Science: Fe-Ni-Cr-Si

William Gilbert, who was Queen Elizabeth’s personal physician but used his spare time to putter with electricity and magnetism, discovered that when iron is hot it loses its magnetism. That was about 1600. Late in the 19th Century, Pierre Curie, husband of Marie Curie, discovered that—although magnetism is gradually lost with rising temperature—an abrupt change occurs at a certain heat above which iron, nickel and cobalt cease in effect to be magnetic. This critical temperature chemists call the Curie point. These two discoveries underlie the operating principle of a new alloy announced last week in Instruments (“The Magazine of Measurement and Control”).

Metallurgist L. R. Jackson and Physicist Howard Willis Russell of the Battelle Memorial Institute (Columbus, Ohio) realized that if they could vary the ingredients of an alloy so as to set the Curie point at any desired temperature, they would have a highly sensitive substance for thermostatic control. Experimenting with several mixtures, they finally got what they wanted with an alloy of iron, nickel, chromium, silicon.

Since it can be made to operate switches and contactors at the critical temperature, the Jackson-Russell alloy can be used to shut off costly machines at the point of overheating; for automatic fire alarms and sprinklers; for air conditioning, refrigeration, household heating. So far the alloy has no name except the “Fe-Ni-Cr-Si system,” from the symbols of the four chemical elements which compose it.