1) Refractory metal 
Nisil is an alloy of nickel and silicon. Typically, the alloy is mostly nickel alloyed with 4.4% silicon. Nisil melts at 1341 °C and has a density of 8.55 g/cm³. It is often used in conjunction with Nicrosil in type N thermocouples. In this use, it serves as the negative leg of the thermocouple. ...