As a part of the current study on decrease of the solubility of gypsum fiber, preparation of gypsum hemihydrate fiber incorporating phosphate ion and the decrease of its solubility were reported in our previous paper. Studies were made to investigate decrease of the solubility of gypsum fibers by substitution of Ca
2+_??_Sr
2+, simultaneous substitutions of Ca
2+_??_Sr
2+ and SO
42-_??_HPO
42- into the hemihydrate fiber. Characteristics of solid solutions were investigated by means of X-ray diffraction, thermal analysis (TG-DTA), scanning electron microscopic observation and dissolution test.
The incorporation of strontium ion in the hemihydrate fiber by the aqueous reaction in CaCl
2-SrCl
2-H
2SO
4-CH
3OH system at 80°C was synthesized by adding a H
2SO
4-CH
3OH solution into a CaCl
2-SrCl
2 solution. Changes in lattice constants caused by the substitution of Ca
2+_??_Sr
2+ in the hexagonal hemihydrate fiber were found by X-ray diffraction. The upper limit of the incorporation was 33 mol per cent (Sr
2+/Ca
2+mol ratio 0.5). This finding was also supported from data of TG-DTA and scanning electron microscopic observation. The solid solution had an aspect ratio of about 350 (diameter 0.2μm, length 70μm). However, the decrease of the solubility of strontium ion-incorporated hemihydrate fiber did not improved against that of phosphate ion-incorporated hemihydrate fiber reported by a previous paper.
Whereas simultaneous substitutions of both Ca
2+_??_Sr
2+ (Sr
2+/Ca
2+mol ratio 0.1) and SO
42-_??_HPO
42- (HPO
42-/SO
42-mol ratio 0.15) into hemihydrate fiber were attempted by the aqueous reaction in CaSO
4-SrCl
2-Na
2HPO
4-CH
3OH system at 65°C. The solid solution was formulated as Ca
0.9 Sr
0.1 (SO
4)
0.85 (HPO
4)
0.15·1/2H
2O and had a high flexibile fiber as an aspect ratio of about 200 (diameter 0.3μm, length 60μm). Its solubility after dipping in water for 24 h decreased to about 1/30 against that of gypsum dihydrate.
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