Mapping the parameter space for direct-spun carbon nanotube aerogels

Industrial-scale use of carbon nanotube (CNT) materials and prototype development is limited by the availability of economic, high-throughput production methods. Recent investigations have demonstrated the feasibility of producing direct-spun macroscopic CNT materials via floating catalyst chemical vapour deposition. However, few quantitative results have been reported regarding process yield and correlations with product quality. Validation of results is therefore challenging as identification of the key fundamental process parameters is hindered. This first meta-analysis quantifies atomic input rates and correlates them with product outputs to map the current parameter space of 55 successful conditions leading to spinnable aerogels. All mapped processes fall within a bulk residence time of 5–240 s, operating temperature of 1100–1500 °C and an atomic S:Fe of 0.1–10. Low (high) S/Fe ratios favour single (multi)-wall CNTs in the direct-spun product. A high atomic carbon dilution, with only 3% of the input atoms being C, is a common feature across many systems. Furthermore, we connect the findings to known catalyst and product growth behaviour, as well as the thermodynamics of intermediates, to create an emerging picture of direct-spun CNT product formation. Elucidation of the most important factors influencing material synthesis, and the relationships between them, provides opportunities for gains in industrial-scale synthesis.