CaO/Al_2O_3/SiO_2 系玻璃非均匀形核的研究

Study on the heterogeneous nucleationof CaO/Al2O3/SiO2 system glasses

使用ＤＴＡ，ＸＲＤ，ＳＥＭ和ＥＤＡＸ方法研究了氧化铝瓷基片和ＣａＯ／Ａｌ２Ｏ３／ＳｉＯ２（ＣＡＳ）系玻璃在高温下的相互作用，发现晶体同时从玻璃表面和氧化铝界面处形核并生长，中间仍是玻璃态，没有均匀形核，晶体从玻璃表面以枝晶状向玻璃内部生长，晶化层厚度大于氧化铝界面处晶化层厚度，氧化铝界面处晶化层主要是由氧化铝晶粒和晶粒间的一些其他球晶组成。非均匀形核的主要位置是晶核剂表面的结构缺陷，晶核剂具有选择性。非均匀形核速率更多地被动力学势垒ΔＧＤ所决定，接触角函数ｆ（θ）的影响较弱。母体玻璃相的化学组成对形核起一定的促进作用。

A block of polished alumina crystal substrate containing wAl2O3=95% above was put in the center of the CaO/Al2O3/SiO2 (CAS) system glasses in the alumina crucible and heated together to a high temperature (above 1500℃) to melt the glasses. The alumina crystal substrate and the melting glasses were kept at the high temperature for a long time and quenched to a temperature slightly above Tg, and then continued to be heated at a constant rate (10℃/min) to a temperature slightly above Tp. The methods of DTA, XRD, SEM and EDAX were used to study the samples which crystallized both on the surface of the glasses and in the interface between alumina crystal substrate and the glasses studied. The crystal layer on the surface which grew by the shape of dendrite from the surface to interior was thicker than that in the interface which mainly consisted of alumina crystal grain and spherulite among the alumina crystal grains. The parts between glass surface and alumina substrate were still glasses, that shown homogeneous nucleation did not take place. The most important sites for heterogeneous nucleation are structure defects on the surface of nucleation agents. The rate for heterogeneous nucleation is mainly decided by the kinetic barrier to nucleation (ΔGD). The f(θ) has a slightly effect on the rate of heterogeneous nucleation. The chemical constitute of base glasses plays an accelerating role in nucleation.