Coagulation rate silica

The colloidal stability of silica Suspensions in the present work was assessed by sediment volumes and from the optical coagulation rate constant. In the first method, 50 mg of silica was dispersed in 5 cm3 polymer solution (concentration 10-2 g cm 3) in a narrow tube and the sediment height found at equilibrium. Coagulation rates of the same systems were found by plotting reciprocal optical densities (500nm, 1cm cell) against time. When unstable dispersions were handled, the coagulation was followed in... 

The sediment volume of silica in CCl solutions of poly (methyl methacrylate) was approximately 9 cc g-l but variable results were found in solutions of polystyrene, depending on the molecular wt. of the polymer. Lower M.W. samples are poor stabilizers and the dispersions are so unstable that optical coagulation rates could not be measured with confidence. Figure 5 shows the general trend in CCl. All polymers, whatever their composition, are superior to the pure solvent. 

Colloid stability assessments of silica dispersions in CCI4 by sediment volume and coagulation rate are in general concordance and confirm the pattern previously reported by Barron and Howard... 

Figure 8. log(coagulation rate/min-l) of silica 186 in CCI4 solutions of polymers with various styrene contents. Squares, block polymers circles, random copolymers or homopolymers. 

Ionic Medium. Silica dispersions were freshly prepared for each experiment in solutions buffered with 10"3M HC03"/C02. The amount of species dissolved from the amorphous silica surface during the experiment was negligible because of the small rate of dissolution reactions. The ionic medium in which coagulation and adsorption studies were carried out was kept constant I = 1.0 to 2.0 X 10 3M. The conditions in all agglomeration and adsorption experiments were such that no Al(OH)3 precipitated within the period of observation. 

In an experimental study of mixed iron-silica colloids we found the opposite phenomenon, stabilization of colloids of iron hydroxide by silica colloids, which is manifested very clearly in undialyzed iron hydroxide sols of average concentration with a ratio of Fe203 SiOj = 1 3. Colloidal iron in mixed solutions proved to be more resistant to the action of electrolytes than in isolated sols of iron hydroxide. Only colloidal silica shows any stabilizing effect on sols of iron hydroxide dilute solutions undersaturated with Si(OH)4 are not stabilizers. It is characteristic that colloidal silica is capable of stabilizing colloidal iron in the same pH ranges in which pure silica sols are stable in acid (pH < 4) and alkaline (pH > 8) environments. In slightly acid environments (pH = 5-6) iron-silica sols are unstable and decompose to form mixed sediments, which sometimes are not uniform due to different rates of coagulation and deposition. 

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