Oxidation barrier of Cu and Fe powder by Atomic Layer Deposition

Atomic Layer Deposition (ALD) is a vapor based technique which allows to deposit uniform, conformal films with a thickness control at the atomic scale. In this research, Al2O3 coatings were deposited on micrometer-sized Fe and Cu powder (particles) using the thermal trimethylaluminum (TMA)/water (H2O) process in a rotary pump-type ALD reactor. Rotation of the powder during deposition was required to obtain a pinhole-free ALD coating. The protective nature of the coating was evaluated by quantifying its effectiveness in protecting the metal particles during oxidative annealing treatments. The Al2O3 coated powders were annealed in ambient air while in-situ thermogravimetric analysis (TGA) and in-situ x-ray diffraction (XRD) data were acquired. The thermal stability of a series of Cu and Fe powder with different Al2O3 thicknesses were determined with TGA. In both samples a clear shift in oxidation temperature is visible. For Cu and Fe powder coated with 25 nm Al2O3, we observed an increase of the oxidation temperature with 300-400°C. For the Cu powder a thin film of only 8 nm is required to obtain an initial increase in oxidation temperature of 200°C. In contrast, for Fe powder a thicker coating of 25 nm is required. In both cases, the oxidation temperature increases with increasing thickness of the Al2O3 coating. These results illustrate that the Al2O3 thin film, deposited by the thermal ALD process (TMA/H2O) can be an efficient and pinhole-free barrier layer for micrometer-sized powder particles, provided that the powder is properly agitated during the process to ensure sufficient vapor-solid interaction.