抄録
In continuing the previous report [This Journal, No. 12, p. 537-541 (1954)] the present authors reported the results of further studies on the special gypsum-dolomite plaster (abridged name by the present authors as “Gypster”). The main points of the present report are as following : (1) two samples of calcined dolomite grains (20-30 mm) were obtained by calcining at 950°C of two kinds of dolomite from (a) Kuzuu, Tochigi Prefecture and (b) Ibuki, Gifu Prefecture, (2) three samples of by-product crystal gypsum (CaSO4·2H2O) from three salt making plants (a) Hofu, Yamaguchi Prefecture, (b) Ako, Hyogo Prefecture and (c) Takuma, Kagawa Prefecture, (3) 70, 75, 80, or 85 parts of calcined dolomite grains were mixed with 30, 25, 20, or 15 parts of crystal gypsum powder, (4) 100 parts of these mixtures were slaked by 35-40 parts of water with strong stiring, (5) these slaked masses were aged at 150-170°C of slaking heat for one day, and then ground and wind sieved to the special gypsum-dolomite plaster as Gypster, (6) several samples of thus prepared Gypster were tested and compared on their chemical compositions, and physical properties as fineness, amount of mixing water, setting and hardening time, viscosity of kneaded mass, hardness, soundness, whiteness and bending strendgth of hardened test pieces, etc., by the method of the Japan Industrial Standards for mixed gypsum plaster (JIS A 6904), (7) the good results were obtained by the samples containing not les than 14-15 % of calcined gypsum or semihydrated gypsum as gypsum plaster (CaSO4·1/2H2O), which is showing that the Gypster of the best quality can be obtained by mixing 80-70 % calcined dolomite grain with 20-30 % crystal gypsum powder and slaking with 35 % water, and these studies are now further continuing and comparing by using other by-product crystal gypsum from various chemical industrial plants, which results will be reported in the next third report.
