Aluminium oxide, effect

Davis, J.A, Gloor, R. (1981) Adsorption of dissolved organics in lake water environments by aluminium oxide Effect of molecular weight. Environ. Sci. Technol. 15., 1223-1227. 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

Radiochemical studies indicate that the pore base is the actual site of formation of aluminium oxide, presumably by transport of aluminium ions across the barrier-layer, although transport of oxygen ions in the opposite direction has been postulated by some authorities. The downward extension of the pore takes place by chemical solution, which may be enhanced by the heating effect of the current and the greater solution rate of the freshly formed oxide, but will also be limited by diffusion. It has been shown that the freshly formed oxide, y -AljOj, is amorphous and becomes slowly converted into a more nearly crystalline modifipation of y-AljO . 

If the preference for hydrogen ion exchange shown by lime-soda glasses can be reduced, then other cations will become involved in the ion exchange process and the possibility of an electrode responsive to metallic ions such as sodium and potassium exists. The required effect can be achieved by the introduction of aluminium oxide into the glass, and as shown in Table 15.2, this approach has led to new glass electrodes of great importance to the analyst. 

Since the literature cited did not reveal a significant effect of the differing pore systems of the various types of layer the aluminium oxide and silica gel types (60, 80, 100, etc.) are not specified. The same applies to binders, fluorescence indicators and trace impurities in the sorbents. 

Acid (pH 3) ammonium oxalate has been widely used to dissolve iron and aluminium oxides and release bound trace metals since its introduction in 1922 (Tamm, 1922) (Tamm s reagent). Typically McLaren et al. (1986) used 0.17moll-1 ammonium oxalate +0.1 moll- 1 oxalic acid. The extraction is sensitive to light (Mitchell and Mackenzie, 1954) and particularly to ultraviolet light (Endredy, 1963). Schwertmann (1964) showed that in the dark the amorphous iron oxides were mainly attacked and under ultraviolet illumination the crystalline phases were dissolved as effectively as by the dithionite reagent. Heavy metals are released, with the exception of lead and cadmium whose oxalates are poorly soluble and which coprecipitate with calcium oxalate. The use of oxalic... 

Type of Layer. The influence of the type of thin-layer was investigated by Caissie and Mallet (51) and it was shown to have an important effect on the fluorescence of pesticides. For instance, the spectral data vary from one layer to another (Table VII) some pesticides are fluorescent on basic aluminium oxide layers but they are not fluorescent on acidic layers. All these experiments demonstrate the flexibility of using fluorometric procedures and the selectivity that could be achieved if desired. 

Temperature influences the structure of TiC>2 synthesized as a nanolayer on SiC>2 and AI2O3. After 12 cycles at temperatures below 350°C on SiC>2, only anatase is formed. Above 600°C predominantly rutile is formed. At intermediate temperatures a mix of the two phases is formed. On aluminium oxide however, at low temperature the biphase system is formed. At 600°C 100%, anatase is formed on AI2O3. This illustrates the effect of the mutual influence of the matrix surface and the nanolayer on phase transformations in core-shell system. 

According to the results of our experiments in vitro, the highest adsorptive capacity with reference to proteins and protein-associated phospholipids and triglycerides of blood serum was characteristic of the highly disperse silica modified with aluminium oxide. The mechanism of the therapeutic effect of HDS on treatment for intestinal infections seems to involve the following major aspects. 

Since wet purification methods are insufficiently effective, solid sorbents are used. The systems based on calcium and aluminium oxides and hydroxides are promising as such sorbents. A sorbent should provide a minimum gas dynamic resistance, therefore, it is produced as the granules of complicated shape. Sorbents based on lime and aluminium hydroxide are good fluorine absorbers. However, lime sorbents do not possess sufficient mechanical strength, while the use of aluminium hydroxide alone as a sorbent is limited by its high cost. 

Aluminium oxide has a very high melting point, so a more easily melted compound of aluminium, sodium hexafluoroaluminate(lll), called cryolite (Na3AIF6), was added. What will be the effect on the melting point of aluminium oxide of adding this impurity ... 

The development of stress during calcination is shown in Fig. 8.20 for boehmite membranes calcined at 600°C (thickness after calcination is 5 pm). Curve c in Fig. 8.20 represents the curve which is corrected for support effects (see the preceding section on this subject). Three heating and cooling cycles are shown. During the first heating the Al-hydroxide particles of the gel are transformed to boehmite and subsequently to (hydrated) y-aluminium oxide particles and the shape of the first peak of curve c differs from the subsequent peaks. The maximum tensile stress calculated from the deflection amounts about 30 MPa. 

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