Need Tin/lead alloy melting points.

[AJ Peacock]

I've looked around quite a bit and haven't been able to find a definitive list of melting points for tin/lead alloys. I've found the common alloy's 50/50, 40/60, etc. But Not a nice spreadsheet with the melting points for every percentage.

The reason I need this is as follows. I have some unknown solder ingot's that I would like to analyse to figure the tin/lead composition. I've taken samples and weighed them in and out of water to calculate a density. According to the density (assuming they are tin/lead only), the composition would be 77%Tin and 23%lead (SG of 8.25). If I could get a spreadsheet with all the melting points, then I could melt it and have a second data point that may corroborate my guess.

Here are the alloy/melting points that I already have.

Solder Alloy______Melting Point (°C)__Melting Point (°F)
100Pb_______________327.4__________621.3
5Sn-95Pb____________307____________585
0.5Sn-92.5Pb-2.5Ag___280____________536
WW (approx)_________263____________505
Sn/5Sb______________243____________469
100Sn_______________232____________450
Linotype_____________230____________475
99.3Sn-0.7Cu________227____________440
96.5Sn-3.5Ag_________221____________430
Sn/3.0Ag/0.5Cu_______219____________426
Sn/3.8Ag/1.0Cu_______217____________423
Sn/3.5Ag/1.0Cu/3Bi____213____________415
50In-50Pb____________209____________402
45Sn-55Pb___________204____________400
55Sn-45Pb___________193____________379
60Sn-40Pb___________186____________368
63Sn-37Pb___________183____________361
62Sn-36Pb-2Ag_______179____________354
97In-3Ag____________143____________289
Sn/57Bi______________139____________282
52In-48Sn___________118____________244

If I've missed the data and it's already around here someplace, let me know. Thanks.
AJ

[AJ Peacock]

Anybody?

[Matt_G]

I'm not finding much to help you out AJ.
Maybe this will fill a few holes in your data...

http://www.kester.com/en-US/technical/alloy.aspx

[rob45]

If I were a manufacturer of solder, then I would want my customers to know at what temperature the product is totally melted, so as to determine suitability for a particular application. That makes sense to me, as one would not want to use a solder that requires a high melting point in an application where high heat may weaken the parent metal. So the listed melting points are most likely for suitability purposes, not identification purposes.

I am not a metallurgist, so perhaps others (including yourself) know more on the subject than I do, but I'll tell you what I do know. Only pure metals and eutectic alloys have a melting point that is easily identifiable using home methods (thermometer).

I use the same melting point concept to which you are referring, but I use it to identify if the scrap "pure" lead or tin I purchase is indeed pure. Pure lead (99.85% pure or better) will both melt and solidify at 621 F. Pure tin will do it at 449 F. Eutectic linotype (composition of 4/12/84) will do it at 465 F.
The only reason I want to identify these materials is because if I know for sure what I'm working with, then I can be assured of reasonable accuracy when I later blend for specific alloys. So that's the same intent as you have. But it also gives me peace of mind to know that I actually got what I paid for. If the person told me it was pure tin, then I know how to tell if it is!

The eutectic for tin/lead alloys has a composition of 63Sn/37Pb. Such composition will change state from solid to liquid at 362 F. Any other solder alloy that is not eutectic, such as 50/50, 30/70, etc., will not be easily identifiable by the melting test. The reason relates to the test method itself- since we do not know exactly the point it melts, we have to determine when it solidifies.

Remember, a eutectic alloy (or pure metal) will melt and solidify at the same temperature. The way to do this at home is to melt the metal and then turn off the heat and plot the temperature decrease while it solidifies. I use a thermometer, stopwatch, and graph paper. Using the graph paper, I take a temp reading every 15 seconds, then note that temp on the graph paper. As it becomes solid, there will be a flat spot in the temperature curve you just graphed. After it has solidified, the curve will then resume, which is simply the cooling of the solid metal and pot. In a eutectic alloy (or pure metal), that flat spot is the melting point. If the alloy is noneutectic, then there will not be a flat spot upon solidification, just a steady curve. That is why we cannot pinpoint (by the temperature method) the composition of an alloy that is not eutectic. The only exception I have found to this is 60/40 solder, which appears to have a curve so shallow that it appears "flat", and is very close to the eutectic 63/37 solder.

So using a temp test to identify an unknown material really isn't very reliable. As an example, look at your list and you will note that 50In/50Pb has an advertised melt temp of 402 F, while 45Sn/55Pb has an advertised melt temp of 400 F. That is close enough to be indiscernible to us, yet one solder has tin and one does not. And do not forget that we probably cannot easily determine the exact melting point of a noneutectic by using home methods, due to the varying properties of solidification. The properties of a noneutectic alloy are such that it does not solidify and melt at the same time, so the temp test is only accurate if using a pure metal or eutectic alloy. Everything else simply gives a curve with no flat spot, and two totally different alloys can give a similar curve.

How much solder are you dealing with? If it's a large batch, it may be worthwile to send a sample in for analysis (assay, x-ray test, etc.) If I'm dealing with unknown solder scrap and must know the composition, I usually wait till I've built a few hundred pounds, then melt it all together and send a sample in for professional analysis.

I hope this helps you out, because by no means do I wish to discourage your efforts. I'm simply stating what I have learned the very hard way. I do like your idea of the specific gravity test. But I would not use a temp test to back it up; the only thing the temp test will reliably ascertain is whether your alloy is eutectic or not. To summarize, your test for specific gravity is far more reliable than a temp test when dealing with an unknown.

[AJ Peacock]

Rob45,

Thanks for you response. I agree with it entirely. However, I'm not trying to identify a solder solely by it's melting point. I already have it's density which limits the possible alloy's to a finite set. Because it doesn't react to Muriatic acid, I know it has no zinc. It cuts and dents like a high tin alloy and the other scraps I received from the same source (old plumbing supplies) has a bunch of known Tin components.
So I'm really just looking for some supporting evidence. For example, Matt G pointed me at the following paper (http://www.sjsu.edu/faculty/selvaduray/page/phase/binary_p_d.pdf) that has a phase diagram for Tin/lead (page 18). If indeed I have a 77%/23% Sn/Pb ingot, it should melt at around 200C (392F). I planned on melting the lead in my pot and setting my thermometer in the first 1/8" of the surface. My pot will be solid at under 500"F. I'll use the surface of the lead by touching the solder to the surface at every 5 degree increment to see it's melt temperature.
As you've pointed out, this won't identify the solder. However, it will eliminate some possibilities from the set. If it does melt near the expected temperature, I'll be confident enough of it's composition to use for my purposes.

Again, thanks for the well thought out and descriptive response.

AJ

[montana_charlie]

ron45,
That was an informative, and interesting dissertation on the subject. As I read along, I had in mind what I would say about 'melting temperatures', then I came to where you discussed that same thing. What you said is (sorta) the reverse of what I thought is true, but my 'knowledge' comes from reading...not doing.

I thought that any non-eutectic alloy would show the flat spot in the graph of decreasing temperature, and only eutectic ones would be a straight drop.
I was under the impression that the presence of the 'slush stage' caused the flat spot.

But, never having needed the data produced by the graphing, I have never done it, myself.

Although what you say is different from what I believed, it is a great piece to keep for reference...even if only as a reminder that not all 'knowledge' is a true reflection of fact...and personal experimentation is often more valid that what 'experts' write.

CM