daniel on fri 4 jun 04
Hi All,
At my class last night my teacher posed the following question to me. What
actually causes the carbon trap effect in a carbon trap shino ? I read too
much and know too little, but my best guess was that the soda ash breaks
down into soda, carbon and oxygen under the influence of the reducing
atmosphere. My theory is that the oxygen is liberated from the soda to
satisfy the combustion requirements of the excess gas. This led to a bunch
of questions on my part because soda ash has an LOI of CO2 doesn't it ? So
is this all happening below the decomposition temperature ?
She suggested that the body may have something to do with it but I wasn't
sure as it seems that you can trap on a variety of bodies.
Anyhow, we're both curious. So I said I'd ask you guys.
Thanx
D
Belmont, California, USA
(ex terra australis)
Ivor and Olive Lewis on sat 5 jun 04
Dear Daniel,
I like your speculation relating to the behaviour of Soda Ash, Better
known as Sodium Carbonate.
Who gave you the idea that there is LOI from Na2CO3?
My Chemistry Book tells me that this substance is almost unreactive
and contrary to popular opinion does not behave like Whiting by
discharging Carbon dioxide when it is heated before it melts.
Experiments show that it decomposes very slowly, not at a rate which
would be noticeable enough to create bubbles in a molten glaze unless
there is some form of silica around for it to work with. Then you get
Sodium Silicate.
Given a melting temperature of just over 800 =C2=BA C and a dirty
atmosphere in the kiln up to that point soda ash will melt and seal
soot into the glaze preventing oxidation except for that which is
possible through diffusion of oxygen.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
----- Original Message -----
From: "daniel"
To:
Sent: Saturday, 5 June 2004 7:02
Subject: Carbon Trap Shino Chemistry
> Hi All,
>
> At my class last night my teacher posed the following question to
me. What
> actually causes the carbon trap effect in a carbon trap shino ? I
read too
> much and know too little, but my best guess was that the soda ash
breaks
> down into soda, carbon and oxygen under the influence of the
reducing
> atmosphere. My theory is that the oxygen is liberated from the soda
to
> satisfy the combustion requirements of the excess gas. This led to a
bunch
> of questions on my part because soda ash has an LOI of CO2 doesn't
it ? So
> is this all happening below the decomposition temperature ?
>
> She suggested that the body may have something to do with it but I
wasn't
> sure as it seems that you can trap on a variety of bodies.
>
> Anyhow, we're both curious. So I said I'd ask you guys.
>
> Thanx
> D
>
> Belmont, California, USA
> (ex terra australis)
>
>
______________________________________________________________________
________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
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> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
daniel on sat 5 jun 04
Hi Ivor,
> Who gave you the idea that there is LOI from Na2CO3?
> My Chemistry Book tells me that this substance is almost unreactive
> and contrary to popular opinion does not behave like Whiting by
> discharging Carbon dioxide when it is heated before it melts.
My own lack of knowledge led me to this. I was unable, at the time of my
post to check this with any authority, so I just put my theory forward
hoping to be appropriately corrected. I need more chemistry. Of course, I
need to make more pots too :)
Dave Finkelnburg sent me a response that, in essence, is the same as yours
- soot and a low temparture melter to seal it in. This raises further
questions like, how does glaze thickness affect this - it certainly seems to
in some simple tests I've done and seen. Also, it seems that this is an
effect that is likely to occur relatively near the glaze surface. I plan to
break a test piece I have and examine the glaze to see if this is
noticeable. Really need to get that hand lense.
Thanx
D
Belmont, California, USA
(ex terra australis)
daniel on sat 5 jun 04
Hi Ivor,
>
> Who gave you the idea that there is LOI from Na2CO3?
> My Chemistry Book tells me that this substance is almost unreactive
> and contrary to popular opinion does not behave like Whiting by
> discharging Carbon dioxide when it is heated before it melts.
I went to the books and the web and the software and both hydrous and
anhydrous sodium carbonate are reported to have CO2 as a volatile. Of
course, the hydrous soda ash also has H2O. Rhodes reports Na2O being the
oxide that enters fusion, leaving CO2 out of his fired weight. John Conrad,
in his Advanced Ceramic Manual does the same. DigitalFire's
ceramicmaterials.info site does so, reporting CO as 41.51 % by weight as a
volatile in the anhydrous compound and 15.38 % in the hydrous, due to the
large amount of water - 10H2O by Conrad's reckoning.
So here's my question then. We can ignore the water (I hope ?) so that
leaves some proportion of CO2 according to these sources. I do not
understand how melting and decomposition (if this is the correct word) take
place. Would CO2 leave before the substance melts or would it be driven from
the molten substance ? Is you reading of your chemistry reference, that this
would not happen at all up to the maturity of the glaze ? or that it would
happen somewhere above the melting point ? or ... Certainly GM 2.0 and
Insight 5 both register an LOI for this material.
(Apologies for the "?" in the middle of sentences but I rather write the way
I speak, besides I rather like them)
Mel, point taken regarding this glaze, but I am the cat who will be felled
by his curiosity I'm afraid :-)
Thanx
D
Belmont, California, USA
(ex terra australis)
Earl Krueger on sun 6 jun 04
On Sunday, Jun 6, 2004, at 14:09 US/Pacific, Ron Roy wrote:
> Hamer says decomposition is at 860C for soda ash and 270 for the
> bicarbonate - and often lowered by interaction.
> RR
>
>>> Who gave you the idea that there is LOI from Na2CO3?
>>> My Chemistry Book tells me that this substance is almost unreactive
>>> and contrary to popular opinion does not behave like Whiting by
>>> discharging Carbon dioxide when it is heated before it melts.
For your reading enjoyment.
Handbook of Chemistry and Physics
43rd Edition 1961-1962
Chemical Rubber Publishing
Sodium Carbonate (Soda Ash)
Na2CO3,
Melting Point - 851=BAC,
Boiling Point - Decomposes (no Temp given).
Sodium Oxide
Na2O
Melting Point - not applicable
Boiling Point - sublimes (evaporates from solid) 1275=BAC
Sodium Carbonate (Washing Soda)
Na2CO3.10H2O,
Melting Point - 32.5 - 34.5=BAC,
Boiling Point - -H2O, 33.5=BAC
Sodium Bicarbonate (Baking Soda)
NaHCO3,
Melting Point - -CO2 @ 270=BAC,
Boiling Point - not applicable (doesn't exist)
Calcium Carbonate (Whiting)
CaCO3,
Melting Point - Decomposes @ 825=BAC,
Boiling Point - not applicable (doesn't exist)
Calcium Oxide
CaO
Melting Point - 2580=BAC
Boiling Point - 2850=BAC
This is for the pure material. Mix it with something else,
like silica, feldspar, clay, and all bets are off.
Earl K...
Bothell, WA, USA
Ron Roy on sun 6 jun 04
Hamer says decomposition is at 860C for soda ash and 270 for the
bicarbonate - and often lowered by interaction.
RR
>> Who gave you the idea that there is LOI from Na2CO3?
>> My Chemistry Book tells me that this substance is almost unreactive
>> and contrary to popular opinion does not behave like Whiting by
>> discharging Carbon dioxide when it is heated before it melts.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Lee Love on mon 7 jun 04
Edouard's book arrived today. It is full of things to try!
Only glanced, trying to get some pots thrown. Will take it to bed.
Tony and I were talking about calcinating reformulated hiratsu
shino, to get the coarser texture found in the original shino
feldspar. Much of the original shino's texture comes from the
coarseness of the feldspar and appears in the application before
firing. It will also reduced carbon trapping that is not found in
Japanese shinos.
In Edouard's materials substitution book, he mentions that
after calcinating soluble materials, they may have to be re-ground.
So I think we are on the right track in making a coarser mix.
Hiratsu shino feldspar cost over $100.00 for 40kilos. I figure
my substitute will only cost under $25.00 a kilo and will not required
7 to 12 days to fire.
--
Lee in Mashiko, Japan http://mashiko.org
http://journals.fotki.com/togeika/Mashiko/ Commentary On Pottery
Ivor and Olive Lewis on mon 7 jun 04
Dear Ron Roy,
Sodium Bi-Carbonate decomposes at the lower temperature through the
destruction of the Bi-Carbonate Ion (HCO3+). (2NaHCO3 =3D Na2CO3 + H2O
+ CO2)
Janet and Frank Hamer might like to reveal the source of their
chemical knowledge in stating the decompostion temperature of Sodium
Carbonate is 860=BA C. Have you checked what is said in their
references? Durrant is explicit, saying of Sodium Carbonate " It melts
at 852=BA C and is not decomposed by heat.*". The (*) refers to a
footnote which I have already quoted in a previous post.
I would rather trust CRC "Handbook of Chemistry and Physics" or Kaye
and Laby, "Tables of Physical and Chemical Constants" for factual
information. Those are the books University Science Students are
directed to for information and the books used in industrial research.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
Sent: Monday, 7 June 2004 6:39
Subject: Re: Carbon Trap Shino Chemistry
> Hamer says decomposition is at 860C for soda ash and 270 for the
> bicarbonate - and often lowered by interaction.
>
> RR
>
>
> >> Who gave you the idea that there is LOI from Na2CO3?
> >> My Chemistry Book tells me that this substance is almost
unreactive
> >> and contrary to popular opinion does not behave like Whiting by
> >> discharging Carbon dioxide when it is heated before it melts.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
>
______________________________________________________________________
________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Joyce Lee on tue 8 jun 04
ok
----- Original Message -----
From: "Ivor and Olive Lewis"
To:
Sent: Sunday, June 06, 2004 10:42 PM
Subject: Re: Carbon Trap Shino Chemistry
Dear Ron Roy,
Sodium Bi-Carbonate decomposes at the lower temperature through the
destruction of the Bi-Carbonate Ion (HCO3+). (2NaHCO3 = Na2CO3 + H2O
+ CO2)
Janet and Frank Hamer might like to reveal the source of their
chemical knowledge in stating the decompostion temperature of Sodium
Carbonate is 860º C. Have you checked what is said in their
references? Durrant is explicit, saying of Sodium Carbonate " It melts
at 852º C and is not decomposed by heat.*". The (*) refers to a
footnote which I have already quoted in a previous post.
I would rather trust CRC "Handbook of Chemistry and Physics" or Kaye
and Laby, "Tables of Physical and Chemical Constants" for factual
information. Those are the books University Science Students are
directed to for information and the books used in industrial research.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
Sent: Monday, 7 June 2004 6:39
Subject: Re: Carbon Trap Shino Chemistry
> Hamer says decomposition is at 860C for soda ash and 270 for the
> bicarbonate - and often lowered by interaction.
>
> RR
>
>
> >> Who gave you the idea that there is LOI from Na2CO3?
> >> My Chemistry Book tells me that this substance is almost
unreactive
> >> and contrary to popular opinion does not behave like Whiting by
> >> discharging Carbon dioxide when it is heated before it melts.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> Fax: 613-475-3513
>
>
______________________________________________________________________
________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Ivor and Olive Lewis on tue 8 jun 04
Dear Earl,
I have the 1996 edition. Well worth the money. The credentials of the
sub editors and other contributors attest to the quality of the
information.
Pure stuff! Well as pure as they can get it, usually between 4/9s and
5/9s.
Sodium Monoxide reacts with Carbon Dioxide in damp air. No prizes for
guessing the name of the residue.
Best regards,
Ivor
<
Handbook of Chemistry and Physics
43rd Edition 1961-1962
Chemical Rubber Publishing>>
John Britt on tue 8 jun 04
Ivor,
I checked the internet for alternative sources. Search for soda ash
decomposition temperature or MSDS.
I found MSDS sheets like:
http://216.239.39.104/search?
q=cache:nA553izsX24J:site.ivenue.com/atpinc_2/MSDS/SODA_ASH_MSDS.pdf+soda+a
sh+decomposition+temperature&hl=en
It states: The decomposition of soda begins at 440 C and CO2 is evolved at
high temperatures 1000 C /1832 F or with acids.
Or:
http://216.239.51.104/search?q=cache:Zbf_V4lY1jYJ:www.espimetals.com/msds%
27s/sodiumcarbonate.pdf+sodium+carbonate+decomposition+temperature&hl=en
Melting point 851 C, - 400 C begins to evolve CO2.
Maybe you can resolve this for us?
John Britt
John Britt on wed 9 jun 04
Ivor,
I was kinda hoping you would test it for us??
>It is, as you know, a simple task to test such data.
>In whom do you put your trust?
>Best regards.
>Ivor Lewis
What do you think?
John Britt
John Britt on wed 9 jun 04
Ivor,
I am going with the world's major producer, Solvay.com and their MSDS.
http://www.sodaash.com/product/MSDS/0,5376,-_EN-1000013,00.html
What do you think?
John Britt
Ivor and Olive Lewis on wed 9 jun 04
Dear John Britt,
I trust CRC "Handbook of Physical and Chemical Constants" and Kay and
Laby, "Tables of Physical and Chemical Constants", a publication which
began life at the Cavendish Laboratory, Cambridge (UK).
It is, as you know, a simple task to test such data.
In whom do you put your trust?
Best regards.
Ivor Lewis
Ivor and Olive Lewis on fri 11 jun 04
Dear John Britt,
Sounds like a good idea except..... Porcelain crucibles are not hard
to come by but in $Au Platinum Crucibles fro J & M are a bit rich for
my pocket. Nor do I have access to analytical grade scales.
Anyway, it would be far better if a third party were to repudiate the
information I have provided.
I might suggest that someone use a clean loop of Nichrome Wire, dip
this in some moist Soda ash and heat it in a strong gas/air flame.
Several attempts may be required to collect enough to make a molten
bead. Observe what happens and report back to the group.
Best regards,
Ivor.
Lee Love on sat 12 jun 04
Lee Love wrote:
>
>
> Hiratsu shino feldspar cost over $100.00 for 40kilos. I figure
> my substitute will only cost under $25.00 a kilo and will not required
> 7 to 12 days to fire.
Correction:
Hiratsu is actually about $100.00 for 25 kilos . And my
substitution about $25.00 for 40 kilos
--
in Mashiko, Japan http://mashiko.org
http://journals.fotki.com/togeika/Mashiko/ Commentary On Pottery
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