UNIVERSITY OF SIEGEN

Investigation of hydration mechanisms of alpha and beta hemihydrate

Gypsum-based binders are generally based on the reaction between calcium sulfate hemihydrate (HH) and water to form calcium sulfate dihydrate (DH). Often gypsum can be used as a raw material to obtain hemihydrate. In this study, the obtained alpha hemihydrate consists of large crystals that have more or less lattice defects according to its production process while beta hemihydrate is characterize by a large surface area and fast setting time. The dissolution rate and setting time of α-HH are relatively lower than β-HH, therefore, large dihydrate crystals with fewer branches were formed. The dissolving rate of β-HH and nucleation density of the crated dihydrate was very high due to its high surface area. The gypsum stone which was created from the hydration process out of α-HH is characterized by its higher compressive strength and slower reaction.

1 Introduction

Calcium sulfate hemihydrate [CaCO4 ∙ 0.5H2O(s)] can be found naturally in very dry climate regions in Egypt, Australia, Death valley and Kuwait as bassanite, but in the presence of water or humid atmosphere it can convert to dehydrate [1, 2]. Therefore, the production of hemihydrate industrially has been studied widely through the dehydration process of dihydrate. Based on the dehydration process, the hemihydrate exists in two forms: alpha and beta. Many investigations showed that the symmetry and the water content vary between alpha and beta hemihydrate which might be due to...

Related articles:

Issue 2016-7-8 WO 2016/073393 A1

Microwave heating for gypsum manufacturing processes

(22) 03.11.2015 (43) 12.05.2016 (57) Methods of making calcium sulfate whiskers are provided. In one aspect, a method includes autoclaving a slurry of calcium sulfate hemihydrate and water to form...

more
Issue 2017-5 WO 2017/045519 A1

Method for producing wet-process phosphoric acid and ­byproducing alpha-hemihydrate gypsum and high-purity and high-whiteness alpha-hemihydrate gypsum

(22) 26.08.2016 (43) 23.03.2017 (57) Provided is a method for producing wet-process phosphoric acid and by-producing alpha-hemihydrate gypsum and high-purity and high-whiteness alpha-hemihydrate...

more
Issue 2015-5 UNIVERSITY OF SIEGEN

Investigations of the hydration of calcium sulfate hemihydrate

1 Introduction Gypsum is one of the most used materials in the world; 119 million tons of natural gypsum were extracted worldwide in 2006 (MINERAL COMMODITY 2007). Additionally another...

more
Issue 2015-7-8 WO?2015/085139?A1

Gypsum composite modifiers

(22) 05.12.2014 (43) 11.06.2015 (57) Anhydrite calcium sulfate whiskers are prepared by combining alpha calcium sulfate hemihydrate and water to form a slurry, autoclaving the slurry to form alpha...

more
Issue 2020-9 US 2020/0123055 A1

Recycling method of dihydrate gypsum from waste gypsum boards

(22) 22.10.2019 (43) 23.04.2020 (57) Gypsum derived from waste gypsum boards is calcined and converted into gypsum granules including hemihydrate and/ or anhydrous type III gypsum. The calcined gypsum...

more