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| CSIRO | SOLVE | Issue 11 | MAY 07 | |
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ARTICLE
MATERIALS SCIENCE:
Coatings That Heal Themselves By Rebecca Thyer
Protective barriers that actively treat corrosion as it occurs could reduce maintenance costs and replace toxic materials now in useAn ambitious international research project to develop coatings that are responsive to their environment could substantially reduce maintenance costs and replace the toxic materials used in protective coatings. The coatings have applications in aerospace, pipelines, industrial plants and other types of infrastructure. Called ‘self-healing’ coatings, these protective barriers would be built to last for decades by actively treating damage, such as corrosion, before the performance of the system deteriorates. They could be used wherever recoating is difficult or expensive.
With two to five per cent of GDP in Western countries spent on mitigating corrosion each year, self-healing coatings could bring massive benefits across many industries, say researchers from CSIRO, its Dutch counterpart TNO, the Netherlands Organisation for Applied Scientific Research, and the Netherlands’ Technical University of Delft (TU Delft), who have joined forces to modernise the way coatings work. Self-healing coatings could have particular application in Australia, with its population concentration in coastal areas where corrosion is a major maintenance issue. CSIRO’s Dr Tony Hughes says that while heavy rain cleans surfaces, light rain and high humidity only moisten salts on surfaces and this promotes corrosion. Dr Hughes and TNO’s Dr Hartmut Fischer want to develop coatings that are responsive to their environment, unlike traditional coatings that are often engineered with built-in redundancy to cope with any situation that arises. As part of this brief, they also want to develop a coating that replaces chromate, which is used as a corrosion barrier for aluminium, magnesium and their alloys. Worldwide, environmental legislators now require that less-toxic alternatives be used. Dr Hughes says the need for a new generation of coatings is twofold. “We want to improve coatings to reduce maintenance requirements and also to replace the environmentally unfriendly and dangerous chemicals used as corrosion inhibitors,” he says. The concept of self-healing could take various forms from total repair to partial repair, where the coating is fixed for long enough for maintenance programs to respond. “It could also incorporate a signalling function to indicate to maintenance managers the health of the surface,” he says. The science behind self-healing coatings is to incorporate nano additives (microscopic particles) into special polymers. These additives, designed to function on a molecular scale, will have the capacity to change a coating’s properties in response to particular external or internal stimuli. Dr Hughes says that functionality may include different types of biological and corrosion inhibition properties to prevent damage, or diffusion and reconstruction properties for healing the polymer. “We have some ideas on what we want to work on,” he says. Dr Fischer, who is a senior researcher at TNO and also a lecturer with TU Delft, says the researchers are hoping to have a prototype in two years. He says the worldwide move towards self-healing materials is gaining momentum. “Globally, there are substantial efforts to understand the basics of self-repair systems. “There’s a big initiative in the Netherlands, with the government investing 10 million euros in it. They’ve also invested 2 million euros in the TU Delft program on self-healing materials.” Dr Fischer says self-healing materials are made viable by understanding the basics of material science. It is here that the research partners hope to make their mark, with each organisation bringing different but important skills to the project. CSIRO has already developed non-chromate replacement technologies for architectural and aerospace aluminium applications and will look to take this knowledge further.
Dr Hughes says CSIRO has a well-developed understanding of coated metal systems’ degradation mechanisms and of how particular electrochemical factors affect the interfaces and layers of a metal/oxide coating system. “Our research aims to integrate these aspects to develop chromate-free coatings with longer lives, lower toxicity and capacity to self-repair.” TNO and TU Delft will bring knowledge of encapsulation technology, controlled chemical release and basic concepts of self-repair based on different chemical and physical actions to the joint effort, says Dr Fischer. Dr Hughes and Dr Fischer say self-healing materials have the potential to transform material design to increase component life in critical applications. “This could add value and increase competitiveness of final products by increasing longevity and reducing maintenance costs.” For further information contact: |
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