Crystallization Of Calcium Sulfate Dihydrate Research Articles

Improvement of Plasterboard Properties by the Control of Polymethylhydrosiloxane Dosage, Stirring Time, and Drying Temperature Applied to the Calcium Sulfate Hemihydrate and Water Mixture.

Plasterboard is an important building material in the construction industry because it allows for quick installation of walls, partitions, and ceilings. Although a common material, knowledge about its performance related to modern polymers and fabrication conditions is still lacking. The present work analyzes how some manufacturing factors applied during the plaster board fabrication impact on some plasterboard properties, including water absorption, flexural strength, and thermal conductivity. The manufacturing variables evaluated are the dose (D) of polymethylhydrosiloxane (PMHS), the agitation time of the mixture (H), and the drying temperature of the plaster boards after setting (T). The results suggest that factors D, H, and T induce changes in the porosity and the morphological structure of the calcium sulfate dihydrate crystals formed. Performance is evaluated at two levels of each factor following a statistical method of factorial experimental design centered on a cube. Morphological changes in the crystals of the resulting boards were evaluated with scanning electron microscopy (SEM) and the IMAGEJ image analysis program. Porosity changes were evaluated with X-ray microcomputed tomography (XMT) and 3D image analysis tools. The length-to-width ratio of the crystals decreases as it goes from low PMHS dosage to high dosage, favoring a better compaction of the plasterboard under the right stirring time and drying temperature. In contrast, the porosity generated by the incorporation of PMHS increases when going from low-level to high-level conditions and affects the maximum size of the pores being generated, with a maximum value achieved at 0.6% dosage, 40 s, and 140 °C conditions. The presence of an optimal PMHS dosage value that is approximately 0.6-1.0% is evidenced. In fact, when comparing trails without and with PMHS addition, a 10% decrease in thermal conductivity is achieved at high H (60 s) and high T (150 °C) level conditions. Water absorption decreases by more than 90% when PMHS is added, mainly due to the hydrophobic action of the PMHS. Minimum water absorption levels can be obtained at high drying temperatures. Finally, the resistance to flexion is not affected by the addition of PMHS because apparently there are two opposing forces acting: on one hand is the decrease in the length-width ratio giving more compactness, and on the other hand is the generation of pores. The maximum resistance to flexion was found around a dosage of 0.6% PMHS. In conclusion, the results suggest that the addition of PMHS, the correct agitation time of the mixture, and the drying temperature reduce the water absorption and the thermal conductivity of the gypsum boards, with no significant changes in the flexural resistance.

Mechanical and Thermal Properties of Thermally Conductive Enhanced Paraffin/Gypsum Composites

The low thermal conductivity of gypsum-based composites containing phase change materials (PCMs) has limited their application in construction materials. In this study, the mechanical and thermal properties and microstructures of paraffin (PA)/gypsum composites containing iron powder, copper powder, and expanded graphite were characterized by a universal testing machine, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The PA/gypsum composites had optimal mechanical properties when the PA content was 20 wt.%. The compressive and flexural strengths were 9.46 MPa and 3.57 MPa, respectively. When the copper powder content increased, the densities and porosities of the PA/gypsum composites containing the copper powder did not largely change. The average density and porosity of the composites were 1.17 g/cm3 and 46%, respectively. The compressive and flexural strengths of the PA/gypsum composite containing 8 wt.% copper powder were optimal. A phase change temperature of 48.8 °C was obtained when 8 wt.% copper powder was added to the PA/gypsum composite. The thermal conductivities of the PA/gypsum composites were lower than those of PA/gypsum composites with 8 wt.% iron powder, 8 wt.% copper powder, or 8 wt.% expanded graphite. Parts of coarse calcium sulfate dihydrate crystals were present at the interfaces between the gypsum and PA, which indicated that the growth of calcium sulfate dihydrate crystals was affected by the copper powder.

Experimental Study of Salicylic Acid as a Calcium Sulfate Dihydrate Scale Inhibitor, Analyzed from Surface Properties and Crystal Growth.

Static and dynamic experiments were carried out to study the antiscale performance of salicylic acid (SA) to calcium sulfate dihydrate (CSD) scale. The CSD scale formed in the reuse of processing of wastewater of phosphorite flotation. The scale surface physicochemical properties have been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ζ potential, and contact angle measurements. The antiscale mechanisms of SA to CSD were studied from surface properties and crystal growth. The results showed that the scale inhibition efficiency of SA to CSD reached 98.9% (6 mg/L) under static conditions. Under dynamic conditions, the faster the fluid velocity, the less CSD formed. The order of scaling capability on different material surfaces was 20#CS > 304SS > PC > PE. The growth of CSD was inhibited by SA resulting in the surface becoming porous. The deprotonated SA could easily interact with the Ca2+ to make the CSD surface potential negative. The wettability properties of the CSD are greatly improved when the contact angle is reduced. The surface tension values of CSD without and with 6 mg/L SA are 19.06 and 240.69 mN/m2, respectively. SA as a scale inhibitor can significantly inhibit crystallization of CSD.

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.

Nucleation and crystal growth of calcium sulfate dihydrate from aqueous solutions: Speciation of solution components, kinetics of growth, and interfacial tension

Experimental results of an investigation of crystallization of calcium sulfate dihydrate by potentiometry, conductometry, redoxmetry and photometry are presented and discussed. The chemical species participating in the crystallization process are determined and the dominant role of CaSO40 complexes is demonstrated. It is found that: (1) spontaneous homogeneous crystallization kinetics follows linear dependence on absolute supersaturation, which is characteristic of diffusion-controlled crystals growth, (2) the induction period for nucleation the interfacial tension of the nuclei 7.04 mJ/m2 and 9.69 mJ/m2, and (3) the abrupt change in the interfacial tension occurs when initial concentrations (Ca2+)0 ≈ (SO42−)0 and is associated with the recharging of the micelle that can aggregate to form a transitional amorphous phase.

Investigating the Effectiveness of Phosphonate Additives in Hindering the Calcium Sulfate Dihydrate Scale Formation

The effects of 20 ppm 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP), amino trimethylene phosphonic acid (ATMP), polyamino poly(ether methylene phosphonic acid) (PAPEMP), diethylene triamine penta (methylene phosphonic acid) (DTPMPA), and bis(hexamethylene triamine penta (methylene phosphonic acid)) (BHMTPMPA) on the room-temperature crystallization of calcium sulfate dihydrate (gypsum) were investigated by in situ UV–vis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), and scanning electron microscopy (SEM) techniques. A comparison between additive-containing and additive-free experiments showed that BHMTPMPA was the most efficient antiscalant by completely inhibiting crystallization. Due to the chain length of the BHMTPMPA molecule, the crystallization kinetics decreased to a larger extent than DTPMPA. The increase in pH of the solution from ∼4 to ∼7 positively enhanced the efficiency of the phosphonates in inhibiting crystallization. Our results revealed that partially deprotonated phosphonate additives were strongly associated with gypsum crystals and/or potentially taken up into the crystal matrix, resulting in a sudden and sharp increase in turbidity plots. Furthermore, phosphonate additives altered the thin, twinned gypsum crystals into thick needles.

Influence of the polymeric additives on the process of calcium sulfatedihydrate crystallization

The research is aimed to the clarification of the calcium sulfatedihydrate crystals growth and formation of in the presence of the different polymers based functional additives. The calcium sulfatedihydrate crystals have been synthesized both in the pure form and with the additives. The additives have included a super plasticizer based on a sulfonated melamine-formaldehyde resin (SMF), a methylcellulose (MC) and a redispersible polymer powder based on vinyl acetate, ethylene and vinyl chloride copolymers (VAEVC). The X-ray analysis and the electron microscopy have been applied to identify an influence of the polymer additives over the configuration and size of the calcium sulphate dihydrate crystals. The structural and strength characteristics of the gypsum materials have been also investigated.

Structurally controlled synthesis of calcium sulphate dihydrate from industrial wastes of spent sulphuric acid and limestone

Abstract All types of gypsum binders are obtained mainly from the natural gypsum and man-made products. As a sustainable analogue of these materials, synthetic gypsum as a product of spent dilute sulphuric acid and calcium carbonate was proposed. We investigated the effect of various technological parameters on the production of calcium sulphate dihydrate particles with a given morphology. The sizes of calcium sulphate dihydrate crystals with optimal values of technological parameters and exposure time up to 4.5 h increased from 18 to 28 μ m and combined into agglomerates with sizes that mostly lie in the range from 200 to 600 μ m. Synthesized calcium sulphate crystals acquiring a prismatic shape instead of a needle shape which simplified and accelerated the industrial filtration process. Our study shows that a promising sustainable and cheap source of gypsum-containing raw materials is synthetic gypsum, obtained by reacting a suspension of calcium carbonate and spent sulphuric acid.

Substitution of Calcium with Ce, Nd, Er, and Tb in the Structure of Microcrystals of Calcium Sulfates with Controlled Hydration Water: A Proposed Mechanism

To interpret the mechanism of cocrystallization and sorptive properties of rare earth elements (REE) with calcium sulfate dihydrate (CSD) crystallization, synthetic crystals were prepared by the crystallization of CSD from solutions containing Ce, Nd, Er, and Tb as heavy and light REE. The obtained crystals were characterized using an array of characterization techniques, including X-ray diffraction, thermogravimetric analysis, differential thermal analysis, time-of-flight secondary ion mass spectrometry, high resolution scanning electron microscopy, and transmission electron microscopy. The results showed that the heavy REE are less prone to enter the CSD structure than the light REE. Further, the main mechanism of incorporation of REE in the CSD structure is via a surface adsorption process rather than an isomorphous substitution process into the CSD crystal lattice.

Effectiveness of Green Additives vs Poly(acrylic acid) in Inhibiting Calcium Sulfate Dihydrate Crystallization

ABSTRACT: The effects that 20 ppm poly(epoxysuccinic acid) (PESA), poly(aspartic acid) (PASP), and two poly(acrylic acid) (PAA) compounds with molecular weights of ∼2000 and ∼100000 have on the crystallization of gypsum were evaluated at 21 °C byin situ UV−vis spectrophotometry. XRD and SEM were utilized for phase and morphological studies, while the way these additives are associated with the final gypsum crystals was evaluated by XPS. The comparison showed that PASP performed far better than the other antiscalants as it completely inhibited the formation of gypsum. In contrary, the presence of the low molecular weight PAA decreased the rate of crystallization far more than the larger molecular weight PAA. When the pH in the reacting solution was switched from ∼4 to∼7, the efficiency of the low molecular weight PAA in inhibiting gypsum formation increased, while in the presence of the higher molecular weight PAA the opposite effect was observed.

THE EFFECT OF NANOADDITIVES ON THE HYDRATION OF GYPSUM BINDING AGENTS

The results of investigation of hydration processes of gypsum with carbon nanomodifiers are presented in the article. Gypsum modification by multilamellar carbon nanotube (CNT) results in the improvement of its compression strength. Experiments proved that at the nanotubes content of 0,18 %, strength improvement by up to 30 % is observed. Chemical functionalization of carbon nanotube surface facilitates the reduction of the sedimentation effect inherent to the nanoparticles, enables more uniform nanostructure dispersion throughout the modified material volume and provides the chemical interaction between nanotubes and the substance matrix. Quantum-chemical analysis methods confirm that the interaction of calcium sulfate dihydrate molecule with the dihydrate -like surface is the chemical process. The improvement of CNT-containing gypsum composite strength is due to the accelerated process of calcium sulfate dihydrate crystallization at the graphene surface. Therefore, it may be assumed that CNTs act as “crystallization nuclei” in the gypsum composite. The analysis of the microstructure of gypsum composition samples showed that without the modifying additive, loose structure of the gypsum samples is formed with a significant number of pores.It may be assumed that nanodispersed CNT additives act as “crystallization nuclei” on the surface of which calcium sulfate matrix structuring occurs with the improvement of the gypsum composition structural characteristics. This is due to the fact that during growth, crystals partly penetrate into each other and form three-dimensional network permeating and incorporating the entire gypsum stone into a body.

Hydroxyethyl methyl cellulose as a modifier of gypsum properties

The study is focused on the influence of a water-soluble polymer (in weight fraction up to 1.5%), cellulose derivatives—hydroxyethyl methyl cellulose, on gypsum properties. Gypsum setting involves two processes: gypsum hydration/crystallization and probably formation of a polymer film in material pores. The processes are studied by various methods such as setting time and mechanical measurements, scanning electron microscopy and differential scanning calorimetry. The additive acts as a retarder (an increase in setting time), and it modifies the morphology of calcium sulfate dihydrate crystals, leading to the change in mechanical properties—an increase in bending stress. The mechanism of gypsum crystal growth during hemihydrate hydration is predicted to be a nucleation control process (the Avrami equation is applied). The value of nucleation rate constant decreases with an increasing additive content.

In Situ Polymorphic Alteration of Filler Structures for Biomimetic Mechanically Adaptive Elastomer Nanocomposites.

A mechanically adaptable elastomer composite is prepared with reversible soft-stiff properties that can be easily controlled. By the exploitation of different morphological structures of calcium sulfate, which acts as the active filler in a soft elastomer matrix, the magnitude of filler reinforcement can be reversibly altered, which will be reflected in changes of the final stiffness of the material. The higher stiffness, in other words, the higher modulus of the composites, is realized by the in situ development of fine nanostructured calcium sulfate dihydrate crystals, which are formed during exposure to water and, further, these highly reinforcing crystals can be transformed to a nonreinforcing hemihydrate mesocrystalline structure by simply heating the system in a controlled way. The Young's modulus of the developed material can be reversibly altered from ∼6 to ∼17 MPa, and the dynamic stiffness (storage modulus at room temperature and 10 Hz frequency) alters its value in the order of 1000%. As the transformation is related to the presence of water molecules in the crystallites, a hydrophilic elastomer matrix was selected, which is a blend of two hydrophilic polymers, namely, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer and a terpolymer of ethylene oxide-propylene oxide-allyl glycidyl ether. For the first time, this method also provides a route to regulate the morphology and structure of calcium sulfate nanocrystals in a confined ambient of cross-linked polymer chains.

The Effect of Disinfectant on the Microstructure of Dental Stone at Different Time Intervals

Gypsum products have been considered to be among the most widely used model and die materials. Modifications of these materials by adding chemicals or salts result in a change in their structure. This study was designed to evaluate the effect of the addition of Calcium Hypochlorite disinfectant on the microstructure of dental stone.Calcium Hypochlorite disinfectant in aqueous solution in different concentrations (0.5, 1.0, 1.5 and 2.0%) was added to type III dental stone. The microstructure of the dental stone samples was examined under the microscope and then photo scoped, pictures were taken at different time intervals (immediately, after 10, 30 min., 1and 2 hours) for all the test groups.The results of this study showed that at different time intervals, from the beginning of mixing of dental stone with Calcium Hypochlorite disinfectant solution, deformation in the microstructure was produced (calcium sulfate dihydrate crystals).Microscopically appearance of dental stone samples mixed with Calcium Hypochlorite disinfectant solution revealed a deformation in size and shape of the calcium sulfate dihydrate crystals when compared with the control group.

Revealing the working principle of sodium trimetaphosphate as state of the art anti-creep agent in gypsum plaster

Sodium trimetaphosphate (STMP) is a state of the art anti-creep agent for gypsum plasterboards. It counteracts the deformation of gypsum in a humid environment under load. Despite the fact that STMP is the industrial standard as anti-creep agent, its working mechanisms is not yet thoroughly understood or published. In this work, the role of sodium trimetaphosphate as anti-creep agent of gypsum is reviewed with fundamentally new approaches and modern analytical methods. The surface interaction of trimetaphosphate with calcium sulfate dihydrate crystals is studied in dependence of different crystallographic facets. Via this approach, it was ultimately possible to reveal the working principle of STMP as a highly effective anti-creep agent and deduce a general understanding for anti-creep agents. These insights could help to find and judge new substances in light of their working principle as anti-creep agents.

Influence of Microwave Irradiation of Tempering Water on the Process of Crystallization of Calcium Sulfate Dihydrate

It is established that water treatment by a microwave field influences the processes of formation and growth of calcium sulfate dihydrate crystals. Results of investigation of calcium sulfate dihydrate crystals by the methods of x-ray phase analysis, electron microscopy, and thermal analysis are presented.

Determination of the Effects of Carboxylic Acids on Calcium Sulfate Dihydrate Crystallization

AbstractCalcium sulfate dihydrate crystallization was carried out using a mixed‐suspension mixed‐product removal (MSMPR)‐type crystallizer in pure media and in the presence of three different types of carboxylic acid: propionic acid, oxalic acid, and propane‐1,2,3‐tricarboxylic acid. The crystal size distributions and filtration rates of the calcium sulfate dihydrate crystals were measured, and the crystals obtained were analyzed using a thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer and mass spectrometer (TGA‐FTIR‐MS). The average particle size, length‐to‐width ratio of the crystals, and the filtration rate of calcium sulfate dihydrate crystals were decreased in the presence of all three carboxylic acids when compared to the pure media. TGA‐FTIR‐MS indicated that all carboxylic acids adsorbed onto the calcium sulfate dihydrate crystals.

A mechanism to explain the creep behavior of gypsum plaster

Gypsum plaster is a widely used building material, as it is inexpensive and mechanically strong. However, the main disadvantage of gypsum is its significant loss of mechanical strength in a humid environment. As a result for instance gypsum wallboards bend when exposed to humidity. Despite intense research on this topic, the origin of the mechanisms that ultimately cause this deformation of bulk gypsum, i.e., the creep of gypsum is not yet thoroughly understood.In this work, the creep of gypsum is reviewed with fundamentally new experimental design approaches and modern analytical methods. The surface reactions of calcium sulfate dihydrate crystals are related to the macroscopic behavior of polycrystalline gypsum. The acquired data supports a model for moisture-triggered, pressure solution creep as the fundamental mechanism for the deformation of gypsum under mechanic load in a moist atmosphere.

Characterization and Kinetics of Calcium Sulfate Dihydrate Crystallization in the Presence of Trimesic Acid

AbstractIn this study, calcium sulfate dihydrate crystallization was studied within a mixed‐suspension, mixed‐product‐removal‐type crystallizer at 65 °C and 2.5 pH in pure media and in the presence of trimesic acid. The experiments were performed at different trimesic acid concentrations (250, 1000, and 2500 p.p.m.) through the reaction of calcium carbonate solution with sulfuric acid solution. The crystal size distributions (CSDs) and filtration rates of calcium sulfate dihydrate crystals were measured, and the crystals obtained were also analyzed by thermogravimetric analysis–coupled with Fourier transform infrared–mass spectrometry and scanning electron microscopy. It was determined that the length/width ratio of the crystals obtained in the trimesic acid additive media decreased compared with the crystals obtained in the pure media. Both the filtration rate and the average particle size decreased with an increase in trimesic acid concentration. The kinetics of crystal growth of calcium sulfate dihydrate has been analyzed on the basis of McCabe's ΔL law. It has been found that the growth rate of crystals depends on the particle size, which was specified using Abegg, Stevens, and Larson, Canning and Randolph, two‐parameter Mydlarz and Jones, and three‐parameter Mydlarz and Jones size‐dependent growth models. Results indicated that three‐parameter Mydlarz and Jones model ideally fitted for the characterization of the system because it has high relative coefficient and low square deviation. The presence of trimesic acid also led to a decrease in the growth rate of calcium sulfate dihydrate crystals. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

The Effects of Inorganic Additives on the Nucleation and Growth Kinetics of Calcium Sulfate Dihydrate Crystals

The effects that 50–500 mM aqueous Li+, Na+, K+, and Mg2+ have on the crystallization kinetics of calcium sulfate dihydrate (gypsum; CaSO4·2H2O) were determined by in situ and time-resolved UV–vis spectrophotometry. The mechanisms of surface or structural associations between these additives and the end-product gypsum crystals were evaluated through a combination of inductively coupled plasma mass and/or optical emission spectrometric analyses of digested end-products and X-ray photoelectron spectroscopy of the surface of the solids. Furthermore, X-ray diffraction and scanning electron microscopy were utilized for determining any changes in phase composition and growth morphologies of the formed crystals. Our results revealed that Mg2+, even at low concentrations, decreased the nucleation and growth kinetics 5–10 fold more than Li+, Na+, and K+. In all cases, the additives also changed the shapes and sizes of the formed crystals, with Mg2+ and Li+ resulting in longer and narrower crystals compared to the additive-free system. In addition, we show that, regardless of concentration, Mg2+, Li+, and K+ only adsorb to the newly forming surfaces of the growing gypsum crystals, while ∼25% of Na+ becomes incorporated into the synthesized crystals.