Basics about theory behind alloys?

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solar_plasma

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Here on the forum and in Ammen's I learned about metals that would not dissolve into each other like the extraction process with lead and zinc or the fact that iron would not dissolve in silver. I would like to learn more about that, but I don't know the keywords to search, why some metals behave one way or the other and which metals beside those mentioned do behave like this.

It would help me, if someone could tell me, what this part of the science is called (now don't say "metallurgy" :lol: ) or which authors have written about that.
 
necromancer said:
http://en.wikipedia.org/wiki/Metallurgy :lol:

i think this is a question for GSP.

Not me. Probably Lou or 4metals. Or download a metallurgy text.

https://www.google.com/search?q=theory+of+alloying+metals&ie=utf-8&oe=utf-8

Solar,

This question is obviously not something that can be answered simply and I'm not sure that the answer would benefit anyone else, as far as refining goes. The answer to "why" in a lot of aspects is mostly theory and to me, theory is at the bottom of the list (see my signature) of important things to know. Much more important is to learn "what" happens to this or that when you do this or that to it - the more of those things you know, the more successful you'll be as a refiner. Graduate chemists know tons of theory but, when it comes to refining PM's, they don't usually have a clue. Also, why ask others to waste their time on a huge write-up, when you can search it out for yourself and answer your own questions.
 
Look around in the oil and gas online community (articles, patents, SPE papers). The industry is at the front of the alloy metal industry. The last company I worked for (Baker Hughes) developed an alloy with properties like aluminum (light) but strength like steel. They are always looking for new technology in that field. The deeper they go down, the more weight that is applied to the completion string that has to be anchored like a straw within a straw and withstand 20,000psi and 400F for 10 years or more. The easy oil is gone. Fracking has made it much easier and cheaper but eventually that will be gone and we will look deeper and farther in the sea, new alloys will be important.
 
Some general directions...

1. alloy theory (from a metallurgist's viewpoint) is part of the field of "Material Science." There are lots of introductory texts on this. There are a lot of mechanisms at play, so it does get a little complex.

2. very generally speaking, actual alloys (solid solutions between 2 or more metals, resulting in a single phase solid) are governed by the relative size of the metal atoms (and to a lesser extent, the similarity in the outer electronic structure).

a). Similar sized metal atoms can "substitute" for one another in the crystal lattice of a solid - an example would be Fe-Ni or Ni-Co alloys - the actual atoms are similarly sized. Plain brass (Cu and Zn) is another (note that Cu and Zn are in neighboring groups on the periodic table - similar electronic structures also).

b). The other broad class of alloying is "interstitial", which occurs when atoms of dramatically DIFFERENT sizes can alloy because the small atoms can fit in the spaces between the large atoms. An example would be plain carbon steel - the very small carbon atoms can fit in between the iron atoms in the crystal lattice.

c). you can have a combination of interstitial and substitutional alloying - an example could be old stainless steels - Fe+C+Ni+Cr. The C is dissolved interstitially in the Fe matrix. The Ni and Cr substitute for Fe in the Fe matrix. Modern stainless steels tend to be low carbon, so you don't see much of this anymore...

3. A metallurgist/materials scientist could model the interaction of elements to estimate alloying behaviour. The equations are complex. The more usual approach is to use a PHASE DIAGRAM - this is a diagram usually developed experimentally that shows the solubility of various metals in various other metals. With a sufficient database, these diagrams can also be created theoretically (estimated) using software - a classic example is the program CALPHAD. It is pricey. However, there are a lot of books of phase diagrams, called "atlases" that show these diagrams for all kinds of metals. Two element diagrams are called "binary", while 3 element diagrams are called "ternary" phase diagrams. Beyond 3 elements, people make "pseudo-ternary" diagrams, because it isn't possible to represent graphically otherwise. These are a series of ternary-style diagrams where the fourth element is held fixed at a certain percentage.

If you search, you will find lots of examples of binary phase diagrams, along with the instructions on how to read them.

Enjoy the journey!

Best Regards, G
 
Good post, Geraldo. I will reread it several times until it soaks in.

Solar,

I was probably a little extreme in my last post. What I was saying is, for example, I know that silver and iron won't alloy (actually it does at about 1 part per thousand) and that iron will readily alloy with gold. The main reasons I know these things is because I've seen them happen in practice. What more do I need to know? I could care less "why" these things happen. All I care about is that I know that this is the way that it is. I know these things to be facts and I will do things with these facts always in mind. I probably know 10,000 facts like this and these are what I need to make the right decisions on how to process something or how to pick the best option. Refining PM's is a practical thing. I know you are a theory type guy. But, in my mind, like my signature says, as far as refining is concerned, "A pocketful of theory and $3 will buy you a cup of coffee almost anywhere." In other words, theory is essentially worthless in a practical field. I'll never be convinced otherwise.

I guess this is just me. I love practical things. After differential equations, I took linear algebra, which I detested - nothing but zeros and ones. Boring, boring, boring. But then, I took a 10 hour course, "Advanced Engineering Mathematics." 100% practical. I loved it. Different strokes for different folks.
 
I am probably wrong, but my thoughts are the iron is oxidized in the melt with silver, with silver taking in so much oxygen at these temperatures, and how easily iron forms oxides.
 
butcher said:
I am probably wrong, but my thoughts are the iron is oxidized in the melt with silver, with silver taking in so much oxygen at these temperatures, and how easily iron forms oxides.

You may be right but how is this important, Richard? The end results are that essentially no iron ends up alloyed with the silver. That's the only important thing to know. Knowing "why" it happens won't even buy you a cup of coffee, unless you have $3 to go with it.
 
Thank you all for your answers!

Geraldo, you have given lots of good keywords to do my own search now and even more than I asked, you have already explained a lot! I had a diffuse feeling of, it could have to do with the things you mentioned, like electrons, crystal structures, space between atoms, but I just didn't know, which words to search for. Thank you so much!

GSP, you are right. It is just that, what I told my lady yesterday, when I told her proudly from my successful making of a shiny silver button within a school lesson of 45min - from recovering from some silver plated spoons a student gave to me, over refining, washing and finally melting with a cheap little bunsen burner within 5 min - and just when the school bell rang, I handed out the button to the student.

That this was possible for me is only because of the knowledge I gained from you guys, PRACTICAL knowledge. Of course working that fast causes losses of 50%, but I know, where the losses are and they will be recovered another time. There will be a huge army of teachers, who are better than me to explain the theory, but I believe there are only a few, who could have done this trick at all or at least within that short time.

Understand my approach of view, I am not a chemist, my expertise is to catch the interest of young students for the many small miracles of nature - with the intention, they will open their eyes and want actively to gain personal knowledge about it. From the school books they learn some tiny facts about alloys. My intention is to know a little more than those books, so I can make it a little more interesting for them, but they would only listen, if they get the subjective feeling, that I am some kind of "expert" who knows, what he is talking about. I do not need to be able to understand it all, I don't have to build bridges of steel like engineers, but enough to make it interesting for the kids. It would not surprise me, if one or the other boy or girl, who followed the school experiments and the stories with glittering eyes, would become a chemical engineer or a metallurgist in the future.

When you understand me as a theory guy, this is not the whole truth. I absorb all the practical knowledge and the skills I find here every day, it is only because of my profession's socialization, that I tend to ask (mostly myself) questions, that on the surface have no or only little relevance or value for the practice of refining. I believe, there is a lot different kinds of "refiners", some have ores to process, others scrap jewelry, some are owners of whole plants, others do it as a hobby. When I use experiments related to refining in school to explain some matters the students have to learn about, I am as much a refiner, as everyone else on the board and because of the board - with challenges, problems and approaches to just this setting of mine.

I am sure, I am not the only teacher on the board, so I think, this approach is not more off-topic, than when some workers from a plant join in and have some mysterious problems with their cells, even when they only know their own limited process and neither do need or do know, what are basics to most of us, to do their work.

And no, I didn't feel your answer to be extreme, I understand your point of view and when you answer in the way you did, there are two possibilities: I didn't explain myself good enough and you got me wrong OR I am just wrong and off-topic. Both are valid and no reasons to feel bad, but to learn from this and make it better next time.

While writing this, another footnote comes to mind: It is one of the most effective ways to prevent burn-out to take a little from one's hobbies into the one's labour and to take a little labour into the hobbies.

Once again, thank you all so much!
 
As Geraldo mentioned, phase diagrams can be helpful. I use them a lot. They give you a visual picture of how metals (or non-metals) combine at various temperatures. I rarely use tertiary (3 metals) phase diagrams due to their complexity, but the binary (2 metals) ones are often quite handy. To search for any of them, say silver/copper, just type in: Ag-Cu phase diagram. Some binary ones, such as Ag-Cu, are simple, but many are more complex. Note on the attached Ag/Cu diagram how the liquid (L) curve temperature is at it's lowest point at 28.1% Cu/71.9% Ag, by weight. This lowest melting point is called the eutectic. The melting point of this combination is 778.1C, which is far below the melting points of either silver (961.8C) or copper (1085C). On the diagram, you can see the melting point of sterling silver (92.5% Ag/7.5% Cu - not a eutectic) is a little under 900C (actually 893C).

Most common 2 metal solders and brazes are composed at their eutectic combinations. For example, the eutectic 63Sn/37Pb (commonly called 60/40) melts at about 180C. The Au/Sn braze used to attach gold plated lids to IC packages is commonly about 80Au/20Sn, a eutectic which melts at about 280C.
 

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In the mid-1960's, when I first became interested in chemistry, I owned a very enjoyable book written by a famous British metallurgist named William Hume-Rothery. The title was, "Electrons, Atoms, Metals and Alloys", 3rd edition, 1963, published by Dover Publications. It's now out of print. The whole thing was a 300+ page, somewhat argumentative dialogue between 2 characters, the Old Metallurgist and the Young Scientist. It was very interesting. If I remember right, it was written in a fairly non-technical manner and that's probably why I liked it so much. It's possibly now out-of-date but, maybe not.

I couldn't find it as a free download but I found it used in several places for between $15-$20. I think Amazon had 3 used copies.

Hume-Rothery set up a series of rules on alloying which you might find useful

http://www.synl.ac.cn/org/non/zu1/knowledge/Hume-Rothery-rules.pdf
.
https://www.google.com/search?q=hume+rothery+rules+pdf&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:eek:fficial&client=firefox-a&channel=sb

Lots on YouTube.
https://www.youtube.com/watch?v=qHqAyk8wwxI
https://www.youtube.com/results?search_query=phase+diagrams
 
Wow! I would never have found those with my poor English. Thanks a lot again, now, this reading answers all questions I have. Highly interesting!
 
This is an old post and I think the "basics" part of the question was answered by Geraldo and subsequent textbooks, but if you are still curious, the sort of end all knowledge base is the American Society of Metals. Almost every university library has full access to their online trove. If you are out of school, you can usually get limited access just by asking for it (UT will let you access everything for 1 hour a day if you just ask) or if you have a kid get their login. The actual print versions of their materials take up entire shelves in he university stacks. It's more than you could ever learn, but if you wanted to dive deep, that would be the "Marianas Trench" of alloy knowledge.

Www.asminternational.org
 
http://en.wikipedia.org/wiki/Miscibility
Immiscible metals are unable to form alloys with each other. Typically, a mixture will be possible in the molten state, but upon freezing the metals separate into layers. This property allows solid precipitates to be formed by rapidly freezing a molten mixture of immiscible metals. One example of immiscibility in metals is copper and cobalt, where rapid freezing to form solid precipitates has been used to create granular GMR materials.
There also exist metals that are immiscible in the liquid state. One with industrial importance is that liquid zinc and liquid silver are immiscible in liquid lead, while silver is miscible in zinc. This leads to the Parkes process, an example of liquid-liquid extraction, whereby lead containing any amount of silver is melted with zinc. The silver migrates to the zinc, which is skimmed off the top of the two phase liquid, and the zinc is boiled away leaving nearly pure silver.

More on this:
https://www.google.com/search?q=theory+of+alloying+metals&ie=utf-8&oe=utf-8#q=Miscibility+of+metals
 
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