Electrical Resistivity of Alloys

## Resistivity Fundamentals Electrical resistivity (rho) measures opposition to current flow, in microohm-cm. Conductivity is the reciprocal. The IACS standard defines annealed copper as 100%. ## Values Across Engineering Metals | Metal/Alloy | Resistivity (microohm-cm) | % IACS | Application | |------------|--------------------------|--------|-------------| | Silver | 1.59 | 108 | Contacts | | Copper (C11000) | 1.72 | 100 | Wiring | | Aluminum (1350) | 2.83 | 62 | Transmission lines | | Carbon steel | 14-17 | 10-12 | Magnetic circuits | | 304 Stainless | 72 | 2.4 | Structural | | Nichrome (Ni80Cr20) | 108 | 1.6 | Heating elements | | Kanthal A1 (FeCrAl) | 139 | 1.2 | Furnace elements | ## Temperature Coefficient of Resistance (TCR) Pure metals have high TCR (copper: +3,930 ppm/degree C). Heavily alloyed materials have near-zero TCR (Manganin: +/-15 ppm/degree C), making them ideal for precision resistors. ## Resistance Heating Alloys **Nichrome**: Maximum element temperature 1150 degrees C. The standard for toasters, kilns, and industrial furnaces. **Kanthal A1**: Maximum 1400 degrees C. Higher resistivity and better oxidation resistance than nichrome due to alumina scale. ## Conductor Alloys **C11000 ETP Copper**: 101% IACS. Standard for wiring and bus bars. Excellent conductivity but soft. **C17200 Beryllium Copper**: 22% IACS but 1280 MPa strength. For contact springs and connectors requiring conductivity plus spring force. ## Superconductivity NbTi wire (Tc = 9.8 K) is the workhorse of MRI magnets and particle accelerators, drawn into fine filaments embedded in a copper stabilizing matrix.