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 …
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 …
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 …
In contrast, as the hydration process developed, the dihydrate gypsum crystals gradually encapsulated the fluorogypsum particles, hindering the dissolution and hydration of fluorogypsum from ...
The CAC used in this study was composed of 62% CA and 38% CA 2 while β-hemihydrate consisted of about 85.6% β-hemihydrate and 14.4% anhydrite. Dihydrate gypsum was provided by China National Pharmaceutical Industry Corporation ltd. The chemical compositions of CAC, β-hemihydrate, and dihydrate are listed in Table 1; their …
In this work, the dehydration pathways of gypsum and the rehydration mechanism of soluble anhydrite were mainly investigated by thermodynamic modeling …
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.
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].
Gypsum is one of the most widely-used building materials in the world. It is applied in several interior building uses, including in wallboard. Normally, calcium sulphate dihydrate (CaSO 4 •2H 2 O) is used as a raw material and a subhydrate such as hemihydrate (CaSO 4 •0.5H 2 O) or anhydrite (CaSO 4) is produced. The subhydrate is …
The apparent empirical activation energies (Ea) suggest that the transition from gypsum to hemihydrate is mainly controlled by nucleation and growth mechanism, while the transition from gypsum to γ-anhydrite is mostly followed by phase boundary …
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.
In this introduction, we'll explore the definition and composition of gypsum. Gips – Lubin, Poland Original image of the Gypsum crystal. You can see luminescence of the crystal in the next photo. Gypsum, Red River Floodway, Winnipeg, Manitoba, Canada. Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate (CaSO4·2H2O).
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.
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 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 …
At 2.5 GPa, gypsum starts to dehydrate around 428 K, by forming bassanite, CaSO 4 hemihydrate, which completely dehydrates to γ-anhydrite at 488 K.
The hydration rate of α-HH–DH increases considerably with the decrease of temperature and ... In a second step, the hemihydrate crystals are recrystd. to calcium sulfate dihydrate/gypsum. With the phosphate ore, impurities enter the prodn. processes. ... The same is true for the opposite process of anhydrite hydration to gypsum. …
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 ...
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the …
The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble...
The effects of different dosages of gypsum on the hydration and hardening properties of AMCSA, such as setting time, hydration rate, compressive strength and hydration products, were studied. The results show that the mineral content of ye'elimite, C 2 S, C 3 S and iron phase in the calcined AMCSA clinker are 48.5 wt.%, 32.6 wt.%, 11.7 …
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 ...
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.
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.
1 a) Represents the solubility curves of gypsum, anhydrite, ... (HH) and water to form calcium sulfate dihydrate (DH). Often gypsum can be used as a raw material to obtain hemihydrate. In this study, the obtained alpha hemihydrate consists of large crystals that have more or less lattice defects according to its production process while beta ...
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 …
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
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 …
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.
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 …
(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
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.
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.
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 …
