Silicon carbide parts for protection of blast furnace tuyere noses

Abstract

666.762.852:669.162.221 In recent years in a number of countries silicon carbide refractories have become widely used for lining blast furnaces [1][2][3][4]. At each level of the furnace lining the refractory is subjected to the aggressive action of physicochemical, thermomechanical, and thermotechnical factors. In the tuyere zone the most important are thermal shocks and the action of alkali and zinc vapors and heated gases containing particles of dust and carbon. The tuyere noses, which, in addition to the above factors, undergo the mechanical and abrasive actions of solid, liquid, and gaseous reaction products, are under even more complex service conditions 9A chemically inert, heat resistant, and mechanically strong refractory capable of resisting the action of these factors is necessary for lining the tuyere nose. In this case the problem of development of parts of self-bonded silicon carbide, which would meet the requirements imposed to the greatest degree, has arisen. The essence of obtaining self-bonded silicon carbide parts is synthesis of the silicon carbide parts is synthesis of the silicon carbide binder during firing of the compacts. There are a number of methods of formation of silicon carbide binders from secondary fl-SiC [5][6][7]. The most common is production of /3-SIC from crystalline silicon and carbon by siliciding the solid component by Si vapors or liquid. Formation of the structure and phase composition occurs in reaction sintering, which occurs under conditions of nonoxidizing heating.To study the processes occurring in firing of silicon carbide compacts containing crystalline silicon and carbon investigations were made of specimens of mixtures of Si and C, Sit 2 and C, and also SiC) 2, Si and C. The compositions of the charges were based on the possibility of formation of SiC as the result of the following reactions between the components: Si + C --, SiC; Sit 2 + 3C --, SiC + 2CO; Si + Sit 2 + 4C --, 2SiC + 2CO.Crystalline silicon, quartzite, and petroleum coke were used for preparation of the binder. All of the materials were ground until obtaining of the freer than 0.06-mm fraction. The pressed and dried specimens were fired in argon, nitrogen, and carbon monoxide (crushed coke) atmospheres. In firing of specimens in argon they did not contract since the volume effect of the reaction (zSq) Siso 1 + Cso I --, SiCso I is negative (Aq = -29.8%). In all of the investigated compacted specimens the density after firing dropped by about 0.06-0.09 g/cm 3 and a direct relationship of density of the fired specimens to density of the green specimen is established.In firing of specimens in nitrogen and CO other reactions occur: 3Si + N 2 + Sit = Si2ON 2 -Aq (+41,8 %), 3SiC + 2CO = Sit 2 + 3C -Aq (+247,4 %), 3SiC + 2N 2 = Si.~Na + 3C -/~q (+64,4 %).These reactions occur with a positive effect with compaction and strengthening of the specimens. The results presented show that by changing the charge composition, temperature, and gaseous atmosphere and compaction of the compacts it is possible to ...