Growth kinetics of primary and secondary solid phases in Sr(NO_3)-H_2O peritectic system

摘要

The growth behavior of the primary α phase (Sr(NO_3)_2) and the secondary β phase (Sr(NO_3)_2·4H_2O) in Sr(NO_3)_2-H_2O peritectic system was observed in situ in a solution flow system. The two phases grew simultaneously below the peritectic temperature in the solution with the composition near the peritectic point. The β phase grew much faster than the α phase due to the difference in both supersaturation and kinetic property for two phases. This resulted in the peritectic structure that the β phase engulfed the α phase. Using Michelson interferometry, growth rate was measured on the most widely developed faces, the (111) face of the α phase and the (110) face of the β phase. The β phase had the larger growth rate and step velocity and the smaller hillock slope than the α phase at a given supersaturation. The kinetic coefficient β_s and the edge free energy α_s of steps were evaluated as follows: β_s = 5.1 x 10~(-2) cm/s and α_s = 3.6 mJ/m~2 for the α phase; β_s = 5.3 x 10~(-1) cm/s and α_s = 18 mJ/m~2 for the β phase. This indicates that the step kinetics influences the growth of the two phases more significantly than that of the surface energy of step edge.