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Thermal decomposition kinetics of some aromatic azomonoethers

Part II. Non-isothermal study of three liquid crystals in dynamic air atmosphere

Journal of Thermal Analysis and Calorimetry
Authors: A. Rotaru, Anna Kropidłowska, Anca Moanţă, P. Rotaru, and E. Segal

Abstract  

Thermal analysis of three azomonoether dyes, exhibiting liquid-crystalline properties, was performed in dynamic air atmosphere. Thermal stability studies and the evaluation of the kinetic parameters of each physical or chemical transformations are essential for a full characterization, before attempting accurate thin films’ depositions of such materials used in non-linear optical applications. New synthesized dyes with general formula:

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where R is a nematogenic group: CN, CF3 or a highly polarizable group: NO2 were investigated using TG, DTG, DTA and DSC techniques, under non-isothermal regime. The evolved gases were analyzed by FTIR spectroscopy. The activation energies of the first decomposition step were evaluated for each compound, the obtained results revealing complex mechanisms.

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This paper describes the influences of some parameters relevant to biomass pyrolysis on the numerical solutions of the nonisothermal n th-order distributed activation energy model (DAEM) involved the Weibull distribution. Investigated parameters are the integral upper limit, the frequency factor, heating rate, the reaction order and the shape, scale and location parameters of the Weibull distribution. Those influences can be used for the determination of the kinetic parameters of the nonisothermal n th-order Weibull DAEM from thermoanalytical data of biomass pyrolysis.

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Abstract  

The Eu tris(dibenzoylmethanato)phenanthroline complex doped xerogel has been synthesized by a catalyst-free sol-gel roure. The non-isothermal kinetic analysis is calculated by Friedman isoconversional method and multivariate non-linear regression method. The overall decomposition process below 600C is fitted by an Fn model (n order reaction), corresponding to the dehydration of the matrix, and a two-step consecutive reaction of Cn model (n order autocatalytic reaction), corresponding to the decomposition of organic complex. Correlation coefficient is 0.99986. The lifetime values of xerogel, defined as the 5% decomposition of europium organic complex, indicate that the xerogel can find application at near room temperature.

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Abstract  

Kinetics of exothermal decomposition of 2-nitrophenylhydrazine (2-NPH) and 4-nitrophenylhydrazine (4-NPH) was investigated by differential scanning calorimetry. The isoconversional methods, Friedman and Flynn-Wall-Ozawa, were applied to determine the activation parameters from the common analysis of multiple curves measured at different heating rates. For the processes involving two-step reactions the multivariate non-linear regression was used. A good agreement between the experimental and the fitted data was found.

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Abstract  

The complex of [Tb2(o-MBA)6(PHEN)2] (o-MBA: o-methylbenzoate and PHEN:1,10-phenanthroline) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behavior of [Tb2(o-MBA)6(PHEN)2] in dynamic nitrogen atmosphere was investigated by TG-DTG techniques. The thermal decomposition process of the [Tb2(o-MBA)6(PHEN)2] occurred in three consecutive stages at Tp 294, 427 and 512C. The kinetic parameters and mechanisms of first decomposition stage from analysis of the TG-DTG curves were obtained by the Malek method.

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Abstract  

Criteris for deciding upon the support effect by the thermal decomposition of precursor/support systems are discussed. Instead of the linear relationship between lgA and E, two new criteria determined by the calculated rate maximum were suggested. Dimensionless criteria based on the rate, conversion and temperature values at the inflexion point of the TG diagram lead to a parameter able to describe the support effect in a synthetic and quantitative manner. The experimental data were the TG-curves for the decomposition of ammonium metavanadate, molybdic acid and ammonium phosphomolybdate, supported on carborundum and silica.

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Abstract  

The thermal decompositions of ammonium metavanadate, molybdic acid and ammonium phosphomolybdate supported on carborundum or silica were subjected to non-isothermal kinetic study. The compensation effect is discussed in connection with the quantitative estimation of the support effect.

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Abstract  

The non-isothermal decomposition process of the powder sample of palladium acetylacetonate [Pd(acac)2] was investigated by thermogravimetric (TG) and the X-ray diffraction (XRD) techniques. Model-free isoconversional method of Tang, applied to the investigated decomposition process, yield practically constant apparent activation energy in the range of 0.05≤α≤0.95. It was established, that the Coats-Redfern (CR) method gives several statistically equivalent reaction models, but only for the phase-boundary reaction models (R2 and R3), the calculated value of the apparent activation energy (E) is nearest to the values of E obtained by the Tang’s and Kissinger’s methods. The apparent activation energy value obtained by the IKP method (132.4 kJ mol−1) displays a good agreement with the value of E obtained using the model-free analysis (130.3 kJ mol−1). The artificial isokinetic relationship (aIKR) was used for the numerical reconstruction of the experimental integral model function, g(α). It was established that the numerically reconstructed experimental function follows R3 reaction model in the range of α, taken from model-free analysis. Generally, decomposition process of Pd(acac)2 starts with initial nucleation which was characterized by rapid onset of an acceleratory reaction without presence of induction period.

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