Research On The Preparation Of Calcium Sulfate Whisker Using Salt Gypsum

Whisker is a kind of single crystal which cross section is aptotic, figure is even and inner structure is perfect. Since the80’s, carborundum whisker, aluminum borate whisker, potassium chloride whisker, potassium titanium acid and calcium carbonate whisker etc have been prepared successfully at home, which have been used in lots of industrial fields. Even so, most of them have not brought about industrialization because of its high cost. It is possible of whisker’s industrialization because of the successful preparation of Calcium sulfate whisker (CSW). Calcium sulfate whisker is single crystal of calcium sulfate, which is same as gypsum that has three types:no crystal water crystal、 half crystal water crystal and two water crystal, at the same time it can be used as intensifier of moderate intensity because of its characteristic for instance:innocuous, high intensity and toughness, temperature resistance, anticorrosive, easy surface modification, strong appetency with polymer for instance rubber and plastic etc. Though its excellent performances, calcium sulfate whisker has not been developed extensively because of the problems about preparation craft and surface modification.There are abundant mineral salt resources of gypsum type in our country. The calcium sulfate and the sodium chloride are both precipitated by evaporation and concentration of the brine in the process of vacuum salt production process. After the separation of the mixture, sodium chloride was separated and calcium sulfate was discarded as a kind of dregs--he salt gypsum. With such features of little grain size, high salinity and squatting hardness, the salt gypsum has been a kind of solid wastes which do great harm to the environment. One of the main components contained in the salt gypsum is anhydrous calcium sulfate. As a kind of cementitious material, anhydrous calcium sulfate can hydrate in the water, during which calcium sulfate dehydrate can be generated. Because of its merits like larger average particle diameter and easier separation from the mother liquor, the matter calcium sulfate dehydrate can be used as a kind of construction gypsum and cement retarder.Calcium sulfate whisker which morphology is homogeneous and controllable was synthesized by means of hydrothermal method using hydration salt gypsum as raw material in this paper firstly. The hydration process:the optimal conditions of the crystal transformation process were ascertained under25℃as follows:the concentration of the activator solution was0.20mol/L, the total time of the crystal transformation was54hours, the stirring rate was200r/min and the mass ratio of the salt gypsum and the water was10:1. Under the above conditions, the average particle diameter of the crystal was76.49μm and the degree of hydration could be up to about70%. Preparation of calcium sulfate whisker by hydrothermal process:effects of reaction temperature and time, slurry concentration and stirring rate on the preparation and morphology of CSW were investigated in detail and the author discussed the effect mechanism of craft factor. Through SEM and X-ray diffraction analysis as the direct analysis method, optimum process conditions of calcium sulfate whiskers were obtained as follows:reaction temperature was130℃, mass fraction of slurry was5%, stirring rate was120r/min and reaction time was2h. Under these conditions calcium sulfate whisker product with average diameter of2.3μm and L/D ratio of70-100was obtained. Conclusion drawn from the experiment will play an important guiding role in the industrial production of calcium sulfate whiskers.