Aspects of generation of destructive crystal growth pressure

Growth of some salt crystals, e.g. Na2SO4 circle 10H(2)O circle Na2S2OP3 circle 5H(2)O, etc., from their supersaturated solutions is often, though not invariably, associated with crumbling of porous materials. Usually, both crystal growth and development of damage-causing pressure are treated using isothermal, equilibrium thermodynamics. The implicit assumption is that crystals have their equilibrium habits. However, experimental and natural crumbling have been associated with the formation of acicular crystals, e.g. Na2S2O3 circle 5H(2)O from its melt, Ca(OH)(2) in the hydration of CaO, etc. Slow formation of large crystals, in conditions approaching equilibrium and isothermal requirements, has not been associated with any damage. To resolve the above contradiction, the literature on crystal growth has been critically examined. This examination shows that in most studies the following has not been properly considered: (1) a growing crystal is neither in equilibrium nor in equi-thermal state with the supersaturated solution, (2) supersaturated solutions contain ion agglomerates of larger sizes, (3) different crystallographic faces have different solubility. A similar non-uniform material deposition also occurs in the vapour deposition of metals on irregular particles. More metal accrues on the tips or heights than on planes and sides. A mechanism has been proposed to explain the crumbling of porous materials. (c) 2005 Elsevier B.V. All rights reserved.