Metal alumina

The increasing use of siliconized coatings for weather durability 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—alumina-on-ceramic honeycomb catalysts offered economically attractive results. 

Alumina is a porous, high-surface-area form of aluminum oxide. The surface has more polar characteristics than silica gel does therefore, it has both acidic and basic characteristics, reflecting the nature of the metal. Alumina has a high melting point, slightly over 2000°C, which is also a desirable property for a support due to its thermal stability. Alumina is composed of aluminum trihydroxides, Al(OH)3 aluminum oxyhydroxides, AIO(OH) and aluminum oxide, Al203n(H20). 

Detailed HRTEM characterization of the specimens showed that all metal-ceramic interfaces in the two different nanocomposites had thin ( 1 nm thick) amorphous films (see Fig. 11.5). In addition, occluded particles were found inside the alumina grains which also had thin amorphous films at their interfaces with alumina. Analytical microscopy showed the films to contain Ca, Si, and Al.41 Hamaker coefficients were calculated for metal-ceramic interfaces in the presence of a Si02-based film, which indicated that a stronger attractive force is expected for intergranular films at metal-alumina interfaces,... 

Element (atomic state) Hi Fused silica, glass, metals, alumina, graphite, ice... 

Particles of 50. diameter have about one-fourth of their total number of atoms on the surface and 200X particles have about one-fifteenth of their atoms on the surface. It is evident that the behavior of metal-alumina contacts could be influenced by surface states not presently understood. However even if this possibility is neglected, major complications can arise in applying the Schottky theory to small particles. 

F.S. Ohuchi and M. Kohyama, Electronic Structure and Chemical Reactions at Metal/ Alumina and Metal/Aluminum Nitride Interfaces, Journal of Amercian Ceramic Society, Vol.74(No.6), 1991, p.1163. 

C. Aromatic Hydrocarbons, Steam Dealkylation.—Research on steam dealkylation has thrown light on the mechanism of reforming. Rabinovich and other Russian workers, following their earlier research in this area which is summarized by Grenoble, concluded that the toluene reaction with steam over precious metal/alumina catalysts proceeds by simultaneous-consecutive reactions ... 

Figure 2. Profiles of metal-alumina FGM coatings produced for joining experiments. Numbers indicate different experimental series Ni-20%A1 (58,61), and NiCoCrAlY (59,62-65).

On the basis of the results on the isotopic exchange between gaseous and 1 0 of the support in precious metals/alumina catalysts, it can be concluded that ... 

As expected from the above discussion, the amounts of cracked products and methane increase by a factor of 2 to 2.5. However, the DHC products (naphthenes and toluene) increase by a factor of 12. Under the experimental conditions, DHC can be both mono- or bi-([metal + alumina]-) functional. The rate of dehydrogenation of MCH to toluene (not shown) actually decreases for the bimetallic catalyst, from 45 to 12 mol/h/kg. 

E ddently, an intensive H-D exchange between molecular hydrogen and the hydrocarbon intermediates proceeds already at normal pressure on our catalysts. On metal/alumina catalysts such exchange is known only at elevated pressure [10]. This result means that one or some intermediate dehydrogenation steps are reversible... 

CS-metal/alumina complexed nanocomposites could be promising candidates for antimicrobial agents in the cosmetic, food and textile industries. Quaternised CS and CS-iodine could be future materials with enhanced biocidal properties. Improving our understanding of antimicrobial mechanisms will enable the continued design of new biocidal polymers, which is necessary in order to combat the development of microbial resistance. 

HM 9) Excellent electrical insulator and also wear-resistent. Insoluble in water, insoluble in strong mineral acids, readily soluble in strong solutions of alkali metal hydroxides, attacked by HE and NH4HE2. Owing to its corrosion resistance under an inert atmosphere in molten metals such as Mg, Ca, Sr, Ba, Mn, Sn, Pb, Ga, Bi, As, Sb, Hg, Mo, W, Co, Ni, Pd, Pt, and U, it is used for crucibles for these liquid metals. Alumina is readily attacked under an inert atmosphere by molten metals such as li, Na, Be, Al, Si, Ti, Zr, Nb, Ta, and Cu. Maximum service temperature 1950 °C. 

Because of the widespread use of chlorinated hydrocarbons in industry, the presence of halogens in exhaust gas impurities is very common. This has caused problems, particularly with platinum group metal (PGM) catalysts, which make up about 75% of the catalysts used for VOC destruction. Reportedly, the problem lies with the catalyst carrier or wash coat rather than with the catalytic metals. Alumina, which is usually used as the carrier, reacts with chlorine compounds to form aluminum chloride, which can cover or otherwise degrade the metal catalysts. According to Parkinson (1991), alternate carriers are being developed to avoid this problem. 

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