NaF-BaTiO_3平均原子溶解熵与共晶形态研究

Study on the Average Entropy of Solution Per Atom and Eutectic Morphology of NaF-BaTiO_3

依照Taylor和Fidler分别计算固溶体和化合物平均原子溶解熵的基本思想,建立了计算NaF,BaTiO3共晶两相平均原子溶解熵ΔSf的模型,并计算出NaF,BaTiO3的ΔSf分别为44.568 J/mol.K,59.382 J/mol.K,两者均超过临界值23 J/mol.K.实验研究发现NaF,BaTiO3共晶两相均呈小片面生长,从而使上述计算结果得到验证.同时发现NaF和Ba-TiO3两相形成以BaTiO3为树枝晶,枝晶间分布NaF的共晶组织形态,这种形态不同于Cro-ker对共晶凝固组织七种分类中的任一类.共晶中BaTiO3能够促发NaF异质形核,而NaF不能促发BaTiO3异质形核,说明形核非互惠原则对两相均为小平面相的共晶亦起作用.

Based on the concept that Taylor and Fidler adopted to calculate the average entropy of solution per atom （ASf） of solid solution and compound, the model for calculating △Sf of NaF and BaTiO3 in the NaF-BaTiO3 eutectic is established. The calculated △Sf of NaF and BaTiO3 are 44. 568 and 59. 382 J/mol · K respectively and both exceed the critical value of 23J/mol · K. It is found that NaF and BaTiO3 manifest as facet behavior, which improved the calculated results. Experimental results indicate that in the NaF-BaTiO3 eutectic,which is different from any kind of 7 eutectic microstructures classified by Croker, BaTiO3 is formed as dendrite among which there are NaF phase. In the eutectic, BaTiO3 can catalyze NaF heterogeneous nucleation, not vice versa, which indicates that in facet-facet binary eutectic, the principle of nonreciprocity nucleation acts as in nonfacet-facet binary eutectic.