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ceramic/resistance

updated wed 9 apr 08

 

Dave Finkelnburg on fri 4 apr 08


Claudia,
Can you please explain what you mean by
resistance? Are you referring to hardness, as in
resistance to abrasion or wear?
IF that is the case, both chemical and mechanical
durability are, in my opinion, functions of glaze
chemistry rather than firing atmosphere. In general a
glass with adequate silica and enough alumina, say a
10:1 ratio of silica to alumina, will be most durable.
Good potting,
Dave Finkelnburg


Date: Fri, 4 Apr 2008 20:04:51 -0300
Hi Everyone,
I woul like to know if I could have more resistance
on the ceramic body in the oxidation or reduction.
If one atmosphere coul be hardest them the other, and
why.
Thanks in advance!
Cláudia Rimmer
São Paulo- Brasil



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Claudia Rimmer on fri 4 apr 08


Hi Everyone,
I woul like to know if I could have more resistance
on the ceramic body in the oxidation or reduction.
If one atmosphere coul be hardest them the other, and why.
Thanks in advance!
Cl=E1udia Rimmer
S=E3o Paulo- Brasil

Claudia Rimmer on sat 5 apr 08


Hi Dave,
It=B4s exactaly about hardness.
But I=B4m talking about the clay.If a good clay will be as hard in oxidatio=
n
as in reduction.
I would like to know if in different atmospheres - oxidation or reduction-
has influence on hardness at the same clay.
Sorry poor english...
Thank you Dave!
Cl=E1udia Rimmer
S=E3o Paulo- Brasil

2008/4/5, Dave Finkelnburg :
>
> Claudia,
> Can you please explain what you mean by
> resistance? Are you referring to hardness, as in
> resistance to abrasion or wear?
> IF that is the case, both chemical and mechanical
> durability are, in my opinion, functions of glaze
> chemistry rather than firing atmosphere. In general a
> glass with adequate silica and enough alumina, say a
> 10:1 ratio of silica to alumina, will be most durable.
> Good potting,
> Dave Finkelnburg
>
>
> Date: Fri, 4 Apr 2008 20:04:51 -0300
> Hi Everyone,
> I woul like to know if I could have more resistance
> on the ceramic body in the oxidation or reduction.
> If one atmosphere coul be hardest them the other, and
> why.
> Thanks in advance!
> Cl=E1udia Rimmer
> S=E3o Paulo- Brasil
>
>
>
>
> _________________________________________________________________________=
___________
> You rock. That's why Blockbuster's offering you one month of Blockbuster
> Total Access, No Cost.
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>
>
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Hank Murrow on sat 5 apr 08


On Apr 5, 2008, at 6:28 AM, Claudia Rimmer wrote:

> Hi Dave,
> It=B4s exactaly about hardness.
> But I=B4m talking about the clay.If a good clay will be as hard in =20
> oxidation
> as in reduction.
> I would like to know if in different atmospheres - oxidation or =20
> reduction-
> has influence on hardness at the same clay.
> Sorry poor english...
> Thank you Dave!
> Cl=E1udia Rimmer
> S=E3o Paulo- Brasil

Dear Claudia;

My clay bodies do seem a bit more melted and consolidated when fired =20
in reduction, but it is a very minor gain at cone 10_11. I fire =20
around half my work in oxidation at those temperatures, so I have a =20
basis for comparison. I think there is also a minor improvement of =20
the bond created at the clay/glaze interface in reduction fires.

Cheers, Hank=

Dave Finkelnburg on mon 7 apr 08


Claudia,
Yes, clay fired in reduction will be more
vitrified, glassier, thus more dense, than the same
clay body fired in oxidation IF there is iron in the
clay body. Very white porcelains don't show this much
because there isn't much iron present. But, high iron
clay bodies are very different.
Ron Roy explained this to me several years ago,
that the iron in reduction works like a flux, to make
the clay more dense.
Good potting,
Dave Finkelnburg

Date: Sat, 5 Apr 2008 10:28:11 -0300
From: Claudia Rimmer

It´s exactaly about hardness.
But I´m talking about the clay.If a good clay will be
as hard in oxidation
as in reduction.
I would like to know if in different atmospheres -
oxidation or reduction-
has influence on hardness at the same clay.




____________________________________________________________________________________
You rock. That's why Blockbuster's offering you one month of Blockbuster Total Access, No Cost.
http://tc.deals.yahoo.com/tc/blockbuster/text5.com

Ivor and Olive Lewis on tue 8 apr 08


Dear Claudia,

Dave Finkelnburg's note reminded me of study I did on the question of =
Iron Oxide acquiring fluxing properties.

This is what I think happens. Many of the chemical compounds we use =
react together to form new compounds with properties that we =
unconsciously exploit. ( This is detailed in Singer and Singer, =
"Industrial Ceramics".)

Under reducing condition red iron oxide (Fe2O3) changes first into =
Magnetite Fe3O4, (a mixed oxide of FeO and Fe2O3). The FeO then =
combines with Silicon dioxide (SiO2) forming Fayalite, an Iron Silicate =
which has a melting point of 1205 deg C (2201 deg F). Given that there =
will be excess free Silica, unchanged Magnetite and Fayalite there is =
potential for a Eutectic reaction. If this does happen then a liquid =
phase will form in your clay as low as 1140 deg C (2084 deg F).=20

I think this adequately explains why Terra Cotta clays melt =
catastrophically when heated into the stoneware firing range.

Best regards,

Ivor Lewis.
Redhill,
South Australia.


=20