Unusual route for preparation of manganese(II), cobalt(II), zinc(II) and cadmium(II) carbonate compounds: synthesis and spectroscopic characterizations

The manganese(II) carbonate, MnCO₃·H₂O, cobalt(II) carbonate, CoCO₃·4H₂O, zinc(II) carbonate, ZnCO₃ and cadmium(II) carbonate, CdCO₃, respectively, were synthesis by a new simple unusual route during the reaction of aqueous solutions of MnX₂, CoX₂, ZnX₂ and CdX₂, where (X = Br⁻ and ClO₄⁻) with urea at high temperature within ∼ 90°C for 6 h. The infrared spectra of the reaction products clearly indicate the absence of the bands of urea, but show the characteristic bands of ionic carbonate, CO₃²⁻. A general mechanism describing the preparation of manganese(II), cobalt(II), zinc(II) and cadmium(II) carbonate compounds are discussed.     

Characterization of zinc carbonate hydroxides synthesized by precipitation from zinc acetate and potassium carbonate solutions

Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation of a white solid, whose composition and structure depend on the initial concentrations of the reagents. Hydrozincite, Zn₅(CO₃)₂(OH)₆, forms when the K₂CO₃ concentration is low and a new K-containing zinc carbonate hydroxide phase forms when the K₂CO₃ concentration is high. The chemical formula of the new phase has been determined to be Zn(CO₃)_0.61(OH)_0.780.233K₂CO₃ by TGA, CHNO and AA analysis. The new phase is insoluble in water and extensive water washing of the new phase does not change its composition or structure, suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified CO₂ causes disproportionation to separate phases of ZnCO₃ and K₂CO₃. Pure ZnCO₃ was synthesized for comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal synthesis of ZnCO₃.     

Kinetics of carbothermic reduction of zinc sulfide in the presence of calcium carbonate

The kinetics of the carbothermic reduction of zinc sulfide in the presence of calcium carbonate was investigated by an atomic absorption spectrometer (AAS) and a thermogravimetric analysis system (TGA). Experimental results indicate that TGA data accompanying with the equation derived from two-stage mechanism can be used to calculate the zinc yield properly. The results of TGA revealed that the rate of reduction in the presence of calcium carbonate was close to that in the presence of calcium oxide. The reduction rate was found to increase with increasing the reaction temperature, the initial molar ratio of C/ZnS, or the initial molar ratio of CaCO₃/ZnS and with decreasing the argon flow rate, the sample height, the size of carbon aggregate, the size of calcium carbonate aggregate or the initial bulk density. An empirical rate expression of zinc yield has been regressed based on the experimental data obtained.     

Formation of Pb(Ti,Zr)O3, from thermal decomposition of oxalate precursors

Lead zir conyl oxalate hexahydrate (LZO) and lead titanyl zirconyl oxalate hydrate (LTZO) are prepared and characterized. Their thermal decompositions have been investigated by thermoanalytical and gas analysis techniques. The decomposition in air or oxygen has three steps — dehydration, decomposition of the oxalate to a carbonate and the decomposition of carbonate to PbZrO₃. In non oxidising atmosphere, partial reduction of Pb(II) to Pb(0) takes place at the oxalate decomposition step. The formation of free metallic lead affects the stoichiometry of the intermediate carbonate and yields a mixture of Pb(Ti,Zr)O₃ and ZrO₂ as the final products. By maintaining oxidising atmosphere and low heating rate, direct preparation of stoichiometric, crystalline Pb(Ti,Zr)O₃ at 550°C is possible from the corresponding oxalate precursor.     

In situ preparation of calcium carbonate films

The in situ preparation of calcium carbonate films in an ultra high vacuum (UHV) is inhibited by the decomposition of CO₂ molecules at the surface and the absence of CO₂ bulk diffusion. Therefore, it is not possible to prepare such films simply by CO₂ exposure to a calcium layer.We investigated different approaches for the preparation of CaCO₃ films in an UHV. Among these, only the simultaneous evaporation of Ca atoms in a mixed O₂ and CO₂ atmosphere is able to produce well defined stoichiometric calcium carbonate films. Metastable Induced Electron Spectroscopy, Ultraviolet Photoelectron Spectroscopy and X-ray Photoelectron Spectroscopy are employed to verify quality and purity of the films.     

Preparation,characterization and application of Fe3O4/ZnO core/shell magnetic nanoparticles

Fe₃O₄ magnetic nanoparticles (MNPs) were synthesized by a co-precipitation method. The phase purity was confirmed by X-ray powder diffraction (XRD) analysis. The crystal size was found to be 10 nm from transmission electron microscopy (TEM). It is evidenced that the surface of Fe₃O₄ MNPs was modified by sodium citrate. The Fe₃O₄/ZnO core/shell MNPs were obtained by coating the MNPs with direct precipitation using zinc acetate and ammonium carbonate. The precursor was firstly dried and then calcined at 350 °C. The antioxidation tests indicated that the core/shell MNPs give better antioxidation than that of the Fe₃O₄ MNPs. The photocatalytic degradation of methyl orange revealed that the core/shell MNPs have higher photocatalytic activity than that of the ZnO nanoparticles. Separation of the core/shell MNPs from the aqueous suspension using a magnet provides an easy way to recycle the core/shell MNPs. After four-time recycling, the photocatalytic degradation percentage of the core/shell MNPs is about 70%.     

Mechanical Activation of Diopside in CO2

The mechanical activation (MA) of diopside in a controlled CO₂ atmosphere was studied using different grinding facilities. The results demonstrate that diopside may sorb CO₂ by two mechanisms, depending on the nature of the MA process. If grinding is not accompanied by structure breakdown, the sorption process is similar to that reported for metal oxides, and the adsorbate consists of undistorted CO₃ ^2- groups. If the MA process leads to diopside amorphization, CO₂ is sorbed in the form of distorted carbonate groups, and the IR spectrum contains a split absorption band (1433 and 1522 cm^–1) similar to the CO₃ ^2- band in the spectra of carbonate-containing silicate glasses. After ball milling in an AL-1000 mechanical activator in CO₂ for 580 min, diopside contains up to 15 wt % CO₂. Subsequent heating ensures partial or complete removal of the carbonate. Acid treatment of diopside after MA in CO₂ leads to decomposition of the carbonate and almost complete leaching of the Ca and Mg cations.     

Manganese in apatites,chemical, ligand-field and electron paramagnetic resonance spectroscopy studies

Hydroxapatites precipitated with different amounts of carbonate and Mn²⁺ were studied. Infrared spectra, X-ray diffraction lattice parameters and thermal behaviour indicate that the presence of Mn²⁺ does not have any effect on the formation and properties of the carbonate apatites obtained. Interaction of apatite with a Mn²⁺-containing aqueous solution reveals that the molar uptake of Mn²⁺ by the apatite is higher than the Ca²⁺ released by it. Ligand-field and electron paramagnetic resonance spectroscopy results show that in Mn²⁺-doped Cd₅(PO₄)₃Cl, Mn²⁺ replaces Ca²⁺ in the apatite lattice, but in precipitated carbonate apatite it is in an MnO phase. The conclusion that Mn²⁺ in precipitated carbonate apatites is not incorporated in the apatite crystal is discussed in the light of the size differences between Mn²⁺ and Ca²⁺.     

Study of Mechanical Activation of Diopside in a CO2 Atmosphere

Interaction of natural diopside CaMgSi₂O₆ with CO₂ during mechanical activation in a CO₂ atmosphere has been studied. It has been shown that, depending on the kind of mechanical activator used, two types of CO₂ sorption by diopside are possible. If grinding is not accompanied by crystal structure disordering, the sorption of CO₂ on the diopside surface is similar to the sorption on metal oxides in the form of undistorted CO₃ ^2– groups, resulting in a nonsplit absorption band at 1430 cm^–1 in the infrared spectrum. If the mechanical activation of diopside leads to amorphization of the sample, it absorbs CO₂ in the form of distorted carbonate groups, which results in the appearance of a double carbonate band with maxima at 1433 and 1522 cm^–1 in the infrared spectrum of the ground sample. This band is similar to the one corresponding to CO₃ ^2– groups in the infrared spectra of carbonate-containing silicate glass. The carbonate content in the diopside sample reaches about 15% CO2 (or 35% CaCO₃) after mechanical activation in an AL-1000 activator in the CO₂ atmosphere for 580 min. X-ray diffraction, infrared spectroscopic data, carbonate content, and BET surface area measurements indicate that CO₂ molecules are likely to penetrate the structurally disordered diopside sample by a tribosorption mechanism. The results on the relaxation of the activated diopside sample during heating are presented.     

High‐Performance Aqueous Zinc–Ion Battery Based on Layered H2V3O8 Nanowire Cathode

Rechargeable aqueous zinc–ion batteries have offered an alternative for large‐scale energy storage owing to their low cost and material abundance. However, developing suitable cathode materials with excellent performance remains great challenges, resulting from the high polarization of zinc ion. In this work, an aqueous zinc–ion battery is designed and constructed based on H₂V₃O₈ nanowire cathode, Zn(CF₃SO₃)₂ aqueous electrolyte, and zinc anode, which exhibits the capacity of 423.8 mA h g⁻¹ at 0.1 A g⁻¹, and excellent cycling stability with a capacity retention of 94.3% over 1000 cycles. The remarkable electrochemical performance is attributed to the layered structure of H₂V₃O₈ with large interlayer spacing, which enables the intercalation/de‐intercalation of zinc ions with a slight change of the structure. The results demonstrate that exploration of the materials with large interlayer spacing is an effective strategy for improving electrochemical stability of electrodes for aqueous Zn ion batteries.     

On the morphological nature of Na2CO3 produced by thermal decomposition from NaHCO3 and from Na2CO3 · 10H2O

Reactivity of sodium carbonate toward SO₂ is dependent upon Na₂CO₃ microstructure. In this paper we obtained sodium carbonate by thermal decomposition of NaHCO₃ and Na₂CO₃. 10H₂O. The first reaction is a gas-solid process while the second one proceeds via liquid-phase. Accordingly the sodium carbonate surface area and porosity from NaHCO₃ are higher than those the product obtained from Na₂CO₃.10 H₂O. These properties can be related to the higher degree of reactivity observed in the conversion to sodium sulfite of Na₂CO₃ from NaHCO₃. The role of water vapor pressure in controlling the sodium carbonate morphology from NaHCO₃ has been proved to be important.     

Mg2+ content control of aragonite whisker synthesised from calcium hydroxide and carbon dioxide in presence of magnesium chloride

Abstract

This research is concerned with thermodynamic control of inorganic whisker synthesis in existence of some additives. The polymorphism and morphology control of calcium carbonate (CC) is an active research area because of wide applications of CC. Magnesium chloride has been used to improve the formation of aragonite whisker synthesised from Ca(OH)₂ and CO₂. However, the reaction kinetics and the purity of final products affected by MgCl₂ have not been theoretically studied. In the present research quantitative thermodynamic calculation showed that MgCl₂ can decrease relative supersaturation by several orders of magnitude and so is favourable to the formation of aragonite. High reactant ratio of MgCl₂/Ca(OH)₂ will give a marked decrease in pH within the transformation of Ca(OH)₂ into Mg(OH)₂, but a small decrease in pH in the following CaCO₃ formation, which is disadvantageous to the control of the synthesis with pH. Both solid Mg(OH)₂ and MgCO₃ may exist in aragonite product, but can be avoided by pH control. Maximum MgCO₃ content in aragonite product is <1·00 wt-% and MgCO₃ can be removed by slightly decreasing pH using excessive CO₂ adsorption, which will result in a negligible decrease in Ca²⁺ conversion and an increase in carbonate ion concentration. High carbonate ion concentration, unfortunately, is disadvantageous to the reuse of MgCl₂ solution. The present study gives a guidance of synthesising aragonite in the presence of inorganic salts such as MgCl₂.     

Analysis of growth parameters for hydrothermal synthesis of ZnO nanoparticles through a statistical experimental design method

Nanocrystalline ZnO particles were synthesized from an aqueous solution composed of zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) and urea (H₂NCONH₂). A precipitating precursor, basic zinc carbonate (Zn₅(CO₃)₂(OH)₆), was first formed by hydrothermally treating the solution at 120 °C for 2–4 h. Nanocrystalline ZnO particles were then obtained by calcining the precursors at 350–650 °C for 0.5–2 h. The synthesis products were characterized using thermogravimetry–differential scanning calorimetry–mass spectrometry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. Based on the experimental results, a possible reaction mechanism for the ZnO formation was proposed. The effects of experimental parameters (namely, the hydrothermal treatment time, the calcination time, and the calcination temperature) on the characteristics of the resulting ZnO products (i.e., the crystalline size and the photoluminescence properties) were analyzed by the Taguchi method to attain the optimum synthesis conditions. By using the appropriate parameters derived from this method, we verified that the optimized synthesis provided a yield of ~70% and that the resulting ZnO particles possessed the characteristics of a ~25 nm crystalline size and a satisfactory photoluminescence property.     

Microwave-assisted hydrothermal synthesis of zinc oxide particles starting from chloride precursor

Zinc oxide (ZnO) was synthesized using a microwave assisted hydrothermal (MAH) process based on chloride/urea/water solution and under 800 W irradiation for 5 min. In the bath, Zn²⁺ ions reacted with the complex carbonate and hydroxide ions to form zinc carbonate hydroxide hydrate (Zn₄CO₃(OH)₆·H₂O), and the conversion from Zn₄CO₃(OH)₆·H₂O to ZnO was synchronously achieved by a MAH process. The as-prepared ZnO has a sponge-like morphology. However, the initial sponge-like morphology of ZnO could change to a net-like structure after thermal treatment, and compact nano-scale ZnO particles were finally obtained when the period of thermal treatment increased to 30 min. Pure ZnO nanoparticles was obtained from calcination of loose sponge-like ZnO particles at 500 °C. The analysis of optical properties of these ZnO nanoparticles showed that the intensity of 393 nm emission increased with the calcination temperature because the defects were reduced and the crystallinity was improved.     

The synthesis of porous Co3O4 micro cuboid structures by solvothermal approach and investigation of its gas sensing properties and catalytic activity

The cobalt carbonate cuboids are prepared by adopting a simple solvothermal approach by using diethylene glycol and water in specific ratio as solvent. The prepared cobalt carbonate is subjected to different instrumentation to investigate its morphology and other properties. It is clear from the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the product is distinct cuboid in shape with a size of approximately 3 μm from each face of the cube. Each particle of cuboid cobalt carbonate seems to comprise of layer by layer assembly of unit cells that consequently leads to a cuboid geometry. The cuboid cobalt carbonate was calcined at 700 °C in a furnace under argon atmosphere that decompose cobalt carbonate into porous Co₃O₄ with the loosely packed arrangement of nano architectures. The gas sensing properties and catalytic activity of porous cuboids Co₃O₄ are also investigated.     

Evolution of corrosion products and metal release from Galvalume coatings on steel during short and long-term atmospheric exposures

Non-treated Galvalume (55% Al, 43.4% Zn and 1.6% Si by weight) coatings have been studied through a combination of surface, near surface and bulk analysis after exposure at marine conditions, and for comparison also in an urban test site and in successively more complex short-term laboratory exposures. Slightly polished Galvalume surfaces exhibit dendritic aluminum-rich areas with higher Volta potential compared with interdendritic zinc-rich areas. These effects were not observed on bare as-received surfaces due to the overall presence of aluminum oxide. As a result, preferential corrosion occurred initially in interdendritic areas. The zinc release rate followed the same time-dependence as the surface coverage of zinc-containing phases at the marine exposure condition with zinc predominantly released compared to aluminum. Short term laboratory exposures generated the same main phases as formed at marine conditions. This confirms that the evolution of corrosion products and time dependence of zinc release rates can be explained by the uniform formation of less soluble Al₂O₃, AlOOH and Al(OH)₃ compared to observed zinc-containing phases, e.g. ZnO, zinc hydroxycarbonate and zinc hydroxychloride. The same underlying mechanism is believed to operate also during exposure of Galvalume in the urban site studied.     

Synthesis and dielectric investigations of ZnTiO3 obtained by a soft chemistry route

In this paper, we report a strategy for preparing an inorganic zinc titanate precursor by applying a chemical bath deposition method (CBD) to ZnO nanocrystals in an aqueous layered titanate colloid. The zinc titanate precursor, obtained as a precipitate, undergoes profound changes under the influence of elevated temperatures in normal atmospheric conditions and allows us to obtain zinc titanate ZnTiO₃ with a rhombohedral symmetry. Investigations of its dielectric properties enabled us to determine a dielectric permittivity (?) of 25, a low loss factor tan(δ) < 10⁻³, and a temperature coefficient (τ_?) of 18 ppm at the frequency of 1.15 MHz. The density of the zinc titanate ceramic was equal to approximately 80% of the theoretical density of the ZnTiO₃ crystals.     

Hydrous oxides of titanium: cation exchange properties and kinetics of exchange

The ion exchange properties of hydrous titania gels of different particle sizes, precipitated from titanous chloride through the agency of ammonium carbonate and hydroxide have been studied. Such studies were carried out under acidic and alkaline conditions with respect to Cu²⁺, Ni²⁺, Co²⁺ and Cr³⁺ ions.In the case of gels precipitated by ammonium carbonate, oxygen gas was used as the oxidizing agent whereas with ammonium hydroxide as precipitant, oxidation was performed with hydrogen peroxide.Ion exchange capacities were determined by visible spectrophotometry. Increasing the pH of preparation lead to an increase in exchange capacities of the hydroxide precipitated gels that are characterized to be mesoporous. Such an increase is not observed in the case of carbonate precipitated microporous gels. It is shown that in the latter case the NH ₄ ⁺ ions generated by the initial interaction of (NH₄)₂CO₃ with the acidic titanous chloride lead to the formation of titania exchangers that are predominantly in the ammonium form. The textural characteristics of the exchanger resulting from different conditions of preparation is a significant contributing parameter to the resulting data.Ageing of the microporous titania samples markedly reduces the exchanger capacity of the smaller Ni²⁺ ions but increases that of the bulkier Cr³⁺ as a result of the presence of some wide pores that appear upon agglomeration. The presence of Cr³⁺ ions in the hydroxo form in solution seems to inhibit its exchange with the appropriate surface species.Studies on the kinetics of exchange with respect to the Ni²⁺ ions seem to indicate that a particle diffusion mechanism is partly or completely responsible for the rate of exchange.     

Thermodynamics and kinetics of methane hydrate formation and dissociation in presence of calcium carbonate

Huge amount of gas hydrate deposits are identified in deep marine sediments, which may be considered as a future source of energy. Since carbonate is one of the major components of marine sediments, in the present study attention has been given to characterize methane hydrate formation and dissociation in presence of calcium carbonate. Experiments were performed with 0%, 2%, 4%, 6% and 10% by weight of calcium carbonate in distilled water. Extensive investigations have been done on pressure-temperature equilibrium behavior of hydrate formation and dissociation at varying concentrations of calcium carbonate. Hydrate formation rate was found to vary with concentration of calcium carbonate as the solubility of calcium carbonate in water is controlled by the presence of simultaneous chemical equilibria involving a high number of species like Ca²⁺, CO₃^2?, HCO₃^?, CO₂, etc. Induction time for hydrate formation has also been measured at different concentrations of carbonate. Nucleation point for the hydrate formation was observed to be slightly higher at higher concentration of calcium carbonate due to increased heat absorption. Dissociation enthalpy of hydrates was calculated by using Clausius-Clapeyron at different measured conditions. Moles consumption of methane gas during hydrate formation at different concentrations of carbonate was measured using real gas equation and found to be minimum at 10?wt%.     

Solubilities of Carbon Dioxide in Aqueous Potassium Carbonate Solutions Mixed with Physical Solvents

The solubilities of carbon dioxide in aqueous potassium carbonate (K₂CO₃) solutions mixed with physical solvents were measured at 298.2 and 323.2 K with a CO₂ partial-pressure range of 5 kPa to 2 MPa. 1,2-propanediol and propylene carbonate were selected as physical solvents. The aqueous solutions treated in this study were 5 mass% K₂CO₃–15 mass% 1,2-propanediol, 5 mass% K₂CO₃–30 mass% 1,2-propanediol, 5 mass% K₂CO₃–7.5 mass% propylene carbonate, and 5 mass% K₂CO₃–15 mass% propylene carbonate. The experimental solubility results were presented by the mole ratio of CO₂ and K₂CO₃ contained in the liquid mixture. The addition of 1,2-propanediol to 5 mass% K₂CO₃ solution lowered the solubility of CO₂ at constant temperature and pressure conditions within the CO₂ partial-pressure range of 5 kPa to 2 MPa. In the case of propylene carbonate, the addition of propylene carbonate increased the experimental solubilities in the region of low CO₂ partial pressures and decreased as the CO₂ partial pressure was increased above atmospheric. The solubilities of CO₂ decreased with increasing temperature in the range of 298.2 to 323.2 K.