|MadSci Network: Physics|
Hi Mike, I checked the US Mint web site at http://www.usmint.gov/circulating/specifications.cfm for the composition of the nickel. You are correct that the Jefferson nickel contains 25% nickel. The remainder of the alloy (mixture of two or more metals) is copper. A metallurgist uses a phase diagram to predict the crystal structure and magnetic properties of alloys. The phase diagram for copper- nickel alloys has a curie temperature of about 300 degrees centigrade when the weight percent of nickel exceeds 50%. A curie temperature is the temperature at which a magnetic material becomes non-magnetic. A nickel copper alloy with more nickel than copper will be magnetic. The phase diagram in the reference book does not show temperatures less than 200 degrees C. I cannot tell from the phase diagram the exact percentage of nickel that will be magnetic at room temperature. The room temperature percentage is somewhere between 25 and 50%. The percentage of magnetic elements in an alloy does not always determine if the alloy is magnetic. Many alloys can be either magnetic or non- magnetic depending upon the crystal structure. These alloys, when heated above a transition temperature, change crystal structure and become magnetic or non-magnetic. A metallurgist uses phase diagrams to predict crystal structures and magnetic properties of alloys. Bob Novak Specialist, Process R&D Carpenter Technology
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