Question:
Which of the following refractories is best for handling molten steel with high oxygen activity?
Which of the following refractories is best for handling molten steel with high oxygen activity?
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Magnesia-carbon is the standard lining material for the slag-line region of steel ladles and basic oxygen furnaces (BOF) due to its superior resistance to both chemical corrosion and thermal cycling.
Updated On: Jul 3, 2026
- Carbon-based refractories
- Magnesia-carbon
- Silica
- Fireclay
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Question:
The question asks to identify the refractory material that is most suitable for lining furnaces or vessels that contain molten steel with a high concentration of dissolved oxygen (high oxygen activity).
Step 2: Key Formula or Approach:
Refractories must be chemically compatible with both the molten metal and the slag to minimize corrosion and dissolution.
High oxygen activity in molten steel promotes the oxidation of carbon and other elements:
\[ \text{C(refractory)} + \underline{\text{O}}\text{(dissolved)} \rightarrow \text{CO(g)} \]
Step 3: Detailed Explanation:
• Limitation of Pure Carbon: Carbon-based refractories (Option A) have excellent thermal conductivity and slag resistance, but they are highly susceptible to rapid oxidation and decarburization when exposed to molten steel with high dissolved oxygen levels.
• Advantages of Magnesia-Carbon (MgO-C):
- Magnesia-carbon refractories consist of high-purity magnesia (MgO) grains bound with carbon (graphite and resin).
- Magnesia is a highly stable basic oxide with a very high melting point (\( 2852^\circ\text{C} \)) that does not easily reduce or react with dissolved oxygen.
- The presence of graphite provides excellent thermal shock resistance and slag non-wetting properties.
- Decarburization of the surface carbon leaves behind a dense sintered MgO layer that shields the remaining refractory from further oxidation and wear.
• Other Options:
-
Silica (Option C) is an acidic refractory and reacts aggressively with basic slags, making it unsuitable for ladle linings or basic steelmaking.
-
Fireclay (Option D) has a relatively low melting point and poor resistance to metallurgical slag and thermal shock compared to MgO-C.
Step 4: Final Answer:
Therefore, Magnesia-carbon refractories are best for handling molten steel with high oxygen activity, matching Option (B).
The question asks to identify the refractory material that is most suitable for lining furnaces or vessels that contain molten steel with a high concentration of dissolved oxygen (high oxygen activity).
Step 2: Key Formula or Approach:
Refractories must be chemically compatible with both the molten metal and the slag to minimize corrosion and dissolution.
High oxygen activity in molten steel promotes the oxidation of carbon and other elements:
\[ \text{C(refractory)} + \underline{\text{O}}\text{(dissolved)} \rightarrow \text{CO(g)} \]
Step 3: Detailed Explanation:
• Limitation of Pure Carbon: Carbon-based refractories (Option A) have excellent thermal conductivity and slag resistance, but they are highly susceptible to rapid oxidation and decarburization when exposed to molten steel with high dissolved oxygen levels.
• Advantages of Magnesia-Carbon (MgO-C):
- Magnesia-carbon refractories consist of high-purity magnesia (MgO) grains bound with carbon (graphite and resin).
- Magnesia is a highly stable basic oxide with a very high melting point (\( 2852^\circ\text{C} \)) that does not easily reduce or react with dissolved oxygen.
- The presence of graphite provides excellent thermal shock resistance and slag non-wetting properties.
- Decarburization of the surface carbon leaves behind a dense sintered MgO layer that shields the remaining refractory from further oxidation and wear.
• Other Options:
-
Silica (Option C) is an acidic refractory and reacts aggressively with basic slags, making it unsuitable for ladle linings or basic steelmaking.
-
Fireclay (Option D) has a relatively low melting point and poor resistance to metallurgical slag and thermal shock compared to MgO-C.
Step 4: Final Answer:
Therefore, Magnesia-carbon refractories are best for handling molten steel with high oxygen activity, matching Option (B).
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