Phase aluminum

The small (10 -lm) coating particles are typically aluminum oxide [1344-28-1/, Al O. These particles can have BET surface areas of 100 to 300 m /g. The thermal and physical properties of alumina crystalline phases vary according to the starting phase (aluminum hydroxide or hydrate) and thermal treatment (see ALUMINUM COMPOUNDS, ALUMINUM OXIDE). 

Adsorption HPLC is the classification in which the highly polar silica particles are exposed (no adsorbed or bonded liquid phase). Aluminum oxide particles fit this description too and are also readily available as the stationary phase. As mentioned earlier, this classification can also be thought of as normal phase... 

There seems to be even less structural similarity for many other metal halides as the crystalline systems are compared with the molecules in the vapor phase. Aluminum trichloride, e.g., crystallizes in a hexagonal layer structure. Upon melting, and then, upon evaporation at relatively low temperatures, dimeric molecules are formed. At higher temperatures they dissociate into monomers (Figure 9-58) [107], The coordination number decreases from 6 to 4 and then to 3 in this process. However, at closer scrutiny, even the dimeric aluminum trichloride molecules can be derived from the crystal structure. Figure 9-59 shows another representation of crystalline aluminum trichloride which facilitates the identification of the dimeric units. A further example is chromium dichloride illustrated in Figure 9-60. The small oligomers in its vapor have structures [108] that are closely related to the solid structure [109], Correlation between the molecular composition of the vapor and their source crystal has been established for some metal halides [110],... 

In view of the matrix-isolation infrared studies, the theoretical calculations, and those studies of aluminum beam-water reactions, it is of considerable interest to probe the electronic structure of aluminum metal atom hydration reaction intermediates and products Isolated in rare-gas matrices. Such a study will form a useful adjunct to the infrared research. A mapping of the electronic structure of these species will provide a data set to which further theoretical calculations may compare. A more focused elucidation of the nature of the gas-phase aluminum hydration reaction s chemiluminescent continuum emitter may be provided... 

Figure 9.11 Powder X-ray diffraction profiles of the three phases of AIH3 before and after mechanical milling. O = a-phase, = Aluminum, n=p-phase and A = Ref [23].

The occurrence of coordination numbers greater than four for the aluminum is another feature of the phosphate-based solids in comparison with the zeolites. For example, in some phases aluminum adopts five-fold (trigonal bipyramidal) or sixfold (octahedral) coordination. In these cases, anionic species such as hydroxy or... 

The primary means of producing EB from the 1930s to about 1980 was the liquid phase aluminum chloride catalyst process. Although the aluminum chloride catalyst process is still in use at many plants, its share of worldwide EB production is diminishing as all new plants use a solid acid catalyst. 

In the gas phase, aluminum chloride exists as a dimer (a unit of two) with the formula Al2Clg. Its skeletal structure is given by... 

A number of hydrogen-transfer reactions involving carbonyl groups are known in organic chemistry however, these are for the most part limited to liquid-phase, homogeneously catalyzed systems. In this paper there is described a vapor-phase surface-catalyzed reaction which like the liquid-phase aluminum alkoxide catalyzed reductions of Meerwein-Ponndorf-Verley (J) will selectively reduce a carbonylic group in conjugation with a carbon-carbon double bond. 

There seems to be even less structural similarity for many other metal halides when the crystalline systems are compared with the molecules in the vapor phase. Aluminum trichloride, for example, crystallizes in a hexagonal layer structure. Upon melting and then evaporation at relatively low temperatures, dimeric molecules are formed. At higher temperatures, they dissociate into monomers (Figure 9-60) [9-60]. The coordination number decreases from six to four and then to three in this process. 

The ionic liquid process has a number of significant advantages over the industrial Cosden process. This system uses a supported or liquid phase aluminum(lll) chloride catalyst. Using the ionic liquid process, the polymer forms a separate layer, which is substantially free of catalyst and ionic liquid solvent. This effect greatly enhances the degree of control available to reduce undesirable secondary reactions (i.e., isomerization) without requiring alkali quenching of the reaction. 

It is witnessed that combustion products of the mixture AIF3 -I- 3NaNg over nitrogen pressure 4 MPa consist of three phases aluminum nitrogen, sodium aluminum hexafluoride, and sodium fluoride. On the assumption of the reflex magnitude relation it is fair to assume that Nag AlFg < AIN < NaF. 

Some modifications of this method have been developed by companies including Dow Chemical, BASF, Shell Chemical, Monsanto, and Union Carbide. Most of their efforts were focused on the development of various complex catalyst systems based on liquid-phase (aluminum chloride-based catalysts) and vapor-phase (solid acid-based catalysts, such as phosphoric acid catalysts) processes. 

Stationary phase Aluminum-backed silica gel (Kieselgel 60) TLC plates (Merck). 

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