2.2.3 Resistors and Heating

Resistors

Basic requirements for resistors (still one of the most numerous component in circuits) are:
  • Large region of R values (= device resistance in W) within one production technology.
  • Small (ideally vanishing) temperature coefficient .
  • Minimal noise.
  • Small dependence of r on production parameters (good repeatability).
  • No Ageing.
  • Small thermoelectrical coefficients to Cu (you want a resistor, not a thermoelement).
Materials of choice include
Ta, Ta based alloys, and in particular "Constantan" (55% Cu, 44% Ni, 1% Mn), a resistor material with an especially small temperature coefficient ar, but a large thermoelectric coefficient).
Strange mixtures of conductors and insulators including "Cermet" (short for Ceramics - Metals), e.g. Cr - SiO2.
Details and data in the (future) link.

Heating

Basic requirements for heating elements are:
  • High melting point.
  • Chemical stability at high temperatures and in potentially corrosive environments.
  • Mechanical strength at high temperatures.
The choice of a materials depends significantly on the range of temperatures envisioned. We have:
FeNiCr, FeNiAl alloys.
Pt, W, Ta, Mo - stable elements with a high melting point.
MoSi2 Among more industrial applications also used as heaters in dish washers - this is very aggressive environment!
Graphite (up to 3000 K in non-oxidizing gas).
Some details and data can be found in the links.
Overview of resistivity and temperature range for some materials
Maximum temperatures for some materials

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