Which of the following is not an alumino-silicate refractory material?

Introduction / Context:
Refractory linings are selected by matching slag chemistry and thermal service with suitable brick chemistries. Alumino-silicate refractories comprise silica and alumina phases (e.g., fireclay, mullite, sillimanite). Basic refractories include magnesia and doloma systems, which are chemically incompatible with acidic slags but excel in basic environments. This question asks you to identify the non-alumino-silicate among common brick types.

Given Data / Assumptions:

• Alumino-silicates include fireclay, high-alumina, mullite, and sillimanite families.
• Tar-bonded dolomite bricks belong to the basic refractory class (MgO·CaO with tar pitch binder).
• We focus on the primary refractory system, not minor additives.

Concept / Approach:
Because tar dolomite bricks are magnesia-lime based (after calcination), they do not contain the alumina-silicate backbone that defines the alumino-silicate family. In contrast, fireclay (Al2O3-SiO2), mullite (3Al2O3·2SiO2), high-alumina bricks, and sillimanite (Al2SiO5) are classic alumino-silicates used across furnaces, kilns, and regenerators where slag chemistry permits.

Step-by-Step Solution:
List alumino-silicates: fireclay, high-alumina, mullite, sillimanite.Identify basic system: tar dolomite (doloma + tar pitch).Select the outlier (non-alumino-silicate): tar dolomite bricks.

Verification / Alternative check:
Materials catalogues and steelmaking texts place tar dolomite within basic refractories, often used in converters and ladles exposed to basic slags rich in CaO and MgO, underscoring that it is not an alumino-silicate.

Why Other Options Are Wrong:
Fireclay, mullite, high-alumina, sillimanite: all are alumino-silicate systems.

Common Pitfalls:
Confusing “mullite” with “magnesite” due to similar sounds.Assuming tar bonding changes the basic chemical classification; the matrix remains doloma-based.

Final Answer:
Tar dolomite bricks