Study On Morphology Control And Performance Of ?-hemihydrate Gypsum By The Glycerol Water Method At Atmospheric Pressure

With the rapid development of phosphate fertilizer industry in China, by the end of 2015, the total accumulation of phosphorus gypsum in China has been more than 500 million tons. Large amounts of gypsum storage not only take up too much land, but also cause serious pollution of water, atmosphere and environment. So the utilization of phosphogypsum and preventing secondary pollutions are the urgent problems. The a-hemihydrate gypsum with different sizes was prepared by the glycerol water method in atmospheric pressure, by taking full advantage of the characteristics of phosphogypsum such as high grade and powder in hygrometric state. The influences of glycerol centration, the reaction temperature and time, solid-to-liquid ratio, pH value and crystal modifiers on the content of crystal water and crystal morphology of a-hemihydrate gypsum were studied. And this article also does a research of organic acid modification mechanism. The study found that:The optimal technological conditions of preparing a-hemihydrate gypsum were determined as follows:the concentration of glycerol centration 50%, reaction temperature 105?, reaction time 2 h, pH value 5. Its crystal form appeared fine fibrous, surface smooth, aspect ratio about 90:1?60:1, when solid-to-liquid ratio was 1:9. Its crystal form appeared rod-shaped, aspect ratio about 12:1-8:1, which compressive strength of 24 hours was 13.26 MPa, when solid-to-liquid ratio was 1:5.The influence of crystal morphology was little when inorganic salts and macromolecules were crystal modifier. The crystal growth of c-axis direction was evidently inhibited when surfactants and organic acids were crystal modifier. The results showed that:hexagonal prism shape crystal with aspect ratio about 3:1 to 1:1 were obtained. By analyzing occurrence state of organic acids on the crystal surface, the complexation reaction between ionizing carboxyl functional groups of organic acids in aqueous solution and calcium ion was carried on. The complex compound selectively adsorbed on the (111) crystal face of crystallite, suppressing the growth of this crystal surface, so as to achieve the purpose of changing the product crystal morphology.The bonding of Whiskers/PP composite with different modified was better than that of without modifiers, the comprehensive properties of which was improved. The experimental results showed that tensile strength increased 11.40% and 4.89% respectively than pure polypropylene when the content of whiskers modified with the silane coupling agent KH-550 and sodium stearic acid was 10%, the toughening effect of the former was better than the latter, and the elongation was larger.