Urea, its use in refining

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HAuCl4 said:
Is there a simple procedure to make silver "blacks"?. (i.e. super fine powders of pure silver).


Ascorbic acid reduce very fine powder from AgNO3.
It will not be black though :mrgreen:

I have a picture i can upload later when i get home, if you want.
Edit: scratch that... can't find the picture...
 
4metals said:
Sure simply atomize pure silver! :lol:
Next time I have a chance with this alloy and solution of nitrates, I'll try ultra fine pure silver foil in a shaker to cement Pd and Pt, before filtering and retrieving the silver.

Why is HCl better for dropping the silver chloride, than NaCl or KCl in powder form?. One would have less liquid and much less nitric acid, that's an advantage that I can clearly see?. :?:
 
HAuCl4 said:
Next time I have a chance with this alloy and solution of nitrates, I'll try ultra fine pure silver foil in a shaker to cement Pd and Pt, before filtering and retrieving the silver.

Save your time. Been there done that.
Silver will not cement even a microgram of Pd and i suspect neither it will cement Pt.
 
Hello all , how are tricks today?
I hope all is well!
I was looking for information on a different subject this morning , and I came across the following (link) and remembered this thread , thinking that someone was looking for silver powder.
(I also found some of the information in the Datasheets section quiet interesting) ;
http://heraeus-thickfilm.com/en/productsapplications/preciousmetalpowders/precious_metal_powders_1.aspx
samuel-a said:
I have a picture i can upload later when i get home, if you want.
Edit: scratch that... can't find the picture...
I did find this image of fine Ag powder ;
http://www.natureer.com/uploadfile/201012/26/0E213240437.jpg
All the best everybody , and kind regards ,
Chris :mrgreen:
 
4metals,

I had very good success with Pt and Pd after eliminating the nitric with sulfamic. The AR contained up to 50% nitric and, therefore, it ended up with lots of sulfuric and little HCl.

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Concerning black silver powder. In general, for any metal I have seen, the smaller the particle size, the darker the powder. I think that it has to do with our sight limitations of reflections. I would experiment with different reductants at different solution strengths, reductant strengths, temperatures, etc. However, I have only seen very dark silver a few times and I can't remember the conditions. Most is medium gray or whiter.

With gold, it is different in that a range of shades - from light tan to black (to colloidal pink/purple) - are fairly common. Although dark gold powder often indicates low purity, it can also be due to particle size.
 
You hit the nail on the head Chris. Cruddy gold is usually very fine while really high quality gold is spongy and very light in color.

I believe this is best described with statistical mechanics (like any nucleation theory). I'd be glad to get more into it if y'all are keen on hearing my thoughts.


I will take some photographs of crappy gold and really nice gold under the electron microscope.

Really nice gold rinses well. Really crappy gold doesn't. Pore structure and relative surface area to volume ratios must be at play.
 
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