Structure 78-80 Aluminium source

Methods. The crystallization of silicoaluminate mixtures into zeolite omega in the temperature range 105-130°C was performed in the presence of a structure-directing mixture (SDM) (10,11). The method gives minimum overlap between the nucleation and growth steps as indicated by the very homogeneous distribution of size of the crystals in the final product. The use of kaolinite as the aluminium source presents two main advantages (10). First, the low solubility of the clay under the crystallization conditions prevents the formation of a gel. Second, under the low supersaturation levels achieved, secondary nucleation is hindered. 

The facility was operated for the first time in May 1969, and since 1973 it is out of operation because of corrosion problems in the structural aluminium tubes and in the spacing plates, one of them particularly highly corroded. At present, the fuel is kept in storage boxes, and the tank is empty. The neutron source is in its storage device, which is appropriately shielded. The fuel cylinders are in good condition and are periodically inspected thoroughly by visual and X ray inspection. 

The key property required of the inorganic species is ability to build up (polymerize) around the template molecules into a stable framework. As is already evident in this article, the most commonly used inorganic species are silicate ions, which yield a silica framework. The silica can be doped with a wide variety of other elements (heteroatoms), which are able to occupy positions within the framework. For example, addition of an aluminium source to the synthesis gel provides aluminosilicate ions and ultimately an aluminosilicate mesoporous molecular sieve. Other nonsilica metal oxides can also be used to construct stable mesoporous materials. These include alumina, zirconia, and titania. Metal oxide mesophases, of varying stability, have also been obtained from metals such as antimony (Sb), iron (Fe), zinc (Zn), lead (Pb), tungsten (W), molybdenum (M), niobium (Nb), tantalum (Ta), and manganese (Mn). The thermal stability, after template removal, and structural ordering of these mesostructured metal oxides, is far lower, however, than that of mesoporous silica. Other compositions that are possible include mesostructured metal sulfides (though these are unstable to template removal) and mesoporous metals (e.g., platinum, Pt). 

The surfaces of colloidal particles are often charged and these changes can arise from a number of sources. Chemically bound ionogenic species may be found on the surface of particles such as rubber or paint latex particles. Charged species may be physically adsorbed if ionic surface active materials, for example, have been added. A charged surface may occur on a crystal lattice. An example is the isomorphous substitution of lower valency cations such as aluminium for silicon in the lattice structure of clays. A further example is the adsorption of lattice ions... 

A wide choice of precoated thin-layer plates may be purchased from commercial sources. These plates are standardised, both by their textural structure and granulometry. In general, their quality is superior to the manually prepared plates. In addition, the discovery and use of organic polymer binders permit excellent adherence of the layers. The thin-layer support is generally glass, aluminium, or plastic sheets, supplied as plate or sheets, but sometimes rolls are also available. 

Source of Activity in other Siliceous Catalysts.—Although various oxides can be combined with silica to give amorphous, acidic catalysts, the replacement of aluminium in zeolites (specially non-faujasitic zeolites) has proved to be very difficult with any element other than gallium. Materials of ZSM-5 structure with iron or boron in place of aluminium have been claimed recently, but it is not yet certain that either iron or boron is part of the zeolite lattice or that the catalytic activity observed is not due to residual lattice aluminium. 

The electrical properties of the films were determined on aluminium/insu-lator/gold (MIM) structures. The capacitance was measured with a LCR Meter (Agilent 4284 A) at a frequency of 1 kHz. The specific resistance and the breakdown field strength were measured using a Source-Measure-Unit (SMU, Keithley 6430). The film thickness was determined by scanning electron microscopy (SEM). 

For the preparation of washcoated monoliths the suspensions of sol-aluminium hydroxide with pseudoboehmite structure have been used. This sol formed during the reaction between the hydroxide and nitric acid serves both as a binder and a source of y-A Oa in the final product after calcination. Salts of additives were introduced into sol. The influence of the following parameters on the formation of thermostable washcoated layer have been studied concentration of anhydrous alumina in the sol amount of added HNO3 dipping time number of dippings drying and calcination duration. 

In some of the AlP04-n molecular sieves discovered in 1982 [1], it is possible to substitute part of the P and Al framework elements with Si [2]. In the resulting SAPO-n materials, isolated Si atoms occupy P sites, while patches of Si atoms replace locally P as well as Al atoms [3,4]. The degree of Si substitution and the substitution mechanism depend on the topology of the framework and on the synthesis method [4,5]. While the synthesis method does not seem to be critical for the incorporation of traces of Si in SAPO-5 and SAPO-11, extensive Si incorporation in these structures can be achieved only by using very specific synthesis recipes [4,6]. Silicon-rich crystals of SAPO-5 and SAPO-11, e.g., can be prepared by using aluminium isopropoxide as a source of aluminium and specific templates, viz. dipropylamine for SAPO-11 and cyclohexylamine for SAPO-5 [4,6]. 

Aluminosilicate gels are prepared by the mixing of reactive sources of alumina and silica. These include fumed silica, silica sols and alkoxides of silica, and aluminium, aluminates, aluminium salts and alkoxides of aluminium. Other synthetic routes have been explored that use structured aluminosilicate precursors, such as zeolites themselves, to supply aluminate and silicate species to... 

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