Abstract
Al/Ni bimetallic core-shell pigments with flake Al particle as core and metallic Ni as shell were synthesized via a galvanic displacement method and studied with X-ray diffraction, scanning electron micrograph (SEM), specific surface area analysis (BET), thermogravimetry-differential thermalanalysis (TG/DSC), and visible-near infrared-infrared reflectance spectroscopy. The influence of reactant ratio (Al:Ni2+) and order of addition on phase structure, surface morphology, optical properties, and high temperature oxidation resistance properties were studied systematically. The results show that the local concentration of Ni2+ at solid-liquid interfaces can be effectively modulated by adjusting the reactant ratio and order of addition. A high local concentration of Ni2+ improves the rate of displacement reaction resulting in more metallic Ni on the surface of the flake Al powders. This increases the relative content of Ni in the shell. The change of displacement reaction rate also leads to a different surface morphology and roughness of the Ni shell. The thick and rough Ni shell has a strong absorption extinction due to the intense light scattering and absorption-this substantially reduces the spectral reflectance of the flake Al core. Infrared reflectance in particular is influenced by light scattering and absorption of the rough surface. In addition, the Ni shell can enhance the high temperature oxidation resistance of the Al core by preventing contact between the metallic Al substrate and oxygen. The oxidation resistance is also associated with the processing parameters of the galvanic displacement reaction.
Highlights
Flake aluminum powders offer high spectral reflectance, good electric conductivity, excellent shielding capacity, and low cost
Bimetallic Al/Ni core-shell pigments have been synthesized with a simple galvanic displacement reaction
The relative content and surface morphology of the Ni shell mainly depends on the rate of reaction
Summary
Flake aluminum powders offer high spectral reflectance, good electric conductivity, excellent shielding capacity, and low cost. They are widely used in automobile metallized coatings, energy saving coatings, electromagnetic shielding coatings and infrared stealth coatings [1,2,3,4,5,6]. The galvanic displacement method is an effective method to prepare the bimetallic core-shell powder with controllability, high cladding rates, low costs, and simple processing [14,15,16]. The effect of processing parameters on phase structure, morphology, optical, and antioxidant properties of Al/Ni core-shell pigments were investigated systematically
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