Jim Murphy on sat 4 oct 03

IMHO, for perhaps the most recent and well written text on clay-charge
theory, checkout the book "Ceramic Processing and Sintering" by M.N.
Rahaman, published 7-31-2003, (ISBN 0-8247-0988-8) from your library.

Chapter 4 of this book entitled, "Science of Colloidal Processing" has 'the
stuff'.

Note - it (the book) apparently is not widely available - my library had to
get it from another out-of-state library for me.

Kudos to Ivor Lewis for directing us to this book's existence in his 8/3/03
post to Clayart regarding "Ceramic Technology - Modern Texts".

Best wishes,

Jim Murphy

on 10/4/03 7:23 AM, Louis Katz at louis.katz@MAIL.TAMUCC.EDU wrote:

> I could use a short chapter of good material to read.

piedpotterhamelin@COMCAST.NET on sat 4 oct 03

"I would like some opinions about which are the best element to have
> > associated with the clay if you are preparing a plastic body, that is
> > a good strong throwing body. Should they all be eliminated, if that
> > were possible, or are some to be preferred and others avoided?".
Ivor's statement
Hello Ivor
I hope all is well with you and yours.
Specific to the question of the clays,if I imagine a large, say 12 inch diameter magnet activated in an area covered, for example, with nails being our ions, I would get more nails collecting on the circumferance than on a six inch diameter magnet, keeping the nails an equal size. Although two six inch magnets would potentially attract an equal amount of nails as the 12 inch magnet.
As particle size increases and the ion ring lengthens around the edge, how does this relate to defloc/floc?
In other words, are larger particle clays in the range of 10-13 million particles per square millimeter (I remember in my fog of memory reading this to be non-plastic kaolin, correct me if I am wrong) more easily defloc/flocculated than extremely fine clays surpassing the 20 million particles per square millimeter (this being attributed to highly plastic ball clays) conditions because of the larger ion fence that they are able to create?
Now, knowing (assuming that I correctly remember) that a combined clay body of 18 million particles per square millimeter allows for us to have a good throwing body, this would be from having the combination of large and small particles as described above. If I lay coffee can lids side by side touching their edges, I have more open edge area than if I introduce cat food lids in between to touch the open areas.Placing in silver dollars increases the contact area. Thus more edge length is touching than if there were only one particle size alone. Does this also increase the ion bonding? In other words, is it not simply a question of ion charge but of the amount of contact area between the particles? Any ions falling into the spaces would have to respond to some adjacent particle as the spacing becomes smaller.
Does an equal amount of deflocculant added to equal weight of non-plastic kaolin or to a highly plastic ball clay or to a bentonite clay have the same effect as added it to a well blended clay body being a mixture of the above?


--
"Many a wiser men than I hath
gone to pot." 1649

iandol on sun 5 oct 03

Dear Louis Katz,=20

You prompt <but the ions that get attached to the clay crystal edges that are the =
cause of flocculation and deflocculation.>>

This has been my understanding as well, though Lawrence and West show =
Calcium Ions embedded within rings of water molecules. Another confusing =
factor is the way Rado treats residual elements (see Appendix 1.1, An =
Introduction to Ceramic Technology) He makes the assumption that the =
Alkali Metals are derived from Felspars.

I hope we get to a resolution on this topic.

Best regards,
Ivor Lewis, Redhill, South Australia.

iandol on sun 5 oct 03

My dear Friend,
You have certainly taken to my "Magnetic Analogy" and I fear you are =
tormenting it like a fox terrier with a raw bone.
I refuse to think about deflocculating any clay. I am not a slip caster =
so it is useless to my purpose. I want to know how to increase the =
plastic strength of my clay ! ! ! !=20
But your argument seems to approach a conclusion or hypothesis that a =
slip which is made form a variety of clays of several dimensions will =
require more deflocculant than a coarse grained clay. This proposition =
can be tested.
Best regards,
Ivor Lewis. Redhill, South Australia

Louis Katz on sun 5 oct 03

Thanks
Will try interlibrary loan, one of the best services a University can
offer.
On Saturday, October 4, 2003, at 11:27 AM, Jim Murphy wrote:

> IMHO, for perhaps the most recent and well written text on clay-charge
> theory, checkout the book "Ceramic Processing and Sintering" by M.N.
> Rahaman, published 7-31-2003, (ISBN 0-8247-0988-8) from your library.
>
> Chapter 4 of this book entitled, "Science of Colloidal Processing" has
> 'the
> stuff'.
>
> Note - it (the book) apparently is not widely available - my library
> had to
> get it from another out-of-state library for me.
>
> Kudos to Ivor Lewis for directing us to this book's existence in his
> 8/3/03
> post to Clayart regarding "Ceramic Technology - Modern Texts".
>
> Best wishes,
>
> Jim Murphy
>
> on 10/4/03 7:23 AM, Louis Katz at louis.katz@MAIL.TAMUCC.EDU wrote:
>
>> I could use a short chapter of good material to read.
>
> _______________________________________________________________________
> _______
> 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.
>

piedpotterhamelin@COMCAST.NET on mon 6 oct 03

Hello.
I am not really sure what it is that I postulate.
I can imagine that if the ions which collect onto the edge of the particle must as well touch the next particle to either create an attraction or repulsion. If the particles are of a similar size, it demands that the open space in between the particles must be saturated with the charge to create some sort of continuity. Hence, more acid or alkali is required to have an effect as this void or pool must be filled.
But if that space is filled with smaller particles which allow for more touching and less voids, then less acid or alkali is required.
So, no matter if it is the task of separating or attracting these particles, the continuity of the charge is effected and improved particle to particle by have a greater variety of dimensions. So Ivor, does a coarse non-plastic kaolin clay plasticity improve with increased acidity? If so, per measure, as one adds ball clay to keep an equal test weight, is the added acidity reduced not only because of the benefits of the size of the ball clay but also because of the touching/continuity? Years ago, I experimented with adding yeast to my clay and aging it. It was greatly improved, as I read, because of the acidity given off. At the time, Ceramics Monthly had articles concerning this improvement to Porcelain, but I was working with earthenware.
Or as you are understanding it, perhaps it is the other way.
This is not tormenting. It is actually quite refreshing. ClayArt has me revisiting ideas that I have put on the shelf for many years.
Stay happy



--
"Many a wiser men than I hath
gone to pot." 1649

Jim Murphy on mon 6 oct 03

Hello again to all,

Here's some further info below regarding clay plasticity from M.N. Rahaman's
book - "Ceramic Processing and Sintering".

Take note of his descriptions for "Adsorption" and "Isomorphic Substitution"
and imagine how they may apply to two clay particles in a plastic clay body
as they (the two clay particles) approach one another in a clay-water
system.

Best wishes,

Jim Murphy

Ceramic Processing and Sintering
Chaper 4 - Science of Colloidal Processing
4.5 Electrostatic Stabilization
A. Charges on Particles in a Liquid

Adsorption of Ions From Solution
In the process of preferential adsorption of ions from solution, an
electrolyte such as an acid, a base, or a metallic salt is added to the
solution. Ions prferentially adsorb onto the surface of the particles,
leading to a charge on the particle surface. Because the system consisting
of the particle and the electrolyte must be electrically neutral, an equal
and opposite counter-charge exists in the solution. Most oxide surfaces are
hydrated; for an oxide of metal M, there will be MOH groups on the surface.
In acid solutions, adsorption of H+ ions (or hydronium ions, H3O+) produces
a positively charged surface, whereas in basic solutions, adsorption of OH-
ions (or the dissociation of H+ ions) leads to a negatively charged surface.
Thus oxide surfaces are positively charged at low pH and negatively charged
at high pH. At some intermediate pH, referred to as the point of zero charge
(PZC), the adsorption of H+ ions will balance that of the OH- ions, and the
particle surface will be effectively neutral.
For oxides, the PZC is related to the acidity or basicity of the
surface groups. Acidic oxides such as SiO2 have a low PZC, whereas basic
oxides such as Al2O3 have a high PZC. For an oxide of a metal M, the
adsorption of H+ and OH- ions can be written
MOH + H+ goes to MOH2+ (process is reversible)
MOH + OH- goes to MO- + H2O (process is reversible)

Isomorphic Substitution
Isomorphic substitution is commonly found in clays. In the crystal lattice,
some of the cations are replaced by other cations of lower valence without
altering the crystal structure; for example, Si4+ ions are replaced by Al3+
or Mg2+ ions, and Al3+ ions by Mg2+ ions. This process leads to a deficit of
positive charges, which is balanced by other positive ions (e.g., Na+, K+,
or Ca2+) adsorbed on the surface of the clay particles. In the case of the
mineral pyrophyllite, Al2(Si2O5)2(OH)2, isomorphic substitution in which
Mg2+ replaces some of the Al3+ ions in the lattice leads to montmorillonite
, Na 0.33(Al 1.67 Mg 0.33)(Si2O5)2(OH)2, another mineral with the same
crystal structure in which the charge deficit is balanced by Na+ ions on the
particles surfaces. When the clay mineral montmorillonite is dispersed in
water, the Na+ ions pass freely into solution, leaving negatively charged
particles.
The extent of isomorphic substitution is dictated by the nature of
the clay, and this is expressed by the cation exchange capacity (CEC). The
CEC of a clay is the number of charges on the clay that can be replaced in
solution. For a given clay it (CEC) is not sensitive to variables such as pH
or concentration of the electrolyte in solution.

Ron Roy on tue 7 oct 03

Hi Ivor,

First we need to know - what cone will it be fired at? low fire is one
thing, midfire another and high fire needs some careful compounding - if
too much CaO and MgO are present (see Red Art) you are in for some
cristobalite problems. To much iron and you need to counteract it in
reduction.

I am used to looking at the chemical analysis of the clays I deal with. I
cannot tell anything about the working properties from that. Much has to do
with particle size and distribution but I don't use that either.

I go by the standard plasticity test - coil around the finger - shrinkage -
wet to dry and overall to glaze temp.

To answer you directly - it really does depend on final temperature and the
amounts present.
If there are soluble salts involved - well they can be delt with if
necessary but I avoid them when I can.

Certainly alkaline salts are to be avoided if possible.

If I have an analsis I can make some comparisons and be more specific.

RR


>I am still at the Raw Clay Stage. Nothing to do with a prepared body
>mixture!!! No Neph Sy in sight!!! Just a shovel full of clay.
>
>As an example, if you review Chappell's list of analyses for American
>Clays is shows the elements as molecular oxides. These include Iron as
>well as group 1 and 2 elements. When I wrote to Spinks some years ago they
>provided a summation of the Minerals present.
>
>I would like some opinions about which are the best element to have
>associated with the clay if you are preparing a plastic body, that is a
>good strong throwing body. Should they all be eliminated, if that were
>possible, or are some to be preferred and others avoided?
>
>Thanks for coming back on this one.
>
>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.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513