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1 Introduction Calcium sulfate hemihydrate [CaCO 4 ∙ 2 O s ] can be found naturally in very dry climate regions in Egypt Australia Death valley and Kuwait as bassanite but in the presence of water or humid atmosphere it can convert to dehydrate [1 2] Therefore the production of hemihydrate industrially has been studied widely through the dehydration process of dihydrate
·The conversion of hemihydrate to dihydrate appears to be a simple process but the exact mechanism is still not clear According to LeChatelier as quoted by Desch 1 the hemihydrate being more soluble than the dihy drate produces a highly supersaturated solution with respect to gypsum as soon as it comes in contact to water
·The hydration of calcium sulphate hemihydrate CaSO4· leading to the crystallization of gypsum calcium sulphate dihydrate CaSO4·2H2O has been the subject of several investigations
·Hemihydrate phosphogypsum HPG formed by direct PG dehydration at temperatures around 180 ℃ is mainly composed of calcium sulfate hemihydrate CaSO 4 · H 2 O [8] [9] When hydrated from CaSO 4 · H 2 O to CaSO 4 · 2 H 2 O HPG exhibits obvious self hardening properties and can be used as a cementitious material HPG is a strong
Loading rate effect and energy dissipation mechanism of dihydrate gypsum under confining pressures LI Dong1 REN Gaofeng1 2 KE Bo1 2 ZHANG Congrui1 2#br# 1 School of Resources and Environmental Engineering Wuhan University of Technology Wuhan Hubei 430070 China；2 Key Laboratory of Mineral Resources Processing and
sulfate And the classical dihydrate technique is the main process to produce phosphoric acid in fertilizer industries Additionally anhydrite and hemihydrate gypsum are unstable with the extension of the accumulation time they slowly hydrate into dihydrate gypsum Therefore the main component of PG is calcium sulfate dihydrate CaSO
·facets of the hemihydrate In this work epitaxial growth of gypsum crystals on the hemihydrate grains was not observed 1 Introduction Gypsum plaster or stucco or plaster of Paris is the material made by the hydration of calcium sulfate hemihydrate CaSO 4 2 O resulting in the formation of calcium sulfate dihydrate or gypsum
·Contrary to the gypsum behavior at 90 °C in the experiments performed at elevated temperatures inside the autoclave the transformation process proceeded faster and a different transformation mechanism was the experiments performed at 150 °C more than 90% of gypsum transformed to hemihydrate after 2 h retention time but no anhydrite
·1 Introduction Gypsum CaSO 4 ·2H 2 O also known as dihydrate plaster is one of the earliest building materials elaborated by mankind and gypsum plasterboard is used widely as indoor building material because of its easy fabrication feature environmental friendliness fire resistance aesthetics low price etc The global production of gypsum in
·A promising alternative is the transformation of PG into α hemihydrate gypsum α HH through dehydration via heating in saturated steam or aqueous solutions [19 21] α HH is a valuable resource with applications in gypsum based self leveling mortars mold gypsum and fiber reinforced gypsum boards among others However the fibrous
·Gypsum is a calcium sulfate dihydrate CaSO 4 ·2H 2 O which occurs in different countries and its use is widespread all over the world It can be used in both natural and burnt forms Natural gypsum is used in agriculture and in Portland cement plants
·At its core gypsum is a naturally occurring mineral composed of calcium sulfate dihydrate CaSO 4 ·2H 2 O It forms primarily through the evaporation of seawater in large basins This chemical formula reveals that each molecule of gypsum contains one calcium atom one sulfur atom four oxygen atoms and two water molecules
·The three common phases of calcium sulfate are anhydrite CaSO 4 hemihydrate CaSO 4 ·1/2H 2 O and gypsum CaSO 4 ·2H 2 O Lu et al 2012; Rolnick 1954; Serafeimidis and Anagnostou 2015 In the Ca SO 4 H 2 O system gypsum and anhydrite are the two stable phases that can occur as geologic deposits and hemihydrate can occur as the
·It is still uncertain whether β hemihydrate and dihydrate gypsum influence the properties especially the phase conversion of white calcium aluminate cement CAC Therefore in this study we prepared CAC pastes/mortars containing β hemihydrate
·Lime pretreated phosphogypsum PG was calcined at 500 °C to produce anhydrate gypsum cement Due to the slow hydration of anhydrate gypsum additives K2SO4 and hemihydrate gypsum were selected to accelerate the hydration of anhydrate The hydration characteristics the resistance to hydrodynamic water and the mineralogical studies were
·The phase transformation of anhydrite to gypsum and hemihydrate can be identified with Bruker s X ray Diffraction D8 Discover instrument with Cu K radiation in the 10° to 60° range at a scanning rate of 1°/min and a scan rate of s/step Preparation of calcium sulfate dihydrate and calcium sulfate hemihydrate with controllable
·The calcium sulphate dihydrate gypsum CaSO 4 ·2H 2 O is the most common sulphate evaporite mineral on our planet evaporites play an important role in Earth s sulphur cycle and are
·stability and transformation of hemihydrate and gypsum calcium sulfate dihydrate and a new precipitation mechanism is revealed It is widely known that gypsum is the most stable phase at low temperatures and hemihydrate is metastable at all temperatures MacDonald 1953; Freyer and Voigt 2003 The reported typical transition temperature for
·Fig 6 SEM analysis of hemihydrate gypsum hemihydrate phosphogypsum and processed hemihydrate phosphogypsum obtained in the autoclave a c and microwave reactor d f
·α Calcium sulfate hemihydrate α HH is an important cementitious material which can be prepared by hydrothermal method from calcium sulfate dihydrate DH in an electrolyte solution Study of the conversion kinetics of DH to α HH in NaCl solution is helpful for understanding the control process In this paper X ray diffraction XRD patterns were applied
·This article focuses on the hydration and associated microstructure development of β hemihydrate to dihydrate gypsum The sound velocity is used to quantify the composition of the fresh slurry as Expand 5 PDF Save Preparation of α Calcium Sulfate Hemihydrate from Phosphogypsum in CaCl2 Solution under Atmospheric Pressure
·The phase change of hemihydrate to dihydrate gypsum at different pH was followed by XRD As shown in Fig 10 the typical diffraction peak 2 theta = ° PDF card No 41 0224 of hemihydrate was outstanding in early hydration time at all pH It was about 30 min that the peak of hemihydrate disappeared in the reference sample
