An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)2 have been processed.
Authors:K. Chrissafis, K. Efthimiadis, E. Polychroniadis, and S. Chadjivasiliou
In this work we study the influence of Mo admixtures on the crystallization process of amorphous Fe78-xMoxSi9B13 (x=1, 2, 3 and 4) alloys by measurements of differential scanning calorimetry and on the soft ferromagnetic properties of the
alloys by magnetic measurements. The addition of Mo by replacing Fe, results in magnetic hardening of materials. In DSC curves
two peaks appear which are distinct when the concentration of Mo is 1 at.% and partly overlap when the Mo content is 2 at.%.
Further increase in the Mo content leads to the appearance of just one peak. The activation energy was calculated both with
Kissinger's and isoconversional Flynn, Wall and Ozawa methods.
Authors:J. Yi, F. Zhao, S. Xu, L. Zhang, X. Ren, H. Gao, and R. Hu
The decomposition reaction kinetics of the double-base (DB) propellant (No. TG0701) composed of the mixed ester of triethyleneglycol
dinitrate (TEGDN) and nitroglycerin (NG) and nitrocellulose (NC) with cerium(III) citrate (CIT-Ce) as a combustion catalyst
was investigated by high-pressure differential scanning calorimetry (PDSC) under flowing nitrogen gas conditions.
The results show that pressure (2 MPa) can decrease the peak temperature and increase the decomposition heat, and also can
change the mechanism function of the exothermal decomposition reaction of the DB gun propellant under 0.1 MPa; CIT-Ce can
decrease the apparent activation energy of the DB gun propellant by about 35 kJ mol−1 under low pressure, but it can not display the effect under high pressure; CIT-Ce can not change the decomposition reaction
mechanism function under a pressure.
Authors:Nicoleta Birta, N. Doca, Gabriela Vlase, and T. Vlase
The thermal behavior of sorbitol was studied under non-isothermal conditions, in both air and nitrogen atmosphere. The main
process is a deep and continuous dehydration.
For the kinetic analysis, the TG/DTG data obtained at five heating rates were processed by three different methods: Friedman,
Budrugeac-Segal and non-parametric kinetic, respectively. This analysis indicates a complex reaction with a preponderant chemical
process, described by a conversion function (1−α)3/2, accompanied by diffusion.
The decomposition of series of supramolecular compounds, namely inclusion compounds, was studied by means of different thermoanalytical
methods, i.e., traditional thermogravimetry, quasi-equilibrium thermogravimetry, and thermomechanical analysis. The series
of compounds included the intercalates on the base of fluorinated graphite C2F, the clathrates on the base of carbamide and on the base of coordination compounds and microporous inclusion compounds on
the base of coordination compounds. Kinetic parameters of decomposition processes were estimated within the approaches of
the non-isothermal kinetics (“model-free” kinetics, linear and non-linear regression methods for the topochemical equation
detection). The kinetic stability of the inclusion compounds under heating, the flexibility of the matrix structure, and the
thermodynamic stability of the intermediate phases are discussed.
Authors:S. Li, L. Liu, H. Jiang, D. Liu, S. Chen, and Z. Yang
The crystal C81H78N12O6Cd3 was synthesized and its structure was determined by single crystal X-ray diffraction method. The complex crystallizes in
the monoclinic system space group P21/n with cell parameters, a=15.959(4) , b=26.222(3) , c=25.907(6) , β=101.60(2). The non-isothermal kinetics of the crystal
was studied by use of non-isothermal TG and DTG curves. The kinetic parameters were analyzed by means of integral and differential
methods, and mechanism functions of the thermal decomposition reaction for its second step were proposed. The kinetic equation
of thermal decomposition is expressed as:
dα/dt=Aexp(-E/RT)1.5(1-α)4/3[1/(1-α)1/3-1]−1. The average values of E(kJ mol−1) and lnA/s−1 are 339.25, 43.95, respectively.
Authors:T. Vlase, Gabriela Vlase, A. Chiriac, and N. Doca
Summary In order to obtain catalysts, the thermal decomposition of the precursors is a compulsory step. However, kinetic analysis of the decomposition data obtained under non-isothermal conditions lead very seldom to the intimate reaction mechanism. There is also a lack of information because in non-isothermal kinetics, the compensation effect, is rather a rule and unfortunately a source of debate. In order to discriminate between these processes, and the influence of conversion, respectively temperature on the reaction rate, the NPK (non-parametric kinetic - Sempere and Nomen) method was used. This method is based on the singular value decomposition algorithm (SVD) applied on the matrix of reaction rate at corresponding conversion and temperature. This method allows a less speculative determination of the conversion functions and of the kinetic parameters.
Authors:H. Ye, N. Ren, H. Li, J. Zhang, S. Sun, and L. Tian
The complex of [Nd(BA)3bipy]2 (BA = benzoic acid; bipy = 2,2′-bipyridine) has been synthesized and characterized by elemental analysis, IR spectra, single
crystal X-ray diffraction, and TG/DTG techniques. The crystal is monoclinic with space group P2(1)/n. The two–eight coordinated Nd3+ ions are linked together by four bridged BA ligands and each Nd3+ ion is further bonded to one chelated bidentate BA ligand and one 2,2′-bipyridine molecule. The thermal decomposition process
of the title complex was discussed by TG/DTG and IR techniques. The non-isothermal kinetics was investigated by using double
equal-double step method. The kinetic equation for the first stage can be expressed as dα/dt = A exp(−E/RT)(1 − α). The thermodynamic parameters (ΔH≠, ΔG≠, and ΔS≠) and kinetic parameters (activation energy E and pre-exponential factor A) were also calculated.
Authors:L. Tian, N. Ren, J. Zhang, H. Liu, S. Sun, H. Ye, and K. Wu
The two complexes of [Ln(CA)3bipy]2 (Ln = Tb and Dy; CA = cinnamate; bipy = 2,2′-bipyridine) were prepared and characterized by elemental analysis, infrared
spectra, ultraviolet spectra, thermogravimetry and differential thermogravimetry techniques. The thermal decomposition behaviors
of the two complexes under a static air atmosphere can be discussed by thermogravimetry and differential thermogravimetry
and infrared spectra techniques. The non-isothermal kinetics was investigated by using a double equal-double steps method,
the nonlinear integral isoconversional method and the Starink method. The mechanism functions of the first decomposition step
of the two complexes were determined. The thermodynamic parameters (ΔH≠, ΔG≠ and ΔS≠) and kinetic parameters (activation energy E and the pre-exponential factor A) of the two complexes were also calculated.