Synthesis Mechanism and Material Characterization of C4AF Obtained by the Self-propagating Combustion Reaction Method

To investigate the influence of preparation process on the properties of synthesized C(4)AF, the powder was prepared via the self-propagating combustion reaction (SPCR) method using urea as fuel and metal nitrates as cation precursors. Synthesis mechanism of the SPCR method, calculation and adjusting principles of urea dosage were detailedly introduced. Material characterization of synthesized C(4)AF was performed with the aid of X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Al-27 nuclear magnetic resonance and isothermal microcalorimetric technique. Remaining content of transition phase of calcium carbonate in synthesized C(4)AF was determined by quantitative analysis of X-ray diffractometry. It was found that there was no difference in the hydration behavior of C(4)AF synthesized by the SPCR method and the traditional solid-state reaction (SSR) method. C(3)AH(6) and amorphous iron (III) hydroxide (Fe(OH) 3) would be formed during the hydration of C(4)AF while CH not. Crystallite size of synthesized C(4)AF was 16.1 angstrom and the apparent activation energy was 36.2 kJ/mol. Coordinated condition of Al in C(4)AF can be detected by Al-27 NMR technique, but the peaks were broadened and the intensities were relatively low, supporting the use of Al-27 NMR for the quantitative analysis of C(3)A in Portland cements.