Failure of self-bonded silicon carbide under dynamic pressure

Translated from Poroshokovaya Metallurgiya, No. 4(304), 78–83, April, 1988.     

Reaction between zirconium carbide and silicon powders

Conclusions A study was made of the reaction of zirconium carbide and silicon powders over the temperature range 800–1700C.Translated from Poroshkovaya Metallurgiya, No. 11(83), pp. 61–65, November, 1969.     

硅粉常压直接氮化过程的非催化气固反应模型

以平均粒径2.2μm、纯度99.99%的硅粉为原料,采用纯度99.993%的高纯氮气作为反应气体,在1350和1400℃下进行了氮化时间为10~30 min的氮化实验,得出了不同温度下硅粉转化率随反应时间的变化关系.将硅氮反应看成非催化气固反应,建立了硅颗粒氮化动力学模型.通过对实验数据的拟合,得出两个模型参数:硅氮反应速率常数和氮气在产物层中的扩散系数.假定反应速率常数和扩散系数均满足阿伦尼乌斯公式,求得化学反应激活能和指前因子分别为2.71×10⁴J·mol^-1和3.07×10^-5m·s^-1,扩散激活能和指前因子分别为1.06×10⁵J·mol^-1和1.12×10^-9m²·s^-1.利用本文得出的氮化动力学模型对各温度下不同粒径硅粉的转化曲线进行了预测,预测曲线与文献中的实验数据在趋势上吻合较好.     

High-temperature zirconium carbide heating elements

Conclusions A batch of carbide filament heating elements was produced and tested. The tests showed that carbide heating elements twisted from filaments withstand heating in an inert atmosphere to temperatures of up to 2640°C at rates of 30–1000, and cooling at a rate of 2400 deg C/h.Translated from Poroshkovaya Metallurgiya, No. 7(223), pp. 33–35, July, 1981.     

On the kinetics of carbide precipitation during reaction between graphite and Fe-Ti liquids under microgravity

Experiments on the reaction between graphite and liquid Fe-Ti alloys were performed with a mirror furnace on board an airplane during parabolic flights. Small Fe-Ti alloy samples were melted in contact with graphite and held for some seconds at a temperature of 1550 °C. The samples were melted and solidified during a microgravity period. Carbon and titanium atoms reacted in the melt and titanium carbides were formed. In the experiments, a precipitation zone with faceted titanium carbide crystals dispersed in high carbon Fe-C-Ti alloy matrix was obtained near the graphite/alloy interface. The thicknesses of the carbide precipitation zones were measured and effects of alloy composition on the growth rates of the carbide zones were revealed by experiments and calculations. It was shown that the process was controlled by the diffusion of titanium in the liquid at low titanium concentrations and by diffusion of carbon through the precipitation layer at high titanium concentrations in the melt. Supersaturation of the carbide in front of the reaction interface was predicted from the calculations. The analysis showed that homogeneous nucleation of titanium carbide can readily occur in the alloys. Carbide morphologies were analyzed, and the mechanisms which lead to their formation are discussed.     

烧结温度对反应烧结碳化硅组织与性能的影响

本文研究了1450、1550、1650℃不同烧结温度制备的反应烧结SiC材料的密度、硬度、抗弯强度、显微组织、显微硬度及断裂行为。结果表明:烧结温度对材料密度影响较小。低温反应烧结的SiC晶粒的晶体结构不够完整,存在亚晶界等缺陷,晶粒强度较低,烧结材料的硬度和抗弯强度较低。高温反应烧结的SiC晶粒的晶体结构完整性增加,晶粒强度较高,烧结材料的硬度和抗弯强度较高。因此为了提高反应烧结碳化硅的力学性能,应该适当提高烧结温度或延长烧结时间。     

Formation of silicon carbide in the reaction of reduction of silica by carbon

Conclusions In the initial stages of heat treatment of H₂SiO₃ and sucrose a mixture of highly dispersed defective SiO₂ particles and carbon material is formed. Then as the result of contact interparticle interaction of a radical character disintegration (activation) of the carbon particles and envelopment of them by a layer of SiO₂ accompanied by deformation of the Si-O-Si bonds occur. Filling of the pores of the carbon material with silicon oxide creates in subsequent higher temperature treatment favorable conditions for formation of SiC. The particles formed as the result of the relatively low-temperature solid-state reaction are non-uniform in composition. Their core consists of uninteracted carbon and after it follow a layer of silicon carbide and an outer layer of SiO₂. A switch to the area of high synthesis temperature makes it possible to approach a stoichiometric composition of the silicon carbide.Translated from Poroshkovaya Metallurgiya, No. 9(321), pp. 57–62, September, 1989.     

Interactions of boron carbide with titanium and zirconium carbides under pressure

The reactions of boron carbide with titanium and zirconium carbides have been examined under various conditions. Reactive sintering of the initial mixtures produces a heterophase material based on B₄C–MeB₂ via a stage of lower boride formation. The reaction completeness is increased by adding boron and boron silicide. The material has a finely divided structure and high hardness (42–45 GPa). Promising mixture compositions have been identified together with ways of optimizing the sintering modes. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos 1-2, pp. 52–55, January–February, 1998.     

Solid state reactions between silicon carbide and (Fe,Ni, Cr)-alloys: reaction paths,kinetics and morphology

Solid state reactions between silicon carbide and various (Fe, Cr, Ni)-alloy compositions are studied. The different phases present in the reaction scale, their chemical composition and morphology are determined. The reaction path and the reaction kinetics are also measured. A typical composition distribution and morphology of the reaction scale is associated to each alloy element: iron yields broad α-iron zones with randomly distributed graphite precipitates; the presence of nickel results in typical reaction scales made of alternating bands of pure silicide and other bands of silicide containing a high density of carbon precipitates; chromium leads to large chromium carbide precipitates on the alloy side. The solid state reactions between SiC and (Fe, Cr, Ni)-alloys can be described as the dissolution of silicon carbide by iron and nickel, resulting in the formation of silicon-rich compounds (α-, τ-phase, Ni₅Si₂ or Ni₂Si) and in the precipitation of graphite flakes.