Silver Chloride Conversion Problem - Sulfuric / Iron in Tumbler - Heat / Caking

[Yggdrasil]

Yes, I'm melting silver oxide (what I assume to be silver oxide).

Molten silver oxide is one thing I was wondering. But everywhere I've seen on this form is along the lines of simply "melt the silver oxide directly". I could, of course, be assuming too much.

There are a few scientific demonstration videos [on YouTube] where silver oxide is heated to produce silver powder - but these demonstrations stop there. The silver is not actually melted. So I also wonder if the oxide to elemental silver conversion needs to be a more controlled heating step, and I've made things complicated by putting in too much heat too quickly?

Thank you

I did a search on the net.
Silver Oxide decompose at 195C so a slow heating to some 200-250C and good stirring might be the way.
If it becomes liquid it will have much less surface area to give off the Oxygen.
According to Wikipedia it decomposes at 280C.
One question. Did you use some kind of flux?

 

[MGH]

One question. Did you use some kind of flux?

Just borax. There was some already in the dish, and I added a little more during the melt.

 

[Yggdrasil]

Just borax. There was some already in the dish, and I added a little more during the melt.

Maybe try without.
After all you shold be way below the melting point of Borax.

 

[snoman701]

You lost silver. That looks crumbly, which means it has minimal water.

 

[snoman701]

Oh, and when melting silver that you have converted, you should always melt with soda ash and borax, then melt as slow as possible with a lid. The goal being if there is any chloride remaining, it gets reduced by the sodium carbonate.

 

[MGH]

Following up here with a humble acknowledgement that snowman701 was right.

At first I just didn’t want to believe that I had silver chloride left in my solids. After further trials, and some additional help from a kind forum member, I think I somehow had MOSTLY silver chloride in what I had assumed was completely converted and nicely washed silver oxide. Also, after the fact, I see that there are a few other similar examples here on the forum that I had missed. This is not a unique scenario.

I will not go into exhaustive details here. Suffice to say, the unknown black/brown slag was actually melted silver chloride. Ultimately I melted two 200g aliquots of my starting material with essentially the same results. I was able to capture and re-grind the melted silver chloride, mix it 1:1 with soda ash, then melt to produce elemental silver. I then mixed the remaining starting material 1:1 with soda ash, and melted, to combine the steps in one, with a little bit better overall yield.

The melting in a 5 inch melt dish was not optimal, to say the least. It’s all I have available. It required slow heating, a lot of torch play, and multiple pour-offs of the slag so that I could continue to melt the metal remaining in the dish. Hopefully I don’t have to do this again, but if I do, I’ll certainly be looking for a furnace and larger crucible.

As you can see in the table below, I have what I consider to be a decent yield from this trial (albeit in the form of ugly, slag-covered partial bars which need to be remelted). I’m sure I lost some silver along the way. At this scale, I’m not too concerned about it. I’ll consider it the price of an education if I can avoid dealing with this again in the future.

Thanks as always, GRF!

 

[Lou]

One thing I always did when I was tumbling was to test the finished cement product by torch melting in a cupel. If I saw any metallic bluish purple slag that smoked white...it was AgCl and needed more time.

The smell of molten silver chloride is not a good one!

 

[orvi]

One thing I always did when I was tumbling was to test the finished cement product by torch melting in a cupel. If I saw any metallic bluish purple slag that smoked white...it was AgCl and needed more time.

The smell of molten silver chloride is not a good one!

It need some few test trials before you "see what you should see". Colour and smoke are good clues.

Some folks I know did pseudo-photochemical test, when they distinguished between NaCl and AgCl smoke by placing small piece of clean wet towel over the sample of say silver cement, hit it with oxy/propane torch and let it "fume" the piece of wet towel. Then placed that towel on direct sunlight or under strong light. If there was AgCl, you seen that as darkening. But it wasn´t completely consistent in my hands to be honest... I dunno how they done that on day to day basis with very good accuracy.

My analytical way in the beginnings was to take sample, wash it with water until all soluble salts were washed away and cover with ammonia. Swirl it for some minute, let it settle, decant the clear liquid (or filter if necessary) and after that sprinkle some sodium borohydride in. If there was any silver, grey merky solution will form. Or neutralize the solution with HCl - there should be colourless solution afterwards if there is no silver in.

There are many ways... however that distinct behaviour upon contact with torch is by far the easiest one. Once you train yourself to see what you are supposed to see, that´s basically it Similarly as with gold in solution. Even with heavily contamined solutions, you can spot that AuCl4- right away when you swirl the beaker