Does anyone know of any electromagnetic core materials that either do not oxidize or who's magnetic and physical strength doesn't change much when it does oxidize? I need to make a room temperature electromagnet for hydrodynamic propulsion experiments. My first experiments used an air core but the results were insignificant. Design: Electromagnet covered in aluminum (foil) and suspended in the center of an aluminum pipe which is submerged in a saline (salt water) solution. The original magnet had about 1cm diameter and about 10cm length with approximately 300 turns of magnet wire. Two AA batteries were used in series and a potentiometer wired as a voltage divider, the anode and cathode (aluminum) were connected in series with the electromagnet. The resulting lorentz force should be radial causing a blower-like effect where the rotating water creates a propulsion force. The actual results were that the rotation of the water within the aluminum pipe was minimal and halted after a few minutes of operation. The observed forces after a few minutes seem to have changed from radial to going directly from the magnet core to the aluminum pipe. I suspect that the AIR core is too weak of a magnet to use for this purpose and an IRON core would quickly oxidize (rust) and become useless. So what I need to know is what core materials could be used for an electromagnet which is designed for salt-water operation.