Development of AlN/AlO（OH） Composite Film with Enhanced Thermal Conductivity by the Steam Coating Process

To address growing demand for heat-dissipating components, AlN/AlO（OH）composite films were fabricated using the steam coating process on a commercially pure aluminum alloy. Thermally oxidized AlN particles that had been treated at 1050 ℃ and 1150 ℃ in air to impart water resistance were introduced into the process to improve the thermal conductivity of conventional AlO（OH）films. During coating, AlO（OH）crystals were formed not only on the aluminum substrate but also on the AlN particle surface. Particularly at higher oxidation temperatures, α-Al2O3 films that had formed on the AlN particles during thermal oxidation suppressed the conversion of AlN to AlO（OH）. The resulting composite films exhibited a dense interfacial structure, into which AlO（OH）crystals derived from both the substrate and AlN particles were co-integrated, thereby filling voids at the film/particle interface. The AlN particles possess higher intrinsic thermal conductivity than AlO（OH）. Their inclusion led to measurable improvement in the composite film's thermal conductivity. The greatest enhancement was observed in the composite film containing the largest volume fraction of AlN, obtained using AlN particles oxidized at 1050 ℃. Potentiodynamic polarization measurements of a 5 wt% NaCl aqueous solution showed that the composite films suppressed the current density by a factor of approximately 10−1 compared to the pure AlO（OH）film. Improved heat dissipation performance and densification via crystal growth are anticipated, highlighting the potential of this environmentally benign process for thermal management applications.