The curve of the hemihydrate solubilities is largely based on the data of Partridge and White (), Posnjak (), D'Ans et al. and Power et al. yielding a gypsum to hemihydrate transition temperature of 99 ± 4°C, which is in reasonable agreement with the values of 97.5°C (Posnjak 1938) and 97°C (D'Ans et al. 1955).According to Fig. 2 the hemihydrate can be prepared from …
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These two experiments clarified that: i) increasing gypsum amount up to 4.5% of binder mass effectively reduced free shrinkage strain subjected to 30 degree of ambient temperature, ii) this free ...
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Gypsum content determined from gravimetry of precipitated BaSO 4 as related to gypsum content from loss of its crystal water between three temperature intervals: 70 to 90°C, 70 to 105°C, and 70 ...
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Temperature ( °C) Fig. 1. Example of TGA mass and mass loss rate curves (Type C gypsum board heated at 20 °C/min). ARRHENIUS-RATE THERMAL DECOMPOSITION KINETICS . Consider an experiment in which a (small) specimen of a material that is heated uniformly so that its temperature . T. rises with increasing time . t. It is assumed that the ...
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Figure 2 shows an overlay of gypsum DSC curves obtained with open crucibles in STA at atmospheric pres- sure and in DSC at 1, 16, 34, 50, and 67 bar. ... gypsum). The temperature at which ...
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The temperature and humidity dependent formation of different crystalline phases CaSO 4 ·xH 2 O with 0 ≤ x ≤ 2 was investigated by in situ X-ray powder diffraction using a Bruker D8 diffractometer equipped with an Anton Paar CHC + cryo−/ humidity chamber. By isothermal measurements over time ranges up to 60 h at temperatures between 76 °C and 140 °C the …
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The above process, known as "dehydration" or "calcination" of gypsum, takes place at the temperature range between ∼80 °C and ∼250 °C, depending on the heating rate, of the gypsum board, and its composition [1], [10], [11].
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Using a heating rate of 5°C min −1, the very slow dehydration of CaSO 4 ·2H 2 O and impurities in the gypsum samples start at temperatures lower than 95°C.
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dehydration temperature and the required energy are still not certain [3–7]. This can be caused by the physical properties such as the composition and the microstructure of the investigated gypsum. Therefore, in the present study, the dehydration reaction was studied. The dehydration of …
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Water saturation has a weakening effect on the high-strength gypsum remolded sample. After high-temperature dehydration, the strength of the sample decreased by 73.09%. It can be observed that high-temperature dehydration has obvious weakening effect on the sample. 3.2.2. Triaxial Compression
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Download scientific diagram | Pressure^temperature graph showing the gypsum-out curve from Zen (1965), the metastable bassanite-in curve of McConnell et al . (1987), 30 8 C km À 1 and 15 8 C km ...
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An in situ dehydration kinetics study of gypsum under water-saturated condition was performed in the temperature and pressure ranges of 383-423 K and 343-1085 MPa by using a hydrothermal diamond ...
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The effects of gypsum dehydration are assessed by using two alternative modelling approaches, an effective specific heat model and a solid reaction kinetics model; the obtained predictions are compared to a benchmark test case, where no such phenomena are modelled. ... The integral of the temperature-specific heat curve, owed to the additional ...
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Figure 1: (left) Mass vs. temperature curves of gypsum during heating as measured by TGA. Two experiments were performed: open and closed. The one step process under open conditions is replaced by a two step dehydration …
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According to the thermal curves, the gypsum dehydration comports two steps described by the following equations: CaSO 4 •2H 2 O( s )→CaSO 4 •1/2H 2 O( s )+3/2H 2 O( g ) (I)
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In the low-temperature and high water vapor zone above curve AB in Figure 2, gypsum is thermodynamically stable; in the ABC zone, CaSO 4 ·2H 2 O will partially dehydrate its crystal water to form β-CaSO 4 ·0.5H 2 O, and as the temperature is increased, gypsum undergoes a two-step dehydration process (CaSO 4 ·2H 2 O → γ-CaSO 4 → β-CaSO ...
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From the weight loss curves obtained by DVS it is evident that the humidity has an important influence on the dehydration process. The time to weight equilibrium shortens drastically with …
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Gypsum plaster is an inorganic binder that is prepared in a two-step process. The first step is dehydration: heated to 100–200 °C, gypsum (CaSO 4 ·2H 2 O) releases water as vapor [1, 2] and, depending on temperature and water vapor partial pressure (p H2O) [3, 4] forms either hemihydrate (CaSO 4 •½H 2 O) or γ-anhydrite (CaSO 4), the main components of the …
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Download scientific diagram | European fire testing standard time/temperature curves (ISO 834 = curve #1). from publication: Enhanced Gypsum Panels for Fire Protection | The fireproofing materials ...
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The first mass loss between 100 and 250 °C [36][37][38][39] [40] [41][42] can be ascribed to the release of water molecules of gypsum which occurrs in two steps as described by Equations 1 and 2 ...
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Using this calibration curve, levels as low as 0.5% dehy-drate may be determined in the hemihydrate. A high sensitivity and precise TGA (such as the TA Instruments TGA 2950 or …
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The autoclave method operated gypsum dehydration under elevated temperature and pressure [19], resulting in high running cost. ... The curve of the particle size distribution in Fig. 1 (b) presents fine particles in the FGD gypsum, and the particle sizes are mainly concentrated in 0–80 μm. Statistically, 90% of the total volume diameters is ...
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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 ...
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Methods. The dehydration process of FGD gypsum was performed with simultaneous TG/DSC analysis (NETZSCH STA 409 Luxx, Selb/Bavaria, Germany) at N 2 atmosphere with a gas flow of 20 mL min −1.Non-isothermal analysis was carried out at different heating rate (2−20 K min −1).Isothermal analysis was conducted in the temperature range of …
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Thermogravimetric and differential thermal analysis curves reveal that dehydration occurs in two stages. The diffraction peaks of β-hemihydrate with the trigonal space group P3121 gradually...
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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 3008C, …
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An experimental investigation was also developed by Ghazi Wakili and E. Hugi in 2009, dealing with thermal properties of the materials and comparing the fire behaviour of four types of gypsum ...
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DSC curves as a function of sample temperature and heat ramp curves for the chemically bound water dehydration reaction of a commercial gypsum board (a and c) and …
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The sigmoidal fraction of conversion curves with complete gypsum dehydration (obtained at 92 °C, 88 °C and 84 °C measurement temperature) were fitted using the JMAK model as given above. ... A crystallographic study of the low-temperature dehydration products of gypsum, CaSO 4 · 2H 2 O: hemihydrate CaSO 4 · 0.5H 2 O, and γ-CaSO 4. Am ...
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At this stage, the dehydration could be attributed to the removal of the physically absorbed moisture and partial dehydration of the gypsum accompanied by the formation of calcium sulfate ...
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Nuclear magnetic resonance (NMR) is used to non-destructively measure the moisture and dehydration profiles in gypsum during one sided heating to temperatures of 400 ... Three curves are shown: temperature (T), hydrogen content (H), and the approximated vapour pressure (P v). The moisture peak is highlighted in grey.
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The dependence of the solubility of gypsum on temperature is nonlinear, reaching a maximum at 43°C. ... = Curves for gypsum and. ... that gypsum dehydration occurs widely.
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This article investigates the thermal performance of gypsum boards in the dehydration temperature region, where pronounced chemical reactivity is anticipated. ... Curve of the differential ...
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From the weight loss curves obtained by DVS, it is evident that humidity has an important influence on the dehydration process. The time-to-weight equilibrium shortens …
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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 hydration time, and the …
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Figure 11. Temperature curves of the unexposed side of gypsum plasterpanel (W=P 06) according thicknesses. Figure 12. Temperature curves of the unexposed side of panels (thick-ness 37mm) according to bullet5ller amount.Trans IChemE, Vol 81, Part A, October 2003 1234 FE´JEAN et al. shown in Figure 13(b) and (c).
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