Ron Roy on tue 15 apr 03
Vansil?)
Hi Jim,
I work with a lot of cone 6 bodies and most are fluxed with combinations of
low fire red clays, neph sy, and spar - one with talc.
First it does not follow that alkalies produce high expansion bodies - in
fact MgO and CaO are going to increase the production of cristobalite in
mid fire bodies - a little - which increases expansion - dolomite does it
better than CaO and MgO by themselves. Increased body expansion is a good
anti craze up to a point - with low expansion glazes - well you don't want
to wind up there.
CaO/MgO are not wanted at higher temps - you want the KNaO to gobble up
that cristobalite as it is forming. Porcelains are an exception but I have
not done the experiments to say at what levels.
If you want 50% none plastics and you get more melting you may find
yourself in a jam - certainly - as you add MgO/CaO you will need to cut
back on the spar to control melting - you will have to replace that none
plastic with another.
I'm not say it is imposible - I'm not saying it's not desirable either -
just saying it's tricky and you better have a way to guage the expansion
factores as you go along.
I have a dilatometer - I would be willing to share that if you are willing
to share the chemistry.
RR
>In my original post, I wondered how Wollastonite, a source of CaO, along
>with Potash Feldspar (high K2O) may be used in ceramic bodies to reduce
>maturation temperature and improve vitrification. Specifically, in midfire
>clay bodies.
>
>Why midfire bodies ? To me - a newbie reading pottery books, literature,
>etc. - there seems to be some sort of fork-in-the-road mentality for
>developing these midfire clay bodies. The majority appear to take the path
>of relying on Soda Feldspar, Neph Sy, or combinations thereof with Potash
>Feldspar for midfire clay body maturation and vitrification.
>
>I'm particularly interested in midfire casting bodies, so, 50% plastics
>(clay) and 50% nonplastics along with water and defloculant(s) is a normal
>starting point. Those rascally high Na oxide-bearing Spars and Neph Sy can
>present some unwanted clay body behavior such as high expansion, solubility
>issues, warping, etc.
>
>Perhaps, "the road less traveled by" for midfire clay bodies may be built
>around lime causing a sharp increase in the fusibility of potash feldspar.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on fri 18 apr 03
Vansil?)
Hi Jim,
I don't realy have much experience - none with CaO - all I can say is 50 lb
of talc in a white stoneware clay - dry mix is 1100 lb - does the trick but
it depends on what materials you plan to use - some are easier to melt than
others of course.
If you want to tell me what materials you plan to use I can give you some
idea based on the experience I have with talc - and tell me what amounts of
non plastics you would like to start with.
RR
>Ron, do you have any idea or guesstimate for how much CaO in a Cone 6
>vitrified or semi-vitrified body may be too much ?
>
>For his cones - midfire and up - Herman Seger kept CaO/K2O constant and
>incrementily varied Al2O3 and SiO2. For casting body test samples, perhaps a
>relatively small number of test recipes may be formulated and tested by
>holding KNaO, Al2O3 and SiO2 "somewhat" constant with variations of CaO.
>
>Now, the following is NOT my planned starting point. I understand, in a clay
>body, it's not about the "pure-oxides" which is why I said "'somewhat'
>constant" above. It's more about clay body physics, particle diversity,
>Potash Feldspar viscosity during the "melt", etc.
>
>Again, this is only an example: To simplify, IF I were talking about a
>triaxial body starting point, the recipe total % of clay, flux (Pot spar
>with or w/o Wollastonite) and flint would remain constant, e.g. 50% Clay,
>30% Flux, 20% Flint. The 30% Flux would be made-up of different proportions
>of Potash Feldspar and Wollastonite in different test samples. Only the
>proportion of Pot spar to Wollastonite changes. Firing below, at, and above
>the intended working temperature would be necessary to properly evaluate the
>test samples.
>
>> I have a dilatometer - I would be willing to share that if you are willing
>> to share the chemistry.
>
>I'll have to give that some more thought. Thanks for the offer.
>
>Best wishes,
>
>Jim Murphy
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
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>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on mon 21 apr 03
Vansil?)
Hi Jim,
I don't have an analysis for the FC 340 ball so I used C&C - I can give a
better answer maybe - if I have that analysis.
I have compared to a couple of cone 6 porcelains which use Neph Sy as flux
and your seems a little tight in comparison - that will be needed given the
inability of G200 to melt enough at cone 6. Neph sy is an ideal material
for slip casters it seems to me - some deflocculation from the sodium not a
negative. Why not try some tests subbing in some Neph Sy replacing some of
the G200 if you need more melt.
I also compared yours to a cone 6 white stoneware fluxed with Talc and spar
yours was short of refractories but that again may be just right.
Spar is just not a good melter at cone 6 and the amount of wollastonite is
small so I am guessing you will need more melt - the neph sy will be a
quick way to get it. I am guessing that you will need to increase the
wollastonite a lot to get the kind of melting you expect.
Theory does not get you very far in all this - we just don't stay at top
temperature long enough to get the kind of reactions you see in phase
diagrams.
I compared your molecular formula with what I get and everything is close
except the SiO2 - perhaps I do need the analysis for that ball clay - it
might be high in silica. If not then I suspect another material definition
is way out.
I am interested in what you are doing Jim - if I can be part of it I would
l would like that. Feel free to be in contact whenever you care to.
RR
>> If you want to tell me what materials you plan to use I can give you some
>> idea based on the experience I have with talc - and tell me what amounts of
>> non plastics you would like to start with.
>
>Sure Ron,
>
>For discussion purposes, feel free to comment on this "totally imaginery"
>(hasn't been tested) casting body recipe below - targeted to mature around
>Cone 6 - using 50% Clay, 30% Flux (K-spar + Wollastonite) and 20% Flint:
>
>FC-340 Ball Clay......... 25.00
>TILE #6 KAOLIN........... 15.00
>VELVACAST KAOLIN......... 10.00
>G-200 FELDSPAR........... 28.00
>WOLLASTONITE............. 2.00
>SILICA................... 20.00
> =========
> 100.00
>
> CaO 0.11 1.38%w 1.65%m
> MgO 0.02 0.21%w 0.34%m
> K2O 0.17 3.53%w 2.51%m
> Na2O 0.07 0.94%w 1.02%m
> TiO2 0.04 0.68%w 0.57%m
> Al2O3 1.00* 22.04%w 14.52%m
> SiO2 5.45 70.84%w 79.22%m
> Fe2O3 0.01 0.39%w 0.16%m
>
>Thanks in advance,
>
>Jim Murphy
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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