Calcium Chloride Aqueous Solution Research Articles

Melting and recrystallization in modified porous nylon-6 membranes

For the porous membranes prepared from a calcium chloride–methanol solution of nylon-6, the behaviors of melting and recrystallization were investigated by DSC measurements. For thin samples annealed at 200 °C, a double peak was observed on the DSC curve. Further immersing them in an aqueous solution of calcium chloride or magnesium chloride and then drying, the higher side peak intensity decreased with the immersion time and disappeared finally. The residual single peak temperature for samples with magnesium ions was 7 °C higher than those with calcium ions, reflecting the increase of three structural units of crystal length during the heating process. The structural models adsorbed calcium and magnesium ions are proposed.

Controlling the kinetic versus thermodynamic crystallisation of calcium carbonate

Calcium carbonate was grown by diffusion of gaseous carbon dioxide into an aqueous solution of calcium chloride. The interplay between kinetic and thermodynamic control of the growth was investigated. It was found that the calcium ion is the dominant species in producing thermodynamic growth of rhombohedral calcite, while kinetic growth is preferentially controlled by carbon dioxide. This was evidenced by the formation of vaterite as the partial pressure of carbon dioxide increased for a given calcium ion concentration. The different morphological and polymorphic forms grown were examined by scanning electron microscopy and powder X-ray diffraction, respectively.

Improvement of physical properties of crosslinked alginate and carboxymethyl konjac glucomannan blend films

AbstractBlend films from carboxymethyl konjac glucomannan and sodium alginate in different ratios were prepared by blending 4 wt % sodium alginate aqueous solution with 2 wt % konjac glucomannan aqueous solution. After crosslinking with 5 wt % calcium chloride aqueous solution, the blend films formed a structure of semi‐interpenetrating networks. The structure and physical properties of both uncrosslinked and crosslinked films were characterized by Fourier transformed infrared spectra (FTIR), differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile tests. The results indicated that the mechanical properties and the thermal stability of the films were improved by blending sodium alginate with carboxymethyl konjac glucomannan due to the intermolecular hydrogen bonds between sodium alginate and carboxymethyl konjac glucomannan. The crosslinked blend films with Ca2+, compared with uncrosslinked blend films, exhibited further improved physical properties due to the formation of a semi‐IPN structure. Furthermore, the degree of swelling of the crosslinked films was also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2554–2560, 2002

Thermodynamics of the interactions of calcium chloride with α-chymotrypsin

High sensitivity differential scanning calorimetry (d.s.c.) and uv-visible spectrophotometry have been used to study the thermal unfolding of α -chymotrypsin in presence of calcium chloride at pH = 2.8, 3.4, 5.0, 7.0, and 8.2. Quantitative thermodynamic parameters accompanying the thermal transitions have been evaluated. In the absence of calcium ions, the thermal denaturation of α -chymotrypsin is a reversible process giving a ratio of the van’t Hoff to calorimetric enthalpy of 0.92 at pH = 2.8. At pH values higher than 5.0, the thermal denaturations in the absence of calcium chloride were observed to be completely irreversible. In the presence of calcium chloride, α -chymotrypsin undergoes irreversible thermal denaturation and its thermal transitions are found to be scan-rate dependent fitting to the model N2→ I, yielding an average activation energy of (419 ± 16)kJ · mol−1using different approaches at pH = 2.8. It is also observed that at pH = 2.8 and 3.4, calcium reduces the transition temperature of the protein. However, at pH = 5.0, 7.0, and 8.2, it stabilizes initially, and at higher concentrations the salt acts as a destabilizer of the native structure of α -chymotrypsin. The surface tension values of aqueous calcium chloride solutions were measured and it is observed that the role of surface tension of the medium is not dominant in providing thermal stability of this protein.

Corn Kernel Structural Integrity: Analysis Using Solvent and Heat Treatments

ABSTRACTMost corn (Zea mays, L.) processing is accomplished by causing a structural change to the kernel. Associations between corn endosperm structural components were characterized using textural analysis after solvent and heat treating kernels. Intact Asgrow 405W and B73xMo17 kernels were incubated and treated at 20, 40, 55, and 90°C for 1, 24, and 48 hr in static air, in acetone, and in aqueous solutions of water, calcium chloride, sodium chloride, sodium bisulfite, lactic acid, lime, lye, ethanol urea, and sodium dodecyl sulfate (SDS). After treatment, kernels were compressed between flat platens. Acetone did not significantly soften endosperm structure. Ethanol reduced kernel fracturability by weakening cell‐to‐cell (wall) bonds, but ethanol did not effectively reduce kernel hardness. Water and aqueous solvents swelled and softened kernels by plasticizing structural components. Bisulfite and SDS softened kernels more than water only soaks because they denatured matrix proteins. Alkaline soaks reduced fracturability and softened the kernel by dissociating both cell‐to‐cell and intracellular (starch‐protein) bonds. Soaking for longer periods and at higher temperatures increased aqueous‐based solvent softening effect. Urea imbibition into the kernel and its softening effects were highly dependent on time and temperature of soak. Endosperm structural integrity is the governed by a combination of cell‐to‐cell bonds and intra‐cellular (starch‐protein) bonds. Reagents that denatured the endosperm matrix proteins and disrupted hydrogen bonds resulted in the greatest alterations to kernel structural integrity. Ultimately a better understanding of kernel structural integrity will lead to the development of improved hybrids and process technologies designed to facilitate desirable structural changes.

Investigation of heat and mass transfer in a gauze-type structured packing liquid desiccant dehumidifier

In this experimental investigation, a packed bed column suitable for 5-ton hybrid cooling system has been designed to study the absorption of water vapour from moist air by contact with aqueous solutions of calcium chloride. The packing material used in the study was two elements of the BXPEP structured packing and the height of the each element was 17 cm. This packed bed dehumidifier handles desiccant flow rates from 10 to 321/min. This paper presents results from a detailed experimental investigation of the heat and mass transfer between a liquid desiccant (calcium chloride) and air in a gauze-type structured packing dehumidifier. The effects of different independent variables such as air inlet absolute humidity, desiccant inlet temperature, flow rate and its concentration on the performance of the dehumidifier have been investigated.

EFFECT OF ANNEALING ON CALCIUM PECTIN GEL FORMATION BY THERMOMECHANICAL ANALYSIS

Pectin solutions were annealed at various temperatures and time intervals. Calcium pectin gels were prepared by mixing aqueous solutions of pectin and calcium chloride (CaCl2). The degree of Na to Ca substitution (DS) was calculated based on the data obtained by atomic absorption spectrometry. DS increased with increasing Ca content and levelled off at the characteristic Ca content which corresponds to the saturated value assuming all -COOH was converted into -COO2Ca. The characteristic saturated values depended annealing temperature and time at sol state. DS was calculated and it was found that DS decreased with increasing annealing temperature. Viscoelastic properties of gels in water were investigated using a thermomechanical analyzer (TMA). Dynamic modulus increased and tanδ decreased with increasing DS. Swelling ratio of gels decreased with increasing annealing temperature and time at sol state showing a similar tendency to the results of DS. It can be concluded that a large network structure was formed when the samples were annealed at high temperature for a long time at sol state.

Usefulness as guided bone regeneration membrane of the alginate membrane

Alginate membrane is a new bioabsorbable, guided bone regeneration (GBR) membrane, which is placed directly on the surface of the bone defect. It is designed to drop a calcium chloride aqueous solution into the bone defect, which is filled with sodium alginate aqueous solution. Alginate membrane is an excellent agent for this procedure due to its close assimilation to the surface of the bone. In this study, we evaluated the short-term biocompatibility of alginate membrane in the bone defects of rat tibiae. GBR membrane availability was also examined. Consequently, we found that the healing process in bone defects covered with an alginate membrane was delayed in comparison with that of controls; however, the defect was restored to nearly original condition. In contrast, in the controls, bone defect repairs exhibited partitioning as a result of connective tissue involvement. Furthermore, we observed a relation between the sodium alginate concentration and the rate of absorption of the sodium alginate membrane. Absorption of a 1.5% sodium alginate membrane was slow. As a result, the compound was not absorbed completely and bone repairs resembled an hourglass. Moreover, the inflammatory response was absent surrounding the alginate membrane. The present findings suggested that the alginate membrane functions effectively as a GBR membrane. In addition, the alginate membrane derived from 3% calcium chloride and 1% sodium alginate was most suitable as a GBR membrane.

Isentropic Compressibility and Viscosity of Aqueous and Methanolic Calcium Chloride Solutions

Speeds of sound and viscosities of aqueous and methanolic calcium chloride solutions were measured as functions of concentration [0.0040 ≤ m/(mol·kg-1) ≤ 7.151 and 0.1903 ≤ m/(mol·kg-1) ≤ 3.252 for aqueous and methanolic calcium chloride solutions, respectively] and temperature (273.15 ≤ T/K ≤ 323.15). Isentropic compressibility isotherms of aqueous calcium chloride solutions converge at 5.1 mol·kg-1. In the case of methanolic calcium chloride solutions, isentropic compressibility isotherms vary smoothly with the increase in concentration and converge at 5.66 mol·kg-1 on extrapolation. Total solvation numbers of calcium chloride in water and methanol media were estimated to be 10.9 and 5.5, respectively.

High-Density Monomer System for Formation Consolidation/Water-Shutoff Applications

Summary This paper describes an in-situ polymerizable organic monomer hydrogel system for formation consolidation during deepwater drilling applications in which a water-soluble vinyl monomer solution is polymerized in-situ to seal and consolidate unstable geological zones. In deepwater wells, shallow zones may have pore pressures close to parting pressures. In these situations, lost circulation or flowing zones can be difficult to control and can lead to a complete loss of the well. Hydroperoxide and azo initiators are used for polymerizing solutions of 2-hydroxyethyl acrylate monomer in aqueous solutions of synthetic seawater, sodium chloride (NaCl), calcium chloride (CaCl2), calcium bromide (CaBr2), and zinc bromide (ZnBr2), with densities from 8.6 to 17.5 lbm/gal. These monomer solutions undergo controlled polymerizations in the formation to yield a crosslinked hydrogel matrix that can withstand high differential pressures. A similar monomer system has been used for water-shutoff applications but had never been formulated in heavy brines or used in the cool temperatures (50 to 60°F) typical of the shallow water-flow zones. The use of a high-density hydrogel for consolidation purposes would be an advantage in shallow water-flow zones because the gelant solution of the hydrogel could be spotted over, and allowed to flow into, the problem zone where the gelant flow is driven by the hydrostatic pressure of the treatment fluid. This process enables the use of the monomer system in wells where high-pressure injection of the treatment fluid into the formation is not an option. This article describes the hydrogel system's development, including gel-time curves and compressive strengths of consolidated sandpacks, and discusses factors affecting the performance and application of the system.

Homogeneous Precipitation of Calcium Carbonates by Enzyme Catalyzed Reaction

Catalytic decomposition of urea by urease in aqueous calcium chloride solutions was used to rapidly prepare calcium carbonate polymorphs at room temperature. The nature of the resulting particles depended on the concentration of the enzyme and, in a strong manner, on the agitation of the reacting solutions. In an undisturbed system an amorphous precipitate is formed first, which readily crystallized to vaterite and upon aging changed to calcite. Under the influence of magnetic stirring, the amorphous phase could be not observed; instead smaller particles were initially obtained, which aggregated to vaterite and calcite. Similarly, the application of ultrasonic energy produced small vaterite particles at the early stages. It is apparent that enzyme macromolecules are important in the development of calcite faces and, as such, they exert significant influence on calcite morphology, without being present in detectable amounts in the resulting solids.

Long period gratings as solution concentration sensors

The on-line concentration measurement of solutions is of great interest in many industrial processes as a means of quality production control, in order to measure concentrations of harmful solutions or solutions that cannot be reached by the operator. An optical fiber long-period grating (LPG), tested for the refractometry of sodium chloride, calcium chloride and ethylene glycol aqueous solutions, is presented. Resolution values comparable to or even better than those offered by an Abbe refractometer, that is typically used in these types of measurements, are obtained.

Isopiestic study of (calcium chloride + water) and (calcium chloride + magnesium chloride + water) atT = 313.15 K

The osmotic coefficients of aqueous calcium chloride solutions were experimentally determined atT= 313.15 K by the isopiestic method. Magnesium chloride served as the isopiestic standard for the calculation of osmotic coefficients. The molality range covered in this study correspond to about 0.1mol · kg−1to 3.0mol · kg−1. In addition, the osmotic coefficients of aqueous mixtures of calcium chloride and magnesium chloride were determined over the range of ionic strength levels of about 0.1mol · kg−1to 9mol · kg−1and at various mole fractions. The results obtained were correlated by the Pitzer equation.

A Concentration and Temperature Combined Convection due to the Melting of a Horizontal Square Ice Bar.

This paper is concerned with the double diffusive convention due to the melting of a horizontal square ice bar into a calcium chloride aqueous solution inside a insulated square cavity. The temperature in the ice bar suddenly decreases just after the melting begins, however, the temperature gently decreases during the melting process. The concentration induced convection appears above in the liquid, and the temperature induced convection appears below in the liquid. The present ideal numerical model predicts approximately the temperature decrease in the ice bar, the mean melting mass and the mean melting Nusselt number.

Sandbed Consolidation with Mineral Precipitation

A new method has been developed to prevent sand reentrainment during oil production from unconsolidated or poorly consolidated reservoir formations. Consolidation of the zformation around the well is achieved through in situ precipitation of a sparingly soluble salt, namely, calcium phosphate. Control of the depth of salt formation is achieved by alternating injection, mixing, and reaction of two aqueous solutions of calcium chloride and potassium phosphate. Calcium phosphate crystals precipitate and grow on the grain surfaces, forming sufficiently uniform coatings. The formation of relatively uniform coatings on the grains causes an acceptably small decrease of the permeability, which is a feature of primary importance for oil production. The grains are gradually “cemented” with bridges of calcium phosphate crystallites and form a consolidated and still porous structure. As a result, the rate of hydrocarbon production for the problematic reservoir can be increased considerably without undesirable reentrainment of sand. The proposed method for consolidation has been successfully tested in sandbeds. Several series of experiments have been carried out under diverse conditions to establish the optimum parameter values for the implementation of this method. A set of optimum conditions at 25°C were determined and these conditions gave satisfactory consolidation with permeability loss of ca. 60% of the initial value. The conditions of precipitation were chosen so that the precipitated phase was octacalcium phosphate [Ca4H(PO4)3·2.5H2O], along with its byproduct hydroxyapatite [Ca5(PO4)3OH]. Experiments were also carried out at 70°C and have shown that it is feasible to consolidate loose sandpacks at oil reservoir conditions.

The role of vaterite and aragonite in the formation of pseudo-biogenic carbonate structures: implications for Martian exobiology

A simple synthesis of various forms of calcium carbonate with spherical and ‘floral’ morphologies is reported. Vaterite formation occurs at ∼25°C, aragonite at ∼70°C and calcite at about ∼80°C. These are produced when CO 2 is reacted with an aqueous solution of calcium chloride in the presence of ammonia. These conditions may have existed at the surface of Mars in the past, leading us to conclude that such mineral formations may be common there. Although the initial phases are modified over time with changing temperature and pressure conditions, they still influence the final morphology of the carbonates observed. A comparison of these structures with those found in the Martian meteorite ALH84001 suggests, but does not confirm, a non-biogenic origin for the ALH84001 carbonates.

Calcium chloride and calcium bromide aqueous solutions of technical and analytical grade in Lemna bioassay

Saturated water solutions of calcium chloride, calcium bromide and their 1:1 mixture are commonly used as “high density brines” for pressure control in oil wells. To compare the effect of these chemicals of technical grade with the effect of the chemicals of analytical grade the Lemna test was used. The multiplication rate, fresh weight, dry to fresh weight ratio, area covered by plants and chlorophyll content were measured as toxicity parameters. The concentrations of tested chemicals were 0.025, 0.05, 0.075 and 0.1 mol dm −3. Generally, the chemicals of both technical and analytical grade in concentrations of 0.025 mol dm −3 stimulated the Lemna minor growth, while tested chemicals in concentrations of 0.05 mol dm −3 did not affect the growth significantly. The exceptions were results obtained by measuring fresh weight. Most of tested chemicals in concentrations of 0.075 mol dm −3 and all chemicals in concentrations of 0.1 mol dm −3 reduced the growth. No major differences between effects of tested chemicals of technical and analytical grade on plant growth were observed, except that tested chemicals of analytical grade in concentrations of 0.1 mol dm −3 increased dry to fresh weight ratio much stronger than chemicals of technical grade. All tested chemicals in all concentrations increased chlorophyll content. After treatment with chemicals of analytical grade much higher increase of chlorophyll a concentration in comparison to increase of chlorophyll b was noticed, while chemicals of technical grade caused more prominent increase of chlorophyll b.

Fire resistance test for fire protection materials with high water content

It is known that moist fire protection materials show good fire resistance characteristics. For this reason, these materials are usually made of mixtures of cement mortar and high water content materials such as silica gels or moist perlites. The latent heat of water plays an important role in the resistance of heat propagation in these materials. In this study, a fire resistance test of a material with high water content is conducted and the temperature response of the test is obtained. Also, the water content of the test materials is measured. The test material consists of a mixture of perlite mortar and gel. The gel absorbs the aqueous solution of calcium chloride, which serves as a water storage mechanism. The numerical predictions to simulate the fire resistance test were conducted and the results were compared with the experimentally obtained temperature responses.

Thermal and water storage characteristics of super-absorbent polymer gel which absorbed aqueous solution of calcium chloride

This paper describes the thermal and water storage characteristics of a super-absorbent polymer gel which has absorbed an aqueous solution of calcium chloride. It is expected that the gel could be used as a heat absorbent material in a fire protection material during the course of the fire. Gels which absorbed calcium chloride solutions of 10 – 40 mass% were tested. The maximum absorbency of polymer and latent heat of the gel were measured using a thermal analyzer of TG/DTA. The water storage characteristics of the gel were obtained leaving the gel in a room whose temperature was controlled and measuring changes in weight of the gel. Also, an equilibrium concentration of the calcium chloride solution in gel and the latent heat of the gel were obtained.

Preparation and characterization of apatite deposited on silk fabric using an alternate soaking process.

Apatite-deposited silk fabric composite materials were developed using a new alternate soaking process. The characteristics of deposited apatite were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), and X-ray photoelectron spectroscopy (XPS). Apatite weight increased with alternating soaking in a calcium solution [200 mM aqueous calcium chloride solution buffered with tris(hydroxymethyl) aminomethane and HCl (pH 7.4)] and a phosphate solution (120 mM aqueous disodium hydrogenphosphate) changed every hour. SEM showed that apatite deposited after 21 or more repeated soakings was over 20 microm thick. XRD showed that with alternate soakings, the apatite crystals deposited on silk fabric elongated along the c axis. FTIR and XPS indicated the existence of carbonate, HPO(4)(2-), and Na(+) ions in addition to constituent ions of hydroxyapatite. A loss of HPO(4)(2-) and Na(+) ions in the deposit upon further soaking might be associated with an increasing apatite crystallinity. Apatite deposited on silk by the alternate soaking process was a deficient apatite containing carbonate, HPO(4)(2-), and Na(+) ions as in a natural bone tissue. Thus, this apatite-silk composite material might be potentially bioactive.