Ivor and Olive Lewis on tue 6 jun 06
Dear Friends,
I continue to study.
One of the things I have found is that the reaction for the =
decomposition of Black Copper Oxide to Red Copper oxide, fundamental in =
the generation of Copper Red Glazes, can take place at atmospheric =
pressure above a temperature of approx 1122 Deg Celsius. Given =
(Greenwood and Earnshaw) that Carbon dioxide will decompose under these =
condition adding Carbon monoxide to the atmospheric broth, Oxygen =
discharged from Copper(2)oxide will be scavenged allowing the reaction =
to proceed to completion. Thermodynamic numbers become favourable at a =
slightly higher temperature, but well inside the temperature range for =
Cone 6 workers.
Obviously a kiln vent will eliminate burnt Volatiles including Carbon =
dioxide from an electric kiln equipped with this device, counter =
productive with respect to Electric Copper Red. I also think that =
sealing the interior with an impervious coating (ITC 100 ???) might be =
advantageous in controlling air diffusion
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Brian Fistler on wed 7 jun 06
On Tue, 2006-06-06 at 15:42 +0930, Ivor and Olive Lewis wrote:
> Dear Friends, I continue to study. One of the things I have found is
> that the reaction for the decomposition of Black Copper Oxide to Red
> Copper oxide, fundamental in the generation of Copper Red Glazes, can
> take place at atmospheric pressure above a temperature of approx 1122
> Deg Celsius. Given (Greenwood and Earnshaw) that Carbon dioxide will
> decompose under these condition adding Carbon monoxide to the
> atmospheric broth, Oxygen discharged from Copper(2)oxide will be
> scavenged allowing the reaction to proceed to completion.
> Thermodynamic numbers become favourable at a slightly higher
> temperature, but well inside the temperature range for Cone 6 workers.
> Obviously a kiln vent will eliminate burnt Volatiles including Carbon
> dioxide from an electric kiln equipped with this device, counter
> productive with respect to Electric Copper Red. I also think that
> sealing the interior with an impervious coating (ITC 100 ???) might be
> advantageous in controlling air diffusion Best regards, Ivor Lewis.
> Redhill, South Australia.
Ivor,
Since you are saying that CO2 is decomposing to CO + O, (I know it would
be 2CO2 --> 2CO + O2)... Why would the loose CO molecule be more likely
to scavange an Oxygen molecule from the copper oxide, therefore reducing
it, rather than recombining with the free Oxygen molecule present in the
kiln that is there as a result of the original decompositiong of the CO2
molecule?
Brian
Des & Jan Howard on thu 8 jun 06
Ivor
Easy way to test this.
I'll borrow a cylinder of Beer gas (compressed CO2 used to pressurise
beer barrels)
from the village pub & bleed it into the kiln via a sealed fitting in
the bottom spyhole.
Diffusion of outside air could be prevented by having the kiln at a
slight positive pressure,
excess gases could be vented via the top venthole.
Worth a try?
Des
Ivor and Olive Lewis wrote:
>One of the things I have found is that the reaction for the decomposition of Black Copper Oxide to Red Copper oxide, fundamental in the generation of Copper Red Glazes, can take place at atmospheric pressure above a temperature of approx 1122 Deg Celsius. Given (Greenwood and Earnshaw) that Carbon dioxide will decompose under these condition adding Carbon monoxide to the atmospheric broth, Oxygen discharged from Copper(2)oxide will be scavenged allowing the reaction to proceed to completion. Thermodynamic numbers become favourable at a slightly higher temperature, but well inside the temperature range for Cone 6 workers.
>Obviously a kiln vent will eliminate burnt Volatiles including Carbon dioxide from an electric kiln equipped with this device, counter productive with respect to Electric Copper Red. I also think that sealing the interior with an impervious coating (ITC 100 ???) might be advantageous in controlling air diffusion
>
>
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Ivor and Olive Lewis on fri 9 jun 06
Dear Fred Parker,
Local reduction is achieved by incorporating into your glaze an additive =
that will react chemically with the colourant in your glaze.
The most common one would be Silicon Carbide.
You need -600# or smaller and only as small amount is needed, possibly =
less than one percent.
If you set up and balance the equation of CuO +SiC=3D> Cu2O + CO2 +SiO2 =
you should be able to estimate how much will be needed.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Des & Jan Howard on mon 12 jun 06
Ivor
A number of queries.
Can or does the thermal decomposition from black copper oxide
to red copper oxide progress to elemental copper?
Are the colours of copper red glazes produced by the formation
of red copper oxide or by the formation of elemental copper?
Are the colours a result of one of the above or some proportion of both?
Do you have an idea of the sequence/s that could produce the red
effects from either?
Des
Ivor and Olive Lewis wrote:
>One of the things I have found is that the reaction for the decomposition of Black Copper Oxide to Red Copper oxide, fundamental in the generation of Copper Red Glazes, can take place at atmospheric pressure above a temperature of approx 1122 Deg Celsius. Given (Greenwood and Earnshaw) that Carbon dioxide will decompose under these condition adding Carbon monoxide to the atmospheric broth, Oxygen discharged from Copper(2)oxide will be scavenged allowing the reaction to proceed to completion.
>
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Ivor and Olive Lewis on tue 13 jun 06
Dear Des,=20
I have Copper on the list of substances to investigate via the =
Thermodynamic route.
I do know that when you heat Copper metal under the torch it oxidises. =
If you can change the air setting to reduce oxygen passing through the =
flame you can observe colour changes on the surface as the oxide film =
moves in and out of the reduction zone. Best to use a Oxy-acetylene =
torch if you can lay your hands on one.
This note is speculative, based on my assumption that Copper does not =
form compounds with Silica as do the 1A alkali elements (Monosilicates =
(M2O.SiO2), Metasilicates (2M2O.SiO2) and Di-silicates (M2O.2SiO2). If =
it did it would have greater stability towards acid attack. Be it as =
metal, or cuprous ions or oxide, it remains suspended in the glaze as a =
colloidal entity. Read what is written in "Handbook for Australian =
Potters". When it is found associated with silica it is in the form of a =
"complex" containing Carbonate ions an water molecules (as is Copper =
Sulphate pentahydrate).
An interesting experiment is to add a saturated solution of Copper =
Sulphate to Sodium Silicate and leave it to dry out. During =
crystallisation, a black residue is ejected or precipitated. Borax bead =
test this and identify the element. interesting chemistry.
Sorry I cannot give cast iron answers to your questions.
Best regards,
Ivor
Maggie Woodhead on tue 13 jun 06
Hello Des,
My recipe for Copper Red Glaze is - Pete Pinnell's adjusted for local
materials and the ingredient for the copper is ".3 % red copper oxide".
I can only say it seems to work well. Maggie. N.Z.
of red copper oxide or by the formation of elemental copper?>
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