Electric-Field Generation by Gas-Solid Combustion

The combustion of metal particles may generate a temporal electrical field due to a difference in the electrochemical potential across the growing oxide shell, which usually is a mixed ionic electronic conductor. A novel measurement technique enables simultaneously measurement of the temporal electrical field and temperature generated by a planar reaction wave during highly exothermic gas–solid reactions. The voltage formed after the rate of the temperature rise reached its maximum value, but before the temperature attained its maximum. For both simple (TiO2, Fe2O3, MgO) and complex oxides (LiMn2O4, SrFe12O19, PbFe12O19, BaTiO3) the voltage grew to its maximum value within 0.2–0.6 s, irrespective of the distance between the measuring probes. The decay of the voltage signal was slower than its rise. Increasing the distance between the measuring probes increased the period during which the voltage decayed. The difference between the time at which the temperature attained its maximum and the electrical signal vanished depended on both the distance between the two probes, and on the difference in time at which the voltage and temperature attained their maximum. Changing the exothermicity of the reaction (by dilution of the reactant mixture) can shift the time of the voltage decay relative to that at which the maximum temperature occurs. © 2004 American Institute of Chemical Engineers AIChE J, 50: 241–248, 2004