The changes in reaction rate of a carbon char with conversion in the temperature range 500-1200 K are followed by using an electrodynamic balance (EDB). This device allows, in a temperature range wider than in other apparatus, in situ measurements of mass, diameter, density, surface area, rate of reaction, and temperature for a single, suspended submillimeter particle as the reaction takes place. A synthetic char (Spherocarb) has been used because of its low ash and volatile matter contents and its spherical shape. The results on oxidation kinetics obtained in an EDB are compared with low-temperature reaction rate data, obtained by conventional thermogravimetric apparatus on Spherocarb, and with the data obtained in an entrained-flow reactor at temperatures typical of pulverized-fuels combustors. The correlation between all the data in the temperature range 500-2300 K is examined. EDB data can be combined with entrained-flow data to depict a sharp change in reaction regime from a chemical kinetic to an internal diffusion control. A simple Thiele analysis, considering different classes of pores, yields results that suggest pores in the 100-1000 nm range are responsible for diffusional constraints that cause the kinetic data to depart from the chemical regime.
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