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Reduction atmosphere in kiln


#1

Hi! I imagine co2 (carbon dioxide) would produce a reduction
atmosphere in the kiln. Co2 is readily available and cheap; it is
heavier than air and if you flood the kiln through the peephole in
the top it will eventually displace all the air, particularly if you
flood it continousley at about 1 or 2 psi … that is my theory
anyway … if someone tries it I’ll be interested in hearing about it
regards Jo


#2

CO2 is relatively non-reactive to the materials we work with but is
not a reducing agent. To be a reducing agent it must combine with
oxygen or oxides to burn or reduce the available oxygen or oxides.
Unless the kiln shell is air tight you will not be able to displace
all the oxygen with another gas. I have tried with both argon, and
nitrogen. If you want to control the atmosphere in the kiln
interior it really must be a gas tight shell around the kiln
insulation or a sealed retort inside the kiln. Otherwise you are
just wasting your money on gas.

Filling the kiln with charcoal will work as a reducing atmosphere
because the charcoal turns into CO (carbon monoxide which is a
reducing gas) when it interacts with the oxygen that is present
inside the kiln but it reduces the protective oxide layer on the
kiln elements which causes them to burn up rapidly. So it is not a
good idea for the life of the kiln. It also is a safety hazard due
to the fact that you now have a mass of burning charcoal that must
some how be put out and it releases CO into your studio.

Jim

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#3

You might also try Argon gas. It would also eliminate the oxygen in
the the chamber, is fairly cheap and available at any welding supply
store

Mike & Dale Lone Star Technical Service, The ultrasonic repair guys.


#4
    You might also try Argon gas.  It would also eliminate the
oxygen in the the chamber, is fairly cheap and available at any
welding supply store 

The firebrick or ceramic fiber is just too porous to allow for
creating a controlled atmosphere in a kiln that is not specially
fabricated for this purpose. The air just continues to come in
through the brick. I have wasted a lot of argon in trying this out.

Jim
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#5

I have had fair success in creating a reducing atmosphere in the
kiln by using carbon to absorb the free oxygen. I simply placed
graphite sheets inside the kiln, lining the bottom and sides. I use
this for annealing gold, and the metal comes out both annealed and
shiny…oxide free. The graphite will soon begin to disappear and
will need to be replaced occasionally. I got a great deal on
graphite sheets on eBay.

For very fine wire or small parts, I place them in a covered tin,
like a watch parts can, filled with powdered charcoal. Again,
everything comes out shiny and soft.

I know that for furnace soldering, most ovens use anhydrous ammonia
to create a reducing environment, but this is obviously not
something you want to try in a kiln not built for that purpose.

Doug Zaruba


#6
    I know that for furnace soldering, most ovens use anhydrous
ammonia to create a reducing environment, but this is obviously not
something you want to try in a kiln not built for that purpose. 

G’day; I offer here just a very slight amendment. As mentioned above,
anhydrous ammonia (NH3) is used, but not as such. The ammonia gas is
passed through a red hot tube wherein the nitrogen and hydrogen
components are disassociated. This means that the reducing
atmosphere is of nitrogen and hydrogen gases in the correct ratio; no
longer ammonia, and used because it doesn’t explode so easily. At a
laboratory in which I worked we used that mixture - called ‘forming
gas’ or ‘cracked ammonia’ - in several small furnaces, it being less
dangerous (!?!?!) than pure hydrogen. Until one day a big cylinder
of ammonia leaked… – Cheers for now,

John Burgess; @John_Burgess2 of Mapua Nelson NZ


#7

Doug, Did you run into any problem with removing the protective
oxide from the heating elements? Notice any reduction in element
liftime after several sessions in a reducing atmosphere? Bob Williams


#8

Forming gas is 5 % hydrogen in nitrogen . it is fire safe and is
used for a lot of furnace work. Dissociated ammonia is often
cheaper . The 5% hydrogen blend will often be better as the
components are usualy purer than the ammonia. Jesse


#9

For creating an reducing atmosphere for tool making in a large oven,
normally a small steel box is used. This box is often made from a
square tube steel. The backside is closed and a long tube is welded
on hole in this backside. The steel tube (10-12 mm) is connected to
an inert gas. This gas can be CO2, Argon ect.

The box is place in the oven with the tube coming out the oven. The
front of the box is close with a piece of steel or brick. The closer
the better Now you have created a chamber where you only need a very
small amount of gas 0.2-1 litre per minute. I hope you can do
something with this.

Martin Niemeijer


#10

As Mr. John Burgess correctly stated, the jewelry industry mostly
uses a forming gas composed of a mixture of nitrogen/hydrogen at I
believe a 85/15 ratio instead of ammonia or anhydrous. This forming
gas comes premixed in cylinders like oxygen, acetylene, etc. and is
cheaper than argon also I think. All of the more modern casting
machines and furnaces use it, Memco, Manfredi, etc. Those Manfredi
platinum casting machines are AWESOME! One should take a look at
VICENZAORO magazine’s OROMACCHINE issue that comes out every year
about the show there. It has all the latest technology with forming
gas, chain soldering machines, furnaces, etc. What you need is a
pressure vessel inside a furnace or kiln, then you don’t affect the
element. A simple air tight metal enclosure with one side that opens
should work and you could pipe the gas in through metal tubing to it
and let the whole thing heat up inside the oven with your work
sealed inside with the forming gas. Ideally, it would not leak and
it should only require enough gas to displace the ambient atmosphere
inside the enclosure. Shouldn’t be too difficult to convert a
standard kiln to do this, don’t you think?

Ricky Low


#11

Bob, I’ve been using this process in my kiln for over 10 years now,
and the elements still work fine. I have to say that I don’t anneal
metal in the kiln every day, just every couple of weeks.

Doug Zaruba