WhatsApp)WhatsApp)
Thermal expansion of gypsum is strongly anisotropic being larger along the b axis mainly due to the weakening of H2 O1 hydrogen bond. Dehydration of gypsum has been investi gated in isothermal conditions within the 348–403 K range with a temperature increase of 5 K. Dehydration proceeds through the CaSO 42H 2O ?
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).
Synthetic anhydrite is obtained when gypsum is dehydrated at the temperature of 600 to 800ºC. There is little knowledge about the influence of the dehydration temperature on the physical and mechanical properties of anhydrite binder.
temperature interval for the dehydration of gypsum plaster board at fire conditions is between 100°C and 200°C.
The temperature close to the sliding surface is remarkably stable at ∼100 °C during the dehydration reaction of gypsum. Microstructural and Xray diffraction investigations show that dehydration occurs at the very beginning of the test, and progresses into the bulk as slip increases.
lowtemperature dehydration of gypsum has been investigated for many years. The first analysis of the process is attributed to Flörke (1952), which indicated a twostep process CaSO 4·2H 2O →CaSO 4· 2O →γCaSO early study of the kinetics of dehydration of gypsum was performed, in vacuo, by Molony Ridge (1968) whose results, based on Xray powder diffraction, indicated ...
ABSTRACT: 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 temperature .
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 temperature and water vapor ...
Gypsum is moderately watersoluble (~– g/l at 25 °C)and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures.
DEHYDRATION OF GYPSUM. 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 90140 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 ...
The main dehydration of the calcium sulphate dehydrate part of synthetic gypsum occurs between 95 and 170°C (heating rate 5°C min −1) and seems to proceed via a process with an activation energy of 392 ± 100 kJ mol −1 for αvalues between 0 and
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 the gypsum
The temperature close to the sliding surface is remarkably stable at ∼100 °C during the dehydration reaction of gypsum. Microstructural and Xray diffraction investigations show that dehydration occurs at the very beginning of the test, and progresses into the bulk as slip increases. In the hottest parts of the sample, anhydrite crystal growth is observed. The halfthickness of the ...
Dehydration of gypsum in the water suspension J. KAZIMÍR Research institute of Civil Engineering, ... increase in temperature was 5°C/min. The DTA curve is shown in Fig. 2. Discussion It is evident from the DTA curve in Fig. 2 that the hydration of gypsum in water suspension under hydrothermal conditions proceeds according to the reaction (A) in accordance with papers [1—4]. The ...
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.
Influence of the gypsum dehydration temperature and alkali additives on the properties of anhydrite cement . By Leskeviciene V ., Sarlauskaite I., Nizeviciene D. and Kybartiene N. Cite . BibTex; Full citation; Abstract. While dehydrating gypsum with additives at the temperatures of 800°C and 900°C the influence of alkali additives on both the crystalline structure of anhydrite and properties ...
(1) In an atomsphere, the primary dehydration temperature of natual dihydrated gypsum used as a test sample is 133°C while its secondary dehydration temperature being 192°C.
and/or mass loss rate as a function of time and/or temperature (see Fig. 1 for an example). 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). ARRHENIUSRATE THERMAL DECOMPOSITION KINETICS
MEASUREMENT OF THERMAL PROPERTIES OF GYPSUM BOARD AT ELEVATED TEMPERATURES ... To accommodate the gas generation incurred from dehydration, the sample, reference and standard measurements utilized aluminum pans that were sealed except for a 50 μm pinhole in the lid. Measurements were performed with a heating rate of 20 oC /min under a constant .
Dehydrationinduced damage and deformation in gypsum and implications for subduction zone processes N. Brantut,1,2 A. Schubnel,1 E. C. David,3 E. Héripré,4 Y. Guéguen,1 and A. Dimanov4 Received 28 July 2011; revised 25 December 2011; accepted 19 January 2012; published 10 March 2012. [1] Experimental heating tests were performed on Volterra gypsum to study the .
Gypsum (CaSO 2 O) contains about % by mass chemically combined water, which is readily lost at an elevated temperature, this phenomenon is called dehydration, the dehydration reaction is endothermic, that is, an amount of energy is needed to break the crystal water (Yuand and Brouwers,2012; Ang and Wang,2009).
specimens of gypsum (Type X) with temperature. The results are represented in Fig. 6. As can be seen, between 100°C to 160°C about % of the initial mass is lost, which indicates the first dehydration reaction and the release of water of crystallization ( × 21% = %) as well as the evaporation of the free water (less than 3%). They also noticed a mass loss at 650°C which ...
The temperatures range from 200 o C at a position of 0 mm to 230 o C further into the material, which is signifficantly higher than the ffirst front. The temperatures measured on this front are comparable to the temperatures related to the second dehydration of gypsum.
ability data for dehydrating gypsum (R3). [3] Gypsum has repeatedly been used as an analog material principally for its abundance and its low dehydration temperature. Ballirano and Melis [2009] concluded that in air, at a water vapor partial pressure of ca. kPa, and in the temperature range of 348 to 403 K, gypsum (CaSO 4•2H 2O)
شركة Shanghai A&C © 2000-2020 حقوق النشر. خريطة الموقع(WhatsApp)
