How many calcium sulfate hemihydrates are there?

Calcium sulfate hemihydrate is one of the most consumed construction materials. In spite of its widespread use, its crystal structure remains a matter of debate. Two different types of hemihydrate, α and β, are known. Their different reactivity has until now been related to their different microstructure, with the α- being more reactive (i.e., providing a faster setting). Recent research conducted at the ESRF has introduced the possibility that a single crystal may contain multiple structural domains. Here, we intend to analyze calcium sulfate hemihydrate samples from diverse sources, including industrial and commercial samples with known high reactivity. Our goal is to establish connections between crystal structure and reactivity, investigating whether variations are attributable to microstructural features like surface area or differences in atomic structure. The results from this experiment will be of high value for the development of materials with tunable reactivity.

半水硫酸钙（calcium sulfate hemihydrate）是目前应用最为广泛的建筑材料之一。尽管其应用范围极广，但其晶体结构至今仍存在争议。目前已知存在α型与β型两种半水硫酸钙晶型，此前学界普遍认为二者反应活性的差异源于微观结构的不同，其中α型半水硫酸钙的反应活性更强，即凝结速度更快。欧洲同步辐射光源（European Synchrotron Radiation Facility，ESRF）近期的研究提出了一种新的可能性：单颗晶体内部可能存在多个结构畴域。本研究旨在对不同来源的半水硫酸钙样品展开分析，其中包括已知具备高反应活性的工业与商用样品。本研究的目标在于厘清晶体结构与反应活性之间的关联，探究反应活性的差异是否源于比表面积这类微观结构特征，或是原子结构层面的不同。本实验的研究成果将对开发具备可调谐反应活性的材料具有重要价值。