Calcium Sulfate Dihydrate Research Articles

Геополимерный бетон с использованием многотоннажных техногенных отходов

Introduction. Currently, in all countries, Portland cement is used as a binder in the production of concrete, and its global production accounts for 10 % of the total carbon dioxide emitted into the atmosphere. Therefore, Portland cement can be partially or fully replaced by new cement-free binders, made of large-tonnage technogenic waste with a cementing effect, for example, by finely ground blast furnace slag, fly ash generated by thermal power plants and ash formed during the combustion of rice hulls. Aqueous alkaline solutions (NaOH and Na2SiO3 or KOH and K2SiO3) should be used as activators of setting and hardening of such binders, and calcium sulfate dihydrate can be used to adjust the setting time. Concrete containing new cement-free binders is called geopolymer concrete. Materials and methods. In order to reduce mixing water consumption and maintain the required workability of the fine-grained concrete mixture, a polycarboxylate superplasticizer was introduced into its composition. All raw materials, except for the superplasticizer, were of the Vietnamese origin. The following research methods were used: the composition of the geopolymer concrete mixture was analyzed using the absolute volume method, the workability of the concrete mixture was determined according to ASTM C1611-18 и TCVN 3106:2007, compressive and tensile strength of the concrete, subjected to bending, were tested pursuant to GOST 10180-2012, and the average density of concrete was tested according to GOST 12730.1-78. Results. The co-authors have developed the composition of the geopolymer concrete containing the alkaline cement-free binder. As a result of the heat treatment of the 28-days-old concrete for 6 hours at 100 °C, its compressive strength reaches about 60 MPa; hence, it can be used in the hot and humid climate of Vietnam. Conclusions. This cement-free concrete, in addition to its high strength, has good water resistance and low water absorption. This concrete has economic benefits, and its production will help to protect the environment due to the lower consumption of natural resources and the applicability of large-tonnage technogenic waste.

A Novel One-Pot Synthesis and Characterization of Silk Fibroin/α-Calcium Sulfate Hemihydrate for Bone Regeneration

This study aims to fabricate silk fibroin/calcium sulfate (SF/CS) composites by one-pot synthesis for bone regeneration applications. The SF was harvested from degummed silkworm cocoons, dissolved in a solvent system comprising of calcium chloride:ethanol:water (1:2:8), and then mixed with a stoichiometric amount of sodium sulfate to prepare various SF/CS composites. The crystal pattern, glass transition temperature, and chemical composition of SF/CS samples were analyzed by XRD, DSC, and FTIR, respectively. These characterizations revealed the successful synthesis of pure calcium sulfate dihydrate (CSD) and calcium sulfate hemihydrate (CSH) when it was combined with SF. The thermal analysis through DSC indicated molecular-level interaction between the SF and CS. The FTIR deconvolution spectra demonstrated an increment in the β-sheet content by increasing CS content in the composites. The investigation into the morphology of the composites using SEM revealed the formation of plate-like dihydrate in the pure CS sample, while rod-like structures of α-CSH surrounded by SF in the composites were observed. The compressive strength of the hydrated 10 and 20% SF-incorporated CSH composites portrayed more than a twofold enhancement (statistically significant) in comparison to that of the pure CS samples. Reduced compressive strength was observed upon further increasing the SF content, possibly due to SF agglomeration that restricted its uniform distribution. Therefore, the one-pot synthesized SF/CS composites demonstrated suitable chemical, thermal, and morphological properties. However, additional biological analysis of its potential use as bone substitutes is required.

Detection of unexpected copper sulfate decay compounds on late Gothic mural paintings: Assessing the threat of environmental impact

A multianalytical study was proposed for the study of late-gothic wall paintings preserved inside the Romanic church of Saint Ementerio and Saint Celedonio of Goikolexea (Basque Country, Spain), erected in the 15th century and then renewed in the 17th. Raman spectroscopy coupled with energy-dispersive X-ray fluorescence was used in the in situ analysis in order to identify the nature of the original compounds and those used in the restoration works. The mortar composition and some original pigments (haematite, carbon black, cinnabar, goethite) were characterized. However, the identification of the original pictorial layer was difficult by the presence of chromatic retouching and mainly by the presence of the protective acrylic resin layer applied in modern times. Thus, the information obtained by the portable technique was used to select the sampling areas to perform laboratory Raman measurements especially in the green areas in which different shades appeared, because no antique green pigments were identified during the in situ analyses. Although the church was restored a couple of decades ago, the presence of salt crystallization was noted during the field campaign. Thus, some samples of salt efflorescences were collected to complete the analyses in the laboratory. Sulphate (calcium sulphate dihydrate CaSO4·2H2O and thenardite Na2SO4·10H2O) and nitrate compounds, (nitratine NaNO3 and nitromagnesite Mg(NO3)2·6H2O) were identified. Even, an extensive biodeterioration phenomenon was detected on the samples in the form of calcium oxalates whewellite and weddellite. All these decay products are strictly related to the characteristics of the surrounding natural environment and they represent the main factors that endanger the integrity of the masonry and consequently the substrate of the wall paintings. In particular, the presence of humidity of the walls and of the organic matter around the church seems to be the main factors of the formation of decay products. In addition, the hydrated sulphate copper connellite, generally identified as a product of corrosion of archaeological pieces in copper or bronze, was identified on the wall painting samples as a degradation product of malachite, the only original green pigment found in the mural paintings.

3D-printed composite, calcium silicate ceramic doped with CaSO4·2H2O: Degradation performance and biocompatibility

Calcium silicate is a common implant material with excellent mechanical strength and good biological activity. In recent years, the addition of strengthening materials to calcium silicate has been proven to promote bone tissue regeneration, but its degradation properties require further improvements. In this paper, calcium silicate was used as the matrix, and 10 wt% hydroxyapatite and 10 wt% strontium phosphate were added to im prove the biological activity of the scaffold. The effect of adding different amounts of calcium sulfate dihydrate (CaSO4·2H2O) on the degradation of the scaffold was explored. A porous ceramic scaffold was prepared by digital light processing (DLP) technology, and its performance was evaluated. Cell experiments showed that the addition of calcium sulfate improved cell proliferation and differentiation. Simulated body fluid (SBF) immersion tests showed that small amounts of apatite deposits appeared on the fourth day, larger deposits appeared on the 14th day, and degradation occurred on the surface after 28 days of immersion. Mechanical tests showed that the addition of 5 wt% CaSO4·2H2O improved the compressibility of the composite. After soaking in SBF for 14 days, it retained its compressive strength (11.8 MPa), which meets the requirements of cancellous bone, demonstrating its potential application value for bone repair.

Physical and Geotechnical Perspectives of Gypsum on Lime Stabilized Expansive Soil: A Critical Appraisal

The gypsum is the source of sulphate commonly found in the soils throughout the world. The expansive soils are considered as problematic soils as they exhibit uncertain swelling and shrinkage in presence of moisture. The expansive soils are treated with different stabilizers to suppress the swelling behaviour. Lime is most effective stabilizer used to stabilize the expansive soil. Researchers reported that expansive soil when treated with lime encounters the gypsum it regenerates the swelling. This regenerated expansion of lime treated soil in presence of sulphate may have alarming signs for sulphate bearing soils. The presence of sulphate alters the mineralogical behaviour of expansive clay. The stabilization additive used f or such soils needs more attention. A comprehensive approach towards proper understanding of the effects of gypsum on lime stabilized soil is required in order to understand the future threats of expansive soils. In this paper, an attempt has been made to present a comprehensive review on the effects of (Gypsum) calcium sulphate dihydrate on the physical properties of untreated and lime treated expansive soil have.

ОСОБЛИВОСТІ СТРУКТУРОУТВОРЕННЯ КОМПОЗИЦІЙНИХ ГІПСОВАПНЯНИХ В’ЯЖУЧИХ ДЛЯ НЕАВТОКЛАВНОГО ГАЗОБЕТОНУ

The crystalline phases of hydration products of the gypsum-lime binder were identified using XRD analysis. The physical and chemical regularities of the structure formation processes in the model system “gypsum – quicklime – metakaolin – amorphous silica – water – borax” were established. The influence of the quicklime type and gypsum binder brand on the morphology and the size of the calcium sulfate dihydrate crystals were investigated. The relationship between processesof the structure formation of composite gypsum-lime binders under normal hardeningconditions and the physical and mechanical characteristics of the stone was established.

High toughness resorbable brushite-gypsum fiber-reinforced cements

The ideal bone substitute material should be mechanically strong, biocompatible with a resorption rate matching the rate of new bone formation. Brushite (dicalcium phosphate dihydrate) cement is a promising bone substitute material but with limited resorbability and mechanical properties. To improve the resorbability and mechanical performance of brushite cements, we incorporated gypsum (calcium sulfate dihydrate) and diazonium-treated polyglactin fibers which are well-known for their biocompatibility and bioresorbability. Here we show that by combining brushite and gypsum, we were able to fabricate biocompatible composite cements with high fracture toughness (0.47 MPa·m1/2) and a resorption rate that matched the rate of new bone formation. Adding functionalized polyglactin fibers to this composite cement further improved the fracture toughness up to 1.00 MPa·m1/2. XPS and SEM revealed that the improvement in fracture toughness is due to the strong interfacial bonding between the functionalized fibers and the cement matrix.This study shows that adding gypsum and functionalized polyglactin fibers to brushite cements results in composite biomaterials that combine high fracture toughness, resorbability, and biocompatibility, and have great potential for bone regeneration.

High-quality gypsum binders based on synthetic calcium sulfate dihydrate produced from industrial waste

Synthetic calcium sulfate dihydrate, obtained from sulfuric acid waste of chemical plants and waste of the fine fraction of limestone, is a potential source of gypsum-containing raw materials. We investigated the processing of synthetic calcium sulfate dihydrate from sulfuric acid waste to gypsum, high-strength gypsum binder, and anhydrite. The effects of technological parameters on the strength indicators of binders were studied. It was found that the obtained samples of binders (based on synthetic gypsum) meet all standards and even exceed the performance of binders obtained from natural gypsum stone. Our studies show that synthetic gypsum is a promising gypsum-containing raw material for the production of gypsum binders and can be a promising alternative to natural gypsum stone.

Clean production of sustainable backfill material from waste gold tailings and slag

Gold tailings (GT) and slag disposed of in the landfill affect the environment. This study investigated the green process for the utilization of non-radioactive gold tailings and granulated blast furnace slag (GBFS) to synthesize a green and sustainable backfill material. The following mix design ratios of GBFS:GT were investigated; 100, 10:90, 20:80,30:70, 40:60, 50:50. Maximum dry density, optimum moisture content, and strength were studied. The elemental composition, mineralogy, micrography, and evolution of particle size distribution were studied for raw materials and developed stabilized specimens. The mix design containing 20% GBFS and 80% GT yielded the optimum strength of 0.9 MPa. Calcium magnesium carbonate and calcium sulfate dihydrate were some of the products formed. There was a significant change in the microstructure of the GBFS blended GT with the increment in GBFS content. From the evolution of the volume distribution, the generation of finer particles was evident with the stabilization of GT. There was a significant modal size change with the mix designs investigated. Particle size distribution (PSD) proved to have an impact on the strength development of GBFS modified GT. The specimen developed met the requirement for backfill bearing material, for the strength of 0.3–0.7 MPa for conventional engineering design and the strength below 1 MPa for freestanding backfilling material. The evaluation of stabilized material for environmental impact showed that the concentrations of the contaminants were within the stipulated standards. This study proved that readily available wastes were beneficiated to produce value-added construction material and solve environmental pollution challenges.

Tetracalcium Phosphate/Monetite/Calcium Sulfate Hemihdrate Biocement Powder Mixtures Prepared by the One-Step Synthesis for Preparation of Nanocrystalline Hydroxyapatite Biocement-Properties and In Vitro Evaluation.

A modified one-step process was used to prepare tetracalcium phosphate/monetite/calcium sulfate hemihydrate powder cement mixtures (CAS). The procedure allowed the formation of monetite and calcium sulfate hemihydrate (CSH) in the form of nanoparticles. It was hypothesized that the presence of nanoCSH in small amounts enhances the in vitro bioactivity of CAS cement in relation to osteogenic gene markers in mesenchymal stem cells (MSCs). The CAS powder mixtures with 15 and 5 wt.% CSH were prepared by milling powder tetracalcium phosphate in an ethanolic solution of both orthophosphoric and sulfuric acids. The CAS cements had short setting times (around 5 min). The fast setting of the cement samples after the addition of the liquid component (water solution of NaH2PO4) was due to the partial formation of calcium sulfate dihydrate and hydroxyapatite before soaking in SBF with a small change in the original phase composition in cement powder samples after milling. Nanocrystalline hydroxyapatite biocement was produced by soaking of cement samples after setting in simulated body fluid (SBF). The fast release of calcium ions from CAS5 cement, as well as a small rise in the pH of SBF during soaking, were demonstrated. After soaking in SBF for 7 days, the final product of the cement transformation was nanocrystalline hydroxyapatite. The compressive strength of the cement samples (up to 30 MPa) after soaking in simulated body fluid (SBF) was comparable to that of bone. Real time polymerase chain reaction (RT-PCR) analysis revealed statistically significant higher gene expressions of alkaline phosphatase (ALP), osteonectin (ON) and osteopontin (OP) in cells cultured for 14 days in CAS5 extract compared to CSH-free cement. The addition of a small amount of nanoCSH (5 wt.%) to the tetracalcium phosphate (TTCP)/monetite cement mixture significantly promoted the over expression of osteogenic markers in MSCs. The prepared CAS powder mixture with its enhanced bioactivity can be used for bone defect treatment and has good potential for bone healing.

Low‐energy technology for producing anhydrite in the CaCO3–H2SO4–H2O system derived from industrial wastes

AbstractBACKGROUNDA high‐quality anhydrite binder could be produced due to the exergy of sulfuric acid in the CaCO3–H2SO4–H2O system derived from industrial wastes. Waste of sulfuric acid derived from the production of heat‐resistant fibers and wastes of limestone that was formed on the metallurgical enterprise were used for the synthesis of anhydrite. Such a product is safe from an environmental point of view and has many advantages, both operational and economic, over standard gypsum binders.RESULTSThe optimal technological parameters have been established and a technological scheme for producing anhydrite excluding the stage of calcium sulfate dihydrate formation has been proposed. Anhydrite production in the CaCO3–H2SO4–H2O system, due to the exergy of sulfuric acid, is a promising technology to replace the traditional thermal technology for producing anhydrite. This technology can reduce fuel costs because the required synthesis temperature is 95–105 °С, instead of 800–1000 °С in the traditional one, and this significantly reduces the cost of manufactured products.CONCLUSIONThe maximum yield of synthetic anhydrite was provided by a limestone suspension taken in a stoichiometric amount. This neutralizing agent makes it possible to obtain particles of a prismatic shape, the size of which is generally more than 20 μm. © 2021 Society of Chemical Industry (SCI).

Fabrication of highly interconnected porous carbonate apatite blocks based on the setting reaction of calcium sulfate hemihydrate granules

Interconnected porous carbonate apatite (CO3Ap) blocks that emulate cancellous bone have potential as an alternative to autografts. The present study aimed to evaluate the feasibility of fabricating a block via a stepwise compositional transformation to CO3Ap through dissolution-precipitation reactions of an interconnected porous calcium sulfate dihydrate (CSD) block, which was obtained by the setting reaction of calcium sulfate hemihydrate (CSH) granules. Exposure of the CSH granules to water resulted in a setting reaction. However, the gaps between the granules were clogged, preventing the fabrication of interconnected porous structures. Removing the water in the gaps using filter paper was beneficial in avoiding gap clogging and in fabricating interconnected porous CSD blocks. Although the CSD blocks transformed into CaCO3 blocks, which maintained the interconnected porous structure through a dissolution-precipitation reaction in a Na2CO3 solution, their mechanical strength was quite low (diametral tensile strength: DTS = 75 kPa). In contrast, a CaCO3 block with a much greater mechanical strength (DTS = 0.98 MPa) was fabricated when a calcium sulfate anhydrous block made via the heat treatment of the CSD block was used as a precursor. The CaCO3 block transformed into a CO3Ap block (DTS = 2.1 MPa), maintaining the interconnected porous structure through a dissolution-precipitation reaction when immersed in a Na2HPO4 solution. The CO3Ap block had macropores initiated by the gaps between the granules and micropores created by the setting reaction of CSH granules and the dissolution-precipitation reactions to form CO3Ap. The results obtained in the present study demonstrate that this method is useful for fabricating interconnected porous CO3Ap blocks.

Development of a novel three‐dimensional printing technology for the application of “raised” surface features

AbstractA simple procedure to ink‐jet print raised images using two water‐soluble inorganic inks is reported and it has the potential to be utilised in domestic and commercial environments. The advantages of such a procedure lies in the ability to print moulded objects, Braille type and to engineer special gonio‐specific effects that may have value in the security printing area. The study focuses on printing gypsum through the ready precipitation of calcium sulphate dihydrate by co‐jetting calcium chloride and ammonium sulphate solutions. The results in this preliminary study are encouraging and offer a potential method for durable surface structuring of material surfaces with haptic and visual effects for both the blind and the sighted.

Incorporation of Calcium Sulfate Dihydrate into a Mesoporous Calcium Silicate/Poly-ε-Caprolactone Scaffold to Regulate the Release of Bone Morphogenetic Protein-2 and Accelerate Bone Regeneration.

Tissue engineering and scaffolds play an important role in tissue regeneration by supporting cell adhesion, proliferation, and differentiation. The design of a scaffold is critical in determining its feasibility, and it is critical to note that each tissue is unique in terms of its morphology and composition. However, calcium-silicate-based scaffolds are undegradable, which severely limits their application in bone regeneration. In this study, we developed a biodegradable mesoporous calcium silicate (MS)/calcium sulfate (CS)/poly-ε-caprolactone (PCL) composite and fabricated a composite scaffold with 3D printing technologies. In addition, we were able to load bone morphogenetic protein-2 (BMP-2) into MS powder via a one-step immersion procedure. The results demonstrated that the MS/CS scaffold gradually degraded within 3 months. More importantly, the scaffold exhibited a gradual release of BMP-2 throughout the test period. The adhesion and proliferation of human dental pulp stem cells on the MS/CS/BMP-2 (MS/CS/B) scaffold were significantly greater than that on the MS/CS scaffold. It was also found that cells cultured on the MS/CS/B scaffold had significantly higher levels of alkaline phosphatase activity and angiogenic-related protein expression. The MS/CS/B scaffold promoted the growth of new blood vessels and bone regeneration within 4 weeks of implantation in rabbits with induced critical-sized femoral defects. Therefore, it is hypothesized that the 3D-printed MS/CS/B scaffold can act both as a conventional BMP-2 delivery system and as an ideal osteoinductive biomaterial for bone regeneration.

Model development for estimating calcium sulfate dihydrate, hemihydrate, and anhydrite solubilities in multicomponent acid and salt containing aqueous solutions over wide temperature ranges

Thermodynamic solubility of calcium sulfate in multicomponent electrolyte aqueous solutions is of significant importance in many disciplines in science and engineering. A knowledge of environmental chemistry and aqueous solubility of calcium sulfate and several of its hydrates; anhydrite (CaSO4), hemihydrate (CaSO4.0.5H2O), and dihydrate (CaSO4.2H2O); in acid and salt-containing media is of huge practical and theoretical importance. In this study, a solubility calculation model was developed based on coupling of Least Squares Support Vector Machine and Coupled Simulated Annealing (CSA-LSSVM) to model the solubility of various forms of calcium sulfate in aqueous solutions over wide temperature ranges. Comparing the model results to 3079 experimental data gathered from the literature yields a correlation coefficient of 0.9897 and RMSE of 0.0068. The model is able to present accurate solubility results for calcium sulfate dihydrate (CaSO4.2H2O) in aqueous solutions containing H2SO4, ZnSO4, CuSO4, NiSO4, MnSO4, H3PO4, NaCl, CaCl2, MgCl2, KCl, FeCl2, Na2SO4, HNO3, Ca(NO3)2, HCl, AlCl3, Ca(HCO3)2, NaNO3, LiNO3, Li2SO4, MgSO4, Al2(SO4)3, NaClO4, NaOH, KOH at temperatures up to 100 °C, calcium sulfate hemihydrate (CaSO4.0.5H2O) in solutions containing NaCl, CaCl2, MgCl2, KCl, FeCl2, HCl at temperatures up to 125 °C, and calcium sulfate anhydrite (CaSO4) in solutions containing H2SO4, NaCl, CaCl2, MgCl2, Na2SO4, HNO3, HCl, NaNO3, LiNO3, NiSO4, MgSO4, Al2(SO4)3, Mg(NO3)2 at temperatures up to 350 °C. Comparison of the CSA-LSSVM model results to those of Pitzer ion interaction model as well as BR-ANN model in binary, ternary, and multicomponent mixtures reveals the superiority of the CSA-LSSVM model developed in this study in all cases.

The effect of calcium phosphate and silk fibroin nanofiber tuning on properties of calcium sulfate bone cements

Calcium sulfate (CS) bone cements have been used as bone substitutes for a long time, but their clinical use is currently limited due to their rapid degradation rate and brittleness. This work aimed to study the effect of α-tricalcium phosphate (α-TCP) and silk fibroin nanofibers (SFF) on CS bone cements. The bone cements were prepared from α-CS hemihydrate (α-CSH), calcium sulfate dihydrate (CSD; as a setting accelerator) and varying α-TCP contents (0%, 5%, 10%, 15%, 20% and 25%), with SFF solution or deionized water as the solidification solution at the same liquid/solid ratio. Scanning electron microscopy, particle size distribution, x-ray diffraction and Fourier transform infrared spectroscopy were used to measure the composition and characterize the properties of the materials. The compressive strength, setting time and weight loss rate of samples were also tested. Cytotoxicity was evaluated by a Cell Counting Kit-8 assay. The results suggest that the tuning of α-TCP and SFF has an important role in determining the compressive strength and degradation rate of CS bone cements, and the properties could be changed by varying the content of α-TCP. Moreover, cell experiments showed no toxicity of the samples towards MC3T3 cells. Thus, the materials prepared from α-CSH, CSD, α-TCP and SFF in this work could provide the basis for research into CS-based bone repair materials.

Crystallization Kinetics and Mechanisms of Calcium Sulfate Dihydrate: Experimental Investigation and Theoretical Analysis

In this work, four influencing factors including temperature, stirring speed, pH value, and polymer concentration were chosen to investigate crystallization kinetics of calcium sulfate dihydrate (C...

Polycarboxylate superplasticizer modified by phosphate ester in side chain and its basic properties in gypsum plaster

In this study, 2-hydroxylethyl methacrylate phosphate was introduced as side chain to modify polycarboxylate superplasticizers (PCEs), and its performance in gypsum paste was systematically investigated. The results show that the introduction of phosphate ester can increase the water reduction ratio from 24% to 58%, and also extend the final setting time, showing excellent dispersing ability and retarding effect. The excellent dispersion was due to the stronger adsorption capacity of phosphate ester leading to high adsorption amount and high absolute value of zeta potential. In addition, the negative effect of the high adsorption amount on the crystal precipitation of calcium sulfate dihydrate is considered to be an important reason for retarding effect.

Selective Crystal Growth Regulation by Chiral α-Hydroxycarboxylic Acids Improves the Strength and Toughness of Calcium Sulfate Cements.

Natural biominerals, such as bones and teeth, use acidic matrix biomolecules to control growth, morphology, and organization of the brittle hydroxyapatite crystals. This interplay provides biominerals with outstanding mechanical properties. Recently, we reported that the l-enantiomer of chiral tartaric acid has a potent regulatory effect on the crystal structure and mechanical performance of brushite cement, a mineral with a monoclinic crystal system. We hypothesized that this strategy could be applied using various chiral α-hydroxycarboxylic acids to enhance the mechanical performance of calcium sulfate dihydrate cements, another mineral belonging to the monoclinic crystal system. Calcium sulfate cements are widely used in dentistry, medicine, and construction, but these cements have low mechanical properties. In this work, we first determined the impact of different chiral α-hydroxycarboxylic acids on the properties of calcium sulfate cements. After that, we focused on identifying the regulation effect of chiral tartaric acid on gypsum crystals precipitated in a supersaturated solution. Here, we show that the selective effect of α-hydroxycarboxylic acid l-enantiomers on calcium sulfate crystals improved the mechanical performance of gypsum cements, while d-enantiomer had a weak impact. Compare to the calcium sulfate cements prepared without additives, the presence of l-enantiomer enhanced the compressive strength and the fracture toughness of gypsum cements by 40 and 70%, respectively. Thus, these results prove the generalizability of this approach and help us to fabricate high-strength cements.

Kinetics and Mechanism of the Dehydration of Calcium Sulfate Dihydrate: A Comprehensive Approach for Studying the Dehydration of Ionic Hydrates under Controlled Temperature and Water Vapor Pressure

We studied the kinetics and mechanism of the dehydration reaction of calcium sulfate dihydrate to hemihydrate under controlled temperature and water vapor partial pressure. From kinetic and reactio...