The self-propagating combustion reaction（SPCR）method was employed to synthesize C4AF using metal nitrates as cation precursors and urea as fuel.Thermal decomposition behavior of dried gels,phase identification and c...The self-propagating combustion reaction（SPCR）method was employed to synthesize C4AF using metal nitrates as cation precursors and urea as fuel.Thermal decomposition behavior of dried gels,phase identification and crystallinity of synthesized C4AF,and impact of urea to metal nitrates（UR/MN）molar ratio on synthesis effect were investigated with the aid of differential thermogravimetric analysis,X-ray diffraction and Fourier transform inferred spectrometry.It is found that pure C4AF can be prepared by the SPCR method in 2 h at 500℃.The UR/MN molar ratio plays a significant role in the thermal decomposition behavior of dried gel,purity,crystallinity and crystallite size of synthesized C4AF.Ignition temperature should be not lower than 500℃but higher temperatures were unnecessary.No trace of free lime in synthesized C4AF is detected and calcium carbonate is the transition phase.Further calcining the synthesized C4AF at high temperatures is beneficial for increasing crystallinity,purity and crystallite size.Reaction activation energy of the further calcination process is 119.6 kJ/mol.It is more efficient to improve the synthesis effect by increasing UR/MN molar ratio than further calcination at high temperatures.展开更多
To investigate the influence of preparation process on the properties of synthesized C4AF,the powder was prepared via the self-propagating combustion reaction（SPCR）method using urea as fuel and metal nitrates as cat...To investigate the influence of preparation process on the properties of synthesized C4AF,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 C4AF was performed with the aid of X-ray diffractometry,Fourier transform infrared spectrometry,scanning electron microscopy,energydispersive X-ray spectroscopy,^27Al nuclear magnetic resonance and isothermal microcalorimetric technique.Remaining content of transition phase of calcium carbonate in synthesized C4AF was determined by quantitative analysis of X-ray diffractometry.It was found that there was no difference in the hydration behavior of C4AF synthesized by the SPCR method and the traditional solid-state reaction（SSR）method.C3AH6 and amorphous iron（III）hydroxide（Fe（OH）3）would be formed during the hydration of C4AF while CH not.Crystallite size of synthesized C4AF was 16.1 A and the apparent activation energy was 36.2 kJ/mol.Coordinated condition of Al in C4AF can be detected by ^27Al NMR technique,but the peaks were broadened and the intensities were relatively low,supporting the use of ^27Al NMR for the quantitative analysis of C3A in Portland cements.展开更多
基金Funded partly by the National "973" Program of China(No.2015CB655101)National Natural Science Foundation of China(No.51379163)
文摘The self-propagating combustion reaction（SPCR）method was employed to synthesize C4AF using metal nitrates as cation precursors and urea as fuel.Thermal decomposition behavior of dried gels,phase identification and crystallinity of synthesized C4AF,and impact of urea to metal nitrates（UR/MN）molar ratio on synthesis effect were investigated with the aid of differential thermogravimetric analysis,X-ray diffraction and Fourier transform inferred spectrometry.It is found that pure C4AF can be prepared by the SPCR method in 2 h at 500℃.The UR/MN molar ratio plays a significant role in the thermal decomposition behavior of dried gel,purity,crystallinity and crystallite size of synthesized C4AF.Ignition temperature should be not lower than 500℃but higher temperatures were unnecessary.No trace of free lime in synthesized C4AF is detected and calcium carbonate is the transition phase.Further calcining the synthesized C4AF at high temperatures is beneficial for increasing crystallinity,purity and crystallite size.Reaction activation energy of the further calcination process is 119.6 kJ/mol.It is more efficient to improve the synthesis effect by increasing UR/MN molar ratio than further calcination at high temperatures.
基金Funded partly by the National“973”Program of China(No.2015CB655101)National Natural Science Foundation of China(No.51379163)
文摘To investigate the influence of preparation process on the properties of synthesized C4AF,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 C4AF was performed with the aid of X-ray diffractometry,Fourier transform infrared spectrometry,scanning electron microscopy,energydispersive X-ray spectroscopy,^27Al nuclear magnetic resonance and isothermal microcalorimetric technique.Remaining content of transition phase of calcium carbonate in synthesized C4AF was determined by quantitative analysis of X-ray diffractometry.It was found that there was no difference in the hydration behavior of C4AF synthesized by the SPCR method and the traditional solid-state reaction（SSR）method.C3AH6 and amorphous iron（III）hydroxide（Fe（OH）3）would be formed during the hydration of C4AF while CH not.Crystallite size of synthesized C4AF was 16.1 A and the apparent activation energy was 36.2 kJ/mol.Coordinated condition of Al in C4AF can be detected by ^27Al NMR technique,but the peaks were broadened and the intensities were relatively low,supporting the use of ^27Al NMR for the quantitative analysis of C3A in Portland cements.
