Sciencemadness Discussion Board

Pyrophoric Iron

Forest Innovations - 24-9-2014 at 03:38

Hello.

Could anyone tell me at what particle size iron powder becomes pyrophoric and also at what temperature?

I'm making good progress refining iron powder in my wife's old blender, to then use in some sintering experiments.

Currently the powder is approximately 25um particle size and is reaching a temperature of about 40 deg C as the blender works its magic.

What I don't want to do is set fire to my workshop accidentally.

Thank you very much for your help with this.

blogfast25 - 24-9-2014 at 10:58

Quote: Originally posted by Forest Innovations  
I'm making good progress refining iron powder in my wife's old blender, to then use in some sintering experiments.



You're achieving 25 micron with a blender? What's your secret? ;)

HgDinis25 - 24-9-2014 at 11:32

"The Pyrophoric Iron particles, when viewed under a microscope, are determined to be from approximately 100 nm to 1 micron in size."
Quote from the following video: http://www.youtube.com/watch?v=vinu8ZzNvRw

25um should already be pyrophoric. Are you sure it's 25um? How are you measuring it?

Little_Ghost_again - 24-9-2014 at 11:43

Quote: Originally posted by Forest Innovations  
Hello.

Could anyone tell me at what particle size iron powder becomes pyrophoric and also at what temperature?

I'm making good progress refining iron powder in my wife's old blender, to then use in some sintering experiments.

Currently the powder is approximately 25um particle size and is reaching a temperature of about 40 deg C as the blender works its magic.

What I don't want to do is set fire to my workshop accidentally.

Thank you very much for your help with this.


Thank you. I have shown this to my mum to prove that it is perfectly normal practice to use the kitchen blender for chemistry. It's still a no though

bbartlog - 24-9-2014 at 12:02


To my understanding, 25µm is still too large to be pyrophoric. That's still far larger (by about 100x) than the '100 nm to 1 micron in size' quoted above. Here's a link to some investigations of a 'pyrophoric' iron system, with particle sizes in the 1-10µm range - but notice that their particles are not spontaneously pyrophoric, they need some additional heat to ignite them: http://download.springer.com/static/pdf/947/art%253A10.1007%...

I expect that to see spontaneous ignition in air you would need to get particle sizes well under a micron.

aga - 24-9-2014 at 12:21

Quote: Originally posted by Little_Ghost_again  
perfectly normal practice to use the kitchen blender for chemistry

No, it isn't.

Food and Chemistry should never cross paths, apart from Analysis of what shit it is that someone not observing this Rule put in the food you just bought.

The Big Secret is the existence of Used Blender #2 bought off ebay for a fiver that lives in your Lab.

Little_Ghost_again - 24-9-2014 at 12:22

Quote: Originally posted by bbartlog  

To my understanding, 25µm is still too large to be pyrophoric. That's still far larger (by about 100x) than the '100 nm to 1 micron in size' quoted above. Here's a link to some investigations of a 'pyrophoric' iron system, with particle sizes in the 1-10µm range - but notice that their particles are not spontaneously pyrophoric, they need some additional heat to ignite them: http://download.springer.com/static/pdf/947/art%253A10.1007%...

I expect that to see spontaneous ignition in air you would need to get particle sizes well under a micron.

Wouldnt it also be a biological hazard under 10 micron?

Artemus Gordon - 24-9-2014 at 12:26

I am surprised blender blades are hard enough to pulverize iron, but if it is working for you, that is interesting to know.
You say it is reaching temps of 40c, but I assume that is the bulk temperature of the iron powder. What you have to watch out for is just a few particles being heated to ignition temp and then igniting the rest of the powder. When grinding steel, sparks are generated that have individual temps hot enough to melt pits in a <a href="http://forum.atomiczombie.com/archive/index.php/t-4526.html">car windshield</a> while the mass of the steel is cool enough to hold with bare hands.
If I were trying this, I would work with very small batches, keeping the rest of my powder in a closed container, and I would try to keep iron dust from settling on my work surface.

HeYBrO - 24-9-2014 at 13:58

Quote: Originally posted by Forest Innovations  
Hello.

Could anyone tell me at what particle size iron powder becomes pyrophoric and also at what temperature?

I'm making good progress refining iron powder in my wife's old blender, to then use in some sintering experiments.

Currently the powder is approximately 25um particle size and is reaching a temperature of about 40 deg C as the blender works its magic.

What I don't want to do is set fire to my workshop accidentally.

Thank you very much for your help with this.


Perhaps you should look into iron oxalate, which when heated creates pyrophoric iron. But beware as it also creates carbon monoxide which is very dangerous.

[Edited on 24-9-2014 by HeYBrO]

Ozone - 24-9-2014 at 16:37

To the best of my knowledge, the oxalate decomposes to (mostly) CO2. This is nice because it blankets (heat the oxalate in an ampoule) your pyrophoric iron keeping it safe long enough to seal for later use (like starting a campfire or somesuch).

If your batches are small, say a gram or two, I wouldn't worry myself to death about the CO.

Cheers,

O3

bbartlog - 24-9-2014 at 18:10

According to Hurd, pyrolysis of ferrous oxalate yields roughly equal quantities of the oxide and the metal, which would imply roughly equal amounts of CO and CO2 are released. It's always possible that different temperature regimes would yield different results, though.

Ozone - 24-9-2014 at 20:08

Interesting. I always got a fine grey (didn't look much like either ferrous or ferric oxide) powder. There was no evidence of flammable gas exiting the ampoule, but maybe CO just won't burn if there is a bunch of CO2 with it. In any case, the blanket was always successful, and the material (so long as you didn't overheat it and blob the particles) would always catch fire.

If the quantities are small, and the experiment performed with adequate ventilation (if larger), the only risks I see are fire (I used a MAPP gas torch), hot glass, and the product itself.

Cheers,

O3