“Carborundum” crucibles: chemically, carborundum is which compound commonly used for making crucibles for non-ferrous melting?

Introduction / Context:
“Carborundum” is a trade/vernacular name historically associated with silicon carbide (SiC). SiC is valued for high thermal conductivity, good thermal shock resistance, and chemical durability, making it suitable for crucibles used in non-ferrous melting and holding furnaces.

Given Data / Assumptions:

• Question asks for the chemical identity behind the name “carborundum.”
• Application context is non-ferrous crucibles (e.g., aluminum, copper alloys).

Concept / Approach:
SiC’s covalent bonding and stable structure provide strength at elevated temperature and excellent resistance to cracking under thermal cycling. In oxidizing conditions, a protective SiO2 layer can form, further enhancing corrosion resistance against some melts.

Step-by-Step Solution:

Verification / Alternative check:
Materials catalogs list SiC crucibles as “carborundum” types; silicon nitride (Si3N4) is used for thermocouple protection tubes and bearings, not typically as “carborundum” crucibles.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing trade names; assuming any silicon-based ceramic is “carborundum”.

Final Answer:
Silicon carbide