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Effect of humidity on calcium sulphate hemihydrate
Author(s) -
Torrance A.,
Darvell B. W.
Publication year - 1990
Publication title -
australian dental journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.701
H-Index - 71
eISSN - 1834-7819
pISSN - 0045-0421
DOI - 10.1111/j.1834-7819.1990.tb05399.x
Subject(s) - hemihydrate , calcium , context (archaeology) , humidity , atmospheric pressure , chemistry , water vapor , vapour pressure of water , inorganic chemistry , materials science , metallurgy , gypsum , organic chemistry , thermodynamics , meteorology , geology , paleontology , physics
The conversion of calcium sulphate hemihydrate powders to dihydrate by reaction with atmospheric water vapour has been re‐examined gravimetrically. Storage is usually said to be safe at less than ‘70 per cent RH’, but this is shown to be an inadequate criterion (water vapour pressure being more useful in the context) and based on an inappropriate experiment. At 23°C, greater than about 2.3 kPa water vapour pressure caused rapid reaction, and this may be taken as a more reliable critical value.