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| Section3 = | Section5 = }} Dodecacalcium hepta-aluminate (12CaO·7Al2O3, Ca12Al14O33 or C12A7) is an inorganic solid that occurs rarely in nature as the mineral mayenite. It is an important phase in calcium aluminate cements and is an intermediate in the manufacture of Portland cement. Its composition and properties have been the subject of much debate, because of variations in composition that can arise during its high-temperature formation.〔Taylor, H F W (1990) ''Cement Chemistry'', Academic Press, ISBN 0-12-683900-X, pp. 36–38〕 ==Synthesis== Polycrystalline C12A7 can be prepared via a conventional solid-state reaction, i.e., heating a mixture of calcium carbonate and aluminium oxide or aluminium hydroxide powders, in air. It is not formed in oxygen or in moisture-free atmosphere. It can be regrown into single crystals using the Czochralski or zone melting techniques. In Portland cement kilns, C12A7 is an early reaction product of aluminium and calcium oxides in the temperature range 900–1200 °C. With the onset of melt-phases at higher temperatures, it reacts with further calcium oxide to form tricalcium aluminate. It thus can appear in under-burned kiln products. It also occurs in some natural cements. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dodecacalcium hepta-aluminate」の詳細全文を読む スポンサード リンク
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