In situ quantification of electrochemical dissolution of hafnium-tantalum alloys in acidic media

• Hf–Ta alloys electrochemical dissolution was studied in a wide compositional range.
• A flow-type scanning droplet cell microscope was used for acidic media dissolution.
• Downstream analytics were used for the quantification of Hf and Ta amounts dissolved.
• Hf and Ta dissolution rates were in the ng and pg s− 1 cm− 2 range, respectively.
• A dissolution enhancement of minor species was identified in Hf–Ta alloys.

A thin film hafnium-tantalum combinatorial library with a compositional spread of over 70 at.% was used for electrochemical dissolution experiments in nitric acid. Surface microstructure analysis and crystallographic characterization of individual Hf–Ta alloys confirmed a hexagonal to tetragonal transition from pure Hf to pure Ta accompanied by a change in the surface grain structure. A flow-type scanning droplet cell microscope coupled to downstream analytics was used for the quantification of Hf and Ta dissolution rates along the entire compositional spread. Potentiostatically applying 3 V vs. SHE for 120 s for an electrolyte flow of 0.46 ml min− 1 resulted in dissolution rates of pure Hf and pure Ta in the ng s− 1 cm− 2 and pg s− 1 cm− 2 range, respectively. For both species, the average dissolution rate was independent of the compositional gradient, indicating a dissolution enhancement of minor species. A decrease in their activation energy for dissolution triggered by a surface energy modification was the reason for the observed behavior.

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