Boehmite microporous

Boehmite is itself decomposed at c. 400—450°C. As expected, the calcined products have much lower specific surface areas than the activated aluminas produced from the trihydroxides. However, the results of de Boer and his co-workers (de Boer, 1972) indicate that a sample prepared at 580°C was highly microporous and that up to this temperature there was only a small change in the external area. 

Ilford uses nearly exclusively resin-coated true photobase for their wide format and desktop media. The ink-receiving layers (IRL) are based on proprietary technology and are apphed in a multi-layer photo-like cascade or curtain coating process. Ilford developed ink receiving layers which are based on either polymers (e.g., gelatin CMC, PVA) or microporous layers based on sUica or lanthanum doped boehmite, or a combination of both. ... 

Commonly used aluminum sources in the synthesis of zeolites include sodium aluminate (NaA102, Na20 54%), pseudo-boehmite, home-made aluminum hydroxide, and aluminum isopropoxide, which is the mostly used in the synthesis of microporous aluminophosphates. The structures of the two most important aluminum sources are shown in Figure 5.11 and Figure 5.12, respectively. 

Figure 2. Microstructure with typical cluster of micropores in a submicrometer sintered alumina ceramic produced from a boehmite sol with corundum (a-Al203) seeds <0.2 pm.

A good illustration of the importance of the order in which reactants are mixed is given in Figure 7.4, which shows the differences in XRD for aluminum hydroxide precipitation at pH 9 [18]. Each procedure led to a different compound microporous boehmite (aluminum nitrate added to sodium carbonate), bayerite (sodium carbonate added to aluminum nitrate), or fibrillar boehmite (simultaneous addition). 

During the gibbsite decomposition slit-shaped micropores are produced whose size is dependent on the pressure of the water vapour above the material [8]. At higher temperatures the boehmite itself decomposes to form alumina. 

Rouquerol [9,10] studied the effect of water vapour pressure on the decomposition, at low pressure, of 1 pm crystallites of gibbsite using a vacuum thermobalance and constant reaction rate regimes. He showed that, at pressures of less than 1,33 Pa, the formation of boehmite is minimised and the gibbsite decomposes directly to produce a highly microporous alumina. He found that the BET surface areas could be varied from 40 to 430 m g" by changing the pressure of water vapour over the solid from 5 to 130 Pa. 

Conunercial production of activated alumina is performed exclusively by thermal dehydration or activation of aluminum trihydrate, Al(OH)3, or gibbsite (MacZura et al., 1977). The oldest form, which is stUl widely used, is made from Bayer a-trihydrate, which is a by-product of the Bayer process for aqueous caustic extraction of alumina from bauxite. The trihydrate, in the form of gibbsite, is heated or activated in air to 400°C to form crystalline )// )-alumina with a minor amount of boehmite and has a surface area of 250 m /g. Alternatively, the trihydrate is heated very rapidly at 400-800 °C to form an amorphous alumina with a higher surface area, 300-350 m /g. The major impurity in these products, besides water (typically 6%), is Na20 at nearly 1%. The micropore volume is shown in Figure 6.1, but there is a considerable number of pores with sizes... 

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