PhD Thesis

Corrosion of Ta in Acidic Fluoride Media

Anodic Dissolution Mechanism of Ta in Acidic Fluoride Media

• The corrosion of Ta is studied from conventional weight loss experiments performed at various temperatures and concentrations.

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• The key species (HF dissociated species) assisting the corrosion of Ta in acidic fluoride media are identified as (HF2)-  and equilibrium HF.

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• H2 evolution reaction that occurs during the corrosion process is rapid from the surface of Ta and hence can be neglected.

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• A mathematical model is developed to estimate the corrosion rate of Ta.

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• Electrochemical experiments are performed to measure the corrosion rate or polarisation resistance to support the weight loss experiments. 

• The anodic dissolution mechanism of Ta in acidic fluoride media was studied using potentiodynamic polarization and electrochemical impedance spectroscopy

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• The anodic polarization was performed in four different concentrations at room temperature, and it shows active-passive regions in all concentrations studied.

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• The impedance spectra were taken in one active and two passive regions for two concentrations.

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• A four-step mechanism with two intermediate adsorbed species and two dissolution pathways was developed to describe the anodic dissolution of Ta in active and passive regions.

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• The mechanistic analysis also shows that the chemical dissolution is assisted by equilibrium HF, and electrochemical dissolution is assisted by both undissociated HF and (HF2)- species present in the solution.