The formation process of calcium suphoaluminate（C4A3S） was investigated by the X-ray diffraction technique and then the thermodynamics was analyzed, finally the kinetics of which was studied by SC-132. XRD results show that the formation of C4A3S is accomplished in three different kinds of ways： one is by solid reaction of Ca （OH）2/ CaO, Al2O3 and CaSO4, other two ways are through such interstitial products as CaO·Al2O3 and CaO·2Al2O3. The formation thermodynamics shows that C4A3S begins to form at 900 ℃-1 000 ℃ and increases as temperature rising; the quantity of reaches the highest at 1 300 ℃-1 350 ℃ and then falls at 〉1350℃. Kinetics study shows that the formation rate of C4A3S can be described as first-order kinetics at high temperature, and it belongs to the random nucleation growth mechanism. The apparent activation energy is 456.37 kJ·mol-1 and pre-exponential factor is 1.545×1012.
The Co2O3-doping effect on the formation of 3CaO · 3A12O3· CaSO from CaCO3-A12O3-CaSO4, 2H20 mixtures was investigated by means of SO2 emission behavior, chemical analysis, X-ray diffraction, differential thermal analysis and scanning electron microscopy. The experimental results show that CO2O3 addition increases the reactivity of the CaCO3-A12O3-CaSO4·2H2O system significantly, by reducing SO2 emissions in combustion andf-CaO contents in the clinkers, promoting the nucleation and growth of 3CaO·3A12O3-CaSO4, and intensifying the formation of 3CaO·3A12O3·CaSO4. Moreover, CO2O3 addition lowers the formation temperature of 3CaO·3A12O3·CaSO4 by 18 ℃, and similarly increases the thermal stability of it at a wider temperature range.
The reference test methods are carried out parallelly, by means of chemical analysis, X-ray diffraction, differential scanning calorimetry-thermogravimetry, scanning electron microscopy and polarized optical microscope to study the formation of C4A3S in the presence and absence of nucleating agent. The results show that nucleating agent with high calcium and low heat consumption as tricalcium silicate （C3S） promotes the formation of C4A3S and increases desulfurization degree obviously. During calcining raw meals doped with C3S, the grain sizes of C4A3S are larger compared with that without C3S. And at the same calcining level, the mass loss and the heat consumption belonged to CaCO3 decomposition is reduced.
