Silica sol–gel anchoring on aluminum pigments surface for corrosion resistance based on aluminum oxidized by hydrogen peroxide

• XRD and FTIR results proved that boehmite formed by H2O2 oxidized aluminum.
• FTIR proved that silica sol–gel anchored on aluminum surface by forming Al–O–Si.
• Encapsulated media pH between 9 and 10 conducted the best anchorage efficiency.
• High or low H2O2 proportion is unfavorable for anchorage.
• Opposite charges of sol–gel and boehmite on aluminum are favorable for anchorage.

The waterborne aluminum pigments were prepared by sol–gel encapsulation method using tetraethoxysilane and γ-aminopropyl triethoxysilane as precursors with H2O2 as anchoring agent. Fourier transformation infrared and X-ray diffraction results indicated that the boehmite formed by H2O2 oxidizing aluminum can successfully reacted with silanol to make the silica sol–gel film anchored on the aluminum surface in the encapsulation process. The reaction conditions were optimized and the products were characterized by scanning electron microscopy, optical microscopy and stability test. It was found that when controlling the pH value of encapsulation media at about 9.5 and H2O2 concentration of 5.1 × 10−5 mol/m2 of aluminum flake surfaces, the boehmite on aluminum flake surfaces carried a strong positive charge and the silica sol–gel film carried a negative charge, which conduct the most anchorage efficiency. A crack free, smooth and dense coating was formed and exhibited best corrosion resistance on the aluminum flake surfaces.