The electrochemical impedance spectroscopy （EIS） was used to evaluate the water transport and dielectric properties of polyurethane films filled with nano-TiO2 at different pigment/base （P/B） values in 0.5 mol/L NaCl solutions. EIS results were compared with gravimetric measurements on the freestanding films. The amount of water absorption showed great discrepancy between the two methods. The diffusion coefficient in the polyurethane film with P/B：30% was the smallest among those filled with nano-TiO2 pigments. The dielectric constant ε of the polyurethane varnish film obtained from the initial capacitance was in the range of typical values of polymers. SEM was used to measure the distribution of nano-TiO2 particles in the polyurethane films.
For a long time, chromate incorporated conversion coatings have been drawn special attention in corrosion protection of aircraft-used aluminum alloys. However, ever-increasing environmental pressures requires that non-chromate conversion coatings be developed because of the detrimental carcinogenic effects of the chromate compounds. In recent years, the sol-gel coatings doped with inhibitors were developed to replace chromate conversion coatings, and showed real promise; A sol-gel coating was prepared and its anti-corrosion behavior was investigated using the potentiodynamic scanning （PDS） and the electrochemical impedance spectroscopy （EIS）. It is found that the sol-gel coating obtained by the hydrolysis and condensation of 3-glycidoxypropyltrimethoxysilane （GPTMS） and tetramethoxysilane （TMOS） is prone to form defects if cured at the room temperature, whereas if cured at a higher temperature （100℃）, these flaws can be avoided. Furthermore, it can be seen that addition of anti-foam agents and surfactants will reduce the faults if cured at the room temperature. Effects of the corrosion inhibitors, CeCl3 and mercaptobenzothiazole （MBT）, in the sol-gel coatings on 2024-T3 aluminum alloy were also investigated. Results show that the corrosion resistance of the sol-gel coatings containing CeCl3 proves to be better than that of the pure and MBT added sol-gel coatings by the electrochemical methods.
SHI Hong-wei LIU Fu-chun HAN En-hou SUN Ming-cheng
