Evaluation of kinetic parameters from thermogravimetri traces

The thermal decarboxylation of TI(GLA)3 (where GLA stands for the anion ofglycollic acid) was studied by TG, DTG and DTA techniques. The results showed the escape of all three glycollic acid moieties in a single step. The I R spectra of the ligand and the complex indicated the bidentate character of carboxylate ion and the fact that the proton from the hydroxy group is not replaced during complex formation, The various kinetic and thermodynamic parameters were estimated from analysis of the TG, DTG and DTA curves of the sample, employing several computational methods. Precise results were then obtained by the method of least squares and are discussed.The thermal decomposition of metal carboxylates has attracted great interest during recent years [1,2]. However, work on the thermal decomposition of heavy metal carboxylates started only a short time ago [3]. Recently, we reported on the thermal dehydration and decomposition of metal complexes of salicylic and nuclear substituted salicylic acids [4][5][6][7][8][9]. The work on the thermal decomposition of metal complexes of hydroxy acids is very limited. As an extension of our previous studies [4][5][6][7][8][9], the present report deals with the thermal decarboxylation of TI(III) glycollate, with a view to understanding the mechanism of the decomposition and the nature of the decomposition products. The characterization ofTl(IlI) glycollate was carried out through elemental analysis, IR spectra, TG, DTG and DTA studies. Attempts were also made to estimate the kinetic parameters from thermal studies, employing different computational methods, e.g. the Horowitz-Metzger

Section: Resultssupporting

confidence: 94%

Section: Regression Analysis Of the Datasupporting

confidence: 92%

Structure and thermal characterization of tris-thallium(III) glycollate

Khadikar

1987

“…the highest value of the correlation coefficient. In the cases where more than one equation gives linear curves, the reaction mechanism is chosen from the function g (a) which gives kinetic parameters in agreement with the corresponding non-mechanistic method, as suggested by Fong and Chen [15]. All the 24 sets of TG data were analyzed with the nine equations and the reaction mechanism was chosen from the 216 kinetic curves by applying the above two criteria.…”

Section: Reaction Mechanismmentioning

confidence: 99%

Kinetics and mechanism of thermal decomposition of insitu generated calcium carbonate

Ninan

Krishnan

Krishnamurthy

1991

Thermogravimetric studies on two varieties of calcium carbonate viz., analytical reagentgrade and insitu generated from calcium oxalate monohydrate, were carried out. The kinetics and mechanism of their solid-state thermal decomposition reaction were evaluated from the TG data using integral methods and the effect of procedural factors such as heating rate, sample mass and method of computation on them were also studied. The procedural variables in the range studied had no marked influence on the results; however the kinetic parameters were marginally higher for the insitu generated calcium carbonate. This trend is explained by the presence of more micropores in the insitu generated calcium carbonate as well as the mechanism of its decomposition following phase boundary reaction with cylindrical symmetry.The thermal decomposition of calcium carbonate has been extensively studied over the years [1, 2]. It is a high temperature reversible decomposition reaction involving a relatively large mass-loss associated with the evolution of carbon dioxide and hence used as a model reaction for the study of the influence of many experimental variables. A number of TG studies dealing with the kinetics and mechanism of the thermal decomposition of calcium carbonate have been reported [3][4][5][6][7]. The kinetic parameters viz., energy of activation E and preexponential factor// for the reaction, were found to be influenced by experimental conditions such as heating rate, sample mass, furnace atmosphere and the partial pressure of carbon dioxide.Widely varying values (E =40 to 900 kcal.mo1-1 and A = 104 to 10157S -1) have been reported under varying experimental conditions [3-5]. Empirical

“…The thermal dehydroxylation of magnesium hydroxide has been investigated in some detail by Fong and Chen [19]. The experimental data from two thermal curves have been processed by two methods, using 17 mechanistic equations.…”

Section: Resultsmentioning

confidence: 99%

Compensation effect resulting from the use of mechanistic equations, and its physical significance

Somasekharan

Kalpagam

1987

A compensation effect is observed in the activation parameters resulting from various mechanistic equations; the T computed from the slope of the E* vs In A plot matches the observed DTG peak.In the Arrhenius equation(1) the activation parameters A and E*, instead of being independent, have sometimes been found to exhibit a correlation, A increasing with E* through a series of reactions. Such ~ compensation effect was first reported in connection with catalytic studies [1]. Evidence for such a kinetic compensation has since been reported in other fields as well [2][3][4][5][6][7][8][9][10][11], even though many of the reports have subsequently been disputed. Several theories and explanations that account for such compensation behaviour have also been put forward [2,4,7,[12][13][14][15][16].The kinetic parameters reported for solid-state reactions differ widely; for example, the estimates of the activation energy for the decomposition of calcium carbonate vary between 26 and 377 kcal/mol, while those of the pre-exponential factor vary between 102 and 1069. Procedural factors such as the heating rate, sample size, sample pretreatment, container shape and the atmosphere are implicated in the widely differing calculated parameters. Zsak6 has suggested [17] that thermal decomposition processes can be better characterized by means of compensation parameters, since the shapes and positions of the TG curves can be greatly influenced by the working conditions, whereas the compensation parameters are independent of them. We have thus been able to identify the mechanisms of thermal decomposition of some copolymers using a compensation parameter "Sp = E*/log A [18], in spite of the wide scatter in the computed kinetic parameters.John Wilev& Sons, Limited, Chichester Akad~miai Kiad6, Budapest