The influence of morphology of ultra-fine calcite particles on decomposition kinetics

The decomposition kinetics of reference calcite and three ultra-fine samples with different morphologies are investigated. The kinetic parameters and rate equation are obtained according to the methods reported in our previous studies. Compared with the reference calcite, a considerable diminution of the activation energy E _a up to 70–80 kJ mol⁻¹ is observed in the case of three ultra-fine samples. There are also some distinct differences concerning the activation energy of each of the ultra-fine sample. This may have something to do with the particle morphology revealed by TEM and SEM measurements. XRD measurements of four calcite samples show that large strain exists in the crystal lattice in the case of ultra-fine calcite samples. This may give a reason to their abnormal decomposition behavior.     

Kinetic study of pyrolysis of waste water treatment plant sludge

Activated sewage sludge samples obtained from two different waste water treatment plants were investigated by thermogravimetric analysis. Due to a very high content of water in the sludge samples, these had to be dried at 160°C in an electrical oven in order to remove all adsorbed water. To ensure pyrolysis conditions, nitrogen atmosphere was applied. The pyrolysis decomposition process was carried out in the temperature range from ambient temperature to 900°C at three different heating rates: 2 K min⁻¹, 5 K min⁻¹, 10 K min⁻¹. TGA and DTG curves of the decomposition processes were obtained. Temperature of onset decomposition, final temperature of decomposition, maximum decomposition rate, and decomposition temperature were determined by thermogravimetric analysis for both sludge samples used. The main decomposition process takes place at temperatures in the range from 230°C to 500°C. Above this temperature, there are only small changes in the mass loss which are often attributed to the decomposition of carbonates present in the sewage sludge samples. To determine the apparent kinetic parameters such as the activation energy and the preexponential factor, the so called Friedman isoconversional method was used. Because of the requirements of this method, initial and final parts of the decomposition process, where crossings of the decomposition lines occurred, were cut off. Obtained dependencies of the apparent activation energies and preexponential factors as a function of conversion were used backwards to calculate the modeled decomposition process of sewage sludge and the experimental data were in good accordance with the data obtained by simulation.     

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.     

Heating rate effect on the DSC kinetics of oil shales

This research was aimed to investigate the combustion and kinetics of oil shale samples (Mengen and Himmetoğlu) by differential scanning calorimetry (DSC). Experiments were performed in air atmosphere up to 600°C at five different heating rates. The DSC curves clearly demonstrate distinct reaction regions in the oil shale samples studied. Reaction intervals, peak and burn-out temperatures of the oil shale samples are also determined. Arrhenius kinetic method was used to analyze the DSC data and it was observed that the activation energies of the samples are varied in the range of 22.4–127.3 kJ mol⁻¹ depending on the oil shale type and heating rate.     

The effect of zinc stearate on thermal degradation of paraffin wax

In this research, the effects of zinc stearate addition on paraffin wax degradation were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energies of wax decomposition in nitrogen and air atmospheres were determined as 76 and 37 kJ mol⁻¹, respectively applying Kissinger method to TG data. The degradation rate constants of paraffin containing zinc stearate (0.1–0.5%) were found to be almost two times greater than that of paraffin only in air atmosphere. However, zinc stearate did not affect the rate constants in nitrogen significantly.     

Effect of particle size on pyrolysis characteristics of Elbistan lignite

In this study, the relationship between particle size and pyrolysis characteristics of Elbistan lignite was examined by using the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. Lignite samples were separated into different size fractions. Experiments were conducted at non-isothermal conditions with a heating rate of 10°C min⁻¹ under nitrogen atmosphere up to 900°C. Pyrolysis regions, maximum pyrolysis rates and characteristic peak temperatures were determined from TG/DTG curves. Thermogravimetric data were analyzed by a reaction rate model assuming first-order kinetics. Apparent activation energy (E) and Arrhenius constant (A _r) of pyrolysis reaction of each particle size fraction were evaluated by applying Arrhenius kinetic model. The apparent activation energies in the essential pyrolysis region were calculated as 27.36 and 28.81 kJ mol⁻¹ for the largest (−2360+2000 μm) and finest (−38 μm) particle sizes, respectively.     

Oil shale kinetics by differential methods

In this research, pyrolysis and combustion behavior of three different oil shale samples from Turkey were characterized using thermal analysis techniques (TG/DTG). In pyrolysis experiments, two different mechanisms causing mass loss were observed as distillation and cracking. In combustion experiments, two distinct exothermic peaks were identified known low and high temperature oxidation. On the other hand, determination of activation energies are required for the estimation of oil extraction conditions from the oil shales. Differential methods are used to determine the activation energies of the samples where various f(α) models are applied from the literature. It was observed that the activation energies of the all oil shale samples are varied between 13.1–215.4 kJ mol⁻¹ in pyrolysis and 13.1–408.4 kJ mol⁻¹ in combustion experiments which are consistent with other kinetic results.     

Effect of poly(bisphenol A acryloxyethyl phosphate) on the activation energy in thermal degradation of urethane acrylate

Poly(bisphenol A acryloxyethyl phosphate) (BPAAEP) was blended in different ratios with a commercial urethane acrylate to obtain a series of UV curable flame-retardant resins. The thermal oxidative degradation mechanism of their cured films in air were studied by thermogravimetric analysis at several heating rates between 5 and 20°C min⁻¹. The activation energies were determined using Kissinger method, Friedman method, Flynn-Wall method, Horowitz-Metzger method and Ozawa method. The results showed that the activation energies of the blends were lower than that of pure urethane acrylate at lower degree of degradation, whereas the higher activation energies were obtained at higher degree of degradation.     

Thermal studies on polymorphic structures of tibolone

Tibolone polymorphic forms I (monoclinic) and II (triclinic) have been prepared by recrystallization from acetone and toluene, respectively, and characterized by different techniques sensitive to changes in solid state, such as polarized light microscopy, X-ray powder diffractometry, thermal analysis (TG/DTG/DSC), and vibrational spectroscopy (FTIR and Raman microscopy). The nonisothermal decomposition kinetics of the obtained polymorphs were studied using thermogravimetry. The activation energies were calculated through the Ozawa’s method for the first step of decomposition, the triclinic form showed a lower E _a (91 kJ mol⁻¹) than the monoclinic one (95 kJ mol⁻¹). Furthermore, Raman microscopy and DSC at low heating rates were used to identify and follow the thermal decomposition of the triclinic form, showing the existence of three thermal events before the first mass loss.     

Study on thermal decomposition kinetics of N,N′-bis(5,5-dimethyl-2-phospha-2-thio-1,3-dioxan-2-yl)ethylenediamine in air

The thermal decomposition kinetics of the N,N′-bis(5,5-dimethyl-2-phospha-2-thio-1,3-dioxan-2-yl) ethylenediamine (DPTDEDA) in air were studied by TGDTG techniques. The kinetic parameters of the decomposition process for the title compound in the two main thermal decomposition steps were calculated through the Friedman and Flynn-Wall-Ozawsa (FWO) methods and the thermal decomposition mechanism of DPTDEDA was also studied with the Coats-Redfern and Achar methods. The results show that the activation energies for the two main thermal decomposition steps are 128.03 and 92.59 kJ·mol⁻¹ with the Friedman method, and 138.75 and 106.78 kJ·mol⁻¹ with the FWO method, respectively. Although there are two main thermal decomposition steps for DPTDEDA in air, the thermal decomposition mechanism of DPTDEDA in the two steps are the same, i.e. f(α) = 3/2(1 − α)^4/3[(1 − α)^−1/3 − 1]⁻¹. __________ Translated from Acta Chimica Sinica, 2008, 66(9) (in Chinese)     

Oxidation of Saturated Fatty Acids Esters DSC investigations

Oxidation of saturated fatty acids ethyl esters: laurate, myristate, palmitate and stearate was investigated by means of DSC techniques under isothermal and non-isothermal conditions. The activation energies of isothermal oxidation were similar to each other (112–123 kJ mol⁻¹) and no influence of carbon length on the rate of oxidative decomposition was observed. Results obtained from non-isothermal experiments were similar only for the first stage of oxidation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetic analysis of the thermal decomposition of copper (I) complexes with heterocyclic thiones

Two series of copper (I) halide complexes formulated as [(L)CuX(μ₂-L)₂CuX(L)] and [(L)₂Cu(μ₂-L)₂Cu(L)₂]²⁺ 2Χ⁻, respectively (X = Cl, Br and L = 4,6-dimethylpyrimidine-2-thione (dmpymtH)) were prepared. From the thermogravimetric curves it was found that among the four studied materials, [Cu₂(dmpymtH)₆]²⁺2Cl⁻ presents a lower thermal stability. For the determination of the activation energy (E) two different methods have been used comparatively, since every method has its own error. These methods were the isoconversional methods of Ozawa, Flynn and Wall (OFW), and Friedman. The dependence of the E on the value of the mass conversion α, as calculated with OFW and Friedman’s methods, can be separated in three distinct regions. The decomposition mechanism is very complex and can be described using at least three different mechanisms with different activation energies. The best fitting of experimental data with theoretical models gave nth-order for all the three mechanisms (Fn–Fn–Fn).     

Thermal analysis of <Emphasis Type="Italic">cis</Emphasis>-(dithiocyanato)(1,10-phenanthroline-5,6-dione)(4,4′-dicarboxy-2,2′-bipyridyl)ruthenium(II) photosensitizer

Thermal behavior of [cis-(dithiocyanato)(1,10-phenanthroline-5,6-dione)(4,4′-dicarboxy-2,2′-bipyridyl)ruthenium(II)], cis-[Ru(L1)(L2)(NCS)₂] (where the ligands were L1 = 1,10-Phenanthroline-5,6-dione, L2 = 4,4′-dicarboxy-2,2′-bipyridyl) was investigated by DTA/TG/DTG measurements under inert atmosphere in the temperature range of 298–1473 K as well as by XRD analysis of the final product. After making detailed analysis and comparison of thermogravimetrical and MS measurements of ruthenium complex, the decomposition mechanism of that complex was suggested. The values of activation energy and reaction order of the thermal decompositions were calculated by Ozawa Non-isothermal Method for all decomposition stages. The calculated activation energies vary in between 32 and 49 kJ mol⁻¹.     

Thermogravimetric analysis of cellulose insulation and determination of activation energy of its thermo‐oxidation using non‐isothermal,model‐free methods

The aim of the work was to determine the effect of heating rate on initial decomposition temperature and phases of thermal decomposition of cellulose insulation. The activation energy of thermo‐oxidation of insulation was also determined. Individual samples were heated in the air flow in the thermal range of 100°C to 500°C at rates from 1.9°C min^?1 to 20.1°C min^?1. The initial temperatures of thermal decomposition ranged from 220°C to 320°C, depending on the heating rate. Three regions of thermal decomposition were observed. The maximum rates of mass loss were measured at the temperatures between 288°C and 362°C. The activation energies, which achieved average values between 75 and 80.7 kJ mol^?1, were calculated from the obtained results by non‐isothermal, model‐free methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetic parameters and geometry of the transition state of acyl radical decarbonylation

Experimental data on acyl radical decomposition reactions (RC^·O → R^· + CO, where R = alkyl or aryl) are analyzed in terms of the intersecting parabolas method. Kinetic parameters characterizing these reactions are calculated. The transition state of methyl radical addition to CO at the C atoms is calculated using the DFT method. A semiempirical algorithm is constructed for calculating the transition state geometry for the decomposition of acyl radicals and for the reverse reactions of R^· addition to CO. Kinetic parameters (activation energy and rate constant) and geometry (interatomic distances in the transition state) are calculated for 18 decomposition reactions of structurally different acyl radicals. A linear correlation between the interatomic distance r ^#(C…C) (or r ^#(C…O)) in the transition state the enthalpy of the reaction (δH _e) is established for acyl decomposition reactions (at br _e = const). A comparative analysis of the enthalpies, activation energies, and interatomic distances in the transition state is carried out for the decomposition and formation of acyl, carboxyl, and formyl radicals.     

Decomposition kinetics of iron (III)-diclofenac compound

Non-isothermal decomposition of iron (III)-diclofenac anhydrous salt was investigated by thermogravimetry (TG) under different conditions in opened and closed α-alumina pans under nitrogen atmosphere. To estimate the activation energy of decomposition, the Capela and Ribeiro isoconversional method was applied. The results show that due to the lid cover different activation energies were obtained. From these curves a tendency can be seen where the plots maintain the same profile for closed lids and almost run parallel to each other. Independently of the different experimental conditions no remarkably different results have been obtained.     

The highly crosslinked dimethacrylic/divinylbenzene copolymers

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, [BMIM]Br, and 1-n-octyl-3-methylimidazolium bromide, [OMIM]Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition temperature, previously determined from fast scan TG experiments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 °C interval in the range 533–573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of [BMIM]Br and [OMIM]Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol⁻¹, respectively. The moisture absorption kinetics of these ILs at 25 °C and 30% relative humidity (RH) and at 85 °C and 85% RH were also studied. Water uptake of ILs exposed at 25 °C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 °C/85%RH fortuitously fit into the Henderson–Pabis model.     

Studies of the rates of thermal decomposition of glycine,alanine, and serine

Rates of thermal decomposition of glycine, alanine, and serine are described by the equation of first order reaction in the temperature range 200–300°C. Apparent rate constants and apparent activation energies of decomposition of α-amino acids were evaluated. It was found that the main gaseos reaction product is carbon dioxide.     

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.     

Kinetic and thermodynamic studies of MgHPO<Subscript>4</Subscript> · 3H<Subscript>2</Subscript>O by non-isothermal decomposition data

The thermal decomposition of magnesium hydrogen phosphate trihydrate MgHPO₄ · 3H₂O was investigated in air atmosphere using TG-DTG-DTA. MgHPO₄ · 3H₂O decomposes in a single step and its final decomposition product (Mg₂P₂O₇) was obtained. The activation energies of the decomposition step of MgHPO₄ · 3H₂O were calculated through the isoconversional methods of the Ozawa, Kissinger–Akahira–Sunose (KAS) and Iterative equation, and the possible conversion function has been estimated through the Coats and Redfern integral equation. The activation energies calculated for the decomposition reaction by different techniques and methods were found to be consistent. The better kinetic model of the decomposition reaction for MgHPO₄ · 3H₂O is the F _1/3 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the decomposition reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous without connecting with the introduction of heat.