a b s t r a c tTraditional bearing materials contain different amounts of lead (Pb) because of its friction reducing properties. However, in view of the negative health and environmental impact of Pb, there is growing emphasis on restricting the usage of Pb in engine bearings. Owing to this, new bearing materials that provide at least comparable tribological performance to that of Pb containing alloys are being developed and some new Pb-free materials are being already used in engine bearing applications. It is, however, still unclear how these new engine bearing materials would perform in mixed and boundary lubricated conditions. In this study, a block-on-ring test setup was employed to investigate the tribological performance of several bi-metal and multi-layer Pb-free bearing materials with different compositions of bearing lining and overlay plating. Pb-containing bearing material was also studied as a reference material. Friction and wear properties of these bearing materials were investigated and their wear mechanisms under lubricated conditions have been analysed. Bearing material with Polyamide-Imide based overlay containing graphite and MoS 2 exhibited better friction and wear properties than Pb-based and Al-Sn based materials. Pb-containing bearing material shows higher wear of material and Al-Sn based material has shown higher friction compared with the other test materials.

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and Pb contents of commercially available Ethiopian black tea (Wushwush, Gumero, and Black Lion) and their infusions were analyzed by flame atomic absorption spectrometry (FAAS). In black tea leaves the order of metal content was found to be: K (11503-13780 mg/kg) > Ca (3821-4419 mg/kg) > Mg (3219-3538 mg/kg) > Mn (1242-1421 mg/kg) > Fe (319-467 mg/kg) > Zn (20.2-21.6 mg/kg) > Cu (9.1-11.5 mg/kg). Co, Cd and Pb were too low to be detected by the method (FAAS). In tea infusion, prepared in a laboratory condition following Ethiopian tea making procedures, the range of metal contents was found as follows: K (110-124 mg/L) > Mg (14.5-16.3 mg/L) > Ca (10.0-10.7 mg/L) > Mn (8.5-13.4 mg/L) > Fe (0.98-1.56 mg/L) > Zn (0.098-0.100 mg/L) > Cu (0.038-0.063 mg/L). The metal contents of the black tea leaves were higher than those of tea infusions. The extraction was highest for K (47.1%) and lowest for Ca (12.5%).

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