Studies on the surface passivated aluminum nanoparticles and the characteristics of thermal spray coatings
NiAl composite thermal spray coatings can be used as the adhering substrate layer for ceramic coatings and as the anti-oxidation coatings. Aluminum particles of average size about 80 nm were prepared by evaporation-condensation method. Because of their high surface activities, these particles were passivated so to form a dense oxide membrane on their surfaces. Ni/Al clad powders were then obtained using the nano aluminum particles as the wrapping materials. SAXS (small angel X-ray scattering) was used to characterize the particle size of the nanometer aluminum powder. SEM, HRTEM and TG-DSC were employed to study the structures of the Al nano particles, the composite powder and the coatings. The results show that the composition and the coverings of the Ni/Al clad material is highly homogeneous, dense and complete. The melting reaction temperature is low and highly exothermic. The results further show that the coatings are of typical lamellar structure and with high binding strength with the substrate materials.