Study on plasma drying of expandable graphite and influencing factors

Expandable graphite is synthesized by homogeneously mixing graphite, an oxidant, and an intercalation agent at a controlled temperature, followed by washing, filtration, and drying. To prevent over-expansion during drying, conventional techniques such as low-temperature (≤ 50℃) or vacuum drying are typically employed; However, these methods are often associated with slow drying rates and high energy consumption. Electrohydrodynamic (EHD) drying represents an energy-efficient, non-thermal technology particularly suitable for dehydrating heat-sensitive materials. To avoid structural alterations induced by high temperatures, this study applied EHD drying to expandable graphite, with a focus on investigating the influence of key operational parameters, including discharge electrode polarity, needle tip curvature radius, discharge voltage, discharge gap, and gas flow rate, on the drying kinetics in a single-needle configuration. Throughout the process, sample temperature variations, ion-wind velocity distribution, corona discharge characteristics, and scanning electron microscopy morphology before and after EHD treatment were systematically monitored. The experimental results indicate that optimal drying performance was achieved using a needle electrode with a tip curvature radius of 0.2 mm under the following conditions: an applied voltage of -35.0 kV, a discharge gap of 5.0 cm, and a gas flow rate of 5.0 L/min. Moreover, the EHD drying process induced no measurable temperature rise in the material and had no significant effect on its microstructure.