Powder Preparation and Milling Questions and Answers

Answer: C

The first two are correct. The third describes the opposite of coprecipitation, whose whole advantage is that mixing happens in solution at a scale no mechanical method can approach. Homogeneity at that scale is what shortens the later calcination.

Answer: D

Correct answer: a large proportion of organic binder to be added

Injection moulding requires the feedstock to flow into the mould under pressure, so the powder is compounded with 30 to 50 per cent by volume of thermoplastic binder. That is far more than any other forming route uses, and it is why the removal of it afterwards is the process’s central difficulty.

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 the mechanism. Half the volume of the moulded part is binder, and once it begins to leave the part is held together by very little. It must therefore be removed slowly - days rather than hours - by solvent extraction, catalytic decomposition or careful thermal cycles, and debinding dominates the process time.

Answer: B

Correct answer: False

Binder makes forming easier and firing harder. More of it means more gas to remove, a longer and more delicate burnout, greater shrinkage and more porosity left behind. The right quantity is the least that will do the job, and the balance differs for every forming route.