Research On The Preparation And Densification Of Si₂N₂O-SiC Ceramic

Si2N2O and Si2N2O-SiC ceramic were prepared by pressureless sintering method in nitrogen atmosphere using Si,SiO2 and SiC powder.The bulk density,phase composition,microstructure,rockwell hardness and thermal expansion coefficient of the samples were represented by Archimedes law,XRD,SEM,Digital display rockwell hardness tester and Horizontal expansion coefficient apparatus.The effect of sintering temperature,nitrogen pressure,the kind and amount of sintering aids,SiC content,grain composition of SiC on the densification and properties of Si2N2O and Si2N2O-SiC ceramic were researched in this paper.The results show that:(1)When the Si2N2O ceramics were synthesized by presureless sintering method with Si and SiO2 powder as raw materials,the synthesize temperature was from 1000? to 1550?.The temperature range for Si2N2O stable existence was from 1450? to 1550?.The density,hardness and thermal expansion coefficient of Si2N2O sample increased with the sintering temperature rised and reached maximum at 1550?.Si2N2O was decomposed to Si3N4 at 1600?.The temperature at which Si2N2O began to decompose would be lower with the N2 pressure increased.The density of Si2N2O sample would significantly improved when added sintering aids.The density of Si2N2O sample reached maximum when synthesized at 1550? under 0.2MPa N2 pressure with Si/SiO2 was 3 and added 5wt%MgO.The maximum density of Si2N2O sample was 2.43 g/cm3.The Si2N2O had dense structure,uniform grain size(1-2?m)and plate-shape crystalline grain.The Rockwell hardness and thermal expansion coefficient of Si2N2O was 81.3 and 3.20×10-6?-1 respectively.(2)When the Si2N2O-SiC ceramics were synthesized by presureless sintering method with Si,SiO2 and SiC powder as raw materials,compact Si2N2O-SiC ceramic can be synthesized at 1450? for 2h with 70wt%SiC and 1.5wt%MgO when the mass ratio of SiC particle size was m(297?m:23?m)=4:3.The density of Si2N2O-SiC sample was 2.43g/cm3.The Rockwell hardness and thermal expansion coefficient of Si2N2O-SiC sample was 73.3 and 3.71×10-6?-1 respectively.The phase composition was SiC for 61.29%and Si2N2O for 36.06%which nearly close to the theoretical calculation.The reaction rate of Si2N2O would increase for addition suitable additive and the growth of Si2N2O grain was improved accordingly.The decompose temperature of Si2N2O-SiC would be lower compared with Si2N2O sample.Si2N2O-SiC ceramic began to decompose at 1500? and complete at 1550?.