Reactivity of Gypsum-Based Materials Subjected to Thermal Load: Investigation of Reaction Mechanisms

Abstract

The thermal stability of gypsum-based materials, and in this context, especially their long-term behavior, is the background of our current research activities. A comprehensive investigation program was compiled in which detailed examinations of various model materials exposed to thermal loads were carried out. The understanding of the partly not entirely consistent state of knowledge shall be sharpened especially by in situ observations of the thermally induced conversion reaction of gypsum into hemihydrate. The temporal course of the reaction was investigated non-destructively by in situ investigations in a high-resolution X-ray computed tomography setup, and the experiment was accompanied by detailed characterizations of the microstructure and composition. In this contribution, selected results of experiments with a high-purity natural gypsum rock as the model substance are presented. Studying the influence of temperature on the reaction showed that, even under supposedly dry conditions, the reaction could take place at much lower temperatures than usually reported in the literature. It was demonstrated that the transformation of gypsum into hemihydrate could take place at a temperature of already 50 °C. The results indicated that even under “classical” heating conditions in a conventional oven, the dissolution and crystallization processes in water films on the mineral surfaces could be suggested to be a driving force for the reaction. A corresponding reaction model, which took these aspects into account, was proposed in this work.

Investigative study of the potentialities of noble applications for the Brazilian calcium sulfate α-hemihydrate

“…According to the graph, the first occurrence of mass loss occurred under the maximum temperature value of 43.65°C, probably related to a loss of free water still existing in the sample. The second mass loss event, occurred with a maximum of 138.55°C, most likely related to the loss of part of the crystallization water, these values detected in this analysis referring to the temperatures of partial dehydration of the gypsum with its consequent conversion to the form hemihydrate are in accordance with research reports related to the investigation of this type of ore published in the literature (Krause et al 2020;Ritterbach & Becker 2020). Some discrete events were perceived at temperatures above 450°C suggesting the presence of thermally active components, which were not detected by XRD analysis.…”

In Vitro Comparison of Differences in Setting Time of Premixed Calcium Silicate-Based Mineral Trioxide Aggregate According to Moisture Content of Gypsum

“…The pores in dental gypsum occur when air is trapped in the material during the mixing process, and pores form between crystals when the crystals of gypsum powder grow [ 31 ]. The pores of this dental gypsum can be identified as dark areas in scanning electron microscope images ( Figure 2 ) [ 32 ]. In this experiment, the plaster, which was a grade 2 gypsum, showed large spaces created by pores as dark areas during mixing, and some pores appeared as dark areas between the particles ( Figure 2 (a-1)).…”

Nonlinear Optical Studies of Water at Gypsum–Air and Gypsum–Aqueous Interfaces

“…Furthermore, data showed that the surface-bound crystalline, or structural, water remains intact even when the gypsum surface is in contact with aqueous solution. These results have important implications for bulk-surface exchange rates, solvation dynamics, and general reactivity at this ubiquitous mineral/aqueous interface …”

“…These results have important implications for bulksurface exchange rates, solvation dynamics, and general reactivity at this ubiquitous mineral/aqueous interface. 37 While AFM is a powerful tool for studying the overall waterinfluenced behavior of gypsum surfaces, this technique can only infer whether water is present and, if so, where. Simulations can suggest relative orientations, and the force curves resulting from AFM studies can be used to infer specific molecular−material interactions, but conclusions are necessarily indirect.…”