Pick the wrong statement about insulating and special refractories used in furnace practice.
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AInsulating (light-weight) refractories are often variants of regular bricks but processed to have high porosity and lower density.
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BGraphite refractories are also known as plumbago refractories.
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C“Superduty” fireclay bricks correspond to a pyrometric cone equivalent (PCE) of about 26–28.
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DCalcined magnesite is commonly referred to as “dead-burnt” magnesite.
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ESilica insulating bricks rely on air-filled pores to lower thermal conductivity.
Answer
Correct Answer: “Superduty” fireclay bricks correspond to a pyrometric cone equivalent (PCE) of about 26–28.
Explanation
Introduction / Context:Terminology around refractory classes and properties (e.g., “superduty,” “dead-burnt,” “plumbago”) is frequently tested in metallurgical GK. Distinguishing correct statements from mislabeling avoids costly misapplications in furnace design.
Given Data / Assumptions:
- Insulating bricks derive low conductivity from high porosity.
- Graphite is historically termed plumbago.
- PCE (pyrometric cone equivalent) bands define duty classes for fireclay bricks.
- Dead-burnt magnesite denotes highly calcined MgO with minimal reactivity.
Concept / Approach:The misleading statement is the PCE band for “superduty” fireclay. Typical classifications place superduty significantly higher than 26–28 cones; values around the low-to-mid 30s (e.g., ~33–38) are cited for superduty, whereas 26–28 aligns more with medium-to-high duty. The other statements match standard usage: insulating bricks are processed to be light-weight; graphite ≡ plumbago; calcined magnesite is “dead-burnt”; and insulating silica bricks reduce conductivity via pores.
Step-by-Step Solution:Check each statement against conventional definitions.Identify PCE bands: 26–28 is not “superduty”.Confirm remaining terms are correctly matched to industry practice.Select statement (c) as the wrong one.
Verification / Alternative check:Fireclay classification tables list approximate PCE ranges: low duty (~19–23), medium (~23–29), high (~29–33), and superduty (~33–38), confirming the discrepancy.
Why Other Options Are Wrong:(a) Correct: light-weight refractories are compositionally similar but highly porous.(b) Correct: “plumbago” is a traditional name for graphite.(d) Correct: dead-burnt magnesite is the calcined, low-reactivity form.(e) Correct: air-filled porosity reduces heat transfer in insulating bricks.
Common Pitfalls:Assuming duty labels are interchangeable across manufacturers; while exact numbers vary, superduty is well above cone 28.
Final Answer:“Superduty” fireclay bricks correspond to a pyrometric cone equivalent (PCE) of about 26–28.