Although the dissolution/precipitation mechanism for hemihydrate hydration is widely recognized, this study gives more detailed information for the hydration of hemihydrate by in-situ observation using environmental scanning electron microscope (ESEM). The hydration process was also monitored through numerous parameters, including phase, hydration degree, ion concentration, particle size, and morphology evolution with hydration time. The results indicated that the hemihydrate particles are porous containing numerous nanopores. It dissolves from the surface available to water, forming a transient flocculent intermediate with widen pores. Afterwards, large particles break to small particles due to crack connection and then continue to dissolve, leaving a few stubborn spots last to disappear. At the same time, gypsum precipitates in the first few minutes and evolves to the final crystal structure through three main stages. This work not only provides the most direct evidence for the hydration mechanism, but also gives new insights to enrich it further. It is helpful to adjust the hydration process of gypsum plaster and provide a significant reference for modeling.

尽管半水合物水合的溶解/沉淀机制已被广泛认可，但本研究通过环境扫描电子显微镜（ESEM）的原位观察为半水合物的水合提供了更详细的信息。水合过程还通过许多参数进行监测，包括相、水合度、离子浓度、粒径和形态随水合时间的演变。结果表明，半水合物颗粒是多孔的，含有许多纳米孔。它从水可利用的表面溶解，形成具有加宽孔的瞬时絮凝中间体。之后，大颗粒因裂纹连接而破碎成小颗粒，然后继续溶解，留下一些顽固的斑点最后消失。同时，石膏在最初的几分钟内沉淀，并通过三个主要阶段演变为最终的晶体结构。这项工作不仅为水化机制提供了最直接的证据，而且为进一步丰富它提供了新的见解。有助于调整石膏灰泥的水化过程，为建模提供重要参考。