Attempts to use Electrohydrodynamic (EHD) flow for propulsion have been made since the last century 1 . Limited success has been registered particularly due to the inhomogeneous generation of the thrust, and also the very light weight and frail nature of the devices versus the power supply weight needed hover the craft 2 . However, EHD propulsion can offer a greater thrust to power ratio than any of the current propulsion technologies 3 . Rotary EHD devices have been employed as demo units for a long time 4,5 , but it was unknown if they could produce enough thrust and vertical lift to lead to device liftoff. We designed EHD propellers which spin and eventually lift off and fly independently for a short while. The propeller is balanced on and powered through a high voltage pin/shaft while an intense electric field is created by the presence of a surrounding ground electrode 6 . Multiple propeller electrode designs and ground counter electrodes are able to support propeller rotation and liftoff. Propellers up to 27.8 g and 25.5 cm in diameter were studied with a liftoff voltage range of negative 9.5 kV to 60 kV and rotational speeds up to 80 rot/s. It appears that these are the first EHD devices to liftoff and fly on their own without carrying a power supply 7 . This validates a rotary-based system as a new principle for propulsion with potentially improved stability and control characteristics versus the current EHD devices. Design optimization and scaling seem possible and EHD drone design feasible. Other applications may include EHD motors, fans, or sensors.

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We developed a new procedure for synthesizing highly crystalline FeCO 3 by hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea, starting from ferric ammonium sulfate and Na 4 EDTA as the main precursors. Single phase FeCO 3 microcrystals with a size in the range of 50−200 μm have been obtained after high pressure−temperature treatment time between 15 and 26 h at 230 and 250 °C. Without changing the concentrations of the precursors and synthesis temperature, we have investigated the kinetics of phase transitions between 2 and 40 h of high pressure−temperature treatment time. A transition from hematite (in the first 4 h) to magnetite microoctahedrons with superparamagnetic behavior at room temperature, via a single phase of iron carbonate microcrystals, has been recorded.

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