セッコウの熱間膨張収縮とその制御

抄録

On heating to 1000°C, gypsum expands below 100°C, and then shrinks by dehydration up to 500°C, and over 600°C shrinks strongly, remaining the derormated crystals. It was recognized that the strong shrinkage over 600°C would be originated in this deformation. Procedures to control this shrinkage by mixing refractory materials to gypsum, or by adding materials to prevent crystal deformation were tested, and following results were obtained.
Addition of glycerine, quartz, carbon, magnesia, metaphosphoric acid and chromium (III) oxide have small effect.
Addition of glycerine and quartz, silicone, ammonium dihydrogen phosphate and hydrochloric acid, magnesium chloride and ammonia water, aluminium chloride, and water : glass have respectable effect.
Addition of phosphoric acid, aluminium chloride and phosphoric acid, aluminium chloride and ammonia water, and chromium (VI) oxide have strong effect.
The gypsum samples which were added strongly effective materials expand on reheating to 1000°C and shrink on cooling both corresponding to temperature, remaining small residual shrinkage and weight loss due to the decomposition of gypsum.
X-ray analysis of these gypsum samples indicate the existence of refractory materials such as AlPO₄, 3CaO·Al₂O₃, Al₂O₃·Cr₂O₃ respectively.
ESCA analysis indicates that those refractory materials exist on the surface of gypsum crystals, and so prevent the deformation.
Compressive strength of gypsum descends to 1/2 -1/5 of that of nonadded one according to added material, and it degrades to 1/2-1/5 of each one by calcination at 260° and 500°C.