Non-Parametric Kinetic (NPK) Analysis of Thermal Oxidation of Carbon Aerogels

Abstract

In recent years, much attention has been paid to aerogel materials (especially carbon aerogels) due to their potential uses in energy-related applications, such as thermal energy storage and thermal protection systems. These open cell carbon-based porous materials (carbon aerogels) can strongly react with oxygen at relatively low temperatures (~ 400°C). Therefore, it is necessary to evaluate the thermal performance of carbon aerogels in view of their energy-related applications at high temperatures and under thermal oxidation conditions. The objective of this paper is to study theoretically and experimentally the oxidation reaction kinetics of carbon aerogel using the non-parametric kinetic (NPK) as a powerful method. For this purpose, a non-isothermal thermogravimetric analysis, at three different heating rates, was performed on three samples each with its specific pore structure, density and specific surface area. The most significant feature of this method, in comparison with the model-free isoconversional methods, is its ability to separate the functionality of the reaction rate with the degree of conversion and temperature by the direct use of thermogravimetric data. Using this method, it was observed that the Nomen-Sempere model could provide the best fit to the data, while the temperature dependence of the rate constant was best explained by a Vogel-Fulcher relationship, where the reference temperature was the onset temperature of oxidation. Moreover, it was found from the results of this work that the assumption of the Arrhenius relation for the temperature dependence of the rate constant led to over-estimation of the apparent activation energy (up to 160 kJ/mol) that was considerably different from the values (up to 3.5 kJ/mol) predicted by the Vogel-Fulcher relationship in isoconversional methods

Keywords

• thermal oxidation
• carbon aerogel
• non-parametric kinetic model
• nanostructure
• oxidation kinetics