An extract of juice from the fruit of date palms like the ones shown here in Morocco could be used as the basis of a nontoxic anti-corrosive agent for aluminum alloys commonly used in aircraft structures. (Source: Wikimedia Commons/Erg Chebbi)
Given what sugars and fruit juice can do to the enamel on one's teeth, this result is a surprise to me. I suppose teeth are far more porous than aluminum, which could explain some of the differences. Nevertheless, using juice extracts as a way to prevent corrosion as opposed to toxic materials--you can't argue with that kind of green development.
Beth, that is an interesting development. Using non-toxic organics will probably result in production processes that are less toxic as well. Then the issue is can we grow enough of the organic compound to keep up. I doubt that is an issue with dates.
Beth, it's not just a difference in porosity between tooth enamel and aluminum, it's the fact that they are entirely different physical and chemical structures. What happens between aluminum and the fruit juice extract is an electrostatic interaction, which is very different from what occurs between that extract and enamel.
@ Ann: Do you have the name of the tree (common or scientific)? A friend just came back from Morocco and mentioned a tree that's being promoted heavily for export products. I'm curious to see if it's the same tree.
@Ann: If you have access to the article, can you tell us what the Icorr is, with and without the coating?
Icorr is the corrosion current (usually measured in mA/cm²), and is directly related to the corrosion rate. For example, if Icorr without the coating is 4 times more than Icorr with the coating, then the coating reduces the corrosion rate by a factor of 4.
In an article released earlier this year, Dr. Gerengi showed that the extract of a certain South American hardwood tree could reduce the corrosion rate of low carbon steel in hydrochloric acid by as much as factor of 3.
While this research into "green" corrosion inhibitors is interesting, the effects documented so far have been relatively modest. Many commercial corrosion inhibitors and coatings can reduce corrrosion rates by a factor of 10 or more.
Also, there are cultural issues that might hamper the adoption of such "green" corrosion inhibitors. If I suggested to management that we begin using fruit juice as a corrosion inhibitor for aluminum, I doubt it would be taken seriously.
Dave, corrosion current density values (Icorr) appear several times in different contexts. Without an inhibitor it's 3.47, at 100 ppm it's 2.32, at 500 1.84, at 1500 1.25 and at 2000ppm it's 0.98. Regarding management not taking to the idea of using fruit juice, I think that has more to do with our Western culturally-induced industrial paradigms. People in other areas of the world, usually with a less complex economic infrastructure and greater reliance on local natural resources, take this research and its potential applications seriously. We have much to learn, or re-learn, it seems to me.
@Ann: Thanks for the data. It looks like this coating will reduce the corrosion rate by a factor of about 3.5 at the highest concentration.
I agree with you that a dismissive attitude towards natural products is a prejudice we can ill afford. That being said, it looks like, in this case, the performance of the natural product doesn't match the performance of industrial products.
@Dave: You are absolutely right that taking a dismissive attitude towards exploration of natural products as substitutes for industrial products is short sighted. Maybe this particular strain doesn't stand toe to toe with the industrial offering, but hopefully over time, with some research and exploration, it will.
I sense a bit of a recurring theme. Often mechanical designers turn to natural design to solve complicated physical problems. It seems "natural" that a chemist would turn to nature for clues to chemical problems. When considering all the lifecycle costs (including byproducts, disposal and toxicity issues) some "natural" solutions just might be better than existing "artificial solutions" in the long run.
Chuck, at present it's a potential OEM or aftermarket anti-corrosive coating on aluminum alloys used on automotive and aerospace components. Whether it could be incorporated into other materials hasn't been determined yet.
This is an interesting development indeed. But my question is how well does it prevent corrosion in an evironment of saturated salt solution, which is more typical of the road salt contamination in this southeast corner of Michigan. Our salt is more brutal than seawater, and it is present about half of the year, until it all washes away.
My other question is about the economics of the process as compared to other methods of protection.