Silica-ceria particle interaction

Relaxations in the double layers between two interacting particles can retard aggregation rates and cause them to be independent of particle size [101-103]. Discrepancies between theoretical predictions and experimental observations of heterocoagulation between polymer latices, silica particles, and ceria particles [104] have promptetl Mati-jevic and co-workers to propose that the charge on these particles may not be uniformly distributed over the surface [105, 106]. Similar behavior has been seen in the heterocoagulation of cationic and anionic polymer latices [107]. 

The selectivity of alcohol depends on the carbide preparation. A maximum in alcohol is achieved for the sample WC/Ti02 (T3) for which the preparation of the carbide combines reduction and carburization steps at moderate temperatures (respectively, 873 K and 1073 K). In this case, anionic vacancies stabilized by mixed oxides are formed, associated with carbon vacancies in mixed carbides resulting in a better interaction of carbidic and oxidic phases. On silica, ceria and zirconia, the extent of carburization is too high and the interaction of the carbide phase with the oxide support is suppressed giving larger isolated particles of tungsten carbide with low dispersion. 

Silicate ions of varying concentrations were added to ceria dispersions in order to study the electrostatic interaction between ceria particles and silicate ions. It was observed that the zeta potential of ceria becomes less positive or more negative. With an increase in Na2Si03 concentration, the isoelectric point shifts to lower pH values. At high silicate concentration, the zeta potential of ceria particles follows a trend similar to that of silica. This is a clear indication that the silicate ions adsorb onto the ceria particles [30,31]. 

An instrumentation approach was explored by Abiade et al. [32] who investigated ceria-silica interactions using atomic force microscopy (AFM) and SEM. Based on these studies, a model for silica polishing with ceria particles is illustrated in Fig. 13.23. 

Interactions between the ceria abrasives and the oxide surface have been investigated using both the chemical and the instrumental approaches. Suphantharida and Osseo-Asare [27] used zeta-potential measurements, silicate adsorption, and polishing experiment to investigate the role of ceria abrasives-Si02 surface interaction. T o determine the effect of pH on the surface charges, the zeta potentials of abrasive particles were measured (Fig. 13.21). The points of zero charge (pzc) or isoelectric point is at pH 6.0 for ceria and pH 1.5 for silica. These values are consistent with those reported by others [28,29]. 

Figure 13.23a shows the first mechanism, which is mainly chemical in nature. The silica removal rate is accelerated by the ceria-silica interactions, which results in the improved dissolution of the silica substrate during polishing. Figure 13.23b shows the second mechanism, which is based on physicochemical particle-surface interactions in which the ceria-silica bonding does not result in direct modification of the silica substrate but enhances the... 

The purpose of this study was to explore the interaction between slurry particles and wafer surfaces by the measurements of their zeta potentials. The zeta potentials of slurry particles such as fumed and colloidal silica, alumina, ceria and MnOj and substrates such as silicon, TEGS, W, and A1 have been measured by electrophoretic and electroosmosis method to evaluate the electrical properties of surfaces, respectively. The zeta potential of oxide and metal surfaces showed similar values to those of particles as a function of pH. The interaction energy between alumina and silica particles and TEOS, W and A1 substrate were calculated based on DLVO theory. No deposition of silica particles on TEOS and the heavy deposition of alumina particles on metal substrates were observed in the particle deposition test. Experimental results were well agreed with the theoretical calculation. 

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