Non-isothermal decomposition kinetics of synthetic serrabrancaite (MnPO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O) precursor in N<Subscript>2</Subscript> atmosphere

The thermal decomposition of synthetic serrabrancaite (MnPO₄ · H₂O) was studied in N₂ atmosphere using TG-DTG-DTA. Thermal analysis results indicate that the decomposition occurs in two stages, which are assigned to the dehydration and the reduction processes and the final product is Mn₂P₂O₇. X-ray powder diffraction, FT-IR and FT-Raman techniques were used for identification of the solid decomposition product. The decomposition kinetics analysis of MnPO₄ · H₂O was performed under non-isothermal condition through isoconversional methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). The dependences of activation energies on the extent of conversions are observed in the dehydration and the reduction reactions, which could be concluded the “multi-step” processes.     

Decomposition study of Ni–La–Mg–O precursors using thermal analysis

The thermal decomposition process of La₂O₃/MgO (La/Mg = 2, 1 and 0.5) supported nickel (15% mass/mass Ni) precursor was investigated. Thermal analysis results show distinct processes of decomposition of the samples in accordance with the composition. The mass loss at higher temperature is associated to distinct stages of decomposition of lanthanum precursors. The thermal analysis results agree with the FTIR spectra showing change in the band corresponding to carbonates and nitrates species. XRD results also confirmed the precursor’s decomposition. It can be concluded that the thermal decomposition of La₂O₃–MgO-nickel precursor depends on the La/Mg ratio and of the residual species.     

Thermal Stability of Some Textile Dyes

The effect of thermal treatment at 25–800°C on the structure of some textile dyes (rhodanine' derivatives) has been investigated. The general formula of these dyes are;[(R)–C₆H₄–C₃NS₂O–C₅H₄N–CH=CH–C₆H₄N(CH₃)₂]; 2-[p-dimethylamino-styryl]-6-[5-(3-aryl)-rhodanine]-1,2-dihydropyridine and its derivatives, R=H (I), o-OCH₃ (II), p-OCH3 (III) and p-OH (IV). The techniques employed were TG, IR, UV, NMR and elemental analysis. The results showed that the thermal stability of these dyes depends on the nature of the substituent (R) alkyl radical present and its position in the benzene ring. On the basis of the application of a non-isothermal kinetic equation, it was found to be a first order reaction. Some kinetic and thermodynamic parameters for the thermal decomposition process in each stage have been evaluated by the application of two different calculation methods. To support the above results a simple quantum study was reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

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.     

Synthesis,characterization, and thermal behavior of palladium(II) coordination compounds containing isonicotinamide

Palladium(II) coordination compounds of general formula trans-[PdX₂(isn)₂], X = Cl⁻ (1), N₃ ⁻ (2), SCN⁻ (3), NCO⁻ (4), isn = isonicotinamide; were synthesized and characterized in solid state by elemental analysis, infrared spectroscopy, and simultaneous TG–DTA. TG experiments reveal that the compounds 1–4 undergo thermal decomposition in three or four stages, yielding Pd⁰ as final residue, according to calculus and identification by X-ray powder diffraction.     

Phase polymorphism and thermal decomposition of hexadimethylsulphoxidemagnesium(II) chlorate(VII)

Differential scanning calorimetry (DSC) measurements were performed over the temperature range 93–480 K and three enantiotropic (at 323, 409, and 461 K) and one monotropic (at 271 K) phase transitions were detected. Thus, four solid phases (three of them stable and one metastable) and one liquid phase were found. It was concluded, from the entropy change (ΔS) values of these phase transitions that two of them are stable rotational phases and two are crystalline phases (one stable and one metastable). The thermal decomposition of [Mg((CH₃)₂SO)₆](ClO₄)₂, which was studied using thermogravimetry (TG) with simultaneous differential thermal analysis (SDTA), takes place in two main stages. The gaseous products of the decomposition were identified on-line by a quadruple mass spectrometer (QMS). In the first stage, which starts just above ca. 432 K, the compound loses two dimethylsulphoxide (DMSO) molecules per one formula unit. In the second stage (502–673 K) [Mg(DMSO)₄](ClO₄)₂ decomposes explosively and Cl₂, O₂, H₂, and MgSO₄ are finally produced.     

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.     

Role of CH, CH3, and OH Radicals in Organic Compound Decomposition by Water Plasmas

Decomposition of acetone, methanol, ethanol, and glycerine by water plasmas at atmospheric pressure has been investigated using a direct current discharge. At torch powers of 910–1,050 W and organic compound concentrations of 1–10 mol%, the decomposition rate of methanol and glycerine was over 99%, while those of acetone and ethanol was 95.4–99%. The concentrations of H₂ obtained were 60–80% in the effluent gas for any compounds by pyrolysis. Based on the experimental results, the decomposition mechanism of organic compounds in water plasmas was proposed and the roles of intermediate species such as CH, CH₃, and OH have been investigated; CH radical generated from organic compounds decomposition was easily oxidized to form CO; incomplete oxidation of CH₃ leads to C₂H₂ generation as well as soot formation; and negligible amount of soot observed from glycerine decomposition even at high concentration indicated that oxidation of CH_×(×:1–3) was enhanced by OH radical.     

Electrochemistry of praseodymium in LiF–CaF<Subscript>2</Subscript>

The electrochemical behaviour of PrF₃ was studied in the LiF–CaF₂ (79/21 molar ratio) at 1,213 K. Inert (W) and reactive (Ni) electrodes were used. Pr(III) ions are reduced in a single, three electron exchange. The redox potential of the Pr(III)/Pr couple at the inert electrode was observed very close to the decomposition potential of the LiF–CaF₂ melt. Experiments using reactive working electrode were done. The results show the potential shift connected to the alloying reactions of Pr and Ni. Deposition of Pr–Ni layer was confirmed by SEM-EDX analysis. Conclusions for the Pr separation possibilities from spent nuclear fuel were done.     

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.     

On the sol–gel preparation of different tungstates and molybdates

The preparation and characterization of the M′–M′′–O nitrate–tartrate (M′ = Ca, Ba, Gd and M′ = W, Mo) precursor gels synthesized by simple, inexpensive, and environmentally benign aqueous sol–gel method is reported. The obtained gels were studied by thermal (TG/DSC) analysis. TG/DSC measurements revealed the possible decomposition pathway of synthesized M′–M′′–O nitrate–tartrate gels. For the synthesis of different metal tungstates and molybdates, the precursor gels were calcined at different temperatures (650, 800, and 900 °C). According to the X-ray diffraction (XRD) analysis data, the crystalline compounds CaMo_1-x W _x O₄ doped with Ce³⁺ ions, BaMo_1-x W _x O₄ doped with Eu³⁺ ions and Gd₂Mo₃O₁₂ were obtained from nitrate–tartrate gels annealed at 650–900 °C temperatures. The XRD data confirmed that the fully crystalline single-phase powellite, scheelite, or Gd₂(MoO₄)₃ structures were formed already at 650 °C. Therefore, the suggested sol–gel method based on the complexation of metal ions with tartaric acid is suitable for the preparation of mixed tungstates–molybdates at relatively low temperature in comparison with solid-state synthesis.     

Thermal characteristics of bitumen pyrolysis

The pyrolysis behavior of bitumen was investigated using a thermogravimetric analyzer–mass spectrometer system (TG–MS) and a differential scanning calorimeter (DSC) as well as a pyrolysis-gas chromatograph/mass spectrometer system (Py-GC/MS). TG results showed that there were three stages of weight loss during pyrolysis—less than 110, 110–380, and 380–600 °C. Using distributed activation energy model, the average activation energy of the thermal decomposition of bitumen was calculated at 79 kJ mol⁻¹. The evolved gas from the pyrolysis showed that organic species, such as alkane and alkene fragments had a peak maximum temperature of 130 and 480 °C, respectively. Benzene, toluene, and styrene released at 100 and 420 °C. Most of the inorganic compounds, such as H₂, H₂S, COS, and SO₂, released at about 380 °C while the CO₂ had the maximum temperature peaks at 400 and 540 °C, respectively. FTIR spectra were taken of the residues of the different stages, and the results showed that the C–H bond intensity decreased dramatically at 380 °C. Py-GC/MS confirmed the composition of the evolved gas. The DSC revealed the endothermic nature of the bitumen pyrolysis.     

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.     

Thermal transformations of the supramolecular compound of cucurbit[8]uril with cobalt(III) complex {<Emphasis Type="Italic">trans</Emphasis>-[Co(en)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>]@CB[8]}Cl·17 H<Subscript>2</Subscript>O

The thermal decomposition of hydrated cucurbit[8]uril C₄₈H₄₈N₃₂O₁₆·20H₂O (CB[8]) and the inclusion compound of cucurbit[8]uril with cobalt(III) complex {trans-[Co(en)₂Cl₂]@CB[8]}Cl·17 H₂O was studied in the inert atmosphere by TG, TM, and DSC methods. The dehydration of (C₄₈H₄₈N₃₂O₁₆)·20H₂O (at 320–390 K), and the decomposition of cucurbituril itself (at 620–720 K) are accompanied by a decrease in the sample volume. The inclusion compound loses water molecules at 320–380 K; dehydration is accompanied by an increase in the sample volume. The decomposition (pyrolisis) of the anhydrous compound takes place at 620–720 K; the decomposition is forestalled by a continued increase in the sample volume with an endothermic peak (490–600 K), and only the mass loss (620–720 K) is accompanied by a decrease in the sample volume. The included guest complex does not lose amines until the decomposition process is complete; the previously observed increase in the sample volume is explained by the expansion of cavitand molecules due to a distortion of the included [Co(en)₂Cl₂]⁺ complex on heating.     

Thermoanalytical, magnetic and structural study of Co(II) complexes with substituted salicylaldehydes and neocuproine

In this study, simultaneous TG/DTG-DTA technique was used for two cobalt(II) complexes with neocuproine(neoc) and the anion of a substituted salicylaldehyde ligand (X-salo) (X?=?3-OCH₃, or 5-CH₃) with the general formula [Co(X-salo)₂(neoc)], to determine their thermal degradation in inert atmosphere, which was found to be a multi-step decomposition related to the release of the ligand molecules. The solid material at 1300?°C (verified with PXRD) was a mixture of carbonaceous metal cobalt. Evolved gas analysis by coupled TG-MS verified the elimination of a formaldehyde molecule in the first decomposition stage, initially proposed by the percentage mass loss data. By single-crystal X-ray diffraction analysis an octahedral geometry of the complex [Co(3-OCH₃-salo)₂(neoc)] was found. The variable temperature magnetic susceptibility measurements showed a paramagnetic nature of the complexes, in accordance with their molecular structure. Finally, for the determination of the activation energy (E) two different methods (the isoconversional methods of Ozawa, Flynn and Wall (OFW) and Friedman) were used comparatively.     

Studies on thermal decomposition and oxidation of CoSb<Subscript>3</Subscript>

Thermal durability of CoSb₃ in vacuum, helium and air was investigated over the temperature range of 20–850 °C. A scanning electron microscope (SEM) and X-ray powder diffraction technique were used to investigate the microstructure and to carry out the phase analysis of the degradation products. The analysis of a non-isothermal and isothermal decomposition and oxidation of the CoSb₃ powders and polycrystalline samples were performed using simultaneous TG/DTA technique. More detailed studies were carried out on the oxidation in the temperature range 400–600 °C. It was established that the decomposition products are CoSb₂ and a volatile antimony. In case of oxidation a complex three-layered scale is formed, consisting of CoSb₂O₄, CoSb₂O₆ and Sb₂O₄ layers. Both the decomposition and the oxidation kinetics are determined by a diffusion through the growing layers of products. The electrical resistivity and Seebeck coefficient measurements have been also performed on pure and oxidized samples, which showed a large influence of the oxidation on the electrical properties.     

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).     

Thermal decomposition and antimicrobial activity of zinc(II) 2-bromobenzoates with organic ligands

New zinc(II) 2-bromobenzoate complex compounds with general formula Zn(2-BrC₆H₄COO)₂·nL·xH₂O (where L = urea, nicotinamide, N-methylnicotinamide, N,N-diethylnicotinamide, isonicotinamide, phenazone n = 0–2, x = 0–2) were prepared and characterized by elemental analysis, IR spectroscopy and thermal analysis. The thermal decomposition of hydrated compounds started with dehydration process. During the thermal decomposition organic ligand, carbon dioxide and bis(2-bromophenyl)ketone were evolved. The solid intermediates and volatile products of thermal decomposition were proved by IR spectroscopy and mass spectrometry. The final solid product of the thermal decomposition heated up to 1073 K was zinc oxide. Antimicrobial activity of the prepared compounds was tested against various strains of bacteria, yeasts and filamentous fungi (E. coli, S. aureus, C. albicans, R. oryzae, A. alternate and M. gypseum). It was found that the selected bacteria were more sensitive to the studied zinc(II) complex compounds than the yeast and the filamentous fungi.