Aqueous Solutions Of Ca Research Articles

Synergistic effect of CaCO3 particles and porous carbon towards the removal of Zn2+ ions in aqueous solutions

This work describes the preparation of an adsorbent containing CaCO3 particles dispersed in activated carbon and its use for the removal of Zn2+ ions from aqueous solutions. The combination of the large porosity of the activated carbon support with the easy ion exchange occurring at the surface of the carbonate particles led to the achievement of fast adsorption kinetics and excellent ion removal capacity for the composite adsorbent. The material was synthesized by wet impregnation of the porous carbon support with an aqueous solution of Ca(NO3)2, followed by evaporation of the solvent with subsequent heat treatment in an inert atmosphere. X-ray diffraction results demonstrated the presence of CaCO3 crystals in the material, but with broad and low intensity diffraction peaks, corresponding to an average crystallite size of 20 nm; solid-state 13C NMR spectroscopy confirmed the presence of this phase by means of the identification of the signal relative to the 13C nuclei of the CO32− group at ∼170 ppm. The carbon-based adsorbent containing the CaCO3 particles showed excellent ability to remove Zn2+ ions from aqueous solutions, with essentially all ions removed after 30 min of contact time. In addition, the kinetic analysis data were properly fitted using the pseudo-second order model, pointing to the occurrence of chemisorption as the rate limiting of the process. The equilibrium adsorption isotherms were correctly described by the Langmuir model, indicating that the adsorption takes place with the formation of a monolayer on the adsorbent surface. The results evidenced a synergistic effect of the porous carbon and the CaCO3 particles regarding the Zn2+ ions removal, with a fast adsorption kinetics at the initial stage of adsorption attributed to the high availability of the dispersed CaCO3 particles on the carbon surface.

Effect of temperature and time on the synthesis of calcium phosphate obtained by microwave hydrothermal method

Bioceramics are materials used in biomedical devices for bone replacement, and calcium phosphate derivatives are widely used in cases of bone defect repair. The aim was to evaluate the influence of temperature and time on the synthesis of calcium phosphate obtained by the microwave hydrothermal method on its structural and morphological characteristics with a view to application as a bone graft. The calcium phosphate powders (calcium octophosphate, hydroxyapatite and calcium triphosphate) were produced using the microwave hydrothermal method. To obtain the calcium phosphate powders, aqueous solutions of Ca (OH)2 and H3 PO4 were used and subjected to the microwave hydrothermal method at temperatures of 110°C and 130°C for 30 and 60 minutes, then calcined at 700°C for 1 hour and characterized using XRD, FTIR, SEM, particle size distribution, apparent density, and apparent porosity. The results obtained by the techniques confirm crystalline and morphological modifications, and homogeneous distribution of the particles, and the phases of interest, octophosphate, hydroxyapatite and calcium β-triphosphate, were identified. The formation of the β-TCP phase was predominant in the samples in which the microwave hydrothermal synthesis was carried out over a longer time and at a higher temperature. It was found that the proposed synthesis method was effective in terms of time/temperature, offering advantages over conventional techniques, such as improving the primary characteristics for choosing a biomaterial to be used in cases of bone regeneration.

Brushite mineralised Scots pine (Pinus sylvestris L.) sapwood - revealing mineral crystallization within a wood matrix by in situ XRD.

Dicalcium phosphate dihydrate (CaHPO4·2H2O, DCPD, brushite) crystals were synthesised within Scots pine sapwood via a wet-chemistry route from aqueous solutions of Ca(CH3COO)2 and NH4H2PO4 salts. SEM/EDS analysis was used to assess the saturation of the wood cell lumina and cell wall as well as morphological features and elemental composition of the co-precipitated mineral. Brushite mineral crystallization and crystallite growth within the wood matrix was studied by in situ XRD. The chemical composition of the mineral before and after the dissolution was evaluated using FTIR spectroscopy. The overall impact of brushite on the thermal behaviour of wood was studied by TGA/DSC and TGA/DTA/MS analysis under oxidative and pyrolytic conditions. Bending and compression strength perpendicular and parallel to the fibre directions as well as bending strengths in longitudinal and transverse directions of the mineralised wood were also evaluated. Results indicate the viability of the wet-chemistry processing route for wood reinforcement with crystalline calcium phosphate (CaP)-based minerals, and imply a potential in producing hybrid bio-based materials that could be attractive in the construction sector as an environmentally friendly building material.

High-Strength and Heat-Insulating Cellular Building Concrete Based on Calcined Gypsum

A cellular concrete with a fine porous structure was experimentally made using the corrosion technique for aluminum powder as an expanding agent in an aqueous solution of Ca(OH)2. The originality of this paper was the use of our own production method for the fine aluminum powder through atomizing the recycled molten waste of this metal using concentrated jets of nitrogen. Additionally, the waste melting technique involved our own microwave heating method. A high weight proportion of calcined gypsum (maximum 82.3%) represented the main concrete binder. Using moderate contents of coal fly ash (3.6-11.1%) together with perlite (4.6-6.4%) to reduce the pore size and silica fume (0.3-1.2%) with pozzolanic properties, the aim was to obtain a macrostructure characterized by a very low pore size and to increase the compressive strength (by up to 4.1 MPa), despite the relatively low density (below 641 kg/m3). An industrial method of increasing the mechanical strength by steam curing fresh concrete was applied.

Powders Based on Ca2P2O7-CaCO3-H2O System as Model Objects for the Development of Bioceramics

Nanoscale powders of hydrated Ca2P2O7, CaCO3, and a product of mixed-anionic composition containing P2O74− and CO32− anions were synthesized from aqueous solutions of Ca(CH3COO)2, pyrophosphoric acid (H4P2O7), and/or (NH4)2CO3. Pyrophosphoric acid was previously obtained on the basis of the ion exchange process from Na4P2O7 solution and H+-cationite resin for further introduction into the reactions as an anionic precursor. The phase composition of powders after the syntheses was represented by bioresorbable phases of X-ray amorphous hydrated Ca2P2O7 phase, calcite and vaterite polymorphs of CaCO3. Based on synthesized powders, simple cylindrical constructions were prepared via mechanical pressing and fired in the temperature range of 600–800 °C. Surface morphology observation showed the presence of bimodal porosity with pore sizes up to 200 nm and 2 μm, which is likely to ensure tight particle packing and roughness of the sample surface required for the differentiation of osteogenic cells. Thus, the prepared ceramic samples can be further examined as model objects for bone tissue repair.

Thickness Controlled Physical Properties of Chemically Synthesized Nanostructured Calcite Thin Films

Calcite thin films on pre-cleaned glass substrate were deposited by a simple chemical dipping technique at room temperature by varying number of dips. The as prepared calcite thin films could be utilized for the controlled application of the complex carbonation process. This study presented nano flower like microstructure of the thin films. The petals of nanoflower of the thin films changes from sharp edges to blurred edged with increase in the growth of the thin films.

Solvent and cosolute dependence of Mg surface enrichment in submicron aerosol particles.

The formation of multicomponent aerosol particles from precursor solution droplets often involves segregation and surface enrichment of the different solutes, resulting in non-homogeneous particle structures and diverse morphologies. In particular, these effects can have a significant influence on the chemical composition of the particle–vapor interface. In this work, we investigate the bulk/surface partitioning of inorganic ions, Na+, Mg2 +, Ca2 +, Cl− and Br−, in atomiser-generated submicron aerosols using synchrotron radiation based X-ray photoelectron spectroscopy (XPS). Specifically, the chemical compositions of the outermost few nm thick surface layers of non-supported MgCl2/CaCl2 and NaBr/MgBr2 particles are determined. It is found that in MgCl2/CaCl2 particles, the relative abundance of the two species in the particle surface correlates well with their mixing ratio in the parent aqueous solution. In stark contrast, extreme surface enrichment of Mg2 + is observed in NaBr/MgBr2 particles formed from both aqueous and organic solution droplets, indicative of core–shell structures. Structural properties and hydration state of the particles are discussed.

Chloride Ingress Control and Promotion of Internal Curing in Concrete Using Superabsorbent Polymer

Chloride ingress into concrete from the surrounding environment can result in the corrosion of the embedded steel reinforcement and cause damage to the concrete. Superabsorbent polymer (SAP) with fine particle size was incorporated into the structure of concrete for controlling the chloride ingress and improving its compressive strength via promotion of internal curing. The SAP used in this study was evaluated for its absorbency property when exposed to cementitious environment such as aqueous solution of Ca (OH)2 and cement slurry. The results were compared to that in sodium chloride solution, the environment where absorbency of most of the SAP found in the market are well studied. Results showed that although SAP absorbency decreased with increasing concentration of Ca (OH)2 and cement, the results suggest that water containing cementitious materials are able to be absorbed by SAP. Chloride ingress into 28-day cured concrete specimens were determined using Rapid Chloride Penetration Test (RCPT) method employing 60V DC driving force. Concrete samples with size of 50 mm height x 100 mm diameter were prepared using a M25 mix design with 0.4 and 0.45 water to cement ratios and different percentages of SAP such as 0.05%, 0.1% and 0.15% with respect to cement mass. Results showed that concrete with 0.15% SAP gave the best result with 14% less chloride permeability than concrete with no SAP for a 0.4 water to cement ratio. Concrete samples for compressive strength tests with size of 200 mm height x 100 mm diameter were prepared using the same mix design and percentages of SAP and cured for 28 days. Results showed that the best results for compressive strength was found at 0.1% SAP at a 0.4 water to cement ratio which can be attributed to internal curing provided by SAP.

Peculiarities of using slurry fuels in thermal power plants

The study regards the issues of increasing the thermodynamic efficiency of a typical condensing thermal power plant using coal-water and organic coal-water fuels as the main source. The attention is paid to the use of the phase transition heat of the water vapor of the flue gas. We have shown that it is possible to increase the power plant efficiency by about 3.7% (gross) relative to the base value (in the case of using pulverized coal). We propose to use the flue-gas desulfurization technology for creating fuel slurries in which a liquid incombustible base will be replaced, for example, with aqueous solutions of Ca(OH)2. This will create a closed water cycle, improve the efficiency of Sox flue gas purification and improve the performance of scrubbers.

Preparation and in vitro apatite-forming ability of hydroxyapatite and β-wollastonite composite materials

This paper provides a one-step method of preparation of the ceramic powders, containing various amounts of hydroxyapatite (HA) and β-wollastonite (WT), based on the salt coprecipitation and subsequent thermal treatment of the synthesis products at 1000 °C. Aqueous solutions of Ca(OH)2, H3PO4 and Na2SiO3 were used as precursors of Ca10(PO4)6(OH)2 and β-CaSiO3, as a minimal amount of by-product is formed during such an interaction of reagents. Variation of the concentration of the initial reagents allows the preparation of ceramic powders containing from 0 to 100 wt% of apatite. All composites were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), laser diffraction analysis and an adsorption method (BET). Degradability of composite powders was analyzed in the Tris-HCl buffer solution. The apatite-forming ability of synthetic composites was investigated by soaking composite ceramics in a simulated body fluid (SBF). The results that were obtained reveal an increase in the dissolution rate of powders with wollastonite addition. Soaking of the composite ceramics in SBF leads to the formation of a bone-like apatite spherical particle layer on their surfaces, which become thicker while the content of β-СаSiO3 in the samples increases.

One-Step Lining and Deacidification of Aged Newspapers with Double-sided Writing

AbstractThe one-step lining and deacidification process of aged newspapers with double-sided writing combines deacidification and reinforcement processes. Wheat starch paste or carboxymethyl cellulose were prepared using an aqueous solution of Ca(OH)2. The newspapers were lined with Japanese tissue (9 g/m2), using the alkaline adhesive in order to mechanically reinforce the newspapers and at the same time increase the pH of the paper. After treatment, the pH value of the newspaper samples reached an ideal range between 8.0–8.5 when thew.1% Ca(OH)2was used. More notably, the Japanese tissue lining doubled strength and folding endurance. The treatment had little impact on the visual appearance of the writing and even increased the degree of whiteness of the paper. The increase of tensile strength and whiteness was not diminished even when the treated newspaper samples were exposed to accelerated thermal ageing.

Study on the early crystallization of calcium silicate hydrate (C-S-H) in the presence of polycarboxylate superplasticizers

Calcium silicate hydrate (C-S-H) presents the strength-providing phase in hardened cement and concrete. Its nucleation and very early overall growth are not yet fully understood. Here, the impact of methacrylate ester-based PCEs (a common type of dispersant used to fluidize concrete) on the nucleation and crystallization of C-S-H precipitated from aqueous solutions of Ca(NO3)2 and Na2SiO3 was investigated. It was found that in the absence of PCEs, most unexpectedly globular nanoparticles of C-S-H with a diameter of ∼20–60 nm are favored. Thereafter, within less than 1 h the globuli convert to the well-known nanofoils of C-S-H. According to these observations, the very early C-S-H is formed following a non-classical nucleation mechanism. In the presence of PCEs, the initial globules show a core-shell morphology, presumably with PCE polymers as shell which delays the conversion to the nanofoils for several hours. The PCE polymers exhibiting higher anionicity delayed the transformation to nanofoils more than the PCEs possessing lower anionic charge.

A TEM study on the very early crystallization of C-S-H in the presence of polycarboxylate superplasticizers: Transformation from initial C-S-H globules to nanofoils

Polycarboxylate superplasticizers (PCEs) present common admixtures to adjust the rheology of concrete. Previous studies revealed that they can also influence the crystallization of cement hydrates, such as e.g. ettringite. In this study, we investigated the impact of methacrylate ester-based PCEs on the nucleation and crystal growth of C-S-H precipitated from aqueous solutions of Ca(NO3)2 and Na2SiO3. TEM imaging revealed that in the absence of PCEs following a non-classical nucleation mechanism C-S-H initially precipitates as metastable, globular nanoparticles (droplets, d ~ 20–60 nm) which within less than one hour convert to the characteristic nanofoils of early C-S-H. In the presence of PCEs, the initial globuli exhibit a core-shell morphology, presumably with PCE as shell. The shell was found to delay the conversion to nanofoils for several hours by stabilizing the metastable globules. The PCE polymer exhibiting higher anionicity delayed the conversion to nanofoils more than the PCE possessing fewer carboxylate groups.

Thermal stability of brushite with chitosan samples

In this paper, the powders of brushite from an aqueous solution of Ca(NO3)2- (NH4)2HPO4 with different content of chitosan were synthesized. XRD data revealed that all samples are single-phase and are brushite (CaHPO4·2H2O). By FT-IR spectroscopy and BET methods, it was found that chitosan adsorbs onto the surface of powders. With increase of the content of the additive, the average size of crystallites increases 4.0 – 4.8 – 11.8 μm, respectively, and the dissolution rate in isotonic solution also decreases. The thermal stability of the composite powders was studied. It was established that the highest destruction of samples occurs in the range 473-673 K by removing of adsorption and crystallization water and partial change of the structure of the mineral and chitosan. At a temperature of 873 K, carbonization of the organic additive occurs.

Laser Recovery of Subsurface Damages in Chemomechanically Polished Silicon Wafers

Silicon wafers are the most widely used semiconductor substrates. It has been considered that silicon wafers after chemomechanical polishing (CMP) have no subsurface defects. However, in fact, defects such as dislocation and latent microcracks will remain in the wafers if CMP is performed under unsuitable conditions. In this study, we confirmed the existence of subsurface damages at a depth of submicron level in a silicon wafer after CMP, then used a nanosecond pulsed Nd:YAG laser to repair the subsurface damages. It was found that subsurface defects were recovered to a single crystalline structure by laser irradiation without changing the surface topography. The phase transformation of silicon before and after laser irradiation was confirmed by laser Raman spectroscopy and chemical etching using saturated aqueous solution of Ca(OH)2. The findings from this study contributes to improve the quality of silicon wafers for high-performance semiconductors.

In situ pore-forming alginate hydrogel beads loaded with in situ formed nano-silver and their catalytic activity.

An aqueous mixture of sodium carbonate (Na2CO3) and sodium alginate (Na-ALG) was added dropwise into an aqueous solution of Ca(NO3)2, leading to the formation of calcium alginate (Ca-ALG) hydrogel beads. Meanwhile Na2CO3 as a pore-forming precursor was transformed in situ into CaCO3 nanoparticles (CaCO3 NPs). SEM images show that CaCO3 NPs aggregates with a size of ∼10 μm were uniformly distributed in the Ca-ALG hydrogel beads. After subsequent erosion using acetic acid, Ca-ALG hydrogel beads with a uniform microporous structure were obtained. The porosity and specific surface area of such in situ pore-formed hydrogel beads are 16 and 14 times higher than those of the beads prepared in the absence of Na2CO3. Additionally, their porous structure can be modulated by varying the amount of Na2CO3. The obtained porous Ca-ALG hydrogel beads were further immersed into an aqueous solution of AgNO3. Under UV irradiation, the Ag(+) ions adsorbed in the Ca-ALG were in situ reduced to Ag nanoparticles (Ag NPs). SEM and TEM images show that Ag NPs with a size of ∼10 nm were uniformly distributed in the matrix of the hydrogel beads. The loading amount of Ag in the beads can also be modulated by varying the amount of Na2CO3. Furthermore, the resultant Ca-ALG beads loaded with Ag NPs (Ag/Ca-ALG) were used as catalysts. Their catalytic activity was evaluated by using the reduction reaction of 4-nitrophenol as a model reaction. The rate constant of the reaction in the presence of dry porous Ag/Ca-ALG beads was found to be 36 times higher than that in the presence of beads prepared in the absence of Na2CO3. Such a high catalytic efficiency can be attributed to their porous structure and consequent high Ag-loading capacity.

Steam gasification of Indonesian subbituminous coal with calcium carbonate as a catalyst raw material

The effect of Ca catalysts prepared from CaCO3 on the steam gasification of Indonesian subbituminous coal at 700–800°C is examined. The char obtained by pyrolyzing the coal with 0.59wt.% of Ca (dry basis) showed conversions in steam gasification at 750 and 800°C of around 70 and 90wt.% (dry ash and catalyst free basis), which were 2 and 1.5 times larger than those of the coal without the Ca catalyst, respectively. The activity of this Ca catalyst was as high as that prepared using an aqueous solution of Ca(OH)2. The TPD and XRD measurements demonstrated that the Ca catalyst from CaCO3 was initially present in the ion-exchanged form, and as a finely dispersed calcium species after pyrolysis. These results confirm that CaCO3 is effective as a catalyst raw material in the steam gasification of subbituminous coal, even at low catalyst loadings.

ChemInform Abstract: Ultrathin Ca‐PO4‐CO3 Solid Solution Nanowires: A Controllable Synthesis and Full‐Color Emission by Rare‐Earth Doping.

AbstractUltrathin Ca‐PO4‐CO3 solid solution nanowires are synthesized from aqueous solutions of Ca(NO3)2, Na2CO3, and Na3PO4 containing octadecylamine, EtOH, and oleic acid (autoclave, 90—220 °C, 12 h).

Multinuclear complex formation in aqueous solutions of Ca(ii) and heptagluconate ions

The equilibria and structure of complexes formed between the Ca(2+) ion and the heptagluconate (Hglu(-)) ion in both neutral and alkaline solutions have been studied. In alkaline solutions an uncharged, multinuclear complex is formed with the composition of Ca3Hglu2(OH)4 (or [Ca3Hglu2H(-4)](0)) with an unexpectedly high stability constant (lg β(32-4) = 14.09). The formation of the trinuclear complex was deduced from potentiometry and confirmed by freezing-point depression measurements and conductometry as well. The binding sites of Hglu(-) were determined from NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms proved to be the most probable sites for Ca(2+) binding.

Hydration of the calcium(ii) ion in an aqueous solution of common anions (ClO4−, Cl−, Br−, and NO3−)

Raman spectra of aqueous calcium salt solutions, Ca(ClO(4))(2), CaCl(2), CaBr(2), and Ca(NO(3))(2), were measured from the concentrated solution stage to more dilute solutions (6.08-0.1 mol L(-1)) at 23 °C in water and heavy water down to 40 cm(-1). In aqueous Ca(ClO(4))(2) solutions a strongly polarized band at 283 cm(-1) (full width at half height (fwhh) = 68 cm(-1)) was observed. The mode at 283 cm(-1) was assigned to the Ca-O symmetric stretching vibration of the hexa-aqua Ca(2+) ion, [Ca(OH(2))(6)](2+), and the integrated band intensity showed a linear dependency with Ca(ClO(4))(2) concentration. In a Ca(ClO(4))(2) solution of heavy water a similar band was observed at 268 cm(-1) (fwhh = 64 cm(-1)) of the deuterated species, [Ca(OD(2))(6)](2+). In the OH stretching region of water a band of weakly H-bonded O-H oscillators was detected at 3550 cm(-1) due to O-H···ClO(4)(-). In D(2)O solutions a similar band was found at 2590 cm(-1) due to O-D···ClO(4)(-). The band at 283 cm(-1), in addition to the restricted translation mode of water at ~180 cm(-1), was also observed in dilute to moderately concentrated CaCl(2) and CaBr(2) solutions. This fact is strong evidence that neither Cl(-) nor Br(-) penetrate the first hydration sphere of Ca(2+) in solution with mol ratio H(2)O : CaCl(2)/CaBr(2)≥ 18 : 1 and the coordination number is unchanged. Furthermore, the influence of CaCl(2) on the water bands of the librational band region (300-900 cm(-1)), the deformation band of water and the O-H stretching region has been described. In a hydrate melt and very concentrated solutions of CaCl(2) with a mol ratio H(2)O : CaCl(2)≤ 9 : 1, however, contact ion pairs between Ca(2+) and Cl(-) are formed and the 283 cm(-1) band vanishes. Preliminary DFT calculations on the contact ion pair, [Ca(OH(2))(5)Cl](+), confirm its existence in such hydrate melts. In aqueous solutions of Ca(NO(3))(2), NO(3)(-) penetrates the first hydration sphere and spectroscopic evidence of weak nitrato-complex formation could be detected. This is the first comprehensive report on the symmetric stretching vibration of the hydrated Ca(2+) ion, [Ca(OH(2))(6)](2+), in aqueous solution. DFT calculations concerning geometry optimizations and frequency calculations at the B3LYP/6-311+G(d,p) level on the hexa-aqua Ca(2+) ion in the gas phase and including a solvation-sphere were performed. The calculations on [Ca(OH(2))(6)](2+) and [Ca(OD(2))(6)](2+) with a solvation-sphere allowed the determination of the six CaO(6) skeletal modes and supported the assignment of the symmetric stretching mode, ν(1)CaO(6) of [Ca(OH(2))(6)](2+) and [Ca(OD(2))(6)](2+). Discrete cluster calculations on a cluster with six inner sphere and twelve outer sphere water molecules, [Ca(OH(2))(6)(OH(2))(12)](2+) at the same level of theory, led to a Ca-O internuclear distance at 2.383 Å and 4.475 Å for the inner sphere and the outer sphere respectively.