REVIEW 3 major objections 6 minor 1 references
Investigating the real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS
T0 review · 3 major / 6 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read A single-phase Al1.5TiVCr alloy corrodes incongruently: aluminum dissolves one to two orders of magnitude faster than vanadium, chromium, and especially titanium, which stays put until breakdown.
desk verdict First real-time element-resolved dissolution data for a CCA; the qualitative incongruent-dissolution story holds, but the quantitative partial currents rest on a valence assumption the paper's own XPS undercuts. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is atomic emission spectroelectrochemistry (AESEC), a scanning electrochemical flow cell whose outlet is coupled to an ICP-MS so that dissolved Al, Ti, V, and Cr are quantified continuously during open-circuit exposure and potentiodynamic polarization. Measured ion concentrations are converted to instantaneous mass dissolution rates via v_M = C_M f / A, and then to partial elemental current densities i_Mx+ via Faraday's law using fixed oxidation states (Al3+, Ti4+, V3+, Cr3+). The sum itot is compared with the potentiostat current ipstat to infer surface film formation. X-ray photoelectron spectroscopy depth profiling, using argon cluster sputtering, supplies the companion surface film composition and metal/oxide balance. The machinery's work is to make element-specific dissolution rates visible in real time, which no conventional electrochemical test can do.
What would settle it
Run the same AESEC polarization while measuring dissolved vanadium and chromium speciation (e.g., by ion chromatography coupled to ICP-MS, or by UV-vis on collected fractions). If dissolved V is predominantly V5+ and Cr is Cr6+, then the reported iV3+ and iCr3+ values would need to be multiplied by roughly 5/3 and 6/3, respectively, which could shift the relative dissolution rates and the inference of which element dominates.
Extended reading notes
Core claim
The central claim is that dissolution of the single-phase CCA Al1.5TiVCr is incongruent in real time and in situ. In quiescent 0.1 M NaCl, the partial ion dissolution currents follow iAl3+ >> iV3+ >> iCr3+ > iTi4+ at open circuit; during potentiodynamic polarization, Al3+ remains the dominant dissolved species, Cr and V show distinct increases at around +0.3 and +0.45 V, and Ti4+ only rises sharply at ~+0.7 V SCE, the alloy breakdown potential. Since itot < ipstat at all times, not all applied charge goes into metal dissolution; a surface film forms. XPS reveals that film is principally Al oxide, with the less reactive elements partly trapped as unoxidized metal, and that the outer film after polarization is more fully oxidized. The paper presents this as the first AESEC study of a CCA and as direct validation that CCA corrosion involves incongruent dissolution.
Load-bearing premise
The reported dissolution currents are computed from ICP-MS mass fluxes using fixed oxidation states (Al3+, Ti4+, V3+, Cr3+), yet the paper's own XPS data show vanadium and chromium reaching higher valence states after polarization, so if those higher charges are the ones dissolving, the calculated currents and the element ranking would change.
Editorial extensions
If this is right
- The element-resolved dissolution rates provide a quantitative basis for predicting selective leaching from CCAs: aluminum is the preferential anodic species, so Al-rich CCAs may lose load-bearing Al while retaining Ti, V, and Cr in a surface film.
- Because itot < ipstat throughout, the passivity of Al1.5TiVCr is consistent with film formation consuming most of the anodic charge; equivalent corrosion models that assume all charge goes to dissolution would overestimate the corrosion rate for this alloy.
- The near-zero Ti dissolution until ~+0.7 V SCE identifies titanium as a key stabilizer of the film: if Ti's repassivation contributes to suppressing V, Cr, and Al release, alloy designs that raise Ti content should improve resistance.
- The XPS finding of unoxidized metal inside the surface film means that the film is not a simple passive oxide; any model of CCA passivity must account for a mixed oxide-metal layer whose protective character is not yet mechanistically explained.
Reading between the lines
- If oxidation states shift as XPS suggests (V to V4+/V5+, Cr to higher valence) during polarization, the true partial currents for V and Cr would be larger than reported, potentially closing some of the gap with aluminum; the element ranking might change if this correction were applied.
- The same AESEC+XPS protocol could be applied to other single-phase CCAs to test whether the 'aluminum-first, titanium-last' pattern is general, or whether it is controlled by the relative Gibbs energies of oxide formation of the constituents.
- The observation that the outer surface film after polarization is almost fully oxidized, while the native film contains substantial metal, suggests a testable prediction: pre-polarized surfaces should show different early-stage dissolution kinetics than as-polished surfaces, because the oxide/metal balance differs.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports the first application of atomic emission spectroelectrochemistry (AESEC, using inline ICP-MS) to a compositionally complex alloy, Al1.5TiVCr, in 0.1 M NaCl. Element-resolved dissolution rates (iAl3+, iTi4+, iV3+, iCr3+) are measured during open-circuit exposure and potentiodynamic polarization, and the results are correlated with XPS depth profiles of the native and post-polarization surface films. The paper claims that dissolution is incongruent, with Al dissolving 1–2 orders of magnitude faster than V, Cr, and Ti; that Ti does not dissolve appreciably until breakdown near +0.7 VSCE; that the sum of partial currents itot remains below the applied current ipstat, indicating surface film formation; and that XPS shows a surface film dominated by Al oxide with unoxidised metal present for all four elements. The authors conclude that this demonstrates, for the first time, element-resolved real-time dissolution behavior for a CCA.
Significance. If the results hold, this is a valuable methodological contribution: it extends AESEC to CCAs and provides direct, element-resolved evidence of incongruent dissolution in a single-phase multi-principal-element alloy, with supporting surface chemistry from XPS. The qualitative picture—preferential Al dissolution, suppressed Ti dissolution, and a film enriched in Al oxide with metallic species—is consistent with prior indirect work and is likely to be of interest to the corrosion and high-entropy alloy communities. However, the quantitative partial currents and the associated claims of precise dissolution rates depend on assumed oxidation states for dissolved ions, which the manuscript itself flags as uncertain; this limits the strength of the quantitative conclusions as currently presented.
major comments (3)
- [Methods (AESEC); Results; General discussion] The conversion of ICP-MS elemental mass fluxes to partial current densities (iAl3+, iTi4+, iV3+, iCr3+) via Faraday's law assumes fixed oxidation states (Al3+, Ti4+, V3+, Cr3+). The manuscript's own XPS data (General discussion; Fig. 3d) show that the fraction of V4+/V5+ in the surface film increases from ~30% to ~60% and that Cr5+ also increases after anodic polarization. If dissolved V and Cr carry higher charges (e.g., V5+ or Cr6+), then iV3+ and iCr3+ are systematically underestimated—by up to ~67% for V and ~100% for Cr. This directly affects the quantitative claims in the Conclusions that Al3+ dissolution is 1–2 orders of magnitude greater than V, Cr, and Ti, and the 'ground truth dissolution rates' wording in the Results. Please provide a sensitivity analysis for the assumed valences or clearly frame the partial currents as lower-bound estimates, and temper the 'ground truth' language.
- [Results (Fig. 2b/c)] The inference that itot < ipstat at all times indicates the development of a surface film rests on the sum of partial currents computed under the same fixed-valence assumption. If V and Cr dissolve with higher valences, itot would increase and the margin below ipstat would shrink, weakening the quantitative support for the film-formation inference. In addition, ipstat includes non-faradaic contributions (capacitive charging, film growth), so the comparison should be discussed with this caveat. The qualitative conclusion that a film is present may still hold, but the quantitative statement as written is not robust without addressing these effects.
- [Methods (AESEC); Results (Fig. 2)] The claim that Ti essentially does not dissolve until breakdown near +0.7 VSCE is based on Ti concentrations that may be close to the ICP-MS detection limit (0.5 µg/L for Ti, as stated in Methods). Without presenting the raw concentration profiles or signal-to-noise information, it is not clear whether the reported Ti dissolution is truly negligible or merely below the instrument's detection capability. Please include detection-limit-relative data or error estimates to support the 'essentially no dissolution' statement.
minor comments (6)
- [Title/Abstract/Methods] The method is called 'atomic emission spectroelectrochemistry (AESEC),' but the experimental setup uses ICP-MS, which measures mass spectra rather than atomic emission. This terminology is historically associated with ICP-OES; please clarify the relationship or use a more accurate descriptor such as 'inline ICP-MS spectroelectrochemistry.'
- [Fig. 3 caption and text] The 'repeat' test after 60 min of etching compares a native surface briefly exposed to air with an anodically polarized surface kept under vacuum for three days; these two conditions differ in both prior electrochemical history and storage environment, so the comparison of re-oxidation behavior should be qualified accordingly.
- [Results, paragraph 3] The sentence 'It is noteworthy that Ti4+ is the fastest metal cation that reaches to a lower and stable ion dissolution current' contains a grammatical error ('reaches to') and is ambiguous in meaning; please rephrase for clarity.
- [Throughout] The term 'in-congruent' is used with a hyphen; the standard spelling is 'incongruent' (also in the Conclusions).
- [General discussion] The phrase 'the precise quantification of ion dissolution rates indicates the corrosion rate' is imprecise because only anodic dissolution is measured; suggest using 'anodic dissolution rate' to avoid implying that cathodic or other contributions are included.
- [References] The introduction cites the 2004 Yeh paper for the HEA concept; for readers, a more recent review of HEAs and CCAs (beyond the authors' own references) would improve context.
Circularity Check
No circular derivation: the dissolution measurements are new inline ICP-MS data, and the fixed-valence assumption is a stated limitation rather than an input–output equivalence.
full rationale
The paper's derivation chain is not circular. The central claims—incongruent dissolution with Al3+ dominant, minimal Ti until breakdown, and XPS-detected surface oxide with unoxidized metal—are supported by two independent measurements: real-time element-resolved ICP-MS mass fluxes (Methods, AESEC) and XPS depth profiles (Figure 3). The conversion of ICP-MS mass fluxes to partial currents via Faraday's law uses fixed ionic charges (Al3+, Ti4+, V3+, Cr3+); the paper explicitly flags that ICP-MS cannot determine oxidation state and that V and Cr valences may change during polarisation (General discussion). That is an acknowledged accuracy limitation, not a circular step: the assumed valences are not derived from the dissolution conclusions, nor do the conclusions define the valences. Self-citations (refs 4, 11, 21) provide alloy identity and XPS spectrum-fitting conventions from prior work by the same group, but the dissolution data are new, direct, and measured in this study, and the AESEC methodology is attributed to external work by Ogle (refs 14–16). No quantity is fitted to a subset of data and then predicted; no uniqueness theorem is invoked; no conclusion is equivalent by construction to an input. The fixed-valence assumption could bias the quantitative partial currents, but this is a scientific accuracy risk, not circularity. Accordingly, no circular step is identified.
Assumptions & free parameters
free parameters (1)
- Assumed oxidation state of dissolved ions for Faraday conversion =
Al3+, Ti4+, V3+, Cr3+
assumptions (3)
- standard math Faraday's law with fixed ion charge converts measured mass flux to equivalent current density.
- domain assumption The ICP-MS mass flux corresponds to dissolved ionic species, with no significant loss to particles or undetected species.
- domain assumption The as-arc-melted Al1.5TiVCr is single-phase B2 as verified by EBSD and TEM, and the observed behaviour reflects that single phase.
Cite this review
Pith. "Pith review of Investigating the real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS." pith.science (2026). https://pith.science/paper/HXLYIA63
@misc{pith2026190804493,
author = {Pith},
title = {Pith review of: Investigating the real-time dissolution of a compositionally complex alloy using inline ICP and correlation with XPS},
year = {2026},
howpublished = {\url{https://pith.science/paper/HXLYIA63}},
note = {Machine review of arXiv:1908.04493}
}
read the original abstract
The real-time dissolution of the single-phase compositionally complex alloy (CCA), Al1.5TiVCr, was studied using an inline inductively coupled plasma method. Compositionally complex alloys (CCAs), a term encompassing high entropy alloys (HEAs) or multi-principal element alloys (MPEAs), are - in general - noted for their inherently high corrosion resistance. In order to gain an insight into the dissolution of Al1.5TiVCr alloy, atomic emission spectroelectrochemistry was utilised in order to measure the ion dissolution of the alloy during anodic polarisation. It was revealed that incongruent dissolution occurred, with preferential dissolution of Al, and essentially no dissolution of Ti, until the point of alloy breakdown. Results were correlated with X-ray photoelectron spectroscopy, which revealed a complex surface oxide inclusive of unoxidised metal, and metal oxides in disproportion to the bulk alloying element ratio.
Reference graph
Works this paper leans on
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[1]
Data availability All relevant data are available from authors upon reasonable request
Al, Ti, Cr and V. Data availability All relevant data are available from authors upon reasonable request. 9 Acknowledgements We thank the Monash Centre for Electron Microscopy (MCEM). Dr. Mark Gibson is also gratefully acknowledged for technical assistance with alloy production. Author contribution Yao Qiu : D esigned the alloy, did all the electron micro...
work page 2004
Reviewed August 14, 2026 · model on record in the stance chip above.
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