Microstructure of nitrate polycrystals solidified under ultrasonic vibration

Molten nitrates in the system (1 - x)NaNO₃-xBa(NO₃)₂ were solidified in the presence of a power ultrasound of 20 kHz. Their microstructures were compared with those of controlled samples which were solidified normally. Grain size in the controlled sample of monolithic NaNO₃ (x = 0) was reduced by sonication. In the hypo-(x = 8 wt. %) and the hypereutectic (x = 28 wt. %) binary samples, the sonication completely eliminated the dendritic structure of the primary crystals and induced equiaxed particles of the primary phase. At eutectic (x = 18 wt. %), the sonication removed oriented structures of the eutectic lamellae. Several mechanisms of the microstructural modification were mentioned.