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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 mol−1)
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Volume 941, 1 September 2024, 173756. MgO-based supersulfated cement with different industrial by-product gypsum: Experiments and molecular dynamics simulation ... 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 ...
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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 …
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Volume 262, Part 1, 1 December 2024, 119849. Review article. ... Macroscopically, they can affect the hydration of gypsum dehydration products, prolong the hydration time, reduce the mechanical properties of the products, and shorten their service life. Microscopically, they can cause the crystal morphology to be in an irregular shape ...
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High-temperature, high-pressure experiments indicate that gypsum remains as hemihydrate gypsum at depths up to 5000 m, converting entirely into anhydrite at 6700 m, signifying a continuous dehydration process for gypsum. The theoretically released crystalline water from gypsum dehydration equals 48.6% of the gypsum volume (Lin et al. 2005).
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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). However the reaction is associated with a net volume increase as the water produced has a greater volume than the pore space.
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Volume 545, 10 October 2012, Pages 141-147. Gypsum board dehydration kinetics at autogenous water vapour partial pressure. ... 0.7 (step II). The two-step process for gypsum …
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The product obtained in pilot scale has a purity of 95% and the α-HH crystals are mostly a prismatic morphology, with volume weighted mean diameter (D[3,4]) in the range of 52.9–84.0 ... which results in the variation of the apparent rate of FGD gypsum dehydration.
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The dehydration of gypsum CaSO 4.2H 2 O has been studied, at negligible water vapour pressure, by in situ infrared (IR) spectroscopy and by thermogravimetry to determine whether intermediate phases (CaSO 4. n H 2 O) exist, other than the hemihydrate with n =0.5, and also to compare the mechanism of the dehydration process when measured by two techniques with …
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ture at which the dehydration events occur increases (T dehydration = 425.5 K in an open system, T dehydration = 439 K in a sealed system, in the presence of excess water). …
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The dehydration reaction at 160°C is nearly double that at 100°C and four times that at 70°C, using one particle size. Generally, as the grain size of gypsum becomes less than about 0.13 mm an abrupt increase in the dehydration process occurs with any slight decrease in …
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The U.S. Department of Energy's Office of Scientific and Technical Information
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In the present research, dehydration mechanisms of gypsums from different sources and grades are studied by Raman spectroscopy. Two temperature profiles, one aggressive and another at moderate…
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Abstract Calcium sulfate dihydrate has been widely characterized by both differential scanning calorimetry and thermogravimetry (TG). Two dehydration processes were reported to be partially overlapping. High resolution TG and water vapor self generated atmosphere pin-hole lid strategies were used to increase the resolution of both dehydration …
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An illustration of the volume changes for a dehydration of gypsum as the reaction proceeds to completion, assuming no compaction. Definitions of symbols are given in the Ap- pendix. The example is if)r: CaSO4.2tt,O. ~ CaSO4" 5H20+ i )zH,O . gypsum bassanile water total volume increase, solid volume increase Terzaghi's (1923) pioneering work on ...
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Mineralogical transformations between gypsum, the dominant mineral, and its dehydrated form, anhydrite involve a 39% change in volume (Jowett et al., 1993); gypsum dehydrates to the denser ...
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This study examined the thermal dehydration characteristics of CaSO4∙2H2O in a constant-volume rotary vessel. The experiment used CaSO4∙2H2O particles obtained from the crushed waste gypsum board.
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The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. ... The reversal process leads to a volume decrease of ~29 % ...
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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 posing serious engineering problems …
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4) and dehydration of gypsum (CaSO 4Æ2H 2O) lead to alternating volume changes, thereby posing serious engineering problems to both soil and concrete structures. Gypsification of anhydrite is associated with up to 63% swelling and dehydration of gypsum to form anhydrite results in a maximum volume reduction of 39% (Zanbak and Ar-thur 1986).
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volume change in the dehydration reaction the slope of the P-T line for the coexistence of gypsum and the hemihydrate at 385.65 K and 1000 bars was calculated to be 85.5 bars K- 1, which is close to the experimentally measured value of 81.1 bars K-1. ... DEHYDRATION OF GYPSUM TO BASSANITE ...
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This study verified that alpha-gypsum can be trouble free prepared by gypsum dehydration in solution of a number chloride salts, among others CaCl2, MgCl2 or NaCl.
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Where φg is the volume fraction of gypsum, m hydration degree, vh/vw the specific volume ratio of hemihydrate/free water (0.36 for α- and 0.38 for β-hemihydrate), vn/vw the specific volume ratio of crystal water/free water (0.81 for α- and 0.71 for β-hemihydrate), w the water/hemihydrate ratio, and w0 the water requirement for 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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At standard thermodynamic conditions, the molar volume of gypsum, bassanite, and water are 74.7, 53.8, and 18 cm 3 /mol, ... The dehydration reaction of gypsum into bassanite and water induces a large …
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Transactions of the Indian Ceramic Society Volume 44, 1985 - Issue 2. Submit an article Journal homepage. 9 Views 6 CrossRef citations to date 0. Altmetric Original Articles. Thermoanalytical Studies on Gypsum Dehydration ... There is no general agreement regarding the mechanism of gypsum dehydration. Different authors have come to different ...
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Volume 73, Issue 3 p. 721-723. Gypsum Dehydration During Comminution and Its Effect on Cement Properties. G. Goswami, G. Goswami. Dalmia Institute of Scientific and Industrial Research, Rajgangpur 770017, India. Search for more papers by …
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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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The grinding temperature should never exceed 110°C in order to prevent excessive gypsum dehydration. On the contrary, the temperature must not be lower than 90°C as this will result in a risk of poor gypsum dehydration. ... The higher this ratio the more volume of cement we produce.
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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 …
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