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Fast in-situ X-ray scattering reveals stress sensitivity of gypsum

Here, we perform fast, time-resolved synchrotron X-ray scattering on natural alabaster samples, finding that a small elastic load accelerates the dehydration reaction …

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Understanding gypsum in 3 diagrams

Beta hemihydrate is formed when gypsum is heated up to around 100°C in a normal open kettle or rotary kiln. Alpha hemihydrate is formed in an autoclave above 100°C in a water (suspension autoclave) or in a steam autoclave. 5 - 7 This is possible as, above 100°C, hemihydrate becomes less soluble than dihydrate. The solubility of dihydrate ...

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Innovative synthesis of high-strength α-hemihydrate gypsum: …

High-strength gypsum is the recognized designation for α-hemihydrate gypsum, often referred to as α-HH (CaSO 4 ·0.5H 2 O), which is a cementitious material with low water requirement and high strength [8].The strength of α-HH is generally between 25 and 50 N/mm 2, which is three times that of ordinary building plaster, and has superior working performance. α …

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From atom level to macroscopic scale: Structural mechanism of gypsum

Plaster, made of calcium sulfate hemihydrate (CaSO 4 •½H 2 O) and/or γ-anhydrite (CaSO 4) is obtained by dehydration of gypsum (CaSO 4 ·2H 2 O) at 100–200 °C. When mixed with water, it dissolves while new gypsum crystals precipitate. Plaster's microstructures affect its reactivity and setting properties, but are poorly understood due to confusion between crystals …

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What is the Difference Between Alpha and Beta Hemihydrate

The process of converting gypsum into alpha hemihydrate involves heating gypsum at a specific temperature to remove water molecules, resulting in a more concentrated and stable form of calcium sulfate. The term "alpha" in alpha hemihydrate refers to the unique crystal structure formed during this dehydration process. The alpha form exhibits ...

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Quantitative determination of anhydrite III from dehydrated gypsum …

Gypsum (calcium sulfate dihydrate, Fluka, 99.9% purity) samples were dehydrated at temperatures from 85 up to 800 °C 25 g of substance was weighed in corundum crucibles of 60 ml size and dehydrated in two different furnace types to cover the complete temperature range.The furnaces were calibrated with thermo elements.

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Utilization of low-quality desulfurized ash from semi-dry flue …

Alpha-hemihydrate gypsum B a Alpha-hemihydrate gypsum a a a a a a b Dihydrate gypsum b b b c Calcium hydroxide d Calcium carbonate e Hemihydrate calcium sulfite c c c d e d d e e Fig. 1. Particle size distributions and XRD patterns of hemihydrate gypsum and desulfurized ash. H. Li, et al. Fuel 255 (2019) 115783 2

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The influence of calcium formate on the hydration of calcium …

The gypsum powder was stored for 24 h in a 100 °C oven, where mainly it dehydrated into hemihydrate, next to small amounts of anhydrite. ... The calculated saturation indices from porewater data of both gypsum and hemihydrate are reflecting one another in each sample and follow the sulfur concentrations (Fig. 6). The saturation of hemihydrate ...

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Fast in-situ X-ray scattering reveals stress sensitivity of gypsum

The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, and due to the global use of plaster ...

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Development of alternative for gypsum-based plaster using …

Nesquehonite (NQ) can be activated via thermal treatment under 50–175°C, after which the dehydrated nesquehonite can hydrate to form a plaster-like product, like gypsum-based plaster. Here, we developed different blends of NQ and hemihydrate (dehydrated gypsum) to produce plaster.

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Influence of calcination and GGBS addition in preparing β-hemihydrate

This is because the main composition of PG is dihydrate gypsum (CaSO 4 ⋅2H 2 O), which can be dehydrated to form synthetic hemihydrate gypsum, like natural mineral gypsum. Depending on the temperature and condition of the dehydration process, natural gypsum exists in four different phases, namely hemihydrate gypsum (CaSO 4 ⋅0.5H 2 O), III ...

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Preparation of α High-Strength Gypsum from FGD Gypsum by …

This paper introduced the characteristics of α high-strength gypsum preparation from FGD gypsum by autoclaved semi-dry process. The compositions of the product in different stages of the reaction and the effects of crystal modifiers on the morphology of the α-HH crystals were examined and compared. The properties of α-HH and the feature of hydration products of α …

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Dehydration Pathways of Gypsum and the Rehydration Mechanism …

The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite was also studied by Monte Carlo (MC) simulations. The thermodynamic calculation results reveal that the dehy …

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Structural evolution during the dehydration of gypsum materials

It is found that the dehydration of gypsum to anhydrite proceeds via the hemihydrate and γ-anhydrite phases and the interplay and behaviour of these phases has been determined …

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Formation of α-Hemihydrate Inside of a Gypsum Crystal during …

Gypsum crystal partly dehydrated, cleaved along cleavage plane, with observable dihydrate, α β α-hemihydrate and β-hemihydrate. Yellow circle = still dihydrate, blue circle = alpha hemihydrate, red circle = beta hemihydrate, black arrow = alpha hemihydrate growing direction of …

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2 Gypsum dehydration during cement production

Depending on the mill temperature, the gypsum becomes partially or completely dehydrated to hemihydrate or anhydrite respectively. According to [8] the temperatures at which gypsum dehydration to hemihydrate can take place lie between 95 and 170 °C. The results of [9] indicate that gypsum dehydration can even begin at temperatures below 70 °C.

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Discrimination of bassanite and anhydrite III dehydrated from …

Gypsum_120 120 h 120(±5) °C Gypsum_180 16 h 180(±5) °C Gypsum_250 16 h 250(±5) °C Gypsum_380 16 h 380(±5) °C Gypsum_550 16 h 550(±5) °C For the dehydrated gypsum samples the loss on ignition was determined. To determine the experimental loss on ignition a reference gypsum sample was dehydrated at 800 °C and weighed out.

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Dehydration Pathways of Gypsum and the …

Abriel et al. studied the dehydration mechanism of gypsum using neutron and X-ray diffraction (XRD) and proposed a novel gypsum …

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Gypsum hydration: a theoretical and experimental study

Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in two …

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Why is Calcium Sulphate Hemihydrate called Plaster of Paris?

Calcium Sulphate Hemihydrate is called Plaster of Paris because it is derived by heating gypsum (calcium sulfate dihydrate) to around 150°C, which removes water and forms the hemihydrate. This process was historically centred in Paris, where large gypsum deposits were found and widely used for making quick-setting materials.

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Modification on the Performance of the Hemihydrate Gypsum …

The objective of this study was to assess the feasibility of using the plant-source polymer of the matcha powder as a composite admixture for hemihydrate gypsum. Hemihydrate gypsum was mixed with different contents of matcha powder, and then the water requirement for the normal consistency, setting times, density, strength, hydration and microstructure of the …

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Insight into the influences of β-hemihydrate and dihydrate gypsum …

Dihydrate and β-hemihydrate gypsum exhibit relatively higher solubility and dissolve more quickly than CaSO 4. However, there is little information on their incorporation in CAC. Although Zhang et al. [19] analysed the influence of the type and dosage of calcium sulphate on the properties of CAC-based materials, they did not study phase ...

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Formation of α-Hemihydrate Inside of a …

This work firstly shows that the observed crystallization inside of gypsum during dehydration is the formation of alpha-hemihydrate. Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials …

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The thermal dehydration of synthetic gypsum

A high hemihydrate content results in false setting of the cement, thus a maximum percentage of the hemihydrate is required in gypsum samples [3]. It is shown in the literature that the decomposition of calcium sulphate dihydrate proceeds via two reactions [4, 5] CaS04- 2H20 (s) -. CaS04 -0.5H20 (s) + 1.5Hz0 (g) CaS04 -0.5H20 (s) ~ CaS04 (s ...

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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 ...

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Gypsum: an investigation of microstructure and mechanical …

dehydration still needs further investigation, especially the behaviour of the β-hemihydrate and gypsum produced from it is still poorly understood. This article focuses on the role of water on the properties of gypsum produced from a β-hemihydrate due to its combined effect on both hydration and dehydration.

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Structural evolution during the dehydration of gypsum materials

A 'zero-water hemihydrate' is observed before refinement in the higher symmetry γ-anhydrite cell is possible. The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum materials.

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Influence of dehydration method on the morphology of …

Gypsum raw material (reagent gypsum, phosphogypsum and processed phosphogypsum) was dehydrated by dry method (i.e. in dry air environmental) and wet method (i.e. saturated water vapour...

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Soil stabilization with gypsum: A review

Factors affecting these results include the type of added gypsum (for example when hemihydrate calcium sulfate, i.e. bassanite, is used instead of gypsum, or when solid waste byproducts such as titanium gypsum, phosphorous gypsum, and desulfurization gypsum are used instead of pure gypsum), the type and percentage of fine portion of the soil ...

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From atom level to macroscopic scale: Structural mechanism of …

Plaster, made of calcium sulfate hemihydrate (CaSO 4 •½H 2 O) and/or γ -anhydrite (CaSO 4) is obtained by dehydration of gypsum (CaSO 4 ·2H 2 O) at 100–200 °C. When …

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