— Structural evolution during the dehydration of gypsum materials - Volume 73 Issue 3 ... Jorgensen, J.D. and Hinks, D.G. (1984) A crystallographic study of the low …

 — 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 ...

4-1 Temperature Change in Drying and Dehydration of Gypsum in a Fluidized Bed Fig. 2 illustrates a typical change of interior tempera-tures with time during the drying and …

 — Introduction. Gypsum products are created from two simple reactions [1]: the calcination reaction − CaSO 4 ·2H 2 O + heat → CaSO 4 ·½H 2 O + 3/2H 2 O (g), and the rehydration reaction − CaSO 4 ·½H 2 O + excess water → CaSO 4 ·2H 2 O + excess water (g). An ore of calcium sulfate dihydrate should exhibit four distinct thermal …

temperature dehydrated gypsum rock was treated with different hydration time, and the gypsum rock samples in three states were subjected to ultrasonic test, density test and uniaxial compression test. The results show that the main components of natural gypsum minerals were gypsum dihydrate (71%), dolomite (27%) and potassium chloride (2%). …

 — The performance of composite gypsum at elevated temperatures depends on the treatment temperature and reflects the combined effects of gypsum phase change and the filler effects of silica flour or talc powder. ... There was tremendous pore water loss, and gypsum dehydration happened at 100 °C and 200 °C, leading to a porous structure that ...

 — The thermal decomposition of zinc acetate dihydrate was studied by TG–DSC to better understand its thermal stability and decomposition temperature. Fig. 4 (a) shows typical TGA and DSC curves of zinc acetate dihydrate in an air flow of 100 sccm at a heating rate of 2 °C min −1. The process starts with an endothermic reaction …

 — In the low-temperature and high water vapor zone above curve AB in Figure Figure2 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 …

 — The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor …

 — The crystal structure of the grown crystals was confirmed to be very similar to that of calcium sulfate dihydrate (CaSO4·2H2O, gypsum). The temperature at which dehydration and evaporation of ...

 — 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 …

 — Gypsum of chemical formula CaSO 4 ·2H 2 O, also called calcium sulfate dihydrate, is a versatile material used in several sectors of activity such as cement industry, plaster manufacturing and agriculture [1, 2].It is also found in the formulation of many useful products like paper, glass and paints [3, 4].Gypsum production is carried out in two …

Calcium sulfate dihydrate (gypsum) is a commonly found mineral in the nature, and it is an important building ... produced only when the decomposition occurred at high P H 2O and below 115 C, while the anhydrite was formed above 115 C and at low P H ... focused on the FGD gypsum dehydration behavior until now [26]. The origin, i.e., different ...

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.

 — 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 …

 — This subhydrate material is mixed with water at a construction site to form dihydrate (gypsum) again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were ...

phase decomposition of dihydrate to hemihydrate, the temperature inside of the crystal should not increase above the decompositio n temperature in which dihydrate beta-hemi- hydrate can be formed.

 — 1. Introduction1.1. General context. 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 …

 — Gypsum wallboard has been used for over 100 years as a barrier to the spread of fire in residential and commercial structures. The gypsum molecule, CaSO 4 ·2H 2 O, provides two crystalline waters that are released upon heating providing an endothermic effect. Manufacturers have recognized that the source of the gypsum ore is …

and/or mass loss rate as a function of time and/or temperature (see Fig. 1 for an example). 0.0 0.2 0.4 0.6 0.8 1.0 0 20 40 60 80 100 0 200 400 600 800 1000 / ° C)) 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

 — Semantic Scholar extracted view of "The thermal dehydration of synthetic gypsum" by C. Strydom et al. ... 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 ... calcium sulphate dihydrate undergoes dehydration as …

 — At higher temperatures the super-saturation is lower and the expected reaction speed is lower. However, as the ions can move faster at higher temperature, the speed of the hydration reaction is increased. With a higher temperature fewer seeds are formed and the gypsum crystals can grow larger (Figure 3d - f).

THE differential thermograms of calcium sulphate dihydrates (gypsums) show two relatively large endothermic effects in close sequence below 250° C. There is general agreement1,2 that these two effects represent the two-step decomposition of the dihydrate to hemihydrate and to soluble anhydrite. A third small endothermic effect, which is always associated …

 — In general, it seems not necessary to decompose the 0.3-hydrate, which is only possible at temperatures of about 180 °C, since the decomposition at lower pressure takes place with monohydrate as intermediate phase which decomposes at much lower temperatures. This is beneficial for a thermochemical storage since the decomposition …

This subhydrate material is mixed with water at a construction site to form dihydrate (gypsum) again. Therefore, the dehydration process of gypsum and the rehydration of hemihydrate were investigated in several studies; the given references will give an overview of the research conducted up to now [3–15].

Figure 1 shows the TG/DTA results for dihydrate gypsum. A 30mg sample was placed in a semi-hermetically sealed container, which was a hermetically sealed aluminum container with a pinhole in the lid. The atmosphere was 200ml/min of air …

 — The plot of the solubility product values against pressure and temperature according to Eqs. 2 to 4, for both gypsum and anhydrite, is shown in Fig. 5.

 — 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 …

 — 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].

 — Referring to the literature, the first major peak observed at about 140°C, which accounts for 75% of the total mass loss, is attributed to the partial dehydration of the gypsum giving calcium ...