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首页> 美国卫生研究院文献>Journal of Synchrotron Radiation >A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate
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A kinetic and mechanistic study into the transformation of calcium sulfate hemihydrate to dihydrate

机译：硫酸钙半水合物转化为二水合物的动力学和机理研究

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The conversion of CaSO4·0.5H2O to CaSO4·2H2O is of great importance industrially, being the reaction behind plasterboard production and the setting of medical plasters. A detailed kinetic and mechanistic study of this process was conducted using time-resolved synchrotron X-ray diffraction in this work. The CaSO4·2H2O product is very similar regardless of whether the α- or β-form of CaSO4·0.5H2O is used as the starting material, but the reaction process is very different. The induction time is usually shorter for α-CaSO4·0.5H2O than β-CaSO4·0.5H2O, and a greater conversion percentage is observed with the former (although in neither case does the reaction proceed to 100% completion). The temperature of the system, widely used in industry as an indirect measure of the extent of the hydration process, is found to be a poor pr­oxy for this, with the maximum temperature reached well before the reaction is complete. The Avrami–Erofe’ev and Gualtieri models could both be fitted to the experimental data, with the fits being substantially closer in the case of α-CaSO4·0.5H2O. The rate of reaction in the Avrami model tends to increase with the amount of gypsum seeds added to accelerate the process, and the importance of nucleation declines. The Gualtieri analysis suggested that the rate of nucleation increases substantially with the amount of seeds added, while there are less distinct changes in the rate of crystal growth. At low seed concentrations (<0.5% w/w) the rate of crystal growth is greater than the rate of nucleation, but at concentrations above 0.5% w/w nucleation is faster. These findings represent the first synchrotron study of the conversion of CaSO4·0.5H2O to CaSO4·2H2O, and will be of importance to gypsum producers globally.
机译：CaSO4·0.5H2O向CaSO4·2H2O的转化在工业上非常重要，这是石膏板生产和医用石膏固化的反应。在这项工作中，使用时间分辨的同步加速器X射线衍射对该过程进行了详细的动力学和机理研究。无论是以CaSO4·0.5H2O的α还是β形式作为起始原料，CaSO4·2H2O的产物都非常相似，但是反应过程却大不相同。通常，α-CaSO4·0.5H2O的诱导时间比β-CaSO4·0.5H2O的诱导时间短，并且前者的转化率更高（尽管在任何情况下反应都不会进行到100％完成）。发现该系统的温度在工业上广泛用作水合过程程度的间接指标，但对于这一点而言，它的效果较差，最高温度要在反应完成之前就可以达到。 Avrami–Erofe’ev和Gualtieri模型都可以拟合到实验数据，对于α-CaSO4·0.5H2O，拟合则更加接近。 Avrami模型中的反应速率往往会随着石膏种子添加量的增加而增加，以加速该过程，而成核的重要性下降。 Gualtieri分析表明，成核速率随所添加种子的数量而显着增加，而晶体生长速率的变化却不那么明显。在低种子浓度（<0.5％w / w）下，晶体生长速率大于成核速率，但在高于0.5％w / w浓度下，晶体生长速率更快。这些发现代表了对CaSO4·0.5H2O转化为CaSO 4 ·2H 2 O的首次同步加速器研究，对全球石膏生产者具有重要意义。

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