Titania, isoelectric point

Abrasive particles are a key component in CMP slurry. The most commonly used abrasive particles include silica, alumina, ceria, zirconia, titania, and diamond. Table 21.1 listed a set of information on each type of abrasive particles such as density, microhardness, and isoelectric points (lEP). It is important to point out that the specific values for these properties depend highly on the preparation techniques and the specific states of the samples. The values listed in the table represent an average of the most commonly reported data. For example, the isoelectric point for silica is a function of the number of hydroxyl groups, type and level of adsorbed species, metal impurity in the solid matrix, and the treatment history of the materials [1]. There are three major types of silica according to their preparation methods fumed, colloidal, and precipitated. The common sources for obtaining these abrasive particles are listed in Table 21.2. As examples, some of the more specific information on... 

Rezwan, K., Meier, L.P, and Gauckler, L.J., A prediction method for the isoelectric point of binary protein mixtures of bovine serum albumin and lysozyme adsorbed on colloidal titania and alumina particles, Langmuir, 21, 3493, 2005. 

It is well known that alumina, titania [10,11,12] and magnesium oxide [13,14] dissolve in acidic aqueous solutions and even at pH values close to the isoelectric point [15,16], In this study, it will be shown that these support surfaces were modified with promoters to increase the inertness thereof to acidic/aqueous environments, and not to stabilise the support against sintering and loss in surface area at high temperatures [17,18], This paper will deal with the modification of alumina and titania supports for cobalt based slurry phase Fischer-Tropsch catalysts to ensure the successful operation of slurry phase bubble column reactors on commercial scale,... 

This finding is consistent with the rule of thumb of electrokinetics that the isoelectric point of a mixed surface is the surface-area-weighted average of the isoelectric point values of the components (15). Hence it appears that this surface concentration regime corresponds to the completion of silica monolayer surface coverage of titania particles. This... 

Figure 12. Isoelectric points of DS-coated titanias O, titania dispersed in aqueous silica , dried, coated titania powders. The hose titania was 20 m2/g.

This method is useful for monitoring the surface charge characteristics of the coated titania either after or during deposition. There is a difference of ca. 3 pH units between the isoelectric point of titania (ca. pH 5) and that of silica (ca. pH 2), and the progressive shift in the isoelectric point as coating proceeds indicates the extent of silica... 

An additional advantage of this synthetic approach is that the mesopores of silica restrict the size of the TiO species in the mixed oxide materials. Furthermore, Liu et al. were able to control the homogeneity of the mixed oxide materials by changing the pH value of the initial sol-gel mixture. pH values lower than the isoelectric point of sihca (2.0) lead to uniformly dispersed titania domains, whereas at higher pH values phase separation is observed due to the instability of the titanium-citric acid complexes. A similar approach has been reported by Oki et al. [56] for the synthesis of Ti02—Si02 mixed oxides by addition of various alk)d amines such as hexylamine, dodecylamine, and octadecylamine or even... 

A wide variety of materials have been implemented as abrasive particles in CMP processes. They include alumina, silica, ceria, zirconia, titania, and diamond. The effectiveness and suitability of these particles in CMP with particular applications are greatly influenced by their bulk properties (density, hardness, particle size, crystallinity etc.) and the surface properties (surface area, isoelectric electric point (lEP), OH content, etc.). This section will focus on the evaluation of alumina, silica, diamond, and ceria as the major abrasives used for the CMP of metals. 

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