Refractory classification check: which of the following is not a neutral refractory material?

Introduction / Context:
Refractories are commonly grouped as acidic, basic, and neutral based on their chemical behavior with slags and atmospheres. Correct classification is essential for selecting lining materials in steelmaking, non-ferrous metallurgy, and high-temperature process equipment. This question asks you to identify the item that does not belong to the neutral class.

Given Data / Assumptions:

• Neutral refractories are broadly compatible with both acidic and basic slags.
• Basic refractories react favorably with basic slags but are attacked by acidic slags.
• We consider typical industrial compositions and usage.

Concept / Approach:
Typical neutral refractories include chromite, alumina, graphite, and silicon carbide—materials that exhibit relative chemical inertness to both acidic and basic environments (within limits). Magnesite (magnesia, MgO), however, is a classic basic refractory extensively used in basic oxygen furnaces, electric arc furnaces, and ladle linings where basic slag chemistry prevails. Therefore, magnesite is not neutral; it is basic.

Step-by-Step Solution:
List neutral candidates: chromite, graphite, alumina, silicon carbide.Identify basic material: magnesite (MgO).Select the non-neutral: magnesite (MgO).

Verification / Alternative check:
Materials handbooks and steelmaking references classify MgO, doloma, and spinel systems as basic refractories, contrasting with neutral materials like chromite and alumina that tolerate a wider slag chemistry range.

Why Other Options Are Wrong:
Silicon carbide: generally treated as neutral/inert to many slags.Chromite: considered neutral for many service conditions.Graphite: chemically inert carbon; grouped as neutral in refractory practice.SiC-bonded alumina: engineered neutral behavior in many applications.

Common Pitfalls:
Assuming “carbon” implies reducing behavior only and not classifying it as neutral.Confusing spinel or doloma with chromite when memorizing families.

Final Answer:
Magnesite (MgO)