Kinetic Effects of Alcohol Addition on the Anodic Behavior of Silicon in Acid Fluoride Media

Cattarin, Sandro; Musiani, Marco

doi:10.1021/jp055714g

Cited by 3 publications

(3 citation statements)

References 36 publications

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“…7 are obtained. On this basis, a simple qualitative explanation of the main experimental findings is possible: ͑i͒ under polarization, protons are produced at the electrode surface in Reactions 2 and 4 and cause a local pH decrease; ͑ii͒ due to chemical equilibria ͑Reactions 5 and 6͒, an increase in the concentrations of HF and HF 2 − results; these species attack and dissolve the TiO 2 surface in a reaction similar to that valid for SiO 2 , 12,13 producing, e.g., fluoride complexes…”

Section: Electrode Reactions and Acid-basementioning

confidence: 92%

Electrochemical Etching of NiTi Alloy in a Neutral Fluoride Solution

Cattarin

Guerriero

Musiani

et al. 2009

J. Electrochem. Soc.

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Electrochemical etching of NiTi alloy in a pH 6 fluoride solution is proposed as a convenient, less dangerous procedure than traditional chemical etching in oxidizing HF media. Anodic polarization produces protons at the electrode surface, and local acidification increases the concentration of HF that efficiently dissolves the surface oxides, promoting a sustained dissolution current that decreases with increasing mass-transfer rate. The voltammetric pattern includes a "pseudoplateau" at low potentials, in which only a metal dissolution takes place, and a steady current increase at higher potentials due to the onset of oxygen evolution. The treatment produces a semilustrous rough surface, showing a structure of shallow microscopic cavities in scanning electron microscopy images. Impedance spectra recorded in the pseudoplateau region are similar to those observed during anodic polarization of Ti in HF, and their analysis indicates a formation of a thin barrier film whose thickness increases linearly with potential.The NiTi alloy is a material of great technological interest because of its unique thermomechanical properties, 1 including an excellent shape memory effect, the ability to recover apparently permanent deformations of about 8-10% by heating, and superelasticity, with a pseudoelastic field of up to 10-12% in strain. For these reasons, the Ni-Ti alloy is successfully applied in manufacturing special devices for several industrial applications 2 and appears especially attractive in the biomedical field. 3 Due to the stability of Ni in alkaline media and of the native oxide TiO 2 in ordinary acids, only a few aggressive mixtures are suitable for chemical or electrochemical NiTi dissolution. The use of methanolic sulfuric acid has been recently proposed to perform electropolishing of freshly polished samples. 4,5 However, to efficiently etch aged and heated samples with a tough surface oxide layer, HF solutions are the media of choice. 6 HF is a very dangerous substance for the operator: it is a clear, colorless, volatile substance ͑with a boiling point of 19.5°C͒, and its small undissociated molecule penetrates tissues by nonionic diffusion, causing deep damage such as necrosis of soft tissues, bone erosion, and systemic poisoning. 7,8 ͓Search the Web for hydrofluoric acid safety information.͔ Even a trivial skin contact without immediate pain may cause severe delayed damage. Operation with HF requires strict safety measures, rigorous personnel training, and uncomfortable cohabitation with a severe risk. Neutral fluoride solutions are much less dangerous but are also ineffective etchants, so there seems to be an inherent contradiction between effectiveness and safety.Electrochemical treatments can change the local conditions at the electrode surface by current flow, e.g., the local pH by generation of protons or hydroxyl ions, and in some cases, this property may be used to drive in a desired way the chemical reactivity at the electrode/solution interface. This strategy has been recently applied to prepare h...

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Section: Electrode Reactions and Acid-basementioning

confidence: 92%

Electrochemical Etching of NiTi Alloy in a Neutral Fluoride Solution

Cattarin

Guerriero

Musiani

et al. 2009

J. Electrochem. Soc.

Self Cite

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“…On this basis a simple qualitative explanation of the main experimental findings is possible: (i) under polarization, protons are produced at the electrode surface in Reactions [2] and [4] and cause a local pH decrease; (ii) due to chemical equilibria (Reactions [5] and [6]), an increase in the concentration of HF and HF 2 results; these species attack and dissolve the surface TiO 2 in a reaction similar to that valid for SiO 2 (12,13), producing, e.g., fluoride complexes…”

Section: Electrode Reactions and Acid-base Equilibriamentioning

confidence: 94%

Electrochemical Etching of NiTi Alloy in a Neutral Fluoride Solution

et al. 2010

View full text Add to dashboard Cite

Electrochemical etching of NiTi alloy in a pH 6 fluoride solution is proposed as a convenient alternative to chemical etching in oxidizing HF media. Anodization produces protons at the electrode surface, and local acidification increases the concentration of HF that efficiently dissolves the surface oxides, promoting a sustained dissolution current that decreases with increasing mass-transfer rate. The voltammetric pattern includes a "pseudoplateau" at low potentials, in which only a metal dissolution takes place, and a steady current increase at higher potentials due to the onset of oxygen evolution. The treatment produces a semilustrous rough surface, showing a structure of shallow microscopic cavities in SEM images. EIS spectra recorded in the pseudoplateau region are similar to those observed during anodic polarization of Ti in HF and their analysis indicates formation of a thin barrier film of thickness increasing linearly with potential.

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“…This is due to the fact that on diluting the HF acid, the dissociation of hydrogen bonds present in the concentrated hydrofluoric acid, 35 contributes to an enhanced availability of fluoride ions attacking the silicon anode. Therefore, one can deduce that the amount of the internal noise is regulated by the concentration of the fluoride ions in the electrolyte solution.…”

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confidence: 99%