Lead silver phase diagram 509 B.Sc. chemistry

B.Sc. chemistry
lead silver system
ZINC CADMIUM SYSTEM
phase rule
phase diagram
TY SEMESTER 5 & 6

1. LEAD-SILVER SYSTEM CECH-509 UNIT-4(B) BY – Ms MAYURI R SOMPURA HJD INSTITUTE - KUTCH

2. These metals are completely miscible in liquid state. They do not form any compound together.

3. Pure lead melts at 327℃. Addition of silver lowers its melting point. Pure silver melts at 961℃. Addition of lead lowers its melting point. Along AB solid lead and solution (melted) is present. Along BC solid silver and solution (melted) is present. System is monovariant among AB & BC.

4. B is the eutectic point where three phases solid lead, solid silver and both their liquid forms si present. The temperature of eutectic point is 303 ℃. Composition of the solution phase is 2.6% silver.

5. the phase diagram of Pb -Ag system has special significance in connection with the ‘derivation of lead’. The argentiferous lead consisting of a very small percentage of silver is first heated to a temperature well above its melting point. So, system only consists of the liquid phase represented by point a’’in the figure.

6. It is then allowed to cool. As soon as the point a’ is reached, lead will began to crystallize and solution will contain relatively increasing amount of Ag. Further cooling will shift line along a’a . Lead continues to separate out and is constantly removed from the melted solution.

7. The melted liquid will constantly become richer and richer in silver until point a is reached, where the % of Ag rises to 2.6% Thus, the original argentiferous lead which might have contained 0.1% or less of silver can now contain upto 2.6% of Ag. This process is known as ‘ P attinson’s process ’.

8. assignment :- Explain two component system with the reference of Pb -Ag system.

9. ZINC-CADMIUM SYSTEM CECH-509 UNIT-4(B) BY – Ms MAYURI R SOMPURA HJD INSTITUTE - KUTCH

10. Pressure is kept constant at 1.0 atm. Degree of freedom is decreased by 1.0. The reduced phase rule ( F = C – P + 1 ) is used. No compound is formed in this system.

11. Point A shows the melting point of pure zinc. When Cadmium is added the melting point of Zn is decreased along AO. B is the freezing point of pure cadmium. When Zn is added the freezing point decreases along BO.

12. We get minimum melting point at O, when three phase are in equilibrium – solid Zn, solid Cd and liquid. This is the eutectic point. The eutectic mixture contains 17% Zn and 83% Cd.

13. assignment :- Explain two component system with the reference of Zn-Cd system.