Magnesite (basic) refractories are preferred for furnace construction under which combined conditions of service?

Introduction / Context:
Magnesite refractories are basic (MgO-rich) materials valued for high refractoriness and resistance to basic slags. However, they have limitations in thermal shock resistance. Choosing them correctly requires balancing chemical and thermal service demands.

Given Data / Assumptions:

• Chemical environment: basic slags are possible.
• Thermal environment: high operating temperatures are expected.
• Operational pattern: prefer steady temperature with limited cycling.

Concept / Approach:

Magnesite bricks excel in high-temperature, basic environments but generally have poorer thermal shock resistance than some alumino-silicate refractories. Hence, they are best in applications aimed at attaining and maintaining high temperatures with minimal rapid temperature swings. Avoid using them where severe quenching or frequent temperature cycling occurs.

Step-by-Step Solution:

Verification / Alternative check:

Material datasheets commonly warn of thermal shock concerns with basic bricks while emphasizing their high-temperature chemical resistance.

Why Other Options Are Wrong:

(a): Opposite of where magnesite shines; it is chosen precisely for basic environments. (b) only: Ignores their primary value at high temperature. (c) only: Ignores thermal shock limitation consideration.

Common Pitfalls:

Assuming a single property (temperature rating) determines selection; overlooking thermal shock behavior in service scheduling.

Final Answer:

Both (b) and (c)