Metal aluminate

The increasing use of sihconized coatings for weather durabiUty caused severe masking problems for the all-metal, filter mesh-like catalyst elements available in the 1970s. Interest in catalytic afterburners increased when dispersed-phase precious metal—alumin a-on-ceramic honeycomb catalysts offered economically attractive results. 

NOTE Spinels are very hard metal aluminates or ferrates. 

B. B. Patel. Fluid composition comprising a metal aluminate or a viscosity promoter and a magnesium compound and process using the composition. Patent EP 617106,1994. 

Bolt, H. 1994. Transition metal-aluminate formation in alumina-supported model catalysts. PhD thesis, University of Utrecht. 

A central question with respect to supported metal catalysts is that of the structure of the metal-support interface. Various possibilities have been proposed, varying from interfaces consisting of a mixed metal aluminate or silicate layer [17] or the presence of metal ions which serve as anchors between particle and support [18] to the attractive interaction between ions of the support and the dipoles that these ions induce in the metal particle [19]. EXAFS highlights the atomic surroundings of an atom in the catalyst, and if the supported metal particles are sufficiently small, oxygen atoms in the metal-support interface give a measurable contribution to the EXAFS spectrum. 

Lappert and coworkers also found that such rare-earth metal aluminate complexes can be readily transformed into methyl derivatives by addition of equimolar amounts of donor Lewis base molecules such as pyridine or tetrahydrofuran (Lappert s concept of donor-induced aluminate cleavage, Scheme 1) [10]. Depending on the Lewis acidity of the Ln(III) center homo-... 

Most of the knowledge about aluminate and alkylaluminum coordination stems from X-ray crystallographic studies. The basic idea of this section is to compile a rare-earth metal aluminate library categorizing this meanwhile comprehensive class of heterobimetallic compounds. Main classification criteria are the type of homo- and heterobridging aluminate ligand (tetra-, tri-, di-, and mono alkylaluminum complexes), the type of co-ligand (cyclopen-tadienyl, carboxylate, alkoxide, siloxide, amide), and the Ln center oxidation state. In addition, related Ln/Al heterobimetallic alkoxide complexes ( non-alkylaluminum complexes) are surveyed. Emphasis is not put on wordy structure discussions but on the different coordination modes (charts) and important structural parameters in tabular form. An arbitrary collection of molecular structure drawings complements this structural report. 

Commonly used fuels are polymers, e.g. HTPB or polyethylene which can be metallized (aluminized) in order to increase the specific impulse. Common oxidizers include gaseous or liquid oxygen or nitrous oxide. 

High volatility limits the selection of many otherwise useful materials. Use of silica, all alkali, and alkaline earth metals higher than magnesium as components in any substrate or supporting material cannot be recommended. Catalysts with the least amount of volatility include palladium and iron oxides. It may also be possible to form complex oxides with other transition metal oxides, such as Mn, Ni or Co, which could have an acceptable activity and stability. For example, the formation of transition metal aluminates could lower volatility and increase sintering resistance, but at the expense of decreased activity. 

Hot dipping. Zinc, tin and tin/lead coatings are commonly applied by hot dipping, i.e. dipping of the object to be coated in molten coating metal. Aluminizing by this method is less widespread, because Al makes the process more difficult to operate. 

Borovkova, L.B. et al. (1992) Hardening of alkaline earth metal aluminates I. Barium monoaluminate (in Russian). Tsement (Moscow), pp. 18-24. 

Infrared absorption spectra of synthetic alkali and alkaline earth metal aluminate. 

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