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Fabrication of High Thermal Conductivity Cu/Diamond Composites By Electrodeposition
Diamond has a very high thermal conductivity (1000-2000 W m-1 K-1). Metal/diamond composites have been extensively investigated for heat dissipation applications.1,2) Typically, metal/diamond composites are formed under high temperature and pressure conditions.3) However, composites made by sintering do not yield improved thermal conductivities because of the formation of gaps between the metal matrix and diamond particles due to low wettability. In comparison, fabrication of metal/diamond composites using an electrodeposition technique can be carried out at room temperature and atmospheric pressure, and there are no issues regarding wettability. We have already reported the fabrication of nickel/diamond composites by electrodeposition and an investigation of their thermal conductivities.4)
In this study, Cu/diamond composites were fabricated by electrodeposition and their thermal conductivity was evaluated.
Experimental
The Cu/diamond composite plating bath was prepared using a copper sulfuric bath (0.85 M CuSO4·5H2O + 0.55 M H2SO4) as the base, to which diamond particles (mean diameters of 10, 25, 45, 195 and 230 μm) were mixed. Electrodeposition was carried out under galvanostatic conditions. Pure copper plates were used for the cathode and the anode. The electrodes were arranged horizontally with the cathode set at the bottom position. First, diamond particles were precipitated on the cathode in the plating bath; electrodeposition was then carried out to fill the gaps between the diamond particles.
Surface and cross-sectional morphologies of the composites were observed by field-emission scanning electron microscopy (FE-SEM). A cross-section polisher was used to prepare cross-sectional samples. The thermal conductivity was calculated as a product of the density, specific heat capacity and thermal diffusivity. The thermal diffusivity was measured by a xenon laser flash thermal property analyzer.
In order to estimate the net current density during formation of the Cu/diamond composites, the Butler-Volmer equation was used. The exchange current density and the transfer coefficient were obtained from a Tafel plot.
Simulation of the thermal conductivity of the Cu/diamond composites was carried out using the Hasselman-Johnson equation, for comparison with the measured values.
Results and Discussion
Figures 1 and 2 show cross-sectional SEM images of the Cu/diamond composite at two magnifications. No voids or cracks were observed between the Cu matrix and diamond.
The thermal conductivities of the fabricated Cu/diamond composites were almost consistent with the simulation values. The largest value was 687 W m-1 K-1, using 230 μm size diamond particles with a diamond content in the composite of 61 vol%.
Estimation of the net current density during the formation of the composites will be discussed at the meeting.
References
1) J. Flaquer, A. Ríos, A. Martín-Meizoso, S. Nogales, H. Böhm, Computational Materials Science, 41, 156-163 (2007).
2) M-T. Lee, M-H. Fu, J-L. Wu, C-Y. Chung, S-J. Lin, Diamond & Related Materials, 20, 130-133 (2011).
3) H. Feng, J. K. Yu, W. Tan, Materials Chemistry and Physics, 124, 851-855 (2010).
4) S. Arai, Y. Tashiro, V. Hoang, Y. Suzuki, Abstract of the 220th ECS Meeting, #2337 (2011).