不同品位菱镁矿合成镁锆复相材料性能的研究

Study on the Properties of Magnesia Zirconia Composite Materials Synthesized from Different Grades of Magnesite

为了实现真空循环脱气(RH)精炼炉用耐火材料无铬化,以海城一级菱镁矿、海城二级菱镁矿、岫岩二级菱镁矿(Mg CO_(3))三种不同品位菱镁矿和脱硅锆(ZrO_(2))为原料,制备镁锆质复相材料试样。检测了试样的体积密度、显气孔率、热震稳定性和物相组成,分析了试样的显微结构。研究了不同烧结温度对镁锆质复相材料的烧结性能和热震稳定性的影响。结果表明:随着温度的升高,试样的体积密度升高,显气孔率下降,线收缩率升高,岫岩二级菱镁矿与脱硅锆在1700℃烧后制备的镁锆复相材料体积密度最高为3.26 g/cm^(3),海城二级菱镁矿与脱硅锆在1700℃烧后制备的镁锆复相材料显气孔率最小为5.69%。三种不同品位的菱镁矿和ZrO_(2)均形成c-ZrO_(2)固溶体(Zr_(0.875)Mg_(0.125)O_(1.875)),菱镁矿中SiO_(2)、CaO杂质与MgO化合形成低熔点物相,提高了试样致密度,促进烧结;岫岩二级菱镁矿与脱硅锆制备的镁锆复相材料在1700℃下形成CaZrO_(3)和c-ZrO_(2)(Zr_(0.8)Ca_(0.2)O_(1.8));在冷却过程中,CaZrO_(3)和c-ZrO_(2)与方镁石的热膨胀系数失配产生微裂纹增韧效应以及ZrO_(2)相变增韧效应,使岫岩二级菱镁矿与脱硅锆在1700℃下制备的镁锆复相材料试样热震稳定性最佳。

The samples of magnesia zirconia composite materials were prepared with three kinds of different grades of magnesite,namely Haicheng grade I magnesite,Haicheng grade II magnesite and Xiuyan II grade magnesite(MgCO_(3))and desilication zirconium(ZrO_(2))as raw materials in order to produce substitute for magnesia−chromite brick of RH refining furnace.The bulk density,apparent porosity,thermal shock resistance and phase composition of the samples were tested.The microstructure of the samples was analyzed.The effects of different sintering temperatures on the sintering properties and thermal shock resistance of magnesia zirconia composite were investigated.The results show that the bulk density was increased,the apparent porosity was reduced,and the linear shrinkage was increased with the temperature increasing.The maximum bulk density of the magnesia zirconia composite prepared with Xiuyan Grade II magnesite and desiliconized zirconia fired at 1700℃was 3.26 g∙cm−3.The minimum apparent porosity of the magnesia zirconia composite prepared with Haicheng Grade II magnesite and desiliconized zirconia fired at 1700℃was 5.69%.The c−ZrO_(2)solid solution(Zr_(0.875)Mg_(0.125)O_(1.875))was formed from three different grades of magnesite and ZrO_(2).The impurities of SiO_(2)and CaO in magnesite were combined with MgO to form low melting point phase,which increased the density of samples and promoted sintering;The CaZrO3 and c−ZrO_(2)(Zr_(0.8)Ca_(0.2)O_(1.8)Zr_(0.8))were formed at 1700℃from the magnesia zirconia composite prepared from Xiuyan Grade II magnesite and desiliconized zirconia;The mismatch of the thermal expansion coefficients of CaZrO_(3)and c−ZrO_(2)with periclase resulted in microcrack toughening and ZrO_(2)phase transformation toughening during the cooling process,which made the magnesia zirconia composite sample prepared from Xiuyan Grade II magnesite and desiliconized zirconia at 1700℃have the best thermal shock resistance.