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The reaction kinetics of three
different Zr–Nb alloys with Zr-0.7 wt% Nb, Zr-2.5 wt% Nb, and Zr-5
wt% Nb were investigated using the thermogravimetric technique in
the temperature range of 723-790 K. Analysis of the oxidation curves
revealed that, at all oxidation temperatures, the reaction follows
initially parabolic and then linear oxidation reaction mechanism.
The X-ray powder diffraction pattern of the oxidation products
revealed the formation of ZrO0.27 and Nb0.20Zr0.80O2.10 at each
temperature. The rate constants were evaluated using rate equation
and the activation energy by Arrhenius equation in both the
parabolic and linear regions of each alloy. The activation energies
of Zr-0.7 wt% Nb, Zr-2.5 wt% Nb, and Zr-5 wt% Nb alloys in the
parabolic region are 225, 222, and 198 kJ/mol, respectively, whereas
in the linear region, the activation energies of the corresponding
alloys are 156, 136, and 123 kJ/mol.
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