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.     

Thermoanalytical investigations of the decomposition course of copper oxysalts

The thermal decomposition course of copper acetate monohydrate (CuAc) was examined on heating up to 600°C at various rates, by TG, DTA and DSC. Non-isothermal kinetic and thermodynamic parameters were determined in air or nitrogen. SEM was used to describe the decomposition course and the solid products were identified by IR and XRD analysis. The results indicated that CuAc was dehydrated at 190°C and then partially decomposed at 220°C, giving rise to CuO in addition to a minor portion of Cu₂O and Cu₄O₃. The last two oxides seemed to facilitate the decomposition of the rest of the anhydrous acetate. Cu₂O and Cu₄O₃ were oxidized in air at >400°C, in a process that did not occur in nitrogen.It is a pleasure to thank the Queen's University of Belfast, particularly the staff of the Electron Microscope Unit for assistance in obtaining the electron micrographs. Thanks are also due to the Egyptian Government for the granted fellowship.     

Thermoanalytical investigation of the decomposition course of copper oxysalts

The thermal decomposition of copper nitrate trihydrate (CuNTH); Cu(NO₃)₂·3H₂O was studied up to 600°C by thermogravimetry (TG) and differential thermal analysis (DTA) in a dynamic atmosphere of air. The thermal events occurring throughout the decomposition course were characterized on the basis of spectral analyses using infrared spectroscopy (IR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Non-isothermal kinetic parameters were determined. The results showed that the decomposition course involves two main processes, firstly the formation of hydroxy copper nitrate and secondly, the decomposition of this compound to yield CuO. Pathways were suggested that may be involved in the decomposition course.     

Thermoanalytical investigations of decomposition course of copper oxysalts

The thermal decomposition of basic copper carbonate (malachite; CuCO₃·Cu(OH)₂) in a dynamic atmosphere of air or nitrogen was studied via TG, DTA and DSC at different heating rates. The non-isothermal kinetic and thermodynamic parameters were estimated. The decomposition course was thoroughly followed by examining the structural and morphological consequences of calcining the material at elevated temperatures by IR, XRD and SEM. The results obtained showed that in air CuCO₃·Cu(OH)₂ released 0.5 H₂O at 195°C, transforming into the azurite structure 2CuCO₃·Cu(OH)₂. Decomposition then commenced, through two endothermic steps maximized at 325 and 430°C. The resultant product maintained the water released from the decomposition process up to 650–750°C. A schematic decomposition pathway has been proposed in terms of the thermal and physicoanalytical results.     

Kinetic of thermal decomposition of residues from different kinds of composting

Non-isothermal kinetic parameters regarding to the thermal decomposition of the ligninocellulosic fraction present in compost from urban solid residues (USR) obtained through stack covered (SC) with composted material, comes from the usine in composing of Araraquara city, Săo Paulo state, Brazil, and from stack containing academic restaurant organic solid residues (SAR). The samples were periodically revolved round 132 days of composting. Results from TG, DTG and DSC curves obtained on inert atmosphere indicated that the lignocellulosic fraction present, despite the slow degradation during the composting process, is thermally less stable than other substances originated during that process. The lignocellulosic fraction decomposition, between 200 and 400°C, were kinetically evaluated through non-isothermal methods of analysis. By using the Flynn-Wall and Ozawa isoconversional method, the medium activation energy, Ea, and pre-exponential factor, lgA, were 283.0±14.6, 257.6±1.3 kJ mol^-1 and 25.4±0.8, 23.2±0.2 min^-1, to the SC and SAR, respectively, at 95% confidence level. From E _a and lgA values and DSC curves, Malek procedure could be applied, suggesting that the SB (Sesták-Berggren) kinetic model is suitable for the first thermal decomposition step. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetics of thermal decomposition of nickel sulfate hexahydrate

The paper describes the kinetics of all the recorded steps of thermal decomposition of nickel sulfate hexahydrate in air. The thermal decomposition of the salt in air led to NiO at about 1060 K. The kinetic parameters, the activation energyE and the preexponential factorA, and the thermodynamic parameters, the entropy, enthalpy and free energy of activation were evaluated for the dehydration and decomposition reactions. Tentative reaction mechanisms are suggested for each step of the thermal decomposition.     

Kinetics of thermal decomposition of nickel oxalate dihydrate in air

Thermal decomposition taking place in solid state complex, NiC₂O₄·2H₂O, has been investigated in air by means of TG–DTG/DTA, DSC, XRD. TG–DTG/DTA curves showed that the decomposition proceeds through two well-defined steps with DTA peaks closely corresponding to the weight loss obtained. XRD showed that the final decomposition product of NiC₂O₄·2H₂O was NiO. Kinetics analysis of NiC₂O₄·2H₂O decomposition steps was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Flynn–Wall–Ozawa (FWO) methods, and the most possible kinetic model function has been estimated through the multiple-linear regression method. The activation energies for the two decomposition steps of NiC₂O₄·2H₂O were 171.1 ± 4.2 and 174.4 ± 8.1 kJ/mol, respectively.     

Preparation of mixed-ligand complexes of nickel via thermal decomposition

If heated to around 270° in argon, [Ni(HSal)₂] (H₂Sal=salicylic acid) gives off gaseous H₂Sal and forms [NiSal], which reacts with monoprotic ligands HL (e.g. 8-hydroxyquinoline) to form mixed-ligand complexes [NiHSalL], or with diprotic ligands H₂L' (e.g. quadratic acid) to form dinuclear complexes [HSalNiL'NiHSal].

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Zusammenfassung Die Komplexverbindung [Ni(HSal)₂] spaltet beim Erhitzen auf 270 °C in Argon Salicylsäure ab und liefert [NiSal], das mit Monoproton-Liganden HL (z. B. 8-Hydroxychinolin) zu Gemischtliganden-Komplexen [NiHSalL], mit Zweiprotonen-Liganden H₂L' (z. B. Quadratsäure) dagegen Zweikernkomplexe [HSalNiL'NiHSal] bildet.

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[Ni(HSal)₂] 270°, [NiSal], HL (., 8-) [NiHSalL] H₂L [HSalNiLNiHSal].

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The preparative and thermoanalytical part of this work was performed by C. Gribi, D. Noukakis and M. Piccand, who also drew the Figures.

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This research was supported by the Swiss National Science Fundation, grant No. 2.053-0.99.     

Study of the decomposition of supported nickel acetylacetonate by thermal techniques

The decomposition of supported nickel acetylacetonate (AcacNi) was studied by using thermal techniques to evaluate the nature of the calcination products. Thermogravimetric techniques used in this work indicated transformations occurring during preparation and calcination steps. Results demonstrated the important influence of support modifications upon the catalyst nature finally obtained.     

Synthesis of nanocrystalline nickel ferrite by thermal decomposition of organic precursors

Nickel ferrite powders were synthesized by thermal decomposition of the precursors obtained in the redox reaction between the mixture of Ni(NO₃)₂·6H₂O and Fe(NO₃)₃·9H₂O with polyalcohol: 1,4-butanediol, polyvinyl alcohol and also with their mixture. During this reaction the primary C?COH groups were oxidized at ?CCOOH, while secondary C?COH groups at C=O groups. The carboxylic groups formed coordinate to the present Ni(II) and Fe(III) cations leading to carboxylate type compounds, further used as precursors for NiFe₂O₄. These precursors were characterized by thermal analysis and FT-IR spectrometry. All precursors thermally decomposed up to 350?°C leading to nickel ferrite weakly crystallized. By annealing at higher temperatures, nanocrystalline nickel ferrite powders were obtained, as resulted from XRD. SEM images have evidenced the formation of nanoparticulate powders; these powders present magnetic properties characteristic to the oxidic system formed by magnetic nanoparticles.     

Changes in crystallite size and microstrains of hematite derived from the thermal decomposition of synthetic akaganeite

The thermal decomposition of akaganeite, β-FeOOH, in air is studied. The structural properties of the dehydroxylation product, identified as hematite, are determined at different temperatures. From the results on crystallite size and microstrains, a change of crystallite shape has been shown to occur in the range of temperatures of 300 to 485°C. A marked increase in crystallite size and a diminution in microstrains is observed at 525°C. This change is related to the occurrence of an exothermic peak in the DTA and DSC curves of akaganeite at about 512°C. The peak is thus ascribed to a recrystallization process of hematite. Electron micrographs support the most relevant observations of changes in particle size and shape.     

Investigation of thermal decomposition of polymer nanocomposites with different char residues

The pyrolysis process of polypropylene (PP), PP‐based nanoclay composites, acrylonitrile‐butadiene‐styrene (ABS), and ABS/metal hydroxide nanorods (MHR)/grapheme nanosheets (GNS) composites in a cone calorimeter test was simulated with a recently developed numerical codes, the Federal Aviation Administration ThermaKin. First, the heat release rate (HRR) and the surface temperature as a function of time were compared with experiment data. With reasonable input parameters, the pyrolysis behaviors were predicted reasonably. Subsequently, the influence of the properties of char residue on the HRR was discussed. The char residue of PP/nanoclay acted as a heat transfer barrier, while the char layer of ABS/MHR/GNS acted as a mass transfer barrier. Finally, the sensitivity of the residue characteristic parameters to the model output was discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of nickel(II) oxide on the thermal decomposition of alkali persulfates

The thermal decomposition of Na₂S₂O₈ and K₂S₂O₈ has been studied derivatographically in the presence of NiO at various molar mixtures. Experiments have proved that the first decomposition stage (persulfate into pyrosulfate) is independent of the amount of the oxide present. During the second decomposition stage (pyrosulfate into sulfate) which occurs in the melt, NiO plays the role of lowering the melting, the initial and final decomposition temperatures of pyrosulfates. The lowest melting temperatures recorded for Na₂S₂O₈ and K₂S₂O₈ are 320 and 280°C, respectively.A mechanism has been proposed to describe the catalytic action of NiO on the thermal decomposition of alkali pyrosulfates. The mechanism makes use of the semiconductivity of NiO and the availability of electron-rich centers in the pyrosulfate group to help the formation of an adsorption complex between them.NiO reacts to some extent with alkali pyrosulfates forming the yellow NiSO₄ and alkali sulfates as separate products.NiO and NiSO₄ form eutectic mixtures with alkali sulfates melting at temperatures lower than those of the pure salts.     

A thermal decomposition study of some nickel(II)thioureachloride complexes

TG/DTA and Thermal Degradation Mass spectrometry (TDMS) data are presented for a series of nickel(II)thiourea chloride complexes: NiL₄Cl₂:L=thiourea or methyl-, dimethyl-, tetramethyl-, di-n-butyl, naphthyl-, ethylene- or allylthiourea. Two different thermal decomposition mechanisms are proposed for these complexes, and it is apparent that the thermal decomposition mechanism adopted by a particular complex depends on the structure of the relevant thiourea ligand and not on the nature of the halide ligand or on the existence of geometrical isomerism for these complexes.

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Zusammenfassung Durch TG, DTA und thermodegradative Massenspektrometrie (TDMS) von Nickel(II)-thioharnstoff-chlorid-Komplexen, NiL₄Cl₂ (L=Thioharnstoff oder Methyl-, Dimethyl-, Tetramethyl-, Di-n-butyl-, Naphthyl-, Vinyl- oder Allylharnstoff), erhaltene Daten werden angegeben. Zwei verschiedene Mechanismen werden für die thermische Zersetzung vorgeschlagen. Es ist offensichtlich, daß der Mechanismus, nach der die thermische Zersetzung eines gegebenen Komplexes verläuft, von der Struktur des relevanten Thioharnstoffliganden und nicht von der Natur des Halidliganden oder vom Vorliegen einer geometrischen Isomerie abhängt.

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/ - NiL₄Cl₂, L= , -, -, -, ---, -, - . . , .

     

Combustion and thermal decomposition characteristics of composite solid propellan

The role of thermal decomposition of the binder and the oxidiser in the thermal decomposition, ageing and combustion of composite solid-propellants has been investigated. The present study shows that the burning rate and ageing of polystyrene and ammonium perchlorate propellant are related to the thermal decomposition of the propellant itself and ammonium perchlorate.     

Changes in asphaltene surface topography with thermal treatment

The impact of thermal cracking reaction on asphaltene structure and morphology has been investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structural and morphological changes at a microscopic level were monitored by comparing the parent asphaltenes from different vacuum residues (VRs) to their corresponding thermally treated asphaltenes, obtained from the by-product pitch after thermal treatment. The SEM analysis indicated that the asphaltene aggregates extracted from atmospheric residues have smooth and rough surfaces with agglomerate particles and bright inclusions. The SEM images of asphaltene aggregates that are extracted from the pitch samples after mild cracking demonstrated cleavage fracture morphology with obvious reduction in inclusions sizes and intensities. The TEM analysis, on the other hand, indicated that the asphaltenes from residual oils have tangled structures, with edges similar to a cauliflower. The tangled structure is mainly credited to the alkyl side-chains that impede the aromatic sheets from stacking. At mild cracking (400 °C), the asphaltene began to exhibit well-ordered layer structures near the edges due to the rupture of the alkyl side-chains. However, the tangled structure has been preserved in the interior of the sample. As the reaction severity increases (415 °C), the stacking of aromatic sheets became more evident even in the sample interior. At the most severe cracking condition (430 °C), an obvious reduction in the cluster diameter has been observed, which mainly resulted from the reduction in the number of aromatic sheets per stack.     

Comparative thermal decomposition characteristics and fire behaviors of commercial cables

Journal of Thermal Analysis and Calorimetry - The decomposition and fire behaviors of two commonly used cables were studied by a calorimeter. The effects of the cable type, the incident heat flux,...     

Thermal decomposition of nickel azide

The results on the thermal decomposition of anhydrous nickel azide prepared by reacting nickel azide solution with AnalaR Me₂CO are reported in the temperature range 490–525 K. The sample starts to decompose immediately after it is raised to the decomposition temperature and the rate of decomposition continuously decreases. The decomposition kinetics have been explained in terms of exponential decay law for α?0.19 and contracting volume law for α > 0.19. The domain of exponential decay law corresponds to the initial decomposition pertaining to surface nucleation and two dimensional surface growth of the product phase, while contracting volume law explains the growth of the product phase into the bulk. The role of defects has been explained by electrical conduction studies on the sample.     

A study of solid-state thermal decomposition characteristics of some metallo-organic compounds

The solid-state dehydration of the hydrated Ca(II), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) salts of pyridine-2-carboxylic acid (picolinic acid) and subsequent decarboxylation of the corresponding anhydrous salts have been studied by simultaneous TG, DTA and DTG. The sequences of thermal stability of the hydrated and the anhydrous compounds have been established from analysis of the TG, DTA and DTG traces for dehydration of the hydrated salts and for decarboxylation of the anhydrous compounds. Thermal parameters such as activation energy, enthalpy change and order of reaction for the different stages of each process have been computed by standard methods. An attempt has been made to account for the observed trend in the thermal stability of the anhydrous salts towards decarboxylation. A mechanism of thermal decraboxylation of calcium picolinate has been proposed.

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Zusammenfassung Die Dehydratisierung der hydratisierten Ca(II)-, Mn(II)-, Co(II)-, Ni(II)-, Cu(II)- und Zn(II)-Salze der Pyridin-2-carboxylsäure (Picolinsäure) in fester Phase und die nachfolgende Decarboxylierung der entsprechenden wasserfreien Salze wurden mittels simultaner TG, DTA und DTG untersucht. Aus den thermoanalytischen Kurven wurde die der thermischen Stabilität entsprechende Reihenfolge der hydratisierten und wasserfreien Verbindungen ermittelt. Thermische Parameter wie Aktivierungsenergie, Enthalpieänderung und Reaktionsordnung wurden für die einzelnen Schritte jedes Prozesses nach Standardmethoden berechnet. Es wurde ein Versuch unternommen, den Trend in der thermischen Stabilität der wasserfreien Salze gegenüber Decarboxylierung zu erklären. Ein Mechanismus der thermischen Decarboxylierung von Calciumpicolinat wird vorgeschlagen.

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