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 microstructure s 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 hype reutectic (x = 28 wt. %) binary samples, the sonication completely eli minated the dendritic structure of the primary crystals and induced eq uiaxed particles of the primary phase. At eutectic (x = 18 wt. %), the sonication removed oriented structures of the eutectic lamellae. Seve ral mechanisms of the microstructural modification were mentioned.