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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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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In gypsum, the structure is layered, parallel to the b direction. Tetrahedral SO 4 anions are linked by Ca cations as chains parallel to c, which form as double sheets interlayered with sheets of water molecules. Dehydrated forms of gypsum range isostructurally from CaSO 4 ·2H 2 …
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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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Gypsum crystal partly dehydrated, cleaved along cleavage plane, with observable dihydrate, α-hemihydrate and β-hemihydrate. Yellow circle = still dihydrate, blue circle = alpha hemihydrate, red ...
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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 by full structural 'Rietveld' refinement. In the study of the pure gypsum system, the hemihydrate structure is shown to be preserved as water is lost.
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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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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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Once dehydrated, the resulting product is mixed with several additives and water. It is then placed onto cardboard running on a conveyor belt. It soon takes the shape of a needle-like structure that combines to form what we commonly know as gypsum plasterboards.
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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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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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GASES UPON DEHYDRATED GYPSUM Robert F. Benson1 and George D. Blyholder Department of Chemistry, University of Arkansas, Fayetteville, Arkansas 72701 ABSTRACT: This work explores surface interactions between gypsum and selected prominent gaseous emissions in to the atmosphere. Gypsum is a common air-borne mineral particulate that has a potential
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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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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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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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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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In this work, the dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite were mainly investigated by thermodynamic modeling and MC simulations. The …
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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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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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The polyscrystalline phase that formed when monocrystals of gypsum were dehydrated had hexagonal symmetry and showed preferred orientation relative to the monoclinic parent crystal. the c sub O axis of the dehydration product was aligned approximately perpendicular to the direction in the original single crystal. /Author/
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Rebecca C. Hildyard, Sergio Llana-Fúnez, John Wheeler, Daniel R. Faulkner, David J. Prior, Electron Backscatter Diffraction (EBSD) Analysis of Bassanite Transformation Textures and Crystal Structure Produced from Experimentally Deformed and Dehydrated Gypsum, Journal of Petrology, Volume 52, Issue 5, May 2011, Pages 839–856, https://doi ...
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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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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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The proportions of gypsum, hemihydrate and anhydrite are individually optimized for each type of cement [7]. The dehydration of gypsum to hemihydrate normally takes place during the grinding process in the cement mill. Depending on the mill temperature, the gypsum becomes partially or completely dehydrated to hemihydrate or anhydrite respectively.
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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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Reagent grade gypsum was dehydrated at 85 °C for 144 h in order to get pure bassanite und at 550 °C for 16 h in order to obtain pure anhydrite II (Table 1). ...
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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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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 of gypsum can be observed using thermo-gravimetric measurement and differential scanning calorimetry. Depending on the parameters of …
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