What is nickel-iron alloy?
Nickel-iron alloy is an alloy of nickel and iron, as might be inferred from the question. By combining nickel and iron in different proportions, we can manufacture a number of extremely useful alloys. Invar is just one of them, and it is important because it has the lowest rate of thermal expansion of any known metal or metal alloy (up to a few hundred degrees C). This makes for a good metal-to-glass seal in products that don’t get super hot. Nickel and iron alloys have been essential in many applications in the manufacture of thermostats. The chances of your having at least one in your home are excellent. The “magic” in these nickel-iron alloys has been known for well over a hundred years, though they have been refined throughout all this time.
