CarbonX: A process design tool for gas-phase synthesis of metal nanoparticles and carbon nanotubes

Carbon nanotubes (CNTs) exhibit exceptional electrical, optical, and mechanical properties that make them promising candidates for applications in energy storage, sensing, and advanced composites. Chemical vapor deposition (CVD) synthesis offers advantages in terms of scalability, cost-effectiveness, and control over nanotube characteristics compared to other methods such as laser ablation and arc vaporization. However, controlling the CNT morphology and yield in floating-catalyst CVD (FCCVD) reactors remains challenging due to the complex interplay between chemical kinetics, catalyst nanoparticle evolution, and carbon deposition mechanisms. This work presents CarbonX, an object-oriented package designed to simulate FCCVD reactors for predicting the gas-phase synthesis of single- and multi-walled carbon nanotubes and metallic (Fe, Ni, and Co) nanoparticles. The framework integrates four coupled components: a detailed chemical kinetics submodule, a surface kinetics submodule accounting for catalyst activation, deactivation, and hydrogenation, a particle dynamics submodule for tracking the evolution of the morphology of nanoparticles during inception (nucleation), surface growth, coagulation, and sintering, and a CNT dynamics submodule for predicting nanotube length, diameter, and wall number. Different surface kinetics models are adapted from those in the literature for substrate-based CVD reactors and extended for use in FCCVD reactors. Using a machine learning submodule integrated into the package, the generated parametric maps are classified into distinct zones that identify the specific process conditions (e.g., temperature, pressure, and catalyst concentration) required for the formation of single- and multi-walled CNTs. The package submodules are comprehensively benchmarked against experimental measurements from multiple CVD reactor configurations.