New Titanium Alloy is Hardest Ever Discovered: Good News for Dodgy Hips

Gone are the days when a gentleman scientist of reasonable intelligence could singlehandedly make new scientific discoveries by mixing random chemicals together and seeing what happens. It is now rare for the lone genius to come up with a breakthrough in a classic Eureka! moment. Science, at its heart, is now a very collaborative endeavour. That isn’t to say that each scientist or group of scientists doesn’t desperately want to be the ones to make the kind of revelation that has their names mentioned in the same sentences as the word Nobel. Science is also extremely competitive; as it should be.

Another rare avenue of discovery is that of the accidental finding. Most of us have heard about Fleming and penicillin or Roentgen and x-rays, but these are most definitely exceptions to the rule of hard graft and incremental progress. Not so, however, in an open access paper published in Science Advances last week where Serendipity should perhaps be listed as first author.

Researchers at Rice University in Texas were working on creating new types of magnets made from a titanium-gold alloy. They needed to test the properties of their new magnet by grinding some up with a diamond-coated pestle and mortar; except, they couldn’t, it was too hard.

As we know, titanium is already pretty hard. It’s also very lightweight and so is the metal of choice for many high performance, top end applications. Very importantly, it is biocompatible, i.e. non-toxic, non-corrosive and has low ion formation levels in aqueous environments; this makes it ideal for dental implants and knee and hip replacements. Even titanium struggles under the pressure of daily life, though, and many artificial hips have to be replaced after a decade or so (which just makes me think: how amazing are our bones?!).

The new titanium-gold alloy, Ti3Au, is four times harder than pure titanium and has a very low coefficient of friction and so opens up the potential for prosthetic joints lasting as long as the human that houses them. Most crucially, the new alloy has retained the key property of titanium: osseointegration. This is where the living bone of the host is able to bind directly to the surface of the implant without there being any subsequent movement or slippage. It is this essential requirement that excludes other much harder metals and alloys from being used medically.

I find it absolutely fascinating the way you can combine two elements and get unusual properties from the resultant compound. Why would combining hard titanium and soft gold result in something super hard? It’s like when the people of the Stone Age realised you could combine copper and tin, two soft metals, and create bronze, an alloy much harder than either of its components.

In this instance the increase in hardness comes as a result of the atoms forming a rigid, cubic structure, the length of the bonds between the atoms being shorter and a higher valence electron density. No, me neither. Well it turns out that if something has a higher valence electron density then there are more electrons available to form lovely tight bonds with neighbouring atoms.

Applications of the new alloy are not limited to medical implants. Given that a diamond-coated pestle and mortar couldn’t break the stuff it’s no surprise to hear that there has been interest expressed from the drilling industry.

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