Furnace for sintering ceramics, carbon heater used therefor and process for sintering ceramics

A process for firing a shaped ceramic body comprising a mixture of non-oxide ceramic powder and sintering aids, comprising:

• surrounding said body with insulating layers composed of a carbon fiber mat;
• protecting said body from exposure to said insulating layers by interposing sheets consisting of laminated graphite leaves having an ash content of not more than 0.3% by weight, between said insulating layers and said body;
• and
• firing said body at a high temperature in an inert gas atmosphere.

A furnace for sintering non-oxide ceramics, comprising:

• furnace walls defining a space for accommodating a shaped ceramic body;
• carbon heaters arranged directly around the shaped ceramic body in said space, said carbon heaters comprising a high purity graphite consisting essentially of, in weight %, 99.9980% carbon, not greater than 5 ppm silicon, and not greater than 9 ppm iron;
• heat insulating layers of carbon fiber mat disposed on and covering inner surfaces of said furnace walls;
• and
• sheets consisting of laminated graphite leaves having an ash content of not greater than 0.3% by weight, said sheets being provided over said insulating layers such that said sheets protect said shaped ceramic body from exposure to said insulating layers.