On the Volta potential measured by SKPFM – fundamental and practical aspects with relevance to corrosion science

Abstract

The Volta potential is an electron-sensitive parameter and describes the thermodynamic propensity of a metal to take part in electrochemical reactions. It has found widespread acceptance among corrosion researchers due to its connection to the corrosion potential and its easy measurability in local scale, being often used to study localised corrosion phenomena and micro-galvanic activities. The principle object of this paper is to provide a comprehensive, fundamental insight into the meaning of the Volta potential and to define a polarity convention of measured potentials by the scanning Kelvin probe force microscopy (SKPFM) in order to assess local nobilities in microstructures. Conditions to relate the Volta potential with the mixed-potential theory are discussed and a possible connection to corrosion phenomena explained. The limitations of the Volta potential as well as the SKPFM technique are also aimed to be explained, with some practical information to maximise the output of high quality data.

Corrosion inhibition of copper in ferric chloride solutions with organic inhibitors

“…This interpretation is, however, contradictory to what the potentiodynamic curves indicate and to the reported dominant anodic inhibition action of Trp + CTAB 37 , MBTA (though classified as a mixed-type inhibitor) 21 , and BTA 67 . We believe that the trend seen in the SKP results, namely the lowering of the Volta potential difference, is due to the chemical nature of the coatings, in particular oxygen vacancies and defects in the oxide films 50,68 . The chemical nature of the MBI-induced film is probably more complex.…”

“…The Volta potential is of electrostatic nature, does not account for chemical interactions, and therefore does not always correlate with the corrosion potential, in particular when the measurements are conducted in "dry" air 50,63 . Yet, it does reflect the tendency of a metal to corrode, and has therefore been used to study localized corrosion, micro-galvanic couples in the microstructure, coating/ paint delamination, and effectiveness of conversion coatings.…”

“…With MBI-inhibited solution, the film is evidently non-uniform (±0.15 V). With all inhibitors except MBI, the Volta potential difference at the etched surface was lower than that of Cu, suggesting that the films were positively charged 50 . In contrast, after exposure to an MBIinhibited solution, the Volta potential difference was on average higher than that of Cu, suggesting it was negatively charged, in agreement with the energy-dispersive X-ray spectroscopy (EDS) results showing that after exposure to MBI-inhibited solution, the film contained significantly more chloride (see Supplementary Table 4).…”

Influence of Aging on Corrosion Behaviour of the 6061 Cast Aluminium Alloy

“…It describes the driving force of a metal used in chemical or electrochemical reactions. If the tip is biased, low potential indicates that the cathodic region is protected, while high potential indicates that the anodic area is susceptible to corrosion [ 30 ]. Therefore, a high Volta potential indicates a low electrochemical nobility, and thus, the Volta potential value can be considered a standard for predicting corrosion behaviour.…”

Electrografting of 4-Nitrobenzenediazonium Salts on Al-7075 Alloy Surfaces—The Role of Intermetallic Particles

“…Intermediate positive potential figures were recorded for the Si domains. A much more detailed explanation on the nobility, polarity, referencing, and other precautions when working with SKPFM are provided in the seminal contributions reported by Örnek et al [ 50 , 51 ].…”