Low-temperature synthesis of C₄AF by self-propagating combustion reaction

Low-temperature synthesis of tetracalcium aluminoferrite (C₄AF) by the self-propagating combustion reaction (SPCR) method using urea as fuel and metal nitrates as cation precursors is studied, and the mechanism of the combustion reaction is also introduced. Decomposition behaviour of metal nitrates and urea is analysed by differential thermogravimetric analysis, and characterisation of synthesised C₄AF is performed by X-ray diffractometry and Fourier transform infrared spectroscopy. It is found that C₄AF with good crystallinity and high purity could be synthesised in a straightforward way by the SPCR method in 2 h at 500°C. The free lime content of synthesised C₄AF is below the detection limit. Further calcination of synthesised C₄AF at higher temperatures is only beneficial for improving the crystallinity. It has no effect on chemical structure, and the corresponding hydration behaviour.