Silicon carbide (SiC) refractories: which property is “very low” for SiC bricks among the listed choices?

Introduction / Context:
Silicon carbide refractories are widely used in high-temperature applications such as kiln furniture, heat-treatment furnaces, and waste-to-energy units. Their industrial popularity stems from a bundle of excellent properties: very high refractoriness, high thermal conductivity, impressive resistance to thermal shock, good abrasion resistance, and acceptable oxidation resistance depending on grade and binder system. This question checks whether learners can correctly reject incorrect negative statements about SiC performance.

Given Data / Assumptions:

• We consider typical high-quality SiC refractory bricks or shapes.
• Operating temperatures often exceed 1700°C for service limits.
• Thermal shock resistance is benchmark-high compared with many alumino-silicates.

Concept / Approach:
Evaluate each property qualitatively. SiC has high refractoriness (not “very low”); high thermal conductivity (not “very low”); and very good thermal shock resistance (again, not “very low”). The “trap” in the stem is the phrase “have very low,” which is untrue for these key performance attributes. Therefore, none of the given negatives applies—“None of these” is the correct selection.

Step-by-Step Solution:
Check refractoriness: SiC service limits are well above 1700°C → not low.Check conductivity: SiC is a highly conductive ceramic → not low.Check thermal shock: SiC resists spalling/cracking from temperature swings → not low.Conclusion: all given “very low” claims are incorrect; choose “None of these.”

Verification / Alternative check:
Materials handbooks consistently list thermal conductivity of SiC far above that of fireclay and many high-alumina bricks, and thermal-shock indexes confirm superior behavior under rapid heating/cooling cycles.

Why Other Options Are Wrong:
“Low refractoriness”: contradicts SiC's high-temperature capability.“Low thermal conductivity”: false; SiC is used precisely for good heat transfer.“Low thermal-shock resistance”: opposite of observed performance.“Low oxidation resistance”: modern SiC grades form protective SiO2 scales; not “very low.”

Common Pitfalls:
Assuming all ceramics are insulating; SiC is an exception with high conductivity.Equating “high hardness” with “brittle under shock”; SiC still outperforms many bricks in thermal shock tests.

Final Answer:
None of these