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Further, the coating, distribution of gypsum, and its dehydration temperature were discussed. 2. When the grinding temperature is above 130°C., the strength of cement began to decrease to a small extent, and this tendency became more marked with …
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Dehydration, driers, drying, equilibrium moisture content, evaporation, water activity. Introduction the product is heated at a specified temperature and pressure (usually atmospheric pressure or a specified vacuum) for a specified time to remove all moisture (, dry
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When gypsum plaster is heated in a fire, the dehydration follows the reaction in Equation (1) as solid gypsum is converted back to a powdery form. Significant energy is required to evaporate the free water and make the chemical change which releases the water in the crystal structure. Complete dehydration does not occur until the temperature
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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. Temperature measurements at pre-selected board locations indicated three distinct stages of gypsum …
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cases the total dehydrated, at 170–190 °C, form-ing anhydrite CaSO 4 (26), so it is crucial to cement industry to know the temperature and the kinetic dehydration of different calcium sulphate forms to attempt to control the milling temperature and avoid the formation these damaging gypsum components during the industrial cement production.
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26/10/2022 · 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 dehydration of gypsum proceeded through one step,, CaSO 4 ·2H 2 O → γ-CaSO 4 (γ-anhydrite) or two steps,, CaSO 4 ·2H 2 O → …
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· The temperature close to the sliding surface is remarkably stable at ∼100 °C during the dehydration reaction of gypsum. Microstructural and X-ray diffraction investigations show that dehydration occurs at the very beginning of the …
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The present study investigates the significant rise in thermal conductivity of dehydrated gypsum plaster board between 200 and 800 °C, reaching the initial hydrated value of W/(m·K). It is shown that the main reason for this increase is independent of radiative and convective heat transfers and only due to an enhancement of the conduction between the single crystals …
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· The study of a gypsum single crystal was carried out using in situ thermo-Raman spectroscopy in the temperature range of 80–870 K. The conventional peak fitting approach was used to qualitatively determine the temperature ranges of …
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Gypsum Dehydration During Comminution and Its Effect on Cement Properties. G. Goswami, G. Goswami. (1200 cm×260 cm), because of the rising temperature during grinding, gypsum was dehydrated to hemihydrate, while there was no …
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05/07/2022 · A new experimental determination of the stability relationships for the dehydration of gypsum to the hemihydrate mineral bassanite at elevated temperature and pressure is described. The experimental method used depends on the observation of very small changes in pressure on the onset of reaction due to the potential volume change in the reaction.
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15/09/2022 · The commercial rock gypsum studied generates both hemihydrate and anhydrite at 128°C, and its impurities do not dehydrate until the temperature is increased to 500°C. 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
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01/01/2022 · Read "Thermal conductivity of gypsum boards beyond dehydration temperature, Fire and Materials" on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips.
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The structure of the low-temperature (T < 383 K) dehydration products of gypsum (CaSO 4· 2 O and γ-CaSO 4) was studied using time-of-flight neutron powder diffraction Clarify-ing the pioneer studies,33,34 these authors conclude that, even though bassanite presents an overall structure very similar to γ-CaSO 4 (P6 2
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19/02/2022 · This thesis contributes to our understanding of temperature driven dehydration of rock forming minerals. It investigates the impact of crystallographic preferred orientation (CPO) on the dehydration of gypsum to bassanite through in …
Get PriceDehydration: Rock into plaster Gypsum rock is converted into gypsum plaster by driving off some of the chemically combined water. Heating gypsum at 120°C for one hour results in a hemi-hydrate (CaSO ⁄2H 2O) – with three quarters of the water removed. Gypsum hemi-hydrate is also known as Plaster of Paris.
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Lager G A, Armbruster T, Rotella F J, Jorgensen J D, Hinks D G (1984) A crystallographic study of the low-temperature dehydration products of gypsum, CaSO 4 ·2H 2 O: hemihydrate CaSO 4 · 2 O, and γ-CaSO 4, American Mineralogist, 69, 910-918
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placing gypsum in a glass tube immersed in a paraffin bath and slowly heating the latter while recording the temperature of the gypsum by means of a thermometer. At 1280C and at 1680C there were breaks in the otherwise even rise of temperature, indicating that heat was being absorbed and an endothermic reaction was occurring.
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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 dehydration mechanism of gypsum significantly depended on ambient …
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· This thesis contributes to our understanding of temperature driven dehydration of rock forming minerals. It investigates the impact of crystallographic preferred orientation (CPO) on the dehydration of gypsum to bassanite through in …
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In a triaxial compression test at 5 kb pressure, we observe a tenfold strength decrease (from to kb) in sealed polycrystalline gypsum cylinders if the temperature is increased from 100° to 150° C. This marked decrease is interpreted as being due to the dehydration of gypsum with consequent rise in fluid (pore) pressure to a value
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This dehydration of gypsum by heat is called calculations. The calculations result in a covering over the materials that stop it to undergo combustion and allows the material near them to maintain a lower safer temperature. 3. Acoustic Property of Gypsum. Gypsum products are constructed to focus more on sound insulation and acoustic properties.
Get Price30/01/2022 · As shown in Figure 7, it is verified that the dehydration temperature of epsomite gradually increased with the rise in pressure. This positive relation between dehydration temperature and pressure was coincident with the result of other similar hydrated sulfates (gypsum, chalcanthite and blödite) [11,12,13].
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19/02/2022 · 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 GPa pressure. The investigation revealed a fine structure in the dehydration boundaries of gypsum …
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The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum materials. Finally, high temperature data are re-examined in the search for a variation of the anhydrite structure. KW - Dehydration
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Gypsum is a water soluble compound but its solubility decreases with an increase in temperature. When gypsum is heated, water vapors are lost from it and it gets converted in a compound with chemical formula CaSo4. 12H2O, named as "plaster of Paris".
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Dehydration Temperature of Gypsum JST. In general, the true specific gravity of semihydrated gypsum produced by dehydration under pressure is greater than that produced at normal pressure. (5) Semihydrated gypsum prepared under pressure of nitrogen in unsaturated water vapor is found to be a well developed form of α-semihydrated gypsum.
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The y form results from the dehydration of the hy drates and is regarded as the low-temperature species, although it is apparently metastable and even at room temperature very slowly converts to the "high-tem perature" species, /3-CaS04 [2]. The …
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e ect is influenced by wide equilibrium temperature ranges in the process of the transformation of dihydrate gypsum into semi-aqueous gypsum and anhydrite. In the process of the dehydration of phases, the instability of the CaSO4-H2O system occurs at a temperature of 45 C. The first intense dehydration of the dihydrate into hemihydrate occurs in
Get PriceGypsum rock can be obviously weakened by high-temperature dehydration. With increasing the dehydration time, the crystal structure and shape of gypsum rock change gradually and the numbers of micro-cracks and micro-voids increase gradually, which leads to the deterioration of the physical and mechanical properties of gypsum rock.
Get PriceThis shifts the dehydration of the hemihydrate to higher temperatures thereby improving the separation of the two processes. The gypsum content in cement is usually in the percent range. From stoichiometric considerations, dehydration of the dihydrate is expected to give a total mass loss of %, made up of steps of % (dihydrate
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· The results showed that the simulation results were consistent with the experimental results. The dehydration time of 40 mm FGD gypsum under the three relative humidity conditions of 55%, 75% and 82% at 20℃ was about 350 h, 450 h and 500 h, respectively. The lower the relative humidity was, the longer the dehydration time of FGD gypsum was
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· However, this temperature threshold may be lower in non-pure gypsum, as the activation energy for the dehydration of gypsum is lower in soils than in pure mineral 25.
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Studies of the dehydration of gypsum in dry air atmospheres have shown that the hemihydrate of calcium sulfate is not a stable phase in the temperature range 90-140 deg C. The final product of dehydration was always anhydrous. Discontinuities in the weight loss versus time curves for powdered gypsum at a point corresponding to the loss of about 75 percent of the original …
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floors, due to the endothermic gypsum dehydration process that takes place in high temperature. When a gypsum board is subjected to fire, the free and chemically bound water is released and transferred through the board, absorbing energy and thus reducing the mean wall temperature. This phenomenon can be of great importance from the safety point
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temperature over the course of the dehydration reaction. Thermogravimetric curves were obtained at heating rate of 10 °C/min between ambient and 650 °C in argon atmosphere (20 ml/ min) and the sample mass was between 45 and 50 mg. Kinetic study The kinetic study of the dehydration of PG was performer with Differential Scanning Calorimetry
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· It can be seen that the transformation related to the dehydration of the gypsum–polymer composites occurs in a similar temperature range as the gypsum itself (117–128 °C). A difference, however, can be seen in the …
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wallboard, gypsum must be partially dehydrated or calcined to produce calcium sulfate hemihydrate (CaSO4 ½H 2O), commonly called stucco. A flow diagram for a typical gypsum process producing both crude and finished gypsum products is shown in Figure -1. In this process gypsum is crushed, dried, ground, and calcined.
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produced from titanium gypsum by dehydration at 110–150°C. It is formed according to following equation stored in a desiccator at room temperature to avoid any contamination.
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The main reason for the high resistance of fire spreading through plasterboards is the dehydration phenomenon: a chemical endothermic reaction occurring in the temperature range ≈90°C–250°C, whereby the chemically bounded water contained in the gypsum crystal structure is released as vapour. 1,2 The vapour is then driven by pressure and
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