No abstract

The rdf for the 21.4 wt % sample differs from the ones for the samples with lower loading, especially with respect to the relatively high intensity of the peak at 0.3 nm. This points to a high degree of polymerization, which is in accordance with the expected formation of precipitates. This rdf also differs from that of the AHM reference compound. This suggests that the precipitate has a different structure. No attempt was made to unravel this structure. The amount of Mo(IV) present in this sample is still consistent with the adsorption model, however.During the preparation of catalysts by impregnation, the time allowed to reach equilibrium is often about 1 h or even less. In the case of the AHM/y-Al203 system, the EXAFS results indicate that 1 h is too short for equilibrium to be attained, since it was found that in the impregnated sample less Mo(IV) is present than in the material obtained in an adsorption experiment. ConclusionsThe present EXAFS study has resulted in a modification of the model describing the adsorption of AHM onto 7-Al203. It appears that two adsorption sites are necessary: (1) basic OH groups, leading to adsorption of Mo(IV); (2) coordinatively unsaturated Al3+ sites, leading to adsorption of Mo(VI).Of the site-blocking reactions employed here, the F exchange of basic OH groups gives results in line with the above adsorption model, but the reaction of Al3+ sites with acacH leads to more ambiguous results.A normal catalyst impregnation time of about 1 h is too short for the reaction of AHM with the basic OH groups to proceed to completion.

No abstract

No abstract

No abstract

No abstract

No abstract

The driving force behind the research on advanced materials has largely been aerospace and defense applications. In such applications the customer-induced limitations and infrastructural economic factors are secondary to the application-oriented parameters. Automobiles, on the other hand, represent the primary consumers of advanced materials in civilian applications. Automobiles are high-technology, low-cost machines which need to be robust for various climatic conditions and driver behavior. Advanced materials play an important role in the design and fabrication of various components of automobiles, and the use of new materials continues to increase. Recent interest in developing highly fuel efficient vehicles with low emissions has focused efforts toward materials, designs, and devices and is spurring research into advanced materials for weight reduction. The goal is to achieve fuel efficiency by weight reduction and a more efficient powertrain. In this review article, we summarize the efforts of the 1970s and the 1980s on the development of ceramic gas turbine engines with emphasis on materials processing and properties. This is followed by a discussion of metal-matrix composites and reinforced plastics, the structural materials of current interest. The materials issues related to automotive exhaust reduction catalysts are discussed since materials continue to play an important role in designing catalysts to meet the new EPA regulations. The understanding of materials chemistry is expected to play an important role in designing new materials and developing new processes that can be used economically to mass produce vehicle components. We also summarize reports based on ceramic precursor technology and sol-gel processes that show promise in the fabrication of automotive components.