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Gypsum, scientifically known as Calcium Sulfate Dihydrate (CaSO 4 ·2H 2 O), is a naturally occurring mineral primarily formed from the evaporation of ancient bodies of sea water and lakes. It is a soft, transparent to translucent crystal that is typically white or colorless but can take on other hues when impurities are present.
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This work firstly shows that the observed crystallization inside of gypsum during dehydration is the formation of alpha-hemihydrate. Gypsum crystal at (a) 135 • C, and (b) 142 • C. Crystals ...
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Past studies on gypsum (or hemihydrate) crystallization in phosphoric acid solutions usually involve the study of crystal. 2015 American Chemical Society. Figure …
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The first way is that water breaks the surface of a dihydrate crystal when the pressure inside of the crystal increases because of the higher mobility of the water …
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Alabaster, a form of gypsum. Credit: Wikimedia Commons. Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate (CaSO4·2H2O). It is renowned for its wide use in the manufacturing ...
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The mineral gypsum comes in two different crystal forms: Calcium sulfate dihydrate (CaSO4 2H2O) is how the molecule is found in nature. Calcium sulfate hemihydrate (2 CaSo4 H2O) is created through a process of grinding and heating the calcium sulfate dihydrate molecules. This gypsum cycle diagram shows the two …
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Here, we study the crystallization of calcium sulfate within track-etched membranes and reveal that oriented gypsum forms in 200 nm diameter pores, bassanite in 25–100 nm pores and anhydrite in...
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A microscope study has been made of the development of crystals of calcium sulphate hemihydrate produced on, or in, sheets of the dihydrate in the form of selenite by calcining under controlled ...
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Of the precipitates, calcium sulfate – crystallizing mainly in the form of gypsum, calcium sulfate dihydrate (CaSO 4 ·2H 2 O) – is one of the most common representatives, which is present (or may form) in a large variety of natural and industrial processes, such as acidic wastewater treatment, phosphonic acid production, wet flue …
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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 …
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Gypsum: Composed of calcium sulfate dihydrate (CaSO4·2H2O), gypsum often forms as flat, translucent crystals or as a massive, fine-grained material. Anhydrite: This mineral is composed of calcium sulfate (CaSO4) and lacks water molecules compared to gypsum. Anhydrite can be found in various crystal forms, and its color may range …
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Effects of citric acid on crystalline habit and crystal morphology of gypsum dihydrate were analyzed in great detail. The retarding mechanism of citric acid was also discussed from the standpoint ...
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Chemical Hazards, gypsum is the dihydrate form of calcium sulfate. It is a naturally occurring mineral ... and satin spar (a silky and fibrous transparent crystal form)—and in various purities. It is usually found collectively with other mineral deposits such as quartz, halite, sulfur, pyrites, carbonates, and clays.
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Forms of Calcium Sulfate. Anhydrous calcium sulfate: Also known as anhydrite, it is the dehydrated form of calcium sulfate. It lacks water in its crystal structure, which differentiates it from gypsum. Dihydrate: This form, also referred to as gypsum, includes two water molecules in its structure. It is this hydrated form that is commonly used ...
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Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate (CaSO4·2H2O). It is commonly found in sedimentary rock formations and is often associated with other minerals such as anhydrite, halite, and sulfur. The name "gypsum" is derived from the Greek word …
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The hydration of calcium sulphate hemihydrate (CaSO 4 ·0.5H 2 O) leading to the crystallization of gypsum (calcium sulphate dihydrate – CaSO 4 ·2H 2 O) has been the subject of several investigations over a long period and a vast amount of data is widely distributed throughout in the literature. In this review article an overall picture of the …
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A microscope study has been made of the development of crystals of calcium sulphate hemihydrate produced on, or in, sheets of the dihydrate in the form of selenite by calcining under controlled conditions. The crystal forms were shown to be strongly dependent upon both temperature and ambient water vapour pressure. A …
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The transition temperature in aqueous solution for the gypsum-bassanite (dihydrate to hemihydrate) is in the 40°C-66°C range. Under normal climatic conditions, on monuments, the precipitation of calcium sulfate from aqueous solution will therefore be predominantly gypsum. Anhydrite forms when the temperature in solution is higher than 40°-60°C.
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Since gypsum is dissolved in the water over a period of time, only on rare occasions it can be found in the form of sand, and hence mostly it is found in the crystal form. The gypsum crystal of more than 3 metres or of almost 10 feet in length, and of 0.4 metres or almost about 1.5 feet in diameter, was found in the Braden mine of Chile.
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Selenite is a crystallized form of the mineral gypsum. It may also be known as desert rose, satin spar, or gypsum flower depending on certain characteristics. All four varieties, however, can be grouped together and referred to as selenite. This mineral is composed of calcium sulfate dihydrate. While the name might lea
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the final crystal form). The dihydrate process is the earliest developed industrial phosphoric acid production technology. Despite its drawbacks, which include relatively low acid ... filtration is carried out to separate acid from gypsum crystals. The overall productivity is closely correlated to the efficiency of the filtration step, which ...
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CaSO 4 will combine with water molecules to form dihydrate gypsum. At the same time, CaSO 4 will dissolve and ions will enter the water, ions in the water will crystallize, forming crystals and reaching a new equilibrium state. Anhydrous gypsum will increase in volume during the hydration process, and if constrained, it will produce a …
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Naturally occurring crystals are calcium sulfate dihydrate, CaSO 4 ·2H 2 O, known as gypsum, and anhydrous calcium sulfate, II-CaSO 4. When gypsum is heated, dehydration occurs to form hemihydrates, CaSO 4 ·1/2H 2 O, followed by anhydrite, III-CaSO 4. The hemihydrates and the anhydrite have two modifications, α and β, respectively.
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The crystals of gypsum form immediately, due to heterogeneous nucleation onto the hemihydrate particles. Later, secondary or even homogeneous nucleation may occur.
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A XRD pattern of β-calcium sulfate hemihydrate (Fig. 1, a), a SEM image (Fig. 1, b), and the dependence of the strength of gypsum on the temperature of its dehydration (Fig. 1, c) are shown in Fig. 1.The XRD pattern of β-calcium sulfate hemihydrate is fully assigned by the XRD pattern of hemihydrate as reported in …
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A review with 9 refs. Calcium sulfate, commonly known as natural gypsum, is found in nature in different forms, mainly as the dihydrate (CaSO4.2H2O) and anhydrite (CaSO4). They are products of partial or total evapn. of inland seas and lakes. Both the dihydrate and the anhydrite occur in nature in a variety of forms.
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Diagram 1 - Dehydration. The first process is the formation of hemihydrate or anhydrite from dihydrate. To obtain more information about this step, gypsum …
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The effects of phosphoric acid (H3PO4) in pressurized aqueous solution on the dehydration of CaSO4·2H2O to form α-hemihydrate gypsum (α-HH) phase and the regulation of crystal shape were studied in this paper in order to provide guidance for the low-cost and high-value utilization of phosphogypsum. The results showed that H3PO4 …
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H3PO4•1/2H2O on dihydrate gypsum surface largely degraded dry strength and porosity by transforming short-range electrostatic attraction among dihydrate gypsum crystals into hydrogen bonds.
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Alpha hemihydrate is a form of calcium sulfate hemihydrate with a dense crystal structure known for its rapid setting time and high setting expansion in gypsum products. Beta hemihydrate, on the other hand, is a form of calcium sulfate hemihydrate with a more open crystal structure, often used in specialized applications.
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