Authors:N. Ionescu, N. Jaeger, P. Plath, and C. Hornoiu
Activation energies of ignition for the thermokinetic oscillations obtained during the heterogeneous catalytic oxidation of
ethanol on Pd/Al2O3 in a dynamic calorimeter were obtained using the minimum values of the temperature oscillations. These activation energies
of ignition are greater than the activation energies of the corresponding oscillations. The obtained results are discussed
by assuming a PdOx redox cycle.
Sol–gel auto combustion process was employed to synthesize nanosized Mn–Zn ferrite at different pH values (<1, 5, 6, 7, 8
and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective combustion was observed
at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH < 1 showed localized burning. Thermogravimetric
(TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size
and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction
at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the
value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air)
of powders P1 and P6 synthesized at pH < 1 and pH 6 were also determined. B–H loop results showed that calcined powder C6
was more ferromagnetic than C1 due to fully developed spinel phase and larger particle size.