Research On Controlled Preparation Of Ettringite

The hydrated calcium aluminium, ettringite, one of the primary hydration product of cement, accounts for most of expansive properties of cement-based composite materials. The researches of the past on ettringite usually aim at improving the performance of cement, but pay less attention on the property of ettringite itself. This paper carried out a systematic study, which focused on the influences of the reaction parameters to the crystal structure, micro morphology and dehydration properties of ettringite. The ettringite is synthesized through hydrothermal method to ensure high purity, but not the usual way which is solid state reaction method. The design of experiment procedure follow the rule of control variable method.The ettringite in this paper were synthesized by Al2(SO4)3 and Ca(OH)2 through hydrothermal method, and investigated by the techniques of the X-ray diffraction, infrared spectrum, scanning electron microscope and differential scanning calorimeter. This paper researched the influences of the reaction temperature, time and the p H of reactive liquid to ettringite.This paper finds out that the reaction parameters have no influence to the crystal structure of ettringite, but it has a lot influence to the micro morphology of ettringite. The rising of reaction temperature and time both can benefit the coarsening of crystal. However the decline of the p H can benefit the grain refinement. This paper also point out that the ettringite can be commercial production because of that the concentration of reactant does not have any influence to the crystal structure of ettringite or micro morphology of ettringite. There exists several types of ettringite in SEM micrograph, such as group bunch of pellet, curl thin laminated shape, stubby needle clavate as well as staggered tall and slender needle clavate.Besides, this paper put forward one of the best process parameters to carry out ettringite through hydrothermal method and find out that the most possible way to contaminated ettringite is by carbonization. The result of related experiment also prove several information on the thermal stability of ettringite. When the temperature of the environment is 50℃, ettringite can keep a good structural stability. However if the temperature of heat treatment rise up to 90℃, the structure of ettringite will transform into some undefined structure. But it is reversible if the ettringite get water again. And when the temperature of heat treatment is 400℃, the structure of ettringite can only end up in complete destruction.