Difficulty: Easy
Correct Answer: hydrated aluminium silicate
Explanation:
Introduction / Context:
Fire clay is the base material for refractory bricks and shapes. Understanding its chemistry explains thermal stability and suitability for furnaces and kilns.
Given Data / Assumptions:
Concept / Approach:
Fire clay is rich in kaolinitic minerals, essentially hydrated aluminium silicate. This composition provides high melting point, low fluxing, and good thermal shock resistance compared to clays with higher iron/lime content.
Step-by-Step Solution:
Verification / Alternative check:
Refractory standards specify Al2O3 and SiO2 within ranges typical of kaolinitic clays, with low Fe2O3 and CaO.
Why Other Options Are Wrong:
Lime and magnesium act as fluxes reducing refractoriness; iron oxide also lowers softening temperature and can cause deformation under heat.
Common Pitfalls:
Assuming “iron-rich” clay is better—iron reduces refractoriness.
Final Answer:
hydrated aluminium silicate
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