The Effect of Growth Kinetics on the Formation of Peritectic Microstructures in a Sr(NO3)2–H2O System

We evaluated the growth and dissolution behavior of the primary α phase, Sr(NO 3 ) 2, and peritectic β phase, Sr(NO 3 ) 2 ·4H 2 O, coexisting in aqueous solutions above or below the peritectic temperature ( T p ) in situ. Above T p, when the two phases simultaneously grew in close proximity, the metastable β phase began to partially dissolve where it approached the α phase, although the remaining portion of the β phase was still growing. Overall, the growing α phase could not approach the dissolving face of the β phase; thus, a peritectic microstructure with the α phase enclosing the β phase was not formed. Conversely, below T p, regardless of whether the metastable α phase was growing or dissolving, the stable β phase engulfed the α phase, resulting in a peritectic microstructure with the β phase enveloping the α phase. This demonstrated that it is necessary for the stable phase to dominate the metastable phase in growth kinetics for bringing about a peritectic microstructure consisting of the metastable phase in the core and the stable phase in the periphery.