Permeability of gypsum samples dehydrated in air

An interplay between reaction progress and rock permeability becomes evident when one compares the molar volumes [e.g., Deer et al., 1992] of the educt and solid products involved in the transformation of gypsum (74.53 cm 3 /mol) to bassanite (53.17 cm 3 /mol) and anhydrite (45.68 cm 3 /mol), respectively. One notices that, at ambient conditions, the solid …

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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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Frontiers | Solubility of anhydrite and gypsum at temperatures …

Estimations of the temperature, where gypsum is dehydrated to anhydrite in water vary between 30°C and 60°C. The extremely slow crystallization kinetics of anhydrite at T < 90°C prevents a direct determination of this transition temperature. In the present work the different approaches to fix this temperature are discussed.

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

Dehydration of axially pre-stressed, heated discs of natural gypsum rock (Volterra alabaster) was monitored in a purpose-built loading cell while collecting 2D small- and wide …

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An in situ real-time monitoring of the hydration and dehydration of

The SO 4 2-and water molecules in dehydrated gypsum are known to have lattice and internal vibrational bands in three ranges (500–400, 400–1200, and 3300–3360 cm −1) [35]. The 3300–3360 cm −1 are assigned to vibrational bands of water molecules. In our study, the bands are located at 3386 cm −1 and 3472 cm −1 (Fig. 3). Depending ...

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Electron Backscatter Diffraction (EBSD) Analysis of Bassanite

Dehydration reactions have important effects on fluid flow, porepressure and brittle failure in the Earth.The rates and mechanismsof reaction are relevant to understanding those effects.The micro-structures ofa set ofsamples containing bassanite and gypsum fromdehydration experiments on Volterra gypsum have been analysed byconventional transmitted light …

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Quantitative Determination of Anhydrite III from Dehydrated Gypsum …

DOI: 10.1016/J.CEMCONRES.2009.06.018 Corpus ID: 96616635; Quantitative Determination of Anhydrite III from Dehydrated Gypsum by XRD @article{Seufert2009QuantitativeDO, title={Quantitative Determination of Anhydrite III from Dehydrated Gypsum by XRD}, author={Sebastian Seufert and Christoph Hesse and Friedlinde Goetz-Neunhoeffer and …

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Dehydration Pathways of Gypsum and the …

The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite...

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The thermal dehydration of synthetic gypsum

As for the dehydration of CaSO 4 ·2H 2 O, the dehydration of synthetic gypsum proceeds via multi-step reactions. Using a heating rate of 5°C min −1, the very slow …

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From atom level to macroscopic scale: Structural mechanism of …

The microstructures formed by the dehydration of gypsum under controlled conditions of temperature and water vapor partial pressure were characterized using in situ X …

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(PDF) Thermal conductivity of gypsum plasterboard beyond …

The present paper deals with the thermal conductivity of the dehydrated gypsum up to 500°C and provides some insight into the responsible effects by using different investigation methods. THERMAL CONDUCTIVITY Three gypsum samples of 250mm × 250mm × 10mm were conditioned in an oven at three different temperatures (200, 350 and 500°C).

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Gypsum hydration: a theoretical and experimental study

1. Ultrasonic results indicate gypsum hydration reaction consists of two stages: the dissolution of hemihydrate in the first stage and the nucleation and precipitation of dihydrate in the second stage. 2. Gypsum hydration is strongly influenced by water amount. Spread flow test is suitable to determine the water demand for gypsum hydration.

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Permeability of gypsum samples dehydrated in air

We report on changes in rock permeability induced by devolatilization reactions using gypsum as a reference analog material. Cylindrical samples of natural alabaster were dehydrated in air (dry ...

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Gypsum

Etymology and history. The word gypsum is derived from the Greek word γύψος (gypsos), "plaster". [9] Because the quarries of the Montmartre district of Paris have long furnished burnt gypsum (calcined gypsum) used for various purposes, this dehydrated gypsum became known as plaster of Paris.Upon adding water, after a few dozen minutes, plaster of Paris becomes …

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Discrimination of bassanite and anhydrite III dehydrated from gypsum …

Request PDF | Discrimination of bassanite and anhydrite III dehydrated from gypsum at different temperatures | Technical OPC normally contains mixed sulphate carriers in varying amounts. Gypsum ...

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Dehydration‐induced damage and deformation in …

The dehydration reaction of gypsum into bassanite and water induces a large porosity increase, which is partially compacted. The higher the effective stress, the larger the compaction. Application of a constant …

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Gypsum

Flooring Applications:Calcined gypsum, a dehydrated form of Egyptian gypsum, plays a crucial role in floor leveling compounds. It ensures a smooth, even surface for the installation of tiles, wood flooring, or other floor coverings. Fire Protection:Egyptian gypsum's inherent fire resistance is a significant safety benefit. When exposed to ...

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Gypsum

Gypsum Mineral Description. Gypsum is a hydrated calcium sulfate with composition CaSO 4 ·2H 2 O. It commonly occurs as a chalky powder or occasionally as small crystals. In gypsum, the structure is layered, parallel to the b direction. ... Dehydrated forms of gypsum range isostructuraly from [CaSO 4 ·2H 2 O] to [CaSO 4]. The hemihydrate ...

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Anion water in gypsum (CaSO4·2H2O) and hemihydrate …

This was also observed by Hamad [21] by the study on the image and lattice of a dehydrated gypsum by electron microscope. 3.1. Absorption bands of water molecule [22–24] The presence of water in a sample can be detected by its two characteristic absorption bands in the 3600–3200 cm −1 region and in the 1650 cm −1 region.

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Gypsum, bassanite, and anhydrite at Gale crater, …

Analyses by the CheMin X-ray diffraction instrument on Mars Science Laboratory show that gypsum, bassanite, and anhydrite are common minerals at Gale crater. Warm conditions (~6 to 30 °C) within CheMin drive gypsum dehydration to …

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Insights Into the Micromechanics of Dehydration‐Induced Gypsum …

Gypsum is an anisotropic hydrous mineral found abundantly in fold-thrust belts along with its dehydrated forms (bassanite and anhydrite). Because gypsum contains water in its structure, it can accommodate large shear deformation under external load.

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The thermal dehydration of synthetic gypsum

Mass losses vary between 13.7 and 16.5% and heat of dehydration values between 377 and 420 J g −1 for the dehydration of ground and mixed inhomogeneous gypsum samples. As for the dehydration of CaSO 4 ·2H 2 O, the dehydration of synthetic gypsum proceeds via multi-step reactions. Using a heating rate of 5°C min −1, the very slow …

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Gypsum Skimming Plaster 40KG

TACKTILE Gypsum Skimming Plaster 40Kg SKU: PL40TACK1 Tacktile Gypsum Skimming Plaster is a high-quality interior finishing product designed for easy application. Simply mix the powder with clean water for a consistent, creamy slurry. This lightweight plaster is made from dehydrated gypsum mineral and sets by chemically recombining with water. It's versatile, …

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Microstructural modifications resulting from the dehydration of gypsum

Various faces of dehydrated gypsum-cleaved blocks and single crystals have been investigated using optical microscopy, SEM, and TEM. The orientation of the cracks with respect to the initial gypsum structure and the Miller indices of all possible crack planes have been determined. These crack planes have been found to be few and to correspond ...

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Dehydration behavior of FGD gypsum by simultaneous TG and

Methods. The dehydration process of FGD gypsum was performed with simultaneous TG/DSC analysis (NETZSCH STA 409 Luxx, Selb/Bavaria, Germany) at N 2 atmosphere with a gas flow of 20 mL min −1.Non-isothermal analysis was carried out at different heating rate (2−20 K min −1).Isothermal analysis was conducted in the temperature range of …

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Evolution of microstructure and elastic wave velocities in …

and that the unaltered gypsum in the core is very dense. Finally, the SEM cross section in Figures 1e and 1f (Sample 7, 398 K) highlights the transition from the porous rim to gypsum this time containing dispersed bassanite fibers. [12] The absence of bassanite in the gypsum core of all samples dehydrated at 388 K and its concurrent occurrence

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Formation of α-Hemihydrate Inside of a Gypsum Crystal

The surface character of the dehydrated gypsum was analyzed in SEM, additionally. It is obvious that the layer's burst and broken parts and cracks are formed at the surface. The surface of the hemihydrate is much larger than that of the dihydrate crystal. Formed cracks are shown in Figure 5a,b. Larger, cross-like cracks can be observed beside ...

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The dehydration process of gypsum under high pressure

The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy and synchrotron X-ray diffraction with an externally heated diamond anvil cell. At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely dehydrates to γ-anhydrite at 488 K. …

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Understanding gypsum in 3 diagrams

Figure 1: a: Gypsum crystals produced from sodium sulphate and calcium chloride; b: Natural gypsum cut along black lines; c: Gypsum crystals from a, with directions from Figure 2 marked with arrows, on side from Figure 3 marked with yellow, on cleavage plane with red; d: Crystal from a) along c-axis marked in black.

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Effect of soluble phosphate on strength development of anhydrite

The obtained dehydrated gypsum contained combined gypsum phases of dihydrate, hemihydrate, and II-anhydrite. Cao et al. [23] also found that the soluble phosphate content decreased after calcination at 500 °C. All the experimental results of previous researches have illustrated that the content of soluble phosphates in the dehydrated PG ...

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