材料分相初期动力学研究

A Study on Kinetics of Phase Separation at the Beginning Process

分相有两种机理,即形核生长机理和 Spinodal 机理,而具体的分相过程又可分为两个阶段,即开始的波动阶段和随后的扩散阶段.经典的形核生长动力学方程 I=Ioexp[-(（△FA+△F*）/（KT）]只能描述某一时刻单位体积材料中形成的稳定晶核数,不能描述波动阶段的具体过程,而 Spinodal 分解动力学方程 c（r,t）-co=PQ2exp[R2（β）·t]cos（β·r）只能描述分相的扩散阶段的具体过程,分相的波动阶段动力学至今没有合适的方程描述,本文以波动方程为基础,推导出了分相初期波动阶段的动力学方程为 c（r,t）-co=Pcos（βWt）·cos（β·r）,以此方程为基础,分析了一个稳定的不均区域的形成过程是区域大小在临界值附近来回波动且趋于稳定的过程,其浓度值同时逐渐趋于一定值.在分相的波动阶段形成的稳定的不均区域,为后续的扩散阶段创造了起始条件.

Total process of phase separation contains two stages that are the firstly fluctuating stage and the secondly diffusing stage.Simultaneously according to the thermodynamics,the mechanism of phase separation can again be divided into the nucleation-growth and spinodal decomposition.The classic kinetics equation for nucleation-growth,Ⅰ=Ⅰ_0 exp[-(△F_a+△F~*)/(KT)],can only describe that in the stage of fluctuating how many numbers of stable nucleus for unit volume at some time are formed but cannot describe the detailed program for phase separation. The kinetics equation for Spinodal decomposition,c(r,t)-c_0=PQ_2exp[R_2(β)· t]cos(β·r),can only describe the phase separation in the diffusing stage.Until now there is not a suitable equation describing the program of phase separation in the fluctuating stage.On the basis of the fluctuating process,this paper proposes a kinetics equation,c(r,t)-c_0=Pcos(βWt)·cos(β·r),describing the fluctuating stage.According to the equation the process forming a stablely non- uniform region is that first the size of the non-uniform region fluctuate around the critical value and the degree of fluctuation decreases gradually and simultaneously the concentrations of composite tend to stability.These stablely non-uniform regions provide the beginning condition for either nucleation-growth or spinodal decomposition.