The direct growth of single-walled carbon nanotubes (SWCNTs) with narrow chiral distribution remains elusive despite substantial benefits in properties and applications. Nanoparticle catalysts are vital for SWCNT and more generally nanomaterial synthesis, but understanding their effect is limited. Solid catalysts show promise in achieving chirality-controlled growth, but poor size control and synthesis efficiency hampers advancement. Here, we demonstrate the first synthesis of refractory metal nanoparticles (W, Mo, and Re) with near-monodisperse sizes. High concentrations (N = 10⁵ to 10⁷ cm⁻³) of nanoparticles (diameter 1 to 5 nm) are produced and reduced in a single process, enabling SWCNT synthesis with controlled chiral angles of 19° ± 5°, demonstrating abundance >93%. These results confirm the interface thermodynamics and kinetic growth theory mechanism, which has been extended here to include temporal dependence of fast-growing chiralities. The solid catalysts are further shown effective via floating catalyst growth, offering efficient production possibilities.

We analyze the magnetization relaxation effects of a ferrofluid film flow governed by the ferrohydrodynamics encompassing the Fokker–Planck magnetization equation in a Couette–Poiseuille configuration subject to an applied uniform stationary magnetic field perpendicular to the boundaries. A solver based on OpenFOAM is programmed to find solutions numerically for the velocity, spin velocity, and magnetization in ferrofluid films under the combined pressure gradient, boundary flow, and magnetic field forcing. The solver is validated by comparison with the classical Couette–Poiseuille flows and the analytic solutions of the magnetization relaxation problem when the product of flow vorticity and relaxation time is much smaller than unit, $\Omega {\tau }_B\ll 1$ . We compare the effects of magnetization relaxation obtained from the phenomenological magnetization equation with those from the equation derived microscopically. The results obtained from the former equation are not suitable for the description of ferrofluid film flows. Due to the magnetization relaxation effects, a misalignment between the local magnetization and the local magnetic field is observed. The net effects are that the flow is hampered by magnetic fields and it manifests as diminished slopes of vorticity profiles and reduced volumetric flow rates. The magnetization relaxation effects also slow down the spin velocity of particles or change their direction, which leads to an enhanced effective viscosity. The total tangential stress exerted on the moving boundary is higher than that of the classical Couette–Poiseuille flow owing to the addition of a magnetic stress. The magnetization relaxation effect is more significant in cases of ferrofluids with higher relaxation times.

Larger radical levitation force is favorable for enhancing energy dissipation in ferrofluid dampers. Utilization of composite magnet structures is one of the candidate methods to increase this force. The numerical, analytical and experimental methods of obtaining the levitation force exerted on composite magnet structures in ferrofluid dampers are summarized. The levitation forces of six composite structures are examined using these methods. It is shown that this force can be effectively increased by using composite structures compared with that by only one whole magnet. More than four times of increase of levitation force was obtained in our experiments. The analytical and numerical methods overestimate the levitation force, especially the analytical one. In comparison with the analytical results, the numerical results are much closer to the experimental ones, whose maximum deviation is 14.2%. The levitation force increases with the length and number of magnets composed of the composite structures. Other factors affecting the levitation force include pole spacing, permanent magnet moment and the permeability of ferrofluid. It is predicted by the analytical method that there is a positive correlation of the force with them in ferrofluid dampers.