Does anybody here know the solubility of antimony...

[Harry O]

in tin? I have read that the solubility of antimony in lead is about 6% (the weight of antimony equaling 6% of the weight of lead is fully absorbed -- alloyed -- in the mixture).

I know that using straight monotype for casting does not work well. The mixture is very brittle and breaks easily with a crystaline-looking break. I take it that this means there is a lot of pure antimony that collects (solidifies) between the lead/tin/antimony crystals.

The monotype I have is 7.5% tin, 19.5% antimony and 73% lead. I surmise that approx 4.4% of the antimony (that is 73% x 6%) is absorbed in the lead. That leaves 15.1% antimony. How much of it is absorbed in the tin? Obviously, the 7.5% tin in the monotype is not enough by itself. How much extra tin is needed to absorb all of the antimony?

I have added enough tin to give a 15% tin, 15% antimony, and 70% lead mix. That seems to work well enough to give a non-brittle bullet. So, that is an upper limit. The question is, how much can I reduce the amount of tin added before I have antimony precipitate problems again. The key to that is how soluble antimony is in tin. I have not been able to find that number. If anyone knows, that would give me a starting point to experiment with.

[polara426sh]

I did a quick search and it's solubility appears to be between 6 and 8% at room temperature.

[geargnasher]

I understand that lead and antimony are soluble in one another from zero to 100 percent, but that solubility is dependent upon temperature and will separate upon cooling to solid, I'm assuming you want to eliminate the propensity of antimony to precipitate upon cooling.

I also understand that tin and antimony are infinitely soluble in one another, and that in a liquid lead/tin/antimony solution the tin and antimony form an intermetallic bond that is about equal parts by weight. Whether Pb, Sn, PbSn, or Sn precipitates out first or whether the alloy is eutectic is totally dependent upon proportions of the three.

The Metals Handbook has the Ph, D version of the explanation you're looking for, but Lyman Cast #3 has a pretty good explanation, I quote from p. 46: "Pb is the first solid to form when casting wheel weights or Lyman No. 2 alloy, SbSn will be the first solid to form when casting ordinary monotype which contains 15% antimony and 7% tin. As with the binary lead-antimony alloy, ternary compositions which have (Sb) or SbSn as the primary phase are characterized by extreme brittleness." (bold is mine.) It is NOT the Sb that is freezing first in your monotype, it is actually the intermetallic SbSn, but only at those proportions. At WW proportions, the lead is what solidifies first.

If you have a copy of either of these publications, check out the phase phase chart for the Pb/Sb/Sn ternary, it will explain the relationship of proportion/phase/temperature.

Gear

[geargnasher]

[snip]
I have added enough tin to give a 15% tin, 15% antimony, and 70% lead mix. That seems to work well enough to give a non-brittle bullet. So, that is an upper limit. The question is, how much can I reduce the amount of tin added before I have antimony precipitate problems again. The key to that is how soluble antimony is in tin. I have not been able to find that number. If anyone knows, that would give me a starting point to experiment with.

Ok, I studied your question again. You want to know how much tin has to be added before the antimony precipitates again. That is impossible to answer directly because the amount of tin needed changes with the percentage of antimony present in the ternary alloy. For example, and alloy of 15% antimony and 7% tin will not precipitate antimony crystals upoin cooling, but anything above 11% antimony will precipitate antimony crystals unless balanced by tin in varying proportions: 11% Sb, 0% Sn, Sb precipitates first. at 2% Sn, Sb percentage needs to be above 11% to precipitate pure Sb. Again, at 10% Sn, Sb has to be above 20% to precipitate any out first. The precipitate points vary greatly with temperature.

I don't think the "key" is how soluble antimony is in tin, in fact I think that's the wrong question. I would ask instead "what is the phase trough of Sb and Sn in the Pb/Sb/Sn ternary?" and adjust my proportions based upon that to get the results I was after.

Gear

[runfiverun]

at what point does the antimony become free from the sbsn chain.
i know in lower amounts the chain remains [or seems to] even though there is more sb than sn.
sn will tear away as an alloy with more sn than sb cools. even in low amounts like 1% sb,3% sn
but at what point does the sb tear away from the chain? or does it?
1%sn to 10% sb? or does it depend on the whole percentage?
like anything above 19%sb and anything less than 19% sn.

[troy_mclure]

i dont know if it helps you, but i made around 50lbs of 50/50 - tin/antimony. the antimony dissolved into the tin well below the 1100f melting point.

the ingots from it made very good lyman #2.

[lwknight]

This kind of stuff make my head hurt.
A basic rule of thumb for rednecks like me is that something about 1 tin to 3 antimony parts just works. The balance of lead does not seem not to matter for general casting.

[excess650]

HarryO,
What are your intentions for the 70-15-15 mix? I wouldn't even consider using that for boolits. It WOULD make for a good enrichment mixture to add into softer mixtures.

[lwknight]

I mix 1 pound of tin to 10 pounds of rotomtrals superhard to make 9-27-64. The reason is that it is hard to cast superhard into small ingots because the antimony gets slushy and wants to float. Adding the tin makes the antimony behave and cast smooth even ingots.

Then I can mix 3.5 pounds lead to 1 pound of my 9-27-64 to make hardball ( 2-6-92) .

[geargnasher]

at what point does the antimony become free from the sbsn chain. At any point above the Sb/Sn trough in the ternary phase diagram. It is somewhat temperature dependent, also.
i know in lower amounts the chain remains [or seems to] even though there is more sb than sn. That's my understanding of it, too.
sn will tear away as an alloy with more sn than sb cools. even in low amounts like 1% sb,3% sn "Overtinned" alloy will precipitate pure tin upon cooling, and this makes soft inclusions that are very prone to rubbing off in the bore.
but at what point does the sb tear away from the chain? or does it? Alloys with little to no tin seem to lead barrels by abrasion. As far as it goes when cooling, the primary field of crystallization will be Sb if Sb percentage is over 11 and tin is less than one, or on up the trough line to the eutectic Linotype, where any amount of sb over 12% will be the first to crystallize in the liquid solution as it cools. With tin percentages higher than four, Sb must be more than 12% in order to freeze first in the solution,but not all if it will freeze first since some is tied up in the intermetallic Sb/Sn, which may or not freeze next depending on Pb concentration.

1%sn to 10% sb? or does it depend on the whole percentage?
like anything above 19%sb and anything less than 19% sn. I don't know exactly, it seems that Sb/Sn isn't necessarily a 1:1 ratio, and it also seems to change based on total concentrations. An alloy with 3% Sb and 2% Sn will form pure Pb first, followed by Sb nodules and Sb/Sn filling in the remainder. But raise the proportions to 15% Sb and 10% Sn, and Sb/Sn will be the component that freezes out first, but I'm not really sure how the percentages roll as the alloy cools.

I'm not really sure that for the hobby caster there is much to be gained from an advanced understanding of these interactions, only knowing what standard alloys work best and some of the general rules for boolit alloys should be plenty. There really isn't anything new under the sun when it comes to our common ternary, although there sure seems to be lots of room for discovery in the realm of Zink alloy casting and copper alloys.

Gear

[odoh]

I mix 1 pound of tin to 10 pounds of rotomtrals superhard to make 9-27-64. The reason is that it is hard to cast superhard into small ingots because the antimony gets slushy and wants to float. Adding the tin makes the antimony behave and cast smooth even ingots.

Then I can mix 3.5 pounds lead to 1 pound of my 9-27-64 to make hardball ( 2-6-92) .

That post floats the boat. My first experience w/SH was a major mystery. Seemed like the melt wanted to jump up and crawl out of the ingot mould. Now I know why and that it wasn't only me.
Made a copy for my records ~ thanks!

[Harry O]

HarryO,
What are your intentions for the 70-15-15 mix? I wouldn't even consider using that for boolits. It WOULD make for a good enrichment mixture to add into softer mixtures.

I posted something a while back about bullets I made from a very hard alloy. This was to allow me to use a plain base bullet at full pressure rifle loads (I have not been able to find a gascheck bullet that will feed in this rifle). The Lyman 375167 weighs about 270gr with a normal mix. The 70-15-15 mix was 245gr. However, it worked up to full pressures (appox 42,000psi-45,000psi). BTW, the bullet was dropped into water directly from the mould. It checked at Bhn 37-39 after about a week and a half.

I tried the straight monotype first, but the bullets were way too brittle. I would like to find a mix that will work with less tin. Remember that straight monotype had 7.5% tin in it and that was not enough. 15% is enough. I guess I could try halfway between them, find out which way I have to go and half it again.

[lwknight]

Thats pushing the materials cost to about 4 dollars per pound or so.
Still its way far less than buying jaxxeted bullets. A 300 grain boolit would be about 20 cents .

[geargnasher]

An alloy having 15% antimony will precipitate Sb/Sn in the primary phase if the Sn is 7% or more, and alloys that precipitate Sb/Sn first are going to be very, very brittle no matter how much more tin you add. If you stay under 7% Sn the alloy should precipitate Sb first, but that will still be very brittle.

You have to stay under 10% Sb and use an equal amount or less of Sn, you should be ok on the brittleness side, but probably not as hard as you want.

Something you might try for would be the pseudo-binary eutectic point of 10% Sb/10% Sn. I was just reading through Lyman #3 again and they say that such an alloy will act as a binary, with Pb and Sb/Sn both freezing at the same temperature (473*F), and there will be no antimony or Sb/Sn crystals floating about. This looks like it might be a really tough alloy with not so much crystalline brittleness. What I was thinking was make some of this up, air-cool your boolits, then do a thorough oven heat-treat. Since you know the freeze point of the alloy exactly, you can approach it very closely with your heat-treat temperature without slumping the boolits, and that way you can make them as hard as possible, much harder than water-dropping.

Gear

[Harry O]

The Metals Handbook has the PhD version of the explanation you're looking for, but Lyman Cast #3 has a pretty good explanation, I quote from p. 46: "Pb is the first solid to form when casting wheel weights or Lyman No. 2 alloy, SbSn will be the first solid to form when casting ordinary monotype which contains 15% antimony and 7% tin. As with the binary lead-antimony alloy, ternary compositions which have (Sb) or SbSn as the primary phase are characterized by extreme brittleness." (bold is mine.) It is NOT the Sb that is freezing first in your monotype, it is actually the intermetallic SbSn, but only at those proportions. At WW proportions, the lead is what solidifies first.

If you have a copy of either of these publications, check out the phase phase chart for the Pb/Sb/Sn ternary, it will explain the relationship of proportion/phase/temperature.

Gear

I have the Lyman cast books (along with the E.H. Harrison book and Veral Smiths book), but have not found the answer to what I was asking. Either that or I did not understand what was said. There is a 2-phase lead/tin diagram, a 2-phase lead/antimony diagram, which are a great start, but there is not an antimony/tin diagram. There is also a 2-phase lead/zinc diagram (which is useless) and a 3-phase lead/tin/antimony diagram, but it only shows melting temperature, not solubility.

Any idea where I can find an antimony/tin diagram? It would be great to find a 3-phase lead/tin/antimony diagram, but three dimensions are hard to depict on a two dimensional piece of paper.

[Harry O]

You have to stay under 10% Sb and use an equal amount or less of Sn, you should be ok on the brittleness side, but probably not as hard as you want.

Something you might try for would be the pseudo-binary eutectic point of 10% Sb/10% Sn. I was just reading through Lyman #3 again and they say that such an alloy will act as a binary, with Pb and Sb/Sn both freezing at the same temperature (473*F), and there will be no antimony or Sb/Sn crystals floating about. This looks like it might be a really tough alloy with not so much crystalline brittleness.

Gear

80-10-10 sounds like a possibility. That "might" be hard enough. Or, it might not. Only shooting would tell for sure.

The 70-15-15 mixture is not as ductile as any normal lead mix, but it is tough enough. It is MUCH tougher than straight monotype. Torturing them in a vise with pliers and a hammer showed that it tore most of the way before fracturing. The straight monotype bullet broke through when I crimped the case into the bullet crimping groove. It was a rough crystaline break.

[Harry O]

Thats pushing the materials cost to about 4 dollars per pound or so.
Still its way far less than buying jaxxeted bullets. A 300 grain boolit would be about 20 cents .

Normally, that would be true. However, I got about 250-300lbs of monotype for free many years ago. The tin I am adding is from rolls of solder my wife gets for me at garage or estate sales. I figure, the tin is costing me less than half of buying it straight. The bullets are pretty cheap.

[geargnasher]

It's the fact that 80-10-10 behaves like a eutectic (all freezes at once) combined with the ability to heat treat at a much higher temp than an alloy that has a "slush" phase that had me pointing that out. You might get it harder than water-dropping your 70-15-15.

Gear

[runfiverun]

the 473 is the freeze point i don't think you could go much over 375-390 without the tin sweating.

gear understandin the proportions could help in guessing the mystery alloy.

it's like when you watch a binary alloy cool. 4/6 will still be floatin alloy in the sprue pool but i can cut the sprue off and have solid boolits underneath, just like watching good lino cool in a mold where it solidifies and the center is just flowin around under the surface.

you would have a proportion 25-50% tin to guess at in the total. 4/6 or 4/12
then if the alloy was weighed.
ie you know that 250 gr mold pours at 257 with ww's and 263 with lead and at 246 with lino.
a boolit poured from the mystery metal that you just watched cool similar to lino does
and let freeze in the pot at 566* and it weighs 249.
it could be guessed at a 2/6 alloy or a 5/5 alloy with a hardness test.
you could narrow things down considerably.

the 2/6-5/5 alloys would be pretty similar in all the above except for the cooling and the watching test.
make sense?

[Harry O]

I finally did manage to find an Sb-Sn phase diagram. The original monotype (17.5% Sb) had a rather large area of Sb2Sn3 to go through while it was cooling down. From what I could find, that is pretty brittle stuff. That is probably why the original bullets broke so easily.

It also looks like at 10% antimony, the mix would bypass the Sb2Sn3 area altogether. I am definitely going to try the 80-10-10 mix and see what happens.

[geargnasher]

I don't know if we're speaking the same language, but I think we arrived at the same conclusion. I got there from the ternary phase diagram, you got there from a solubility chart.

Gear