# Melting point of metals



## Shark (Aug 4, 2019)

Wasn't sure where to ask this ...

Knowing the melting points of pure metals such as gold at 1945F or zinc at 747F and so on, is there a way to calculate the melting point of different mixtures of metals? 

It seems most of the time if you mix a high melting point metal with one of a lower melting point it reduces the point at which they melt. Is this the basis for using lead instead of other metals when cupeling? 

I know I have other questions as well but this will do until I can get a better thought process of what I am wanting to learn.


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## FrugalRefiner (Aug 4, 2019)

I don't think there is a mathematical formula. You'd need to consult charts where someone has already done the work. Some curves can be smooth, but I've seen others with jigs and jogs that appear unpredictable.

Dave


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## Lino1406 (Aug 4, 2019)

From the attached chart you can evaluate MP of a two components mixture. Always there is a chance of getting a MP which is lower than the lowest MP in the couple


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## Shark (Aug 5, 2019)

Thanks guys, that got me pointed back in the right direction. 

It is odd how knowing the right terminology can get things moving again.

Eutectic.


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## Geraldo (Aug 5, 2019)

Well, in case you haven't come across all the correct terminology yet...

These are called "phase diagrams."

A 2 component diagram is called a "binary phase diagram."
A 3 component diagram is called a "trinary phase diagram."
More than 3 components are called "ternary phase diagrams." These are stacks of trinary diagrams - you can think of it as a 3-d object that has been sliced into 2-d sheets so that it can be depicted on paper.

People publish papers on specific phase diagrams that they develop. You can search online databases for these papers. Free ones are searchable on gen.lib.rus.ec - check the "scientific papers" checkbox when searching.

People collect all the developed phase diagrams into books called "Atlas of Phase Diagrams." They are often specific to a certain metal - for example, "Atlas of Lead Phase Diagrams" which have lead + some alloying element (tin, arsenic, copper, antimony, bismuth etc.).

If you live near a real University e.g. one with a decent engineering school, you can find these atlases in their technical library. Ideally, the university offers degrees in metallurgical or materials engineering. These programs are sometimes folded into the Mining Engineering School or the Chemical Engineering School.

There are now electronic databases of phase diagram data. They are attached to programs that will generate a phase diagram based on the database. Two that I recall are HSC Chemistry and FactSAGE. Unfortunately, the license fee for these programs runs 1000's of dollars a year. Again, good Universities will have a license - you would have to get cozy with the right, friendly professor or doctoral student.

Have fun!

Geraldo


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## Shark (Aug 6, 2019)

Geraldo said:


> Well, in case you haven't come across all the correct terminology yet...
> 
> These are called "phase diagrams."
> 
> ...




Thanks very much. 

While I am in over my head with this, I love picking at it until it is understandable to a small degree. I have some ideas rambling around in my head that I hope to move forward with later after a bit more understanding.


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## peter i (Aug 11, 2019)

And even a “simple”binary composition like Cu/Zn can have an quite complicated phase diagram with different crystal structures at different compositions and temperatures.


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## butcher (Aug 11, 2019)

We use these diagrams often in tempering and hardening of the metal.


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## anachronism (Aug 11, 2019)

butcher said:


> We use these diagrams often in tempering and hardening of the metal.



I'd really love to learn about that Richard- however there are so many things to learn and just not enough hours in the day. 8) 8) 

Jon


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## butcher (Aug 11, 2019)

I never have enough time in any day.

But every day I do have time to learn something.

Hardening, quenching, tempering, locking in the crystal structure...

https://link.springer.com/content/pdf/10.1007%2FBF03215089.pdf


https://www.google.com/search?q=gold+phase+diagram&source=lnms&tbm=isch&sa=X&ved=0ahUKEwikkfuii_vjAhXnGDQIHVkKBykQ_AUIESgB&biw=1280&bih=881


The melting point of mixed metals (lowest) Eutectic

https://vacaero.com/information-resources/vacuum-brazing-with-dan-kay/1268-eutectics-the-good-and-the-bad.html

https://www.google.com/search?biw=1280&bih=881&tbm=isch&sa=1&ei=Py5QXdXlCs3J-gTuoqHQAw&q=gold+eutectic++diagram&oq=gold+eutectic++diagram&gs_l=img.12...62002.68463..71309...0.0..0.95.721.9......0....1..gws-wiz-img.......0i7i30j0i8i7i30.5LFbo5EC1uw&ved=0ahUKEwiVga6ti_vjAhXNpJ4KHW5RCDoQ4dUDCAY


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## anachronism (Aug 12, 2019)

Cheers!


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## Shark (Aug 12, 2019)

Thanks butcher, those links have kept me busy for a while, and still some to go.


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## butcher (Aug 13, 2019)

When tempering metals hardening and annealing, the phase diagrams are extremely important, like when making tools, knives, car parts, bearing races... We can heat metal to a certain temperature and hold that temperature for a period of time and grow a crystalline structure and lock it in with quenching, making the metal extremely hard like glass, we can then reheat the metal to another crystal matrix to relax some of the hardness to get the desired toughness, hard but not so hard to be brittle...

Very little changes in the chemistry of steel or mixture of metals can have a large difference in how the metal reacts to being hardenable, and at what temperature range the crystalline structure of the metal changes or develops so phase diagrams are needed to work these metals, we use them often in welding, and in almost any field where metals are used...

A bit off subject, pure gold is very soft, but when rolled or hammered the crystal structure changes hardening the gold, so hard that it can crack, bringing the gold to red hot under the torch to change the internal crystal structure and allowing the gold to cool will change the crystalline structure of the gold making it soft and malleable again, copper and silver act similar.


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## butcher (Aug 14, 2019)

For those still interested Here is more on the subject discussing 18K gold.
https://infoscience.epfl.ch/record/144083/files/EPFL_TH4635.pdf


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## FrugalRefiner (Aug 14, 2019)

That's *deep*!

Dave


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## Shark (Aug 16, 2019)

I am still reading. And Dave is right, that is deep, way deep over my head....for now.


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## butcher (Aug 16, 2019)

These Phase diagrams are very useful and important in many areas where we use metals, although they can be helpful to jewelers, they can become much more important to the race boat driver who just had his drive shaft straightened or maybe to a structural engineer where some workers are welding on his newly-built bridge and the welds are critical, many fields besides metallurgy use this information.


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## johnny309 (Nov 30, 2019)

butcher said:


> These Phase diagrams are very useful and important in many areas where we use metals, although they can be helpful to jewelers, they can become much more important to the race boat driver who just had his drive shaft straightened or maybe to a structural engineer where some workers are welding on his newly-built bridge and the welds are critical, many fields besides metallurgy use this information.



An in many cases they use some other science.....like inert gases(aka welding with argon gas),high pressure melting( ( aka plasma)....or vacuum melting(( as an example Tantalum)... 
Way too much technology that we are not aware of.
But thanks....my own library is getting bigger.


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