Physical Vapor Deposition (PVD) is a widely utilized process in various industrial applications, serving as a protective and hard coating. However, its presence in fields like fashion has only recently emerged, as electroplating processes had previously dominated this reality. The future looks toward the replacement of the most hazardous and toxic electrochemical processes, especially those involving Cr(VI) and cyanide galvanic baths, which have been restricted by the European Union. Unfortunately, a complete substitution with PVD coatings is not feasible. Currently, the combination of both techniques is employed to achieve new aesthetic features, including a broader color range and diverse textures, rendering de facto PVD of primary interest for the decorative field and the fashion industry. This review aims to outline the guidelines for decorative industries regarding PVD processes and emphasize the recent advancements, quality control procedures, and limitations.
Various formulations for electroless deposition, to obtain continuous nanometre-sized and micrometre-sized films of palladium on copper, were compared. We deposited ultrathin films using displacement plating formulations. We obtained continuous films with an equivalent thickness between 6 and 22 nm, measured by exploiting the K-ratio method with SEM-EDS of Pd layers. The Pd films obtained in this step of the work represent a cost-effective catalytic substrate. As a second step, we selected chemical plating as the procedure to obtain palladium films with a thickness in the micrometre range. An ammonia-based Pd chemical plating bath represent one of the most effective chemical plating formulations. To prevent copper substrates from being damaged by ammonia, displacement plating with palladium was also applied as a pre-treatment to make the use of these plating baths a viable way to obtain thicker palladium coatings. Palladium films showing good adherence, compact morphology, and a thickness over 1.5 μm were obtained, proving that the combination of two different electroless techniques was the key to develop a sustainable procedure for micrometre-sized palladium coatings, which could substitute electroplating of Pd in galvanic industry for decorative applications.
Steel is a cheap renewable material with many interesting properties but its presence in the electroplating sector is very limited due to adhesion difficulties. Stainless steel contains approximately 10.5% chromium, which forms a surface oxide layer that passivates the steel, making it resistant to corrosion [1]. It is the presence of this surface oxide film that makes it difficult to electroplate steel. The aim of electroplating steel is to refine it by depositing nobler metals of the desired color, such as ruthenium and gold. The activation of steel involves the remotion of the oxide layer. The main method of electroplating stainless steel is generally through the deposition of nickel, but the intensive use of nickel baths makes these processes inappropriate for the sustainability paths taken by the electroplating industry. Even when nickel-based galvanizing processes are not used, it is possible that steel objects do not pass the nickel release test. This is because the steel itself contains nickel, so the removal of the surface oxide layer during the electroplating process may facilitate the release of nickel. The nickel release mechanism is not yet fully clear but bring to allergenic issues in the final product [2]. We performed a systematic study electroplating various metals and alloys on steel to evaluate which one performed better as barrier against the release of nickel and shed light on this issue. The steel substrate was characterized microscopically and spectroscopically before and after the release test. The amount of nickel was evaluated in the solution that simulates human sweat to evaluate its release in µm·cm-2·week-1 according to the standard EN 1811:2015. The authors acknowledge Regione Toscana POR CreO FESR 2014-2020 – azione 1.1.5 sub-azione a1 – Bando 1 “Progetti Strategici di ricerca e sviluppo” which made possible the projects “A.C.A.L. 4.0” (CUP 3553.04032020.158000165_1385), “A.M.P.E.R.E.” (CUP 3553.04032020.158000223_1538), “GIGA 4.0” (CUP 3553.04032020.158000105_1242) and “GoodGalv” (3647.04032020.157000060). References [1] Olsson, C. O. A.; Landolt, D. Passive films on stainless steels—chemistry, structure and growth. Electrochim. Acta. 2003, 48, 1093-1104, doi:10.1016/S0013-4686(02)00841-1. [2] Yuan, J.P.; Li, W.; Wang, C.; Ma, C.Y.; Chen, L.X.; Chen, D.D. Nickel release rate of several nickel-containing stainless steels for jewelries. J. Iron Steel Res. Int. 2015, 22, 72-77, doi: 10.1016/S1006-706X(15)60012-7.
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