Academic literature on the topic 'Hemihydrate de sulfate de calcium'

The existing α-hemihydrate gypsum preparation process has low production efficiency and high energy consumption. In this paper, α-type hemihydrate gypsum was prepared by microwave irradiation using phosphogypsum as the raw material, calcium chloride solution as the reaction medium, and succinic acid and aluminum sulfate as crystal-transforming agents. Both aluminum sulfate and succinic acid were studied to determine the mechanism influencing the effect on the growth of α-type hemihydrate gypsum crystals. This study found that, without added succinic acid or aluminum ions, the crystal transformation rate of α-calcium sulfate hemihydrate reached 96% with the average length-diameter ratio reaching 21 after 1 h; when the dosage of succinic acid was 0.02%, the crystal transformation rate of α-calcium sulfate hemihydrate reached 96% with the average length-diameter ratio reaching 1.5 after 1.5 h; and when the aluminum ion dosage was 5 mM, the crystal transformation rate of α-calcium sulfate hemihydrate reached 97% with the average length-diameter ratio reaching 12.3 after 1 h. In addition, it was discovered that the reaction time was significantly shortened under microwave irradiation, and with an increase in succinic acid content, the regulation of the microscopic morphology of the calcium sulfate hemihydrate crystals was continuously enhanced and the aspect ratio of the crystals was continuously reduced. The EDS and Fourier transform infrared spectroscopy (FTIR) analysis showed that succinic acid did not adsorb onto the hemihydrate gypsum crystal during the reaction under microwave irradiation. The X-ray photoelectron spectroscopy (XPS) analysis revealed that aluminum ions affected crystal growth by incorporating into calcium sulfate hemihydrate crystals after reacting with sulfate radicals.

The influence of sodium citrate on the hydration capacity of hemihydrate calcium sulfate whiskers was investigated. The products were characterized by FTIR, SEM and XRD.The results show that the absorption of the sodium citrate on the surface of the hemihydrate calcium sulfate whiskers is not uniform, and the adsorption state also changed with the amount of sodium citrate. Sodium citrate plays role on the hydration capacity of hemihydrate calcium sulfate whiskers.

Modifying crystal morphology was the key technology of the preparation of α-calcium sulfate hemihydrate from flue gas desulphurization gypsum using the hydrothermal method under atmospheric pressure. For exploring the mechanism of butane diacid effect on crystal morphology of α-calcium sulfate hemihydrate in preparation from flue gas desulphurization gypsum, the crystal morphology, convert ratio, and reaction process of α-calcium sulfate hemihydrate were studied by scanning electron microscope observation, and crystal water testing. The results showed, firstly, crystal modifier made the growth rates of crystal in all directions equal and made the crystal into hexagonal short column, by selectivity adsorbing on (111) crystal plane of α-calcium sulfate hemihydrate to form buffer film layer which hindered combining and growing of crystallization unit on the crystal plane of c-axis direction. Secondly, butane diacid was a good crystal modifier. When adding butane diacid of optimal amount of 0.02%~0.05%, the crystal morphology of α-calcium sulfate hemihydrate was satisfactory, the crystal length-diameter ratio was 1:1, but the convert ratio was only 91%~93%.