Fabrication and properties of carbon-matrix silver particle composites
Alex, Liju Varghese
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Carbon-matrix silver particle (flakes) composites in monolithic and thick-film forms that are superior to those of the prior art have been attained using a low-cost method of fabrication. The method involved a single cycle of carbonization of mesophase pitch powder that had been partly dissolved in a solvent, namely tetrahydrofuran. In the absence of a solvent for the pitch, the resulting composite was more porous and less hard mechanically. The porosity was lower and the pores were smaller for monolithic composites than for similarly prepared thick-film (on alumina) composites. The silver addition decreased the electrical resistivity, increased the thermal conductivity and decreased the specific heat. In relation to the electrical conduction behavior, the percolation threshold was at 6 vol. % for monolithic composites, compared to a value of 12 vol.% for thick-film composites of similar compositions, due to a reduction in pore size. The electrical resistivity attained ranged from 10 -4 to 10 2 ohm.cm for monolithic composites having 20vol. % silver to no silver. The thermal conductivity attained was up to 4.6 W/m.K (for monolithic composite containing 20.0 vol .% silver). The addition of glass powder (15 vol. %) enhanced the scratch resistance of the thick-film composites (the scratch width being reduced from 7 mm to 1 mm, as measured by scratch testing), though the electrical resistivity was increased and the percolation threshold was increased to 14 vol. %.