Fabrication of thick-walled polyacrylonitrile (PAN) with high uniformity by an easily assembled double-T droplet generator

Abstract

Low density carbon shells are required in inertial confinement fusion (ICF) experiments. Polyacrylonitrile (PAN), as a common raw material of carbon, was studied and adopted to prepare thick-walled microspheres with the outer diameter ranging from 300 μm to 800 μm; wall thickness around 50–120 μm; sphericity (OOR): <2 μm; and wall thickness uniformity (ΔT_w): <9 μm. The preparation of PAN microspheres was based on an assembled double T-junction droplet generator. The major challenge in this experiment was to simultaneously meet the requirements and restrictions on both wall thickness and its uniformity. In order to improve the wall uniformity of thick-walled PAN microspheres, two major factors, the viscosity and the temperature which affect the density-matching solutions between the O₁/W compound droplet and the O₂ phase, were tested. The calculated results of OOR and ΔT_w showed that the optimal density gap between the O₁/W compound droplet and the O₂ phase would be around 0.015 g cm⁻³ when the temperature is at 10 °C or the viscosity ratio λ is near 3.6 times (the viscosity ratio λ is defined as the ratio of the W phase to the O₂ phase). Under this circumstance, the wall thickness uniformity and sphericity were largely improved. Furthermore, the experiment established that wall thickness uniformity was more sensitive to the temperature and the viscosity than the sphericity.