Alumina xerogel

For other adsorptives the experimental evidence, though less plentiful than with nitrogen, supports the view that at a given temperature the lower closure point is never situated below a critical relative pressure which is characteristic of the adsorptive. Thus, for benzene at 298 K Dubinin noted a value of 017 on active carbons, and on active charcoals Everett and Whitton found 0-19 other values, at 298 K, are 0-20 on alumina xerogel, 0-20-0-22 on titania xerogel and 017-0-20 on ammonium silicomolybdate. Carbon tetrachloride at 298 K gives indication of a minimum closure point at 0-20-0-25 on a number of solids including... 

Aluminate cement, 2 415-416 Aluminate ions, silica sols and, 22 394s Aluminates, 2 273-279 analysis, 2 275-276 chemical reactions, 2 273-274 dispersants, 8 710t economic aspects, 2 275 health and safety factors, 2 276 manufacture, 2 274-275 physical properties of, 2 273-274 uses of, 2 276-277 Alumina trihydrate (ATH), 2 274 in synthetic fillers, 11 314-315 Alumina whisker reinforcement, 5 574t Alumina xerogels, X-ray diffraction of, 23 78... 

EDX-analyses reveal observation of stretched xerogel clusters which fill almost entirely the channels of the PAA after sequential spin-on deposition followed by heat treatment. Unlike to all our earlier works with titania or alumina xerogel, the proposed technology does not allow fabrication of YAG xerogel monolith, whereas only occasional clusters are observed inside the mesoscopic channels of PAA-Fig. 2. 

The silica hydrogel network constitutes the framework of the silica-alumina gel. From a textural point of wiev, a silica-alumina xerogel seems to be an "image" of the starting silica hydrogel. Depending on the alumina content the silica-alumina gels exhibit predominantly a silica-like texture or an alumina-like texture. 

Table 4 Comparison of crush strength and attrition rate of sol-gel-derived y-alumina xerogel granules with commercial sorbents...

Figure 2. SEM (a,b) and TEM (c) micrographs of the structure xerogel/anodic alumina (a) - as anodized anodic alumina film of 5 pm thick fabricated on Si, (b) - after one spin-on deposition of Eu-doped titania xerogel (c) - ultramicrotomed sections of the terbium-doped alumina xerogel/PAA structure of 30 pm thick. Bottom of the pore was filled with terbium-doped alumina xerogel after five spin-on depositions.

The structures alumina xerogel/PAA doped with Tb demonstrated very low thermal PL quenching which is untypical for lanthanide-doped films [17]. The thermal quenching does not exceed a factor of two within a temperature range from 10 to 300 K. It is much lower in comparison with (i) Tb-doped titania xerogel, (ii)... 

Tb-implanted thermally grown silicon dioxide film, and (iii) Tb-doped alumina xerogels fabricated onto monocrystalline silicon. Thus, the terbium-doped alumina xerogel/PAA structure was proposed as a basis for green room-temperature luminescent images [17]. 

The alumina aerogel (490 m2.g-l, 1.3 cm. g-l micro-mesopore volume) was prepared from aluminum sec - butoxide dissolved in sec - butanol by hydrolysis with a stoichiometric amount of water. The alcogel was then dried in an autoclave under supercritical conditions with respect to sec - butanol [4]. Two conventional alumina xerogels ( Degussa 110 m2.g-l and R.P. 100 m2.g-i ) were also used as supports of Pd and Pt-Rli catalysts. 

An amorphous alumina xerogel is prepared by the nonhydrolytic method according to... 

Modification of silica-alumina xerogel texture by changing the mixing mode of reactants which give the silica hydrogel implies that ... 

Tables 1 and 2 give more details on the textural characteristics of silica and silica-alumina hydrogels (table 1), and of the corresponding xerogels (table 2). The main effect of the semi-continuous addition of the reactants is an increase of the mean pore radius of the silica-alumina xerogels when duration of the reactant addition increases.

Textural characteristics of silica and silica-alumina xerogels... 

The characteristics of silica-alumina xerogels evaluated from nitrogen adsorption-desorption isotherms (B.E.T. - surface area B.J.H. calculations for pore r us and volume evaluations) are presented in table 5. The effects evidenced in this table are almost similar to those detected by thermoporometry opening of the texture for simultaneous introduction of silica reactants. This effect exists for addition durations no longer than 600 s. 

Textural characteristics of silica-alumina xerogels from nitrogen adsorption-desorption isotherms... 

Silica hydrogels prepared in acid conditions conduct to silica-alumina xerogels having pores smaller than those obtain in basic conditions. 

Monolithic alumina xerogels produced by the Yoldas process and heated to SOO C. From Yoldas (164),... 

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