John Hesselberth on tue 22 apr 08
On Apr 21, 2008, at 7:00 PM, Steve Slatin wrote:
> One of the things that happens with
> lithium when you apply it in the form
> of lithium carb is -- because it is
> soluble -- permeates the clay,
> carried in solution by the water.
Hi Steve,
I wonder about this. I know there is pretty good evidence that high
amounts of lithium sourced as lithium carbonate can cause strange
things to happen (like crazing and shivering on the same piece), but
I am not at all sure we understand why. Let's look at some numbers.
Lithium carbonate is not highly soluble in water. It is more in the
category of slightly soluble.
The reported solubility of of lithium carbonate in water is about 1.5
grams per 100 ml of water. Glaze slurries normally have about 100 ml
of water per 100 grams of dry glaze. So I would expect that in a
glaze having a lithium carbonate level of 1.5% most of it would
dissolve. But in a glaze having 10% lithium carbonate only a small
fraction of it would dissolve (the same amount as a glaze having 1.5%
lithium carbonate). The solution would then be saturated and the rest
of the lithium carbonate would remain undissolved just like most of
the other glaze ingredients. So why is there a difference in the way
the 2 glazes behave? My point is that the water in the glaze slurry
would have exactly the same concentration of lithium carbonate
whether the glaze contained 2% or 20% lithium carbonate. So why does
one seem to cause problems and the other not???
What am I missing here? I think there must be something else going
on. Anybody have any ideas?
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Michael Wendt on tue 22 apr 08
I think the cause is migration to edges
because these have the most surface area
with respect to cross section.
We used to make Taco Holders by casting
and regularly saw glaze problems on the
rims if we fan dried them, but no problems
if they dried in the damp box. In the extreme,
the sodium silicate whiskers would sometimes
form on the nearly dry pieces.
In similar fashion, other solubles like lith carb
would migrate towards edges and result in
higher concentrations there, accounting for
shivering while depleting areas where the
calculations would indicate they should
not craze.
I suggest a test:
Glaze two similar pieces with the same
glaze at the same time. Fast dry one.
Cover the other with a cardboard box an slow
dry it. Fire them side by side with a cone pack
between them and see if this has any effect.
While not definitive, it offers a possible pathway
to an explanation.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com
John wrote:
Hi Steve,
I wonder about this. I know there is pretty good
evidence that high
amounts of lithium sourced as lithium carbonate can
cause strange
things to happen (like crazing and shivering on the
same piece), but
I am not at all sure we understand why. Let's look at
some numbers.
Lithium carbonate is not highly soluble in water. It is
more in the
category of slightly soluble.
The reported solubility of lithium carbonate in water
is about 1.5
grams per 100 ml of water. Glaze slurries normally have
about 100 ml
of water per 100 grams of dry glaze. So I would expect
that in a
glaze having a lithium carbonate level of 1.5% most of
it would
dissolve. But in a glaze having 10% lithium carbonate
only a small
fraction of it would dissolve (the same amount as a
glaze having 1.5%
lithium carbonate). The solution would then be
saturated and the rest
of the lithium carbonate would remain undissolved just
like most of
the other glaze ingredients. So why is there a
difference in the way
the 2 glazes behave? My point is that the water in the
glaze slurry
would have exactly the same concentration of lithium
carbonate
whether the glaze contained 2% or 20% lithium
carbonate. So why does
one seem to cause problems and the other not???
What am I missing here? I think there must be something
else going
on. Anybody have any ideas?
Regards,
John
Tony Ferguson on tue 22 apr 08
John,
I am not sure by what process exactly, but I believe lithium will condense (in the case of one of my glaze with higher about of lithium in it) to the underside of the lid and bucked walls. Perhaps a certain amount of lithium is migrating out of the glaze and imbalancing the glaze somehow and the process of remixing is having a variance of in and out of solution lithium particles?
Also, a real pleasure to meet you again and thank you so much for your part in PA Guild of Craftsmen workshop. You folks have an inspiring level of membership and what you are doing for your members! Thanks for having me and take care of Nick--he is doing an impressive job with the guild.
Tony Ferguson
John Hesselberth wrote: On Apr 21, 2008, at 7:00 PM, Steve Slatin wrote:
> One of the things that happens with
> lithium when you apply it in the form
> of lithium carb is -- because it is
> soluble -- permeates the clay,
> carried in solution by the water.
Hi Steve,
I wonder about this. I know there is pretty good evidence that high
amounts of lithium sourced as lithium carbonate can cause strange
things to happen (like crazing and shivering on the same piece), but
I am not at all sure we understand why. Let's look at some numbers.
Lithium carbonate is not highly soluble in water. It is more in the
category of slightly soluble.
The reported solubility of of lithium carbonate in water is about 1.5
grams per 100 ml of water. Glaze slurries normally have about 100 ml
of water per 100 grams of dry glaze. So I would expect that in a
glaze having a lithium carbonate level of 1.5% most of it would
dissolve. But in a glaze having 10% lithium carbonate only a small
fraction of it would dissolve (the same amount as a glaze having 1.5%
lithium carbonate). The solution would then be saturated and the rest
of the lithium carbonate would remain undissolved just like most of
the other glaze ingredients. So why is there a difference in the way
the 2 glazes behave? My point is that the water in the glaze slurry
would have exactly the same concentration of lithium carbonate
whether the glaze contained 2% or 20% lithium carbonate. So why does
one seem to cause problems and the other not???
What am I missing here? I think there must be something else going
on. Anybody have any ideas?
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
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Steve Slatin on tue 22 apr 08
John --
Edouard also thinks I'm wrong ... so
I guess the odds are increasingly good
that I am. I still have an affection
for the idea, though -- so I'm -- for
the time being -- putting it into the
category of 'maybe' from its former
classification of 'maybe-likely.'
I still have some anecdotal experience
of lithium as a carbonate behaving
differently from lithium in spodumene
(that is, what should be good
substitutions don't 'work' similarly).
There could, of course, be different
reasons for this -- the particle size
of the spodumene, for example, or
variations in its chemical constituents.
And let's not forget that the spodumene
lithium is already inside of a fairly
stable bond, where the carbonate is fairly
reactive at STP.
Whatever makes it work, I get nice
little crystals very readily.
Best wishes -- Steve Slatin
--- On Tue, 4/22/08, John Hesselberth wrote:
> From: John Hesselberth
> Subject: Re: copper reds (ron roy #204A)--now lithium carbonate
> To: CLAYART@LSV.CERAMICS.ORG
> Date: Tuesday, April 22, 2008, 4:15 AM
> On Apr 21, 2008, at 7:00 PM, Steve Slatin wrote:
>
> > One of the things that happens with
> > lithium when you apply it in the form
> > of lithium carb is -- because it is
> > soluble -- permeates the clay,
> > carried in solution by the water.
>
> Hi Steve,
>
> I wonder about this. I know there is pretty good evidence
> that high
> amounts of lithium sourced as lithium carbonate can cause
> strange
> things to happen (like crazing and shivering on the same
> piece), but
> I am not at all sure we understand why. Let's look at
> some numbers.
> Lithium carbonate is not highly soluble in water. It is
> more in the
> category of slightly soluble.
>
> The reported solubility of of lithium carbonate in water is
> about 1.5
> grams per 100 ml of water. Glaze slurries normally have
> about 100 ml
> of water per 100 grams of dry glaze. So I would expect that
> in a
> glaze having a lithium carbonate level of 1.5% most of it
> would
> dissolve. But in a glaze having 10% lithium carbonate
> only a small
> fraction of it would dissolve (the same amount as a glaze
> having 1.5%
> lithium carbonate). The solution would then be saturated
> and the rest
> of the lithium carbonate would remain undissolved just like
> most of
> the other glaze ingredients. So why is there a difference
> in the way
> the 2 glazes behave? My point is that the water in the
> glaze slurry
> would have exactly the same concentration of lithium
> carbonate
> whether the glaze contained 2% or 20% lithium carbonate. So
> why does
> one seem to cause problems and the other not???
>
> What am I missing here? I think there must be something
> else going
> on. Anybody have any ideas?
>
> Regards,
>
> John
____________________________________________________________________________________
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Neon-Cat on thu 24 apr 08
No, Jon, not really although I looked basically only to the lithium
carbonate reaction chemistry for my previous post.
It is late -- I've raked a million leaves this week and have forty million
or so to go; I'm on my way out of town; last night I discovered my roof
leaks; I quit school but signed up for a new one; I dropped my boyfriend;
and now I'm of a mind to make something nice and soothing from clay and call
it a night.
Have a restful night,
Marian
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of jonathan
byler
Sent: Thursday, April 24, 2008 9:09 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: copper reds (ron roy #204A)--now lithium carbonate
It is late, and I have had a long day, and I am not sure if I
completely understand all of what you just wrote... Does this all not
happen when the lithium is supplied by minerals such as spodumene?
or is the problem the same/similar? if not, then it explains why
Lithium carbonate is less desirable to use in a ^10 glaze for more
than solubility reasons.
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
Ivor and Olive Lewis on thu 24 apr 08
Dear John Hesselberth,=20
You ask <<...My point is that the water in the glaze slurry would have =
exactly the same concentration of lithium carbonate whether the glaze =
contained 2% or 20% lithium carbonate. So why does one seem to cause =
problems and the other not???
What am I missing here? I think there must be something else going on. =
Anybody have any ideas? ,,,,>>
I think you have to consider the volume of water involved.
Say, as and illustration only, a kilogram of glaze requires one litre of =
water, Mass 1000 grams. So of the glazes the one with 20% Lithium Carb =
will have 200 grams of Lith carb. Of this 15 grams will dissolve in 1000 =
grams of water. This leaves 185 grams to contribute fluxing action to =
the glaze. The recipe containing 2% will contribute 20 grams but the =
water content remains constant, 1000 grams. The solubility does not =
alter, still 15 grams/ litre. This only leaves 5 grams to contribute =
fluxing qualities to the glaze.
Now I am unsure that answers your question.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
John Hesselberth on thu 24 apr 08
Hello Ivor,
No it doesn't get at my question. The "potter's lore" has been that
it is because Li2CO3 is soluble that is causes problems. Problems
that result from the dissolved lithium migrating and concentrating
more in some areas than others. As you and I both pointed out, the
concentration of lithium carbonate in the water will be the same in
either case. So it seems unlikely that dissolved lithium carbonate is
the cause of the problem.
As I thought about it more I am leaning toward the following
hypothesis to replace the "solubility" hypothesis. Lithium carbonate
melts at 618C whereas the insoluble forms of lithium (lepidolite,
petalite, and spodumene) are reported to melt in the range of 1150C
to 1250C. So when the carbonate is used the melting occurs much
earlier and the melt pool may be (hypothesis) much lower viscosity
for a period of time until all the other ingredients are incorporated
into the melt pool. Therefore, what is essentially melted lithium
carbonate is much more mobile to move through the bisque and
concentrate at corners or edges. Makes sense to me anyhow. Comments
from anyone else are welcome.
Regards,
John
On Apr 23, 2008, at 9:50 PM, Ivor and Olive Lewis wrote:
> Say, as and illustration only, a kilogram of glaze requires one
> litre of water, Mass 1000 grams. So of the glazes the one with 20%
> Lithium Carb will have 200 grams of Lith carb. Of this 15 grams
> will dissolve in 1000 grams of water. This leaves 185 grams to
> contribute fluxing action to the glaze. The recipe containing 2%
> will contribute 20 grams but the water content remains constant,
> 1000 grams. The solubility does not alter, still 15 grams/ litre.
> This only leaves 5 grams to contribute fluxing qualities to the glaze.
>
> Now I am unsure that answers your question.
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Neon-Cat on thu 24 apr 08
John wrote: "As I thought about it more I am leaning toward the following
hypothesis to replace the "solubility" hypothesis. Lithium carbonate
melts at 618C whereas the insoluble forms of lithium (lepidolite,
petalite, and spodumene) are reported to melt in the range of 1150C
to 1250C. So when the carbonate is used the melting occurs much
earlier and the melt pool may be (hypothesis) much lower viscosity
for a period of time until all the other ingredients are incorporated
into the melt pool. Therefore, what is essentially melted lithium
carbonate is much more mobile to move through the bisque and
concentrate at corners or edges. Makes sense to me anyhow. Comments
from anyone else are welcome."
Hi John, you and others may wish to stick me in a kiln and crank it up - I
can't buy your hypothesis. Let me offer a quick alternative before things
heat up.
Lithium Carbonate (Li2CO3) decomposes upon firing to form lithium oxide,
also called "lithia" (Li2O) and carbon dioxide (CO2). According to various
data sources it does this at about 1310?C at its boiling point temperature.
Just for the record, various melting points are given for lithium carbonate,
from 618? to 723? C. It should be remembered that the solubility of lithium
carbonate decreases at higher temperatures. There is a dependence of the
equilibrium constant on temperature so during the reaction the available
concentration of lithium oxide within molten lithium carbonate will vary
with the temperature at that time. For example, at 7500 - 8800 C (13820 -
16160 F) the available lithium oxide in the melt is approximately 25% of the
lithium carbonate on a mole-to-mole basis.
Li2CO3 (s) ---heat--> Li2O (s) + CO2 (g)
Side reactions may also occur within the glaze melt at or below
decomposition temperatures. Here are two examples:
Li2CO3 + H2O ---heat--> 2LiOH + CO2 (lithium hydride formation)
2Li2CO3 + O2 ---heat--> 2Li2O2 + 2CO2 (lithium peroxide formation)
If this happens an additional step or two is required before the original
lithium carbonate yields lithium oxide through the thermal decomposition of
lithium hydroxide or lithium peroxide.
You might think of decomposition as evaporation of the substances, in fact
many texts and references do just that. Suppliers of lithium carbonate
commonly advise customers who wish to use this material as a fluxing agent
to do so at temperatures below 1250? C (2282? F) to avoid the evaporation of
Li2CO3. This would put the evaporation of our lithium carbonate between a
firing range of cone 7 and 8. The effects of a loss of flux and the spin-off
reactions caused by its loss are naturally noticed first in those areas such
as corners, edges, rims, handles, lips, or exterior joints of functional
ware or sculptural clay forms because they receive the most exposure to the
heat and actions of flue gases within our kilns.
Three crucial problems for the high temperature potter or ceramic artist
arise as our lithium carbonate flux evaporates (artisans firing in the mid
or low temperature range remain generally unaffected):
1) flux work from both our lithium carbonate and the lithium oxide decrease
or vanish altogether and so are unavailable to do useful work for us;
2) the production of carbon dioxide causes bubbles to form that remain in
the melt or are released from the glaze surface. While useful for chemical
mixing of the melt components bubbling can cause serious problems that may
lead to pinholing in the clay body or glaze, and glaze crazing and
shivering.
3) supersaturation increases near the glaze surface as evaporation takes
place triggering surface nucleation processes (the onset of a phase
transition, signaled by the formation of bubbles or crystals in a liquid
within a small region). Crystals of various elements and compounds may form
aided by micron to
sub-micron bubbles so tiny they're not even seen by many test instruments
(bubbles may serve as nucleation sites for crystals). Increased holding
times at higher temperatures can contribute to this crystallization,
especially of non-lithium-based crystals. While crystals are beautiful and
often a desirable glaze effect their presence deep within the glaze where it
bonds to the clay body is not conducive to achieving a good clay body-glaze
fit. A further point about crystals - with this glaze (the 204 that began
this thread) you may be making kinds you never considered - everything from
calcite (CaCO3) crystals to needle-like or fiber-like shaped crystals
composed of Li2O.SiO2 such as lithium disilicate (Li2Si2O5). These crystals
may form a mass of sheet-like structures on the glaze surface, within the
glaze, or on the surface of the clay body. Depending on what's in your glaze
and/or clay body other non-crystalline compounds may form that could impact
glaze deposition and fit. Silicon carbide (SiC) deposits from a SiO2 +
Li2CO3 melt are one example.
An additional point worth remembering - lithium oxide (and lithium
hydroxide), while present and active, are very corrosive and may dissolve
ceramic pigments within the glaze melt.
My email program has lost its ability to produce subscripts -- sorry about
that. I had them all in WORD, but alas you'll have to do without.
You all make me think too much. Then again, I can't get in too much trouble
thinking about clay and glaze, something to be grateful for:>)
Marian Gooding
Neon-Cat Ceramics
neon-cat.com
neoncat@flash.net
jonathan byler on thu 24 apr 08
It is late, and I have had a long day, and I am not sure if I
completely understand all of what you just wrote... Does this all not
happen when the lithium is supplied by minerals such as spodumene?
or is the problem the same/similar? if not, then it explains why
Lithium carbonate is less desirable to use in a ^10 glaze for more
than solubility reasons.
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Apr 24, 2008, at 8:07 PM, Neon-Cat wrote:
> John wrote: "As I thought about it more I am leaning toward the
> following
> hypothesis to replace the "solubility" hypothesis. Lithium carbonate
> melts at 618C whereas the insoluble forms of lithium (lepidolite,
> petalite, and spodumene) are reported to melt in the range of 1150C
> to 1250C. So when the carbonate is used the melting occurs much
> earlier and the melt pool may be (hypothesis) much lower viscosity
> for a period of time until all the other ingredients are incorporated
> into the melt pool. Therefore, what is essentially melted lithium
> carbonate is much more mobile to move through the bisque and
> concentrate at corners or edges. Makes sense to me anyhow. Comments
> from anyone else are welcome."
>
> Hi John, you and others may wish to stick me in a kiln and crank it
> up - I
> can't buy your hypothesis. Let me offer a quick alternative before
> things
> heat up.
>
> Lithium Carbonate (Li2CO3) decomposes upon firing to form lithium
> oxide,
> also called "lithia" (Li2O) and carbon dioxide (CO2). According to
> various
> data sources it does this at about 1310?C at its boiling point
> temperature.
> Just for the record, various melting points are given for lithium
> carbonate,
> from 618? to 723? C. It should be remembered that the solubility of
> lithium
> carbonate decreases at higher temperatures. There is a dependence
> of the
> equilibrium constant on temperature so during the reaction the
> available
> concentration of lithium oxide within molten lithium carbonate will
> vary
> with the temperature at that time. For example, at 7500 - 8800 C
> (13820 -
> 16160 F) the available lithium oxide in the melt is approximately
> 25% of the
> lithium carbonate on a mole-to-mole basis.
>
> Li2CO3 (s) ---heat--> Li2O (s) + CO2 (g)
>
> Side reactions may also occur within the glaze melt at or below
> decomposition temperatures. Here are two examples:
> Li2CO3 + H2O ---heat--> 2LiOH + CO2 (lithium hydride formation)
> 2Li2CO3 + O2 ---heat--> 2Li2O2 + 2CO2 (lithium peroxide formation)
> If this happens an additional step or two is required before the
> original
> lithium carbonate yields lithium oxide through the thermal
> decomposition of
> lithium hydroxide or lithium peroxide.
>
> You might think of decomposition as evaporation of the substances,
> in fact
> many texts and references do just that. Suppliers of lithium carbonate
> commonly advise customers who wish to use this material as a
> fluxing agent
> to do so at temperatures below 1250? C (2282? F) to avoid the
> evaporation of
> Li2CO3. This would put the evaporation of our lithium carbonate
> between a
> firing range of cone 7 and 8. The effects of a loss of flux and the
> spin-off
> reactions caused by its loss are naturally noticed first in those
> areas such
> as corners, edges, rims, handles, lips, or exterior joints of
> functional
> ware or sculptural clay forms because they receive the most
> exposure to the
> heat and actions of flue gases within our kilns.
>
> Three crucial problems for the high temperature potter or ceramic
> artist
> arise as our lithium carbonate flux evaporates (artisans firing in
> the mid
> or low temperature range remain generally unaffected):
> 1) flux work from both our lithium carbonate and the lithium oxide
> decrease
> or vanish altogether and so are unavailable to do useful work for us;
> 2) the production of carbon dioxide causes bubbles to form that
> remain in
> the melt or are released from the glaze surface. While useful for
> chemical
> mixing of the melt components bubbling can cause serious problems
> that may
> lead to pinholing in the clay body or glaze, and glaze crazing and
> shivering.
> 3) supersaturation increases near the glaze surface as evaporation
> takes
> place triggering surface nucleation processes (the onset of a phase
> transition, signaled by the formation of bubbles or crystals in a
> liquid
> within a small region). Crystals of various elements and compounds
> may form
> aided by micron to
> sub-micron bubbles so tiny they're not even seen by many test
> instruments
> (bubbles may serve as nucleation sites for crystals). Increased
> holding
> times at higher temperatures can contribute to this crystallization,
> especially of non-lithium-based crystals. While crystals are
> beautiful and
> often a desirable glaze effect their presence deep within the glaze
> where it
> bonds to the clay body is not conducive to achieving a good clay
> body-glaze
> fit. A further point about crystals - with this glaze (the 204 that
> began
> this thread) you may be making kinds you never considered -
> everything from
> calcite (CaCO3) crystals to needle-like or fiber-like shaped crystals
> composed of Li2O.SiO2 such as lithium disilicate (Li2Si2O5). These
> crystals
> may form a mass of sheet-like structures on the glaze surface,
> within the
> glaze, or on the surface of the clay body. Depending on what's in
> your glaze
> and/or clay body other non-crystalline compounds may form that
> could impact
> glaze deposition and fit. Silicon carbide (SiC) deposits from a SiO2 +
> Li2CO3 melt are one example.
>
> An additional point worth remembering - lithium oxide (and lithium
> hydroxide), while present and active, are very corrosive and may
> dissolve
> ceramic pigments within the glaze melt.
>
> My email program has lost its ability to produce subscripts --
> sorry about
> that. I had them all in WORD, but alas you'll have to do without.
> You all make me think too much. Then again, I can't get in too much
> trouble
> thinking about clay and glaze, something to be grateful for:>)
>
> Marian Gooding
> Neon-Cat Ceramics
> neon-cat.com
> neoncat@flash.net
>
> ______________________________________________________________________
> ________
> Clayart members may send postings to: clayart@lsv.ceramics.org
>
> You may look at the archives for the list, post messages, change your
> subscription settings or unsubscribe/leave the list here: http://
> www.acers.org/cic/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots2@visi.com
Ivor and Olive Lewis on fri 25 apr 08
Dear Marian Gooding
You give us a most comprehensive overview of the Chemistry of Lithium =
and its compounds.
Perhaps you would also share your sources of information with us .
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on fri 25 apr 08
Dear John=20
Seems to me to be plausible. I suppose it would depend on distribution =
and pore size, as well as the Lithium Carbonate ratio between the two =
fabrics.
I had thought that there might be a reaction between the Li2CO3 and any =
of the silicate minerals in the two fabrics, but the melting point of =
Lithium Metasilicate is over 1200 deg C. If that reaction did happen the =
silicate would solidify and cease acting as a melting flux.=20
It might pay to search Wikipedia for information about elemental =
Lithium, its compounds and their reactions with silicate minerals.
Best regards,
Ivor
John Hesselberth on fri 25 apr 08
On Apr 24, 2008, at 9:07 PM, Neon-Cat wrote:
> Hi John, you and others may wish to stick me in a kiln and crank it
> up - I
> can't buy your hypothesis. Let me offer a quick alternative before
> things
> heat up.
Hi Marian,
No, not at all and I doubt things will heat up. This is the kind of
discussion that puts all but a few of us to sleep. But I can't buy
your hypothesis either. In fact I'm not sure I found it. All I saw,
for sure, was was a recitation of the some of the properties and
behaviors of lithium carbonate. Are you suggesting that lithium
carbonate decomposes to the oxide and the oxide selectively
evaporates from parts of the pot? If so how can this be when lithium
oxide does not even melt until >1700C in my handbook? In addition you
suggest the carbonate does not decompose to the oxide until 1310C--
above cone 10. Even if that were to happen between cones 7 and 8 as
you suggest, this phenomena (described in the next paragraph) is
known to happen at lower temperatures also.
To repeat from previous messages, the question I am wrestling with is
"why does lithium sourced as lithium carbonate in levels above 2 or
3% lithium carbonate behave so differently than lithium sourced from
spodumene or petalite or lepidolite". It is known to sometimes result
in weird behavior of the glaze when sourced that way--such as crazing
and shivering on the same pot. The working hypothesis has been that
because lithium carbonate is soluble in water it is free to migrate
and concentrate (or be depleted) immediately after glaze application
with the water that is in the glaze slurry. As my previous messages
point out this makes no sense to me as the amount of lithium
carbonate dissolved in the water will be the same whether the glaze
contains 2% or 20% lithium carbonate. This weird phenomena of crazing
and shivering on the same pot does not happen at 2% but has been
observed at higher percentages of lithium carbonate. Nor does it
happen, even with high percentages of lithium, when the lithium is
sourced from spodumene, petalite, or lepidolite.
So if the different levels of migration (between 2% and 20% lithium
carbonate) does not happen as a result of lithium carbonate dissolved
in water, when and how does it happen? It seems to me the next
opportunity for it to happen is when the lithium carbonate melts and
whether it melts at 618C or 723C is totally irrelevant. It is melting
way before anything else in the glaze does--even sodium chloride
which might be present as a contaminant does not melt until 800C--and
lithium carbonate must exist for a short time as a fairly pure liquid
scattered through the powdered glaze. That would be a perfect
opportunity for it to begin to move and be wicked by capillary action
through the powdered glaze or the porous bisque. Lithium sourced from
spodumene, petalite, or lepidolite does not become mobile until it
either melts or dissolves into the forming melt pool. This would
occur at significantly higher temperatures--after the molten lithium
carbonate has already migrated.
Your message offered a blizzard of" factoids" about lithium
carbonate, but I could not see any relevance of much of it to the
problem at hand. Nor could I find a hypothesis (unless it is a
variant of what I have tried to state in the first paragraph) that
explains this crazing/shivering phenomena in your writing. If I have
missed it could you please write it in a nice short paragraph
comparable to the one directly above so I can try to understand what
you are hypothesizing?
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Neon-Cat on sun 27 apr 08
~ Mel, hello! Would you please put this post through if you have not already
seen it? It was sent early Sat. afternoon and has not yet appeared. Thank
you! ~
John, thank you so much for your post - it's important for me to learn about
those Clayart folks who read and are interested in certain subjects and how
they might like to receive information or engage in discussion. And yes,
John, I do love factoids - doesn't everyone? Factoids define the dance and
with lithium carbonate in the kiln it can often be a strangely manic dance.
To reiterate -- lithium carbonate, melted or not, is not going to migrate or
get wicked too far afield in or on ware in a kiln environment. It will just
dance around at record breaking speeds in its general area before it or one
of its many species do a few of the things I suggested might happen in my
previous post and a few more things I will point out in this post.
John, you suggested that lithium carbonate melts first and wanders around
the dance floor alone. But does it? Recall, we are having this discussion
because lithium carbonate is known to be and is used as a vigorous flux. By
definition this means it lowers the melting point of the glaze ingredients
(and in our case, probably the clay body ingredients at their body surface,
too) and promotes fusion at lower temperatures than would otherwise possible
without its use making your theory moot. However, in my theory, by fluxing
its dance partners into a like environment the lithium carbonate may cause
the entire dance floor to flow off edges of the stage or do other weird
things on the floor while in a state of flux and nonequilibrium (the two
states not necessarily being related). Our lithium carbonate molecule will
be very busy, maybe changing and growing or flat out disassociating, right
in the vicinity where it started at the beginning of the dance (glaze
firing). Using special techniques and equipment you might get a lithium ion
to migrate some distance but you'd probably never achieve that within a hot
kiln.
Instead, once we have some lithium ions generated before and after the
production of lithium oxide we can observe that in the presence of carbon or
in a carbon atmosphere (CO2) the lithium ions will diffuse to the surface of
the glaze and there react with the carbon to regenerate lithium carbonate
that remains and deposits at the surface where it causes some unrest (high
temperatures tend to amplify and encourage this effect). Due to the
regeneration of lithium carbonate at the surface of the glaze during firing
the lithium ion concentration in the vicinity of the glaze surface
temporarily decreases. Since, however, lithium ion is easily movable in the
glaze melt (lithium ion has a large diffusion coefficient), lithium ion
inside the glaze in this immediate vicinity moves toward the glaze surface
so as to cover a decrease in the lithium ion concentration near the surface
and the generation of lithium carbonate at the glaze surface proceeds in a
seemingly endless cycle until there is no more lithium carbonate left to
react or in the case of excess lithium carbonate the kiln is shut down and
reactions automatically cease. A lithium ion craves stability and it is not
going to patiently travel or migrate clear across ware surfaces looking for
a partner - given its very reactive nature it cannot. Thus we are almost
back at our starting point with respect to the addition of lithium carbonate
except that as firing proceeds, instead of being dispersed throughout the
glaze melt it is constantly created anew on the surface of the glaze where
it forms a film as it cools (appearing as a subtle yellowing or fogging on a
clear glaze). With the bubbles from the release of carbon dioxide within the
glaze and at the bottom of the melt all trying to rise to the surface along
with all the other things going on in the glaze melt a very lively, almost
manic environment is created indeed.
To add excess amounts of lithium carbonate is just asking for a totally wild
time within the glaze. To mention yet another problem regarding the use of
lithium carbonate as a glaze flux, silicon dioxide (SiO2) and aluminum oxide
(Al2O3), already present in our clays or added as fillers or adjustments to
a glaze along with the addition of oxides such as titanium dioxide (TiO2)
all increase the number of available charge carriers within the glaze melt
and enhance the lithium ion dissociation already occurring. To increase the
amount of lithium carbonate above the 1-2% in current popular use only
increases overall volatility within the melt throwing our already highly
disordered system further out of whack. Electrolyte conductivity is reduced
resulting in a further roughing of the glaze surface and its contact area
with the clay body at the bottom of the melt possibly further impeding glaze
fit. To mention just a few more deleterious effects, reduced conductivity
also makes the formation of a uniform glaze harder to achieve and negatively
impacts a glaze's chemical and thermal stability, as well as its strength
and permeability.
For the two reasons stated above in the paragraphs immediately preceding
this one, and for other reasons we sometimes lose the working advantages of
our lithium carbonate and its lithium oxide as a mere flux agent during
firing or we seriously upset equilibrium processes, especially at higher
temperatures. If all ions have not disassociated or can be drawn out of the
cycle of surface lithium carbonate film creation then the ions, molecules,
and any new lithium compounds formed will have a chance to wreck additional
havoc with our clay body surface, the glaze (all areas), and the clay-glaze
fit at the bottom of the melt. As they say, there's a price for the use of
this volatile flux but its not because as you theorize, melted lithium
carbonate is migrating or being wicked to concentrate on distant parts of
the functional or sculptural ware through a porous bisque. The mechanism for
(near) surface deposition of lithium carbonate is in the solid solution
lithium carbonate reaction chemistry.
I still like my hypothesis (briefly touched on in the 1-3 under the "crucial
problems" section of my previous post and entertained here in more detail)
that lithium carbonate chemistry is creating unwanted substances within the
glaze, on the glaze surface, or at the glaze-clay boundary surface and am
sorry not to have communicated it to you better the first time around. Part
of this is due to a haste to communicate and an omission in a previous post
of a paragraph on the production of both CO2 and lithium oxide as these
processes relate to temperature. Like water that begins to bubble before it
boils, the lithium carbonate may produce carbon dioxide or begin to react
during the early stages of heating in the kiln.
Now would be a good time for a basic chemistry mini review - you all tend to
read and utilize your references without regard to real time (real "life")
situations - references are generally in terms of a system (in our case, a
glaze) that has reached equilibrium. In our kiln setting there will be all
kinds of reactions going on involving various species of lithium in varying
and constantly changing concentrations as firing proceeds and the glaze melt
attempts to move toward equilibrium through different kiln temperatures.
It is my hypothesis that it is in this nonequilibrium phase that we run into
problems - everything from the constant cycle of surface deposition of
lithium carbonate, to outright vaporization of materials to the deposition
of ingredients and their relatives (common and new) on the clay body or
glaze surface, to the precipitation of substances such as silicon carbide
onto our clay body surface, to CO2 bubble formation, to crystal formation
and crystal deposition (most crystals would be clear and ever-so very tiny),
to inclusions of lithium disilicate glass, to the effects of reduction (CO
and CO2 atmosphere) vs. oxidation (O2 atmosphere) firing, the reduced
conductivity within the melt, etc. All these things affect the glaze and
account for the strange effects reported. To take one example to extreme
think what a sorry glaze it would be if where the glaze is thinnest, as on
edges and rims, it ended up being almost entirely a film of deposited
lithium carbonate. In thicker more protected areas the glaze may seem fine
even if slightly filmed by lithium carbonate surface deposits but suffer
from internal stresses and strain, contain spurious and unwanted substances
(as mentioned above), or fail to fit to a lithium carbonate induced
roughened clay body surface. The key to the creation of any deposit,
precipitate, crystal, or what-have-you is in the reaction chemistry and it
should be remembered that any such grouping of a created substance will act
like a mini-glaze within the glaze, each having its own thermal expansion
value which may not make for a good fit with its nearest neighbor. Thus a
heterogeneous glaze may fail in part while not necessarily failing entirely
as a whole.
Carbonates are rather odd compounds and lithium carbonate seems to have a
little extra pizzazz within our field and in other industry applications or
systems. For us this may spell trouble, but in some applications outside of
our field it makes for success. None of the three other useful lithium
containing compounds you mentioned, Spodumene, Petalite, or Lepidolite, are
carbonates and their behavior in a glaze melt will never come close to
resembling that of lithium carbonate.
Spodumene, lithium aluminium inosilicate, LiAl(SiO3)2 or LiAlSi2O6, is so
very different from lithium carbonate - it's much less reactive. Overlooking
the volume expansion it undergoes upon heating and an occasional variety
that releases carbon dioxide one can assume that its lithium hydroxide and
lithium ion contribution to the glaze melt goes smoothly since the compound
is made of materials already within the clay body and glaze. In those
Spodumene varieties that releases carbon dioxide, reduction firing may
occasionally facilitate the creation of small amounts of lithium carbonate
film on the glaze surface as the carbon in the kiln environment reacts with
any lithium ions or lithium compounds susceptible to such a reaction.
Petalite, LiAlSi4O10, is another aluminum silicate mineral and like its
buddy Spodumene it is totally unlike lithium carbonate as a chemical
reactant.
Lepidolite, (KLi2Al(Al,Si)3O10(F,OH)2), a phyllosilicate mica mineral, is
similar to Petalite and Spudumene in that, dispite its own slight quirks, it
seems to have none of the reaction complications accociated with lithium
carbonate chemistry.
Many things may remain unknown to us at our present level of human
knowledge, testing, and evaluation but ideally at the end of our discussion
I'd like us together as a Clayart group to be able to formulate some better
guidelines for the use of lithium carbonate in glazes by potters and ceramic
artists. All this discussing and thinking is of no value unless we make it
practical. With so many variables at work there would seem to be no one easy
explanation to the problems encountered with the use of lithium carbonate or
one easy solution. Impurities in the glaze materials or clay body may have a
larger impact than we are use to in glazes without lithium carbonate. So,
too, the addition of oxides and colorants may have similar exaggerated
impacts on the final glaze and its fit to the body. So many times what's
tried and true proves its worth within our field while we await more
complete and comprehensible answers. It's a given that lithium carbonate
based glazes are subject to failure especially when lithium carbonate is
added in excess. Here is where a compilation of experiences using lithium
carbonate might serve our community better than any partial scientific
answer to the question of exactly why lithium carbonate causes a given
effect.
I hope this post helps add to our knowledge about lithium carbonate
chemistry. I'm out of time so will leave you all to your thoughts. And Ivor,
on email group lists I don't normally give references since it's such a time
consuming and tedious process, especially for these informal chat
situations.
Have a nice weekend everyone!
Marian
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of John
Hesselberth
Sent: Friday, April 25, 2008 7:13 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: copper reds (ron roy #204A)--now lithium carbonate
Hi Marian,
No, not at all and I doubt things will heat up. This is the kind of
discussion that puts all but a few of us to sleep. But I can't buy
your hypothesis either. In fact I'm not sure I found it. All I saw,
for sure, was was a recitation of the some of the properties and
behaviors of lithium carbonate. Are you suggesting that lithium
carbonate decomposes to the oxide and the oxide selectively
evaporates from parts of the pot? If so how can this be when lithium
oxide does not even melt until >1700C in my handbook? In addition you
suggest the carbonate does not decompose to the oxide until 1310C--
above cone 10. Even if that were to happen between cones 7 and 8 as
you suggest, this phenomena (described in the next paragraph) is
known to happen at lower temperatures also.
To repeat from previous messages, the question I am wrestling with is
"why does lithium sourced as lithium carbonate in levels above 2 or
3% lithium carbonate behave so differently than lithium sourced from
spodumene or petalite or lepidolite". It is known to sometimes result
in weird behavior of the glaze when sourced that way--such as crazing
and shivering on the same pot. The working hypothesis has been that
because lithium carbonate is soluble in water it is free to migrate
and concentrate (or be depleted) immediately after glaze application
with the water that is in the glaze slurry. As my previous messages
point out this makes no sense to me as the amount of lithium
carbonate dissolved in the water will be the same whether the glaze
contains 2% or 20% lithium carbonate. This weird phenomena of crazing
and shivering on the same pot does not happen at 2% but has been
observed at higher percentages of lithium carbonate. Nor does it
happen, even with high percentages of lithium, when the lithium is
sourced from spodumene, petalite, or lepidolite.
So if the different levels of migration (between 2% and 20% lithium
carbonate) does not happen as a result of lithium carbonate dissolved
in water, when and how does it happen? It seems to me the next
opportunity for it to happen is when the lithium carbonate melts and
whether it melts at 618C or 723C is totally irrelevant. It is melting
way before anything else in the glaze does--even sodium chloride
which might be present as a contaminant does not melt until 800C--and
lithium carbonate must exist for a short time as a fairly pure liquid
scattered through the powdered glaze. That would be a perfect
opportunity for it to begin to move and be wicked by capillary action
through the powdered glaze or the porous bisque. Lithium sourced from
spodumene, petalite, or lepidolite does not become mobile until it
either melts or dissolves into the forming melt pool. This would
occur at significantly higher temperatures--after the molten lithium
carbonate has already migrated.
Your message offered a blizzard of" factoids" about lithium
carbonate, but I could not see any relevance of much of it to the
problem at hand. Nor could I find a hypothesis (unless it is a
variant of what I have tried to state in the first paragraph) that
explains this crazing/shivering phenomena in your writing. If I have
missed it could you please write it in a nice short paragraph
comparable to the one directly above so I can try to understand what
you are hypothesizing?
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
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