Chemically bonded phosphate ceramic coating on a metal substrate (black region) (50x original magnification). Credit: EonCoat
Corrosion is expensive. The cost of corrosion to industrialized nations is about 3 percent of GDP. In the United States that adds up to $2-4 trillion per decade, which equates to rebuilding Hurricane Katrina-scale infrastructure three or four times.
A recent online article published by Environmental Protection reports on a new protective coating based on chemically bonded phosphate ceramics. CBPCs are a class of materials that were developed originally at Argonne National Lab (pdf) and Battelle (pdf) to stabilize mercury-containing DOE wastes. A Raleigh-Durham Research Triangle company, EonCoat, has picked up the technology and developed it into a corrosion resistant coating.
The DOE reports linked above describe the CBPC acid-base synthesis reaction between magnesium oxide and a mono-potassium phosphate solution (KH2PO4). The chemical reaction yields MgKPO4-6H2O, a hard, dense material.
The EonCoat product is applied as a two-component system that is sprayed simultaneously in a 1:1 ratio using standard plural spray equipment. The components react with the substrate in a mildly exothermic reaction, which “creates an alloyed metal surface rather than a layer that sits on top of the substrate,” the EP story says, and that “makes it virtually impossible for corrosion promoters like oxygen and humidity to get behind the coating…”
The coatings have the additional advantage of being able to accommodate flexure up to 19 percent. According to the company website, “fibers and fillers with an acicular structure…create toughness and additional ductility (flexibility).” Most ceramics cannot accommodate such additives because they burn during firing, however the heat released by the CBPC synthesis reaction raises the temperature by only 7-40 °C, which is survivable by a wide range of additive materials.
EonCoat has found that the chemical reaction works best when the steel surface is slightly oxidized, so surface preparation is modest. A commercial blast (NACE 3) or high pressure water blast (NACE 5) is enough.
Coatings for corrosion protection are 3-9 mils thick and cost about $1.50 per square foot. The coatings also can be applied for chemical resistance (6-20 mils) or severe abrasion resistance (5 mils to 0.25 in.) with commensurate costs.
The National Academy of Engineering released a report last fall titled “Research Opportunities in Corrosion Science and Engineering,” that summarized the corrosion problem and identified grand challenges for corrosion research and opportunities for basic and applied research in corrosion. After a rigorous discovery process, four research “grand challenges” were identified. Paraphrasing, they are
1. Development of cost-effective, environmentally friendly corrosion-resistant materials and coatings;
2. Modeling to predict corrosion degradation in service environments;
3. Accelerated corrosion testing correlated to long-term behavior in service environments; and
4. Accurate forecasting of remaining service time, i.e., corrosion prognosis.
Bottom line, there is big money to be made in meeting the NAE’s first challenge to develop corrosion-resistant materials and coatings.