Aluminum mixed structures

Tape and film adhesives are most often used to bond large areas, such as for applications in the aerospace industry. For example, the joining of aluminum honeycomb structure to flat metal skins is often accomplished with thermosetting epoxy film adhesives. These films (Fig. 13.1) can easily be applied without the need to mix, meter, or apply a liquid coating. 

Catalysts on the basis of complexes of cobalt or iron salts [e.g., cobalt(II) chloride/ pyridine, cobalt(II) acetate/AlR2Cl] yield mixed structures with more than 20% 1,2 double bonds and rubber elastic-like polymers [325,326]. Rare earth catalysts have also been described [327]. A crystalline c/ -1,4 polymer with a melting point of 198°C and a molecular weight of 100 000 is obtained with aluminum alkyls/neodymium compounds at a molar ratio of 31 1. The yield is in the range of 30%. Cobalt(II) acetate in combination with diethylaluminum chloride or rhodium salts also yields a cis-, A polymer [328,329]. 

Thermally activated mixed metal hydroxides, made from naturally occurring minerals, especially hydrotalcites, may contain small or trace amounts of metal impurities besides the magnesium and aluminum components, which are particularly useful for activation [946]. Mixed hydroxides of bivalent and trivalent metals with a three-dimensional spaced-lattice structure of the garnet type (Ca3Al2[OH]i2) have been described [275,1279]. 

In order to accomplish the goals of this reviewer in a logical and systematic manner, the first systems to be described will be those of aluminum derivatives that appear to be the most readily discussed in terms of their structures and bonding, followed by the Group II derivatives of beryllium and magnesium, and, finally, by a discussion of the lithium derivatives and of the mixed-metal species, which clearly represent the most difficult systems to describe properly. 

Aluminum forms mixed oxides with many other metals which either replace Al3+ in octahedral positions or occupy tetrahedral sites. The spinel structure of MgAl204, an important prototype, has been investigated by photoelectron spectroscopy.122 Vibrational and solid state NMR methods are also useful for studying aluminate structures.12 125... 

---