Alumina forms

Alkali metal haHdes can be volatile at incineration temperatures. Rapid quenching of volatile salts results in the formation of a submicrometer aerosol which must be removed or else exhaust stack opacity is likely to exceed allowed limits. Sulfates have low volatiHty and should end up in the ash. Alkaline earths also form basic oxides. Calcium is the most common and sulfates are formed ahead of haHdes. Calcium carbonate is not stable at incineration temperatures (see Calcium compounds). Transition metals are more likely to form an oxide ash. Iron (qv), for example, forms ferric oxide in preference to haHdes, sulfates, or carbonates. SiHca and alumina form complexes with the basic oxides, eg, alkaH metals, alkaline earths, and some transition-metal oxidation states, in the ash. 

When aluminium is immersed in water, the air-formed oxide film of amorphous 7-alumina initially thickens (at a faster rate than in air) and then an outer layer of crystalline hydrated alumina forms, which eventually tends to stifle the reaction In near-neutral air-saturated solutions, the corrosion of aluminium is generally inhibited by anions which are inhibitive for iron, e.g. chromate, benzoate, phosphate, acetate. Inhibition also occurs in solutions containing sulphate or nitrate ions, which are aggressive towards iron. Aggressive anions for aluminium include the halide ions F ,... 

Seeding. This process relies on addition of approximately 2 percent of / "-alumina seeds to powders, which increases the amount of / " -alumina formed. 

Alumina - Alumina forms a variety of oxides and hydroxides whose structures have been characterized by X-ray diffraction (16). From the catalytic viewpoint y-alumina is the most important. This is a metastable phase that is produced from successive dehydration of aluminum trihydroxide (gibbsite) to aluminum oxide hydroxide (boehmite) to y-alumina, or from dehydration of boehmite formed hydrothermally. y-alumina is converted into a-alumina (corundum) at temperatures around 1000 C. 

At the O/S interface, for each molecule of alumina formed inside the oxide layer, i.e., three O2- ions transferred across the O/S interface, six hydrogen ions are formed. Thus, the acidity at the interface tends to rise to an extent which depends on the rate removal of these ions by some mechanism. In view of Eqs. (13) to (15), this should lead to oxide dissolution and a further decrease... 

PNNL [25] describes preliminary joining experiments using flexible foils made from an alumina-forming ferritic steel, DuraFoil [26], This foil was brazed to Haynes 214 alloy on the bottom side using BNi-2 braze tape. The foil was also brazed to YSZ (component of a cell) on the top side using Ag-4 mol% CuO. The foil was in... 

Conjugate addition of RN02 to enones. Primary nitroalkanes and a, (3-enones when activated by alumina form conjugate addition products that are oxidized in situ by alkaline hydrogen peroxide to 1,4-diketones. A similar reaction of nitromethane with a vinyl ketone provides 1,4,7-triketones. 

Lippens (48) has studied the texture of the catalytically active aluminas by means of diffraction and adsorption techniques. He concluded that the structure of tj-alumina formed from bayerite consists of lamellae with an average thickness of about 15 A and a distance of about 25 A. y-Alumina prepared from gelatinous boehmite is composed of fibrillar-shaped particles of about 30 X 30 A. Both structures can easily account for the pseudosolvent effect of alumina, which will be referred to in more detail in the forthcoming discussion. 

High-area aluminas (AI2O3) can be easily prepared by precipitating alumina from aqueous solution and drying and heating as for silica. This material is ciystaUine, and the major phase is called y-alumina with a surface area up to -200 mVg. Alumina forms a porous network as the water is removed. 

Alumina forms hydroxide in aqueous alkaline solution. The reaction is slow. The products, aluminum hydroxides (hydrated aluminas), contain hexacoordinated aluminohydroxide anion ... 

The Al203 Si02 ratio influences the dehydration characteristics of analcite only to a limited extent. Both high and low alumina Na-analcites dehydrate in a continuous fashion. However, the high alumina form undergoes water loss beginning at lower temperatures and is more nearly reversible. The overall crystal chemical relationships are summarized in Table II. 

The relationship between the two catalytic components is quite complex. Interactions between the support and the hydrogenation component can alter this relationship. For example, Larson et- al. (6) showed that, with platinum on silica-alumina, a selective adsorption of platinum by acid sites causes a reduction in catalyst acidity. Similarly, nickel reacts with the acid sites on silica-alumina forming nickel salts of the silica-alumina acid sites. It has been suggested (J) that one of the effects of sulfiding a nickel on... 

Figure 3.13. Top when annealed at high temperature, a thin film of Cu on monocrystalline alumina breaks and forms micron-size particles. Bottom SEM micrograph of a Cu monocrystalline particle on (0001) face of alumina formed after annealing at 1040 C. The facet on the top of the particle is a (111) plane. From (Soper et al. 1996) [11],...

Work on one particular ferritic steel, Fecralloy, for fabrication of catalyst substrates was pioneered by the United Kingdom Atomic Energy Authority at Harwell and Johnson Matthey, in collaboration with Resistalloy, which developed technology for producing thin strip [32]. This and related alloys, in addition to iron, chromium, and aluminum, contain low levels of elements such as yttrium (0.1-3.0%), thought to enhance the protective properties of the surface alumina layer. Alumina forms by the oxidation of bulk... 

We have found out the volume expansion coefficient could be reached 3.1 that is larger than previously reported maximum values of 1.6-1.7 [6]. The high volume expansion coefficient is caused by enhancing of the sulphuric content inside porous alumina formed at high field anodising. The high volume expansion also results in low porosity of alumina, which was about 3%. This is smaller than known minimal porosity of 5% for a sulphuric electrolyte [1]. 

Porous anodising at high current densities provides the formation of selfordering structures without pretexturing treatment [1], Fig. 3 shows SEM images of porous alumina formed at 70 V. Self-ordering occurs with the porous growth (Fig. 3a). 

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