Question about reduction firing

[shawnhar]

Maybe this is daft, but it seems like reduction is just the removal of some or all oxygen from the kiln, so.... why couldn't I just hook up a nitrogen tank to my kiln vent intakes and create a reduced oxygen environment inside my electric kiln? There has to be something else going on, carbon interaction with the glaze or something, right?

[Fred Sweet]

Shawn- 

It’s not so much the removal of oxygen from the kiln, as it is removing oxygen from the molecules and compounds which make up the clay and glazes. This is not to say that your hypothesis won’t work, but I think it does need some mechanism  to help remove the oxygen from the molecules as well. I’ve seen some articles regarding adding non- combustible gases to kilns, but can’t remember which gases were used nor the sources of the articles. Web search in order???

Will leave further discussion to those better founded in chemistry and its theory.

Regards,

Fred

[Hulk]

Good question!

Is "reduction" directly related to carbon monoxide's hunger for oxygen? 

...o'course, we don' mess with CO, as it deadly; proceed with caution. A lil' sooty flame in your kiln's intake, perhaps, however, how the kiln's elements react ain' so good.

http://www.lakesidepottery.com/HTML Text/Tips/ReductionFiring.htm

[shawnhar]

Found a CN article that explains it pretty well, looks like the burning fuel is what produces the carbons needed to produce the effect in the glaze/clay body, without that added carbon the reaction won't take place. Would still be interesting to see what would happen to a cone 6 oxy glaze in a "less than neutral" environment.

https://ceramicartsnetwork.org/daily/firing-techniques/gas-kiln-firing/demystifying-the-reduction-firing-process/

[Hulk]

CO is more deadly than N2, as in a lil' bit of CO is bad, however, enough nitrogen aroun' displaces the O2, net result equally bad.

"Unconsciousness can occur within one or two breaths..."

Insert steel mill close call story here, an' power plant tank welding tragedy there.

Yep:

"CO and soot both deliver electrons to the surface of your pottery in the kiln. CO reacts with oxygen at the surface and forms CO2, leaving electrons behind. Soot will flow and adhere to the surface of whatever it touches in the kiln as incredibly small, free-radical black carbon particulate. As small carbon particulates build up on pottery surfaces, they begin to aggregate as soot and oxidize, causing a small flow of electrons into the ceramic surfaces. These processes result in the metals in your glazes gaining electrons, which means the net charge or oxidation state is reduced."

[Bill Kielb]

14 hours ago, Hulk said:

CO is more deadly than N2, as in a lil' bit of CO is bad, however, enough nitrogen aroun' displaces the O2, net result equally bad.

"Unconsciousness can occur within one or two breaths..."

Insert steel mill close call story here, an' power plant tank welding tragedy there.

Yep:

"CO and soot both deliver electrons to the surface of your pottery in the kiln. CO reacts with oxygen at the surface and forms CO2, leaving electrons behind. Soot will flow and adhere to the surface of whatever it touches in the kiln as incredibly small, free-radical black carbon particulate. As small carbon particulates build up on pottery surfaces, they begin to aggregate as soot and oxidize, causing a small flow of electrons into the ceramic surfaces. These processes result in the metals in your glazes gaining electrons, which means the net charge or oxidation state is reduced."

Yep!

easiest way to do this is CO for chemistry reasons. Reduction is actually the gaining of electrons or an increase in negative charge. There have been folks that have injected CO into their electric kilns and have  reportedly successfully reduced. Carbon is important though. Only three primary  things are basically reduced:  copper, Iron, tin.  There are certainly others but primary is the operative word.

it is far easier to understand the potters definition that a flame starved for oxygen is removing oxygen from the glazes.

Very simplified type pottery reduction explanation here, might be helpful. It does emphasize other aspects of these firings such as carbon trapping and the actions of iron as a flux.

 

[neilestrick]

http://community.ceramicartsdaily.org/topic/19108-electric-reduction-firing/?tab=comments#comment-150404