STUDY OF KBR/PB(NO3)2 GROWTH AND CRYSTAL MORPHOLOGIES BY ACOUSTIC-EMISSION AND PHOTOMICROGRAPHIC TECHNIQUES

Simultaneous optical and acoustic information was used to elucidate the mechanism of acoustic emission (AE) generation during growth of pure and Pb(NO3)2 doped KBr crystals. The mechanism of generation is postulated as one of inter-crystal interaction. The use of AE for monitoring the growth of different crystal structures was examined by studying different KBr morphologies grown with varying degrees of Pb dopant (0-32000 ppm). The AE profiles collected during the crystal growth of the dendritic form of KBr (4080-8120 ppm Pb dopant), and the doped forms of 12210 ppm Pb and above were found to give the best agreement with the image whitening profiles collected simultaneously. The dendritic form of KBr observed between 4080 and 8120 ppm consisted of finger-like outgrowths, that spread outwards from the evaporating droplet. Scanning electron microscopy showed these fingers to consist of contiguous chains of tiny (< 25 mum) octahedra, a microscopic structure that provided many potential sources of emission. The total AE observed during the growth of the different KBr morphologies was found to vary in a reproducible manner over 60 experiments. The mass of crystals grown was less than 0.12 g for all samples. Acoustic waveform analysis showed that these signals arising during growth were distinguishable from artificially produced signals of bulk dendrite fracture and crystal impact.