High thermal conductive silicon nitride sintered body and method of producing the same

A high thermal conductive silicon nitride sintered body containing:

• 2.0-7.5% by weight of a rare earth element in terms of an oxide thereof;
• 0.2-30% by weight of at least one compound selected from the group consisting of the oxides, carbides, nitrides, silicides and borides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W;
• at most 2.0% by weight of aluminum compound calculated as alumina, aluminum nitride or mixtures thereof;
• at most 0.3% by weight of Li, Na, K, Fe, Ca, Mg, Sr, Ba, Mn and B as impurity cationic elements in terms of total amount thereof, and comprising a silicon nitride crystal phase and a grain boundary phase.

A method of producing a high thermal conductive silicon sintered body, comprising the steps of:

• forming a compact by molding a mixture obtained by adding 2.0-7.5% by weight of a rare earth element in terms of the amount of an oxide thereof, and at most 2.0% by weight of alumina, aluminum nitride or mixtures thereof, to a silicon nitride powder which contains at most 1.7% by weight of oxygen, at most 0.3% by weight of Li, Na, K. Fe, Ca, Mg, Sr, Ba, Mn and B as impurity cationic elements in terms of total amount thereof, and at least 90% by weight of alpha-phase type silicon nitride, and which has an average grain size of at most 0.8 .mu.m;
• degreasing said compact;
• sintering said compact at a temperature of 1800.degree.-2000.degree. C. while pressurizing the atmosphere around said compact to form a sintered body;
• and
• cooling the sintered body at a cooling rate of at most 100.degree. C. per hour until the temperature is reduced to a point at which a liquid phase formed of said rare earth element during the sintering step solidifies.

A method of producing a high thermal conductive silicon nitride sintered body, comprising the steps of:

• forming a compact by molding a mixture obtained by adding 2.0-7.5% by weight of a rare earth element in terms of the amount of an oxide thereof, and 0.2-3.0% by weight of at least one compound selected from the group consisting of the oxides, carbides, nitrides, silicides and borides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, to a silicon nitride powder which contains at most 1.7% by weight of oxygen, at most 0.3% by weight of Li, Na, K, Fe, Ca, Mg, Sr, Ba, Mn and B as impurity cationic elements in terms of total amount thereof, and at least 90% by weight of alpha-phase type silicon nitride, and which has an average grain size of at most 0.8 .mu.m;
• degreasing said compact;
• sintering said compact at a temperature of 1800.degree.-2000.degree. C. while pressurizing the atmosphere around said molding to form a sintered body;
• and
• cooling the sintered body at a cooling rate of at most 100.degree. C. per hour until the temperature is reduced to a point at which a liquid phase formed of said rare earth element during the sintering step solidifies.

A method of producing a high thermal conductive silicon nitride sintered body, comprising the steps of:

• forming a compact by molding a mixture obtained by adding 2.0-7.5% by weight of a rare earth element in terms of the amount of an oxide thereof, 0.2-3.0% by weight of at least one compound selected from the group consisting of the oxides, carbides, nitrides, silicides and borides, of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, and 0.1-2.0% by weight of alumina, aluminum nitride or mixtures thereof to a silicon nitride powder which contains at most 1.7% by weight of oxygen, at most 0.3% by weight of Li, Na, K, Fe, Ca, Mg, Sr. Ba, Mn and B as impurity cationic elements in terms of total amount thereof, and at least 90% by weight of alpha-phase type silicon nitride, and which has an average grain size of at most 0.8 .mu.m;
• degreasing said compact;
• sintering said compact at a temperature of 1800.degree.2000.degree. C. while pressurizing the atmosphere around said compact to form a sintered body;
• and
• cooling the sintered body at a cooling rate of at most 100.degree. C. per hour until the temperature is reduced to a point at which a liquid phase formed of said rare earth element during the sintering step solidifies.