Aluminum oxide acid-base character

Metals typically form basic oxides and nonmetals typically form acidic oxides, but what about the elements that lie on the diagonal frontier between the metals and nonmetals Along this frontier from beryllium to polonium, metallic character blends into nonmetallic character, and the oxides of these elements have both acidic and basic character (Fig. 10.7). Substances that react with both acids and bases are classified as amphoteric, from the Greek word for both. For example, aluminum oxide, A1203, is amphoteric. It reacts with acids ... 

The product in this case is sodium aluminate, a compound that contains the aluminate ion, [Al(OH)4]. Because aluminum oxide reacts with both acids and bases, it is classified as amphoteric. Other main-group elements that form amphoteric oxides are shown in Fig. J.3. As you can see, these elements lie in a diagonal band across the table from beryllium to polonium. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (see Chapter 16). 

The characteristics of this group are that the elements possess a valence of 3, and that the oxides, M2O3, have but a weakly developed basic character. Boron, in fact, shows practically no base-forming properties, but forms rather a weak acid. The oxide of aluminum displays both basic and acidic properties that is, it is amphoteric. The remaining elements are more distinctly base-forming than aluminum, without, however, approaching in any way the alkaline earth metals in this respect. 

Metal atoms on the metal surface, as mentioned earlier, are soft acid, and hence they combine with anions of soft base on the metal surface. Once these metal surface atoms are ionized, they form metal ions such as iron ions and aluminum ions, and the metal surface turns to be hard acid. The metal ions then combine with anions of hard base such as hydroxide ions, OH, oxide ions, 02, and sulfate ions, SO4, to form insoluble metal oxides and salts of ionic bonding character. The two-dimensional concentration of surface metal ions increases with the electrode potential of the metal, and hence the metal surface gradually becomes harder in the Lewis acidity with increasing electrode potential until it combines with anions of hard base such as oxide ions to form a metal oxide film adhering firmly to the metal surface. The passivation potential of a metal is thus regarded as a threshold potential where the metal surface grows hard enough in the Lewis acidity to combine with a hard base of oxide ions. 

Boron oxide particles were incorporated to silicone rubber-based mixes containing fumed silica (reinforcing filler) and reference mineral fillers - aluminum hydroxide, wollastonite, calcined kaolin, mica (phlogipite) and surface modified montmorillonite with dimethyl-dihydrogenatedtal-low quaternary ammonium salt. Acidic character of boron oxide, which can disturb the peroxide curing process, was compensated by addition of magnesium oxide. The influence of boron oxide particles on properties of composites was determined and mechanism of their ceramization process studied. 

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