Protecting materials is necessary at sea. Many protective paints, however, are banned because they’re too toxic. Rik Breur is looking for environmentally friendly alternatives.
At the ‘Materials at sea’ symposium, he demonstrated that engineers can learn a thing or two from sponges.
”Protection of materials at sea is a bare necessity, just like a good choice of materials,” Rik Breur stated at last week’s symposium. The ocean is among the most aggressive environments for materials. Salts, high amounts of UV-radiation, and diverse sea organisms quickly corrode them. Sea pox, for instance, can be really nasty. They built calcium shells in the grid of a heat exchanger where seawater passes through. This causes all kinds of turbulence in the heat exchanger that in turn speeds up the corrosion.
And when the bottom of a ship is covered with algae and sea pox the ship uses more fuel and has a lower maximum speed. ”It can be lowered by as much as ten percent. That has a big economic impact, especially with big ships like oil tankers.”
At the moment paints with heavy metals and toxic organo-tin compounds prevent corrosion and growth of algae and pox on seafaring vessels. From a technical point of view these systems work well. ”Unfortunately there’s an environmental issue clinging to nearly each one of these effective methods,” Breur says.
Anti corrosives usually contain heavy metals like chromium and zinc. Moreover, growth-inhibiting paints often contain organo-tin compounds, which will be banned globally from 2003 onwards. In its quest for more environmentally friendly alternatives, TNO Industries is trying to learn from nature. Sponges in the ocean are never covered with algae and sea pox. ”They discharge some kind of chemicals to prevent that. So two of my colleagues got lucky and were able to go diving for sponges all over the world,” says Breur, a material science engineer who works for TNO in Den Helder and hopes to receive his doctorate from TU Delft this summer.
”In the end we managed to extract ten active chemicals from the sponges.” They turned out to be organic materials that are simple to synthesise and easily degradable in the environment.
The first tests with these chemicals were successful. Hardly any growth was detected on test areas on ships that sailed the oceans for more than a year. ”Currently, together with a paint producer, we’re developing a binder to make paint out of the materials from the sponges.”
Sugar coating
A ship not only needs this growth inhibiting paint, but also an environmentally friendly anti-corrosion layer. Breur uses bacteria to help prevent rusting. The bacteria is used to make a protectivephosphate layer that forms an oxygen barrier. ”It’s not a perfect system yet, but it does significantly inhibit rust formation. So the principle works,” says Breur.
Other types of bacteria can produce something like a sugar layer. This polysaccharide layer can be applied as a coating layer, but it’s also possible to incorporate it in the paint instead of the chromates. Until now, it’s been possible to increase the corrosion resistance as much as a factor seventy. ”We don’t know exactly why it works yet. So far all we’ve done is a feasibility investigation. The hardest part is applying the bacteria layers in a solid coating.” It would be ideal if the organism kept growing, creating a kind of self-restoring system with bacteria growing back when part of the layer breaks off.
Also, some bacteria have been proven to produce anti-corrosive compounds. Micro-organisms need small amounts of many kinds of metals for their metabolism. That’s why they have chemicals in their cells that can form complexes with very low concentrations of metals. Chemicals like that can be used as corrosion inhibitors because they catch metal particles and then precipitate on the surface. TNO is currently working with TU Delft biotechnologists to produce these chemicals in a bioreactor so that they can test them practically.
Breur expects that the chemicals he’s borrowed from nature will be used mainly on large ships. Small ships use less and less growth-inhibiting coatings with biocides. The use of paints containing copper and tributyl are already banned on ships smaller than 25 meters. ”You can protect small ships by cleaning them four times a year or by using extra smooth coatings. A ten percent increase in fuel use is much less of a problem for them than for large, unwieldy oil tankers.”
Protecting materials is necessary at sea. Many protective paints, however, are banned because they’re too toxic. Rik Breur is looking for environmentally friendly alternatives. At the ‘Materials at sea’ symposium, he demonstrated that engineers can learn a thing or two from sponges.
”Protection of materials at sea is a bare necessity, just like a good choice of materials,” Rik Breur stated at last week’s symposium. The ocean is among the most aggressive environments for materials. Salts, high amounts of UV-radiation, and diverse sea organisms quickly corrode them. Sea pox, for instance, can be really nasty. They built calcium shells in the grid of a heat exchanger where seawater passes through. This causes all kinds of turbulence in the heat exchanger that in turn speeds up the corrosion.
And when the bottom of a ship is covered with algae and sea pox the ship uses more fuel and has a lower maximum speed. ”It can be lowered by as much as ten percent. That has a big economic impact, especially with big ships like oil tankers.”
At the moment paints with heavy metals and toxic organo-tin compounds prevent corrosion and growth of algae and pox on seafaring vessels. From a technical point of view these systems work well. ”Unfortunately there’s an environmental issue clinging to nearly each one of these effective methods,” Breur says.
Anti corrosives usually contain heavy metals like chromium and zinc. Moreover, growth-inhibiting paints often contain organo-tin compounds, which will be banned globally from 2003 onwards. In its quest for more environmentally friendly alternatives, TNO Industries is trying to learn from nature. Sponges in the ocean are never covered with algae and sea pox. ”They discharge some kind of chemicals to prevent that. So two of my colleagues got lucky and were able to go diving for sponges all over the world,” says Breur, a material science engineer who works for TNO in Den Helder and hopes to receive his doctorate from TU Delft this summer.
”In the end we managed to extract ten active chemicals from the sponges.” They turned out to be organic materials that are simple to synthesise and easily degradable in the environment.
The first tests with these chemicals were successful. Hardly any growth was detected on test areas on ships that sailed the oceans for more than a year. ”Currently, together with a paint producer, we’re developing a binder to make paint out of the materials from the sponges.”
Sugar coating
A ship not only needs this growth inhibiting paint, but also an environmentally friendly anti-corrosion layer. Breur uses bacteria to help prevent rusting. The bacteria is used to make a protectivephosphate layer that forms an oxygen barrier. ”It’s not a perfect system yet, but it does significantly inhibit rust formation. So the principle works,” says Breur.
Other types of bacteria can produce something like a sugar layer. This polysaccharide layer can be applied as a coating layer, but it’s also possible to incorporate it in the paint instead of the chromates. Until now, it’s been possible to increase the corrosion resistance as much as a factor seventy. ”We don’t know exactly why it works yet. So far all we’ve done is a feasibility investigation. The hardest part is applying the bacteria layers in a solid coating.” It would be ideal if the organism kept growing, creating a kind of self-restoring system with bacteria growing back when part of the layer breaks off.
Also, some bacteria have been proven to produce anti-corrosive compounds. Micro-organisms need small amounts of many kinds of metals for their metabolism. That’s why they have chemicals in their cells that can form complexes with very low concentrations of metals. Chemicals like that can be used as corrosion inhibitors because they catch metal particles and then precipitate on the surface. TNO is currently working with TU Delft biotechnologists to produce these chemicals in a bioreactor so that they can test them practically.
Breur expects that the chemicals he’s borrowed from nature will be used mainly on large ships. Small ships use less and less growth-inhibiting coatings with biocides. The use of paints containing copper and tributyl are already banned on ships smaller than 25 meters. ”You can protect small ships by cleaning them four times a year or by using extra smooth coatings. A ten percent increase in fuel use is much less of a problem for them than for large, unwieldy oil tankers.”
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