Sintering of phosphate-added MgO and the reaction between phosphates and magnesia were studied by means of thermal dilatometry and high-temperature X-ray diffraction analysis.
Some magnesium pyrophosphate-added MgO compacts, exanding temporaily on the formation of Mg₃ (PO₄) ₂ from MgO and Mg₂P₂O₇, shrank to a great extent compared with those containing other phosphates. The shrinkage rates of phosphate-added magnesia compacts began to increase at about 1000°C, while MgO compacts containing no phosphate shrank rapidly above 1100°C. The formation or the presence of Mg₃ (PO₄) ₂ accelerated shrinkage and sintering of MgO compacts.

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Steam and autoclave-cured pastes of supersulphate slag cement prepared from blast furnace slag, gypsum and slaked lime were investigated by means of scanning electron microscopic observation, measurement of pore-size distribution, X-ray analysis, test of compressive strength and determination of slag reacted. Rate and mechanism of slag reaction were discussed.
1) The hardened paste of 80-10-10 (slag-gypsum-slaked lime) cement cured for 12 hours at 70°C has been found to be effective for development of strength. It has a compressive strength of 259 kg /cm², a total pore volume of 0.1771 cm²/g and a distribution of main micropore from 37.5Å to 750Å, and consists of C-S-H, ettringite and unreacted cement materials. On the other hand, under autoclave curing at 180°C, paste of above cement consists of plazolite, C-S-H, ettringite, anhydrite and unreacted cement materials, which are not contribute to development of strength.
2) The rates of hydration of slag of 80-10-10 cement paste cured at 70°C are 3. 2% for 2 hours, 10. 9% for 5 hours and 25.9% for 12 hours form beginning of curing respectively. The value of N was calculated as using formula of [1- (1-α) ^1/3] ^N = k.t. The N is expressed as N<1 from 2 to 5 hours, N≅1 form 5 to 12 hours and N > 2 from 12 to 24 hours. The hydration of the paste for development of compressive strength seems to proceed via boundary reaction for considerable period in early hydration stage.
3) The compressive strength or hydration process of supersulfate slag cement are strongly influenced by mixing proportion of cement materials and curing condition.

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The shrinkage of Mg (H₂PO₄) ₂-2H₂O was measured by heating compressed specimens from room temperature up to 800°C at atmospheric pressure or under reduced pressures. The morphology of the resultant specimens was also examined.
The specimens obtained under reduced pressures had larger shrinkage coefficients than those at atmospheric pressure. Under reduced pressures the shrinkages which occurred in the ranges of 100-200°C, 250-350°C, and over 450°C were mainly attributed to dehydration, the formation of magnesium metaphosphate glass and its softening, respectively. The shrinkage was found to increase in the softening process.
At atmospheric pressure, the morphology of the grains at 400°C was plate-like and fibrous, while under reduced pressures the original rectangular-prism-like grains remained unchanged. The coalescence of grains at 600°C may be caused by softening of the glass.

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