Mechanochemical Synthesis of Tricalcium Aluminum Hydrate from Calcium Hydroxide-Boehmite Mixtures by Room Temperature Grinding.

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Tricalcium aluminum hydrate (3CaO·Al2O3·6H2O：C3AH6) is synthesized mechanochemically from mixtures composed of calcium hydroxide (Ca(OH)2) and pseudo-boehmite (γ-AlO(OH)) powders by room temperature grinding using a planetary ball mill. Use of the boehmite sample with inferior crystallinity is more favorable for the mechanochemical synthesis rather than that with well crystalline one. The time required to form C3AH6 from the Ca(OH)2-γ-AlO(OH) mixture is much longer than that from the Ca(OH)2-gibbsite (Al(OH)3) one. Adsorbed water from air during grinding plays a significant role in the formation of C3AH6 from the former mixture. After water addition to Ca(OH)2-γ-AlO(OH) mixtures ground for various times, excess hydrated calcium aluminates such as C2AH8, C3AH8-12 and C2A0.5H6.5 are formed in the starting and the short time ground mixtures, while a few amount of these compounds is formed in these hydrated mixtures after prolonged grinding. Formation of these excess hydrated compounds, which belong to layered structural materials, is enhanced in the presence of free Ca, Al compounds and water.