Ruthenium (Ru)

Ruthenium is the cheapest of the platinum group metals and the one most people have never heard of, which is odd given that there are probably several thousand pieces of it within arm's reach of anyone reading this. Every surface-mount chip resistor on a circuit board contains ruthenium dioxide, and a modern phone contains hundreds of resistors. It is an element that achieved ubiquity without ever achieving recognition.

Three claims, two withdrawals, one Kazan pharmacist

The Ural platinum deposits produced a stubborn insoluble residue after the platinum was dissolved out with aqua regia, and three separate chemists announced new elements in it.

Jędrzej Śniadecki, working in Vilnius in 1808, reported a metal he called vestium. Nobody could reproduce his results and he withdrew the claim. In 1828 Gottfried Osann at Dorpat, examining residues supplied to Berzelius, announced three new metals — pluranium, polinium and ruthenium. Berzelius could not confirm any of them, and Osann retracted as well.

Karl Ernst Claus, a Baltic German pharmacist who became professor of chemistry at Kazan, went back to the same residues in 1844 with a much better separation scheme and produced several grams of a genuinely new metal, characterised it, and demonstrated it to Berzelius's satisfaction. He could have named it whatever he liked. He kept Osann's name, writing that he did so in honour of his homeland — Ruthenia being the Latin name for Rus' — which gives the element the unusual distinction of being named by the man who failed to find it and confirmed by the man who did.

Later work found that Osann's preparations had, in fact, contained the element. Being right and being able to prove it are different achievements, and the priority conventions of chemistry reward the second.

The card above ends up with one man's year beside another man's name. Its 1827 is Osann's — reference works date his announcement to 1825, 1827 or 1828 depending on which notice they count, and the earliest English-language report of it ran in the Philosophical Magazine late in 1827 — while the credit line reads Claus, whose proof is seventeen years further on. Neither half is wrong and the pair cannot be reconciled, because a single date and a single name cannot describe a discovery that took three chemists thirty-six years to complete.

The layer that stopped hard disks shrinking

By the late 1990s magnetic recording had run into the superparamagnetic limit: make the magnetic grains on a disk small enough and thermal energy flips them at random, erasing the data. IBM's answer, announced in 2001 and marketed as antiferromagnetically coupled media, was to split the recording layer in two and separate the halves with a ruthenium film about three atoms thick.

At that precise thickness — and it has to be close to precise — the exchange coupling through the ruthenium is negative, so the two magnetic layers align in opposition. The pair behaves as a single, more thermally stable unit while presenting a smaller net signal, which buys several years of continued density growth. IBM's marketing called the ruthenium layer "pixie dust", to the visible discomfort of the physicists involved. Ruthenium remains part of the layer stack in perpendicular recording media, and drives are still one of the element's larger markets.

Resistors, chlorine and ammonia

Ruthenium's industrial uses cluster around conductive oxides and catalysis, and the two largest are almost invisible.

• Thick-film resistors. A chip resistor is made by screen-printing a paste of ruthenium dioxide particles in a glass frit onto a ceramic substrate and firing it. The ratio of oxide to glass sets the resistance; the fired glass makes it stable and rugged. The overwhelming majority of resistors manufactured anywhere work this way.
• Dimensionally stable anodes. Chlorine used to be produced on graphite anodes that eroded continuously and had to be replaced. Henri Beer's titanium anodes coated with ruthenium and iridium oxides, introduced in the late 1960s, do not erode, run at lower voltage, and cut the electricity consumption of the whole chlor-alkali industry substantially. Almost all chlorine now comes from a ruthenium oxide surface.
• Ammonia synthesis. Ruthenium on a graphite support is the active phase in the Kellogg Advanced Ammonia Process, which runs at lower pressure than conventional iron-catalysed Haber–Bosch plant. It has not displaced iron, but it is the only commercially proven alternative.

In organic chemistry, ruthenium carbene complexes — the Grubbs catalysts — made olefin metathesis a routine bench reaction rather than a specialist technique, work recognised with the 2005 Nobel Prize in Chemistry shared by Robert Grubbs, Richard Schrock and Yves Chauvin. The reason those catalysts spread so quickly is not that ruthenium is uniquely active but that it is uniquely forgiving: unlike earlier molybdenum systems, Grubbs catalysts tolerate air, water and most functional groups, so ordinary laboratories could use them.

Ruthenium also hardens platinum and palladium for electrical contacts and jewellery, and ruthenium polypyridyl dyes were the sensitisers that made dye-sensitised solar cells work.

The oxide that will not stay put

Ruthenium tetroxide is a volatile, strongly oxidising yellow solid that sublimes readily. That volatility is a persistent problem in nuclear fuel reprocessing, where ruthenium is a significant fission product and refuses to stay in the aqueous phase like the other metals; managing its escape into off-gas systems is a recognised design constraint.

It is also, in all likelihood, why detectors across Europe picked up ruthenium-106 in the autumn of 2017. The concentrations were far too low to affect health and far too high to be background, and the isotope arrived unaccompanied by anything else — the signature of a release from a facility handling separated fission products rather than a reactor accident. Atmospheric back-tracking pointed to the southern Urals, and the Mayak reprocessing complex, though Russian authorities have consistently denied any release.

Isotopes, and a plaque the size of a shirt button

Ruthenium has seven natural isotopes, an unusually rich set for a platinum group metal. The one that gets used is not among them. Ruthenium-106, thrown off by fission and lasting about 374 days per half-life, decays to a daughter that emits energetic beta particles and almost no penetrating gamma.

That combination is close to ideal for treating tumours inside the eye. A small curved plaque carrying ruthenium-106 is sutured to the outside of the eyeball over the tumour and left in place for a few days, delivering a steep dose to the lesion while the sclera shields everything behind it. Ruthenium plaques have preserved vision in a great many patients with ocular melanoma who would previously have lost the eye.

No ruthenium mine

Ruthenium is never the reason a mine exists. It is recovered from the platinum group metal concentrates of the Bushveld Complex in South Africa and from the nickel-copper ores of Norilsk in Russia, making up a small percentage of the PGM content in each. Annual world production is measured in tens of tonnes — a few truckloads for the entire planet — and it moves with platinum and palladium output rather than with any demand for ruthenium itself.