Curie Point Demonstration Apparatus

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By Timothy Raney…Bald Engineer Guy with Glasses

The Curie point demonstration apparatus is one version of a “thermo-magnetic motor” or oscillator. It converts thermal to kinetic energy directly by using a ferrous metal’s Curie temperature. This motor’s operating principle makes use of a specific physical property of ferromagnetic substances i.e., the Curie temperature, a point where the metal loses its intrinsic magnetic properties as a function of temperature. This motor essentially functions as a mechanical oscillator and uses nickel metal with its relatively low Curie point. When a heat source raises the nickel armature’s temperature to its Curie point, it becomes nonmagnetic and swings away from the attracting magnet. Once cooled below its Curie point, it swings back to the magnet. I modeled this motor after Nikola Tesla’s 1889 United States Patent for a “Thermo Magnetic Motor[1]”.

Demonstration Purpose and Theory
The purpose of this demonstration is to show a novel means of energy conversion. This particular apparatus converts heat energy directly to kinetic energy by the taking advantage of nickel’s Curie point. The resulting mechanical oscillator depends on the loss of nickel's magnetic properties at a certain temperature[2]. Similar to Tesla’s patent, this design resembles a horizontal pivoted pendulum rod with a piece of ferromagnetic material on one end. In this case, I used nickel based on its relatively low Curie temperature (358OC)[3]. In principle, the oscillator operates via the magnetic attraction of nickel and its subsequent demagnetization once heated to its Curie point. As the nickel-tipped pendulum-armature swings away from the magnet and away from the heat source, it cools.  The magnet attracts the nickel again when the ambient environment cools it below its Curie point. The cycle then repeats itself. Cooling the nickel quickly via an efficient heat sink significantly increases the oscillation frequency.

This apparatus is suitable for demonstrating a novel means of converting thermal to mechanical energy by alternatively heating and cooling a ferromagnetic material in the presence of a strong magnetic field.

[1] N. Tesla, Thermo Magnetic Motor, United States Patent Number 396,121, issued 15 January 1889.

[2] H.F Meiners (Ed.) Heat, Electricity and Magnetism, Optics, Atomic and Nuclear Physics, Volume II of Physics Demonstration Experiments, The Ronald Press Company, New York, 1970, pg. 976.

[3] R.C. Weast (Ed.), Handbook of Chemistry & Physics (64th Ed.), CRC Press, Inc. Boca Raton, FL, 1984, p. E-107.

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