Sustainable synthesis of diamond-like carbon and carbon fibres from hyperbaric ethanol–water mixtures through the critical point

• Carbon fibres with DLC coatings were grown from ethanol-water mixtures up to 90 bars. • Growth suppressed near the CP due to thermal diffusion effects. • Max growth rate was 100 µm/s within 6–20 bars; minimal rate was 2–6 µm/s within 80–90 bars. • Reaction order (n ≈ 2.5) was linked proportionally to ethanol pressure, and water enhances it. • Fluid convection > 20 cm/s and porous DLC observed around CP of the mixtures. Freestanding carbon fibres with diamond-like carbon content were grown from ethanol-water mixtures using hyperbaric-pressure laser chemical vapour deposition. Pressures of up to 103 bar were investigated, through the critical point of the precursor fluid. Rapid fibre axial growth rates of up to 100 μ m/s were observed. Process-structure relationships and a Raman spectral P-T phase diagram were developed, providing a potential route to optimising sp 3 -bonding. Most fibre growth was mass transport limited, but near the critical point, a kinetically-limited regime emerged. Due to divergent thermophysical properties of the precursor fluid, and the thermal diffusion effect, growth rates were suppressed at/near the critical point.