The thermal decomposition of pure and doped cadium carbonate: I. Kinetics

The thermal decomposition of both pure and doped cadmium carbonate has been studied. Doping was effected by adding 1, 5 and 10 atom-% of Al³⁺, Li⁺, Zn²⁺, Ca²⁺, and Ba²⁺. Differential thermal analysis, as well as the kinetics of isothermal decomposition of the various carbonates, has been investigated between 310 and 560 °C. The decomposition of both the pure and doped samples was found to obey Mampel's theory. Rate constants were evaluated and found to be appreciably affected by the presence of foreign ions. Application of the Arrhenius equation gave an activation energy of 22.5 kcal/mol for pure cadmium carbonate which is comparable with the standard enthalpy of the reaction which is 22.0 kcal/mol. On the other hand, in applying the Arrhenius equation to the rate constant of the doped samples, no straight lines could be obtained indicating a continuous decrease in the activation energy with a rise of temperature. The activation energies were found to vary between 4.0 and 44.0 kcal/mol. Discussion is presented to account for the effect of the various dopes on the mechanism of thermal decomposition.     

Catalytic activity of pure and doped ceria

Structural and phase changes accompanying the thermal dehydration of pure and doped hydrated eerie oxide have been followed by thermogravimetric analysis, differential thermal analysis, and X-ray diffraction studies. Doping has been affected by either Zn²⁺, Al²⁺ or U⁶⁺ ions. Texture investigation has been studied by analysis of nitrogen adsorption isotherms. Variation in porosity due to annealing and/or doping, as well as mechanisms of foreign ion incorporation, have been correlated with catalyst activity towards decomposition of isopropanol.     

Effect of Impurities on Monoclinic (II)-Cubic (I) Transformation of Lithium Sulphate

The monoclinic (II)-cubic (I) transformation of lithium sulphate is a reversible reconstructive transformation associated with high activation energy. Cationic impurities like Na⁺, K⁺, Mg²⁺, Zn²⁺, Cd²⁺ and Al³⁺ have been doped in pure lithium sulphate and their effect on the kinetics and energetics of its transformation studied. By employing d.t.a., the enthalpy and energy of activation for the transformation of pure and doped samples of lithium sulphate have been calculated and compared.     

Features of the phase transformations in titanium-containing zinc aluminosilicate glasses doped with cobalt oxide

We demonstrated the efficiency of the Raman spectroscopy method in the study of the process of the formation of the amorphous zinc aluminotitanate (ZAT) phase during the phase decomposition of the titanium-containing zinc aluminosilicate glasses doped with cobalt oxide. The quantitative dependences of the variation of the intensity of the Raman bands characteristic for amorphous and crystalline phases on the temperature of the thermal treatment and the cobalt oxide concentration have been obtained. The speed of phase decomposition with the separation of the nanosize crystals of zinc aluminate spinel (gahnite) and ZAT phase increases at low-temperature thermal treatments with increasing cobalt oxide concentration. The addition of cobalt oxide increases the amount of the amorphous ZAT phase separated during phase decomposition and increases its thermal stability during high-temperature treatments. It has been shown that the Co²⁺ ions enter the zinc aluminate spinel (gahnite) crystals precipitated during phase decomposition. It has been supposed that the composition of the residual glass is close to that of the quartz glass and it contains a very small amount of titanium-oxygen tetrahedra.     

Continuous dynamically controlled low-temperature combustion synthesis of ultrafine Co3O4 powders: Experiment and theoretical analysis

Ultrafine cobalt oxide (Co₃O₄) powders were prepared by bubbling bed technique, an efficient and low energy consuming process of combustion synthesis technology. In this paper, discussed are the thermal decomposition of cobalt(II) oxalate dihydrate (CoC₂O₄·2H₂O), stability of a bubbling layer, air flow velocity, and heat distribution in the system under consideration. Key factors for regulating the process parameters are (a) reaction heat of cobalt oxalate decomposition, (b) air flow velocity and (c) reaction temperature. The optimum combustion temperature of 320–450°C and air velocity larger than the critical velocity by a factor of 1.5–2.0 can be achieved through variation in the ratio of material supply to air flow velocity.     

Correlation between the morphology of cobalt oxalate precursors and the microstructure of metal cobalt powders and compacts

Metal cobalt powders of well-controlled size and morphology were synthesized by thermal decomposition under hydrogen of precipitated cobalt oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strength of the metal compacts was measured.A precipitation from ammonium oxalate and oxalic acid gives rise to the formation of β-CoC₂O₄·2H₂O particles of parallelepipedic and acicular morphology, respectively. An increase in the length to diameter ratio of the precursor particles favours an entanglement of the elementary grains during the thermal decomposition. Therefore, irregular and rough metal particles have been obtained. This specific morphology favours a mechanical interlocking of the particles during the compaction, leading to high values of green density and green strength of the metal compacts.     

Investigation of antimicrobial properties and in-vitro bioactivity of Ce3+-Sr2+dual-substituted nano hydroxyapatites

Dual doped calcium apatite has been widely focused as it enhances the osteoconductive property for the possible applications in orthopedic and dental implants. In this work, we investigate the antimicrobial and bioactive properties of cerium/strontium (Ce³⁺/Sr²⁺) co-substituted hydroxyapatite (HA) nanoparticles synthesized by sol-gel assisted precipitation method. The structure, morphology, functional groups, photoluminescence, and thermal stability of the developed systems are examined. The comparative studies performed among the pure HA, Sr²⁺, and Ce³⁺-substituted HA nanoparticles illustrate higher antibacterial activity with lowered apatite-forming ability and biocompatibility for the Ce³⁺-substituted HA. However, the Ce³⁺/Sr²⁺co-substituted HA exhibits better biocompatibility, apatite-forming ability, and good antimicrobial properties. Sr²⁺ ion inclusion leads to better biological properties and compromise the cytotoxic nature of the Ce³⁺-HA. In addition, the Ce³⁺/Sr²⁺-HA nanoparticles prevent thermal decomposition up to 700°C, pointing also toward the possibility of this co-substituted HA in bone implant applications.     

Effect of Intentional Impurities,Aging, Particle Size and Pre-Irradiation on the Thermal Decomposition of Hydrazinium Diperchlorate

The effect of dopants, aging, particle size and pre-irradiation on the thermal decomposition of hydrazinium diperchlorate (HP-2) has been investigated. Data on the uptake of N₂H₆S04 indicate that these impurities are distributed homogenously in HP-2. Anion vacancies have been found to sensitize the decomposition while cation vacancies desensitize. The mechanism of the decomposition has been discussed in terms of the migration of ionic species and electron transfer from CIO₄⁻ ion to N₂H₆²⁺ ion. The decomposition is found to desensitize with age. The aging effect is attributed to a decrease in anion vacancy concentration with age. Particle size does not seem to have any effect on the decomposition of HP-2. Pre-irradiation is found to affect the decomposition appreciably only when HP-2 is irradiated for longer durations (> 1 hr), the effect being observed only during the later stages of the decomposition (01 > 0.3).     

Thermal Decomposition Performance of Unsymmetrical Dimethylhydrazine (UDMH) Oxalate

The thermal decomposition behavior of unsymmetrical dimethylhydrazine (UDMH) oxalate was studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TG/DTG), and thermogravimetric analysis combined with infrared spectroscopy (TG‐IR). The endothermic decomposition of UDMH oxalate occurred at temperatures between 180.4 °C and 217.6 °C, the maximum decomposition temperature is 199.2 °C. The kinetic parameters of the decomposition reaction were calculated based on the Kissinger equation. The TG‐IR spectra indicated that the thermal main decomposition products of UDMH oxalate are CO₂,H₂O and NH₃.     

Effects of impurities on the properties of BaTiO3 synthesized from barium titanyl oxalate

The effects of impurities, such as H⁺/Cl^? and Zr⁴⁺, on the tetragonality (=c/a) of BaTiO₃ were examined to determine their effect on the synthesis of nano-sized particles with a high dielectric constant. The quantity of incorporated impurities was adjusted by controlling the milling and washing processes, which are essential for the preparation of BaTiO₃ using an oxalate method. The tetragonality decreased with increasing impurity concentration, which can be actual proof of the assumption that impurities decrease the tetragonality due to the enhanced internal strain fields. Moreover, the experimental results showing a tetragonality of 1.0068 for a particle size of 119 nm suggest that the dielectric properties of BaTiO₃ prepared by the oxalate route may be comparable with those prepared by solid-state reactions by optimizing the process parameters.     

Influence de l'antimoine et du cuivre sur la cementation du cobalt par le zinc

Zinc sulphate solution (160g/l Zn²⁺) used for zinc electrowinning is purified for cobalt by cementation with metallic zinc powder. Industrial practice shows that considerable acceleration of this operation is achieved by the presence of trace impurities in solution. Eventually, CuSO₄ and Sb₂O₃ are deliberately added to the solution. The aim of this work is to elucidate the mechanism of action of those impurities.Zn²⁺ ions present in the solution are responsible for the slow speed of cobalt deposition (160g/l Zn²⁺; 10 mg/l Co²⁺).The cathodic part of the cementation reaction was simulated on a flat electrode through potentiostatic deposits at ?730 mV/ENH (potential at zero current of metallic zinc in the solution). The deposits were studied by anodic dissolution, radioactive tracers, X-ray diffraction and fluorescence, atomic absorption spectrophotometry, optical and electronic microscopy (transmission and scanning). The results were compared with cementation on zinc plate and zinc powder.Antimony and copper are deposited together with cobalt and form alloys with reduced cobalt activity. Total voltage available to overcome the inhibitor effect of zinc ions is thus increased and the reduction of cobalt ions accelerated. Antimony, copper and cobalt triple alloys resist particularly well to corrosion with hydrogen evolution. Copper has a higher accelerating effect on cobalt cementation than antimony, but the latter stabilizes the deposit very effectively.The electrochemical methods used and the knowledge of the mechanism of action of the impurities open new trends for industrial practice.     

TPR and XPS study of cobalt–copper mixed oxide catalysts: evidence of a strong Co–Cu interaction

In this work the results of a TPR and XPS investigation of Co_xO_y–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N₂ at 723 K for 24 h of singlephase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co²⁺[Co³]₂O₄ (Co₃O₄) spinel phase. The coppercontaining catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co²⁺[Co³⁺]₂O₄, Co _1-x ²⁺ Cu _x ²⁺ [Co³⁺]₂O₄ and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co²⁺, Co³⁺ and Cu²⁺ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co₃O₄ and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N₂ formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu⁺Co³⁺O₂ compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO₂ phase was the main component. A further addition of copper led to the formation of CuCoO₂ and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N₂calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.     

The effect of Co2+, Cu2+, Fe2+ and Fe3+ during electrowinning of nickel

The effects of the impurities Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺ on the current efficiency, physical appearance, purity, crystallographic orientation and surface morphology of the deposit and on nickel deposition polarization behaviour during nickel electrowinning were determined. The current efficiency did not change significantly in the presence of these impurities over the concentration range studied, but certain changes in the purity and physical appearance of the deposit were observed. Based on the physical appearance of the electrodeposited nickel, the tolerance limits of the impurities in the electrolyte are reported. The tolerance limit of Co²⁺ was a maximum at 500 p.p.m. and a minimum at 5 p.p.m. in the case of Fe²⁺. No deviation of nickel structure from fcc was observed in the presence of any of these impurities but the peak height values for different orientations showed variations with all the impurities and the values also changed with increase in the impurity concentrations. The surface morphology of electrodeposited nickel also changed in the presence of the impurities. The potentiodynamic scan curves for electrodeposition of nickel showed deviations in the presence of all the impurities except Cu²⁺. Based on the results, an attempt is made to correlate the effects of the various factors investigated.     

The chemistry of organosulphur compound types occurring in heavy oils: 4. the high-temperature reaction of thiophene and tetrahydrothiophene with aqueous solutions of aluminium and first-row transition-metal cations

In the reactions of thiophene and tetrahydrothiophene with aqueous solutions of first-row transition-metal and aluminium cations at 240 °C and 3.4 MPa all the metal species accelerated the decomposition of the thiophenes in relation to equivalent reactions with pure water. Al³⁺, Sc³⁺, VO²⁺, Cr³⁺, Ni²⁺ and Cu²⁺ were most reactive towards thiophene and Al³⁺, VO²⁺, Cr³⁺ and Cu²⁺ were most reactive towards tetrahydrothiophene. Principal products were H₂S and complex mixtures of organic products. The presence of CO₂ and oxygen-containing organic products revealed that water was involved in direct chemical reaction with the substrates. It is likely that these model reactions parallel more complex processes that occur during the steam-stimulated recovery of oil-sand bitumen and other high-sulphur oils.     

Synthesis and catalytic behaviors of cobalt nanocrystals with special morphologies

Cobalt nanocrystals with highly ordered snowflake-like, cauliflower-like, ball-like morphologies, and some less ordered shapes were prepared through the reduction of Co(NO₃)₂ by hydrazine hydrate in the solution of methanol, ethanol, ethylene glycol, and 1,2-propanediol. Based on the characterization results of X-ray powder diffraction and scanning electron microscope, crystal and morphologic structures of cobalt particles were correlated with the reaction conditions of temperature, Co(NO₃)₂ concentration, and the alcohols used. By changing temperature and/or Co(NO₃)₂ concentration, pure hexagonal close-packed (hcp) cobalt or a mixture of hcp and face-centered cubic (fcc) cobalt was obtained. The catalytic performance of as-prepared cobalt nanocrystals for the thermal decomposition of ammonium perchlorate (AP) was evaluated by differential scanning calorimetry. The decomposition temperature of AP was significantly decreased, and the apparent decomposition heat was over doubled when 2 wt.% cobalt was added into AP. Among the samples tested, snowflake-like cobalt showed the best performance in the aspect of decreasing the decomposition temperature of AP while the ball-like cobalt exhibited the highest apparent decomposition heat.     

Oxalate Ion Decomposition under UV Light from Low Pressure Mercury Vapor Lamps

Kinetics of oxalate ion decomposition under UV light from low pressure mercury vapor lamps (LPMVL) was studied in a batch reactor. The effects of UV light intensity (1.38×10^?6 to 5.27×10^?6 EL^?1s^?1, where E: Einstein or 1 mole of photons), temperature (15?35°C), initial oxalate concentration ((2.05?21.1)?×?10^?5 M), initial pH (5.45?8.94) and alkalinity (0–50 mg L^?1 as CaCO₃) on the photodecomposition kinetics of oxalate in de-ionized water were investigated. Oxalate decay followed split-rate pseudo-first-order kinetics. The decay rate constants decreased with increasing initial oxalate concentration, initial pH, alkalinity and temperature, but increased with UV light intensity. Solution pH increased during oxalate decomposition and reached a plateau as oxalate reached the analytical detection limit in de-ionized water. Addition of carbonate alkalinity virtually eliminated the pH profile. Time-dependent profiles for non-purgeable organic carbon (NPOC) and total carbon (TC) showed that the carbon not accounted for in NPOC is likely to have been converted to CO₂. The pH profile of oxalate decay was estimated using closed system carbonate equilibrium analysis. The dissolved oxygen (DO) utilization during oxalate decay ranged between 0.3–0.8 mol O₂ / mol oxalate. The effect of DO and the decay of natural dissolved organic carbon (DOC) were also explored. Natural DOC retarded oxalate photodecomposition. The decay rate constants were slightly lower in the absence of DO.     

Optimization of preparation for Co3O4 by calcination from cobalt oxalate using response surface methodology

The conditions of technique to prepare Co₃O₄ by calcination from cobalt oxalate were optimized using response surface methodology. A quadratic equation model for decomposition rate was built and effects of main factors and their corresponding relationships were obtained. The statistical analysis of the results showed that in the range studied the decomposition rate of cobalt oxalate was significantly affected by the calcination temperature and calcination time. The optimized calcination conditions were as follows: the calcination temperature 680.86 K, the calcination time 44.7 min, and the mass of material 3.04 g, respectively. Under these conditions the decomposition rate of cobalt oxalate was 99.06%. The validity of the model was confirmed experimentally and the results were satisfactory.     

New hydrogel containing sulfur compound prepared by γ irradiation and its application for metal recovery

A new hydrogel that contains sulfur is prepared by radiation polymerization and its application for recovery of Hg²⁺, Pb²⁺, Cd²⁺, and Cu²⁺ ions is discussed. The metal hydrogel complexes are isolated and characterized by using different spectroscopic techniques (UV‐visible, IR, NMR, and mass), thermal analysis (TGA and DSC) measurements, and SEM. Also, the mode of complexation is determined using IR and NMR spectroscopy. The scanning electron micrographs show that the hydrogel has a great ability to recover the metal ions in the following order: Hg²⁺ > Cd²⁺ > Pb²⁺ > Cu²⁺. TGA thermograms are used to investigate the mechanism of thermal decomposition. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 955–966, 2000     

Separation of Nickel and Cobalt by Electrodialysis Using Ion-Exchange Membranes in the Presence of EDTA

Abstract

Electrodialytic separation of Ni²⁺ and Co²⁺ cations has been realized by using ion-exchange membranes in the presence of EDTA by preferentially complexing Ni²⁺(Ni²⁺ concentration = EDTA concentration). The degree of complexation is calculated as a function of the pH and of the concentration by using data taken from the literature. Due to a systematic study of the influence of the different separation parameters (nature of the membranes, flow rate, electric current intensity, pH), the conditions_of_separation have been optimized on a computer, and then pure solutions of nickel and cobalt ions have been obtained experimentally. The decomplexation of Ni²⁺ is accomplished in acidic medium by cooling.     

Structural investigation and optical properties of cobalt aluminate pigments derived from thermal decomposition of mixed-metal nitrate co-crystals

In this study, the coloration mechanism of cobalt aluminate spinel materials derived by thermal decomposition of the co-crystallized mixed-metal precursors has been reported. The structural alteration of cobalt aluminates, along with the origins of chroma values at the different calcination temperatures from 600 °C to 1200 °C were thoroughly investigated by combining XRF, XRD, XAS, UV-VIS DRS, FT-IR, and FT-Raman techniques. In-depth analyses of structural information and corresponding optical properties suggested that the coloration can be modified by controlling Co²⁺/Co³⁺ contents and their site occupancies in the spinel structure by adjusting calcination temperatures and selecting the counter ions with appropriate oxidizing power. The interplays among (1) the oxidation process at low temperatures, (2) the deoxidation process at high temperatures, (3) the reduction in the degree of spinel inversion (toward the emerging of normal-spinel CoAl₂O₄ structure), and (4) the existence of the minor Al₂O₃ domains are found to be key imperatives for tailoring the color appearances of cobalt aluminate powders in the broad range from black, dark-green, green, greenish-blue, dark-blue, towards bright-blue. Herein, we reveal the correlation between the synthetic parameters and the structural features of the obtained spinel-based materials, which could further exhibit the crucial procedure to control the coloration of inorganic pigments systematically.