Amount Of Calcium Sulfate Research Articles

The potential of thermally conductive polymer composites regarding crystallization fouling mitigation

AbstractThe fouling kinetics and amount of calcium sulfate and calcium carbonate, respectively, on different polypropylene/graphite composites in a flat plate heat exchanger are determined and compared to the reference material stainless-steel. For a straight evaluation of the fouling susceptibility of the materials the formation of bubbles on the materials is considered by optical imaging or excluded by a degasser. The results are interpreted using surface free energy and roughness of the surfaces.The results show that when bubble formation is avoided, the polymer composites have a very low fouling tendency compared to stainless steel. This is particularly the case when turbulent flows are present or when sandblasted specimen are used. Sandblasting also continues to increase heat transfer compared to untreated samples by increasing thermal conductivity and creating local turbulences. Depending on the test conditions, the fouling resistance formed on the stainless-steel surface is an order of magnitude greater than on the polymer composites. In addition, the fouling layers adhere only weakly to the composites, which indicates an easy cleaning in place after the formation of deposits.

Influence of calcium hydroxide and calcium sulfate on early-age properties of non-expansive calcium sulfoaluminate belite cement

Calcium sulfoaluminate belite (CSAB) cements are currently being promoted as alternative low CO2 cements. CSAB cements have ye'elimite as their primary phase. Ye'elimite hydrates rapidly to form ettringite which contributes towards high early-age strength. The hydration characteristics of ye'elimite are influenced by the presence of calcium sulfate and calcium hydroxide, which can also extend to the mechanical properties. Further, this change in phase composition can modify a non-expansive binder into an expansive binder. In this study, the influence of phase composition on hydration characteristics, expansion, pore structure, and mechanical properties was investigated using CSAB binders with varying gypsum and calcium hydroxide levels. The expansion was directly affected by the amount of calcium sulfate and calcium hydroxide. The differentiating factor between expansive and non-expansive systems was the critical pore size of CSAB binders. Expansive CSAB binders exhibited lower critical pore size than non-expansive binders, highlighting the role of supersaturation. The addition of calcium hydroxide accelerated the kinetics of ye'elimite hydration and increased the expansion. Moreover, the change from a non-expansive to expansive system did not lead to the deterioration of the CSAB binder matrix.

Application of Anhydrous Calcium Sulfate as a Weighting Agent in Oil-Based Drilling Fluids.

The hydrostatic pressure exerted during the drilling operation is controlled by adding a weighting agent into drilling fluids. Various weighting materials such as barite, calcium carbonate, hematite, and ilmenite are used to increase the density of drilling fluids. Some weighting additives can cause serious drilling problems, including particle settling, formation damage, erosion, and insoluble filters. In this study, anhydrite (calcium sulfate) is used as a weighting additive in the oil-based drilling fluid (OBDF). Anhydrite is an abundantly available resource used in the preparation of desiccant, plaster of Paris, and Stucco. Anhydrite application in drilling fluids is discouraged because of its filter cake removal issue. This study investigated anhydrite (anhydrous CaSO4) as a weighting agent and its filter cake removal procedure for OBDFs. The anhydrite performance as a weighting agent in OBDFs was evaluated by conducting several laboratory experiments such as density, rheology, fluid loss, and electrical stability and compared with that of commonly used weighting materials (barite, calcium carbonate, and hematite). The anhydrite was mixed in three different concentrations (62, 124, and 175 ppb) in a base-drilling fluid. The results showed that calcium sulfate enhanced rheological parameters such as plastic viscosity, yield point, apparent viscosity, and gel strength. CaSO4 reduced the fluid loss and provided better control over the fluid loss than other tested weighting materials tested at the same concentration of 124 ppb. Similarly, the emulsion stability was decreased with the increase in the amount of calcium sulfate in the OBDF. The calcium sulfate filter cake can be removed easily from the wellbore with an efficiency of 83 to 91% in single-stage and multistage removal processes, respectively using the newly developed formulation consisting of 20 wt % potassium salt of glutamic acid-N,N-diacetic acid (K4GLDA) as a chelating agent, 6 wt % potassium carbonate, and 10% ethylene glycol monobutyl ether. The introduction of anhydrite as a weighting agent can be more beneficial for both academia and industry.

Quantitative in Situ X-ray Diffraction Analysis of Early Hydration of Belite-Calcium Sulfoaluminate Cement at Various Defined Temperatures

The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied at 25, 40 and 60 °C by in situ X-ray powder diffraction. The Rietveld refinement method was used for quantification. The degree of hydration after 24 h was highest at ambient temperatures, but early hydration was significantly accelerated at elevated temperatures. These differences were more noticeable when we increased the temperature from 25 °C to 40 °C, than it was increased from 40 °C to 60 °C. The amount of calcium sulfate added controls the amount of the precipitated ettringite, namely, the amount of ettringite increased in the cement with a higher molar ratio. The results showed that temperature also affects full width at half maximum of ettringite peaks, which indicates a decrease in crystallite size of ettringite at elevated temperatures due to faster precipitation of ettringite. When using a calcium sulfate to calcium sulfoaluminate molar ratio of 1, higher d-values of ettringite peaks were observed at elevated temperatures, suggesting that more ions were released from the cement clinker at elevated temperatures, allowing a higher ion uptake in the ettringite structure. At a molar ratio of 2.5, less clinker is available in the cement, therefore these differences were not observed.

Effects of sulfates on the hydration of Portland cement – A review

Presented within is a critical overview of the effect of sulfates on cement hydration, properties, and optimum sulfate content in Portland cement. Calcium sulfate is used in Portland cement to control the C3A reaction to induce the optimum hydration of C3S to occur. The amount of calcium sulfate in the Portland cement influences the hydration, rheology, setting, phase assemblage, porosity distribution, and strength in cementitious materials. If added in excess, it can also lead to durability problems, thus a better understanding is needed about the mechanisms of sulfate on C3A and C3S hydration. The optimum sulfate content is well known as a key pathway to produce workable, good strength, and durable concretes. Despite many years of research, questions regarding sulfate optimization remain. Further investigation on the influence of clinker and calcium sulfate characteristics, the use of different supplementary cementitious materials and chemical admixtures, and the curing conditions on the sulfate demand of Portland cement are needed. The main methods used to determine the optimum SO3 content are reported, and the advantages and disadvantages are examined. Finally, recommendation for future research is also discussed.

Effect of Waste-Derived Calcium Sulfate Additions on the Tribological Properties of Sintered Steel-Based Material

This study examined the effect of waste-derived calcium sulfate additions (2 to 8 weight percent) on the tribological properties of a sintered high-carbon steel material, commonly used for frictional applications. The calcium sulfate powder was obtained by crushing and subsequent calcination of waste plaster molds previously used for slip casting of ceramics. Samples were made using the powder metallurgy method. Powder mixtures were uniaxially die compacted and sintered at 1,100°C for 30 minutes in a reducing atmosphere. It was found that the density of the samples decreased with increased amounts of calcium sulfate. This was due to the lower theoretical density of the calcium sulfate as well as volumetric expansion of the samples. Ball-on-disc tribological testing was performed at room temperature. The addition of calcium sulfate resulted in an increase of the kinetic friction coefficient. The measured wear volume was slightly reduced with the addition of calcium sulfate less than 6 weight percent, beyond which the wear increased. The hardness of the samples was reduced with the addition of calcium sulfate. Increased calcium sulfate content decreased the sample deformation resistance while increasing the kinetic friction coefficient and the wear. This was likely due to the microstructural changes of the samples, which will be discussed.

Early strength development in cement-treated sand using low-carbon rapid-hardening cements

Soil stabilization through cementation is a commonly-adopted ground improvement technique in which Ordinary Portland Cement (OPC) is widely used as the binding material. This paper explores the applicability of a low–carbon, rapid-hardening calcium sulfoaluminate (CSA) cement for an accelerated and sustainable soil treatment. This study extensively investigates the early strength development in cement-treated sand with two commercially available CSA cements, through the ultrasonic pulse velocity (UPV) test and the unconfined compressive strength test. UPV evolution curves for the first 24 h are obtained, and the effects of different cement contents and types on pulse velocity and compressive strength at early age are studied. The CSA cements used in this study contain ye’elimite as the main cementing phase with different amounts of calcium sulfate. It is shown that the presence of the calcium sulfates, or lack thereof, significantly influences the initial strength and stiffness gained by the CSA-treated sand. CSA with calcium sulfate develops higher strength in the first 12 h than CSA without calcium sulfate, whereas the 1-day strength is higher for CSA with more ye’elimite phase. The 1-day compressive strength of CSA-treated sand is 2–9 times higher than that of OPC-treated sand, depending upon the cement type and content.

Acceleration of OPC by CAC in binary and ternary systems: The role of pore solution chemistry

In dry-mortar-formulations calcium aluminate cement (CAC) is often used as a set accelerator for ordinary Portland cement (OPC). However, a critical amount of CAC is able to delay not only the silicate reaction but also the renewed C3A dissolution of an OPC. This delay can be counteracted by adding an appropriate amount of calcium sulfate (C$) to the mix OPC/CAC. The initial hydration period is dominated by fast ettringite formation from CA (CAC) and CaSO4 from OPC generating early strength. High aluminum and low calcium concentrations in the pore solution probably hinder C-S-H seeding and precipitation, thus preventing alite dissolution. Aluminum has to be initially removed by precipitating hydrate phases to change the pore solution chemistry. The start of the silicate reaction is then induced by increasing the calcium concentration in the pore solution.

REMOVAL OF SULFUR DIOXIDE FROM FLUE GAS USING ABSORBENT PREPARED BY WATER AND STEAM HYDRATION

Active absorbent for flue gas desulfurization was prepared from coal fly ash, calcium oxide (CaO) and calcium sulfate (CaSO4 ) by hydro-thermal process; steam and water hydration. The absorbents were examined and compared for its micro-structural properties. The experiments were conducted based on Design of Experiments (DOE) according to 24 factorial design. The effect of various absorbent preparation variables such as hydration period (Factor A), ratio of CaO to fly ash (Factor B), amount of calcium sulfate used (Factor C) and drying temperature (Factor D) towards the BET surface area of the absorbent were studied. The BET surface area of the absorbent was in the range of 12.9-169.3 m2/g. Fisher’s test showed that there is a strong influence of factor A, B and D towards the absorbent surface area, while its dependence on factor C is negligible. Comparison between absorbents prepared from water and steam hydration showed that the BET surface area of absorbents prepared from water hydration gives a higher surface area, but at a lower rate. The optimum BET surface area for the prepared absorbent 169.3 m 2 /g, was obtained at the following absorbent preparation variables using water hydration; hydration period of 24 hours, ratio of CaO to fly ash of 1:2, CaSO4 amount of 3 g and drying temperature of 200°C.

Properties of Sintered Bronze-Graphite Containing Calcium Sulfate Derived from Waste Plaster Molds

This study examined the effect of calcium sulfate additions on the microstructure and frictional properties of a 95bronze-5graphite material, commonly used for frictional applications. The samples were prepared using a powder metallurgy process. The calcium sulfate powder was obtained from recycled plaster molds previously used for ceramic slip casting. The plaster molds were cleaned, crushed and ball milled to obtain powder, which was calcined at 400 °C for 4 hours and screened. 2 to 8 weight percent calcium sulfate powder was added to a premixed powder composed of copper and tin and mixed before the graphite was added. The powder mixture was compacted into a disc shape under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minutes in a reducing atmosphere. It was found that the green density of the samples decreased with increased amounts of calcium sulfate. After sintering, the densities were found to have decreased due to sample expansion. A finer microstructure was observed in the samples containing calcium sulfate powder, possibly due to a grain boundary pinning effect. The addition of calcium sulfate resulted in the reduction of both the measured friction coefficient and wear of the bronze-graphite samples. However, the addition of calcium sulfate powder above 6 weight percent appeared to show decreasing effects.

A reaction range for hydration of calcium sulfoaluminate with calcium sulfate and calcium hydroxide: theory and experimental validation

To better investigate and understand the hydration of calcium sulfoaluminate (CSA) cement, a theory reaction range for the hydration of CSA with calcium sulfate and calcium hydroxide was established by theoretical calculation with a hypothetical hydration reaction system. With different amounts of calcium sulfate and calcium hydroxide in the reaction systems, their hydration processes, hydration products and stoichiometric water/solid ratios showed regular changes. A preliminary experimental validation was made by analysing the hydration products (curing time 28 d and water/solid ratio of 10) of several composition points in the theory reaction range by means of x-ray diffraction and thermogravimetric analysis. The process for calculation of the theory reaction range and some of the experimental validation results are presented in this paper.

Premixed calcium silicate cement for endodontic applications

Calcium silicate-based materials (also called MTA) are increasingly being used in endodontic applications. However, the handling properties of MTA are not optimal when it comes to injectability and cohesion. Premixing the cements using glycerol avoids these issues. However, there is a lack of data on the effect of common cement variables on important properties of premixed cements for endodontic applications. In this study, the effects of liquid-to-powder ratio, amount of radiopacifier and amount of calcium sulfate (added to control the setting time) were screened using a statistical model. In the second part of the study, the liquid-to-powder ratio was optimized for cements containing three different amounts of radiopacifier. Finally, the effect of using glycerol rather than water was evaluated in terms of radiopacity. The setting time was found to increase with the amount of radiopacifier when the liquid-to-powder ratio was fixed. This was likely due to the higher density of the radiopacifier in comparison to the calcium silicate, which gave a higher liquid-to-powder ratio in terms of volume. Using glycerol rather than water to mix the cements led to a decrease in radiopacity of the cement. In conclusion, we were able to produce premixed calcium silicate cements with acceptable properties for use in endodontic applications.

Sulfate resistance of blended cements containing fly ash and rice husk ash

In this paper, the sulfate resistance of mortars made from ordinary Portland cement containing available pozzolans viz., fly ash and ground rice husk ash (RHA) was studied. Class F lignite fly ash and RHA were used at replacement dosages of 20 and 40% by weight of cement. Expansion of mortar prisms immersed in 5% sodium sulfate solution and the change in the pH values of the solution were monitored. The incorporation of fly ash and RHA reduced the expansion of the mortar bars and the pH values of the solutions. RHA was found to be more effective than fly ash. Examination of the fractured surface of mortar prisms, after a period of immersion, by scanning electron microscopy confirmed that sulfate attack of blended cement mortars was restricted owing to the reductions in calcium hydroxide and C/S ratio of the C–S–H gel in the blended cement mortar. In comparison to Portland cement mortar, less calcium sulfate and much less ettringite formations were found in the mortars made from blended cement containing RHA. The amounts of calcium sulfate and ettringite found in the blended cement mortar containing fly ash were also small but were slightly more than those of RHA mortar. Up to 40% of Portland cement could be replaced with these pozzolans in making blended cement with good sulfate resistance.

Optimizing the specific surface area of fly ash-based sorbents for flue gas desulfurization

High performance sorbents for flue gas desulfurization can be synthesized by hydration of coal fly ash, calcium sulfate, and calcium oxide. In general, higher desulfurization activity correlates with higher sorbent surface area. Consequently, a major aim in sorbent synthesis is to maximize the sorbent surface area by optimizing the hydration conditions. This work presents an integrated modeling and optimization approach to sorbent synthesis based on statistical experimental design and two artificial intelligence techniques: neural network and genetic algorithm. In the first step of the approach, the main and interactive effects of three hydration variables on sorbent surface area were evaluated using a full factorial design. The hydration variables of interest to this study were hydration time, amount of coal fly ash, and amount of calcium sulfate and the levels investigated were 4–32 h, 5–15 g, and 0–12 g, respectively. In the second step, a neural network was used to model the relationship between the three hydration variables and the sorbent surface area. A genetic algorithm was used in the last step to optimize the input space of the resulting neural network model. According to this integrated modeling and optimization approach, an optimum sorbent surface area of 62.2 m 2 g −1 could be obtained by mixing 13.1 g of coal fly ash and 5.5 g of calcium sulfate in a hydration process containing 100 ml of water and 5 g of calcium oxide for a fixed hydration time of 10 h.

Preparation and characterization of sorbents prepared from ash (waste material) for sulfur dioxide (SO2) removal

Sorbents synthesized from various types of ash (coal fly ash, coal bottom ash, oil palm ash, and incinerator ash) for flue gas desulfurization were investigated. The sor- bents were prepared by mixing the ashes with calcium oxide and calcium sulfate using the water hydration method. The effects of various sorbent preparation variables, such as the hydration period, the ratio of calcium oxide to ash, and the amount of calcium sulfate, on the Brunauer-Emmett- Teller (BET)-specific surface area of the resulting sorbent were studied using a two-level full factorial design. The surface area of the sorbents obtained range from 15.4 to 122.1 m 2 /g. Regression models were developed to correlate the significant variables to the surface area of the sorbents. An analysis of variance (ANOVA) showed that the model was significant at a confidence level of 95%. It was found that apart from all the individual variables studied, interac- tions between variables also exerted a significant influence on the surface area of the sorbent. From the activity test results, it was found that sorbents prepared from coal fly ash and oil palm ash have the highest SO2 absorption capacity. Scanning electron microscope (SEM) analysis showed that the sorbent was composed of a compound with a high struc- tural porosity, while an X-ray diffraction spectrum showed that calcium aluminum silicate hydrate compounds are the main products of the hydration reaction.

Optimum conditions for preparation of flue gas desulfurization absorbent from rice husk ash

Several previous studies have reported the preparation of absorbents from coal fly ash variations as a source of siliceous material for the preparation of absorbents for flue gas desulfurization. On the other hand, this study presents findings from an experimental investigation of the preparation of absorbents from rice husk ash as the source of the siliceous material. The effect of various absorbent preparation variables such as hydration period, amount of rice husk ash, amount of calcium sulfate (CaSO 4) and hydration temperature on the BET (Brunner–Emmett–Teller) specific surface area of the absorbent were investigated. Based on the Central Composite Design (CCD) of experiments, a third order mathematical model was developed to correlate the absorbent preparation variables to the surface area of the absorbent. The predicted surface area was found to agree satisfactory with the experimental values. The model indicated that lower hydration period and temperature favor the formation of absorbent with higher surface area. Sulfation activity test on the absorbent revealed that the absorbent prepared from rice husk ash does have a high capacity in sulfur dioxide (SO 2) absorption.

Influence of calcium sulfate in belite-rich cement on the change in fluidity of mortar with time

The fluidity of mortar containing a polycarboxylate-based high-range water-reducing AE agent was studied with respect to the change in fluidity with time after the mixing, and the influence of the kind and amount of calcium sulfate in the belite-rich cement with a low interstitial phases was discussed. The flow of belite-rich cement mortar immediately after the mixing initially increased and then decreased with the increase in the saturation ratio of the liquid phase with respect to CaSO4·2H2O. On the other hand, the flow loss continuously decreased with the increase in the saturation ratio. The saturation ratio of the liquid phase strongly depended on the amount of CaSO4·0.5H2O, and was hardly affected by the other kinds of calcium sulfate. The adsorption of the agent inversely corresponded to the mortar flow immediately after the mixing. However, the flow loss did not coincide with the adsorption tendency. It is suggested that the steric hindrance remains to some degree after the hydrate partially covers the agent adsorbed on the cement particles.

Effect of Phytic Acid on the Texture of Tofu and the Precipitaion Reaction in Tofu Making

Soybean curd or tofu is widely used as daily foods by people in Indonesia. One of the delicate steps in the preparation of tofu is the addition of a salt to precipitate soy protein. The common salt of calcium sulfate and the peeled soybeans were used to produced the non phytic acid soybean milk. Futhermore the adjustment of phytic acid content in soybean milk was done by addition of phytic acid. The result showed that phytic acid is the most important factor in the formation of precipitated protein aggregate in tofu at above isoelectric point. Weight and moisture content werw affected by both phytic acid and amount of calcium sulfate as a coagulant. The results may conclude that either natural phytic acid present in soybean seeds or phytic acid added to soybean milk, have a significant effect on the texture of tofu. The higher the phytic acid content in soybean milk is the stronger the interaction among soybean protein, calcium and phytic acid. This is important in producing tofu of desirable hardness.

An Improved Acid for Calcium Sulfate-Bearing Formations

Abstract An improved acid for the treatment of sulfate-containing limestones and dolomites is described. The acid is designed to reduce the reprecipitation of dissolved calcium sulfate and the possibility of plugging permeable flow channels. In addition, this improved acid has a much lower reaction rate than that of regular acid; the advantages of a "retarded" acid are obtainable. Field testing of the acid has shown it suitable for use in sulfate-containing formations. Substantial improvements in productivity generally resulted. Introduction Acid treatments of limestones, dolomites and other formations bearing carbonate deposits are frequently unsuccessful when the calcareous formation contains sulfate, either as anhydrite (CaSO4) or gypsum (CaSO4 2H2O). Preliminary dissolution in acid followed by redeposition of calcium sulfate appears to be a major factor contributing to poor well performance after acidizing. The precipitate is usually the gypsum form of calcium sulfate, but in higher temperature formations it may be anhydrite. The freshly precipitated crystals are nearly always very small and needlelike. They may occupy a gross volume many times that of the original anhydrite crystals and will obviously constitute an impediment to flow through newly enlarged flow channels. It is believed that the redeposition problem is most severe when anhydrite lines the fracture systems and large pores which supply the effective permeability of a formation. Microscopic inclusions of calcium sulfate also present large sulfate surface areas for dissolution in acid. In either case, great amounts of calcium sulfate may dissolve before the acid can be spent on formation carbonates. For regular spent acid (originally 15 per cent hydrochloric acid) the precipitate could be as much as 270 lb gypsum/1000 gal acid. Two techniques have been applied by the industry for reducing sulfate plugging during acidizing. The method commonly employed in the field is the attempted removal of a quantity of regular treating acid before it has reacted completely with the formation. This is practiced because the solubility of calcium sulfate is greater in a solution that is still acidic than in one which has been largely spent on the formation rock. The chance of precipitative plugging is therefore reduced if the withdrawal is successful. However, it is often impossible to get the acid out of the formation before precipitation occurs.