UNAMBIGUOUS DEMONSTRATION OF DESTRUCTIVE CRYSTAL-GROWTH PRESSURE

At 48 degrees C sodium thiosulphate pentahydrate, Na2S2O3.5H(2)O melts in its own water of crystallization forming a concentrated solution. On cooling, this melt forms a highly supersaturated solution and subse quently Na2S2O3.5H(2)O crystallizes out directly without any intermedi ate anhydrous phase. Pyrex glass test tubes or beakers, containing mor e than a critical volume of this melt, crack when stored in a refriger ator at 5 degrees C. Prolonged storage of the cracked containers in th e refrigerator causes an increase in the apparent diameter of the crys talline mass. This cracking and subsequent expansion unambiguously dem onstrate the existence of destructive crystal growth pressure. Necessa ry conditions for a damage to occur to a porous matrix due to crystal growth pressure have been delineated. (C) 1997 Elsevier Science Ltd.