Surface modification for aluminium pigment inhibition

Preparation of the Yellow-Colored Aluminum Pigments with Double-Layer Structure Using a Crosslinked Copolymeric Dye

Colorization for fabricating aluminum pigments has broad application prospects in recent years. In this study, yellow-colored aluminum pigments with the double-layer structure Al@SiO₂@PFMV were prepared using a sol-gel method. A crosslinked copolymeric dye (PFMV) was firstly synthesized by radical polymerization using vinyl triethoxysilane (VTES) and a small molecular dye (FGMAC) as monomers. Then, colored aluminum pigments were prepared by hydrolysis and condensation of the copolymers on the surface of aluminum pigments. SEM, AFM, FTIR, and XPS were used to characterize the surface morphology and chemical structure of the colored aluminum pigments. It was found that the colored aluminum pigments have a heterogeneous and smooth surface layer. The anticorrosion results showed that the colored aluminum pigments had better chemical stability with significantly improving corrosion resistance compared to raw aluminum pigments and Al@SiO₂ with the single-layer coating. Chromatism analysis indicated that the lightness of Al@SiO₂@PFMV pigments decreased slightly and the color changed from silver-gray to yellow.

Preparation and Angle-Dependent Optical Properties of Brown Al/MnO2 Composite Pigments in Visible and Infrared Region

Traditional low infrared emissivity coatings based on aluminum flakes cannot own low IR emissivity and low lightness simultaneously. Herein, a new simple efficient method for the synthesis of brown Al/MnO₂ composite pigments with low IR emissivity and low lightness is reported, through forming MnO₂ layer on aluminum flakes by thermal cracking, then altering the shape and forming nanoshell by stirring in hot flowing liquid. The results indicate that the MnO₂ particles, which have tetragonal structure with high crystallinity, are needlelike and forming a complete shell on the aluminum flakes. The optical properties of composite pigments can be tuned by mass of KMnO₄ added in precursor and time of hot flowing. Strong angle-dependent optical effects are observed in five different angles through multi-angle reflectance spectrum, while low lightness and low IR emissivity are preserved. This work is expected to provide a new route for the preparation of colored aluminum effect pigments in low infrared emissivity coatings.

Adsorption of sodium dodecyl sulfate and sodium dodecyl phosphate on aluminum, studied by QCM-D, XPS, and AAS

The adsorption of two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl phosphate (SDP), at surfaces of aluminum and aluminum oxide has been studied by means of atomic absorption spectrometry (AAS), X-ray photoelectron spectroscopy (XPS), and quartz crystal microbalance with dissipation monitoring (QCM-D). It was shown that more SDP than SDS binds to the surface and that SDP prevents dissolution of aluminum in water whereas SDS does not. This was not obvious, since the adsorption isotherms of the two surfactants to aluminum pigment powder are quite similar, as shown in an earlier work. The decreased aluminum dissolution with SDP compared to SDS was explained by the formation of a more compact protective layer with less permeability on the aluminum surface with SDP than with SDS. This is explained by differences in complexing ability between the surfactants and the aluminum pigment surface. While SDP is expected to form an inner-sphere complex with aluminum, leading to a lower accessibility of aluminum sites to water, SDS is likely to form a weaker outer-sphere complex.