# When reducing the colored powders??



## KCGreg (May 4, 2009)

Right now when reducing the colored powders, the only way I can really check to see if I'm doing this too quickly or not is to check by holding ice in a glass beaker over the smoke and making sure there isn't any colored condensation on the outside of the glass. I just did this while reducing 20 grams of the orange platinum ammonium chloride, everything seemed to be going ok. When it had finished, I was left with only 6.4 grams of Pt. That seems low, I'm thinking that somewhere I bumped the heat up too high and burned some pt off perhaps?? What would be an acceptable level of loss here? Does anyone have an idea of what 20 grams of the colored powder should reduce to when properly calcined?? Thanks


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## 4metals (May 4, 2009)

Assuming you started with pure ammonium chloroplatinate, and it was dry. (Usually for analytical purposes the salt is dried for a few hours at 225 degrees F and cooled in a dessicator) The salt is anhydrous so it can and will pick up moisture from the air. 

Anyway the molecular weight of ammonium chloroplatinate is 443.87 and the molecular weight of platinum is 195.084 so if you do the math the salt is 43.95% platinum. Your 20 grams should have produced 8.79 grams.

It's not uncommon when rinsing the powders for refiners to use saturated ammonium chloride, that often leaves crystals of ammonium chloride in with the powder giving erroneously high weights. Rinsing with a 15% solution of ammonium chloride is better. Never rinse with water as the salt is slightly soluble in water.


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## KCGreg (May 4, 2009)

At least I didn't burn off as much as I thought. Thanks for the info, I really needed to know that breakdown to match up with my results to see how much room for improvement there is. 

Has anyone ever tried formic acid to reduce the colored powders? I recall Hoke saying that losses are minimized and there are less corrosive fumes when that method is used instead of calcining the colored powders. Why wouldn't this method be preferred over heating?


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## 4metals (May 4, 2009)

Formic reduction yields the "blacks" which is the oxide of the metal. 
It will also reduce the palladium salt as well forming the oxide too. Calcining yields pure metal sponge. I've reduced it with hydrazine but it's nasty stuff and probably a carcinogen. (at least California thinks so)


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## Lou (May 5, 2009)

Yawn.

The formate, borohydride, hydrazine, pyrolysis, and even H2 reduction methods have all been covered here.

4metals is indeed correct about erroneous weight resulting from ammonium chloride which coats your ammonium hexachloroplatinate. It will do this for virtually all ammonium hexachloro'PGM'ates.

I'd like to see a reference as to the blacks being the oxides of the metal. That would be news to me!

Hydrazine drops out a gray sand, while formate/borohydride gives the hard to filter, and perhaps pyrophoric (in the case of Pd especially) metal black.

Low and slow is the method for pyrolysis. Here are some photos and a limited discussion of what is going on:

http://www.sciencemadness.org/talk/viewthread.php?tid=9721#pid113781


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