Electrical conduction of refractories: except for which material listed below, most refractories are poor conductors of electricity (i.e., have low electrical conductivity)?

Introduction / Context:
In furnace design and linings, electrical properties of refractories influence heating methods, arc stability, and safety. Most oxide refractories are insulators, but a few materials conduct electricity well. Recognizing the standout conductor helps avoid misapplication in electrically heated systems or when stray currents are possible.

Given Data / Assumptions:

• “Bad conductors” refers to low electrical conductivity typical of oxide refractories.
• We are comparing common refractory classes used industrially.
• We need the notable exception that conducts readily.

Concept / Approach:
Graphite, a crystalline form of carbon, has delocalized electrons moving in basal planes, giving it high electrical and thermal conductivity. By contrast, fireclay, chromite, and silica are largely ionic/covalent oxides with minimal free carriers at moderate temperatures. Silicon carbide is semiconducting and its conductivity rises with temperature, but graphite remains the classic good conductor among refractories, widely used as electrodes and susceptors.

Step-by-Step Solution:
List candidates: oxide refractories vs carbonaceous/semiconducting.Recall graphite’s electron mobility → high conductivity.Compare with SiC (semiconductor) and oxides (insulators).Select graphite as the clear exception.

Verification / Alternative check:
Industrial practice uses graphite electrodes in electric arc furnaces, directly evidencing its strong electrical conduction compared with insulating oxide bricks surrounding the vessel.

Why Other Options Are Wrong:
Fireclay/Chromite/Silica: typical low-conductivity oxides.Carborundum (SiC): semiconducting, but not as conductive as graphite at comparable conditions and not the standard “exception” cited in GK.

Common Pitfalls:
Equating rising SiC conductivity at high T with metallic-like conduction; graphite remains the definitive conductor in refractory lists.

Final Answer:
Graphite (carbon)