Electro-osmosis .
wrings water out of clay

From 'POPULAR SCIENCE’ magazine

Ceramicist Ron du Bois had a prob-
lem: His large clay projects took five
to six days to stiffen, and uneven dry-
ing sometimes caused cracks. The
water in the clay—up to 25 percent of
the weight—simply took a long tume to
evaporate, and it took a lot of gas for
the final kiln drying, too. Du Bois took
his problem to Dr. Herb Pohl, a phys-
iciat and colleague at Oklahoma State
University, and together they devel-
oped a drying process that not only
works for clay, but may have energy-
saving applications in other fields, as
well.

Pohl and du Bois placed moist clay
samples between wire grids and con-
nected a 35-V DC power source to
them. When the power was turned on,
a pool of water formed under the bot-
tom, negative electrode in two
minutes, and the clay became as atiff
as leather, Measuring the amount of
water from several samples, Pohl cal-
culated that about 100 molecules of
water were drawn off for each positive
ion passing through the clay. He
explains this surprising effect by
painting out that water dissociates, or
disselves, positive ions—potassium,
sodium, and calcium—from the clay,
while the negative ions remain fixed
in the clay matrix. In the electric field,
the metallic ions migrate toward the
negative electrode and thereby create
an osmotic effect: The water in the
clay is drawn toward the solution with
a higher concentration of free dissoci-
noted ions.

Pohl believes that the drying pro-
cess that he calls electro-osmosis
has obvious potential in manufactur-
ing processes that use clay—high-volt-
age insulators, electrical components,
and, of course, pottery and china. But
it may also be valuable for products
that have a composition similar to
clay and that are usually dried by
costly heating,

a TE = mo
™, SS
' ir
CLAY . OL ay
PARTECLE i : PAATECLE
i]
t
J =,

Electric field in wat clay attracts positive
ions to negative slactrode; water follows
concentration of jong, Negative ions re
main fimed in clay

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