The Valve Metal Character of Zirconium as inferred from anode potential measurements in mineral acid solutions |
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| Authors: | Prof. Dr. S. Darwish Dr. M. W. Khalil Dr. M. A. Abdel Rahim Porf. Dr. I. A. Ammar |
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| Affiliation: | Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt |
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| Abstract: | A study on the value metal character of Zr in 0.1 M solutions of H2SO4, HNO3, and H3PO4 has been performed using the anode potential as the primary variable in galvanostatic, potentiostatic, and capacity measurements. A method of surface pre-treatment, which suppresses both O2 evolution and metal dissolution, has been described. Kinetic parameters of oxide growth have been calculated. The results indicate that: - (i) the high field approximation is applicable following an exponential law, and
- (ii) the height and activation distance of the energy barrier for ion transport through the oxide phase (Verwey model) are the same three acids.
Measurements have been also made on the dielectric breakdown of oxide, and this occurs at potentials above 200 V. Direct capacity measurements give similar results as those based on reciprocal capacity calculated from galvanostatic experiments. It is concluded that the dominant anodic oxide species is ZrO2 having a dielectric constant of 25. Open circuit potential measurements show that Zr is spontaneously oxidized in the three acids. |
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