Fire clay used for refractory products contains which principal constituent in a comparatively pure form? Choose the single correct option relevant to refractories and heat resistance.

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:

  • We are focusing on the main compound present in fire clay.
  • Impurities like iron oxide and lime are kept low because they lower refractoriness.


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:

1) Identify the desired refractory constituent: aluminosilicate with structural water.2) Hydrated aluminium silicate (kaolinite group) matches fire clay chemistry.3) Therefore, the correct option is hydrated aluminium silicate.


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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