Effect of impurities on the metastable zone width of solute-solvent systems

摘要

The novel approach to interpret the metastable zone width obtained by the polythermal method using the classical theory of three-dimensional nucleation proposed recently [K. Sangwal, Cryst. Growth Des. 9 (2009) 942] is extended to describe the metastable zone width of solute-solvent systems in the presence of impurities. It is considered that impurity particles present in the solution can change the nucleation rate J by affecting both the kinetic factor A and the term B related with the solute-solvent interfacial energy γ. An expression relating metastable zone width, as defined by the maximum supercooling △T_(max) of a solution saturated at temperature T_0, with cooling rate R is proposed in the form: (T_0/△T_(max))~2 = F(1-ZlnR), where F and Z are constants. The above relation can also be applied to describe the experimental data on maximum supercooling △T_(max) obtained at a given constant R as a function of impurity concentration c_i by the polythermal method and on maximum supersaturation σ_(max) as a function of impurity concentration c_i by the isothermal method. Experimental data on △T_(max) obtained as a function of cooling rate R for solutions containing various concentrations c_i of different impurities and as a function of concentration c_i of impurities at constant R by the polythermal method and on σ_(max) as a function of impurity concentration c_i by the isothermal method are analyzed satisfactorily using the above approach. The experimental data are also analyzed using the expression of the self-consistent Nyvlt-like approach [K. Sangwal, Cryst. Res. Technol. 44 (2009) 231]: In(△T_(max)/T_0) = Φ+β In R, where Φ and β are constants. It was found that the trends of the dependences of Φ and β on impurity concentration c_i are similar to those observed in the trends of the dependences of constants F and Z on c_i predicted by the approach based on the classical nucleation theory.