リン酸イオンの固溶によるセッコウの難溶化

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The conditions for direct preparation: of fibrous II-gypsum anhydride having the lowest solubility in gypsum modifications by the reaction in CaCl_2-H_2SO_4-CH_3OH system were reported in a previous paper. Studies were made on investigate the relationship between the incorporation of phosphate ion and the decrease of both solubilities of needle-like form (produced by the reaction of CaCl_2-Na_2SO_4-Na_2HPO_4 system) and fibrous form (produced by the reaction of Ca SO_4- Na_2HPO_4- CH_3OH system) of gypsum hemihydrate. Phosphate ion into the needle- like hemihydrate was incorporated by adding a CaCl_2 solution to a mixed solution (pH 8) of Na_2 SO_4 and Na_2HPO_4 at 100℃. Changes in lattice constants caused by the substitution of SO_4^2→HPO4^<2-> in gypsum hemihydrate crystal were found by X-ray diffraction. The upper limit of the iacorporation was 7 per cent (HPO_4^<2->/S O_4^<2-> molar ratio 0.07). This finding was also supported from data of TG-DTA, IR spectra and scanning electron microscopic observation. However, the upper limit was raised up to 15 per cent (HPO_4^<2->/S O_4^<2-> molar ratio 0.15), if pH of the mixed solution was adjusted to 9 from 8 by adding NaOH solution. On the other hand, the fibrous hemihydrate was incorporated with phosphate ion by the reaction on between Na_3HPO_4 solution and gypsum organogel which was produced by adding methanol to a saturated solution of gypsum dihydrate at 65℃. The upper limit of the incorporation of phosphate ion was also 15per cent. This fibrous solid solution had a very high water-resistivity as 0.4×10^<-3> Ca^<2+> mol dm^<-3> after dipping in water for 1h retaining the original fibrous form. Moreover, fibrous II-anhydride produced by heating this fibrous solid-solution showed a good water-resistivity as decreasing to about 1/50 against that of gypsum dihydrate (1.52×10^<-2>Ca^<2+> mol dm^<-3> after dipping in water for 1h).
社団法人日本セラミックス協会の論文
1990-05-01

リン酸イオンの固溶によるセッコウの難溶化

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