title: Effect of humidity on calcium sulphate hemihydrate.
abstract: 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 degrees C, greater than about 2.3 kPa water vapour pressure caused rapid reaction, and this may be taken as a more reliable critical value.
authors.affiliation: Dental Technology Unit, University of Hong Kong.
authors.forename: A
authors.initials: A
authors.lastname: Torrance
authors.forename: B W
authors.initials: BW
authors.lastname: Darvell
mesh_terms: D002133:Calcium Sulfate; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003764:Dental Materials; D006813:Humidity; D008422:Materials Testing; D013696:Temperature; D014867:Water
chemical_list: D003764:Dental Materials; D014867:Water; D002133:Calcium Sulfate