Original Date: 04/24/2007
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Best Practice : Corrosion Inhibitors
The University of New Orleans, College of Engineering has obtained patents on the use of lithium as a corrosion inhibitor. It developed aluminum-lithium alloys that have improved corrosion resistance without the use of a coating or chemical treatment. The University of New Orleans, College of Engineering also developed a paintable chemical film treatment for aluminum alloys and is researching the use of scandium as a corrosion-resistant alloy (with aluminum) with exceptional weight and strength advantages.
Corrosion affects a metal’s strength, conductivity, durability, and resistance to external influences. Several different technologies have been used to combat this problem. Chromium, copper, lead, cadmium, and zinc metals are among the materials used as corrosion inhibitors. However, each of these has health issues associated with them. For a corrosion inhibitor to be effective, the surface of the metal being protected may have galvanic and passivity properties. Lithium can provide both of these properties.
The University of New Orleans, College of Engineering (UNO COE) developed the use of lithium with aluminum for a corrosion inhibitor. The UNO COE’s patented coating proved to make an aluminum alloy less reactive, less prone to corrosion, and with improved electrical conductivity. Also, using an aluminum-lithium (Al-Li) alloy allows for a lighter-weight aluminum alloy to provide the same structural properties as that of heavier aluminum alloys. With lithium alloyed into the aluminum creating an Al-Li alloy, it is determined that this alloy has all the properties of having the Al-Li coating provided on top of the metal. Heating this alloy also provides other properties due to the lithium migrating to the surface. Heating the Al-Li alloy to 350oC provides the best results; however, heating it over 600oC will vaporize the lithium and reduce corrosion advantages. In accelerated testing, a two-mil (thousandths of an inch) coating of Al-Li pigmented paint provided corrosion resistance that lasted up to 10 years. A chemical film- treated surface of aluminum is not as corrosion-resistant as a painted surface; however, it can be painted later to improve on the intermediate surface protection. Since aluminum is especially susceptible to saltwater corrosion, the Al-Li may provide substantial protection for aircraft. The UNO COE is studying this now.
The UNO COE is also studying methods that will prevent the effects a copper or copper-oxide-coated ship has on plants and wildlife. Copper-hull ships kill the surrounding plant life, causing the wildlife that feed on plants either die or leave. International researchers have developed Seal Coat™, an epoxy with embedded Teflon fibers. This method of antifouling and several others show promise. The UNO COE is studying whether this epoxy can be used in place of copper on ships to prevent the damage these ships have on their surrounding environment. The UNO COE is also studying the use of scandium, which acts as a natural corrosion-inhibitor for aluminum. This would mean aluminum-scandium-based alloys generally will not need paint or chemical film to resist corrosion. The alloy is strong, lightweight, and corrosion-resistant, making it ideal for maritime and aerospace applications.
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