The Elements Inside a Phone

Take the back off a phone and you can see maybe eight materials. Analyse it properly and you find around thirty of the 118 elements, most present in quantities of a few milligrams, several of them doing a job that no cheaper element can do at all.

That last point is what makes the list interesting. A phone is not made of common metals because common metals were affordable; it is made of a very specific set of elements chosen because each one has a property nothing else quite has, and a fair number of them come out of the ground in places where getting them out has a cost that never appears on the receipt.

The screen is three elements you cannot see doing anything

The glass itself is an alkali aluminosilicate: silicon and oxygen, with aluminum worked into the network to toughen it. Its scratch resistance comes from a chemical trick rather than a coating. The finished sheet is bathed in a molten potassium salt, and potassium ions — noticeably larger than the sodium ions already in the glass — swap places with them near the surface. The oversized ions do not fit comfortably, so the outer skin of the glass ends up under permanent compression, and a crack cannot open in a surface that is already being squeezed shut.

On top of that sits the layer that makes touch work: indium tin oxide, roughly nine parts indium oxide to one part tin oxide. It is the awkward material at the heart of every touchscreen, because it is simultaneously transparent and electrically conductive, and almost nothing else is both. Indium is not mined for its own sake anywhere on Earth. It comes out of the leftovers of the zinc industry, which means the amount available each year is decided by how much zinc the world happens to want. Every serious attempt to replace it — silver nanowires, graphene, conducting polymers — exists because that dependency makes engineers uncomfortable.

The magnets are the reason your phone is not thicker

There are several magnets in a handset: one in the earpiece, one in the loudspeaker, one in the microphone, one in the vibration motor, and more if it charges wirelessly. All of them are neodymium-iron-boron, the strongest permanent magnets ever made, which is what allows a speaker loud enough to hear on a train to be thinner than a coin.

Neodymium gives the alloy its enormous magnetic field. But NdFeB has a weakness — it loses coercivity as it warms, and a phone under load warms considerably — so a few per cent of dysprosium or terbium is substituted into the lattice specifically to hold the magnetism together at temperature. Dysprosium is the expensive part of the magnet by a wide margin, and reducing how much of it a motor needs is an active field of materials research in its own right.

Both are lanthanides, and the phrase attached to them is misleading in a way worth a whole separate argument: they are not, in any geological sense, rare.

The battery is two elements and an argument

A phone cell is lithium cobalt oxide on one side and graphite — carbon, increasingly blended with a little silicon — on the other, with copper foil collecting current from the anode and aluminum foil from the cathode. Lithium is there for the reason lithium is always there: it is the lightest metal and it gives up its outer electron readily, so you get the most charge for the least mass.

Cobalt is the contentious one. It stabilises the cathode's layered structure through hundreds of charge cycles, and consumer electronics has been slower than the car industry to move away from it because a phone cell prizes energy density over cost. Well over half of global production originates in one country, the Democratic Republic of the Congo, and a substantial minority of that output — estimates run from a fifth to about 30 per cent — is dug by artisanal miners working outside any formal mine. Amnesty International's 2016 investigation traced cobalt from sites using child labour into the supply chains of major electronics brands, and documented children as young as seven working for under two dollars a day. UNICEF had estimated around 40,000 children working in mines across the southern DRC two years earlier. The DRC government subsequently committed to ending child labour in mining by 2025. That commitment was not met.

The board: gold where it must not corrode, tantalum where there is no room

The circuit board is where the element count really climbs.

• Gold plates the connectors, the SIM contacts and the bond wires inside chip packages. A handset contains only a few tens of milligrams of it, and it is there for one reason: it is the only good conductor that does not grow an oxide film. A corroded contact is an intermittent fault, and gold does not corrode.
• Tantalum makes the capacitors. Its oxide is an exceptionally good insulator and can be grown vanishingly thin, so a tantalum capacitor stores far more charge per cubic millimetre than a ceramic one. In a device where board space is the scarcest resource, that wins.
• Gallium handles the radio. Gallium arsenide and gallium nitride amplifiers switch faster and survive higher power densities than silicon, which is why the part of the phone that talks to a cell tower is not made of the same semiconductor as the processor. Gallium itself is another by-product metal, extracted during aluminum refining, and arsenic appears here in one of its few uses that has nothing to do with poison.
• Tin, silver and copper make the solder. Lead solder was designed out of consumer electronics by European legislation in 2006, and the replacement alloy is mostly tin with a few per cent silver and copper.
• Tungsten is the counterweight. A vibration motor works by spinning a deliberately unbalanced mass, and the denser that mass, the stronger the buzz for a given volume. Only a handful of elements are that dense, and tungsten is the affordable one.

Four of them have their own law

Tin, tantalum, tungsten and gold are known in the trade as 3TG, and they are singled out because all four have been mined in eastern DRC and neighbouring countries under the control of armed groups. Section 1502 of the US Dodd-Frank Act, passed in 2010, requires listed companies to investigate and disclose whether those four metals in their products originate there. It is the only piece of financial regulation that most people encounter as a footnote in a phone manufacturer's annual report, and it is the reason a smelter audit exists as an industry.

The recovery side is much weaker than the extraction side. The UN's Global E-waste Monitor found that under a quarter of the world's discarded electronics was documented as formally collected and recycled, and the elements present in single-milligram amounts are the hardest to justify recovering. Gold and copper get pulled out because they are worth it. Indium, gallium, tantalum and the magnet lanthanides mostly do not, which is a strange outcome for materials whose supply everybody describes as critical.

Ordinary metals, irreplaceable ones, and cobalt

The elements in a phone divide into three groups. A few — silicon, copper, aluminum, carbon, iron — are ordinary materials doing ordinary jobs. A few more are chosen for one irreplaceable property: indium because it conducts while transparent, gold because it will not oxidise, tantalum because its oxide is thin and tough, tungsten because it is dense, neodymium because it is magnetic beyond anything else available. And a handful — cobalt above all — are there for good technical reasons and arrive through a supply chain that no one involved is entirely comfortable describing.

The device is a genuinely impressive piece of applied chemistry. It is also, element by element, a map of where the world's inconvenient extraction happens.