Chromite refractories: Select the correct combined statements about bonding, thermal fatigue resistance, and slag resistance.
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AThey can be bonded with lime and clay during manufacture.
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BSilica-free chromite refractories show better thermal fatigue resistance than silica and magnesite refractories.
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CThey are resistant to basic slags in service.
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DAll of the statements (a), (b) and (c) are correct.
Answer
Correct Answer: All of the statements (a), (b) and (c) are correct.
Explanation
Introduction / Context:Chromite refractories (based on FeO·Cr2O3 spinel compositions) are widely used in metallurgical furnaces where a neutral-to-basic refractory is advantageous. Their behavior against thermal cycling and basic slags influences lining life in steel and nonferrous operations.
Given Data / Assumptions:
- Bonding systems for chromite shapes include lime and clay additions.
- Thermal fatigue (spalling) resistance depends on thermal expansion, thermal conductivity, and microstructural stability.
- Basic slag resistance is a key selection criterion for certain vessels.
Concept / Approach:Chromite (especially low-silica grades) exhibits good resistance to basic slags and thermal shock/fatigue relative to some silica and magnesite products in specific operating windows. Traditional manufacturing used lime/clay bonding; modern products may use synthetic spinel or resin bonds, but the statement remains broadly correct in a classical context.
Step-by-Step Solution:
Validate (a): Lime/clay bonding for chromite bricks is historically established.Validate (b): Silica-free chromite tends to show favorable thermal fatigue resistance versus pure silica and some magnesite grades.Validate (c): Chromite’s chemistry gives good basic slag resistance.Hence, all three statements are correct.Verification / Alternative check:Handbooks on refractories list chromite as neutral-basic refractory with the cited properties and bonding systems, supporting the combined statement.
Why Other Options Are Wrong:
- Choosing any single option omits the full, correct property set; the combined choice reflects established practice.
Common Pitfalls:Assuming all magnesite bricks outperform chromite in every respect; resistance comparisons depend on grade, impurities, and operating environment.
Final Answer:All of the statements (a), (b) and (c) are correct.