【作者】 马宪法；

【导师】 官宝红；

【作者基本信息】 浙江大学 ， 环境工程， 2008， 硕士

【摘要】 α半水石膏因其性能优良而有广泛的应用领域。常压盐溶液法工艺是将二水石膏配制成盐溶液体系,在常压下转化生成α半水石膏。盐溶液中石膏相变规律并不清楚,α半水石膏的稳定性缺乏明确的判断。因此研究一些具有代表性的盐溶液体系中的石膏相变以及α半水石膏的稳定性,对于盐溶液法制备α半水石膏具有重要意义。实验主要研究了常压、80-105℃之间,0.0-10.0wt%的氯化钾盐溶液中二水石膏、α半水石膏和无水石膏三种石膏相的溶解度及其相变过程。实验过程中采用固定的固液比,石膏原料置于预定温度的不同浓度的氯化钾溶液中,得到三种石膏相的溶解度及旺半水石膏水化、重结晶、脱水反应的历程,绘制出理论相转化图和实际相转化图,确定α半水石膏的稳定区间。在0.0-10.0wt%氯化钾盐溶液中,二水石膏在85、90、95、100℃的氯化钾盐溶液中的最人溶解度分别为0.67、0.71、0.66、0.69g CaSO₄/100ml,α半水石膏在90、95、100℃的氯化钾盐溶液中的最人溶解度为0.68、0.63、0.59g CaSO₄/100ml,无水石膏在85、90、95、100℃的氯化钾盐溶液中的最人溶解度分别为0.65、0.97、0.85、0.91g CaSO₄/100ml。同一温度下,氯化钾浓度升高,二水石膏的溶解度逐渐升高,而α半水石膏和无水石膏的溶解度先升高后下降。这可能是温度和氯化钾共同作用的结果。常压、80-105℃的氯化钾盐溶液中,α半水石膏的相变分为四个方式:水化,重结晶,先水化后脱水,直接脱水。α半水石膏的相变具体历程取决于反应温度和氯化钾盐溶液的浓度。α半水石膏在氯化钾盐溶液中可划为4个相区。二水石膏在Ⅰ区是稳定相,在Ⅲ区是亚稳相;无水石膏在Ⅲ和Ⅳ两个区是稳定,同时伴随有钾石膏的生成;α半水石膏仅在Ⅱ区是亚稳的。氯化钾盐溶液中存在α半水石膏亚稳态窗口:反应温度在89-105℃之问,氯化钾盐溶液的浓度相应的设定在0.0-3.0%范围内,同时反应时间需要控制在5-6hr内。通过α半水石膏的反应制得的实际相转化图和通过溶解平衡法绘制的理论相转化图之间有一定的偏差,并且在理论相转化图中α半水石膏存在两个亚稳区。如果要得到比较纯的α半水石膏产品,必须严格、精确的控制反应温度和氯化钾盐溶液的浓度在Ⅱ区。更多还原

【Abstract】 a-calcium sulfate hemihydrate（α-HH） has been applied in comprehensive areas due to its superior workability and high strength.It could be prepared through salt solution method under atmospheric pressure.Considering the uncertainties of the phase-transition among CaSO₄ phases and the stability ofα-HH in salt solutions,it is need to investigate phase-transitions of CaSO₄ phases andα-HH’s stablility in some representative salt solutions.The solubility and phase-transitions of calcium sulfate dihydrate（DH）,α-HH, calcium sulfate anhydrite（AH） in KC1 solutions（0.0-10.0%） were studied under conditions of atmospheric pressure and（80-105）℃.The gypsum in a fixed ratio to the solution was added into KC1 solutions at an expected temperature with different concentration.The purpose was to measure the solubility of three gypsum phases in KC1 solutions,to sketch out the path forα-HH’s recrystallization,hydration or dehydration, the theoretical and actual phase-transition diagrams.Finally,the stability ofα-HH in KC1 solutions could be presented.In 0.0-10.0wt%KC1 solutions,the maximal solubility for DH at 85,90,95,100℃was （0.67,0.71,0.66,0.69） g CaSO₄l00ml respectively,the maximal solubility forα-HH at 90,95,100℃were（0.68,0.63,0.59） g CaSO4/100ml correspondingly,and the maximal solubility for AH at 85,90,95,100℃was（0.65,0.97,0.85,0.91） g CaSO₄/100ml respectively.At the same temperature,the solubility of DH increased with KC1 concentration,the solubility ofα-HH and AH increased with KC1 concentration,after passing a maximum,the solubility would decline.This may be related with the combined effect of temperature and KCl concentration.It was found that the stability ofα-HH in KC1 solution relied heavily on KC1 concentration and temperature.The phase-transition for calcium sulfate is successfully outlined as a function of KC1 concentration and temperature.DH is stable in regionⅠand metastable in regionⅢ.AH is stable in regionsⅢandⅣ,coexisted with potassium pentacalcium sulfate monohydrate（goergerite）.Only in regionⅡ,α-HH is metastable.A narrow operating window forα-HH’s recrystallization has been determined.This window is limited by KC1 concentration and reaction temperature,even the reaction time.This window is outlined as 0.0-3.0wt%concentration for KC1 solution and 89-105℃for reaction temperature,and in general the reaction time should be controlled within certain time,for example,5-6h.Meanwhile,there are discrepancies between the actual phase-transition diagram gained byα-HH’s reaction in KC1 aqueous solution and the theoretical phase-transition diagram obtained by solubility measurement.In the theoretical diagram,there are two regions forα-HH to be metastable,but in higher concentration region it would dehydrate to AH in a short time.更多还原