Abstract
Nanometric carbides of transition metals and silicon are obtained by using precursors. Control of the course of these processes require data concerning transformations of single precursor, transformations of precursor in the presence of reducing agent and synthesis of the carbide. In this work, the way of investigating such processes is described on the example of thermal decomposition of (NH4)6Mo7O24·4H2O (precursor) in argon. The measurements were carried out by TG–DSC method. The solid products were identified by XRD method, and the gaseous products were determined by mass spectrometry method. There was demonstrated that the investigated process proceeded in five stages. Kinetic models (forms of f(α) and g(α) function) most consistent with experimental data and coefficients of Arrhenius equation A and E were determined for the stages. The Kissinger method and the Coats–Redfern equation were applied. In case of the Coats–Redfern equation, the calculations were performed by analogue method. In this way good consistency between the calculated and determined conversion degrees α(T) at practically constant values of A and E were obtained for distinguished stages and different sample heating rates.
Highlights
In theory of kinetics of non-catalytic heterogeneous reactions, it is assumed that the reaction rate depends on temperature and conversion degree [1,2,3,4,5]r 1⁄4 da 1⁄4 /ðT; aÞ: ð1Þ dtUnder conditions of thermogravimetric measurements, the influence of pressure is negligible [8]
The solid products were identified by XRD method, and the gaseous products were determined by mass spectrometry method
The gaseous products were determined by mass spectrometry method using Pfeifer Vacuum ThermoStar GDS 601 apparatus
Summary
In theory of kinetics of non-catalytic heterogeneous reactions, it is assumed that the reaction rate depends on temperature and conversion degree [1,2,3,4,5]. The size and direction of the arrows of n operator in the plane (T, a) should reflect the course of the change This is the traditional form of kinetic equation. B const, in a given series of measurements This notation indicates that under non-isothermal conditions, at a constant sample heating rate, for each stage of the process, the form of the function k(T), and the parameters A and E of the form of the function f(a) should be maintained [4, 14]. If appropriate correct values of kinetic parameters are achieved by this method It is often impossible, for example, when the peaks of the DTG charts are narrow and are located very close to Tm values for the different sample heating rates. A good approximation (10), easier for use in kinetic calculations, is the Coats–
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