Question

Difference between alpha hemihydrate and beta hemihydrate

Answer 1

Difference between alpha hemihydrate and beta hemihydrate

The alpha-hemihydrate is produced from gypsum calcined in a steam-saturated atmosphere, the beta-hemihydrate where the partial pressure of water vapor is low. The nature of a hemihydrate prepared under intermediate conditions is not known for certain. The author has employed differential thermal analysis, with precautions, to show the presence of two main phases only. It is also possible that there are slight differences between different preparations of both alpha and beta-hemihydrates.

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Answer 2

Difference between alpha hemihydrate and beta hemihydrate

THE existence of α- and β-forms of calcium sulphate hemihydrate has been the subject of much controversy. At present it is considered that the difference between the two forms is in the perfection of their crystallites1–4. These differences are manifested in their thermodynamic properties3, density2–4, gauging water demand1,5, particle size and shape5, and more recently their differential thermal analysis exotherms6,7. Attempts to differentiate between the α- and β-forms by X-ray diffraction have been unsuccessful7–10.

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