Growth kinetics of primary and secondary solid phases in Sr(NO 3)–H 2O peritectic system

Abstract

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 (1 1 1) face of the α phase and the (1 1 0) 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=5.1×10 −2 cm/s and α s=3.6 mJ/m 2 for the α phase; β s=5.3×10 −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.