Gretchen Zinkan on mon 17 dec 01
Thank you for the information so far received....
let me clarify a bit more
Over the last month or so much discussion has taken place regarding
lithium...amounts, if used at all should be less that 2% - so in checking
all my glazes...I was initially just looking at lithium, then I realized
spodomene and petalite were also lithium related so....should I be just as
cautious with spodomene and petalite as with lithium?
Thanks again,
Gretchen
British Columbia
Craig Martell on mon 17 dec 01
Gretchen axed:
>Over the last month or so much discussion has taken place regarding
>lithium...amounts, if used at all should be less that 2% - so in checking
>all my glazes...I was initially just looking at lithium, then I realized
>spodomene and petalite were also lithium related so....should I be just as
>cautious with spodomene and petalite as with lithium?
Hello Gretchen:
Petalite and Spodumene are lithium feldspathoids. This means that they are
feldspars that don't really fit the definition of a "true feldspar". They
are materials that contain lithium, alumina, and silica, plus other trace
oxides. When you add these to a glaze you are adding a lot more alumina
and silica than lithium so they can be tolerated in larger
percentages. When you add around 20%, more or less, you may be at or near
the limit. To acertain the "limit" you need to look at the Seger Formula
of the glaze. For a cone 8-10 glaze, Orton limits say no more than 0.2 for
lithium oxide.
Lithium Carbonate will contribute a lot more lithium oxide per gram than
Petalite or Spodumene so we need to be a bit more stingy with this
stuff. Expressed chemically, lithium carbonate is: Li2CO3. When Lithium
Carb is fired, CO2 is liberated and you end up with Li2O, Lithium
Oxide. The liberated CO2 is about 60% of what you weigh out for your glaze
so you are only getting about 40% Li2O. Still, Lithium is such a light
metal oxide that gram for gram you get a lot of Lithium atoms.
regards, Craig Martell in Oregon
Paul Lewing on mon 17 dec 01
on 12/17/01 6:35 AM, Gretchen Zinkan at gzinkan@CYBERLINK.BC.CA wrote:
> let me clarify a bit more
>
> Over the last month or so much discussion has taken place regarding
> lithium...amounts, if used at all should be less that 2% - so in checking
> all my glazes...I was initially just looking at lithium, then I realized
> spodomene and petalite were also lithium related so....should I be just as
> cautious with spodomene and petalite as with lithium?
Gretchen, we need to clarify a bit more than that. The rule of thumb about
not using more than 2% lithium should read "less than 2% lithium CARBONATE".
Lithium carbonate supplies nothing but Li2O to the fired glaze, whereas
spodumene and petalite also supply a lot of Al2O3 and SiO2. Lithium is a
very strange atom, and is the third lightest element, after helium and
hydrogen. So it's really interesting to compare a materials recipe that
contains lithium carbonate to a flux unity analysis of the same glaze, and
to a molar percentage and a weight percentage analysis for the same glaze.
Just making up numbers here, but in a typical set of analyses you might see
2% lithium carbonate in the raw ingredients making up .4 Li2O in the flux
unity figures (that's 40% of the number of flux oxides), .2 Li2O as a molar
percentage (20% of all the oxides present in the fired glaze), and 1%
lithium oxide in the percentage by weight figures. Lead, on the other hand,
is very heavy, so the same comparisons would be just as skewed, but in the
other extreme.
So you can't just say "less than 2% lithium". It needs to be "less than 2%
lithium carbonate in a recipe of raw materials".
Paul Lewing, Seattle
iandol on tue 18 dec 01
Just for the record :-
Lithium Carbonate melts at 723 =BA Celsius and Decomposes at 1265 =BA =
Celsius (ref Kaye and Laby "Tables of Physical and Chemicalc Constants"
Regards,
Ivor Lewis
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