Identify the acidic refractory: among the following options, which material is classified as an acidic refractory for furnace and kiln applications?

Introduction / Context:
Refractory selection begins with matching the chemical class of the lining to the expected slag chemistry. Acidic refractories resist acidic slags, basic refractories resist basic slags, and neutral refractories serve in mixed or variable conditions. This question asks you to pick the acidic member from a list of common materials.

Given Data / Assumptions:

• “Fireclay” refers to alumino-silicate bricks with significant SiO2 content.
• Magnesite, dolomite, and chrome-magnesite are basic refractories.
• Magnesia–spinel compositions are also basic/neutral leaning due to MgO-rich chemistry.

Concept / Approach:
Acidic refractories are dominated by SiO2 chemistry (silica and many fireclay compositions). They are compatible with acidic slags but are corroded by basic slags. In contrast, MgO (magnesite), CaO·MgO (dolomite), and MgO–Cr2O3 (chrome magnesite) are basic and resist basic slags. Therefore, the only acidic refractory in the list is fireclay.

Step-by-Step Solution:
Classify each option by oxide chemistry.Identify SiO2-rich fireclay as acidic.Recognize MgO/CaO–MgO/Cr2O3–MgO systems as basic.Select “Fireclay.”

Verification / Alternative check:
Standard classification tables place fireclay and silica in the acidic group, while magnesia and doloma families are basic, confirming this choice.

Why Other Options Are Wrong:

• Magnesite/dolomite/chrome magnesite/magnesia–spinel: all basic or neutral-basic; not acidic.

Common Pitfalls:
Confusing alumino-silicate families at very high Al2O3 (neutral/basic) with fireclay grades that remain acidic due to higher silica content.

Final Answer:
Fireclay