Composite ceramics and method of making the same

A sintered ceramic material consisting essentially of:

• a matrix of first particles of at least one compound selected from the group consisting of TiN, TiB.sub.2, TiC, ZrN, ZrC, ZrB.sub.2, Cr.sub.2 N, Cr.sub.3 C.sub.2, CrB, HfN, HfC, TaN, TaC, TaB.sub.2, NbN, NbC, NbB.sub.2, WC, W.sub.2 C, Mo.sub.2 N, Mo.sub.2 C, MoB, VN, VC, WSi.sub.2, TiSi.sub.2, ZrSi.sub.2, NbSi.sub.2, TaSi.sub.2, CrSi.sub.2, MoSi.sub.2, Cr.sub.7 C.sub.2, CeC.sub.2, each having an electric resistivity not greater than 10.sup.-3 .OMEGA.cm;
• and a second particles consisting essentially of silicon nitride and whiskers consisting essentially of silicon nitride;
• wherein said first particles of the compound are interlocked with each other by means of said second particles and said whiskers, said sintered material having a porosity of 5 to 30%, and the amount of said whiskers being 1 to 70% by weight based on the sum of said second particles and said whiskers;
• said sintered material having a resistivity ranging from 4.2.times.10.sup.-5 to 2.8.times.10.sup.0 .OMEGA.cm, being substantially free from glass phase and having a bending strength ranging from 140 to 510 MN/m.sup.2 at 1200.degree. C., said bending strength being substantially the same as that at room temperature.

A sintered ceramic material produced by the process comprising the steps of:

• preparing a molded article comprising a first powder of metallic silicon and/or ferrosilicon powder;
• a second powder of at least one compound selected from the group consisting of TiN, TiB.sub.2, TiC, ZrN, ZrC, ZrB.sub.2, Cr.sub.2 N, Cr.sub.3 C.sub.2, CrB, HfN, HfC, TaN, TaC, TaB.sub.2, NbN, NbC, NbB.sub.2, WC, W.sub.2 C, Mo.sub.2 N, Mo.sub.2 C, MoB, VN, VC, WSi.sub.2, TiSi.sub.2, ZrSi.sub.2, NbSi.sub.2, TaSi.sub.2, CrSi.sub.2, MoSi.sub.2, Cr.sub.7 C.sub.2, CeC.sub.2, each having an electric resistivity not greater than 10.sup.-3 .OMEGA.cm;
• and a binder for forming said first and second powders into said article;
• subjecting said binder to decomposition so as to make said article porous so that gaseous substances can permeate into the pores of said article;
• and
• sintering said porous article in a nitrogen atmosphere containing less than 50 ppm of oxygen at an elevated temperature of at least 1350.degree. C., whereby nitrogen gas reacts with said first powder to form particles consisting essentially of silicon nitride and whiskers containing essentially of silicon nitride, the amount of said whiskers being 1 to 70% by weight based on the sum of said particles and whiskers consisting essentially of silicon nitride so as to interlock particles of said second powder.

A sintered ceramic material produced by a process comprising the steps of:

• preparing a molded article comprising a first powder of metallic silicon and/or ferrosilicon powder;
• a second powder having an average particle size no greater than 100 microns and of at least one compound selected from the group consisting of carbides, oxides, nitrides, borides, oxynitrides and silicides of elements belonging to IIIa, IIIb, IVa, IVb, Va, VIa and VIII of the Periodic Table, wherein said at least one compound includes a member having an electric resistivity not greater than 10 .OMEGA.cm;
• and a binder for forming said first and second powders into said article;
• subjecting said binder to decomposition so as to make said article porous so that gaseous substances can permeate into the pores of said article;
• and
• sintering said porous article in a nitrogen atmosphere containing less than 50 ppm of oxygen at an elevated temperature of at least 1350.degree. C., whereby nitrogen gas reacts with said first particles to form particles consisting essentially of silicon nitride and whiskers consisting essentially of silicon nitride, the amount of said whiskers being 1 to 70% by weight based on the sum of said particles and whiskers consisting essentially of silicon nitride so as to interlock particles of said second powder.

A sintered ceramic material produced by a process comprising the steps of:

• preparing a molded article comprising a first powder of metallic silicon and/or ferrosilicon powder;
• a second powder of at least one compound selected from the group consisting of carbides, oxides, nitrides, borides, oxynitrides and silicides of elements belonging to IIIa, IIIb, IVa, IVb, Va, VIa and VIII of the Periodic Table, wherein at least one compound includes a member having an electric resistivity not greater than 10 .OMEGA.cm;
• and a binder for forming said first and second powders into said article;
• subjecting said binder to decomposition so as to make said article porous so that gaseous substances can permeate into the pores of said article;
• and
• sintering said porous article in a nitrogen atmosphere containing less than 50 ppm of oxygen at an elevated temperature of at least 1350.degree. C., whereby nitrogen gas reacts with said first powder to form particles consisting essentially of silicon nitride and whiskers consisting essentially of silicon nitride, the amount of said whiskers being 1 to 70% by weight based on the sum of said particles and whiskers consisting essentially of silicon nitride so as to interlock particles of said second powder.