Mo 2C intermediate layers for the wetting and infiltration of graphite foams by liquid copper

Abstract

Since copper does not wet graphite foams (GFs), a method for the synthesis of Mo 2C coatings throughout the GFs was developed for improving the wetting between GFs and copper and for the preparation of GF/copper composites. The coatings were formed on the GFs in a reaction medium consisting of ammonium paramolybdate, which decomposed to fine MoO 3, in a mixture of molten NaCl–KCl salts. The formation mechanism and microstructure of the Mo 2C coatings on GFs were investigated. Then the microstructure, thermal conductivity and thermal expansion behavior of the obtained GF/copper composites were studied. Results indicated the formation of Mo 2C coatings occurred in two steps, namely, the reduction of MoO 3 to MoO 2 and the reduction of MoO 2 to Mo 2C. Copper was infiltrated into the Mo 2C-coated GFs without external pressure and the nearly pore-free GF/copper composites were obtained. The thermal conductivity of the composite with a density of 5.76 g/cm 3 reached 268.4 W/mK. Significant reduction in coefficient of thermal expansion of the composite compared with that of copper (8.91 versus 18.59 ppm/K) was obtained.