Bruce Girrell on thu 5 feb 04
Reboot!
Whoa! Let's start this thing over.
Flocculation is a "drawing together", but it occurs in a disorganized,
clumping form. The house of cards analogy is intended to convey the
disordered state of the flocs - jumbled, randomly oriented platelets. As a
result there remains a lot of interstitial space which is usually filled
with water.
Deflocculation results when something (like sodium silicate) gets added to
the clay/water mix that allows the surface charges on the platelets to be
largely neutralized. The platelets then no longer repel one another and can
lie more in alignment, i.e., more like a deck of cards (a _deck_ of cards,
not a _house_ of cards). In this arrangement they take up less space and are
mechanically stronger. Perhaps it may help to think of them as rows of laid
bricks as opposed to a pile of bricks.
Mix up a thin slip consisting only of clay and an overabundance of water in
a clear container. The clay particles will eventually settle to the bottom
forming a layer of a given thickness which you can measure. The clay is in a
naturally flocculated state. Mix it up again, add in a deflocculant and let
it settle out again for the same amount of time. You will note two
differences: 1) The clay particles will settle out faster and 2) the clay
layer at the bottom of the container will be thinner than it was when you
measured it the first time. It settles out faster because the platelets are
no longer electrically repelling one another to as great a degree and the
clay layer is thinner because the platelets are now more aligned with one
another.
Another physical indication of the alignment of the clay platelets is the
pesky mold mark seen in slip cast pieces (which use deflocculated clay). You
can scrape or sand the mold mark smooth in the green state, but it magically
reappears after firing. That is because the shrinking due to firing is
greater in the direction between the platelets and less along the axis of
the platelets. I just wrote a bunch trying to describe this but deleted it
because it gets very confusing without a picture. Hamer and Hamer has a
diagram of the effect. If you want I can get a reference.
Bruce "any questions?" Girrell
Vince Pitelka on thu 5 feb 04
> Deflocculation results when something (like sodium silicate) gets added to
> the clay/water mix that allows the surface charges on the platelets to be
> largely neutralized. The platelets then no longer repel one another and
can
> lie more in alignment, i.e., more like a deck of cards (a _deck_ of cards,
> not a _house_ of cards). In this arrangement they take up less space and
are
> mechanically stronger. Perhaps it may help to think of them as rows of
laid
> bricks as opposed to a pile of bricks.
Whoa! No no no. Deflocculation introduces like electric charges and causes
the particles to REPEL one another, while flocculation causes them to
attract, or floc together. It is true that they take up less space, but
that is because they are repelling one another and therefore need much less
water to retain a liquid slip state.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
daniel on fri 6 feb 04
Hi Bruce, Ivor, Andrew, Vince, everyone,
I'm following this all with great interest. It seems that in each post
there are things that come from the same sort of source and support each
other and things that contradict. This is all to the good I guess and
indicates that this whole thing is yet to be fully understood.
So, time to do some tests.
I had already considered the clay settling test. The defloc is a nice
addition and then I think adding a floc would be interesting. It would be
very interesting if this showed the greatest settled clay volume of the
three. My problem is this. Adding a defloc to something like say ball clay
will likely give me a substance that will take a month to fully settle out
if that - I'll end up with a sig. So perhaps I should get some EPK and try
that as kaolin is what people theorize about initially. Purer (in theory
simpler I guess). Any suggestions for a floc agent and a defloc agent would
be good. I expect I'll use either lye or sodium silicate as the defloc.
Flocs I'll look up in my ever growing library of books on ceramics, but any
preferences let me know.
Ivor, on the magnets thing. I have been thinking a lot about it. I will try
it soon. I want to look at using large amounts of iron filings added
progressively and see if I can get it to slump as would overly wet clay. I
would also like to add large pieces of non-magnetic material, representing
non-plastics and see what affect that has. It is also potentially
interesting to add varying size magnets and varying strength ones to
simulate other blends. I don't know yet what I can get hold of yet but I'll
try a few variations.
Andrew, read your post, will look up the reference you gave. What you put
down tied in nicely with Vince's comments about charge being involved in
flocc. and with Bruce's comments about flocc'd clay occupying more volume.
Its got me thinking about the whole face versus edges thing which I'll need
to read more on.
Thanx
D
> Reboot!
>
> Whoa! Let's start this thing over.
>
> Flocculation is a "drawing together", but it occurs in a disorganized,
> clumping form. The house of cards analogy is intended to convey the
> disordered state of the flocs - jumbled, randomly oriented platelets. As a
> result there remains a lot of interstitial space which is usually filled
> with water.
>
> Deflocculation results when something (like sodium silicate) gets added to
> the clay/water mix that allows the surface charges on the platelets to be
> largely neutralized. The platelets then no longer repel one another and can
> lie more in alignment, i.e., more like a deck of cards (a _deck_ of cards,
> not a _house_ of cards). In this arrangement they take up less space and are
> mechanically stronger. Perhaps it may help to think of them as rows of laid
> bricks as opposed to a pile of bricks.
>
> Mix up a thin slip consisting only of clay and an overabundance of water in
> a clear container. The clay particles will eventually settle to the bottom
> forming a layer of a given thickness which you can measure. The clay is in a
> naturally flocculated state. Mix it up again, add in a deflocculant and let
> it settle out again for the same amount of time. You will note two
> differences: 1) The clay particles will settle out faster and 2) the clay
> layer at the bottom of the container will be thinner than it was when you
> measured it the first time. It settles out faster because the platelets are
> no longer electrically repelling one another to as great a degree and the
> clay layer is thinner because the platelets are now more aligned with one
> another.
>
> Another physical indication of the alignment of the clay platelets is the
> pesky mold mark seen in slip cast pieces (which use deflocculated clay). You
> can scrape or sand the mold mark smooth in the green state, but it magically
> reappears after firing. That is because the shrinking due to firing is
> greater in the direction between the platelets and less along the axis of
> the platelets. I just wrote a bunch trying to describe this but deleted it
> because it gets very confusing without a picture. Hamer and Hamer has a
> diagram of the effect. If you want I can get a reference.
>
> Bruce "any questions?" Girrell
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
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Ivor and Olive Lewis on sat 7 feb 04
Dear Daniel,
Do not use Iron Filings for the Magnetic Model, they are unsuitable.
You need Lab Grade Iron Powder, the stuff that is 99.99% pure. If you
use Iron Filings the material is Steel and already polarised to a
degree with Magnetism. This will contaminate your observations.
Remember that what you are modelling is less than 5mu across, even as
small as 50mmu.The slumping of the model is an interesting thought but
it is possible to postulate a good reason from the model if you apply
the concepts of Dislocation and Grain Boundary Shear (See Kingery et
al)
Best regards,
Ivor Lewis. Redhill, South Australia
daniel on mon 9 feb 04
Hi Ivor,
-100 mesh Iron powder on the way. As are some round disc magnets with the
poles on the flat faces. Let the games begin I guess - well later in the
week at the earliest ...
Kingery ? Sorry not familiar with the name. Do you have a book title,
reference or paper ? I'll do the usual checks but a leg up would help me
out.
Many thanx
D
> Dear Daniel,
> Do not use Iron Filings for the Magnetic Model, they are unsuitable.
> You need Lab Grade Iron Powder, the stuff that is 99.99% pure. If you
> use Iron Filings the material is Steel and already polarised to a
> degree with Magnetism. This will contaminate your observations.
> Remember that what you are modelling is less than 5mu across, even as
> small as 50mmu.The slumping of the model is an interesting thought but
> it is possible to postulate a good reason from the model if you apply
> the concepts of Dislocation and Grain Boundary Shear (See Kingery et
> al)
> Best regards,
> Ivor Lewis. Redhill, South Australia
>
> ______________________________________________________________________________
> 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.
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