Solving Sn-Pb Phase Diagram Questions

AI Thread Summary
A lead-tin alloy of 30 wt% Sn and 70 wt% Pb begins to melt at 183°C, with the first liquid phase having a composition of 61.9 wt% Sn. Complete melting occurs at approximately 250°C, with the last solid phase before complete melting having a composition of 15 wt% Sn. There is some confusion regarding the interpretation of the liquid phase composition, as it can refer to either the composition of the liquid itself or the overall alloy composition. Clarification indicates that the question specifically seeks the composition of the liquid phase, not the proportion of liquid in the total alloy. Accurate answers to the questions were confirmed, emphasizing the importance of using a tie line on the phase diagram for determining compositions.
soul
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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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Hard to help without having phase diagram at hand.
 
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.
 
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.
 
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.
 
ternary Zr-Nb-Y

Please help me do you have ternary phase diagram of Zr-Nb-Y
alloy.
thanks in advance
 
what is the structural difference between eutectic & proeutectic alpha?
 
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...
 
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