A kinetic analysis of thermal decomposition of polyaniline/ZrO<Subscript>2</Subscript> composite

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO₂ composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO₂ composite and PANI are all D₃, and the corresponding function is ƒ(α)=1.5(1−α)^2/3[1−(1-α)^1/3]−1. The correlated kinetic parameters are E _a=112.7±9.2 kJ mol⁻¹, lnA=13.9 and E _a=81.8±5.6 kJ mol⁻¹, lnA=8.8 for PANI/ZrO₂ composite and PANI, respectively.     

Influence of heating rate on kinetic quantities of solid phase thermal decomposition

Thermogravimetric analyses of thermal decomposition (pyrolysis, thermal dissociation and combustion) of 9 different samples were carried out in dynamic conditions at different heating rates. The kinetic parameters (E, A and k_m) of thermal decomposition were determined and interrelations between the parameters and heating rate q were analyzed. There were also relations between Arrhenius and Eyring equations analyzed for thermal decomposition of solid phase. It was concluded that Eyring theory is an element, which interconnects used thermokinetic equations containing Arrhenius law and suggests considering kinetic quantities in way relative to 3 kinetic constants (E, A and k_m). Analysis of quantities other than km (i.e. E, A, Δ⁺H, Δ⁺S) in relation to heating rate is an incomplete method and does not lead to unambiguous conclusions. It was ascertained that in ideal case, assuming constant values of kinetic parameters (E and A) towards heating rate and satisfying both Kissinger equations, reaction rate constant k_m should take on values intermediate between constants (k_m)₁ and (k_m)₂ determined from these equations. Whereas behavior of parameters E and A towards q were not subjected to any rule, then plotting relation k_m vs. q in the background of (k_m)₁ and (k_m)₂ made possible classification of differences between thermal decomposition processes taking place in oxidizing and oxygen-free atmosphere.     

Kinetics of methoxy-NNO-Azoxymethane hydrolysis in strong acids

The kinetics of methoxy-NNO-azoxymethane (I) hydrolysis in concentrated solutions of strong acids (HBr, HCl, HClO₄, and H₂SO₄) has been investigated by a manometric method. The gas evolution rate is described by the equation corresponding to two consecutive first-order reactions, with the rate constant of the second reaction considerably exceeding the rate constant of the first reaction, i.e., k ₂ {ie17-1} k ₁. The temperature dependences of k ₁ (s⁻¹) in 47.59% HBr in the temperature range from 60 to 90°C and in 64.16% H₂SO₄ between 80 and 130°C are described by Arrhenius equations with IogA= 12.7 ± 1.5 and 13.6 ± 1.4 and E _a = 115 ± 10 and 137 ± 10 kJ/mol, respectively. The parameters of the Arrhenius equation for the rate constant k ₂ for the reaction in 64.16% H₂SO₄ between 80 and 130°C are IogA= 9.1 ± 2.5 and E _a = 91 ± 18 kJ/mol. An analysis of the UV spectra of compound I in concentrated H₂SO₄ shows that I is a weak base $ (pK_{BH^ + } \approx - 6) $ (pK_{BH^ + } \approx - 6) . The rate-determining step of the hydrolysis of I is the attack of the nucleophile on the carbon atom of the MeO group of the protonated molecule of I. The resulting methyldiazene dioxide decomposes via a complicated mechanism to evolve N₂, NO, and N₂O. The pseudo-first-order rate constant k ₁ of the reaction at 80°C depends strongly on the acid concentration and on the type of nucleophile (Br⁻, Cl⁻, or H₂O). The relationship between k ₁ and the rate constant k of the bimolecular nucleophilic substitution reaction (S_N2) is given by the linear equation log$ [k_1 /(C_H + C_{Nu} )] = m^ \ne m*X_0 + \log (k/K_{BH^ + } ) $ [k_1 /(C_H + C_{Nu} )] = m^ \ne m*X_0 + \log (k/K_{BH^ + } ) , where $ C_{H^ + } $ C_{H^ + } and C _Nu are the concentrations of H+ and nucleophile, respectively; X ₀ is the excess acidity; and m ^≠ and m* are coefficients. The Swain-Scott equation log$ (k_{Nu} /k_{H_2 O} ) = ns $ (k_{Nu} /k_{H_2 O} ) = ns , where n is the nucleophilicity factor and s is the substrate constant (s = 0.72), is applicable to the rate constants k of the S_N2 reactions of the protonated molecule of I with Br⁻, Cl⁻, and H₂O.     

Capacity factors and peak widths in the gradient elution reversed phase separation of high molar mass polystyrenes

Summary A simplex method for determining the constantsS andk _o from the equation lnk’=lnk _o−S ϕ (was developed and applied to the reversed phase separation of high molar mass polystyrenes using gradients of any curvature. Experimental retention times described using the equation had a standard deviation of 1.1%. The inclusion of a quadratic term in the equation was found to be unwarranted. BothS and lnk _o varied linearly with ln molar mass. The logarithm of peak width of an eluting polystyrene peak was found to be a linear function of the mobile phase composition at elution. The slope was equal toS.     

Kinetics of the reaction CH + N2 rarr; [M]⇒[M] products in the range 10–620 torr and 298–1059 K

The gas-phase reaction of CH(X² Π) radicals with molecular nitrogen was studied in the temperature range 298–1059 K at total pressures between 10 and 620 torr. CH radicals were generated by excimer laser photolysis of CHCIBr₂ at 248 nm and were detected by laser-induced fluorescence. The investigated reaction shows a strong temperature and pressure dependence. At pressures of 20, 100, and 620 torr the Arrhenius plots exhibit a strong decrease of the rate constant with increasing temperature. The rate constant is well described by, with E₀ in kJ/mol. The pressure dependence was studied at temperatures of 298, 410, 561, and 750 K. The rate constants for each temperature were fitted by the Troe formalism. From the calculated values of k₀ and k_infinity, the Arrhenius expressions, were obtained with E₀ (k₀) and E_A (k_infinity) in units of kJ/mol. Within the range of 298–750 K the temperature dependence of the broadening factor is well described by F_c = 0.029 + (173.3/T). © 1996 John Wiley & Sons, Inc.     

Criterion of the existence of compensation relationship for non-isothermal kinetics

If, for a series of similar-type chemical transformations in non-isothermal kinetics, identical or closely similar values of T _cr are observed in the equation 1/T _cr =1/T _si + + (R/E _i)·ln (E _i q/RT _si ² the existence of the compensation relationship lnA _i= =E _i/RT _cr may regularly be assumed.     

Thermal decomposition of complexes of cadmium(II) and mercury(II) with triphenylphosphanes

A series of substituted triphenylphosphane complexes of the type CdL₂X₂ (L= triorthotolylphosphane or trimetatolylphosphane; X=Cl⁻, Br⁻ or I⁻) and HgL₂X₂ (L=triphenylphosphane or triorthotolylphosphane) was prepared fresh. The thermal decomposition was carried out in air with heating rate programmed at 10°C min⁻¹ and it revealed that the complexes with ortho derivative were less stable and the triphenylphosphane moiety leaves along with halogen in the first step. All the complexes were stable up to 210°C. However, the stability order of the tetrahedral complexes was X=Cl>Br. Values of n, E, lnA and ΔS ^# have been approximated and compared. Complexes having Br have higher E _a, lnA and ΔS ^# values than that having Cl.     

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) initiated by Ce(CIO4)3 in the excited state

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) (1) to adamantanone (2) initiated by Ce(ClO₄)₃ in the excited state in the MeCN−CHCl₃ (2∶1) mixture was studied. The bimolecular rate constants of quenchingk _q were determined from the kinetics of quenching of Ce^3+* by dioxetane at different temperatures. The Arrhenius parameters of the quenching were calculated from the temperature dependence ofk _q:E _a=3.2±0.3 kcal mol⁻¹ and logA=11.6±6. The quantum yields of photolysis of 1 depending on its concentration and the rate constant of the chemical reaction of Ce^3+* with 1 were determined. The latter coincides withk _q:k _ch=(2.6±0.3)·10⁹ L mol⁻¹ s⁻¹ (T=298 K). The fact that the maximum quantum yield of decomposition of dioxetane is equal to 1 indicates the absence of physical quenching of Ce^3+* with 1. Nonradiative deactivation of Ce^3+* in solutions of MeCN and in MeCN−CHCl₃ mixtures was studied. It is caused by the replacement of H₂O molecules in the nearest coordination surroundings of Ce³⁺ by solvent molecules and reversible transfer of an electron to the ligand. The activation parameters of the nonradiative deactivation of Ce^+* were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 724–729, April, 1997.     

Kinetic of decomposition of some complexes under non-isothermal conditions

Kinetics of thermal decomposition of three structurally similar complexes Co₂Cu(C₂O₄)₃ (R-diam)₂, where R is ethyl, 1,2-propyl or 1,3-propyl, was studied under non-isothermal conditions and nitrogen dynamic atmosphere at heating rates of 5, 7, 10, 12 and 15 K min⁻¹. For data processing the Flynn-Wall-Ozawa and a modified non-parametric kinetic methods were used. By both methods the activation energy are in the range of 97–102 kJ mol⁻¹. The formal kinetic is r=kα(1−α)². Also a compensation effect between lnA and E was evidenced. The kinetic analysis lead to the conclusion of an identic decomposition mechanism by a single step process.     

Arrhenius parameters for the reactions CH3. + C4H10 → CH4 + C4H9. and C2H5. + C4H10 → C2H6 + C4H9.

Study of n-butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions and of the Arrhenius parameters of the reactions Established data for k₁/k₂ allow estimation of k₁ for 951°K and this, with recent thermochemical data, yields the result log k_?1 (l.mole s^?1) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k₃k₄ (l.²mole^?2s^?2) is found to be associated with the Arrhenius parameters log (A₃A₄) = 21.90 ± 0.6 and (E₃ + E₄) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A₄ = 10.5 ± 0.4 (l.mole^?1s^?1) and E₄ = 20.1 ± 1.7 kcal/mole, hence log A₃ = 11.4 ± 0.8 (l.mole^?1s^?1) and E₃ = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical–alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.     

Nonisothermal kinetic analysis of the chemiluminescence from tetramethyl-1,2-dioxetane

A computerized method is given for the evaluation of Arrhenius parameters which describe the chemiluminescent decomposition of tetramethyl-1,2-dioxetane. The parameters were determined in several solvents by linear regression methods and the equation ln ln \documentclass{article}\pagestyle{empty}\begin{document}$ [(\sum\nolimits_0^\infty I - \sum\nolimits_0^t I)/(\sum\nolimits_0^\infty I - \sum\nolimits_0^t I - \sum\nolimits_0^{t + \Delta t} I)] = \ln\, (A_1 \Delta t) - E_1 /RT$\end{document}, where I refers to photons counted by increments of Δt, and E₁ and A are the first-order Arrhenius parameters. The average of E₁ and log A₁ (s^?1) from this method from six runs in CCl₄ with initial concentrations of 4.9 × 10^?5-8.45 × 10^?4M were 27.21 ± 0.88 kcal/mol (113.7 ± 3.7 kJ/mol) and 13.88 ± 0.50, respectively. Simulated curves of chemiluminescence versus time were obtained with the use of a computer program and an auxiliary plotter.     

Application of non-isothermal cure kinetics on the interaction of poly(ethylene terephthalate) — Alkyd resin paints

Samples of paint (P), reused PET (PET-R) and paint/PET-R mixtures (PPET-R) were evaluated using DSC to verify their physical-chemical properties and thermal behavior. Films from paints and PPET-R are visually similar. It was possible to establish that the maximum amount of PET-R that can be added to paint without significantly altering its filming properties is 2%. The cure process (80–203°C) was identified through DSC curves. The kinetic parameters, activation energy (E _a) and Arrhenius parameters (A) for the samples containing 0.5 to 1% of PET-R, were calculated using the Flynn-Wall-Ozawa isoconversional method. It was observed that for greater amounts of PET-R added, there is a decrease in the E _a values for the cure process. A Kinetic compensation effect (KCE), represented by the equation InA=−2.70+0.31E _a was observed for all the samples. The most suitable kinetic model to describe this cure process is the autocatalytic Šesták-Berggreen, model applied to heterogeneous systems.     

Kinetic characterization of the reduction of silica supported cobalt catalysts

Abstact  The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

Abstraction of chlorine atoms from chloroalkanes. III. The kinetics of liquid phase reactions of trichlorosilyl radicals with chloromethanes

The kinetics of chlorine atom abstraction from the chloromethanes (ClM), CCl₄, CHCl₃, CH₂Cl₂, and CH₃Cl by radiolytically generated trichlorosilyl radicals was studied in the liquid phase by a competitive method. Arrhenius parameters of chlorine atom abstraction from chloromethanes relative to that of bromine atom abstraction from cyclohexyl bromide (RBr) were as follows: The error limits are two standard deviations (2σ) from least mean square Arrhenius plots. From the linear correlation between E_cl values derived from the reactions of SiCl₃ and cyclohexyl radicals with the ClM series it is estimated that E_cl (R + CH₃Cl) ? 16 kcal/mole. In addition the relative Arrhenius parameters for the hydrogen atom abstraction from SiHCl₃ and chlorine atom abstraction from CCl₄ by cyclohexyl radicals were obtained log A_H/A_cl = 0.12 ± 0.15 and E_H ? E_cl = 0.24 ± 0.26. The E_H ? E_cl value was combined with existing data on E(R + CCl₄) to yield the E_H(R + SiHCl₃) value.     

[Cu(TO)2(H2O)4](PA)2的制备、结构表征和热分解机理研究

[Cu（TO）2（H2O）4]（PA）2 was prepared by the reaction of aqueous 1,2,4-triazol-5-one （TO） solution with the solution of copper picrate Cu（PA）2 and characterized by elemental analysis, FT IR and X-ray powder diffraction analysis. The title complex has been studied by means of TG-DTG and DSC under conditions of linear temperature increase. The thermal decomposition residues were examined by FT IR analysis. Thermal decomposition mechanism of the title complex was proposed. In the temperature range of 30-680 ℃, the thermal decomposition process was composed of four major stages. The first stage was an endothermic process with the loss of four coordination water molecules. Since the dehydration product was unstable, when it was heated, it would be decomposed much more easily. The second stage was composed of an acute endothermic process and a continued strong exothermic process and the main decomposed residues were CuCO3, Cu（NCO）2 and polymers during this stage. The third stage was a sharp exothermic process, which resulted from the decomposition of the polymer. After the forth stage, the final decomposed residues were certainly copper oxide. The Arrhenius parameters have been also studied on the dehydration process and the first-step exothermic decomposition of [Cu（TO）2（H2O）4]（PA）2 using Kissinger＇s method and Ozawa-Doyle＇s method. The results using both methods were consistent with each other. The Arrhenius equation can be expressed as in k=24.0-179.8 × 10^3/RT for the dehydration process and in k= 16.7-206.0 × 10^3/RT for the first-step exothermic decomposition, on the basis of the average of Ea and In A through the two methods.     

Comment on the evaluation of the arrhenius parameters by the least squares method

Arrhenius parameters are frequently evaluated incorrectly by applying the least squares method to the logarithmic form of the Arrhenius equation without simultaneously transforming the statistical weights as required for the change of variable from k to ln k. This has been mentioned briefly in an earlier paper. In the present communication the correct procedures are discussed and illustrated by several examples of evaluations. In particular, Arrhenius parameters calculated by the Taylor series expansion of the exponential form of the Arrhenius equation are compared with those calculated from the logarithmic form, using an exact and two approximate transformations of the statistical weights. The comparisons indicate thatthe preferred procedure for obtaining Arrhenius parameters is either the Taylor series method or the logarithmic method with proper transformation of the experimentally determined statistical weights of the rate constants k_i. The common approximation of assuming equal statistical weights of ln k_i when the logarithmic form of the Arrhenius expression is used is shown not to be always appropriate, and reasons forthis are given.     

The oxidation of HI at low temperatures and the heat of formation of HO2

The kinetics of the oxidation of hydrogen iodide (HI + O₂) at low temperature (414–499 K) in the gas phase by the method of iodination kinetics is complicated by a heterogeneous reaction between hydrogen iodide and oxygen. Present work leads to an upper limit for the bimolecular rate constant k₁ for the first and rate-determining step (1) These data are combined with an estimated A factor A₁ = 10^9.3±0.2 L/mol·s (assuming a tight linear I···H···O— transition state), to calculate the lower limit of the activation energy for the forward reaction E₁. This leads to a minimum value for the heat of formation of the HO₂ radical, ΔH_f298^°(HO₂) < 3.0 kcal/mol.     

Relative rate constants of the gas-phase decomposition reactions of the s-butoxy radical

s-Butoxy radicals have been generated by reacting fluorine with s-butanol: Over the temperature range 398.6 to 493.3 K the s-butoxy radical decomposes by two different pathways to yield acetaldehyde and propionaldehyde, acetaldehyde being the major product: The ratio k₁/k₂ was found to be temperature dependent. An Arrhenius plot of the data (398.6 to 493.3 K) yields the relative Arrhenius parameters, E₁ - E₂ = ?11.2 ± 0.8 kJ mol^?1 and (A₁/A₂) = 0.59 ± 0.14. The ratio of rate constants k₁/k₂ was shown to be independent of total pressure (80–600 torr) and of the pressure of s-butanol (2–13 torr). The kinetic results for these s-butoxy decomposition reactions are discussed in relation to the literature data and in terms of the thermochemistry of the reactions.     

Reactivity of C<Subscript>3</Subscript>-C<Subscript>8</Subscript> alkanes with nitronium ions in sulfuric acid

We have determined the parameters of the Arrhenius equation (E, log A) for reactions between \textNO₂⁺ {\text{NO}}_2^{+} ions and C₃-C₈ alkanes in HNO₃–93 wt.% H₂SO₄ solutions at 277–353 K, and we have also estimated the activation parameters E _j , log A _j for secondary and tertiary C—H bonds of these alkanes. We show that the following compensation relations are satisfied: E = 2.3R βlog A + C with isokinetic temperature β = 360 ± 65 K, and also E _j =2.3Rβ _j log A _j  + C _j , for secondary C—H bonds, β₂ =300 ± 60, and for tertiary C—H bonds, β₃ =310 ± 50.     

Kinetics of the reaction Cl + HO2 = HCl + O2, using molecular modulation spectrometry

The rate constant for the reaction (1), Cl + HO₂ → HCl + O₂, was measured using molecular modulation spectrometry to investigate HO₂ radical kinetics in the modulated photolysis of Cl₂? ;H₂? O₂ mixtures at 760 torr pressure. HO₂ was monitored directly in absorption at 220 nm, and k₁ was determined from computer simulations of the observed kinetic behavior of HO₂, using a simple chemical model. The results gave where k₄ is the rate constant for the reaction of Cl with H₂. A consensus value of k₄ gave k₁ = 6.9 × 10^?11 cm³/molecule sec, independent of temperature in the range of 274–338 K with an overall uncertainty of ±50%. The relative importance of reaction (1) for the conversion of Cl to HCl in the stratosphere is discussed briefly.