Decrease of Bubbles caught in Gypsum Plaster Molds

概要

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This is the study on the relation between the bubbles caught in gypsum plaster molds and the pH value of the suspension of calcined gypsum, and on the method of decreasing the bubbles by the pH control with addition of a few Ca compounds. The results of this study are summarized as follows : (1) The pH value of the suspension of calcined chemical gypsum, CaSO4·1/2 H2O, produced in acidic range is less than that of the gypsum, CaSO4·2 H2O and lower than that of commercial plaster. (2) The bubbles increase in proportion to the acidity of the suspension. (3) When the pH value of the suspension of calcined gypsum is less than 7, the bubbles are especially numerous. (4) It is difficult to raise the pH above 7 by dipping the gypsum in Ca (OH) 2 saturated solution after washing, but it is easy by addition of CaCO3 or Ca (OH) 2 fine powder to calcined or dried gypsum. (5) It is possible to decrease the bubbles without lowering the qualities of the plaster by raising the pH value above 7 with addition of CaCO3 or Ca (OH) 2. (6) Optimum pH range are 7.1-7.3 in CaCO3 and 12.5-12.6 in Ca (OH) 2. (7) In utilization for manufacturing, CaCO3 is more profitable than Ca (OH) 2 and the method using of CaCO3 seems to be easy.
無機マテリアル学会の論文