PHASE-TRANSITION OF KNO(3) MONITORED BY ACOUSTIC-EMISSION TECHNIQUE AND THE HEALING EFFECT ON THE GAMMA-]ALPHA TRANSITION

The alpha --> beta phase transition of KNO3 on heating and the beta --> gamma --> alpha transitions on cooling were monitored by simultaneous acoustic emission-differential thermal analysis (AE-DTA) measurements and were observed by high-temperature microscopy, using powder and single crystal samples. The gamma --> alpha transition was affected by the temperature (160-450-degrees-C) from which the samples were cooled, whereas the alpha --> beta and beta --> gamma transitions , were independent of this temperature. It is first noted that the temperature effect on the former transition was associated with a healing effect operating at 220-280-degrees-C, which sweeps out the defects formed by the alpha --> beta transition. The cumulative AE counts were 1 or 2 orders of magnitude greater for the gamma --> alpha transition than for the other two transitions. The healing effect and the greater cumulative counts for the gamma --> alpha transition are discussed in connection with the structural relationship of the three phases.