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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