Sodium thermal reduction of tantalum powders from melts with tantalum pentaoxide additions

The effect of the oxygen concentration in a melt on the characteristics of sodium-reduced tantalum powders, which were produced from potassium heptafluotantalate-based melts with tantalum pentaoxide additions, is studied. An increase in the oxygen content in the initial melt from 0.35 to 2.0 wt % leads to an increase in the specific surface of the formed powder from 1.2 to 3.5 m²/g. The specific charge of anodes made from these powders is 37800–70700 CV/g.     

Sintering of dispersed tantalum powders

Translated from Poroshkovaya Metallurgiya, No. 12 (360), pp. 11–16, December, 1992.     

Some chemical properties of tantalum germanide powders

Conclusions A study was made of the resistance of tantalum germanides to the action of some liquid aggressive media and atmospheric oxygen. It is shown that tantalum germanides are fairly resistant to attack by various acids and their mixtures, but react with solutions containing fluorine ions, Perhydrol, and concentrated sulfuric acid. Their resistance to the action of liquid reagents grows with rise in their tantalum content. A study was made also of the atmospheric oxidation resistance of the germanides at various temperatures.Translated from Poroshkovaya Metallurgiya, No. 11 (119), pp. 13–17, November, 1972.     

Preparation of palladium-based alloy powders by the thermal decomposition of binary complex ammonium oxalate salts

The possibility of obtaining powder alloys (solid solutions) by thermal decomposition of salts of the types [Pd(NH₃)₄[M(C₂O₄)₂] and (M(NH₃)_n[Pd(C₂O₄)₂] was investigated. Salts of the desired compositions were synthesized by double decomposition of the ammonium and oxalate complexes of the metals in aqueous solution. The production of new compounds was confirmed by x-ray diffraction analysis. It was shown that pyrolysis of the salts (Pd(NH₃)₄][M(C₂O₄)₂] occurs in stages: initially one of the oxalate groups migrates to the cationic part, and later the products obtained, (Pd(NH₃)₂](C₂O₄)] and MC₂O₄, decompose. The decomposition temperatures of the salts obtained correlated with those of MC₂O₄. Pyrolysis of [Pd(NH₃)₄] [M(C₂O₄)₂] produced highly dispersed solid solution powders of palladium with copper, nickel, and copper, respectively, with the atom ratio Pd:M = 1:1, and the intermetallic compound PdZn. The powder particle sizes did not exceed 1 m. Initial salts, intermediate products, and oxides were not detected in the powders.Krasnoyarsk State Academy of Nonferrous Metals and Gold. Institute of Chemical and Chemical-Metallurgical Processes. Siberian Division of the Russian Academy of Sciences. Translated from Poroshkovaya Metallurgiya. Nos. 3/4(384), pp. 6–10, March–April. 1996. Original article submitted December 12. 1994.     

Magnesium-thermic reduction of tantalum oxide by self-propagating high-temperature synthesis

The magnesium-thermic reduction of tantalum pentoxide is studied during self-propagating high-temperature synthesis, i.e., under the conditions of manufacturing solid products in an autowave combustion mode. The effects of the charge density, the charge temperature, the particle size of reagents, and thermal ballast on the combustion rate and the maximum process temperature are investigated. Depending on the charge parameters, the combustion rate changes from 1.6 to 13 mm/s and the measured combustion temperatures varies in the range 1100–1885°C.     

溶胶凝胶-碳热还原法制备Si_3N_4纳米粉末

以硅溶胶为硅源,有机碳为碳源,有机氮和氮气为氮源,先采用溶胶-凝胶法制备前驱体,然后进行碳热还原制备Si3N4陶瓷纳米粉体.主要研究了硅碳比、反应温度、氮气流量、保温时间等工艺因素对氮化硅粉体生成的影响.碳热还原制备Si3N4纳米粉体的最佳工艺条件为:碳硅比(摩尔比)为3.5: 1,氮气流量为3L/min,煅烧温度为1 500℃,保温时间2h.在以上最佳工艺条件下,可制备出纯的Si3N4纳米粉体,其中α-氮化硅为90.8%,β-氮化硅为9.2%,平均粒径为43.82nm.     

缺碳预还原MoO3+氢气深脱氧工艺制备超细钼粉

以炭黑为还原剂还原MoO₃制备存在少量MoO₂的预还原Mo粉,然后对预还原Mo粉进行氢气深还原,成功制备出平均粒径为99～190 nm的超细钼粉,研究了碳热还原温度对Mo粉平均粒度和残碳量的影响。结果表明,在同一还原温度下,当C/MoO₃摩尔比从2.0增加到2.1时,产物的粒径变化很小。碳热还原温度对产物粒径和纯度有显著影响。当C/MoO₃摩尔比为2.1时,还原温度从950 ℃增加到1150 ℃,氢还原后钼粉的平均粒径从100 nm增加到190 nm,且残碳量（质量分数）由0.030%降低到0.009%。     

Preparation and photoluminescence of Eu-doped oxyfluoride borosilicate glass ceramics

Eu-doped transparent oxyfluoride borosilicate glass ceramics containing Ba2GdF7 nanocrystals were prepared by controlling crys-tallization of melt-quenched glass fabricated under a reductive atmosphere.In the oxyfluoride borosilicate glass ceramics,the mean crystal size of Ba2GdF7 nanocrystals was about 30 nm,which could be observed by X-ray diffraction(XRD) and transmission electron microscopy analysis.The photoluminescence spectra of the samples excited at 392 nm showed that,besides the characteristic sharp emissions of Eu3+ ions,a very intense broadband emission of Eu2+ ions centered at 450 nm appeared.The photoluminescence intensity of Eu3+ and Eu2+ ions in the glass ceramics was much stronger than that in the as-made precursor.The long decay lifetimes of Eu3+ and Eu2+ ions evidenced the partitions of Eu3+ and Eu2+ ions into the Ba2GdF7 nanocrystals.The energy transfer from Gd3+ ions to Eu3+ and Eu2+ ions was confirmed by the excita-tion and emission spectra.     

电炉半钢转杯离心粒化制备铁粉工艺

摘要：为了实现钛精矿电炉冶炼副产品半钢的高附加值利用,提出了以半钢为原料,采用转杯与冷却水幕相结合的转杯离心粒化工艺制备铁粉,并作为硫酸法钛白还原剂的新工艺。实验研究了转杯直径和转速对铁粉粒度的影响规律,结果表明铁粉粒度随着转杯直径和转速的增大而减小;转杯直径为150mm、转速为1800r/min时,颗粒粒径小于0.45mm 的铁粉占比达到90.45%（质量分数）;建立了适用于转杯离心粒化颗粒粒度的预测模型,平均相对误差为 11.43%;利用扫描电镜观察了铁粉颗粒截面的显微结构,铁粉颗粒表面存在一层铁的氧化物;利用热重分析法研究了水幕对铁粉颗粒氧化程度的影响。论文最后提出了铁粉制备、余热回收与钛白制备相结合的新工艺。     

Effect of the conditions of sintering of sodium-reduced tantalum powders on their characteristics

The effect of the granulation and heat treatment of sodium-reduced tantalum powders with a specific surface area of 2.5–3.6 m²/g on the bulk density, the powder flow time, and the specific surface area of the powders and the specific capacitance of the anodes made of them is studied. It is shown that heat treatment of a granulated powder in vacuum at 1100°C or in a mixture with magnesium at 800°C makes it possible to achieve the required powder flow time.     

Properties of molybdenum powders obtained by reduction in moving beds

We have studied the process of decomposition of ammonium paramolybdate and reduction of the molybdenum oxides in moving beds with rotation of the working chamber. We have shown that agglomerated disperse molybdenum powders are formed under these conditions. Movement of powder beds during reduction ensures continuous contact between the oxides being reduced and the hydrogen, rapid removal of water vapor from the reaction zone, and establishment of nearly kinetic reduction conditions. As a result the metallic molybdenum powders are strong, highly porous agglomerates, similar to the MoO₃ particles in size and shape. The powders have high bulk (as-poured) density and good flowability, and their dispersity depends only on the reduction temperature.