Reach On Processing Conditions For Preparation Of Calcium Sulfate Whisker From Gypsum At Atmospheric Pressure

Gypsum is one kind of the richest minerals in our country. The reverses of gypsum leap into the front ranks of the world. However, it is mainly used in the architectural industry and lacks of economic benefits. Therefore, further processing of gypsum is the only way for gypsum industry. Calcium sulfate whisker is an environmental friendly owing to its special properties of high strength, high elastic modulus, resistance to temperature and low price. It has broad application prospects and practical value and is often used as enhanced material, coating paper filling material, friction material, environmental filter material.Hydrothermal synthesis of CaSO₄·0.5H₂ O whisker is one of the main methods which have been researched most. However hydrothermal method requires high temperature and pressure, this leads to high energy consumption, high equipment requirements. It is difficult for this method to be used in industry because of low yield and uneven topography.In order to solve these problems, a new preparation of CaSO₄·0.5H₂ O whiskers at atmosphere pressure has been proposed. CaSO₄·0.5H₂ O whiskers have been prepared from gypsum under the conditions of atmosphere pressure and lower temperature. The diameters of CaSO₄·0.5H₂ O whiskers we obtained are 3⁵?m, and the aspect ratio is about 40. The influence of processing conditions?the form control agent and its concentration, the reaction temperature and time, pH, slurry concentration, stirring rate? on crystal morphology was researched. Recovered using of the reaction solution and Surface Modification were also studied. The main work and conclusions were as follow:?1?The form control agent ZH-1 was used to adjust the solubility of CaSO₄·2H₂O and CaSO₄·0.5H₂ O to reduce the transition temperature.?2?The optimum condition is follows: the mass percentage of ZH-1 is 12%, The mass proportion of gypsum and reaction solution is 3:20, the stirring rate is 120r/min, pH is 7, the reaction temperature is 96? and the reaction time is 1.5h.?3?Na₂SO₄ has an obvious promoting role on the growth of CaSO₄·0.5H₂ O whiskers. The optimum adding amount of Na₂SO₄ is 8.3% of the raw material.?4?The reaction solution was recycled 5 times, and the obtained CaSO₄·0.5H₂ O whiskers did not change significantly.?5?Sodium stearate was used to modify the CaSO₄·0.5H₂ O whiskers, and the amount of sodium stearate, modification temperature and time were studied. The optimum condition is follows: the mass of the modifier is 5% of the CaSO₄·0.5H₂ O whiskers, modification temperature is 90? and the modification time is 20 min. The activation index is up to 0.73 in optimal conditions.