Study On The Synthesis Of Calcium Sulphoaluminate Mineral And Its Thermodynamic Parameters

Calcium sulphoaluminate is a kind of active mineral with early strength and it is widely used in sulphur aluminate cement and desulfurization at high temperature.However,the thermodynamic properties of the mineral have not been widely studied especially using experimental test.In this work,the molar specific heat capacity,the standard formatio n enthalpy,standard generation entropy,and standard Gibbs free energy are calculated by combining experiment method with the quantum chemistry calculation.Firstly,the calcium sulphoaluminate is synthesized from two components（CaO·Al₂O₃,CaSO₄·2H₂O）and three components（CaCO₃,Al（OH）₃,CaSO₄·2H₂O）.Effects of CaSO₄decomposition,reaction atmosphere（O₂,CO₂,N₂）and mixing method of raw materials on the purity of products are investigated by using TG and XRD techniques.The results show that the two components method have less by-reactions than the three components method at the same temperature,and can generate the product of higher purity.Overall,O₂ atmosphere can reduce the decomposition of CaSO₄,thereby reducing generation of the by-reactions and improving the product purity.The wet mixing method can achieve better mixing effect because its hydrolysis process can increase the reactant activity and facilitate the production of the calcium sulphoaluminate.The mass fraction of the calcium sulphoaluminate in the product（1593.15 K,O₂ atmosphere and wet mixing method）by using the two components method reaches 88.14%.Subsequently,TG and DSC are used to test the specific heat capacity of the calcium sulphoaluminate from 298.15 to 608.15 K,and the specific heat capacity is further fitted and expressed as the function of temperature from 298.15 to 1553.15 K.The enthalpy change of the formation reaction at 1553.15 K is measured.The thermodynamic cycle is designed according to the Hess’s law.Standard enthalpy of formation,standard entropy of formatio n,and standard Gibbs free energy of the calcium sulphoaluminate are calculated as-8537.20kJ·mol^-1,-1.55 kJ·mol^-1·K^-1 and-8074.02 kJ·mol^-1.Then,a crystal structure model of the calcium sulphoaluminate is established.Combining the first principle and density functional theory,the function expression of the specific heat capacity from 298.15K to 1553.15K is obtained.Standard enthalpy of formatio n,standard entropy of formation,and standard Gibbs free energy are calculated as-7997.79kJ·mol^-1,-1.66 kJ·mol^-11 and-7503.46 kJ·mol^-1.