Enhancement of the effective thermal conductivity of iron oxide‐coated hexagonal boron nitride/polyimide composite sheets using samarium–cobalt magnets

Abstract The orientation and distribution of the filler in hexagonal boron nitride (hBN) coated with iron oxide (Fe 3 O 4 @hBN)/polyimide (PI) composite sheets were controlled via magnetic field treatment (MFT) to enhance the effective thermal conductivity (TC) in the out‐of‐plane direction. Filler chain structures gradually formed in the direction of the magnetic field in the precursor solution. The effective TC of the Fe 3 O 4 @hBN/PI sheet after MFT was much higher than that of pristine hBN/PI. The effective TC of the composites was preferably improved by placing the sample near a one‐sided magnet instead of in the middle of a pair of magnets. The effective TC of 10, 20, and 30 vol% Fe 3 O 4 @hBN/PI composites improved by 59%, 53%, and 35%, respectively, compared to that of pristine hBN/PI for a magnet distance of 10 mm and with the sample placed 2 mm from the bottom magnet. These values are in good agreement with those reported in the literature using MFT. The tensile strengths of the 10, 20, and 30 vol% Fe 3 O 4 @hBN/PI composites prepared using MFT were 33%, 33%, and 22% lower, respectively, than those of the composites prepared without MFT.