Aqueous Solutions Of Calcium Research Articles

Rapid formation of nanocrystalline apatite

Nanocrystalline plate-shaped particles of hydroxyapatite, with ca. 300 nm edges were directly precipitated from dilute calcium chloride and sodium phosphate solutions, at ambient temperature and pH 7.4. This pH was selected to make the hydroxyapatite appropriate for medical applications. The precipitated crystallites were loosely aggregated in spherulites of 2–4 μm dimensions. The direct precipitation of hydroxyapatite was achieved by submitting the aqueous solutions of calcium and phosphate to microwave irradiation immediately after mixing. The nanocrystals were remarkably stable, not requiring any liquid or stabilizing agent, remaining free flowing after 3 years of storage in non-hermetically closed containers. An explanation for the direct precipitation of hydroxyapatite from water solution, which allows the formation of nano-particles is suggested.

Retardation of a heat front in a porous medium containing an evaporating liquid

We have investigated heat transfer in a layer of silica gel impregnated with a liquid (water, aqueous solutions of calcium and magnesium chlorides, formic acid, and carbon tetrachloride). The layer was arranged on a substrate impenetrable for vapor and it was heated from above by a concentrated light flux. It has been found that the evaporation of the liquid contained in the pores of silica gel substantially slows down the propagation of the heat front into the layer so that the effective thermal conductivity of the layer can be reduced to 0.01 W/(m·K); this value is approximately 4–20 times smaller than the values typical of the majority of standard heat-insulating materials. The time of the front lag depends on the layer thickness, density of the incident heat flux, amount of liquid in the pores, and evaporation heat of the liquid. The observed trends in the motion of the front have been described by a simple one-dimensional model that takes into account phase transition (liquid evaporation) in the interior of the porous matrix.

Crystallization of Amorphous Precursors in the Calcia–Alumina System: A Differential Scanning Calorimetry Study

Amorphous powders were synthesized by spray‐drying aqueous solutions of calcium and aluminum nitrates, followed by calcination in order to completely decompose the salts. The formation of pure calcium aluminates—C3A, C5A3, C12A7, CA, CA2, and CA6 (C = CaO and A = Al2O3)—has been studied by DSC and XRD. A number of compositions first crystallized to metastable structures without partitioning, i.e., without phase separation. This is the case for orthorhombic C5A3, orthorhombic CA, and γ‐Al2O3 solid solution which may incorporate up to about 25 mol% CaO. o‐C5A3 ultimately partitioned into a mixture of C12A7 and CA according to the equilibrium diagram. o ‐CA transformed partitionless into the stable monoclinic m ‐CA, and the stable CA6 compound was obtained pure at low temperature from γ‐Al2O3 solid solution through a second exotherm. Among all the calcium aluminates studied, C3A was the only one for which an intermediary amorphous precursor could not be obtained, CaO crystallizing as the nitrates were decomposed. Phase transitions involving metastable materials are often fast and release heat over a narrow temperature range leading to steep exothermal DSC signals even at a relatively low heating rate (5°C/min). The present results are consistent with current understanding of partitionless crystallization. They clearly show the ability of the synthesis used to achieve homogeneous mixing at the molecular level. Amorphous precursors formed in a large composition range may be advantageously used as glass models.

The hydrolysis and carbonate complexation of strontium and calcium in aqueous solution. Use of molecular modeling calculations in the development of aqueous thermodynamic models

The hydrolysis and carbonate complexation of the alkaline earth cations Ca2+and Sr2+were investigated by using a combined experimental and modeling approach. The modeling approach uses both macroscopic thermodynamic models and molecular modeling at the density functional theory (DFT) level. The molecular modeling calculations identify possible speciation schemes in the thermodynamic modeling and provide molecular level insight into the macroscopically observed thermodynamic measurements. In order to develop accurate thermodynamic models valid to high electrolyte concentration and to test for the possible existence of species suggested by the molecular models, experimental measurements were made on the solubility of Ca(OH)2, Sr(OH)2·8H2O, and carbonate compounds extending to high base molality (≈5 mol<@TBLEND>kg−1), or carbonate molality (≈2 mol<@TBLEND>kg−1). A thermodynamic model is developed that satisfactorily explains the macroscopic aqueous thermodynamic data and correlates with the molecular modeling results. The first published values of the equilibrium constants for the formation of Sr(CO3)2−2(aq) and Ca(CO3)2−2(aq), and of the solubility product of Sr(OH)2·8H2O are also provided. In certain cases, specifically when the DFT calculations suggest that the hydroxyl groups are more closely associated with the first hydration layer of water molecules than directly with the central alkaline earth cation, the thermodynamic relations for these cation–hydroxyl interactions are described by means of Pitzer ion-interaction parameters, rather than by the explicit introduction of an aqueous hydrolysis species.

Novel poly-glutamic acid functionalized microfiltration membranes for sorption of heavy metals at high capacity

Various sorbent/ion exchange materials have been reported in the literature for metal ion entrapment. We have developed a highly innovative and new approach to obtain high metal pick-up utilizing poly-amino acids (poly- l-glutamic acid, 14,000 MW) covalently attached to membrane pore surfaces. The use of microfiltration (0.2–0.6 μm) membrane-based sorbents containing multiple functional groups is a novel technique to achieve high metal sorption under convective flow conditions. For our studies, both commercial membranes and laboratory prepared cellulose membranes containing aldehyde groups were used for the attachment of poly-amino acids. Cellulose membranes were prepared by converting cellulose acetate microfiltration membranes to cellulose (using alkali treatment), subsequent oxidation of hydroxyl groups to aldehyde using sodium periodate, and attachment of poly- l-glutamic acid via Schiff base chemistry. Extensive experiments (pH 3–6) were conducted (under convective flow mode) with the derivatized membranes involving the heavy metals: lead, cadmium, nickel, copper, and selected mixtures with calcium in aqueous solutions. Metal sorption results were found to be a function of derivatization (aldehydes) density of membranes and degree of attachment of the polyfunctional groups, number of functional groups per chain, membrane surface area, and the type of metals to be sorbed. We have obtained metal sorption capacities as high as 1.5 g metal/g membrane. Of course, depending on the desired goals the membrane containing metal could be regenerated or stabilized for appropriate disposal.

5665144 Method and apparatus utilizing hydrocarbon pollutants from glycol dehydrators : Hill D Jeffre; Wiggins E Tod Edmond, OK, United States

Calcium phosphate whiskers have been suggested to be effective as the reinforcement in improving mechanical properties of composite biomaterials. Therefore, composite scaffolds of varying compositions were prepared by freeze drying of gelatin foams containing increasing amounts of calcium phosphate whiskers/fibrous spherulites, up to 50 wt%. The whiskers were attempted to synthesize in acidic solutions under thermal conditions using two different methods: aging of a highly crystalline beta-tricalcium phosphate powder in H2O2 solution, and the precipitation−hydrolysis method using aqueous solutions of calcium and phosphate ions in HNO3 solution and urea as an additive. The morphology and phase analysis of the whiskers were studied by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The results proved that the whiskers could not be obtained by first method at an appropriate period, but using the second method, a mixed plate-like and long whiskers, and fibrous spherulites could be formed. The XRD patterns revealed the biphasic mixture of octacalcium phosphate (OCP) and dicalcium phosphate anhydrate (DCPA). The composite scaffolds containing whiskers obtained by freeze drying were characterized by SEM, Fourier transform infrared spectroscopy and compressive mechanical test. Scaffolds with interconnective pores in a range of 150–350 μm and porosity of 65–74%, as well as homogenous dispersion of the whiskers could be produced which indicates their potential to use in bone tissue engineering applications. The prepared scaffolds showed the compressive yield strength of 4.3−6.2 MPa and Young modulus of 28−38 MPa. In the view of mechanical and microstructural features, the composite of 25 wt% calcium phosphate phase was introduced as the optimal composite for bone tissue engineering.

5665149 Anti-corrosion pigment and use thereof : Gotzmann Karl; Dorn Karlheinz; Numl agerl Hans-Dieter; Guml obelbecker Sieghard Budenheim, Germany assigned to Chemische Fabrik Budenheim

Calcium phosphate whiskers have been suggested to be effective as the reinforcement in improving mechanical properties of composite biomaterials. Therefore, composite scaffolds of varying compositions were prepared by freeze drying of gelatin foams containing increasing amounts of calcium phosphate whiskers/fibrous spherulites, up to 50 wt%. The whiskers were attempted to synthesize in acidic solutions under thermal conditions using two different methods: aging of a highly crystalline beta-tricalcium phosphate powder in H2O2 solution, and the precipitation−hydrolysis method using aqueous solutions of calcium and phosphate ions in HNO3 solution and urea as an additive. The morphology and phase analysis of the whiskers were studied by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The results proved that the whiskers could not be obtained by first method at an appropriate period, but using the second method, a mixed plate-like and long whiskers, and fibrous spherulites could be formed. The XRD patterns revealed the biphasic mixture of octacalcium phosphate (OCP) and dicalcium phosphate anhydrate (DCPA). The composite scaffolds containing whiskers obtained by freeze drying were characterized by SEM, Fourier transform infrared spectroscopy and compressive mechanical test. Scaffolds with interconnective pores in a range of 150–350 μm and porosity of 65–74%, as well as homogenous dispersion of the whiskers could be produced which indicates their potential to use in bone tissue engineering applications. The prepared scaffolds showed the compressive yield strength of 4.3−6.2 MPa and Young modulus of 28−38 MPa. In the view of mechanical and microstructural features, the composite of 25 wt% calcium phosphate phase was introduced as the optimal composite for bone tissue engineering.

Effect of Surfactants and of Ultrasonic Mixing in the Determination of Calcium, Magnesium, Copper and Zinc in Whole Blood by Flow Injection Flame Atomic Absorption Spectrometry

The behaviour of five non-ionic surfactants of different chain lengths was studied in relation to the improvement in sensitivity that their use affords as a sample pre-treatment procedure for the determination of calcium, magnesium, copper and zinc in real samples by flow injection flame atomic absorption spectrometry. The results show that the sensitivity changed with surfactant concentration, length of the hydrophobic chain and ultrasonic agitation time. Higher outputs were obtained with Triton X-100, which is the surfactant with the shortest chain length. In this case, the sensitivity of the atomic absorption signal increased 2.2, 2.2, 2.3 and 2.5-fold for aqueous solutions of calcium, magnesium, copper and zinc, respectively. The data also showed that ultrasonic agitation of the sample probe considerably improved the sensitivity, regardless of the element under evaluation. A relative precision between 0.6 and 3.3% was achieved with a smaller sample consumption than by the conventional atomic absorption method. The results obtained from the proposed sample pre-treatment procedure for the analysis of the elements under study were in good agreement with those obtained by microwave-assisted mineralization and flow injection AAS (for zinc and copper) and flame AAS (for calcium and magnesium).

Charge reversal seen in electrical double layer interaction of surfaces immersed in 2:1 calcium electrolyte

Interactions between charged surfaces immersed in aqueous calcium solutions were measured using the surface force apparatus and the atomic force microscope. With the surface force apparatus, good agreement with previously reported measurements was found for mica surfaces in dilute solutions up to 0.1 M. However, at higher concentrations large discrepancies were observed. Compared to the earlier work, the strength of the force was lower by two or three orders of magnitude and the range was diminished. Experiments using the atomic force microscope indicated similar force-distance profiles for the interaction between silicon nitride and mica. With this technique concentrations as high as 5 M can be investigated, and owing to the small radius of curvature much higher pressures can be recorded. Results obtained by both methods confirm that the force is strongly attractive at very small surface separations, in agreement with the theoretical predictions based on calculations of ion correlations. Just outside of that interval the interaction is repulsive, and it can be quantitatively explained by taking into account the adsorption of hydrated ions onto the surface (sign reversal of the effective surface charge) and the layering of co- and counterions. At larger surface separations, the behavior indicates a balance between the double layer repulsion and the van der Waals attraction (the presence of a secondary minimum).

THE PARAGENETIC RELATION BETWEEN CHAROITE MINERALIZATION AND ALKALI METASOMATISM

The genesis of the recently discovered and highly attractive jewelry stone charoite at its only known occurrence remains controversial. The authors present the hydrothermal-metasomatic nature of the charoite paragenesis, including charoite and associated minerals (tinaksite, canasite, miserite, and fedorite, etc.). Formation of charoite metasomatites is related to calc-alkaline metasomatism of mesocratic and melanocratic fenite, shonkinite, and alkaline minettes. The metasomatic column includes circum-ore metasomatites (dark, intermediate in color and composition, light orthoclase zone), charoite ore (lilac zone), and an axial quartz zone. The order of differential mobilities of components (from inert to most mobile) was: SiO2, (K2O + Na2O), (CaO + TiO2), AL2O3, Fe203, (FeO + MnO). Concentrated aqueous solutions of calcium and potassium chlorides were found in fluid inclusions in quartz associated with high-quality charoite.

Ion-Exchange Equilibrium of Ca2+, Mg2+, K+, Na+, and H+Ions on Amberlite IR-120: Experimental Determination and Theoretical Prediction of the Ternary and Quaternary Equilibrium Data

Abstract A study of the cation-exchange equilibria between Amberlite IR-120 resin and aqueous solutions of calcium, magnesium, potassium, and sodium chlorides and hydrochloric acid has been made. Experiments were carried out at 283, 303, and 323 K with solutions having total cation concentrations of approximately 0.1, 0.3, and 0.5 N. Experimental data for the ion-exchange equilibria of the ternary and quaternary systems are reported. These systems exhibit nonideal characteristics in both phases. The predictions have been based on the reaction equilibrium constants and correlations for the activity coefficients in both phases. A model which allows the prediction of multicomponent ion-exchange equilibria from binary data has been developed. Predictions of ternary and quaternary systems based solely on the binary data are in good agreement with the experimental results.

Studies on the long-term storage of mature, green tomato fruit

SummaryGreenhouse-grown mature-green tomato fruit (Lycopersicon esculentum cv. Caruso) were stored under air or modified atmospheres (MA-3% 02 plus 2% C02) at 6 and 12°C followed by ripening for seven days at 22°C. Treatments with aqueous solutions of calcium, EDTA, EGTA, BHT, a-tocopherol and paclobutrazol were applied as dips to assess their ability to prevent chilling injury (Cl) or retard senescence. Chemical treatments were not beneficial to the quality attributes of the fruit relative to the control, and MA storage did not alleviate Cl symptoms relative to the air stored samples. Greenhouse-grown fruit could be stored for at least 30 days in the mature-green state at 12°C under MA with no detectable changes in quality, but samples kept at 6°C showed marked deterioration after 15 days of storage under both air and MA. Samples stored at 12°C under an air atmosphere for 30 days ripened completely. Field-grown mature green tomato fruit (Lycopersicon esculentum cv. Heinz 91-29) stored at 12°C under MA co...

Ion-exchange equilibria between solid aluminium pectinates and Ca, MnII, CuII and FeIII ions in aqueous solution

The ion-exchange equilibria between solid aluminium pectinates and aqueous solutions of calcium, manganese, zinc, copper and iron(III) nitrates have been studied at 298 K. The equilibria are generically represented by the equation: (z–i) Al(OH)2P(s)+ M(OH)(z– i)+i(aq)⇌ M(OH)i P(z–i)(s)+(z–i) Al(OH)+2(aq) where P is the active site of pectinates containing (z–i) carboxy groups and their molecular surroundings, and M(OH)(z– 1)+i represents Ca(OH)+, Mn(OH)+, Zn(OH)+, Cu(OH)+, Fe(OH)+ and Fe(OH)2+. The equilibrium constants were determined using pectins with different degrees of methylation of the carboxy groups. The results are discussed in terms of interactions occurring in the ionic exchange for each of the metallic nitrates. Together with data from the literature it is possible to establish the following order of preference in bonding with pectins: FeIII > Al > Cu > Pb > Cd > Zn > Ni > Co > Sr ≈ Ca ≈ Mn > Mg.

Effect of inorganic phosphate on serum ionized calcium concentration in vitro: A reassessment of the “trade-off hypothesis”

The development of secondary hyperparathyroidism in uremia is thought to be due, in part, to the retention of inorganic phosphate which, as proposed by the "trade-off hypothesis", lowers serum ionized calcium by means of CaHPO4 complex formation. To study this hypothesis, free from hormonal or physiological influence, the effect of changes in inorganic phosphate concentration on calcium ion concentration was examined in vitro in serum and protein-free aqueous solutions. The findings of this study demonstrate that the mean change in ionized calcium in aqueous solution is -0.019 +/- 0.001 mM per 1 mM change in inorganic phosphate, and is not significantly different in serum where the mean change in ionized calcium is -0.018 +/- 0.003 mM per 1 mM change in inorganic phosphate. The results in both aqueous solutions and sera agree closely with values predicted from the K'CaHPO4. Based on these results, the serum inorganic phosphate would have to increase by 1.2 mM (3.7 mg%) before the serum ionized calcium would fall sufficiently (0.025 mM) to stimulate the parathyroid glands. These results indicate that an increase in serum inorganic phosphate to as great as 1 mM/liter does not produce a fall in serum ionized calcium by means of direct physicochemical CaHPO4 complex formation great enough to account for the development of secondary hyperparathyroidism.

Thermodynamics of ion association in aqueous solutions of calcium- and magnesium-substituted hydroxybenzoates using an ion-selective electrode technique

Thermodynamics of ion association in aqueous solutions of calcium- and magnesium-substituted hydroxybenzoates using an ion-selective electrode technique

GELS IN THE SYSTEM CaO-Al2O3-SiO2 PREPARATION AND STRUCTURAL EVOLUTION

Gels in the system CaO-Al2O3-SiO2 were prepared by the sol destabilization method. Aqueous solutions of calcium and aluminium nitrate were added to a colloidal silica solution. In order to avoid a selective precipitation of calcium and aluminium hydroxide, the gelation was done at definite pH. The ranges of gel formation in the binary systems Al2O3-SiO2 and CaO-SiO2 have been established. They lie from 100 to 75 mole % SiO2 and from 100 to 25 mole % SiO2 respectively. The range of formation in the ternary system CaOAl2O3-SiO2 was displaced towards the compositions rich in calcium and gels containing up to 75 mole % CaO were prepared. The gelation time was reduced by calcium ions while the aluminium ions increased it. The structural evolution of these gels were followed as a function of temperature by X-ray diffraction. Calcium nitrate crystals occured at low temperature and decomposed as the temperature increased. This decomposition was facilited in the composition domain rich in aluminium.

An electrokinetic study of the interactions between glass fibers and aqueous solutions of calcium

The interactions of glass fibers of different compositions with Ca II solutions have been studied using streaming potential techniques. This study clearly showed the formation, on the glass surface, in basic medium, of a layer enriched in Ca(II), giving the glass a better resistance to corrosion in slightly acid medium. This surface layer is characterized by an isoelectric point (IEP) superior to the one of the untreated fiber.

Dissociation of Micelles and Intermicellar Concentrations of Aqueous Solutions of Calcium and Sodium Decyl Sulfates

Abstract Activities of the surfactant ions and the counterions were calculated from the electromotive forces of concentration cell with ion-exchange membranes for the aqueous solutions of calcium (Ca(DeS)2) and sodium (NaDeS) decyl sulfates. Moreover, the mean activities and the activity coefficients were obtained. From these activities, the valence effects of the counterions on the dissolved state of micellar solutions were studied. The following results were obtained: (1) The mean activities were not constant, but increased with the increase in the concentration of the two surfactants above the CMC; the slope of curve of the mean activity for Ca(DeS)2 against its concentration was smaller than that for NaDeS. (2) The CMCs were 6.4 for Ca(DeS)2 and 32.8 mmol dm−3 for NaDeS, respectively. (3) For the mechanism of micelle formation, the phase separation model was set up in both cases. (4) From this model, the degrees of dissociation of the micelles were calculated as 0.12 for Ca(DeS)2 and 0.28 for NaDeS, respectively. (5) The intermicellar concentrations of the Ca2+, the Na+, and the decyl sulfate (DeS−) ions were calculated; those of the counterions increased but those of the DeS− ions decreased with the increase in their surfactant concentrations. Moreover, those of the DeS− for Ca(DeS)2 changed slowly while those for NaDeS changed steeply.

Film Boiling in a Scaling Liquid

Film boiling experiments were carried out in an aqueous-calcium sulfate solution. The experimental results indicate that scale formation on heating surfaces during evaporation of a calcium sulfate solution can be avoided under carefully controlled conditions. Experimental heat transfer results for both distilled water and aqueous calcium solutions compare very well with analytical predictions. In addition, for high heat fluxes, contact between liquid and heating surface was found to exist during stable film boiling in a quiescent, saturated or almost saturated liquid.

Quantitative Evaluation of Degree of Internal Standardization in X-ray Fluorescence Analysis Using Scattered X-rays

The “degree of internal standardization” for the scattered radiation method of compensation for matrix effects in x-ray fluorescence analysis is defined as the closeness of agreement between the results of analyses of specimens containing identical concentrations of analyte but with differing over-all elemental constituencies. The definition is derived in mathematical terms and is applied to experimental data of analyses of calcium in aqueous solutions containing different dissolved substances as matrix variants. The matrix compensation effectiveness of various wavelengths of scattered radiation can be clearly indicated. Interpretation of the results in terms of basic spectroscopic parameters is offered.