Abstract
The difference of degree of peptization in two kinds of ferric hydroxide powders prepared by heat-dry (105°, 6 hr) and freeze-dry methods was investigated in aqueous hydrochloric acid solution. The characteristics of both kinds of powders were estimated by measurements of zero point of charge, particle size distribution and X ray diffraction patterns. Ferric hydroxide was peptized by adding the powder into a hydrochloric acid solution and boiling for 8 hours. The degree of peptization was evaluated by the concentration of ferric hydroxide in the sol thus formed. The concentration was determined by chelatometry after dissolving the colloidal particles into ferric ions. The degree of peptization in freeze-dried was higher than that in heat-dried samples however, peptization was higher in undried samples. The pH values in which 80% of the added amount of ferric hydroxide was peptized were about 2.6, 1.8 and 1.5 for undried, freeze-dried and heat-dried samples, respectively. The efficiency of peptization tended to be higher in lower pH region but it decreased abruptly around pH 1. The mechanism of peptization in these samples was considered from the view point of electrochemical phenomena caused by the adsorption of hydrogen ions on the ferric hydroxide particles and the ionic strength of the systems.
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