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RELATION BETWEEN THE TEMPERATURE CURVE AND THE EXPANSION CURVE IN THE SETTING OF PLASTER 1
Author(s) -
Williams F. J.,
Westendick F. C.
Publication year - 1929
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1929.tb18063.x
Subject(s) - muffle furnace , hemihydrate , thermal expansion , gypsum , calcination , mineralogy , volume (thermodynamics) , chemistry , thermodynamics , volume expansion , materials science , mathematics , metallurgy , physics , medicine , biochemistry , catalysis
The plan of the investigation was to determine the relation between the expansion curve and the temperature curve in the setting of plaster of Paris, which is manufactured by calcining gypsum at about 145°C in muffle or rotary cylinders. The setting of plaster results from the fact that when it is mixed with water the latter dissolves some of the hemihydrate which unites with the water to form the dihydrate. The first volume change is a contraction followed by expansion, due to the fact that the calcium‐hemihydrate (2CaSO 4 ‐H 2 O) goes into solution, thus decreasing the volume. An equilibrium is reached when the solution is saturated and then the dihydrate (CaSO 4 ‐H 2 O) crystallizes out, causing expansion. Apparatus, methods of testing, data, calculations and curves are given.