The main focus of current research in polymeric matrix brake composites is on searching out a replacement for copper, which has been recently proved to be a hazard to human health and the environment. In this paper, rare earth lanthanum oxide was explored for the replacement of copper in composites. The mechanism of the role of lanthanum oxide in brake composites to replace copper was analyzed. Four series of polymeric matrix brake composites with various amounts of copper (15, 10, 5 and 0 wt %) and rare earth lanthanum oxide (0, 5, 10 and 15 wt %) were developed, in which the copper was gradually replaced by lanthanum oxide in the formula. These series were characterized in terms of physical, thermo-physical and mechanical properties. The results show that lanthanum oxide can be successfully used as a replacement for copper in brake composites. Brake composites with 15 wt % lanthanum oxide that are copper-free are considered optimal, where tribo-properties are considered best. Compared with the addition of copper in brake composites, lanthanum oxide is more conducive to the formation of compacted friction films and transfer films, which is beneficial to the tribological properties of the brake composites. The addition of La₂O₃ to the brake composites can cause the reaction between La₂O₃ and Al₂O₃ to form LaAlO₃, and the reaction between Al₂O₃ and BaSO₄ can produce Ba18Al12O36 and Al₂SO₄ during the friction and wear processes, which can effectively improve the tribological properties of the brake composites at elevated temperature. This research was contributive to the copper-free, metal-free and eco-friendly brake composites.
Keywords: brake composites; copper; lanthanum oxide; polymeric; rare earth; tribological properties.