A heavy-duty ½-inch electric drill with a 9-volt motor and a maximum speed of 500 rpm should provide sufficient mixing to disperse fine carbon powder in your ethanol/water mixture.  The recommended impeller options are either a 12-inch diameter propeller (hydrofoil) or a 10-inch diameter pitched-blade turbine.  These impellers will fully load the drill, smaller impellers or lower speeds may be adequate to accomplish the mixing.