Colloidal Systems - Surface and Colloid Chemistry: Principles and Applications - page 159

Some industrial products in which the foregoing characteristics are of primary
importance include paints, inks, food products, and pharmaceuticals.
The potential differences, ψ, at different phase boundaries, as mentioned before,
have been found to have many industrial applications. The application of electro-
phoresis to the separation and purification of proteins has also been discussed. Both
electrophoresis and electroosmosis have attained a certain amount of industrial
application.
They are often used in the purification of natural colloids. For example, the col-
loids may be separated from uncharged or oppositely charged impurities by elec-
trophoresis deposited on an electrode. The electrophoretic purification of clay and
kaolin may serve as an example. The clay is made into a negatively charged sludge
whose charge may be increased by the addition of small quantities of a base (poten-
tial-determining OH ions) so that the suspension stable colloid while the impurities
settle out. The suspension is then subjected to electrophone; thus, the colloidal par-
ticles are deposited on a rotating metallic cylinder that serves as an anode in which
they can be scraped off continuously. The clay is dehydrated during production.
The colloidal particles are often deposited on metallic electrodes in the form
of adsorbed coatings. Rubber and graphite coatings can be formed in this way,
using solvent mixtures (water-acetone) as the dispersion media. The advantage
of this method is that additives can firmly be codeposited with, for example,
rubber latex. Thermionic emitters for radio valves are produced in a similar
manner. The colloidal suspensions of alkaline earth carbonates are deposited
electrophoretically on the electrode and are later converted to oxides by using an
ignition process.