Solubilities of MgO in H2SO4 solutions were measured and X‐ray analyses of over 100 neat cement samples were used to construct an isothermal phase diagram for the system MgO‐H2SO4‐H2O at 23°±3°C. The phases MgO, Mg(OH)2, 3Mg(OH)2 MgSO4·8H2O (3·1·8), MgSO4·7H2O, MgSO4·6H2O, and MgSO4·H2O were stable at 23°C. The phases Mg(OH)2· MgSO4·5H2O (1·1·5) and MgSO4·4H2O were observed but are considered to be metastable, resulting from overheating during reaction. Invariant liquids were located at 8.2±0.2 MgO, 17.4±0.5 wt% H2SO4 in equilibrium with Mg(OH)2 and 3·1·8; at 8.6±0.2 MgO, 21.2±0.5 wt% H2SO4 in equilibrium with 318 and MgSO4·7H2O; at 6.9±0.2 MgO, 42.4±1.0 wt% H2SO4 in equilibrium with MgSO4·7H2O and MgSO4·6H2O; and at 6.0±0.5 MgO, 48±2 wt% H2SO4 in equilibrium with MgSO4·6H2O and MgSO4·H2O. The diagram indicates that cements containing >50 wt% 3·1·8 cannot be made from MgO and MgSO4 solutions at 23°C. Steam curing, however, offers some possibilities for increasing binder‐phase content. Mg(OH)2 formed in the system provides X‐ray patterns which indicate an exaggerated sheet morphology. Copyright © 1980, Wiley Blackwell. All rights reserved


Materials Science and Engineering

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1551-2916; 0002-7820

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Article - Journal

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Publication Date

01 Jan 1980