Platinum sponge from hydrazine sulfate

[skippy]

4metals, I think your puzzlement stems from there are now two different uses being discussed here - using the tube for the reduction of accumulated PGM compounds, and using the tube setup to extract PGMs as halide from substrates. I believe Steve was outlining the use of the tube furnace setup for the later.

 

[skippy]

Neat plan! I bet 8" quartz fittings cost a pretty penny though so you won't be saving money there!

 

[HAuCl4]

Steve said;

The reaction tube is the one that is heated and the collection tube is the one where your values condense.

A little clarification here please, I've calcined a lot of platinum salts in my day in furnaces without a reducing atmosphere. The values never volatilized and re-condensed and I wonder why they would in your rig?

I have never been a big fan of filling those finger shaped silica boats with metal salts for reduction. Plus there is a limited capacity in a small diameter tube. Factor in that I've become frugal in my old age and I have some ideas for building a atmospheric reducing chamber that will fit into my assay furnace.

I spoke to my glassblower and he can make me a 8" diameter 6" deep quartz glass chamber with the tubes I've sketched in the drawing. The top will have a tapered glass joint lid to open the top fully. I would mount this on a replacement door / shelf arrangement which I can slide into my assay oven. Once loaded with a silica tray full of salts it can be slid into place while the kiln door remains open and out of the way. Then I can hook up a vacuum to the top an a hydrogen cylinder to the bottom.

This will out-gas some nasty chlorine fumes so I'd use a venturi in a closed loop to pull vacuum and scrub the fume in the water at the same time. The top of the venturi tank can go to the exhaust. Now I can heat the oven and when it gets to temperature (around 200 C) turn on the hydrogen gas and evacuate at the same time with the vacuum.

This should work on both small and relatively large lots and since I don't need a tube furnace and controller, should be 4 or 5 thousand cheaper than Lou's estimate.

Opinions?

Took your idea and drawing and changed it a bit. Crucible inside crucible, and quartz glass disk on top (need good coupling here, but if operated at small vaccuum the seal shouldn't be critical) with the quartz tube fused in one piece. Can add another tube on the left (blue) for the hydrogen, but I think for Pt and Pd not really needed?. (Corfirmation of this?).

It shouldn't cost more than a few hundred dollars plus the temperature adjustable fire assay furnace?. I hope it helps someone.

What do you think 4metals?.

http://advaluetech.com/chemical_processing_crucibles.html

edited to add: I think I wouldn't attempt this with hydrogen feed tube unless I could attain a really good seal on the top between outer crucible and glass disk.

 

[4metals]

Lou is really the expert on this method. The hydrogen is needed for Pt and Pd. My reasoning for mounting on the door of a kiln was that the 2 quartz glass tubes can be fused to prevent the leakage you are concerned about around the top of the crucible.

I'm working with a guy that processes a lot of Pd/Ag scrap and has enough metal to reduce using this method. I've been in contact with my glassblower and he is concerned about the top seal in my design as the way I envisioned it was a large (6 or 8") glass stopper on top. He is afraid the condensing gasses will make the sintered glass frit too difficult to remove after processing. He is suggesting a conical opening with a blank cover and a monel clamp. I'm awaiting pricing.

The reduction of platinum and or palladium salts does not require super hot conditions and the reducing atmosphere of the hydrogen does the work. What Steve is suggesting in his tube furnace is for a different application.

 

[HAuCl4]

I've done the whole thing with just straight calcination. Works fine for platinum if you go nice and easy, and to a lesser extent Pd and Rh (I usually let them cool under a soft H2 flame).

I was thinking (El-Cheap-O!) to achieve a seal using a 75-25 mix of borax and boric acid in between joints at the top. Using no H2.

To break the seal, after the reduction (calcination really) is complete, rise temperature to 1,200 degC and pull. Can't tell if it'll work till I see it, but I think it will, as borax liquefies a lot in that range from 700 to 1,200 degC.

Lou said that pure calcination will work too (see quote). Probably at much higher temperature (700-800?) than H2 reduction (200-400?).

Maybe one day soon I'll have the metal stuff to really find out for myself!. :roll:

 

[Oz]

It is worth noting that it is best to have fault tolerant seals when dealing with H2 even with exposure to the atmosphere, not to mention a furnace environment.

 

[HAuCl4]

It is worth noting that it is best to have fault tolerant seals when dealing with H2 even with exposure to the atmosphere, not to mention a furnace environment.

That's my thinking too. I do not like that high temperature "seal", in either design, very much without H2, and not at all with H2.

If H2 can't be avoided then I'd go for some other design that has no joints at such high temperature.

I'll try to post a couple of diagrams later on how I'd approach it on a budget, but I can't see it being cheaper than avoiding H2 altogether.

Hoke speaks of calcining both palladium and platinum salts (no H2), but I'm sure there are good reasons for choosing to reduce with H2 at lower temperatures.

Maybe less losses or purer metal or both, or faster?. I hope Lou, 4metals chime in on why H2 is preferred.

 

[4metals]

You will have to get much hotter without the H2 than with it. These devices only help you prevent losses, if you want to be el cheapo, you can throw it in a crucible and place it in a gas furnace that is barely hot enough to stay lit. (that is back in the day of forced air gas furnaces)
When the white smoke stops it's done. You will have losses though, the kind you cannot recover, so the el cheapo methods aren't always so cheap.

The tube muffle furnaces don't need a seal but I've never liked the skinny little silica boats to feed the salts into. I guess the boats can get larger in a larger ID tube if the production quantity warrants.

 

[HAuCl4]

That makes sense. Thanks again 4metals. I'll throw an idea diagram of mine for your evaluation and/or modification in a few minutes for an H2 tube furnace. Please be advised that I do not have practical expertise on processing these metals, and I'm only going with hopefully good engineering common sense gathered from experience in other applications.

 

[HAuCl4]

Drawing not to scale, of course. Tube is wide enough to load and withdraw the silica boat(s ?) and long enough for the temperature to drop so that a Teflon plug (green) can be used?. The H2 enters on the right through a smaller diameter tube fused to the larger tube and a disk. And a vaccuum to the "glass frits" and scrubber on the left.

I do not have a glassblower to quote me a price, but it looks simple enough to fabricate.

Feel free to criticize, modify, improve, etc, etc.

If Teflon plug not suitable, I'd like to learn the shape and workings of the glass connection and seal.

I don't know anything about the "glass frits" and how they work either.

Cheers!.

 

[HAuCl4]

Quartz frits and other quartz products:
http://www.technicalglass.com/product_pages/fused_quartz_wool/fritted_discs.html

They have a price list online, which is both rare and helpful if you are estimating your cost of materials without having to make 343 phone calls.

I have "modified" the design above to make it round on the right side of the big tube. Closing the tube with a flame is much easier than soldering a disk, insert small tube as the hole is closing. Two pieces to join for the glassblower instead of 3.

I wonder how a "removable frit" looks like and the shape of the joints to make and break the connection. Any pictures anyone?.

I guess a 50 mm 00 frit is more than enough for this job?.

http://technicalglass.thomasnet.com/item/fused-quartz-wool-and-frits/quartz-frits/qpd5000?&seo=110

If you want it all glass instead of the teflon plug, I guess a flange, a tube fused to a hollow disk, a viton gasket, and a mechanical clamp can do the job too on the left side. Piece of cake for a glassblower.

 

[HAuCl4]

I believe these designs will need the addition of a sublimate chamber to catch the NH4Cl solids from calcination, and I'm not sure about the H2 reduction. As they stand, they are incomplete non-working designs that will likely clog or otherwise fail.

I will try to find out some more about tube furnaces.

 

[skippy]

HAuCl4, you should hollow out the plugging portion of your stopper, otherwise a very slight temperature rise can crack your expensive tube like nothing.
I learned this lesson the not so hard way, with a $10 round bottom flask's joint cracking after I tried heating it with a solid teflon stopper in place.

Also quartz doesn't conduct heat very strongly, but the atmosphere in the tube will convect, so you might consider putting some sort of permeable insulation in there to keep heat away from your stopper, like a wad of quartz wool.

 

[HAuCl4]

Thanks skippy. I think I'll do away with the teflon plug design. A pure glass setup seems better. The glass wool is a great idea to avoid clogging the frit. A look at an actual working rig would help a lot.

 

[skippy]

HAuCl4, once I hollowed out the solid PTFE stopper it was fine - I even took the whole flask stopper and all to 150C. Whereas the solid stopper broke the ground glass joint before it ever hit 50C.
WIth some glass or quartz wool you can keep the plug for your tube cooler than 50C. So Your teflon plug could work fine, although I agree
that if this is something you plan on keeping and using often it'll be worth it to have it built all glass.

Me, If I were to do teflon I would add a ground taper socket to the end of the tube and plug that with a tapered, hollow teflon stopper.
On a straight tube, I'd machine it like the flanges here http://www.mtixtl.com/vacuumsealingassemblyfor80-82mmdiatubefurnacewithvalvevacuummeter-eq-fl-82.aspx , but that's getting pretty involved.

 

[HAuCl4]

Thanks skippy. I'm not sure on the proper design yet.

4metals : How are you going to make the top glass-glass seal effective in your design?. Some type of gasket?.

Am I correct in that in the "H2 reduction method", there are no sublimates of NH4Cl and the effluents become all gases, whereas in the "calcination method" there are a lot of sublimates of NH4Cl to collect and reclaim?.

 

[HAuCl4]

Lou: Any chance of a picture of your rig for reduction of Pt in a tube furnace?.

 

[Lou]

I suppose I can post a picture of the tube or some CAD drawings?

Give me some time--busy man lately :-(

Hydrogen, mole for mole is super cheap. You also get a nice gray precipitate. I like 4metals idea as I see the ability to put a tare-able quartz pan or crystallization dish...so I can heat till constant mass. Just make sure you can heat and pull a bit of a vacuum though, it's important to get the absorbed H2 off of the metal. I've lost some hair before to metal that still was H2-saturated.


Time to get some shuteye.

FYI, I've done a bit of business with TGP, and so too does my glassblower (great guy too!). Best prices. Their shop is pretty good too. TGP is close to home as well

 

[HAuCl4]

Take your time Lou. I'm in no hurry. CAD drawings would be nice, and a photo(s) of your tube furnace, glass joints, removable frit joints, etc, even better!. 8)

 

[HAuCl4]

Found these photos on the web for the reduction chamber.