# What Is Flux??



## Tomac1 (Oct 23, 2011)

What is it used for, what is it made of, how do you make it, different types and applications, etc... Just curious I hear the term being thrown around a lot. 

Best Regards


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## element47 (Oct 24, 2011)

Flux does several things, all at the same time. Probably the most important thing it does is to help prevent oxidation of very hot metals which are in a chemically active state precisely because they are hot. Heat, in almost all cases speeds, accentuates, intensifies chemical reactions. Oxides of metals tend to have much higher melting points than the raw metals themselves, and they also tend to be lighter per unit volume. That means they will tend to float on a pool of molten metal. This is why when melting zinc and aluminum, the crud that floats on top is usually skimmed off and discarded. Without flux, many metals will "skin over" with their high melting point oxide, the oxygen coming from the surrounding air. The oxide then prevents heat (from your torch) from hitting the surface of a blob of metal you're trying to melt, so the metal then cools and then the oxide (a pollutant, obviously, if you are trying to refine) gets embedded in the surface of the metal. This usually gives a powdery, gritty, rough appearance. This completely sucks, it's exactly the opposite of what you're trying to achieve. It also represents a loss of values. If your silver enters into a chemical reaction, then it is no longer available to be nice shiny metal. 

Flux is also a wetting agent, when molten it is a "wetter" liquid than the liquid metal. It has a lower surface tension, it has a greater tendency to wet surfaces. At the same time, it does not, or should not, react with the molten metal. So in the case of silver and gold in a melting dish, it produces a smooth, very low friction surface that the molten metal can be rolled around on. It smooths the surface of a melting dish by wetting and being partially absorbed into the porous ceramic material of the melting dish. 

Some fluxes aggressively attack and absorb oxides and other impurties. Acid flux, as used in solder, does this. But, it leaves a residue that is well, acidic. So it is not to be used with electronic soldering, because the residual acid over time attacks other items next to the solder joint you're making. This isn't a problem with soldering copper pipe, but a good plumber will wipe away excess flux with a wet rag from a "sweated" (soldered) copper-to-copper or copper-to-brass plumbing joint because over time, excess flux will crystallize and turn green if there is moisture around that reactivates the excess acid left behind. Especially copper-to-brass where there is zinc in the brass part. You've seen that on old plumbing joints. For electronic applications, you use "resin" flux which is extracted from pine wood. Flux which doesn't boil away floats on top of the molten solder, protecting it from oxidation, wets the items being soldered, and shields the joint from oxidation as it cools. If any excess is there, it doesn't turn into an acid. Elect flux doesn't have to be so aggressive because we are not heating up the materials to torch-level heat. 

So flux does all three of these things, in varying amounts, depending on the exact application. Wetting agent, oxidation preventer, pollutant scavenger. In many applications, the use of flux can be reduced somewhat by carefully controlling the atmosphere in which melting takes place. That might mean an oven with an inert atmosphere or, carefully keeping the melt in the reducing portion of a torch flame. 

It is different substances for different applications. Borax is used a lot for silver and gold. You do not make it, it's super cheap to buy.


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## butcher (Oct 26, 2011)

Flux is a very broad term,
It is a substance used to make soldering easier by cleaning joint when soldering, or can be used to keep metals from oxidizing by high temperature's when welding or brazing.

In recovery and refining of metals flux is mixed with metals to be melted, this can be for many different reasons depending on what the goal is, flux can be a simple crushed glass or quartz sand, or borax, these will usually make melt more liquid, give melt a cover to keep oxygen from outside atmosphere, or from our heating source, from oxidizing melt and a slag cover (glass for base oxidized metals to go into), sometimes we want an oxidizing flux, like sodium nitrate or potassium nitrate to oxidize the base metals, other times we may want to do the opposite like reducing flux (remove the oxides in the melt here we would use a carbon source like flour, sugar, charcoal, and so on, sometimes we may use sodium carbonate that will act as reducer and make melt more liquid, or we may use a little fluoride to act as an acid in melt, or we may add a metal in the melt to collect values like lead , litharge, or silver, we may also add a metal like iron to pick up sulfides from another metal. 

Flux in my thinking, is a chemical we use to change the property of metals in the melt, basically a chemical reaction, or to improve melting environment to give us the desired results we seek.


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## Tomac1 (Oct 26, 2011)

Thanks those were both great responses.

But, how is the flux then extracted from the metal being refined, does it just burn out? Is wet chemestry required to extract the flux? 

Regards


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## philddreamer (Oct 26, 2011)

Hard ones are chipped off with a hammer or some other proper tool; softer, like borax, can be dissolved boiled in a 10% sulphuric & water solution.


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## Tomac1 (Oct 26, 2011)

How would one go about detirmining what type of flux to use?


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## philddreamer (Oct 26, 2011)

What are you welding, melting, smelting?


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## qst42know (Oct 26, 2011)

Far to many possible fluxes for far to many processes for a simple list. You must specify the project at hand to get a meaningful answer. Both material and goal.


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## element47 (Oct 26, 2011)

> How would one go about determining what type of flux to use?



Read, study, ask questions, see what other people are using, and copy them. 

The chances of you discovering something new in the world of metalworking; whether casting, welding, soldering, refining, smelting, brazing, etc; etc; etc; are for all practical purposes, zero. That's not meant to be an insult. All of this stuff has been done before, often, for over 100, 300, 500 years. At the same time, NONE of it is secret. Nobody has any secret processes (that you'll have to worry about for your first 5 years doing this) Anything you can learn by copying and duplicating what others are doing is something that you will not have to burn yourself over, blind yourself over, poison yourself or destroy your lungs over, waste chemicals on, lose values over, set your house on fire, or any of several other hazards you can't know about because you don't know what questions to ask. 

As a matter of practice, any time you imagine you're on track to invent something new....it's virtually certain you are not. You really have to get to know the established procedures and processes in this game.


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## Acid_Bath76 (Oct 26, 2011)

This is an awesome thread. Thanks for sharing the knowledge. This brought so many questions to mind. Do you guys recommend any good books on this subject?


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## philddreamer (Oct 26, 2011)

Hi Acid!
I'm sure you can find many books like, @ the Library or on the net, but the question again would be, flux for what metal? 
Just for starters, try a book on fluxes for steel. Different grades of steel use different fluxes. Then go to, lets say, copper & so on. 

Take care!

Phil


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## qst42know (Oct 26, 2011)

Flux for what? 

Pottery clays and glazes, enameling, glass making? 

Please, you really must be specific.


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## Acid_Bath76 (Oct 26, 2011)

Lol.. if I wanted a flux for pottery... I would be on the pottery glazing forum.. or whatever it would/is be called. That had me crack a smile! You're right though, specificity is key. With all the standard washing steps of hot HCL, heating your product until read hot, another hot HCL wash, boiling water, another HCL bath, Hot water, etc.. all this after AR, and then casting shot. Inspecting your product, and then making a decision to either repeat all this or sit satisfied with your product... is there a way to incorporate a flux somewhere in here to speed things up. I work with e-scrap almost 80% of the time. Copper, tin, and all the other rascals seem to be hiding almost everywhere I turn. Granted, a lot of these can be taken care of with a good wash in HCL. I don't want to quote Harold, and I might have read something and confused it with something he had said on here, but my impression from what I've read on here is that a flux would just make it "look" pretty. Looks are only skin deep though, and the tarnish will reappear if you don't grab the impurities from within. With that said, if a flux can't really pull out all the garbage like we can with acids and heating your specimen until red hot (oxidize some of the impurities prior to another wash cycle), what's the use of all these expensive fluxes that contain ten different chemicals? I'm all for speeding things up, once I have a beaker full of brown lumpy sand, all I want to do is see it melt! I realize though, after blundering through early on, that this just creates a nice recipe for a manure hogie. I want to learn how, and when to properly introduce a flux into cleaning gold powders. I'm curious if it could bypass any of these steps. Right now, I use a little borax. A little to coat the crucible as I slowly heat the dish, and a small pinch as it cools... IF i see a little something that doesn't agree with me. If that happens, it's a real temptation not to start over. After all, it's my name behind this product. To clean some of the dirtier crucibles, I use sodium bicarbonate, and then borax to bring it all together and out. That stuff gets processed at the end of the month. 

For anyone interested, these guy seem to have a fantastic site on certain crystalline glazes... they might have something on fluxes :lol: 

http://s3.excoboard.com/crystal


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## philddreamer (Oct 26, 2011)

Hi Acid!
You got it right, we glaze our melting dishes with borax. Now, if we MELT pure gold or silver, we don't need to "flux" the bead. But if we are melting "dirty" gold or silver & we want it to look better we should add some "flux". Borax, soda ash, some nitrate... These will help with making the bead look cleaner or purer, it has been explained before. 
Here are a couple of pic's of my last ingot before shipping. It was 1.7 Toz
of .730. Notice how shiny the surface is. I used borax & soda ash, but it didn'y make it much purer, just look smoother & cleaner. I poured it into my "adjustable" mild steel mold.

Now for SMELTING, that's when you need the right recipe for a flux. Someone else is going to have to help you with that one. :mrgreen: 

I hope this helps some.

Phil

P.S. The question still remains, what does Tomac want to flux!? :roll: :lol:


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## Acid_Bath76 (Oct 26, 2011)

Nice load you have there!! As far as a making a bar look pretty.. that's really not too complicated. You're spot on though. What we should be talking about it SMELTING. I'll get on that Until I really get my brain around it, I'll be doing it as it's been preached on here. It might take a while, but the results are solid.


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## philddreamer (Oct 27, 2011)

Well, Tamac1 started this post & he never mentioned what flux his interested in. 
Now, if smelting fluxes is what you are interested in, then here is a thread you might be interested in: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=11244
by Dan72ccx. Check it out.

Take care! 

Phil


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## Tomac1 (Oct 27, 2011)

So my real question is, can someone suggest a flux formula to try when smelting crushed ceramic from a 60%pt,20%pd,20%rh honeycomb style autocatalyst?

Here is my idea, and it might be a stupid one, you tell me. One man named Graham on finishing.com claimed to have pulled off something similar to this. 

Crush up the ceramic honeycomb, smelt with suitable flux in order to effect a separation of the ceramic and PGMs, that is PGMs in a conglomerate at the bottom and ceramic on top, let cool then break the ceramic and PGM conglomerate apart probably with a hammer, dissolve PGM conglomerate in AR, use usual methods as described by Hokes book from there. 

I need a reducing flux (because of palladiums tendency to oxidize) that will also make the melt wetter (insure a seperation), also something that decreases the melting point of PGMs will be needed, otherwise I'll have to get a furnace that gets hot enough to melt platinum at its nonaltered melting point about 3200 degrees, I have carbonates to deal with due to the nature of a spent cat. Also someone on this forum told me I'd need to use sodium hexaforaluminate aka "cyrite" to dissolve the ceramic. 

Brainstorm with me. 



A good flux formula is what I need.


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## Acid_Bath76 (Oct 27, 2011)

I wouldn't be the one to guide you with flux's, but there's plenty of stuff on the forum on processing cat's. Check out Lazersteve's posting on it. He also has a video for $25. I bought it a while ago. Worth every penny.


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## nuggetpond (Jun 6, 2013)

I am interested in a flux recipe for gold/silver bars with impurities of zinc, iron, lead and copper. Can anyone point me in the right direction? Also looking for what each chemical does to drive the reaction. Using a furnace with a crucible and pouring bullion bars.


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## TomVader (Jun 6, 2013)

something that decreases the melting point of PGMs will be needed,

Tomac,
Flux won't alter the melting point of any metals.


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## Geo (Jun 6, 2013)

nuggetpond said:


> I am interested in a flux recipe for gold/silver bars with impurities of zinc, iron, lead and copper. Can anyone point me in the right direction? Also looking for what each chemical does to drive the reaction. Using a furnace with a crucible and pouring bullion bars.



are you trying to refine by fluxing?


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## alexxx (Jun 6, 2013)

butcher said:


> Flux is a very broad term,
> It is a substance used to make soldering easier by cleaning joint when soldering, or can be used to keep metals from oxidizing by high temperature's when welding or brazing.
> 
> ...or we may use a little fluoride to act as an acid in melt, *or we may add a metal in the melt to collect values like lead* , litharge, or silver, we may also add a metal like iron to pick up sulfides from another metal.
> ...



Butcher,

Any idea on what flux needs to be added into a gas furnace for melting crt leaded glass to recover the lead inside the glass ?

cheers,
Alex


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## butcher (Jun 7, 2013)

alexxx,
I am not really qualified to give a good answer here.
Why would anyone even want to try, unless they were a huge company with free fuel.
the heavy thick front glass on CRT, monitors, or TV this panel glass has almost no lead, but has around 10% barium oxide (BaO) to absorb Xray's, the thinner back part funnel glass can contain about 20% lead oxide PbO in the glass matrix, as lead glass.

I have heard they can make brick out of the glass in some country's to recycle the glass, but I am unsure if they separate the two types of glass and only use one type of the glass like the BaO or if they also make the brick out of the lead-glass portion also, since the lead in the glass is actually part of the glass itself as lead oxide, it would need a carbon source in the flux to reduce the lead back to metal, charcoal, flour, or something that would generate carbon, the carbon takes the oxygen from the PbO to form carbon dioxide gas in the melt, reducing lead back to metalic lead, also with this much lead oxide in the glass I expect the viscosity of the melt would need something like a little bit fluorite to make it more fluid so lead would settle from the slag glass when poured to a mold (this flux would be hard on crucibles tending to attack them also in the melt), and then of course the other basics to the flux recipe like borax and soda ash (sodium carbonate, washing soda), the glass already has an abundance of silica, then you would also need to have a lot of money to spend on fuel, in my opinion it would be worthless and dangerous to try this, unless you were a company who got paid to recycle the CRT, then you would be better of becoming a manufacture of CRT monitors and use them to make new CRT's or bricks out of them.

Messing with CRT's for the most part I see as a bad Idea, caution the are under a vacuum and can implode (explode inwards) if broken, there is a little tit of glass on the back portion where the pins electrical connections are, taking a pair of pliers, and breaking off this tit of glass will let the tube suck in air, and make it safe from implosion, if dropped or miss handled, also TV's or monitors can have large capacitors which can hold a dangerous charge, these should be shorted with a screw driver, and a jumper wire installed across capacitor terminals to keep the capacitor shorted (capacitors can regenerate a charge by sitting it is rare but it happens).

basically I would say forget this idea, and find a better Idea.


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## g_axelsson (Jun 7, 2013)

Alexxx, if smelting the CRT glass for extraction of the lead could be done at a commercial level somebody would already be doing it and there wouldn't be a problem to get rid of our CRT:s.

Here is a report discussing recovery of CRT tubes (2004). http://www.environmental-expert.com/articles/materials-recovery-from-waste-cathode-ray-tubes-crts-3069

And a newer report (2013) that mentions that ordinary lead smelters accept the lead glass for usage in fluxes but needs payment to do so. It also states that some development is ongoing for small scale lead recovery.
http://www.calrecycle.ca.gov/Actions/Documents/77/20132013/835/Overview%20of%20CRT%20Issues%20and%20the%20CEW%20Program.pdf

Göran


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## alexxx (Jun 7, 2013)

Thanks to Butcher & Goran for your kind replies.

Crt glass remains a day to day problem for small & large recyclers.
At this moment, I have to pay to get rid of some 6000 lbs weekly.
In my province, there's no government supported programs to monetize this hazardous material.
Glass to glass market is already flooded...
Lead smelters are charging more than the actual disposal cost + time needed to arrange transport...

Separating the panel from the leaded funnel glass is not a problem for me...
I'm really curious to experiment with some flux in order to recover some lead out of this glass.
If the challenge of recovering lead can be achieved, selling clean glass as an agregate would be easy...

I will try a few melts with various fluxes and will post results...

cheers,

Alex


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## bswartzwelder (Jun 8, 2013)

It will be very interesting to see your results. I hope it works out well for you.


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