G to prevent the growth of the particles and

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Unformatted text preview: ing concentrations, e.g. to prevent the growth of the particles and consequent precipitation. E.g. sols of various oxides have been prepared by hydrolysis of salts. 2. Dispersion Methods Material (bulk) is disintegrated into particles of colloidal dimensions by various methods. a) Peptization (Greek pepticos, promoting digestion), the disintegration is brought about by the action of a substance known as a peptizing agent. e.g. cellulose is peptized by the addition of organic solvents, such as ethanolether mixtures, leading to the familiar "collodion" sol. In this case, the solvent is itself the peptizing agent, but frequently something else must be added; thus, precipitates of certain metal hydroxides in water can be peptized by dilute alkali hydroxides. b) Colloid mill A method using physical dispersion in which the dispersion medium and the substance to be dispersed are passed, grinds the material into colloidal particles. c) Electrical disintegration An arc is struck between metal electrodes under water, with the production of a metal sol (Brady’s method). 2 L IGHT SCATTERING BY CO LLOIDAL PARTICLES When light passes through a medium that contains no particles larger than about 10-9 m i n diameter, the pa th of l i g ht cannot be detected and the medi...
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This note was uploaded on 10/25/2012 for the course CHEMISTRY 570.448 taught by Professor Billball during the Fall '10 term at Johns Hopkins.

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