Silicon nitride-based sintering composition

Claim 1

A silicon nitride-based sintering composition in powder form containing magnesium oxide and aluminum oxide as densification aids, the composition consisting essentially of Si 3 N 4 in a particle size not exceeding 1μ, and the MgO and Al 2 O 3 as independent particles of a particle size less than the particle size of the Si 3 N 4 , the total amount of the Al 2 O 3 and MgO being up to 6% by weight of the composition and at least sufficient to impart a density of more than 3.10 g/cm 3 to a body formed of the composition by pressureless hot sintering, and the MgO:Al 2 O 3 weight ratio being from 10:1 to 1:3.

Claim 5

A method of manufacturing Si 3 N 4 objects from a silicon nitride-based sintering composition in powder form containing magnesium oxide and aluminum oxide as densification aids, the composition consisting essentially of Si 3 N 4 in a particle size not exceeding 1μ, and the MgO and Al 2 O 3 as independent particles of a particle size less than the particle size of the Si 3 N 4 , the total amount of the Al 2 O 3 and MgO being up to 6% by weight of the composition and at least sufficient to impart a density of more than 3.10 g/cm 3 to a body formed of the composition by pressureless hot sintering, and the MgO:Al 2 O 3 weight ratio being from 10:1 to 1:3, said method comprising the steps of: (a) compacting the powdered composition in the cold state into the form of the required object, (b) subjecting the preformed object in the cold state to an isostatic pressure of at least 1 T/cm 2 , (c) degassing the object passed in the cold state by heating under reduced pressure, and (d) heating the degassed object for 2 to 20 minutes between 1650° and 1830° C. in an atmosphere composed essentially of nitrogen, so as to obtain the required sintering and densification.

Claim 6

A method of manufacturing Si 3 N 4 objects from a silicon nitride-based sintering composition in powder form containing magnesium oxide and aluminum oxide as densification aids, the composition consisting essentially of Si 3 N 4 in a particle size not exceeding 1μ, and the MgO and Al 2 O 3 as independent particles of a particle size less than the particle size of the Si 3 N 4 , the total amount of the Al 2 O 3 and MgO being up to 6% by weight of the composition and at least sufficient to impart a density of more than 3.10 g/cm 3 to a body formed of the composition by pressureless hot sintering, and the MgO:Al 2 O 3 weight ratio being from 10:1 to 1:3, said method comprising the steps of: (a) compacting the powdered composition in the cold state into the form of the required object, (b) subjecting the preformed object in the cold state to an isostatic pressure of at least 1 T/cm 2 , (c) degassing the object passed in the cold state by heating under reduced pressure, and (d) heating the degassed object for 2 to 20 minutes between 1650° and 1830° C. in an atmosphere composed essentially of nitrogen, so as to obtain the required sintering and densification.