John Sankey on thu 10 apr 08
The best iron colour responses in this series were obtained with 0.10 molar
CaO, 0.03-0.06 MgO, 0.01-0.02 P2O5.
Using this base, the best reds were obtained with 8-11% added red iron
oxide,
Full results are at
http://sankey.ws/glazeiron.html
Glazes in this series containing more than 12% Fe2O3 heated up in a
microwave, those with 20% or more were too hot to touch within seconds on
high.
John Sankey
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Steve Slatin on fri 11 apr 08
Marian --
You've gone much wider than I was thinking,
so let me address just a few of this things
you brought up (as you brought up a mountain
of stuff, most of which I know little or nothing
about).
Do we normally think of atoms, or oxides,
and not other (more complex) compounds?
Often we do. I suspect it is because otherwise
the possibilities are so complex that we'd
never get anywhere. Evaluating just the
oxides (like when doing a COE/CTE on
a glaze) gives you some rough idea of where
you are, and using the simple oxide solutions
to most problems generally (not always!)
works. But, it's better than nothing. And if
you even considered all of the possible
compounds that could be, at some point
in the melting and cooling, created, disappated,
and reformulated, you'd never finish anything.
The heat of firing is so great that it could permit
lots of things (many of which are not likely to
withstand the cooling).
So while it's a weakness to think of things
simply, we often have to do it.
All I know about whitlockite is that it's
rare and it's clear in its gem incarnation.
I don't actually know anything else about
it. I googled it quickly, and some
references say it's piezoelectric?
I know there are some ceramic piezoelectric
substances (like the squeeze ignition
systems for some gas grills) but I don't
have any information on them -- I don't
know how closely they resemble a glaze
or clay-glaze mix.
I do vaguely recollect an experiment when
a quartz crystal was subjected to a transient
voltage, and it changed shape slightly. I
presume from that (& the general rule that
except for entropy, everything goes both
ways, if you've got the energy to make it)
that the usual piezo function of pressure
= electrical current will go the other way;
that is, current will = pressure, and more
likely than not, pressure can dissipate
to heat energy.
There are odds and ends of the mug
that burns your hand that I can't make
'come out' with my level of knowledge.
Because John S. got the thing to create
the heat with iron and phosphorus, and
the iron glazes I couldn't get to heat up
in the microwave were low or no phosphorus,
I got to thinking about the possibility
that it was phosphorus, or phosphorus-iron
that was doing something.
But I knew that phosphorus was normally
an insoluble non-conductor (though highly
chemically reactive). That got me as far
as the idea of conductive phosphorus
compounds; but I don't know anything
about them.
As the senator said in that terribly old
joke, that's my story and I'm sticking
to it -- Best wishes -- good luck with
the cactus -- Steve Slatin
Neon-Cat wrote:
Steve Slatin wrote: "I know that normally phosphorus is an electrical
non-conductor. I have a nagging memory of reading somewhere that
electroless nickel plating depended on phosphorus is the solution ...
probably a non-relevant coincidence, but do you know of any circumstances
under which phosphorus compounds might be electroconductive?"
Steve, I'm going skip your question entirely and ask why it is that many of
us on-list are more accustomed to thinking of elements and compounds as
stand-alone additions to our glazes and clay bodies than as participants in
chemical reactions that form new materials?
Looking at John Sankey's interesting report, particularly the section that
references the iron with phosphorous additions and resultant color changes,
makes me think that crystalline and non-crystalline calcium phosphate
ceramic materials like a-whitlockite [a-Ca3(PO4)2] and others have been
created and colored within the glaze(s). They are often best colored by the
use of our standard transition metal oxides like iron oxide, nickel oxide,
cobalt oxide, manganese oxide, copper oxide and related compounds.
The formation of calcium phosphate salts in aqueous solutions like our
glazes takes place following the development of supersaturation. At very
high supersaturations calcium phosphate precipitates spontaneously, in both
stable and unstable forms. Supersaturation may be developed by increasing
the amount of calcium and phosphate material in the solution and/or by
adjusting the pH of the glaze. A temperature increase naturally contributes
to supersaturation development as a glaze is fired; nucleation takes place
following the establishment of supersaturation.
The sintering we do in our kilns (from low to high temperature firing) is a
powerful process affecting many changes in the composition of our clay
bodies and clay-based glazes. The materials formed may be useful, of no
significance, or detrimental to our work as potters and sculptural artists.
Perhaps the differences experienced during the microwave heating of mugs can
be explained, in part, by the distinct ceramic materials we've created on or
in a clay body in independent firings using various recipes, additives, and
firing parameters. Each independently created mug will have its own unique
material composition with its own set of thermal characteristics.
These are just my thoughts - how I look at ceramics. It's a vast field - who
knows? Fortunately we have a whole body of already established workable
techniques and reliable clays or glazes that both beginners and
professionals in our field can utilize. Anyway, I'm about to finish up
another semester of school and have a 5-foot (about 1.5 meters) Saguaro
cactus to finish this weekend (it's a beauty, now standing at 20 inches
tall) and a striking western rattlesnake (21 inches tall) to finish
decorating. My oxide and stain experiments have gone either extremely well
or horribly wrong. My technical abilities to manipulate clay have increased
giving me confidence. I just signed up to become a fine arts (clay) major
and hope that pans out, money-wise. My experiments with a paperclay
preservative have gone well and I'm tweaking the anti-fungal additive now
with a second anti-bacterial additive. In classroom experiments the
paperclay (in various clay bodies) successfully patched 80% or more of all
student cracks in greenware, bone dry work, or bisqued pieces. During the
Stay-at-Home Mug Exchange Connie Christensen (Colorado) sent me a wonderful
mug. I could market Connie's work anywhere I take the mug - people love it
(and I do, too)! My clay professor has taken Connie's mug from me three
different times now to admire it while I've had it at school. I am looking
forward to some time off to get back into my river clay experiments (it's
very relaxing, earthy, and "grounding" hobby that helps me learn more about
clay body chemistry).
Clayart is fun and educational - and I love the mix of ideas and thoughts
you all express on so many subjects within our field. When I'm thinking
about something, wrestling with a concept, fretting about the future, or
just plain tired, someone posts something that meets my need. So ... you all
keep posting!
Marian
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Nobody Special on fri 11 apr 08
On Thu, 10 Apr 2008 23:34:57 -0400, John Sankey wrote:
>The best iron colour responses in this series were obtained with 0.10 molar
>CaO, 0.03-0.06 MgO, 0.01-0.02 P2O5.
---snip---
>
>Glazes in this series containing more than 12% Fe2O3 heated up in a
>microwave, those with 20% or more were too hot to touch within seconds on
>high.
>
John...
If it might help you figure this thing out, the radar glaze I used contains
.61 Ca, .14 Mg, and .103 P, and 11% added Fe. Very subjectively, from your
description of heating, my glaze seems to be far less "active" than yours.
I read the abstract Fred linked to on dispersion factors (not terribly
daunting reading, as I had feared), which lead me to a lot of other stuff on
microwaves (I need to get a life). Really interesting stuff, but after all
the reading I think there is another meritorious possibility:
My reading pointed to a microwave effect whereby an ungrounded metallic
object will actually become a virtual heating element through absorption of
the EMF, and not through electrical arcing (aluminum foil and baggie tie
principle) nor through excitation by the microwaves per se (dissipation
factor). It is my understanding of this effect (usual caveat applies) that
the object in question need not be incredibly electrically conducive.
If this principle can be properly identified, and explained in layman's
terms (perhaps Eva G's microwave physicist friend), and if you can figure
out why some iron glazes become sufficiently "metallic", I think there is a
really great and useful CM article in here.
Be well.
...James
Nobody Special on fri 11 apr 08
---snip---
Very subjectively, from your
>description of heating, my glaze seems to be far less "active" than yours.
>
---snip---
...or my microwave is just less powerful than yours. Duh. Sorry, brain
lost traction for a second there.
...James
Steve Slatin on fri 11 apr 08
John --
Good tests, delightful pictures. The
SEM photo of the differentiation/
layering was especially interesting.
As I read your page, I am increasingly
curious about the effect of the phosphorus,
which you found necessary for color
development.
I know that normally phosphorus is
an electrical non-conductor. I have a
nagging memory of reading somewhere
that electroless nickel plating
depended on phosphorus is the
solution ... probably a non-relevant
coincidence, but do you know of
any circumstances under which
phosphorus compounds might
be electroconductive?
This could explain the frustratingly
different results we get with microwave
heating -- one person finds a mug
heats up with more than so much
iron in it, another person takes a
similar (but not identical) base glaze
and their mugs remain cool no matter
how much iron is in the glaze.
Best wishes, and sorry for leaning
on you for insight when you've done
so much already -- Steve Slatin
Sorry for leaning on you when you've
done so much good work already, but
I've got neither background nor source
material on the physics side.
John Sankey wrote:
The best iron colour responses in this series were obtained with 0.10 molar
CaO, 0.03-0.06 MgO, 0.01-0.02 P2O5.
Using this base, the best reds were obtained with 8-11% added red iron
oxide,
Full results are at
http://sankey.ws/glazeiron.html
Glazes in this series containing more than 12% Fe2O3 heated up in a
microwave, those with 20% or more were too hot to touch within seconds on
high.
John Sankey
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Neon-Cat on fri 11 apr 08
Steve Slatin wrote: "I know that normally phosphorus is an electrical
non-conductor. I have a nagging memory of reading somewhere that
electroless nickel plating depended on phosphorus is the solution ...
probably a non-relevant coincidence, but do you know of any circumstances
under which phosphorus compounds might be electroconductive?"
Steve, I'm going skip your question entirely and ask why it is that many of
us on-list are more accustomed to thinking of elements and compounds as
stand-alone additions to our glazes and clay bodies than as participants in
chemical reactions that form new materials?
Looking at John Sankey's interesting report, particularly the section that
references the iron with phosphorous additions and resultant color changes,
makes me think that crystalline and non-crystalline calcium phosphate
ceramic materials like a-whitlockite [a-Ca3(PO4)2] and others have been
created and colored within the glaze(s). They are often best colored by the
use of our standard transition metal oxides like iron oxide, nickel oxide,
cobalt oxide, manganese oxide, copper oxide and related compounds.
The formation of calcium phosphate salts in aqueous solutions like our
glazes takes place following the development of supersaturation. At very
high supersaturations calcium phosphate precipitates spontaneously, in both
stable and unstable forms. Supersaturation may be developed by increasing
the amount of calcium and phosphate material in the solution and/or by
adjusting the pH of the glaze. A temperature increase naturally contributes
to supersaturation development as a glaze is fired; nucleation takes place
following the establishment of supersaturation.
The sintering we do in our kilns (from low to high temperature firing) is a
powerful process affecting many changes in the composition of our clay
bodies and clay-based glazes. The materials formed may be useful, of no
significance, or detrimental to our work as potters and sculptural artists.
Perhaps the differences experienced during the microwave heating of mugs can
be explained, in part, by the distinct ceramic materials we've created on or
in a clay body in independent firings using various recipes, additives, and
firing parameters. Each independently created mug will have its own unique
material composition with its own set of thermal characteristics.
These are just my thoughts - how I look at ceramics. It's a vast field - who
knows? Fortunately we have a whole body of already established workable
techniques and reliable clays or glazes that both beginners and
professionals in our field can utilize. Anyway, I'm about to finish up
another semester of school and have a 5-foot (about 1.5 meters) Saguaro
cactus to finish this weekend (it's a beauty, now standing at 20 inches
tall) and a striking western rattlesnake (21 inches tall) to finish
decorating. My oxide and stain experiments have gone either extremely well
or horribly wrong. My technical abilities to manipulate clay have increased
giving me confidence. I just signed up to become a fine arts (clay) major
and hope that pans out, money-wise. My experiments with a paperclay
preservative have gone well and I'm tweaking the anti-fungal additive now
with a second anti-bacterial additive. In classroom experiments the
paperclay (in various clay bodies) successfully patched 80% or more of all
student cracks in greenware, bone dry work, or bisqued pieces. During the
Stay-at-Home Mug Exchange Connie Christensen (Colorado) sent me a wonderful
mug. I could market Connie's work anywhere I take the mug - people love it
(and I do, too)! My clay professor has taken Connie's mug from me three
different times now to admire it while I've had it at school. I am looking
forward to some time off to get back into my river clay experiments (it's
very relaxing, earthy, and "grounding" hobby that helps me learn more about
clay body chemistry).
Clayart is fun and educational - and I love the mix of ideas and thoughts
you all express on so many subjects within our field. When I'm thinking
about something, wrestling with a concept, fretting about the future, or
just plain tired, someone posts something that meets my need. So ... you all
keep posting!
Marian
neoncat@flash.net
www.neon-cat.com
Neon-Cat on sat 12 apr 08
Steve, thanks for your note!
Calcium phosphates are/were used in dental applications and show some
promise as synthetic bone materials. In general they are white and
translucent. Pretty fascinating. They are also studied and their properties
exploited in the industries involved in wastewater processing (and
phosphorus recovery). I "get off" on science when stressed and I'm
experiencing end-of-term deadline anxiety. I'd write more about calcium
phosphates but can't or I'd just keep tripping off down the highways and
byways of chemistry, journeying through imaginary clay lattices, or sinking
mentally into glaze melts.
Good and bad news about the cactus - it can only be 53 inches tall, the
height of our largest school kiln. Bad in that it will be less dramatic,
good in that there is now less cactus to construct. Tonight while at the
school studio waiting for clay to dry I had the presence of mind to take a
few kiln measurements. I could make the cactus in segments and assemble them
for greater height but then I'd have to make more clay, a chore I just hate
since it is accomplished by hand and drill attachment mixing. I have some
too-moist clay here now at home drying on my floor furnace. Thank goodness
it's cool in my neck of Texas tonight so I can run the furnace without
overheating the cats and dog. Last time I heated clay at home the smoke
detectors all went off, the animals freaked, and a neighbor came running to
my door so I'm paying a little more attention to my late-night project. It's
a paperclay body so force drying is fine.
I do wish we potters and sculptural types had the material my dentist used
the other day on one of my teeth he was rebuilding where I'd chipped it -
that stuff, a ceramic material, he cured with a few seconds of visible light
application. I could use a light activated, fast drying and hardening clay
body right about now.
Your "story" is nice and not a bad one to stick to - I do know that ferrous
oxide encourages heat absorption. I haven't had time to explore the iron and
iron-phosphorus connection with regard to this current list thread. Although
everything I'm using tonight and will be using in the days to come is 'tried
and true' (and a cause for gratitude) I got involved in thinking about what
seldom thought-of materials we might be creating in the kiln when I began
purposefully creating (during firing) a specific compound in my river clay
body - but more about that later... I've got an incomplete cactus calling my
name...
Marian
John Sankey on sun 13 apr 08
"phosphorus [is] normally an insoluble non-conductor"
Elemental phosphorus is a metal, conductivity 10 milliohm-cm. For
comparison: iron (again, elemental) is 9.7, magnesium 4.4
What we need is the conductivity of the compounds in our glazes:
oxides or more complex molecules in almost all cases. A search is
in progress - any help is appreciated.
John Sankey
---------
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filter.
I can only read text mail, no attachments.
Ivor and Olive Lewis on mon 14 apr 08
Dear John Sankey,=20
<<"phosphorus [is] normally an insoluble non-conductor"
Elemental phosphorus is a metal, conductivity 10 milliohm-cm. For =
comparison: iron (again, elemental) is 9.7, magnesium 4.4>>
I am not sure which definitions of Metal and Non Metal you are using. =
Since there is a clear conflict here, perhaps you would provide =
definitions.
Phosphorus is not listed by Kaye and Laby,"Tables of Physical and =
Chemical Constants", in their table of Resistivities of Metallic =
Elements, PP 102-3,=20
My experience of handling Phosphorus is that it is a Semi Transparent =
Yellow Wax like substance that stored under water and is easily cut with =
the blade of a knife, or a red powder. I would go for it being Non =
Metallic.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Luke Nealey on mon 14 apr 08
Dear Ivor,
The text used in my class, Chemistry by Chang (general college intro) shows
phosphorus clearly as a non-metal on the periodic chart. Element P forms a
molecular crystal,(which aren't that "crystalline" compared to Diamond,
quartz (covalent crystals) or salts (ionic crystals)) like CO2, ice, Iodine
or elemental sulpher. In general molecular crystals are soft, melt easily
and are poor conductors of heat and electricity (Metallic crystals(sort of a
misnomer) are nucleui in kind of an electron soup. The electrons are very
free to move about (electric conduction) also the lack of specific bonds
make it ductile etc.). Phosphourus in its elemental form is a P4 molecule.
This is white phosphorus, it is highly reactive with air (used in
explosives, a lot in Vietnam). It is pretty insoluble in water (stored this
way) and is the yellow waxy material you mention. Red Phosphorus is a
polymer of these P4 molecules and is much more stable than the white
phosphorus.
In nature we find it as Phosphates(PO4 3- ion), which as a class are
insoluble in water except of course the alkali metal salts and the ammonium
salt.
Best regards,
Luke Nealey
Rankin Co. MS
On 4/14/08, Ivor and Olive Lewis wrote:
>
> Dear John Sankey,
>
> <<"phosphorus [is] normally an insoluble non-conductor"
>
> Elemental phosphorus is a metal, conductivity 10 milliohm-cm. For
> comparison: iron (again, elemental) is 9.7, magnesium 4.4>>
>
> I am not sure which definitions of Metal and Non Metal you are using.
> Since there is a clear conflict here, perhaps you would provide definitions.
>
> Phosphorus is not listed by Kaye and Laby,"Tables of Physical and Chemical
> Constants", in their table of Resistivities of Metallic Elements, PP 102-3,
>
> My experience of handling Phosphorus is that it is a Semi Transparent
> Yellow Wax like substance that stored under water and is easily cut with the
> blade of a knife, or a red powder. I would go for it being Non Metallic.
>
> Best regards,
>
> Ivor Lewis.
> Redhill,
> South Australia.
>
>
> ______________________________________________________________________________
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>
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>
John Sankey on tue 15 apr 08
I seem to be having a bad day!
"I assume you meant oxidized from FeO to Fe2O3 in your last sentence."
Yes :-(
I can't find the site I got the conductivities from that I quoted, but a
more careful check has found
half a dozen (e.g.
http://environmentalchemistry.com/yogi/periodic/electrical.html) that
confirm a
low conductivity and non-metallic state for phosphorus.
My apologies.
John Sankey
-----------
Include 'Byrd' in the subject line of your reply to get through my spam
filter.
I can only read text mail, no attachments.
Ivor and Olive Lewis on tue 15 apr 08
Dear Luke Nealey,=20
Thank you for publishing your notes about the non metallic nature of =
Elemental Phosphorus. I agree with you. I was hoping John Sankey might =
have reassessed his position.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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