Oscillatory Thermopower Waves Based on Bi2Te3 Films

Exothermic chemical reactions that are coupled to Bi2Te3 porous layers, which are deposited onto terracotta or alumina (Al2O3) substrates, are used to produce self-propagating thermal waves that are guided along the surface. Nitrocellulose is used as the highly reactive chemical. Bi2Te3 is employed because of its large Seebeck coefficient and high electrical conductivity. For the Al2O3 based structures, the thermal conduction of the substrate results in strong oscillations of the output signals. Such thermopower waves produce a power as large as 10 mW and voltages as high as 150 mV. The power per mass ratio of the developed system is quite remarkable, namely, on the order of 1 kW kg(-1). Depending on the thermal conductivity of the substrate used, the wave front average propagation velocity is either slow (ca. 0.009 m s(-1) for terracotta) or much faster (on the order of 0.4 m s(-1) for Al2O3). We have used a mathematical model based on two coupled heat transport equations, in conjunction with the chemical reaction equation, to predict the behavior of the system, which describes the average propagation velocity and the time between oscillation peaks.