| Gypsum is a kind of material that has been used in the ancientry. It is considered as the mainstay of binding material with lime and cement. According to the different preparing methods, it can change to α hemihydrate gypsum or β hemihydrate gypsum. The properties of them are quite different, the crystal structure of a hemihydrate gypsum is close-grained, crystal shape of α hemihydrate gypsum is the key factor affected the strength, α hemihydrate gypsum was applied in a lot of fields, such as mechanics automobile, manufacture, construction, ceramics, medicine, odontology and so on.α hemihydrate gypsum was prepared by autoclave technology in this paper. With arthogonality experiment method and SEM, TG-DTA, the properties of α hemihydrate gypsum and the factors of influence on them were studied, and the optimum condition of autoclave technology was determined. Under the optimum condition, the compressive strength of a hemihydrate gypsum which prepared by autoclave technology is more than 14MPa. Compare the difference of the sample that was prepared by autoclave technology, aqueous salt solution method and heated aqueous solution method.Adding crystal modifier in gypsum, a hemihydrate gypsum was prepared by autoclave technology under the optimum condition. The result shows that the crystal shape was ideal by add organic crystal modifier. Then the paper discussed dehydration mechanism of gypsum based on a lot of references, and studied the function of crystal modifier in the transform from gypsum to a hemihydrate gypsum.A kind of super high strength gypsum was prepared from industrial a hemihydrate gypsum. It also studies the effect of additive on the setting time, standard consistency of gypsum, the compressive strength and bending strength of a hemihydrate gypsum, analyses the microcosmic structure by scanning electron micrograph. The compressive strength of α hemihydrate gypsum is more than 14Mpa after 2 hours and the dry compressive strength is more than 60MPa.
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