# Using a gold melting furnace to calcined Pt crystals



## Kalahari_Harry (Sep 3, 2014)

Hi, would it be advisable to use a small electrical induction furnace to calcinate Pt colored crystal powder to Pt metal powder at 800 degrees Celsius? As seen on YouTube?


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## FrugalRefiner (Sep 3, 2014)

When you calcine PMG salts, you must carefully control the heat. If you use too high a heat, you will lose some of your values. I doubt you could control an induction furnace close enough to avoid losses.

You'll find much more accurate information here on the forum than on youtube.

Dave


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## etack (Sep 3, 2014)

kadriver was doing it on a hot plate and pyroceram dish.

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=51&t=14881&start=100

Eric


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## g_axelsson (Sep 4, 2014)

Kalahari_Harry said:


> Hi, would it be advisable to use a small electrical induction furnace to calcinate Pt colored crystal powder to Pt metal powder at 800 degrees Celsius? As seen on YouTube?


You can't use an induction furnace to calcinate Pt salts, induction only works on metallic objects, not salts.

Göran


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## 4metals (Sep 4, 2014)

Reduce it with Hydrazine, no losses, no ammonium chloride fume.


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## Harold_V (Sep 5, 2014)

g_axelsson said:


> Kalahari_Harry said:
> 
> 
> > Hi, would it be advisable to use a small electrical induction furnace to calcinate Pt colored crystal powder to Pt metal powder at 800 degrees Celsius? As seen on YouTube?
> ...


Depends on the frequency of the induction furnace. Pretty much anything can be heated if the oscillation rate is high enough. Think microwave oven. 
However, an induction furnace wouldn't be my choice, not by a long shot. 

Harold


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## g_axelsson (Sep 5, 2014)

Harold_V said:


> g_axelsson said:
> 
> 
> > Kalahari_Harry said:
> ...


There's a huge difference between induction heating and micro wave ovens, they are based on two different principles.

- Induction induces a current into a metallic object and the rotating current heats the object by resistive heating. Anything that doesn't conduct current is unaffected by an induction oven. Glass, ceramics, tree, salt, water... is unaffected. Solid metal objects conducts current and is heated. Metallic powders does conduct current but the contact points between the grains usually gives high resistivity so the current goes down and the heating effect is lower. By increasing the frequency small loops inside each grain can be formed and you get higher effect and melts the metal.

- Microwave heating targets the molecules in an object. For example the domestic microwave oven is tuned to the rotation frequency of water molecules. That's why glass isn't affected so much while the water inside the glass is heated. Another effect is when we try to thaw something frozen, the water locked up in ice doesn't rotate so most of the microwave passes through the ice and is absorbed in already thawed pieces, you can cook a part of a frozen fish before everything has thawed. Rapidly rotating water molecules bumps into other molecules and that is what we see as heat transfer.
By varying the frequency you can target other molecules so in theory you could build an oven that heats the glass while the water stays cool.

Göran


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## Harold_V (Sep 5, 2014)

Yep! I agree with all you said. 
Induction furnaces create eddy currents in the metal, heating in the process. It is the eddy currents that create the rather ambitious stirring that is common to induction furnaces. 

It should be noted that the size of the charge determines the required frequency, which gets higher as the volume decreases. I have no clue where there would be a cross-over, but I fully expect that an induction furnace, operated at a frequency that rivals that of a microwave, would behave in an identical way. Frequency is key to the outcome. Please correct me if I'm wrong, as I am not schooled in this arena. 

I think my point was that one can perform the operation via the use of such a device---call it an induction furnace or microwave. It just wouldn't be a good idea, as the fumes would have to be addressed, and I expect corrosion would be a concern. 

Harold


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## 4metals (Sep 5, 2014)

Calcining Pt salts results in copious quantities of thick dense ammonium chloride fume. Passes right through a caustic scrubber. Plus the fume takes its toll on every bit of metal it encounters, very corrosive. Unless you are doing large quantities, stick with a chemical reduction.


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## butcher (Sep 5, 2014)

Health hazards would be a big concern with these fumes.


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## 4metals (Sep 6, 2014)

Refiners are like Bill Clinton, we never inhale!


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## g_axelsson (Sep 6, 2014)

Harold_V said:


> Yep! I agree with all you said.
> Induction furnaces create eddy currents in the metal, heating in the process. It is the eddy currents that create the rather ambitious stirring that is common to induction furnaces.
> 
> It should be noted that the size of the charge determines the required frequency, which gets higher as the volume decreases. I have no clue where there would be a cross-over, but I fully expect that an induction furnace, operated at a frequency that rivals that of a microwave, would behave in an identical way. Frequency is key to the outcome. Please correct me if I'm wrong, as I am not schooled in this arena.
> ...


I understand that it can be hard to see the difference between induction and microwaves if you don't know more about the underlying physics. I have thought a lot about how to describe it in simple terms to show it is a fundamental difference between induction and microwaves. You got a good grasp on how induction works, the charge (the metal to melt) can be seen as the secondary side in a transformer and that it is short circuited. You would get the same effect by running a DC current through the charge, the frequency only depends on the size of the melt and the material to melt.

For microwaves the size of the object to heat isn't vital, it's the chemical bonds and the microwave absorption of the object that matters. It has more in common with friction than with induction. In a normal microwave oven you use the electromagnetic wave to violently shake the water molecules to heat the water.

For me as a physicist to say that induction and microwave in principle is the same is probably comparable to you when you hear people mixing melting and smelting.

To turn an induction oven into a micro wave oven you would have to change everything except the wall plug. The way the signal is formed, the transmission, the way it is delivered to the melt, the geometry of the antenna, the type of material that is melted. Microwaves travels on the surface of conductors so it would be useless to use on metals.

So, to summarize it in the simplest way:
- Induction : Heating by running a current through the object. Works on conductors.
- Microwave : Heating by violently shaking the atoms. Works on isolators.

I'm sorry, I just can't let this slide. 8) 

Göran


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## Harold_V (Sep 7, 2014)

g_axelsson said:


> I'm sorry, I just can't let this slide. 8)
> 
> Göran


Nor should you, Göran. I left the door open for clarification, as I am a firm believer that readers should not be exposed to misinformation, and the source doesn't matter (I am not exempt). If I am wrong, I hope to be corrected. That's how we grow as humans, and I'm hoping I have learned something from our exchange. We'll see how much of this I remember tomorrow! :lol: 

You might wish to rethink the concept of not being able to melt with a microwave, by the way. While I don't understand the physics involved, there are folks who sell an insert in which you can melt small amounts of metal, using your microwave oven. I gather, from what little I've read, that the insert is primarily a huge insulating device, so the heat created is contained within. I fully expect such a device would function for calcining, although it certainly would be a poor choice. 

Harold


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## butcher (Sep 7, 2014)

Microwave can be reflected (like from the walls of the microwave oven) and will not heat the walls, microwave at a specific frequency has a certain size of wave, this wave if bigger than a hole in the metal will not pass through the hole. note the window on the home microwave door has a metal screen with holes in it these holes are sized so that the microwave cannot pass through the door, the frequency of the microwave creates a wave bigger than the holes.

Microwave also travels in a straight line. it can be reflected (with metal) like a light beam of light with a mirror, it will not go through the metal, it will not go over or through a mountain.

Microwave cooks food by vibrating the molecules of water, note that objects without water do not normally get hot.
metals that reflect the microwave do not get hot.

Most home microwave oven if we put metal in them would blow fuse and normally the high voltage diode and possibly the radar tube.

Some foods can not be heated very well in a microwave, without the water, or moisture content which can act as a receptor of the microwave energy, like bread, Have you ever looked inside the package from a Hot-Pocket sandwich , that you heat up in a microwave, the inner side of the card board is lined with a microwave susceptor, to heat the bread.

To heat object like a metal gold we would need a microwave susceptor, or receptor that would absorb the microwave energy (not just reflect it), if we were melting impure gold powder we may have a susceptor in the impurities, or we could use a flux that included a microwave susceptor that would not effect the purity of our melted gold.

The susceptor is what absorbs the microwave energy and will generate the heat that will melt the gold. 

if melting in the microwave the insulation (soft fire brick or ceramic fiber-wool) needed to protect the microwave walls (and the microwave, from the heat that normally would not be there when we cook food, this insulation can also help hold the heat inside generated by the susceptor.

Goran,
Thank you for that clarification, and short introduction to the difference of induction heating verses microwave, it makes a lot of sense, I kind of get it, and somewhat understand it, but I would need more study to understand it better, maybe when I have some more time, I will have to put that on my list of interesting things to look into further, (note it is a long list).

The tube in your home microwave is basically a radar tube, a man who was working on radar tubes had a candy bar near his work bench, when his candy bar melted, he got the idea he could cook food with the radar tube, or the microwave energy generated by the radar tube.

https://www.google.com/search?newwindow=1&site=&source=hp&q=microwave+receptors&oq=microwave+receptors&gs_l=hp.13..0i22i30.2270.19977.0.26609.19.14.0.5.5.0.159.1425.8j6.14.0....0...1c.1.53.hp..0.19.1478.70xIzyqbOhA
https://www.google.com/search?newwindow=1&site=&source=hp&q=melting+gold+microwave+receptor&oq=melting+gold+microwave+receptor&gs_l=hp.3...3298.22266.0.23905.33.25.1.7.7.0.150.2316.18j7.25.0....0...1c.1.53.hp..4.29.2043.tG16iHFewq4

https://www.google.com/search?newwindow=1&q=melting+gold+microwave+susceptor&oq=melting+gold+microwave+susceptor&gs_l=serp.12...172062.185217.0.188198.17.17.0.0.0.0.124.1658.7j9.16.0....0...1c.1.53.serp..7.10.1063.Bd-8H3CVUG4


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## justinhcase (Sep 7, 2014)

Has any one look at the interaction of Micro waves and matter already in a plasma state.
I read a little about it being used in propulsion devices to increasing the efficiency of fuel.
The effect is quite startling and if uncontrolled creates large bolts that look like man made ball lightning.
I was toying with the idea of seeing if a small microwave generator would help the efficiency of a furnace if directed into the combustion chamber.
I know it sound a bit mad but there are several patents that have given good results in the air craft industry.


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## g_axelsson (Sep 7, 2014)

I assure you Harold that I have learned so much from you, I'm glad to be able to give something back.

When melting metal in a microwave oven you heat the crucible, not the metal directly. Just as Butcher writes, metals are mirrors for microwaves. But there are some materials that are good absorbents for microwave, among others are (if I remember correctly) magnetite and silicon carbide, if you mix it into the crucible then it will heat up. The rest is to enclose it in a material that is transparent to micro waves but isolate well, like ceramic fibers.

A fun experiment is to take a piece of glass and heat a spot until it almost glowing and then put it in the micro. Hot glass absorbs microwaves while cold glass isn't affected, the glass starts to melt where heated. Only do this experiment with an old micro, it might get damaged from this experiment.

Göran


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## Harold_V (Sep 8, 2014)

g_axelsson said:


> I assure you Harold that I have learned so much from you, I'm glad to be able to give something back.


My only comment is that there are individuals on this board who are astounding! They have so much to offer in the way of knowledge, and are humble beyond belief. To think that I may have been instrumental (in any way) in aiding you when you sought information is very flattering. 

Thank you, kind sir. 

Harold


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## g_axelsson (Sep 8, 2014)

Harold_V said:


> g_axelsson said:
> 
> 
> > I assure you Harold that I have learned so much from you, I'm glad to be able to give something back.
> ...


That was very nice said. 8) 

Your posts together with GSP, Lazersteve and a few others are the one I first search for answers when I research a topic. How much wisdom you have shared over the years will become clear when I make my new project public. I'm working on a gold refining wiki where the references mostly points back into the forum. If I manage to configure the web server correct it will only be open to members of the forum, trying to make it as a integral part and a reference newbies can be directed to. The information on the forum is getting harder to find the more standard questions are asked and I felt something had to be done.

Göran


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## Harold_V (Sep 12, 2014)

g_axelsson said:


> I'm working on a gold refining wiki where the references mostly points back into the forum. If I manage to configure the web server correct it will only be open to members of the forum, trying to make it as a integral part and a reference newbies can be directed to. The information on the forum is getting harder to find the more standard questions are asked and I felt something had to be done.


Sorry for the late response, Göran. I've been trying to spend a little more time on the board checking posts, so I'm spread all the more thin these days.

I really like your idea, and I thank you for the effort you are dedicating to making the board more useful. I should also note that your contributions to the board discussions are much appreciated. Knowing you don't live in the US, I'm quite impressed with your command of the English language. 

Harold


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## g_axelsson (Sep 12, 2014)

Ooops... did I post that on the forum? I thought I wrote it in a PM.... my bad!  

But there's no secrets in the post so it can stay out in the open. It was not my intention to reveal my wiki just yet. I was planning to do it in a month or so since it's still quite rough and lacking some pieces.

Harold, I have realized a long time ago the truth in your signature, "You are what you write". That is all you are on the net. (Unless you make youtube videos :mrgreen: ) So it's important to try your best when writing any reply on the forum. Usually I rewrite half of what I've written as it always looks strange when I press the "Preview"-button. More people should try that button, it makes you look better!
... and I always appreciate when people correct my mistakes.

And Harold, never feel bad if you don't answer any of my posts. If it's important I'll remind you and we all know and appreciate the important work you do for the forum.

Göran


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