| abstract |
The invention belongs to the field of ceramic preparation, in particular to a method for preparing silicon nitride ceramics with high strength and high thermal conductivity by two-step sintering. In this method, silicon nitride powder and sintering aid are mixed with organic solvent in a certain proportion, after granulation, pressing and degreasing, firstly pretreatment under low temperature, normal pressure and nitrogen flow for 1 to 5 hours, and then in Sintering is carried out at high temperature and under nitrogen pressure of 0.9 to 10 MPa. In the first step of pretreatment, the content of magnesia sintering aid was adjusted according to the oxygen content of the silicon nitride powder, and the oxygen content of the green body was reduced before sintering by using the low-temperature reaction characteristics of magnesium oxide and silicon dioxide on the surface of the silicon nitride powder. Carry out the second step of air pressure sintering. Compared with the unpretreated sintered body, the two-step sintered silicon nitride ceramic has higher density, the total oxygen content and the second phase content are significantly reduced, and the thermal conductivity can be prepared to be greater than 90W/m·K , Silicon nitride ceramics with flexural strength greater than 750MPa. |