Some considerations regarding the kinetics of solid-state reactions

Simon, J.

doi:10.1007/bf01950374

Cited by 51 publications

(13 citation statements)

References 45 publications

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“…Previous investigators [13,14] have shown that the process of preparing VN from V 2 O 5 is very complicated because it is difficult to control the experimental parameter of the reaction. The literature data [15,16] have shown that experimental factors such as mass and shape, particle size, ambient pressure, and heating rate can affect significantly the course of the solid-state reactions. The weak control of these parameters may be expected to be the cause of discrepancies and uncertainties.…”

Section: Introductionmentioning

confidence: 99%

Carbothermal synthesis of vanadium nitride: Kinetics and mechanism

Ortega

Roldán

Real

2006

Int J of Chemical Kinetics

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Constant rate thermal analysis (CRTA) has been used for the first time to study the kinetics of the carbothermal reduction of V 2 O 5 in nitrogen to obtain vanadium nitride. It is noteworthy to point out that CRTA method allows both a good control of pressure in the sample surroundings and the use of reaction rates low enough to keep temperatures gradients at a negligible level to avoid any heat or mass transfer phenomena. This method allows one to control the texture and the structure of many materials through kinetic control of the thermal treatment of the precursors. The precise control of the external parameters of the reaction shows that CRTA is an attractive method for kinetic studies and leads to more reliable kinetic data. It has been shown that the carbothermal synthesis of vanadium nitride is best described by a three-dimensional diffusion kinetic model (the Jander equation) with an activation energy which falls in the range of 520-540 kJ/mol. C

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Section: Introductionmentioning

confidence: 99%

Carbothermal synthesis of vanadium nitride: Kinetics and mechanism

Ortega

Roldán

Real

2006

Int J of Chemical Kinetics

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“…On the other hand, besides other influences, the literature reports on the dependence of the kinetic parameters on the heating rate in thermoanalytical studies on other desorption processes by means of linear heating schedules [4][5][6].…”

Section: Nh4naymentioning

confidence: 99%

Temperature-programmed desorption (TPD) studies of the deammoniation kinetics of NH4NaY zeolites using a hyperbolic temperature programme

Hunger

Hoffmȧnn

1983

Journal of Thermal Analysis

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TPD studies on the kinetics of deammoniation of an NH4NaY zeolite showed that the use of a hyperbolic temperature programme led to kinetic parameters agreeing with those resulting from a linear heating process. Because of the progressive increase of the heating rate in the case of hyperbolic heating schedules, the parameters can be considered as independent of the heating rate within certain limits. The better resolution of complex desorption spectra with hyperbolic programmes Js an additional reason for their use.The thermal activation of NH4NaY zeolites is connected with the desorption of water and ammonia, the latter occurring in the temperature interval from 473 to 673 K and resulting in two overlapping peaks [1--3]: NH4NaY> HNaY + NH 3 ?Desorption of the high-temperature form of the sorbed NH 3 can be well described over a relatively large range of coverage by a rate equation of first order without readsorption [3]. The activation energies of the desorption process on zeolites with different ammonium contents are very suitable for characterizing the acidity of the appropriate H forms [3], provided, however, that the activation energies calculated are widely independent of the experimental conditions and of the method of evaluation.On the other hand, besides other influences, the literature reports on the dependence of the kinetic parameters on the heating rate in thermoanalytical studies on other desorption processes by means of linear heating schedules [4][5][6].The application of non-linear, especially hyperbolic, temperature programmes could be very useful to obtain information about the influence of the heating rate:Furthermore, this kind of temperature guidance would permit a correction-free integral evaluation [7,8]. In comparison with linear heating schedules, the shape index would advantageously be a function of reaction order only or of the mechanism of the desorption process in the case of hyperbolic temperature programmes [9,10],

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“…However, if the reaction rate is modified because of mass transfer effects, it is well known: [5][6][7] that an increase in the sample weight gives rise to a movement of the TG curve at higher temperatures, while a broadening of the reaction temperature range takes place. These facts mean that if Wil> Wi~ (i.e., c > 1), the data taken at the same temperature from both TG curves satisfy the relationships:…”

Section: Woomentioning

confidence: 99%

Remarks on the suitability of Chatterjee's method for the kinetic analysis of TG traces

Criado

1981

Journal of Thermal Analysis

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It is shown that Chatterjee's method cannot be used at all to determine the value of n in reactions of thermal degradation of solids following n-order kinetics. It has been demonstrated that, if heat and mass transfer effects are avoided, the reaction order obtained from this method will be equal to one whatever the reaction mechanism.Chatterjee's method [1] has been widely used for the kinetic analysis of TG data. Gupta and Dwarakanath [2] have recently used this method to evaluate the reaction order of the thermal degradation of polystyrene and styrene acrylonitrile copolymer and they have concluded that both reactions follow first-order kinetics.The scope of the present paper is to analyse whether the above method is an appropriate one for determining the value of the reaction order.Chatterjee represents the rate of decomposition in the following form:where W is the active weight of the material remaining at time t, n is the reaction order and k is the rate constant. For the calculation of n by Chatterjee's method, two TG curves from two different initial weights of sample must be recorded, all the other experimental conditions being kept constant. Then, sets of W1 and IV,, values and the corresponding (-dW/dt)land (-dW/dt) 2, taken at the same are substituted into the following relationship, temperature from each diagram, derived from Eq. (1):log Wl-lOg W 2However, we must bear in mind [3,4] that the rates of thermal decompositions of solids following n-order kinetics must fit the following expression:where ~ is the fraction reacted at time t and k t is the "true" rate constant of the reaction, given by the Arrhenius law.

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Some considerations regarding the kinetics of solid-state reactions

Cited by 51 publications

References 45 publications

Carbothermal synthesis of vanadium nitride: Kinetics and mechanism

Carbothermal synthesis of vanadium nitride: Kinetics and mechanism

Temperature-programmed desorption (TPD) studies of the deammoniation kinetics of NH4NaY zeolites using a hyperbolic temperature programme

Remarks on the suitability of Chatterjee's method for the kinetic analysis of TG traces

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