Volterra gypsum in an evaporitic rock, and groups (up to centimeter scale) of neighboring grains with similar crystal orientations are commonly found (see Fusseis et al. for a detailed investigation of the fabric of Volterra gypsum). The onset of dehydration can thus be marked by the development of heterogeneities in elastic properties.
LTP weathering. And gypsum dehydration is the significant process of CO 2 LTP weathering. However, the other changes in composition and structure of sam-ples were not detected using our Raman method. Acknowledgements: This work was supported Key Laboratory of Planetary Sciences of Chinese Academy of Sciences(PSL14_04), the National
The gypsum dehydration capability determined under the given test conditions of about 26% in the vertical stirred media mill can be considered as relatively low compared with the dehydration capability of ball mills (up to ). Comparable grinding trials in a semi-industrial horizontal SMM have shown that with fairly long operating times ...
The invention provides a technology for FGD gypsum dehydration, and relates to the FGD flue gas desulphurization field. When a wet method FGD technology is used, gypsum slurry outputted by an FGD absorbing tower is subjected to solid-liquid separation by utilization of the provided method. The technology comprises dehydration steps. The dehydration steps comprise a …
Find the latest published documents for gypsum dehydration, Related hot topics, top authors, the most cited documents, and related journals
Conference: Gypsum dehydration, agent of salt diapirism Gypsum dehydration, agent of salt diapirism. Full Record; Other
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 …
Therefore, anhydrite appears in evaporitic settings through gypsum dehydration. When these anhydrite-dominated deposits are exhumed above the reaction isotherm, and enough water is available, they will convert back to gypsum (e.g., Conley and Bundy 1958; Murray 1964; Ossorio et al. 2014).
dehydration of β-CaSO 4·0.5H 2 O. 7−10 McAdie11 studied the gypsum dehydration process at 124.3 °C under different water vapor partial pressures. Their experimental results reveal that gypsum dehydration proceeds through only a single CaSO 4· 2H 2 O → γ-CaSO 4 step when the ambient water vapor pressure
Keywords: gypsum dehydration, non-isothermal kinetic, thermal analysis Introduction The thermal behaviour of gypsum was frequently investigated due to its use as construc-tion material. The thermal decomposition of gypsum depends on the experimental condi-tions. Among them the heating rate and the atmosphere of the thermal treatment are par-
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 …
The second peak related to dihydrate gypsum dehydration at around 120 °C becomes weaker compared to that of 7-day pastes, implying increased involvement of dihydrate gypsum in subsequent hydration reactions. However, the weight loss of all pastes from 105 °C to 150 °C increases, primarily due to weight loss of hydration products in this ...
Gypsum (CaSO 4 ·2H 2 O) dehydration kinetics were investigated through energy dispersive X-ray diffraction (EDXD), under reduced pressure (100 Pa), in the temperature range 313–353 K. The process follows the JMAK (Johnson-Mehl-Avrami Kinetic) model. The fitting procedure of the Arrhenius expression provides an activation barrier of 18(2) kcal/mol.
Gypsum board dehydration. Gypsum board dehydration takes place at the temperature range between ∼80 °C and 250 °C, depending on the heating rate and the composition of the gypsum board [1], [10], [16], [17]. During this process the chemically bound water dissociates from the crystal mesh and, together with the free moisture content, evaporates.
The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
The microstructures formed by the dehydration of gypsum under controlled conditions of temperature and water vapor partial pressure were characterized using in situ X …
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 dehydration pathways of gypsum are largely determined by ambient temperature and …
Gypsum dehydration has been previously proven to negatively influence the air void structure of air-entrained concrete. Ettringite, nucleating from tricalcium aluminate and calcium sulfate, influences the adsorption and mode of action of anionic-based polycarboxylate ether admixtures. The authors suspected the admixture's air-entraining ...
The hemihydrate (CaSO 4.0.5H 2 O) obtained after thermal dehydration of Gypsum. Upon mixing with water, the hemihydrate can immediately react with water, producing Gypsum, which can be shown b following reaction [5]: (1) CaSO 4.0.5H 2 O+ 1.5 H 2 O → CaSO 4 ·2H 2 O + Heat
At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO4 hemihydrate, which completely dehydrates to c-anhydrite at 488 K.
Gypsum (CaSO4 center dot 2H(2)O) dehydration kinetics were investigated through energy dispersive X-ray diffraction (EDXD), under reduced pressure (100 Pa), in the temperature range 313-353 K. The process follows the JMAK (Johnson-Mehl-Avrami Kinetic) model. The fitting procedure of the Arrhenius expression provides an activation barrier of 18(2) …
Labelled gypsum soil consisted of an artificial soil resulting from heating natural gypsum soil at 100 ºC for three days to promote dehydration and loss of gypsum crystallization water and then, re-hydrating it with deuterated water obtained by adding 1 ml of deuterium oxide (99.9% atom D, CAS, Sigma-Aldrich, Germany) to 5 litres of ...
As gypsum is a very clean and well defined material we have also used is as a benchmark material to study the processes like interpret moisture and/or dehydration at high temperatures. Gypsum is also from an NMR point of view a nice material because it does not contain any paramagnetic impurities.
The kinetics of gypsum dehydration in non-isothermal conditions with constant heating rate as well in quasi-isotherm, quasi-isobar regime, was investigated. The latter ones of these methods allowed putting in evidence the autocatalytic character of the dehydration, as well as the change of the activation energy with the conversion.The activation energy change was explained by …
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 ...
The gypsum dehydration process is an essential step for plaster production. This section of the paper examines the thermal properties of HPO 4 2− ions within the CaO–SO 3 –H 2 O system, focusing on understanding their behavior during the transition from PG to HPG.
This study examined the thermal dehydration characteristics of CaSO 4 ∙2H 2 O in a constant-volume rotary vessel. The experiment used CaSO 4 ∙2H 2 O particles obtained from the crushed waste gypsum board. The particle size ranged from 850 to 2000 μm, and the experiment was carried out at varying rotation speeds of 1, 10, and 35 rpm, with the vessel temperature heated …
The dehydration of gypsum (CaSO 4 ·2H 2 O) into calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O) and anhydrites (γ-CaSO 4 andβ-CaSO 4) was carried out by heating under a constant pressure of water vapor using Controlled transformation Rate Thermal Analysis.No intermediate formation of calcium sulfate hemihydrate occurred under a pressure of water …
Gypsum dehydration experiments were carried out in the temperature range 313–353 K. In a typical run the pellet was inserted into the environmental chamber that was subsequently closed and evacuated. At this point the heating cycle was started under X-ray monitoring. As temperature reached the set value, counting time (1) where Iobs is the ...
The effects of gypsum dehydration and the associated water vapour release have been investigated by using a dedicated solid reaction kinetics model, which allowed, for the first time, quantification of the gypsum dehydration induced water vapour; relevant predictions of water vapour production and dispersion have been presented.
Cement milling and gypsum dehydration. Because the cement gets hot due to the heat generated by grinding, gypsum can be partly dehydrated, forming hemihydrate, or plaster of Paris - 2CaSO 4.H 2 O. On further heating, hemihydrate dehydrates further to a form of calcium sulfate known as soluble anhydrite (~CaSO 4). This is calcium sulfate with a ...
Consequently, a portion of the dihydrate gypsum may undergo drying and dehydration, forming β-hemihydrate gypsum. Compared with α-HH, β-hemihydrate gypsum …
During gypsum dehydration (Stage 3 on Fig. 7), the increase of bassanite content is still associated with the development of continuous R 1 Riedel shears and P foliation planes. The increase of bassanite content allows the progressive maintenance of newly formed pores in relatively strong bassanite aggregates inducing permeability change from ...
Gypsum (CaSO 4 ·2H 2 O) dehydration kinetics were investigated through energy dispersive X-ray diffraction (EDXD), under reduced pressure (100 Pa), in the temperature …
Harrison T N (2012) Experimental VNIR reflectance spectroscopy of gypsum dehydration: investigating the gypsum to bassanite transition, American Mineralogist, 97, 598-609 Robertson K, Bish D (2013) Constraints on the distribution of CaSO 4 ·nH 2 O phases on Mars and implications for their contribution to the hydrological cycle, Icarus, 223 ...
low-temperature dehydration of gypsum has been inves-tigated for many years. The rst analysis of the process is attributed to Flörke (1952), which indicated a two-step process CaSO 4 ·2H 2 O CaSO 4 ·0.5H 2 O -CaSO 4.An early study of the kinetics of dehydration of gypsum was performed, in vacuo, by Molony & Ridge (1968) whose
the dehydration of gypsum due to the effects. of high pressure and temperature during. burial. However, Sonnenfeld (1984) suggested that high pressure and temperature.
Gypsum, calcium sulfate dihydrate (CaSO4·2H2O), is known to form crystals larger than one meter in several locations worldwide. ... From 5.3 to 2.6 Ma [7,26,27], the …
Gypsum dehydration is necessary for it to become an effective set moderating agent. Gypsum itself is insolouble and therefore cannot moderate the setting of the C3A in cement clinker. For that to happen soluble sulphate must be present. Dehydration of gypsum to hemihydrate renders it soluble.
