Ivor and Olive Lewis on wed 15 mar 06
Dear Jim Murphy,=20
You start by saying ..[edge-to-surface] bone dry clay structure.>...Now, I cannot understand =
how this can be if the particles of clay have aligned themselves in =
parallel sheets as pressure is applied during throwing or rolling.
I am not sure how to use the other information you gave. Apart from =
conferring a pH of about 3 or 4 to the solution of acetic acid with =
water what you have said tells us nothing about the purpose of Acetic =
acid. Do you have values for the dimensional and force relationships of =
the model you are proposing ? Or are these just approximate proportions =
and estimates ?
As I see it, the questions still remain unanswered. What is happening =
when Vinegar is used to join hardening or hard clay and why do Hamer and =
Fournier give opposite opinions.
Thanks for considering the question.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Jim Murphy on wed 15 mar 06
on 3/14/06 11:01 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> You start by saying ..> bone dry clay structure.>...Now, I cannot understand how this can be if the
> particles of clay have aligned themselves in parallel sheets as pressure is
> applied during throwing or rolling.
Hi Ivor,
"Parallel sheets" in the 'wet-state', yes/maybe.
However, as the free ["unstructured"] water-layer gradually dries from
surrounding particles in a moist "plastic" claybody, clay particles approach
each other more closely and a higher percentage of positively-charged
"edges" would tend to "tilt" by attraction to negatively-charged clay
particle Silica-like "surfaces".
As more free-water dries, we reach the "bone-dry" state where clay particle
orientations are more random, i.e. more edge-to-surface contacts, AND clay
particle charge-strength decreases.
> As I see it, the questions still remain unanswered. What is happening when
> Vinegar is used to join hardening or hard clay
When bone-dry clay is "rehydrated" by an acid, once again, clay particle
"edges" become positively-charged while - for Kaolin - the Silica-like
surface becomes negatively-charged and the AluminumHydroxide-like surface
becomes positively-charged.
So, once again, a means has been provided for 'wet' clay particle repulsive
separation followed by "attraction" [edge-to-surface] as free-water dries,
allowing new bonds to form.
> and why do Hamer and Fournier give opposite opinions.
Though I returned my Brownell book - "Structural Clay Bodies" - to the
library long ago, perhaps these "double-layer theory" notes from Chapter 4
regarding "flocculation" and "deflocculation" may help justify the two
possibilities. Of critical importance though Ivor is that BOTH the
Geuy-Freundlich' "diffuse-double-layer" AND Lawrence's "thermodynamic"
theories apply ONLY to the origin and development of charges on clay
particles in the 'wet' state. Here's a few notes [two paragraphs] from
Brownell below:
"According to the double-layer theory, the negative charge on clay
particles is small when the fixed layer is composed of (OH)- ions, and the
diffuse layer contains a preponderance of (OH3)+ ions. This would also be
true when highly charged cations such as Ca2+, Mg2+, and Al3+, are added to
the system by way of an electrolyte, because the adsorbed negative charge is
neutralized in a short distance by ions of larger charge. With a thin
diffuse layer, particles can approach each other closely without repulsion;
then Van der Walt forces of attraction exceed repulsive forces and particle
aggregates are formed. This is called flocculation."
"Deflocculation occurs in the diffuse layer theory when electrolytes are
added which increase the thickness of the diffuse layer, the zeta potential,
and the apparent charge on the particle. This is accomplished by adding some
monovalent ions such as Li+ and Na+ to the clay-water system. These ions are
less able to neutralize the adsorbed (OH)- ions unless they are introduced
in excessive quantities. In addition, they do not approach the surface as
closely as (OH3)+ ions because of their lower mobilities. More precisely,
they have lower mobilities than the proton. Deflocculation results from the
charged particles repelling each other and approaching a stable colloid that
does not settle out appreciably with time."
FWIW Ivor, Brownell also notes this disadvantage of Lawrence' thermodynamic
theory: "It is, unfortuneately, completely independent of the size of the
water hull or the structure built up around the clay particles."
Accordingly, we may expect 'pore-structure' in bone-dry clay to have some
impact on the affect of added vinegar on clay particle charge-strength
development.
Hope this helps,
Jim
Ivor and Olive Lewis on fri 17 mar 06
Dear Jim Murphy,
Sad to say your highly theoretical explanation does not give practical, =
technical or scientific reasons why it is possible for Vinegar to be a =
flocculant (Hamer's view) and a deflocculant (Fournier's view). Brownell =
has one entry for Acetic acid but that is not for the chapter you quote =
at length.
It make sense to suggest that if a clay or glaze has become =
deflocculated due to the addition of a caustic deflocculant, be that =
deliberate or accidental as in using a Sodium rich flux in a clay or =
glaze, to neutralise the alkali by using a raw acid or an acidic salt. =
Hence Vinegar should, in theory, be appropriate. But to understand how =
an acid, in this case Acetic acid in solution with water, is able to =
cause deflocculation, imitating a base or alkali, is a bit hard to =
swallow. Need I say more?
One bit of information to chew on. This morning I weighed out 70 grams =
of ball clay and 30 grams of water. This made a stiff plastic paste. =
When tested with the pH Meter the reading was pH 5.4. The water was =
fresh rain water which scaled at pH7.2. So my Ball clay/Water system is =
slightly acidic. Vinegar scaled at pH3.
Thanks for joining in the fun. I think we keep Mel amused.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Jim Murphy on fri 17 mar 06
So ... Ivor ... with respect to your understanding of how clay particles are
oriented in "bone dry" clay, are the clay particles oriented: (a) in
parallel-sheet formation; or (b) in a more random edge-to-surface type
fashion ???
And again, I'm asking with regard to "bone dry" clay [per your original
vinegar bond question] rather than a colloidal-solution of clay-water.
The devil is in the details my friend ... ;o)
Best wishes,
Jim Murphy
on 3/16/06 11:09 PM, Ivor and Olive Lewis at iandol@WESTNET.COM.AU wrote:
> Dear Jim Murphy,
>
> Sad to say your highly theoretical explanation does not give practical,
> technical or scientific reasons why it is possible for Vinegar to be a
> flocculant (Hamer's view) and a deflocculant (Fournier's view). Brownell has
> one entry for Acetic acid but that is not for the chapter you quote at length.
>
> It make sense to suggest that if a clay or glaze has become deflocculated due
> to the addition of a caustic deflocculant, be that deliberate or accidental as
> in using a Sodium rich flux in a clay or glaze, to neutralise the alkali by
> using a raw acid or an acidic salt. Hence Vinegar should, in theory, be
> appropriate. But to understand how an acid, in this case Acetic acid in
> solution with water, is able to cause deflocculation, imitating a base or
> alkali, is a bit hard to swallow. Need I say more?
>
> One bit of information to chew on. This morning I weighed out 70 grams of ball
> clay and 30 grams of water. This made a stiff plastic paste. When tested with
> the pH Meter the reading was pH 5.4. The water was fresh rain water which
> scaled at pH7.2. So my Ball clay/Water system is slightly acidic. Vinegar
> scaled at pH3.
Ivor and Olive Lewis on sun 19 mar 06
Dear Jim Murphy,=20
You ask..."with respect to your understanding of how clay particles are
oriented in "bone dry" clay, are the clay particles oriented: (a) in
parallel-sheet formation; or (b) in a more random edge-to-surface type
fashion ???"....
Good question Jim, Good question ! ! All I can say is, at the macro =
level with a naked eyeball, flow structures are laminar but they are =
composed of granular fragments which, when stirred, break down into =
undifferentiated residue.=20
Until I have a consistent way of stabilising dry clay I cannot make =
samples for observation. At the moment I am limited to a magnification =
of about X 200 with my microscope though I hope to get a X 6 eyepiece =
this week which will get me up to a limit of about X 1000. This is still =
somewhat short of what is needed to see things that are in the minus 100 =
nm range of many clay particles. That is one for the Electron Microscope =
types.
Until I have done that I regard what has been illustrated and written as =
science fiction. Best regards,
Ivor
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