iandol on mon 3 dec 01
Dear Logan Oplinger,
and others who may be interested in these topics
Information in your response to Paul Taylor is interesting and I respect =
your caveat that you claim no expertise relating to the subject. =
However, I wondered about your reference to Prof Lawrence's text as I =
could not recall any mention in it of Phase Diagrams or Eutectics. I =
have the 2nd Ed. and the information you cite has been eliminated from =
the text as have the lists of binary and ternary eutectics. However, the =
lists are contained as Appendix 4 in Handbook for Australian Potters, =
DeBoos et al. with a footnote recording their source.
Two points arise out of this. The first is to consider why, when Dr =
.West collaborated with Prof Lawrence for the 2nd Ed, did they eliminate =
this information and reference to Phase Transformation Diagrams if they =
are such important factors in Ceramic Science and the Preparation of =
Glaze Recipes. The second is to ask, what does this information convey =
and is it correct.
The first I cannot answer, but the second issue is clear. Eutectic =
compositions which give such low melting points are not always made from =
mixtures of metallic and non metallic oxides. Such examples are =
exceptional and I will give examples later. If the first in that list =
compiled by Prof Lawrence, that given as the Eutectic between Potassium =
Oxide and Boron Oxide, is examined it is crystal clear from the =
Equilibrium Phase Diagram the Eutectic Composition is between Potassium =
Di-Borate and Potassium Tetra-Borate, two independent chemical =
compounds. Similarly, and this is a mixture I have tested, there is a =
eutectic at 1170 Celsius in the CaO-Al2O3-SiO2 system. This is not =
between lime, silica and corundum, a mixture of which shows no sign of =
fusion or even sintering at Cone 9. But when compounded from the =
minerals given in the phase diagram melts to a dull green glass fired to =
that temperature.
Only in exceptional examples do pure oxides form eutectics. This may be =
the case for Lead and Copper oxides and for some Beryllium oxide =
mixtures, eg BeO/UO2, BeO/Y2O3 but in many other cases of binary =
eutectics it is between solid solutions, that is when one oxide seems to =
be seriously contaminated by the other and they are formed during the =
cooling from a melt, not by melting the pure solid oxides.
This is a field of knowledge where there are some serious =
misunderstandings within the constituency of clay artists. The popular =
definition is misleading since those who use it seldom specify the =
conditions under which the systems are operating or take the trouble to =
learn how to interpret Equilibrium Phase Diagrams.
In considering the manufacture of Frits, I believe it might be better to =
use proportions of chemicals which will not form Equilibrium Eutectics =
(See a recent posting for definitions of Eutectics) but instead, to =
attempt to create glasses. I suspect that these would become thermally =
active at lower temperatures, and hence prove to be more useful in =
acting as a solvents for other materials which contribute to a glaze =
recipe.
Although attempts may be made to shave me with Ockhams Razor, I propose =
that a new class of materials be investigated which I would term =
"Solution Eutectics". These would be derived from line blends of =
minerals where specimens show unequivocal evidence of fusion and =
solution to give transparent glasses on cooling. This might involve =
several tests at succeively lower temperatures with fresh specimens if =
the first trials showed several examples of the phenomeon. The =
temperature at which only one mixture melted and remained transparent =
would provide the Solution Eutectic for that system.
I trust you find this interesting and wish you all the best,
Ivor Lewis. Redhill, South Australia
Khaimraj Seepersad on mon 3 dec 01
Hello to All ,
Ivor ,
I don't pretend to fully understand all you have posted
, but I work at the lower temperatures [ below 983 deg.c.]
and have used the eutectics listed at the lower ranges
to help create glazes and enamels.
Multiple oxide mixes really.
[I work only in oxides,carbonates and bi-carbonates ]
Most of those eutectic glasses for below 983 deg,c are
normally too high in expansions to fit a normal clay body
and will only hit the eutectic temperatures after being
fritted . As frits in the melt flowing off the body , or
dissolving in water as a glass ,etc.
Same goes for metals having refractory oxides , but as
metals are lower melting , they only work when fritted.
However often a multi-metal mix substituted into a Eutectic
will often yield a stable glass and a lower deformation
and flow temperature.
Instinctively , I would not use any Borate Frit containing
only B203 and alkaline metal , it is stable only in water
and even then there are the conditions of cold , warm or
hot , as well as ph.
I would always use a base of at least 1B203 to 2Si02
plus alkaline metal oxides.
Often in a useful frit/s your looking for -
[1] It's ability to attack more Si02 in the glaze melt.
[2] Low viscosity , to aid in the above.
[3] The frit/s ability to be stable in a wet glaze mix.
[4] Qualities contributed -
Chemical durability / Abrasion resistance / Expansion
qualities and probably elasticity.
I use high gloss as my optimum point [ hopefully full
fusion ].
Apologies , I do this so much by instinct now and the
terms are often my own words evolved for my own
understanding.
Khaimraj
-----Original Message-----
From: iandol
To: CLAYART@LSV.CERAMICS.ORG
Date: 03 December 2001 7:47
Subject: Frits, Eutectic Mixtures and Related Topics
Dear Logan Oplinger,
and others who may be interested in these topics
Information in your response to Paul Taylor is interesting and I respect
your caveat that you claim no expertise relating to the subject. However, I
wondered about your reference to Prof Lawrence's text as I could not recall
any mention in it of Phase Diagrams or Eutectics. I have the 2nd Ed. and the
information you cite has been eliminated from the text as have the lists of
binary and ternary eutectics. However, the lists are contained as Appendix 4
in Handbook for Australian Potters, DeBoos et al. with a footnote recording
their source.
Two points arise out of this. The first is to consider why, when Dr .West
collaborated with Prof Lawrence for the 2nd Ed, did they eliminate this
information and reference to Phase Transformation Diagrams if they are such
important factors in Ceramic Science and the Preparation of Glaze Recipes.
The second is to ask, what does this information convey and is it correct.
The first I cannot answer, but the second issue is clear. Eutectic
compositions which give such low melting points are not always made from
mixtures of metallic and non metallic oxides. Such examples are exceptional
and I will give examples later. If the first in that list compiled by Prof
Lawrence, that given as the Eutectic between Potassium Oxide and Boron
Oxide, is examined it is crystal clear from the Equilibrium Phase Diagram
the Eutectic Composition is between Potassium Di-Borate and Potassium
Tetra-Borate, two independent chemical compounds. Similarly, and this is a
mixture I have tested, there is a eutectic at 1170 Celsius in the
CaO-Al2O3-SiO2 system. This is not between lime, silica and corundum, a
mixture of which shows no sign of fusion or even sintering at Cone 9. But
when compounded from the minerals given in the phase diagram melts to a dull
green glass fired to that temperature.
Only in exceptional examples do pure oxides form eutectics. This may be the
case for Lead and Copper oxides and for some Beryllium oxide mixtures, eg
BeO/UO2, BeO/Y2O3 but in many other cases of binary eutectics it is between
solid solutions, that is when one oxide seems to be seriously contaminated
by the other and they are formed during the cooling from a melt, not by
melting the pure solid oxides.
This is a field of knowledge where there are some serious misunderstandings
within the constituency of clay artists. The popular definition is
misleading since those who use it seldom specify the conditions under which
the systems are operating or take the trouble to learn how to interpret
Equilibrium Phase Diagrams.
In considering the manufacture of Frits, I believe it might be better to use
proportions of chemicals which will not form Equilibrium Eutectics (See a
recent posting for definitions of Eutectics) but instead, to attempt to
create glasses. I suspect that these would become thermally active at lower
temperatures, and hence prove to be more useful in acting as a solvents for
other materials which contribute to a glaze recipe.
Although attempts may be made to shave me with Ockhams Razor, I propose that
a new class of materials be investigated which I would term "Solution
Eutectics". These would be derived from line blends of minerals where
specimens show unequivocal evidence of fusion and solution to give
transparent glasses on cooling. This might involve several tests at
succeively lower temperatures with fresh specimens if the first trials
showed several examples of the phenomeon. The temperature at which only one
mixture melted and remained transparent would provide the Solution Eutectic
for that system.
I trust you find this interesting and wish you all the best,
Ivor Lewis. Redhill, South Australia
iandol on fri 7 dec 01
Dear Paul Taylor,
I have no problems with using line blends. Have a tile on the glazing =
bench at the moment, crossing Soda felspar with Amblygonite. An =
enlightening empirical study which none of the computer glaze programs =
might predict. And I intend making more of these darling little patches =
of fired enlightenment What always get up my nostrils is the insistence =
that things used in glazes become glazes because of the "Eutectics" =
which continue to occur as temperature rises. Such statements are =
Oxymoronic. Those who disagree with me should read, read, read, then =
think, to discover the error of their ways.
Your best reference for making Frits has got to be Daniel Rhodes, Second =
(revised) Edition 1979 of "Clay and Glazes for the Potter". It even lays =
out the mathematics just to make it easy for those with the PC programs. =
See Ch. 19 Fritted Glazes. Someone else can say if Robin Hopper left =
this in or deleted it from his revision.
Deformation Eutectics are not defined in a Scientific sense but by the =
behaviour of mixtures as they are heated. Samples are in the form of a =
standard cone, and the temperature of the bending point is the pyrometer =
reading when the tip moves to 1 o'clock. This is the lowest temperature =
at which it is agreed (convenient)to say that motion has happened.
Having said that, I hope you have a lot of success with this program of =
work, and expect to enthusiastic reports about it in the near future.
Best regards,
Ivor Lewis. Redhill. South Australia
Paul Taylor on fri 7 dec 01
Dear Ivor, Khaimrajand Logan
Thanks for your involvement . I under stand from your arguments that " It
depends " is again the answer to a ceramic question.
What I have learned from it is, that at the scientific sharp end there are
still controversy over the logical sets that would give us better
understandings - and eutectics is one of these.
Do you name the high point of your reaction as the deforming
temperature or the glass forming temperature? And the temperature that may
be the most scientifically convenient may not be the most empirically
useful- such things fascinate me.
From what Ivor says there are imitations to eutectics that I should be
aware of. Using pure chemicals may not give me the results I expect - if
any.
This discussion also applies to other endeavors to classify things in
ceramics - like expansion coefficients in bodies and glazes - one ends up
with so many variables and caveats that a good old set of judicious and
empirical line blends may be more economic of time and effort for the
jobbing potter that in depth know how and calculation.
Such rudimentary approaches like line blending or throwing stuff in a
bucket may be annoying to the analytical mind, but for the alchemist 'bung
ho' potter it is like sailing in an uncharted water, that is as liable to
come up with interesting glazes . In some ways its a nice thought that
ceramic reactions are complex, varied and difficult to quantify. This makes
one feel that invention and discovery are still possible.
But you can not beat understanding so I better get a copy of the prof
Lawrence book. Glad I did not read it as a student it probably would have
frightened the life out of me.
I prefer to make as much of all approaches and do as much calculation
as possible so again thank you for taking the time to further my
understanding. When I do bung stuff in a bucket to make these frits I will
now have a better chance of success.
--
Regards from Paul Taylor
http://www.anu.ie/westportpottery
> From: iandol
> Reply-To: Ceramic Arts Discussion List
> Date: Mon, 3 Dec 2001 15:48:13 +1030
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Frits, Eutectic Mixtures and Related Topics
>
> Dear Logan Oplinger,
>
> and others who may be interested in these topics
>
> Information in your response to Paul Taylor is interesting and I respect your
> caveat that you claim no expertise relating to the subject. However, I
> wondered about your reference to Prof Lawrence's text as I could not recall
> any mention in it of Phase Diagrams or Eutectics. I have the 2nd Ed. and the
> information you cite has been eliminated from the text as have the lists of
> binary and ternary eutectics. However, the lists are contained as Appendix 4
> in Handbook for Australian Potters, DeBoos et al. with a footnote recording
> their source.
>
> Two points arise out of this. The first is to consider why, when Dr .West
> collaborated with Prof Lawrence for the 2nd Ed, did they eliminate this
> information and reference to Phase Transformation Diagrams if they are such
> important factors in Ceramic Science and the Preparation of Glaze Recipes. The
> second is to ask, what does this information convey and is it correct.
>
> The first I cannot answer, but the second issue is clear. Eutectic
> compositions which give such low melting points are not always made from
> mixtures of metallic and non metallic oxides. Such examples are exceptional
> and I will give examples later. If the first in that list compiled by Prof
> Lawrence, that given as the Eutectic between Potassium Oxide and Boron Oxide,
> is examined it is crystal clear from the Equilibrium Phase Diagram the
> Eutectic Composition is between Potassium Di-Borate and Potassium
> Tetra-Borate, two independent chemical compounds. Similarly, and this is a
> mixture I have tested, there is a eutectic at 1170 Celsius in the
> CaO-Al2O3-SiO2 system. This is not between lime, silica and corundum, a
> mixture of which shows no sign of fusion or even sintering at Cone 9. But when
> compounded from the minerals given in the phase diagram melts to a dull green
> glass fired to that temperature.
>
> Only in exceptional examples do pure oxides form eutectics. This may be the
> case for Lead and Copper oxides and for some Beryllium oxide mixtures, eg
> BeO/UO2, BeO/Y2O3 but in many other cases of binary eutectics it is between
> solid solutions, that is when one oxide seems to be seriously contaminated by
> the other and they are formed during the cooling from a melt, not by melting
> the pure solid oxides.
>
> This is a field of knowledge where there are some serious misunderstandings
> within the constituency of clay artists. The popular definition is misleading
> since those who use it seldom specify the conditions under which the systems
> are operating or take the trouble to learn how to interpret Equilibrium Phase
> Diagrams.
>
> In considering the manufacture of Frits, I believe it might be better to use
> proportions of chemicals which will not form Equilibrium Eutectics (See a
> recent posting for definitions of Eutectics) but instead, to attempt to create
> glasses. I suspect that these would become thermally active at lower
> temperatures, and hence prove to be more useful in acting as a solvents for
> other materials which contribute to a glaze recipe.
>
> Although attempts may be made to shave me with Ockhams Razor, I propose that a
> new class of materials be investigated which I would term "Solution
> Eutectics". These would be derived from line blends of minerals where
> specimens show unequivocal evidence of fusion and solution to give transparent
> glasses on cooling. This might involve several tests at succeively lower
> temperatures with fresh specimens if the first trials showed several examples
> of the phenomeon. The temperature at which only one mixture melted and
> remained transparent would provide the Solution Eutectic for that system.
>
> I trust you find this interesting and wish you all the best,
>
> Ivor Lewis. Redhill, South Australia
>
| |
|
