Preparation,characterisation and thermal decomposition of barium zirconyl oxalate

Barium zirconyl oxalate hydrate (BZO) is prepared and characterised by chemical analysis and IR spectral studies. Thermal decomposition studies have been made using TG and DTA techniques. The decomposition has been found to proceed through four steps. The first step involves a two-stage dehydration (100–190°C, 190–260°C) and the second step the decomposition of oxalate (260–460°C). The third step involves the evolution of carbon monoxide present in the lattice and partial decomposition of carbonate. The fourth step involves the final stage decomposition of carbonate (760–920°C) giving barium zirconate as an end product. The identification of compounds at various stages has been done by IR spectra. The X-ray diffraction pattern of BZO confirms that it is a crystalline compound.     

Pyrolysis of Nickel Zirconyl Oxalate

Nickel zirconyl oxalate hexahydrate (NiZrOx) is δ prepared and characterised by I.R. spectral and chemical analysis. Its thermal decomposition has been investigated by employing TG, DTG, DTA and chemical analysis. End product was identified by X-ray diffraction studies. The decomposition proceeds through four steps i) dehydration of NiZrOx in two steps, ii) partial decomposition of oxalate to give an oxalate carbonate intermediate, iii) decomposition of oxalate to give a non-stoichiometric carbonate and iv) decomposition of this non-stoichiometric carbonate to give the end product a mixture of NiO+ZrO₂. On the basis of the results obtained, a tentative scheme for the decomposition of NiZrOx is proposed.     

Thermal studies on beryllium titanyl/zirconyl oxalates

Beryllium titanyl oxalate tetrahydrate and beryllium zirconyl oxalate tetrahydrate were prepared in aqueous medium and characterized by elemental analyses, magnetic susceptibility measurements and IR spectral studies. The thermal behaviour of these compounds under non-isothermal conditions was investigated by thermogravimetric, derivative thermogravimetric and differential scanning calorimetric (DSC) techniques. The intermediates obtained at the end of the various thermal decomposition steps were identified on the basis of elemental analyses and IR spectral studies. The decomposition proceeds through three major steps, viz, dehydration of the hydrate, decomposition of the oxalate to carbonate and decomposition of the carbonate to oxide. The graphical method of Coats and Redfern was employed to calculate kinetic parameters such as apparent activation energy and order of reaction. Heats of reaction for the different decomposition steps were calculated from the DSC curves.     

A kinetic and mechanistic study of thermal decomposition of strontium titanyl oxalate

Thermal decomposition of anhydrous strontium titanyl oxalate proceeds through a series of complex reactions to form strontium metatitanate at high temperature. Among them the decomposition of oxalate is the first major thermal event. A kinetic study of oxalate decomposition in the temperature range 553-593 K has been carried out by cooled gas pressure measurement in vacuum. Results fitted the Zhuravlev equation for almost the entire α-range (0.05-0.92) indicating the occurrence of a diffusion-controlled, three-dimensional rate process. The activation energy has been calculated to be 164 ± 10 kJ mol⁻¹. Results from elemental analysis, TGA, IR and SEM studies of undecomposed and partially decomposed samples have been used to supplement kinetic observations in formulating the mechanism for oxalate decomposition.     

Thermal decomposition of rare-earth trioxalatocobaltates

The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C₂O₄)₃ · x H₂O, where Ln  La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates.     

Thermal decomposition of manganese(II)bis(oxalato)nickelate(II)tetrahydrate

Summary A mixed metal oxalate, manganese(II)bis(oxalato)nickelate(II)tetrahydrate, has been synthesized and characterized by elemental analysis, IR spectral and X-ray powder diffraction (XRD) studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound decomposed mainly to Mn₂O₃, MnO₂ and NiO at ca.1000°C, via. the formation of several intermediates. DSC study in nitrogen upto 500°C showed the endothermic decomposition. The tentative mechanism for the thermal decomposition in air is proposed.     

Preparation and thermal decomposition of some oxomolybdenum(VI) oxalates

Anionic oxomolybdenum(VI) oxalates having the general formula A₂[Mo₂O₆(C₂O₄)], where A = K⁺ and NH⁺₄, are prepared and characterized by chemical analysis and IR spectra, and their thermal decomposition studied using TG and DTA techniques. Both the compounds are anhydrous and the decomposition of oxalate takes place in a single step. The ammonium compound decomposes between 255 and 320°C to give MoO₃ as the end product, while the potassium compound decomposes between 300 and 380°C to give K₂Mo₂O₇ as the end product. Both the products were characterized by chemical analysis, IR and X-ray studies. The X-ray diffraction patterns of the two oxalato complexes confirm that they are crystalline compounds.     

The influence of the environment on the thermal decomposition of oxysalts

The environment can influence the thermal decomposition of an oxysalt by;

1. causing a change in the course of chemical decomposition or
2. causing an alteration in the physical nature of the solid product or solid intermediates.

The environment can also effect the equilibrium condition or the course of the kinetics. The use of special techniques such as thermogravimetry, differential thermal analysis, or differential scanning calorimetry to study the decomposition means that a special environment is imposed on the oxysalt and this effects the thermal decomposition process. The influence of the environment in changing the course of a chemical reaction can be illustrated by reference to the decomposition of zinc oxalate and nickel oxalate. The DTA shows that the decompositions are endothermic in inert atmospheres but exothermic in air or oxygen. The reasons are different however in each case. Thus although the product of decomposition of zinc oxalate is zinc oxide the change in character of the decomposition from endothermic to exothermic is due to the catalytic oxidation of carbon monoxide to carbon dioxide in the presence of oxygen. The similar change in the character of nickel oxalate decomposition is however due to nickel formation in an inert atmosphere but nickel oxide in air or oxygen. The alteration in the physical nature of the solid products is illustrated by surface area measurements on solid residues from the decomposition of carbonates or oxalates. The kinetic and chemical equilibrium studies showing the influence of environment are illustrated by reference to dehydration studies, carbonate and oxalate decompositions.     

Copper(II) oxalate obtained through the reaction of 1,2-ethanediol with Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·3H<Subscript>2</Subscript>O

The paper presents the experimental results of the structural investigations and thermal analysis of copper(II) oxalate, a polynuclear coordination compound, obtained by a new method, through the reaction of 1,2-ethanediol with Cu(NO₃)₂·3H₂O. The reaction between 1,2-ethanediol and Cu(NO₃)₂·3H₂O occurs, under some working conditions, with the oxidation of 1,2-ethanediol to the oxalate anion (L). The synthesized polynuclear coordination compound, [CuL·0.3H₂O]_n, was characterized by chemical analysis, electronic and vibrational spectra and thermal analysis. The thermal properties of the polynuclear coordination compound have been investigated by TG, DTG and DSC. The obtained decomposition product is CuO. Powder XRD (X-ray diffraction), IR spectroscopy and TEM (transmission electron microscopy) were used to characterize the composition, the crystalline structure and the surface morphology of the copper oxide obtained through thermolysis. The thermal conversion product, copper(II) oxide, has a microporous structure with a large specific area.     

Thermochemistry of decomposition of manganese(II) oxalate dihydrate

Differential scanning calorimetry (DSC) has been used to determine the enthalpy of dehydration of manganese(II) oxalate dihydrate and the enthalpies of decomposition in nitrogen and in oxygen of the anhydrous oxalate. The thermodynamic data have been related to the activation energies reported in kinetic studies and to the mechanisms proposed for the thermal decomposition and oxidation processes.     

Thermal decomposition of hydrated iron(II) oxalate and manganese(II) oxalate in vacuum

The thermal decomposition of hydrated iron(II) oxalate and manganese(II) oxalate under high vacuum conditions (10^–5 mm Hg) has been studied by differential thermal analysis. The decomposition in vacuum of iron(II) oxalate is exothermic, while that of manganese(II) oxalate is endothermic. An explanation is offered for this behaviour.The financial support by National Bureau of Standards, U.S.A., through a PL-480 scheme is gratefully acknowledged.     

Synthesis and study of structure and physicochemical properties of dicopper(II) (diaqua)benzene-1,2,4,5-tetracarboxylate

Layered complexes of copper(II) with benzene-1,2,4,5-tetracarboxylic acid has been prepared for the first time. The data of elemental analysis, X-ray diffraction analysis, IR spectroscopy, and differential thermal analysis have confirmed the purity of the complex compound. Its chemical composition has been elucidated, and thermal decomposition has been studied. The prepared complex contained no water molecules, and the polymeric layered structure has been retained.     

Thermal studies on beryllium,magnesium and calcium hafnyl oxalates

Beryllium hafnyl oxalate tetrahydrate, magnesium hafnyl oxalate tetrahydrate and calcium hafnyl oxalate tetrahydrate abbreviated as BHO, MHO and CHO, respectively, have been prepared in an aqueous medium and characterized by elemental analysis, magnetic susceptibility measurements and infrared spectral data. The thermal behaviour of these compounds in non-isothermal conditions have been investigated by employing TG, DTG and DSC techniques. The intermediates obtained at the end of various thermal decomposition steps were identified on the basis of elemental analysis and infrared spectral studies. The graphical method of Coats and Redfern has been employed to evaluate the kinetic parameters such as apparent activation energy and order of reaction. Heat of reaction for different decomposition steps have been calculated from the DSC curves.     

A comparative study on the thermal decomposition of some transition metal maleates and fumarates

Thermal decomposition of M(mal/fum)·xH₂O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500°C employing TG-DTG-DTA, XRD and IR spectroscopic techniques. After dehydration the anhydrous maleate salts decompose to metal oxalate in the temperature range of 320–360°C, which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The anhydrous fumarate salts have been found to decompose directly to oxide phase. A comparison of thermal analysis reveals that fumarates are thermally more stable than maleates.     

Quantitative calibration of a TPD-MS system for CO and CO2 using calcium carbonate and calcium oxalate

A method is described for calibrating quantitatively a temperature-programmed decomposition, mass-spectrometric (TPD-MS) system by monitoring the gases evolved during the thermal decomposition of a chemical within the TPD reactor. A method for calibrating for evolved CO and CO₂ is described using the thermal decompositions of calcium carbonate and calcium oxalate. The method takes into account the production of CO⁺ ions from CO₂⁺ ions and secondary reactions in the thermal decomposition of calcium oxalate.     

Kinetics and mechanism of the thermal decomposition of barium titanyl oxalate

Thermal analysis of barium titanyl oxalate reveals that the decomposition proceeds through four distinct rate processes. Among them, the decomposition of oxalate occurs in the temperature range 230–350°C, and has been studied by TG and gas pressure measurements, supplemented by IR spectroscopy, electron microscopy and chemical analysis. Oxalate decomposition proceeds differently in vacuum and in flowing gas atmospheres. Analytical results indicate the formation of a complex carbonate together with CO, CO₂ and water vapour below 400°C. Schemes for each type of decomposition are proposed and discussed. For decomposition in vacuum, kinetic observations fitted the three-dimensional, diffusion controlled, rate equation for almost the entire α-range (0.028≤α≤0.92). The activation energy is calculated to be3 189±6 kJ mol⁻¹. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Effect of γ irradiation on non-isothermal decomposition kinetics,X-ray diffraction pattern,infrared spectrum and antibacterial property of tris(1,2-diaminoethane)nickel(II)oxalate

Thermal decomposition, X-ray diffraction pattern, infrared (IR) spectrum and antibacterial property of tris(1,2-diaminoethane)nickel(II)oxalate were studied before and after γ-irradiation. Irradiation enhanced thermal decomposition. From X-ray diffraction studies, unirradiated and irradiated samples of the complex are found to be tetragonal. A change in lattice parameters was observed upon irradiation. Position and intensity of IR bands of –NH₂ and >C=O group were found to be changed upon irradiation. Antibacterial studies showed that irradiation induced activity towards B. cereus.     

Thermal study of zinc(II) 4-chlorosalicylate complex compounds with bioactive ligands

Three new complex compounds of general formula Zn{4-ClC₆H₃-2-(OH)COO}₂⋅L₂⋅nH₂O (where L=thiourea (tu), nicotinamide (nam), caffeine (caf), n=2,3), were prepared and characterized by chemical analysis, IR spectroscopy and their thermal properties were studied by TG/DTG, DTA methods. It was found that the thermal decomposition of hydrated compounds starts with the release of water molecules. During the thermal decomposition of anhydrous compounds the release of organic ligands take place followed by the decomposition of salicylate anion. Zinc oxide was found as the final product of the thermal decomposition performed up to 650°C. RTG powder diffraction method, IR spectra and chemical analysis were used for the determination of products of the thermal decomposition.     

Thermal decomposition kinetics of strontium oxalate

The thermal decomposition behavior in air of SrC₂O₄ · 1.25H₂O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO₃ and the decomposition of SrCO₃ to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO₃. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D₂), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R₃). The values of activation parameters obtained using different methods were compared and discussed.     

Thermal study of zinc(II) salicylate complex compounds with bioactive ligands

Five new complex compounds of general formula Zn(Hsal)_2·L₂·nH₂O (where Hsal=OHC₆H₄COO^-, L=thiourea (tu), nicotinamide (nam), caffeine (caf), theobromine (tbr), n=2-4), were prepared and characterized by chemical analysis, IR spectroscopy and studied by methods of thermal analysis (TG/DTG, DTA). It was found that the thermal decomposition of hydrated compounds starts with the release of water molecules. During the thermal decomposition of anhydrous compounds the release of organic ligands take place followed by the decomposition of salicylate anion. Zinc oxide was found as the final product of the thermal decomposition heated up to 800°C. RTG powder diffraction method, IR spectra and chemical analysis were used for the determination of products of the thermal decomposition. This revised version was published online in August 2006 with corrections to the Cover Date.