Configured Semiconductor/Insulator Coatings For Corrosion Prevention
Semiconductor and insulator coatings, appropriately configured in Metal-Semiconductor (MS) and Metal-Insulator (≈20–100Å)-Semiconductor (MIS) structural formats, are shown to result in the formation of a built-in active electronic barrier on metal surfaces. This interfacial electronic barrier impedes the transfer of electrons from the metal to oxidizing species present at the metal surface, thereby providing protection against corrosion. The effectiveness of the electronic barrier concept has been confirmed using weight-loss, and cathodic and anodic polarization measurements on aluminum samples coated with indium tin oxide ITO (semiconductor) and SiO2 (thin oxide/insulator) films. In particular, Al-ITO, Al-ITO-Si3N4, Al-SiO2-ITO, and Al-SiO2-ITO-Si3N4 structures were fabricated and tested in a 1% NaCl, pH-2 solution. The films were grown using chemical vapor deposition (CVD) and spray techniques to ensure high quality and reproducibility. Aluminum samples tested included commercial purity, high purity (polycrystalline and single crystalline), and alloy (7075-T6). The MS and MIS configurations were found to provide superior corrosion protection as compared to conventional insulating films (e.g., Al-Si3N4). The active electronic barrier approach is a generic methodology to inhibit corrosion, and it can be realized using other semiconductor/insulator combinations including semiconducting polymer coatings.