Advanced Characterization of Silica–Encapsulated Aluminum Pigments

Abstract

For environmental reasons, the paints industry shifts from solvent-borne towards water-borne formulations. This change is challenging the business of aluminum pigments, as the hydrogen released by the reaction of aluminum with water degrades the optical properties, besides being a safety concern. In this work, industrial-grade aluminum pigments are encapsulated, by a well-known method, in a silica matrix by sol-gel process using isopropanol - a more suitable solvent for the industry. The effectiveness of the encapsulation process is proven by advanced physical methods (Scanning Electron Microscopy, Energy Dispersive X-Ray Analysis, Selected Area Electron Diffraction, Fourier Transformed InfraRed Spectroscopy, Thermo-Gravimetric Analysis) and by industry-relevant tests (stability in water, hiding power, flop and granulometry). Moreover, advanced surface-applied physical methods (High Resolution Transmission Electron Microscopy combined with Selected Area Electron Diffraction and Scanning Transmission Electron Microscopy, and FT-IR microscopy) clearly show the homogeneity of the resulting pigments, a quality which is highly desirable for practical applications. The results demonstrate that stability comparable to that of pigments passivized by chromium-based inhibitors is easily achieved, for a variety of operating conditions. However, accomplishing a homogeneous silica layer of the right thickness is the determining factor for good optical properties.

An overview of the science and art of encapsulated pigments: Preparation, performance and application

“…48 Results showed that in the transformation of liquid to solid interface (sol to gel) the sol microemulsion system was automatically demulsified, and the praseodymium-zirconium silicate pigment obtained a uniform spherical size of 0.785 μm, which was suitable for ink-jet printing. In a recent study by Dragnea et al, 49 a silica-encapsulated aluminum pigment was produced for industrial applications, where pigment homogeneity is a desirable property for the achievement of good optical properties.…”