Zinc Powder 3000 mesh with no Cab-O-Sil

[kadriver]

Found this Ebay vendor that sells very fine powdered zinc with NO Cab-O-Sil.

http://www.ebay.com/itm/Zinc-Metal-Powder-5Lb-3000-Mesh-LOWEST-PRICE-EBAY-/120937712896?pt=LH_DefaultDomain_0&hash=item1c28730d00

I have used this zinc to precipitate PGMs. I have ordered 7 lbs so far. He also sells 1 lb containers - I have two of those.

Zinc powder that has been treated with Cab-O-Sil as an additive will be very smooth and flow easily with no lumps.

If you use zinc powder that has Cab-O-Sil in it, then the Cab-O-Sil will be introduced as a contaminant into your metals.

The Cab-O-Sil contamination may appear as a grey sludge in your precipitated mixed black PGM powders.

If you order zinc powder from the above vendor, then be sure and get a mortar & pestle because the zinc is very lumpy just like in the picture.

The lumps are easily broken into fine powder for precipitating PGMs.

kadriver

 

[goldsilverpro]

Being so fine, it could be self igniting in air.

 

[kadriver]

I did not think of that - like a flour mill explosion.

 

[goldsilverpro]

I remember seeing a science demonstration where a guy sprinkled some very fine Al powder from about 6' up. It ignited, white hot, just from the friction in the air. Since then, I don't keep any ultrafine metal powders around, especially those near the top of the electromotive series.

 

[kadriver]

Chris:

I had no idea that the powder was that unstable.

It works so well for precipitating the metals out of solution.

I also have a pound or so of zinc turnings that are pure zinc metal.

I am going to divide my pregnant solutions in two.

Then use powder in one and turnings in the other to get a feel for the difference between each form.

Thanks for the warning - kadriver

 

[ericrm]

Chris:

I had no idea that the powder was that unstable.

It works so well for precipitating the metals out of solution.

I also have a pound or so of zinc turnings that are pure zinc metal.

I am going to divide my pregnant solutions in two.

Then use powder in one and turnings in the other to get a feel for the difference between each form.

Thanks for the warning - kadriver

do you mind posting your result? that would be a very good addition to the knowledge of the forum

 

[goldsilverpro]

The particle size of 3000 mesh is about 5-6 microns. It sounds pretty fine to me and, personally, I wouldn't want it around my shop. I always used 325 mesh "zinc dust" with no additives and that's dangerous enough. One time I stupidly put some in a small ceramic rock tumbler to try and break up the clumps and it ignited from the friction and badly cracked the tumbler. I think it ignites at about 900F and burns at about 2700F. Blinding white. Copious white zinc oxide fumes.

I just read that, in the MSDS, when you dissolve zinc in acids or NaOH, the heat of reaction can be enough to ignite the hydrogen evolved. Here's the MSDS for bulk Zn.
http://www.sciencelab.com/msds.php?msdsId=9925476

Here's the MSDS for 200 mesh and 325 mesh Zn powder. Notice it has a fire rating of 3.
http://www.sciencelab.com/msds.php?msdsId=9925472

Just be very careful, work in increments, and keep the additions small. Store it properly - with moisture it will release hydrogen. Although Cab-O-Sil is an undesirable when refining, it absorbs moisture and makes storage and shipping safer. If that 3000 mesh stuff contains no silica, I would think that, when shipping, it's a fire waiting to happen. Is there one of those silica gel pouches in the container when you receive it?

As an aside, I once bought a product for killing silverfish. It was an ultrafine silica powder in a plastic squeeze bottle. The silverfish were immediately dehydrated and died. Very effective. The problem was that the powder was also in the air and some got in my lungs. There was an immediate feeling of being unable to breathe. A mask may have worked but they didn't mention that on the label. I haven't seen it on the market since.

 

[kadriver]

Chris, thank you for the info on this zinc dust. It sounds dangerous! I had no idea.

It comes in a sealed plastic bottle with red tape securing the lid shut.

I add it in very small increments - about 1 or 2 grams at a time.

I wait for all the gas to stop before I add more.

I always do these reactions outdoors.

Also, I did not realize that H2 gas was being given off.

I know hydrogen is not flamable all by itsef, but HIGHLY flamable (explosive) when mixed with oxygen (air).

I have not had any problems so far, and now I know a little more to take proper precautions.

Thank you.

kadriver

 

[BAMGOLD]

GREAT Info here! I'd say best thing I've learned all week!

 

[qst42know]

As an aside, I once bought a product for killing silverfish. It was an ultrafine silica powder in a plastic squeeze bottle. The silverfish were immediately dehydrated and died. Very effective. The problem was that the powder was also in the air and some got in my lungs. There was an immediate feeling of being unable to breathe. A mask may have worked but they didn't mention that on the label. I haven't seen it on the market since.

Diatomaceous earth is sold to kill insects it acts like broken glass in their soft body joints and in their gut causing dehydration. Silicon dioxide skeletons of an ocean microbe as I recall. It is sold to organic gardeners. It lacks the lasting toxic effects of a pesticide however they likely down play the hazards of breathing the material.

 

[goldsilverpro]

As an aside, I once bought a product for killing silverfish. It was an ultrafine silica powder in a plastic squeeze bottle. The silverfish were immediately dehydrated and died. Very effective. The problem was that the powder was also in the air and some got in my lungs. There was an immediate feeling of being unable to breathe. A mask may have worked but they didn't mention that on the label. I haven't seen it on the market since.

Diatomaceous earth is sold to kill insects it acts like broken glass in their soft body joints and in their gut causing dehydration. Silicon dioxide skeletons of an ocean microbe as I recall. It is sold to organic gardeners. It lacks the lasting toxic effects of a pesticide however they likely down play the hazards of breathing the material.

My great aunt, Jennie E. Harris, lived up the street from us most of my early life and we were quite close. She was a science writer and was published in some top journals. One article I remember was about diatoms, the source of diatomaceous earth. She was also the librarian and I remember she wouldn't let me check out "Peyton Place."
http://www.google.com/search?q=diatoms+jennie+e+harris&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a#hl=en&client=firefox-a&rls=org.mozilla:en-US%3Aofficial&sclient=psy-ab&q=diatoms+%22jennie+e.+harris%22&oq=diatoms+%22jennie+e.+harris%22&gs_l=serp.3...131725.138584.0.139147.3.3.0.0.0.0.176.369.1j2.3.0...0.0...1c.4xGLK0m5Lq0&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=27c3459139b6440d&biw=1116&bih=463

 

[butcher]

http://www.google.com/search?q=diatoms+jennie+e+harris&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a#hl=en&gs_nf=1&gs_mss=diatoms%20se&pq=diatoms%20&cp=24&gs_id=l1&xhr=t&q=diatoms+serve+modern+man&pf=p&client=firefox-a&rls=org.mozilla:en-US%3Aofficial&sclient=psy-ab&oq=diatoms+serve+modern+man&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=798ff7e45f6d12e&biw=1920&bih=899

 

[Noxx]

The particle size of 3000 mesh is about 5-6 microns. It sounds pretty fine to me and, personally, I wouldn't want it around my shop. I always used 325 mesh "zinc dust" with no additives and that's dangerous enough. One time I stupidly put some in a small ceramic rock tumbler to try and break up the clumps and it ignited from the friction and badly cracked the tumbler. I think it ignites at about 900F and burns at about 2700F. Blinding white. Copious white zinc oxide fumes.

I don't believe that it ignited due to friction.

Back in the days when I was doing pyrotechnic stuff, I was reading about ball mills fires:

Some people reported that they have put some metal (can't remember which) in their ball mill and let it run for 24 hours or more. As they opened the ball mill, it caught fire immediately.

The explanation was that the powder was so finely divided that is had a huge surface area. When they opened it up, air got in and oxidized the newly divided powder. This went so fast that the temperature spiked and it caused a metal fire...

 

[goldsilverpro]

The particle size of 3000 mesh is about 5-6 microns. It sounds pretty fine to me and, personally, I wouldn't want it around my shop. I always used 325 mesh "zinc dust" with no additives and that's dangerous enough. One time I stupidly put some in a small ceramic rock tumbler to try and break up the clumps and it ignited from the friction and badly cracked the tumbler. I think it ignites at about 900F and burns at about 2700F. Blinding white. Copious white zinc oxide fumes.

I don't believe that it ignited due to friction.

Back in the days when I was doing pyrotechnic stuff, I was reading about ball mills fires:

Some people reported that they have put some metal (can't remember which) in their ball mill and let it run for 24 hours or more. As they opened the ball mill, it caught fire immediately.

The explanation was that the powder was so finely divided that is had a huge surface area. When they opened it up, air got in and oxidized the newly divided powder. This went so fast that the temperature spiked and it caused a metal fire...

You're right, Noxx. It didn't ignite until it was opened and air got in. Ignition was immediate.

 

[kadriver]

ericrm:

here is the post comparing using zinc turnings to zinc powder:

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=14920

kadriver