To Hf or Hf not? Who cares about Hafnium?
Perhaps the recent history of Hafnium can best illustrate the question – ‘What are minor metal merchants for?’
A minor metals trader of the 1970s, it is fair to say, could safely get through his career without breathing the two letters –‘Hf’. After all, the element was only first separated in 1923 and has few uses even today.
If pressed, today’s traders of Cobalt or Molybdenum, probably know of its application in the strategic world of nuclear physics where Hafnium’s property of repelling neutrons means it is used in control rods to slow the nuclear reaction. Perhaps they would also know of Hafnium’s high melting point of 2233°C.
But, today, applications are moving on swiftly. Not a hundred years since its discovery, Hafnium now has two growing non-nuclear uses. In plasma cutting tips and as an addition in directionally solidified alloys and single crystal alloys for the hot parts of gas turbine engines.
In the former, a tiny tip made of Hafnium is needed to survive the high temperatures generated by a spark between a negative electrode and the metal to be cut. In DS alloys the Hf migrates to grain boundaries, pins them, preventing movement / cracks / fracture / fatigue.
All well and good – ‘Let’s mine more Hafnium’, you might think; except that minor metals are rarely substances to be bought ‘off-the-shelf’ like Heinz Baked Beans. And in the case of Hafnium, there are no Hafnium mines…which makes it a long and circuitous journey from bean to can.
As with so many ultra-minor elements, metallurgists and engineers tend to devise outstanding uses for metals that can transform an industry. However, the same materials scientists are not paid to be concerned where they come from. Such is the case of Hafnium, where its growing use in complex alloys is gradually leading those who use it to ask – ‘Where does Hafnium come from?’ and ‘How much of it is available in the form needed in the market?’
So where does Hafnium come from? In nature, while rare, it is not the rarest – for it is found at 1 part to every 50 parts in Zirconia (1:50). With 1.2 mln tons of Zirconia mined each year there should be plenty. In fact, at 65% ZrO2, there should be 15,600 mt of the stuff. So why is there only 55mt produced per year?
It is, actually, a frustratingly simple question to answer. For, in all Zirconia’s main uses (ceramics, refractory bricks, catalyst substrates and others) hafnia is not deleterious. Therefore, it is not removed.
The only time it is recovered, is when nuclear grade Zirconium is required. So, let’s go back to our nuclear reaction. In the nuclear reaction, neutrons are used to bombard the weak Uranium atoms causing the atom to split and release further neutrons which split further uranium atoms (the chain reaction). Only Hafnium-free Zirconium may be used in the fuel assemblies which are used to contain the Uranium – because Hafnium would block neutrons and slow the reaction.
It is something of a startling fact to think this is the only reason that Hafnium is ever commercially generated and this is the cause of the great inelasticity in the market. Removing Hafnium is a costly process and, at the time of writing, no other route to its production is conceived of. So the world is reliant on those who carry out this process – and they are companies to be found in the great nuclear powers – USA, France and to some extent Russia. China is trying to de-hafniate but is not there yet.
All would perhaps be well. After all, the nuclear industry was until recently in something of an upturn and the need for more Zirconium would have generated more Hafnium. But then it was hit by two factors. Following the Fukushima Tsunami in March 2011, the world briefly stepped back from nuclear power. Japan closed all 48 reactors and Germany pledged to remove all of theirs by 2022. In other parts of the world, the so-called nuclear renaissance was stopped in its tracks.
From 6000mtpy of Zirconium production, the industry slimmed to not more than about 3000 mtpy, and with less Zirconium metal production, it will mean less Hafnium by-product and hence it seems likely that fresh Hf output will be no more than about 50mt – all of which could be easily consumed in turbine alloy orders.
Meantime, its growing use in super alloy is easy to understand. As turbines run hotter, those substances that assist the engine to withstand high temperatures are in greater demand, and so use of Hafnium-bearing alloys are applied to increase engine efficiency and reduce emissions. Key to this development, is the application of a series of alloys devised by Martin Marietta Corp of which MAR M 002 and MAR M 247 (Hf 1.5%) are best known. So far has engine design travelled, that it is today inconceivable that an industrial gas turbine could be operated without these alloys at the core of the engine.
So what is the correct role of the minor metal merchant in all this?
Well, companies like ours, who have been trading the metal for 20 years, took an interest in its supply-demand when there was no imperative to do so. This was not genius on our part – rather, when Russia/Ukraine first came to export such elements following the Soviet break-up in the 1990s, they needed counterparties ready to invest time and effort to find outlets for the often absurdly illiquid market of Hafnium. At that time, it was illiquid in demand, today it is illiquid in supply and we find ourselves at least with sufficient trading experience to understand the relative grades, where to convert and who to sell to.
It is a minor, minor metal story and one to justify the much maligned world of metal merchants. Perhaps someone has to take the time to study these things; but when all is going swimmingly in other markets, poring over supply/demand patterns of Hafnium, is more likely to get you put out to pasture than a pat on the back.
Twenty years ago, when my staff asked me for guidance on what they should say at the MMTA Dinner should anyone ask what we were trading, I said ‘Hafnium’ (as we were not trading it). This year I have suggested ‘Lutetium’.
Published: The Crucible (Nov 2015)
Anthony Lipmann 05.10.2015