Vanadium (V)

Andrés Manuel del Río found vanadium in 1801, named it, described it — and then publicly took it back. He is the name on the data card above, and he is the one person in the story who formally disclaimed the discovery.

Persuaded out of it

Del Río was Spanish-born and taught mineralogy at the Royal School of Mines in Mexico City. Working on a brown lead ore from Zimapán, he concluded it contained an unknown metal, and named it panchromium for the range of colours its compounds produced. He revised that to erythronium after noticing that the salts turned red on heating.

He gave samples to Alexander von Humboldt, who was passing through on his American expedition and who forwarded them to Paris. Hippolyte-Victor Collet-Descotils analysed them and reported that the material was chromium with impurities. Humboldt accepted that verdict, and del Río — deferring to the metropolitan laboratory over his own bench — accepted it too and withdrew his claim.

Twenty-nine years later, Nils Gabriel Sefström in Sweden found an unrecognised element while examining iron from the Taberg ore, and named it after Vanadís, a name of the Norse goddess Freyja, because its compounds were so beautifully coloured. Friedrich Wöhler had del Río's original Mexican material in hand at the same period and was slowed by illness — he was recovering from hydrogen fluoride poisoning sustained in his own attempts on fluorine — and Sefström published first. Wöhler then established what nobody had checked in three decades: Sefström's vanadium and del Río's erythronium were the same element, and Collet-Descotils had simply been wrong.

Henry Enfield Roscoe finally reduced it to reasonably pure metal in 1867, more than sixty years after del Río first held its ore.

A rebar standard moved the world price

Something like eighty-five to ninety per cent of vanadium production goes into steel, added as ferrovanadium in quantities of a few tenths of one per cent.

That tiny addition works by microalloying. Vanadium forms carbides and nitrides that precipitate as extremely fine particles during rolling and cooling, and those particles both pin the grain boundaries — keeping the grains small, which raises strength and toughness simultaneously — and obstruct the movement of dislocations. The result is a stronger steel without raising the carbon content, which matters because carbon is what makes steel difficult to weld.

The consequences for the vanadium market are dramatic and largely invisible to anyone outside it. In 2018 China revised its national rebar standard, GB 1499, eliminating the weakest grade and banning a cheap quench-and-temper strengthening route that mills had been using to meet specification without alloying. Producers had to microalloy instead. Vanadium demand from a single country's construction code jumped, and the price roughly tripled over the course of the year.

The older and more famous application is Henry Ford's. Ford put vanadium steel into the Model T's critical components, and the story he told — that he had picked up a valve stem from the wreck of a French racing car at Palm Beach and been struck by the quality of the metal — is one he promoted himself and is difficult to verify independently. What is documented is that the Model T used vanadium alloy steel at a time when American mills barely knew how to make it, and that Ford underwrote the capability.

The battery that uses one element on both sides

A redox flow battery stores energy in two liquid electrolytes held in external tanks and pumped through a cell stack. Every such system has the same fundamental weakness: the two electrolytes are different chemistries separated by an imperfect membrane, and over time each contaminates the other, degrading the battery permanently.

Vanadium's four accessible oxidation states remove that problem entirely. Maria Skyllas-Kazacos and colleagues at the University of New South Wales built systems in the 1980s using vanadium on both sides — the +2/+3 couple in one tank, the +4/+5 couple in the other. Ions that cross the membrane cause an efficiency loss and a state-of-charge imbalance that can be corrected simply by remixing the two electrolytes. Nothing is irreversibly lost. Vanadium flow batteries have demonstrated tens of thousands of cycles with electrolyte that does not need replacing.

Their other structural advantage is that power and energy are decoupled: the stack size sets how fast the battery can deliver, the tank size sets how long it can deliver for, and the two can be specified independently. That is exactly wrong for a vehicle, where the whole system has to be carried, and increasingly attractive for grid storage, where a warehouse of electrolyte is acceptable.

Those same oxidation states are why vanadium solutions are a standard teaching demonstration. The +5, +4, +3 and +2 states are yellow, blue, green and lavender respectively, so a stepwise reduction walks visibly through the spectrum.

Sea squirts, and nobody knows why

Tunicates — sea squirts — concentrate vanadium in specialised blood cells called vanadocytes at levels that can exceed the surrounding seawater by a factor of a million or more, holding it in strongly acidic vacuoles in a reduced oxidation state.

This has been known for over a century and remains unexplained. Oxygen transport was the first hypothesis and has been effectively ruled out, since the vanadium does not bind oxygen reversibly under physiological conditions. Hardening of the tunic, chemical defence against predators and fouling organisms, and antimicrobial action have all been proposed and none convincingly demonstrated. An organism spending considerable metabolic effort accumulating a metal for no identified purpose is an unusually clean open question in biochemistry.

Elsewhere in biology vanadium turns up in genuinely functional roles. Some nitrogen-fixing bacteria carry a vanadium-based nitrogenase as an alternative to the usual molybdenum enzyme, used when molybdenum is scarce; marine algae use vanadium haloperoxidases to make brominated compounds; and the fly agaric mushroom accumulates it in a distinct complex called amavadin, whose function is also unknown.

The catalyst under the world's largest chemical industry

Vanadium pentoxide is the catalyst in the contact process, which oxidises sulfur dioxide to sulfur trioxide on the way to sulfuric acid. Since sulfuric acid is manufactured in greater quantity than any other industrial chemical, this makes vanadium a quiet participant in an enormous fraction of the world's chemistry.

It works because vanadium cycles easily between the +5 and +4 states: it hands an oxygen atom to the sulfur dioxide, is reduced, and is reoxidised by air, over and over. A catalyst charge lasts years. It displaced finely divided platinum, which did the same job and was poisoned by trace impurities in the gas stream that vanadium tolerates.

An isotope that should not be there

Vanadium-51 accounts for essentially all natural vanadium. A quarter of a per cent is left over, and that quarter of a per cent is one of the strangest entries on the isotope chart.

Vanadium-50 has 23 protons and 27 neutrons, both odd. That combination is almost invariably unstable — fewer than ten odd-odd nuclides survive in nature at all — and vanadium-50 only just counts as one of them, at a half-life near 10¹⁷ years. It also cannot decide which way to fall: some nuclei capture an electron and become titanium-50, others emit a beta particle and become chromium-50, and both channels run at once.

How it got here is a separate puzzle. The two neutron-capture chains that assemble most of the heavy elements run past vanadium-50 without depositing anything in it, which leaves photon-driven reactions in the shock front of a supernova as the only mechanism anyone has been able to propose. That puts vanadium-50 in the class of p-nuclei, whose production remains one of the looser threads in the theory of how the elements were made.