Subject: Materials Engineering/Chemical Engineering (2019)

(a) Sketch the plane with Miller indices (111) in a unit cell. (2 Marks) (b) Calculate the planar atomic density of the (111) plane in FCC gold. (Hint: Use the relationship between lattice constant, a and radius of atom, R). (2.5 Marks) (c) 24-karat gold is pure gold and is extremely soft. In comparison 14-karat gold is only 58.33wt% gold and the rest being mostly copper and some silver. These additional elements make 14-karat gold much harder, but also cheaper. (i) The atomic radius of gold is 0.144nm and the radius of copper is 0.128nm. What type of solid solution is formed in the 14-karat gold? Justify your answer. (1 Mark) (ii) List down the criteria which must be satisfied to form a solid solution which is completely soluble in each other. (2 Marks)