On the nature of isomerism in oxalatecopper(II) diammine thermal decomposition of α-, β-, and γ-Cu(C2O4)(NH3)2

The mechanisms of the thermal decompositions of various isomers of Cu(C₂O₄)-(NH₃)₂ were studied in this work. Data were obtained by the DSC technique and Derivatograph as well as infrared spectra and chemical analysis. The destruction of the complexes was found to take place in three steps—the first two of them being endothermic, and the third one exothermic. The values of ΔH₁, apparent activation energy and stoichiometry of the first step of destruction suggest that certain differences in bonding of the oxalate groups in each isomer lead to quite significant differences in their thermal decomposition.     

Thermoanalytical characterization of polyphenylacetylene

Differential scanning calorimetry, thermogravimetry, thermogravimetry/mass spectrometry and infrared spectroscopy were used to study the thermal behaviour of high polyphenylacetylene obtained through the Mo(CO)₆ catalyzed metathesis polymerization of phenylacetylene. The exothermic peaks observed in nitrogen are explained by crystallization or a solid state transition, initiation and decomposition to aromatic compounds, and the endothermic peaks by volatilization. In oxygen the exothermic peaks are explained by crystallization or a solid state transition, initiation, oxidation, cross-linking and decomposition. The TG and MS results indicate that the polymer is stable to ca. 250°C with solvent molecules trapped in the polymer matrix evolving below this temperature.     

Thermal decomposition of hydrated iron(II) oxalate and manganese(II) oxalate in vacuum

The thermal decomposition of hydrated iron(II) oxalate and manganese(II) oxalate under high vacuum conditions (10^–5 mm Hg) has been studied by differential thermal analysis. The decomposition in vacuum of iron(II) oxalate is exothermic, while that of manganese(II) oxalate is endothermic. An explanation is offered for this behaviour.The financial support by National Bureau of Standards, U.S.A., through a PL-480 scheme is gratefully acknowledged.     

A comparative study of the thermal reactivities of some transition metal oxalates in selected atmospheres

A comparative investigation has been made of the nonisothermal, solid-state thermal decompositions of the oxalates of six divalent transition metals (cations: manganese, iron, cobalt, nickel, copper and zinc) in alternative flowing atmospheres, inert (N₂, CO₂), reducing (H₂) and oxidizing (air). Derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) response peak maxima, providing a measure of reaction temperatures, have been used to determine salt reactivities and thus to characterize the factors that control the relative stabilities of this set of chemically related reactants. Two trends were identified. Trend (1): in the inert and reducing atmospheres, the decomposition temperature (salt stability) increased with rise in enthalpy of formation of the divalent transition metal oxide, MO. It is concluded that the rupture of the cation-oxygen (oxalate) bond is the parameter that determines the stability of salts within this set. Trend (2): the diminution of decomposition temperatures from values for reactions in inert/reducing atmosphere to those for reactions in an oxidizing atmosphere increased with the difference in formation enthalpy between MO and the other participating oxide (MO_3/2 or MO_1/2). The change of cation valence tended to promote reaction, most decompositions in O₂ occurred at lower temperatures, but the magnitude of the effect varied considerably within this set of reactants. Observed variations in stoichiometric and kinetic characteristics with reaction conditions are discussed, together with the mechanisms of thermal decompositions of these solid oxalates.This approach to the elucidation of crystolysis reaction mechanisms emphasizes the value of comparative investigations within the group of chemically related reactants. Previous isothermal kinetic studies had been made for each of the reactants selected here. From these, much has been learned about the form of the (isothermal) solid-state yield-time curves, often interpreted to provide information about the geometry of interface development for the individual rate processes. However, identification of the controls of reactivity, reaction initiation (nucleation) and advance (nucleus growth), is much more difficult to characterize and less progress has been made towards elucidation of the interface chemistry. The trends of reactivity changes with salt compositions, identified here, offer a complementary approach to that provided by the study of single salts. Much of the recent literature on thermal decompositions of solids has been concerned with individual reactants, but many results and conclusions are not presented in the widest possible perspective. Comparisons between systematically related reactants are identified here as providing a chemical context for the elucidation of the chemical steps that participate in interface reactions. The article advocates the use of a more chemical approach in investigations of crystolysis (solid-state chemical) reactions.     

Analysis of thermodynamic and kinetic stabilities in the thermal decomposition of the trinuclear μ-oxoacetates Fe 2 III MIIO(CH3OO)6(H2O)5, with M=Mn,Fe, Co or Ni

The thermal analysis of acetate clusters of general formula [Fe ₂ ^III M^IIO(CH₃COO)₆(H₂O)₃]·2H₂O, with M=Mn, Fe, Co or Ni, was performed in dynamic and quasi-isothermal regimes. The thermal decompositions of these compounds proceed in the interval 40–310° and consist of two endothermic and three exothermic stages. Dependence on the nature of the transition metal M is evidenced most explicitly in the parameters of the second stage, proceeding in the interval 103–170°. For this stage the sequences of thermodynamic stability and kinetic stability were established. The effect of the nature of the metal on the thermodynamic and kinetic parameters of the thermal decomposition processes involving the heteronuclear acetates was analyzed. Mechanisms for the first two stages of thermal decomposition are suggested.     

Determination of the kinetic constants of endothermic decompositions of the type Asol f Bsol + Cgas

The present work describes the endothermic decompositions of calcium carbonate and nickel carbonate, recorded on a MOM derivatograph in the non-isothermal mode at different heating rates. The possibility and advantages of determining the kinetic parametersE, Z, andn for reactions proceeding in one step, as well as the detection of simultaneous (parallel or concurrent) reactions in the decomposition process, are discussed. The results obtained permit the conclusion that the thermal decomposition of calcite occurs in one step. In this case, the kinetic equation has the following form: $$\lg \left[ {\frac{{d\alpha }}{{(1 - \alpha )^n }}} \right] = \lg \frac{Z}{q} - \frac{E}{{2.3R}} \cdot \frac{1}{T}$$ where f(α)=(1?α)ⁿ,n=0.3, andE=176.8 kJ/mol. In the case of nickel carbonate the results of treating the experimental data have been obtained only in the graphical form. From the shape of the curves obtained, it is clearly seen that the decomposition of nickel carbonate in open air proceeds in several steps (i.e. several simultaneous reactions take place), which cannot be described by the equations for a one-step reaction.     

TG/DTA/MS of poly(methyl methacrylate), The Role of the Oxidative Environment

Degradation of relatively large particle size, 0.5 mm of Type-G PMMA (Rohm and Haas) were conducted with thermogravimetric analysis and evolved gas measurements using quadrupole mass spectrometer under conditions of mass transport limitation. In addition, differential thermal analysis was performed in order to furnish information with regards to exothermic or endothermic reactions associated with the degradation. The tests were conducted in an inert environment of pure N₂ and oxygenated environment. The results indicated one step degradation process in pure N₂ and the degradation process is endothermic. As the O₂ fraction increases the degradation process is transformed to exothermic. This revised version was published online in July 2006 with corrections to the Cover Date.     

Monitoring of the Gas Phase Composition: A Prerequisite for Unravelling the Mechanism of Decomposition of Solids. Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products. Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Co_met, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Co_met. The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H₂, Co_met oxidation under rich and lean oxygen conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of cerium oxalate and mixed cerium-gadolinium oxalates

Cerium oxalate and mixed cerium-gadolinium oxalates containing 20 and 50 mol% gadolinium were subjected to thermal decomposition. Thermal analysis showed that cerous oxalate is transformed to cerium oxide in two steps. The first step involves the endothermic removal of 10 mol of water, with a calculated activation energy of 78.2 kJ/mol. The second step involves the exothermic decomposition of the anhydrous oxalate, with an activation energy of 112.6 kJ/mol. The water content in the mixed cerium-gadolinium oxalates decreases with increasing gadolinium content, while the temperature of exothermic decomposition of the anhydrous oxalate increases with it.

---

Zusammenfassung Zeroxalat und Zer-Gadolinium-Mischoxalat mit 20 bzw. 50 mol% Gadolinium wurden einer thermischen Zersetzung unterzogen. Die Thermoanalyse zeigte, da\ Zeroxalat in zwei Schritten in Zeroxid überführt wird. Der erste Schritt mit der Aktivierungsenergie von 78.2 kJ/mol besteht in der endothermen Abgabe von 10 mol Wasser. Der zweite Schritt mit der Aktivierungsenergie 112.6 kJ/mol umfa\t die exotherme Zersetzung des wasserfreien Oxalates. Der Wassergehalt der Zer-Gadolinium-Mischoxalate nimmt mit steigendem Gadoliniumgehalt ab und die Temperatur für den exothermen Zersetzungsvorgang der wasserfreien Oxalate nimmt mit steigendem Gadoliniumgehalt zu.

     

Fire safety evaluation of expanded polystyrene foam by multi-scale methods

Microscale thermal analysis, bench scale cone calorimetric and real scale burning tests were conducted to evaluated fire safety performance of expanded polystyrene (EPS) foam. Simultaneous thermal analysis was used to study the thermal degradation of the foam in nitrogen, air, and oxygen environments at four heating rates. An endothermic effect is observed only in nitrogen environment, while two exothermic effects are observed in oxygen and air environments. In the nitrogen environment, the onset temperature of the endothermic effect and the endothermic peak temperature are much higher than that of the exothermic processes observed in air and oxygen environments. The Flynn–Wall–Ozawa method is utilized to analyze the degradation kinetics of the non-isothermal thermogravimetry. The activation energies calculated for an air environment, in a conversion range α = 20–70 %, are lower than those for an oxygen environment. The temperature range for this conversion range is 275–371 °C. The enthalpies of the first exothermic effect exceed that of the oxygen environment by 10–45 %. Bench scale cone calorimetric tests were carried out at incident heat flux of 25, 35, and 50 kW m^?2 with two sets of cone equipment. Heat release rate, ignition time, effective heat of combustion, and critical heat flux required for ignition is obtained. In real scale burning tests, the EPS boards were ignited in sandwich structures. Fire spread speeds were derived from temperature measurement inside sandwich structure.     

Structural, microstructural, thermal, and electrical properties of Ni/YSZ cermet materials

Ceramic?Cmetal composites (cermets) containing 4?mol% yttria-zirconia (4YSZ) and Ni particles as anode materials in solid oxide fuel cells were prepared by two methods. The first method involves nickel oxalate dihydrate precipitation on the 4YSZ powder and decomposition at 360?°C in inert Ar atmosphere. The second method consists of impregnation of the 4YSZ pellets with an aqueous solution of nickel nitrate. The temperature of oxalate decomposition was determined on the basis of TG/DTA experiments. Gaseous products of decomposition were analyzed by mass spectrometry. The structure of the materials was characterized by X-ray diffraction, scanning electron microscopy, porosity studies, and particle size measurements. The thermal expansion coefficient (TEC) was determined by dilathometric method. Electrochemical impedance spectroscopy was used to determine the electrical conductivity. Thus, determined TECs, porosity, and electrical properties were found suitable for anode materials of fuel cells.     

The use of the temperature signal and its derivative in a TG-DTA simultaneous unit

Simultaneous TG-DTA units have a work station which allows plots to be made of temperature against time, as well as the conventional TG and DTA plots. These time-temperature plots and their derivatives can be used to show details of both exothermic and endothermic events. The melting behavior of zinc is used as illustrative of endothermic phase changes. Solid-solid transitions are exemplified by noting the transitions in quartz. Examples of chemical reactions being treated to temperature-time plots are the decomposition's of zinc oxalate in nitrogen (an endothermic event) and the oxidation of carbon black in air (a sustained exothermic event). This wide selection of exothermic and endothermic events serves to illustrate the details which can be drawn from any thermogravimetric plot irrespective of the other associated equipment present, which serves to reinforce the data presented in the present study.     

Thermal decomposition kinetics of strontium oxalate

The thermal decomposition behavior in air of SrC₂O₄ · 1.25H₂O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO₃ and the decomposition of SrCO₃ to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO₃. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D₂), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R₃). The values of activation parameters obtained using different methods were compared and discussed.     

Thermal decompositions of scandium(III) 2,4-dinitrobenzoate, 3,5-dinitrobenzoate, 2,4-dichlorobenzoate and 3,4-diaminobenzoate in air atmosphere

The thermal decompositions of scandium 2,4-dinitrobenzoate, 3,5-dinitrobenzoate, 2,4-dichlorobenzoate and 3,4-diaminobenzoate were studied. On heating, the carboxylates decompose in two steps. The hydrated complexes first lose crystallization water and are transformed to Sc₂O₃. The dehydration of the complexes is accompanied by an endothermic effect and decomposition of the anhydrous or monohydrate complezes by strong exothermic effects. Scandium 2,4-dinitrobenzoate and 3,5-dinitrobenzoate decompose explosively.     

Thermal decomposition of lead titanyl oxalate tetrahydrate

The thermal behaviour of PbTiO(C₂O₄)₂·4H₂O (PTO) has been investigated, employing TG, quantitative DTA, infrared spectroscopy and (high temperature) X-ray powder diffraction.The decomposition involves four main steps. The first is the dehydration of the tetrahydrate (30–180°C), followed by a small endothermic (270–310°C) and a large exothermic decomposition of the oxalate. The main (exothermic) oxalate decomposition (310–390°C) results in a stable oxide-carbonate PbTiO₂₅.(CO₃)_0.5. In the last step a phase transition, release of CO₂ and ordering of the crystalline cubic PbTiO₃ lattice can be detected (460–530_C).It can be argued that for thermodynamic reasons the presence of lead-oxo- carbonates in the oxide-carbonate intermediate is not possible.No differences could be found in thermal behaviour of two crystallographically different synthetic forms of PTO, of which one has an orthorhombic lattice.     

Mössbauer studies of thermal decomposition of metal(II) hexacyanoferrates(II)

The thermal decompositions of metal(II) hexacyanoferrates(II) (Co, Ni and Zn) were studied in air with Mössbauer, infrared, thermal analysis and magnetic susceptibility techniques. Dehydration is almost complete at 200° and decomposition starts at 250° in the cases of cobalt and nickel hexacyanoferrates(II), and at 300° for zinc hexacyanoferrates (II). Finally, ferrites are formed as decomposition products.     

Thermal behaviour of lignins extracted from different raw materials

The thermal degradation of lignins extracted from bagasse, rice straw, corn stalk and cotton stalk, have been investigated using the techniques of thermogravimetric analysis (TG) and differential thermal analysis (DTA), between room temperature and 600°C. The actual pyrolysis of all samples starts above 200°C and is slow. The results calculated from TG curves indicated that the activation energy, Efor thermal degradation for different lignins lies in the range 7.949–8.087 kJ mol^?1. The DTA of all studied lignins showed an endothermic tendency around 100°C. In the active pyrolysis temperature range, thermal degradation occurred via two exothermic process at about 320 and 480°C, and a large endothermic pyrolysis region between 375 and 450°C. The first exothermic peak represents the main oxidation and decomposition reaction, the endothermic effect represents completion of the decomposition and the final exothermic peak represents charring.     

Thermal decomposition of ammonium vanadyl oxalate supported on various oxides

The thermal decomposition of ammonium vanadyl oxalate supported on La₂O₃, MgO, SiO₂, Al₂O₃, ZrO₂, TiO₂, SAPO-5, and ZSM-5 oxides in a dynamic atmosphere of dry air was compared by thermal gravimetric analysis (TG) and differential thermal analysis (DTA). The calcined catalysts were characterized by X-ray diffractometry (XRD). The TG and DTA results demonstrate that the surface acid-base properties of the oxides play a significant role in the decomposition behaviour of the supported ammonium vanadyl oxalate, i.e. the basic oxides exhibit an endothermic effect and the acidic oxides show an exothermic effect. Two mechanisms are suggested for thermal decomposition of ammonium vanadyl oxalate on basic and acidic oxides, respectively. After transformation of the ammonium vanadyl oxalate to vanadia, subsequent rearrangement of the vanadia on the surface of the supports was also observed. During the thermal treatment or calcination in air, solid state reactions of vanadia with the surface of oxides such as La₂O₃, ZrO₂ and TiO₂ took place to form new phases.     

DSC characterisation of chemically reduced electrolytic manganese dioxide

The thermal decomposition of electrolytic manganese dioxide (EMD), in an inert atmosphere, and the effect of chemical reduction on EMD, using 2-propanol under reflux (82°C), was investigated by differential scanning calorimetry (DSC). This study is an extension of a study investigating the thermal decomposition of EMD and reduced EMD by TG-MS (J. Therm. Anal. Cal., 80 (2005)625)). The DSC characterisation was carried out up to 600°C encompassing the water loss region up to 390°C and the first thermal reduction step. Water removal was observed in two distinct endothermic peaks (which were not deconvolved in the TG-MS) associated with the removal of bound water. For the lower degrees of chemical reduction, thermal reduction resulted in the formation of Mn₂O₃; for higher degrees of chemical reduction, the thermal reduction resulted in Mn₃O₄ at 600°C. In the DSC the thermal reduction of the EMD and chemically reduced specimen was observed to be endothermic. The reduced specimens, however, also showed an exothermic structural reorganisation.     

苯胺溶剂中偶氮二异丁腈热分解特性及动力学

偶氮二异丁腈(AIBN)是一种典型的相变吸热与分解放热重叠的物质, 该重叠现象的存在不利于其动力学规律的研究. 为了正确解析AIBN相变吸热对其分解放热的影响, 并研究AIBN在溶剂中的非等温热行为, 利用差示扫描量热仪(DSC)对苯胺、AIBN及AIBN-苯胺溶液(22.18%(w))进行动态扫描, 得到不同升温速率下AIBN在苯胺溶剂中起始分解温度T_onset的范围为79.90-94.47 ℃, 比放热量较固态AIBN高291 J·g^-1左右, 该数值可以视为其比相变热. 基于Kissinger法计算的AIBN与AIBN-苯胺溶液的活化能E和指前因子A的结果相差不大. 采用Friedman法对AIBN与AIBN-苯胺溶液的热分解过程进行计算, 发现固态AIBN相变吸热对其分解放热的影响主要发生在反应进度α小于0.20的范围内, 当α大于0.20后, 两者活化能E(α)和ln(A(α)·f(α))随α的变化趋势基本一致. 分析认为, 相对于AIBN的分解反应而言, 苯胺可以视为一种惰性溶剂, 即其不会干扰AIBN的分解机理. AIBN在苯胺溶剂中的分解机理可以视为固态AIBN的分解机理. 结合Friedman法的计算结果, 采用一般积分法, 即Coats-Redfern法得到AIBN在苯胺溶剂中分解反应的机理函数为G(α)=α^3/2, 符合Mampel power法则,平均表观活化能为139.93 kJ·mol^-1.