Where are magnesite refractories generally not used? Identify the application least suited to MgO-based bricks.

Introduction / Context:
Magnesite (MgO) refractories are classic basic bricks with strong resistance to basic slags and high refractoriness under load. They are favored in steelmaking and cement burning zones but are not universally optimal across all furnace walls or atmospheres. This question probes where MgO is generally not the preferred choice.

Given Data / Assumptions:

• Electric furnaces vary widely (arc furnaces for steel, induction furnaces for non-ferrous, etc.).
• Basic open-hearth and steel melting furnaces employ basic slags.
• Cement kiln burning zones are traditionally lined with basic materials (e.g., magnesia-chrome, magnesia-spinel).

Concept / Approach:
Although many steel arc furnaces use basic linings (including MgO-C), not all “electric furnace walls” are suitable for MgO. In several electric furnace applications—particularly non-ferrous or special atmospheres—high-alumina or silica refractories may be preferred due to chemistry, volatility of slags, and oxidation/reduction cycles. In contrast, basic steelmaking and cement burning zones explicitly demand basic refractories, making MgO a natural fit there. Hence, among the generic choices, “electric furnace walls” is the least consistently compatible category and is the most reasonable selection for “generally not used.”

Step-by-Step Solution:

Verification / Alternative check:
Industry practice shows cement kilns (burning zone) and basic steelmaking furnaces employing MgO-rich linings; by contrast, various electric furnaces (e.g., induction for copper/aluminum, certain resistance furnaces) lean on high-alumina/silica systems.

Why Other Options Are Wrong:

Common Pitfalls:
Overgeneralizing from steel EAF practice to all electric furnaces; ignoring non-ferrous chemistries where MgO is unsuitable.

Final Answer:
Electric furnace walls