Boron nitride particle filled paraffin wax as a phase-change thermal interface material

Wax (predominantly tricosane paraffin wax, with a melting temperature of 48°C) filled with hexagonal boron nitride (BN) particles (5-11 μm) was found to be an effective phase-change thermal interface material. The thermal contact conductance, as measured with the interface material between copper surfaces, decreased with increasing temperature from 22 to 48°C, but increased with increasing temperature from 48 to 55&C. The melting of the wax enhanced the conductance, due to increased conformability to the mating surfaces. For a given BN volume fraction and a given temperature, the thermal contact conductance increased with increasing contact pressure. However, a pressure above 0.30 MPa resulted in no significant increase in the conductance. The conductance increased with BN content up to 6.2 vol. %, but decreased upon further increase to 8.6 vol. %. The highest conductance above the melting temperature was 18 × 10⁴ W/m².°C, as attained for a BN content of 4.0 vol. % at 55°C and 0.30 MPa. Below the melting temperature, the highest conductance was 19 × 10⁴ W/m ².°C, as attained for a BN content of 6.2 vol. % at 22°C and 0.30 MPa.