Experimental Study On The Morphology And Structure Of Calcium Sulphate Regulated By Microwave In Glycerin Aqueous Solution

Calcium sulphate(commonly known as gypsum)is one of the natural inorganic minerals with large reserves on the earth and is widely used in many industries such as construction,ceramics,and moulds.The output of various industrial by-product calcium sulfate(or gypsum slag)is also rising,and its stacking constitutes a great environmental pressure.Undoubtedly,it is important to study phase transformation,structural design,and functional modification of calcium sulfate mineral materials which will expand their potential of resource utilization.In this study,the dehydration modification and the morphological structure tuning of calcium sulfate dihydrate were investigated by using microwave glycerol thermal system and chelating agents EDTA and ATMP.The phase transformation and mechanism of morphological structure regulation were discussed.The effects of basic conditions such as glycerol concentration,reaction temperature,reaction time,suspension concentration,and heating rate on the phase change of calcium sulfate dihydrate were investigated by using a temperature-increasing recrystallization process.The results show that high glycerol concentration is not conducive to product separation.The glycerol mass concentration of 60%～70%,the reaction temperature of 110℃,the reaction time of 3 hours,and the DH concentration of 1%are prefer to this experiment.If the glycerol concentration was decreased,the temperature or time should be increased accordingly.A higher heating rate can promote calcium sulfate phase transition.The effect of EDTA on the phase transition and morphology of calcium sulfate was investigated.EDTA chelates the Ca2+,retarding the phase transition of calcium sulfate and changing its crystal morphology.The higher the concentration of EDTA,the smaller the aspect ratio of calcium sulfate crystals.Using NaCl can decrease the inhibition of EDTA.Microwave irradiation delays the phase transition of calcium sulfate,which is beneficial to the regulation of the morphological structure of calcium sulfate crystals.When 8mM of EDTA was used,the prepared HH crystals were β-HH.The HH heated by oil bath is in the shape of a hexagonal prism while heated by microwave tend to be spherical.Increasing the phase transition time helps the conversion of hexagonal prismatic crystals to spherical crystals.The effect of ATMP on the modification of calcium sulfate was investigated.It was found that when the ATMP is 30-60mM and the glycerol concentration is greater than 60%,the petal microspheres calcium sulfate can be prepared.Glycerol significantly affects the morphology of the microspheres.However,the reaction temperature has little effect on the morphology of the sample.ATMP changes the morphology of calcium sulfate because ATMP can chelate with Ca2+ on the specific plane of calcium sulfate dihydrate and participate in its growth.Compared with the raw material,the pore volume and specific surface of the petal microspheres are significantly increased.The dissertation has a certain reference value for the development of traditional methods for the modification of inorganic mineral materials and the preparation of novel calcium sulfate functional materials to expand their application potential.