Dodecacalcium Hepta Aluminate
Dodecacalcium Hepta-Aluminate
Dodecacalcium hepta-aluminate (12CaO·7Al2O3), also known by its mineral name mayenite, is an inorganic compound of significant interest in the field of calcium aluminate cements. Its chemical formula is sometimes expressed as Ca12Al14O33. This compound is one of the primary phases in calcium aluminate cements and is known for its reactivity and influence on the hydration processes of these cements.
Properties and Synthesis
Dodecacalcium hepta-aluminate can be synthesized through a conventional solid-state reaction. This involves heating a mixture of calcium carbonate and aluminium oxide or aluminium hydroxide powders in the presence of air. Notably, it is not formed in oxygen-rich or moisture-free environments. The synthesis occurs within a temperature range of 900–1200 °C, which facilitates the reaction between aluminium and calcium oxides.
Role in Calcium Aluminate Cements
In the context of calcium aluminate cements, dodecacalcium hepta-aluminate plays a crucial role during the hydration process. This compound contributes to the early stages of strength development in aluminous cements. However, due to its high reactivity, which can lead to excessively rapid hydration, the amount of C12A7 in aluminous cements is generally kept low or omitted altogether.
When exposed to higher temperatures, C12A7 can react with additional calcium oxide to form tricalcium aluminate, indicating its transitional presence in under-burned kiln products.
Related Phases
C12A7 is part of a larger group of calcium aluminates that influence the properties of cements. Other related compounds include:
- Monocalcium aluminate (CA)
- Tricalcium aluminate (C3A)
These compounds collectively contribute to the complex chemistry that governs the performance and application of calcium aluminate cements.
Applications
The involvement of dodecacalcium hepta-aluminate in cement chemistry makes it valuable for applications requiring rapid hardening and high-performance cements. It is particularly beneficial in scenarios where the rapid development of strength is crucial, such as in repair works and situations where quick setting is essential.