Material · Synthetic

Carbon fibre

Filaments of near-pure carbon with extraordinary stiffness-to-weight, used in composites rather than alone.

Carbon fibre is drawn from a polymer precursor, usually polyacrylonitrile, which is oxidised and then carbonised until little but carbon remains, arranged in sheets aligned along the fibre.

Its headline strength figures are real but directional, and that qualification is essential rather than pedantic. Fibres are enormously strong along their length and weak across it. A carbon fibre component's real properties are set by how the fibres are laid up, which is why it is a design material rather than a drop-in substitute for metal.

Processing

Carbon fibre is made by controlled decomposition rather than by melting or drawing. A polymer precursor — usually polyacrylonitrile — is spun into filaments, then stretched and oxidised in air at a few hundred degrees so the chains cross-link and will not melt.

The oxidised fibre is then carbonised in an inert atmosphere at temperatures above a thousand degrees, driving off nitrogen and hydrogen until almost only carbon remains, arranged in sheets aligned along the fibre axis. Higher temperatures give stiffer, less strong fibre; lower ones the reverse. The surface is finally treated and sized so that resin will bond to it, without which the composite fails at the interface.

Uses

Aerospace was the first market and remains the most demanding: large parts of modern airliner structures are carbon composite, chosen because weight saved is fuel saved over decades of service.

Wind turbine blades are now a large consumer, since blade length is limited by what the material can hold up under its own weight. Automotive use is concentrated in performance and electric vehicles, sporting goods take a visible share, and pressure vessels for compressed hydrogen and natural gas depend on carbon fibre overwrap. Cost and the difficulty of recycling the cured composite are the two limits on wider adoption.

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.

is composed of

Carbon — element · 92–100% · carbonised from a polymer precursor until little but carbon remains

is an alternative to

Aluminium — element · in aerospace structure: better stiffness for its weight than any metal, against cost, a failure that is sudden rather than gradual, and damage that can be invisible from outside
Aramid fibre — material · aramid is tougher and better in tension and impact, carbon fibre is stiffer and far better in compression. Hybrid laminates use both, which is the usual answer
Invar — alloy · as mould tooling that must not change size relative to the composite curing on it — Invar is heavy and predictable, carbon tooling is light and matches the part exactly

is used as

Structural engineering — application · where stiffness per unit mass justifies the cost — aircraft structure, pressure vessels, and the reinforcement of existing concrete
Textiles — application · as the fibre in a composite rather than as fabric in its own right, though it is woven first

is used in

Aerospace manufacture — industry · primary structure since the 1990s — a modern wide-body wing and fuselage are more composite than metal
Wind turbine blade — object · in the spar caps of the longest blades, where stiffness stops the tip striking the tower

is a component of

Carbon fibre composite — material · and quoting the filament's strength for the laminate overstates it by a factor of several, which is the commonest error made about the material

is produced by

Pyrolysis — process · polyacrylonitrile filament, first oxidised in air at 200 to 300 °C so it will not melt, then carbonised above 1,000 °C — and the final temperature sets the stiffness, because it sets how ordered the carbon is

Sources

Material World
Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Carbon fibre 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

Carbon fibre → is composed of (carbonised from a polymer precursor until little but carbon remains) → Carbon → is produced by (as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind) → 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
Carbon fibre → is produced by (polyacrylonitrile filament, first oxidised in air at 200 to 300 °C so it will not melt, then carbonised above 1,000 °C — and the final temperature sets the stiffness, because it sets how ordered the carbon is) → Pyrolysis → takes as input (to make coke, and the coal gas that came off it lit European cities for a century as the by-product) → Coal → is sourced from (every coal seam in the world was a peat bog. Bury it, compress it, heat it, and it passes through lignite and bituminous coal to anthracite, losing water and volatiles at each step) → Peat → is sourced from (waterlogging is the whole mechanism: a bog is anoxic below a few centimetres, so the organisms that would decompose the plant matter cannot work, and it accumulates instead) → Water → is sourced from (by desalination, where energy is cheap and coastline available — the only route that adds fresh water rather than moving it) → Seawater
Carbon fibre → is produced by (polyacrylonitrile filament, first oxidised in air at 200 to 300 °C so it will not melt, then carbonised above 1,000 °C — and the final temperature sets the stiffness, because it sets how ordered the carbon is) → Pyrolysis → takes as input (and what comes off was the point for most of history: methanol, acetic acid and acetone all came from wood distillation before petroleum) → Wood
Carbon fibre → is composed of (carbonised from a polymer precursor until little but carbon remains) → Carbon → is produced by (as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind) → Acheson process → takes as input (as silica sand, the silicon half of the charge) → Quartz
Carbon fibre → is composed of (carbonised from a polymer precursor until little but carbon remains) → Carbon → is produced by (as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind) → 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
Carbon fibre → is composed of (carbonised from a polymer precursor until little but carbon remains) → Carbon → is produced by (as synthetic graphite, made by driving the reaction past silicon carbide until the silicon boils away and leaves the carbon behind) → 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

These are the most distinct paths back. Carbon fibre can be traced through others besides.

Downstream — what it becomes

Carbon fibre → is used in (in the spar caps of the longest blades, where stiffness stops the tip striking the tower) → Wind turbine blade → is used in (and it is the part of a turbine with no established end-of-life route, where the tower and foundation are steel and concrete) → Energy generation
Carbon fibre → is a component of (and quoting the filament's strength for the laminate overstates it by a factor of several, which is the commonest error made about the material) → Carbon fibre composite → is used as (aircraft primary structure since the 1990s, where stiffness per unit mass is what is being bought) → Structural engineering
Carbon fibre → is used as (where stiffness per unit mass justifies the cost — aircraft structure, pressure vessels, and the reinforcement of existing concrete) → Structural engineering
Carbon fibre → is used as (as the fibre in a composite rather than as fabric in its own right, though it is woven first) → Textiles
Carbon fibre → is used in (primary structure since the 1990s — a modern wide-body wing and fuselage are more composite than metal) → Aerospace manufacture
Carbon fibre → is a component of (and quoting the filament's strength for the laminate overstates it by a factor of several, which is the commonest error made about the material) → Carbon fibre composite → is used in (primary structure — a modern wide-body wing and fuselage are more composite than metal) → Aerospace manufacture