High-purity Powder Research Articles

Valence states, impurities and electrocrystallization behaviors during molten salt electrorefining for preparation of high-purity titanium powder from sponge titanium

High-purity titanium powder was prepared by molten salt electrorefining from sponge titanium in NaCl–KCl–TiClx salts. The titanium valence, purity and electrocrystallization during electrolysis process were studied. The XPS analysis showed that the titanium valences are mainly +4, +3 and +2 at the earlier, medium and later stages of electrolysis, respectively. During the electrolysis process, the contents of impurities Si, Cr, Mn, Al vary little, and the contents of impurities Fe, Cu, Ni decrease markedly, while the contents of impurities O, N, H increase obviously. The residual impurities are usually distributed in small tunnel of dendritic crystals. Enhancing the electrolysis temperature and prolonging the electrolysis time can increase the titanium particle size. The TEM analysis showed that the electrodeposited titanium is not a single crystal, but contains many nanostructured grains and subgrains, with grain size of 100–500 nm. The electrolysis mechanisms were also discussed.

Characterization of Nickel Ions in Nickel‐Doped Yttria‐Stabilized Zirconia

The distribution of Ni2+ ions in NiO‐doped 10YSZ powder is examined with Superconducting Quantum Interference Device magnetometry, a technique that is able to distinguish between randomly distributed Ni2+ ions in solid solution and ordered Ni2+ ions within NiO with high precision. Very high purity powders containing 0.01, 0.1, 0.5, and 1.0 mol% NiO in 10YSZ (all levels below the solid solubility limit of NiO in 10YSZ) were made from acetate precursors and a modified EDTA (ethylenediaminetetraacetic acid)‐citrate synthesis method. The powders were calcined in air at either 873 or 1273 K. The 873 K calcination leads to single phase YSZ particles about 10 nm in diameter, and almost all of the NiO dopant exists in complete solid solution. The 1273 K calcination leads to a larger YSZ particle size (55–95 nm), and also to the formation and/or growth of NiO particles, the amount of which depends on the length of time of calcination. Upon sintering the powders in air (1773 K, 1 h), the NiO dissolves back into 10YSZ. The results demonstrate that particle growth during calcination leads to the exsolution of Ni2+ ions to form NiO. This has important implications for the synthesis of NiO‐doped 10YSZ from chemical precursors.

Preliminary Information of Laboratorial Tantalum Recovery and Considerations for a Potential Solution for Conflict Mineral and Wildlife Conservation

Tantalum is a rarely occurring transition metal which is chiefly used to manufacture capacitors for electronic appliances such as mobile phones. The demand for tantalum is expected to show an annual growth rate of about 5%; however, tantalum produced in the Democratic Republic of Congo is considered a conflict mineral due to illegal mining which is accelerating the extinction of lowland gorillas. Although tantalum recycling is desirable, the recycling technology has been poorly developed. Phase separation was applied to recover tantalum. It was expected that a copper phase could absorb tantalum, but tantalum was slightly transferred into an iron-rich phase in the Cu-Fe-C system. When ferric oxide was applied as an auxiliary, the tantalum was concentrated as precipitate on the surface of the iron-rich phase. In terms of practical application, a theoretical prediction suggests that the addition of a reductant will make it possible to recover tantalum as a high-purity powder. Since conflict, illicit exploration and hunting (bush-meat trade) have caused a decline in the population of wild animals, it is considered that a feasible tantalum recycling system will be helpful in solving such problems.

Prepare dispersed CIS nano-scale particles and spray coating CIS absorber layers using nano-scale precursors

In this study, the Mo-electrode thin films were deposited by a two-stepped process, and the high-purity copper indium selenide-based powder (CuInSe2, CIS) was fabricated by hydrothermal process by Nanowin Technology Co. Ltd. From the X-ray pattern of the CIS precursor, the mainly crystalline phase was CIS, and the almost undetectable CuSe phase was observed. Because the CIS powder was aggregated into micro-scale particles and the average particle sizes were approximately 3 to 8 μm, the CIS power was ground into nano-scale particles, then the 6 wt.% CIS particles were dispersed into isopropyl alcohol to get the solution for spray coating method. Then, 0.1 ml CIS solution was sprayed on the 20 mm × 10 mm Mo/glass substrates, and the heat treatment for the nano-scale CIS solution under various parameters was carried out in a selenization furnace. The annealing temperature was set at 550°C, and the annealing time was changed from 5 to 30 min, without extra Se content was added in the furnace. The influences of annealing time on the densification, crystallization, resistivity (ρ), hall mobility (μ), and carrier concentration of the CIS absorber layers were well investigated in this study.

不同形貌纳米镍粉的制备

以粗镍粉(平均粒径为24.6 μm)和氯化钠为原料，将两者按不同的摩尔比混合，700℃下氯化得到氯化镍与氯化钠的低共熔混合物。在900℃加热使低共熔物熔化挥发，氢气还原挥发物即得到不同形貌和粒径的高纯镍粉。当NaCl/Ni摩尔比为4.0，制备出了平均粒径为97.42 nm的球形钠米镍粉；当NaCl/Ni摩尔比为2.0，制备出了平均粒径为101.92 nm的立方体形超细镍粉；没有氯化钠添加，制备出的镍粉颗粒是烧结在一起的，并且没有规则形状。导致以上现象的可能原因被探讨了。Some anhydrous eutectics composed of nickel chloride and sodium chloride were obtained by chlorinating the mixtures of sodium chloride and row nickel (average particle size 24.6 μm) with different molar ratios at 700°C. The eutectics were smelt and vaporized at 900°C and the vaporized eutectics were reduced by H2 into nickel powders of high purity with different shapes and different particle sizes. When the molar ratio of NaCl/Ni was 4.0, some spherical nanoparticles of nickel with average particle size 97.42 nm were synthesized. When the molar ratio of NaCl/Ni was 2.0, some cubic superfine particles of nickel with average particle size 101.92 nm were synthesized. Without addition of NaCl, some sintered nickel particles of irregular shape were synthesized. The plausible reasons were given to explain above phenomena.

Effects of element addition on the β→α transformation in tin

The influence of 1 wt.% Pb, Cu, Ge and Si on the transformation kinetics of the β-Sn→α-Sn transformation in high-purity powder mixtures was examined using synchrotron powder X-ray diffraction. Pb and Cu were found to be effective in suppressing α–tin growth. Ge and Si inhibited the β→α transformation. The kinetics of the transformation are largely determined by the nucleation of α-Sn.

Low-temperature densification and excellent thermal properties of W–Cu thermal-management composites prepared from copper-coated tungsten powders

High-density W–20wt.%Cu composites containing a Cu-network structure and exhibiting good thermal properties were fabricated by low-temperature hot-press sintering from high-purity copper-coated tungsten powders. The relative density of W–20wt.%Cu composites sintered at 950°C–100MPa–2h was 98.4%. The low-temperature densification of W–Cu composites occurs because the sintering mode of the coated particles involves only sintering of Cu to Cu, rather than both Cu to W and Cu to Cu, as required for conventional powder particles. The microstructure shows that a network of high-purity Cu extends throughout the composites, and that the W is distributed homogeneously; the interfaces between W and Cu show good contact. The composites have excellent thermal conductivity (239W/(mK)) and a relatively low coefficient of thermal expansion (7.4×10−6/K), giving them some of the best properties reported to date for thermal-management materials. The excellent performance is mainly because of their structure, which arises from the characteristics of the high-purity copper-coated tungsten powders.

Quantitative determination of trace metals in high-purity silicon carbide powder by laser ablation inductively coupled plasma mass spectrometry without binders

We have developed a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method to directly determine the concentrations of trace metals in high-purity powdery silicon carbide (SiC) samples. The sample preparation procedure is simple and rapid. The sample was formed into pellets using no binders and heated at 1000°C for 2h. The operation parameters for LA and ICP-MS were optimized to achieve a table signal intensity and high sensitivity. National Institute of Standards and Technology Standard Reference Materials glasses were chosen as calibration standards, with 29Si chosen as the internal standard. The relative sensitivity factor obtained from the glass matrix was used to calculate the concentrations of analytes in the SiC ceramic samples. The regression correlation coefficients of the calibration curves for elements with internal standard correction ranged from 0.9981 to 0.9999, which are better than those obtained with an external standard correction method only. The relative standard deviation of the measured trace element concentrations was less than 5%. The limits of detection were 0.02, 0.08, 0.04, 0.005, 0.01, 0.02, 0.004, 0.07, and 0.006mgkg−1 for B, Ti, Cr, Mn, Fe, Ni, Co, Cu, and Sr, respectively. The method was applied to analyze SiC samples with two different particle sizes. The analysis showed good agreement with the results of inductively coupled plasma optical emission spectrometry. The reliability of the proposed method was confirmed by determining the contents of B, Ti, Cr, Mn, Fe, Ni, and Cu in BAM-S003.

Copper nanopowder synthesis by electrolysis method in nitrate and sulfate solutions

Chemical electrodeposition (electrolysis) is one of the methods which can be used for production of high-purity copper powder. In this work, synthesis of nano-sized copper powder particles by means of electrolysis has been investigated. Parameters such as electrolysis solution, type of current (direct and pulse), and nitric acid concentration have been studied. The media of study were nitrate and sulfate. Particle size of powder obtained by the direct current in the nitrate solution was even smaller than those of the pulse current state in the sulfate. Thus, the nitrate solution was chosen for investigation of the nitric acid concentration (25–45g/L). The obtained powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and laser particle size analyzing (LPSA) methods. The powders produced in the sulfate solution (in pulse state along with the polyvinylpyrrolidone (PVP) additive) were less than 200nm in size; however, those produced in the nitrate solution (in direct state without additive) were less than 100nm. Current efficiency of the nitrate solution (about 30%) was significantly less than that of the sulfate solution (about 70%). The powders produced in the nitrate solution were of high purity, similar to the sulfate solution.

Synthesis of high pure Ti3AlC2 and Ti2AlC powders from TiH2 powders as Ti source by tube furnace

Titanium aluminum carbide (Ti3AlC2 and Ti2AlC) powders were synthesized from TiH2 powders instead of Ti powders as Ti source by a tube furnace under argon atmosphere without preliminary dehydrogenation. 95 wt% pure Ti3AlC2 powders were synthesized from TiH2/1.1Al/2TiC at 1 450 °C for 120 min. High-purity Ti2AlC powders were also prepared from 3TiH2/1.5Al/C and 2TiH2/1.5Al/TiC powders at 1 400 °C for 120 min. The as-synthesized samples were porous and easy to be ground into powders. Sn or Si additives in starting materials increased the purity of synthesized Ti3AlC2 obviously and expanded the temperature range for the synthesis of Ti3AlC2. With Si or Sn as additives, high pure Ti3AlC2 was synthesized at 1 200 °C for 60 min from TiH2/x Si/Al/2TiC and TiH2/x Sn/Al/2TiC (x = 0.1, 0.2), respectively.

Transparent Ceramics for Photonic Applications

AbstractThe International Symposium on Transparent Ceramics for Photonic Applications is an annual international conference since 2005. The previous LCS events were held in Poland (2005), Japan (2006), France (2007), China (2008), Spain (2009), Germany (2010), and Singapore (2011). The 8th LCS was held in Russia in the city of Nizhny Novgorod on December 4–7, 2012. The aim of the symposium was to provide a forum for material scientists, chemists and physicists, to discuss the state of the art of optical transparent ceramics, including basic aspects and promising applications, and to give an insight into future advances and research possibilities in this field.The symposium program included invited talks as well as contributed presentations. This year the main focuses of the symposium were:– Synthesis of high purity powders and transparent ceramics– Optical spectroscopy and characterization of physical properties– New materials and novel fabrication methods– Ceramic lasers and amplifiers– Composite structured laser ceramics.The International Program Committee had 24 members from 16 countries worldwide (http://www.8lcs.iapras.ru/committees.html). The OSA representative in the International Program Committee was academician S. N. Bagayev. After revision, the symposium program consisted of 42 reports, including 13 invited talks (invited speaker names can be found on the webpage: http://www.8lcs.iapras.ru/invited.html). Among the 67 participants of the LSC 2012, 44 were from Russia, 9 from P.R. China, 6 from Japan, 3 from Ukraine, 2 from South Korea, 1 from UK, 1 from Germany, and 1 from Singapore. The oral presentations were given in English.The symposium took four days and was divided into three sessions: “Ceramics fabrication ”, “Ceramics characterization ” and “Ceramic lasers ”.As representatives of the industry, Dr. Hideki Yagi from Konoshima Chemical Co. Ltd. (Japan) gave the interesting review “Transparent ceramics for photonic applications ” and Dr. Ken‐ichi Ueda from Hamamatsu Photonics K.K. (Japan) told about important applications of laser ceramics in his lecture “Thermal lens free ceramic laser ”.The fellow of the Optical Society of America, director of the Institute of Extreme Light (France), Gerard Mourou, has visited the technical sessions and a subsequent discussion of the Laser Ceramics Symposium.The LCS has brought together leading experts from around the world, stimulated active discussions and contacts between the scholars and gave a brilliant opportunity for the participants to start further fruitful research collaborations.The four‐days LCS 2012 was attended by 67 scientists and engineers from around the world. Pictures could be found in the gallery at: http://www.8lcs.iapras.ru/photoshots.html.The next, the 9th Laser Ceramics Symposium will be held in Seoul, South Korea in 2013.

화학적 처리를 적용한 Slurry 분리 및 비교분석 검증 연구

The use of slurry with a mix of abrasives and coolant for making Wire Saw in the photovoltaic industry has sharply increased with the semiconductor wafer. In this paper, the slurry was isolated, purified and dried by microwave drying method with high-purity silicon carbide powder obtained through chemical processing. Dried slurry bulk was first pulverized and chemical treatment was applied to produce powder. The produced slurry powder was then analyzed by going through the following analysis; thermal analysis, particle size analyses: SEM shots, elemental analysis, XRF and XRD. The results of this study found the recovery rate of the power obtained though the chemical processing to be higher than the one obtained from mineral processing. The results anticipate infrastructure building and active responses to increasingly stronger domestic and international environmental regulations through the integration and recycling of large amounts of slurry in the photovoltaic industry.

Study of Nitrogen Concentration in Silicon Carbide

This work focused on studying the nitrogen concentration (C N) in SiC. The variations of C N in the synthesis of SiC powder as well as the transport during SiC crystal growth have been investigated for broad ranges of temperature and Ar pressure. Before SiC crystal growth, SiC powders were synthesized from high-purity silicon and carbon powders. The concentrations of nitrogen, free C, and free Si in the as-prepared powders were all measured. C N in the SiC source powder decreased with increasing temperature and decreasing Ar pressure, whereas it did not show a remarkable trend with the molar ratio of free Si to free C. SiC crystal was then grown by the physical vapor transport (PVT) technique using the as-prepared powder. The distribution of C N in the remaining material indirectly indicated the temperature field of crystal growth. In addition, compared with introducing N2 during SiC crystal growth, doping with nitrogen during synthesis of the SiC source powder might be a better method to control C N in SiC crystals.

Effect of synthesis atmosphere, wetting, and compaction on the purity of AlB2

Abstract AlB2 is attractive as an energetic fuel because of its large heat of combustion on a volumetric basis. The formation of AlB2 from its elements is thermodynamically limited by decomposition into liquid aluminum and α-AlB12 at temperatures approaching 950 °C, and kinetically limited in the reverse reaction, making synthesis of high-purity powders difficult. Minimizing unreacted Al and B makes AlB2 more resistant to moisture degradation. AlB2 yield for similarly prepared samples was observed to be significantly higher in He–6% H2 or vacuum compared to a high-purity Ar atmosphere. Lower AlB2 yield was generally associated with higher Al2O3 content in the reaction products, suggesting that poor Al wetting on oxide surfaces generated by the reaction of Al with B2O3 and other sources of oxygen prevented complete reaction. Compaction decreased the amount of oxygen available to the interior of the pellet, and the vacuum and He–6% H2 environments reduced the amount of oxide impurities in the system, possibly by reducing or subliming them. By optimization of synthesis parameters the purity of AlB2 was measured as 93 wt%, which was better than the previously reported bulk syntheses. Accounting for unreacted boron is important when using XRD to assess purity since the quantification of secondary phases, such as Al, Al2O3, and Al3BC, allow the amount of boron, which is not easily detected in the scan, to be calculated.

Activation measurements of fast neutron radiative capture for 139La

The neutron capture cross section of the neutron magic isotope 139La has been measured relative to that of 27Al by means of the activation method. The fast neutrons were produced via the 3H(d,n)4He reaction on Pd-300 neutron generator. The natural high-purity La2O3 powder was used as target material. Induced gamma activities were measured by a high-resolution gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The new values for En=13.5±0.2, 14.1±0.2, and 14.8±0.2MeV are found to be 1.30±0.08, 1.15±0.08 and 0.99±0.07mb, respectively. Results were discussed and compared with some corresponding values found in the literature.

Fabrication of transparent Nd:YAG ceramic by vacuum sintering with CaF2 additive

Abstract Neodymium-doped yttrium aluminum garnet (Nd:YAG) ceramics were fabricated via a solid-state reaction method using high-purity Y2O3, Al2O3 and Nd2O3 powders as the raw materials. The mixed powder compacts were sintered at 1 750 °C for 5 h under vacuum. The Nd:YAG bulk without doped CaF2 was opaque. A transparent Nd:YAG ceramic was obtained with tiny amounts of CaF2 addition. The bulk had a uniform microstructure containing grains with an average size of 20 μm. No porosity could be detected in the sintered bulk. The maximum optical transmittance of the sample is 44 % in the visible range.

Synthesis of Nanocrystalline Electron Emissive Materials with Homogenous Composition in Nanoscale

In this research, specific stoichiometric mixture of nanocrystalline barium carbonate, calcium carbonate, and aluminum oxide was fabricated by using the sol-gel combustion method. This mixture is used as emissive materials on impregnated cathodes which make up high power vacuum microwave tubes such as klystrons. Composition uniformity and particle size of emissive materials affect the electron emission properties of impregnated cathodes. In this study, dry gel and heat treated powder at 500 °C are investigated by thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The results show that dry gel combusts at 260 °C , and that during combustion transforms from an amorphous phase to a nanocrystalline phase. The average crystallite size of the powders which is calculated by Debye-Scherrer's method based on the XRD patterns is under 45 nm. The results of SEM and EDX of powder after heat treatment at 500 °C show that the particle size of powder is under 100 nm, and the chemical composition of emissive material is uniform at nanoscale. technique and ball-milling method. They reported that the emission properties of cathode synthesized by sol-gel technique were better than that of cathode produced through ball-milling method. They claimed that small particles and more uniform mixing bring about good emission capability of scandate cathode synthesized by sol-gel technique. Generally, the sol-gel combustion method is a novel technique for the production of crystalline and high purity powders. Sol-gel combustion technique is based on a chemical sol-gel and the subsequent combustion process. During the sol-gel process, an aqueous solution containing salts of the desired metal and an organic fuel form a gel. After the gel obtained, ignition occurs in the gel due to combustion process. The product of this step is voluminous and fluffy with a large surface area. This technique is characterized by inexpensive raw materials, low temperature synthesis, and obtaining nanocrystalline powder with homogenous composition (9). Studies have shown that using emissive materials with uniform composition and crystallite size at nanoscale improve emission performance of cathode. Wang et al. (10) fabricated oxide cathode using nano emissive materials which is produced by liquid-gas method. They reported that the emission current density of oxide cathode used nano emissive materials is significantly higher than that of the conventional oxide cathode under the same condition. The main goals of this work were to synthesize appropriate mixture of emissive materials by sol-gel combustion technique and investigation of crystalline structure and the composition uniformity of synthesized powder.

A Study on Trapping CO2 Using Molecular Sieve for 14C AMS Sample Preparation

At the Seoul National University accelerator mass spectrometry (AMS) laboratory, we are planning to develop an automated sample preparation system for higher throughput of radiocarbon dating. This system will consist of several sections, including a combustion line, CO2 trap, graphitization system, and so on. We usually collect CO2 by cryogenic trapping. However, since handling liquid nitrogen is expected to be rather difficult, we are interested in replacing the cryogenic method with the molecular sieve method for the collection of CO2. In this study, we compare the performance of the cryogenic trapping method and molecular sieve method. Zeolite 13X is used as a molecular sieve, and as test samples we use the oxalic acid standard (NIST SRM 4990C), high-purity graphite powder, and archaeological charcoals. The pMC values and the radiocarbon ages (BP) obtained from samples prepared by the above 2 methods are very similar. We especially focused on the memory effect of the molecular sieve, meaning the CO2 contamination from a previous sample, which can cause errors in age determination. To reduce this effect, we flowed He gas through a zeolite container for several minutes at a high temperature before the CO2 was introduced. By the adding this step, we have obtained more reliable results.

A Study on Trapping CO2 by Using a Molecular Sieve for 14C AMS Sample Preparation

At the Seoul National University accelerator mass spectrometry (AMS) laboratory, we are planning to develop an automated sample preparation system for higher throughput of radiocarbon dating. This system will consist of several sections, including a combustion line, CO2 trap, graphitization system, and so on. We usually collect CO2 by cryogenic trapping. However, since handling liquid nitrogen is expected to be rather difficult, we are interested in replacing the cryogenic method with the molecular sieve method for the collection of CO2. In this study, we compare the performance of the cryogenic trapping method and molecular sieve method. Zeolite 13X is used as a molecular sieve, and as test samples we use the oxalic acid standard (NIST SRM 4990C), high-purity graphite powder, and archaeological charcoals. The pMC values and the radiocarbon ages (BP) obtained from samples prepared by the above 2 methods are very similar. We especially focused on the memory effect of the molecular sieve, meaning the CO2 contamination from a previous sample, which can cause errors in age determination. To reduce this effect, we flowed He gas through a zeolite container for several minutes at a high temperature before the CO2 was introduced. By the adding this step, we have obtained more reliable results.

On the Bi2O3-Al2O3-PbO system

The present work is dedicated to the description of the pseudo-binary Al2O3-Bi2O3 and the isothermal section at 600°C of the system Al2O3-Bi2O3-PbO according to a Calphad approach. It takes part of the complete description of the complex system Pb-Bi-Fe-(Al,Cr)-O. Such study is of high interest for the nuclear community that aims to develop protective coatings for the MEGAPIE spallation target to prevent the T91 steel from corrosion due to contact with lead-bismuth eutectic liquid. A survey in literature has revealed a discrepancy between equilibrium phases diagrams related to the Al2O3Bi2O3 system where four different compounds were reported. Therefore, an experimental reinvestigation of the system was necessary. Samples were prepared from mixtures of powders of high purity at different compositions then annealed at different temperatures. Different techniques were used to characterize the samples: XRD, SEM (EDS and WDS) and DTA. Only two stoichiometric compounds were found to be stable at low temperature, and invariant transformations were determined. The same process was used in case of addition of PbO. A modeling of the binary is also proposed.