Explain briefly the differences between jet milling, vibratory milling, and agitated ball milling.

(ii) Which technique would you use if you wanted to obtain a particle size of less than 1 µm and why?

(iii) Which technique would you use and why if maintaining the purity of your powder was your primary concern?

(b) Keramica-UG

Keramica-UG is a new company that wants to manufacture alumina furnace tubes, and they hire you as a consultant. You are asked to propose a process for the fabrication of such tubes. Give a general description of the process you would propose. Explain the roles of the different steps involved.

(c) Comparison of Wet and Dry Milling

With the aid of a plot, compare wet and dry milling. Enumerate factors that affect the milling rate in ball milling.

Question 2:

(a)

(i) Explain briefly the types of shaping operations in manufacturing.

(ii) With the aid of a diagram, explain sintering.

(iii) Distinguish between isostatic and uniaxial pressing.

(b)

(i) Draw the LaMer diagram for the precipitation process.

(ii) Plot the free energy versus nucleus radius diagram for the nucleation process, including the resultant curve and surface and volume contributions.

(iii) From question 2(b)(ii), and assuming that crystals are spherical particles with radius 

$r$

r, derive an expression for the critical size beyond which the crystal is stable during homogeneous nucleation.

(c) Using an appropriate flow diagram or chemical equations, explain sol-gel processing.

Question 3:

(a) Describe briefly an experiment to determine the fluidity of molten metal.

(b) A large steel sand casting shows the characteristic signs of penetration defect—a surface consisting of a mixture of sand and metal.

(i) What steps can be taken to correct the defect?

(ii) What other possible defects might result from taking each of these steps?

(c) The total solidification times of three casting shapes are to be compared: (a) a sphere with a diameter of 10 cm, (b) a cylinder with diameter and length both 10 cm, and (c) a cube with each side 10 cm. The same casting alloy is used in the three cases.

(i) Determine the relative solidification times for each geometry.