Non-clay Raw Materials Questions and Answers

Answer: A

It is hard, chemically resistant, a good electrical insulator and available in quantity at a price that many applications will bear. Nothing else matches that particular combination across so wide a range of uses. It accounts for the great majority of technical ceramic tonnage.

Answer: B

The Bayer process dissolves the alumina from bauxite in caustic soda and precipitates it as hydroxide, which is then calcined. Purity and particle size are both controlled during that sequence. The Bayer process is the same one that feeds aluminium smelting.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the necessity. Technical alumina is made by the Bayer process, dissolving bauxite in caustic soda, precipitating aluminium hydroxide and calcining it, then milling to a controlled particle size. No natural deposit offers 99.5 per cent purity with a submicron size distribution, and both are needed - impurities form glassy grain boundary phases that destroy high-temperature strength, and coarse particles will not sinter to full density.

Answer: D

The transformation of tetragonal to monoclinic zirconia at a crack tip absorbs energy and resists propagation. Ceramics are otherwise brittle, so this mechanism is a genuinely unusual property. The mechanism is often described as ceramic armour against its own brittleness.

Answer: A

Correct answer: involves a volume increase that closes the crack

The tetragonal to monoclinic transformation carries a volume increase of three to five per cent. The stress field ahead of an advancing crack triggers it in the grains there, and the expansion puts that region into compression, squeezing the crack closed and absorbing energy. It is the reason zirconia has a fracture toughness several times that of alumina, and the reason it is called ceramic steel.

Answer: B

Both are true and the reason gives the purpose: the toughening depends on the transformation being available to happen at a crack tip, which requires the tetragonal phase to be present and poised rather than already converted.

Answer: C

It transforms on cooling with a volume change large enough to crack the piece apart. Stabilisers are not an optional refinement but a requirement for the material to survive firing at all. The volume change on transformation is several per cent.

Answer: D

Correct answer: hardness and high thermal conductivity

Silicon carbide is one of the hardest materials known, close behind diamond and boron carbide, and it conducts heat better than most metals while remaining a ceramic. That pairing explains its uses: abrasives and wear parts from the hardness, and kiln furniture, heat exchangers and heating elements from the conductivity. It is also chemically inert, which is why the acid solubility option is the opposite of the truth.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives both halves. The greater strength allows a thinner section to carry the same load, and the high thermal conductivity keeps the thin section from developing damaging gradients as the kiln heats and cools. The result is furniture of far lower mass - which matters because every kilogram of it is heated and cooled on every cycle at the ware’s expense.

Answer: B

Its low thermal expansion gives it unusual tolerance of rapid temperature change, and it keeps its strength where metals soften. The difficulty is that it does not sinter readily and needs additives or applied pressure.