Reduction kinetics of molybdenum oxide in slag

The reduction rate of Mo oxide in slag by iron-carbon melt under different stirring conditions, reaction temperatures and slag composition has been investigated. Results indicate that the reduction of Mo oxide is a fast reaction; both stirring and temperature have evident influence upon the reaction; while the initial concentration of Mo oxide and content of fluoride in slag have also some influence upon the reaction. The reduction of Mo oxide is an apparent first order reaction. At 1440–1500°C, the reduction rate of Mo oxide is mainly controlled by Mo transfer in slag, with its diffusion activation energy of 223 kJ/mol. At 1500–1590°C, the transfer of Mo in metal turns to be the main limiting step, with its diffusion activation energy of 81.5 kJ/mol.     

Reduction of tungsten oxide to tungsten metal

Tungsten oxide, WO_2.96, was reduced toα-W in hydrogen for various time periods over the temperature range 500°C to 900°C. Intermediate oxides were determined using X-ray diffraction analysis of the semireduced powders. Several dopant conditions were used, to find the effect on oxide structures and reaction kinetics of the usual dopants K, Si and Al. The scanning electron microscope was employed to determine the morphology of the crystallites at intermediate and final stages of reduction. This research was supported in part by the U.S. Energy Research and Development Administration, Contract E(11-1)-1198.     

Structural mechanism and character of redistribution of tungsten and molybdenum in their reduction from a mixed oxide

Conclusions At temperatures of 600°C and higher the mixed oxide (W_0.5Mo_0.5)O₃ is reduced with the starting uniform distribution of tungsten and molybdenum being retained in the end product, which is due to a single mechanism being operative in the process. As a result, a virtually homogeneous alloy is formed. At 400–600°C the reduction of tungsten and molybdenum from the mixed oxide involves two different structural mechanisms, which brings about a regrouping of the metals, disturbs their uniform starting distribution, and hence lowers the degree of homogeneity of the end product.Translated from Poroshkovaya Metallurgiya, No. 3(255), pp. 1–7, March, 1984.     

氧化钨氢还原动力学的研究进展

超细钨粉是目前制备多种硬质合金和结构材料的重要原料,其主要制备方法为氢还原法.在对大量文献资料进行查阅及分析的基础上,综述了氧化钨氢还原动力学的研究现状,包括氧化钨氢还原的基本原理、不同动力学条件下的还原历程以及物相转换.介绍了国内外学者在不同钨氧化物的氢还原过程中,通过改变动力学参数对产物钨粉的粒度、形貌、结构和性能的影响,以及实际工业生产的现状和存在的问题.重点介绍了目前氢还原动力学的几种模型及其方程,并对可能适用于氧化钨氢还原动力学研究的动力学模型进行了展望.      

Reduction characteristics and kinetics of iron oxide by carbon in biomass

The characteristics and kinetics of iron oxide reduction by carbon in biomass composites were studied. Iron oxide can be reduced by biomass very rapidly, and the degree of metallisation and reduction increases with temperature. Iron oxide reduction by carbon in biomass can be divided into two stages: reduction by volatile carbon followed by reduction by non-volatile carbon. The reduction times of the two stages both decrease with increasing temperature. The first reduction is controlled by gas diffusion, whereas the second stage is dominated by carbon gasification.     

Electrochemical synthesis of tungsten and molybdenum borides in a dispersed condition

Electrolytic deposition of tungsten and molybdenum boride particles from ionic melts is studied. Conditions are found for preparing different boride phases. If the anode material is graphite and the voltage in the bath does not exceed 2.5 V the cathode deposit consists mainly of tungsten and molybdenum metals. A mixture of phases (M, M₂B, MB, MB₂, M₂B₅) is produced on the cathode with U=2.5–3.5 V, while with U=2.3–3.5 V, while with U=3.5–4.5 V the deposit consists of the higher boride MB₄. On the whole the process of electrochemical synthesis for molybdenum and tungsten borides is governed by the following interconnected parameters: electrolytic bath composition, voltage in the bath, temperature, and duration of electrolysis.Institute of General and Inorganic Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 1 (361), pp. 8–11, January, 1993.