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.     

Non-isothermal decomposition kinetics of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized using egg white solution route

The thermal decomposition kinetics of nickel ferrite (NiFe₂O₄) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different heating rates. The activation energy (E _α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS), which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe₂O₄ precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.     

Kinetics of thermal decomposition of CeO2 nanocrystalline precursor prepared by precipitation method

The thermal decomposition of CeO₂ nanocrystalline precursor prepared by chemical precipitation method was investigated using thermo-gravimetric/differential scanning calorimetry (TG/DSC) and X-ray powder diffraction (XRD). In particular, the differential thermal analysis curves for the decomposition of CeO₂ nanocrystalline precursor were measured at different heating rates in air by a thermal analyzer (NETZSCH STA 449C, Germany). The kinetic parameters of the thermal decomposition of CeO₂ nanocrystalline precursor were calculated using the Kissinger method and the Coats-Redfern method. Results show that the apparent active energy E of the reaction is 105.51 kJ/mol, the frequency factor lnA is 3.602 and the reaction order n is 2. This thermal decomposition process can be described by the anti-Jander equation and a three-dimensional diffusion mechanism. Tanslated from Journal of Central South University (Science and Technology), 2007, 38(3): 428–432 [译自: 中南大学学报(自然科学版]     

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.     

Study on thermal decomposition of calix[6]arene and calix[8]arene

Thermal decomposition kinetics of calix[6]arene (C6) and calix[8]arene (C8) were studied by Thermogravimetry analysis (TG) and Differential thermal analysis (DTA). TG was done under static air atmosphere with dynamic heating rates of 1.0, 2.5, 5.0, and 10.0 K min⁻¹. Model-free methods such as Friedman and Ozawa–Flynn–Wall were used to evaluate the kinetic parameters such as activation energy (E _a) and pre-exponential factors (ln A). Model-fitting method such as linear regression was used for the evaluation of optimum kinetic triplets. The kinetic parameters obtained are comparable with both the model-free and model-fitting methods. Within the tested models, the thermal decomposition of C6 and C8 are best described by a three dimensional Jander’s type diffusion. The antioxidant efficiency of C6 and C8 was tested for the decomposition of polypropylene (PP).     

Phase transition of YBO<Subscript>3</Subscript>

Yttrium orthoborate crystallizes in the vaterite-type structure and has two polymorphous forms, viz. a low- und a high temperature one. DTA measurements of YBO₃ confirmed a reversible phase transition with a large thermal hysteresis. The phase transition has been accurately characterized by the application of different heating and cooling rates (β). Consequently, the extrapolation of the experimental data to zero β yields the transition points at 986.9°C for the heating up and at 596.5°C for the cooling down cycle. These values correspond to samples just after treatment at 1350°C. For samples with a different ‘thermal history’ other phase transition temperatures are observed, (e.g. after having performed several heating and cooling cycles). The linear relationship between the associated DTA signal ΔT=T _onset–T _offset and the square root of the heating rate β was confirmed, but the relation between T _onset and square root of β is not found here. From the empirical data a good linear fitting between T _onset and ln(β+1) can be derived. From the kinetic analysis (Kissinger method) of the phase transformation of YBO₃ an apparent activation energy of about 1386 kJ mol^–1 for heating and of about 568 kJ mol^–1 for cooling can be determined     

Non-isothermal kinetics of the thermal decomposition of sodium oxalate Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The thermal transformation of Na₂C₂O₄ was studied in N₂ atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na₂C₂O₄ and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (E _α) of Na₂C₂O₄ decomposition were found to be consistent. Decreasing E _α at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R₂ or F_1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.     

Kinetics of decomposition of different acid calcium phosphates

The kinetics of thermal decomposition of Ca(H₂PO₄)₂·H₂O under non-isothermal conditions was studied. The TG/DTG curves were obtained at five heating rates: 5, 7, 10, 12 and 20 K min^–1. The kinetic analysis was performed by means of three methods: Friedman, Budrugeac–Segal and NPK by Sempere and Nomen. An important dependence of the activation energy vs. the conversion degree was observed and also a compensation effect. The decomposition consists of water loss and is due to the elimination of crystallization water and an intermolecular condensation, respectively.     

Coupled thermogravimetric-IR techniques and kinetic analysis by non-isothermal decomposition of Cd<Superscript>2+</Superscript> and Co<Superscript>2+</Superscript> vinyl-phosphonates

The thermal behavior of Cd²⁺ and Co²⁺ vinyl-phosphonates was studied using two different experimental strategies: the coupled TG–EGA (FTIR) technique by decomposition in nitrogen, respectively, air, and the kinetic analysis of TG data obtained in dynamic air atmosphere at four heating rates. The both compounds exhibited a good thermal stability: in nitrogen, only an endothermic dehydration step was observed. In air the Cd²⁺ salt presents the same dehydration step whereas by the Co²⁺ salt two simultaneous processes take place dehydration, respectively, thermooxidative destruction of the vinyl group. The kinetic analysis of the TG data was performed with the Flynn–Wall–Ozawa, Friedman’s, and modified non-parametric kinetic methods. By means of the coupled techniques, some spectroscopic arguments on the reaction mechanism were obtained. The values of the activation energy by the three methods are in good agreement and support the two different suggested mechanism.     

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.     

Thermal behavior of drugs

Data on the thermal stability of drugs was required to obtain information for handling, storage, shelf life and usage. In this study, the thermal stability of two nonsteroidal anti-inflammatory drugs (NSAIDs) was determined by differential scanning calorimetry (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the naproxen and celecoxib occurs in the temperature ranges of 196–300 and 245–359 °C, respectively. The TG/DTA analysis of compounds indicates that naproxen melts (at about 158.1 °C) before it decomposes. However, the thermal decomposition of the celecoxib started about 185 °C after its melting. The influence of the heating rate (5, 10, 15, and 20 °C min⁻¹) on the DSC behavior of the both drug samples was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the values of activation energy obtained by various methods, the following order for the thermal stability was noticed: naproxen > celecoxib. Finally, the values of ΔS ^#, ΔH ^#, and ΔG ^# of their decomposition reaction were calculated.     

Synthesis of electrospun BaSrTiO<Subscript>3</Subscript>/PVP nanofibers

Ba_1−x Sr _x TiO₃(x = 0–0.5, BST) nanofibers with diameters of 150–210 nm were prepared by using electrospun BST/polyvinylpyrrolidone (PVP) composite fibers by calcination for 2 h at temperatures in the range of 650–800 °C in air. The morphology and crystal structure of calcined BST/PVP nanofibers were characterized as functions of calcination temperature and Sr content with an aid of XRD, FT-IR, and TEM. Although several unknown XRD peaks were detected when the fibers were calcined at temperatures less than 750 °C, they disappeared with increasing the temperature (above 750 °C) due to its thermal decomposition and complete reaction in the formation of BST. In addition, the FT-IR studies of BST/PVP fibers revealed that the intensities of the O–H stretching vibration bands (at 3430 and 1425 cm⁻¹) became weaker with increasing the calcination temperature and a broad band at 540 cm⁻¹, Ti–O vibration, appeared sharper and narrower after calcination above 750 °C due to the formation of metal oxide bonds. However, no effect of Sr content on the crystal structure of the composites was detected.     

Preparation, characterization, and the molecular structure of 2,4,6-trinitro-mesitylene

We reported in this study the synthesis, culture of crystal, and single-crystal X-ray crystallography of the 2,4,6-trinitro-trimethylbenzene (TNTM) compound. We found the crystal belongs to the Triclinic system with space group P-1. The compound was also characterized by FT-IR,¹H NMR, and MS spectroscopy techniques. Density functional theory (DFT) B3LYP was employed to optimize structure and calculate frequencies of TNTM. The calculated geometrical parameters are close to the corresponding experimental ones. The thermal decomposition of TNTM was investigated by DSC and TG–DTG methods at heating rate 10°C/min. The results indicate that TNTM has high heat-resistant ability.1

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Thermal decomposition kinetics of potassium iodate

The thermal decomposition of potassium iodate (KIO₃) has been studied by both non-isothermal and isothermal thermogravimetry (TG). The non-isothermal simultaneous TG–differential thermal analysis (DTA) of the thermal decomposition of KIO₃ was carried out in nitrogen atmosphere at different heating rates. The isothermal decomposition of KIO₃ was studied using TG at different temperatures in the range 790–805 K in nitrogen atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of KIO₃. The non-isothermal decomposition of KIO₃ was subjected to kinetic analyses by model-free approach, which is based on the isoconversional principle. The isothermal decomposition of KIO₃ was subjected to both conventional (model fitting) and model-free (isoconversional) methods. It has been observed that the activation energy values obtained from all these methods agree well. Isothermal model fitting analysis shows that the thermal decomposition kinetics of KIO₃ can be best described by the contracting cube equation.     

Thermal stability and degradation of Co(II), Cd(II), and Zn(II) complexes with <Emphasis Type="Italic">N</Emphasis>-benzyloxycarbonylglycinato ligand

Thermal behavior of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand was investigated using the results of TG, DSC and DTG analysis obtained at different heating rates (2.5 to 30 °C min⁻¹), from room temperature to about 900 °C. Mechanisms of complex degradation, as well as enthalpies of the degradation processes were determined. It is shown that thermal stability of investigated complexes correlates with their crystal structures, especially with the presence of crystallization and coordinated water molecules. The values of dehydration enthalpies are discussed and correlated with composition of the complexes. Kissinger’s, Ozawa’s, and Friedman’s isoconversion methods were used for the determination of kinetic parameters: the pre-exponential factor A and the apparent activation energy E _a. For all three complexes and all steps of degradation, the values of kinetics parameters obtained by Kissinger’s and Ozawa’s methods are in good agreement. The results obtained by Friedman’s method showed that some decomposition steps are simple and some others are complex ones.     

Preparation of ferrites from the thermal decomposition of magnesium and calcium <Emphasis Type="Italic">tris</Emphasis>(succinato)ferrates(III) precursors

The complexes of general formula Ln(btfa)₃L, where Ln=Eu or Tb, btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione, L=1,10-phenanthroline (phen) or 2,2-bipyridine (bipy), were synthesized by reacting the corresponding metal chloride with the proper β-diketone and the other ligand. The complexes were obtained in the powder form and were characterized by photoluminescence and TG. Their thermal decomposition was studied by non-isothermal thermogravimetric techniques. The Eu(btfa)₃bipy complex presented the highest thermal stability and it melts before being decomposed. The complex Eu(btfa)₃phen presented the largest activation energy for a heating rate of 5°C min^–1.     

Phase transition and thermal decomposition of [Al(DMSO)<Subscript>6</Subscript>]Cl<Subscript>3</Subscript>

Phase transition and thermal decomposition of hexadimethylsulfoxidealuminium chloride were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and simultaneous differential thermal analysis (SDTA). The gaseous products of the decomposition were on-line identified by a quadrupole mass spectrometer (QMS). In the temperature range of 95–300 K, [Al(DMSO)₆]Cl₃ indicates one phase transition at T _c^h=244.96 K (on heating) and at T _c^c=220.87 K (on cooling). Large thermal hysteresis of the phase transition (∼24 K) indicates its first order character. Large value of transition entropy (ΔS≈40 J mol⁻¹ K⁻¹) suggests its configurational character. Thermal decomposition of the title compound proceeds in four main stages. In the first stage, which starts just above ca. 300 K, the compound loses two DMSO molecules per one formula unit and undergoes into [Al(DMSO)₄]Cl₃. In the second stage, the next three DMSO ligands are released and simultaneously decomposed. The third stage, which continues up to ca. 552 K, is connected with a loss of the last DMSO ligand and the formation of AlCl₃. In the fourth stage AlCl₃ reacts with carbon monoxide that originates from the decomposition of DMSO, and first aluminium oxychloride and next solid Al₂O₃ plus carbon are created.     

Characterization and phase transformation study of TlSbSe2 crystals

TlSbSe₂ monocrystals were grown using the modified Bridgman–Stockbarger method and were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Reflectivity spectra have been registered in the range 50 to 4000 cm^–1 for E parallel to a and E parallel to b polarizations, on the cleavage plane. A remarkable anisotropy at two directions was verified. With regard to previous observations, additional peaks were discriminated and the fundamental phonon parameters were determined using classical dispersion relations. The material presents a complex phase transformation – with two thermal effects – that was examined using differential scanning calorimetry (DSC). Non-isothermal measurements, at different heating and cooling rates (β), were used to study the thermal phenomena. The main effect is attributed to a structural displacement and the second one to a cation exchange procedure. The phase transformation temperature depends strongly on the cooling rate and the peaks are shifted by 30 K with the increase of this rate, on the contrary to the increase of the heating rate that has a smaller effect. Phenomena related with the influence of the previous, repeated heating and cooling cycles on the transformation are also examined and analytically discussed.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition behaviors of β-cyclodextrin,its inclusion complexes of alkyl amines,and complexed β-cyclodextrin at different heating rates

The present work revealed there was a conceptual difference in the thermal decomposition behaviors between the complexed β-cyclodextrin (CD) in an inclusion system and the β-CD complex of guest. The thermal decomposition behaviors of the solid inclusion complexes of β-CD with ethylenediamine (Eda), diethylenetriamine (Dta) and triethylamine (Tea) were investigated using nonisothermal thermogravimetry (TG) analysis based on weight loss as a function of temperature. In view of TG profiles, a consecutive mechanism describing the formation and thermal decomposition of the three solid supermolecules of β-CD was presented. Heating rate has very different effects on the thermal decomposition behaviors of these complexes. The faster the heating rate is, the higher the melting-decomposition point of the complexed β-CD in an inclusion system is, and on the whole the bigger the rate constant (k) of the thermal decomposition reaction of the complexed β-CD is. The thermal decomposition process of the complexed β-CD for each inclusion system is determined to be simple first-order reaction using Ozawa method. The apparent activation energies (E _a) and frequency factors (A) of the thermal decomposition reactions of the complexed β-CD molecules have been also calculated. It is found that when the decomposition reaction of the complexed β-CD encountered a large value of E _a, such as that in Dta–β-CD system, an apparent compensation effect of A on E _a can provide enough energy to conquer the reaction barrier in prompting the k value of thermal decomposition reaction of the complexed β-CD according to Arrhenius equation.