Thermal Decomposition Of Co Research Articles

Thermal decomposition of Co xLa y(C 2O 4)( x+1.5 y)

A series of Co(II)-La(III)-oxalate codepositions have been prepared and their molecular formulae can be expressed as Co x La y (C 2O 4)( ( x +1.5 y ). The results of X-ray diffraction showed that these codepositions were solid solutions rather than simple mixtures. Thermal decomposition of Co x La y (C 2O 4)( x+1.5 y ) in Ar and H 2 was investigated by GC, and it was found that methanation of the CO and CO 2 produced during the decomposition in hydrogen took place, and that the catalytic activity depended on the La/Co ratio.

Oxidation of ammonia evolved by thermal decomposition of co(III) ammine complexes

Thermal decomposition of various compounds containing Co(III) ammine complex cations was studied by use of a differential thermal analysis-thermogravimetry instrument. When heated in an air atmosphere, remarkable exothermic peaks corresponding to NH 3 liberation were observed for the sulfato double complexes such as [Co(NH 3) 6][Ln(SO 4) 3]· nH 2O, where Ln is a trivalent rare earth metal, whereas simple salts gave endothermic peaks in the same temperature range with liberation of the coordinated NH 3 as a gaseous product. This exothermic effect was found to be due to oxidation of the liberated NH 3 on the surface of the sample holders, but only if they are made of Pt or Pd. The thermal analytical data were examined to find the conditions under which the oxidation of NH 3 takes place effectively after liberation from compounds of various compositions. In addition to the presence of oxygen and of Pt or Pd as catalysts, the temperature and rate of NH 3 liberation seem to be important factors, but their involvement is quite complicated.

Mechanism of cobalt atomization from different atomizer surfaces in graphite-furnace atomic-absorption spectrometry

The mechanism of cobalt atomization from different atomizer surfaces in graphite-furnace atomic-absorption spectrometry has been investigated. The atomizer surfaces were pyrolytically coated graphite, uncoated electrographite, and glassy carbon. The activation energy of the rate-determining step in the atomization of cobalt (taken as the nitrate in aqueous solution) in a commercial graphite furnace has been determined from a plot of log k s vs. 1/ T (for T values greater than the appearance temperature), where k s is a first-order rate constant for atom release, and T is the absolute temperature. The activation energy E a, can be correlated either with the dissociation energy of CoO (g) or with the heat of sublimation of Co (s), formed by carbon reduction of CoO (s), the latter being the product of the thermal decomposition of Co(NO 3) 2. The mechanism for Co atomization seems to be the same for the pyrolytically coated graphite and the uncoated electrographite surfaces, but different for the glassy carbon surface. The suggested mechanisms are consistent with the chemical reactivity of the three atomizer surfaces, and the physical and thermodynamic properties of cobalt and its chemical compounds in the temperature range involved in the charring and atomization cycle of the graphite furnace.

ARAS measurements on the thermal decomposition of CO2 behind shock waves

The dissociation rate coefficient of COi has been measured behind reflected shock waves in the temperature range 2400<T<4400 K at pressures 1.2<p <2.0 bar. By the use of the atomic resonance absorption spectroscopy, the formation of O atoms could directly be observed in the postshock reaction zone. The experiments have been performed in mixtures of CCh highly diluted in argon. The initial COi concentrations varied from 10 to 5000 ppm. The Arrhenius expression for the thermal decomposition of COz, CCh + M_^iCO + O + M was found to be k = 3.65 x 10 14exp(-52,525 K/T) cm3mol~1 s1. The effect of impurities was minimized by keeping background pressures in the shock tube below 5x 10 ~7 mbar.

Thermal decomposition of Co(II), Cu(II) AND Zn(II) methanesulfonates

The thermal decomposition of Co(II), Cu(II) and Zn(II) tetrahydrated methanesulfonates has been studied in air, under vacuum and in N 2 flow. Dehydration enthalpies were measured from the DSC curves, and degradation products of anhydrate salts were identified by X-ray diffraction.

The mechanism of thermal decomposition of Co(NO3)2 · 2H2O

The mechanism of thermal decomposition of Co(NO3)2 · 2H2O was found to involve stages in which Co(NO3)3 and Co2O3 · H2O are formed both of which decompose to Co3O4. During the process, the total cobalt enters the +3 oxidation state, which is consistent with the results reported by Mehandjiev [2].

Electrochemical surface properties of Co3O4 electrodes

The electrochemical behaviour of Co3O4 layers deposited by thermal decomposition of Co(NO3)2 at 200–500°C on titanium supports with and without an interlayer of RuO2 has been studied by cyclic voltammetry, chronopotentiometry and potential step experiments in alkaline solutions. Such variables as the calcination temperature, the solution pH, the potential sweep rate and the oxide loading have been investigated in detail to determine their influence on voltammetric peaks and voltammetric charge. Insight has been gained into the relevance of the latter to surface area determination and to proton diffusion into the oxide layer. The role of the support-active layer interface and especially that of the RuO2 interlayer has been scrutinized. The importance of surface studies for the understanding of the electrocatalytic behaviour of Co3O4 electrodes has been analysed.

Effect of calcination temprature on the surface properties of Ti/RuO 2-supported Co 3O 4 layers. A spectroscopic investigation

Co 3O 4 layers prepared by the thermal decomposition of Co (NO 3) 2 at 200—400°C were deposited on Ti supports with an interlayer of RuO 2. The surface composition and the depth concentration profile were analyzed by Rutherford backscattering, X-ray photoelectron and Auger electron spectroscopies. Results have shown that: (i) inter-diffusion takes place at the RuO 2/Co 3O 4 phase boundary but Ru does not reach the surface in the temperature range explored; (ii) the samples are partly hydrated to an extent which decreases as the annealing temperature is increased; (iii) the surface composition does not depend appreciably on the calcination temperature but the procedure of preparation may play a role in the actual non-stoichiometry; and (iv) there is weak but ambigous evidence that the Co(III)/Co(II) ratio is higher on the surface.

Effect of calcination temprature on the surface properties of Ti/RuO 2-supported Co 3O 4 layers. A spectroscopic investigation

Co 3O 4 layers prepared by the thermal decomposition of Co (NO 3) 2 at 200—400°C were deposited on Ti supports with an interlayer of Ru

Properties of catalysts prepared by pyrolysis of Co 2(CO) 8 on silica containing surface Ti ions

Catalysts prepared by thermal decomposition of Co 2(CO) 8 on modified silica were studied by magnetic susceptibility and by IR and ESR spectroscopy, and were tested in CO hydrogenation. The modification of SiO 2 by Ti ions made it possible to diminish the size of metallic Co particles. The effect was the most pronounced for modification by hydride complexes of a low-valent titanium. An increase of Co dispersion was accompanied by a drop in the metal activity in CO hydrogenation and by a rise of the relative yield of light hydrocarbons and alcohols, especially that of ethanol.

Crystallite size and microstrains of Co 3O 4 derived from CoOOH and Co(OH) 2

The variation of crystallite size and microstrains in Co 3O 4 derived from the thermal decomposition of CoOOH and Co(OH) 2 is studied by X-ray diffraction line broadening analysis in several crystallographic directions. The results show that the low-temperature oxide derived from CoOOH produces lower crystallite size and microstrains, due to the development of cracks in the particles instead of a porous system which is characteristic of the sample derived from Co(OH) 2. On the other hand, microstrains decrease and crystallite size increases with temperature for both parent compounds, but the changes are dependent on the crystallographic direction. The shape of crystallites is anisotropic at low temperature but the isotropy increases on heating, specially for the samples obtained from CoOOH.

Mechanistic study of C12 evolution at Ti-supported Co3O4 anodes

Co3O4 layers were prepared by thermal decomposition of Co(NO3)2 at various temperatures in the range 200–500° C on a Ti support with and without an interlayer of RuO2. Kinetic studies were carried out with and without dissolved Cl2 at various partial pressures in NaCl solutions of concentration in the range 0.5–5 mol dm−3. The effect of the solution pH was especially investigated. Kinetic measurements were carried out both close to and far from equilibrium. The following parameters were determined: transfer coefficient, Tafel slope, stoichiometric number, reaction orders with respect to Cl−, H+ and surface sites, activation energy. The most intriguing feature observed was the retarding effect of acidity on the anodic Cl2 reaction. This has been ascribed to the complex surface behaviour of oxides in solution. A detailed mechanistic scheme has been proposed and discussed. The stability of the oxide surface was monitored by measuring the voltammetric charge in alkaline solution after sets of experiments.

The point of zero charge of Co 3O 4: Effect of the preparation procedure

Co 3O 4 powder samples were prepared by thermal decomposition of Co(NO 3) 2 6H 2O in the range of temperature from 200 to 800°C. The point of zero charge (pzc) was measured by acid-base potentiometric titration in KNO 3 solutions. The isoelectric point was also determined by measuring the electrophoretic mobility of the dispersed oxide particles. The pzc was found to be independent of the calcination temperature between 200 and 500°C (mean value 7.5 + −0.1) whereas it rose as the temperature was increased further. The results have been discussed within the framework of existing semi-empirical theories of the acid-base properties of oxides. The experimental data were also processed according to the Grahame model of the electrical double layer. This approach has enabled the “electrochemical” surface area and the inner layer capacity to be estimated. A value for the potential of zero charge has also been derived, E σ−0 = 0.50 V (SHE).

Thermal decomposition and thermofracto-chromatographic studies of metal citrates

The thermal decomposition and kinetic parameters of thermal decomposition of Mg(II), Ca(II), Al(III), Cr(III), Fe(III), Co(II), Ni(II), Zn(II), Mn(II) and Cd(II) complex salts with citric acid were investigated on the basis of the respective thermal curves. The values of the activation energy (Ea) and reaction order (n) of the thermal decomposition were compared. Thermofractochromatograph constructed in our laboratory complies with the requirements of apparatus for separation, evolution and identification of products formed during the heating of the investigated samples in the temperature range of 293 to 600 K.

Physicochemical characterization of Co 3O 4 prepared by thermal decomposition I: Phase composition and morphology

Co 3O 4 was prepared by thermal decomposition of Co(No 3) 2·6H 2O and CoCl 2·6H 2O as both powders and coatings on quartz and titanium supports. The samples were characterized by thermogravimetric analysis, X-ray analysis (phase composition, crystal structure, crystallite size and crystallinity), surface area determination using the Brunauer-Emmett-Teller method and by direct observation with the scanning electron microscope.

Vibrational analysis of the products from thermal decomposition of OCS and CO 2

The thermal decomposition of CO 2 and OCS has been studied using a shock tube and cw CO probe laser. The energies of activation are in good agreement with the values of other workers. It has been shown that the CO formed from OCS has an initial non-thermal vibrational distribution with a large excess in ν = 0.

Pulsed laser atom-probe study of the dissociation of CO on molybdenum

The thermal decomposition of molecular CO on molybdenum surfaces has been studied using the pulsed laser atom-probe (PLAP). Field emitter tips, cleaned by vacuum field evaporation, were dosed with CO at low temperatures (<60 K) and heated to 180–350 K under fieldfree conditions. The fraction of undissociated CO + ions compared to all carbon- and oxygen-containing species appearing in subsequently recorded PLAP mass spectra was taken as a measure of the extent of surface CO dissociation. Molecular (virgin) CO was found to convert to dissociated (β) CO at temperatures between 200—300 K. The analyzed surface area included both flat single crystal planes and stepped regions. Assuming first-order kinetics, the dissociation occurred with an activation energy of 0.7 ± 0.1 eV. The dissociation on the flat (110) plane, measured using the same technique but with the rest of the surface masked, occurred with a 0.12 eV higher activation energy.

Thermal decomposition of CO on a stepped Ni surface

The adsorption-desorption behaviour of CO on the stepped Ni(S) [5(111) × (11̄0)] and the smooth Ni(111) plane are compared by using LEED, thermal flash desorption and AES. Above room temperature flash desorption from the Ni(111) face yields a single α peak characteristic of molecularly adsorbed CO whereas from the stepped surface in addition to the a peak α second desorption peak (β2) appears around 550°C which is assigned to associative CO desorption. If carbon and oxygen are separately chemisorbed on Ni(111) associative desorption of CO leads to a desorption peak around 350° C. It is concluded that steps lower the activation energy for CO decomposition but increase the activation energy for associative desorption.

Vaporization and thermal decomposition of transition metal salts in flameless atomic absorption spectrometry with a carbon tube atomizer

Vaporization and thermal decomposition of Cr, Mn, Fe, Co, Ni and Cu salts were investigated by measuring the absorption spectra observed when aqueous solutions of these salts were heated in the carbon tube atomizer. Gaseous metal halides are vaporized in the atomizer at temperatures above 300–500° C. SO 2 and NO are produced by thermal decomposition of metal sulfates and nitrates, respectively. The vaporization of metal halides is also confirmed by the spectra for solutions of metals in hydrochloric acid and for mixtures of metal nitrates and ammonium halides.

Complexes of cobalt(II) and nickel(II) nitrates and perchlorates with substituted imidazoles

A series of complexes of the general formulae ML n X 2 (M = Co, Ni; X = ClO 4 −, NO 3 −; n = 4 or 6; L = 1-vinyl; 1-vinyl 2-methyl; 1-ethyl; 1-propyl; 2-ethyl and 2-phenyl imidazole) have been prepared and characterised by magnetic susceptibility, electronic spectra and molar conductivity in nonaqueous solvents and IR spectra. Octahedral complexes are obtained when n = 6 for both Co(II) and Ni(II); but, when n = 4 tetrahedral Co(II) complexes and either square-planar or strongly distorted tetragonal Ni(II) complexes are obtained. Evidences for NO 3 − coordination were found in Co(1-vinyl 2-methyl imidazole) 3 (NO 3) 2 possessing tetrahedral structure with one NO 3 − group involved in unidentate coordination and in NI(1-propyl imidazole) 2 (NO 3) 2, which has an octahedral structure achieved through bidentate coordination of both the nitrate groups. Ni(1-propyl imidazole) 4 (ClO 4) 2 and Ni(1-propyl imidazole) 2 (NO 3) 2 were obtained by the thermal decomposition of the corresponding hexakis complexes. Thermal decomposition of Co(1-ethyl imidazole) 6 (ClO 4) 2 gave 4-coordinate, tetrahedral Co(1-ethyl imidazole) 4 (ClO 4) 2, whereas that of Ni(1-ethyl imidazole) 6 (ClO 4) 2 gave Ni(1-ethyl imidazole) 5 (ClO 4) 2 which is shown to be a high-spin, penta-coordinate complex involving ionic ClO 4 − groups.