Complementarity methodology as applied for solution of the inverse problem for solid-phase reaction kinetics III

Mathematical analysis has shown that invariant kinetic parameters (IKP) correspond to the real kinetic curve even in the case when the equation prescribing this curve is not used for the calculation of parameters. It has been proved that IKP values coincide with those obtained for isothermal conditions. The theory is verified by calculations using model experimental data. The IKP stability to random experimental errors is studied.     

Some aspects of mathematical statistics as applied to non-isothermal kinetics

As a numerical characteristic of the sensitivity of the kinetic parameter calculation method to the form of the kinetic function in non-isothermal kinetics, the value of the curvature of the line plotting residual dispersionvs. formal reaction order at the minimum point is suggested. The efficiency of this characteristic is exemplified.     

Kinetics of azobenzene nitrene oxidation by molecular oxygen in glassy propylene carbonate

The kinetics of azobenzene nitrene oxidation by molecular oxygen dissolved in a matrix was studied in glassy propylene carbonate. The reaction was carried out in excess oxygen within its concentration range 0.008 to 0.048 M. The oxidation kinetics, controlled by oxygen diffusion, is not described by the exponential function. A specific reaction rate decreases in the course of the process. The higher the oxygen concentration in the matrix, the sharper is the decrease in the reaction rate. It is shown that at all concentrations, the oxidation kinetics is described in the framework of the model of heterogeneous matrix with a characteristic size of heterogeneities of 1.5 nm and a dispersion of the activation energy of oxygen molecule jump of 4 kJ/mol. The reaction radius is about 0.5 nm.     

The √t law in solid-phase reactions. Analysis of the hypothesis on rate constant distribution

The reaction C₂H₅ + O₂ → C₂H₅O₂ in glassy methanol-d₄ and the H-atom abstraction by CH₃, C₂H₅, and n-C₄H₉ radicals in C₂H₅OH + C₂D₅OH and CD₃CH₂OH + C₂D₅OH glassy mixtures have been studied by electron spin resonance. The analysis of the dependence of the reaction rates on the concentration of O₂ (oxidation) and C₂H₅OH, CD₃CH₂OH (H-atom abstraction) has shown that the √t law is not conditioned by the existence of regions characterized by different rate constants.     

Ammonium nitrate-polymer glasses: a new concept for phase and thermal stabilization of ammonium nitrate

Dissolving of ammonium nitrate in highly polar polymers such as poly(vinylpyrrolidone) and/or poly(acrylamide) can result in the formation of single-phase glassy solid materials, in which NH 4 (+) and NO 3 (-) are separated through an ion-dipole interaction with the polymer matrix. Below the glass transition temperature of the polymer matrix the resulting materials remain phase and thermally stable as demonstrated through the absence of decomposition as well as the solid-solid transitions and melting of ammonium nitrate. The structure of the materials is explored by Fourier transform infrared spectroscopy and density functional calculations. Differential scanning calorimetry, thermogravimetry, and isoconversional kinetic analysis are applied to characterize the thermal behavior of the materials.     

Effect of substituents in aromatic amines on the activation energy of epoxy-amine reaction

Differential scanning calorimetry has been used to study the kinetics of epoxy-amine curing reaction between diglycidyl ether of 4,4'-bisphenol and aromatic amines with different electron-withdrawing/-donating substituents. The substituents include -NO2, -CN, -OCH3, -OH, and -CH3 groups. An advanced isoconversional method has been employed to determine the effective activation energy of the respective processes. An attempt has been made to link the experimental values with the results of quantum chemistry calculations. It has been found that regardless of the electron-withdrawing/-donating properties the presence of a substituent of a large negative charge in the ortho position causes an increase in the activation energy to approximately 100 kJ mol-1 from the normally observed values of 50-60 kJ mol-1.