Nickel (Ni)

Around 1.85 billion years ago something several kilometres across hit what is now northern Ontario. The crater it left is one of the largest and oldest confirmed impact structures on Earth, and the melted crust that pooled in it separated on cooling into layers, concentrating nickel-copper sulfides along the base of the melt sheet. The Sudbury Basin has been mined continuously since the 1880s and supplied a substantial share of the world's nickel for most of the twentieth century.

An ore body that arrived from space

That the structure is an impact crater was not obvious and was not conceded easily. For decades it was read as a volcanic or intrusive feature, which was the respectable interpretation at a time when geologists were reluctant to explain anything on Earth by collision.

Robert Dietz argued in 1964 that Sudbury was an astrobleme, resting his case largely on shatter cones — distinctive fractured rock structures that form only under shock pressures no volcano can generate. The evidence accumulated through shocked quartz and the recognition of the impact melt, and the impact origin is now standard. It remains one of the few places where an impact directly produced an economically enormous ore deposit rather than merely a hole.

Two kilometres below the surface in Sudbury's Creighton Mine sits SNOLAB, and its predecessor detector settled the solar neutrino problem: the Sun appeared to produce only a third of the expected electron neutrinos, and the Sudbury Neutrino Observatory demonstrated that the missing two-thirds had changed flavour in transit, which requires neutrinos to have mass. Art McDonald shared the 2015 physics Nobel for it. The depth of rock that shields the detector from cosmic rays exists because somebody wanted the nickel.

The devil's copper

Saxon miners working a red-brown ore in the Ore Mountains expected copper from it and got nothing. They called it Kupfernickel — copper-nickel, where Nickel was a mischievous spirit blamed for worthless rock, the same sort of figure that English calls Old Nick.

Axel Fredrik Cronstedt, working in Sweden in 1751, extracted a new white metal from that ore and kept the goblin's half of the name. The mineral is now called nickeline, and the miners had a point: it is a nickel arsenide, which is why nothing they tried yielded copper and why smelting it made people ill. Cobalt's name has a closely parallel origin in the same mining tradition and the same period.

Chromium makes it stainless; nickel makes it austenitic

Stainless steel resists corrosion because of chromium. What nickel contributes is entirely different and equally necessary, and it is the reason the most common stainless grade is 18% chromium with 8% nickel rather than chromium alone.

Iron at room temperature is body-centred cubic. Heat it and it converts to a face-centred cubic form called austenite, which is denser-packed, tougher, non-magnetic and much easier to form. Left alone it reverts on cooling. Nickel stabilises the austenite phase all the way down to room temperature and below, so an 18/8 steel keeps that structure permanently.

Everything people notice about type 304 follows from this. It is non-magnetic, which is the kitchen test people use to distinguish it from cheaper ferritic grades. It work-hardens rather than cracking, so it can be deep-drawn into a sink. And it stays tough at cryogenic temperatures, where body-centred cubic steels turn brittle, which is why liquefied gas tanks are made from it.

Around two-thirds of world nickel consumption goes into stainless steel. Batteries have grown rapidly as the second destination, since high-nickel cathode chemistries store more energy and use less cobalt, but stainless remains dominant.

Two different metals with one price

Nickel trades as though it were a single commodity and it is not. Class 1 nickel is refined metal of high purity — briquettes, cathode, powder — and it is what a battery manufacturer requires. Class 2 is ferronickel and nickel pig iron, cheaper products containing substantial iron, which suit a stainless mill perfectly well because the iron is going into the steel anyway.

The London Metal Exchange contract is deliverable only in Class 1, which is a minority of world production. That mismatch broke the market on 8 March 2022. Tsingshan, the Chinese group that had pioneered nickel pig iron, held a very large short position hedging Class 2 output it could not deliver against the contract. As prices climbed on supply fears following the invasion of Ukraine, the short was squeezed: nickel went from around $25,000 a tonne to briefly above $100,000 intraday. The LME suspended trading and then cancelled several hours of transactions worth billions of dollars, a decision that triggered years of litigation and a lasting argument about whether an exchange may unwind trades to protect a participant.

The supply picture behind it has shifted just as sharply. Indonesia banned exports of unprocessed nickel ore in 2020 to force smelting onshore, and now accounts for more than half of world mine production, mostly from laterite deposits rather than the sulfide ores that Sudbury and Norilsk represent.

The most common contact allergy there is

Nickel allergy is the single most frequent cause of allergic contact dermatitis, affecting something in the region of one in ten people in Europe and considerably more women than men — a disparity attributed largely to ear piercing, which introduces the metal through broken skin at the point of greatest sensitising potential.

Denmark regulated nickel release from consumer items in 1990 and the EU followed with the Nickel Directive, restricting how much nickel may leach from anything in prolonged skin contact: jewellery, watch cases, spectacle frames, jean studs, belt buckles. Danish and later European studies found measurably lower sensitisation rates in cohorts growing up after the rules took effect, which is an unusually clean demonstration that regulating an exposure reduces an allergy at population scale. Euro coins were nevertheless issued containing nickel, over dermatological objections that were noted and overruled.

The nucleus that beats iron

Iron-56 is routinely described as the most stable nucleus in existence. The claim is very nearly true and, stated that way, slightly wrong.

Nickel-62 has the highest binding energy per nucleon of any nuclide — about 8.7945 MeV, marginally above iron-56. Iron-56, meanwhile, has the lowest mass per nucleon. Both statements are correct and they differ because a neutron is heavier than a proton, so converting protons to neutrons changes the mass ledger and the binding-energy ledger by different amounts. Which nuclide counts as "most stable" depends on which quantity you meant.

Neither is what stars actually accumulate, and that is the more interesting point. Silicon burning does not search for the true energy minimum; it proceeds through a quasi-equilibrium of photodisintegration and capture reactions in a matter of seconds, at a proton-to-neutron ratio set by the conditions rather than by thermodynamics. The result is dominated by nickel-56, which then decays. The universe ends up with iron because of reaction kinetics, not because iron won the stability contest.

Catalysis by a metal full of holes

Murray Raney patented in 1926 a method of making a nickel-aluminum alloy and then dissolving the aluminum out with caustic soda, leaving a nickel skeleton riddled with pores and enormously high in surface area, saturated with adsorbed hydrogen.

Raney nickel became the workhorse hydrogenation catalyst of the chemical industry, adding hydrogen across double bonds in everything from pharmaceutical intermediates to the vegetable oils hardened into margarine. Its enormous reactive surface makes the dry material pyrophoric, and it is consequently stored and shipped under water — a property of the material rather than a procedure.