コロイド系粉体の凝集
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概要
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The stability of hydrophobic colloids is mainly governed by the magnitude of the potential energy of repulsion due to the superposition of electrical double layers and van der Waals attraction between approaching particles. In the absence of potential barriers, every collision between particles leads to adhesion (rapid coagulation), and in the presence of potential barriers, the probability of collision is decreased, thus leading to slow coagulation. A quantitative theory was given by Reerink and Overbeek to describe the influence of the double layer thickness at constant Stern potential on colloid stability, a situation which occurs when indifferent inorganic electrolytes are added to sols. While, Ottewill, Rastogi and the present author gave a theory which treated the case where the change in the Stern potential occurs due to adsorption. An extended theory of coagulation was also given which treated the general case of changing ionic strength and potential.<BR>The experimental verification of the theory thus obtained was carried out by measuring the coagulation kinetics of positively charged silver iodide sols spectrophotometrically. Electrokinetic measurements were also made by using ultramicroelectrophoresis. The agreement between the theory and experiments was very good and a reasonable value of the van der Waals constant was obtained. Experiments were also shown which were carried out by employing the twin dropping mercury electrodes polarized at various potentials in electrolytic solutions. The condition of coalescence of the mercury droplets, i. e. the relation between the ionic strength and the critical potential of coalescence, was proved to be in excellent agreement with the theory of coagulation of colloid particles. Thus, the interaction between finely dispersed particles in hydrophobic colloids is essentially the same as that acting between macroscopic mercury droplets.
- 社団法人 粉体粉末冶金協会の論文