刚玉-莫来石-锌铝尖晶石复相材料的合成与烧结

SYNTHESIS AND SINTERABILITY OF CORUNDUMMULLITEZnO·Al_(2)O_(3 ) MULTIPHASE MATERIALS

热力学计算表明:在Al2O3SiO2ZnO三元体系中,硅酸锌(Zn2SiO4)和锌铝尖晶石(ZnAl2O4)生成Gibbs自由能在温度为1326.85℃以下是负值,莫来石(3Al2O3·2SiO2)的Gibbs生成自由能在温度为426.85℃以上是负值。系统中Al2O3富存的条件下,Al2O3可与Zn2SiO4反应生成锌铝尖晶石。以ZnO,SiO2,Al(OH)3为原料,通过固相反应合成刚玉莫来石锌铝尖晶石复相材料。研究烧结温度和气氛对刚玉莫来石锌铝尖晶石复相材料的合成与烧结性能的影响。用X射线衍射分析复相材料中的物相成分。用扫描电子显微镜观察复相材料的显微结构。结果发现:Al2O3SiO2ZnO三元体系在所选择的配料点,1300℃及1600℃时均能生成刚玉、莫来石、锌铝尖晶石3种物相,不会出现低熔点的硅酸盐相,这明显区别于Al2O3MgOSiO2三元体系,该体系在1500℃左右会出现低熔点相。试样在900℃烧成后出现锌铝尖晶石相。随着温度升高,试样的致密化过程加快,部分抵消了1300℃左右莫来石形成所产生的体积膨胀。当烧结温度高于1300℃时,试样的致密化过程大大加快。还原性气氛不利于刚玉莫来石锌铝尖晶石复相材料的合成与烧结。

Thermodynamics analysis indicates that in Al_2O_(3)SiO_2ZnO ternary system, Gibbs free energies of Zn_2SiO_(4) and ZnAl_2O_(4) are all negative under the temperature of 1 326.85 ℃ and the Gibbs free energy of mullite (3Al_2O_(3)·2SiO_(2)) is negative only above the temperature of 426.85 ℃. Al_2O_(3) can be reacted with Zn_2SiO_(4) to form ZnAl_2O_(4) if Al_2O_(3) content is rich (enough) in the system. The analysis proved that using ZnO, SiO_(2) and Al(OH)_(3) as raw materials corundummulliteZnO ·(Al_2O_3) multiphase materials were synthesized by the solid-state reaction. Effects of sintering temperatures and atmosphere on the synthesis and sintering properties of the multiphase materials were studied. The mineral phase was characterized by X-ray diffraction (XRD) and the microstructure of corundummulliteZnO ·Al_(2)O_(3) multiphase materials was observed by scanning electron microscope (SEM). Results show the distinction between the ternary system of Al_2O_(3)SiO_(2)ZnO and (Al_(2)O_(3))MgOSiO_(2). Namely, in the former ternary system there is no low melt silicate phase found but corundum, mullite and ZnO·Al_(2)O_(3) are formed above 1 300 ℃ and 1 600 ℃ under the proper condition. However, low melt phase is found in Al_(2)O_(3)MgOSiO_(2)system at about 1 500 ℃.ZnO·Al_(2)O_(3)is formed at about 900 ℃. With the increase of the temperature, the densification process is accelerated, which can partially counteract the bulk expansion from mullite solid-state reaction at about (1 300 ℃). As the sintering temperature is above 1 300 ℃, the densification process is accelerated dramatically. The reducing atmosphere is unfavorable for the synthesis and sinterability of corundummulliteZnO·Al_(2)O_(3) multiphase materials.