Effects of TiB2 addition on performance of Si3N4-SiC refractories
To improve the performance,reaction sintered Si3N4-SiC refractories were prepared by reaction sintering at 1 400 ℃ for 2 h using SiC(particles and fines)and Si powder as the raw materials,TiB2 fine powder as the additive.The effects of the TiB2 fine powder addition(0,0.2％,0.4％,0.6％,and 0.8％,by mass)on the bulk density,modulus of rupture,phase composition,and microstructure of the reaction sin-tered Si3N4-SiC refractories were studied using MIP,XRD,and SEM,and the densification mechanism was analyzed.The results show that:(1)adding an appropriate amount of TiB2 helps to improve the bulk densi-ty and hot modulus of rupture at 1 200 ℃,increasing the proportion of small pores(≤ 1 μm);(2)with the increasing TiB2 addition,the content of Si2N2O impurity phase decreases,the nitridation rate of silicon pow-der improves;Si3N4 exists as a whisker structure at the beginning,then evolves into well-developed long rods,and finally grows abnormally;(3)the densification mechanism is as follows:a small amount of TiB2 can increase the partial pressure of SiO gasous phase and promote the growth of Si3N4 whiskers,which fol-low the gas-solid growth mechanism;when increasing the TiB2 addition to 0.6％,Si3N4 develops into long-rod shapes under moderate high-temperature liquid phase,forming a three-dimensional network structure;when continuing to increase the TiB2 addition to 0.8％,the liquid phase in the samples increases again,and the rod-shaped Si3N4 grows abnormally;(4)when the TiB2 addition is 0.6％,the comprehensive perform-ance of samples is the best,with the bulk density of 2.75 g·cm-3,apparent porosity of 11.6％,cold mod-ulus of rupture of 40.2 MPa,and hot modulus of rupture at 1 200 ℃ of 47.4 MPa.
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