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STUDIA UNIVERSITATIS BABEŞ-BOLYAI, CHEMIA, LIV, 3, 2009 ISOCONVERSIONAL LINEAR INTEGRAL KINETICS OF THE NON-ISOTHERMAL EVAPORATION OF 4-[(4-chlorobenzyl)oxy]-4’-trifluoromethyl-azobenzene ANDREI ROTARU a , MIHAI GOŞA b,c , EUGEN SEGAL d ABSTRACT. The activation energy of the linear non-isothermal evaporation of 4-[(4-chlorobenzyl)oxy]-4’-trifluoromethyl-azobenzene has been determined by various linear integral isoconversional methods. Activation energy may be evaluated using several isoconversional methods as the well-known Tang et al. method, Generalized KAS method, but also by means of two so-called “local linear integral” (Tang & Chen) and ”average linear integral” (Ortega) isoconversional methods. A comparison study has been carried out in order to understand how the activation energy values are affected when using different approaches. Keywords: azomonoether dyes, non-isothermal kinetics, linear integral, local linear integral and average linear integral isoconversional methods. INTRODUCTION Dyes from the category of azoic aromatics have been intensively studied since they are of large interest from the point of view of possible applications [1-4]. Thermal characterizations and stability studies are usually required before choosing them to be part of composite materials, moreover since they are used in thermal-controlled devices. Kinetic studies are required for predicting their behaviour in other conditions than in those that are accessible for normal runs [5-9]. This paper aims to present a isoconversional kinetic study of the linear non-isothermal evaporation of 4-[(4-chlorobenzyl)oxy]-4’-trifluoromethylazobenzene liquid crystal that has been previously investigated [7] only by KAS (Kissinger-Akahira-Sunose) [10,11] and FWO (Flynn-Wall-Ozawa) [12,13] a INFLPR – National Institute for Laser, Plasma and Radiation Physics, Laser Department, Bvd. Atomistilor, Nr. 409, PO Box MG-16, RO-077125 Magurele, Bucharest, Romania, andrei.rotaru@inflpr.ro b University of Craiova, Faculty of Automatics, Computers and Electronics, Bvd. Decebal, Nr. 107, Craiova, Romania c KineTAx, Str. Ştefan cel Mare, nr. 3, bl. L, sc. B, ap. 1, 200137 Craiova, Romania, mihai.gosa@kinetax.com d University of Bucharest, Faculty of Chemistry, Bvd. Regina Elisabeta Nr. 4-12, Bucharest, Romania, esegal@gw-chimie.math.unibuc.ro
186 ANDREI ROTARU, MIHAI GOŞA, EUGEN SEGAL isoconversional methods. Since for our early papers we have used regular calculations, we were able to report results only for a few methods and conversions. The new software package TKS-SP [14,15] for kinetic analysis allows the rapid evaluation of the activation energy by means of isoconversional methods (integral and differential), as well as by other more complex procedures. With the increasing number of papers dealing with the approximation of the temperature integral, its evaluation improved [16-22] and led to the general opinion that other methods should be used instead of those consecrated ones [10-13]. The method of Tang et al. [16] and the generalized KAS [17, 18] methods have been used here, together with the new “local linear isoconversional” of Tang & Chen [19] and ”average linear integral”of Ortega [20] methods as well. RESULTS AND DISCUSSION Thermal behaviour of 4-[(4-chlorobenzyl)oxy]-4’-trifluoromethyl-azobenzene was investigated in a previous paper [7], together with a couple of other liquid crystals from the same category of aromatic azomonoethers. Before evaporating in the temperature range of 190-310 o C (endothermic effect), at 155 o C the compound melts. The FTIR spectrum of the evolved gases perfectly matches to the FTIR spectrum of the solid compound. No influence of the gas atmosphere (air or inert flow) was found. The complexity of a physical or chemical process can be expressed from the activation energy dependence on the conversion degree. Usually, “model-free” kinetic methods are the most popular. Such applications require the use of isoconversional methods for the evaluation of the activation energy. 1) Regular linear integral methods (Tang et al. and Generalized KAS) Here we made use of several isoconversional methods: The methods of Tang et al. [16] (very close to KAS method) and Generalized KAS [17,18]; are the isoconversional integral linear ones, based on the following integral form of the reaction rate: α dα A α g( α ) = ∫ = ∫ e f ( α ) β T 0 0 E RT A dT = I( E β where β is the heating rate, R is the universal gas constant, g(α) is the integral conversion function and I(Eα ,Tα) represents the temperature integral. Substitution of I(Eα,Tα) in the equation (1) by various approximation mathematical expressions, provides various equations − therefore a multitude of isoconversional methods. − α , T α ) (1)
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R /(mol m -2 s -1 ) 0.06 0.05 0.04
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ANA-MARIA CORMOS, JOZSEF GASPAR, AN
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Studia Universitatis Babes-Bolyai C
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6 PROFESSOR IOAN BÂLDEA AT HIS 70
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MARCELA ACHIM, DANA MUNTEAN, LAURIA
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STUDIA UNIVERSITATIS BABEŞ-BOLYAI,
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STUDIES ON WO3 THIN FILMS PREPARED
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PREPARATION AND CHARACTERIZATION OF
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MATHEMATICAL MODELING FOR THE CRYST
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STUDY OF THE CHROMATOGRAPHIC RETENT
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THE INTERACTION OF SILVER NANOPARTI
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MELINDA-HAYDEE KOVACS, DUMITRU RIST
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IRON DOPED CARBON AEROGEL AS CATALY
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128 ANDRADA MĂICĂNEANU, HOREA BED
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E / mV vs. SCE POTASSIUM-SELECTIVE
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