Theory of solid-state thermal decomposition reactions

A case is presented to recommend strongly that scientists interested in thermal chemistry should make comprehensive, conscientious, clinical and critical analyses of the strengths and weaknesses of The L??vov Thermochemical Theory (L??vov, Thermal decomposition of solids and melts??new thermochemical approach to the mechanism, kinetics and methodology, Springer, Berlin, 2007), used to interpret the kinetics and mechanisms of reactions that occur on heating. The shortcomings underlying the theory (some originally developed for solid decompositions) currently uncritically accepted in this field are reviewed, and these deficiencies are contrasted with the successes of L??vov??s approach. To promote the use of this alternative theory, features that may have discouraged researchers unfamiliar with its assumptions, methodology and applications are discussed here. A new scientific theory cannot be ignored or discounted without adequate consideration and testing, particularly in a stagnant area of chemistry that lacks guiding principles and unifying concepts. Novel ideas in the literature (L??vov 2007) deserve recognition, critical appraisal and, if possible, exploitation to maintain the progress of scientific research.     

Kinetic analysis of thermal decomposition reactions

The effect of⁶⁰C0-gamma radiation on the kinetic parameters of the thermal decomposition of potassium bromate crystals has been investigated. Radiation did not modify the mechanism of thermal decomposition reaction, but resulted in a decrease in activation energy and frequency factor with a rate which is large at small doses and decreases at higher doses. The results showed that the increase in the concentration of decomposition nuclei tends to be more important than the increase in the porous character of the solid.     

较快一级化学反应的热动力学研究法: 热弛豫法

分析了非稳态传热情况下热导式热量计的动态性能,通过对输出信号的剖析,建立了热导式热量计冷却常数的经验动态模型。通过对热弛豫现象的分析,建立了可用于研究快速化学反应的热动力学研究法-热弛豫法,应用此种量热研究法可用于研究速率常数小于5s^-^1的一级化学反应。研究了25℃下乙酸甲酯、甲酸乙酯和甲酸甲酯在水溶液中的皂化反应,其计算结果与文献值相吻合,从而验证了热弛豫法的正确性。     

Kinetics of solid state thermal decomposition reactions

The author wishes to thank Prof. C. G. R. Nair, Dr. V. R. Gowarikar, Mr. M. R. Kurup and Dr. K. V. C. Rao for their encouragements. Thanks are due to Prof. P. M. Madhusudanan and Dr. K. Krishnan for helpful discussions and to Director, VSSC for the kind permission to publish this work.     

Superfast thermal decomposition reactions of polymers and crystallohydrates

Evidence of the existence of a high-limit degradation temperature for polymers is reported. At this high-limit temperature, the rate of polymer thermolysis exceeds the reaction rate predicted by the Arrhenius law by many orders of magnitude. An explanation is proposed for the observed behaviour, based on the disappearance of intermolecular interactions. For the study of degradation reactions under high-limit temperature conditions, new methods of fast (pulsed) thermal analysis are presented. The investigated samples, as very thin films, are brought into tight contact with a hot moving metal surface. Under these conditions, the heating rate exceeds 10⁴ deg/s, allowing estimation of accompanying decomposition rates for heating times of the order of 0.01 s.     

慢对峙反应的热动力学对比参量法

根据热动力学基本理论,推导了对峙反应的热动力学对比参量方程,建立了对峙反应对比参量法的数学模型。该法利用特征时间t~m和2t~m时对应的热谱数据计算反应的对比参量,进而解析出较慢对峙反应的速率常数和平衡常数。利用该法分别研究了硝基乙烷与氨和三(羟甲基)氨基甲烷质子转移反应的热动力学,实验结果表明了较慢对峙反应对比参量法的正确性。     

Continuous determination of carbon monoxide evolved during thermal decomposition reactions

A device suitable for the continuous detection of carbon monoxide evolved during themal decomposition processes is described. The detector can be connected directly to thermoanalytical equipment of controlled gas atmosphere. Carbon monoxide collected by the carrier gas is passed through the device containing hopcalite catalyst. In the presence of oxygen carbon monoxide is converted to carbon dioxide in the cell and the temperature change caused by the heat of reaction is measured. According to experience, the change of temperature is linearly proportional to the amount of carbon monoxide released.The signal curve of the detector can be compared to the simultaneously recorded thermoanalytical curves and used to determine the step in which carbon monoxide was released.The detector is not completely selective to carbon monoxide, but in most cases the interferring gases can be removed from the carrier gas by various packings placed between the detector and the thermoanalytical equipment.

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Zusammenfassung Es wird ein geeignetes GerÄt zur kontinuierlichen Detektierung von in thermischen Zersetzungsprozessen freigesetztem Kohlenmonoxid beschrieben. Der Detektor kann direkt an eine thermoanalytische Apparatur mit überwachter GasatmosphÄre angeschlossen werden. Das vom Carriergas aufgenommene Kohlenmonoxid wird durch das GerÄt geleitet, das einen Hopcalit-Katalysator enthÄlt. In Gegenwart von Sauerstoff wird das Kohlenmonoxid in Kohlendioxid überführt und die durch die ReaktionswÄrme verursachte TemperaturÄnderung gemessen. ErfahrungsgemÄ\ ist die TemperaturÄnderung proportional der entwickelten Menge Kohlenmonoxid.Das Detektorsignal kann mit den gleichzeitig aufgezeichneten thermoanalytischen Kurven verglichen und zur Bestimmung dessen benutzt werden, in welchem Teilschritt Kohlenmonoxid freigesetzt wird.Der Detektor zeigt keine vollstÄndige SelektivitÄt, jedoch können Störgase durch verschiedene Füllungen zwischen Thermoanalysator und Detektor vom Carriergas getrennt werden.

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The authors thank Dr. A. Felinger for his kind help in the computer processing of the recordings.     

Ring-expansion reactions in the thermal decomposition of tert-butyl-1,3-cyclopentadiene

The thermal decomposition of tert-butyl-1,3-cyclopentadiene has been investigated in single-pulse shock-tube studies at shock pressures of 182-260 kPa and temperatures of 996-1127 K. Isobutene (2-methylpropene), 1,3-cyclopentadiene, and toluene were observed as the major stable products in the thermolysis of dilute mixtures of the substrate in the presence of a free-radical scavenger. Hydrogen atoms were also inferred to be a primary product of the decomposition and could be quantitatively determined on the basis of products derived from the free-radical scavenger. Of particular interest is the formation of toluene, which involves the expansion of the ring from a five- to a six-membered system. The overall reaction mechanism is suggested to include isomerization of the starting material; a molecular elimination channel; and C-C bond fission reactions, with toluene formation occurring via radical intermediates formed in the latter pathway. These radical intermediates are analogous to those believed to be important in soot formation reactions occurring during combustion. Molecular and thermodynamic properties of key species were determined from G3MP2B3 quantum chemistry calculations and are reported. The temperature dependence of the product spectrum was fit with a detailed chemical kinetic model, and best-fit kinetic parameters were derived using a Nelder-Mead simplex minimization algorithm. Our mechanism and rate constants are consistent with and provide experimental support for the H-atom-assisted routes to the conversion of fulvene to benzene that have been proposed in the literature on the basis of theoretical investigations.     

Analysis of thermal decomposition behaviors with consecutive reactions by TG

Thermal decomposition behaviors of a fluororubber are observed with linear heating mode at constant rate, controlled rate mode and isothermal mode of TG/DTA, and, with isothermal mode of TG/mass-spectrometer. The results suggest that this material decomposes with, at least, three consecutive reactions. From the results of TG/DTA and TGMS in isothermal mode, it is considered that the first reaction is the first-order reaction, the second reaction is chain reaction and the last reaction is vaporization of residue. Supposing these three consecutive reactions, the decomposition behaviors of the rubber is simulated. The observed curves of fraction of mass loss, , against time, t, are well reproduced by the simulation. The relationship between d/dt and is reproduced also, though the differences between observed and the calculated values of d/dt are slightly larger than noise level of d/dt.     

Continuous determination of carbon dioxide evolved during thermal decomposition reactions

A simple device suitable for continuous monitoring of carbon dioxide evolved during thermal decomposition reactions is described. Carbon dioxide is transported by a carrier gas through the device connected to thermoanalytical equipment and absorbed by soda lime reagent. The reaction heat released is linearly proportional to the amount of carbon dioxide absorbed.     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.     

A thermovoltaic detector (TVD) for thermal decomposition reactions

The construction of a pulse calorimeter is described. In the temperature range 400 K to 1500 K the specific heat, the electric resistivity, and the total hemispherical emittance can be measured simultaneously on electric conductors in the shape of a wire of about 3 mm in diameter. First measurements on pure nickel are presented.     

The study of decomposition reactions through the exchange of thermal energy

In many decomposition reactions, the reaction velocity can be described as a product of two functions: a temperature dependent part K(T) and the kinetic function f(1 – α), where T designates the temperature and α the fraction of reactant that has decomposed. The physical interpretation of these functions is discussed for both solid and homogeneous systems. A method is described by which f(1 – α) and K(T) can be determined from kinetic data. The mechanism of decomposition can subsequently be identified which should be consistent with the derived kinetic parameters. The method has been applied to analyze the kinetics of the thermal decomposition of nitromethane. © 1994 John Wiley & Sons, Inc.     

On the non-isothermal determination of activation energy for thermal decomposition reactions

Attention is called to the frequently encountered linear sector in the isothermal course of the topochemical processes which is used in the kinetic treatment of the differential curves of thermal CoOOH decomposition. The effect of sample weight and heating rate on the values of the activation energy of this process under polythermal conditions has been investigated. Most of the values obtained are in good agreement among themselves as well as with those found isothermally. Existing differences have been explained satisfactorily.     

Comparative method to evaluate reliable kinetic triplets of thermal decomposition reactions

Reliable kinetic information for thermal analysis kinetic triplets can be determined by the comparative method: (1) An iterative procedure or the KAS method had been established to obtain the reliable value of activation energy E _a of a reaction. (2) A combined method including Coats-Redfern integral equation and Achar differential equation was put forward to confirm the most probable mechanism of the reaction and calculate the pre-exponential factor A. By applying the comparative method above, the thermal analysis kinetic triplets of the dehydration of CaC₂O₄·H₂O were determined, which apparent activation energy: 81±3 kJ mol^-1, pre-exponential factor: 4.51·106-1.78·10⁸ s^-1, the most probable mechanism function: f(α)=1 or g(α)=α, which the kinetic equation of dehydration is dα/dt=Ae^-E _a ^/RT. This revised version was published online in August 2006 with corrections to the Cover Date.     

特征参量法 2: 可逆反应

根据几类可逆反应通用的微分动力学方程和热动力学变换方程,本文建立了可逆反应的特征参量研究法。应用该法在两个温度下研究了硝基乙烷分别与氨和Tris反应的热动力学, 实验结果验证了可逆反应特征参量法的正确性。     

NMR studies of the thermal decomposition and branching reactions of aromatic esters

Poly(chlorophydroquinone terephthalate) is an aromatic polyester containing mainly chlorohydroquinone and terephthalate. Thermal stability of this aromatic polyester has been a problem during the processing. In order to characterize the melt reactions of this polyester, the thermal degradation of the model compound chlorohydroquinone dibenzoate was studied. The chlorohydroquinone dibenzoate was characterized by high resolution ¹³C-NMR. All experiments for studyng degradation of chlorohydroquinone dibenzoate were designed to test the following environmental parameters: (1) atmosphere, (2) temperature, (3) time, (4) additives, (5) container material. The analysis of the degradation products were carried out mainly using NMR; in some cases GC/MS and HPLC were also used to aid in separation and identification of the degradation products. The major degradation products produced in various experimental conditions were identified as chlorohydroquinone benzoates, hydroquinone dibenzoate, dichlorohydroquinone dibenzoate, 9-fluorenone, benzoic acid, Fries products, and hydrogen chloride     

The catalytic effects of metal oxides on thermal decomposition reactions,III

The catalytic activity of a series of iron oxides on the thermal decomposition of potassium chlorate was investigated by methods of thermal analysis. Structural and electronic defects were introduced into the oxide by doping, heat treatment in different atmospheres, and irradiation with-rays. These induced defects changed in a systematic way the conductive properties of the iron oxides and correspondingly, their catalytic activity. The results are consistent with ann-type semiconductive behavior of the oxides.

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Zusammenfassung Die katalytische Aktivität einer Reihe von Eisenoxiden gegenüber der thermischen Zersetzung von Kaliumchlorat wurde durch Methoden der Thermoanalyse untersucht. Strukturelle und elektronische Defekte wurden in das Oxid durch Dosierung, Wärmebehandlung in verschiedenen Atmosphären und Bestrahlung mit-Strahlen eingebaut. Diese induzierten Defekte änderten systematisch die Leitfähigkeitseigenschaften der Eisenoxide und dementsprechend ihre katalytische Aktivität. Die Ergebnisse stimmen mit dem Halbleiterverhalten desn-Typs der Oxide gut überein.

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This work was supported by the U.S. Army Edgewood Arsenal under Project No. DA-18-035-AMC-341(A). The authors are grateful to Mr. B. Zeffert and Mr. Harry A. Brown for valuable discussions and useful suggestions.

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The authors also wish to acknowledge Brent Boldt for the laboratory work which he conducted on this program.