V2O5碳热还原合成碳化钒粉末的反应过程

为了实现小批量连续化制备碳化钒粉末,以工业级V2O5和纳米炭黑为原料,利用碳热还原法,在常压下碳管炉中得到了V8C7。通过X射线衍射仪(XRD)、扫描电镜(SEM),分析了合成过程。结果表明:在较低的温度下,纳米炭黑将V2O5还原为VO2;随着合成温度的升高,还原为更低价的V2O3,但没有VO生成;接着发生碳化反应,生成VC1-x、V8C7,合成的各阶段相互重叠;在合成过程中,试样的显微组织因物相不同而有所不同,生成的钒氧化物为炭黑附着的颗粒状大团聚体,VC1-x粉末颗粒呈类球形,但大小不均匀;随着温度升高,合成的最终产物V8C7粉末颗粒呈球形或类球形,大小均匀,粒度为1μm左右;还原碳化过程中,产生的气体有CO、CO2。     

Interaction of vanadium carbide with a nickel-molybdenum alloy

Melting and solidification temperatures for Ni-Mo alloys (the ratio of these elements is 3:1) containing 10% (by weight) of vanadium carbide are determined. Introduction of vanadium carbide into Ni-Mo alloy reduces the melting temperature by 20°C. The alloys consist of two phases: a solid solution based on nickel and a carbide component resembling needle-shaped inclusions of the eutectic type. Traces of eutectic are observed with 1% VC in a sample. Dissolution of vanadium in the Ni-Mo alloy mentioned does not exceed 1% (by weight). The presence of two phases and their approximate composition in the alloys are confirmed by x-ray diffraction analysis. The solid solution based on nickel contains molybdenum (10–20%) and vanadium (1–6%). The carbide component is a vanadium-containing phase based on molybdenum with a crystal lattice of the Mo₂C type.Scientific Research Institute of Refractory Metals and Hard Alloys. Moscow. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 59–62, January–February, 1994.     

纳米碳化钒粉末制备的研究现状

概述了碳化钒粉末的优良性能和国内外的研究进展。详细介绍了目前制备纳米碳化钒粉末的4种主要方法:碳热还原法、气相还原法、前驱体法和机械合金化法,同时阐述了每种制备方法的优缺点及最新研究进展。最后,对纳米碳化钒粉末的发展前景进行了展望。     

Diffusion interaction of vanadium carbide with powdered steels

Conclusions The processes of diffusion interaction of vanadium carbides with cast and powdered steels are largely analogous. Differences are mainly due to unequal diffusional mobility of the components in cast and powdered materials.In cast and powdered steels equal boundary concentration of vanadium are established on the boundary with the carbides, and these concentrations are determined by the carbon content of the steel and by the temperature.The interdiffusion coefficient in ferrite does not depend on the carbon content, and it is the same for cast and powdered steels. The interdiffusion coefficient in austenite increases with increasing carbon content, and it is noticeably larger in powdered steels than in cast steels.The activation energy of interdiffusion in the austenite of powdered steels (220–230 kJ/mole) is noticeably lower than in cast steels (260–270 kJ/mole); this is due to the substantial contribution of the processes of surface diffusion to the overall mass transfer in porous materials.Translated from Poroshkovaya Metallurgiya, No. 11(323), pp. 40–45, November, 1989.     

An electron microscopy study of carbide precipitation in vanadium

The precipitation of carbon from supersaturated solid solution in vanadium has been investigated using transmission electron microscopy techniques on thin foils. High purity vanadium strip was doped to a carbon content of about 0.2 at. pct and rapidly quenched in high vacuum, followed by aging treatments for various times in the temperature range from 300° to 600°C. The strip was then thinned for transmission electron microscopy. The carbon is observed to precipitate initially as very finely dispersed carbides visible through structure factor contrast. With increasing aging the precipitate distribution coarsens, and the carbides appear as very thin coherent platelets on {310} planes, showing a pronounced displacement fringe contrast. The coherent precipitate appears to have a bcc structure closely related to that of the matrix. With further aging these platelets are observed to thicken and partially lose coherency, punching out prismatic dislocation loops and helices having axes in 〈111〉 directions. This semicoherent precipitate is found to be the hexagonal V₂C phase described by other researchers, and its orientation relationship with the matrix may be expressed: (110)v‖(00.1)v₂c, [•111]v‖[•110] v₂C. The dislocation loops are a result of the specific volume difference between the V₂C precipitation and the matrix, and have Burgers vector b = a/2〈111〉. Formerly Research Assistant, Department of Metallurgy and Mining Engineering, University of Illinois at Urbana-Champaign, Urbana Ill.     

Fe-V-C系奥氏体中VC析出动力学计算

以材料热力学及动力学为基础,以Fe-V-C三元系为研究对象,研究了1 130℃恒温条件下碳化物VC在奥氏体中从形核、长大到熟化的连续过程。各元素在碳化物-基体界面处达到局部平衡,根据基体成分以及每个碳化物颗粒的大小分别计算出生长速度。当碳化物生长进入熟化阶段,在Gibbs-Thomson效应作用下,小颗粒开始回溶,大颗粒继续长大,表现为总颗粒数量减少,平均半径变大;当保温时间达到1×104s时,析出量接近平衡状态,VC体积分数为1.51%、平均半径为0.72μm。     

Interaction between vanadium carbide and aluminum and copper melts

The effect of low-frequency vibrations on the interaction between molten metals (Al,Cu) and vanadium carbide is studied. These vibrations are shown to initiate wetting of the V8C7 carbide by a copper melt and a chemical interaction in the Al-V8C7 system, resulting in the formation of vanadium aluminides and aluminum carbide.     

Structural mechanism of oxygen implantation in the vanadium carbide lattice

Conclusions An investigation was carried out into the variation of the completeness of the elementary cell of the VC_xO_y phase forming during the progressive implantation of oxygen into the lattices of the carbides VC_0.7–0.9, and the types of solid solutions forming under these conditions were determined. The hypothesis is advanced that metal evolution in this process can be a result also of a redistribution of atoms within the matrix being formed, with the appearance of new elementary cells. In addition, the possibility cannot be ruled out of disproportionation reactions occurring during the oxidation of, inter alia, VC_x and VC_xO_y phases.Translated from Poroshkovaya Metallurgiya, No. 2(206), pp. 75–78, February, 1980.     

Microstructural analysis of vanadium carbide/steel surface-alloyed materials fabricated by high-energy electron-beam irradiation

This study is concerned with the microstructural analysis of vanadium carbide (VC)/steel surface-alloyed materials fabricated by high-energy electron-beam irradiation. The mixtures of VC powders and MgO-CaO flux were deposited on a plain carbon steel substrate, and then electron beam was irradiated on these mixtures using an electron-beam accelerator. Microstructures of the irradiated surface regions were examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. Residual pores were found in the specimen processed without flux, but hardly found in the specimens processed with a considerable addition of flux. As a result of irradiation, vanadium content was homogeneously maintained throughout the melted region, and fine vanadium carbides were formed in the melted region. These microstructural modification including the formation of vanadium carbides greatly improved hardness, especially high-temperature hardness up to 500 °C.     

The influence of annealing in the ferrite-plus-austenite phase field on the stability of vanadium carbide precipitates

The influence of rapid excursions into the ferrite-plus-austenite two-phase field on V₄C₃ precipitates formed by tempering in the ferrite phase was explored. The iron-based alloy studied contained 0.14 carbon and 0.49 vanadium in wt pct. A fine distribution of V₄C₃ particles was obtained through solution treatment followed by quench and tempering at 973 K. Samples were then rapidly heated to 1088 K for various times between 50 and 300 seconds. The plate-shaped V₄C₃ precipitates in regions that maintained their original ferrite matrix exhibited a continuous coarsening and decrease in their aspect ratio with increasing hold times. The V₄C₃ precipitates in regions that transformed to austenite were observed to dissolve by a reversion process if they were below a certain size. If the V₄C₃ particles were above that size, the matrix change caused them to coarsen and reduce their aspect ratio. Based upon the size of V₄C₃ particles that did show reversion, the interphase interfacial surface energy between the V₄C₃ partieles and aus tenite in the nonequilibrium orientation relationships produced in this study was determined to be between 1125 and 1840 mJ/m². When samples where reversion was observed were retempered at 973 K, the original distribution of fine, plate-shaped V₄C₃ particles could be reproduced accompanied by a measurable secondary hardening response.     

高炉煤气精脱硫技术的半工业试验

 高炉煤气中有机硫(主要是COS)含量高,无机硫含量低,硫的脱除难度大。针对以上特点,在山东某金属公司进行了干法精脱硫工艺的半工业试验。具体的工艺方案为,脱硫设备布置在高炉TRT设备之后,高炉煤气通过旁通管从高炉煤气管网上接入脱硫试验装置。水解和脱硫反应器均为填充床形式,采用“一级水解+脱硫”串联“二级水解+脱硫”的两级串联设计方案。在相应的水解和脱硫反应器中分别填充一种改进型的Al₂O₃基低温水解催化剂和氧化铁基脱硫剂。水解催化剂促使煤气中的有机硫(COS)与水蒸气反应生成H₂S,再由脱硫剂与H₂S反应生成Fe₂S₃,从而实现煤气中硫的脱除。在半工业试验中,进入脱硫设备的煤气流量为400 m3/h,煤气温度为80~100 ℃,COS的体积分数约为70%,H₂S的体积分数约为25%,煤气中硫浓度为145 mg/m3。经过300 h的连续试验,结果表明,该脱硫工艺全过程废水零排放;高炉煤气中有机硫(COS)转化为无机硫(H₂S)的转化率约为99%;煤气中硫分的脱除率大于96%;能够保证煤气燃烧后烟气中SO₂浓度小于10 mg/m3。