Abstract
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.
Highlights
During braking, the wear debris, which contains several hazardous elements, has been recently proven as a threat to human and aquatic life [1,2,3]
We found that rare earth lanthanum oxide can significantly improve the mechanical and tribological properties of the brake composites
This study aims to use its findings as a guide to the development of Cu -free, metal-free and eco-friendly brake composites
Summary
The wear debris, which contains several hazardous elements (e.g., copper, lead, zinc, antimony), has been recently proven as a threat to human and aquatic life [1,2,3]. In 2010, California and Washington State pioneered new laws to restrict copper and other heavy metals in brake pads [4]. The development of copper-free, metal-free and eco-friendly brake composites will be a trend in this field. The non-metallization of the polymeric matrix brake composites must be realized by looking for substitute materials of copper. Copper is an important component in polymeric matrix brake composites and plays a crucial role in the friction properties of the brake composites. The positive effects of copper on brake composites can be summarized in three aspects. Copper has high thermal conductivity and can effectively conduct away heat from the friction interface, contributing to the good heat resistance of the brake composites [5,6]. Copper is often used in the friction material industry as a solid lubricant
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