that the dehydration phenomenon is more temperature dependent than pressure-dependent',4,6,7. In fact, the tran sition temperature of gypsum to bassanite linearly shifts upwards with pressure8. The transition sequence and the individual phases were earlier studied by many techniques, including IR and Raman spectroscopic methods'9'2.
Like most dehydration reactions, the breakdown of gypsum involves a reduction in the solid molar volume, which leads to the formation of porosity (29% when fully dehydrated).
The estimation of apparent activation energy for each individual step of the thermal dehydration of gypsum sample was obtained using isoconversional Fr, KAS and FWO methods, as indicated by Eqs. ( 8 ), ( 10 ) and ( 12 ), in α interval ranged between 0.2 and 0.8 with step of 0.05.
Certain workplace types, e.g. the "Stucco plasterers / plasterers" and "Crane drivers in the manufacture of products from concrete, cement and gypsum" and also "Screed and terrazzo layers in the working and processing of natural stone" also have very high sickness rates, but comparatively few insured persons are employed in these areas, and so individual cases with long-drawn-out illnesses may ...
The dependence of the intermediate products of gypsum dehydration on the measurement conditions and the state of sample was confirmed. A detailed analysis of the temperature behavior of ν 1 (SO 4 ) in a single crystal indicated the coexistence of CaSO 4 ·2H 2 O + γCaSO 4 (380–440 K) and γ-CaSO 4 + β-CaSO 4 (680–740 K) phases, which was ...
Gypsum plaster, white cementing material made by partial or complete dehydration of the mineral gypsum, commonly with special retarders or hardeners added. Gypsum Plaster Market Swot Analysis by Key Players VANS Gypsum, Shreenath Gyptech, Sherlock Industries - The Cowboy Channel
Dehydration starts at 40°C and reaches a level corresponding to the semi-hydrate (bassanite) at 70-90°C. Above 100°C or even 200°C, the salt still contains about 0.01 mole of water per mole. Gypsum is formed in two ways: by crystallization from an aqueous solution, or by the hydration of anhydrite. It crystallizes as monoclinic prisms.
Gypsum undergoes brittle-ductile transition at moderate pressure (around 10 to 20 MPa confining pressure [Brantut et al., 2011]) and dehydration at less than 150 C, which is easily attainable is a triaxial apparatus using oil as a confining medium [e.g., Ko et al., 1997]. [5] In this paper we present a series of dehydration tests
Xylem water was distilled at 130 °C, whereas gypsum soils were distilled in two steps: first at 35 °C, and then at 130 °C to separate free and crystallization water and ensure almost complete dehydration of gypsum (Freyer and Voigt, 2003; Palacio et al., 2014b). Between the first and second distillation, sample tubes were kept in a ...
This article investigates the thermal performance of gypsum boards in the dehydration temperature region, where pronounced chemical reactivity is anticipated. Gypsum board samples were gradually heated up to 300°C, using a low heating rate. ... If you have an individual …
Gypsum alabaster has a very low starting porosity and permeability meaning that fluid can be efficiently overpressured at the onset of dehydration. If the fluid pressure during reaction exceeds the confining pressure sufficiently, hydrofracturing may occur and fractures could form preferential fluid pathways ( Zhu et al., 2016 ).
Gypsum dehydration experiment Four gypsum samples constituting the main polycrystalline habits of gypsum (alabaster, massive, satin spar, and selenite) were obtained from Ward's Natural Science and dehydrated to examine changes in the reflectance spectrum over the 350–2500 nm wavelength region and to determine if habit has any effect on the
The gypsum discharge pump sends calcium sulfate slurry from the absorption tower to the gypsum dehydration system. 3.1 absorption tower The absorption tower is an air tight structure, in order to ensure the integrity of the shell structure, welding connections are used as much as possible, flanged and bolted connections are used only if necessary.
In the process of tunnel construction, gypsum rock is often encountered, and the volume of gypsum rock expands when encountering water, which is easy to cause the occurrence of rock fall, collapse, and other disasters, bringing serious challenges to the safe construction of the tunnel. Therefore, in this paper, four groups of samples under different moisture content are tested by ...
The estimation of apparent activation energy for each individual step of the thermal dehydration of gypsum sample was obtained using isoconversional Fr, KAS and FWO methods, as indicated by Eqs.
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12%The estimation of apparent activation energy for each individual step of the thermal dehydration of gypsum sample was obtained using isoconversional Fr, KAS and FWO methods, as indicated by Eqs. ( 8 ), ( 10 ) and ( 12 ), in α interval …
~ 110-200º C: wt/ loss due to gypsum crystal water ~ Dehydration of calcium hydroxide thereafter. As it is quite evident that the wt. loss in case of cement due to the presence of gypsum is very small, therefore a separate curve has been made using the alumina-gypsum composite containing 0-5 wt.% of gypsum in the composite.
Gypsum plaster, white cementing material made by partial or complete dehydration of the mineral gypsum, commonly with special retarders or hardeners added.Applied in a plastic state (with water), it sets and hardens by chemical recombination of the gypsum with water. For especially hard finish plaster, the gypsum is completely dehydrated at high temperature, and such chemicals as alkali ...
Gypsum undergoes brittle-ductile transition at moderate pressure (around 10 to 20 MPa confining pressure [Brantut et al., 2011]) and dehydration at less than 150°C, which is easily attainable is a triaxial apparatus using oil as a confining medium [e.g., Ko et al., 1997].
Gypsum is the name given to a mineral categorized as calcium sulfate mineral, and its chemical formula is calcium sulfate dihydrate, CaSO 4 ⋅ 2H 2 O. However, a broader definition includes all the calcium sulfates, including calcium sulfate hemihydrate, CaSO 4 ⋅ 0.5H 2 O, which is known as plaster or plaster of Paris (POP). Figure 6 summarizes the polymorphism of calcium sulfate; 'g ...
In this thesis, the dehydration of single gypsum crystals are examined at 80°C and 110°C in NaCl solutions saturated with respect to gypsum. Indeed, no dehydration of gypsum is observed at 80°C or at 110°C if the ionic strength is low. At 110°C and high ionic strength, there is evidence of gypsum dissolution, but it occurs only after ...
[3] Gypsum has repeatedly been used as an analog material principally for its abundance and its low dehydration temperature. Ballirano and Melis [2009] concluded that in air, at a water vapor partial pressure of ca. 1.4 kPa, and in the temperature range of 348 to 403 K, gypsum (CaSO 4 •2H 2 O) dehydrates to γ -anhydrite (CaSO 4 ) via an ...
NOV.1985 Thermal Analysis of Gypsum 1. Introduction Gypsum has long been used as a building material and is used for that purpose in the following items. • Setting retarder for Portland cement • For gypsum plaster, gypsum board, ceramic molding tools, and arts and crafts • Auxiliary material for nickel smelting and a source of sulfur
McCormak (1926) likewise concluded that temperature was a more important factor than pressure in the dehydration of gypsum. He added, however, that pressure plus time in the geologic sense is an unknown factor and may have more influence on the dehydration of gypsum than any laboratory experiments could indicate.
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 …
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 …
Individual crystals are platy on (0001) and typically smaller than 10 ... of the gypsum–bassanite equilibrium was largely observed in order to explain the topotactic transformation of gypsum into bassanite by natural dehydration, especially in arid environments such as the Sahara Desert (e.g., Mees and Stops, 2003, and references therein). ...
The historical horizon of gypsum-related technology covers at least 11,000 years. The thermal behavior of gypsum (CaSO 4 · 2 H 2 O) plays a central role in the production of gypsum-based binders and the range of applications of the materials. Even hundreds of years ago, the details of process control in binder production, such as the use of water vapor, were already documented and discussed ...
Some Observations on the Process of Dehydration and Rehydration of Gypsum by Means of Proton Magnetic Resonance. Bulletin of the Chemical Society of Japan 1961, 34 (10), 1454-1457.
Gypsum (CaSO 4 ·2H 2 O) is a rock-forming mineral that also occurs in soil 1.Gypsum outcrops are widespread throughout the Earth, being present in the five continents 2.They are particularly ...
