The objective of this research was to understand the dehydration mechanism of technical dihydrate and the variation of the physical properties of β-hemihydrate after the first hydration-dehydration process. In this study, the recycling mechanism of different hemihydrate types as raw material was investigated. The influence of the first hydration-dehydration process on the hydration rate, microstructure, and mechanical properties of recycled hemihydrate were characterized by differential calorimetric analysis (DCA), calcium ion-selective electrode (Ca²⁺-ISE), conductivity, particle size distribution (PSD), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the formed hemihydrate after the first hydration-dehydration process differs in its properties than the unrecycled hemihydrate in some characteristics such as the morphological structure, number of surface, and side defects due to the grinding process after the first hydration step. In addition to the grinding step, the calcination process was responsible for increasing the number of defects on the crystal surface, which leads to a change in setting time and the microstructure of the recycled hemihydrate. Therefore, after the 1st reaction cycle of β-HH, the compressive strength decreases due to a decrease in the hemihydrate crystal size, an increase in the surface area, and an increase in the amount of water required to perform the hydration reaction. The obtained hemihydrate after the first hydration-dehydration process was in β form due to the applied calcination process after the first cycle.

中文翻译：

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纯α-和β-CaSO4•0.5H2O的第一水合-脱水循环的机理

本研究的目的是了解工业二水合物的脱水机理以及在第一次水合-脱水过程后β-半水合物的物理性质的变化。本研究以半水合物为原料，研究了其循环机理。通过差示量热分析（DCA），钙离子选择电极（Ca ²⁺）表征了第一次水合脱水过程对循环半水合物的水合速率，微观结构和机械性能的影响。-ISE），电导率，粒度分布（PSD），扫描电子显微镜（SEM）和X射线衍射（XRD）。结果表明，第一次水合-脱水过程后形成的半水合物在性质上与未回收的半水合物在某些特征上有所不同，例如由于第一次水合步骤后的研磨过程而导致的形态结构，表面数量和侧面缺陷。除研磨步骤外，煅烧过程还导致晶体表面缺陷数量的增加，这导致凝固时间和循环半水合物微观结构的改变。因此，在β的第一个反应周期之后-HH，由于半水合物晶体尺寸的减小，表面积的增加以及进行水合反应所需的水量的增加，抗压强度降低。在第一水合-脱水过程之后获得的半水合物由于在第一循环之后进行的煅烧过程而呈β形式。