

Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

NASA Astrophysics Data System (ADS)

Bathula, Sivaiah; Gahtori, Bhasker; Jayasimhadri, M.; Tripathy, S. K.; Tyagi, Kriti; Srivastava, A. K.; Dhar, Ajay

2014-08-01

Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si80Ge20 alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si80Ge20 alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.

The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering

PubMed Central

Cui, Guodong; Wei, Xialu; Olevsky, Eugene A.; German, Randall M.; Chen, Junying

2016-01-01

High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. The compressive strength and energy absorption characteristics of the FPSPS processed specimens are examined here to be correspondingly improved as a result of the refined microstructure. PMID:28773617

Spark plasma sintering synthesis of porous nanocrystalline titanium alloys for biomedical applications.

PubMed

Nicula, R; Lüthen, F; Stir, M; Nebe, B; Burkel, E

2007-11-01

The reason for the extended use of titanium and its alloys as implant biomaterials stems from their lower elastic modulus, their superior biocompatibility and improved corrosion resistance compared to the more conventional stainless steel and cobalt-based alloys [Niinomi, M., Hattori, T., Niwa, S., 2004. Material characteristics and biocompatibility of low rigidity titanium alloys for biomedical applications. In: Jaszemski, M.J., Trantolo, D.J., Lewandrowski, K.U., Hasirci, V., Altobelli, D.E., Wise, D.L. (Eds.), Biomaterials in Orthopedics. Marcel Dekker Inc., New York, pp. 41-62]. Nanostructured titanium-based biomaterials with tailored porosity are important for cell-adhesion, viability, differentiation and growth. Newer technologies like foaming or low-density core processing were recently used for the surface modification of titanium alloy implant bodies to stimulate bone in-growth and improve osseointegration and cell-adhesion, which in turn play a key role in the acceptance of the implants. We here report preliminary results concerning the synthesis of mesoporous titanium alloy bodies by spark plasma sintering. Nanocrystalline cp Ti, Ti-6Al-4V, Ti-Al-V-Cr and Ti-Mn-V-Cr-Al alloy powders were prepared by high-energy wet-milling and sintered to either full-density (cp Ti, Ti-Al-V) or uniform porous (Ti-Al-V-Cr, Ti-Mn-V-Cr-Al) bulk specimens by field-assisted spark plasma sintering (FAST/SPS). Cellular interactions with the porous titanium alloy surfaces were tested with osteoblast-like human MG-63 cells. Cell morphology was investigated by scanning electron microscopy (SEM). The SEM analysis results were correlated with the alloy chemistry and the topographic features of the surface, namely porosity and roughness.

Plasma Methods of Obtainment of Multifunctional Composite Materials, Dispersion-Hardened by Nanoparticles

NASA Astrophysics Data System (ADS)

Sizonenko, O. N.; Grigoryev, E. G.; Pristash, N. S.; Zaichenko, A. D.; Torpakov, A. S.; Lypian, Ye. V.; Tregub, V. A.; Zholnin, A. G.; Yudin, A. V.; Kovalenko, A. A.

2017-09-01

High voltage electric discharge (HVED) in disperse system "hydrocarbon liquid - powder" due to impact of plasma discharge channel, electromagnetic fields, shock waves mechanical impact, hydro flows and volume microcavitation leads to synthesis of nanocarbon, metal powders dispersion and synthesis of micro- (from 10-6 to 10-7 m) and nanosized (from 10-7 to 10-9 m) composite powders of hardening phases. Spark plasma sintering (SPS) of powder mixtures allows targeted control of grain growth rate and thus allows obtainment of multifunctional composite materials dispersion hardened by nanoparticles. Processes of HVED synthesis of micro- and nanosized powders of new compositions from elemental metal powders and their mixtures with the subsequent application of high-speed SPS of obtained powders create conditions for increase of strength (by 10-20 %), hardness and wear-resistance (by 30-60 %) of obtained materials.

Strength and fracture mechanism of iron reinforced tricalcium phosphate cermet fabricated by spark plasma sintering.

PubMed

Tkachenko, Serhii; Horynová, Miroslava; Casas-Luna, Mariano; Diaz-de-la-Torre, Sebastian; Dvořák, Karel; Celko, Ladislav; Kaiser, Jozef; Montufar, Edgar B

2018-05-01

The present work studies the microstructure and mechanical performance of tricalcium phosphate (TCP) based cermet toughened by iron particles. A novelty arises by the employment of spark plasma sintering for fabrication of the cermet. Results showed partial transformation of initial alpha TCP matrix to beta phase and the absence of oxidation of iron particles, as well as a lack of chemical reaction between TCP and iron components during sintering. The values of compressive and tensile strength of TCP/Fe cermet were 3.2 and 2.5 times, respectively, greater than those of monolithic TCP. Fracture analysis revealed the simultaneous action of crack-bridging and crack-deflection microstructural toughening mechanisms under compression. In contrast, under tension the reinforcing mechanism was only crack-bridging, being the reason for smaller increment of strength. Elastic properties of the cermet better matched values reported for human cortical bone. Thereby the new TCP/Fe cermet has potential for eventual use as a material for bone fractures fixation under load-bearing conditions. Copyright © 2018 Elsevier Ltd. All rights reserved.

Si-Ge Nano-Structured with Tungsten Silicide Inclusions

NASA Technical Reports Server (NTRS)

Mackey, Jon; Sehirlioglu, Alp; Dynys, Fred

2014-01-01

Traditional silicon germanium high temperature thermoelectrics have potential for improvements in figure of merit via nano-structuring with a silicide phase. A second phase of nano-sized silicides can theoretically reduce the lattice component of thermal conductivity without significantly reducing the electrical conductivity. However, experimentally achieving such improvements in line with the theory is complicated by factors such as control of silicide size during sintering, dopant segregation, matrix homogeneity, and sintering kinetics. Samples are prepared using powder metallurgy techniques; including mechanochemical alloying via ball milling and spark plasma sintering for densification. In addition to microstructural development, thermal stability of thermoelectric transport properties are reported, as well as couple and device level characterization.

WSi2 in Si(1-x)Ge(x) Composites: Processing and Thermoelectric Properties

NASA Technical Reports Server (NTRS)

Mackey, Jonathan A.; Sehirlioglu, Alp; Dynys, Fred

2015-01-01

Traditional SiGe thermoelectrics have potential for enhanced figure of merit (ZT) via nano-structuring with a silicide phase, such as WSi2. A second phase of nano-sized silicides can theoretically reduce the lattice component of thermal conductivity without significantly reducing the electrical conductivity. However, experimentally achieving such improvements in line with the theory is complicated by factors such as control of silicide size during sintering, dopant segregation, matrix homogeneity, and sintering kinetics. Samples were prepared using powder metallurgy techniques; including mechano-chemical alloying, via ball milling, and spark plasma sintering for densification. Processing, micro-structural development, and thermoelectric properties will be discussed. Additionally, couple and device level characterization will be introduced.

Plasma methods of obtainment of multifunctional composite materials, dispersion-hardened by nanoparticles

NASA Astrophysics Data System (ADS)

Sizonenko, O. N.; Grigoryev, E. G.; Zaichenko, A. D.; Pristash, N. S.; Torpakov, A. S.; Lipyan, Ye V.; Tregub, V. A.; Zholnin, A. G.; Yudin, A. V.; Kovalenko, A. A.

2016-04-01

The new approach in developed plasma methods consists in that dispersionhardening additives (TiC, TiB2 in particular) are not mechanically added to powder mixture as additional component, as in conventional methods, but are instead synthesized during high voltage electric discharges (HVED) in disperse system “hydrocarbon liquid - powder” preservation of ultrafine structure is ensured due to use of spark plasma sintering (SPS) as a consolidation method. HVED in disperse system “hydrocarbon liquid - powder” due to impact of plasma discharge channel, electromagnetic fields, shock waves mechanical impact, hydro flows and volume microcavitation leads to synthesis of nanocarbon, metal powders dispersion and synthesis of micro- (from 10-6 to 10-7 m) and nanosized (from 10-7 to 10-9 m) composite powders of hardening phases. SPS is the passage of pulsed current (superposition of direct and alternating current) through powder with the simultaneous mechanical compressing. The formation of plasma is initiated in gaseous phase that fills gaps between particles. SPS allows targeted control of grain growth rate and thus allows obtainment of multifunctional composite materials dispersion hardened by nanoparticles. Processes of HVED synthesis of micro- and nanosized powders of new compositions from elemental metal powders and their mixtures with the subsequent application of high-speed SPS of obtained powders create conditions for increase of strength (by 10 - 20%), hardness and wear-resistance (by 30 - 60%) of obtained materials.

Emerging Ceramic-based Materials for Dentistry

PubMed Central

Denry, I.; Kelly, J.R.

2014-01-01

Our goal is to give an overview of a selection of emerging ceramics and issues for dental or biomedical applications, with emphasis on specific challenges associated with full-contour zirconia ceramics, and a brief synopsis on new machinable glass-ceramics and ceramic-based interpenetrating phase composites. Selected fabrication techniques relevant to dental or biomedical applications such as microwave sintering, spark plasma sintering, and additive manufacturing are also reviewed. Where appropriate, the authors have added their opinions and guidance. PMID:25274751

Multi-Scale Microstructure and Mechanical Properties of High Carbon Eutectic Tantalum Carbide Reinforced with Carbon Nanotubes

DTIC Science & Technology

2012-07-02

more effective grain growth inhibitors. Transverse Rupture Strength of TaC reinforced with shorter CNTs displayed highest strength/density ratio with...microstructural features. 6. Strength to density ratio of CNT reinforced TaC increased from 17 to 28, which is an increase of ~ 65%. 7. Oxidation behavior of... reinforced with carbon fibers for space applications [15,16]. In recent years, Spark Plasma Sintering (SPS) also known as Electric Field Assisted Sintering

Wear resistance of Ti/TiB composites produced by spark plasma sintering

NASA Astrophysics Data System (ADS)

Ozerov, M.; Stepanov, N.; Zherebtsov, S.

2017-12-01

The tribological characteristics of Ti/TiB composites were studied in as-sintered condition and after isothermal multiaxial forging. A mixture of commercially pure Ti and TiB2 powders was used to produce Ti/TiB composites with 8.5 and 17 vol % of TiB via in-situ Ti+TiB2→Ti+TiB reactions during spark plasma sintering at 1000°C. During isothermal multiaxial forging (MAF), the material was exposed to successive compressions along three orthogonal directions at a temperature of 700°C and strain rate of 10-3 s-1 to cumulative strains e = 5.2. The microstructure of the as-sintered composites consisted of TiB whiskers nonuniformly distributed within the Ti matrix. In the forged composites, intensive shortening of TiB whiskers occurred. The hardness of the composites increased greatly compared to that of commercially pure Ti; the hardness also increased with increasing the TiB fraction. The hardness in the forged composites decreased by ˜20% for both composite states. Tribological tests using a standard ball-on-disk geometry showed that the friction coefficient of the Ti/TiB composites increased in comparison with Ti. Increasing the TiB fraction in the composites increased the friction coefficient and decreased the wear factor. It was shown that the tribological characteristics after isothermal multiaxial forging were changed but slightly.

Mechanical properties of thermoelectric n-type magnesium silicide synthesized employing in situ spark plasma reaction sintering

NASA Astrophysics Data System (ADS)

Muthiah, Saravanan; Singh, R. C.; Pathak, B. D.; Dhar, Ajay

2017-07-01

Thermoelectric devices employing magnesium silicide (Mg2Si) offer an inexpensive and non-toxic solution for green energy generation compared to other existing conventional thermoelectric materials in the mid-temperature range. However, apart from the thermoelectric performance, their mechanical properties are equally important in order to avoid the catastrophic failure of their modules during actual operation. In the present study, we report the synthesis of Mg2Si co-doped with Bi and Sb employing in situ spark plasma reaction sintering and investigate its broad range of mechanical properties. The mechanical properties of the sintered co-doped Mg2Si suggest a significantly enhanced value of hardness ~5.4  ±  0.2 GPa and an elastic modulus ~142.5  ±  6 GPa with a fracture toughness of ~1.71  ±  0.1 MPa  √m. The thermal shock resistance, which is one of the most vital parameter for designing thermoelectric devices, was found to be ~300 W m-1, which is higher than most of the other existing state-of-the-art mid-temperature thermoelectric materials. The friction and wear characteristics of sintered co-doped Mg2Si have been reported for the first time, in order to realize the sustainability of their thermoelectric modules under actual hostile environmental conditions.

Applying "Spark Plasma Sintering" Technology to Enhance the Resistance to Contact Fatigue of Sintered Steel Based on Astaloy CRL

NASA Astrophysics Data System (ADS)

Rodziňák, D.; Čerňan, J.; Puchý, V.

2017-12-01

The article deals with the effect of porosity on the contact fatigue of sintered material type Astaloy CrL with 0.3 and 0.4% C. Sets of samples were used with densities beginning from the value of 7000 kg.m-3 to the value of almost 7859 kg.m-3 which represents almost zero porosity (compact material). It has been found out that the increase of compacting pressure applied simultaneously with temperature results in the reduction of porosity from the value of 9.10% to 0.0005% and increase in hardness from 145 to 193 HV10, depending on the carbon content. Logically there is also an increase in the fatigue life by the contact fatigue tests for the value of 50×106 cycles from the value of 900 MPa to 1150 MPa for samples with 0.3% of C and from 900 MPa to 1300 MPa for samples with 0.4% C. These investigations were also carried out in the past, but to achieve the reduction of porosity, different technonologies were used at each level such as double pressing, hot pressing, saturation, hot forging, etc. In this case, the single technology of "spark plasma sintering" making use of compacting at high temperatures is capable to continuously reduce porosity to zero.

PTCR characteristics and microstructure of porous (Ba,Sr)TiO3 ceramics prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Lee, Ki-Ju; Tang, Dongxu; Park, K.; Cho, Won-Seung

2010-02-01

Porous Y-doped (Ba,Sr)TiO3 ceramics were prepared by the spark plasma sintering of (Ba,Sr)TiO3 powders with different amounts of carbon black, and by subsequently burning out the carbon black acting as a pore precursor. The microstructure, PTCR and gas-sensing characteristics for porous Y-doped (Ba,Sr)TiO3 ceramics were investigated. Spark plasma sintered (Ba,Sr)TiO3 ceramics revealed a very fine microstructure containing submicron-sized grains with a cubic phase and revealed an increased porosity after the carbon black was burned out. As a result of reoxidation treatment, the grain size of the (Ba,Sr)TiO3 ceramics increased to a few μm and the cubic phase transformed into a tetragonal phase. The phase transformation of (Ba,Sr)TiO3 ceramics was affected by grain size. The PTCR jump in the (Ba,Sr)TiO3 ceramics prepared by adding 40 vol.% carbon black showed an excellent value of 4.72 × 106, which was ten times higher than the PTCR jump in (Ba,Sr)TiO3 ceramics. The electrical resistivity of the porous (Ba,Sr)TiO3 ceramics was recovered as the atmosphere changed from a reducing gas (N2) to an oxidizing gas (O2) under consecutive heating and cooling cycles.

The Influence of Milling and Spark Plasma Sintering on the Microstructure and Properties of the Al7075 Alloy

PubMed Central

Málek, Přemysl; Minárik, Peter; Novák, Pavel; Průša, Filip

2018-01-01

The compact samples of an Al7075 alloy were prepared by a combination of gas atomization, high energy milling, and spark plasma sintering. The predominantly cellular morphology observed in gas atomized powder particles was completely changed by mechanical milling. The continuous-like intermetallic phases present along intercellular boundaries were destroyed; nevertheless, a small amount of Mg(Zn,Cu,Al)2 phase was observed also in the milled powder. Milling resulted in a severe plastic deformation of the material and led to a reduction of grain size from several µm into the nanocrystalline region. The combination of these microstructural characteristics resulted in abnormally high microhardness values exceeding 300 HV. Consolidation through spark plasma sintering (SPS) resulted in bulk samples with negligible porosity. The heat exposition during SPS led to precipitation of intermetallic phases from the non-equilibrium microstructure of both gas atomized and milled powders. SPS of the milled powder resulted in a recrystallization of the severely deformed structure. An ultra-fine grained structure (grain size close to 500 nm) with grains divided primarily by high-angle boundaries was formed. A simultaneous release of stored deformation energy and an increase in the grain size caused a drop of microhardness to values close to 150 HV. This value was retained even after annealing at 425 °C. PMID:29614046

Biocompatibility assessment of spark plasma-sintered alumina-titanium cermets.

PubMed

Guzman, Rodrigo; Fernandez-García, Elisa; Gutierrez-Gonzalez, Carlos F; Fernandez, Adolfo; Lopez-Lacomba, Jose Luis; Lopez-Esteban, Sonia

2016-01-01

Alumina-titanium materials (cermets) of enhanced mechanical properties have been lately developed. In this work, physical properties such as electrical conductivity and the crystalline phases in the bulk material are evaluated. As these new cermets manufactured by spark plasma sintering may have potential application for hard tissue replacements, their biocompatibility needs to be evaluated. Thus, this research aims to study the cytocompatibility of a novel alumina-titanium (25 vol. % Ti) cermet compared to its pure counterpart, the spark plasma sintered alumina. The influence of the particular surface properties (chemical composition, roughness and wettability) on the pre-osteoblastic cell response is also analyzed. The material electrical resistance revealed that this cermet may be machined to any shape by electroerosion. The investigated specimens had a slightly undulated topography, with a roughness pattern that had similar morphology in all orientations (isotropic roughness) and a sub-micrometric average roughness. Differences in skewness that implied valley-like structures in the cermet and predominance of peaks in alumina were found. The cermet presented a higher surface hydrophilicity than alumina. Any cytotoxicity risk associated with the new materials or with the innovative manufacturing methodology was rejected. Proliferation and early-differentiation stages of osteoblasts were statistically improved on the composite. Thus, our results suggest that this new multifunctional cermet could improve current alumina-based biomedical devices for applications such as hip joint replacements. © The Author(s) 2015.

Electrically-conductive proppant and methods for making and using same

DOEpatents

Cannan, Chad; Roper, Todd; Savoy, Steve; Mitchell, Daniel R.

2016-09-06

Electrically-conductive sintered, substantially round and spherical particles and methods for producing such electrically-conductive sintered, substantially round and spherical particles from an alumina-containing raw material. Methods for using such electrically-conductive sintered, substantially round and spherical particles in hydraulic fracturing operations.

[Study on friction and wear properties of dental zirconia ceramics processed by microwave and conventional sintering methods].

PubMed

Guoxin, Hu; Ying, Yang; Yuemei, Jiang; Wenjing, Xia

2017-04-01

This study evaluated the wear of an antagonist and friction and wear properties of dental zirconia ceramic that was subjected to microwave and conventional sintering methods. Ten specimens were fabricated from Lava brand zirconia and randomly assigned to microwave and conventional sintering groups. A profile tester for surface roughness was used to measure roughness of the specimens. Wear test was performed, and steatite ceramic was used as antagonist. Friction coefficient curves were recorded, and wear volume were calculated. Finally, optical microscope was used to observe the surface morphology of zirconia and steatite ceramics. Field emission scanning electron microscopy was used to observe the microstructure of zirconia. Wear volumes of microwave and conventionally sintered zirconia were (6.940±1.382)×10⁻², (7.952±1.815) ×10⁻² mm³, respectively. Moreover, wear volumes of antagonist after sintering by the considered methods were (14.189±4.745)×10⁻², (15.813±3.481)×10⁻² mm³, correspondingly. Statistically significant difference was not observed in the wear resistance of zirconia and wear volume of steatite ceramic upon exposure to two kinds of sintering methods. Optical microscopy showed that ploughed surfaces were apparent in zirconia. The wear surface of steatite ceramic against had craze, accompanied by plough. Scanning electron microscopy showed that zirconia was sintered compactly when subjected to both conventional sintering and microwave methods, whereas grains of zirconia sintered by microwave alone were smaller and more uniform. Two kinds of sintering methods are successfully used to produce dental zirconia ceramics with similar friction and wear properties.
.

Effect of spark plasma sintering on the microstructure and in vitro behavior of plasma sprayed HA coatings.

PubMed

Yu, L-G; Khor, K A; Li, H; Cheang, P

2003-07-01

The crystalline phases and degree of crystallinity in plasma sprayed calcium phosphate coatings on Ti substrates are crucial factors that influence the biological interactions of the materials in vivo. In this study, plasma sprayed hydroxyapatite (HA) coatings underwent post-spray treatment by the spark plasma sintering (SPS) technique at 500 degrees C, 600 degrees C, and 700 degrees C for duration of 5 and 30 min. The activity of the HA coatings before and after SPS are evaluated in vitro in a simulated body fluid. The surface microstructure, crystallinity, and phase composition of each coating is characterized by scanning electron microscopy and X-ray diffractometry before, and after in vitro incubation. Results show that the plasma sprayed coatings treated for 5 min in SPS demonstrated increased proportion of beta-TCP phase with a preferred-orientation in the (214) plane, and the content of beta-TCP phase corresponded to SPS temperature, up to 700 degrees C. SPS treatment at 700 degrees C for 30 min enhanced the HA content in the plasma spray coating as well. The HA coatings treated in SPS for 5 min revealed rapid surface morphological changes during in vitro incubation (up to 12 days), indicating that the surface activity is enhanced by the SPS treatment. The thickest apatite layer was found in the coating treated by SPS at 700 degrees C for 5 min.

Microstructural study and densification analysis of hot work tool steel matrix composites reinforced with TiB{sub 2} particles

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

Fedrizzi, A., E-mail: anna.fedrizzi@ing.unitn.it; Pellizzari, M.; Zadra, M.

2013-12-15

Hot work tool steels are characterized by good toughness and high hot hardness but are less wear resistant than other tooling materials, such as high speed steel. Metal matrix composites show improved tribological behavior, but not much work has been done in the field of hot work tool steels. In this paper TiB{sub 2}-reinforced hot work tool steel matrix composites were produced by spark plasma sintering (SPS). Mechanical alloying (MA) was proposed as a suited process to improve the composite microstructure. Density measurements and microstructure confirmed that MA promotes sintering and produces a fine and homogeneous dispersion of reinforcing particles.more » X-ray diffraction patterns of the sintered composites highlighted the formation of equilibrium Fe{sub 2}B and TiC, as predicted by thermodynamic calculations using Thermo-Calc® software. Scanning electron microscopy as well as scanning Kelvin probe force microscopy highlighted the reaction of the steel matrix with TiB{sub 2} particles, showing the formation of a reaction layer at the TiB{sub 2}-steel interface. Phase investigations pointed out that TiB{sub 2} is not chemically stable in steel matrix because of the presence of carbon even during short time SPS. - Highlights: • TiB{sub 2} reinforced steel matrix composites were produced by spark plasma sintering. • TiB{sub 2} was successfully dispersed in the steel matrix by mechanical alloying. • Steel and TiB{sub 2} react during sintering forming equilibrium Fe{sub 2}B and TiC. • The new phases were investigated by means of AFM, Volta potential and XRD analyses.« less

Alloying Behavior and Properties of FeSiBAlNiCo x High Entropy Alloys Fabricated by Mechanical Alloying and Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Wang, Wen; Li, Boyu; Zhai, Sicheng; Xu, Juan; Niu, Zuozhe; Xu, Jing; Wang, Yan

2018-02-01

In this paper, FeSiBAlNiCo x (x = 0.2, 0.8) high-entropy alloy (HEA) powders were fabricated by mechanical alloying process, and the powders milled for 140 h were sintered by spark plasma sintering (SPS) technique. The microstructures and properties of as-milled powders and as-sintered samples were investigated. The results reveal that the final milling products (140 h) of both sample powders present the fully amorphous structure. The increased Co contents obviously enhance the glass forming ability and thermal stability of amorphous HEA powders, which are reflected by the shorter formation time of fully amorphous phase and the higher onset crystallization temperature, respectively. According to coercivity, the as-milled FeSiBAlNiCo x (x = 0.2, 0.8) powders (140 h) are the semi-hard magnetic materials. FeSiBAlNiCo0.8 HEA powders possess the highest saturation magnetization and largest remanence ratio. The SPS-ed products of both bulk HEAs are composed of body-centered cubic solid solution, and FeSi and FeB intermetallic phases. They possess the high relative density above 97% and excellent microhardness exceeding 1150 HV. The as-sintered bulks undergo the remarkable increase in saturation magnetization compared with the as-milled state. The SPS-ed FeSiBAlNiCo0.8 HEA exhibits the soft magnetic properties. The electrochemical corrosion test is carried out in 3.5% NaCl solution. The SPS-ed FeSiBAlNiCo0.2 HEA reveals the better passivity with low passive current density, and the higher pitting resistance with wide passive region.

The Fabrication of All-Solid-State Lithium-Ion Batteries via Spark Plasma Sintering

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

Wei, Xialu; Rechtin, Jack; Olevsky, Eugene

Spark plasma sintering (SPS) has been successfully used to produce all-solid-state lithium-ion batteries (ASSLibs). Both regular and functionally graded electrodes are implemented into novel three-layer and five-layer battery designs together with solid-state composite electrolyte. The electrical capacities and the conductivities of the SPS-processed ASSLibs are evaluated using the galvanostatic charge-discharge test. Experimental results have shown that, compared to the three-layer battery, the five-layer battery is able to improve energy and power densities. Scanning electron microscopy (SEM) is employed to examine the microstructures of the batteries especially at the electrode–electrolyte interfaces. It reveals that the functionally graded structure can eliminate themore » delamination effect at the electrode–electrolyte interface and, therefore, retains better performance.« less

The Fabrication of All-Solid-State Lithium-Ion Batteries via Spark Plasma Sintering

DOE PAGES

Wei, Xialu; Rechtin, Jack; Olevsky, Eugene

2017-09-14

Spark plasma sintering (SPS) has been successfully used to produce all-solid-state lithium-ion batteries (ASSLibs). Both regular and functionally graded electrodes are implemented into novel three-layer and five-layer battery designs together with solid-state composite electrolyte. The electrical capacities and the conductivities of the SPS-processed ASSLibs are evaluated using the galvanostatic charge-discharge test. Experimental results have shown that, compared to the three-layer battery, the five-layer battery is able to improve energy and power densities. Scanning electron microscopy (SEM) is employed to examine the microstructures of the batteries especially at the electrode–electrolyte interfaces. It reveals that the functionally graded structure can eliminate themore » delamination effect at the electrode–electrolyte interface and, therefore, retains better performance.« less

The Structure and Mechanical Properties of High-Strength Bulk Ultrafine-Grained Cobalt Prepared Using High-Energy Ball Milling in Combination with Spark Plasma Sintering

PubMed Central

Marek, Ivo; Vojtěch, Dalibor; Michalcová, Alena; Kubatík, Tomáš František

2016-01-01

In this study, bulk ultrafine-grained and micro-crystalline cobalt was prepared using a combination of high-energy ball milling and subsequent spark plasma sintering. The average grain sizes of the ultrafine-grained and micro-crystalline materials were 200 nm and 1 μm, respectively. Mechanical properties such as the compressive yield strength, the ultimate compressive strength, the maximum compressive deformation and the Vickers hardness were studied and compared with those of a coarse-grained as-cast cobalt reference sample. The bulk ultrafine-grained sample showed an ultra-high compressive yield strength that was greater than 1 GPa, which is discussed with respect to the preparation technique and a structural investigation. PMID:28773514

The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering

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

Cui, Guodong; Wei, Xialu; Olevsky, Eugene

2016-06-01

High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. In conclusion, the compressive strength and energy absorption characteristics of the FPSPS processed specimens are examinedmore » here to be correspondingly improved as a result of the refined microstructure.« less

Preparation of tungsten fiber reinforced-tungsten/copper composite for plasma facing component

NASA Astrophysics Data System (ADS)

He, Gang; Xu, Kunyuan; Guo, Shibin; Qian, Xueqiang; Yang, Zengchao; Liu, Guanghua; Li, Jiangtao

2014-12-01

W fiber reinforced-W/Cu composite is designed as a transition layer between CuCrZr heat sink material and W plasma facing material. A novel method was developed for the preparation of W fiber reinforced-W/Cu composite by combining combustion synthesis with centrifugal infiltration. Cu melt with a transient temperature over 2000 °C produced by the thermite reaction was infiltrated into the W powder and fiber bed with the assistance of a high gravity field. It was found that the W particles were sintered and bonded to the W fibers due to the high temperature produced by the thermite reaction. The bending strength of W/Cu composite improved 12.7% through W fibers reinforcement.

Assessing Effects of Oxidizer Characteristics on Composite Reaction Kinetics

DTIC Science & Technology

2013-12-01

in its spark gap is ionized and creates conductive plasma allowing current flow to the EBW. The EBW is a type of detonator which utilizes shockwaves...flow rate of 70 mL min-1 for the remainder of the cycle. Sintering can occur during heating and melting, ultimately affecting heat transfer in the...argon at a flow rate of 70 mL min-1 for the remainder of the cycle. Sintering can occur during heating and melting, ultimately affecting heat transfer

Mechanism research on arsenic removal from arsenopyrite ore during a sintering process

NASA Astrophysics Data System (ADS)

Cheng, Ri-jin; Ni, Hong-wei; Zhang, Hua; Zhang, Xiao-kun; Bai, Si-cheng

2017-04-01

The mechanism of arsenic removal during a sintering process was investigated through experiments with a sintering pot and arsenic-bearing iron ore containing arsenopyrite; the corresponding chemical properties of the sinter were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The experimental results revealed that the reaction of arsenic removal is mainly related to the oxygen atmosphere and temperature. During the sintering process, arsenic could be removed in the ignition layer, the sinter layer, and the combustion zone. A portion of FeAsS reacted with excess oxygen to generate FeAsO4, and the rest of the FeAsS reacted with oxygen to generate As2O3(g) and SO2(g). A portion of As2O3(g) mixed with Al2O3 or CaO, which resulted in the formation of arsenates such as AlAsO4 and Ca3(AsO4)2, leading to arsenic residues in sintering products. The FeAsS component in the blending ore was difficult to decompose in the preliminary heating zone, the dry zone, or the bottom layer because of the relatively low temperatures; however, As2O3(g) that originated from the high-temperature zone could react with metal oxides, resulting in the formation of arsenate residues.

Development of bismuth tellurium selenide nanoparticles for thermoelectric applications via a chemical synthetic process

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

Kim, Cham; Department of Chemical Engineering, Pohang University of Science and Technology; Kim, Dong Hwan

2011-03-15

Research highlights: {yields} We synthesized a Bi{sub 2}Te{sub y}Se{sub 3-y} nano-compound via a chemical synthetic process. {yields} The compound was sintered to achieve an average grain size of about 300 nm. {yields} The resulting sintered body showed very low thermal conductivity. It is likely caused by the vigorous phonon scattering of the nano-sized grains. -- Abstract: Bismuth tellurium selenide (Bi{sub 2}Te{sub y}Se{sub 3-y}) nanoparticles for thermoelectric applications are successfully prepared via a water-based chemical reaction under atmospheric conditions. The nanostructured compound is prepared using a complexing agent (ethylenediaminetetraacetic acid) and a reducing agent (ascorbic acid) to stabilize the bismuth precursormore » (Bi(NO{sub 3}){sub 3}) in water and to favor the reaction with reduced sources of tellurium and selenium. The resulting powder is smaller than ca. 100 nm and has a crystalline structure corresponding to the rhombohedral Bi{sub 2}Te{sub 2.7}Se{sub 0.3}. The nanocrystalline powder is sintered via a spark plasma sintering process to obtain a sintered body composed of nano-sized grains. Important transport properties of the sintered body are measured to calculate its most important characteristic, the thermoelectric performance. The results demonstrate a relationship between the nanostructure of the sintered body and its thermal conductivity.« less

Effect of boron addition on injection molded 316L stainless steel: mechanical, corrosion properties and in vitro bioactivity.

PubMed

Bayraktaroglu, Esra; Gulsoy, H Ozkan; Gulsoy, Nagihan; Er, Ozay; Kilic, Hasan

2012-01-01

The research was investigated the effect of boron additions on sintering characteristics, mechanical, corrosion properties and biocompatibility of injection molded austenitic grade 316L stainless steel. Addition of boron is promoted to get high density of sintered 316L stainless steels. The amount of boron plays a role in determining the sintered microstructure and all properties. In this study, 316L stainless steel powders have been used with the elemental NiB powders. A feedstock containing 62.5 wt% powders loading was molded at different injection molded temperature. The binders were completely removed from molded components by solvent and thermal debinding at different temperature. The debinded samples were sintered at different temperature for 60 min. Mechanical property, microstructural characterization and electrochemical property of the sintered samples were performed using tensile testing, hardness, optical, scanning electron microscopy and electrochemical corrosion experiments. Sintered samples were immersed in a simulated body fluid (SBF) with elemental concentrations that were comparable to those of human blood plasma for a total period of 15 days. Both materials were implanted in fibroblast culture for biocompatibility evaluations were carried out. Results of study showed that sintered 316L and 316L with NiB addition samples exhibited high mechanical and corrosion properties in a physiological environment. Especially, 316L with NiB addition can be used in some bioapplications.

Assessment of Methods to Consolidate Iodine-Loaded Silver-Functionalized Silica Aerogel

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

Matyas, Josef; Engler, Robert K.

2013-09-01

The U.S. Department of Energy is currently investigating alternative sorbents for the removal and immobilization of radioiodine from the gas streams in a nuclear fuel reprocessing plant. One of these new sorbents, Ag0-functionalized silica aerogels, shows great promise as a potential replacement for Ag-bearing mordenites because of its high selectivity and sorption capacity for iodine. Moreover, a feasible consolidation of iodine-loaded Ag0-functionalized silica aerogels to a durable SiO2-based waste form makes this aerogel an attractive choice for sequestering radioiodine. This report provides a preliminary assessment of the methods that can be used to consolidate iodine-loaded Ag0-functionalized silica aerogels into amore » final waste form. In particular, it focuses on experimental investigation of densification of as prepared Ag0-functionalized silica aerogels powders, with or without organic moiety and with or without sintering additive (colloidal silica), with three commercially available techniques: 1) hot uniaxial pressing (HUP), 2) hot isostatic pressing (HIP), and 3) spark plasma sintering (SPS). The densified products were evaluated with helium gas pycnometer for apparent density, with the Archimedes method for apparent density and open porosity, and with high-resolution scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) for the extent of densification and distribution of individual elements. The preliminary investigation of HUP, HIP, and SPS showed that these sintering methods can effectively consolidate powders of Ag0-functionalized silica aerogel into products of near-theoretical density. Also, removal of organic moiety and adding 5.6 mass% of colloidal silica to Ag0-functionalized silica aerogel powders before processing provided denser products. Furthermore, the ram travel data for SPS indicated that rapid consolidation of powders can be performed at temperatures below 950°C.« less

Mechanically induced self-propagating reaction and consequent consolidation for the production of fully dense nanocrystalline Ti{sub 55}C{sub 45} bulk material

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

Sherif El-Eskandarany, M., E-mail: msherif@kisr.edu.kw; Al-Hazza, Abdulsalam

2014-11-15

We employed a high-energy ball mill for the synthesis of nanograined Ti{sub 55}C{sub 45} powders starting from elemental Ti and C powders. The mechanically induced self-propagating reaction that occurred between the reactant materials was monitored via a gas atmosphere gas-temperature-monitoring system. A single phase of NaCl-type TiC was obtained after 5 h of ball milling. To decrease the powder and grain sizes, the material was subjected to further ball milling time. The powders obtained after 200 h of milling possessed spherical-like morphology with average particle and grain sizes of 45 μm and 4.2 nm, respectively. The end-products obtained after 200more » h of ball milling time, were then consolidated into full dense compacts, using hot pressing and spark plasma sintering at 1500 and 34.5 MPa, with heating rates of 20 °C/min and 500 °C/min, respectively. Whereas hot pressing of the powders led to severe grain growth (∼ 436 nm in diameter), the as-spark plasma sintered powders maintained their nanograined characteristics (∼ 28 nm in diameter). The as-synthesized and as-consolidated powders were characterized, using X-ray diffraction, high-resolution electron microscopy, and scanning electron microscopy. The mechanical properties of the consolidated samples obtained via the hot pressing and spark plasma sintering techniques were characterized, using Vickers microhardness and non-destructive testing techniques. The Vickers hardness, Young's modulus, shear modulus and fracture toughness of as-spark plasma sintered samples were 32 GPa, 358 GPa, 151 GPa and 6.4 MPa·m{sup 1/2}, respectively. The effects of the consolidation approach on the grain size and mechanical properties were investigated and are discussed. - Highlights: • Room-temperature synthesizing of NaCl-type TiC • Dependence on the grain size on the ball milling time • Fabrication of equiaxed nanocrystalline grains with a diameter of 4.2 nm • Fabrication of nanocrystalline bulk TiC material by SPS with minimal grain growth • Dependence of improved mechanical properties on the consolidation techniques.« less

Effect of sintering atmosphere on properties of porous stainless steel for biomedical applications.

PubMed

Dudek, Agata; Włodarczyk, Renata

2013-01-01

This study discusses manufacturing of metallic biomaterials by means of powder metallurgy with consideration for their unquestionable advantages, i.e. opportunities of obtaining materials with controllable porosity. The paper focuses on properties of 316 L stainless steel obtained using the method of powder metallurgy with respect to compacting pressure and sintering atmosphere. All the specimens were compacted at 700, 400 and 225 MPa, and sintered at 1250 °C. In order to analyze the sintering atmosphere, three different media were used: dissociated ammonia, hydrogen and vacuum. The study covered sintering density, porosity, microstructure analysis and corrosion resistance. The proposed method of powder metallurgy allowed for obtaining materials with predictable size and distribution of pores, depending on the parameters of sinter preparation (compaction force, sinter atmosphere). High corrosion resistance of the materials (sintering in the atmosphere of hydrogen and in vacuum) and high porosity in the sinters studied offer opportunities for using them for medical purposes. Copyright © 2012 Elsevier B.V. All rights reserved.

Quasi-intrinsic colossal permittivity in Nb and In co-doped rutile TiO2 nanoceramics synthesized through a oxalate chemical-solution route combined with spark plasma sintering.

PubMed

Han, HyukSu; Dufour, Pascal; Mhin, Sungwook; Ryu, Jeong Ho; Tenailleau, Christophe; Guillemet-Fritsch, Sophie

2015-07-14

Nb and In co-doped rutile TiO2 nanoceramics (n-NITO) were successfully synthesized through a chemical-solution route combined with a low temperature spark plasma sintering (SPS) technique. The particle morphology and the microstructure of n-NITO compounds were nanometric in size. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG)/differential thermal analysis (DTA), Fourier transform infrared (FTIR), and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compound. The results indicated that the as-synthesized n-NITO oxalate as well as sintered ceramic have a co-doped single phase of titanyl oxalate and rutile TiO2, respectively. Broadband impedance spectroscopy revealed that novel colossal permittivity (CP) was achieved in n-NITO ceramics exhibiting excellent temperature-frequency stable CP (up to 10(4)) as well as low dielectric loss (∼5%). Most importantly, detailed impedance data analyses of n-NITO compared to microcrystalline NITO (μ-NITO) demonstrated that the origin of CP in NITO bulk nanoceramics might be related with the pinned electrons in defect clusters and not to extrinsic interfacial effects.

Osteoblastic cell response to spark plasma-sintered zirconia/titanium cermets.

PubMed

Fernandez-Garcia, Elisa; Guillem-Marti, Jordi; Gutierrez-Gonzalez, Carlos F; Fernandez, Adolfo; Ginebra, Maria-Pau; Lopez-Esteban, Sonia

2015-01-01

Ceramic/metal composites, cermets, arise from the idea to combine the dissimilar properties in the pure materials. This work aims to study the biocompatibility of new micro-nanostructured 3 Y-TZP/Ti materials with 25, 50 and 75 vol.% Ti, which have been successfully obtained by spark slasma sintering technology, as well as to correlate their surface properties (roughness, wettability and chemical composition) with the osteoblastic cell response. All samples had isotropic and slightly waved microstructure, with sub-micrometric average roughness. Composites with 75 vol.% Ti had the highest surface hydrophilicity. Surface chemical composition of the cermets correlated well with the relative amounts used for their fabrication. A cell viability rate over 80% dismissed any cytotoxicity risk due to manufacturing. Cell adhesion and early differentiation were significantly enhanced on materials containing the nanostructured 3 Y-TZP phase. Proliferation and differentiation of SaOS-2 were significantly improved in their late-stage on the composite with 75 vol.% Ti that, from the osseointegration standpoint, is presented as an excellent biomaterial for bone replacement. Thus, spark plasma sintering is consolidated as a suitable technology for manufacturing nanostructured biomaterials with enhanced bioactivity. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Low modulus and bioactive Ti/α-TCP/Ti-mesh composite prepared by spark plasma sintering.

PubMed

Guo, Yu; Tan, Yanni; Liu, Yong; Liu, Shifeng; Zhou, Rui; Tang, Hanchun

2017-11-01

A titanium mesh scaffold composite filled with Ti/α-TCP particles was prepared by spark plasma sintering (SPS). The microstructures and interfacial reactions of the composites were investigated by scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The compressive strength and elastic modulus were also measured. In vitro bioactivity and biocompatibility was evaluated by using simulated body fluid and cells culture, respectively. After high temperature sintering, Ti oxides, Ti x P y and CaTiO 3 were formed. The formation of Ti oxides and Ti x P y were resulted from the diffusion of O and P elements from α-TCP to Ti. CaTiO 3 was the reaction product of Ti and α-TCP. The composite of 70Ti/α-TCP incorporated with Ti mesh showed a high compressive strength of 589MPa and a low compressive modulus of 30GPa. The bioactivity test showed the formation of a thick apatite layer on the composite and well-spread cells attachment. A good combination of mechanical properties and bioactivity indicated a high potential application of Ti/α-TCP/Ti-mesh composite for orthopedic implants. Copyright © 2017. Published by Elsevier B.V.

Multiwalled carbon nanotube monoliths prepared by spark plasma sintering (SPS) and their mechanical properties.

PubMed

Uo, Motohiro; Hasegawa, Tomoka; Akasaka, Tsukasa; Tanaka, Isao; Munekane, Fuminori; Omori, Mamoru; Kimura, Hisamichi; Nakatomi, Reiko; Soga, Kohei; Kogo, Yasuo; Watari, Fumio

2009-01-01

Three types of multiwalled carbon nanotube (MWCNT) monoliths without any binders were obtained by spark plasma sintering (SPS) treatment at 2000 degrees C under 80 MPa sintering pressure. Three MWCNTs with different diameters: thin (slashed circle20-30 nm, CNT Co., Ltd., Korea), thick (slashed circle100 nm, Nano Carbon Technologies Co., Ltd., Japan) and spherical thin (slashed circle20-30 nm, granulated diameter = 1-3 microm, Shimizu Corporation, Japan) were employed for SPS. SEM observation confirmed that these materials maintained the nanosized tube microstructure of raw CNT powder after SPS treatment. The densest monolith was prepared with the spherical MWCNTs. The mechanical properties of this material were estimated by the dynamic hardness test. The elastic modulus of the monolith did not depend on the difference of MWCNTs, but the hardness of spherical MWCNTs was higher than that of thick MWCNTs. The high density and hardness of the spherical MWCNTs were caused by the high packing density during the SPS process because of its spherical granulation. Thus, the spherical MWCNTs were most useful for the MWCNT monolith preparation with the SPS process and its application as a bone substitute material and a bone tissue engineering scaffold material was suggested.

Data on the impact of increasing the W amount on the mass density and compressive properties of Ni-W alloys processed by spark plasma sintering.

PubMed

Sadat, T; Hocini, A; Lilensten, L; Faurie, D; Tingaud, D; Dirras, G

2016-06-01

Bulk Ni-W alloys having composite-like microstructures are processed by spark plasma sintering (SPS) route of Ni and W powder blends as reported in a recent study of Sadat et al. (2016) (DOI of original article: doi:10.1016/j.matdes.2015.10.083) [1]. The present dataset deals with determination of mass density and evaluation of room temperature compressive mechanical properties as function of the amount of W (%wt. basis). The presented data concern: (i) measurement of the mass of each investigated Ni-W alloy which is subsequently used to compute the mass density of the alloy and (ii) the raw (stress (MPa) and strain ([Formula: see text])) data, which can be subsequently used for stress/ strain plots.

Data on the impact of increasing the W amount on the mass density and compressive properties of Ni–W alloys processed by spark plasma sintering

PubMed Central

Sadat, T.; Hocini, A.; Lilensten, L.; Faurie, D.; Tingaud, D.; Dirras, G.

2016-01-01

Bulk Ni–W alloys having composite-like microstructures are processed by spark plasma sintering (SPS) route of Ni and W powder blends as reported in a recent study of Sadat et al. (2016) (DOI of original article: doi:10.1016/j.matdes.2015.10.083) [1]. The present dataset deals with determination of mass density and evaluation of room temperature compressive mechanical properties as function of the amount of W (%wt. basis). The presented data concern: (i) measurement of the mass of each investigated Ni–W alloy which is subsequently used to compute the mass density of the alloy and (ii) the raw (stress (MPa) and strain (ΔLL0)) data, which can be subsequently used for stress/ strain plots. PMID:27158658

Structural Evolution during Milling, Annealing, and Rapid Consolidation of Nanocrystalline Fe–10Cr–3Al Powder

PubMed Central

Kumar, Rajiv; Bakshi, S. R.; Joardar, Joydip; Parida, S.; Raja, V. S.; Singh Raman, R. K.

2017-01-01

Structural changes during the deformation-induced synthesis of nanocrystalline Fe–10Cr–3Al alloy powder via high-energy ball milling followed by annealing and rapid consolidation by spark plasma sintering were investigated. Reduction in crystallite size was observed during the synthesis, which was associated with the lattice expansion and rise in dislocation density, reflecting the generation of the excess grain boundary interfacial energy and the excess free volume. Subsequent annealing led to the exponential growth of the crystallites with a concomitant drop in the dislocation density. The rapid consolidation of the as-synthesized nanocrystalline alloy powder by the spark plasma sintering, on the other hand, showed only a limited grain growth due to the reduction of processing time for the consolidation by about 95% when compared to annealing at the same temperature. PMID:28772633

Co-blasting of titanium surfaces with an abrasive and hydroxyapatite to produce bioactive coatings: substrate and coating characterisation.

PubMed

Dunne, Conor F; Twomey, Barry; O'Neill, Liam; Stanton, Kenneth T

2014-01-01

The aim of this work is to assess the influence of two blast media on the deposition of hydroxyapatite onto a titanium substrate using a novel ambient temperature coating technique named CoBlast. CoBlast was developed to address the problems with high temperature coating techniques. The blasting media used in this study were Al2O3 and a sintered apatite powder. The prepared and coated surfaces were compared to plasma sprayed hydroxyapatite on the same substrates using the same hydroxyapatite feedstock powder. X-ray diffraction analysis revealed the coating crystallinity was the same as the original hydroxyapatite feedstock powder for the CoBlast samples while evidence of amorphous hydroxyapatite phases and β-TCP was observed in the plasma sprayed samples. The blast media type significantly influences the adhesive strength of the coating, surface roughness of both the substrate and coating and the microstructure of the substrate. The coating adhesion increased for the CoBlasted samples from 50 MPa to 60 MPa for sintered apatite powder and alumina, respectively, while plasma spray samples were significantly lower (5 MPa) when tested using a modified pull-test. In conclusion, the choice of blast medium is shown to be a key parameter in the CoBlast process. This study indicates that sintered apatite powder is the most suitable candidate for use as a blast medium in the coating of medical devices.

METHOD OF JOINING CARBIDES TO BASE METALS

DOEpatents

Krikorian, N.H.; Farr, J.D.; Witteman, W.G.

1962-02-13

A method is described for joining a refractory metal carbide such as UC or ZrC to a refractory metal base such as Ta or Nb. The method comprises carburizing the surface of the metal base and then sintering the base and carbide at temperatures of about 2000 deg C in a non-oxidizing atmosphere, the base and carbide being held in contact during the sintering step. To reduce the sintering temperature and time, a sintering aid such as iron, nickel, or cobait is added to the carbide, not to exceed 5 wt%. (AEC)

Hexagonal OsB 2: Sintering, microstructure and mechanical properties

DOE PAGES

Xie, Zhilin; Lugovy, Mykola; Orlovskaya, Nina; ...

2015-02-07

In this study, the metastable high pressure ReB 2-type hexagonal OsB 2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB 2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (~80 wt.%) and orthorhombic (~20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulusmore » of 574 ± 112 GPa, indicating that the material is rather hard and very stiff; but, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB 2 bulk ceramics.« less

Manufacturing and characterization of Ni-free N-containing ODS austenitic alloy

NASA Astrophysics Data System (ADS)

Mori, A.; Mamiya, H.; Ohnuma, M.; Ilavsky, J.; Ohishi, K.; Woźniak, Jarosław; Olszyna, A.; Watanabe, N.; Suzuki, J.; Kitazawa, H.; Lewandowska, M.

2018-04-01

Ni-free N-containing oxide dispersion strengthened (ODS) austenitic alloys were manufactured by mechanical alloying (MA) followed by spark plasma sintering (SPS). The phase evolutions during milling under a nitrogen atmosphere and after sintering were studied by X-ray diffraction (XRD). Transmission electron microcopy (TEM) and alloy contrast variation analysis (ACV), including small-angle neutron scattering (SANS) and ultra-small-angle X-ray scattering (USAXS), revealed the existence of nanoparticles with a diameter of 3-51 nm for the samples sintered at 950 °C. Sintering at 1000 °C for 5 and 15 min caused slight growth and a significant coarsening of the nanoparticles, up to 70 nm and 128 nm, respectively. The ACV analysis indicated the existence of two populations of Y2O3, ε-martensite and MnO. The dispersive X-ray spectrometry (EDS) confirmed two kinds of nanoparticles, Y2O3 and MnO. The material was characterized by superior micro-hardness, of above 500 HV0.1.

Manufacturing and characterization of Ni-free N-containing ODS austenitic alloys

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

Kowalska-Mori, A.; Mamiya, H.; Ohnuma, M.

Ni-free N-containing oxide dispersion strengthened (ODS) austenitic alloys were manufactured by mechanical alloying (MA) followed by spark plasma sintering (SPS). The phase evolutions during milling under a nitrogen atmosphere and after sintering were studied by X-ray diffraction (XRD). Transmission electron microcopy (TEM) and contrast variation analysis (ACV), including small-angle neutron scattering (SANS) and ultra-small X-ray scattering (USAXS), revealed the existence of nanoparticles with a diameter of 3-51 nm for the samples sintered at 950 ºC. Sintering at 1000 ºC for 5 and 15 min caused slight growth and a significant coarsening of the nanoparticles, up to 70 nm and 128more » nm, respectively. The ACV analysis indicated the existence of two populations of Y2O3, ε-martensite and MnO. The dispersive X-ray spectrometry (EDS) confirmed two kinds of nanoparticles, Y2O3 and MnO. The material was characterized by superior micro-hardness, of above 500 HV0.1.« less

Manufacturing and characterization of Ni-free N-containing ODS austenitic alloys

DOE PAGES

Kowalska-Mori, A.; Mamiya, H.; Ohnuma, M.; ...

2018-01-17

Ni-free N-containing oxide dispersion strengthened (ODS) austenitic alloys were manufactured by mechanical alloying (MA) followed by spark plasma sintering (SPS). The phase evolutions during milling under a nitrogen atmosphere and after sintering were studied by X-ray diffraction (XRD). Transmission electron microcopy (TEM) and contrast variation analysis (ACV), including small-angle neutron scattering (SANS) and ultra-small X-ray scattering (USAXS), revealed the existence of nanoparticles with a diameter of 3-51 nm for the samples sintered at 950 ºC. Sintering at 1000 ºC for 5 and 15 min caused slight growth and a significant coarsening of the nanoparticles, up to 70 nm and 128more » nm, respectively. The ACV analysis indicated the existence of two populations of Y2O3, ε-martensite and MnO. The dispersive X-ray spectrometry (EDS) confirmed two kinds of nanoparticles, Y2O3 and MnO. The material was characterized by superior micro-hardness, of above 500 HV0.1.« less

Synthesis of [(Ca1-xSrx)2-2y](Ti2-2yLi2y)Si2yO6-y Ceramic and its Application in Efficient Plasma Decomposition of CO2

NASA Astrophysics Data System (ADS)

Li, Ruixing; Tang, Qing; Yin, Shu; Sato, Tsugio

According to both the first principle and materials chemistry, a method for fabricating [(Ca1-xSrx)2-2y](Ti2-2yLi2y)Si2yO6-y ceramic was investigated. It was considered that the sintering was promoted by self-accelerated diffusion due to the formation of point defects caused by doping with Li2Si2O5. Consequently, a concept of non-stoichiometrically activated sintering, which was enhanced by point defects without the help of a grain boundary phase, was systematically studied in the Ca1-xSrxTiO3-Li2Si2O5 system. The mechanical and dielectric properties of [(Ca1-xSrx)2-2y](Ti2-2yLi2y)Si2yO6-y were greatly enhanced by adding Li2Si2O5. To improve CO2 decomposition activity, [(Ca1-xSrx)2-2y](Ti2-2yLi2y)Si2yO6-y, which possesses both high permittivity and high dielectric strength was used as a dielectric barrier to decompose CO2 by dielectric barrier discharges (DBDs) plasma without using any catalyst and auxiliary substance. It successfully generated DBDs plasma and the CO2 conversion was much higher than that using an alumina or a silica glass barrier which was widely used as the dielectric barrier in previous studies.

Method of sintering materials with microwave radiation

DOEpatents

Kimrey, Jr., Harold D.; Holcombe, Jr., Cressie E.; Dykes, Norman L.

1994-01-01

A method of sintering ceramic materials following: A compacted article comprising inorganic particles coated with carbon is provided, the carbon providing improved microwave coupling. The compacted article is then heated by microwave radiation to a temperature and for a period of time sufficient to sinter the compacted article.

Method of forming a ceramic to ceramic joint

DOEpatents

Cutler, Raymond Ashton; Hutchings, Kent Neal; Kleinlein, Brian Paul; Carolan, Michael Francis

2010-04-13

A method of joining at least two sintered bodies to form a composite structure, includes: providing a joint material between joining surfaces of first and second sintered bodies; applying pressure from 1 kP to less than 5 MPa to provide an assembly; heating the assembly to a conforming temperature sufficient to allow the joint material to conform to the joining surfaces; and further heating the assembly to a joining temperature below a minimum sintering temperature of the first and second sintered bodies. The joint material includes organic component(s) and ceramic particles. The ceramic particles constitute 40-75 vol. % of the joint material, and include at least one element of the first and/or second sintered bodies. Composite structures produced by the method are also disclosed.

Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Lee, Kang N.; Miller, Robert A.

2002-01-01

Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.

Examination of the Mass Transfer of Additive Elements in Barium Titanate Ceramics during Sintering Process by Laser Ablation ICP-MS.

PubMed

Sakate, Daisuke; Iwazaki, Yoshiki; Kon, Yoshiaki; Yokoyama, Takaomi; Ohata, Masaki

2018-01-01

The mass transfer of additive elements during the sintering of barium titanate (BaTiO 3 ) ceramic was examined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in the present study. An analytical sample consisting of two pellets of BaTiO 3 with different concentrations of additive elements of manganese (Mn) and holmium (Ho) as well as silicon (Si) as a sintering reagent was prepared and measured by LA-ICP-MS with small laser irradiated diameter of 10 μm to evaluate the distributions and concentrations of additive elements in order to examine their mass transfers. As results, enrichments of Mn and Si as an additive element and a sintering reagent, respectively, were observed on the adhesive surface between two BaTiO 3 pellets, even though Ho did not show a similar phenomenon. The mass transfers of additive elements of Mn and Ho were also examined, and Mn seemed to show a larger mass transfer than that of Ho during the sintering process for BaTiO 3 ceramics. The results obtained in this study shows the effectives of LA-ICP-MS for the future improvement of MLCCs.

SPS Fabrication of Tungsten-Rhenium Alloys in Support of NTR Fuels Development

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

Jonathan A. Webb; Indrajit Charit; Cory Sparks

Abstract. Tungsten metal slugs were fabricated via Spark Plasma Sintering (SPS) of powdered metals at temperatures ranging from 1575 K to 1975 K and hold times of 5 minutes to 30 minutes, using powders with an average diameter of 7.8 ?m. Sintered tungsten specimens were found to have relative densities ranging from 83 % to 94 % of the theoretical density for tungsten. Consolidated specimens were also tested for their Vickers Hardness Number (VHN), which was fitted as a function of relative density; the fully consolidated VHN was extrapolated to be 381.45 kg/mm2. Concurrently, tungsten and rhenium powders with averagemore » respective diameters of 0.5 ?m and 13.3 ?m were pre-processed either by High-Energy-Ball-Milling (HEBM) or by homogeneous mixing to yield W-25at.%Re mixtures. The powder batches were sintered at temperatures of 1975 K and 2175 K for hold times ranging from 0 minutes to 60 minutes yielding relative densities ranging from 94% to 97%. The combination of HEBM and sintering showed a significant decrease in the inter-metallic phases compared to that of the homogenous mixing and sintering.« less

[Application of sintered Ti powder to dental prostheses].

PubMed

Hikosaka, Tatsuya; Tanaka, Yoshinobu; Hoshiai, Kazumoto; Kanazawa, Takeshi; Nakamura, Yoshinori; Tsuda, Kenji; Ohasi, Hideya

2005-04-01

Powder metallurgy is a metal processing technology. Porous titanium produced from powder is widely used. The method is applied to titanium, which is not easy to cast as it sinters under melting point. In prosthetic dentistry, powder metallurgy can be applied to high fusing metal that is biocompatible. In this study, we examined the mechanical characteristics of the Ti sheet produced by sintering and discussed its application to dental prosthesis manufacturing. Ti sheets of 1-mm thickness, in which a binder was added to spherical Ti powder, were produced with the Doctor Blade Method. The sintering was carried out between 900-1150 degrees C at 6 temperatures. The sintered compact was evaluated by dimensional change rate, hardness test, bending strength, tensile strength and SEM observation. Another compact was sintered on the refractory cast. Mechanical strength significantly increased with sintering temperature. In addition, excellent mechanical strength was acquired by adding crushed powder and performing the de-binder process. In the sintering on the refractory cast, pre-baking for more than 100 minutes and sintering at over 1050 degrees C was needed for practical application. It thus seems possible to apply sintered titanium to dental prostheses. However, it will be necessary to examine the control of the shrinkage of the sintered compact in the future too.

Method of forming aluminum oxynitride material and bodies formed by such methods

DOEpatents

Bakas, Michael P [Ammon, ID; Lillo, Thomas M [Idaho Falls, ID; Chu, Henry S [Idaho Falls, ID

2010-11-16

Methods of forming aluminum oxynitride (AlON) materials include sintering green bodies comprising aluminum orthophosphate or another sacrificial material therein. Such green bodies may comprise aluminum, oxygen, and nitrogen in addition to the aluminum orthophosphate. For example, the green bodies may include a mixture of aluminum oxide, aluminum nitride, and aluminum orthophosphate or another sacrificial material. Additional methods of forming aluminum oxynitride (AlON) materials include sintering a green body including a sacrificial material therein, using the sacrificial material to form pores in the green body during sintering, and infiltrating the pores formed in the green body with a liquid infiltrant during sintering. Bodies are formed using such methods.

Method of sintering materials with microwave radiation

DOEpatents

Kimrey, H.D. Jr.; Holcombe, C.E. Jr.; Dykes, N.L.

1994-06-14

Disclosed is a method of sintering ceramic materials. A compacted article comprising inorganic particles coated with carbon is provided, the carbon providing improved microwave coupling. The compacted article is then heated by microwave radiation to a temperature and for a period of time sufficient to sinter the compacted article. No Drawings

Effect of metallic coating on the properties of copper-silicon carbide composites

NASA Astrophysics Data System (ADS)

Chmielewski, M.; Pietrzak, K.; Teodorczyk, M.; Nosewicz, S.; Jarząbek, D.; Zybała, R.; Bazarnik, P.; Lewandowska, M.; Strojny-Nędza, A.

2017-11-01

In the presented paper a coating of SiC particles with a metallic layer was used to prepare copper matrix composite materials. The role of the layer was to protect the silicon carbide from decomposition and dissolution of silicon in the copper matrix during the sintering process. The SiC particles were covered by chromium, tungsten and titanium using Plasma Vapour Deposition method. After powder mixing of components, the final densification process via Spark Plasma Sintering (SPS) method at temperature 950 °C was provided. The almost fully dense materials were obtained (>97.5%). The microstructure of obtained composites was studied using scanning electron microscopy as well as transmission electron microscopy. The microstructural analysis of composites confirmed that regardless of the type of deposited material, there is no evidence for decomposition process of silicon carbide in copper. In order to measure the strength of the interface between ceramic particles and the metal matrix, the micro tensile tests have been performed. Furthermore, thermal diffusivity was measured with the use of the laser pulse technique. In the context of performed studies, the tungsten coating seems to be the most promising solution for heat sink application. Compared to pure composites without metallic layer, Cu-SiC with W coating indicate the higher tensile strength and thermal diffusitivy, irrespective of an amount of SiC reinforcement. The improvement of the composite properties is related to advantageous condition of Cu-SiC interface characterized by well homogenity and low porosity, as well as individual properties of the tungsten coating material.

Microstructure and Mechanical Properties of Nano-Size Zirconium Carbide Dispersion Strengthened Tungsten Alloys Fabricated by Spark Plasma Sintering Method

NASA Astrophysics Data System (ADS)

Xie, Zhuoming; Liu, Rui; Fang, Qianfeng; Zhang, Tao; Jiang, Yan; Wang, Xianping; Liu, Changsong

2015-12-01

W-(0.2, 0.5, 1.0)wt% ZrC alloys with a relative density above 97.5% were fabricated through the spark plasma sintering (SPS) method. The grain size of W-1.0wt% ZrC is about 2.7 μm, smaller than that of pure W and W-(0.2, 0.5)wt% ZrC. The results indicated that the W-ZrC alloys exhibit higher hardness at room temperature, higher tensile strength at high temperature, and a lower ductile to brittle transition temperature (DBTT) than pure W. The tensile strength and total elongation of W-0.5wt% ZrC alloy at 700 °C is 535 MPa and 24.8%, which are respectively 59% and 114% higher than those of pure W (337 MPa, 11.6%). The DBTT of W-(0.2, 0.5, 1.0)wt% ZrC materials is in the range of 500°C-600°C, which is about 100 °C lower than that of pure W. Based on microstructure analysis, the improved mechanical properties of the W-ZrC alloys were suggested to originate from the enhanced grain boundary cohesion by ZrC capturing the impurity oxygen in tungsten and nano-size ZrC dispersion strengthening. supported by the Innovation Program of Chinese Academy of Sciences (No. KJCX2-YW-N35), the National Magnetic Confinement Fusion Science Program of China (No. 2011GB108004), National Natural Science Foundation of China (Nos. 51301164, 11075177, 11274305), and Anhui Provincial Natural Science Foundation of China (No. 1408085QE77)

Study of effective utilization of iron ore sinter through arc plasma

NASA Astrophysics Data System (ADS)

Swain, Biswajit; Samal, S. K.; Mohanty, M. K.; Behera, A.; Mishra, S. C.

2018-03-01

Generation of fines is common in mining, sizing, and beneficiation and also in high-temperature metallurgical processes as the disintegration of agglomerate/compact occurs. Extraction of metallic iron from ore fines is one of the challenging aspects of iron making industries as the liberation of fines blocks, the charge burden porosity and hence hinders the reduction rate. Along with size factor, mineral composition plays a vital role in the extraction process; particularly silica. As silica has the very high tendency towards iron oxide, at comparatively low temperature, the activity of silica should be suppressed to prevent silicate phases. Adjustment of such conditions is controlled by addition of lime, but sometimes excessive slag generation increases the cost of production. In the present work, carbothermic reduction of partially reduced iron bearing pellets has been melted through 20 KW DC arc plasma furnace, and a comparative study has been made for considering different slag chemistry approaches. Pellets as aforementioned are made available from Patnaik Steel and Alloys Ltd, Odisha, having high silica content ore fines (of about 8.6%) as obtained from the chemical analysis. X-Ray analysis and optical image analyzer result of sinter thus obtained reveal that fayalite phase has major fractional value. Smelting works were done for sinter with/without adjustment of slag chemistry, where argon and nitrogen were used as plasma forming gases. A range of recovery rates (between 87-94%) is achieved by charge composition, ionizing gases, and smelting duration. It is observed that use of nitrogen as plasma forming gas increases the recovery rate than that of using only argon plasma; due to high energy flux of nitrogen which increases the enthalpy due to its diatomicity. A maximum recovery rate of about 94% is achieved for process duration of 13minutes utilizing nitrogen plasma. Smelting of charge with the addition of hydrated lime targeting melilite as final slag resulted in the formation of metallic iron as confirmed from XRD and XRF analyses. In the other hand, ferrosilicon is liberated in the metallic parts where smelting of charge was done without adjustment of slag chemistry. Both metal and slag thus obtained are characterized by XRD, XRF, microhardness and wet chemical analysis suitably.

Chemical Synthesis and Oxide Dispersion Properties of Strengthened Tungsten via Spark Plasma Sintering

PubMed Central

Ding, Xiao-Yu; Luo, Lai-Ma; Chen, Hong-Yu; Zhu, Xiao-Yong; Zan, Xiang; Cheng, Ji-Gui; Wu, Yu-Cheng

2016-01-01

Highly uniform oxide dispersion-strengthened materials W–1 wt % Nd2O3 and W–1 wt % CeO2 were successfully fabricated via a novel wet chemical method followed by hydrogen reduction. The powders were consolidated by spark plasma sintering at 1700 °C to suppress grain growth. The samples were characterized by performing field emission scanning electron microscopy and transmission electron microscopy analyses, Vickers microhardness measurements, thermal conductivity, and tensile testing. The oxide particles were dispersed at the tungsten grain boundaries and within the grains. The thermal conductivity of the samples at room temperature exceeded 140 W/m·K. The tensile tests indicated that W–1 wt % CeO2 exhibited a ductile–brittle transition temperature between 500 °C and 550 °C, which was a lower range than that for W–1 wt % Nd2O3. Surface topography and Vickers microhardness analyses were conducted before and after irradiations with 50 eV He ions at a fluence of 1 × 1022 m−2 for 1 h in the large-powder material irradiation experiment system. The grain boundaries of the irradiated area became more evident than that of the unirradiated area for both samples. Irradiation hardening was recognized for the W–1 wt % Nd2O3 and W–1 wt % CeO2 samples. PMID:28773999

Epsilon Metal Waste Form for Immobilization of Noble Metals from Used Nuclear Fuel

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

Crum, Jarrod V.; Strachan, Denis M.; Rohatgi, Aashish

2013-10-01

Epsilon metal (ε-metal), an alloy of Mo, Pd, Rh, Ru, and Tc, is being developed as a waste form to treat and immobilize the undissolved solids and dissolved noble metals from aqueous reprocessing of commercial used nuclear fuel. Epsilon metal is an attractive waste form for several reasons: increased durability relative to borosilicate glass, it can be fabricated without additives (100% waste loading), and in addition it also benefits borosilicate glass waste loading by eliminating noble metals from the glass and thus the processing problems related there insolubility in glass. This work focused on the processing aspects of the epsilonmore » metal waste form development. Epsilon metal is comprised of refractory metals resulting in high reaction temperatures to form the alloy, expected to be 1500 - 2000°C making it a non-trivial phase to fabricate by traditional methods. Three commercially available advanced technologies were identified: spark-plasma sintering, microwave sintering, and hot isostatic pressing, and investigated as potential methods to fabricate this waste form. Results of these investigations are reported and compared in terms of bulk density, phase assemblage (X-ray diffraction and elemental analysis), and microstructure (scanning electron microscopy).« less

Epsilon metal waste form for immobilization of noble metals from used nuclear fuel

NASA Astrophysics Data System (ADS)

Crum, Jarrod V.; Strachan, Denis; Rohatgi, Aashish; Zumhoff, Mac

2013-10-01

Epsilon metal (ɛ-metal), an alloy of Mo, Pd, Rh, Ru, and Tc, is being developed as a waste form to treat and immobilize the undissolved solids and dissolved noble metals from aqueous reprocessing of commercial used nuclear fuel. Epsilon metal is an attractive waste form for several reasons: increased durability relative to borosilicate glass, it can be fabricated without additives (100% waste loading), and in addition it also benefits borosilicate glass waste loading by eliminating noble metals from the glass, thus the processing problems related to their insolubility in glass. This work focused on the processing aspects of the epsilon metal waste form development. Epsilon metal is comprised of refractory metals resulting in high alloying temperatures, expected to be 1500-2000 °C, making it a non-trivial phase to fabricate by traditional methods. Three commercially available advanced technologies were identified: spark-plasma sintering, microwave sintering, and hot isostatic pressing, and investigated as potential methods to fabricate this waste form. Results of these investigations are reported and compared in terms of bulk density, phase assemblage (X-ray diffraction and elemental analysis), and microstructure (scanning electron microscopy).

Thermodynamics analysis of diffusion in spark plasma sintering welding Cr3C2 and Ni

NASA Astrophysics Data System (ADS)

Zhang, Fan; Zhang, Jinyong; Leng, Xiaoxuan; Lei, Liwen; Fu, Zhengyi

2017-03-01

Spark plasma sintering (SPS) welding of chromium carbide (Cr3C2) and nickel (Ni) was used to investigate the atomic diffusion caused by bypassing current. It was found that the diffusion coefficient with bypassing current was enhanced by almost 3.57 times over that without bypassing current. Different from the previous researches, the thermodynamics analysis conducted herein showed that the enhancement included a current direction-independent part besides the known current direction-dependent part. A local temperature gradient (LTG) model was proposed to explain the current direction-independent effect. Assuming that the LTG was mainly due to the interfacial electric resistance causing heterogeneous Joule heating, the theoretical results were in good agreement with the experimental results both in the present and previous studies. This new LTG model provides a reasonable physical meaning for the low-temperature advantage of SPS welding and should be useful in a wide range of applications.

Microstructure and Mechanical Behavior of Amorphous Al-Cu-Ti Metal Foams Synthesized by Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Li, Maoyuan; Lu, Lin; Dai, Zhen; Hong, Yiqiang; Chen, Weiwei; Zhang, Yuping; Qiao, Yingjie

Amorphous Al-Cu-Ti metal foams were prepared by spark plasma sintering (SPS) process with the diameter of 10mm. The SPS process was conducted at the pressure of 200 and 300MPa with the temperature of 653-723K, respectively. NaCl was used as the space-holder, forming almost separated pores with the porosity of 65 vol%. The microstructure and mechanical behavior of the amorphous Al-Cu-Ti metal foams were systematically investigated. The results show that the crystallinity increased at elevated temperatures. The effect of pressure and holding time on the crystallization was almost negligible. The intermetallic compounds, i.e. Al-Ti, Al-Cu and Al-Cu-Ti were identified from X-ray diffraction (XRD) patterns. It was found that weak adhesion and brittle intermetallic compounds reduced the mechanical properties, while lower volume fraction and smaller size of NaCl powders improved the mechanical properties.

Photoconductivity induced by nanoparticle segregated grain-boundary in spark plasma sintered BiFeO3

NASA Astrophysics Data System (ADS)

Nandy, Subhajit; Mocherla, Pavana S. V.; Sudakar, C.

2017-05-01

Photoconductivity studies on spark plasma sintered BiFeO3 samples with two contrasting morphologies, viz., nanoparticle-segregated grain boundary (BFO-AP) and clean grain boundary (BFO-AA), show that their photo-response is largely influenced by the grain boundary defects. Impedance analyses at 300 K and 573 K clearly demarcate the contributions from grain, grain-boundary, and the nanoparticle-segregated grain-boundary conductivities. I-V characteristics under 1 sun illumination show one order of higher conductivity for BFO-AP, whereas conductivity decreases for BFO-AA sample. Larger photocurrent in BFO-AP is attributed to the extra conduction path provided by oxygen vacancies on the nanoparticle surfaces residing at the grain boundaries. Creation of photo-induced traps under illumination and the absence of surface conduction channels in BFO-AA are surmised to result in a decreased conductivity on illumination.

Proportional integral derivative, modeling and ways of stabilization for the spark plasma sintering process

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

Manière, Charles; Lee, Geuntak; Olevsky, Eugene A.

The stability of the proportional–integral–derivative (PID) control of temperature in the spark plasma sintering (SPS) process is investigated. The PID regulations of this process are tested for different SPS tooling dimensions, physical parameters conditions, and areas of temperature control. It is shown that the PID regulation quality strongly depends on the heating time lag between the area of heat generation and the area of the temperature control. Tooling temperature rate maps are studied to reveal potential areas for highly efficient PID control. The convergence of the model and experiment indicates that even with non-optimal initial PID coefficients, it is possiblemore » to reduce the temperature regulation inaccuracy to less than 4 K by positioning the temperature control location in highly responsive areas revealed by the finite-element calculations of the temperature spatial distribution.« less

ZrB2-CNTs Nanocomposites Fabricated by Spark Plasma Sintering

PubMed Central

Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

2016-01-01

ZrB2-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB2 matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB2 grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB2-CNTs composites were compared with those of the micro-grained ZrB2-CNTs composites. Due to the small size and surface effects, the nanograined ZrB2-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m1/2, respectively. PMID:28774087

ZrB₂-CNTs Nanocomposites Fabricated by Spark Plasma Sintering.

PubMed

Jin, Hua; Meng, Songhe; Xie, Weihua; Xu, Chenghai; Niu, Jiahong

2016-11-29

ZrB₂-based nanocomposites with and without carbon nanotubes (CNTs) as reinforcement were prepared at 1600 °C by spark plasma sintering. The effects of CNTs on the microstructure and mechanical properties of nano-ZrB₂ matrix composites were studied. The results indicated that adding CNTs can inhibit the abnormal grain growth of ZrB₂ grains and improve the fracture toughness of the composites. The toughness mechanisms were crack deflection, crack bridging, debonding, and pull-out of CNTs. The experimental results of the nanograined ZrB₂-CNTs composites were compared with those of the micro-grained ZrB₂-CNTs composites. Due to the small size and surface effects, the nanograined ZrB₂-CNTs composites exhibited stronger mechanical properties: the hardness, flexural strength and fracture toughness were 18.7 ± 0.2 GPa, 1016 ± 75 MPa, and 8.5 ± 0.4 MPa·m 1/2 , respectively.

Tantalum-tungsten oxide thermite composites prepared by sol-gel synthesis and spark plasma sintering

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

Kuntz, Joshua D.; Gash, Alexander E.; Cervantes, Octavio G.

2010-08-15

Energetic composite powders consisting of sol-gel derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition-tested and the results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High-Pressure Spark Plasma Sintering (HPSPS) technique, on the sol-gel derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The sol-gel derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta-WO{sub 3}) energetic composite was consolidated to a density of 9.17 g cm{sup -3}more » or 93% relative density. In addition, those samples were consolidated without significant pre-reaction of the constituents, thus retaining their stored chemical energy. (author)« less

Tantalum-Tungsten Oxide Thermite Composite Prepared by Sol-Gel Synthesis and Spark Plasma Sintering

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

Cervantes, O; Kuntz, J; Gash, A

2009-02-13

Energetic composite powders consisting of sol-gel derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition tested and results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High Pressure Spark Plasma Sintering (HPSPS) technique, on the sol-gel derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The sol-gel derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta - WO{sub 3}) energetic composite was consolidated to a density of 9.17more » g.cm{sup -3} or 93% relative density. In addition those parts were consolidated without significant pre-reaction of the constituents, thus the sample retained its stored chemical energy.« less

Proportional integral derivative, modeling and ways of stabilization for the spark plasma sintering process

DOE PAGES

Manière, Charles; Lee, Geuntak; Olevsky, Eugene A.

2017-04-21

The stability of the proportional–integral–derivative (PID) control of temperature in the spark plasma sintering (SPS) process is investigated. The PID regulations of this process are tested for different SPS tooling dimensions, physical parameters conditions, and areas of temperature control. It is shown that the PID regulation quality strongly depends on the heating time lag between the area of heat generation and the area of the temperature control. Tooling temperature rate maps are studied to reveal potential areas for highly efficient PID control. The convergence of the model and experiment indicates that even with non-optimal initial PID coefficients, it is possiblemore » to reduce the temperature regulation inaccuracy to less than 4 K by positioning the temperature control location in highly responsive areas revealed by the finite-element calculations of the temperature spatial distribution.« less

Thermoelectric properties of n-type double substituted SrTiO3 bulk materials.

PubMed

Cui, Yanjie; He, Jian; Amow, Gisele; Kleinke, Holger

2010-01-28

A series of La, Ta double substituted Sr(1-x)La(x)Ti(1-x)Ta(x)O(3), with x = 0.01, 0.05 and 0.10, and La, Nb double substituted Sr(0.90)La(0.10)Ti(0.90)Nb(0.10)O(3) for comparison were investigated in this project. Rietveld refinements were performed to check for purity and symmetry reduction. Electronic structure calculations indicate n-type conduction with steep and flat bands in the vicinity of the Fermi level for x = 0.125. Seebeck coefficient, electrical conductivity, and thermal conductivity measurements on hot-pressed and spark-plasma-sintered samples were performed over a wide range of temperatures. Best results were obtained by spark-plasma-sintering of double substituted Sr(0.99)La(0.01)Ti(0.99)Ta(0.01)O(3) with a thermoelectric figure-of-merit of 0.13 at 660 K.

Sintered rare earth-iron Laves phase magnetostrictive alloy product and preparation thereof

DOEpatents

Malekzadeh, Manoochehr; Pickus, Milton R.

1979-01-01

A sintered rare earth-iron Laves phase magnetostrictive alloy product characterized by a grain oriented morphology. The grain oriented morphology is obtained by magnetically aligning powder particles of the magnetostrictive alloy prior to sintering. Specifically disclosed are grain oriented sintered compacts of Tb.sub.x Dy.sub.1-x Fe.sub.2 and their method of preparation. The present sintered products have enhanced magnetostrictive properties.

Sintered magnetic cores of high Bs Fe84.3Si4B8P3Cu0.7 nano-crystalline alloy with a lamellar microstructure

NASA Astrophysics Data System (ADS)

Zhang, Yan; Sharma, Parmanand; Makino, Akihiro

2014-05-01

Fabrication of bulk cores of nano-crystalline Fe84.3Si4B8P3Cu0.7 alloy with a lamellar type of microstructure is reported. Amorphous ribbon flakes of size ˜1.0-2.0 mm were compacted in the bulk form by spark plasma sintering technique at different sintering temperatures. High density (˜96.4%) cores with a uniform nano-granular structure made from α-Fe (˜31 nm) were obtained. These cores show excellent mechanical and soft magnetic properties. The lamellar micro-structure is shown to be important in achieving significantly lower magnetic core loss than the non-oriented silicon steel sheets, commercial powder cores and even the core made of the same alloy with finer and randomly oriented powder particles.

Method of producing amorphous thin films

DOEpatents

Brusasco, Raymond M.

1992-01-01

Disclosed is a method of producing thin films by sintering which comprises: a. coating a substrate with a thin film of an inorganic glass forming parulate material possessing the capability of being sintered, and b. irridiating said thin film of said particulate material with a laser beam of sufficient power to cause sintering of said material below the temperature of liquidus thereof. Also disclosed is the article produced by the method claimed.

Method of producing amorphous thin films

DOEpatents

Brusasco, R.M.

1992-09-01

Disclosed is a method of producing thin films by sintering which comprises: (a) coating a substrate with a thin film of an inorganic glass forming material possessing the capability of being sintered; and (b) irradiating said thin film of said particulate material with a laser beam of sufficient power to cause sintering of said material below the temperature of liquidus thereof. Also disclosed is the article produced by the method claimed. 4 figs.

Microwave sintering of single plate-shaped articles

DOEpatents

Katz, Joel D.; Blake, Rodger D.

1995-01-01

Apparatus and method for high temperature sintering of plate-shaped articles of alumina, magnesia, silica, yttria, zirconia, and mixtures thereof using microwave radiation. An article is placed within a sintering structure located within a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

Large-scale production of (GeTe) x (AgSbTe 2) 100$-$x (x=75, 80, 85, 90) with enhanced thermoelectric properties via gas-atomization and spark plasma sintering

DOE PAGES

Kim, Hyo-Seob; Ames Lab., Ames, IA; Dharmaiah, Peyala; ...

2017-01-30

(GeTe) x(AgSbTe 2) 100$-$x: TAGS thermoelectrics are an attractive class of materials due to their combination of non-toxicity and good conversion efficiency at mid-temperature ranges. Here in the present work, we have utilized energy and time efficient high-pressure gas atomization and spark-plasma sintering techniques for large-scale preparation of samples with varying composition (i.e., (GeTe) x(AgSbTe 2) 100$-$x where x = 75, 80, 85, and 90). High-temperature x-ray diffraction was used to understand the phase transformation mechanism of the as-atomized powders. Detailed high-resolution transmission electron microscopy of the sintered samples revealed the presence of nanoscale precipitates, antiphase, and twin boundaries. Themore » nanoscale twins and antiphase boundaries serve as phonon scattering centers, leading to the reduction of total thermal conductivity in TAGS-80 and 90 samples. The maximum ZT obtained was 1.56 at 623 K for TAGS-90, which was ~94% improvement compared to values previously reported. The presence of the twin boundaries also resulted in a high fracture toughness (K IC) of the TAGS-90 sample due to inhibition of dislocation movement at the twin boundary.« less

Effect of Sintering on Mechanical and Physical Properties of Plasma-Sprayed Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2004-01-01

The effect of sintering on mechanical and physical properties of free-standing plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coatings (TBCs) was determined by annealing them at 1316 C in air. Mechanical and physical properties of the TBCs, including strength, modes I and II fracture toughness, elastic modulus, Poisson s response, density, microhardness, fractography, and phase stability, were determined at ambient temperature as a function of annealing time ranging from 0 to 500 h. All mechanical and physical properties, except for the amount of monoclinic phase, increased significantly in 5 to 100 h and then reached a plateau above 100 h. Annealing resulted in healing of microcracks and pores and in grain growth, accompanying densification of the TBC s body due to the sintering effect. However, an inevitable adverse effect also occurred such that the desired lower thermal conductivity and good expansivity, which makes the TBCs unique in thermal barrier applications, were degraded upon annealing. A model was proposed to assess and quantify all the property variables in response to annealing in a normalized scheme. Directionality of as-sprayed TBCs appeared to have an insignificant effect on their properties, as determined via fracture toughness, microhardness, and elastic modulus measurements.

Sintering behavior and thermal conductivity of nickel-coated graphite flake/copper composites fabricated by spark plasma sintering

NASA Astrophysics Data System (ADS)

Xu, Hui; Chen, Jian-hao; Ren, Shu-bin; He, Xin-bo; Qu, Xuan-hui

2018-04-01

Nickel-coated graphite flakes/copper (GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes (GFs) being modified by Ni-P electroless plating. The effects of the phase transition of the amorphous Ni-P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity (TC) of the GN/Cu composites were systematically investigated. The introduction of Ni-P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650°C and slightly increased the TC of the X-Y basal plane of the GF/Cu composites with 20vol%-30vol% graphite flakes. However, when the graphite flake content was greater than 30vol%, the TC of the GF/Cu composites decreased with the introduction of Ni-P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.

New ZrO2/Al2O3 Nanocomposite Fabricated from Hybrid Nanoparticles Prepared by CO2 Laser Co-Vaporization

PubMed Central

Bartolomé, José F.; Smirnov, Anton; Kurland, Heinz-Dieter; Grabow, Janet; Müller, Frank A.

2016-01-01

Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO2/Al2O3 dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr(1−x)AlxO(2−x/2) and (γ-, δ-)Al2O3 by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO2 (52.4 vol%) and α-Al2O3 (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σf = 1500 MPa, fracture toughness KIc = 6.8 MPa m1/2) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants. PMID:26846310

New ZrO2/Al2O3 Nanocomposite Fabricated from Hybrid Nanoparticles Prepared by CO2 Laser Co-Vaporization

NASA Astrophysics Data System (ADS)

Bartolomé, José F.; Smirnov, Anton; Kurland, Heinz-Dieter; Grabow, Janet; Müller, Frank A.

2016-02-01

Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO2/Al2O3 dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr(1-x)AlxO(2-x/2) and (γ-, δ-)Al2O3 by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO2 (52.4 vol%) and α-Al2O3 (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σf = 1500 MPa, fracture toughness KIc = 6.8 MPa m1/2) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants.

Surface-selective laser sintering of thermolabile polymer particles using water as heating sensitizer

NASA Astrophysics Data System (ADS)

Antonov, E. N.; Krotova, L. I.; Minaev, N. V.; Minaeva, S. A.; Mironov, A. V.; Popov, V. K.; Bagratashvili, V. N.

2015-11-01

We report the implementation of a novel scheme for surface-selective laser sintering (SSLS) of polymer particles, based on using water as a sensitizer of laser heating and sintering of particles as well as laser radiation at a wavelength of 1.94 μm, corresponding to the strong absorption band of water. A method of sintering powders of poly(lactide-co-glycolide), a hydrophobic bioresorbable polymer, after modifying its surface with an aqueous solution of hyaluronic acid is developed. The sintering thresholds for wetted polymer are by 3 - 4 times lower than those for sintering in air. The presence of water restricts the temperature of the heated polymer, preventing its thermal destruction. Polymer matrices with a developed porous structure are obtained. The proposed SSLS method can be applied to produce bioresorbable polymer matrices for tissue engineering.

Grain growth in uranium nitride prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Johnson, Kyle D.; Lopes, Denise Adorno

2018-05-01

Uranium mononitride (UN) has long been considered a potential high density, high performance fuel candidate for light water reactor (LWR) and fast reactor (FR) applications. However, deployability of this fuel has been limited by the notable resistance to sintering and subsequent difficulty in producing a desirable microstructure, the high costs associated with 15N enrichment, as well as the known proclivity to oxidation and interaction with steam. In this study, the stimulation of grain growth in UN pellets sintered using SPS has been investigated. The results reveal that by using SPS and controlling temperature, time, and holding pressure, grain growth can be stimulated and controlled to produce a material featuring both a desired porosity and grain size, at least within the range of interest for nuclear fuel candidates. Grain sizes up to 31 μm were obtained using temperatures of 1650 °C and hold times of 15 min. Evaluation by EBSD reveal grain rotation and coalescence as the dominant mechanism in grain growth, which is suppressed by the application of higher external pressure. Moreover, complete closure of the porosity of the material was observed at relative densities of 96% TD, resulting in a material with sufficient porosity to accommodate LWR burnup. These results indicate that a method exists for the economic fabrication of an 15N-bearing uranium mononitride fuel with favorable microstructural characteristics compatible with use in a light water-cooled nuclear reactor.

The Influence of Sintering Method on Kaolin-Based Geopolymer Ceramics with Addition of Ultra High Molecular Weight Polyethylene as Binder

NASA Astrophysics Data System (ADS)

Romisuhani, A.; AlBakri, M. M.; Kamarudin, H.; Andrei, S. V.

2017-11-01

The influence of sintering method on kaolin-based geopolymer ceramics with addition of Ultra High Molecular Weight Polyethylene as binder were studied. Geopolymer were formed at room temperature from kaolin and sodium silicate in a highly alkaline medium, followed by curing and drying at 80 °C. 12 M of sodium hydroxide solution were mixed with sodium silicate at a ratio of 0.24 to form alkaline activator. Powder metallurgy technique were used in order to produce kaolin geopolymer ceramics with addition of Ultra High Molecular Weight Polyethylene. The samples were heated at temperature of 1200 °C with two different sintering method which are conventional method and two-step sintering method. The strength and density were tested.

Development of composite ceramic materials with improved thermal conductivity and plasticity based on garnet-type oxides

NASA Astrophysics Data System (ADS)

Golovkina, L. S.; Orlova, A. I.; Boldin, M. S.; Sakharov, N. V.; Chuvil'deev, V. N.; Nokhrin, A. V.; Konings, R.; Staicu, D.

2017-06-01

Powders based on the complex garnet-type oxide Y2.5Nd0.5Al5O12 - x wt. % Ni (x = 0, 10, 20) were prepared using wet chemistry methods. Ceramics based on these compounds were obtained by Spark Plasma Sintering (SPS) with a relative densities: 99%. 4% (TD = 4.77 g/cm3 (0%)), 97.6% (TD = 4.88 g/cm3 (10%)), 94.4% (TD = 5.06 g/cm3 (20%)). The influence of nickel concentration on the mechanical (fracture toughness, microhardness) and thermophysical (thermal conductivity) properties of the composites was studied.

Sintering Uranium Dioxide of Domestic Production. Report No. 78; SINTERIZACION DE DIOXIDO DE URANIO DE PRODUCCION NACIONAL. Informe No. 78

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

Carrea, A.J.

1963-01-01

After a brief indication of the uranium- oxygen equilibrium and the methods for the preparation of UO/sub 2/, the sintering of UO/sub 2/ is considered. The effects of various sintering atmospheres on the properties of the product are discussed and tabulated. The method used for the processing of domestic ores for the preparation of UO/sub 2/ and the fabricition of the sintered UO/sub 2/are described. The properties of the product obtained are illustrated graphically. (J.S.R.)

Extrinsic contributions to the dielectric response in sintered BaTiO3 nanostructures in paraelectric and ferroelectric regimes

NASA Astrophysics Data System (ADS)

Jaffari, G. Hassnain; Rehman, Atiq ur; Iqbal, Asad M.; Awan, M. S.; Saleemi, Mohsin

2017-11-01

Post sintering studies of BaTiO3 (BTO) nanoparticles are presented in detail. Bulk nanostructures were prepared via three different compaction processes, namely, uniaxial cold pressing (UCP), Cold Isostatic Pressing (CIP) and Spark Plasma Sintering (SPS). Effect of compaction technique on microstructures have been investigated and correlated with electrical response for each sample. In addition to the transport properties, temperature and frequency dependent dielectric response of variously sintered samples and bulk counterpart was recorded. Several aspects have been identified that are essential to be taken into account in order to completely understand physical processes. Drastically distinct features were observed in paraelectric (PE) regime well above ferroelectric (FE)-PE transition temperature. These features include intra grain conduction with a reduction in the magnitude of PE to FE peak dielectric constant magnitude. Role of strain, grain boundary conduction associated with observation of Maxwell Wagner relaxation and hopping conduction in dielectric and ferroelectric response have been observed and discussed. Densification with presence of oxygen vacancies, significantly enhances conductivity associated with the hopping of the carriers, in turn deteriorated ferroelectric response.

Microwave sintering of single plate-shaped articles

DOEpatents

Katz, J.D.; Blake, R.D.

1995-07-11

Apparatus and method are disclosed for high temperature sintering of plate-shaped articles of alumina, magnesia, silica, yttria, zirconia, and mixtures thereof using microwave radiation. An article is placed within a sintering structure located within a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled. 2 figs.

Ultrafast Thermal Plasma Preparation of Solid Si Films with Potential Application in Photovoltaic Cells: A Parametric Study

NASA Astrophysics Data System (ADS)

Mostajeran Goortani, Behnam; Gitzhofer, François; Bouyer, Etienne; Mousavi, Mehdi

2009-03-01

An innovative method, namely ultrafast plasma surface melting, is developed to fabricate solid films of silicon with very high rates (150 cm2/min). The method is composed of preparing a suspension of solid particles in a volatile solvent and spreading it on a refractory substrate such as Mo. After solvent evaporation, the resulting porous layer is exposed to the flame tale of inductively coupled RF plasma to sinter and melt the surface particles and to prepare a solid film of silicon. It is shown that by controlling the flow dynamics and heat transfer around the substrate, and managing the kinetic parameters (i.e., exposure time, substrate transport speed, and reaction kinetics) in the reactor, we can produce solid crystalline Si films with the potential applications in photovoltaic cells industry. The results indicate that the optimum formation conditions with a film thickness of 250-700 μm is when the exposure time in the plasma is in the range of 5-12.5 s for a 100 × 50 mm large layer. By combining the Fourier’s law of conduction with the experimental measurements, we obtained an effective heat diffusivity and developed a model to obtain heat diffusion in the porous layer exposed to the plasma. The model further predicts the minimum and maximum exposure time for the substrate in the plasma flame as a function of material properties, the porous layer thickness and of the imposed heat flux.

Titanium dental copings prepared by a powder metallurgy method: a preliminary report.

PubMed

Eriksson, Mikael; Andersson, Matts; Carlström, Elis

2004-01-01

The purpose of this study was to determine if the Procera pressed-powder method can be used to fabricate titanium copings. Commercially pure titanium powder was used to prepare the copings. The powder was pressed onto an enlarged tooth preparation die of aluminum using cold isostatic pressing. The outer shape of the coping was formed using a Procera milling machine, and the copings were vacuum sintered. Titanium copings could be prepared using this method. The density of the sintered copings reached 97% to 99%+ of theoretic density, and the copings showed ductile behavior after sintering. Enlarging the tooth preparation die to compensate for the sintering shrinkage could optimize the final size of the copings. Ductile and dense titanium dental copings can be produced with powder-metal processing using cold isostatic pressing, followed by milling and sintering to final shape. The forming technique has, if properly optimized, a potential of becoming a more cost-efficient production method than spark erosion.

Method for heat treating and sintering metal oxides with microwave radiation

DOEpatents

Holcombe, Cressie E.; Dykes, Norman L.; Meek, Thomas T.

1989-01-01

A method for microwave sintering materials, primarily metal oxides, is described. Metal oxides do not normally absorb microwave radiation at temperatures ranging from about room temperature to several hundred degrees centrigrade are sintered with microwave radiation without the use of the heretofore required sintering aids. This sintering is achieved by enclosing a compact of the oxide material in a housing or capsule formed of a oxide which has microwave coupling properties at room temprature up to at least the microwave coupling temperature of the oxide material forming the compact. The heating of the housing effects the initial heating of the oxide material forming the compact by heat transference and then functions as a thermal insulator for the encased oxide material after the oxide material reaches a sufficient temperature to adequately absorb or couple with microwave radiation for heating thereof to sintering temperature.

Method of forming a joint

DOEpatents

Butt, Darryl Paul; Cutler, Raymond Ashton; Rynders, Steven Walton; Carolan, Michael Francis

2006-08-22

A method of joining at least two sintered bodies to form a composite structure, including providing a first multicomponent metallic oxide having a perovskitic or fluorite crystal structure; providing a second sintered body including a second multicomponent metallic oxide having a crystal structure of the same type as the first; and providing at an interface a joint material containing at least one metal oxide containing at least one metal identically contained in at least one of the first and second multicomponent metallic oxides. The joint material is free of cations of Si, Ge, Sn, Pb, P and Te and has a melting point below the sintering temperatures of both sintered bodies. The joint material is heated to a temperature above the melting point of the metal oxide(s) and below the sintering temperatures of the sintered bodies to form the joint. Structures containing such joints are also disclosed.

Apparatus and method for direct measurement of coal ash sintering and fusion properties at elevated temperatures and pressures

DOEpatents

Khan, M. Rashid

1990-01-01

A high-pressure microdilatometer is provided for measuring the sintering and fusion properties of various coal ashes under the influence of elevated pressures and temperatures in various atmospheres. Electrical resistivity measurements across a sample of coal ash provide a measurement of the onset of the sintering and fusion of the ash particulates while the contraction of the sample during sintering is measured with a linear variable displacement transducer for detecting the initiation of sintering. These measurements of sintering in coal ash at different pressures provide a mechanism by which deleterious problems due to the sintering and fusion of ash in various combustion systems can be minimized or obviated.

Two-Step Reactive Aid Sintering of BaZr0.8Y0.2O3- δ Proton-Conducting Ceramics

NASA Astrophysics Data System (ADS)

Wang, Siwei; Chen, Yan; Zhang, Lingling; Ren, Cong; Chen, Fanglin; Brinkman, Kyle S.

2015-12-01

Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr0.8Y0.2O3- δ (BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. In this paper, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO3 and B2O3-Li2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering was improved to 19.3% by a TRAS method as compared to 2.6% by the conventional solid date reaction method. The bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.

Two-Step Reactive Aid Sintering of BaZr 0.8Y 0.2O 3-δ Proton-Conducting Ceramics

DOE PAGES

Wang, Siwei; Chen, Yan; Zhang, Lingling; ...

2015-10-14

Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr 0.8Y 0.2O 3-δ (BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. Here, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO 3 and B 2O 3-Li 2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering was improvedmore » to 19.3% by a TRAS method as compared to 2.6% by the conventional solid date reaction method. Moreover, the bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.« less

A comparative study of conventionally sintered and microwave sintered nickel zinc ferrite

NASA Astrophysics Data System (ADS)

Rani, Rekha; Juneja, J. K.; Raina, K. K.; Kotnala, R. K.; Prakash, Chandra

2014-04-01

For the present work, nickel zinc ferrite having compositional formula Ni0.8Zn0.2Fe2O4 was synthesized by conventional solid state method and sintered in conventional and microwave furnaces. Pellets were sintered with very short soaking time of 10 min at 1150 °C in microwave furnace whereas 4 hrs of soaking time was selected for conventional sintering at 1200 °C. Phase formation was confirmed by X-ray diffraction analysis technique. Scanning electron micrographs were taken for microstructural study. Dielectric properties were studied as a function of temperature. To study magnetic behavior, M-H hysteresis loops were recorded for both samples. It is observed that microwave sintered sample could obtain comparable properties to the conventionally sintered one in lesser soaking time at lower sintering temperature.

Effect of Process Parameter on Barium Titanate Stannate (BTS) Materials Sintered at Low Sintering

NASA Astrophysics Data System (ADS)

Shukla, Alok; Bajpai, P. K.

2011-11-01

Ba(Ti1-xSnx)O3 solid solutions with (x = 0.15, 0.20, 0.30 and 0.40) are synthesized using conventional solid state reaction method. Formation of solid solutions in the range 0 ≤ x ≤0.40 is confirmed using X-ray diffraction technique. Single phase solid solutions with homogeneous grain distribution are observed at relatively low sintering by controlling process parameters viz. sintering time. Composition at optimized temperature (1150 °C) sintered by varying the sintering time, stabilize in cubic perovskite phase. The % experimental density increase with increasing the time of sintering instead of increasing sintering temperature. The lattice parameter increases by increasing the tin composition in the material. This demonstrates that process parameter optimization can lead to single phase at relatively lower sintering-a major advantage for the materials used as capacitor element in MLCC.

Sub-second carbon-nanotube-mediated microwave sintering for high-conductivity silver patterns on plastic substrates

NASA Astrophysics Data System (ADS)

Jung, Sunshin; Chun, Su Jin; Han, Joong Tark; Woo, Jong Seok; Shon, Cha-Hwa; Lee, Geon-Woong

2016-02-01

A method of microwave sintering that is mediated by carbon nanotubes (CNTs) has been developed to obtain high-conductivity Ag patterns on the top of heat-sensitive plastic substrates within a short time. The Ag patterns are printed on CNTs formed on plastic substrates and rapidly heated to a great extent by the heat transferred from the microwave-heated CNTs. The conductivity of the microwave-sintered Ag patterns reaches ~39% that of bulk Ag within 1 s without substrate deformation. Furthermore, microwave sintering enhances the adhesion of Ag patterns to the thermoplastic substrates because the sintering causes interfacial fusion between the Ag patterns and the substrates, and CNTs physically connect the patterns with the substrates.A method of microwave sintering that is mediated by carbon nanotubes (CNTs) has been developed to obtain high-conductivity Ag patterns on the top of heat-sensitive plastic substrates within a short time. The Ag patterns are printed on CNTs formed on plastic substrates and rapidly heated to a great extent by the heat transferred from the microwave-heated CNTs. The conductivity of the microwave-sintered Ag patterns reaches ~39% that of bulk Ag within 1 s without substrate deformation. Furthermore, microwave sintering enhances the adhesion of Ag patterns to the thermoplastic substrates because the sintering causes interfacial fusion between the Ag patterns and the substrates, and CNTs physically connect the patterns with the substrates. Electronic supplementary information (ESI) available: Temperature difference in Ag/CNT/PC samples; the carbon content and electrical performance after microwave sintering; microwave sintering of Ag/CNT patterns; physical connection between the substrate and sintered Ag lines; touch-piano (figure and movie). See DOI: 10.1039/c5nr08082g

Silicon nitride sintered body

NASA Technical Reports Server (NTRS)

Suzuki, K.; Shinohara, N.

1984-01-01

The sintering of silicon carbide and it production are described. The method of production is by calcination in which molding is followed by sintering without compression. The invention improves the composition of the silicon carbide ceramic. Six examples of the invention are illustrated and discussed.

Effect of the application of surface treatments before and after sintering on the flexural strength, phase transformation and surface topography of zirconia.

PubMed

Kurtulmus-Yilmaz, Sevcan; Aktore, Huseyin

2018-05-01

To evaluate the effects of airborne-particle abrasion (APA) and Er,Cr:YSGG laser irradiation on 4-point-flexural strength, phase transformation and morphologic changes of zirconia ceramics treated at pre-sintered or post-sintered stage. Three hundred and forty-two bar shaped zirconia specimens were milled with different sizes according to the flexural strength test (n = 10), X-ray diffraction (XRD) (n = 4) and field emission scanning electron microscope (FE-SEM) (n = 4) analyses. For each test protocol, specimens were divided into 4 main groups whether the surface treatments applied before or after sintering and whether the specimens received heat treatment or not as pre-sintered, post-sintered no-heat and post-sintered heat-treated groups, and a group was served as control. Main groups were further divided into 6 equal subgroups according to surface treatment method applied (2 W-, 3 W-, 4 W-, 5 W-, 6 W-laser irradiations and APA). Surface treatments were applied to pre-sintered groups before sintering and to post-sintered groups after sintering. Post-sintered heat-treated groups were subjected to veneer ceramic firing simulation after surface treatments. Flexural strength and flexural modulus values were statistically analysed and monoclinic phase content was calculated. Weibull analysis was used to evaluate strength reliability and fractographic analysis was conducted. Highest flexural strength values were detected at post-sintered no-heat APA and 4W-laser groups (P < 0.05). Pre-sintered groups showed statistically lower flexural strength values. Heat treatment decreased the strength of the specimens. Monoclinic phase content was only detected at post-sintered no-heat groups and the highest amount was detected at APA group. Rougher surfaces and deeper irregularities were detected at FE-SEM images pre-sintered groups. Application of surface treatments at pre-sintered stage may be detrimental for zirconia ceramics in terms of flexural strength. Treating the surface of zirconia ceramic before sintering process is not recommended due to significant decrease in flexural strength values. 2 W-4 W Er,Cr:YSGG laser irradiations can be regarded as alternative surface treatment methods when zirconia restoration would be subjected to veneer ceramic firing procedures. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effect of reducing agent strength on the growth and thermoelectric performance of nanocrystalline bismuth telluride

NASA Astrophysics Data System (ADS)

Nour, Asmaa; Hassan, Nazly; Refaat, Heba M.; Soliman, Hesham M. A.; El-Dissouky, A.

2018-03-01

A novel combination of Trizma, as an environmentally friendly chelating agent, with either weak or strong reducing agent was used to produce n-type bismuth telluride (Bi2Te3) nanocrystals via water-based chemical route. The synthesized powders were consolidated into pellets utilizing spark plasma sintering (SPS). The sintered n-type pellets exhibited potentially high electrical conductivities (5.29 × 105 and 5.23 × 105 S.m‑1) and low lattice thermal conductivities (0.12 and 0.25 Wm‑1K‑1) respectively. These thermoelectric (TE) properties suggested that the partially coherent boundaries permitted significant phonons scattering and electrons transfer. These led to an enhanced figure-of-merit (ZT) values (0.52 and 0.97), which are considered to be significant among the reported ZT values at room-temperature for the undoped synthesized n-type Bi2Te3 nanoparticles. Therefore, the current investigation displayed an efficient method to improve ZT of TE materials via nanostructure orchestrating, resulting in a worthy candidate n-type nanostructured Bi2Te3 for room-temperature TE applications.

Design and characterization of Yb and Nd doped transparent ceramics for high power laser applications: recent advancements

NASA Astrophysics Data System (ADS)

Lapucci, A.; Vannini, M.; Ciofini, M.; Pirri, A.; Nikl, M.; Li, J.; Esposito, L.; Biasini, V.; Hostasa, J.; Goto, T.; Boulon, G.; Maksimov, R.; Gizzi, L.; Labate, L.; Toci, G.

2017-01-01

We report a review on our recent developments in Yttebium and Neodymium doped laser ceramics, along two main research lines. The first is the design and development of Yb:YAG ceramics with non uniform doping distribution, for the management of thermo-mechanical stresses and for the mitigation of ASE: layered structures have been produced by solid state reactive sintering, using different forming processes (spray drying and cold press of the homogenized powders, tape cast of the slurry); samples have been characterized and compared to FEM analysis. The second is the investigation of Lutetium based ceramics (such as mixed garnets LuYAG and Lu2O3); this interest is mainly motivated by the favorable thermal properties of these hosts under high doping. We recently obtained for the first time high efficiency laser emission from Yb doped LuYAG ceramics. The investigation on sesquioxides has been focused on Nddoped Lu2O3 ceramics, fabricated with the Spark Plasma Sintering method (SPS). We recently achieved the first laser emission above 1 W from Nd doped Lu2O3 ceramics fabricated by SPS.

Si

NASA Astrophysics Data System (ADS)

Fiameni, S.; Famengo, A.; Agresti, F.; Boldrini, S.; Battiston, S.; Saleemi, M.; Johnsson, M.; Toprak, M. S.; Fabrizio, M.

2014-06-01

Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion in the middle-high temperature range. The detrimental effect of the presence of MgO on the TE properties of Mg2Si based materials is widely known. For this reason, the conditions used for synthesis and sintering were optimized to limit oxygen contamination. The effect of Bi doping on the TE performance of dense Mg2Si materials was also investigated. Synthesis was performed by ball milling in an inert atmosphere starting from commercial Mg2Si powder and Bi powder. The samples were consolidated, by spark plasma sintering, to a density >95%. The morphology, and the composition and crystal structure of samples were characterized by field-emission scanning electronic microscopy and x-ray diffraction, respectively. Moreover, determination of Seebeck coefficients and measurement of electrical and thermal conductivity were performed for all the samples. Mg2Si with 0.1 mol% Bi doping had a ZT value of 0.81, indicative of the potential of this method for fabrication of n-type bulk material with good TE performance.

Removable partial denture alloys processed by laser-sintering technique.

PubMed

Alageel, Omar; Abdallah, Mohamed-Nur; Alsheghri, Ammar; Song, Jun; Caron, Eric; Tamimi, Faleh

2018-04-01

Removable partial dentures (RPDs) are traditionally made using a casting technique. New additive manufacturing processes based on laser sintering has been developed for quick fabrication of RPDs metal frameworks at low cost. The objective of this study was to characterize the mechanical, physical, and biocompatibility properties of RPD cobalt-chromium (Co-Cr) alloys produced by two laser-sintering systems and compare them to those prepared using traditional casting methods. The laser-sintered Co-Cr alloys were processed by the selective laser-sintering method (SLS) and the direct metal laser-sintering (DMLS) method using the Phenix system (L-1) and EOS system (L-2), respectively. L-1 and L-2 techniques were 8 and 3.5 times more precise than the casting (CC) technique (p < 0.05). Co-Cr alloys processed by L-1 and L-2 showed higher (p < 0.05) hardness (14-19%), yield strength (10-13%), and fatigue resistance (71-72%) compared to CC alloys. This was probably due to their smaller grain size and higher microstructural homogeneity. All Co-Cr alloys exhibited low porosity (2.1-3.3%); however, pore distribution was more homogenous in L-1 and L-2 alloys when compared to CC alloys. Both laser-sintered and cast alloys were biocompatible. In conclusion, laser-sintered alloys are more precise and present better mechanical and fatigue properties than cast alloys for RPDs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1174-1185, 2018. © 2017 Wiley Periodicals, Inc.

B{sub 4}C-SiC reaction-sintered coatings on graphite plasma facing components

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

Valentine, P.G.; Trester, P.W.; Winter, J.

1994-05-01

Boron carbide plus silicon carbide (B{sub 4}C-SiC) reaction-sintered coatings for use on graphite plasma-facing components were developed. Such coatings are of interest in TEXTOR tokamak limiter-plasma interactions as a means of reducing carbon erosion, of providing a preferred release of boron for oxygen gettering, and of investigating silicon`s effect on radiative edge phenomena. Specimens evaluated had (a) either Ringsdorfwerke EK 98 graphite or Le Carbon Lorraine felt-type AEROLOR A05 CFC substrates; (b) multiphase coatings, comprised of B{sub 4}C, Sic, and graphite; (c) nominal coating compositions of 69 wt.-% B{sub 4}C + 31 wt.-% SiC; and (d) nominal coating thicknesses betweenmore » 250 and 775 {mu}m. Coated coupons were evaluated by high heat flux experiments in the JUDITH (electron beam) test facility at KFA. Simulated disruptions, with energy densities up to 10 MJm{sup {minus}2}, and normal operation simulations, with power densities up to 12 MWm{sup {minus}2}, were conducted. The coatings remained adherent; at the highest levels tested, minor changes occurred, including localized remelting, modification of the crystallographic phases, occasional microcracking, and erosion.« less

Graphene addition to MgB{sub 2} superconductor obtained by ex-situ spark plasma sintering technique

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

Aldica, G.; Burdusel, M.; Popa, S.

Highlights: • Graphene-added dense MgB{sub 2} was prepared by ex-situ spark plasma sintering. • There is a limited interaction between graphene and MgB{sub 2}. • Addition of graphene (G) shows a small enhancement of J{sub c} and μ{sub 0}H{sub irr}. • G is one of the least effective C-containing additions. - Abstract: Graphene nanopowder (G) with average thickness particle size of about 6–8 nm was added to MgB{sub 2} commercial powder. Starting composition was (MgB{sub 2}){sub (1−x)}(G){sub x}, x = 0.0125, 0.025, 0.05. Processing was performed by Spark Plasma Sintering (SPS) technique. All added samples have high density (above 95%).more » The critical temperature (T{sub c}) and the lattice parameter a (c-axis lattice parameter is constant) show a small variation suggesting that carbon substitution for boron is low. TEM observations show the presence of un-reacted graphene plates supporting the T{sub c} and structural results. It also indicates that G-addition does not modify the MgB{sub 2} microstructure. Despite this, there is an optimum doped sample (MgB{sub 2}){sub 0.9875}(G){sub 0.0125} for which the critical current density at temperatures below 25 K is slightly higher at high magnetic fields than for the pristine sample. The addition of G is found as one of the least effective C-source additions enhancing J{sub c}. We discuss results as being strongly related to variation of the residual stress.« less

[Translucency of dental zirconia ceramics sintered in conventional and microwave ovens].

PubMed

Yuemei, Jiang; Ying, Yang; Wenhui, Zhan; Guoxin, Hu; Qiuxia, Yang

2015-12-01

To evaluate the effect of microwave sintering on the translucency of zirconia and to compare these effect with those of conventional sintering. The relationship between the microstructure of specimens and translucency was investigated. A total of 10 disc-shaped specimens were fabricated from 2 commercial brands of zirconia, namely, Zenostar and Lava. Each group included 5 discs. Conventional sintering was performed according to the manufacturers' specifications. The maximum temperature for Zenostar was 1,490 °C, whereas that for Lava was 1,500 °C. The dwelling time was 2 h. The sintering temperature for microwave sintering was 1,420 °C, heating rate was 15 °C · min⁻¹, and dwelling time was 30 min. After sintering, the translucency parameter (TP) of the specimens were measured with ShadeEye NCC. The sintered density of the specimens was determined by Archimedes' method. The grain size and microstructure of the specimens were investigated by scanning electron microscopy. Density and translucency slightly increased by microwave sintering, but no significant difference was found between microwave and conventional sintering (P > 0.05). Small and uniform microstructure were obtained from microwave sintering. The mean TP of Lava was significantly higher than that of Zenostar (P < 0.001). The translucency of zirconia sintered by microwave sintering is similar to that of the zirconia sintered by conventional sintering.

Microwave sintering of sol-gel derived abrasive grain

DOEpatents

Plovnick, Ross; Celikkaya, Ahmet; Blake, Rodger D.

1997-01-01

A method is provided for making microwave-sintered, free flowing alpha alumina-based ceramic abrasive grain, under conditions effective to couple microwaves with calcined alpha alumina-based abrasive gain precursor and sinter it at a temperature of at least about 1150.degree. C.

Improved thermoelectric properties of Bi2Te3-xSex alloys by melt spinning and resistance pressing sintering

NASA Astrophysics Data System (ADS)

Cai, Xinzhi; Fan, Xi'an; Rong, Zhenzhou; Yang, Fan; Gan, Zhanghua; Li, Guangqiang

2014-03-01

Starting from bismuth, tellurium and selenium chunks, n-type Bi2Te3-xSex (x ⩽ 0.3) alloys were obtained by melt spinning (MS) combined with a resistance pressing sintering (RPS) process. The phases, microstructures and compositions of the samples were evaluated by x-ray diffraction, field emission scanning electron microscopy, and energy dispersive x-ray spectroscopy during each step in the preparation process, respectively. The influences of Se doping, MS and RPS processes on the thermoelectric (TE) properties of Bi2Te3-xSex alloys were investigated in detail. The Bi2Te3-xSex powders could be well compacted by the RPS process and the relative densities of the bulks prepared by RPS were all higher than 96%. The partially oriented lamellar structure could be observed at some regions of the samples prepared by RPS, and the monolayer thickness of the lamellar structure in the MS-RPS samples was smaller than that in the smelting-RPS sample. The MS process was confirmed as an excellent method to obtain fine microstructures and low lattice thermal conductivity for the TE materials. All evidence about electrical and thermal transport properties suggested that suitably increasing the Se content could effectively improve the ZT value. The maximum ZT value of 0.84 was obtained for the Bi2Te2.7Se0.3 prepared by MS-RPS at 423 K. As opposed to the conventional hot pressing and spark plasma sintering, the RPS method introduced here is more suitable for practical industrial application due to its cost saving and high efficiency.

Grain size effect on the giant dielectric constant of CaCu3Ti4O12 nanoceramics prepared by mechanosynthesis and spark plasma sintering

NASA Astrophysics Data System (ADS)

Ahmad, Mohamad M.; Yamada, Koji

2014-04-01

In the present work, CaCu3Ti4O12 (CCTO) nanoceramics with different grain sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosynthesized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The grain size of CCTO nanoceramics increases from 80 nm to ˜200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-sized ceramics of 2-3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed in CCTO nanoceramics. The dielectric constant increases with increasing the grain size of the nanoceramics with values of 8.3 × 103, 2.4 × 104, and 3.2 × 104 for SPS-800, SPS-900, and SPS-975, respectively. For the micro-sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 104. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.

Formation of Aluminum Particles with Shell Morphology during Pressureless Spark Plasma Sintering of Fe–Al Mixtures: Current-Related or Kirkendall Effect?

PubMed Central

Dudina, Dina V.; Bokhonov, Boris B.; Mukherjee, Amiya K.

2016-01-01

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects when electric current passes through the underdeveloped inter-particle contacts. Until now, inter-particle interactions during pressureless SPS have been studied mainly for particles of the same material. In this work, we focused on the interactions between particles of dissimilar materials in mixtures of micrometer-sized Fe and Al powders forming porous compacts during pressureless SPS at 500–650 °C. Due to the chemical interaction between Al and Fe, necks of conventional shape did not form between the dissimilar particles. At the early interaction stages, the Al particles acquired shell morphology. It was shown that this morphology change was not related to the influence of electric current but was due to the Kirkendall effect in the Fe–Al system and particle rearrangement in a porous compact. No experimental evidence of melting or melt ejection during pressureless SPS of the Fe–Al mixtures or Fe and Al powders sintered separately was observed. Porous FeAl-based compacts could be obtained from Fe-40at.%Al mixtures by pressureless SPS at 650 °C. PMID:28773498

Microstructure and Mechanical Behaviors of Titanium Matrix Composites Containing In Situ Whiskers Synthesized via Plasma Activated Sintering.

PubMed

Sun, Yi; Zhang, Jian; Luo, Guoqiang; Shen, Qiang; Zhang, Lianmeng

2018-04-02

In this paper, titanium matrix composites with in situ TiB whiskers were synthesized by the plasma activated sintering technique; crystalline boron and amorphous boron were used as reactants for in situ reactions, respectively. The influence of the sintering process and the crystallography type of boron on the microstructure and mechanical properties of composites were studied and compared. The densities were evaluated using Archimedes' principle. The microstructure and mechanical properties were characterized by SEM, XRD, EBSD, TEM, a universal testing machine, and a Vickers hardness tester. The prepared composite material showed a high density and excellent comprehensive performance under the PAS condition of 20 MPa at 1000 °C for 3 min. Amorphous boron had a higher reaction efficiency than crystalline boron, and it completely reacted with the titanium matrix to generate TiB whiskers, while there was still a certain amount of residual crystalline boron combining well with the titanium matrix at 1100 °C. The composite samples with a relative density of 98.33%, Vickers hardness of 389.75 HV, compression yield strength of up to 1190 MPa, and an ultimate compressive strength of up to 1710 MPa were obtained. Compared with the matrix material, the compressive strength of TC4 titanium alloy containing crystalline boron and amorphous boron was increased by 7.64% and 15.50%, respectively.

Microstructure and Mechanical Behaviors of Titanium Matrix Composites Containing In Situ Whiskers Synthesized via Plasma Activated Sintering

PubMed Central

Luo, Guoqiang; Shen, Qiang; Zhang, Lianmeng

2018-01-01

In this paper, titanium matrix composites with in situ TiB whiskers were synthesized by the plasma activated sintering technique; crystalline boron and amorphous boron were used as reactants for in situ reactions, respectively. The influence of the sintering process and the crystallography type of boron on the microstructure and mechanical properties of composites were studied and compared. The densities were evaluated using Archimedes’ principle. The microstructure and mechanical properties were characterized by SEM, XRD, EBSD, TEM, a universal testing machine, and a Vickers hardness tester. The prepared composite material showed a high density and excellent comprehensive performance under the PAS condition of 20 MPa at 1000 °C for 3 min. Amorphous boron had a higher reaction efficiency than crystalline boron, and it completely reacted with the titanium matrix to generate TiB whiskers, while there was still a certain amount of residual crystalline boron combining well with the titanium matrix at 1100 °C. The composite samples with a relative density of 98.33%, Vickers hardness of 389.75 HV, compression yield strength of up to 1190 MPa, and an ultimate compressive strength of up to 1710 MPa were obtained. Compared with the matrix material, the compressive strength of TC4 titanium alloy containing crystalline boron and amorphous boron was increased by 7.64% and 15.50%, respectively. PMID:29614842

Comparison of laser and intense pulsed light sintering (IPL) for inkjet-printed copper nanoparticle layers

PubMed Central

Niittynen, Juha; Sowade, Enrico; Kang, Hyunkyoo; Baumann, Reinhard R.; Mäntysalo, Matti

2015-01-01

In this contribution we discuss the sintering of an inkjet-printed copper nanoparticle ink based on electrical performance and microstructure analysis. Laser and intense pulsed light (IPL) sintering are employed in order to compare the different techniques and their feasibility for electronics manufacturing. A conductivity of more than 20% of that of bulk copper material has been obtained with both sintering methods. Laser and IPL sintering techniques are considered to be complementary techniques and are highly suitable in different application fields. PMID:25743631

Numerical Simulation of Sintering Process in Ceramic Powder Injection Moulded Components

NASA Astrophysics Data System (ADS)

Song, J.; Barriere, T.; Liu, B.; Gelin, J. C.

2007-05-01

A phenomenological model based on viscoplastic constitutive law is presented to describe the sintering process of ceramic components obtained by powder injection moulding. The parameters entering in the model are identified through sintering experiments in dilatometer with the proposed optimization method. The finite element simulations are carried out to predict the density variations and dimensional changes of the components during sintering. A simulation example on the sintering process of hip implant in alumina has been conducted. The simulation results have been compared with the experimental ones. A good agreement is obtained.

Spark plasma sintering synthesis of Ni1-xZnxFe2O4 ferrites: Mössbauer and catalytic study

NASA Astrophysics Data System (ADS)

Velinov, Nikolay; Manova, Elina; Tsoncheva, Tanya; Estournès, Claude; Paneva, Daniela; Tenchev, Krassimir; Petkova, Vilma; Koleva, Kremena; Kunev, Boris; Mitov, Ivan

2012-08-01

Nickel-zinc ferrite nanoparticles, Ni1-xZnxFe2O4 (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.

Current-Assisted Diffusion Bonding of Extruded Ti-22Al-25Nb Alloy by Spark Plasma Sintering: Interfacial Microstructure and Mechanical Properties

NASA Astrophysics Data System (ADS)

Yang, Jianlei; Wang, Guofeng; Jiao, Xueyan; Gu, Yibin; Liu, Qing; Li, You

2018-05-01

Spark plasma sintering (SPS) technology was used to current-assisted bond extruded Ti-22Al-25Nb alloy. The effects of bonding temperature (920-980 °C) and bonding time (10-30 min) on the microstructure evolution and shear strength of this alloy were investigated systematically. The temperature distribution in the specimen during the current-assisted bonding process was also analyzed by numerical simulation. It is noted that the highest temperature was obtained at the bonding interface. As the bonding temperature and bonding time increased, the voids in the interface shrank increasingly until they vanished. A complete metallurgical bonding interface could be produced at 960 °C/20 min/10 MPa, exhibiting the highest shear strength of 269.3 MPa. In addition, the shear strength of the bonded specimen depended on its interfacial microstructure. With increased bonding temperature, the fracture mode transformed from the intergranular fracture at the bonding interface to the cleavage fracture in the substrate.

Effect of Spark Plasma Sintering on the Structure and Properties of Ti1−xZrxNiSn Half-Heusler Alloys

PubMed Central

Downie, Ruth A.; Popuri, Srinivas R.; Ning, Huanpo; Reece, Mike J.; Bos, Jan-Willem G.

2014-01-01

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition. PMID:28788234

Transport Properties of La- doped SrTiO3 Ceramics Prepared Using Spark Plasma Sintering

NASA Astrophysics Data System (ADS)

Mehdizadeh Dehkordi, Arash; Bhattacharya, Sriparna; Tritt, Terry M.; Alshareef, Husam N.

2012-02-01

In this work, thermoelectric transport properties of La-doped SrTiO3 ceramics prepared using conventional solid state reaction and spark plasma sintering have been investigated. Room temperature power factor of single crystal strontium titanate (SrTiO3), comparable to that of Bi2Te3, has brought new attention to this perovskite-type transition metal-oxide as a potential n-type thermoelectric for high temperature applications. Electronic properties of this model complex oxide, SrTiO3 (ABO3), can be tuned in a wide range through different doping mechanisms. In addition to A site (La-doped) or B site (Nb-doped) substitutional doping, introducing oxygen vacancies plays an important role in electrical and thermal properties of these structures. Having multiple doping mechanisms makes the transport properties of these perovskites more dependent on preparation parameters. The effect of these synthesis parameters and consolidation conditions on the transport properties of these materials has been studied.

Reflectivity and laser ablation of ZrB2/Cu ultra high temperature ceramic

NASA Astrophysics Data System (ADS)

Yan, Zhenyu; Ma, Zhuang; Zhu, Shizhen; Liu, Ling; Xu, Qiang

2013-05-01

Ultra high temperature ceramics (UHTCs) were thought to be candidates for laser protective materials due to their high melting point, thermal shock and ablation resistance. The ablation behaviors of UHTCs like ZrB2 and its composite had been intensely investigated by the means of arc, plasma, oxyacetylene ablation. However, the ablation behavior under laser irradiation was still unknown by now. In this paper, the dense bulk composites of ZrB2/Cu were successfully sintered by spark plasma sintering (SPS) at 1650 degree C for 3min. The reflectivity of the composites measured by spectrophotometry achieved 60% in near infrared range and it decreased with the increasing wavelength of incident light. High intensity laser ablation was carried out on the ZrB2/Cu surface. The phase composition and microstructure changes before and after laser irradiation were characterized by X-ray diffraction and SEM respectively. The results revealed that the oxidation and melting were the main mechanisms during the ablation processing.

Graphene-copper composite with micro-layered grains and ultrahigh strength

PubMed Central

Wang, Lidong; Yang, Ziyue; Cui, Ye; Wei, Bing; Xu, Shichong; Sheng, Jie; Wang, Miao; Zhu, Yunpeng; Fei, Weidong

2017-01-01

Graphene with ultrahigh intrinsic strength and excellent thermal physical properties has the potential to be used as the reinforcement of many kinds of composites. Here, we show that very high tensile strength can be obtained in the copper matrix composite reinforced by reduced graphene oxide (RGO) when micro-layered structure is achieved. RGO-Cu powder with micro-layered structure is fabricated from the reduction of the micro-layered graphene oxide (GO) and Cu(OH)2 composite sheets, and RGO-Cu composites are sintered by spark plasma sintering process. The tensile strength of the 5 vol.% RGO-Cu composite is as high as 608 MPa, which is more than three times higher than that of the Cu matrix. The apparent strengthening efficiency of RGO in the 2.5 vol.% RGO-Cu composite is as high as 110, even higher than that of carbon nanotube, multilayer graphene, carbon nano fiber and RGO in the copper matrix composites produced by conventional MLM method. The excellent tensile and compressive strengths, high hardness and good electrical conductivity are obtained simultaneously in the RGO-Cu composites. The results shown in the present study provide an effective method to design graphene based composites with layered structure and high performance. PMID:28169306

Bonding of TRIP-Steel/Al2O3-(3Y)-TZP Composites and (3Y)-TZP Ceramic by a Spark Plasma Sintering (SPS) Apparatus

PubMed Central

Miriyev, Aslan; Grützner, Steffen; Krüger, Lutz; Kalabukhov, Sergey; Frage, Nachum

2016-01-01

A combination of the high damage tolerance of TRIP-steel and the extremely low thermal conductivity of partially stabilized zirconia (PSZ) can provide controlled thermal-mechanical properties to sandwich-shaped composite specimens comprising these materials. Sintering the (TRIP-steel-PSZ)/PSZ sandwich in a single step is very difficult due to differences in the sintering temperature and densification kinetics of the composite and the ceramic powders. In the present study, we successfully applied a two-step approach involving separate SPS consolidation of pure (3Y)-TZP and composites containing 20 vol % TRIP-steel, 40 vol % Al2O3 and 40 vol % (3Y)-TZP ceramic phase, and subsequent diffusion joining of both sintered components in an SPS apparatus. The microstructure and properties of the sintered and bonded specimens were characterized. No defects at the interface between the TZP and the composite after joining in the 1050–1150 °C temperature range were observed. Only limited grain growth occurred during joining, while crystallite size, hardness, shear strength and the fraction of the monoclinic phase in the TZP ceramic virtually did not change. The slight increase of the TZP layer’s fracture toughness with the joining temperature was attributed to the effect of grain size on transformation toughening. PMID:28773680

Microwave sintering of nanophase ceramics without concomitant grain growth

DOEpatents

Eastman, Jeffrey A.; Sickafus, Kurt E.; Katz, Joel D.

1993-01-01

A method of sintering nanocrystalline material is disclosed wherein the nanocrystalline material is microwaved to heat the material to a temperature less than about 70% of the melting point of the nanocrystalline material expressed in degrees K. This method produces sintered nanocrystalline material having a density greater than about 95% of theoretical and an average grain size not more than about 3 times the average grain size of the nanocrystalline material before sintering. Rutile TiO.sub.2 as well as various other ceramics have been prepared. Grain growth of as little as 1.67 times has resulted with densities of about 90% of theoretical.

Cathode preparation method for molten carbonate fuel cell

DOEpatents

Smith, James L.; Sim, James W.; Kucera, Eugenia H.

1988-01-01

A method of preparing a porous cathode structure for use in a molten carbonate fuel cell begins by providing a porous integral plaque of sintered nickel oxide particles. The nickel oxide plaque can be obtained by oxidizing a sintered plaque of nickel metal or by compacting and sintering finely divided nickel oxide particles to the desired pore structure. The porous sintered nickel oxide plaque is contacted with a lithium salt for a sufficient time to lithiate the nickel oxide structure and thus enhance its electronic conductivity. The lithiation can be carried out either within an operating fuel cell or prior to assembling the plaque as a cathode within the fuel cell.

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

Wang, Siwei; Chen, Yan; Zhang, Lingling

Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr 0.8Y 0.2O 3-δ(BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. In this paper, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO 3 and B 2O 3-Li 2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering wasmore » improved to 19.3% by a TRAS method as compared to 2.6% by the conventional solid date reaction method. In conclusion, the bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.« less

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

Wang, Siwei; Chen, Yan; Zhang, Lingling

Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr 0.8Y 0.2O 3-δ (BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. Here, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO 3 and B 2O 3-Li 2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering was improvedmore » to 19.3% by a TRAS method as compared to 2.6% by the conventional solid date reaction method. Moreover, the bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.« less

Work Function and Conductivity of Inkjet-Printed Silver Layers: Effect of Inks and Post-treatments

NASA Astrophysics Data System (ADS)

Mitra, Dana; Mitra, Kalyan Yoti; Dzhagan, Volodymyr; Pillai, Nikhil; Zahn, Dietrich R. T.; Baumann, Reinhard R.

2018-03-01

The electronic properties of a printed layer are influenced by a number of factors, including the nature of the ink (nanoparticle- or solution-based), ink composition (solvents, additives, concentration), and post-treatment technologies, especially sintering. One of the major challenges in the field of printed electronics is achieving the desired performance, for example, in terms of conductivity, resistivity, or work function (WF). This work investigates the dependence of sheet resistance and WF on various sintering methodologies. Four different silver nanoparticle inks were inkjet-printed on a flexible polymeric foil and post-treated by thermal sintering (in an oven) or novel sintering processes using infrared or intense pulsed light. The surfaces of the printed and sintered layers were investigated optically, and various inhomogeneities in the layer surface were observed, varying from a smooth to a highly rough appearance with ring-shaped drying structures. An analysis of the sheet resistance revealed notable variation among the various inks and sintering methodologies used. Here, for the very first time, WF is measured and evaluated as a function of sintering methodology and silver ink, and the respective layer formation characteristics realized with the inkjet printing technology. The WF values obtained by ultraviolet photoemission show a similar spread and allow unambiguous trends to be tracked with respect to the type of ink and sintering method used. The values of the WF obtained range from 3.7 eV to 4.3 eV, approaching the reported bulk values of 4.3-4.7 eV. The various silver inks resulted in different WFs when the same sintering method was used, while the same silver ink resulted in different WFs when various sintering methods were applied. Therefore, it is believed that the WF can be tuned over a broad range in a controlled manner to satisfy electronic device requirements.

SINTERING METHOD

DOEpatents

Googin, J.M.

1963-11-01

Methods of making articles by powder metallurgy techniques are presented. An article is made by packing a metal powder into a desired shape, raising the temperature of the powder compact to a sintering temperature in the presence of a reducing gas, and alternately increasing and decreasing the pressure of the gas while the temperatume is being raised. The product has a greater density than can be achieved by sintering for the same length of time at a constant gas pressure. (AEC)

[Effect of compaction pressure on the properties of dental machinable zirconia ceramic].

PubMed

Huang, Hui; Wei, Bin; Zhang, Fu-qiang; Sun, Jing; Gao, Lian

2010-10-01

To investigate the effect of compaction pressure on the linear shrinkage, sintering property and machinability of the dental zirconia ceramic. The nano-size zirconia powder was compacted at different isostatic pressure and sintered at different temperature. The linear shrinkage of sintered body was measured and the relative density was tested using the Archimedes method. The cylindrical surface of pre-sintering blanks was traversed using a hard metal tool. Surface and edge quality were checked visually using light stereo microscopy. The sintering behaviour depended on the compaction pressure. Increasing compaction pressure led to higher sintering rate and lower sintering temperature. Increasing compaction pressure also led to decreasing linear shrinkage of the sintered bodies, from 24.54% of 50 MPa to 20.9% of 400 MPa. Compaction pressure showed only a weak influence on machinability of zirconia blanks, but the higher compaction pressure resulted in the poor surface quality. The better sintering property and machinability of dental zirconia ceramic is found for 200-300 MPa compaction pressure.

Atmospheric Pressure Plasma Jet as a Dry Alternative to Inkjet Printing in Flexible Electronics

NASA Technical Reports Server (NTRS)

Gandhiraman, Ram Prasad; Lopez, Arlene; Koehne, Jessica; Meyyappan, M.

2016-01-01

We have developed an atmospheric pressure plasma jet printing system that works at room temperature to 50 deg C unlike conventional aerosol assisted techniques which require a high temperature sintering step to obtain desired thin films. Multiple jets can be configured to increase throughput or to deposit multiple materials, and the jet(s) can be moved across large areas using a x-y stage. The plasma jet has been used to deposit carbon nanotubes, graphene, silver nanowires, copper nanoparticles and other materials on substrates such as paper, cotton, plastic and thin metal foils.

Improved mechanical properties of thermoelectric (Bi 0.2Sb 0.8) 2Te 3 by nanostructuring

DOE PAGES

Lavrentev, M. G.; Osvenskii, V. B.; Parkhomenko, Yu. N.; ...

2016-06-01

Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.

Improved mechanical properties of thermoelectric (Bi 0.2Sb 0.8) 2Te 3 by nanostructuring

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

Lavrentev, M. G.; Osvenskii, V. B.; Parkhomenko, Yu. N.

Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.

A novel route for processing cobalt–chromium–molybdenum orthopaedic alloys

PubMed Central

Patel, Bhairav; Inam, Fawad; Reece, Mike; Edirisinghe, Mohan; Bonfield, William; Huang, Jie; Angadji, Arash

2010-01-01

Spark plasma sintering has been used for the first time to prepare the ASTM F75 cobalt–chromium–molybdenum (Co–Cr–Mo) orthopaedic alloy composition using nanopowders. In the preliminary work presented in this report, the effect of processing variables on the structural features of the alloy (phases present, grain size and microstructure) has been investigated. Specimens of greater than 99.5 per cent theoretical density were obtained. Carbide phases were not detected in the microstructure but oxides were present. However, harder materials with finer grains were produced, compared with the commonly used cast/wrought processing methods, probably because of the presence of oxides in the microstructure. PMID:20200035

Choosing the optimal Pareto composition of the charge material for the manufacture of composite blanks

NASA Astrophysics Data System (ADS)

Zalazinsky, A. G.; Kryuchkov, D. I.; Nesterenko, A. V.; Titov, V. G.

2017-12-01

The results of an experimental study of the mechanical properties of pressed and sintered briquettes consisting of powders obtained from a high-strength VT-22 titanium alloy by plasma spraying with additives of PTM-1 titanium powder obtained by the hydride-calcium method and powder of PV-N70Yu30 nickel-aluminum alloy are presented. The task is set for the choice of an optimal charge material composition of a composite material providing the required mechanical characteristics and cost of semi-finished products and items. Pareto optimal values for the composition of the composite material charge have been obtained.

Microalloying of transition metal silicides by mechanical activation and field-activated reaction

DOEpatents

Munir, Zuhair A [Davis, CA; Woolman, Joseph N [Davis, CA; Petrovic, John J [Los Alamos, NM

2003-09-02

Alloys of transition metal suicides that contain one or more alloying elements are fabricated by a two-stage process involving mechanical activation as the first stage and densification and field-activated reaction as the second stage. Mechanical activation, preferably performed by high-energy planetary milling, results in the incorporation of atoms of the alloying element(s) into the crystal lattice of the transition metal, while the densification and field-activated reaction, preferably performed by spark plasma sintering, result in the formation of the alloyed transition metal silicide. Among the many advantages of the process are its ability to accommodate materials that are incompatible in other alloying methods.

Powder metallurgy: Solid and liquid phase sintering of copper

NASA Technical Reports Server (NTRS)

Sheldon, Rex; Weiser, Martin W.

1993-01-01

Basic powder metallurgy (P/M) principles and techniques are presented in this laboratory experiment. A copper based system is used since it is relatively easy to work with and is commercially important. In addition to standard solid state sintering, small quantities of low melting metals such as tin, zinc, lead, and aluminum can be added to demonstrate liquid phase sintering and alloy formation. The Taguchi Method of experimental design was used to study the effect of particle size, pressing force, sintering temperature, and sintering time. These parameters can be easily changed to incorporate liquid phase sintering effects and some guidelines for such substitutions are presented. The experiment is typically carried out over a period of three weeks.

Loading Mode Optimization and Structure Tailoring in Spark Plasma Sintering of Monocarbide Powder-based Components for High Temperature Applications

NASA Astrophysics Data System (ADS)

Wei, Xialu

In this study, the spark plasma sintering (SPS) is employed to consolidate poorly sinter-able ultra-high temperature ceramic (UHTC) powders due to the fact that the conjoint application of electric current and mechanical pressure during SPS can largely offset the required processing temperature. Zirconium carbide (ZrC) is selected as target material as it broadly represents properties of typical UHTCs. Investigations on SPS of ZrC are concurrently conducted in two correlated regimes: One regime is used to optimize the SPS densification efficiency by manipulating the loading schematics. The other regime is used to produce complex shape carbide components for high temperature applications via SPS. Both theoretical and experimental studies are involved in the achievement of the formulated research objectives. Consolidation of ZrC has been carried out to form a densification map with determining the optimal processing parameters. The densification of ZrC is studied through the continuum theory of sintering, in which the ZrC power-law creep parameters have been determined through the clarification of electrical and thermal aspects of the employed SPS system. Then the SPS-forging setup is proposed as it is theoretically and experimentally proven to be able to render more densification than the regular SPS. SPS-forging and regular SPS are eventually integrated into a hybrid loading mode SPS regime to combine the advantages of the individual setups to obtain the optimal densification kinetics. Annular shape ZrC pellets have been fabricated using SPS. Finite element modeling framework is constructed to manifest the thermomechanical interactions during the SPS of annular shape ZrC specimens. The fabrication procedures are practically adapted to produce also annular shape carbide composites with excellent high temperature structural strength being used as alternative SPS tooling components. The applicability of annular shape fuel pellet to accommodate volume swelling under its service conditions is investigated. The irradiation-induced swelling phenomena are analyzed by analytical modeling and finite element simulations, in which the generated fission products are considered to be the sources of the fuel pellet swelling.

Spark plasma sintering of tantalum carbide and graphene reinforced tantalum carbide composites

NASA Astrophysics Data System (ADS)

Kalluri, Ajith Kumar

Tantalum carbide (TaC), an ultra-high temperature ceramic (UHTC), is well known for its exceptional properties such as high hardness (15-19 GPa), melting point (3950 °C), elastic modulus (537 GPa), chemical resistance, and thermal shock resistance. To make TaC to be the future material for hypersonic vehicles, it is required to improve its thermal conductivity, strength, and fracture toughness. Researchers have previously reinforced TaC ceramic with carbides of silicon and boron as well as carbon nanotubes (CNTs), however, these reinforcements either undergo chemical changes or induce defects in the matrix during processing. In addition, these reinforcements exhibit a very minimal improvement in the properties. In the present work, we attempted to improve TaC fracture toughness by reinforcing with graphene nano-platelets (GNPs) and processing through spark plasma sintering at high temperature of 2000 °C, pressure of 70 MPa, and soaking time of 10 min. In addition, we investigated the active densification mechanism during SPS of TaC powder and the effect of ball milling time on mechanical properties of sintered TaC. A relative density of >96% was achieved using SPS of monolithic TaC (<3 μm). Ball milling improved the sintering kinetics and improved the mechanical properties (microhardness, bi-axial flexural strength, and indentation fracture toughness). Activation energy (100 kJ/mol) and stress exponent (1.2) were obtained using the analytical model developed for power-law creep. Grain boundary sliding is proposed as active densification mechanism based on these calculations. Reinforcing GNPs (2-6 vol.% ) in the TaC matrix improved relative density (99.8% for TaC-6 vol.% GNP). Also ˜150% and ˜180% increase in flexural strength and fracture toughness, respectively, was observed for TaC-6 vol.% GNP composite. The significant improvement in these properties is attributed to improved densification and toughening mechanisms such as sheet pull-out and crack deflection due to reinforcement of graphene. Uniform dispersion of GNPs in the TaC matrix is observed from microstructural analysis. Raman spectroscopy analysis also indicated that GNPs are successfully retained in sintered TaC-GNP composites without any damage.

Thermal barrier coating life-prediction model development

NASA Technical Reports Server (NTRS)

Strangman, T. E.; Neumann, J.; Liu, A.

1986-01-01

The program focuses on predicting the lives of two types of strain-tolerant and oxidation-resistant thermal barrier coating (TBC) systems that are produced by commercial coating suppliers to the gas turbine industry. The plasma-sprayed TBC system, composed of a low-pressure plasma-spray (LPPS) or an argon shrouded plasma-spray (ASPS) applied oxidation resistant NiCrAlY or (CoNiCrAlY) bond coating and an air-plasma-sprayed yttria partially stabilized zirconia insulative layer, is applied by both Chromalloy, Klock, and Union Carbide. The second type of TBS is applied by the electron beam-physical vapor deposition (EB-PVD) process by Temescal. The second year of the program was focused on specimen procurement, TMC system characterization, nondestructive evaluation methods, life prediction model development, and TFE731 engine testing of thermal barrier coated blades. Materials testing is approaching completion. Thermomechanical characterization of the TBC systems, with toughness, and spalling strain tests, was completed. Thermochemical testing is approximately two-thirds complete. Preliminary materials life models for the bond coating oxidation and zirconia sintering failure modes were developed. Integration of these life models with airfoil component analysis methods is in progress. Testing of high pressure turbine blades coated with the program TBS systems is in progress in a TFE731 turbofan engine. Eddy current technology feasibility was established with respect to nondestructively measuring zirconia layer thickness of a TBC system.

Microwave sintering of multiple articles

DOEpatents

Blake, Rodger D.; Katz, Joel D.

1993-01-01

Apparatus and method for producing articles of alumina and of alumina and silicon carbide in which the articles are sintered at high temperatures using microwave radiation. The articles are placed in a sintering container which is placed in a microwave cavity for heating. The rates at which heating and cooling take place is controlled.

Low-energy plasma-cathode electron gun with a perforated emission electrode

NASA Astrophysics Data System (ADS)

Burdovitsin, Victor; Kazakov, Andrey; Medovnik, Alexander; Oks, Efim; Tyunkov, Andrey

2017-11-01

We describe research of influence of the geometric parameters of perforated electrode on emission parameters of a plasma cathode electron gun generating continuous electron beams at gas pressure 5-6 Pa. It is shown, that the emission current increases with increasing the hole diameters and decreasing the thickness of the perforated emission electrode. Plasma-cathode gun with perforated electron can provide electron extraction with an efficiency of up to 72 %. It is shown, that the current-voltage characteristic of the electron gun with a perforated emission electrode differs from that of similar guns with fine mesh grid electrode. The plasma-cathode electron gun with perforated emission electrode is used for electron beam welding and sintering.

Method of sintering ceramic materials

DOEpatents

Holcombe, Cressie E.; Dykes, Norman L.

1992-01-01

A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density.

Reflow-oven-processing of pressureless sintered-silver interconnects

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

Wereszczak, Andrew A.; Chen, Branndon R.; Oistad, Brian A.

Here, a method was developed to pressurelessly fabricate strong and consistent sinterable-silver joints or interconnects using reflow oven heating. Circular sinterable-silver interconnects, having nominal diameter of 5 mm and 0.1 mm thickness were stencil printed, contact-dried, and then pressurelessly sinter-bonded to Au-plated direct copper bonded ceramic substrates at 250 °C in ambient air. That sintering was done in either a reflow oven or a convective oven (latter being a conventional heating source for processing sinterable-silver). Consistently strong (>40 MPa) interconnects were produced with reflow oven heating and were as strong as those produced with convective oven heating. This is significantmore » because reflow oven technology affords better potential for continuous mass production and it was shown that strong sintered-silver bonds can indeed be achieved with its use.« less

Mechanical parameters of strontium doped hydroxyapatite sintered using microwave and conventional methods.

PubMed

Curran, Declan J; Fleming, Thomas J; Towler, Mark R; Hampshire, Stuart

2011-11-01

The effects of ion substitution in hydroxyapatite (HA) on crystal structure and lattice stability is investigated in the green state and post sintering. The effects of ion incorporation on the biaxial flexural strength and hardness are also investigated. Sintering is carried out at 1200 °C using comparative conventional and microwave regimes. Post sintering, the effects of ion incorporation manifest as an increase in the lattice d-spacings and a reduction of the crystallite size. Some HA decomposition occurs with β-TCP stabilisation in conventional sintering (CS), but this phase is destabilised during microwave sintering (MS), generating α-TCP. Conventional sintering (CS) allows higher densification in the undoped samples. Overall, for the Sr-doped compositions, the MS samples retain higher amounts of HA and experience higher density levels compared to the CS samples. Published by Elsevier Ltd.

Reflow-oven-processing of pressureless sintered-silver interconnects

DOE PAGES

Wereszczak, Andrew A.; Chen, Branndon R.; Oistad, Brian A.

2018-01-04

Here, a method was developed to pressurelessly fabricate strong and consistent sinterable-silver joints or interconnects using reflow oven heating. Circular sinterable-silver interconnects, having nominal diameter of 5 mm and 0.1 mm thickness were stencil printed, contact-dried, and then pressurelessly sinter-bonded to Au-plated direct copper bonded ceramic substrates at 250 °C in ambient air. That sintering was done in either a reflow oven or a convective oven (latter being a conventional heating source for processing sinterable-silver). Consistently strong (>40 MPa) interconnects were produced with reflow oven heating and were as strong as those produced with convective oven heating. This is significantmore » because reflow oven technology affords better potential for continuous mass production and it was shown that strong sintered-silver bonds can indeed be achieved with its use.« less

Method of manufacturing ceramic shaped articles

NASA Technical Reports Server (NTRS)

Inoue, K.

1983-01-01

A method of manufacturing ceramic shaped articles, wherein tapes of ceramic powder material in mixture with a binder material and special additives are shaped and then articles are stamped out from said tapes and sintered in a sintering furnace is described.

Method of joining ITM materials using a partially or fully-transient liquid phase

DOEpatents

Butt, Darryl Paul; Cutler, Raymond Ashton; Rynders, Steven Walton; Carolan, Michael Francis

2006-03-14

A method of forming a composite structure includes: (1) providing first and second sintered bodies containing first and second multicomponent metallic oxides having first and second identical crystal structures that are perovskitic or fluoritic; (2) providing a joint material containing at least one metal oxide: (a) containing (i) at least one metal of an identical IUPAC Group as at least one sintered body metal in one of the multicomponent metallic oxides, (ii) a first row D-Block transition metal not contained in the multicomponent metallic oxides, and/or (iii) a lanthanide not contained in the multicomponent metallic oxides; (b) free of metals contained in the multicomponent metallic oxides; (c) free of cations of boron, silicon, germanium, tin, lead, arsenic, antimony, phosphorus and tellurium; and (d) having a melting point below the sintering temperatures of the sintered bodies; and (3) heating to a joining temperature above the melting point and below the sintering temperatures.

Sintering activation energy MoSi2-WSi2-Si3N4 ceramic

NASA Astrophysics Data System (ADS)

Titov, D. D.; Lysenkov, A. S.; Kargin, Yu F.; Frolova, M. G.; Gorshkov, V. A.; Perevislov, S. N.

2018-04-01

The activation energy of sintering process was calculated based on dilatometric studies of shrinkage processes (Mo,W)Si2 + Si3N4 composite ceramic. (Mo,W)Si2 powders was obtained by solid-phase solutions of 70 wt% MoSi2 and 30 wt% WSi2 by SHS in the ISMAN RAS. The concentration rate Si3N4 was from 1 to 15 wt.%. The sintering was carried out to 1850°C in Ar atmosphere the heating rate of 5, 10, 12 and 15°C/min by the way of dilatometer tests. Based on the differential kinetic analysis method (Friedman’s method), the sintering process activation energy of (Mo,W)Si2 + Si3N4 were calculated. The two-stage sintering process and the dependence of the activation energy on the Si3N4 content was shown. Average value of 370 kJ/mol for Q was obtained.

A new integrated evaluation method of heavy metals pollution control during melting and sintering of MSWI fly ash.

PubMed

Li, Rundong; Li, Yanlong; Yang, Tianhua; Wang, Lei; Wang, Weiyun

2015-05-30

Evaluations of technologies for heavy metal control mainly examine the residual and leaching rates of a single heavy metal, such that developed evaluation method have no coordination or uniqueness and are therefore unsuitable for hazard control effect evaluation. An overall pollution toxicity index (OPTI) was established in this paper, based on the developed index, an integrated evaluation method of heavy metal pollution control was established. Application of this method in the melting and sintering of fly ash revealed the following results: The integrated control efficiency of the melting process was higher in all instances than that of the sintering process. The lowest integrated control efficiency of melting was 56.2%, and the highest integrated control efficiency of sintering was 46.6%. Using the same technology, higher integrated control efficiency conditions were all achieved with lower temperatures and shorter times. This study demonstrated the unification and consistency of this method. Copyright © 2015 Elsevier B.V. All rights reserved.

Tailoring of processing parameters for sintering microsphere-based scaffolds with dense-phase carbon dioxide

PubMed Central

Jeon, Ju Hyeong; Bhamidipati, Manjari; Sridharan, BanuPriya; Scurto, Aaron M.; Berkland, Cory J.; Detamore, Michael S.

2015-01-01

Microsphere-based polymeric tissue-engineered scaffolds offer the advantage of shape-specific constructs with excellent spatiotemporal control and interconnected porous structures. The use of these highly versatile scaffolds requires a method to sinter the discrete microspheres together into a cohesive network, typically with the use of heat or organic solvents. We previously introduced subcritical CO2 as a sintering method for microsphere-based scaffolds; here we further explored the effect of processing parameters. Gaseous or subcritical CO2 was used for making the scaffolds, and various pressures, ratios of lactic acid to glycolic acid in poly(lactic acid-co-glycolic acid), and amounts of NaCl particles were explored. By changing these parameters, scaffolds with different mechanical properties and morphologies were prepared. The preferred range of applied subcritical CO2 was 15–25 bar. Scaffolds prepared at 25 bar with lower lactic acid ratios and without NaCl particles had a higher stiffness, while the constructs made at 15 bar, lower glycolic acid content, and with salt granules had lower elastic moduli. Human umbilical cord mesenchymal stromal cells (hUCMSCs) seeded on the scaffolds demonstrated that cells penetrate the scaffolds and remain viable. Overall, the study demonstrated the dependence of the optimal CO2 sintering parameters on the polymer and conditions, and identified desirable CO2 processing parameters to employ in the sintering of microsphere-based scaffolds as a more benign alternative to heat-sintering or solvent-based sintering methods. PMID:23115065

Method of sintering ceramic materials

DOEpatents

Holcombe, C.E.; Dykes, N.L.

1992-11-17

A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density. 2 figs.

Sintered silicon carbide molded body and method for its production

NASA Technical Reports Server (NTRS)

Omori, M.; Sendai, M.; Ohira, K.

1984-01-01

Sintered silicon carbide shapes are described. They are produced by using a composition containing an oxide of at least one element chosen from the group: Li, Be, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Mo, Ba, Tc, Ta, W and Th as a supplement to known sintering aids.

Feasibility of Plasma Treated Clay in Clay/Polymer Nanocomposites Powders for use Laser Sintering (LS)

NASA Astrophysics Data System (ADS)

Almansoori, Alaa; Seabright, Ryan; Majewski, C.; Rodenburg, C.

2017-05-01

The addition of small quantities of nano-clay to nylon is known to improve mechanical properties of the resulting nano-composite. However, achieving a uniform dispersion and distribution of the clay within the base polymer can prove difficult. A demonstration of the fabrication and characterization of plasma-treated organoclay/Nylon12 nanocomposite was carried out with the aim of achieving better dispersion of clay platelets on the Nylon12 particle surface. Air-plasma etching was used to enhance the compatibility between clays and polymers to ensure a uniform clay dispersion in composite powders. Downward heat sintering (DHS) in a hot press is used to process neat and composite powders into tensile and XRD specimens. Morphological studies using Low Voltage Scanning Electron Microscopy (LV-SEM) were undertaken to characterize the fracture surfaces and clay dispersion in powders and final composite specimens. Thermogravimetric analysis (TGA) testing performed that the etched clay (EC) is more stable than the nonetched clay (NEC), even at higher temperatures. The influence of the clay ratio and the clay plasma treatment process on the mechanical properties of the nanocomposites was studied by tensile testing. The composite fabricated from (3% EC/N12) powder showed ~19 % improvement in elastic modulus while the composite made from (3% NEC/N12) powder was improved by only 14%). Most notably however is that the variation between tests is strongly reduced when etch clay is used in the composite. We attribute this to a more uniform distribution and better dispersion of the plasma treated clay within polymer powders and ultimately the composite.

[Study on preparation and physicochemical properties of surface modified sintered bone].

PubMed

Li, Jingfeng; Zheng, Qixin; Guo, Xiaodong

2012-06-01

The aim of this study is to investigate a new method for preparing a biomimetic bone material-surface modified sintered bovine cancellous bone, and to improve its bioactivity as a tissue engineering bone. The prepared sintered bovine cancellous bones with the same size were randomly divided into two groups, immersing in 1 and 1. 5 times simulated body fluid (SBF), respectively. The three time periods of soak time were 7, 14, and 21 days. After sintered bone was dried, the surface morphology of sintered bone and surface mineralization composition were observed under scanning electron microscopy (SEM). By comparing the effect of surface modification of sintered bone materials, we chose the most ideal material and studied its pore size, the rate of the porosity, the compress and bend intensity. And then the material and the sintered bone material without surface modification were compared. The study indicated that sintered bone material immersed in SBF (1.5 times) for 14 days showed the best effect of surface modification, retaining the original physico-chemical properties of sintered bone.

Low-Thermal-Conductivity Pyrochlore Oxide Materials Developed for Advanced Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Zhu, Dong-Ming

2005-01-01

When turbine engines operate at higher temperatures, they consume less fuel, have higher efficiencies, and have lower emissions. The upper-use temperatures of the base materials (superalloys, silicon-based ceramics, etc.) used for the hot-section components of turbine engines are limited by the physical, mechanical, and corrosion characteristics of these materials. Thermal barrier coatings (TBCs) are applied as thin layers on the surfaces of these materials to further increase the operating temperatures. The current state-of-the-art TBC material in commercial use is partially yttria-stabilized zirconia (YSZ), which is applied on engine components by plasma spraying or by electron-beam physical vapor deposition. At temperatures higher than 1000 C, YSZ layers are prone to sintering, which increases thermal conductivity and makes them less effective. The sintered and densified coatings can also reduce thermal stress and strain tolerance, which can reduce the coating s durability significantly. Alternate TBC materials with lower thermal conductivity and better sintering resistance are needed to further increase the operating temperature of turbine engines.

Field assisted sintering of refractory carbide ceramics and fiber reinforced ceramic matrix composites

NASA Astrophysics Data System (ADS)

Gephart, Sean

The sintering behaviors of silicon carbide (SiC) and boron carbide (B4C) based materials were investigated using an emerging sintering technology known as field assisted sintering technology (FAST), also known as spark plasma sintering (SPS) and pulse electric current sintering (PECS). Sintering by FAST utilizes high density electric current, uniaxial pressure, and relatively high heating rate compared to conventional sintering techniques. This effort investigated issues of scaling from laboratory FAST system (25 ton capacity) to industrial FAST system (250 ton capacity), as well as exploring the difference in sintering behavior of single phase B4C and SiC using FAST and conventional sintering techniques including hot-pressing (HP) and pressure-less sintering (PL). Materials were analyzed for mechanical and bulk properties, including characterization of density, hardness, fracture toughness, fracture (bend) strength, elastic modulus and microstructure. A parallel investigation was conducted in the development of ceramic matrix composites (CMC) using SiC powder impregnation of fiber compacts followed by FAST sintering. The FAST technique was used to sinter several B4C and SiC materials to near theoretical density. Preliminary efforts established optimized sintering temperatures using the smaller 25 ton laboratory unit, targeting a sample size of 40 mm diameter and 8 mm thickness. Then the same B4C and SiC materials were sintered by the larger 250 ton industrial FAST system, a HP system, and PL sintering system with a targeted dense material geometry of 4 x 4 x 0.315 inches3 (101.6 x 101.6 x 8 mm3). The resulting samples were studied to determine if the sintering dynamics and/or the resulting material properties were influenced by the sintering technique employed. This study determined that FAST sintered ceramic materials resulted in consistently higher averaged values for mechanical properties as well as smaller grain size when compared to conventionally sintered materials. While FAST sintered materials showed higher average values, in general they also showed consistently larger variation in the scattered data and consequently larger standard deviation for the resulting material properties. In addition, dynamic impact testing (V50 test) was conducted on the resulting materials and it was determined that there was no discernable correlation between observed mechanical properties of the ceramic materials and the resulting dynamic testing. Another study was conducted on the sintering of SiC and carbon fiber reinforced SiC ceramic matrix composites (CMC) using FAST. There has been much interest recently in fabricating high strength, low porosity SiC CMC.s for high temperature structural applications, but the current methods of production, namely chemical vapor infiltration (CVI), melt infiltration (MI), and polymer infiltration and pyrolysis (PIP), are considered time consuming and involve material related shortcomings associated with their respective methodologies. In this study, SiC CMC.s were produced using the 25 ton laboratory unit with a target sample size of 40 mm diameter and 3 mm thickness, as well as on the larger 250 ton industrial FAST system targeting a sample size of 101.6 x 101.6 x 3 mm3 to investigate issues associated with scaling. Several sintering conditions were explored including: pressure of 35-65 MPa, temperature of 1700-1900°C, and heating rates between 50-400°C/min. The SiC fibers used in this study were coated using chemical vapor deposition (CVD) with boron nitride (BN) and pyrolytic carbon to act as a barrier layer and preserve the integrity of the fibers during sintering. Then the barrier coating was coated by an outer layer of SiC to enhance the bonding between the fibers and the SiC matrix. Microstructures of the sintered samples were examined by FE-SEM. Mechanical properties including flexural strength-deflection and stress-strain were characterized using 4-point bend testing. Tensile testing was performed on the larger 101.6 x 101.6 x 3 mm samples. The microstructures of samples sintered using the 25 ton laboratory FAST system showed a reduction in porosity and good adhesion between the fiber-fiber and fiber-matrix interface. The microstructures of samples sintered on the 250 ton industrial FAST system showed a reduction in porosity, but there was visible reaction of the fiber and fiber coatings with the surrounding matrix. Additionally, there was significant radial cracking of the fibers visible in the microstructures. There is gap in the understanding of sintering behavior between laboratory and industrial scale FAST systems. The vast majority of publications on FAST sintering have been primarily focused on small sample geometries (20 mm diameter, less than 3 mm thick). A study was coordinated to investigate the thermal properties during heating and cooling using a 250 ton industrial FAST system at 900°C using B4C and SiC materials inside the graphite die assembly. The thermal properties were then compared to the resulting material properties of the identically sintered B4C and SiC to approximately 94% relative density, at a temperature of 1950°C, pressure of 45 MPa, 10 minute hold, and heated at a rate of 100°C/min. The study determined that at 900°C there were significant thermal gradients within the system for the examined materials, and that these gradients correlated well with the material property difference of the samples sintered at higher temperatures where the gradients are presumably larger due to an increase in radiative heat loss. The observed temperatures throughout the graphite were significantly different between B4C and SiC. These temperatures also correlated well with the material properties of the sintered products which showed more substantial variation for B4C when compared to SiC which was overall less affected by thermal gradients. This was attributed to the intrinsic thermal conductivity difference between the two subject materials which was manifested as thermal gradients throughout the material and graphite die assembly. Additionally, both the observed temperature gradients throughout the graphite die assembly and the difference in temperature reading between the optical pyrometer and thermocouples were significantly larger for the 250 ton FAST system than previous publications have demonstrated experimentally or via modeling of smaller laboratory scale systems. The findings from this work showed that relative to conventional sintering methods, the FAST process demonstrated comparable or improved material and mechanical properties with a significantly shorter processing cycle. However, the results demonstrated on the 25 ton laboratory scale unit were significantly different compared to results for the same materials sintered using the 250 ton industrial scale unit. The temperature gradients observed on the 250 ton FAST unit were significantly larger than previous reports on smaller FAST units. This result showed future efforts to scale up the FAST sintering process while maintaining similar results will require careful attention to minimizing temperature gradients. This could potentially be achieved by reducing radiative heat loss during processing and/or optimizing the graphite die design and implementing heat spreaders in specific locations dependent on the host material.s thermal and electrical properties as well as the sample geometry.

Chemical Sintering Generates Uniform Porous Hyaluronic Acid Hydrogels

PubMed Central

Cam, Cynthia; Segura, Tatiana

2014-01-01

Implantation of scaffolds for tissue repair has been met with limited success primarily due to the inability to achieve vascularization within the construct. Many strategies have shifted to incorporate pores into these scaffolds to encourage rapid cellular infiltration and subsequent vascular ingrowth. We utilized an efficient chemical sintering technique to create a uniform network of polymethyl methacrylate (PMMA) microspheres for porous hyaluronic acid hydrogel formation. The porous hydrogels generated from chemical sintering possessed comparable pore uniformity and interconnectivity as the commonly used non- and heat sintering techniques. Moreover, similar cell response to the porous hydrogels generated from each sintering approach was observed in cell viability, spreading, proliferation in vitro, as well as, cellular invasion in vivo. We propose chemical sintering of PMMA microspheres using a dilute acetone solution as an alternative method to generating porous hyaluronic acid hydrogels since it requires equal or ten-fold less processing time as the currently used non-sintering or heat sintering technique, respectively. PMID:24120847

The Effects of Atmosphere on the Sintering of Ultrafine-Grained Tungsten with Ti

NASA Astrophysics Data System (ADS)

Ren, Chai; Koopman, Mark; Fang, Z. Zak; Zhang, Huan

2016-11-01

Tungsten (W) is a brittle material at room temperature making it very difficult to fabricate. Although the lack of ductility remains a difficult challenge, nano-sized and ultrafine-grained (UFG) structures offer the potential to overcome tungsten's room-temperature brittleness. One way to manufacture UFG W is to compact and sinter nano-sized W powder. It is challenging, however, to control grain growth during sintering. As one method to inhibit grain growth, the effect of Ti-based additives on the densification and grain growth of nano-W powders was investigated in this study. Addition of 1% Ti into tungsten led to more than a 63% decrease in average grain size of sintered samples at comparable density levels. It was found that sintering in Ar yielded a finer grain size than sintering in H2 at similar densities. The active diffusion mechanisms during sintering were different for W-1% Ti nano powders sintered in Ar and H2.

Dielectric and Piezoelectric Properties of Barium-substituted Sr1.9Ca0.1NaNb5O15 Ceramics

NASA Astrophysics Data System (ADS)

Xie, Rong-Jun; Akimune, Yoshio; Wang, Ruiping; Hirosaki, Naoto; Nishimura, Toshiyuki

2003-12-01

Highly dense piezoelectric ceramics of tungsten bronze-type (Sr1.9Ca0.1)1-0.5xBaxNaNb5O15 (where x=0.1--0.8) were prepared by spark plasma sintering. The crystallographic parameters, dielectric behaviors and piezoelectric properties of the sintered ceramics were investigated, and the effects of the Ba substitution on these electrical properties were discussed. The structural analysis and the electrical property measurements indicate a morphotropic phase boundary (MPB)-like phenomenon at x=0.4--0.5. In all compositions, a diffuse phase transition and a relaxor behavior are observed. The electrical properties are found to be crystallographically dependent.

Effects of sintering temperature on electrical properties of sheep enamel hydroxyapatite

NASA Astrophysics Data System (ADS)

Dumludag, F.; Gunduz, O.; Kılıc, O.; Kılıc, B.; Ekren, N.; Kalkandelen, C.; Oktar, F. N.

2017-12-01

Bioceramics, especially calcium phosphate based bioceramics, whose examples are hydroxyapatite, and calcium phosphate powders have been widely used in the biomedical engineering applications. Hydroxyapatite (HA) is one of the most promising biomaterials, which are derived from natural sources, chemical method, animal like dental enamel and corals. The influence of sintering temperature on the electrical properties (i.e. DC conductivity, AC conductivity) of samples of sintered sheep enamel (SSSE) was studied in air and in vacuum ambient at room temperature. The sheep enamel were sintered at varying temperatures between 1000°C and 1300°C. DC conductivity results revealed that while dc conductivity of the SSSE decreases with increasing the sintering temperature in air ambient the values increased with increasing the sintering temperature in vacuum ambient. AC conductivity measurements were performed in the frequency range of 40 Hz - 105 Hz. The results showed that ac conductivity values decrease with increasing the sintering temperature.

Accelerated sintering in phase-separating nanostructured alloys

PubMed Central

Park, Mansoo; Schuh, Christopher A.

2015-01-01

Sintering of powders is a common means of producing bulk materials when melt casting is impossible or does not achieve a desired microstructure, and has long been pursued for nanocrystalline materials in particular. Acceleration of sintering is desirable to lower processing temperatures and times, and thus to limit undesirable microstructure evolution. Here we show that markedly enhanced sintering is possible in some nanocrystalline alloys. In a nanostructured W–Cr alloy, sintering sets on at a very low temperature that is commensurate with phase separation to form a Cr-rich phase with a nanoscale arrangement that supports rapid diffusional transport. The method permits bulk full density specimens with nanoscale grains, produced during a sintering cycle involving no applied stress. We further show that such accelerated sintering can be evoked by design in other nanocrystalline alloys, opening the door to a variety of nanostructured bulk materials processed in arbitrary shapes from powder inputs. PMID:25901420

Stream-sediment samples reanalyzed for major, rare earth, and trace elements from ten 1:250,000-scale quadrangles, south-central Alaska, 2007-08

USGS Publications Warehouse

Bailey, Elizabeth A.; Shew, Nora B.; Labay, Keith A.; Schmidt, Jeanine M.; O'Leary, Richard M.; Detra, David E.

2010-01-01

During the 1960s through the 1980s, the U.S. Geological Survey (USGS) conducted reconnaissance geochemical surveys of the drainage basins throughout most of the Anchorage, Bering Glacier, Big Delta, Gulkana, Healy, McCarthy, Mount Hayes, Nabesna, Talkeetna Mountains, and Valdez 1:250,000-scale quadrangles in Alaska as part of the Alaska Mineral Resource Assessment Program (AMRAP). These geochemical surveys provide data necessary to assess the potential for undiscovered mineral resources on public and other lands, and provide data that may be used to determine regional-scale element baselines. This report provides new data for 366 of the previously collected stream-sediment samples. These samples were selected for reanalysis because recently developed analytical methods can detect additional elements of interest and have lower detection limits than the methods used when these samples were originally analyzed. These samples were all analyzed for arsenic by hydride generation atomic absorption spectrometry (HGAAS), for gold, palladium, and platinum by inductively coupled plasma-mass spectrometry after lead button fire assay separation (FA/ICP-MS), and for a suite of 55 major, rare earth, and trace elements by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry (ICP-AES-MS) after sodium peroxide sinter at 450 degrees Celsius.

SINTERED REFRACTORY MASS

DOEpatents

Williams, A.E.

1955-09-01

A method is given for joining sintered masses of refractory compounds. It consists in maintaining the masses in contact with each other by application of a moderate pressure, while they are at sintering temperature. The sintered masses are subjected to am applied pressure of about 1/2 to 1 ton per square inch of the surface in contact for about 10 minutes, and the temperature employed may be fropn about 1400 deg C to 2000 deg C. Refractory oxides to which the invention may be applied are beryllia, alumina, thoria, and magnesia.

Sintering behavior and mechanical properties of zirconia compacts fabricated by uniaxial press forming

PubMed Central

Oh, Gye-Jeong; Yun, Kwi-Dug; Lee, Kwang-Min; Lim, Hyun-Pil

2010-01-01

PURPOSE The purpose of this study was to compare the linear sintering behavior of presintered zirconia blocks of various densities. The mechanical properties of the resulting sintered zirconia blocks were then analyzed. MATERIALS AND METHODS Three experimental groups of dental zirconia blocks, with a different presintering density each, were designed in the present study. Kavo Everest® ZS blanks (Kavo, Biberach, Germany) were used as a control group. The experimental group blocks were fabricated from commercial yttria-stabilized tetragonal zirconia powder (KZ-3YF (SD) Type A, KCM. Corporation, Nagoya, Japan). The biaxial flexural strengths, microhardnesses, and microstructures of the sintered blocks were then investigated. The linear sintering shrinkages of blocks were calculated and compared. RESULTS Despite their different presintered densities, the sintered blocks of the control and experimental groups showed similar mechanical properties. However, the sintered block had different linear sintering shrinkage rate depending on the density of the presintered block. As the density of the presintered block increased, the linear sintering shrinkage decreased. In the experimental blocks, the three sectioned pieces of each block showed the different linear shrinkage depending on the area. The tops of the experimental blocks showed the lowest linear sintering shrinkage, whereas the bottoms of the experimental blocks showed the highest linear sintering shrinkage. CONCLUSION Within the limitations of this study, the density difference of the presintered zirconia block did not affect the mechanical properties of the sintered zirconia block, but affected the linear sintering shrinkage of the zirconia block. PMID:21165274

Influence of Grain Refinement on Microstructure and Mechanical Properties of Tungsten Carbide/Zirconia Nanocomposites

NASA Astrophysics Data System (ADS)

Nasser, Ali; Kassem, Mohamed A.; Elsayed, Ayman; Gepreel, Mohamed A.; Moniem, Ahmed A.

2016-11-01

WC-W2C/ZrO2 nanocomposites were synthesized by pressure-less sintering (PS) and spark plasma sintering (SPS) of tungsten carbide/yttria-stabilized tetragonal zirconia, WC/TZ-3Y. Prior to sintering, WC/TZ-3Y powders were totally ball-milled for 20 and 120 h to obtain targeted nano (N) and nano-nano (N-N) structures, indicated by transmission electron microscopy and powder x-ray diffraction (PXRD). The milled powders were processed via PS at temperatures of 1773 and 1973 K for 70 min and SPS at 1773 K for 10 min. PXRD as well as SEM-EDS indicated the formation of WC-W2C/ZrO2 composites after sintering. The mechanical properties were characterized via Vicker microhardness and nanoindentation techniques indicating enhancements for sufficiently consolidated composites with high W2C content. The effects of reducing particle sizes on phase transformation, microstructure and mechanical properties are reported. In general, the composites based on the N structure showed higher microhardness than those for N-N structure, except for the samples PS-sintered at 1773 K. For instance, after SPS at 1773 K, the N structure showed a microhardness of 18.24 GPa. Nanoindentation measurements revealed that nanoscale hardness up to 22.33 and 25.34 GPa and modulus of elasticity up to 340 and 560 GPa can be obtained for WC-W2C/ZrO2 nanocomposites synthesized by the low-cost PS at 1973 K and by SPS at 1773 K, respectively.

Coupling of in-situ X-ray Microtomography Observations with Discrete Element Simulations-Application to Powder Sintering

NASA Astrophysics Data System (ADS)

Olmos, L.; Bouvard, D.; Martin, C. L.; Bellet, D.; Di Michiel, M.

2009-06-01

The sintering of both a powder with a wide particle size distribution (0-63 μm) and of a powder with artificially created pores is investigated by coupling in situ X-ray microtomography observations with Discrete Element simulations. The micro structure evolution of the copper particles is observed by microtomography all along a typical sintering cycle at 1050° C at the European Synchrotron Research Facilities (ESRF, Grenoble, France). A quantitative analysis of the 3D images provides original data on interparticle indentation, coordination and particle displacements throughout sintering. In parallel, the sintering of similar powder systems has been simulated with a discrete element code which incorporates appropriate sintering contact laws from the literature. The initial numerical packing is generated directly from the 3D microtomography images or alternatively from a random set of particles with the same size distribution. The comparison between the information drawn from the simulations and the one obtained by tomography leads to the conclusion that the first method is not satisfactory because real particles are not perfectly spherical as the numerical ones. On the opposite the packings built with the second method show sintering behaviors close to the behaviors of real materials, although particle rearrangement is underestimated by DEM simulations.

Advanced Ceramic Technology for Space Applications at NASA MSFC

NASA Technical Reports Server (NTRS)

Alim, Mohammad A.

2003-01-01

The ceramic processing technology using conventional methods is applied to the making of the state-of-the-art ceramics known as smart ceramics or intelligent ceramics or electroceramics. The sol-gel and wet chemical processing routes are excluded in this investigation considering economic aspect and proportionate benefit of the resulting product. The use of ceramic ingredients in making coatings or devices employing vacuum coating unit is also excluded in this investigation. Based on the present information it is anticipated that the conventional processing methods provide identical performing ceramics when compared to that processed by the chemical routes. This is possible when sintering temperature, heating and cooling ramps, peak temperature (sintering temperature), soak-time (hold-time), etc. are considered as variable parameters. In addition, optional calcination step prior to the sintering operation remains as a vital variable parameter. These variable parameters constitute a sintering profile to obtain a sintered product. Also it is possible to obtain identical products for more than one sintering profile attributing to the calcination step in conjunction with the variables of the sintering profile. Overall, the state-of-the-art ceramic technology is evaluated for potential thermal and electrical insulation coatings, microelectronics and integrated circuits, discrete and integrated devices, etc. applications in the space program.

High coercivity, anisotropic, heavy rare earth-free Nd-Fe-B by Flash Spark Plasma Sintering.

PubMed

Castle, Elinor; Sheridan, Richard; Zhou, Wei; Grasso, Salvatore; Walton, Allan; Reece, Michael J

2017-09-11

In the drive to reduce the critical Heavy Rare Earth (HRE) content of magnets for green technologies, HRE-free Nd-Fe-B has become an attractive option. HRE is added to Nd-Fe-B to enhance the high temperature performance of the magnets. To produce similar high temperature properties without HRE, a crystallographically textured nanoscale grain structure is ideal; and this conventionally requires expensive "die upset" processing routes. Here, a Flash Spark Plasma Sintering (FSPS) process has been applied to a Dy-free Nd 30.0 Fe 61.8 Co 5.8 Ga 0.6 Al 0.1 B 0.9 melt spun powder (MQU-F, neo Magnequench). Rapid sinter-forging of a green compact to near theoretical density was achieved during the 10 s process, and therefore represents a quick and efficient means of producing die-upset Nd-Fe-B material. The microstructure of the FSPS samples was investigated by SEM and TEM imaging, and the observations were used to guide the optimisation of the process. The most optimal sample is compared directly to commercially die-upset forged (MQIII-F) material made from the same MQU-F powder. It is shown that the grain size of the FSPS material is halved in comparison to the MQIII-F material, leading to a 14% increase in coercivity (1438 kA m -1 ) and matched remanence (1.16 T) giving a BH max of 230 kJ m -3 .

Spark Plasma Sintering As a Solid-State Recycling Technique: The Case of Aluminum Alloy Scrap Consolidation

PubMed Central

Paraskevas, Dimos; Vanmeensel, Kim; Vleugels, Jef; Dewulf, Wim; Deng, Yelin; Duflou, Joost R.

2014-01-01

Recently, “meltless” recycling techniques have been presented for the light metals category, targeting both energy and material savings by bypassing the final recycling step of remelting. In this context, the use of spark plasma sintering (SPS) is proposed in this paper as a novel solid-state recycling technique. The objective is two-fold: (I) to prove the technical feasibility of this approach; and (II) to characterize the recycled samples. Aluminum (Al) alloy scrap was selected to demonstrate the SPS effectiveness in producing fully-dense samples. For this purpose, Al alloy scrap in the form of machining chips was cold pre-compacted and sintered bellow the solidus temperature at 490 °C, under elevated pressure of 200 MPa. The dynamic scrap compaction, combined with electric current-based joule heating, achieved partial fracture of the stable surface oxides, desorption of the entrapped gases and activated the metallic surfaces, resulting in efficient solid-state chip welding eliminating residual porosity. The microhardness, the texture, the mechanical properties, the microstructure and the density of the recycled specimens have been investigated. An X-ray computed tomography (CT) analysis confirmed the density measurements, revealing a void-less bulk material with homogeneously distributed intermetallic compounds and oxides. The oxide content of the chips incorporated within the recycled material slightly increases its elastic properties. Finally, a thermal distribution simulation of the process in different segments illustrates the improved energy efficiency of this approach. PMID:28788153

Spark Plasma Sintering As a Solid-State Recycling Technique: The Case of Aluminum Alloy Scrap Consolidation.

PubMed

Paraskevas, Dimos; Vanmeensel, Kim; Vleugels, Jef; Dewulf, Wim; Deng, Yelin; Duflou, Joost R

2014-08-06

Recently, "meltless" recycling techniques have been presented for the light metals category, targeting both energy and material savings by bypassing the final recycling step of remelting. In this context, the use of spark plasma sintering (SPS) is proposed in this paper as a novel solid-state recycling technique. The objective is two-fold: (I) to prove the technical feasibility of this approach; and (II) to characterize the recycled samples. Aluminum (Al) alloy scrap was selected to demonstrate the SPS effectiveness in producing fully-dense samples. For this purpose, Al alloy scrap in the form of machining chips was cold pre-compacted and sintered bellow the solidus temperature at 490 °C, under elevated pressure of 200 MPa. The dynamic scrap compaction, combined with electric current-based joule heating, achieved partial fracture of the stable surface oxides, desorption of the entrapped gases and activated the metallic surfaces, resulting in efficient solid-state chip welding eliminating residual porosity. The microhardness, the texture, the mechanical properties, the microstructure and the density of the recycled specimens have been investigated. An X-ray computed tomography (CT) analysis confirmed the density measurements, revealing a void-less bulk material with homogeneously distributed intermetallic compounds and oxides. The oxide content of the chips incorporated within the recycled material slightly increases its elastic properties. Finally, a thermal distribution simulation of the process in different segments illustrates the improved energy efficiency of this approach.

Effect of grain size on structural and dielectric properties of barium titanate piezoceramics synthesized by high energy ball milling

NASA Astrophysics Data System (ADS)

Verma, Narendra Kumar; Patel, Sandeep Kumar Singh; Kumar, Dinesh; Singh, Chandra Bhal; Singh, Akhilesh Kumar

2018-05-01

We have investigated the effect of sintering temperature on the densification behaviour, grain size, structural and dielectric properties of BaTiO3 ceramics, prepared by high energy ball milling method. The Powder x-ray diffraction reveals the tetragonal structure with space group P4mm for all the samples. The samples were sintered at four different temperatures, (T = 900°C, 1000°C, 1100°C, 1200°C and 1300°C). Density increased with increasing sintering temperature, reaching up to 97% at 1300°C. A grain growth was observed with increasing sintering temperature. Impedance analyses of the sintered samples at various temperatures were performed. Increase in dielectric constant and Curie temperature is observed with increasing sintering temperature.

Method for sintering fuel cell electrodes using a carrier

DOEpatents

Donelson, R.; Bryson, E.S.

1995-03-28

A carrier is described for conveying components of a fuel cell to be sintered through a sintering furnace. The carrier comprises a metal sheet coated with a carbon-based paint, the carbon-based paint comprising an organic binder. The carbon-based paint may be an alcohol or a solvent-based paint or a water-based paint.

Laser surface processing on sintered PM alloys

NASA Astrophysics Data System (ADS)

Reiter, Wilfred; Daurelio, Giuseppe; Ludovico, Antonio D.

1997-08-01

Usually the P.M. alloys are heat treated like case hardening, gas nitriding or plasma nitriding for a better wear resistance of the product surface. There is an additional method for gaining better tribological properties and this is the surface hardening (or remelting or alloying) of the P.M. alloy by laser treatment on a localized part of the product without heating the whole sample. This work gives a cured experimentation about the proper sintering powder alloys for laser surface processing from the point of view of wear, fatigue life and surface quality. As concerns the materials three different basic alloy groups with graduated carbon contents were prepared. Regarding these sintered powder alloys one group holds Fe, Mo and C and other group holds Fe, Ni, Mo and C and the last one holds Fe, Ni, Cu, Mo and C contents. Obviously each group has a different surface hardness, different porosity distribution, different density and diverse metallurgical structures (pearlite or ferrite-pearlite, etc.). ON the sample surfaces a colloidal graphite coating, in different thicknesses, has been sprayed to increase laser energy surface absorption. On some other samples a Mo coating, in different thicknesses, has been produced (on the bulk alloy) by diverse deposition techniques (D.C. Sputtering, P.V.D. and Flame Spraying). Only a few samples have a Mo coating and also an absorber coating, that is a bulk material- Mo and a colloidal graphite coating. All these sintered alloys have been tested by laser technology; so that, many laser working parameters (covering gas, work-speed, focussed and defocussed spot, rastered and integrated beam spots, square and rectangular beam shapes and so on) have been experimented for two different processes at constant laser power and at constant surface temperature (by using a temperature surface sensor and a closed controlled link). For all experiments a transverse fast axial flow CO2 2.5 kW c.w. laser source has been employed.

Post-Plasma SiOx Coatings of Metal and Metal Oxide Nanoparticles for Enhanced Thermal Stability and Tunable Photoactivity Applications

PubMed Central

Post, Patrick; Jidenko, Nicolas; Weber, Alfred P.; Borra, Jean-Pascal

2016-01-01

The plasma-based aerosol process developed for the direct coating of particles in gases with silicon oxide in a continuous chemical vapor deposition (CVD) process is presented. It is shown that non-thermal plasma filaments induced in a dielectric barrier discharge (DBD) at atmospheric pressure trigger post-DBD gas phase reactions. DBD operating conditions are first scanned to produce ozone and dinitrogen pentoxide. In the selected conditions, these plasma species react with gaseous tetraethyl orthosilicate (TEOS) precursor downstream of the DBD. The gaseous intermediates then condense on the surface of nanoparticles and self-reactions lead to homogeneous solid SiOx coatings, with thickness from nanometer to micrometer. This confirms the interest of post-DBD injection of the organo-silicon precursor to achieve stable production of actives species with subsequent controlled thickness of SiOx coatings. SiOx coatings of spherical and agglomerated metal and metal oxide nanoparticles (Pt, CuO, TiO2) are achieved. In the selected DBD operating conditions, the thickness of homogeneous nanometer sized coatings of spherical nanoparticles depends on the reaction duration and on the precursor concentration. For agglomerates, operating conditions can be tuned to cover preferentially the interparticle contact zones between primary particles, shifting the sintering of platinum agglomerates to much higher temperatures than the usual sintering temperature. Potential applications for enhanced thermal stability and tunable photoactivity of coated agglomerates are presented. PMID:28335219

Solvent-Based Synthesis of Nano-Bi0.85Sb0.15 for Low-Temperature Thermoelectric Applications

NASA Astrophysics Data System (ADS)

Kaspar, K.; Fritsch, K.; Habicht, K.; Willenberg, B.; Hillebrecht, H.

2017-01-01

In this study we show a preparation method for nanostructured Bi0.85Sb0.15 powders via a chemical reduction route in a polyol medium, yielding material with particle sizes of 20-150 nm in scalable amounts. The powders were consolidated by spark plasma sintering (SPS) in order to maintain the nanostructure. To investigate influence of the sinter process, the powders were characterized by x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), and scanning electron microscopy (SEM) measurements before and after SPS. Transport properties, Seebeck effect, and thermal conductivity were determined in the low temperature range below 300 K. The samples showed excellent thermal conductivity of 2.3-2.6 W/m × K at 300 K and Seebeck coefficients from -97 μV/K to -107 μV/K at 300 K with a maximum of -141 μV/K at 110 K, thus leading to ZT values of up to 0.31 at room temperature. The results show that Bi-Sb-alloys are promising materials for low-temperature applications. Our wet chemical approach gives access to scalable amounts of nano-material with increased homogeneity and good thermoelectric properties after SPS.

Effects of the addition of municipal solid waste incineration fly ash on the behavior of polychlorinated dibenzo-p-dioxins and furans in the iron ore sintering process.

PubMed

Min, Yi; Liu, Chengjun; Shi, Peiyang; Qin, Chongda; Feng, Yutao; Liu, Baichen

2018-04-11

Raw materials were co-sintered with municipal solid waste incineration (MSWI) fly ash through iron ore sintering to promote the safe treatment and utilization of MSWI fly ash. To assess the feasibility of this co-sintering method, in this study, the effects of the addition of MSWI fly ash on the formation and emission of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) were estimated via iron ore sintering pot experiments. During co-sintering, most of the PCDD/Fs in the added MSWI fly ash were decomposed and transformed into PCDD/Fs associated with iron sintering, and the concentrations of lower- and mid-chlorinated congeners increased. As there was a sufficient chlorine source and the sintering bed permeability was decreased by the addition of MSWI fly ash, the PCDD/F concentration in the exhaust gas increased. The mass emission of PCDD/Fs decreased; however, the emission of toxic PCDD/Fs increased beyond the total emissions from the independent MSW incineration and iron ore sintering processes due to the transformation of PCDD/F congeners. The co-sintering may be an important solution after technological improvements in the flue gas cleaning system and PCDD/F formation inhibition procedures. Copyright © 2018. Published by Elsevier Ltd.

Thermoelectric properties of higher manganese silicide/multi-walled carbon nanotube composites.

PubMed

Truong, D Y Nhi; Kleinke, Holger; Gascoin, Franck

2014-10-28

Composites made of Higher Manganese Silicide (HMS)-based compound MnSi1.75Ge0.02 and multi-walled carbon nanotubes (MWCNTs) were prepared by an easy and effective method including mechanical milling under mild conditions and reactive spark plasma sintering. SEM compositional mappings show a homogeneous dispersion of MWCNTs in the HMS matrix. Electronic and thermal transport properties were measured from room temperature to 875 K. While power factors are virtually unchanged by the addition of MWCNTs, the lattice thermal conductivity is significantly reduced by about 30%. As a consequence, the maximum figure of merit for the composites with 1 wt% MWCNTs is improved by about 20% compared to the MWCNT free HMS-based sample.

Spark plasma sintering of bulk SrAl2O4-Sr3Al2O6 eutectic glass with wide-band optical window.

PubMed

Liu, Jiaxi; Lu, Nan; He, Gang; Li, Xiaoyu; Li, Jianqiang; Li, Jiangtao

2018-06-15

SrAl 2 O 4 -Sr 3 Al 2 O 6 eutectic glass was prepared by using an aerodynamic levitator equipped with a CO 2 laser device. A bulk transparent amorphous sample was obtained by the spark plasma sintering (SPS) of the prepared eutectic glass. XRD, a UV-vis-NIR spectrophotometer and FT-IR were employed to characterize the phase evolution and optical properties. The results show that the bulk SrAl 2 O 4 -Sr 3 Al 2 O 6 samples fabricated by the containerless process and SPS between 852 °C-857 °C were fully amorphous. The amorphous sample has a wide transparent window between 270 nm and 6.2 μm. The average refractive index in the visible light region is 1.680 and the Abbe number is 27.4. The prepared bulk SrAl 2 O 4 -Sr 3 Al 2 O 6 eutectic glass with the wide-band optical window may be a promising candidate for optical applications.

Zirconium Carbide Produced by Spark Plasma Sintering and Hot Pressing: Densification Kinetics, Grain Growth, and Thermal Properties

PubMed Central

Wei, Xialu; Back, Christina; Izhvanov, Oleg; Haines, Christopher D.; Olevsky, Eugene A.

2016-01-01

Spark plasma sintering (SPS) has been employed to consolidate a micron-sized zirconium carbide (ZrC) powder. ZrC pellets with a variety of relative densities are obtained under different processing parameters. The densification kinetics of ZrC powders subjected to conventional hot pressing and SPS are comparatively studied by applying similar heating and loading profiles. Due to the lack of electric current assistance, the conventional hot pressing appears to impose lower strain rate sensitivity and higher activation energy values than those which correspond to the SPS processing. A finite element simulation is used to analyze the temperature evolution within the volume of ZrC specimens subjected to SPS. The control mechanism for grain growth during the final SPS stage is studied via a recently modified model, in which the grain growth rate dependence on porosity is incorporated. The constant pressure specific heat and thermal conductivity of the SPS-processed ZrC are determined to be higher than those reported for the hot-pressed ZrC and the benefits of applying SPS are indicated accordingly. PMID:28773697

Friction and wear of several compressor gas-path seal movements

NASA Technical Reports Server (NTRS)

Bill, R. C.; Wisander, D. W.

1978-01-01

Rub interaction experiments were conducted on a series of sintered and plasma sprayed compressor gas path seal materials in contact with Ti-6Al-4V blade tip and knife edge rotors. The most rub tolerant materials investigated were sintered Nichrome and plasma sprayed nickel 25 percent graphite. The effectiveness of providing a compliant substrate for dense seal material coatings was also demonstrated. In general, it was observed that rotor wear and high frictional energy generation rates accompanied smearing or surface densification of the materials investigated. The onset of smearing was sensitive to rub interaction parameters and seal geometry. Two complementary models were proposed to account for the smearing trends. One is based on thermal effects, the other on particulate escape effects. They were shown to be consistent with the experimental evidence at hand, and together they predict that smearing, with the onset of high energy rub conditions, is favored when incursion rates (radial motion) are low, incursion depths are high, the seal geometry is of a knife-edge character, and the seal particle size is small.

Zirconium Carbide Produced by Spark Plasma Sintering and Hot Pressing: Densification Kinetics, Grain Growth, and Thermal Properties

DOE PAGES

Wei, Xialu; Back, Christina; Izhvanov, Oleg; ...

2016-07-14

Spark plasma sintering (SPS) has been employed to consolidate a micron-sized zirconium carbide (ZrC) powder. ZrC pellets with a variety of relative densities are obtained under different processing parameters. The densification kinetics of ZrC powders subjected to conventional hot pressing and SPS are comparatively studied by applying similar heating and loading profiles. Due to the lack of electric current assistance, the conventional hot pressing appears to impose lower strain rate sensitivity and higher activation energy values than those which correspond to the SPS processing. A finite element simulation is used to analyze the temperature evolution within the volume of ZrCmore » specimens subjected to SPS. The control mechanism for grain growth during the final SPS stage is studied via a recently modified model, in which the grain growth rate dependence on porosity is incorporated. Finally, the constant pressure specific heat and thermal conductivity of the SPS-processed ZrC are determined to be higher than those reported for the hot-pressed ZrC and the benefits of applying SPS are indicated accordingly.« less

Fe-Cr-Mo based ODS alloys via spark plasma sintering: A combinational characterization study by TEM and APT

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

Y. Q. Wu; K. N. Allahar; J. Burns

2013-08-01

Nanoscale oxides play an important role in oxide dispersion strengthened (ODS) alloys for improved high temperature creep resistance and enhanced radiation damage tolerance. In this study, transmission electron microscopy (TEM) and atom probe tomography (APT) were combined to investigate two novel Fe-16Cr-3Mo (wt.%) based ODS alloys. Spark plasma sintering (SPS) was used to consolidate the ODS alloys from powders that were milled with 0.5 wt.% Y2O3 powder only or with Y2O3 powder and 1 wt.% Ti. TEM characterization revealed that both alloys have a bimodal structure of nanometer-size (~ 100 – 500 nm) and micron-size grains with nanostructured oxide precipitatesmore » formed along and close to grain boundaries with diameters ranging from five to tens of nanometers. APT provides further quantitative analyses of the oxide precipitates, and also reveals Mo segregation at grain boundaries next to oxide precipitates. The alloys with and without Ti are compared based on their microstructures.« less

Spark plasma sintering of bulk SrAl2O4-Sr3Al2O6 eutectic glass with wide-band optical window

NASA Astrophysics Data System (ADS)

Liu, Jiaxi; Lu, Nan; He, Gang; Li, Xiaoyu; Li, Jianqiang; Li, Jiangtao

2018-06-01

SrAl2O4-Sr3Al2O6 eutectic glass was prepared by using an aerodynamic levitator equipped with a CO2 laser device. A bulk transparent amorphous sample was obtained by the spark plasma sintering (SPS) of the prepared eutectic glass. XRD, a UV–vis-NIR spectrophotometer and FT-IR were employed to characterize the phase evolution and optical properties. The results show that the bulk SrAl2O4-Sr3Al2O6 samples fabricated by the containerless process and SPS between 852 °C–857 °C were fully amorphous. The amorphous sample has a wide transparent window between 270 nm and 6.2 μm. The average refractive index in the visible light region is 1.680 and the Abbe number is 27.4. The prepared bulk SrAl2O4-Sr3Al2O6 eutectic glass with the wide-band optical window may be a promising candidate for optical applications.

Powder Metallurgy Processing of a WxTaTiVCr High-Entropy Alloy and Its Derivative Alloys for Fusion Material Applications.

PubMed

Waseem, Owais Ahmed; Ryu, Ho Jin

2017-05-16

The W x TaTiVCr high-entropy alloy with 32at.% of tungsten (W) and its derivative alloys with 42 to 90at.% of W with in-situ TiC were prepared via the mixing of elemental W, Ta, Ti, V and Cr powders followed by spark plasma sintering for the development of reduced-activation alloys for fusion plasma-facing materials. Characterization of the sintered samples revealed a BCC lattice and a multi-phase structure. The selected-area diffraction patterns confirmed the formation of TiC in the high-entropy alloy and its derivative alloys. It revealed the development of C15 (cubic) Laves phases as well in alloys with 71 to 90at.% W. A mechanical examination of the samples revealed a more than twofold improvement in the hardness and strength due to solid-solution strengthening and dispersion strengthening. This study explored the potential of powder metallurgy processing for the fabrication of a high-entropy alloy and other derived compositions with enhanced hardness and strength.

Optically- and thermally-stimulated luminescences of Ce-doped SiO2 glasses prepared by spark plasma sintering

NASA Astrophysics Data System (ADS)

Okada, Go; Kasap, Safa; Yanagida, Takayuki

2016-11-01

Rare-earth doped phosphors have been used in many applications including radiation measurements. In the latter applications, the radiation photons are converted to light so that we can indirectly detect the radiation using a conventional photodetector. In this work, we have prepared and characterized a Ce-doped SiO2 glass for dosimeter applications. Unlike conventional techniques such as sol-gel synthesis, the sample was prepared by spark plasma sintering. Although the PL emission seems to be only from the Ce3+ ions in the structure, due to the X-ray induced luminescence, we have also observed optically-stimulated luminescence (OSL), and thermally-stimulated luminescence (TSL), owing to a pair of silylenes and a set of dioxasilirane and silylene in addition to Ce3+. We have measured the detector response vs irradiation dose for both the OSL and TSL. The detector response in both cases is linear over the dose range from at least 1 mGy to 2 Gy. Particularly, the sensitivity of TSL is so high that it should be considered to be a good candidate for practical applications.

Microscopy of Alloy Formation on Arc Plasma Sintered Oxide Dispersion Strengthen (ODS) Steel

NASA Astrophysics Data System (ADS)

Bandriyana, B.; Sujatno, A.; Salam, R.; Dimyati, A.; Untoro, P.

2017-07-01

The oxide dispersed strengthened (ODS) alloys steel developed as structure material for nuclear power plants (NPP) has good resistant against creep due to their unique microstructure. Microscopy investigation on the microstructure formation during alloying process especially at the early stages was carried out to study the correlation between structure and property of ODS alloys. This was possible thanks to the arc plasma sintering (APS) device which can simulate the time dependent alloying processes. The ODS sample with composition of 88 wt.% Fe and 12 wt.% Cr powder dispersed with 1 wt.% ZrO2 nano powder was mixed in a high energy milling, isostatic compressed to form sample coins and then alloyed in APS. The Scanning Electron Microscope (SEM) with X-ray Diffraction Spectroscopy (EDX) line scan and mapping was used to characterize the microstructure and elemental composition distribution of the samples. The alloying process with unification of each Fe and Cr phase continued by the alloying formation of Fe-Cr by inter-diffusion of both Fe and Cr and followed by the improvement of the mechanical properties of hardness.

Diffraction, microstructure and thermal stability analysis in a double phase nanocrystalline Al20Mg20Ni20Cr20Ti20 high entropy alloy

NASA Astrophysics Data System (ADS)

Rameshbabu, A. M.; Parameswaran, P.; Vijayan, V.; Panneer, R.

2017-12-01

An effort has been made to develop a new composition of AlMgNiCrTi high entropy alloy (HEA) with a distinct properties includes squat density, intense strength and hardness, superior corrosion resistance, better oxidation resistance, high temperature resistance, fatigue load and crack resistance to congregate the necessity of aircraft applications. The equivalent atomic percentage for the above defined composition is established using analytical correlation for molar and atom renovation by trial and error method. The alloy is synthesized by powder metallurgy technique through mechanical alloying. Succeeding to mechanical alloying it is elucidated that the metal powder is primarily composed of single BCC solid solution with crystallite magnitude <10 nm. It is also observed that the alloy is thermally stable at prominent temperature about 800°C as it is retained its nanostructure which was revealed using differential scanning caloriemetry (DSC). This alloy powder was consolidated and sintered using spark plasma sintering at 800°C with 50 Mpa pressure to a density of 98.83%. Subsequent to sintering, Titanium carbide FCC phase evolved along with the BCC phase. The alloying behavior and phase transformation were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The homogeneity of the composition is confirmed by energy dispersive spectroscopy (EDS). The hardness of the alloy is found to be 710±20 HV. The evolutions of the phases and hardness imply that this alloy is apposite for both high strength and high temperature applications.

Surface hardening of Al alloys through controlled ball-milling and sintering.

PubMed

Kim, Seek Hyeoun; Kim, Yong Jin; Ahn, Jung-Ho

2012-07-01

One of the drawbacks of aluminum and its alloys is the lack of proper heat-treatment for surface-hardening. In the present work, a new and simple method of hardening the surface of aluminum and its alloys was developed. Low-energy ball-milling using specific process control agents (PCAs) was employed, using subsequent sintering in a controlled atmosphere. The PCAs in the present work were very effective both for milling and the formation of hard nanocrystalline dispersoids during sintering. The residual oxygen in a sintering atmosphere also played an important role in the formation of AIN or Al-O-N dispersoids. Through the proper control of the processing atmosphere and PCAs, the hardness and thickness of the hardened layers could be adjusted. The results of the wear test showed that the present aluminum alloys can be effectively utilized as light-weight components with a good wear resistance. Furthermore, the present method involves a simple forming process of die-compaction and sintering.

Production technology of an electrolyte for Na/S batteries

NASA Astrophysics Data System (ADS)

Heimke, G.; Mayer, H.; Reckziegel, A.

1982-05-01

The trend to develop a cheap electrochemical electric battery and the development of the Na/S system are discussed. The main element in this type of battery is the beta Al2O3 solid electrolyte. Characteristics for this material of first importance are: specific surface, density of green and of sintered material, absence of cracks, gas permeability, resistance to flexion, purity, electrical conductivity, crystal structure and dimensions. Influence of production method on all these characteristics were investigated, e.g., method of compacting powder, tunnel kiln sintering versus static chamber furnace sintering, sintering inside a container or not, and type of kiln material when sintering in a container. In the stationary chamber furnace, beta alumina ceramics were produced with a density of 3.2 g/cm3, a mechanical strength higher than 160 MPa, and an electrical conductivity of about 0.125 Ohm-1cm-1 at 300 C. The best kiln material proved to be MgO and MgAl2O3.MgO ceramics.

Conventional and two step sintering of PZT-PCN ceramics

NASA Astrophysics Data System (ADS)

Keshavarzi, Mostafa; Rahmani, Hooman; Nemati, Ali; Hashemi, Mahdieh

2018-02-01

In this study, PZT-PCN ceramic was made via sol-gel seeding method and effects of conventional sintering (CS) as well as two-step sintering (TSS) were investigated on microstructure, phase formation, density, dielectric and piezoelectric properties. First, high quality powder was achieved by seeding method in which the mixture of Co3O4 and Nb2O5 powder was added to the prepared PZT sol to form PZT-PCN gel. After drying and calcination, pyrochlore free PZT-PCN powder was synthesized. Second, CS and TSS were applied to achieve dense ceramic. The optimum temperature used for 2 h of conventional sintering was obtained at 1150 °C; finally, undesired ZrO2 phase formed in CS procedure was removed successfully with TSS procedure and dielectric and piezoelectric properties were improved compared to the CS procedure. The best electrical properties obtained for the sample sintered by TSS in the initial temperature of T 1 = 1200 °C and secondary temperature of T 2 = 1000 °C for 12 h.

Textured Na x CoO2 Ceramics Sintered from Hydrothermal Platelet Nanocrystals: Growth Mechanism and Transport Properties

NASA Astrophysics Data System (ADS)

Zhang, Wei; Liu, Pengcheng; Wang, Yifeng; Zhu, Kongjun; Tai, Guoan; Liu, Jinsong; Wang, Jing; Yan, Kang; Zhang, Jianhui

2018-05-01

Nanostructuring is an effective approach to improve thermoelectric (TE) performance, which is caused by the interface and quantum effects on electron and phonon transport. For a typical layered structure such as sodium cobalt (NCO), a highly textured ceramic with nanostructure is beneficial for the carrier transport properties due to the strong anisotropy. In this paper, we established a textured NCO ceramic with highly oriented single crystals in nanoscale. The Na0.6CoO2 platelet crystals were prepared by a one-step hydrothermal method. The growth mechanism was revealed to involve dissolution-recrystallization and exchange reactions. NCO TE ceramics fabricated by a press-aided spark plasma sintering method showed a high degree of texturing, with the platelet crystals basically lying along the in-plane direction perpendicular to the press direction. TE properties of the textured NCO ceramics showed a strong anisotropic behavior. The in-plane electrical conductivity was considerably larger than the out-of-plane data because of fewer grain boundaries and interfaces that existed in the in-plane direction. Moreover, the in-plane Seebeck coefficient was higher because of the anisotropic electronic nature of NCO. Although the in-plane thermal conductivity was high, a prior ZT value was enabled for these NCO ceramics along this direction because of the dominant electrical transport. This finding provides a new approach to prepare highly oriented ceramics.

Influence of processing parameters on microstructure and biocompatibility of surface laser sintered hydroxyapatite-SiO2 composites.

PubMed

Kivitz, E; Görke, R; Schilling, A F; Zhang, J; Heinrich, J G

2013-05-01

Silica-doped hydroxyapatite (HA) is a promising material concerning biocompatibility to natural bone, bioactivity and osteoconductive characteristics. HA exhibits phase transformations during sintering which are attendant to the change in volume and thermal strain. To avoid cracks during sintering, the exact knowledge of the phase transition temperatures is necessary. The sintering behavior of HA can be improved by adding amorphous silica with a low coefficient of thermal expansion. Therefore, the phase transformations in the system HA-SiO2 were analyzed by using differential scanning calorimetry followed by quantitative phase analysis by X-ray diffraction with the Riedveld method. The maximum sintering temperature without reversible phase transformation was defined as 1265°C. In laser surface sintered (LSS) samples, amorphous SiO2 , HA, and Si-α-TCP (or α-TCP) were detected. By comparison, only crystalline phases, such as cristobalite, HA, β-TCP, and Si-α-TCP (or α-TCP), were determined after furnace sintering. Scanning electron microscopy micrographs of furnace sintered and LSS samples show the differences in the resulting microstructures. Biocompatibility was determined by measuring cell activity of osteoblasts cultivated on four laser-sintered materials in the HA-SiO2 system in comparison to normal cell culture plastic. Cell proliferation was similar on all surfaces. The level of the cell activity on day 8 varied depending on the composition of the material and increased linearly as the amorphous SiO2 content rose. Taken together a laser-based method to develop novel biocompatible HA-SiO2 ceramics with adjustable properties and possible applications as orthopedic bioceramics are discussed. Copyright © 2012 Wiley Periodicals, Inc.

HSPES membrane electrode assembly

NASA Technical Reports Server (NTRS)

Kindler, Andrew (Inventor); Yen, Shiao-Ping (Inventor)

2000-01-01

An improved fuel cell electrode, as well as fuel cells and membrane electrode assemblies that include such an electrode, in which the electrode includes a backing layer having a sintered layer thereon, and a non-sintered free-catalyst layer. The invention also features a method of forming the electrode by sintering a backing material with a catalyst material and then applying a free-catalyst layer.

Preparation and flash sintering of MgTiO3 nanopowders obtained by the polyacrylamide gel method

NASA Astrophysics Data System (ADS)

Su, Xinghua; Bai, Ge; Zhang, Jing; Zhou, Jie; Jia, Yongjie

2018-06-01

Using a polyacrylamide gel method, phase pure and well-dispersed MgTiO3 nanopowders were prepared at 800 °C for 2 h. It was found that a high mole ratio of monomers to precursors resulted in low formation temperature of MgTiO3, due to the highly mixing homogeneity and smaller particle sizes of precursors. Sintering behaviors of MgTiO3 nanopowders under DC electric field from 500 to 800 V/cm were investigated. Nearly full dense MgTiO3 ceramics can be prepared in 30 s. An abrupt and simultaneous increase in current density and power dissipation were observed in sintering process, which are characteristics of flash sintering. The power dissipation for the flash sintering was found to be 82 mW/mm3. The densities and average grain sizes of samples increase with the increase of the electrical field strength. It was suggested that Joule heating was the main mechanism of flash sintering of MgTiO3 ceramics. Our work provides a useful route for the fabrication of dense MgTiO3 ceramics at low temperature in short time.

Method of manufacture of single phase ceramic superconductors

DOEpatents

Singh, J.P.; Poeppel, R.B.; Goretta, K.C.; Chen, N.

1995-03-28

A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa{sub 2}Cu{sub 3}O{sub x} indicates that sintering kinetics are enhanced at reduced p(O{sub 2}) and that because of second phase precipitates, grain growth is prevented. The density of specimens sintered at 910 C increased from 79 to 94% theoretical when p(O{sub 2}) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O{sub 2}) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910 C resulted in a fine-grain microstructure, with an average grain size of about 4 {mu}m. Post sintering annealing in a region of stability for the desired phase converts the second phases and limits grain growth. The method of pinning grain boundaries by small scale decompositive products and then annealing to convert its product to the desired phase can be used for other complex asides. Such a microstructure results in reduced microcracking, strengths as high as 230 MPa and high critical current density capacity. 25 figures.

Method of manufacture of single phase ceramic superconductors

DOEpatents

Singh, Jitrenda P.; Poeppel, Roger B.; Goretta, Kenneth C.; Chen, Nan

1995-01-01

A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa.sub.2 Cu.sub.3 O.sub.x indicates that sintering kinetics are enhanced at reduced p(O.sub.2) and that because of second phase precipitates, grain growth is prevented. The density of specimens sintered at 910.degree. C. increased from 79 to 94% theoretical when p(O.sub.2) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O.sub.2) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910.degree. C resulted in a fine-grain microstructure, with an average grain size of about 4 .mu.m. Post sintering annealing in a region of stability for the desired phase converts the second phases and limits grain growth. The method of pinning grain boundaries by small scale decompositive products and then annealing to convert its product to the desired phase can be used for other complex asides. Such a microstructure results in reduced microcracking, strengths as high as 230 MPa and high critical current density capacity.

Fabrication of Ce3+ doped Gd3Ga3Al2O12 ceramics by reactive sintering method

NASA Astrophysics Data System (ADS)

Ye, Yong; Liu, Peng; Yan, Dongyue; Xu, Xiaodong; Zhang, Jian

2017-09-01

Ce3+ doped Gd3Ga3Al2O12 (Ce:GGAG) ceramics were fabricated by solid state reactive sintering method in this study. The ceramics were pre-sintered in normal muffle furnace in air at various temperature range from 1410 °C to 1550 °C for 10 h and post-treated by hot isostatic press at 1400 °C/2 h in 200 MPa Ar. The phase and microstructure evolution of Ce: GGAG samples during the densification process were investigated by X-ray diffraction and scanning electron microscope. Pure GGAG phase appeared with the temperature increased to 1200 °C. The fully dense and translucent GGAG ceramics were fabricated by pre-sintering at 1450 °C and followed by HIP treatment.

Studies of Plasma-Sprayed Alumina

NASA Astrophysics Data System (ADS)

Ilavsky, Jan

1994-05-01

Phase transformations and porosity of the plasma sprayed alumina deposits were examined. The dependence of the phase transformations on deposit chemistry was established. Porosity changes during heat treatment were studied and a model for the porosity is proposed. A novel technique in the field of plasma sprayed deposits--small-angle neutron scattering (SANS)--was successfully applied. Deposits were manufactured using the water-stabilized plasma spray system, PAL160, with an input of 160 kW. Phase transformations of the plasma sprayed alumina deposits were studied using XRD and DTA. The deposits were manufactured from 99.9% alumina, alumina-chromia (1.5% Cr_2O_3), gray alumina (3.7% TiO_2) and alumina -titania (17% TiO_2). The addition of chromia increases the temperature of the alpha phase formation by about 40^circ C and the addition of TiO_2 reduces this temperature by about 150^circ C for gray alumina and by about 175^ circC for alumina-titania. The amount of metastable theta phase was found to depend on the chemistry of the feedstock. Porosities of the deposits, made from alumina and gray alumina, were studied using mercury intrusion porosimetry, weighing method (Archimedean porosimetry), image analysis and SANS. Samples were studied in the as -sprayed condition and after heat treatment for 2 hours at 1300^circC and 1500 ^circC. Porosity depends on the deposit chemistry and on the heat treatment and varies from 5% to about 11%. Different porosity measurement techniques yield different results. Surface areas of 1.5 to 7.5 times 10^4 cm^2 /cm^3 (times 10^6 m^{ -1}) were measured using SANS and depend on heat treatment and on the deposit chemistry. The phase transformations can be associated with an increase in pore surface area and decrease in surface area at 1500 ^circC can be associated with sintering. The effective pore radius, R_{ rm eff}, as measured by SANS is a measure of the pore sizes in the 0.08 to 10 μm size range. The R_{rm eff} depends on deposit chemistry and is about 0.7 to 0.9 μm for all deposits, but the gray alumina deposit, heat treated at 1500^ circC for 2h, exhibits an R_ {rm eff} of 2.2 mu m. This increase can be associated with sintering.

Thermal barrier coating life-prediction model development. Annual report no. 2

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

Strangman, T. E.; Neumann, J.; Liu, A.

1986-10-01

The program focuses on predicting the lives of two types of strain-tolerant and oxidation-resistant thermal barrier coating (TBC) systems that are produced by commercial coating suppliers to the gas turbine industry. The plasma-sprayed TBC system, composed of a low-pressure plasma-spray (LPPS) or an argon shrouded plasma-spray (ASPS) applied oxidation resistant NiCrAlY or (CoNiCrAlY) bond coating and an air-plasma-sprayed yttria partially stabilized zirconia insulative layer, is applied by both Chromalloy, Klock, and Union Carbide. The second type of TBS is applied by the electron beam-physical vapor deposition (EB-PVD) process by Temescal. The second year of the program was focused on specimenmore » procurement, TMC system characterization, nondestructive evaluation methods, life prediction model development, and TFE731 engine testing of thermal barrier coated blades. Materials testing is approaching completion. Thermomechanical characterization of the TBC systems, with toughness, and spalling strain tests, was completed. Thermochemical testing is approximately two-thirds complete. Preliminary materials life models for the bond coating oxidation and zirconia sintering failure modes were developed. Integration of these life models with airfoil component analysis methods is in progress. Testing of high pressure turbine blades coated with the program TBS systems is in progress in a TFE731 turbofan engine. Eddy current technology feasibility was established with respect to nondestructively measuring zirconia layer thickness of a TBC system.« less

Method for fabricating prescribed flaws in the interior of metals

DOEpatents

Hsu, David K.; Thompson, Donald O.

1989-03-07

The method for fabricating a metal body having a flaw of predetermined size and shape located therein comprises placing half of the metal powder required to make the metal body in the die of a press and pressing it to create a flat upper surface thereon. A piece of copper foil is cut to the size and shape of the desired interior crack and placed on the upper surface of the powder and centered in position. The remaining powder is then placed in the die to cover the copper foil. The powder is first cold pressed and removed from the press. The powder metal piece is then sintered in a furnace at a temperature above the melting point of the copper and below the melting point of the metal. It is then removed from the furnace, cooled to room temperature, and placed back in the die and pressed further. This procedure results in an interior flaw or crack. Modified forms of the method involve using a press-sinter-press-sinter cycle with the first sinter being below the melting point of the copper and the second sinter being above the melting point of the copper and below the melting point of the metal.

Effect of Soft Phase on Magnetic Properties of Bulk Sm-Co/alpha-Fe Nanocomposite Magnets (Postprint)

DTIC Science & Technology

2012-11-01

plasma sintering , and warm compaction [4][5]–[9]. In our previous study [10], bulk Sm–Co –Fe nanocomposite magnets were fabricated by hot pressing of...no. 5, pp. 2974–2976, Jul. 2003. [8] T. Saito and H. Miyoshi, “Magnetic properties of Sm5Fe17/Fe com- posite magnets produces by spark plasma ...Fe and Fe-Co. Bulk composite magnets have been prepared using compaction techniques such as hot pressing/deforma- tion, dynamic shock compaction, spark

Microstructure, Mechanical and Tribological Properties of Oxide Dispersion Strengthened High-Entropy Alloys.

PubMed

Liu, Xinyu; Yin, Hangboce; Xu, Yi

2017-11-15

A novel metal matrix composite CrMnFeCoNi with Y₂O₃ as reinforcement phase was designed and manufactured by mechanical alloying and spark plasma sintering. After sintering at 900 °C for 5 min, the microstructure consisted of a FCC matrix and Y₂O₃ nanoparticles. The addition of 0.25 wt % Y₂O₃ increased the room temperature tensile strength of the CrMnFeCoNi base from 868 MPa to 1001 MPa, while the mechanical properties of the addition of 0.5 wt % Y₂O₃ composite decreased. In the meantime, the addition of Y₂O₃ had no significant influence on the coefficient of friction, while the addition of 0.25 wt % Y₂O₃ composite shows excellent wear-resistance.

Fast plasma sintering delivers functional graded materials components with macroporous structures and osseointegration properties.

PubMed

Godoy, R F; Coathup, M J; Blunn, G W; Alves, A L; Robotti, P; Goodship, A E

2016-04-13

We explored the osseointegration potential of two macroporous titanium surfaces obtained using fast plasma sintering (FPS): Ti macroporous structures with 400-600 µmØ pores (TiMac400) and 850-1000 µmØ pores (TiMac850). They were compared against two surfaces currently in clinical use: Ti-Growth® and air plasma spray (Ti-Y367). Each surface was tested, once placed over a Ti-alloy and once onto a CoCr bulk substrate. Implants were placed in medial femoral condyles in 24 sheep. Samples were explanted at four and eight weeks after surgery. Push-out loads were measured using a material-testing system. Bone contact and ingrowth were assessed by histomorphometry and SEM and EDX analyses. Histology showed early osseointegration for all the surfaces tested. At 8 weeks, TiMac400, TiMac850 and Ti-Growth® showed deep bone ingrowth and extended colonisation with newly formed bone. The mechanical push-out force was equal in all tested surfaces. Plasma spray surfaces showed greater bone-implant contact and higher level of pores colonisation with new bone than FPS produced surfaces. However, the void pore area in FPS specimens was significantly higher, yet the FPS porous surfaces allowed a deeper osseointegration of bone to implant. FPS manufactured specimens showed similar osseointegration potential to the plasma spray surfaces for orthopaedic implants. FPS is a useful technology for manufacturing macroporous titanium surfaces. Furthermore, its capability to combine two implantable materials, using bulk CoCr with macroporous titanium surfaces, could be of interest as it enables designers to conceive and manufacture innovative components. FPS delivers functional graded materials components with macroporous structures optimised for osseointegration.

Hydrogen Plasma Processing of Iron Ore

NASA Astrophysics Data System (ADS)

Sabat, Kali Charan; Murphy, Anthony B.

2017-06-01

Iron is currently produced by carbothermic reduction of oxide ores. This is a multiple-stage process that requires large-scale equipment and high capital investment, and produces large amounts of CO2. An alternative to carbothermic reduction is reduction using a hydrogen plasma, which comprises vibrationally excited molecular, atomic, and ionic states of hydrogen, all of which can reduce iron oxides, even at low temperatures. Besides the thermodynamic and kinetic advantages of a hydrogen plasma, the byproduct of the reaction is water, which does not pose any environmental problems. A review of the theory and practice of iron ore reduction using a hydrogen plasma is presented. The thermodynamic and kinetic aspects are considered, with molecular, atomic and ionic hydrogen considered separately. The importance of vibrationally excited hydrogen molecules in overcoming the activation energy barriers, and in transferring energy to the iron oxide, is emphasized. Both thermal and nonthermal plasmas are considered. The thermophysical properties of hydrogen and argon-hydrogen plasmas are discussed, and their influence on the constriction and flow in the of arc plasmas is considered. The published R&D on hydrogen plasma reduction of iron oxide is reviewed, with both the reduction of molten iron ore and in-flight reduction of iron ore particles being considered. Finally, the technical and economic feasibility of the process are discussed. It is shown that hydrogen plasma processing requires less energy than carbothermic reduction, mainly because pelletization, sintering, and cokemaking are not required. Moreover, the formation of the greenhouse gas CO2 as a byproduct is avoided. In-flight reduction has the potential for a throughput at least equivalent to the blast furnace process. It is concluded that hydrogen plasma reduction of iron ore is a potentially attractive alternative to standard methods.

Cracks and nanodroplets produced on tungsten surface samples by dense plasma jets

NASA Astrophysics Data System (ADS)

Ticoş, C. M.; Galaţanu, M.; Galaţanu, A.; Luculescu, C.; Scurtu, A.; Udrea, N.; Ticoş, D.; Dumitru, M.

2018-03-01

Small samples of 12.5 mm in diameter made from pure tungsten were exposed to a dense plasma jet produced by a coaxial plasma gun operated at 2 kJ. The surface of the samples was analyzed using a scanning electron microscope (SEM) before and after applying consecutive plasma shots. Cracks and craters were produced in the surface due to surface tensions during plasma heating. Nanodroplets and micron size droplets could be observed on the samples surface. An energy-dispersive spectroscopy (EDS) analysis revealed that the composition of these droplets coincided with that of the gun electrode material. Four types of samples were prepared by spark plasma sintering from powders with the average particle size ranging from 70 nanometers up to 80 μm. The plasma power load to the sample surface was estimated to be ≈4.7 MJ m-2 s-1/2 per shot. The electron temperature and density in the plasma jet had peak values 17 eV and 1.6 × 1022 m-3, respectively.

Understanding proton-conducting perovskite interfaces using atom probe tomography

NASA Astrophysics Data System (ADS)

Clark, Daniel R.

Proton-conducting ceramics are under intense scientific investigation for a number of exciting applications, including fuel cells, electrolyzers, hydrogen separation membranes, membrane reactors, and sensors. However, commercial application requires deeper understanding and improvement of proton conductivity in these materials. It is well-known that proton conductivity in these materials is often limited by highly resistive grain boundaries (GBs). While these conductivity-limiting GBs are still not well understood, it is hypothesized that their blocking nature stems from the formation of a positive (proton-repelling) space-charge zone. Furthermore, it has been observed that the strength of the blocking behavior can change dramatically depending on the fabrication process used to make the ceramic. This thesis applies laser-assisted atom probe tomography (LAAPT) to provide new insights into the GB chemistry and resulting space-charge behavior of BaZr0.9Y0.1O 3--delta (BZY10), a prototypical proton-conducting ceramic. LAAPT is an exciting characterization technique that allows for three-dimensional nm-scale spatial resolution and very high chemical resolution (up to parts-per-million). While it is challenging to quantitatively apply LAAPT to complex, multi-cation oxide materials, this thesis successfully develops a method to accurately quantify the stoichiometry of BZY10 and maintain minimal quantitative cationic deviation at a laser energies of approximately 10--20 pJ. With the analysis technique specifically optimized for BZY10, GB chemistry is then examined for BZY10 samples prepared using four differing processing methods: (1) spark plasma sintering (SPS), (2) conventional sintering using powder prepared by solid-state reaction followed by high-temperature annealing (HT), (3) conventional sintering using powder prepared by solid-state reaction with NiO used as a sintering aid (SSR-Ni), and (4) solid-state reactive sintering directly from BaCO3, ZrO2, and Y2O3 precursor powders with 1 wt. % NiO as a reactive sintering aid (SSRS-Ni). It is observed that oxygen depletion (oxygen-vacancy accumulation) occurs at all GBs. Segregation of the constituent cations, Ba, Zr, and Y, is found to be variable across all samples although zirconium depletion and yttrium accumulation are most prevalent. Additionally, impurities such as Al, Fe, Mg, Ni, Si, and Sr are shown to generally accumulate at the GBs. Finally, LAAPT-derived GB chemistry data is combined with electrostatic modeling to examine the electronic structure of a BZY10 GB, revealing significant non-uniformity in the space charge region at the GB with an average space-charge potential of approximately 580 mV, extending 5--7 nm in width from the GB core. This result demonstrates how LAAPT can not only be used to further understand the role of GB chemistry within oxide materials, but can also be used to examine the electronic structure, allowing for the possibility of engineering these interfaces to improve their electrochemical performance.

Effect on the grain size of single-mode microwave sintered NiCuZn ferrite and zinc titanate dielectric resonator ceramics.

PubMed

Sirugudu, Roopas Kiran; Vemuri, Rama Krishna Murthy; Venkatachalam, Subramanian; Gopalakrishnan, Anisha; Budaraju, Srinivasa Murty

2011-01-01

Microwave sintering of materials significantly depends on dielectric, magnetic and conductive Losses. Samples with high dielectric and magnetic loss such as ferrites could be sintered easily. But low dielectric loss material such as dielectric resonators (paraelectrics) finds difficulty in generation of heat during microwave interaction. Microwave sintering of materials of these two classes helps in understanding the variation in dielectric and magnetic characteristics with respect to the change in grain size. High-energy ball milled Ni0.6Cu0.2Zn0.2Fe1.98O4-delta and ZnTiO3 are sintered in conventional and microwave methods and characterized for respective dielectric and magnetic characteristics. The grain size variation with higher copper content is also observed with conventional and microwave sintering. The grain size in microwave sintered Ni0.6Cu0.2Zn0.2Fe1.98O4-delta is found to be much small and uniform in comparison with conventional sintered sample. However, the grain size of microwave sintered sample is almost equal to that of conventional sintered sample of Ni0.3Cu0.5Zn0.2Fe1.98O4-delta. In contrast to these high dielectric and magnetic loss ferrites, the paraelectric materials are observed to sinter in presence of microwaves. Although microwave sintered zinc titanate sample showed finer and uniform grains with respect to conventional samples, the dielectric characteristics of microwave sintered sample are found to be less than that of conventional sample. Low dielectric constant is attributed to the low density. Smaller grain size is found to be responsible for low quality factor and the presence of small percentage of TiO2 is observed to achieve the temperature stable resonant frequency.

Structural and mechanical characterization of boron doped biphasic calcium phosphate produced by wet chemical method and subsequent thermal treatment

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

Albayrak, Onder, E-mail: albayrakonder@mersin.edu.tr

In the current study, boron doped biphasic calcium phosphate bioceramics consisting of a mixture of boron doped hydroxyapatite (BHA) and beta tricalcium phosphate (β-TCP) of varying BHA/β-TCP ratios were obtained after sintering stage. The effects of varying boron contents and different sintering temperatures on the BHA/β-TCP ratios and on the sinterability of the final products were investigated. Particle sizes and morphologies of the obtained precipitates were determined using SEM. XRD and FTIR investigation were conducted to detect the boron formation in the structure of HA and quantitative analysis was performed to determine the BHA/β-TCP ratio before and after sintering stage.more » In order to determine the sinterability of the obtained powders, pellets were prepared and sintered; the rates of densification were calculated and obtained results were correlated by SEM images. Also Vickers microhardness values of the sintered samples were determined. The experimental results verified that boron doped hydroxyapatite powders were obtained after sintering stage and the structure consists of a mixture of BHA and β-TCP. As the boron content used in the precipitation stage increases, β-TCP content of the BHA/β-TCP ratio increases but sinterability, density and microhardness deteriorate. As the sintering temperature increases, β-TCP content, density and microhardness of the samples increase and sinterability improves. - Highlights: • This is the first paper about boron doped biphasic calcium phosphate bioceramics. • Boron doping affects the structural and mechanical properties. • BHA/β-TCP ratio can be adjustable with boron content and sintering temperature.« less

Applying Massively Parallel Kinetic Monte Carlo Methods to Simulate Grain Growth and Sintering in Powdered Metals

DTIC Science & Technology

2011-09-01

Structure Evolution During Sintering From [19]. ...................................20 Figure 10. Ising Model Configuration With Eight Nearest Neighbors...INTRODUCTION A. MOTIVATION The ability to fabricate structural components from metals with a fine (micron- sized), controlled grain size is one of the...hallmarks of modern, structural metallurgy. Powder metallurgy, in particular, consists of powder manufacture, powder blending, compacting, and sintering

Compositional Design of Dielectric, Ferroelectric and Piezoelectric Properties of (K, Na)NbO₃ and (Ba, Na)(Ti, Nb)O₃ Based Ceramics Prepared by Different Sintering Routes.

PubMed

Eiras, José A; Gerbasi, Rosimeire B Z; Rosso, Jaciele M; Silva, Daniel M; Cótica, Luiz F; Santos, Ivair A; Souza, Camila A; Lente, Manuel H

2016-03-08

Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO₃, such as (K, Na)NbO₃ (KNN) and (Ba, Na)(Ti, Nb)O₃ (BTNN) families. From a ceramic processing point of view, high density single phase KNN and BTNN ceramics are very difficult to sinter due to the volatility of the alkaline elements, the narrow sintering temperature range and the anomalous grain growth. In this work, Spark Plasma Sintering (SPS) and high-energy ball milling (HEBM), following heat treatments (calcining and sintering), in oxidative (O₂) atmosphere have been used to prepare single phase highly densified KNN ("pure" and Cu 2+ or Li 1+ doped), with theoretical densities ρ th > 97% and BTNN ceramics (ρ th - 90%), respectively. Using BTTN ceramics with a P 4 mm perovskite-like structure, we showed that by increasing the NaNbO₃ content, the ferroelectric properties change from having a relaxor effect to an almost "normal" ferroelectric character, while the tetragonality and grain size increase and the shear piezoelectric coefficients ( k 15 , g 15 and d 15 ) improve. For KNN ceramics, the results reveal that the values for remanent polarization as well as for most of the coercive field are quite similar among all compositions. These facts evidenced that Cu 2+ may be incorporated into the A and/or B sites of the perovskite structure, having both hardening and softening effects.

Method of forming and assembly of parts

DOEpatents

Ripley, Edward B.

2010-12-28

A method of assembling two or more parts together that may be metal, ceramic, metal and ceramic parts, or parts that have different CTE. Individual parts are formed and sintered from particles that leave a network of interconnecting porosity in each sintered part. The separate parts are assembled together and then a fill material is infiltrated into the assembled, sintered parts using a method such as capillary action, gravity, and/or pressure. The assembly is then cured to yield a bonded and fully or near-fully dense part that has the desired physical and mechanical properties for the part's intended purpose. Structural strength may be added to the parts by the inclusion of fibrous materials.

Development of a sintering process for recycling oil shale fly ash and municipal solid waste incineration bottom ash into glass ceramic composite

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

Zhang, Zhikun; Zhang, Lei; Li, Aimin, E-mail: leeam@dlut.edu.cn

Highlights: • Glass ceramic composite is prepared from oil shale fly ash and MSWI bottom ash. • A novel method for the production of glass ceramic composite is presented. • It provides simple route and lower energy consumption in terms of recycling waste. • The vitrified slag can promote the sintering densification process of glass ceramic. • The performances of products decrease with the increase of oil shale fly ash content. - Abstract: Oil shale fly ash and municipal solid waste incineration bottom ash are industrial and municipal by-products that require further treatment before disposal to avoid polluting the environment.more » In the study, they were mixed and vitrified into the slag by the melt-quench process. The obtained vitrified slag was then mixed with various percentages of oil shale fly ash and converted into glass ceramic composites by the subsequent sintering process. Differential thermal analysis was used to study the thermal characteristics and determine the sintering temperatures. X-ray diffraction analysis was used to analyze the crystalline phase compositions. Sintering shrinkage, weight loss on ignition, density and compressive strength were tested to determine the optimum preparation condition and study the co-sintering mechanism of vitrified amorphous slag and oil shale fly ash. The results showed the product performances increased with the increase of sintering temperatures and the proportion of vitrified slag to oil shale fly ash. Glass ceramic composite (vitrified slag content of 80%, oil shale fly ash content of 20%, sintering temperature of 1000 °C and sintering time of 2 h) showed the properties of density of 1.92 ± 0.05 g/cm{sup 3}, weight loss on ignition of 6.14 ± 0.18%, sintering shrinkage of 22.06 ± 0.6% and compressive strength of 67 ± 14 MPa. The results indicated that it was a comparable waste-based material compared to previous researches. In particular, the energy consumption in the production process was reduced compared to conventional vitrification and sintering method. Chemical resistance and heavy metals leaching results of glass ceramic composites further confirmed the possibility of its engineering applications.« less

Low temperature sintered giant dielectric permittivity CaCu3Ti4O12 sol-gel synthesized nanoparticle capacitors

NASA Astrophysics Data System (ADS)

Puli, Venkata Sreenivas; Adireddy, Shiva; Kothakonda, Manish; Elupula, Ravinder; Chrisey, Douglas B.

This paper reports on synthesis of polycrystalline complex perovskite CaCu3Ti4O12 (as CCTO) ceramic powders prepared by a sol-gel auto combustion method at different sintering temperatures and sintering times, respectively. The effect of sintering time on the structure, morphology, dielectric and electrical properties of CCTO ceramics is investigated. Tuning the electrical properties via different sintering times is demonstrated for ceramic samples. X-ray diffraction (XRD) studies confirm perovskite-like structure at room temperature. Abnormal grain growth is observed for ceramic samples. Giant dielectric permittivity was realized for CCTO ceramics. High dielectric permittivity was attributed to the internal barrier layer capacitance (IBLC) model associated with the Maxwell-Wagner (MW) polarization mechanism.

Study of structural and magnetic properties of cobalt ferrite nanoparticles sintered at different temperature

NASA Astrophysics Data System (ADS)

Kumari, Mukesh; Bhatnagar, Mukesh Chander

2018-05-01

Cobalt ferrite (CFO) has been synthesized in the form of nanoparticles (NPs) through sol-gel auto-combustion method. The prepared NPs of CFO were sintered for four hours at various temperatures from 300°C to 900°C. The physical properties of the sintered samples have been optimized using X-ray diffraction (XRD), Raman spectroscopy and physical properties measurement system (PPMS). The XRD and Raman studies have confirmed the cubic spinel phase formation of CFO NPs. XRD results showed that as we increase the sintering temperature the crystallite size of particles increases. Whereas the magnetic studies revealed that the saturation magnetization (MS) increases while the coercivity (HC) of nanoparticles decreases with increase of sintering temperature.

Study on selective laser sintering of glass fiber reinforced polystyrene

NASA Astrophysics Data System (ADS)

Yang, Laixia; Wang, Bo; Zhou, Wenming

2017-12-01

In order to improve the bending strength of Polystyrene (PS) sintered parts by selective laser sintering, Polystyrene/glass fiber (PS/GF) composite powders were prepared by mechanical mixing method. The size distribution of PS/GF composite powders was characterized by laser particle size analyzer. The optimum ratio of GF was determined by proportioning sintering experiments. The influence of process parameters on the bending strength of PS and PS/GF sintered parts was studied by orthogonal test. The result indicates that the particle size of PS/GF composite powder is mainly distributed in 24.88 μm~139.8 μm. When the content of GF is 10%, it has better strengthen effect. Finally, the article used the optimum parameter of the two materials to sinter prototype, it is found that the PS/GF prototype has the advantages of good accuracy and high strength.

Sintered silver joints via controlled topography of electronic packaging subcomponents

DOEpatents

Wereszczak, Andrew A.

2014-09-02

Disclosed are sintered silver bonded electronic package subcomponents and methods for making the same. Embodiments of the sintered silver bonded EPSs include topography modification of one or more metal surfaces of semiconductor devices bonded together by the sintered silver joint. The sintered silver bonded EPSs include a first semiconductor device having a first metal surface, the first metal surface having a modified topography that has been chemically etched, grit blasted, uniaxial ground and/or grid sliced connected to a second semiconductor device which may also include a first metal surface with a modified topography, a silver plating layer on the first metal surface of the first semiconductor device and a silver plating layer on the first metal surface of the second semiconductor device and a sintered silver joint between the silver plating layers of the first and second semiconductor devices which bonds the first semiconductor device to the second semiconductor device.

In vitro biodegradation testing of Mg-alloy EZK400 and manufacturing of implant prototypes using PM (powder metallurgy) methods.

PubMed

Wolff, M; Luczak, M; Schaper, J G; Wiese, B; Dahms, M; Ebel, T; Willumeit-Römer, R; Klassen, T

2018-09-01

The study is focussing towards Metal Injection Moulding (MIM) of Mg-alloys for biomedical implant applications. Especially the influence of the sintering processing necessary for the consolidation of the finished part is in focus of this study. In doing so, the chosen high strength EZK400 Mg-alloy powder material was sintered using different sintering support bottom plate materials to evaluate the possibility of iron impurity pick up during sintering. It can be shown that iron pick up took place from the steel bottom plate into the specimen. Despite the fact that a separating boron nitrite (BN) barrier layer was used and the Mg-Fe phase diagram is not predicting any significant solubility to each other. As a result of this study a new bottom plate material not harming the sintering and the biodegradation performance of the as sintered material, namely a carbon plate material, was found.

Effect of sandblasting on surface roughness of zirconia-based ceramics and shear bond strength of veneering porcelain.

PubMed

He, Min; Zhang, Zutai; Zheng, Dongxiang; Ding, Ning; Liu, Yan

2014-01-01

This study aims to investigate the effect of sandblasting on the surface roughness of zirconia and the shear bond strength of the veneering porcelain. Pre-sintered zirconia plates were prepared and divided into four groups. Group A were not treated at all; group B were first sandblasted under 0.2 MPa pressure and then densely sintered; group C and D were sintered first, and then sandblasted under 0.2 MPa and 0.4 MPa pressures respectively. Surface roughness was measured and 3D roughness was reconstructed for the specimens, which were also analyzed with X-ray diffractometry. Finally after veneering porcelain sintering, shear bond tests were conducted. Sandblasting zirconia before sintering significantly increased surface roughness and the shear bond strength between zirconia and veneering porcelain (p<0.05). Sandblasting zirconia before sintering is a useful method to increase surface roughness and could successfully improve the bonding strength of veneering porcelain.

Sintering Behavior of Hypereutectic Aluminum-Silicon Metal Matrix Composites Powder

NASA Astrophysics Data System (ADS)

Rudianto, Haris; Sun, Yang Sang; Jin, Kim Yong; Woo, Nam Ki

Lightweight materials of Aluminum-Silicon P/M alloys offer the advantage of high-wear resistance, high strength, good temperature resistance, and a low coefficient of thermal expansion. An A359 MMC alloy was mixed together with Alumix 231 in this research. Powders were compacted with compaction pressure up to 700 MPa. Particle size and compaction pressure influenced green density. Compacted powders were sintered in a tube furnace under a flowing nitrogen gas. Sintering temperature, heating rate and sintering time were verified to determine best sintering conditions of the alloys. Chemical composition also contributed to gain higher sintered density. Precipitation strengthening method was used to improve mechanical properties of this materials.T6 heat treatment was carried out to produce fine precipitates to impede movement of dislocation. The chemical composition of this materials allow for the potential formation of several strengthening precipitates including θ (Al2Cu) and β (Mg2Si).

Erosion Performance of Gadolinium Zirconate-Based Thermal Barrier Coatings Processed by Suspension Plasma Spray

NASA Astrophysics Data System (ADS)

Mahade, Satyapal; Curry, Nicholas; Björklund, Stefan; Markocsan, Nicolaie; Nylén, Per; Vaßen, Robert

2017-01-01

7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM.

Data on processing of Ti-25Nb-25Zr β-titanium alloys via powder metallurgy route: Methodology, microstructure and mechanical properties.

PubMed

Ueda, D; Dirras, G; Hocini, A; Tingaud, D; Ameyama, K; Langlois, P; Vrel, D; Trzaska, Z

2018-04-01

The data presented in this article are related to the research article entitled "Cyclic Shear behavior of conventional and harmonic structure-designed Ti-25Nb-25Zr β-titanium alloy: Back-stress hardening and twinning inhibition" (Dirras et al., 2017) [1]. The datasheet describes the methods used to fabricate two β-titanium alloys having conventional microstructure and so-called harmonic structure (HS) design via a powder metallurgy route, namely the spark plasma sintering (SPS) route. The data show the as-processed unconsolidated powder microstructures as well as the post-SPS ones. The data illustrate the mechanical response under cyclic shear loading of consolidated alloy specimens. The data show how electron back scattering diffraction(EBSD) method is used to clearly identify induced deformation features in the case of the conventional alloy.

Beam limiter for thermonuclear fusion devices

DOEpatents

Kaminsky, Manfred S.

1976-01-01

A beam limiter circumscribes the interior surface of a vacuum vessel to inhibit collisions of contained plasma and the vessel walls. The cross section of the material making up the limiter has a flatsided or slightly concave portion of increased width towards the plasma and portions of decreased width towards the interior surface of the vessel. This configuration is designed to prevent a major fraction of the material sputtered, vaporized and blistered from the limiter from reaching the plasma. It also allows adequate heat transfer from the wider to the narrower portions. The preferred materials for the beam limiter are solids of sintered, particulate materials of low atomic number with low vapor pressure and low sputtering and blistering yields.

Spark Plasma Sintering of Load-Bearing Iron-Carbon Nanotube-Tricalcium Phosphate CerMets for Orthopaedic Applications

NASA Astrophysics Data System (ADS)

Montufar, Edgar B.; Horynová, Miroslava; Casas-Luna, Mariano; Diaz-de-la-Torre, Sebastián; Celko, Ladislav; Klakurková, Lenka; Spotz, Zdenek; Diéguez-Trejo, Guillermo; Fohlerová, Zdenka; Dvorak, Karel; Zikmund, Tomáš; Kaiser, Jozef

2016-04-01

Recently, ceramic-metallic composite materials (CerMets) have been investigated for orthopaedic applications with promising results. This first generation of bio-CerMets combine the bioactivity of hydroxyapatite with the mechanical stability of titanium to fabricate bioactive, tough and biomechanically more biocompatible osteosynthetic devices. Nonetheless, these first CerMets are not biodegradable materials and a second surgery is required to remove the implant after bone healing. The present work aims to develop the next generation bio-CerMets, which are potential biodegradable materials. The process to produce the new biodegradable CerMet consisted of mixing powder of soluble and osteoconductive alpha tricalcium phosphate with biocompatible and biodegradable iron with consolidation through spark plasma sintering (SPS). The microstructure, composition and mechanical strength of the new CerMet were studied by metallography, x-ray diffraction and diametral tensile strength tests, respectively. The results show that SPS produces CerMet with higher mechanical performance (120 MPa) than the ceramic component alone (29 MPa) and similar mechanical strength to the pure metallic component (129 MPa). Nonetheless, although a short sintering time (10 min) was used, partial transformation of the alpha tricalcium phosphate into its allotropic and slightly less soluble beta phase was observed. Cell adhesion tests show that osteoblasts are able to attach to the CerMet surface, presenting spread morphology regardless of the component of the material with which they are in contact. However, the degradation process restricted to the small volume of the cell culture well quickly reduces the osteoblast viability.

Evaluation of consolidation method on mechanical and structural properties of ODS RAF steel

NASA Astrophysics Data System (ADS)

Frelek-Kozak, M.; Kurpaska, L.; Wyszkowska, E.; Jagielski, J.; Jozwik, I.; Chmielewski, M.

2018-07-01

In the present work, the effects of the fabrication method on mechanical and structural properties of 12%Cr, 2%W, 0.25%Ti, 0.25%Y2O3 steels were investigated. Materials obtained by Spark Plasma Sintering (SPS), Hot Isostatic Pressing (HIP) and Hot Extrusion (HE) methods were studied. The microstructure was characterized by using Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction analysis (EBSD). Mechanical properties of the studied samples were evaluated by using Vickers micro hardness HV0.1, Small Punch Test (SPT) and nanoindentation (NI) methods. The analysis revealed that samples manufactured via HIP and SPS processes exhibit very similar properties, whereas SPS method produces material with slightly lower hardness. In addition, significantly lower mechanical properties of the specimens after HE process were observed. The study described in this article addresses also the problems of mechanical parameters measured in micro- and nano-scale experiments and aims to identify possible pitfalls related to the use of various manufacturing technologies.

Synthesis and characterization of nanocrystalline Nd{sup 3+}-doped gadolinium scandium aluminum garnet powders by a gel-combustion method

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

Su, Jing, E-mail: zlj007@126.com; Miao, Ju-hong; Xu, Lin-hua

2012-07-15

Graphical abstract: The graph shows the emission spectra (λ{sub ex} = 808 nm) of 1 at.% Nd:GSAG powders sintered at different temperatures for 3 h. Compared with the powder sintered at 900 °C, the PL intensity of the powder sintered at 1000 °C decreased significantly. The changes in the PL intensity should mainly due to the crystallinity and dispersion of the powders. Highlights: ► We synthesized Nd:GSAG nano-powders by gel-combustion method successfully. ► We analyzed the structure and the morphology of the heat-treated products. ► We studied the optical characteristics of Nd:GSAG nano-powders. -- Abstract: Nd{sup 3+}-doped gadolinium scandium aluminummore » garnet (Nd:GSAG) precursor was synthesized by a gel combustion method using metal nitrates and citric acid as raw materials. The structure and morphology of the precursor and the sintered powders were studied by means of X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). The results showed that the precursor transformed into pure GSAG polycrystalline phase at about 800 °C, and the powders sintered at 800–1000 °C were well-dispersed with average particle sizes in the range of 30–80 nm. Optical properties of Nd:GSAG nano-powders were characterized by using photoluminescence spectroscopy. The highest photoluminescence intensity was achieved for the powder sintered at 900 °C.« less

Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated by Selective Laser Melting of Powder Produced by Granulation-Sintering-Deoxygenation Method

NASA Astrophysics Data System (ADS)

Sun, Pei; Fang, Z. Zak; Zhang, Ying; Xia, Yang

2017-12-01

Commercial spherical Ti powders for additive manufacturing applications are produced today by melt-atomization methods at relatively high costs. A meltless production method, called granulation-sintering-deoxygenation (GSD), was developed recently to produce spherical Ti alloy powder at a significantly reduced cost. In this new process, fine hydrogenated Ti particles are agglomerated to form spherical granules, which are then sintered to dense spherical particles. After sintering, the solid fully dense spherical Ti alloy particles are deoxygenated using novel low-temperature deoxygenation processes with either Mg or Ca. This technical communication presents results of 3D printing using GSD powder and the selective laser melting (SLM) technique. The results showed that tensile properties of parts fabricated from spherical GSD Ti-6Al-4V powder by SLM are comparable with typical mill-annealed Ti-6Al-4V. The characteristics of 3D printed Ti-6Al-4V from GSD powder are also compared with that of commercial materials.

Preparation of W–Sc{sub 2}O{sub 3} targets and scandate cathodes with film prepared by pulsed laser deposition

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

Zhang, Xizhu; Wang, Jinshu, E-mail: wangjsh@bjut.edu.cn; Liu, Wei

2013-12-15

Graphical abstract: - Highlights: • W–Sc{sub 2}O{sub 3} film containing 5% Sc{sub 2}O{sub 3} and 95% W were prepared by pulsed laser deposition. • W–Sc{sub 2}O{sub 3} film on scandate cathode surface improves emission property. • The film improves Sc distribution uniformity and is favorable for forming Ba–Sc–O layer. - Abstract: Sub-micrometer Sc{sub 2}O{sub 3}–W powder with a narrow particle size distribution has been obtained by a sol–gel method combined with two-step hydrogen reduction process. Based on the obtained powder, the W–Sc{sub 2}O{sub 3} targets have been sintered via spark plasma sintering (SPS) at 1300 °C. The W–Sc{sub 2}O{sub 3}more » targets have the average grain size of about 1 μm. Both the sintering temperature and holding time are much lower than those of the targets prepared with micrometer sized powders. The obtained W–Sc{sub 2}O{sub 3} targets have a high comparative density of 96.4% and rockwell hardness of 86.4 HRC. Using the target, the scandate cathode deposited with a film containing 5% Sc{sub 2}O{sub 3} and 95% W has been obtained by pulsed laser deposition (PLD) method. This cathode has good emission property, i.e., the highest thermionic emission current density reaches 43.09 A/cm{sup 2} of J{sub div} at 900 °C{sub b} after being activated for 8 h, which is much higher than that of scandate cathode without film. Scandium (Sc) supplied by the film on the surface during the activation forms a Ba–Sc–O active layer, which helps to the emission.« less

Development of AlN and TiB2 Composites with Nb2O5, Y2O3 and ZrO2 as Sintering Aids

PubMed Central

González, José C.; Rodríguez, Miguel Á.; Figueroa, Ignacio A.; Villafuerte-Castrejón, María-Elena; Díaz, Gerardo C.

2017-01-01

The synthesis of AlN and TiB2 by spark plasma sintering (SPS) and the effect of Nb2O5, Y2O3 and ZrO2 additions on the mechanical properties and densification of the produced composites is reported and discussed. After the SPS process, dense AlN and TiB2 composites with Nb2O5, Y2O3 and ZrO2 were successfully prepared. X-ray diffraction analysis showed that in the AlN composites, the addition of Nb2O5 gives rise to Nb4N3 during sintering. The compound Y3Al5O12 (YAG) was observed as precipitate in the sample with Y2O3. X-ray diffraction analysis of the TiB2 composites showed TiB2 as a single phase in these materials. The maximum Vickers and toughness values were 14.19 ± 1.43 GPa and 27.52 ± 1.75 GPa for the AlN and TiB2 composites, respectively. PMID:28772681

Sintering of micro-trusses created by extrusion-3D-printing of lunar regolith inks

NASA Astrophysics Data System (ADS)

Taylor, Shannon L.; Jakus, Adam E.; Koube, Katie D.; Ibeh, Amaka J.; Geisendorfer, Nicholas R.; Shah, Ramille N.; Dunand, David C.

2018-02-01

The development of in situ fabrication methods for the infrastructure required to support human life on the Moon is necessary due to the prohibitive cost of transporting large quantities of materials from the Earth. Cellular structures, consisting of a regular network (truss) of micro-struts with ∼500 μm diameters, suitable for bricks, blocks, panels, and other load-bearing structural elements for habitats and other infrastructure are created by direct-extrusion 3D-printing of liquid inks containing JSC-1A lunar regolith simulant powders, followed by sintering. The effects of sintering time, temperature, and atmosphere (air or hydrogen) on the microstructures, mechanical properties, and magnetic properties of the sintered lunar regolith micro-trusses are investigated. The air-sintered micro-trusses have higher relative densities, linear shrinkages, and peak compressive strengths, due to the improved sintering of the struts within the micro-trusses achieved by a liquid or glassy phase. Whereas the hydrogen-sintered micro-trusses show no liquid-phase sintering or glassy phase, they contain metallic iron 0.1-2 μm particles from the reduction of ilmenite, which allows them to be lifted with magnets.

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

NASA Astrophysics Data System (ADS)

Sharma, Payal; Sharma, Chetan; Singh, Kanchan L.; Singh, Anirudh P.

2018-05-01

Doped and co-doped ceria ceramics are used as electrolyte materials in solid oxide fuel cells. In this work, ceria-based oxides, Ce0.90Gd0.06Y0.02M0.02O2-δ (M = Ca, Fe, La, and Sr) were prepared by conventional as well as microwave processing from the precursors prepared by the mixed oxide method. The consolidated calcined powders in pellet form were sintered in microwave energy at 1400°C for 20 min and in an electric furnace of IR radiation at 1400°C for 6 h. The x-ray diffraction analysis confirmed that all the compositions were crystallized into a cubic fluorite structure. Surface morphology of the sintered products was studied using scanning electron microscopy and the microhardness was investigated using the Vickers hardness test. The comparative results analysis shows that the microwave-sintered samples have uniform grain growth, higher density and higher microhardness than the corresponding conventionally sintered products. The microwave-sintered sample of composition Ce0.90Gd0.06Y0.02Sr0.02O2-δ was found to have the highest microhardness among the four compositions due to its high density and smallest grain size.

Method of making a layered composite electrode/electrolyte

DOEpatents

Visco, Steven J.; Jacobson, Craig P.; DeJonghe, Lutgard C.

2005-01-25

An electrode/electrolyte structure is prepared by a plurality of methods. An unsintered (possibly bisque fired) moderately catalytic electronically-conductive or homogeneous mixed ionic electronic conductive electrode material is deposited on a layer composed of a sintered or unsintered ionically-conductive electrolyte material prior to being sintered. A layer of particulate electrode material is deposited on an unsintered ("green") layer of electrolyte material and the electrode and electrolyte layers are sintered simultaneously, sometimes referred to as "co-firing," under conditions suitable to fully densify the electrolyte while the electrode retains porosity. Or, the layer of particulate electrode material is deposited on a previously sintered layer of electrolyte, and then sintered. Subsequently, a catalytic material is added to the electrode structure by infiltration of an electrolcatalyst precursor (e.g., a metal salt such as a transition metal nitrate). This may be followed by low temperature firing to convert the precursor to catalyst. The invention allows for an electrode with high electronic conductivity and sufficient catalytic activity to achieve high power density in an ionic (electrochemical) device such as fuel cells and electrolytic gas separation systems.

Phase composition and in vitro bioactivity of porous implants made of bioactive glass S53P4.

PubMed

Fagerlund, S; Massera, J; Moritz, N; Hupa, L; Hupa, M

2012-07-01

This work studied the influence of sintering temperature on the phase composition, compression strength and in vitro properties of implants made of bioactive glass S53P4. The implants were sintered within the temperature range 600-1000°C. Over the whole temperature range studied, consolidation took place mainly via viscous flow sintering, even though there was partial surface crystallization. The mechanical strength of the implants was low but increased with the sintering temperature, from 0.7 MPa at 635°C to 10 MPa at 1000°C. Changes in the composition of simulated body fluid (SBF), the immersion solution, were evaluated by pH measurements and ion analysis using inductively coupled plasma optical emission spectrometry. The development of a calcium phosphate layer on the implant surfaces was verified using scanning electron microscopy-electron-dispersive X-ray analysis. When immersed in SBF, a calcium phosphate layer formed on all the samples, but the structure of this layer was affected by the surface crystalline phases. Hydroxyapatite formed more readily on amorphous and partially crystalline implants containing both primary Na(2)O·CaO·2SiO(2) and secondary Na(2)Ca(4)(PO(4))(2)SiO(4) crystals than on implants containing only primary crystals. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Finite element method analysis of cold forging for deformation and densification of Mo alloyed sintered steel

NASA Astrophysics Data System (ADS)

Kamakoshi, Y.; Nishida, S.; Kanbe, K.; Shohji, I.

2017-10-01

In recent years, powder metallurgy (P/M) materials have been expected to be applied to automobile products. Then, not only high cost performance but also more strength, wear resistance, long-life and so on are required for P/M materials. As an improvement method of mechanical properties of P/M materials, a densification is expected to be one of effective processes. In this study, to examine behaviours of the densification of Mo-alloyed sintered steel in a cold-forging process, finite element method (FEM) analysis was performed. Firstly, a columnar specimen was cut out from the inner part of a sintered specimen and a load-stroke diagram was obtained by the compression test. 2D FEM analysis was performed using the obtained load-stroke diagram. To correct the errors of stress between the porous mode and the rigid-elastic mode of analysis software, the analysis of a polynominal approximation was performed. As a result, the modified true stress-true strain diagram was obtained for the sintered steel with the densification. Afterwards, 3D FEM analysis of backward extrusion was carried out using the modified true stress-true strain diagram. It was confirmed that both the shape and density of the sintered steel analyzed by new FEM analysis that we suggest correspond well with experimental ones.

Sintering and Microstructure of BaTiO3 Nano Particles Synthesized by Molten Salt Method.

PubMed

Lee, Chang-Hyun; Shin, Hyo-Soon; Yeo, Dong-Hun; Ha, Gook-Hyun; Nahm, Sahn

2016-05-01

In order to establish thinner dielectric layers in thick film electronic components such as MLCC (Multilayer ceramic capacitor), BaTiO3 nanoparticles have been utilized. However, studies on the synthesis of nanoparticles smaller than 20 nm, the characteristics of the BaTiO3 powder, and the powder's sintering are lacking. Therefore, this paper aims to synthesize BaTiO3 particles smaller than 20 nm by using the molten salt method and evaluate the microstructure and dielectric properties by varying the sintering temperature from 750 degrees C to 1200 degrees C. Through the molten salt method and by using KOH-KCl mixed salt, 20 nm BaTiO3 powder was synthesized at a low temperature of 150 degrees C. Sintering the pellets formed from the synthesized 20 nm BaTiO3 nano powder led to the observation of an unusual phenomenon where the particles grew to approximate sizes below 850 degrees C where densification progressed. At sintering temperatures above 950 degrees C, particles that expanded into rod shapes were observed and these particles were identified to be unreacted TiO2 based on the results of the EDX (Energy Dispersive X-ray Spectroscopy) analysis and phase analysis results.

Spark plasma sintering of silicon carbide, multi-walled carbon nanotube and graphene reinforced zirconium diboride ceramic composite

NASA Astrophysics Data System (ADS)

Balaraman Yadhukulakrishnan, Govindaraajan

Scope and Method of Study: Space vehicles re-entering the earth's atmosphere experience very high temperatures due to aerodynamic heating. Ultra-high temperature ceramics (UHTC) with melting point higher than 3200°C are promising materials for thermal protection systems of such space vehicles re-entering the earth's atmosphere. Among several UHTC systems ZrB2 based ceramic composites are particularly important for thermal protection systems due to their better mechanical and thermoelectric properties and high oxidation resistance. In this study spark plasma sintering of SiC, carbon nanotubes (CNT) and graphene nano platelets (GNP) reinforced ZrB2 ultra-high temperature ceramic matrix composites is reported. Findings and Conclusions: Systematic investigations on the effect of reinforcement type (SiC, CNTs and GNP) and content (10-40 vol.% SiC, 2-6 vol.% CNTs and 2-6 vol.% GNP) on densification behavior, microstructure development, and mechanical properties (microhardness, bi-axial flexural strength, and indentation fracture toughness) are reported. With the similar SPS parameters near-full densification (>99% relative density) was achieved with 10-40 vol.% SiC, 4-6 vol.% CNT reinforced composites. Highly dense composites were obtained in 4-6 vol.% GNP reinforced composites. The SiC, CNT and GNP reinforcement improved the indentation fracture toughness of the composites through a range of toughening mechanisms, including particle shearing, crack deflection at the particle-matrix interface, and grain pull-outs for ZrB2-SiC composites, CNT pull-outs and crack deflection in ZrB2-CNT composites and crack deflection, crack bridging and GNP sheet pull-out for ZrB2 -GNP composites.

Double coating protection of Nd-Fe-B magnets: Intergranular phosphating treatment and copper plating

NASA Astrophysics Data System (ADS)

Zheng, Jingwu; Chen, Haibo; Qiao, Liang; Lin, Min; Jiang, Liqiang; Che, Shenglei; Hu, Yangwu

2014-12-01

In this work, a double coating protection technique of phosphating treatment and copper plating was made to improve the corrosion resistance of sintered Nd-Fe-B magnets. In other words, the intergranular region of sintered Nd-Fe-B is allowed to generate passive phosphate conversion coating through phosphating treatment, followed by the copper coating on the surface of sintered Nd-Fe-B. The morphology and corrosion resistance of the phosphated sintered Nd-Fe-B were observed using SEM and electrochemical method respectively. The phosphate conversion coating was formed more preferably on the intergranular region of sintered Nd-Fe-B than on the main crystal region; just after a short time of phosphating treatment, the intergranular region of sintered Nd-Fe-B has been covered by the phosphate conversion coating and the corrosion resistance is significantly improved. With the synergistic protection of the intergranular phosphorization and the followed copper electrodeposition, the corrosion resistance of the sintered Nd-Fe-B is significantly better than that with a single phosphate film or single plating protection.

Consolidation & Factors Influencing Sintering Process in Polymer Powder Based Additive Manufacturing

NASA Astrophysics Data System (ADS)

Sagar, M. B.; Elangovan, K.

2017-08-01

Additive Manufacturing (AM) is two decade old technology; where parts are build layer manufacturing method directly from a CAD template. Over the years, AM techniques changes the future way of part fabrication with enhanced intricacy and custom-made features are aimed. Commercially polymers, metals, ceramic and metal-polymer composites are in practice where polymers enhanced the expectations in AM and are considered as a kind of next industrial revolution. Growing trend in polymer application motivated to study their feasibility and properties. Laser sintering, Heat sintering and Inhibition sintering are the most successful AM techniques for polymers but having least application. The presentation gives up selective sintering of powder polymers and listed commercially available polymer materials. Important significant factors for effective processing and analytical approaches to access them are discussed.

Pressure- and Additive-Mediated Sintering of B4C at Relatively Low Temperatures

NASA Astrophysics Data System (ADS)

Goswami, Ramasis; Qadri, Syed B.; Wollmershauser, James; Kolel-Veetil, Manoj K.; Feygelson, Boris

2017-03-01

A significant improvement in sinterability of B4C was achieved at a relatively low temperature by applying high pressure (2 GPa) and adding a small amount (5 wt pct) of Ni. The sintered B4C and Ni powder mixture showed improved hardness in the range of 21 to 32 GPa and improved modulus as compared to the sintered B4C powder without additive. This is mostly attributed to the formation of Ni4B3, as characterized by Reitveld refinement method and transmission electron microscopy (TEM), which enhances the bonding between B4C particles. These results provide a new avenue toward the development of sintering of B4C at relatively low temperatures (<0.5 T m of B4C).

Formation of TiO2 nanostructure by plasma electrolytic oxidation for Cr(VI) reduction

NASA Astrophysics Data System (ADS)

Torres, D. A.; Gordillo-Delgado, F.; Plazas-Saldaña, J.

2017-01-01

Plasma electrolytic oxidation (PEO) is an environmentally friendly technique that allows the growth of ceramic coatings without organic solvents and non-toxic residues. This method was applied to ASME SB-265 titanium (Ti) plates (2×2×0.1cm) using voltage pulses from a switching power supply (340V) for 10 minutes at frequency of 1000Hz changing duty cycle at 10, 60 and 90% and the electrolytes were Na3PO4 and NaOH. The treated sheets surfaces were analysed by X-ray diffraction and scanning electron microscopy. According to the diffractograms, the duty cycle increase produces amorphous TiO2 coating on Ti sheets and the thickness increases. After sintering at 900°C during 1 hour, the 10% duty cycle generated a combination of anatase and rutile phases at the sample surface with weight percentages of 13.3 and 86.6% and particle sizes of 32.461±0.009nm and 141.14±0.03 nm, respectively. With this sample, the total reduction of hexavalent chromium was reached at 50 minutes for 1ppm solution. This photocatalytic activity was measured following the colorimetric method ASTM-3500-Cr B.

Morphology and phase identification of micron to nanosized manganese oxide (MnO) with variations in sintering time

NASA Astrophysics Data System (ADS)

Sasongko, Muhammad Ilman Nur; Puspitasari, Poppy; Yazirin, Cepi; Tsamroh, Dewi Izzatus; Risdanareni, Puput

2017-09-01

Manganese oxide (MnO) occurs in many rock types and may take the form of minerals. MnO has its drawbacks, namely highly reactive oxidizing species classified as dangerous and explosive at temperatures above 55 °C. Despite this,MnO has excellent magnetic, electrochemical, and conductivity properties, which should be reduced to nano-size to maximize their use and improve the properties of MnO. Phase and morphology characterization of powder this research aims to reduce the grain size of the MnO from micro to nano using the sol-gel method with various sintering times. Sol-gel is a simple synthesis method that has been proven capable of synthesizing a wide variety of micro-sized oxide materials into nano. Sintering time is a technique performed in the synthesis process to dry the material to a temperature above the normal temperature. The temperature used for sintering starting from 600 °C to 1000 °C. Characterizations were done using XRD, SEM, EDX, and FTIR machines. The sintering processes in this study used a temperature of 600 °C with different sintering periods of 30, 60 and 90 minutes. The XRD characterization with a 30-minute sintering time resulted in the smallest MnO in the form crystalline powder of 47.3 nm. The highest intensity (degree of crystallinity) found in MnO sintered for 90 minutes. The results of the morphological characterization of SEM showed a morphological change in MnO from micro-sized triangular to nano-sized spherical shape. The EDX characterization results indicated that the 30-minute sintering caused the lowest change in Mn and the highest change in O. The results of FTIR characterization showed a shift in C-H and Mn-O followed by an increase in the group of N-H, C=O and Mn-O.

40 CFR 63.7851 - Who implements and enforces this subpart?

Code of Federal Regulations, 2012 CFR

2012-07-01

... defined in § 63.90, except for approval of an alternative method for the oil content of the sinter plant feedstock or volatile organic compound measurements for the sinter plant windbox exhaust stream stack as...

40 CFR 63.7851 - Who implements and enforces this subpart?

Code of Federal Regulations, 2011 CFR

2011-07-01

... defined in § 63.90, except for approval of an alternative method for the oil content of the sinter plant feedstock or volatile organic compound measurements for the sinter plant windbox exhaust stream stack as...

40 CFR 63.7851 - Who implements and enforces this subpart?

Code of Federal Regulations, 2014 CFR

2014-07-01

... defined in § 63.90, except for approval of an alternative method for the oil content of the sinter plant feedstock or volatile organic compound measurements for the sinter plant windbox exhaust stream stack as...

40 CFR 63.7851 - Who implements and enforces this subpart?

Code of Federal Regulations, 2013 CFR

2013-07-01

... defined in § 63.90, except for approval of an alternative method for the oil content of the sinter plant feedstock or volatile organic compound measurements for the sinter plant windbox exhaust stream stack as...

Method of preparing uranium nitride or uranium carbonitride bodies

DOEpatents

Wilhelm, Harley A.; McClusky, James K.

1976-04-27

Sintered uranium nitride or uranium carbonitride bodies having a controlled final carbon-to-uranium ratio are prepared, in an essentially continuous process, from U.sub.3 O.sub.8 and carbon by varying the weight ratio of carbon to U.sub.3 O.sub.8 in the feed mixture, which is compressed into a green body and sintered in a continuous heating process under various controlled atmospheric conditions to prepare the sintered bodies.

Method of making a composite refractory material

DOEpatents

Morrow, Marvin S.; Holcombe, Cressie E.

1995-01-01

A composite refractory material is prepared by combining boron carbide with furan resin to form a mixture containing about 8 wt. % furan resin. The mixture is formed into a pellet which is placed into a grit pack comprising an oxide of an element such as yttrium to form a sinterable body. The sinterable body is sintered under vacuum with microwave energy at a temperature no greater than 2000.degree. C. to form a composite refractory material.

Method of making a composite refractory material

DOEpatents

Morrow, M.S.; Holcombe, C.E.

1995-09-26

A composite refractory material is prepared by combining boron carbide with furan resin to form a mixture containing about 8 wt. % furan resin. The mixture is formed into a pellet which is placed into a grit pack comprising an oxide of an element such as yttrium to form a sinterable body. The sinterable body is sintered under vacuum with microwave energy at a temperature no greater than 2000 C to form a composite refractory material.

LiFePO4 Nanostructures Fabricated from Iron(III) Phosphate (FePO4 x 2H2O) by Hydrothermal Method.

PubMed

Saji, Viswanathan S; Song, Hyun-Kon

2015-01-01

Electrode materials having nanometer scale dimensions are expected to have property enhancements due to enhanced surface area and mass/charge transport kinetics. This is particularly relevant to intrinsically low electronically conductive materials such as lithium iron phosphate (LiFePO4), which is of recent research interest as a high performance intercalation electrode material for Li-ion batteries. Many of the reported works on LiFePO4 synthesis are unattractive either due to the high cost of raw materials or due to the complex synthesis technique. In this direction, synthesis of LiFePO4 directly from inexpensive FePO4 shows promise.The present study reports LiFePO4 nanostructures prepared from iron (III) phosphate (FePO4 x 2H2O) by precipitation-hydrothermal method. The sintered powder was characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Inductive coupled plasma-optical emission spectroscopy (ICP-OES), and Electron microscopy (SEM and TEM). Two synthesis methods, viz. bulk synthesis and anodized aluminum oxide (AAO) template-assisted synthesis are reported. By bulk synthesis, micro-sized particles having peculiar surface nanostructuring were formed at precipitation pH of 6.0 to 7.5 whereas typical nanosized LiFePO4 resulted at pH ≥ 8.0. An in-situ precipitation strategy inside the pores of AAO utilizing the spin coating was utilized for the AAO-template-assisted synthesis. The template with pores filled with the precipitate was subsequently subjected to hydrothermal process and high temperature sintering to fabricate compact rod-like structures.

Development of nano-structured duplex and ferritic stainless steels by pulverisette planetary milling followed by pressureless sintering

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

R, Shashanka, E-mail: shashankaic@gmail.com; Chaira, D., E-mail: chaira.debasis@gmail.com

Nano-structured duplex and ferritic stainless steel powders are prepared by planetary milling of elemental Fe, Cr and Ni powder for 40 h and then consolidated by conventional pressureless sintering. The progress of milling and the continuous refinement of stainless steel powders have been confirmed by means of X-ray diffraction and scanning electron microscopy. Activation energy for the formation of duplex and ferritic stainless steels is calculated by Kissinger method using differential scanning calorimetry and is found to be 159.24 and 90.17 KJ/mol respectively. Both duplex and ferritic stainless steel powders are consolidated at 1000, 1200 and 1400 °C in argonmore » atmosphere to study microstructure, density and hardness. Maximum sintered density of 90% and Vickers microhardness of 550 HV are achieved for duplex stainless steel sintered at 1400 °C for 1 h. Similarly, 92% sintered density and 263 HV microhardness are achieved for ferritic stainless steel sintered at 1400 °C. - Highlights: • Synthesized duplex and ferritic stainless steels by pulverisette planetary milling • Calculated activation energy for the formation of duplex and ferritic stainless steels • Studied the effect of sintering temperature on density, hardness and microstructure • Duplex stainless steel exhibits 90% sintered density and microhardness of 550 HV. • Ferritic stainless steel shows 92% sintered density and 263 HV microhardness.« less

Thermal method for fabricating a hydrogen separation membrane on a porous substrate

DOEpatents

Song, Sun-Ju [Orland Park, IL; Lee, Tae H [Naperville, IL; Chen, Ling [Woodridge, IL; Dorris, Stephen E [LaGrange Park, IL; Balachandran, Uthamalingam [Hinsdale, IL

2009-10-20

A thermal method of making a hydrogen permeable composition is disclosed. A mixture of metal oxide powder and ceramic oxide powder and optionally a pore former is formed and pressed to form an article. The article is dried at elevated temperatures and then sintered in a reducing atmosphere to provide a dense hydrogen permeable portion near the surface of the sintered mixture. The dense hydrogen permeable portion has a higher initial concentration of metal than the remainder of the sintered mixture and is present in the range of from about 20 to about 80 percent by volume of the dense hydrogen permeable portion.

Surface-structured diffuser by iterative down-size molding with glass sintering technology.

PubMed

Lee, Xuan-Hao; Tsai, Jung-Lin; Ma, Shih-Hsin; Sun, Ching-Cherng

2012-03-12

In this paper, a down-size sintering scheme for making high-performance diffusers with micro structure to perform beam shaping is presented and demonstrated. By using down-size sintering method, a surface-structure film is designed and fabricated to verify the feasibility of the sintering technology, in which up to 1/8 dimension reduction has been achieved. Besides, a special impressing technology has been applied to fabricate diffuser film with various materials and the transmission efficiency is as high as 85% and above. By introducing the diffuser into possible lighting applications, the diffusers have been shown high performance in glare reduction, beam shaping and energy saving.

Fabrication of thin layer beta alumina

NASA Technical Reports Server (NTRS)

Tennenhouse, G. J.

1977-01-01

Beta alumina tubes having walls 700 microns, 300 microns, and 140 microns were processed by extrusion and sintering utilizing Ford proprietary binder and fabrication systems. Tubes prepared by this method have properties similar to tubes prepared by isostatic pressing and sintering, i.e. density greater than 98% of theoretical and a helium leak rate less than 3 x 10 to the -9th power cc/sq cm/sec. Ford ultrasonic bonding techniques were used for bonding beta alumina end caps to open ended beta -alumina tubes prior to sintering. After sintering, the bond was hermetic, and the integrity of the bonded area was comparable to the body of the tube.

Effect of sintering on structure and magnetic properties of Mn-doped Zn ferrite

NASA Astrophysics Data System (ADS)

Farheen, Atiya; Singh, Rajender

2018-05-01

The Mn-doped zinc ferrites, MnxZn1-xFe2O4 (x= 0 and 0.1) were prepared using co-precipitation method. The as-prepared samples were sintered at different temperatures. The x-ray diffraction pattern for all the samples confirms single phase spinel structure with Fd-3m space group. The lattice parameters have been estimated using Rietveld fitting. The magnetic moment is found to increase with Mn-doping. The magnetization increases as the sintering temperature increases up to 1200°C. The as-prepared samples are super paramagnetic, while the sintered samples are ferrimagnetic in nature.

Silicon carbide sintered products and a method for their manufacturing

NASA Technical Reports Server (NTRS)

Suzuki, K.

1986-01-01

SiC based sinters are produced by pressureless sintering from a SiC-AlN solid solution containing Al2 to 20, N 0.2 to 10, O 0.2 to 5, a Group IIIB element 0 to 15 percent, the remainder being Si and C. Thus, a 90:10 mixture of SiC and AlN powders were cold pressed at 2000 kg/sq cm and sintered for 5 hours at 2100 C in a nitrogen atmosphere. The resulting product had density of 3.11 g/cu cm and bending strength at ambient and 1400 C at 68.5 and 66.3 kg/sq mm.

Enery Efficient Press and Sinter of Titanium Powder for Low-Cost Components in Vehicle Applications

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

Thomas Zwitter; Phillip Nash; Xiaoyan Xu

2011-03-31

This is the final technical report for the Department of Energy NETL project NT01931 Energy Efficient Press and Sinter of Titanium Powder for Low-Cost Components in Vehicle Applications. Titanium has been identified as one of the key materials with the required strength that can reduce the weight of automotive components and thereby reduce fuel consumption. Working with newly developed sources of titanium powder, Webster-Hoff will develop the processing technology to manufacture low cost vehicle components using the single press/single sinter techniques developed for iron based powder metallurgy today. Working with an automotive or truck manufacturer, Webster-Hoff will demonstrate the feasibilitymore » of manufacturing a press and sinter titanium component for a vehicle application. The project objective is two-fold, to develop the technology for manufacturing press and sinter titanium components, and to demonstrate the feasibility of producing a titanium component for a vehicle application. The lowest cost method for converting metal powder into a net shape part is the Powder Metallurgy Press and Sinter Process. The method involves compaction of the metal powder in a tool (usually a die and punches, upper and lower) at a high pressure (up to 60 TSI or 827 MPa) to form a green compact with the net shape of the final component. The powder in the green compact is held together by the compression bonds between the powder particles. The sinter process then converts the green compact to a metallurgically bonded net shape part through the process of solid state diffusion. The goal of this project is to expand the understanding and application of press and sinter technology to Titanium Powder applications, developing techniques to manufacture net shape Titanium components via the press and sinter process. In addition, working with a vehicle manufacturer, demonstrate the feasibility of producing a titanium component for a vehicle. This is not a research program, but rather a project to develop a process for press and sinter of net shape Titanium components. All of these project objectives have been successfully completed.« less

Novel Processing of Boron Carbide (B4C): Plasma Synthesized Nano Powders and Pressureless Sintering Forming of Complex Shapes

DTIC Science & Technology

2008-12-01

Figure 4. B4C plates formed via hot pressing with a curved shape. Commercial B4C shows a large number of lenticular graphitic inclusions, Figure 5...materials and they act as crack initiation points in flexure testing. Figure 5. SEM micrograph showing large lenticular graphitic inclusions in commercial

Improved Ceramic Anodes for Corrosion Protection.

DTIC Science & Technology

1984-11-01

34 . 4 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE(Whi Data Entered) BLOCK 20 (Continued) ferrite over niobium over Ni- Cr -AI-Y...plasma-sprayed lithium ferrite on a valve metal substrate. Donor doped and reduced solid sintered titanate compounds yielded electrically conductive...Traditionally. impressed current systems have used tion (CEGS) 2310. antides that are either inexpensive and very large (high silicon, chromium

Processing, Mechanical and Optical Properties of Additive-Free ZrC Ceramics Prepared by Spark Plasma Sintering.

PubMed

Musa, Clara; Licheri, Roberta; Orrù, Roberto; Cao, Giacomo; Sciti, Diletta; Silvestroni, Laura; Zoli, Luca; Balbo, Andrea; Mercatelli, Luca; Meucci, Marco; Sani, Elisa

2016-06-18

In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS) after 20 min dwell time at 1850 °C starting from powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS) followed by 20 min ball milling. A prolonged mechanical treatment up to 2 h of SHS powders does not lead to appreciable benefits. Vickers hardness of the resulting samples (17.5 ± 0.4 GPa) is reasonably good for monolithic ceramics, but the mechanical strength (about 250 MPa up to 1000 °C) could be further improved by suitable optimization of the starting powder characteristics. The very smoothly polished ZrC specimen subjected to optical measurements displays high absorption in the visible-near infrared region and low thermal emittance at longer wavelengths. Moreover, the sample exhibits goodspectral selectivity (2.1-2.4) in the 1000-1400 K temperature range. These preliminary results suggest that ZrC ceramics produced through the two-step SHS/SPS processing route can be considered as attractive reference materials for the development of innovative solar energy absorbers.

Bone-like apatite layer formation on hydroxyapatite prepared by spark plasma sintering (SPS).

PubMed

Gu, Y W; Khor, K A; Cheang, P

2004-08-01

Hydroxyapatite (HA) compacts with high density and superior mechanical properties were fabricated by spark plasma sintering (SPS) using spray-dried HA powders as feedstock. The formation of bone-like apatite layer on SPS consolidated HA compacts were investigated by soaking the HA compacts in simulated body fluid (SBF) for various periods (maximum of 28 days). The structural changes in HA post-SBF were analyzed with scanning electron microscopy, grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy. It was found that a layer consisting microcrystalline carbonate-containing hydroxyapatite was formed on the surface of HA compacts after soaking for 24h. The formation mechanism of apatite on the surface of HA compacts after soaking in SBF was attributed to the ion exchange between HA compacts and the SBF solution. The increase in ionic concentration of calcium and phosphorus as well as the increase in pH after SBF immersion resulted in an increase in ionic activity product of apatite in the solution, and provided a specific surface with a low interface energy that is conducive to the nucleation of apatite on the surface of HA compacts.

A methodology to investigate the intrinsic effect of the pulsed electric current during the spark plasma sintering of electrically conductive powders

PubMed Central

Locci, Antonio Mario; Cincotti, Alberto; Todde, Sara; Orrù, Roberto; Cao, Giacomo

2010-01-01

A novel methodology is proposed for investigating the effect of the pulsed electric current during the spark plasma sintering (SPS) of electrically conductive powders without potential misinterpretation of experimental results. First, ensemble configurations (geometry, size and material of the powder sample, die, plunger and spacers) are identified where the electric current is forced to flow only through either the sample or the die, so that the sample is heated either through the Joule effect or by thermal conduction, respectively. These ensemble configurations are selected using a recently proposed mathematical model of an SPS apparatus, which, once suitably modified, makes it possible to carry out detailed electrical and thermal analysis. Next, SPS experiments are conducted using the ensemble configurations theoretically identified. Using aluminum powders as a case study, we find that the temporal profiles of sample shrinkage, which indicate densification behavior, as well as the final density of the sample are clearly different when the electric current flows only through the sample or through the die containing it, whereas the temperature cycle and mechanical load are the same in both cases. PMID:27877354

Thermoelectric SnS and SnS-SnSe solid solutions prepared by mechanical alloying and spark plasma sintering: Anisotropic thermoelectric properties

PubMed Central

Asfandiyar; Wei, Tian-Ran; Li, Zhiliang; Sun, Fu-Hua; Pan, Yu; Wu, Chao-Feng; Farooq, Muhammad Umer; Tang, Huaichao; Li, Fu; Li, Bo; Li, Jing-Feng

2017-01-01

P–type SnS compound and SnS1−xSex solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS–pressurizing direction in the temperature range 323–823 Κ. SnS compound and SnS1−xSex solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m−1 K−1 at 823 K for the composition SnS0.5Se0.5. With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS0.2Se0.8 along the parallel direction. PMID:28240324

Microstructure and performance of rare earth element-strengthened plasma-facing tungsten material

PubMed Central

Luo, Laima; Shi, Jing; Lin, Jinshan; Zan, Xiang; Zhu, Xiaoyong; Xu, Qiu; Wu, Yucheng

2016-01-01

Pure W and W-(2%, 5%, 10%) Lu alloys were manufactured via mechanical alloying for 20 h and a spark plasma sintering process at 1,873 K for 2 min. The effects of Lu doping on the microstructure and performance of W were investigated using various techniques. For irradiation performance analysis, thermal desorption spectroscopy (TDS) measurements were performed from room temperature to 1,000 K via infrared irradiation with a heating rate of 1 K/s after implantations of He+ and D+ ions. TDS measurements were conducted to investigate D retention behavior. Microhardness was dramatically enhanced, and the density initially increased and then decreased with Lu content. The D retention performance followed the same trend as the density. Second-phase particles identified as Lu2O3 particles were completely distributed over the W grain boundaries and generated an effective grain refinement. Transgranular and intergranular fracture modes were observed on the fracture surface of the sintered W-Lu samples, indicating some improvement of strength and toughness. The amount and distribution of Lu substantially affected the properties of W. Among the investigated alloy compositions, W-5%Lu exhibited the best overall performance. PMID:27596002

Thermoelectric properties of Si/CoSi2 sub-micrometer composites prepared by melt-spinning technique

NASA Astrophysics Data System (ADS)

Xie, Jun; Ohishi, Yuji; Ichikawa, Satoshi; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke

2017-05-01

We here report on the influence of CoSi2 precipitates on the thermoelectric properties of heavily doped p-type Si. A simple self-assembly process using a melt-spinning technique followed by spark plasma sintering is introduced to prepare bulk Si/CoSi2 composites with a nominal composition of (Si0.99B0.01)95Co5. Scanning and transmission electron microscopy observations present clear evidence of a sub-micrometer CoSi2 phase with a size ranging from 50 to 500 nm. These sub-micrometer precipitates resulted in a retention of the high electrical performance of heavily doped Si, while simultaneously reducing thermal conductivity by over 20% compared to a coarse CoSi2 phase (1-10 μm) in a comparative sample prepared by arc melting and spark plasma sintering. As a result, a figure of merit ZT value of 0.21 at 1073 K was achieved in the sub-micrometer Si/CoSi2, an increase of 16% compared with the ZT value for homogeneous p-type Si with a similar carrier concentration. This suggests that the self-assembled sub-micrometer inclusions effectively enhanced the thermoelectric performance of Si-based thermoelectric materials.

Thermoelectric SnS and SnS-SnSe solid solutions prepared by mechanical alloying and spark plasma sintering: Anisotropic thermoelectric properties.

PubMed

Asfandiyar; Wei, Tian-Ran; Li, Zhiliang; Sun, Fu-Hua; Pan, Yu; Wu, Chao-Feng; Farooq, Muhammad Umer; Tang, Huaichao; Li, Fu; Li, Bo; Li, Jing-Feng

2017-02-27

P-type SnS compound and SnS 1-x Se x solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS-pressurizing direction in the temperature range 323-823 Κ. SnS compound and SnS 1-x Se x solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m -1  K -1 at 823 K for the composition SnS 0.5 Se 0.5 . With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS 0.2 Se 0.8 along the parallel direction.

Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

NASA Astrophysics Data System (ADS)

Jakubowicz, J.; Adamek, G.; Sopata, M.; Koper, J. K.; Siwak, P.

2017-12-01

The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.

Influence of the sintering temperature on the electrical properties of Ce-doped WO3 ceramics prepared from nano-powders

NASA Astrophysics Data System (ADS)

Dong, Liang; Chen, Han-Jun; Wang, Yu; Li, De-Zhu; Li, Tong-Ye; Zhao, Yong

2007-04-01

Using a nm-level powder fabricated by a wet chemical method as precursor, the CeO2-doped WO3 ceramics were prepared by the conventional solid state reaction at sintering temperatures from 600 to 1100 °C. The x-ray diffraction analysis reveals the coexistence of different WO3 phases in the samples sintered at temperatures below 900 °C, whereas a single phase appears in the samples sintered above 1000 °C. No new Ce-W compound appears. As the sintering temperature increases, the electrical properties of the samples display an interesting transformation from linear to nonlinear behaviour. The measurements of scanning electron microscope, complex impedance and electrical stability indicate that a lot of grain boundary regions in the samples sintered at low temperatures strongly influences the electrical transportation. Therefore, the electrical nonlinearity is due to a basic process controlled by the back-to-back Schottky barriers at grain boundaries with suitable thickness as well as the coexistence of phases.

Low-cost optical fabrication of flexible copper electrode via laser-induced reductive sintering and adhesive transfer

NASA Astrophysics Data System (ADS)

Back, Seunghyun; Kang, Bongchul

2018-02-01

Fabricating copper electrodes on heat-sensitive polymer films in air is highly challenging owing to the need of expensive copper nanoparticles, rapid oxidation of precursor during sintering, and limitation of sintering temperature to prevent the thermal damage of the polymer film. A laser-induced hybrid process of reductive sintering and adhesive transfer is demonstrated to cost-effectively fabricate copper electrode on a polyethylene film with a thermal resistance below 100 °C. A laser-induced reductive sintering process directly fabricates a high-conductive copper electrode onto a glass donor from copper oxide nanoparticle solution via photo-thermochemical reduction and agglomeration of copper oxide nanoparticles. The sintered copper patterns were transferred in parallel to a heat-sensitive polyethylene film through self-selective surface adhesion of the film, which was generated by the selective laser absorption of the copper pattern. The method reported here could become one of the most important manufacturing technologies for fabricating low-cost wearable and disposable electronics.

Fabrication and Analysis of the Wear Properties of Hot-Pressed Al-Si/SiCp + Al-Si-Cu-Mg Metal Matrix Composite

NASA Astrophysics Data System (ADS)

Bang, Jeongil; Oak, Jeong-Jung; Park, Yong Ho

2016-01-01

The aim of this study was to characterize microstructures and mechanical properties of aluminum metal matrix composites (MMC's) prepared by powder metallurgy method. Consolidation of mixed powder with gas atomized Al-Si/SiCp powder and Al-14Si-2.5Cu-0.5Mg powder by hot pressing was classified according to sintering temperature and sintering time. Sintering condition was optimized using tensile properties of sintered specimens. Ultimate tensile strength of the optimized sintered specimen was 228 MPa with an elongation of 5.3% in longitudinal direction. In addition, wear properties and behaviors of the sintered aluminum-based MMC's were analyzed in accordance with vertical load and linear speed. As the linear speed and vertical load of the wear increased, change of the wear behavior occurred in order of oxidation of Al-Si matrix, formation of C-rich layer, Fe-alloying to matrix, and melting of the specimen

Effect of sintering temperature on micro structural and impedance spectroscopic properties of Ni0.5Zn0.5Fe2O4 nano ferrite

NASA Astrophysics Data System (ADS)

Venkatesh, Davuluri; Ramesh, K. V.; Sastry, C. V. S. S.

2017-07-01

Ni-Zn nanoferrite Ni0.5Zn0.5Fe2O4 is prepared by citrate gel auto combustion method and sintered at various temperatures 800, 900, 1000, 1100 and 1200°C. The room temperature x-ray diffraction conforms that the single phase spinel structure is formed. Crystallite size and density were increased with increasing of sintering temperature. From Raman spectroscopy all sintered samples are single phase with cubic spinel structure belong to Fd3m space group. From surface morphology studies it is clearly observed that the particle size increased with increasing of sintering temperature. Impedance spectroscopy revel that increasing of conductivity is due to grain resistance is decreased with increasing of sintering temperature. Cole-Cole plots are studied from impedance data. The electrical modulus analysis shows that non-Debye nature of Ni0.5Zn0.5Fe2O4 ferrite.

Strength and fatigue properties of three-step sintered dense nanocrystal hydroxyapatite bioceramics

NASA Astrophysics Data System (ADS)

Guo, Wen-Guang; Qiu, Zhi-Ye; Cui, Han; Wang, Chang-Ming; Zhang, Xiao-Jun; Lee, In-Seop; Dong, Yu-Qi; Cui, Fu-Zhai

2013-06-01

Dense hydroxyapatite (HA) ceramic is a promising material for hard tissue repair due to its unique physical properties and biologic properties. However, the brittleness and low compressive strength of traditional HA ceramics limited their applications, because previous sintering methods produced HA ceramics with crystal sizes greater than nanometer range. In this study, nano-sized HA powder was employed to fabricate dense nanocrystal HA ceramic by high pressure molding, and followed by a three-step sintering process. The phase composition, microstructure, crystal dimension and crystal shape of the sintered ceramic were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties of the HA ceramic were tested, and cytocompatibility was evaluated. The phase of the sintered ceramic was pure HA, and the crystal size was about 200 nm. The compressive strength and elastic modulus of the HA ceramic were comparable to human cortical bone, especially the good fatigue strength overcame brittleness of traditional sintered HA ceramics. Cell attachment experiment also demonstrated that the ceramics had a good cytocompatibility.

Structure and properties of sintered MM-Fe-B magnets

NASA Astrophysics Data System (ADS)

Shang, R. X.; Xiong, J. F.; Li, R.; Zuo, W. L.; Zhang, J.; Zhao, T. Y.; Chen, R. J.; Sun, J. R.; Shen, B. G.

2017-05-01

MM14Fe79.9B6.1 magnets were prepared by conventional sintering method. The Curie temperature of the sintered MM2Fe14B magnet was about 210 °C. When the sintering temperature increased from 1010 °C to 1030 °C, the density of the magnet increased from 6.85 g/cm3 to 7.52 g/cm3. After the first stage tempering at 900 °C, the (BH)max and Hcj had a slight increase. The maximum value of (BH)max = 7.6 MGOe and Hcj = 1080 Oe was obtained when sintered at 1010 °C and tempering at 900 °C, respectively. The grain size grew very large when the sintering temperature increased to 1050 °C, and the magnetic properties deteriorated rapidly. La reduced by ˜ 7.5 at. % in grains, which is almost equal to the increased percentage of Nd. That is mainly because La-Fe-B is very difficult to form the 2: 14: 1 phase.

Toward Interpreting Failure in Sintered-Silver Interconnection Systems

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

Wereszczak, Andrew A; Waters, Shirley B

2016-01-01

The mechanical strength and subsequent reliability of a sintered-silver interconnection system is a function of numerous independent parameters. That system is still undergoing process development. Most of those parameters (e.g., choice of plating) are arguably and unfortunately taken for granted and are independent of the silver s cohesive strength. To explore such effects, shear strength testing and failure analyses were completed on a simple, mock sintered-silver interconnection system consisting of bonding two DBC ceramic substrates. Silver and gold platings were part of the test matrix, as was pre-drying strategies, and the consideration of stencil-printing vs. screen-printing. Shear strength of sintered-silvermore » interconnect systems was found to be was insensitive to the choice of plating, drying practice, and printing method provided careful and consistent processing of the sintered-silver are practiced. But if the service stress in sintered silver interconnect systems is anticipated to exceed ~ 60 MPa, then the system will likely fail.« less

Compositional Design of Dielectric, Ferroelectric and Piezoelectric Properties of (K, Na)NbO3 and (Ba, Na)(Ti, Nb)O3 Based Ceramics Prepared by Different Sintering Routes

PubMed Central

Eiras, José A.; Gerbasi, Rosimeire B. Z.; Rosso, Jaciele M.; Silva, Daniel M.; Cótica, Luiz F.; Santos, Ivair A.; Souza, Camila A.; Lente, Manuel H.

2016-01-01

Lead free piezoelectric materials are being intensively investigated in order to substitute lead based ones, commonly used in many different applications. Among the most promising lead-free materials are those with modified NaNbO3, such as (K, Na)NbO3 (KNN) and (Ba, Na)(Ti, Nb)O3 (BTNN) families. From a ceramic processing point of view, high density single phase KNN and BTNN ceramics are very difficult to sinter due to the volatility of the alkaline elements, the narrow sintering temperature range and the anomalous grain growth. In this work, Spark Plasma Sintering (SPS) and high-energy ball milling (HEBM), following heat treatments (calcining and sintering), in oxidative (O2) atmosphere have been used to prepare single phase highly densified KNN (“pure” and Cu2+ or Li1+ doped), with theoretical densities ρth > 97% and BTNN ceramics (ρth ~ 90%), respectively. Using BTTN ceramics with a P4mm perovskite-like structure, we showed that by increasing the NaNbO3 content, the ferroelectric properties change from having a relaxor effect to an almost “normal” ferroelectric character, while the tetragonality and grain size increase and the shear piezoelectric coefficients (k15, g15 and d15) improve. For KNN ceramics, the results reveal that the values for remanent polarization as well as for most of the coercive field are quite similar among all compositions. These facts evidenced that Cu2+ may be incorporated into the A and/or B sites of the perovskite structure, having both hardening and softening effects. PMID:28773304

Clean recycle and utilization of hazardous iron-bearing waste in iron ore sintering process.

PubMed

Gan, Min; Ji, Zhiyun; Fan, Xiaohui; Chen, Xuling; Zhou, Yang; Wang, Guojing; Tian, Ye; Jiang, Tao

2018-04-18

Applying recycled iron-bearing waste materials (RIM) into iron ore sintering process is the general disposal approach worldwide, while its use is still a thorny problem. Results showed that adding RIM increased contents of hazardous elements (K, Na, Pb, Zn, and Cl) in sinter product, and also enhanced emission concentration of PM 2.5 in flue gas; increasing reaction temperature, and contents of CaO & coke breeze in raw mixtures improved hazardous elements removal. Based on these features, a novel method through granulating natural iron ores and RIM separately and distributing granulated RIM in bottom sintering layers was proposed for clean RIM cycle. When recycling 5% RIM, granulating RIM separately with higher contents of CaO and coke breeze removed hazardous elements effectively, the contents of which in sinter were reduced to comparable level of the case without RIM. Moreover, distributing RIM in bottom sintering layer reached intensive release of hazardous elements and PM 2.5 during sintering, which reduced the flue gas volume needing purification by about 2/3. Through activated carbon purification, about 60% of PM 2.5 comprised high contents of hazardous elements was removed. Novel technique eliminated the negative impact of RIM and has the prospect to reach clean recycle in sinter-making plants. Copyright © 2018. Published by Elsevier B.V.

Panoscopic approach for high-performance Te-doped skutterudite

DOE PAGES

Liang, Tao; Su, Xianli; Yan, Yonggao; ...

2017-02-24

One-step plasma-activated sintering (OS-PAS) fabrication of single-phase high-performance CoSb 3-based skutterudite thermoelectric material with a hierarchical structure on a time scale of a few minutes is first reported here. The formation mechanism of the CoSb 3 phase and the effects of the current and pressure fields on the phase transformation and microstructure evolution are studied in the one-step PAS process. The application of the panoscopic approach to this system and its effect on the transport properties are investigated. The results show that the hierarchical structure forms during the formation of the skutterudite phase under the effects of both current andmore » sintering pressure. The samples fabricated by the OS-PAS technique have defined hierarchical structures, which scatter phonons more intensely over a broader range of frequencies and significantly reduce the lattice thermal conductivity. High-performance bulk Te-doped skutterudite with the maximum ZT of 1.1 at 820 K for the composition CoSb 2.875Te 0.125 was obtained. Such high ZT values rival those obtained from single filled skutterudites. As a result, this newly developed OS-PAS technique enhances the thermoelectric performance, dramatically shortens the synthesis period and provides a facile method for obtaining hierarchical thermoelectric materials on a large scale.« less

Fabrication of Multilayer-Type Mn-Si Thermoelectric Device

NASA Astrophysics Data System (ADS)

Kajitani, T.; Ueno, T.; Miyazaki, Y.; Hayashi, K.; Fujiwara, T.; Ihara, R.; Nakamura, T.; Takakura, M.

2014-06-01

This research aims to develop a direct-contact manganese silicon p/ n multilayer-type thermoelectric power generation block. p-type MnSi1.74 and n-type Mn0.7Fe0.3Si1.68 ball-milled powders with diameter of about 10 μm or less were mixed with polyvinyl butyl alcohol diluted with methylbenzene at pigment volume concentration of approximately 70%. The doctor-blade method produced 45- μm-thick p- and n-type pigment plates. The insulator, i.e., powdered glass, was mixed with cellulose to form insulator slurry. Lamination of manganese silicide pigment layers and screen-printed insulator layers was carried out to fabricate multilayer direct-contact thermoelectric devices. Hot pressing and spark plasma sintering were carried out at 450°C and 900°C, respectively. Four to 30 thermoelectric (TE) p/ n pairs were fabricated in a 10 mm × 10 mm × 10 mm sintered TE block. The maximum output was 11.7 mW/cm2 at a temperature difference between 20°C and 700°C, which was about 1/85 of the ideal power generation estimated from the thermoelectric data of the bulk MnSi1.74 and Mn0.7Fe0.3Si1.68 materials. A power generation test using an engine test bench was also carried out.

Effect of far-field stresses and residual stresses incorporation in predicting fracture toughness of carbon nanotube reinforced yttria stabilized zirconia

NASA Astrophysics Data System (ADS)

Mahato, Neelima; Nisar, Ambreen; Mohapatra, Pratyasha; Rawat, Siddharth; Ariharan, S.; Balani, Kantesh

2017-10-01

Yttria-stabilized zirconia (YSZ) is a potential thermal insulating ceramic for high temperature applications (>1000 °C). YSZ reinforced with multi-walled carbon nanotubes (MWNTs) was processed via spark plasma sintering to produce dense, crack-free homogeneous sample and avoid any degradation of MWNTs when sintered using conventional routes. Despite porosity, the addition of MWNT has a profound effect in improving the damage tolerance of YSZ by allowing the retention of tetragonal phase. However, at some instances, the crack lengths in the MWNT reinforced YSZ matrices have been found to be longer than the standalone counterparts. Therefore, it becomes inappropriate to apply Anstis equation to calculate fracture toughness values. In this regard, a combined analytical cum numerical method is used to estimate the theoretical fracture toughness and quantitatively analyze the mechanics of matrix cracking in the reinforced composite matrices incorporating the effects of various factors (such as far-field stresses, volume fraction of MWNTs, change in the modulus and Poisson's ratio values along with the increase in porosity, and bridging and phase transformation mechanism) affecting the fracture toughness of YSZ-MWNT composites. The results suggest that the incorporation of far-field stresses cannot be ignored in estimating the theoretical fracture toughness of YSZ-MWNT composites.

Structural modifications induced by ion irradiation and temperature in boron carbide B4C

NASA Astrophysics Data System (ADS)

Victor, G.; Pipon, Y.; Bérerd, N.; Toulhoat, N.; Moncoffre, N.; Djourelov, N.; Miro, S.; Baillet, J.; Pradeilles, N.; Rapaud, O.; Maître, A.; Gosset, D.

2015-12-01

Already used as neutron absorber in the current French nuclear reactors, boron carbide (B4C) is also considered in the future Sodium Fast Reactors of the next generation (Gen IV). Due to severe irradiation conditions occurring in these reactors, it is of primary importance that this material presents a high structural resistance under irradiation, both in the ballistic and electronic damage regimes. Previous works have shown an important structural resistance of boron carbide even at high neutron fluences. Nevertheless, the structural modification mechanisms due to irradiation are not well understood. Therefore the aim of this paper is to study structural modifications induced in B4C samples in different damage regimes. The boron carbide pellets were shaped and sintered by using spark plasma sintering method. They were then irradiated in several conditions at room temperature or 800 °C, either by favoring the creation of ballistic damage (between 1 and 3 dpa), or by favoring the electronic excitations using 100 MeV swift iodine ions (Se ≈ 15 keV/nm). Ex situ micro-Raman spectroscopy and Doppler broadening of annihilation radiation technique with variable energy slow positrons were coupled to follow the evolution of the B4C structure under irradiation.

New Bond Coat Materials for Thermal Barrier Coating Systems Processed Via Different Routes

NASA Astrophysics Data System (ADS)

Soare, A.; Csaki, I.; Sohaciu, M.; Oprea, C.; Soare, S.; Costina, I.; Petrescu, M. I.

2017-06-01

This paper aims at describing the development of new Ru-based Bond Coats (BC) as part of Thermal Barrier Coatings. The challenge of this research was to obtain an adherent and uniform layer of alumina protective layer after high temperature exposure. We have prepared a RuAl 50/50 at% alloy in an induction furnace which was subsequently subjected to oxidation in an electric furnace, in air, at 1100C, for 10h and 100h. Mechanical alloying of Ru and Al powders was another processing route used in an attempt to obtain a stoichiometric RuAl. The alloy was sintered by Spark Plasma Sintering (SPS) and then oxidized at 1100C for 1 and10h. The alloys obtained as such were analysed before and after oxidation using advanced microscopy techniques (SEM and TEM). The encouraging results in case of RuAl alloys prepared by induction melting reveal that we obtained an adherent and uniform layer of alumina, free of delta-Ru. The results for the samples processed by powder metallurgy were positive but need to be further investigated. We should note here the novelty of this method for this particular type of application - as a BC part of a TBC system.

Wettability of eutectic NaLiCO3 salt on magnesium oxide substrates at 778 K

NASA Astrophysics Data System (ADS)

Li, Chuan; Li, Qi; Cao, Hui; Leng, Guanghui; Li, Yongliang; Wang, Li; Zheng, Lifang; Ding, Yulong

2018-06-01

We investigated the wetting behavior of a eutectic carbonate salt of NaLiCO3 on MgO substrates at an elevated temperature of 778 K by measuring contact angle with a sessile drop method. Both sintered and non-sintered MgO were prepared and used as the substrates. The sintered substrates were obtained by sintering compacted MgO powders at 500-1300 °C. For comparison purposes, a single crystal MgO substrate was also used in the work. The different sintering temperatures provided MgO substrates with different structures, allowing their effects on salt penetration and hence wettability and surface energy to be investigated. A scanning electron microscope equipped with energy dispersive spectrometry and an atomic force microscope were used to observe the morphology and structures of the MgO substrates as well as the salt penetration. The results showed a good wettability of the carbonate salt on both the sintered and non-sintered MgO substrates and the wettability depended strongly on the structure of the substrates. The non-sintered MgO substrate has a loose surface particle packing with large pores and crevices, leading to significant salt infiltration, and the corresponding contact angle was measured to be ∼25°. The contact angle of the salt on the sintered MgO substrates increased with an increase in the sintering temperature of the MgO substrate, and the contact angle of the salt on the single crystal substrate was the highest at ∼40°. The effect of the sintering temperature for making the MgO substrate could be linked to the surface energy, and the linkage is validated by the AFM measurements of the adhesion forces of the MgO substrates.

Effect of Starch on Sintering Behavior for Fabricating Porous Cordierite Ceramic

NASA Astrophysics Data System (ADS)

Li, Ye; Cao, Wei; Gong, Lunlun; Zhang, Ruifang; Cheng, Xudong

2016-10-01

Porous cordierite ceramics were prepared with starch as pore-forming agent by solid-state method. The green bodies were sintered at 1,100-1,400 °C for 2 h. The characterization was focused on thermal analysis, phase evolution, sintering behavior, porosity and micro-structural changes. The results show that cordierite becomes the main crystallization phase at 1,200 °C. The shrinkage behavior shows the most obvious dependence on the sintering temperature and starch content, and it can be divided into three stages. Moreover, the open porosity increases with the increase of starch content, but the pore-forming effectivity decreases. Nevertheless, compared with the open porosity curves, the bulk density curves are more in line with the linear rule. The microphotographs show the densification process with the sintering temperature and the variation of pore connectivity with the starch content.

Characterizations of Rapid Sintered Nanosilver Joint for Attaching Power Chips

PubMed Central

Feng, Shuang-Tao; Mei, Yun-Hui; Chen, Gang; Li, Xin; Lu, Guo-Quan

2016-01-01

Sintering of nanosilver paste has been extensively studied as a lead-free die-attach solution for bonding semiconductor power chips, such as the power insulated gated bipolar transistor (IGBT). However, for the traditional method of bonding IGBT chips, an external pressure of a few MPa is reported necessary for the sintering time of ~1 h. In order to shorten the processing duration time, we developed a rapid way to sinter nanosilver paste for bonding IGBT chips in less than 5 min using pulsed current. In this way, we firstly dried as-printed paste at about 100 °C to get rid of many volatile solvents because they may result in defects or voids during the out-gassing from the paste. Then, the pre-dried paste was further heated by pulse current ranging from 1.2 kA to 2.4 kA for several seconds. The whole procedure was less than 3 min and did not require any gas protection. We could obtain robust sintered joint with shear strength of 30–35 MPa for bonding 1200-V, 25-A IGBT and superior thermal properties. Static and dynamic electrical performance of the as-bonded IGBT assemblies was also characterized to verify the feasibility of this rapid sintering method. The results indicate that the electrical performance is comparable or even partially better than that of commercial IGBT modules. The microstructure evolution of the rapid sintered joints was also studied by scanning electron microscopy (SEM). This work may benefit the wide usage of nanosilver paste for rapid bonding IGBT chips in the future. PMID:28773686

Characterizations of Rapid Sintered Nanosilver Joint for Attaching Power Chips.

PubMed

Feng, Shuang-Tao; Mei, Yun-Hui; Chen, Gang; Li, Xin; Lu, Guo-Quan

2016-07-12

Sintering of nanosilver paste has been extensively studied as a lead-free die-attach solution for bonding semiconductor power chips, such as the power insulated gated bipolar transistor (IGBT). However, for the traditional method of bonding IGBT chips, an external pressure of a few MPa is reported necessary for the sintering time of ~1 h. In order to shorten the processing duration time, we developed a rapid way to sinter nanosilver paste for bonding IGBT chips in less than 5 min using pulsed current. In this way, we firstly dried as-printed paste at about 100 °C to get rid of many volatile solvents because they may result in defects or voids during the out-gassing from the paste. Then, the pre-dried paste was further heated by pulse current ranging from 1.2 kA to 2.4 kA for several seconds. The whole procedure was less than 3 min and did not require any gas protection. We could obtain robust sintered joint with shear strength of 30-35 MPa for bonding 1200-V, 25-A IGBT and superior thermal properties. Static and dynamic electrical performance of the as-bonded IGBT assemblies was also characterized to verify the feasibility of this rapid sintering method. The results indicate that the electrical performance is comparable or even partially better than that of commercial IGBT modules. The microstructure evolution of the rapid sintered joints was also studied by scanning electron microscopy (SEM). This work may benefit the wide usage of nanosilver paste for rapid bonding IGBT chips in the future.

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

Sudiana, I. Nyoman, E-mail: sudiana75@yahoo.com; Ngkoimani, La Ode; Usman, Ida

Microwave sintering of materials has attracted much research interest because of its significant advantages (e.g. reduced sintering temperatures and soaking times) over the conventional heating. Most researchers compared processes that occurred during the microwave and conventional heating at the same temperature and time. The enhancements found in the former method are indicated as a 'non-thermal effect' which is usually used for explaining the phenomena in microwave processing. Numerous recent studies have been focused on the effect to elucidate the microwave interaction mechanism with materials. Moreover, recent progress on microwave sources such as gyrotrons has opened the possibility for processing materialsmore » by using a higher microwave frequency. Therefore, the technology is expected to exhibit a stronger non-thermal effect. This paper presents results from a series of experiments to study the non-thermal effect on microwave sintered alumina. Sintering by using a wide rage of microwave frequencies up to 300 GHz as well as a conventional furnace was carried out. The linear shrinkages of samples for each sintering method were measured. Pores and grains taken from scanning electron microstructure (SEM) images of cut surfaces were also examined. The results of a comparative study of the shrinkages and microstructure evolutions of the sintered samples under annealing in microwave heating systems and in an electric furnace were analyzed. A notably different behavior of the shrinkages and microstructures of alumina after being annealed was found. The results suggested that microwave radiations provided an additional force for mass transports. The results also indicated that the sintering process depended on microwave frequencies.« less

Method and device for microwave sintering large ceramic articles

DOEpatents

Kimrey, Jr., Harold D.

1990-01-01

A microwave sintering system and method are provided for extremely uniform sintering of large and/or irregular shaped ceramic articles at microwave frequencies of at least 28 GHz in the hundreds of kilowatts power range in an untuned cavity. A 28 GHz, 200 kw gyrotron with variable power output is used as the microwave source connected to an untuned microwave cavity formed of an electrically conductive housing through an overmoded waveguide arrangement which acts in conjunction with a mode promoter within the cavity to achieve unexpected field uniformity. The part to be sintered is placed in the cavity and supported on a removable high temperature table in a central location within the cavity. The part is surrounded by a microwave transparent bulk insulating material to reduce thermal heat loss at the part surfaces and maintain more uniform temperature. The cavity may be operated at a high vacuum to aid in preventing arcing. The system allows controlled increased heating rates of greater than 200.degree. C./min to provide rapid heating of a ceramic part to a selected sintering temperature where it is maintained by regulating the microwave power applied to the part. As a result of rapid heating, the extent of non-isothermal processes such as segregation of impurities to the grain boundaries are minimized and exaggerated grain growth is reduced, thereby strengthening the mechanical properties of the ceramic part being sintered.

A Review of Metal Injection Molding- Process, Optimization, Defects and Microwave Sintering on WC-Co Cemented Carbide

NASA Astrophysics Data System (ADS)

Shahbudin, S. N. A.; Othman, M. H.; Amin, Sri Yulis M.; Ibrahim, M. H. I.

2017-08-01

This article is about a review of optimization of metal injection molding and microwave sintering process on tungsten cemented carbide produce by metal injection molding process. In this study, the process parameters for the metal injection molding were optimized using Taguchi method. Taguchi methods have been used widely in engineering analysis to optimize the performance characteristics through the setting of design parameters. Microwave sintering is a process generally being used in powder metallurgy over the conventional method. It has typical characteristics such as accelerated heating rate, shortened processing cycle, high energy efficiency, fine and homogeneous microstructure, and enhanced mechanical performance, which is beneficial to prepare nanostructured cemented carbides in metal injection molding. Besides that, with an advanced and promising technology, metal injection molding has proven that can produce cemented carbides. Cemented tungsten carbide hard metal has been used widely in various applications due to its desirable combination of mechanical, physical, and chemical properties. Moreover, areas of study include common defects in metal injection molding and application of microwave sintering itself has been discussed in this paper.

Cantilever testing of sintered-silver interconnects

DOE PAGES

Wereszczak, Andrew A.; Chen, Branndon R.; Jadaan, Osama M.; ...

2017-10-19

Cantilever testing is an underutilized test method from which results and interpretations promote greater understanding of the tensile and shear failure responses of interconnects, metallizations, or bonded joints. The use and analysis of this method were pursued through the mechanical testing of sintered-silver interconnects that joined Ni/Au-plated copper pillars or Ti/Ni/Ag-plated silicon pillars to Ag-plated direct bonded copper substrates. Sintered-silver was chosen as the interconnect test medium because of its high electrical and thermal conductivities and high-temperature capability—attractive characteristics for a candidate interconnect in power electronic components and other devices. Deep beam theory was used to improve upon the estimationsmore » of the tensile and shear stresses calculated from classical beam theory. The failure stresses of the sintered-silver interconnects were observed to be dependent on test-condition and test-material-system. In conclusion, the experimental simplicity of cantilever testing, and the ability to analytically calculate tensile and shear stresses at failure, result in it being an attractive mechanical test method to evaluate the failure response of interconnects.« less

Microwave-Assisted Synthesis of High Dielectric Constant CaCu3Ti4O12 from Sol-Gel Precursor

NASA Astrophysics Data System (ADS)

Ouyang, Xin; Cao, Peng; Huang, Saifang; Zhang, Weijun; Huang, Zhaohui; Gao, Wei

2015-07-01

CaCu3Ti4O12 (CCTO) powders derived from sol-gel precursors were calcined and sintered via microwave radiation. The obtained CCTO powders were compared with that obtained via a conventional heating method. For microwave heating, 89.1 wt.% CCTO was achieved from the sol-gel precursor, after only 17 min at 950°C. In contrast, the conventional calcination method required 3 h to generate 87.6 wt.% CCTO content at 1100°C. In addition, the CCTO powders prepared through 17 min of microwave calcination exhibited a small particle size distribution of D50 = 3.826 μm. It was found that a lengthy hold time of 1 h by microwave sintering is required to obtain a high dielectric constant (3.14 × 103 at 102 Hz) and a reasonably low dielectric loss (0.161) in the sintered CCTO ceramic. Based upon the distinct microstructures, the dielectric responses of the CCTO samples sintered by different methods are attributed to space charge polarization and internal barrier layer capacitor mechanism.

Cantilever testing of sintered-silver interconnects

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

Wereszczak, Andrew A.; Chen, Branndon R.; Jadaan, Osama M.

Cantilever testing is an underutilized test method from which results and interpretations promote greater understanding of the tensile and shear failure responses of interconnects, metallizations, or bonded joints. The use and analysis of this method were pursued through the mechanical testing of sintered-silver interconnects that joined Ni/Au-plated copper pillars or Ti/Ni/Ag-plated silicon pillars to Ag-plated direct bonded copper substrates. Sintered-silver was chosen as the interconnect test medium because of its high electrical and thermal conductivities and high-temperature capability—attractive characteristics for a candidate interconnect in power electronic components and other devices. Deep beam theory was used to improve upon the estimationsmore » of the tensile and shear stresses calculated from classical beam theory. The failure stresses of the sintered-silver interconnects were observed to be dependent on test-condition and test-material-system. In conclusion, the experimental simplicity of cantilever testing, and the ability to analytically calculate tensile and shear stresses at failure, result in it being an attractive mechanical test method to evaluate the failure response of interconnects.« less

Design and Fabrication of an Experimental Microheater Array Powder Sintering Printer

NASA Astrophysics Data System (ADS)

Holt, Nicholas; Zhou, Wenchao

2018-03-01

Microheater array powder sintering (MAPS) is a novel additive manufacturing process that uses an array of microheaters to selectively sinter powder particles. MAPS shows great promise as a new method of printing flexible electronics by enabling digital curing of conductive inks on a variety of substrates. For MAPS to work effectively, a microscale air gap needs to be maintained between the heater array and the conductive ink. In this article, we present an experimental MAPS printer with air gap control for printing conductive circuits. First, we discuss design aspects necessary to implement MAPS. An analysis is performed to validate that the design can maintain the desired air gap between the microheaters and the sintering layer, which consists of a silver nanoparticle ink. The printer is tested by printing conductive lines on a flexible plastic substrate with silver nanoparticle ink. Results show MAPS performs on par with or better than the existing fabrication methods for printed electronics in terms of both the print quality (conductivity of the printed line) and print speed, which shows MAPS' great promise as a competitive new method for digital production of printed electronics.

Elaboration of austenitic stainless steel samples with bimodal grain size distributions and investigation of their mechanical behavior

NASA Astrophysics Data System (ADS)

Flipon, B.; de la Cruz, L. Garcia; Hug, E.; Keller, C.; Barbe, F.

2017-10-01

Samples of 316L austenitic stainless steel with bimodal grain size distributions are elaborated using two distinct routes. The first one is based on powder metallurgy using spark plasma sintering of two powders with different particle sizes. The second route applies the reverse-annealing method: it consists in inducing martensitic phase transformation by plastic strain and further annealing in order to obtain two austenitic grain populations with different sizes. Microstructural analy ses reveal that both methods are suitable to generate significative grain size contrast and to control this contrast according to the elaboration conditions. Mechanical properties under tension are then characterized for different grain size distributions. Crystal plasticity finite element modelling is further applied in a configuration of bimodal distribution to analyse the role played by coarse grains within a matrix of fine grains, considering not only their volume fraction but also their spatial arrangement.

Physical properties and microstructure study of 316L SS fabricated by metal injection moulding process

NASA Astrophysics Data System (ADS)

Dandang, Nur Aidah Nabihah; Harun, Wan Sharuzi Wan; Khalil, Nur Zalikha; Ismail, Muhammad Hussain; Ibrahim, Rosdi

2017-12-01

Metal injection moulding (MIM) has been practised to process alloy powders to become components with significant physical and mechanical properties. Dissimilar than other methods, MIM focuses on the production of high volume, a small, and complex shape of products. The performance of the compacts depends on the suitable sintering parameters that governs their strengths in the final phase which determines the excellent properties of the sintered compacts. Three different sintering temperatures were utilised; 1100, 1200, and 1300 °C with two different soaking times; 1 and 3 hours at 10 °C/min heating rate to study their effect on the physical properties and microstructure analysis of 316L SS alloy compacts. The shrinkage measurement, surface roughness, and density measurement had been conducted for physical properties study. Different sintering temperatures give an effect to the physical properties of the sintered compacts. The shrinkage measurement at 1300 °C and 3-hour sintering condition demonstrated the highest percentage reading which was 10.1 % compared to the lowest percentage reading of 6.4 % at 1100 °C and 1-hour sintering conditions. Whereas, the minimum percentage of density measurement can be found at sintering conditions of 1100 °C and 1-hour which is 83.9 % and the highest percentage is at 1300 °C and 3-hour sintering condition which is about 89.51 %. Therefore, it has been determined that there could be a significant relationship between sintering temperature and physical properties in which it can be found from the porosity of the compact based on the microstructure studies.

Grain size effect on the giant dielectric constant of CaCu{sub 3}Ti{sub 4}O{sub 12} nanoceramics prepared by mechanosynthesis and spark plasma sintering

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

Ahmad, Mohamad M., E-mail: mmohamad@kfu.edu.sa; Department of Physics, Faculty of Science, Assiut University in the New Valley, El-Kharga 72511; Yamada, Koji

2014-04-21

In the present work, CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) nanoceramics with different grain sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosynthesized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The grain size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed inmore » CCTO nanoceramics. The dielectric constant increases with increasing the grain size of the nanoceramics with values of 8.3 × 10{sup 3}, 2.4 × 10{sup 4}, and 3.2 × 10{sup 4} for SPS-800, SPS-900, and SPS-975, respectively. For the micro-sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 10{sup 4}. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.« less

Spark plasma sintering and microstructural analysis of pure and Mo doped U3Si2 pellets

NASA Astrophysics Data System (ADS)

Lopes, Denise Adorno; Benarosch, Anna; Middleburgh, Simon; Johnson, Kyle D.

2017-12-01

U3Si2 has been considered as an alternative fuel for Light Water Reactors (LWRs) within the Accident Tolerant Fuels (ATF) initiative, begun after the Fukushima-Daiichi Nuclear accidents. Its main advantages are high thermal conductivity and high heavy metal density. Despite these benefits, U3Si2 presents an anisotropic crystallographic structure and low solubility of fission products, which can result in undesirable effects under irradiation conditions. In this paper, spark plasma sintering (SPS) of U3Si2 pellets is studied, with evaluation of the resulting microstructure. Additionally, exploiting the short sintering time in SPS, a molybdenum doped pellet was produced to investigate the early stages of the Mo-U3Si2 interaction, and analyze how this fission product is accommodated in the fuel matrix. The results show that pellets of U3Si2 with high density (>95% TD) can be obtained with SPS in the temperature range of 1200°C-1300 °C. Moreover, the short time employed in this technique was found to generate a unique microstructure for this fuel, composed mainly of closed nano-pores (<1 μm) and small average grain size (∼4.5 μm). The addition of Mo (1.5 at%) demonstrated no solubility of Mo in the U3Si2 matrix. The interaction of this fission product with the fuel matrix at 1200 °C formed, in the early stages, the stoichiometric U2Mo3Si4 ternary as well as precipitates of free uranium with small quantities of dissolved Si and Mo at the front of the reaction.

Si-Ca species modification and microwave sintering for NiZn ferrites

NASA Astrophysics Data System (ADS)

Yang, Yin-Ju; Sheu, Ching-Iuan; Cheng, Syh-Yuh; Chang, Horng-Yi

2004-12-01

NiZn ferrite particles were precoated with Si-Ca precursor by sol-gel method. Thus convention-sintered particles exhibited small grain size about 2 μm and lowered magnetic permeability as well as increased coercive magnetic field effectively. Microwave sintering could suppress grain growth as the same result of conventional sintering specimens with SiO2-CaO precoating. In microwave process, the grain growth inhibition expressed more obviously for the SiO2-CaO precoated specimens. The magnetic permeability (∼300) after SiO2-CaO precoating became lower than original ferrite (∼800) without SiO2-CaO precoating in conventional sintering. However, the magnetic permeability was lowered no matter whether SiO2-CaO precoating in microwave process. On the other hand, microwave sintering possessed short processing time, for example, 1250 °C/5 min, to prohibit ZnO volatilization in accompanied with grain size reduction. Therefore, such contribution increased resistivity to about 12×106 Ω cm compared to 3×106 Ω cm of original NiZn ferrite. The large coercive magnetic field (Hc) was ascribed to the superposition of small grain size and stress induced by microwave sintering.

Characterizing Sintered Nano-Hydroxyapatite Sol-Gel Coating Deposited on a Biomedical Ti-Zr-Nb Alloy

NASA Astrophysics Data System (ADS)

Jafari, Hassan; Hessam, Hamid; Shahri, Seyed Morteza Ghaffari; Assadian, Mahtab; Shairazifard, Shahin Hamtaie Pour; Idris, Mohd Hasbullah

2016-03-01

In this study, sol-gel dip-coating method was used to coat nano-hydroxyapatite on specimens of Ti-14Zr-13Nb alloy for orthopedic applications. The coated specimens were sintered at three different temperatures and time spans to evaluate the impact of sintering process on microstructure, mechanical, bio-corrosion, and bioactivity properties of the coating. Field-emission scanning electron microscopy and x-ray diffraction were used to analyze the coating microstructure. Coating adhesion and mechanical performance were also investigated by scratch testing. Besides, electrochemical corrosion and immersion tests were performed in simulated body fluid to examine the sintering effect on corrosion performance and bioactivity of the coatings, respectively. The evaluations of coated specimens displayed that sintering at elevated temperatures leads to higher surface integrity and improves crystallinity of the nano-hydroxyapatite to approximately 89% which brings about distinctively enhanced mechanical properties. Similarly, it improved the corrosion rate for about 17 times through sintering at 700 °C. Immersion test proved that the coating increased the bioactivity resulted from the dissolution of calcium phosphates into the corresponding environment. It is noticeable that sintering the dip-coated specimens in the nano-hydroxyapatite improves corrosion performance and maintains bioactive behaviors as well.

Method of electrode fabrication for solid oxide electrochemical cells

DOEpatents

Jensen, R.R.

1990-11-20

A process for fabricating cermet electrodes for solid oxide electrochemical cells by sintering is disclosed. First, a porous metal electrode is fabricated on a solid oxide cell, such as a fuel cell by, for example, sintering, and is then infiltrated with a high volume fraction stabilized zirconia suspension. A second sintering step is used to sinter the infiltrated zirconia to a high density in order to more securely attach the electrode to the solid oxide electrolyte of the cell. High performance fuel electrodes can be obtained with this process. Further electrode performance enhancement may be achieved if stabilized zirconia doped with cerium oxide, chromium oxide, titanium oxide, and/or praseodymium oxide for electronic conduction is used. 5 figs.

Method of electrode fabrication for solid oxide electrochemical cells

DOEpatents

Jensen, Russell R.

1990-01-01

A process for fabricating cermet electrodes for solid oxide electrochemical cells by sintering is disclosed. First, a porous metal electrode is fabricated on a solid oxide cell, such as a fuel cell by, for example, sintering, and is then infiltrated with a high volume fraction stabilized zirconia suspension. A second sintering step is used to sinter the infiltrated zirconia to a high density in order to more securely attach the electrode to the solid oxide electrolyte of the cell. High performance fuel electrodes can be obtained with this process. Further electrode performance enhancement may be achieved if stabilized zirconia doped with cerium oxide, chromium oxide, titanium oxide, and/or praseodymium oxide for electronic conduction is used.

Thermal conductivity of zirconia thermal barrier coatings

NASA Technical Reports Server (NTRS)

Dinwiddie, R. B.; Beecher, S. C.; Nagaraj, B. A.; Moore, C. S.

1995-01-01

Thermal barrier coatings (TBC's) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBC's is of primary importance. Physical vapor description (PVD) and plasma spraying (PS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The PS coatings were applied with either standard power or hollow sphere particles. The hollow sphere particles yielded a lower density and lower thermal conductivity coating. The thermal conductivity of both fully and partially stabilized zirconia, before and after thermal aging, will be compared. The thermal conductivity of the coatings permanently increase upon being exposed to high temperatures. These increases are attributed to microstructural changes within the coatings. Sintering of the as fabricated plasma sprayed lamellar structure is observed by scanning electron microscopy of coatings isothermally heat treated at temperatures greater than 1100 C. During this sintering process the planar porosity between lamella is converted to a series of small spherical pores. The change in pore morphology is the primary reason for the observed increase in thermal conductivity. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the PVD coatings are less susceptible to thermal aging effects, preliminary results suggest that they have a higher thermal conductivity than PS coatings, both before and after thermal aging. The increases in thermal conductivity due to thermal aging for partially stabilized plasma sprayed zirconia have been found to be less than for fully stabilized plasma sprayed zirconia coatings. The high temperature thermal diffusivity data indicates that if these coatings reach a temperature above 1100 C during operation, they will begin to lose their effectiveness as a thermal barrier.

Thermal conductivity of zirconia thermal barrier coatings

NASA Technical Reports Server (NTRS)

Dinwiddie, R. B.; Beecher, S. C.; Nagaraj, B. A.; Moore, C. S.

1995-01-01

Thermal barrier coatings (TBC's) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBC's is of primary importance. Physical vapor deposition (PVD) and plasma spraying (PS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The PS coatings were applied with either standard powder or hollow sphere particles. The hollow sphere particles yielded a lower density and lower thermal conductivity coating. The thermal conductivity of both fully and partially stabilized zirconia, before and after thermal aging, will be compared. The thermal conductivity of the coatings permanently increases upon exposed to high temperatures. These increases are attributed to microstructural changes within the coatings. Sintering of the as-fabricated plasma sprayed lamellar structure is observed by scanning electron microscopy of coatings isothermally heat treated at temperatures greater than 1100 C. During this sintering process the planar porosity between lamella is converted to a series of small spherical pores. The change in pore morphology is the primary reason for the observed increase in thermal conductivity. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the PVD coatings are less susceptible to thermal aging effects, preliminary results suggest that they have a higher thermal conductivity than PS coatings, both before and after thermal aging. The increases in thermal conductivity due to thermal aging for partially stabilized plasma sprayed zirconia have been found to be less than for fully stabilized plasma sprayed zirconia coatings. The high temperature thermal diffusivity data indicate that if these coatings reach a temperature above 1100 C during operation, they will begin to lose their effectiveness as a thermal barrier.

Porous calcium polyphosphate bone substitutes: additive manufacturing versus conventional gravity sinter processing-effect on structure and mechanical properties.

PubMed

Hu, Youxin; Shanjani, Yaser; Toyserkani, Ehsan; Grynpas, Marc; Wang, Rizhi; Pilliar, Robert

2014-02-01

Porous calcium polyphosphate (CPP) structures proposed as bone-substitute implants and made by sintering CPP powders to form bending test samples of approximately 35 vol % porosity were machined from preformed blocks made either by additive manufacturing (AM) or conventional gravity sintering (CS) methods and the structure and mechanical characteristics of samples so made were compared. AM-made samples displayed higher bending strengths (≈1.2-1.4 times greater than CS-made samples), whereas elastic constant (i.e., effective elastic modulus of the porous structures) that is determined by material elastic modulus and structural geometry of the samples was ≈1.9-2.3 times greater for AM-made samples. X-ray diffraction analysis showed that samples made by either method displayed the same crystal structure forming β-CPP after sinter annealing. The material elastic modulus, E, determined using nanoindentation tests also showed the same value for both sample types (i.e., E ≈ 64 GPa). Examination of the porous structures indicated that significantly larger sinter necks resulted in the AM-made samples which presumably resulted in the higher mechanical properties. The development of mechanical properties was attributed to the different sinter anneal procedures required to make 35 vol % porous samples by the two methods. A primary objective of the present study, in addition to reporting on bending strength and sample stiffness (elastic constant) characteristics, was to determine why the two processes resulted in the observed mechanical property differences for samples of equivalent volume percentage of porosity. An understanding of the fundamental reason(s) for the observed effect is considered important for developing improved processes for preparation of porous CPP implants as bone substitutes for use in high load-bearing skeletal sites. Copyright © 2013 Wiley Periodicals, Inc.

Method of producing improved microstructure and properties for ceramic superconductors

DOEpatents

Singh, Jitendra P.; Guttschow, Rob A.; Dusek, Joseph T.; Poeppel, Roger B.

1996-01-01

A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa.sub.2 Cu.sub.3 O.sub.x indicates that sintering kinetics are enhanced at reduced p(O.sub.2). The density of specimens sintered at 910.degree. C. increased from 79 to 94% theoretical when p(O.sub.2) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O.sub.2) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910.degree. C. resulted in a fine-grain microstructure, with an average grain size of approximately 4 .mu.m. Such a microstructure results in reduced microcracking, strengths as high as 191 MPa and high critical current density capacity.

Method of producing improved microstructure and properties for ceramic superconductors

DOEpatents

Singh, J.P.; Guttschow, R.A.; Dusek, J.T.; Poeppel, R.B.

1996-06-11

A ceramic superconductor is produced by close control of oxygen partial pressure during sintering of the material. The resulting microstructure of YBa{sub 2}Cu{sub 3}O{sub x} indicates that sintering kinetics are enhanced at reduced p(O{sub 2}). The density of specimens sintered at 910 C increased from 79 to 94% theoretical when p(O{sub 2}) was decreased from 0.1 to 0.0001 MPa. The increase in density with decrease in p(O{sub 2}) derives from enhanced sintering kinetics, due to increased defect concentration and decreased activation energy of the rate-controlling species undergoing diffusion. Sintering at 910 C resulted in a fine-grain microstructure, with an average grain size of approximately 4 {micro}m. Such a microstructure results in reduced microcracking, strengths as high as 191 MPa and high critical current density capacity. 20 figs.