Solving Sn-Pb Phase Diagram Questions

In summary, the lead-tin alloy is slowly heated from a temperature of 150 C (300F) and it eventually melts. The alloy's composition is 15wt % Sn.
  • #1
soul
62
0
Hi everyone,

Homework Statement



A lead–tin alloy of composition 30 wt% Sn–70 wt% Pb is slowly heated from a temperature
of 150 C (300F).

(a) At what temperature does the first liquid phase form?

(b) What is the composition of this liquid phase?

(c) At what temperature does complete melting of the alloy occur?

(d) What is the composition of the last solid remaining prior to complete melting?

Homework Equations



2f07fxs.jpg


The Attempt at a Solution



It is probably an easy question, but I thought it is a good idea to consult first.
a) At 183 C, the first liquid phase forms.

b) We can draw a tie line and the point intersects with the liquidus line, gives us the composition of liquid. It is 61.9 wt % Sn.

c) It is around 250 C. Because phase diagram is on liquidus line.

d) Composition is 15wt % Sn. We can find it by drawing a tie line.

I am not sure about the question b and d. Because as far as I know composition of this liquid means that the composition of the components in this liquid. For instance, in some specific temperature liquid is composed of 30wt % Sn - 70 wt & Pb. However, in some sources I saw that they interpreted this statement as the composition of liquid phase in the total alloy. Like, again in some temperature, 30 % liquid- 70 % solid. Which one is correct. I am a bit confused. Any help will be greatly appreciated.

Thank you.
 

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  • #2
Hard to help without having phase diagram at hand.
 
  • #3
I have put it below the heading of "relevant equations", but I guess there is a problem about seeing it so I attached it to the problem. Thanks for your warning.
 
  • #4
I can see it now, could be that was my internet playing its dirty tricks, I have serious problems with web access lately.

I think you are right, but I have not analyzed phase diagrams for eons, so second opinion won't hurt.
 
  • #5
Your answers look good to me.

soul said:
I am not sure about the question b and d. Because as far as I know composition of this liquid means that the composition of the components in this liquid. For instance, in some specific temperature liquid is composed of 30wt % Sn - 70 wt & Pb. However, in some sources I saw that they interpreted this statement as the composition of liquid phase in the total alloy.

I think you interpreted it fine, since the question asked for the composition of the liquid phase, not the amount of liquid in the total system.
 
  • #6
ternary Zr-Nb-Y

Please help me do you have ternary phase diagram of Zr-Nb-Y
alloy.
thanks in advance
 
  • #7
what is the structural difference between eutectic & proeutectic alpha?
 
  • #8
your answers of question b&d are absolutely correct..if you want to know the composition in liq. then draw tie line at given temperature , where the tie line cuts the liqidus line drop a vertical line where it cut the x-axis is the correct composition (61.9 wt% sn)...
but if it is asked that what is the amount of liquid at a given temp. & for an particular alloy then u have to use the lever rule...
 

1. What is a Sn-Pb phase diagram?

A Sn-Pb phase diagram is a graphical representation of the relationship between the temperature, composition, and phases of a binary alloy of tin (Sn) and lead (Pb). It shows the different phases that exist at different compositions and temperatures, and the boundaries between these phases.

2. Why is it important to solve Sn-Pb phase diagram questions?

Solving Sn-Pb phase diagram questions helps to understand the behavior and properties of this binary alloy, which is commonly used in soldering and other industrial applications. It also allows for the prediction and control of the microstructure and properties of the alloy, which is crucial for its proper functioning in various applications.

3. How do you read a Sn-Pb phase diagram?

To read a Sn-Pb phase diagram, you need to locate the composition of the alloy on the horizontal axis and the temperature on the vertical axis. The intersection of these two points will correspond to a specific phase or phase boundary on the diagram. The diagram can also provide information on the proportion of each phase present at a given temperature and composition.

4. What are the phases in a Sn-Pb phase diagram?

The phases in a Sn-Pb phase diagram include liquid, alpha (α) solid solution, beta (β) solid solution, eutectic, and eutectic solid solution. The liquid phase exists at high temperatures, while the alpha and beta solid solutions form at lower temperatures depending on the composition. The eutectic is the lowest temperature at which the two solid solutions can coexist, and the eutectic solid solution is a mixture of the two solid solutions at the eutectic temperature.

5. How do you solve Sn-Pb phase diagram questions?

To solve Sn-Pb phase diagram questions, you need to understand the principles of phase equilibria and apply them to the specific alloy composition and temperature given in the question. This involves identifying the phases present, their proportions, and the temperature at which they form. It also requires knowledge of the different phase boundaries and their significance in determining the microstructure and properties of the alloy.

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