Metal-shell char particulate composites using copper-coated particles

Abstract

Optimum conditions to obtain uniform and continuous coatings of copper on 125 Μm size coconut shell char particles (by using Fehling formaldehyde solution, activating char surfaces by copper tartarate complex followed by copper coating) are reported. 30 wt % of copper, in the form of coatings with almost theoretical density, could be depostied on shell char particles in the present investigation. Copper-coated shell char particles were dispersed in Al-11.8 wt % Si alloy melts using the vortex method and the melts were poured into moulds to produce cast Al-alloy shell char particulate composites, with higher recoveries than those obtained with uncoated shell char particles. Copper shell char composites using coated char particles were also successfully made by powder metallurgy techniques. As a result of 4 wt % dispersions of coconut shell char in the as-sintered copper shell char composites (a) hardness decreases from 45 BHN to 35.7 BHN (b) density decreases from 7.9 g cm⁻³ to 7.06 g cm⁻³, (c) electrical resistivity increases from 5 Μ ohm cm to 10.05 Μ ohm cm in close agreement with calculated value, and (d) wear rate and friction coefficient under dry conditions decrease from 6.635× 10⁻¹¹ cm² and 0.250, to 3.89×10⁻¹¹ cm² and 0.129, respectively, suggesting that these composites can be used in antifriction applications. Repressing and annealing increases the density and hardness, and decreases the electrical resistivity values of the as-sintered pieces.