How does Carbon Fiber Transform from Petroleum/Bitumen into "Black gold"?

Can you believe it? The core framework of Olympic champions' rackets capable of smashing shuttlecocks at 300km/h, F1 cars with bodies enduring 0-100km/h sprints in 2.3 seconds, even the outer shells of space rockets piercing the atmosphere – their very backbone stems from the discarded 'black residue' left over after oil refining?

Today we delve into the remarkable rise of carbon fibre, the 'top dog' of materials science. Discover how humble petroleum asphalt overcame countless trials to transform into 'black gold' worth more than silver!

Why is it called "black gold"?
Before embarking on this journey of transformation, let us first address a fundamental question: why is carbon fibre often compared to gold?
(1) Its price is truly 'gold-worthy': standard carbon fibre costs several thousand yuan per kilogram, while high-end aerospace-grade carbon fibre can fetch up to 20,000 yuan per kilogram – more expensive than silver (approximately 5 yuan per gram).

(2) Performance is formidable: Weighing just one-quarter of steel yet boasting tenfold its strength, it resists corrosion in strong acids and remains unfragile at -180°C.

(3) Its scarcity is truly formidable: only a dozen or so nations globally possess mass production technology, with premium carbon fibre classified as a "strategic material" – making it difficult to procure even when desired.

This "all-rounder" originates from asphalt, a byproduct of petroleum refining – akin to extracting diamonds from coal piles, with each step brimming with wonder.

Asphalt to Carbon Fibre: A Five-Step 'Alchemy' Process Where Not a Single Step Can Be Overlooked!

Step One: Material Selection — The Cream of the Crop: Premium Bitumen
Not all bitumen can make a comeback. The bitumen we typically use for road construction contains too many impurities and has low carbon content, rendering it unsuitable. Only "special-grade bitumen" with high purity, high carbon content (90%), and low sulphur and metal content can be used for carbon fibre production.

Engineers employ solvent extraction to "bathe" the asphalt: immersing it in specialised solvents to filter out impurities like sulphur, nitrogen, and heavy metals, much like sifting sand. Distillation then refines its molecular structure, endowing it with the potential to be drawn into filaments and withstand high temperatures.

This stage resembles selecting athletes: only those with "strong foundations" can withstand subsequent intensive training.

Step Two: Spinning — drawing out "golden threads" ten times finer than a strand of hair.
The purified bitumen is heated to 200–300°C, transforming into a honey-like viscous "melt". This melt is then forced through a "spinneret plate" riddled with tiny orifices—each measuring just 5–50 micrometres in diameter (compared to a human hair's 50–100 micrometres), finer than an embroidery needle!

The asphalt filaments extruded through these orifices are immediately immersed in cold water or chilled air to "cool and set", forming continuous "asphalt filament strands". This step demands exceptional technical skill: slightly higher extrusion speed causes the filaments to snap; slightly lower cooling temperatures make them brittle; even a single blocked orifice can render an entire batch of filaments unusable.

One might liken it to "artificially producing silkworm cocoons," except the "filament" extruded is ten times finer than silk.

Step Three: Pre-oxidation — Dressing the filament with a "fireproof suit"
Freshly spun asphalt filament is a delicate little thing: it snaps at the slightest pull and catches fire at the slightest spark. To make it tough and resilient, the first step is to make it fireproof.

The raw filament is placed in an oven heated to 150-300°C, where it undergoes slow heating in air for several hours. During this process, hydrogen and oxygen elements gradually escape from the asphalt filament. Its molecular structure transforms from linear to a networked state, and its colour changes from black to dark brown. Crucially, it becomes fire-resistant!

This step absolutely cannot be skipped: skipping pre-oxidation and proceeding directly to high-temperature processing would cause the asphalt fibre to burn instantly, rendering all prior efforts futile. Moreover, the heating rate must be slow; rushing it would lead to "uneven internal stress" within the fibre, causing cracks.

Step Four: Carbonisation — Refining at high temperatures to produce a "pure carbon skeleton"
The raw filament, now clad in its "fireproof garment", must undergo the "ultimate trial" within the carbonisation furnace. This furnace operates at temperatures ranging from 1000 to 1800°C and must maintain an oxygen-free environment (otherwise the carbon would oxidise into carbon dioxide).

Under these extreme temperatures, the last traces of non-carbon elements (such as hydrogen and nitrogen) within the filament "escape" as gases. What remains is nearly pure carbon (carbon content 90%), with its molecular structure rearranging into orderly "graphite-like crystals". At this stage, the "asphalt filament" is formally upgraded to "carbon fibre precursor"!

The carbonisation temperature directly determines the carbon fibre's value: ordinary industrial-grade carbon fibre can be produced at around 1000°C, whereas aerospace-grade requires temperatures exceeding 2000°C. This results in more orderly carbon crystal arrangements and strength that increases severalfold, naturally driving up the price.

Step Five: Surface Treatment — Establishing Connections for Carbon Fibre
Freshly carbonised carbon fibre boasts a surface as smooth as glass, which tends to 'slip' when bonding with materials like resin or metal – much like two smooth panes of glass pressed together, only to separate with a snap. The treated carbon fibre is then woven into fabric (the carbon fibre cloth discussed earlier) or cut into short fibres, forming the "core skeleton" of composite materials.
At this point, the 2-3 month "metamorphosis" journey that began with asphalt is finally complete.

These little-known facts are unknown to 90% of people!

1.Not all carbon fibre originates from petroleum pitch: alongside petroleum pitch, polyacrylonitrile (PAN) and viscose fibre can also be used to produce carbon fibre. PAN-based carbon fibre accounts for 90% of global production, while pitch-based carbon fibre is better suited for high-end, high-strength applications.

2.Producing one tonne of carbon fibre consumes 20 tonnes of raw materials: from pitch to carbon fibre, the yield rate falls below 5%. No wonder it's so expensive.

3.China has broken the monopoly: previously, high-end carbon fibre was controlled by Europe, America and Japan. Now, China has achieved mass production of T1100-grade carbon fibre (aerospace-grade), priced 30% lower than imports.

What carbon fibre products have you encountered?
Carbon fibre is actually far from distant in our daily lives: beyond aerospace and motorsport, it now features in high-end bicycle frames, drone arms, and even mobile phone casings.

Have you encountered carbon fibre products in your surroundings? Or what future applications do you envision for this material? Share your thoughts in the comments!

The unassuming petroleum asphalt underwent a remarkable transformation over several months, evolving into the "black gold" underpinning high-end manufacturing. Behind this lies the relentless pursuit of millimetre-level precision by countless engineers, as well as humanity's ongoing quest to push the boundaries of materials science. Next time you encounter a carbon fibre product, you might recall: it once began as little more than discarded petroleum residue.