Studies on the thermal decomposition of N,N'-ethylenebis(salicylideneiminato) diaquochromium(III) nitrate

A complex of N,N'-ethylenebis(salicylideneiminato)diaquochromium(III) nitrate, [Cr(salen)(H₂O)₂]NO₃ was characterized and its decomposition mechanism was studied by TG. The IR spectrum and X-ray analysis were examined for the complex. The non-isothermal kinetic data were analyzed by means of the Achar method and the Coats—Redfern method. The most probable kinetic model function was suggested by comparison of the kinetic parameters.This revised version was published online in November 2005 with corrections to the Cover Date.     

Kinetics study of norbixin’s first stage thermal decomposition,using dynamic method

Cis-norbixin isomer obtained by hydrolysis of cis-bixin and isolated by solvent extraction from annatto seeds. The thermal decomposition data of the cis-norbixin samples were analyzed by thermogravimetric analysis at different heating rates in the 25–900°C temperature range. DSC curves showed that thermal decomposition reactions for cis-norbixin occurred in the solid phase. The kinetic parameters, such as activation energy and pre-exponential factor were determined using integral and approximate methods: Coats–Redfern, Madhusudanan, Horowitz–Metzger and Van Krevelen. F1 mechanism describes well the first stage of the thermal decomposition.     

Thermal study of TiO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> yellow ceramic pigment obtained by the Pechini method

TiO₂–CeO₂ oxides for application as ceramic pigments were synthesized by the Pechini method. In the present work the polymeric network of the pigment precursor was studied using thermal analysis. Results obtained using TG and DTA showed the occurrence of three main mass loss stages and profiles associated to the decomposition of the organic matter and crystallization. The kinetics of the degradation was evaluated by means of TG applying different heating rates. The activation energies (E _a) and reaction order (n) for each stage were determined using Horowitz–Metzger, Coats–Redfern, Kissinger and Broido methods. Values of E _a varying between 257–267 kJ mol^–1 and n=0–1 were found. According to the kinetic analysis the decomposition reactions were diffusion controlled.     

Thermal decomposition kinetics of tetraalkylammonium and dimethylpyridinium salts of the complex anion bis(1,3-dithiole-2-thione-4,5-dithiolate) bismuthate (−1)

In the present work, thermal decomposition kinetics of tetraalkylammonium and 1,4-dimethylpyridinium salts of the complex anion bis(1,3-dithiole-2-thione-4,5-dithiolate) bismuthate ([Bi(dmit)₂]⁻) are addressed. Kinetic parameters for the decomposition reactions were obtained utilizing the Ozawa and Coats–Redfern (CR) models. Entropy, enthalpy, and free energy of decomposition processes were calculated from the CR results, providing information on the thermodynamic characteristics of the processes. The most probable mechanisms of thermal decomposition were indicated for the studied systems, along with their kinetic and thermodynamic parameters.     

Thermal degradation kinetics of semi-aromatic polyamide containing benzoxazole unit

The kinetics of the thermal degradation of a new semi-aromatic polyamide containing benzoxazole unit (BO6) have been investigated by thermogravimetric analysis (TG). Thermal degradation of BO6 could be accomplished by one step. The corresponding kinetic parameters of the degradation process are determined by using Kissinger and Flynn–Wall–Ozawa methods, respectively. Coats–Redfern method is also used to discuss the probable degradation mechanism of the BO6. The results show that the activation energy obtained from Kissinger method is in good agreement with the value obtained by using Flynn–Wall–Ozawa method. The solid-state degradation mechanism of the BO6 is a decelerated R ₁ type (phase boundary controlled reaction one-dimensional movement).     

Kinetics and dissociation mechanism of heptaaqua-<Emphasis Type="Italic">p</Emphasis>-nitrophenolatostrontium(II) nitrophenol

A single crystal of heptaaqua-p-nitrophenolatostrontium(II) nitrophenol (HNSN) was grown, and the structure was confirmed by UV–Vis–NIR, FT-IR, FT-NMR, and high-resolution X-ray diffraction (HRXRD) analyses. The dielectric loss, dielectric constant, and the mechanical strength of the crystal have already been reported. The dynamic, non-isothermal thermal analysis was carried out at different heating rates, and TG and DTG data were used for the interpretation of the mechanisms and kinetics of decomposition by means of a model fitting method, Coats–Redfern equation, and a model-free method, Kissinger and Flynn–Wall method. The values of activation energy (E) and the pre-exponential factor (ln A) of each stage of thermal decomposition at various linear heating rates were calculated.     

Synthesis, Characterization and Thermal Studies of Some Iron(III) Complexes of o-Vanillin Oxime

Iron(III) complexes of o-vanillin oxime have been synthesized and characterized by different physicochemical techniques. The complexes containing thiocyanate, iodide and sulphate ionshave been subjected to non-isothermal decomposition studies in N₂ using TGand DTG techniques. The kinetic parameters for both stages of decomposition of these complexes were evaluated by weighted least-squares method using the general approach as well as the Coats–Redfern and Horowitz–Metzger equations. The results indicate that the values of kinetic parameters obtained by these three different approaches agree well. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and non-isothermal degradations of the bridged diacetato–diamido–diamine–uranyl complex

The new bridged diacetato–diamido–diamine–uranyl complex {2[(UO₂)(H₂N)(H₃N)(OOCCH₃)]} was prepared and characterized by elemental analysis, IR measurement as well as TG and DTA analysis. The kinetic parameters; activation energy (E_a), pre-exponential factor (A) and the order of decomposition (n) were calculated from TG curves using Coats–Redfern and Flynn–Wall–Ozawa methods. The mechanism of decomposition has been established from TG and DTA data. The data obtained agree quite well with the expected structure and show that the complex finally decomposes to form UO₃. A general mechanism describing the formation of bridged complex {2[(UO₂)(H₂N)(H₃N)(OOCCH₃)]} is proposed.     

Kinetic study of the polymeric binder burnout in green low temperature co-fired ceramic tapes

The binder decomposition and burnout process of a commercial low temperature co-fired ceramic (LTCC) tape and an alumina tape which is used as a sacrificial tape for the constrained sintering process of the LTCC-tape was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) up to 550 °C at different heating rates (from 1.5 to 10 K min⁻¹) in air. TG revealed a multistage degradation behaviour of the binder system for both tapes, but the temperature range of the different degradation stages varied. The activation energy of decomposition was determined by the Flynn–Wall isoconversional method and the Coats–Redfern method.     

Kinetics of curing and thermal degradation of hyperbranched epoxy (HTDE)/diglycidyl ether of bisphenol-A epoxy hybrid resin

Hyperbranched epoxy resin (HTDE) has relatively low viscosity and high molecular mass and holds great promise as a functional additive for enhancing the strength and toughness of thermosetting resins. In this work, the curing and thermal degradation kinetics of HTDE/diglycidyl ether of bisphenol-A epoxy (DGEBA) hybrid resin were studied in detail using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) techniques by Coats–Redfern model. The effect of molecular mass or generation and content of HTME on the activation energy, reaction order, and curing time were discussed; the results indicated that HTDE could accelerate the curing speed and reduce the activation energy and reaction order of the curing reaction.     

Pyrolysis and combustion characteristics of Bio-oil from swine manure

Pyrolysis and combustion characteristics of bio-oil derived from swine manure were investigated using thermogravimetry techniques. Thermogravimetric analysis of the bio-oils were carried out in O₂ and N₂ atmosphere under different heating rates (5–20 °C/min) to a maximum temperature of 900 °C. The results indicate that the combustion processes of bio-oil occurred in three stages, namely the water and the lighter compound evaporation, i.e., the release of the volatile compounds, ignition and burning of the heavier compounds (mainly carbon), and finally decomposition of the carbonate compounds. The effect of heating rate was also studied, and higher heating rates were found to facilitate the combustion process. Different reaction kinetic mechanisms were used to treat TG data, and showed that diffusion models are the best fit for describing the combustion of bio-oil in air. The kinetic parameters of the three stages were determined using Coats–Redfern method. The study provided reliable basic data for the burning of bio-oil.     

Effect of alpha-tocopherol (vitamin E) on the thermal degradation behavior of edible oils

Alpha-tocopherol (vitamin E) is the most widely used antioxidant for edible oils. The present investigation presents its effect on the thermal degradation behavior of edible oils (sunflower, soybean, and their blend) through the use of dynamic thermogravimetry. The study is based on the comparison of activation energies of decomposition process which were subsequently calculated using preferred and reliable multiple-heating rate methods viz. Kissinger, Friedman, Ozawa–Flynn–Wall, and Coats–Redfern (modified). It is concluded that the role of alpha-tocopherol as antioxidant at higher temperature is nearly accomplished.     

Complexes of biologically important ligands. I. Ternary complexes of nickel(II) comprising 1,10-o-phenanthrolineazosulfonamide derivatives and alkyldithiophosphates

5-[p-(R-Sulfonyl)phenylazo]-1,10-o-phenanthroline (L) and its octahedral complexes of the type [Ni(R₂dtp)₂(L)] (where R₂dtp = diethyl-or dipropyldithiophosphate) with the core NiN₂S₄ have been prepared and characterized by spectral, magnetic, and thermogravimetric methods. The thermal decomposition mechanism of the compounds was proposed and the kinetic parameters of decomposition were calculated making use of the Coats—Redfern and Horowitz—Metzger equations.     

Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements

Dynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps, as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods were used to determine the apparent activation energy (E _a) of the thermal degradation of the cellulose component into the composites. E _a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular, it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion between the components in NFR composites.     

Studies on the thermal decomposition kinetics and mechanism of ammonium niobium oxalate

Ammonium niobium oxalate was prepared and characterized by elemental analysis, XRD and FTIR spectroscopy analysis, which confirmed that the molecular formula of the complex is NH₄(NbO(C₂O₄)₂(H₂O)₂)(H₂O)₃. Dynamic TG analysis under air was used to investigate the thermal decomposition process of synthetic ammonium niobium oxalate. It shows that the thermal decomposition occurs in three stages and the corresponding apparent activation energies were calculated with the Ozawa–Flynn–Wall and the Friedman methods. The most probable kinetic models of the first two steps decomposition of the complex have been estimated by Coats–Redfern integral and the Achar–Bridly–Sharp differential methods.     

Thermogravimetric evaluation of decomposition kinetics of metal surfactant complexes

Thermal behavior of various synthesized transition metal surfactant complexes of the type [M(CH₃COO)₄]²⁻[C₁₂H₂₅NH₃ ⁺]₂ where M: Cu(II), Ni(II), Co(II) has been investigated using Thermogravimetric Analysis (TGA). It was found that pyrolytic decomposition occurs with melting in metal complexes, and that metal oxides remain as final products. The activation energy order obtained, E _Cu > E _Ni > E _Co, could be explained on the basis of size of transition metal ion and metal ligand bond strength. In the course of our investigation on the decomposition of complexes, we carried out a comparative study of different measurement and calculation procedures for the thermal decomposition. A critical examination was made of the kinetic parameters of non-isothermal thermoanalytic rate measurement by means of several methods such as Coats–Redfern (CR), Horowitz–Metzger (HM), van Krevelen (vK), Madhusudanan–Krishnan–Ninan (MKN), and Wanjun–Yuwen–Hen–Cunxin (WYHC). The most appropriate method among these was determined for each decomposition step according to the least-squares linear regression. It was found that the results obtained using CR method differ considerably from HM method, as the former method involves a lot of approximations and is not much reliable. The application of thermoanalytic techniques to the investigation of rate processes has also been discussed.     

Thermoanalytical investigations of niobium(V) complexes of 4-isopropylphenol

Thermal behaviour of newly synthesized niobium(V) aryloxides of composition [NbCl_5−n (OC₆H₄CH(CH₃)₂-4) _n ] (where n = 1 → 5) synthesized by the reactions of niobium pentachloride with 4-isopropylphenol in predetermined molar ratios in carbon tetrachloride has been studied by thermogravimetric (TG) and differential thermal analysis (DTA) techniques. The results showed that thermal decomposition of complex of composition [NbCl₄(OC₆H₄CH(CH₃)₂-4)] resulted in the formation of NbOCl₃ as the ultimate decompositional product while all other complexes yielded Nb₂O₅ as the final product of thermal decomposition. From the mathematical analysis of TG data, the kinetic and thermodynamic parameters viz. energy of activation, frequency factor, entropy of activation, etc. have been evaluated using Coats–Redfern equation.     

Studies on Non-isothermal Kinetics of the Thermal Decomposition of Eu2(BA)6(bipy)2

The thermal decomposition of Eu₂(BA)₆(bipy)₂ (BA=C₂H₅N^– ₂, benzoate; bipy=C₁₀H₈N₂, 2,2'-bipyridine)and its kinetics were studied under the non-isothermal condition by TG-DTG, IR and SEM methods. The kinetic parameters were obtained from analysis of the TG-DTG curves by the Achar method, the Madhusudanan-Krishnan-Ninan (MKN) method, the Ozawa method and the Kissinger method. The most probable mechanism function was suggested by comparing the kinetic parameters. The kinetic equation for the first stage can be expressed as: dα/dt=Aexp(–E/RT)3(1–α)^2/3. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization and kinetic study of sunflower oil and biodiesel

In this study, the physico-chemistry characterization and kinetic study of the thermal decomposition of sunflower oil and its biodiesel were carried out. Sunflower biodiesel was synthesized by the methanol route and basic homogeneous catalysis. The physicochemical characterization of the sunflower oil and biodiesel were performed according to standards set out in the ANP resolution, and both are in accordance to the specifications. The chromatographic analysis was obtained by GC-FID. The yield of conversion of 97.4 wt% of sunflower oil in methyl esters confirms the efficiency of the conversion of the fatty acids into esters. The thermal analysis was performed on a thermobalance, using heating rates of 5, 10, and 20 °C min⁻¹. In these three rates, we observed a single well-defined step of mass loss that describes the volatilization and decomposition of the sunflower oil and the biodiesel. The kinetic study was performed using equations of approximation and integration methods such as Coats–Redfern, Van Krevelen, and Horowitz–Metzger. The kinetic parameters reaction order (n) and apparent activation energy (E _a), obtained by applying these method were correlated.     

Kinetics of dehydroxylation and evaluation of the crystallinity of kaolinite

This study presents results on the kinetics of kaolinite dehydroxylation. The accuracy of various methods of determining the values for the kinetic parameters and their sensitivity in detecting the mechanism of reaction is investigated. In particular, the differential order of reaction method of Baker, the general method of Achar et al., the integral method of Boy and Bohme, and the method of Coats and Redfern as modified by Fong and Chen are considered.

Kaolinites from well-known sources are used to study the influence of crystallinity on the values of kinetic parameters. The statistical significance of the various mathematical methods for the assessment of the data obtained from non-isothermal thermogravimetry is determined by comparison with experimental and theoretical data using a computer programme developed for this purpose. The study demonstrates that the kinetic parameters can be used to quantify the degree of crystallinity of kaolinite and also confirms other findings that the dehydroxylation of kaolinite is a second-order reaction.