Patent GB-936118-A (GB)
Title: Refractory carbide bodies and method of making them
IPC: C04B41/50
Filed: 1959-10-23
Abstract: A porous refractory carbide body such as a carbide of Si, B, Zr, Hf, Ti, V, Ta, Nb, Mo, Cr, W and Th is made oxidation resistant by depositing in situ in said body a layer of molybdenum silicide preferably the disilicide so that both internal and external surfaces of the body are coated.  In the preferred process self bonded SiC with a porosity of up to 35% by volume is impregnated with up to 25% by weight of MoSi2 by immersing the body in a suspension of MoSi2 in polyvinyl alcohol, water and a wetting agent such as disodium dibutyl-orthophenylphenaldisulphonate, drying, then sintering at 1500 DEG C. in helium or argon.  Impregnation may also be effected by heating the SiC body in contact with powdered MoSi2 at 2100 DEG C. in helium.  Up to 50% by weight of powdered Ni or Cr based on the weight of MoSi2 may also be included in the MoSi2 slurry.ALSO:A porous refractory carbide such as a carbide of Si, B, Zr, Hf, Ti, V, Ta, Nb, Mo, Cr, W and Th is impregnated with up to 25% by weight of MoSi2 so that both the external and internal surfaces of the carbide are coated.  Impregnation may be effected by immersion of the carbide in a suspension of MoSi2 in polyvinyl alchol, water and a wetting agent, drying and then sintering in helium or argon at 1500 DEG  C. Alternatively, the carbide is heated in contact with powdered MoSi2 at 2100 DEG  C. in helium.  Up to 50% by weight of Ni or Cr, based on the weight of MoSi2, may also be included in the impregnant.  In the production of resistance heating elements the impregnated SiC body is joined to siliconized SiC cold ends by using a jointing paste of SiC, resorcinol formaldehyde resin, pine oil and paraformaldehyde and heating the assembly to 2000 DEG  C. in a graphite mould, powdered Si being placed around the joint. Alternatively, a paste of SiC or MoSi2 may be used.ALSO:A porous refractory carbide body such as a carbide of Si, B, Zr, Hf, Ti, V, Ta, Nb, Mo, Cr, W and Th is made oxidation resistant by depositing in situ in said body a layer of molybdenum silicide preferably the disilicide so that both internal and external surfaces of the body are coated.  In the preferred process self bonded recrystallised SiC with a porosity of up to 35% by volume is impregnated with up to 25% by weight of MoSi2 by immersing the body in a suspension of MoSi2 in polyvinyl alcohol, water and a wetting agent such as disodium dibutyl-ortho-phenylphenoldi-sulphonate, drying and then sintering at 1500 DEG C. in helium or argon. Impregnation may also be effected by heating the SiC body in contact with powdered MoSi2 at 2100 DEG C. in helium.  Up to 50% by weight of powdered Ni or Cr, based on the weight of the MoSi2 may also be included in the MoSi2 slurry.  For the production of electrical resistance heating elements the impregnated SiC body may be joined to siliconised SiC "cold ends" by using a jointing paste of SiC, resorcinal formaldehyde resin, pine oil or paraformal-dehyde and heating the assembly to 2000 DEG C. in a graphite mould, powdered Si being placed around the joint.  Alternatively a paste of SiC and MoSi2 may be used.