MgO–Al_2O_3–ZrO_2复合粉对氧化锆质定径水口改性的作用

Modification Effect of MgO–Al_2O_3–ZrO_2 Composite Powders on Zirconia Metering Nozzle

用溶胶–凝胶法制备的化学组成不同的MgO–Al_2O_3–ZrO2复合粉作为添加剂,制备改性氧化锆质定径水口,对其体积密度、显气孔率、热震稳定性、耐压强度、物相组成和显微结构进行表征。结果表明:加入MgO–Al_2O_3–ZrO_2复合粉后,随着MgO引入量的增加,改性定径水口的体积密度降低,气孔率上升,耐压强度呈先上升后略微下降趋势,热震之后的残余强度保持率显著升高;复合粉中MgO成分的引入,降低了镁铝尖晶石对原料中MgO稳定剂的消耗,减少了固溶于ZrO_2中MgO稳定剂的脱溶,保证了改性定径水口的稳定度;改性定径水口在烧结过程中生成了大小和分布都较均匀的镁铝尖晶石和收缩微孔,同时,形成的氧化锆晶粒尺寸均匀,结合强度较好,在保证抗侵蚀性和抗冲刷性的同时,可进一步提高样品的抗热震稳定性。MgO引入量为0.65%时,相变量较为合适,定径水口的综合性能最优;当没有引入MgO时,相变量过大,水口性能下降。

The modified zirconia metering nozzles were fabricated with MgO-A1203-ZrO2 composite powders with different compositions prepared by a sol-gel method as additives. The bulk density, apparent porosity, thermal shock, compression strength, mineral phase and microstructure of zirconia metering nozzle were characterized. The results show that the bulk density decreases and the open porosity increases with increasing the mass fraction of MgO addition. The compressive strength firstly increases, and then decreases, and the residual strength ratio after thermal shock becomes greater. The addition of MgO composition in composite powders can reduce the consumption of stabilizer MgO in raw material, which produces magnesium aluminate spinel, thus leading to the decrease of the precipitation of stabilizer MgO that favors the stability degree of the modified metering nozzle. The magnesium aluminate spinel and miniature pore structure in the sintering process with uniform size and dispersed distribution and the formation of strong-bonding zirconia grains with uniform size can improve the thermal shock stability of samples and ensure the erosion resistance and scouring resistance. When the addition of MgO is 0.65% （in mass fraction）, the amount of phase transition is proper and the amount of micro cracks in the sample favor the toughening of the samples, thus obtaining the optimal strength and thermal shock stability. However, the excessive phase transition causes the deterioration of performance of the samples in the absence of MgO addition.