Method for producing high density sintered silicon nitride(Si.sub.3 N.sub.4 )

A method for producing high density sintered silicon nitride (Si.sub.3 N.sub.4) having a relative density of at least 98%, said method comprising:

• forming silicon nitride powder into a desired shape to obtain a silicon nitride green compact;
• presintering said green compact under a nitrogen gas atmosphere ranging in pressure from 1 to 30 atmospheres at a temperature of 1500.degree.-1600.degree. C. for 50-200 minutes into a presintered Si.sub.3 N.sub.4 body whose .alpha.--Si.sub.3 N.sub.4 content ranges from 80-20% and whose .beta.--Si.sub.3 N.sub.4 content ranges from 20-80% and which has relative density of at least 92%;
• removing the presintered body at room temperature from the presintering furnace;
• charging the cooled presintered body into a hot isostatic pressing furnace;
• subjecting said presintered Si.sub.3 N.sub.4 body to hot isostatic pressing without being confined by a capsule in an inert gas atmosphere of a temperature in the range of 1500.degree.-2100.degree. C. and of a nitrogen gas partial pressure of at least 500 atm until a Si.sub.3 N.sub.4 body is obtained of at least 80% .beta.--Si.sub.3 N.sub.4 having a relative density of at least 98%;
• discharging the sintered body at room temperature from the hot isostatic pressing furnace;
• and then
• heat-treating said sintered body at a temperature of 500.degree. C. or higher in a heat treatment furnace.

A method for producing high density sintered silicon nitride (Si.sub.3 N.sub.4) having a relative density of at least 98%, said method comprising:

• forming silicon nitride powder into a desired shape to obtain a silicon nitride green compact;
• presintering said green compact under a nitrogen gas atmosphere ranging in pressure from 1 to 30 atmospheres at a temperature of 1500.degree.-1600.degree. C. for 50-200 minutes into a presintered body in a hot isostatic pressing furnace, said presintered Si.sub.3 N.sub.4 body having a .alpha.--Si.sub.3 N.sub.4 content ranging from 80-20% and a .beta.--Si.sub.3 N.sub.4 content ranging from 20-80% and which has a relative density of at least 92%;
• subjecting said presintered Si.sub.3 N.sub.4 body continuously to hot isostatic pressing without being confined by a capsule in an inert gas atmosphere of a temperature in the range of 1500.degree.-2100.degree. C. and of a nitrogen gas partial pressure of at least 500 atm until a Si.sub.3 N.sub.4 body is obtained of at least 80% .beta.--Si.sub.3 N.sub.4 having a relative density of at least 98%;
• and
• discharging the sintered body at room temperature from the hot isostatic pressing furnace.

A method for producing high density sintered silicon nitride (Si.sub.3 N.sub.4) having a relative density of at least 98%, said method comprising:

• forming silicon nitride powder into a desired shape to obtain a silicon nitride green compact;
• presintering said green compact under a nitrogen gas atmosphere ranging in pressure from 1 to 30 atmospheres at a temperature of 1500.degree.-1600.degree. C. for 50-200 minutes into a presintered Si.sub.3 N.sub.4 body in a hot isostatic pressing furnace, said Si.sub.3 N.sub.4 body having a .alpha.--Si.sub.3 N.sub.4 content ranging from 80-20% and a .beta.--Si.sub.3 N.sub.4 content ranging from 20-80% and having a relative density of at least 92%;
• subjecting said presintered Si.sub.3 N.sub.4 body continuously to hot isostatic pressing without being confined by a capsule in an inert gas atmosphere of a temperature in the range of 1500.degree.-2100.degree. C. and of a nitrogen gas partial pressure of at least 500 atm until a Si.sub.3 N.sub.4 body is obtained of at least 80% .beta.--Si.sub.3 N.sub.4 having a relative density of at least 98%;
• discharging the sintered body at room temperature from the hot isostatic pressing furnace;
• and then
• heat-treating said sintered body at a temperature of 500.degree. C. or higher into a heat treatment furnace.