Alumina, deposition

The decomposition of aluminum alkyls, such as (CH3)3A1 or ( 2115)3Al, in an oxidizing atmosphere, such as O2 orN20, produces alumina deposits in a temperature range of 250-500°C.l l... 

The function of the carbon coating is to contain the byproducts of the fission reaction, thereby reducing the shielding requirements. It also protects the nuclear fuel from embrittlement and corrosive attack and from hydrolysis during subsequent processing steps. CVD coatings of alumina deposited at 1000°C and beryllia deposited at 1400°C have also been studied for that purpose.P l... 

The mineralogy of ferricrete alteration profiles can be complex and varied because of the incorporation of mechanically derived materials and the retained importance of host rock composition after the formation of secondary minerals. In general, ferricrete profiles do not display the progression of alteration minerals observed in laterites. Where ferricretes are formed by mechanical accumulation, they can lie disconformably above unaltered bedrock (Bowden, 1987, 1997). In these instances, the ferricrete mineral assemblage will be inherited, in part, from the derived materials, and in part from later cementation processes that involve remobilised iron and alumina deposited as neo-formed oxyhydroxides. In such examples, determining the sequence of mineralogical transformations becomes exceptionally difficult. 

Equivalent results were obtained with alumina deposited catalysts (figure 5). However in this case ammonia has a very marked inhibiting effect on non-promoted catalysts. It can be seen then that the addition of the promotor strongly increases the stability of the catalysts in the presence of ammonia and of water. However contrary to graphite supported catalysts the addition of a promotor does not allow to stabilize completely the catalyst in the presence of ammonia and of water. 

Commercial fonnulations These catalysts contained Pt and Rh supported on alumina deposited in monolitlis which also contained ceria. 

In order to understand this very peculiar chemisorption step which occurs in the real process of oil recovery and purification, triphenylarsine, and diphenylmer-cury have been used to model the real organometallic poison present in the crude oil. An industrial catalyst made of alumina-deposited nickel, containing 18wt% nickel as about lOnm diameter particles, is used (this corresponds to a dispersion of 10%). In the following, we will see that the smallest size of the nanoparticles is no longer a requirement but the control of such a size becomes a crucial problem ... 

The removal of solvated cadmium ions (Cd ) from water has been studied because ionic cadmium is a toxic element (itai-itm disease in Japan) and one of the main metallic pollutants of industrial aqueous effluents (electrodeposition, Ni-Cd batteries etc.). When alumina-deposited nickel, previously reduced under a hydrogen flow, is suspended in a Cd solution, a quick and strong decrease in pH is observed, followed by a slow pH increase with time. The pH decrease has been interpreted by the reaction ... 

Figure 9.6. Film of beta-alumina deposited using serigraphy...

However, in other cases internal diffusion limitation can be significant even with very thin washcoat thicknesses [127], when temperature is high (> 700°C). This refers, for example, to catalytic combustions, which are extremely fast. Hayes et al. [135] evaluated the extent of intraphase and interphase resistances to the catalytic conversion of low concentrations of carbon monoxide in air in a tube wall reactor (coated with a platinum-alumina deposit). Above 610 K there was strong evidence of both intraphase and interphase resistances to catalytic conversion. In Sections 8.3.2, 8.3.3, and 8.3.4, we provide a systematic analysis for prediction of the extension of external and internal diffusion limitations. 

Fig. 12.5 SEM-EDS cordierite after 6 alumina deposition cycles (a). EDS spectra are in the same order corresponding to those shown SEM images (b). The blank spots indicate the locations analyzed by EDS (NUCAT/PEQ/COPPEAJFRJ) [17]...

Doloma Graphite SENs. Doloma graphite (DG) pouring shrouds were developed in order to reduce and/or eliminate the tendency for alumina deposition in the SEN or SES. The DG tubes have been used primarily for casting stainless steels prone to alumina clogging and aluminum killed carbon steels that are also prone to this problem. Alumina graphite (AG) are typically used in these applications however, alumina deposition is usually the limiting factor for their performance. Properties for several DG materials are shown as compared to a typical AG material in Table 9. 

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