Non-clay Raw Materials Questions and Answers

Answer: C

Both are true and the reason gives the driver: the thermal performance of beryllia is better, so the substitution is made on grounds of safety rather than of technical merit. Toxicity has settled a question that performance alone would not.

Answer: D

The first two are correct. The third inverts the property, since aluminium nitride is valued precisely for being an electrical insulator while conducting heat well. That combination is precisely what an electronic substrate requires.

Answer: A

In a metal both are carried by electrons and go together, but in a ceramic heat can travel by lattice vibrations while charge does not move at all. Aluminium nitride and silicon carbide are practical demonstrations of the point.

Answer: B

Correct answer: about 64 per cent

For the same volume the mass ratio is the density ratio: \[ \frac{2.5}{3.9} = 0.641, \] so about 64 per cent. Inverting it gives the 156 per cent offered. This is the calculation behind boron carbide’s use in armour and neutron shielding - comparable hardness at roughly two thirds of the weight is decisive where the material must be carried.

Answer: C

Correct answer: retains strength to high temperature and resists shock

Mullite melts above 1800 degrees, keeps its strength almost to that point, has a low thermal expansion and so tolerates thermal shock, and resists slag attack well. That combination is why it is the desirable phase in an aluminosilicate refractory and why kyanite is added to generate more of it - the plasticity and low melting options describe clay and glass, which are what mullite is wanted instead of.

Answer: D

Metakaolin converts to mullite above about a thousand degrees, so the mineral appears without anyone having supplied it. Refractory formulations may add mullite as well where more of it is wanted. In-situ formation is a considerable convenience in fireclay refractories.