| The calcium sulfate whiskers, namely, the calcium sulfate single fibrous crystals, have generally been recognized as calcium sulfate dihydrate (CaSO4·2H2O), calcium sulfate hemihydrate (CaSO4·0.5H2O) and anhydrous calcium sulfate (CaSO4). The synthetic anhydrous calcium sulfate whiskers can be further divided into two types including anhydrous soluble and anhydrous dead roasted. Calcium sulfate whiskers are considered to be prosperous reinforced material in application due to their high mechanical properties. Hydrations occur for both of calcium sulfate hemihydrate whiskers and anhydrous soluble calcium sulfate whiskers which cause the transformation of their crystal structures when they are in solution or at moist atmosphere, while no hydration occurs for anhydrous dead roasted calcium sulfate whiskers given by roasting at the temperature of 700℃. Because of high cost it is important to study the hydration process and stabilization of hemihydrate calcium sulfate whiskers and anhydrous soluble calcium sulfate whiskers for commercial production of calcium sulfate whiskers. So this paper has systematically studied on the hydration and the stabilization of calcium sulfate whiskers.Both online and unline oberservations and XRD analysis, carried out through hemihydrate calcium sulfate whiskers'hydration, indicate that the transformation of whiskers' crystalline phase and the reduction of whiskers' aspect ratio are typical characteristics of the mentioned hydration. Based on the observations it can be concluded that the hydration of hemihydrate calcium sulfate whiskers is comprised of three phases, namely, hemihydrate calcium sulfate whiskers'early hydration time, dihydrate calcium whiskers'formation time and their largening and dissolving time which causes another dihydrate calcium crystal shape to form. From this it is deduced that the hydration of hemihydrate calcium sulfate whiskers is different from hemihydrate gypsum's.Both the surface texture and properties of calcium sulfate whiskers were characterized by SEM, FTIR, XRD and XPS, revealed that the surface active site-calcium ion, the surface-OH and the inner channels played important roles in the hydration of calcium sulfate whiskers. The key of the stabilization of calcium sulfate whiskers lies in covering their surface active site and eliminating their inner channels.Calcium sulfate whiskers were calcined at different temperature and then tested by XRD. According to the results, the crystalline phase and crystal structure of calcined calcium sulfate whiskers varied with temperature, and there is highest compactness in whiskers calcined at 600℃for 4h. Further hydration experiments displayed that there is different stability for whiskers at different temperature and the whiskers calcined at 600℃are very stable. The main reasons for stability change are differences of crystal structural and crystalline phase between them.The stabilization process of hemihydrate calcium sulfate whiskers was studied in different additive amounts, reaction times and temperatures with several additives such as sodium oleate, oxalate, lemonade, sodium citrate, sodium lauric acid, neupelex, sodium stearate and sodium phosphate and so on. From the results it can be seen that sodium phosphate can keep the crystal shape of hemihydrate calcium sulfate whiskers only, while sodium oleate, sodium citrate and sodium stearate can make the crystal shape and crystalline phase of hemihydrate calcium sulfate whiskers kept preferably. Moreover, the stabilization of CaSO4·0.5H2O whiskers can be accomplished at 100℃with addition of 0.3% sodium oleate for 20 minutes.Hemihydrate calcium sulfate whiskers before and after stabilized were characterized by FTIR, and then the stabilization mechanism was discussed. It is showed that different additive amounts lead to various absorption state of sodium oleate on the surface of whiskers and that the absorption state of sodium oleate includes both physical and chemical absorption by which calcium oleate is produced on the surface of whiskers. The achievement of stabilization of whiskers attributes to the elimating the active points on the hemihydrate calcium sulfate whiskers surface, the inhibiting CaSO4·0.5H2O dissolution and the changing of hemihydrate calcium sulfate whiskers' surface property by sodium oleate.Experiments exposed that the addition of sodium oleate, sodium stearate and sodium citrate has some influence on the crystallization of whiskers at various critical amount. The absorption of sodium stearate on hemihydrate calcium sulfate whiskers surface is uneven and the absorption state changes with additive amount. The results indicate that reagents have great influence on the nucleation rate and growth ration of hemihydrate calcium sulfate whiskers. The crystal shape of hemihydrate calcium sulfate will change from fibers into plate and column while the level of sodium stearate increases. Furthermore, the integration of preparation and stabilization of hemihydrate calcium sulfate whiskers can be achieved by adding agents in different steps.The stabilization of calcium sulfate whiskers, the method of preventing calcium sulfate whiskers from hydrating by adding agents and the integration mechanism of preparation and stabilization of calcium sulfate whiskers were brought out firstly in this paper. Moreover, the investigations of this paper are very significant for the industrial preparation and application of calcium sulfate whiskers.
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