Paul on sun 22 sep 02
Does anyone know how the flux power of copper carbonate differs from that of
the oxide? I understand that the oxide is about twice as strong of a
colorant as the carbonate; but does this mean that it is twice as strong of
a flux as the carbonate as well? I have not seen this point addressed in any
of my books, so please let me know if anyone knows for sure. thanks
-Paul Borian
Edouard Bastarache on mon 23 sep 02
Hello,
" Copper carbonate is usually written as CuCO3, but chemistry texts say t=
his
"normal" copper carbonate doesn't exist. The green powdery stuff known by
that name is more like CuCO3.Cu(OH)2"
Sorry,
both compounds exist, see the different CAS numbers.
"Basic" copper carbonate is more toxic than copper carbonate;
it is as toxic as copper sulfate by ingestion to cause a severe
intoxication potentially leading to death after such a small dose
as 10 g. The same goes for the oxidule.
A-Copper carbonate
Num=E9ro CAS : 1184-64-1
CCUO3
B-BASIC COPPER(II) CARBONATE
Num=E9ro CAS : 12069-69-1
CH2CU2O5
Main synonyms:
BASIC COPPER CARBONATE
Basic cupric carbonate
CARBONIC ACID, COPPER(2+) SALT, BASIC
COPPER CARBONATE HYDROXIDE
For more information on copper compounds go to:
http://perso.wanadoo.fr/smart2000/cuivre.htm
or
http://digitalfire.com/education/toxicity/materialsafety.html
Later,
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
iandol on mon 23 sep 02
Dear Paul,
I believe the consensus is that Copper Carbonate decomposes, discharging =
Carbon dioxide at a temperature below the melting point of Black Copper =
oxide. This oxide melts at about 1225=B0 Celsius. Hence the contribution =
made to a glaze of either Copper compound as a "Melting Flux" would be =
minimal in a cone 6 glaze but may influence the progress of maturation =
of a full stoneware or porcelain glaze designed to mature above Cone 8 =
or 10 if the recipe contained a substantial amount of either substance.
I suspect that if the glaze recipe contains some form of Borate or =
Alkali Borate Frit the melting effect of Cu2O can be disregarded.
Best regards,
Ivor Lewis. Redhill, South Australia
Roger Graham on mon 23 sep 02
Paul: If it helps, here are some figures re copper oxide and copper
carbonate.
Black copper oxide is CuO
Copper's atomic weight is approx 63.5
Oxygen's atomic weight is 16
So the formula weight of CuO is 63.5 + 16 = 79.5
The percentage of copper in CuO is (63.5 / 79.5) x 100 = 79.5 %
Copper carbonate is usually written as CuCO3, but chemistry texts say this
"normal" copper carbonate doesn't exist. The green powdery stuff known by
that name is more like CuCO3.Cu(OH)2
Adding up all the atomic weights (Carbon = 12, Hydrogen = 1) gives a total
of 221 for the formula weight of this green stuff.
The percentage of copper in it is ( (2 x 63.5)/221) ) x 100 = 57.5 %
Cooked up in a glaze, the carbonate decomposes to oxide well before red
heat, so the end result is the same whichever one you use. But of course,
the black oxide gives you more copper than the green carbonate, weight for
weight. The ratio is (79.5/57.5) = 1.4 approx
So, for example, if the recipe calls for 10 grams of copper oxide, you could
use 14 grams of copper carbonate and get the same effect.
You might have other reasons for choosing the black oxide, or the green
carbonate. Like particle size, for example. But that's another story.
Roger Graham
http://members.optusnet.com.au/~rogergraham
John Hesselberth on wed 25 sep 02
On Sunday, September 22, 2002, at 02:29 PM, iandol wrote:
> I believe the consensus is that Copper Carbonate decomposes,=20
> discharging Carbon dioxide at a temperature below the melting point of=20=
> Black Copper oxide. This oxide melts at about 1225=B0 Celsius. Hence =
the=20
> contribution made to a glaze of either Copper compound as a "Melting=20=
> Flux" would be minimal in a cone 6 glaze but may influence the =
progress=20
> of maturation of a full stoneware or porcelain glaze designed to =
mature=20
> above Cone 8 or 10 if the recipe contained a substantial amount of=20
> either substance.
>
> I suspect that if the glaze recipe contains some form of Borate or=20
> Alkali Borate Frit the melting effect of Cu2O can be disregarded.
I can't explain what is happening, but copper can have a clearly=20
discernable effect on melting at cone 6. A glaze that is marginally=20
melted (or matte due to the formation of crystals on the way down)=20
without copper can be fully melted (or glossy) with the addition of 4-5%=20=
copper. Either copper is aiding in the melting or inhibiting=20
crystallization. I haven't taken the time at this point to figure out=20=
which--but it very clearly has an effect at cone 6. I only use the=20
carbonate, but I would bet the oxide has the same effect IF it gets=20
fully dispersed in the glaze slurry.
Regards,
John
Frog Pond Pottery
PO Box 88
Pocopson, PA 19366
Fax or phone: 610-388-1254
iandol on thu 26 sep 02
Dear John Hesselberth,
I can accept that with some glazes this will happen. I just noted that =
if a glaze was compounded to mature at a particular temperature the =
melting effect of Copper oxide, which has a melting point of 1235=B0 C =
would be of no consequence at Orton Cone 6, 1222=B0 C for large cones. =
But as it dissolves in the melt it will start to make a contribution to =
the properties of the solution.
It is equally probable that once Copper oxide is in solution, Copper =
ions (which seem to be much smaller than other Group One ions) may have =
an effect on viscosity, surface tension or the solubility of other =
compounds which are dissolving into the vitreous silicate melt. I do not =
know which crystals you mean in this instance ..Zinc silicate... =
Wollastonite.. Sphene.. Enstatite? Perhaps Copper has the ability to =
increase the degree of solubility of some of these compounds and so =
assist in suppressing crystallisation during cooling.
Like a lot of questions which are asked, it is sometimes difficult to =
give a defining answer with so little knowledge. What I suggest is =
merely speculation, but might be tested through the examination of draw =
rings taken as the cones drop to signal a mature solution has formed.
One final point. If there is sufficient copper oxide and free silica and =
these compounds are in suitable proportions as well as in intimate =
association, the question of Eutectic melting happening may have to be =
considered. This could be something an interested party may wish to =
investigate. The mixture would be 8% Copper oxide-92%Quartz. Does this =
mixture form a fluid before the glaze (without copper oxide) melts?
Thanks for putting your observations forward.
Best regards,
Ivor Lewis. REDHILL, SOUTH AUSTRALIA
Ron Roy on sat 28 sep 02
Copper carbonate disassociates at about 500C - the melting point of black
copper oxide is 1148C - Basic Copper Carb. disassociates at 500 as well.
That is not the whole story - when materials are combined they melt (and
help flux) at lower temperatures - copper oxide would be a flux at cone 6.
Red Cooper oxide melts at a higher temp. (1230C) but will still help the
melt - even at cone 6.
Adding any oxide to a glaze usually promotes melting - at least for small
amounts.
=46rom Hamer and RR
>I believe the consensus is that Copper Carbonate decomposes, discharging
>Carbon dioxide at a temperature below the melting point of Black Copper
>oxide. This oxide melts at about 1225=B0 Celsius. Hence the contribution
>made to a glaze of either Copper compound as a "Melting Flux" would be
>minimal in a cone 6 glaze but may influence the progress of maturation of
>a full stoneware or porcelain glaze designed to mature above Cone 8 or 10
>if the recipe contained a substantial amount of either substance.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Gavin Stairs on sat 28 sep 02
I would dearly love to have the wherewithal to study melting. Maybe a
Raman spectroscopic telescope and a mass spectrograph in a differential
thermogravimeter.
Anyway, I suspect that some effects of somewhat refractory "fluxes" come
about because of contact melting of eutectic combinations in the powder
phase. Put two slightly refractory powders in close contact and heat to
below their individual melting points, but above their combined eutectic,
and what you will probably see is a melt which forms slowly but inexorably
at the points of contact between particles of the two powders. This is the
basis of sintering, and given the right conditions, it will operate in
liquid phase as well as in a mushy, diffusion capable semisolid. So if the
copper carbonate is in contact with a sodium or calcium salt or oxide, say,
it may convert to oxide and melt at a temperature well below the nominal
decomposition temperature. If this conjecture is correct, it will work
faster the finer the powder. It can also be checked in a
thermogravimeter. And it is consistent with the results reported by John.
Gavin
At 10:03 AM 25/09/2002 -0400, you wrote:
>On Sunday, September 22, 2002, at 02:29 PM, iandol wrote:
>
> > I believe the consensus is that Copper Carbonate decomposes,=20
> > discharging Carbon dioxide at a temperature below the melting point of=20=
>
> > Black Copper oxide. This oxide melts at about 1225=B0 Celsius. Hence =
>the=20
> > contribution made to a glaze of either Copper compound as a "Melting=20=
>
> > Flux" would be minimal in a cone 6 glaze but may influence the =
>progress=20
> > of maturation of a full stoneware or porcelain glaze designed to =
>mature=20
> > above Cone 8 or 10 if the recipe contained a substantial amount of=20
> > either substance.
> >
> > I suspect that if the glaze recipe contains some form of Borate or=20
> > Alkali Borate Frit the melting effect of Cu2O can be disregarded.
>
>I can't explain what is happening, but copper can have a clearly=20
>discernable effect on melting at cone 6. A glaze that is marginally=20
>melted (or matte due to the formation of crystals on the way down)=20
>without copper can be fully melted (or glossy) with the addition of 4-5%=20=
>
>copper. Either copper is aiding in the melting or inhibiting=20
>crystallization. I haven't taken the time at this point to figure out=20=
>
>which--but it very clearly has an effect at cone 6. I only use the=20
>carbonate, but I would bet the oxide has the same effect IF it gets=20
>fully dispersed in the glaze slurry.
>
>Regards,
>
>John
>
>Frog Pond Pottery
>PO Box 88
>Pocopson, PA 19366
>Fax or phone: 610-388-1254
>
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