Heat treatment of very fine palladium powders

Translated from Poroshkovaya Metallurgiya, No. 11(323), pp. 23–26, November, 1989.     

Properties and sintering behaviour of fine spherical iron powders produced by new hydrogen reduction process

Abstract

The most important use of fine spherical iron powders is for metal injection moulding (MIM). For many applications, the high costs of powder based on the carbonyl or atomising production route are a limiting factors. An alternative two-step hydrogen reduction process using a granulated hematite powder, which is a recycling product from steelmaking, has been developed to produce <25 µm spherical powder. The morphology and properties of the powder have been found to depend strongly on the second temperature step of the reduction process. A further important step is enclosed powder processing by milling and sieving to remove agglomerates. The powder properties and sintering behaviour as a function of heat treatment and processing parameters are reported and discussed.     

Production of fine tin powders of various degrees of purity

Conclusions Pneumoacoustic atomization enables the yield of fine tin powder fractions to be increased by 20–30% compared with the pneumatic method. The purity of resultant powders is higher than that of powders comminuted mechanically in the presence of a SAA.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 7–9, May, 1986.     

Production of high-purity microcrystalline molybdenum and rhenium powders by reduction in hydrogen-nitrogen media

Possibilities of producing high-purity microcrystalline molybdenum and rhenium powders by direct single-stage reduction of ammonium compounds of molybdenum [(NH₄)₆Mo₇O₂₄ · 4H₂O] and rhenium [NH₄ReO₄] in hydrogen-nitrogen media are considered. Based on the results of investigations of the influence of technological parameters (degree of purity of the initial reactants, temperature, gas mixture composition, reactant feed rate) on the quality of target products, an optimum regime of the reduction process has been established, which ensures the production of high-purity microcrystalline molybdenum and rhenium powders.     

Production of nickel and iron nanopowders by hydrogen reduction from salts

The formation of nickel and iron nanoparticles produced by a chemical??metallurgical method and steels made of composite iron powders with nanosized nickel additions is studied. A procedure is developed for calculating the nanopowder particle size and the activation energy of sintering. The results obtained make it possible to decrease the temperature of the process of powder production, to decrease the energy consumed for powder sintering, and to predict the powder nanoparticle size.     

Production of very fine TiN-Mo composite powders in a low-temperature plasma stream

Conclusions In the hydrogen reduction of TiCl₄, and thermal decomposition of Mo(CO)₆ in a stream of shf discharge nitrogen plasma the main reaction products are titanium nitride and molybdenum. The impurity elements in the composite (carbon and oxygen) react with the titanium nitride, forming the titanium oxycarbonitride TiN_xO_yC_z (where x + y + z = 1, y < 0.10, and z < 0.05). The formation of nitride particles takes place before the instant of full pyrolysis of Mo(C0)₆, and molybdenum therefore does not cover them, but condenses in the form of free spherical particles whose mean size is about half that of the particles forming during the pyrolysis of the carbonyl without a TiCl₄ addition to the reactor. A characteristic feature of the resultant fine molybdenum-nitride composite powders is a high uniformity of distribution of Ti and Mo in them.Translated from Poroshkovaya Metallurgiya, No. 11(251), pp. 3–8, November, 1983.     

Methods for preparing fine powders based on zirconium dioxide (review)

Mechanical, physical, and chemical methods for producing fine powders based on zirconium dioxide are considered. Their main advantages and disadvantages are reported.Translated from Poroshkovaya Metallurgiya, No. 7(367), pp. 24–30, July, 1993.     

赤铁粉矿在H2气氛中的闪速还原行为

通过高温下的动力学实验对铁粉矿在H_2气氛中的闪速还原行为进行了研究.采用XRD、SEM和金相显微镜对反应后铁粉矿的物相组成和单个粉矿颗粒表面及内部微观形貌的演变规律进行了分析,采用化学分析法获得了反应后赤铁粉矿的还原度.结果表明:铁粉矿高温下发生的闪速还原仍然遵循Fe_2O_3→Fe_3O_4→FeO→Fe的逐级还原规律.粉矿颗粒的剖面由未反应核和产物层构成,符合未反应核模型的描述.采用模型函数配合法得出铁粉矿与H_2在高温下发生闪速还原反应的限制性环节是界面化学反应,进一步基于动力学模型计算得到,闪速还原的表观活化能为311 kJ/mol.     

Kinetics of the reaction of S-carboxymethyl-L-cysteine with palladium(II) chloride

The influence of the acidity and the Cl- concentration on the kinetics of the complex formation between s-carboxymethyl-L-cysteine and Pd(II) chloride was studied with a stopped-flow technique in the pH range from 1.5 to 5.0 at 25 degrees C. The reaction mechanism involving Pd(H2O)4-nCln, LH-, LH2 and LH3+ species was proposed. Fairly good agreement between the computed and experimentally determined rate constants was found.