The effect of dehydration on the strength of gypsum was chosen for investigation partly because of the known occurrence of evaporites along many thrust faults but chiefly because this dehydration was considered to be typical of but more tractable o t laboratory investigation than the hydrous anhydrous reactions of many metamorphic rocks
The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid triggered earthquakes and due to the global use of plaster
The conversion of gypsum to anhydrite upon burial and heating is accompanied by about a 39% volume decrease a four fold increase in thermal conductivity and consumption of heat Accurate "back stripping" of an evaporite basin and tracking its thermal evolution requires a knowledge of the depth of the gypsum anhydrite transition This depth depends on
Gypsum calcium sulfate dihydrate is one of the most used inorganic binding materials in the world During calcination calcium sulfate subhydrates are formed and for technical reasons are mixed with water to form dihydrate again Therefore the dehydration process of gypsum and the rehydration of hemihydrate were investigated This dehydration
Mass losses vary between and % 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 slow
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
The governing equations are integrated numerically using the finite element method The obtained results show a significant correlation between gypsum dehydration and creation of fluid pathways The proposed model can be generalised to describe the effects of dehydration in other minerals carrying water in their crystal structures "
A systematic study was conducted to investigate the correlation between the dehydration of gypsum and the time and temperature of calcination as well as the grain size of the starting was found that the proposed formula may be considered as a real expression of the dehydration raction throughtout the major part of α However the initial and final stages of
The spectral behavior of gypsum dehydration in the visible to near infrared 350 2500 nm wavelength range was investigated by partially dehydrating the four main habits of gypsum alabaster satin spar selenite and massive to form bassanite Powdered samples of gypsum dehydrated at 100 115 °C and hand samples dehydrated at 115 130 °C coinciding with
The final products of the gypsum dehydration process are calcium sulphate anhydrite and water vapour; the latter is transferred through the pore network and is finally released through the surface In depth information regarding the solid reaction kinetics of gypsum dehydration can be found in dedicated publications [7] [8]
dehydration of β CaSO 4· 2 O 7−10 McAdie11 studied the gypsum dehydration process at °C under different water vapor partial pressures Their experimental results reveal that gypsum dehydration proceeds through only a single CaSO 4· 2H 2 O → γ CaSO 4 step when the ambient water vapor pressure
The process of gypsum dehydration the production and the transport of the water vapor inside the gypsum board have been analyzed The temperature field and the propagation of the dehydration front are analyzed for four different heat fluxes The heat absorption during the endothermic dehydration and the transport of water vapor released due
The dehydration of gypsum has been studied at negligible water vapour pressure by in situ infrared IR spectroscopy and by thermogravimetry to determine whether intermediate phases
The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid triggered earthquakes and due to the global use of plaster
The dehydration of gypsum CaSO 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 = and also to compare the mechanism of the dehydration process when measured by two
The opportunities afforded by this methodology are illustrated with the example of gypsum dehydration The remainder of this article is structured as follows First the basic principles of SAXS/WAXS are elucidated We proceed with a brief synopsis of the relevance and current knowledge of gypsum dehydration The experimental cell is introduced
Here we report the first solid like dehydration of gypsum to produce anhydrite at room temperature Specifically a 39 nm thick sulfuric acid film NSF was fabricated to extract water of crystallization from gypsum and simultaneously enable a phase transformation from gypsum to anhydrite via recrystallization Using density functional theory
The effects of pressure on the dehydration of gypsum materials were investigated up to 633 K and 25 GPa by using Raman spectroscopy and synchrotron X ray diffraction with an externally heated diamond anvil cell At GPa gypsum starts to dehydrate around 428 K by forming bassanite CaSO4 hemihydrate which completely dehydrates to γ
Keywords gypsum dehydration non isothermal kinetic thermal analysis Introduction The thermal behaviour of gypsum was frequently investigated due to its use as construc tion material The thermal decomposition of gypsum depends on the experimental condi tions Among them the heating rate and the atmosphere of the thermal treatment are par
Gypsum quantitative determination in cements may be done from their thermogravimetric analysis TG data which uses the mass of the water released from its gypsum dehydration during cement analysis to determinate its content stoichiometrically Depending on the operational conditions used to mill the gypsum with clinker its partial dehydration may
