Electrical Heating Materials — Selection for Resistance Wire Which metal or alloy is most commonly used for making electrical resistance wire in electric furnaces and heating elements (due to stable high resistivity and oxidation resistance at elevated temperature)?

Introduction / Context:
Heating elements in electric furnaces, toasters, and industrial heaters rely on materials that can convert electrical energy into heat efficiently and survive long-term exposure to high temperatures in air. The right resistance wire must maintain resistivity, resist oxidation and scaling, and avoid rapid creep or embrittlement. This question tests familiarity with standard heater-wire materials used across electrical and thermal engineering applications.

Given Data / Assumptions:

• Application: electric furnaces and general heating elements operating in air.
• Desired properties: high and stable electrical resistivity, good oxidation resistance, adequate mechanical strength at temperature, and manufacturability into wire/strip.
• Common candidate alloys: Nichrome, Monel, bronzes, Babbitt.

Concept / Approach:
Nichrome (nickel–chromium, often Ni 60–80% with Cr balance plus small Fe) forms a protective chromium-oxide scale that resists further oxidation. Its resistivity is much higher than that of copper-based alloys, enabling practical element lengths and safe current densities. Monel and bronzes lack sufficiently high resistivity and oxidation resistance for typical heater-element duty; Babbitt is a soft bearing metal wholly unsuitable for high-temperature electrical service.

Step-by-Step Solution:
Identify key requirement: stable high resistivity + oxidation resistance at elevated temperature.Screen candidates: Cu- and Ni–Cu-based alloys (Monel, bronzes) have lower resistivity and poorer scaling resistance than Ni–Cr.Select: Nichrome meets all criteria and is the industry standard for resistance heating elements.Confirm by application examples: furnace coils, domestic heaters, lab muffle furnaces use Nichrome or related Ni–Cr grades.

Verification / Alternative check:
Material datasheets list Nichrome’s resistivity (roughly 1.0–1.4 micro-ohm·m depending on grade) and continuous-use temperatures often exceeding 1000°C in air, with stable oxide formation. Practical experience in coil rewinding and industrial furnace maintenance corroborates its dominance.

Why Other Options Are Wrong:

• Babbitt metal: a soft bearing alloy (Sn/Pb–Sb–Cu) for low-friction linings, not for hot resistive elements.
• Monel metal: Ni–Cu alloy; strong and corrosion-resistant but relatively low resistivity and inferior scaling for heater duty.
• Phosphor bronze: Cu–Sn–P alloy; good springs/bearings, not high-temperature heater wire.

Common Pitfalls:
Assuming any nickel-containing alloy will work as heater wire; composition and oxide stability matter tremendously. Also, conflating corrosion resistance in liquids (Monel) with oxidation resistance in hot air can mislead material selection.

Final Answer:
Nichrome