材料期刊网

运用热力学研究了氧化物固溶体相变消除问题。回顾近50年ZrO_2及SiO_2相变消失原因,其中对ZrO_2相变消失是由于固溶体的形成一节各家意见分歧甚大。推导了热力学公式以求固溶体相变消除的条件。这一公式为 x_h(G_l~0—G_h~0)>(ΔG_(mh)-ΔG_(ml)或 x_h(G_h~0-G_l~0)>(ΔG_(ml)-ΔG_(mh))式中 x_h为高温型固溶体内溶剂mol％ G_l~0为纯高温型溶剂在标准状态下自由能 G_h~0为纯低温型溶剂在标准状态下自由能 ΔG_(mh)为高温型同溶体生成时的混合自由能 ΔG_(ml)为低温型固溶体生成时的混合自由能只有当G_l~0与G_h~0差额很大时,这一差额才可大于ΔG_(ml)与ΔG_(mh)的差额,从而使 ΔG>0相变消失。但是由于高温型、低温型氧化物的化学键与配位数相同,它们的G_l~0与G_h~0差额很小,生成固溶体时,相变不能消除。

A thermodynamical study was made of the problem concerning elimination of polymorphism of oxide solid solutions. The understandings on the elimination of polymorphism of ZrO_2 or SiO_2 given by various authors in recent five decades were reviewed, and yet these were contradictory. Derivation on elimination of polymorphism has been performed as:x_h(G_l~0—G_h~0)>(ΔG_(mh)—ΔG_(ml)) where x_h—-the tool % of solvent in high temperature modification of the solid solution, G_l~0 or G_h~0—the free energy of solvent under standard conditions for lower or higher temperature modification respectively and ΔG_(mh) or ΔG_(ml)—the free energy of mixing of the solid solution for higher or lower temperature modification respectively. It is only possibilty of the elimination of polymorphism that the differnce between G_l~0 and G_h~0 is much greater than that of ΔG_(mh) and ΔG_(ml). Due to the identity of the chemical bonds or coordination numbers between high and low temperature modifications of oxides, these differences are very small, thus, the polymorphism of oxide solid solutions which is possesed of polymorphism originally will be not eliminated.