Classifying refractories by basicity: which of the following is NOT a basic refractory material?

Introduction:
Refractories are often categorized as acidic, basic, or neutral depending on their behavior with slags. Correct classification avoids deleterious reactions in service and premature wear.

Given Data / Assumptions:

• Basic refractories: MgO-rich systems such as magnesite, dolomite, chrome-magnesite.
• Neutral refractories: silicon carbide, carbon, alumina in certain contexts.
• Service with basic slags typically needs basic refractories.

Concept / Approach:
MgO and CaO bearing refractories are basic. Silicon carbide is generally classed as neutral (chemically stable to both acidic and basic slags to a degree) and not “basic.”

Step-by-Step Solution:
List basic candidates: magnesite, chrome-magnesite, dolomite (MgO/CaO systems) → basic.Evaluate SiC: considered neutral, not basic.Thus, “Silicon carbide” is the item that is not basic.

Verification / Alternative check:
Textbook tables place SiC among neutral refractories, known for high thermal conductivity and oxidation sensitivity at very high temperatures.

Why Other Options Are Wrong:

• Chrome-magnesite, magnesite, dolomite, and magnesia-spinel are classic basic systems designed for basic slags.

Common Pitfalls:
Assuming “neutral” equals “acidic” or “basic”; neutral refractories have distinct behavior and compatibility ranges.

Final Answer:
Silicon carbide