In Section 2.1, the chemical modification of carbon fibers involves a strong oxidative treatment using CrO₃/H₂SO₄ at 343 K, followed by sequential reactions with NaOH and CuSO₄ to introduce carboxylate copper complexes. However, it is unclear if any post-treatment steps were implemented to fully remove or neutralize residual oxidizing agents, particularly Cr and S-containing species, prior to composite fabrication.
Given that Cr and S residues are known to significantly alter aluminum surface chemistry, promote localized corrosion, or interfere with interfacial bonding during high-temperature processing, could the authors clarify the following points:
Were any rinsing, neutralization, or purification steps carried out after each chemical treatment stage (especially after CrO₃/H₂SO₄ oxidation), and if so, what were the procedures and reagents used?
Did the authors conduct any surface or bulk elemental analyses (e.g., XPS, ICP-OES, EDS mapping with detection limits) to confirm the absence or quantify the level of residual Cr and S species on the CFs or in the final composites?
How do the authors ensure that the observed improvements in infiltration and mechanical strength are not influenced by unintended catalytic or corrosive effects of these residual elements during sintering at 903K?