Patent GB-983911-A (GB)
Title: Improvements in or relating to the manufacture of bodies comprising silicon carbide and/or a high melting transition metal silicide
IPC: C04B41/50
Filed: 1961-03-03
Abstract: The resistance of a body of silicon carbide and/or a high-melting transition metal silicide oxidative decomposition is increased by depositing in and/or on the body phosphoric acid and/or a phosphate. The high-melting transition metal silicide is from a metal of Groups IVB, VB or VIB of the Periodic Table (Handbook of Chemistry and Physics, 44th Edn., page 448) and has a melting-point above 1000 DEG C., e.g. molybdenum or titanium silicide. The impregnation with phosphoric acid may take place in vacuo, and preferably at least two impregnations take place, the body being heated after each impregnation. A fixing agent may also be used with the phosphoric acid, this being to prevent evaporation of the phosphoric acid when heated either by forming an impervious coating on the body, or by reacting with the phosphoric acid to form a heat-stable coating.  The fixing agent may be a high-melting oxide, or a compound which is converted on heating in air to a high-melting oxide, e.g. alumina, aluminum hydroxide, zirconium oxide, zirconium silicate, silicon dioxide, silica gel, polyethyl silicate, aluminium phosphate, borax, titanium silicide, or a synthetic resin may be used, e.g. that formed from furfuryl alcohol and phosphoric acid at 80 DEG  C.  The fixing agent may also be used in conjunction with a bonding agent, i.e. an adhesive substance to prevent the fixing agent and protective coating formed from being detached from the body.  The bonding agent may be polyvinyl acetate, polyvinyl alcohol, dextrin, or nitrocellulose. The impregnations with the various materials may be in any order or all together.ALSO:The resistance of a body of silicon carbide and/or a high-melting transition metal silicide to oxidative decomposition is increased by depositing in and/or on the body phosphoric acid and/or a phosphate.  The high-melting transition metal silicide is from a metal of Group IVb, Vb or VIb of the Periodic Table (Handbook of Chemistry and Physics, 44th Edn., page 448) and has a melting point above 1000  DEG C., e.g. molybdenum or titanium silicide. The impregnation with phosphoric acid may take place in vacuo, and preferably at least two impregnations take place, the body being heated after each impregnation.  A fixing agent may also be used with the phosphoric acid, this being to prevent evaporation of the phosphoric acid when heated either by forming an impervious coating on the body, or by reacting with the phosphoric acid to form a heat-stable coating.  The fixing agent may be a high melting oxide, e.g. alumina, aluminium hydroxide, zirconium oxide, zirconium silicate, silicon dioxide, silica gel, polyethyl silicate, aluminium phosphate, borax, titanium silicide, or a synthetic resin may be used, e.g. that formed from furfuryl alcohol and phosphoric acid at 80  DEG C. The fixing agent may also be used in conjunction with a bonding agent, i.e. an adhesive substance, to prevent the fixing agent and protective coating formed from being detached from the body.  The bonding agent may be polyvinyl acetate, polyvinyl alcohol, dextrin, or nitrocellulose.  The impregnations with the various materials may be in any order or all together.