Study of the thermal decomposition processes of clathrate compounds

The decompositions of the clathrate compounds [M(NCS)₂(4-MePy)₄]·nG (whereM=Mn, Co, Ni or Cd;G=4-methylpyridine (4-MePy), benzene or xylenes) were studied on a Q-derivatograph under quasi-equilibrium conditions and with linear heating. These clathrates can be divided into two groups, in which the loss of guest is either (I) accompanied by destruction of the host complex, or (II) occurs before decomposition of the host complex. Kinetic parameters were obtained.

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Zusammenfassung Die Zersetzung von Clathrat-Verbindungen der Zusammensetzung [M(NCS)₂(4-MePy)₄]·nG (M=Mn, Co, Ni, Cd;G=4-Methylpyridin (4-MePy), Benzen, o-,m, p-Xylen) wurde mittels Q-Derivatograph unter Quasi-Gleichgewichtsbedingungen und bei linearer Aufheizung untersucht.Die studierten Clathrate lassen sich in zwei Gruppen einteilen, je nachdem ob die Abgabe des Gastmoleküls G entweder vor oder unter Gleichzeitiger Zerstörung des Wirtskomplexes erfolgt. Kinetische Parameter wurden ermittelt.

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Q- [M(NCS)₂(4-MePy)₂]·nG, M , , , G — 4- , . , . .

     

Surfactant-assisted low-temperature thermal decomposition route to spherical NiO nanoparticles

Thermal decomposition has been employed to access spherical nickel oxide (NiO) nanoparticles from a new precursor, nickel-salicylate, [Ni(C₇H₅O₃)₂(H₂O)₄]. Surfactants, triphenylphosphine ((C₆H₅)₃P), and oleylamine (C₁₈H₃₅NH₂) were added to control the particle size. The products were characterized by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and thermogravimetric analysis. TEM images showed particles nearly spherical having sizes 5–15?nm. The magnetism of NiO nanoparticles was studied with a vibrating sample magnetometer. Due to smaller particle size and increased surface uncompensated spins, a superparamagnetic behavior is observed. The synthetic process is simple and affords high-purity material at a relatively lower calcination temperature.     

Kinetics of thermal decomposition of barium zirconyl oxalate

Kinetics of the thermal decomposition of anhydrous barium zirconyl oxalate and a carbonate intermediate have been studied. Decomposition of the anhydrous oxalate, though it could be explained based on a contracting-cube model, is quite complex. Kinetics of decomposition of the intermediate carbonate Ba₂Zr₂O₅CO₃ is greatly influenced by thermal effects during its formation. (-t) curves are sigmoidal and obey a power law equation followed by first order decay. Presence of carbon in the vacuum-prepared carbonate has a strong deactivating effect. Decomposition of the carbonate is accompanied by growth in particle size of the product barium zirconate.

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Die Kinetik der thermischen Zersetzung von Barium-zirkonyl-oxalat

Zusammenfassung Es wurde die thermische Zersetzung von wasserfreiem Barium-zirkonyl-oxalat und dem intermediären Karbonat untersucht. Die Zersetzung des wasserfreien Oxalates ist — obwohl über das contracting-cube-Modell erklärbar — sehr komplex. Die Kinetik der Zersetzung des intermediären Karbonates Ba₂Zr₂O₅CO₃ ist stark von den thermischen Effekten während seiner Bildung abhängig. Die (-t)-Kurven gehorchen einem exponentiellen Gesetz, gefolgt von einem Zerfall erster Ordnung. Die Gegenwart von Kohlenstoff im Karbonat hat einen starken desaktivierenden Effekt. Die Zersetzung des Karbonats wird von einem Wachstum der Partikelgröße des Produktes (Bariumzirkonat) begleitet.

     

Formation and thermal decomposition of silicon oxynitride compounds I

The existence of formerly unknown compounds of the type M ₃ ¹ SiNO₂, suggested in previous papers, has been confirmed in reactions of lithium and sodium oxides with silicon oxynitride, Si₂N₂O.     

Formation and thermal decomposition of silicon oxynitride compounds II

In studies on the reactions of silicon oxynitride, Si₂N₂O, with lithium oxide and of lithium metasilicate with lithium nitride, the formation of a previously unknown compound with stoichiometry Li₅SiNO₃ has been observed.

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Zusammenfassung Eine bisher unbekannte Verbindung der Zusammensetzung Li₅SiNO₃ wurde bei Reaktionen von Siliciumoxynitrid (Si₂N₂O) mit Lithiumoxid und von Lithiummetasilikat mit Lithiumnitrid erhalten.

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(Si₂N₂O) , Li₅SiNO₃.

     

A novel method to prepare metal oxide electrode:Spin-coating with thermal decomposition

In this work,we propose a new spin-coating method coupling with high thermal decomposition,to prepare the tin-antimony(Sn-Sb) oxide electrode.The character of the spin-coating electrode was compared with the dip-coating electrode through X-ray diffraction(XRD),scanning electron microscopy(SEM),accelerated life test,cyclic voltammetry,and electrolytic degradability. The results showed that the spin-coating electrode had a better defined crystal form,a smoother and more compact surface than that of the dip-coating electrode.Service time of the spin-coating electrode was determined to be longer than 15 h,and it was less than 2 min for the dip-coating electrode.Electrochemical characterization analysis showed that the electrolytic degradability of the spin-coating electrode is better than that of the dip-coating electrode.     

Superconductivity and crystal structure of the solid solutions of Ba8−δSi46−xGex (0?x?23) with Type I clathrate structure

The solid solutions of barium containing Type I clathrate, Ba_8−δSi_46−xGe_x (0?x?23) were prepared under high-pressure and high-temperature conditions of 3 GPa at 800°C. All the solid solutions showed superconductivity, and the transition temperature (T_c) decreased from 8.0 to 2.0 K as the germanium content increased from x=0 to 23 in Ba_8−δSi_46−xGe_x. The single crystals with five different compositions were obtained and the structures, compositions, and site occupancies were determined from X-ray single-crystal analysis. A slight barium deficiency was observed at Ba1 (2a) sites for all the clathrates. The Ge atoms replaced the Si atoms at the Si3 (24k) site in the composition range of x<8, and then at the Si2 (16i) site. The crystals had a slight deficiency in the covalent (Si, Ge) network and the deficiency increased with the increase of the Ge content.     

Synthesis and thermal decomposition of GAP-Poly(BAMO) copolymer

An energetic copolymer of glycidyl azide polymer (GAP) and poly(bis(azidomethyl)oxetane (Poly(BAMO)) was synthesized using the Borontrifluoride-dimethyl ether complex/diol initiator system. The synthesized copolymer exhibited the characteristics of an energetic thermoplastic elastomer (ETPE). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal decomposition behavior and the results were compared with that of the constituent homopolymers. The main weight loss step in all the polymers coincides with the exothermic dissociation of the azido groups in the side chain. In contrast with the behavior of the homopolymers, the copolymer shows a broad exothermic shoulder peak at 298 °C after the main exothermic decomposition peak at 228 °C. Kinetic analysis was performed by Vyazovkin's model-free method, which suggests that the activation energy of the main decomposition step is around 145 kJ/mol and for the second shoulder it is around 220 kJ/mol. Fourier transform infra red (FTIR) spectra of the degradation residues show that the azido groups in the copolymer decompose in two stages at different temperatures which is responsible for the double decomposition behavior.     

Formation and thermal decomposition of silicon oxynitride compounds. Part III

The formation of a previously unknown compound with stoichiometry Li₆SiN₂O₂ was found during studies on the reactivity of Li₂SiN₂ with Li₂O, of SiO₂ with Li₃N and of Li₃SiNO₂ with Li₃N.

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Zusammenfassung Die Bildung einer bisher unbekannten Verbindung der Stöchiometrie Li₆SiN₂O₂ wurde bei Untersuchungen der Reaktivität von Li₂SiN₂ mit LiO, von SiO₂ mit Li₃N und von Li₃SiNO₂ mit Li₃N beobachtet.

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Li₆SiN₂O₂ Li₂SiN₂ , , Li₃SiNO₂ .

     

Phase evolution of a barium tin 1,2-ethanediolato complex to barium stannate during thermal decomposition

The thermal behaviour of [Ba(C₂H₆O₂)₄][Sn(C₂H₄O₂)₃] used as a BaSnO₃ precursor, and its phase evolution during thermal decomposition are described. The initially formed transient barium tin oxycarbonate phase disintegrates into BaCO₃ and SnO₂, reacting subsequently to BaSnO₃. The existence of the intermediate oxycarbonate phase is evidenced by Fourier transformed infrared (FT-IR), X-ray powder diffraction (XRD) and electron energy loss spectroscopy (EELS (ELNES)) investigations.     

Dispersive kinetic models for isothermal solid-state conversions and their application to the thermal decomposition of oxacillin

The authors recently published works in which the use of two novel equations for modeling the dispersive kinetics observed in various solid-state conversions are described. These equations are based on the assumptions of a ‘Maxwell-Boltzmann (M-B)-like’ distribution of activation energies and a first-order rate law. In the present work, it is shown that it may be possible to expand the approach to include mechanisms other than first-order, i.e. some of those commonly encountered in the field of thermal analysis, thus obtaining ‘dispersive versions’ of these kinetic models. The application of these dispersive kinetic models to the slightly sigmoidal, isothermal conversion-time (x-t) data of Rodante and co-workers for the degradation of the antibiotic, oxacillin, is described. This is done in an effort to test the limitations of the proposed dispersive models in describing kinetic data which is not clearly sigmoidal (i.e. as shown in previous works). Finally, it is demonstrated that, using graphical analysis, the typically sigmoidal x-t plots of first-order dispersive processes are the direct result of (asymmetric) activation energy distributions that are either ‘∩-shaped’ (for heterogeneous conversions) or ‘∪-shaped’ (for homogeneous conversions) in appearance, i.e. when the activation energy is plotted as a function of conversion. This finding lends support to the founding hypothesis of the authors’ approach for modeling dispersive kinetic processes: the existence of ‘M-B-like’ distributions of activation energies.     

Synthesis, characterization and kinetics of thermal decomposition of dimeric peroxycarbamates

Several dimeric peroxycarbamates (PCs) have been synthesized by using cycloaliphatic and aromatic diisocyanates with mono- and di-hydroperoxides. The reactions were carried out under suitable conditions either in the presence of T-12 (dibutyltin dilaurate) as catalyst or in the absence of this catalyst. The products were characterized by IR-spectra and molecular weight measurements from isocyanate and peroxygen analyses. Thermal decomposition kinetics of these PCs were studied in THF solution at 80, 90 and 100 °C; the reactions were found to be first-order and decomposition rate constants (k_d) were found. Activation energies and frequency factors for the decomposition were calculated. Activation energies were found to be in the range 67-121 kJ mol⁻¹ and frequency factors were of the order of 10¹¹-10¹⁵ s⁻¹ depending on the structure of the PC. The results for the PCs agree well with literature values.     

The kinetics and mechanism of induced thermal decomposition of peroxomonosulphate by phase transfer catalysts

The kinetics of induced decomposition of potassium peroxomonosulphate (PMS) by the phase transfer catalysts (PTC), viz. tetrabutylammonium chloride [TBAC] and tetrabutylphosphonium chloride [TBPC] have been investigated. The effect of [PMS], [PTC], ionic strength of the medium and temperature on the rate of decomposition of PMS was studied. The rate of decomposition of PMS was monitored under pseudo-first-order condition at a constant temperature (50 ± 0.1 °C). The rate of decomposition was first order with respect to PMS for TBAC and half order for TBPC. The order with respect of PTC was found to be unity for TBAC and half order for TBPC. A suitable kinetic scheme has been proposed to account for the experimental data and its significance is discussed.     

One-pot hydrothermal synthesis of reduced graphene oxide/zinc ferrite nanohybrids and its catalytic activity on the thermal decomposition of ammonium perchlorate

Reduced graphene oxide/Zinc ferrite (rGO/ZnFe₂O₄) nanohybrids are successfully decorated on the surface of the rGO sheets through a simple, one-step hydrothermal method. ZnFe₂O₄ nanoparticles (NPs) are homogeneously anchored on the rGO sheets. The rGO/ZnFe₂O₄ hybrids are characterized by XRD, FT-IR, XPS, TEM, Raman, BET. The rGO/ZnFe₂O₄ hybrids demonstrate amazing catalytic activity on thermal decomposition of ammonium perchlorate (AP), which is better than that of bare ZnFe₂O₄ NPs. TG-DTA results indicate that the ZnFe₂O₄ NPs in the hybrids with increasing ratio (1%, 3%, 5%) could decrease the second decomposition temperature of AP by 42.7?°C, 55.0?°C, 68.1?°C, respectively, and reduce the apparent activation energy of AP from 160.2?kJ?mol^?1 to 103.8?kJ?mol^?1. This enhanced catalytic performance is mainly attributed to the synergistic effect of ZnFe₂O₄ NPs and rGO.     

Electronic structure and thermal decomposition of 5-methyltetrazole studied by UV photoelectron spectroscopy and theoretical calculations

The electronic properties and thermal decomposition of 5-methyltetrazole (5MTZ) are investigated using UV photoelectron spectroscopy (UVPES) and theoretical calculations. Simulated spectra of both 1H- and 2H-5MTZ, based on electron propagator methods, are produced in order to study the relative tautomer population. The thermal decomposition results are rationalized in terms of G2(MP2) results. 5MTZ yields a HOMO ionization energy of 10.82 ± 0.04 eV and the gas-phase 5MTZ assumes predominantly the 2H-form. Its gas-phase thermal decomposition starts at ca. 195 °C and leads to the formation of N₂,CH₃CN and HCN. N₂ is formed from two competing routes, involving 150.2 and 126.2 kJ/mol energy barriers, from 2H- and 1H-5MTZ, respectively. CH₃CN is formed also from two competing pathways, requiring activation energies of 218.3 (2H-5MTZ) and 198.6 kJ/mol (1H-5MTZ). Conclusions are also drawn in order to explain the formation of HCN from secondary reactions in the thermal decomposition process.     

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decomposition kinetics

The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study [1].     

Mechanisms and kinetics of thermal decomposition of plastics from isothermal and dynamic measurements

The kinetics of decomposition of plastics are of interest from different points of view, i.e. evolution of harmful substances during fires or waste incineration, recovering of chemical raw materials from plastic refuses and designing of recycling procedures. To measure the formal kinetic parameters of the degradation of polymers isothermal and dynamic methods are applied in this work. Dynamic measurements are performed by combined thermogravimetry mass spectrometry (TG-MS), the isothermal measurements are carried out with a new closed loop-type reactor. To evaluate consistent kinetic data from isothermal and dynamic measurements, the energy balance for the sample in dynamic measurements has to be considered to obtain the true sample temperature and heating rate. Subject of this investigation is the exploitation of dynamic and isothermal methods for measuring and interpreting the kinetics of thermal decomposition of plastics. Results for commodity plastics polyethylene and poly(vinyl chloride) (PVC) are presented. The combined application of TG–MS, isothermal experiments in the closed loop-type reactor and DSC leads to new results for the decomposition kinetics of PVC. The dehydrochlorination mechanism at moderate temperature can be distinguished in an endothermal and exothermal part. The benzene formation is identified as a second order reaction. A great advantage of the isothermal method is, that changes in the mechanisms are detectable, i.e. changes in the apparent order of the reaction and the apparent activation energy. From that, new mechanistic aspects of the decomposition kinetics of polyethylene were obtained.     

Theoretical study of thermal decomposition of azomethane

Summary.  Thermal one- and two-bond dissociation processes of cis- and trans-azomethane were studied by ab initio computation with DZP and TZ2P basis sets, using the d(N–C) bond lengths as the reaction coordinates. The geometries were optimized at the MP2 level, and the dissociation energies obtained exploiting a single-point, fourth-order M?ller–Plesset calculations [MP4SDTQ/TZ2P]. At this level of theory including zero-point energies, the trans-isomer is by 9.3 kcal/mol more stable than the cis-isomer. The results show that the energetically more favourable one-bond cleavage proceeds without transition state with the predicted bond dissociation energy D ₀ of 47.8 kcal/mol for trans-azomethane and 38.5 kcal/mol for cis-azomethane. With calculated barrier heights the unimolecular dissociation rate constants have been determined by means of the RRKM theory. The second-order saddle points localized for synchronous decomposition pathways lie 13 (trans)-23(cis) kcal/mol above the one-bond dissociation energies [MP2/DZP]. Received May 28, 1996/Final version received November 1, 1996 / Accepted November 1, 1996     

Synthesis, crystal structure and thermal decomposition study of a new barium acetato-propionate complex

The present study reports on a novel barium acetato-propionate complex, obtained by the reaction of barium acetate with propionic acid, used as an oxide precursor with applications in superconducting thin films deposition. The molecular structure has been determined by X-ray diffraction on single crystals and demonstrated to be [Ba₇(CH₃CH₂COO)₁₀(CH₃COO)₄·5H₂O]. The barium acetato-propionate is a three-dimensional channel-type polymer. The thermal decomposition of the barium precursor has been studied by simultaneous differential thermal analysis-thermogravimetry-mass spectrometry (DTA-TG-MS) in air at a heating rate of 10 °C/min. Based on these analyses, infrared spectroscopy was further used to characterize the precursor solution by the step-wise addition of the reagents. The X-ray diffraction on the precursor powder at different temperatures was performed.     

Thermal decomposition of ammonium perchlorate

This review represents an attempt to summarize literature data on thermal decomposition of ammonium perchlorate. The mechanism of thermal decomposition and various factors which influence on the thermal decomposition of ammonium perchlorate are discussed.