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.