Measurements of heat capacities, temperatures, and absorptivities of single particles in an electrodynamic balance

Abstract

A rapid measurement technique to determine heat capacities, temperatures, and absorptivities of single submillimeter size (50–200 μm diam) particles in an electrodynamic balance (EDB) is described. Accurate estimates of heat capacities and absorptivities are made for single carbon particles at temperatures ranging from 800 to 1200 K with measurement times of less than 0.5 s. Measurements are made by isolating and holding charged particles at the null position in an EDB. Particles are heated using the output from a well-characterized CO2 laser which is modulated to provide heating pulses of 3-ms duration at a repetition rate of 100 Hz. The resulting periodic temperature oscillations are monitored continuously using a single wavelength high-speed optical pyrometer. Heat capacities and absorptivities are determined based on comparisons of the recorded heating and cooling profiles with theoretical predictions obtained from numerical solution of the Fourier equation. Experimentally determined heat capacities for carbon spheres are in excellent agreement (±10%) in terms of their absolute value and temperature dependence when compared with published heat capacity correlations for chars and graphite. Absorptivity estimates are also in excellent agreement with published values for carbons.