Thermal Analysis of Cobalt(II) Salts with some Carboxylic Acids

The thermal analysis of CoC₂O₄·2H₂O, Co(HCOO)₂·2H₂O and Co(CH₃COO)₂·4H₂O was carried out with simultaneous TG-DTG-DTA measurements under non-isothermal conditions in air and argon atmospheres. The intermediates and the end products of decomposition were characterised by X-ray diffraction and IR and UV-VIS spectroscopy. The decomposition of the studied compounds occur in several stages. The first stage of dissociation of each compound is dehydration both in air and argon. The next stages differ in air and argon. The final product of the decomposition of each compound in air is Co₃O₄. In argon it is a mixture of Co and CoO for cobalt(II) oxalate and cobalt(II) formate but CoO for cobalt(II) acetate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monitoring of the Gas Phase Composition: A Prerequisite for Unravelling the Mechanism of Decomposition of Solids. Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products. Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Co_met, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Co_met. The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H₂, Co_met oxidation under rich and lean oxygen conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Peculiarities of polythermic decomposition of iron,cobalt and nickel oxalates within pores of photonic crystals based on SiO<Subscript>2</Subscript> in atmosphere with oxygen lack

Iron(II), cobalt(II) and nickel(II) oxalates were synthesized as nanofractals inside the voids of the photonic crystals based on SiO₂. Guest substances undergone polythermic decomposition within the pores of the photonic crystals in helium atmosphere containing of oxygen traces (∼1 Pa) under static conditions. Pyrolysis of Fe(COO)₂·2H₂O, Co(COO)₂·2H₂O and Ni(COO)₂·2H₂O studied by TG and DSC techniques results in the formation of the metal oxides. The nanoparticles of Fe₂O₃, CoO (Co₃O₄) and NiO populated the interspheric voids of the photonic crystals exhibited no ferromagnetic effects indicating that no metallic inclusions were formed in helium in the presence of O₂ traces. The exothermic effect was observed by the thermal decomposition of the cobalt(II) oxalate only under oxygen lack.     

Non-isothermal Studies on Mechanism And Kinetics of Thermal Decomposition of Cobalt(II) Oxalate Dihydrate

Thermal decomposition of CoC₂O₄⋅2H₂O was studied using DTA, TG, QMS and XRD techniques. It was shown that decomposition generally occurs in two steps: dehydration to anhydrous oxalate and next decomposition to Co and to CoO in two parallel reactions. Two parallel reactions were distinguished using mass spectra data of gaseous products of decomposition. Both reactions run according toAvrami–Erofeev equation. For reaction going to metallic cobalt parameter n=2 and activation energy is 97±14 kJ mol^–1. It was found that decomposition to CoO proceeds in two stages. First stage (0.12<α_II<0.41) proceeds according to n=2, with activation energy 251±15 kJ mol^–1 and second stage (0.45<α_II<0.85) proceeds according to parameter n=1 and activation energy 203±21 kJ mol^–1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Investigations of M[La(C2O4)3]⋅xH2O (M=Cr(III) and Co(III))

The complexes M[La(C₂O₄)₃]⋅xH₂O (x=10 for M=Cr(III) and x=7 forM=Co(III)) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR, reflectance and powder X-ray diffraction (XRD) studies. Thermal investigations using TG, DTG and DTA techniques in air of chromium(III)tris(oxalato)lanthanum(III)decahydrate, Cr[La(C₂O₄)₃]⋅10H₂O showed the complex decomposition pattern in air. The compound released all the ten molecules of water within ∼170°C, followed by decomposition to a mixture of oxides and carbides of chromium and lanthanum, i.e. CrO₂, Cr₂O₃, Cr₃O₄, Cr₃C₂, La₂O₃, La₂C₃, LaCO, LaCrO_x (2<x<3) and C at ∼1000°C through the intermediate formation of several compounds of chromium and lanthanum at ∼374, ∼430 and ∼550°C. Thecobalt(III)tris(oxalato)lanthanum(III)heptahydrate, Co[La(C₂O₄)₃]⋅7H₂O becomes anhydrous around 225°C, followed by decomposition to Co₃O₄, La₂(CO₃)₃ and C at ∼340°C and several other mixture species of cobalt and lanthanum at∼485°C. The end products were identified to be LaCoO₃, Co₃O₄, La₂O₃, La₂C₃, Co₃C, LaCO and C at ∼ 2>1000°C. DSC studies in nitrogen of both the compounds showed several distinct steps of decomposition along with ΔH and ΔSvalues. IR and powder XRD studies have identified some of the intermediate species. The tentative mechanisms for the decomposition in air are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Studies of Copper(II) Squarate Complexes of Diamines in the Solid State

CuL₂C₄O₄ [L=ethane-1,2-diamine (en)], CuL₂C₄O₄⋅2H₂O [L=N-methylethane-1,2-diamine (meen), N-ethylethane-1,2-diamine (eten),N-propylethane-1,2-diamine (pren), N-methyl-N’-ethylethane- 1,2-diamine (meeten) andpropane-1,2-diamine (pn)], CuL₂C₄O₄⋅0.5H₂O [L=N,N’-dimethylethane- 1,2-diamine (dmeen)], CuL₂C₄O₄⋅4H₂O [L=propane-1,2-diamine (pn)]and CuL₂C₄O₄⋅H₂O[L=2-methylpropane-1,2-diamine (ibn)] have been synthesized by the addition of respective diamine to finely powdered CuC₄O₄⋅2H₂O and their thermal studies have been carried out in the solid state. Cu(en)₂C₄O₄ upon heating loses one molecule of diamine with shar pcolour change yielding Cu(en)C₄O₄ which upon further heating transforms to unidentified products. All aquated-bis-diamine species [CuL₂C₄O₄⋅2H₂O, CuL₂C₄O₄⋅0.5H₂O and CuL₂C₄O₄⋅H₂O] upon heating undergo deaquation–anation reaction in the solid state showing thermochromism and transform to CuL₂C⁴O₄, which revert on exposure to humid atmosphere (RH ∼90%). All the squarato bis-diamine species, CuL₂C₄O₄, on further heating transform to unidentified products through the formation of CuLC₄O₄ as intermediates. The mono diamine species, have been isolated pyrolytically in the solid state and can be stored in a desiccator as well as in open atmosphere. They are proposed to be polymeric. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectral, magnetic and thermal investigations of some d-electron element 3-methoxy-4-methylbenzoates

Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methoxy-4-methylbenzoates were investigated and their quantitative composition and magnetic moments were determined. The IR spectra and powder diffraction patterns of the complexes prepared of general formula M(C₉H₉O₃)₂·nH₂O (n=2 for Mn, Co n=1 for Ni, Cu, n=0 for Zn, Cd) were prepared and their thermal decomposition in air was studied. Their solubility in water at 293 K is of the order 10^–2 (Mn)–10^–4 (Cu) mol dm^–3. IR spectra of the prepared 3-methoxy-4-methylbenzoates suggest that carboxylate groups are bidentate bridging. The magnetic moments for the paramagnetic complexes of Mn(II), Co(II), Ni(II) and Cu(II) attain values 5.50, 4.45, 3.16 and 1.79 B. M., respectively. During heating the hydrated complexes lose crystallization water molecules in one step and then the anhydrous complexes decompose directly to oxides MO and Mn3O4. Only Co(II) complex decomposes to Co₃O₄ with intermediate formation CoO.     

Some dn Metal Complexes with 4,4'-bipyridine and Trichloroacetates. Preparation,characterization and thermal properties

The new mixed ligand complexes with formulae Co(4-bpy)₂L₂⋅2H₂O (I), Cu(4-bpy)₂L₂⋅H₂O (II) and Cd(4-bpy)L₂⋅H₂O (III) (4-bpy=4,4'-bipyridine, L=CCl₃COO^–) were prepared. Analysis of the IR spectra indicate that 4-bpy is coordinated with metal ions and carboxylates groups bond as bidentate chelating ligands. The electronic spectra are in accordance with pseudo-octahedral environment around the central metal ion in the Co(II) and Cu(II) complexes. The thermal decomposition of the synthesized complexes was studied in air. A coupled TG-MS system was used to analyse the principal volatile thermal decomposition products of Co(II) and Cu(II) complexes. Corresponding metal oxides were identified as a final product of pyrolysis with intermediate formation of metal chlorides. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,structural characterization and thermal analysis of the cobalt(II) oxalate obtained through the reaction of 1,2-ethanediol with Co(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O

The homopolynuclear coordination compound [CoL · 2.5H₂O]_n with L=C₂O₄ ²⁻ was synthesized by a new unconventional method. It consist in the redox reaction between 1,2-ethanediol and cobalt nitrate in presence of nitric acid. The coordination compound was characterized by chemical analysis, electronic and vibrational spectra respectively, thermal analysis. In the coordination compound the Co(II) ion exists in a high spin octahedral configuration and oxalate anion acts as double-bridge ligand, tetradentate, similar as in CoC₂O₄ · 2H₂O obtained by the classical method. Nonstoichiometric oxide, Co₃O_4+0.25 with deficit in cobalt and normal spinel Co₃O₄ where identified as thermal decomposition intermediates. As final product of decomposition, the oxide CoO was obtained.     

X-ray,Thermal and Infrared Spectroscopic Studies on Potassium,Rubidium and Caesium Uranyl Oxalate Hydrates

M₂UO₂(C₂O₄)₂⋅nH₂O compounds (M=K, Rb and Cs)have been prepared and characterized by chemical and thermal analyses as well as by X-ray diffraction and infrared spectroscopy. X-ray powder data show that the compounds belong to an orthorhombic system. Thermal and infrared studies show that the compounds decompose to M₂UO₄ through the formation of alkali metal carbonate and UO₂ as intermediates. K₂UO₂(C₂O₄)₂⋅3H₂O, and Rb₂UO₂(C₂O₄)₂⋅2H₂O gave K₂UO₄, Rb₂UO₄ at 700 and 600°C respectively, while in the case of Cs₂UO₂(C₂O₄)₂⋅2H₂O, the intermediate products of decomposition reacted to yield Cs₂U₄O₁₃ at 1000°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

CCl<Subscript>4</Subscript> Decomposition in RF Thermal Plasma in Inert and Oxidative Environments

The decomposition of carbon tetrachloride was investigated in an RF inductively coupled thermal plasma reactor in inert CCl₄–Ar and in oxidative CCl₄–O₂–Ar systems, respectively. The exhaust gases were analyzed by gas chromatography-mass spectrometry. The kinetics of CCl₄ decomposition at the experimental conditions was modeled in the temperature range of 300–7,000 K. The simulations predicted 67.0 and 97.9% net conversions of CCl₄ for CCl₄–Ar and for CCl₄–O₂–Ar, respectively. These values are close to the experimentally determined values of 60.6 and 92.5%. We concluded that in RF thermal plasma much less CCl₄ reconstructed in oxidative environment than in an oxygen-free mixture.     

Thermochemistry of the Decomposition of Some Cobalt Compounds

Differential scanning calorimetry (DSC) was used to determine the molar enthalpies of dehydration and decomposition of CoC₂O₄·2H₂O, Co(HCOO)₂·2H₂O and [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O. The first stage of dissociation of each compound is a single-step dehydration both in air and argon atmospheres. The next stages are decomposition processes influenced by experimental parameters. The enthalpies of dehydration and decomposition vary from compound to compound in each atmosphere. The obtained data have been related to the macromechanisms proposed for the thermal decomposition and the parallel-consecutive decomposition-oxidation processes. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Thermal And Structural Study on Lanthanum Hexacyanocobaltate(III) Pentahydrate. Part II

The thermal dehydration of La[Co(CN)₆]⋅5H₂O proceeded through at least three stages from the temperature range of30~230°C, and an abrupt mass loss occurred around 350°C and the perovskite type oxide,LaCoO₃ was obtained at 1000°C. After dehydration, the color of the anhydride changed from white to pale blue around 230°C and furthermore, the color changed to blue around 290°C. These color changes were discussed on the basis of the changes of coordination structures around Co ions. In La[Co(CN)₆]⋅5H₂O, Co³⁺ ions lie at the center of the O_h crystal field consisted of six CN^– ions. However, in the pale blue specimen, Co³⁺ ions were situated in the center of D_4h crystal field which was distorted the O_h one by lengthening of the trans CN^– ions along z-axis. In the blue specimen, Co³⁺ ions were reduced to Co²⁺ ions which were situated in the T_d crystal field formed by four CN^–ions as [Co(CN)₄]^2–. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study on the obtaining of cobalt oxides by thermal decomposition of some complex combinations,undispersed and dispersed in SiO<Subscript>2</Subscript> matrix

In order to obtain cobalt oxides nanoparticles we have used the thermal decomposition of some carboxylate type precursors. These precursors were obtained by the redox reaction between cobalt nitrate and ethylene glycol, either bulk or dispersed in silica matrix. The redox reaction takes place by heating the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution or the Si(OC₂H₅)₄-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels. Thermal analysis of the Co(NO₃)₂·6H₂O-C₂H₆O₂ solution and Si(OC₂H₅)-Co(NO₃)₂·6H₂O-C₂H₆O₂ gels allowed us to establish the optimal value for the synthesis temperature of the carboxylate precursors. By fast heating of the solution Co(NO₃)₂·6H₂O-C₂H₆O₂, the redox reaction is immediately followed by the decomposition of the precursor, which represents an autocombustion process. The product of this combustion contains CoO as unique phase. We have obtained a mixture of CoO and Co₃O₄ by annealing the synthesized carboxylate compounds for 2 h at 400°C. With longer annealing time (6 h), we have obtained Co₃O₄ as unique phase. The XRD study of the crystalline phases resulted by thermal decomposition of the precursors embedded in silica matrix, showed that the formation of Co₂SiO₄ and Co₃O₄, as unique phases, depends on the thermal treatment.     

Thermal and Other Properties of New 4,4'-bipyridine-trichloroacetato Complexes of Mn(II), Ni(II) and Zn(II)

New mixed-ligand complexes of general formulae Mn(4-bpy)(CCl₃COO)₂⋅H₂O, Ni(4-bpy)₂(CCl³COO)₂⋅2H²O and Zn(4-bpy)₂(CCl₃COO)₂⋅2H²O (where 4-bpy=4,4’-bipyridine) were obtained and characterized. The IR spectra, conductivity measurements and other physical properties of these compounds were discussed. The central atoms M(II) form coordinate bonds with title ligands. The thermal behaviour of the synthesized complexes was studied in air. During heating the complexes decompose via different intermediate products to Mn₃O₄, NiO and ZnO; partial volatilization of ZnCl₂was observed. A coupled TG-MS system was used to the analysis of the principal volatile thermal decomposition products of Mn(II) and Ni(II) complexes. The principal volatile mass fragments correspond to: H₂O⁺, OH⁺, CO⁺ ₂, HCl⁺, Cl⁺ ₂, CCl⁺ and other. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hexavalent uranium dicarboxylates with hydrazine. Preparation,characterization and thermal studies

The uranium complexes of composition,UO₂X⋅N₂H₄⋅H₂O, X=succinate or glutarate, UO₂X₂⋅N₂H₄⋅H₂O, X=Hadipate, Hpimelate, Hsuberate, Hazelate and Hsebacate and UO₂X⋅N₂H₄, where X=malate and oxydiacetate have been prepared and characterized by analytical, spectral (IR and electronic), thermal and X-ray powder diffraction studies. Hydrazine acts as a monodentate ligand in uranyl succinate, glutarate, malate and oxydiacetate hydrazinates and bidentate in uranyl adipate, pimelate, suberate, azelate and sebacate hydrazinate hydrate complexes. The dicarboxylate anions bind the uranium through uni- and bidentate fashion depending upon the coordination polyhedra. All the dicarboxylate hydrazinate complexes in this series decompose to give U₃O₈ as the end product through their respective uranyl dicarboxylate intermediates. Malate and oxydiacetate compounds decompose exothermically in a single step. The coordinated water is confirmed from thermal data. The complexes of succinate to sebacate seem to possess hexagonal bipyramidal geometry around uranium, whereas pentagonal bipyramidal geometry has been proposed for both malate and oxydiacetate complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low temperature synthesis of Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposite using a modified sol–gel method

The paper presents a study on the preparation of Co₂SiO₄/SiO₂ nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC₂H₅)₄), cobalt nitrate Co(NO₃)₂·6H₂O and some diols: ethylene glycol (C₂H₆O₂), 1,2propanediol (C₃H₈O₂) and 1,3propanediol (C₃H₈O₂), for a final composition: 30% CoO/70% SiO₂. During the heating of the gels at 140 °C, a redox reaction takes place between NO₃ ⁻ ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co₃O₄ inside the matrices pores. When CoO results, it reacts with SiO₂ at low temperature leading to Co₂SiO₄, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co₂SiO₄ (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co₂SiO₄ nanoparticles are homogenously dispersed inside the silica matrix.     

Hydrazinium Oxydiacetates and Oxydiacetate Dianion Complexes of Some Divalent Metals with Hydrazine

Hydrazinium oxydiacetate salts of formulae N₂H₅(Hoda)⋅H₂oda, N₂H₅(Hoda) and (N₂H₅)₂oda (H₂oda=oxydiacetic acid) and complexes of the types, M(oda)⋅2N₂H₄⋅xH₂O (where M=Co, Ni and Cd; x=0 for Co and Ni;x=1 for Cd) and Zn(oda)⋅N₂H₄⋅H₂O have been prepared and characterized by analytical, spectral, thermal and X-ray powder diffraction data. IR data document the existence of N₂H⁺ ₅ ion in the simple salts and the bidentate coordination of both hydrazine and dianion in the complexes. Complete decomposition of hydrazinium salts takes place via oxydiacetic acid intermediate. Cobalt and nickel complexes decompose in a single step, whereas zinc and cadmium complexes decompose through hydrazinate intermediates. However, all the metal complexes yield metal oxide as the final residue. Isomorphic nature of the cobalt and nickel complexes is evident from XRD data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of mixed Ce and Gd oxalates and thermal properties of mixed Ce and Gd oxides

The aim of the present work is to study the thermal decomposition of the mixed oxalates (Ce_1–xGd_x)₂(C₂O₄)₃·nH₂O. The mechanisms of decomposition of Ce and Gd oxalate are different, and mixed oxalates behave in an intermediate way. Their dehydration stages are more similar to those of Gd oxalate, as not all the molecules of water are equivalent like the cerium oxalate. The decomposition leads to (Ce_1–xGd_x)O_2–x/2. For x close to 0 or to 1 two solid solutions exist, while for the central composition, the presence of a biphasic region can not be excluded.     

Kinetic Analysis of Dissociation of Smithsonite from a Set of Non-isothermal Data Obtained at Different Heating Rates

The heats of hydration reactions for MgCl₂⋅4H₂O and MgCl₂⋅2H₂O include two parts, reaction enthalpy and adsorption heat of aqueous vapor on the surfaces of magnesium chloride hydrates. The hydration heat for the reactions MgCl₂⋅4H₂O+2H₂O→MgCl₂⋅6H₂O and MgCl₂⋅2H₂O+2H₂O→MgCl₂⋅4H₂O, measured by DSC-111, is –30.36 and –133.94 kJ mol^–1,respectively. The adsorption heat of these hydration processes, measured by head-on chromatography method, is –13.06 and –16.11 kJ mol^–1, respectively. The molar enthalpy change for the above two reactions is –16.64 and –118.09 kJ mol^–1, respectively. The comparison between the experimental data and the theoretical values for these hydration processes indicates that the results obtained in this study are quite reliable. This revised version was published online in July 2006 with corrections to the Cover Date.