The Future is Here: Self-Healing Metal

self-healing_metalYou’ve heard of self-healing concrete, you’ve heard of self-healing polymers. And now, it seems that researchers at MIT have found a way to make metals heal themselves after tiny cracks form. As the latest in a series of materials that is capable of maintaining itself, this discovery could very well help pioneer the revolution in manufacturing everyone has been waiting for.

Led by graduate student Guoqiang Xu and professor Michael Demkowicz, the process of getting metals to heal themselves was made almost entirely by accident. The discovery first came when they were modelling a sheet of nickle and tiny microscopic cracks were applied. Once tension was applied, the cracks became smaller and then disappeared as the edges fused together.

crystallineApparently, the key has to do with the fact that most metals are composed of microscopic crystalline grains, the size and orientation of which affect the overall strength and characteristics of the material. Nickel has always been of interest because of its use in so many superalloys, many of which are used in harsh environments – jet turbines, deep sea oil rigs, heavy industry joints.

It turns out that the grains making these materials so strong are not as static as scientists thought. As the metal is pulled outward, the edge of the crystalline grains begins to migrate and can eventually fill in the crack completely. The migration of this crystalline boundary is what heals the gaps in the material. And while it is not exactly polymorphic alloy (see pic below), its certainly big news.

metal_fatigueAnd while researchers have only been able to reproduce this healing behavior with cracks at the microstructural level (known as disclination), these micro-defects are the source of much larger and sometimes catastrophic cracks and metal fatigue. The geometry of disclinations can actually reverse an applied force locally, which is how the tension leads to the metal pulling itself back together.

The team believes this newfound knowledge can be used to prevent superalloys from accumulating structural cracks that could lead to real damage with time. Materials could also be designed to direct damage into disclination-type structures, areas that could absorb damage and then heal themselves. Given time, it could even lead to metals that don’t weaken with age.

t1000Still, you shouldn’t be expecting something like this guy anytime soon! And be sure to enjoy this brief but poignant video of the self-healing effect in action:


The Future is Here: Self-Healing Concrete!

concreteBack in 2009, the US suffered a rather serious embarrassment as the American Society of Civil Engineers gave its national infrastructure a grade ‘D’. To make matters worse, they claimed that getting that grade up to a ‘B’ standard would require roughly $2.2 trillion worth of investment. So, any technology that might make repairing bridges, roads, and buildings easier, and perhaps cheaper, has been welcomed with open arms.

And this might just be a topical solution, not to mention a very impressive sign of things to come. Led by Chan-Moon Chung, a professor of chemistry at Yonsei University in South Korea, researchers have come up with a protective coating for concrete that seals up cracks when exposed to sunlight. Not only would this save billions in infrastructure costs, it would address a central problem civil engineers have always faced.

MODEL5_plus 1..1For starters, concrete is a strong and resilient substance, but a brittle one as well. Tiny fractures appear quite easily over time, and exposure to wind and rain cause these to expand. This new substance addresses that through the polymer microcapsules it contains, which melt when exposed to the sun and fill these in. What’s more, Chung says the agent is relatively inexpensive, and won’t freeze in winter.

And his is not the only proposed solution for a new “smart concrete” system. A team from the Delft University of Technology, in the Netherlands, has developed a living “bio-concrete”, which used a mixture that is impregnated with a bacteria called Bacillus megaterium to produce a crack-filling mineral, called calcite (calcium carbonate). And similar research is being conducted at Northumbria University and the University of Michigan. megaterium

But all of this may take a backseat to Michelle Pelletier of the University of Rhode Island who, along with URI Chemical Engineering Professor Arijit Rose, began work on a self-healing concrete back in 2010. In her specialized concrete matrix, micro-encapsulated sodium silicate is embedded and used as the healing agent, rather than a method that generates silicate.

When cracks form, these silicate capsules rupture and react with calcium hydroxide, which is already present in the concrete. These come together to form a calcium-silica-hydrate gel that heals the cracks and blocks the concrete’s pores, all in the space of about a week. According to Pelletier, this method is more cost-effective than the proposed calcium carbonate solutions and does not require an environmental trigger like sunlight or moisture, just pressure.

smart_concreteThe benefits of these new concepts for “smart concrete” present many benefits. Not only are they likely to save money in maintenance costs for cities everywhere, concrete can be infused with these repairing gels and manufactures cheaply. This puts them in contrast with other proposed “smart-materials”, which offer the possibility of being self-repairing but cost an arm and a leg to produce.