Calcium sulfate additives for industrial applications

Control of the hydration of calcium sulfate hemihydrate (HH) to calcium sulfate dihydrate (known as gypsum) has a number of important industrial applications, for example in the production of plasterboard, dentistry, restorative medicine and medical plasters. Additives, in the form of accelerators and retardants, help to control the setting (crystallisation) time of the gypsum product during manufacture. If the hydration reaction occurs too quickly it can lead to fouling in processing steps but if the process takes too long it is not economically viable for the mass production of materials.

Ball-milled accelerant (BMA) is employed to speed up the conversion reaction and works by seeding the process with small gypsum crystals for nucleation and growth. BMA aids the production of material at large scale but it is known to produce significant batch-to-batch variation.

In order to understand more about the reaction kinetics and mechanisms for the hydration of HH to gypsum and understand the role of additives in the reaction mechanism, a group of scientists from Etex Group used in situ X-ray diffraction at Diamond to explore the effects of both soluble and insoluble additives (ZnSO₄ and K₂SO₄) and retardants (NA₃PO₄ citric and tartaric acid). These additives were shown to be viable alternatives to BMA. The study also showed that temperature is not an effective measure of the progress of the reaction.

Find out what they discovered.

^{Image: Enareksi, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons}