Question

10. In the following phase diagram for Zn-Cu Alloy. Label one eutectic, eutectoid and peritectic point and write down the reactions and all other relevant details. Also explain the eutectoid reaction i.e. why does one solid phase convert to two solid phases as the alloy cools down.....(5 points) a)The figure needs to be part of your answer sheet Composition (at% Zn) 20 1200 40 60 100 12200 80 2000 a+L Liquid 1000 1800 B+L 1600 800 1400 3 B Temperature (°C) Temperature (°F) 8 +L 1200 + 600 7 8 + € 7+L 1000 Z 800 400 + + 7 E+ 600 1 400 200 0 (Cu) 20 10 60 80 100 (Zn) Composition (wt% Zn)

Answer 1

Composition (at% Zn) 0 20 40 60 80 1200 100 2200 2000 a + L Liquid 1000 1800 B+L 1600 800 1400 B Temperature (°C) Temperature (°F) 1200 8,+L B ation 600 + 13 a 2 5+ 7+1000 7 B' € 800 400 7+e 77 B + > B' En 600 1 1 1 200 0 (Cu) 20 40 60 80 400 100 (Zn) Composition (wt% Zn)

When liquid upon cooling converts into two different solids it is known as Eutectic Reaction and the correspoinding point is called Eutectic Point. Example - No such point in the given phase diagram.

When one solid upon cooling converts into two different solids it is known as Eutectoid Reaction and the correspoinding point is called Eutectoid Point. Example - point 2 shown in the phase diagram.

When liquid and solid phase upon cooling converts into another solid it is known as Peritectic Reaction and the correspoinding point is called Peritectic Point. Example - point 3 shown in the phase diagram.

A liquid solution is a single phase, but when it solidifies to the solid state, the different chemical compositions and/or crystal structures are possible and hence a solid may consist of several phases. For the same composition, different crystal structures represent different phases.