Timothy Joko-Veltman on sun 7 oct 07
Resending, because this didn't seem to get through the first time.
=====
I was just reading in the Brazilian industrial ceramics magazine
"Ceramica Industrial" an article entitled (my translation) "High
Temperature Glazes with High Chemical Resistance". ("High
Temperature" here is 1180C/^5)
Skipping the middle - which is interesting enough for me, but might
not be for y'all, the conclusion said this (again, my translation,
also skipping some less relevant parts ...):
"... The presense of anorthite on the surface of the glaze is the
principal cause of deterioration in the glaze when it is submitted to
a standard battery of chemical resistance tests using strong acids.
"Both matte and transparent glazes with improved chemical resistance
were achieved using a frit with a high MgO content ...
"The formation of cordierite when using a frit of appropriate
composition (high in alumina and magnesium oxide, and free of calcium
oxide) is improved when using boric oxide as a flux. In the same way,
the use of spodumene in place of nepheline syenite in the glaze recipe
also promotes the growth of cordierite crystals in the glaze."
For the interested, the whole article (in Portuguese, but with
diagrams and photos) is here:
http://www.ceramicaindustrial.org.br/pdf/v12n01/v12n1a02.pdf
Cheers,
Tim
Ivor and Olive Lewis on mon 8 oct 07
Dear Timothy Joko-Veltman,=20
Interesting conclusions. So the inference is that matt and opaqued =
glazes that contain high proportions of Whiting or other Calcium bearing =
compounds such as Gerstly Borate have inferior resistance to corrosion.
By strong acids would I be correct in considering these to be the major =
mineral acids, Sulphuric, Hydrochloric and Nitric and that high Calcium =
glazes would not be corroded by Acetic, Citric, Tartaric, Tannic and =
Lactic acids.
Thank you for providing the precis,
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on mon 8 oct 07
Hi Tim,
I saved this but I would really like to read it - any chance of finding a
translation anywhere? I wish I was smarter at finding stuff on the web but
I'm not.
Thanks for sending this to ClayArt.
RR
>Resending, because this didn't seem to get through the first time.
>
>=====
>
>I was just reading in the Brazilian industrial ceramics magazine
>"Ceramica Industrial" an article entitled (my translation) "High
>Temperature Glazes with High Chemical Resistance". ("High
>Temperature" here is 1180C/^5)
>
>Skipping the middle - which is interesting enough for me, but might
>not be for y'all, the conclusion said this (again, my translation,
>also skipping some less relevant parts ...):
>
>"... The presense of anorthite on the surface of the glaze is the
>principal cause of deterioration in the glaze when it is submitted to
>a standard battery of chemical resistance tests using strong acids.
>
>"Both matte and transparent glazes with improved chemical resistance
>were achieved using a frit with a high MgO content ...
>
>"The formation of cordierite when using a frit of appropriate
>composition (high in alumina and magnesium oxide, and free of calcium
>oxide) is improved when using boric oxide as a flux. In the same way,
>the use of spodumene in place of nepheline syenite in the glaze recipe
>also promotes the growth of cordierite crystals in the glaze."
>
>For the interested, the whole article (in Portuguese, but with
>diagrams and photos) is here:
>http://www.ceramicaindustrial.org.br/pdf/v12n01/v12n1a02.pdf
>
>Cheers,
>
>Tim
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Timothy Joko-Veltman on tue 9 oct 07
On 10/8/07, Ivor and Olive Lewis wrote:
> By strong acids would I be correct in considering these to be the major mineral acids, Sulphuric, Hydrochloric and Nitric and that high Calcium glazes would not be corroded by Acetic, Citric, Tartaric, Tannic and Lactic acids.
The reagents they used ("acids" is technically incorrect, as the last
is alkaline) were: hydrochloric acid 18%, lactic acid 5%, and
potassium hydroxide 100g.L^-1. Only in the case of the latter did the
high MgO glaze NOT improve on the high CaO glaze (that is, the CaO
glaze already had high resistance to potassium hydroxide).
As for their resistance to the "everyday" acids you mention, no
mention is made in the article of any of them except lactic acid.
Regards,
Tim
Ivor and Olive Lewis on wed 10 oct 07
Dear Timothy Joko-Veltman,
I picked up on the idea of strong acids and I quote your original post
"... The presense of anorthite on the surface of the glaze is the =
principal cause of deterioration in the glaze when it is submitted to a =
standard battery of chemical resistance tests using strong acids."
so I asked the question
"By strong acids would I be correct in considering these to be the major =
mineral acids, Sulphuric, Hydrochloric and Nitric and that high Calcium =
glazes would not be corroded by Acetic, Citric, Tartaric, Tannic and =
Lactic acids."
I discriminate between Mineral Acids which are inorganic in nature and =
Organic acids.In this sense I would not regard any of them as "everyday =
acids" but consider them to be laboratory reagents, thought many organic =
reagents can be found on supermarket shelves.
Thank you for your clarification.
Sincere Regards,
Ivor Lewis.
Redhill,
South Australia.
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