Question

Silica refractories are also known as

• A. Acid refractories
• B. Basic refractories
• C. Neutral refractories
• D. Magnesia refractories

Hint:

Silica refractories resist acidic slags but react with basic slags, hence classified as acidic.

Answer 1

The Correct Option is A

Step 1: Understanding silica refractories.
Silica refractories are primarily composed of silica (SiO$_2$). Their chemical behavior depends on the nature of silica, which reacts readily with basic slags but remains stable in acidic environments.
Step 2: Classification of refractories.
Refractories are classified into acidic, basic, and neutral types based on their chemical resistance to slags. Silica-based materials fall under acidic refractories because they resist acidic slags but react with basic slags.
Step 3: Analysis of other options.
(B) Basic refractories: These include magnesia and dolomite refractories.
(C) Neutral refractories: Examples include alumina and chromite.
(D) Magnesia refractories: These are basic refractories, not silica-based.
Step 4: Conclusion.
Therefore, silica refractories are correctly known as acid refractories.

Answer 2

Refractories are classified by how their chemical composition reacts with slag during high-temperature service. Silica refractory bricks are made almost entirely of \( \text{SiO}_2 \). Let's look at what each option actually implies about that composition and behaviour.

1. Acid refractories: Acid refractories are built from oxides such as \( \text{SiO}_2 \) that combine readily with basic oxides (like \( \text{CaO} \) or \( \text{FeO} \)) but resist attack from acidic slags. Since silica bricks are almost pure \( \text{SiO}_2 \), they slot directly into this category, and this is exactly how silica linings are used in acid open-hearth and electric-arc furnace roofs.
2. Basic refractories: This group is built from basic oxides such as magnesia (\( \text{MgO} \)) or dolomite, which resist basic slags but are rapidly corroded by acidic ones. Silica bricks would fail quickly if used this way, so silica cannot belong here.
3. Neutral refractories: Materials like alumina, chromite, and carbon are chemically inert to both acidic and basic slags. Silica is not chemically neutral, it has a strong acidic character, so it does not fit this class either.
4. Magnesia refractories: Magnesia refractories are a specific type of basic refractory, made from \( \text{MgO} \), the chemical opposite of the acidic \( \text{SiO}_2 \) that makes up silica brick. The two are not interchangeable names.

Since silica is an acidic oxide that resists acidic slag attack while reacting with basic slags, silica refractories fall squarely into the acid refractory group.

Therefore, the correct answer is Acid refractories.