Effect of some technological parameters on structure formation in materials based on reaction-sintered silicon carbide

Abstract

Results of petrographic, x-ray, chemical, and spectral investigations of the structure and composition of materials based on SiC fabricated by reaction sintering of preforms pressed from grainy silicon carbide and its mixtures with petroleum coke in molten and volatilized silicon are presented. It is shown that the structure and composition of reaction-sintered silicon carbide materials can be controlled by changing the proportion of silicon carbide and petroleum coke in the pressed preform, the coarseness of carbide and carbon particles, the density of the pressings, and the temperature of reaction sintering. It is established experimentally that secondary silicon carbide formed as a result of the reaction between petroleum coke and silicon binds the grains of the initial carbide into a dense silicon carbide skeleton, whereas the retained pores are filled with free silicon. A single-phase material consisting entirely of silicon carbide can hardly be obtained by the method of reaction sintering. In practice, this method gives double-phase (SiC-Si) and triple-phase (SiC-Si-C) materials with a maximum content of the principal phase (SIC) equal to 94 -96% (mass fractions).SiC-base materials possess a comparatively low density, a low coefficient of thermal expansion, a high thermal conductivity, and an elevated resistance to oxidation and to the effect of chemically active and abrasive-containing media, which makes them invaluable for various fields of engineering. They are used in linings of heating furnaces, jet mills, facings of pipelines for transporting aggressive fluids, friction pairs operating under conditions of abrasive and chemical wear, and other purposes.In recent years Russia and other countries have been developing research aimed at fabricating and investigating the properties of silicon carbide materials of high density (85-98% of the theoretical value). High-density articles from SiCbase materials were obtained for the first time in the 1950s by the method of hot pressing of powder silicon carbide in graphite molds at 2000-2200QC under a pressure of 100 MPa [1,2]. However, the method of hot pressing is laborious, expensive, and unproductive, which hampered its wide industrial use.

Structural features of a carbon plastic material infiltrated with molten silicon

“…Thus, the infiltration of car- bon fibers with molten silicon may be regarded as a modification of the preparation of SiC components by the method of reactive sintering described in some detail in [1,2,7].…”

“…In this connection, the development and industrial use of composite SiC-materials reinforced with carbon fibers are issues of important concern for technologists, considering that to date there is sufficient experience in the production of SiC components using reactive sintering techniques [1,2] and siliconizing of carbon fabric [7]. Thus, the infiltration of car- bon fibers with molten silicon may be regarded as a modification of the preparation of SiC components by the method of reactive sintering described in some detail in [1,2,7].…”