Study of electroplating processes and production sustainability of an electroplating plant

This PhD thesis was done within the FABER4 project, founded by Fondazione CR Firenze and supported by Fondazione per la Ricerca e l’Innovazione dell’Università degli Studi di Firenze and Confindustria Firenze. This PhD fellowship promotes the third mission of University: the technological transfer between the academic and the industrial world. Starting with this premise the work was done in collaboration with Materia Firenze Lab srl, an electroplating company specialized in electrodeposition of metal alloys on small metal parts for haute couture. The aim was to deepen the fundamental research on industrial metal alloys electrodeposition and multilayer engineering and transfer this knowledge to the factory counterpart, improving the production sustainability of the industrial counterpart. This leads me to understand how the market is evolving and if there are more sustainable competing technologies such as PVD. After analyzing this possibility and evidencing how PVD is not a competitor but a complementary technique, the state-of-the-art and criticalities of sustainability of a decorative electroplating plant were evaluated. Among the critical points highlighted, those addressed in this thesis include the improvement and study of barrier systems, knowledge of the mechanisms of action of additives within formulations and reducing the number and quantity of these additives. Barrier systems play a fundamental role in extending the lifetime of electroplated products, reducing waste, and improving the overall sustainability of the production chain. A cost-effective methodology was developed to characterize such barrier systems using XRF, EDS, and XRD allowing both evaluation of coating effectiveness and kinetic analysis of diffusion phenomena. Several barrier systems employed in high-fashion applications were tested, revealing that anticorrosion coatings are not necessarily effective as diffusion barriers, contrary to common industrial practice. Furthermore, investigations on gold coatings produced under varying current densities demonstrated a correlation between the activation energy of intermetallic diffusion, surface roughness, and crystallite size. Then, as a prototypical electroplating formulation to study additives action, acid copper was selected. Acid copper is central to both Ni-free decorative and electronic industries, yet contemporary bath formulations are still based on patents from the 1940s, which rely on sodium chloride and a trio of organic additives, making these systems complex and difficult to control. To develop a sustainable alternative, a standard AC formulation was modeled and characterized using EDS, XPS, XRD, SEM, and cyclic voltammetric stripping, with data interpreted through molecular dynamics and DFT simulations. Once the functional roles of traditional additives were clarified, L-cysteine (L-Cys) was tested as a single, environmentally friendly additive. The new formulation enabled bright, fine-grained, low-roughness copper deposits, as verified by AFM. DFT-based electronic structure analysis and AR-XPS measurements confirmed that the performance of L-Cys stems from its ability to adsorb planarly on the copper surface via both thiol and carboxylic groups, effectively combining the functions of conventional suppressors and accelerators. In order to perform the theoretical modelling organic additives of acid copper formulations, studies on charge transfer on organic molecules were conducted. In the first one, a DFT-based methodology to asses the charge transfer value on molecular co-crystals was proposed and verified: many population analyses and DFT levels of theory were benchmarked finding that long range corrected functionals coupled with DDEC6 population analysis can reproduce experimental charge transfer accurately. On the second one the IRAV response of radical polycyclic aromatic hydrocarbons was modeled and proved to be caused by the presence of a polaron and a giant IRAV VCD response due to a chiral polaron being theorized. This study was also centered on exploiting various DFT levels of theory, confirming the capability of long range corrected functionals in reproducing correctly the π-polarizability.