Caracterisation du composite titanium diboride-carbone avec l'aluminium liquide et le bain cryolithique des cuves d'electrolyse de l'aluminium (French text).

摘要

It is the aluminum industry which is most interested in titanium diboride (TiB₂) and TiB₂-carbon composites (TCC). The interesting properties of TiB₂ were recognized as early as the 50s.; In this study, both raw materials (anthracite, pitch and TiB₂ powder) and TiB₂-carbon composite were characterized. Results on a comparative microscopic evaluation between TiB₂-carbon composites and conventional anthracite-based carbon cathode samples after laboratory immersion and electrolysis tests are presented.; Inclusions of alumino-silicate and iron oxide types were found in the anthracite aggregates. XRD analysis allowed to differentiate between two types of aggregates: stratified (L_c = 44 nm) and non-stratified (L _c = 15 nm). The principal impurity found in the TiB₂ powder was TiCN and surface analysis of the particles revealed the presence of a contaminant layer composed of C, N, O and Ti; the thickness of this layer varied from 5 nm to 15 nm.; Although pure molten aluminum wets TiB₂ after a latent period and penetrates the composite to a depth of about 100 to 200 μm, the TiB ₂ shows no evidence of dissolution. Liquid aluminum, in direct contact with carbon, reacts readily to form Al₄C₃; the carbon from baked pitch is more reactive than the coarser anthracite particles. Molten bath dissolved TiB₂ grains preferentially along specific atomic planes. The extent of liquid bath penetration is very low for the anthracite carbon cathode, compared to the composite material which is completely impregnated within minutes. In the case of the composite, a ≈500 μm thick coherent layer of TiB₂/Al₄C₃ composite is formed, the carbon being almost completely reacted in this zone.; Following the electrolysis tests, a film of electrolyte containing aluminum nodules and filaments covers the surface of the conventional carbon cathode. In the case of the TiB₂-carbon composite, a continuous film of aluminum metal is observed, wetting the surface of the sample. The penetrating aluminum reacts with the carbon matrix to form a TiB₂/Al₄ C₃ composite sealing the surface to further penetration. (Abstract shortened by UMI.)