Rice husk as a natural ingredient for brake friction material: A pin-on-disc investigation

The addition of the rice husk in a new eco-friendly Cu-free brake pad formulation was investigated in this study. Rice husk (RH) is a natural agro-waste residue with relatively high silica content, which should display abrasive properties that are not easily found in other natural materials. In this study, tribological properties of three friction materials were investigated using a pin-on-disc (PoD) tribometer. The three formulations were prepared adding to a common composition, each one of the following components: 6 wt% of grinded rice husk (material code: F-RH); this same amount of rice husk, after heat treatment at 600 degrees C (material code: F-RHT); and finally 6 wt% of alumina (F-AL) in place of rice husk, respectively. This latter material was meant to characterize the specific role of the natural ingredient. During PoD tests the evolution of the friction coefficient was followed, along with the concentration of the emitted airborne particles. The F-RHT showed very promising properties, depending on the particular characteristics of the friction layer forming onto the pin surface. This layer turned out to be compact and it was highly covering the surface of the F-RHT material, thanks to the positive effect of the silica particles from RH. The F-RH featured good behavior in terms of low wear and low emissions. In both cases, the rice husk showed up as a potential valuable alternative as a natural brake pad ingredient.