C.G.R. Nair

Thermal decomposition studies: Part X. Thermal decomposition kinetics of calcium oxalate monohydrate — correlations with heating rate and samples mass

Abstract Quantitative correlations between kinetic parameters (energy of activation E , pre-exponential factor A ) and procedural factors (heating rate, sample mass) in non-isothermal thermogravimetry have been made for the first time. The effect of heating rate and sample mass on the first two stages of thermal decomposition of calcium oxalate monohydrate in a nitrogen atmosphere has been evaluated in detail using non-isothermal thermogravimetry. Kinetic parameters are calculated from the TG curves using three integral methods (two “exact” and one “approximate”). The values obtained by the “approximate” method are higher than the corresponding values from the “exact” integral methods. For the decomposition of calcium oxalate to carbonate, the kinetic parameters are not much affected by heating rates or sample masses in the ranges studied. For the dehydration of CaC 2 O 4 · H 2 O, the parameters show a systematic decrease with increase in either heating rate or sample mass. The values of E and log A obtained by all three equations are best correlated to heating rate as rectangular hyperbole of the type: The best fits for correlation to sample mass are parabolae of the type E (or log A ) = constant × (mass) 2 − constant × mass ÷ constant SYMBOLS USED A = pre-exponential factor α = fraction decomposed φ = heating rate in deg min −1 E = energy of activation n = order parameter R = gas constant T i = temperature of inception of reaction T f = temperature of completion of reaction T s = DTG peak temperature Δ T = T − T s

Thermal decomposition kinetics. Part XI. Mechanism of thermal decomposition of calcium oxalate monohydrate from a thermogravimetric study — the effects of heating rate and sample mass on kinetic parameters from mechanistic equations

Abstract The mechanisms of the first two stages of the thermal decomposition of calcium oxalate monohydrate have been established from non-isothermal thermogravimetric studies. For both stages, the rate-controlling processes are phase boundary reactions; the dehydration step assumes spherical symmetry whereas the decomposition step follows cylindrical symmetry. The kinetic parameters calculated from mechanistic equations show the same trend as those from mechanism-non-invoking equations. Thus, for the decomposition of CaC 2 O 4 the kinetic parameters are not appreciably affected by heating rate or sample mass. For the dehydration step they show a systematic decrease with increase in either heating rate or sample mass. The best fit correlations can be expressed as follows E (or, log A ) = (Constant/Heating rate) + Constant, (at fixed sample mass) E (or, log A ) = (Constant) × (Mass) 2 − (Constant) × (Mass) + Constant, (at fixed heating rate)

Thermal decomposition studies. Part XII. Kinetics of dehydration of calcium oxalate monohydrate. Multiple correlation with heating rate and sample mass

Abstract The kinetic parameters (energy of activation, E , and pre-exponential factor, A ) from non-isothermal TG data have been correlated, for the first time, with simultaneous variations of both the procedural factors (heating rate and sample mass) by multiple regression analysis. The unique equation based on the mechanism of the reaction as well as three general mechanism-non-invoking integral equations were used to calculate E and A from the TG data for the dehydration of CaC 2 O 4 · H 2 O. The kinetic parameters calculated using all four equations showed a systematic trend and the results can be expressed as E (or log A ) = constant heating rate + constant mass + constant

Thermal decomposition studies. Part XIII. Kinetics of the thermal decomposition of the oxalates of the rare earths, yttrium and titanium

Abstract The thermal decomposition behaviour of the oxalates of La, Ce, Pr, Nd, Sm, Gd, Dy, Y and Ti was studied in detail by TG, DTG and DTA. The kinetic parameters (energy and entropy of activation) for the important stages of dehydration and decomposition were evaluated from TG traces by using the Coats—Redfern equation and the modified Coats—Redfern equation.

Thermal decomposition kinetics: Part XV. Kinetics and mechanism of thermal decomposition of tetrammine copper(II) sulphate monohydrate

Abstract The kinetics and mechanism of the thermal decomposition of tetrammine copper(II) sulphate monohydrate have been studied using non-isothermal thermogravimetry. Kinetic parameters were calculated for each step in the decomposition reaction from the TG curve using four integral methods, three “exact” and one “approximate”. The rate-controlling process for all the four stages of decomposition is random nucleation with the formation of one nucleus on each particle (Mampel equation). The stages of decomposition have been identified from X-ray diffraction and independent pyrolysis.

Thermal decomposition kinetics: Part XVII. Kinetics and mechanism of thermal decomposition of bis(ethylenediamine)copper(II) halide monohydrate

Abstract The thermal decomposition studies of bis(ethylenediamine)copper(II) chloride monohydrate and bis(ethylenediamine)copper(II) bromide monohydrate were carried out using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). The kinetics and mechanism of the dehydration and the deamination stages of both the complexes were evaluated. The different stages of decomposition were identified from TG, DTG and DTA. The intermediate and residue analysis done using optical microscopy and X-ray diffraction showed the formation of CuCl and CuBr at about 450°C and copper as fine linear wires at about 700°C. The kinetic parameters for the dehydration and the deamination reactions were evaluated from the TG and DTA curves using four integral methods. For both the complexes the dehydration and the deamination processes follow the mechanism of random nucleation with the formation of one nucleus on each particle (Mampel equation). The heat of reaction for each stage of decomposition was determined using DTA.

Thermal decomposition kinetics: Part IX. A study of the thermal decomposition of sodium tetraphenyl borate☆

Abstract Sodium tetraphenylborate [NaB(C 6 H 5 ) 4 ] undergoes a two-stage decomposition on heating in air. The DTG peak temperatures are at about 320 and 500°C, the corresponding DTA peaks are at 330 and 520°C. The energies of activation for the two stages are ≈ 220 kJ mol −1 and ≈ 140 kJ mol −1 . The total enthalpy change for the complete decomposition (including combustion of carbonaceous decomposition products) is ≈ − 13,200 kJ mol −1 The ultimate decomposition product in air is NaBO 2 .

Thermal decomposition kinetics.: Part XVI. Kinetics and mechanism of thermal decomposition of diaquobis(ethylenediamine)copper(II) oxalate

Abstract The kinetics and mechanism of thermal decomposition of diaquobis(ethylenediamine)copper(II) oxalate were studied using non-isothermal thermogravimetry (TG) and differential scanning calorimetry (DSC). The stages of decomposition were identified from TG/DTG, independent pyrolysis and X-ray diffraction data. The complex undergoes a three-step decomposition corresponding to dehydration, deamination to mono(amine) complex followed by simultaneous deamination, and decomposition giving rise to copper(II) oxide. The kinetic parameters for the three steps of decomposition were calculated from the TG and DSC curves using four integral methods. The rate-controlling process for all three stages of decomposition is random nucleation with the formation of one nucleus on each particle (Mampel equation). The heat of reaction for each stage of decomposition was determined using DSC.

Thermoanalytical investigations on kinetics and mechanism of deamination of tris(ethylenediamine)copper(II) sulphate

The thermal decomposition of tris(ethylenediamine)copper(II) sulphate has been studied using TG, DTG and DTA. The different stages of decomposition have been identified by these techniques in conjunction independent pyrolysis and X-ray diffraction. The kinetics and mechanism of the first two stages of deamination of the complex were evaluated. The activation parameters for the deamination reaction were computed from the TG and DTA curves using four integral methods. The two stages of deamination follow the mechanism of random nucleation with the formation of one nucleus on each particle (Mampel equation). The thermodynamic parameter namely heat of reaction (DH) for the two deamination processes was also evaluated.ZusammenfassungMittels TG, DTG und DTA wurde die thermische Zersetzung von Tris(ethylendiamin)-kupfer(II)-sulfat untersucht. Anhand dieser Methoden wurden in Verbindung mit einer gesonderten Pyrolyse und Röntgendiffraktion die einzelnen Schritte dieser Zersetzung identifiziert. Weiterhin wurde die Kinetik und der Mechanismus der beiden ersten Schritte der Desaminierung des Komplexes entwickelt. Unter Anwendung von vier Integralmethoden wurden aus den TG- und DTA-Kurven die Aktivierungsparameter der Desaminierungsreaktion berechnet. Beide Schritte der Desaminierung verlaufen nach dem Mechanismus der Random-Keimbildung mit der Bildung von einem Keim pro Partikel (Mampel-Gleichung). Die Reaktionswärme der zwei Desaminierungsprozesse wurde ebenfalls bestimmt.

Quantitative correlations of activation parameters and procedural factors : dependence on reaction type

Abstract The dependence of the correlation of kinetic parameters (energy of activation and pre-exponential factor) and procedural factors (sample mass and heating rate) on the type of reaction in non-isothermal thermogravimetry is established here for the first time. The effect of heating rate and sample mass on the stages of decomposition of diaquabis(ethylenediamine)copper(II) oxalate has been studied non-isothermally. The kinetic parameters, calculated using both the mechanistic and non-mechanistic equations, show a systematic decrease with increase in either heating rate or sample mass for the dehydration and deamination reactions. For the decomposition reaction, the kinetic parameters are not appreciably affected by procedural factors. Mathematical correlations of high reliability are established between kinetic parameters and heating rate/sample mass using both the mechanistic and non-mechanistic equations for the dehydration and deamination reactions. Thus it has been found that the type of reaction is decisive in the correlation of kinetic parameters with procedural factors. The quantification follows a rectangular hyperbolic equation for the dehydration and a parabolic one for the deamination. No quantitative correlations were possible for the final decomposition of the oxalate to oxide. For all three reaction types, the rate-controlling process is random nucleation with the formation of one nucleus on each particle. It is observed that the mechanism of these reactions is not affected by the variations in sample mass and heating rate, or by the reaction type.