The Preparation And Properties Of Robust Mullite Ceramics With Mulllite Whisker And ZrO₂

Mullite ceramic had good high temperature mechanical properties, thermal shock stability, corrosion resistance and so on, the comprehensive performance of mullite was highest in all oxide ceramics, so it was used in various industries. But the room temperature mechanical properties of mullite ceramics was not high, especially the low brittleness had become the main factor that restrict its application. So we needed to enhance the properties of mullite ceramics. As toughening agents, mullite whisker and ZrO2could greatly improve the fracture toughness of mullite ceramics. Therefore they were widely used in ceramic matrix composites.The mullite whisker was first prepared by in situ method in this paper. Then ZrO2/mullite ceramic powder was prepared by pressure sintering. The mixed mullite whisker powder and ZrO2/irmllite ceramics powder with equal quality, after lh grinding, Dense mullite ceramic was obtained by spark plasma sintering (SPS).Mullite whisker is prepared by using pure Al(OH)3, SiO2as raw materials and AIF3, V2O5as additive. Exploring the influence of the content of AIF3and V2O5, sintering temperature, holding time on synthesis of mullite whisker. Results showed that the optimal adding quantity of AF3, V2O5was3wt%, the best sintering temperature was1350℃, the best holding time was2h.ZrO2/mullite ceramic powder was prepared by using pure A1(OH)3and SD2as raw materials, and ZrO2, Y2O3as additive by pressureless sintering. We explored the influence of the content of ZrO2and sintering temperature on the synthesis of mullite ceramics powder. Results showed that the temperature played a decisive role on the synthesis of ZrO2/mullite ceramic powder, the optimal sintering temperature was1600℃, the best level of ZrO2was about30wt%. The addition of ZrO2could inhibit mullite grains grew up.Finally, mixed mullite whisker powder and ZrO2/mullite ceramics powder with equal quality, after1h grinding, dense mullite ceramic was obtained by spark plasma sintering (SPS) at1300-1600℃. The phase and microstructure of mullite dense ceramics were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the mullite whiskers and grains began to melt at941℃and finally crystallized with flaky morphology. The highest relative density of the mullite ceramics was98.2%when the sintering temperature was1600℃. The fracture toughness of mullite ceramics could increase to4.14MPa·m1/2when only mullite whisker is added, while the sample with the co-addition of ZrO2(10wt%) and whisker had the largest fracture toughness value of5.52MPa·m1/2.