COMPUTER-SIMULATION OF THE TOPLEY-SMITH EFFECT

Computer simulation of the layer-by-layer distribution of temperature and dehydration rate J in powdered Li2SO4 . H2O monohydrate as functio ns of the partial pressure P-w of water vapor reveals a substantial se lf-cooling of the sample. The anomalous course of the J=f(P-w) curve w ith increasing P-w, which manifests itself in the appearance of a maxi mum in the curve (the Topley-Smith effect), originates from the compet ition of the depressing action of H2O vapor on the dehydration rate wi th increasing heat transfer from the furnace to the sample. The model accounts for the main features of the Topley-Smith effect, namely, the falloff of decomposition rate for low P-w and the minimum in the J=f( P-w) curve, the variation of the value of P-w corresponding to the max imum of the curve within two orders of magnitude for different hydrate s, and the enhancement of the effect with increasing decomposition tem perature and decreasing grain size of the powder sample. (C) 1998 Else vier Science B.V.