The kinetics of the dehydration of gypsum was investigated by powder diffraction methods. Using the incoherent scattering effect of H with the neutron beam, the background intensity as a measure of the water content was checked in the temperature range 295–623 K.
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Diagram 1 - Dehydration. The first process is the formation of hemihydrate or anhydrite from dihydrate. To obtain more information about this step, gypsum crystals …
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The system Ca S O 4 – H 2 O , characterized by the three dehydration reactions gypsum-anhydrite, gypsum-bassanite, and bassanite-anhydrite, was reexamined by in situ differential pressure analysis in the temperature range of 60 – 350 ° C up to 3.5 GPa pressure. The investigation revealed a fine structure in the dehydration …
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Volume 491, 1 July 2024, 152122. Ingenious approach for retrieving valuable metals from gypsum via dehydration–rehydration two-step phase transition. Author links open overlay panel Jiayi Zheng a e 1, Changzhou Weng a 1, Chen Tian b, Wenchao Zhang b, Jiemin Qin a c, Xiaoqin Li a c, Weizhen Liu a c, Jing Zhang d, Zhang Lin b.
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Abstract The spectral behavior of gypsum dehydration in the visible to near-infrared (350-2500 nm) wavelength range was investigated by partially dehydrating the four main habits of gypsum (alabaster, satin spar, selenite, and massive) to form bassanite. Powdered samples of gypsum dehydrated at 100-115 °C and hand samples dehydrated …
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Understanding the behaviour of natural calcium sulphates is important to ensure the sustainable integrity of civil structures. The phase transitions of these minerals are associated with considerable volume variations, creation of porosity with local defects, and water exchanges. Such changes can jeopardise the integrity of structures when the …
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The dehydration process of a synthetic gypsum indicates that it has an interstitial gypsum phase dehydrating in a similar way to the interstitial phase found in the Terra Alba gypsum.
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Minor changes in specific surface area and total pore volume for anhydrite and halite are observed. Abstract. ... These results confirm that the process of gypsum dehydration is mainly derived by temperature, and usually takes place in the long term. In summary, the XRD results indicate a high level of stability of halite, anhydrite, and …
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Volume 129, Issue 1 e2023JB027098. ... Laboratory experiments show that during gypsum dehydration, the escaping water weakens the rock, facilitating deformation. In our study, we employ microindentation tests …
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obtained average activation volume 3V is equal to 5.69 cm /mol and the calculated activation ... A series of Raman spectra as a function of time acquired during gypsum dehydration at 393 K and 421 ...
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In order to study the physical and mechanical properties of gypsum rock samples in three states (natural, high-temperature dehydration and hydration time), natural gypsum rock was put into high-temperature condition of 220°C for dehydration treatment, and then the high-temperature dehydrated gypsum rock was treated with different …
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The peak at 120∼160 °C (peak 2) mainly corresponds to the dehydration of gypsum and can reflect the gypsum consumption during hydration in PG-slag binder system [33, 53]. Download: Download high-res image (641KB) ... And the long term properties (volume stability and durability, etc.) toward large-scale application should be investigated.
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The phase transitions of these minerals are associated with considerable volume variations, creation of porosity with local defects, and water exchanges. Such changes can jeopardise the integrity of structures when the conditions that trigger the phase transitions are encountered. ... Thermo-poro-mechanics Modelling of Gypsum Dehydration ...
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Volume 13. Issue 12. 10.3390/coatings13122091. ... There was tremendous pore water loss, and gypsum dehydration happened at 100 °C and 200 °C, leading to a porous structure that weakened the strength of the gypsum matrix. After the 300 °C …
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Thermal behaviour and kinetics of dehydration of gypsum in air have been investigated using in situ real-time laboratory parallel-beam X-ray powder diffraction data evaluated by the Rietveld method. Thermal expansion has been analysed from 298 to 373 K. The high-temperature limits for the cell edges and for the cell volume, calculated …
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The conversion of gypsum to anhydrite upon burial and heating is accompanied by about a 39% volume decrease, a four-fold increase in thermal conductivity, and consumption of heat. Accurate "back-stripping" of an evaporite basin and tracking its thermal evolution requires a knowledge of the depth of the gypsum …
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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 dehydration pathways of gypsum are largely determined by …
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The thermodynamic calculation results reveal that γ-CaSO4 has an extraordinary ability to capture water molecules from an extremely dry atmosphere, which is very useful in some fields, such as in drying processes and even for extracting liquid water fromextremely dry atmosphere. The dehydration products of gypsum under different …
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Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are formed and, for technical reasons, are mixed with water to form dihydrate again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated. …
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during experimental dehydration of lizardite and gypsum. [3] Two challenging problems encountered in addressing the possible importance of dehydration embrittlement in ... At standard thermodynamic conditions, the molar volume of gypsum, bassanite, and water are 74.7, 53.8, and 18 cm3/mol, respectively [Robie et al., 1979]. Considering the ...
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The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure.
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A hot and arid climate, fluctuating relative humidity, and an alkaline environment govern the geological evolution and the engineering behaviour of soil deposits in the Arabian Gulf coastal region (Azam 2000).Hydration of anhydrite (CaSO 4) and dehydration of gypsum (CaSO 4 ·2H 2 O) lead to alternating volume changes, thereby …
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As illustrated in Fig. 1, one mole of gypsum (molar volume (V_g=74.69,cm^3,mol^{-1})) produces one mole of hemihydrate ... Gypsum dehydration affects matrix morphology; the porosity changes due to the decrease of solid volume and increase of fluid content. In addition, the increase of pore pressure affects the …
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Abstract The dehydration of gypsum (CaSO4·2H2O) into calcium sulfate hemihydrate (CaSO4·0.5H2O) and anhydrites (γ-CaSO4andβ-CaSO4) 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 …
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Thermo-poro-mechanics Modelling of Gypsum Dehydration 179 1 mol of gypsum Intact Gyp- sum Sample 1 mol of bassanite porosity 1.5 mol of water Reaction products excess Expelled w ater Fig.1. Illustration of the reaction (1) of gypsum into bassanite and water after a temperature increase up to 388oK. 1mol of Gypsum (molar volume 74.69cm3 …
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Abstract. The dehydration behaviors of FGD gypsums from three power plants were investigated at N 2 atmosphere (autogenous and negligible partial pressure of water, ) in non-isothermal and isothermal condition.The dehydration of gypsum proceeded through one step, i.e., CaSO 4 ·2H 2 O → γ-CaSO 4 (γ-anhydrite) or two steps, i.e., …
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(a) Unit-cell volume of the hemihydrate phase during the dehydration study of pure gypsum within a sealed capillary with an excess of water. (b) View of the ab plane of the hemihydrate structure with 0.5 water molecules content at 230ºC.
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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, …
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