Rapid industrialization is inevitable with the population boom and increased demand for goods. However, numerous serious repercussions accompany the growth of this magnitude, which includes waste generation. Currently, wastes are being disposed of in landfills, leading to soil pollution. However, the landfill option will soon be defunct due to the unavailability of free space and its corresponding negative effects on the environment. Hence, according to the waste management legislation in the European Union, it becomes rather imperative to find effective methods to dispose of generated waste without affecting human lives and the environment. Currently, the metallurgy industry produces a significant amount of industrial waste which needs to be urgently and suitably disposed of. However, due to their composition, these wastes are considerably lucrative. One such waste is ferrous slags obtained in steel and blast furnaces, which are currently used in road and building construction and fertilizer production. The steel slags mainly constitute a significant portion of Fe-based oxides, along with CaO, MgO, and MnO among other constituents. These slags require a basic pre-treatment procedure and are thermally stable, which makes them easy to incorporate into specific applications. Lately, due to their composition, slags are being introduced as an ingredient in friction materials intended to be used in automotive braking applications. Depending on their constituents, they can be assumed to effectively function like an abrasive. The studies with the slags essentially focus on friction and wear characteristics. However, the emission analysis of slag containing formulations is quite limited. Hence, keeping this in mind, this study aims at understanding the emission trends and the possibility of its corresponding reduction in a commercially employed, highly optimized friction material formulation with the addition of metallurgical slags from a basic oxygen furnace (BOF) in varying quantities from 6 to 38 wt.%. Initially, the BOF slag was extensively characterized using XRD, SEM, and EDS to gain knowledge of its composition. The friction, wear, and emission analyses on the different compositions were conducted on a pin on disc tribometer while paired with a pearlitic grey cast iron counterface. The testing conditions adopted were a contact pressure of 1 MPa and a sliding velocity of 1.51 m/s to replicate mild braking conditions. The friction coefficient and pin wear magnitude increased with the slag content, emphasizing the role of slag being abrasive. However, the friction and wear magnitudes were within the acceptable limit when compared to the original composition. With the increase in the slag content, a decrease in the emissions was significantly noticed. The average particle concentration dropped from 580 #/cm3 for the original composition to 250 #/cm3 for the composition containing 38 wt.% of slag. Furthermore, the worn pin surfaces were subjected to SEM/EDS analysis. The compositions containing higher slag content displayed extremely smooth, compacted, and extended secondary contact plateaus, which also saw significant slag presence. Through this pilot study, the effective role of BOF slag on the emission reduction of a commercial friction material formulation was highlighted, paving the path for the potential recycling of the waste and possible substitution of raw materials in the composition by slags, thereby leading to a sustainable process.
Dr. Priyadarshini Jayashree, Researcher, University of Trento; Prof. Vlastimil Matejka, Associate Professor, VSB - Technical University of Ostrava; Dr. Mara Leonardi, Materials Development Specialist, Brembo, Italy; Prof. Giovanni Straffelini, Professor, University of Trento, Italy