Development of environmentally friendly corrosion inhibitors for friction materials in automotive braking systems

The transport sector is a fundamental pillar of modern society and a cornerstone of industrial systems. However, it remains one of the primary contributors to environmental pollution, particularly through greenhouse gas (GHG) emissions associated with the extensive use of internal combustion engine (ICE) vehicles. In response to these environmental challenges, electric vehicles (EVs), including battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), have emerged as a viable solution due to their ability to eliminate tailpipe emissions. Despite this advancement, non-exhaust emissions, particularly particulate matter (PM10) generated by brake systems, remain a significant concern. Brake friction material wear is a major source of these particulate emissions and often includes environmentally harmful heavy metals such as copper and zinc. Furthermore, brake disc corrosion contributes to the release of pollutants, presenting additional environmental challenges. Addressing these issues is critical for the development of sustainable and environmentally friendly braking systems in the context of modern electric vehicles. In this frame, the integration of regenerative braking systems in electric vehicles (EVs) has significantly reduced reliance on traditional hydraulic braking systems, particularly in urban driving conditions, where regenerative braking accounts for approximately 90% of braking activity. This shift in braking system design necessitates the development of advanced friction materials that not only minimize particulate emissions but also exhibit enhanced wear resistance and effectively address corrosion-related issues, such as the stiction phenomenon. Specifically, the corrosion of gray cast iron brake discs can result in the strong adhesion of friction material to the disc surface, potentially compromising the reliability and performance of the braking system. To mitigate this issue, metallic zinc is commonly employed as an additive in current friction material formulations. However, regulatory measures, such as the European Union’s Euro 7 standards, are intensifying efforts to reduce brake particle emissions and limit the use of heavy metals in friction material compositions. Consequently, there is a growing need to identify and develop new, more environmentally friendly corrosion inhibitors that can replace metallic zinc in these applications. This highlights the urgent need to identify and develop environmentally friendly, green corrosion inhibitors as sustainable alternatives to metallic zinc. The focus of this thesis is on the development of environmentally friendly corrosion inhibitors for braking systems employing cast iron brake discs. In particular, inorganic as well as organic corrosion inhibitors have been considered, and their inhibition mechanism has been studied using complementary techniques. Furthermore, a new experimental technique, used to induce the stiction phenomenon at a laboratory scale, has been used to characterise the presented inhibitors. This thesis demonstrates that environmentally friendly corrosion inhibitors such as chitosan and phosphates can be effectively employed to limit corrosion issues in automotive braking systems.