Cationic composition ratios

Figure 15 shows a typical variation of the cationic composition ratio with deposition... 

Fig. 15 Typical variation of the cationic composition ratio with deposition temperature when the precursors are Ba(thd)2tetraglyme, Sr(thd)2tetraglyme and Ti(thd)2(0-i-P )2 dissolved in n-buthyl acetate.

Fig. 17 Cationic composition ratios calculated from XRF utilizing a sensitivity factor.

Ligand Metal cation Molar ratio, ligand/eatlon Composition of complex Ethanol of solvation, % Alcohol- % Hydrox- molecules ate ide adduct per cation ... 

Chemical analysis for cation composition, cation/anion ratio, and chemical impurities. 

Notice that in step 2, the weathering of an aluminosilicate mineral by the aggressive attack of "H2S04" waters may result in the release of dissolved silica, as well as cations. The ratio of silica to cations released depends on the composition of the primary mineral weathered and its alteration product. The weathering of a carbonate mineral gives cations and bicarbonate. 

In this paper we shall summarize our recent findings concerning the nature and distribution of species present in silicate and aluminosilicate solutions and gels. Particular attention will be focused on establishing the effects of pH, cation composition, Si/Al ratio, and solvent composition. 

The species distribution of the solution determines the cation composition of the interlayer space of montmorillonite. In equilibrium, the cation exchange sites of montmorillonite are covered by calcium, hydrogen, manganese, and sodium ions (Figure 2.9). Figure 2.13 shows the equivalent fractions (X) of these cations as a function of pH at the ratio of MrnEDTA =1 1. 

Up to now, the precursor solutions for Ba, Sr, and Ti are usually contained in separate reservoirs to permit variation in the input ratio of the cationic elements. However, for mass-production it is much more desirable to use the cocktail source which contains all three precursors in one reservoir for more reproducible deposition. Use of the cocktail source is not proper for research because changing the cationic composition is not easy. Furthermore, the cationic composition of BST films is not only dependent on the input precursor ratio hut also on the deposition temperature, as discussed helow. Therefore, use of a cocktail source is possible only... 

Catalyst Composition. Chemical compositions of typical nickel and cobalt zeolites are summarized in Table 1. Based on the total CEC derived from the initial sodium composition, 23 to 37% of the Zeolon and 8.4% of the Linde SK400 exchange sites are occupied by nickel cations. In Zeolon, 55% of the exchange sites are occupied by cobalt cations. A ratio of 1.41 1 for cobalt to nickel on the Zeolon exchange sites resulted where nickel and cobalt were exchanged under comparable conditions. 

Since pH is known to influence strongly the distribution of silicate anions in alkaline solutions (7.9), one might expect the observed changes in silicate anion distribution with cation size to be a result of changes in pH. Reference to Table 1 shows, however, that for a fixed silicate ratio, the pH of the solutions is relatively independent of the base composition and certainly does not increase with cation size, as might be expected from a consideration of hydroxide dissociation constants (171. This suggests that the influence of cation composition is a consequence of direct cation-anion interactions, rather than an effect of pH. 

Zeolite Si02/Al203 (molar ratio) Cation composition (%) Na" - K - Surface area (m /g) Crystal size (pm)... 

Ionic Solids In crystalline ionic solids, the unit cell contains particles with whole, rather than partial, charges. As a result, the interparticle forces (ionic bonds) are much stronger than the van der Waals forces in atomic or molecular solids. To maximize attractions, cations are surrounded by as many anions as possible, and vice versa, with the smaller of the two ions lying in the spaces (holes) formed by the packing of the larger. Because the unit cell is the smallest portion of the crystal that maintains the overall spatial arrangement, it is also the smallest portion that maintains the overall chemical composition. In other words, the unit cell has the same cation anion ratio as the empirical formula... 

These defects form by the selective addition or loss of one (or more) of the constituents of the crystal and consequently lead to a change in crystal chemistry and the notion of nonstoichiometry discussed below. The basic notion that the composition of compounds is a constant with simple ratios between the numbers of constituent atoms is one that is reiterated in every first-year college chemistry course. For instance, in MgO the cation anion ratio is unity, that for AI2O3 is 2/3, etc. In reality, however, it can be rigorously shown using thermodynamic arguments that the composition of every compound must vary within its existence regime. ... 

These discrepancies could be justified by the fact that clinoptilolite displays different thermal behaviours depending on its Si/(Si+Al) ratio and cation composition (Gottardi and Galli, 1985). Actually, these two authors found that ... 

These ferrites are the basis for many applications. The lattice parameter varies linearly with composition, x, as shown in Fig. 210. The cation radius ratio for tetrahedral sites is large (in four-fold symmetry, the Zn " radius is 0.60 A, while that of Fe is 0.49 A (Shannon, 1976)), and has the strongest influence on the lattice parameter, as well as on the magnetic properties of these solid solutions (Globus, Pascard Cagan, 1977). 

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