Effect of scandia on tungsten oxide powder reduction process

Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction.The particle size of doped tungsten powder,powder morphology and doped tungsten matrix were characterized by scanning electron microscope,X-ray diffrac-tion and laser diffraction particle size analyzer,respectively.The reduction behavior of Sc2O3 doped tungsten oxide and the effect of Sc2O3 on the property of tungsten powder were studied by the temperature programmed reduction.The experimental results showed that the pre-cursor powders prepared by spray drying had spherical shape.The addition of Sc2O3 could decrease the reduction temperature of tungsten oxide.The scandia doped tungsten powder had sub-micrometer size in the range of 0.1 to1 μm and scandium distributed evenly in the powder.By using this kind powder,sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scan-dium were obtained.     

Technology of deep removal of impurities from scandium oxide with the acquisition of high-purity scandium oxide

A new production process for processing off-grade scandium oxide (98%) and scandium oxides 99.0 and 99.9 and the removal of impurities from them with the acquisition of high-purity scandium oxide 99.99% is developed and tested. This process is based on various solubilities of scandium formates and elements of impurities; it involves the dissolution of starting (98–99.8%) Sc₂O₃ in HCl, the processing of the solution with NH₄OH to pH = 5–7, filtering and washing the Sc(OH)₃ precipitate with water, repulpation in formic acid, separating the precipitate of scandium formate from the mother liquor, washing scandium formate with formic acid, and drying and calcinating it with the acquisition of Sc₂O₃ of the OS-99.99 grade.     

Sintering a disperse mixture of W-Sc2O3 powders

The effect of additions of scandium oxide (1, 5, and 10 vol. %) on compaction during sintering of a disperse mixture of W-Sc₂O₃ powder at 2000°C has been studied. It has been found that the scandium oxide particles activate compaction during heating and conversely retard shrinkage of tungsten in the stage of isothermal soaking. The kinetics of compaction during sintering is determined by the geometry of the heterophase system. Depending on how much the tungsten and scandium oxide particles increase in size, the nature of thestructure changes markedly from matrix-statistical to statistical.     

Processing and performance of Cr2O3–Fe2O3 reference electrode powders prepared by oxide coprecipitation

Abstract

Cr₂O₃–Fe₂O₃ based oxide mixtures for reference electrode powders of oxygen sensors were processed using oxide coprecipitation route. A special method for preparing reference electrode powders has been developed by mixing coarse Cr particles with the oxide mixture in the form of Cr–Fe hydroxide. Morphology and size of the mixed oxide powders were characterised by means of scanning electron microscopy and laser diffraction method. With the coprecipitation process, chemically homogeneous and very fine powders with a mean particle size of 1.53 μm were prepared. This powder mixture adhered and loosely coated to Cr particles. The processed reference electrode powders were tested in low level oxygen concentration measurements of steelmaking process under industrial scale. The reference electrode powders showed excellent results in terms of electromotive force reproducibility, response time and accuracy in soluble aluminium predictions at the oxygen concentration measurements. Most of the particles of the reference electrode powder remained separated after dipping to molten steel.     

高性能等离子喷枪用多元复合稀土钨电极研制

本论文以"多元复合稀土钨电极及其制备技术"2008年国家技术发明二等奖为基础,采用喷雾干燥法并结合两段氢气还原成功制备出多元复合稀土掺杂钨粉。经过冷等静压压制、中频感应烧结后制备出等离子喷枪电极。实验结果表明,多元复合稀土的掺杂,降低了钨粉的粒度,进而提高了稀土在电极中元素的分布均匀性,稀土元素分布均匀性的提高降低了钨电极的烧损量,同时采用中频感应烧结制备的电极密度要大于垂熔烧结制备的电极。与目前使用的等离子喷枪电极相比,采用中频感应烧结制备的多元复合稀土钨电极抗烧损性能更好,电极寿命更长。     

微量硅酸钠的掺杂机理及掺杂量对还原钨粉性能的影响

将微量硅酸钠以不同浓度的水溶液形式掺杂到蓝色氧化钨中并在相同的条件下还原成钨粉。结果表明,还原钨粉的粒度随硅酸钠掺杂量的增加而增加,少量掺杂还使还原钨粉的松装密度增加。对还原钨粉表面的扫描电镜及x射线光电子能谱分析结果显示,掺杂到蓝色氧化钨中的硅酸钠最终以Na_2SiO_3和SiO_2二种分子形式存在并以微粒状分布在还原钨粉的表面。掺杂微量硅酸钠还使还原钨粉中的二次颗粒增加。     

Effect of the Phase Composition of Barium-Calcium Alumoscandates on the Emission Properties of Impregnated Cathodes

The effect of scandium oxide additions on the emission properties of impregnated tungsten cathodes was investigated. The synthesis of alumoscandates in the BaO ― CaO ― Sc₂O₃ ― Al₂O₃ system were studied by x-ray diffraction, thermography, and petrographic analysis. The hygroscopic properties of the emission-active material was determined. Based on the results of emission tests the recommended optimal compositions of emission-active material are 2.4 BaO·0.6 CaO·0.1 Sc₂O₃·0.9 Al₂O₃ and 2.6 BaO·1.9 CaO·0.1 Sc₂O₃·0.9 Al₂O₃. Cathodes based on these compositions had lifetimes greater than 10000 h operating in the temperature range 900-1000°C at current densities of 15-20 A/cm² in a vacuum of the order of 10⁻⁶ Torr.

     

溶胶-凝胶法制备稀土CeO2掺杂纳米钨粉的研究

以偏钨酸铵(AMT)、柠檬酸和硝酸铈为原料,用溶胶-凝胶法(sol-gel)制备稀土CeO2掺杂纳米钨粉。通过热重-差热(TG-DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)、比表面积法(BET)等测试手段对复合粉体的合成工艺、物相、颗粒形貌和粒径进行了分析。结果表明:当pH值为1时,还原后的粉体颗粒呈准球形,无团聚,稀土元素以CeO2形式存在且均匀地分布在钨粉中,平均颗粒粒径为80nm左右,满足制备高性能掺杂稀土氧化物亚微米结构浸渍阴极的要求。     

A Study of Scandia Doped Tungsten Nano-Powders

Scandia and rhenium doped tungsten powders were prepared by solid-liquid doping combined with two-step reduction method. The particle size of doped tungsten and distribution of scandia and rhenium were studied by SEM, EDS, XRD and granularity analysis. Experimental results showed that scandia distributed evenly on the surface of tungsten particles. Addition of scandia and rhenium decreased the particle size of doped tungsten, and the more the content of scandia and rhenium, the smaller the doped tungsten particles. Tungsten powders doped with 3 % Sc2O3 and 3 % Re （mass fraction） had an average size of about 80 nm in diameter. The mechanism of the decrease in the tungsten particle size was discussed.     

掺杂氧化铝对纳米钨粉烧结过程的影响

以碳热预还原和氢气深还原两步制备的纳米钨粉作为烧结原料,即先通过碳黑还原脱除三氧化钨中的大部分氧,再以氢还原脱除残留的氧。该方法制备的钨粉颗粒呈球形形貌,平均晶粒度可达90 nm。同时,向钨粉中掺杂质量分数为1%和2%的氧化铝,探究了氧化铝对钨粉烧结行为的影响。通过烧结样品的断口形貌和晶粒的平均尺寸分析发现,氧化铝对烧结后期的晶粒长大有明显的抑制作用,相同的烧结温度下晶粒的尺寸随着氧化铝含量的上升而减小。在1600 ℃时,纯钨粉烧结坯的晶粒平均尺寸为2.75 μm,但添加质量分数为1%和2%氧化铝的烧结样品晶粒平均尺寸约为1.5 μm,这是由于氧化铝能有效地抑制烧结后期的钨粉晶粒长大。纯钨粉和掺杂氧化铝钨粉的烧结坯的硬度随温度升高具有不同的趋势。掺杂钨粉烧结坯的硬度随着温度的升高而升高,且其最大值高于800 HV。但是,纯钨粉烧结坯的硬度随烧结温度增加而先增加后降低,在1400 ℃时取得最大值（473.6 HV）,这是由纯钨粉烧结坯的晶粒在高温下急剧长大所导致。在烧结温度为1600 ℃时,纯钨粉、掺杂质量分数1%和2%的氧化铝掺杂的钨粉的烧结坯的相对密度依次为98.52%、95.43%和93.5%。      

Plasma densification of agglomerated Cr2O3 powder for thermal spray coating

Abstract

Double plasma flame treatments were carried out on spray dried Cr₂O₃ agglomerated powders to increase their apparent density. The powders that were subjected to the first densification treatment didn't show the entirely melted state, and were fully melted only after the second plasma treatment. Plasma densification resulted in powder size decreasing as well as apparent density of particles and also resulted in the fluidity increasing due to the powder melting and surface smoothing effects. However, some parts of the particles after the second treatment showed a hollowed structure, especially for a particle size above 30 µm. The influence of the thermal conductivity of powder and the gas pressure within aggregates exposed to the plasma flame in the particle densification process was discussed in detail. The powder density strongly influenced the structure of plasma sprayed coatings. The dense coatings with high hardness and high bond strength was achieved in the coatings produced from Cr₂O₃ powders after plasma densification.     

喷雾干燥法制备PSZ—3Y粉末的粒度研究

用激光衍射法和BET法（Brunner-Emmett-Teller Method)研究了用喷雾干燥法制备的PSZ－3Y粉末的粒度性能。用喷雾干燥法能制得粒度均匀性好的球状PSZ－3Y粉末。影响粒度的主要因素是料液中（ZrO2 Y2O3)的浓度,其次是送料速度。从颗粒形貌图看出,颗粒表面布满了裂纹,所以这样的粉末经二次处理后,可获得超细粉末。     

Sc2O3掺杂对ScSZ粉体制备过程的影响研究

本文以ZrOCl₂·8H2O和Sc₂O₃为原料,聚乙二醇(PEG800)为分散剂,氨水为沉淀剂,采用共沉淀法制备了不同钪掺杂量的氧化钪稳定氧化锆(ScSZ)复合粉体,并通过TG/DSC热分析、ICP、XRD、Raman和SEM等分析手段对样品进行表征,研究了Sc₂O₃掺杂对ZrO₂前驱体热稳定性和ZrO₂粉体物相、形貌等的影响,还探讨了洗涤方式对所制备的ScSZ粉体形貌的影响。结果表明:ZrO₂和ScSZ前驱体均为无定形状态,经煅烧后ScSZ前驱体的总失重量大于ZrO₂前驱体的总失重量;未掺杂钪所制备的ZrO₂粉体为单斜相,钪掺杂改变了物相,ScSZ粉体为四方和立方相的混合晶型;钪掺杂对ZrO₂粉体的粒径无明显影响,ZrO₂和ScSZ粉体均发生一定团聚,团聚体直径约为0.5~3μm;采用乙醇洗涤有利于减小ScSZ粉体的初级纳米颗粒粒径,减小团聚现象,粉末团聚较松散。     

紫钨喷雾干燥-直接碳化法制备纳米WC-Co复合粉

以WC-6%Co为基本成分,计算原料紫钨、醋酸钴、有机碳及超纯炭黑配料量,称量后加入装有适量纯水的可倾斜式滚动球磨机,湿磨混匀12 h,形成复合盐料浆,然后充分搅拌,进行喷雾干燥后制备的前驱体粉末粒度在10¹00μm,平均粒度为50μm。将喷雾干燥好的粉末装舟(200 g),推入高温钼丝炉中,通入氢气,还原碳化温度950℃,时间30min制备的纳米WC-Co复合粉,粉末粒度分布窄,颗粒粒度在5100μm,平均粒度为50μm。将喷雾干燥好的粉末装舟(200 g),推入高温钼丝炉中,通入氢气,还原碳化温度950℃,时间30min制备的纳米WC-Co复合粉,粉末粒度分布窄,颗粒粒度在5⁴5μm,平均粒度为23.38μm。SEM、BET结果表明WC晶粒度在300 nm左右,由扫描电镜(SEM)、X光微区分析(EDS)及元素面分布图得到,W、Co、C分布均匀、Co相均匀包覆在WC晶粒周围,不存在成分偏析。XRD的半高宽窄,晶粒细小;物相纯净,无η相。     

Synthesis of Scandium Oxide Nano Power and Fabrication of Transparent Scandium Oxide Ceramics

Synthesis of Sc₂O₃ nanopowder from scandium sulfate and hexamethylenetetramine [(CH₂)₆N₄] using a precipitation method was investigated. Fourier transform infrared spectroscopy combined with differential thermal analysis/thermo-gravimetry analysis showed that chemical composition of the precursor precipitates was (Sc(OH)_2.2(SO₄)_0.04)·0.4H₂O. Phase transformation of the precursor precipitated during calcinations was investigated by X-ray diffractometry. A Sc₂O₃ nanopowder with good dispersion and a mean particle size of 80 nm was obtained by calcining the sulfate precursor at 1100 °C for 4 h. The Sc₂O₃ nanopowder was sintered into transparent Sc₂O₃ ceramic by vacuum sintering at 1700 °C for 5 h without any additives.     

Influence of the precursor composition and the reduction conditions on the characteristics of magnesium-thermic niobium powders

The influence of the composition and the conditions of the reduction of niobium oxide compounds with magnesium vapor on the specific surface area of the produced metallic powder is studied. When magnesium niobate Mg₄Nb₂O₉ is used as a precursor, the specific surface of the powder increases by several times compared to that of an Nb₂O₅ precursor. Niobium powders with the specific surface up to 150 m² g^–1 (calculated particle size 4.7 nm) and a bulk density of 0.8 g cm^–3 are formed by the reduction of Mg₄Nb₂O₉. The powders are characterized by a mesoporous structure, and the most part of the specific surface consists of pores with a diameter less than 4 nm.     

Room-Temperature Mechanochemical Synthesis of W2B5 Powders

The mechanochemical synthesis of W₂B₅ powders was successfully carried out at room temperature. WO_2.72, B₂O₃ and Mg powder blends were mixed to form batches according to the metallothermic reduction of WO_2.72 and B₂O₃ with Mg, which were subsequently mechanically alloyed (MA) using a Spex mill at different durations to constitute W₂B₅ + MgO as final products. Following mechanochemical synthesis, MgO was removed from the system by leaching the powders with HCl. Microstructural and morphological characterizations of boride powders were carried out via scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Moreover, atomic absorption spectroscopy (AAS) and differential scanning calorimetry (DSC) experiments were carried out to monitor the purity of the powders at different stages of the process. After mechanical alloying of the powder batches comprising 50 pct stoichiometrically excess amount of B₂O₃ for 30 hours and leaching with a 7 M HCl solution, pure W₂B₅ powders with an average particle size of 226 nm and an average grain size of 55.3 nm were successfully synthesized.     

仲钨酸铵还原制备超粗球形钨粉

以钨酸铵溶液为原料,加入含Li、Na和K碱金属盐的添加剂,在湿氢条件下还原制备粗晶球形钨粉.研究了碱金属盐的种类、含量及还原时间对仲钨酸铵粉末及钨粉的影响.通过扫描电镜、能谱仪、X射线衍射仪和检验分析筛对仲钨酸铵及粗晶钨粉的形貌、成分、物相组成及粒度分布进行表征.研究表明,采用钨酸铵溶液为原料,添加剂（NaCl、KCl和Li₂CO₃）为3 g·L-1,在1000℃湿氢条件下还原180 min,可直接制备出流动性良好、近球形、晶粒发育完整且均匀的粗晶钨粉.其平均粒径达到67μm,最大粒径可达150μm,最大松装密度为13.41 g·cm-3,最佳流动性为每50 g粗晶钨粉用时9 s.      

Extraction of Scandium and Zirconium from Their Oxides during the Electrolysis of Oxide–Fluoride Melts

The main features of scandium and zirconium extraction from their oxides to aluminum during the aluminothermic and electrolytic preparation of Al–Sc and Al–Zr alloys and master alloys in the KF–AlF₃, NaF–AlF₃, and KF–NaF–AlF₃ oxide–fluoride melts with Sc₂O₃ and ZrO₂ additives are studied. The influence of the melt composition and temperature, the synthesis time, the contents of oxides Sc₂O₃ and ZrO₂ in the melts, the mechanical stirring of aluminum, and the cathodic current density on the contents of scandium and zirconium in aluminum and on their extraction from the oxides is determined. The average values of scandium and zirconium extraction are 20–75 and 40–100%, respectively, depending on the synthesis parameters. The electrolytic decomposition of the oxides in the KF–AlF₃, NaF–AlF₃, and KF–NaF–AlF₃ melts results in the enhancement of scandium and zirconium extraction to aluminum. The parameters of the preparation of Al–Sc and Al–Zr alloys and master alloys with the scandium content to 10 wt % and zirconium content to 15 wt % during the electrolysis of oxide–fluoride melts are chosen as a result of the results obtained.