These aggregations were likely unhydrated anhydrite II gypsum, as inferred from the previous analysis and the 7-day hydration rate results of HPG280–40 %. …
Additives, such as the nucleating agent calcium sulphate dihydrate and the accelerator potassium sulphate, increased the rate of the hydration reaction by increasing seeding and the rate of ...
The effects of a 0, 0.2 wt%, 0.6 wt%, 1.0 wt%, 1.4 wt% and 1.8 wt% calcium hydroxide content on the microstructure and performance of super sulfated cement (SSC) were investigated.
AGRICULTURAL GYPSUM Dihydrate vs. Anhydrite The highest quality gypsum for agriculture is natural, a dihydrate, has beneficial trace minerals, and purity levels over 80%. Because Dihydrate is already hydrated with water molecules, as opposed to anhydrite, it dissolves faster in water. If dissolved in the irrigation water, dissolution speed has little …
Both of the two increased the solubility of fluorogypsum, supersaturation of dihydrate gypsum, the nucleation and growth rate of dihydrate gypsum, and inhibited the dissolution of dihydrate gypsum. The compactness of the hardened fluorogypsum was improved and the porosity was reduced.
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 …
In view of the poor hydration activity and difficult utilization of industrial by-product fluorogypsum, the effects of potassium carbonate (K 2 CO 3) and potassium bicarbonate (KHCO 3) on the hydration mechanisms of fluorogypsum (pH-adjusted to 7.3) were investigated and compared through hydration rate, hydration heat, solubility and …
The addition of Na2C2O4 increased the hydration rate of anhydrite, concentrated the hydration heat, shortened the hydration latency period, and accelerated the hydration process, accordingly ...
A hot and arid climate, fluctuating relative humidity, and an alkaline environment govern the geological evolution and the engineering behaviour of soil deposits in the Arabian Gulf coastal region (Azam 2000).Hydration of anhydrite (CaSO 4) and dehydration of gypsum (CaSO 4 ·2H 2 O) lead to alternating volume changes, thereby …
The transformation of gypsum into anhydrite at low temperatures under atmospheric pressure as well as at elevated temperatures (150 °C and 200 °C) inside an autoclave was investigated by monitoring changes in both the liquid and solid phases.The effect of temperature, sulfuric acid addition, anhydrite seeding and addition of sulfate …
The influence of sodium sulfate on the anhydrite hydration process and the crystal morphology of its dihydrate products were studied by the determination of the hydration rate, hydration temperature and the ion concentration in liquid phase, in combina-tion with the investigation of the microstructure of the hardened anhydrite paste. Moreover, the …
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.
The gypsum selected was the analytical reagent calcium sulfate dihydrate (Kermel Co., Ltd) with a purity exceeding 99%. ... The addition of gypsum increases the calcium concentration while decreasing the pH value of the interstitial solution. Increasing the gypsum addition from 2 wt% to 5 wt% makes a minor change in the concentration of …
The speed difference between conventionally ground dihydrate gypsum and a finely-ground anhydrite gypsum product can little if any difference at all. When anhydrite gypsum or dihydrate gypsum are spread in dry granular form, the different dissolving rates can actually be an advantage, if they are used intelligently.
The hydration properties of hemihydrate gypsum and anhydrite affect the quality of MPPG-based materials. Anhydrite has a much slower hydration rate and strength development than hemihydrate gypsum, and is commonly blended with cement, strong alkali or alkali sulfate to increase its hydration activity [15–17].
(2011) found that natural dihydrate gypsum will gradually lose crystal water at 220 C, and its physical and mechanical properties will obviously deterio-rate, but it will recrystallize into dihydrate gypsum after encountering water. Therefore, in the process of underground nuclear waste storage, the stability
Hydration of Anhydrite: Gypsum can also form through the hydration of anhydrite (CaSO₄). Anhydrite is a calcium sulfate mineral that lacks the water molecules present in gypsum. When exposed to water, anhydrite undergoes a hydration reaction, incorporating water molecules into its structure and transforming into gypsum.
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the …
The variation of the amount of gypsum formed and the specific surface area developed during the hydration of anhydrite with hydration time are given in Fig. 2.The amount of gypsum first increases slowly and then appears at a faster rate (Fig. 2a).The rate of formation of gypsum with hydration time is shown in Fig. 2b.The curve shows …
The hydration of an anhydrite of gypsum (CaSO4.II) in a ball mill was studied as a function of time and temperature. The amount of gypsum formed at different intervals of time was determined by ...
anhydrite into gypsum crystals. This transformation takes place via the solution phase, i.e. via anhydrite dissolution and gypsum precipitation. The chemical dissolution and precipitation reactions of gypsum and anhydrite are CaSO 4 2H 2O $ Ca2þ þ SO2 4 þ 2H 2O ð1Þ and CaSO 4 $ Ca2þ þ SO2 4; ð2Þ respectively.
As can be observed in Fig. 4 b, the leaching rate of red gypsum was increased with the increase of reaction temperature. When the reaction temperature was 60 and 70 °C, the dissolution rate of red gypsum rose quickly. When the reaction temperature increased to 80 and 85 °C, the dissolved rate of red gypsum rose slightly.
Gypsum growth combined with water uptake by the clay minerals is the main cause of the swelling process. Iden-tifying the conditions under which gypsum rather than anhydrite …
1. Introduction. Three crystalline phases are known in the CaSO 4 –H 2 O system, distinguishable by their degree of hydration: gypsum (CaSO 4 ·2H 2 O), bassanite (CaSO 4 ·0.5H 2 O), and anhydrite (CaSO 4).On Earth, calcium sulfate is mainly encountered as gypsum or anhydrite related with evaporitic environments (e.g. Buick …
Conversion of gypsum to anhydrite and back to gypsum is common due to the thermodynamic instability of these minerals within the physicochemical range of common geologic environments.
After adding cement, gypsum forms a saturated dihydrate gypsum solution after contacting with water, C 3 A in clinker will react violently with gypsum, which accelerates the hydration reaction. Since Ca (OH) 2 was slightly soluble in water, the pH of the solution increases rapidly, and the solubility of Ca (OH) 2 was less than that of …
Introduction. Various forms of calcium sulphate hydrate have been reviewed by Hand [1]. Depending on the temperature, calcium sulphate exists as anhydrite (CaSO 4), subhydrate ([2]; CaSO 4.xH 2 O, 0
The present paper addresses the gypsum hydration study with the theoretical and experimental method. The microstructure of gypsum changes during the hydration …
DOI: 10.1016/0008-8846(87)90044-5 Corpus ID: 96326600; Strength development and hydrate formation rate. Investigation on anhydrite binders @article{Hajjouji1987StrengthDA, title={Strength development and hydrate formation rate.
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble...