High alumina content

During the period 1940-1962, the cracking catalysts used most widely commercially were the aforementioned acid-leached clays and silica-alumina. The latter was made in two versions low alumina (about 13% AI2O3) and high alumina (about 25% AI2O3) contents. High-alumina-content catalysts showed a higher equilibrium activity level and surface area. 

The relationship between aluminous sepiolite and the magnesian form is not at all clear as yet. The question of whether or not aluminous sepiolite can be precipitated directly from solution should be posed since alumina concentration in alkaline solutions (pH 7-9) is assumed to be quite low. For the present, palygorskite should probably be considered as a phase produced through solid-solution equilibria due to its high alumina content. Possibly most sepiolites are produced in this way. Even the inonomineralic deposits in saline lakes or deep sea cores contain sepiolites with high alumina contents (Parry and Reeves, 1968 McLean, et al., 1972). 

Andreu et ah (11) explained the increased activity (with increasing alumina content of amorphous silica-alumina catalysts) for cracking of sec-butylbenzene by the greater density of acid sites in the high-alumina-content catalysts. Adams et ah (12) proposed that the interaction of several active sites with reactant molecules in mordenite catalysts was partly responsible for the rapid rate of activity loss. 

Abrasiveness at different temperatures of refractories with high alumina content, at a load of 147 kPa and test time 5 h (after Schwiete, 1965)... 

Controlled Pore Size, High Alumina Content Silica—Aluminas... 

To obtain a uniform mineralogical composition with a high alumina content (AI2O3 content > 37%), the raw kaolin is elutriated and simultaneously classified in hydrocyclones, whereupon kaolinite and the other layer silicates are separated from the accompanying quartz and feldspar on the basis of their different particle size distributions. 

Alumina-containing refractory linings are widely utilized in the steel industry. Bricks with high alumina contents are, due to their resistance to alkali slags, also used in the cement and glass industries. 

It is thus reasonable to believe that the Al20Fg species are dominant at low AI2O3 concentration while the Al202F4 species are predominant at high alumina contents. The two species are formed according to the reactions... 

The unit cell dimension of P-L (a-direction) is compatible with the high alumina content observed. However, there is a drastic drop in adsorption capacity which I believe is owing to occlusion of phosphate. Do you think that the larger number of cations explains the lower sorption capacity ... 

Continued research led to improvements so that the first commercial high alumina catalyst was produced by American Cyanamid Co. in 1954, this time in cooperation with Shell Development Co. (53). These catalysts contained about 25% alumina and had significantly higher pore volumes than earlier formulations. These new high-alumina catalysts had higher activity with essentially the same product distribution, exhibited a slower deterioration of activity and had better attrition properties. In later years, with zeolitic catalysts, high alumina contents in the catalyst matrix were employed for stability enhancement, and then for a host of other improvements in overall performance. 

However, specially shaped refractory bricks with curved surfaces (used for manhole arches or for lining circular shapes of furnaces) or with high alumina content of 65-70 % are manufactured only as per special order placed by clients in limited numbers. 

The electrolysis cell is best constructed of a refractory of high alumina content, and containing as little silica as possible, owing to the ready attack of silica by thorium metal. The small-scale cell illustrated in Fig. 7.6, however, uses a silica pot and care is taken to prevent thorium metal contacting the silica wall or base. The small, 6 kg scale, model is heated externally, although a more conventional internal heating system is necessary for a production scale cell. 

All ceramic proppant producers use as feedstock essentially bauxite and, to a lesser extent, other industrial minerals with a high alumina content such as kaolin, nepheline syenite, wollastonite, talc, and feldspars. The final spherical shape is obtained by several processing routes currently used in the ceramics industry for producing beads and other particulate materials. The most common of these processes are pelletizing and sintering, atomization, fire polishing, and flame spraying. 

A refractory cement (non-hydraulic) of high alumina content. 

A high alumina content is required to achieve a high thermal conductivity in alumina-based substrate. This effect is illustrated by the data in Table 2.13, which shows that the thermal conductivity decreases by 13 percent when the alumina content is lowered from 99 to 98 percent, and by 50 percent when the alumina content is lowered to 85 percent. 

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