This dehydration step results in a negative solid volume change because of the decreasing molar volume of the denser product mineral: 74.53 cm 3 /mol for …
Calcium sulfate exists in three forms, namely dihydrate or gypsum (CaSO4·2H2O), anhydrite (CaSO4), and hemihydrate or bassanite (CaSO4·0.5H2O) depending on temperature, pressure, pH, and formation conditions. The formation of calcium sulfates occurs widely in nature and in many engineering settings. Herein, a …
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 …
WEBGypsum hydration: a theoretical and experimental study. Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building material because of its excellent …
The band 3600 cm −1 in hemihydrate is lowered to 3540 cm −1 in gypsum, and the band 3550 cm −1 in hemihydrate to 3400 cm −1 indicates the hydrogen bonding. Hemihydrate contains only one type of water molecule attached to the anion, SO 4 2−, by hydrogen bonding but gypsum contains two types of water molecules out of which one …
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 mechanism for …
Gypsum is a well-known mineral that is obtained from natural resources or from technological processes. Gypsum (calcium sulfate dihydrate) is burned to calcium …
2) Calcium sulfate hemihydrate was formed by the rehydration of gypsum dehydrated in vacuo. This hemihydrate showed the proton resonance spectrum corresponding to the signal of three spin …
1 Introduction . Calcium sulfate hemihydrate [CaCO 4 ∙ 0.5H 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 …
Sustainability of gypsum products as a construction material. N. Lushnikova, L. Dvorkin, in Sustainability of Construction Materials (Second Edition), 2016 β-Hemihydrate binder. β-Hemihydrate (also known as plaster of Paris) is the most commonly used gypsum binder in construction.It is produced in an apparatus connected to air. Different equipment is …
The calcium sulphate dihydrate gypsum (CaSO 4 ·2H 2 O) is the most common sulphate evaporite mineral on our planet 1.Sulphate evaporites play an …
The process of converting gypsum into alpha hemihydrate involves heating gypsum at a specific temperature to remove water molecules, resulting in a more concentrated and stable form of calcium sulfate. ... The main difference between calcium sulfate dihydrate and hemihydrate is their water content. Calcium sulfate dihydrate …
Gypsum (CaSO 4 ·2H 2 O, also as dihydrate) plaster is one of the earliest building materials elaborated by mankind, and gypsum plasterboard is used widely because of …
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. ... 21 52 100 1,3 0,5 0,4 DH natural crystal before storage in furnace point 2 28 21 51 100 1,3 0,6 0,4 DH ...
DOI: 10.1016/j.jcrysgro.2021.126360 Corpus ID: 241731164; Preparation of hemihydrate gypsum with controllable morphology in Glycerol-NaCl-Water solutions with maleic acid @article{Chen2021PreparationOH, title={Preparation of hemihydrate gypsum with controllable morphology in Glycerol-NaCl-Water solutions with maleic acid}, …
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 …
Spin-coated cellulose thin films have been used as model substrates to investigate the crystallization of calcium sulfate dihydrate (gypsum) under industrially relevant conditions using highly concentrated dispersions of calcium sulfate hemihydrate (bassanite).Pre-treatment of the films by regeneration in aqueous solutions of Ca 2+ promotes gypsum …
Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in the world. During calcination, calcium sulfate subhydrates are …
Ground gypsum in and by itself will not get hard when mixed with water. Gypsum has to be converted to a "hemihydrate" by first cooking it. The process of cooking gypsum is called "calcination." As previously mentioned, two molecules of water are part of the gypsum (dihydrate) crystal.
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 ...
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
The present paper investigates aspects of the crystallization of gypsum dihydrate during the artificial "aging" of calcined gypsum binder. ... in producing gypsum binders has received a great deal of attention in recent years owing to the instability of calcined gypsum properties [1]. Gypsum hemihydrate is a material used in the building ...
The synthesis of α-calcium sulfate hemihydrate (α-CSH) from flue gas desulfurization (FGD) gypsum is a good way to realize the comprehensive utilization of FGD gypsum. To obtain α-CSH with the satisfactory performances, a facile hydrothermal-aging pretreatment process for FGD gypsum raw materials was proposed, where FGD …
1. Introduction. Phosphogypsum (PG) is the main solid waste in the phosphorus chemical industry. In the wet process production of phosphoric acid, which is a mainstream process of the phosphorus chemical industry, 4.5–5.5 tons of PG is emitted for each ton of P 2 O 5 production [1], [2], [3].The PG is mainly composed of dihydrate …
The crystallization of gypsum (CaSO 4 ·2H 2 O) from a suspension of calcium sulphate hemihydrate is well-known as the setting of plaster. In this paper we present results concerning the crystallization of gypsum in the presence of different acids. ... The three different stages, observed in Fig. 1, correspond to the hemihydrate …
Using FGD gypsum as the raw material, whitening and large prismatic dihydrate gypsum can be obtained by dissolution‐crystallization and decoloring process with α‐hemihydrate gypsum whiskers prepared in MgSO4‐CaCl2‐H2O solution, which can transform into whitening short columnar α‐hemihydrate gypsum. The effects of aging …
Beta hemihydrate is formed when gypsum is heated up to around 100°C in a normal open kettle or rotary kiln. Alpha hemihydrate is formed in an autoclave above 100°C in a water (suspension autoclave) or in a steam autoclave. 5 - 7 This is possible as, above 100°C, hemihydrate becomes less soluble than dihydrate. The solubility of …
On comparing the solubility of calcium sulfate dihydrate and α-calcium sulfate hemihydrate in the formamide aqueous solution, it was found that the solubility of α-calcium sulfate hemihydrate is ...
Based on the molecular masses of above (1–3) chemical equations, the mass of gypsum hemihydrate generated from 10 g of gypsum dihydrate is calculated as 8.43 g.In similar ways, 7.91 g of gypsum anhydrate is generated, and 9.38 g of gypsum anhydrate is generated from 10 g of gypsum hemihydrate.
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 …
By definition, gypsum is a "mineral of crystalline structure composed of calcium (Ca), sulfate (SO4) combined with two molecules of water.". The chemical equation is: …
Calcium sulfate whiskers (CSWs) are columnar crystalline synthetic microfibers with excellent heat resistance, high elastic modulus, and good processability [20], [21].CSWs not only offer the advantages of a fiber and inorganic filler, but also have the same chemical composition as that of the gypsum matrix, which results in good …
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 …
This is because the main composition of PG is dihydrate gypsum (CaSO 4 ⋅2H 2 O), which can be dehydrated to form synthetic hemihydrate gypsum, ... Hemihydrate gypsum is found in two forms: α-hemihydrate gypsum (α-CaSO 4 ⋅0.5H 2 O) and β-hemihydrate gypsum (β-CaSO 4 ⋅0.5H 2 O) [8]. The α-hemihydrate gypsum …
In the first deceleration period, 0.5%–1% of β-hemihydrate or dihydrate slightly enhanced heat flow in the mortar pastes but contents higher than 1% resulted in a significant decrease. While 0.5% β-hemihydrate or dihydrate significantly extended the induction period, contents higher than 0.5% shortened it.
Calcium sulfate. J L RICCI, ... H ALEXANDER, in Bioceramics and their Clinical Applications, 2008. 14.2.1 Gypsum and its derivatives. CS cements begin as gypsum, or calcium sulfate dihydrate (CaSO 4 · 2H 2 O), which is either mined from the earth or produced through more controlled chemical processes (Randolph, 1971).Gypsum and …
The most prevalent sulfate mineral in the surrounding natural environment is calcium sulfate, which can be found as calcium sulfate dihydrate or gypsum (CaSO 4 ⋅2H 2 O), hemihydrate (CaSO 4 ⋅ ...
Therefore, the mechanism of the HH-CSW formation from gypsum should be such that the two Ca–O–H bonds broken in the gypsum structure release H 2 O and …