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Material World
Process

Acheson process

Baking sand and coke together at nearly 2,500 °C — the route to silicon carbide, and to the synthetic graphite that electrodes and battery anodes are made from.

Edward Acheson was trying to make artificial diamond and made something more useful. Heating a mixture of silica sand and carbon in an electric furnace produced hard blue-black crystals that would scratch anything he tested them against, and he named the product carborundum in the belief that it was a compound of carbon and corundum. It is silicon carbide, and it was the first synthetic abrasive hard enough to matter.

The same furnace does a second job. Push the temperature higher and the silicon boils away, leaving the carbon behind rearranged into graphite — which is how synthetic graphite is made, and why one process appears in both the abrasives industry and the battery one.

Processing

A long trough is filled with a mixture of sand and petroleum coke packed around a carbon core, and a current of several thousand amps is passed through the core for a day or more. The core heats to around 2,500 °C, and silicon carbide crystallises outward from it in zones, the best-formed crystals nearest the centre and progressively less converted material further out.

The furnace is then broken open and the product sorted by hand and by grade — an oddly artisanal end to an enormously energy-intensive operation. Unconverted material from the outer zones is simply returned to the next charge.

Raising the temperature further drives silicon off as vapour and leaves graphite. That is the same reaction taken one stage past its intended stopping point, and it is deliberately exploited: the electrodes used in electric arc steelmaking are made of graphite produced this way.

Economic significance

Silicon carbide's first market was abrasives, and for most of a century that is what the process supplied. Its second is more valuable: silicon carbide is a wide-bandgap semiconductor that tolerates voltages and temperatures silicon cannot, and the power electronics in an electric vehicle's inverter increasingly depend on it.

Synthetic graphite has followed a similar path. It was an electrode material, and it is now also an anode material — and because the process is defined by holding a large mass at extreme temperature for days, its cost is essentially the price of electricity.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

produces

  • Silicon carbide — compound · the product the process was built for, crystallised out of sand and coke at around 2,500 °C
  • Carbon — element · as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind
  • Battery graphite — material · which is where synthetic graphite comes from, and the furnace runs at around 3,000 °C for weeks to convert disordered carbon into ordered sheets

takes as input

  • Quartz — mineral · as silica sand, the silicon half of the charge
  • Sand — material · sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Acheson process back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is sourced from (the ultimate source of most of it — granite weathers, the feldspar becomes clay and washes out, and the quartz survives as grains) → Granite → is composed of (by volume, alongside feldspar and lesser mica) → Quartz
  • Acheson process → takes as input (as silica sand, the silicon half of the charge) → Quartz
  • Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is composed of (almost everywhere, because quartz is what is left when everything else in a rock has weathered away — though a volcanic beach is basalt grains and a tropical one is broken shell) → Quartz
  • Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is sourced from (the ultimate source of most of it — granite weathers, the feldspar becomes clay and washes out, and the quartz survives as grains) → Granite → is composed of (the pink or cream mineral that gives much granite its colour) → Orthoclase
  • Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is sourced from (the ultimate source of most of it — granite weathers, the feldspar becomes clay and washes out, and the quartz survives as grains) → Granite → is composed of (one of the two common micas in granite, alongside biotite) → Muscovite
  • Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is sourced from (the ultimate source of most of it — granite weathers, the feldspar becomes clay and washes out, and the quartz survives as grains) → Granite → is composed of (alongside the potassium feldspar and quartz) → Plagioclase

These are the most distinct paths back. Acheson process can be traced through others besides.

Downstream — what it becomes

  • Acheson process → produces (which is where synthetic graphite comes from, and the furnace runs at around 3,000 °C for weeks to convert disordered carbon into ordered sheets) → Battery graphite → is used in (the anode of essentially every cell ever sold, and roughly twice the mass of the cathode it is paired with) → Lithium-ion cell → is used in (and portable computing came first by two decades) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Acheson process → produces (as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind) → Carbon → is a component of (the element whose proportion separates steel from iron and governs its hardness) → Steel → is associated with (produced in small quantities long before it could be made reliably) → Iron Age complete chain
  • Acheson process → produces (the product the process was built for, crystallised out of sand and coke at around 2,500 °C) → Silicon carbide → is a component of (where abrasion and thermal shock both matter — blast furnace bosh, incinerators and kiln furniture) → Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (fired in a continuous tunnel kiln, the atmosphere governing colour as much as the temperature) → Brick → is used in (load-bearing walls and cladding) → Construction
  • Acheson process → produces (which is where synthetic graphite comes from, and the furnace runs at around 3,000 °C for weeks to convert disordered carbon into ordered sheets) → Battery graphite → is an input to (read from the other end — flotation is how flake graphite is concentrated before any of the anode processing begins) → Froth flotation → is used in (the process that made low-grade disseminated sulfide deposits economic, and therefore made the modern copper industry) → Mining and quarrying → is associated with (steam pumping allowed mines below the water table, which is what made deep coal possible) → Industrial Revolution complete chain
  • Acheson process → produces (which is where synthetic graphite comes from, and the furnace runs at around 3,000 °C for weeks to convert disordered carbon into ordered sheets) → Battery graphite → is used in (the anode, and roughly twice the mass of the cathode) → Smartphone → is used in (and it is where four separate raw-material arguments meet — the 3TG conflict minerals, cobalt, the rare earths, and everything too dispersed to recover) → Electronics manufacture → is associated with (and the supply chain it produced is the deepest and most concentrated in the world economy) → The semiconductor era complete chain
  • Acheson process → produces (the product the process was built for, crystallised out of sand and coke at around 2,500 °C) → Silicon carbide → is used as → Abrasive

These are the most distinct paths onward. Acheson process ends up in others besides.