Corrosion of steel, aluminum, and other structural metals erodes the safety and financial stability of industries and countries alike. Fighting corrosion in ships, tanks, planes, and equipment costs the Pentagon $22.9 billion a year. Corrosion costs advanced industrialized nations about 3.5% of GDP to replace damaged material and components, plus a similar amount due to lost production, environmental impact, disrupted transportation, injuries, and fatalities.

For generations, polymer paints have acted as a physical barrier to keep corrosion promoters such as salt water and oxygen away from steel and aluminum substrates. This works until the paint is scratched, chipped, or breached, and corrosion promoters enter the gap between the substrate and polymer coating. Then the coating can act like a greenhouse—trapping water, oxygen and other corrosion promoters—allowing corrosion to spread.

Placing sacrificial, reactive elements next to steel that will corrode first, such as zinc and galvanized coatings, is another strategy. This works until the sacrificial elements are used up and recoating must be done, usually after a few years. Cathodic protection, where a negative voltage is imposed on steel, can limit corrosion on pipelines or other stationary, continuous metal structures where voltage can be attached. But this can fail if it’s not properly insulated and voltage goes to ground.

For assets that demand long-term corrosion protection, stainless steel alloys work. But with stainless steel costing up to six times more than mild steel, this option is often cost prohibitive. Ideally, engineers, facility managers, and industrial paint contractors would want the long-term corrosion-resistance of a stainless steel part with the lower cost of coating application. A new category of Chemically Bonded Phosphate Ceramics (CBPCs) is now basically making this possible. Unlike polymer paints that simply cover a substrate, CBPCs essentially ‘alloy’ the surface.

Dr. Arun Wagh, a former materials engineer at Argonne National Lab, explains it like this. “When a dual-component spray gun mixes an acid phosphate with base minerals and metal oxides in a water slurry, a chemical reaction occurs on the surface of the steel substrate,” says Wagh. “A hand-held thermometer indicates a 10-12 °F temperature rise, as iron becomes a corrosion-resistant passivation layer of iron oxy hydroxide. Because the passivation layer is electrochemically stable, like gold and platinum, it does not react with corrosion promoters such as water and oxygen.”

Scanning electron microscopy indicates this passivation layer is about 20 microns thick. X-ray diffraction indicates this passivation layer is about 60% iron with components of phosphate, magnesium, silicon, hydrogen, and oxygen.

“History suggests that the new CBPCs passivation layer may resist corrosion indefinitely, as demonstrated by the Iron Pillar of Delhi,” says Wagh. “The Iron Pillar, a 7-meter high, 6-ton Indian artifact that has resisted corrosion for 1600 years with its original inscriptions still legible, has a virtually identical passivation layer to that of the new CBPC.”

In contrast to typical paint polymer coatings that sit on top of the substrate, the new ceramic coating bonds through a chemical reaction with the substrate, so slight surface oxidation actually improves the reaction. This makes it virtually impossible for corrosion promoters like oxygen and humidity to get behind the coating the way they can with ordinary paints.

The corrosion-resistant passivation layer is further protected by a true ceramic outer shell. This dense ceramic outer shell is impermeable to water, and resists impact, abrasion, chemicals, and fire. The ceramic outer shell forms simultaneously with the passivation layer and chemically bonds with it, after acid and base materials mix in the spray gun nozzle then react with the substrate surface. The dual-layer ceramic coating can be used both as a primer and a topcoat, and can be applied in a single pass that’s dry to the touch in a minute, hard dry in 15 minutes, and can be returned to service in an hour.

Though CBPCs such as these have proven themselves in the laboratory and in examples such as the Iron Pillar, Tony Collins knew that the effectiveness of the new material had to be compared to that of traditional anti-corrosion coatings. Duplicating a NASA corrosion test, these new CBPCs have been put to the test against 19 leading anti-corrosion coatings in a live corrosion test, viewable to the public by webcam. Coated samples were scribed, then exposed to 12 hours of sea spray, followed by 12 hours of sunlight (or the UV light equivalent). After 45 days, every other high-performance coating tested failed. Except for the rust on its scribe (gouge) line, the EonCoat sample looked the same as day one.

To monitor another ongoing corrosion test modeled on NASA’s sea spray test, the public can view, zoom, and control a live webcam at www.eoncoat.com. In the latest test, which has passed 120 days and includes brand names matched to numbers, 20 Q panels coated with a popular primer, topcoat, or the new CBPC are sprayed daily with corrosive seawater.

There’s nothing like seeing results with your own eyes. The product has gone more than 10,000 hours with no corrosion in a salt spray ASTM B117 test, but it is believed that engineers, facility managers, and industrial contractors will see value in comparing its effectiveness with leading brands. New CBPCs are a new approach to corrosion protection that should be looked into as aging plants, equipment, and infrastructure need to be safely maintained as long as possible.

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Defense Tech Briefs Magazine

This article first appeared in the December, 2011 issue of Defense Tech Briefs Magazine.

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