Silica stabilized iron particles toward anti-corrosion magnetic polyurethane nanocomposites

A sol-gel method is used to introduce fluorescent silica shells with tunable thickness on the spherical carbonyl iron particles (CIP) by a combined hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Both gelatin B and 3-aminopropyltriethoxysilane (APTES) are used as primers to render the metal particle surface compatible with TEOS. The silica shell is formed through the hydrolysis and condensation of TEOS on the primer-treated CIP and the shell thickness can be controlled by varying the ratio of chemicals, such as TEOS and ammonia. The silica shell on the particle surface is confirmed by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The magnetic and anti-corrosive properties of the CIP and CIP-silica particles have been evaluated. A conformal coating shell is confirmed surrounding the CIP against their etching/dissolution by protons. Polyurethane composites filled with CIP and CIP-silica particles are fabricated with a surface initiated polymerization (SIP) method. A salt fog industrial-level test indicates an improved anti-corrosive behavior of the CIP-silica/PU composites than that of the CIP/PU composites. Both CIP-silica particles and CIP-silica/PU composites exhibit better thermal stability and antioxidation capability than their CIP and CIP/PU counterparts, respectively due to the stronger barrier effect of the noble silica shell. The insulating silica shell decreases the efficiency of the electron transportation among the particles and thus leads to a higher resistivity in the composites.