Xiaoqing Gao

Thermophysical properties of high-density graphite foams and their paraffin composites

Abstract High-density graphite foams (GFs) were prepared from mesophase pitch with or without mesocarbon microbeads at different foaming temperatures and pressures, followed by carbonization and graphitization at 1 273 and 2 973 K, respectively. In one case, pitch was repeatedly infiltrated into the graphitized foam at 573 K followed by carbonization to increase its density. Paraffin was infiltrated into the GFs to form GF/paraffin composites. Factors determining the thermophysical properties of the GFs and thermal behavior of the GF/paraffin composites were investigated. The microstructure and thermophysical properties of the foams were found to be greatly influenced by the pitch fraction, foaming temperature and foaming pressure. The thermal conductivity of the foams determines the thermal behavior of the GF/paraffin composites. The thermal diffusivity of the GF/paraffin composites investigated can be increased 768 to 1588-fold compared with that of paraffin. The latent heat of the composites has an almost linear relationship with the mass fraction of paraffin in the composites. The composites are suitable candidates for passive cooling of electronics.

Microstructure and properties of ultrasonic assisted copper coated graphite foams

Abstract Mesophase pitch based graphite foams were electroplated with copper to obtain the improved mechanical and thermal properties and to extend their applications in heat sinks. A nickel interlayer was electroplated prior to copper to improve the wettability and bonding between copper and the graphite foams. An ultrasonic oscillation device and a rotary cathode were applied to enhance the mass transfer and to ensure the more even coatings throughout the foams from inside. Microstructure and properties of the copper coated foams were studied. Results indicated the copper coatings greatly improved the mechanical and thermal properties of the foams. With the prolonged timescale of plating, the foams possessed enhanced mechanical and thermal properties. After 16 min. of plating, the bending strength of the foams increased from 1·1 to 7·6 MPa, and the thermal conductivity of the foams reached 100·2 from 81·6 W m−1 K−1, while the porosity was reduced only by 4·2%.