Effect of alumina content

Fig. 10. Effect of alumina content on the electrical resistivity of alumina-added yttria stabilized zirconia. From ref. [24], This paper was originally presented at the Fall 1989 Meeting of the Electrochemical Society held in Hollywood, Florida.

A qualitative effect of alumina incorporation in silica has been described alumina is a stabilizing agent for silica hydrogel texture. Thus, it is also interesting to study the effect of alumina content on the texture of silica-alumina gel. 

Fig. 18. Effect of alumina content on specific gravity of heat-treated silica-alumina...

Effect of alumina content on dimethyl ether and methanol yields over catalysts of Cu/ZnO=3/7, together with other oxides... 

TABLE 2.13 Effect of Alumina Content on the Thermal Conductivity of Alumina Substrates... 

For the methanation reaction in the process of converting coal to a high Btu gas, various catalyst compositions were evaluated in order to determine the optimum type catalyst. From this study, a series of catalysts were developed for studying the effect of nickel content on catalyst activity. This series included both silica- and alumina-based catalysts, and the nickel content was varied (Table I). 

Figure 7.19 Effect of solids content in the milling of an alumina slurry on milling rate, expressed as cumulative mass percent fines. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

These results indicate that alumina acts on CrgOg phase to prevent its clustering and segregation with high coordinate Cr + ions. This dispersive effect of the support provides a suitable environment for the formation on the surface of low coordinate chromium ions (ref. 2). However this effect of alumina tends to depress when the content of chromium exceeds 30 % at 410°C. This result seems to Indicate a saturation of the surface sites of the support which interact with the chromium (surface of alumina covered with a layer of chromium oxide). Then an excess of Cr O deposited leads to its clustering and crystallization. Consequently the coordination of chromium ions changes from tetrahedral (low coordination) to octahedral (high coordination). 

The results are reported of a study of plate-out in PVC extrusion carried out using several analytical techniques, including DSC, SEM-EDX, FTIR spectroscopy and laser ionisation mass spectrometry. A special die and calibrator unit developed to investigate plate-out are illustrated and the reproducibility of the method evaluated. The effects of water content and anti-plate-out additives, such as alumina and silica, on plate-out are discussed and mechanisms explaining the formation of plate-out are proposed. 11 refs. 

Fig. 23. Effect of phosphorus content on the transition temperatures of alumina x in AIP3 refers to the atomic percentage of phosphorus. O (Ti), transition from amorphous to 7-alumina (A), transition from y-alumina to a-alumina [reprinted with permission from Abbattista et al. (26) copyright 1990 the Royal Society of Chemistry].

FIG. 21-184 Effect of liquid content of surface fracture, a-alumina and 5 wt % Celacol in water, with die (D = 9.5 mm, L = 3.14 mm) at a velocity V = 1.2 mm/s. Benbow and Bridgwater, Paste Flow and Extrusion, Ovford University Press, 1993, with permission.)... 

The newer data (106), showing complete restoration of the maximum activity by only about 5 x 10 ev/gm, are harder to reconcile with a water-removal mechanism, although the absolute amount of water to produce the sensitive catalyst cannot be estimated, since this sample was prepared by a 200° evacuation of the raw catalyst rather than by back-addition of water to a thoroughly pumped one. More data on the effect of water content on activity are obviously necessary if we wish to be able to judge the feasibility of water removal as a mechanism for the radiation effect on alumina. 

Figure 5 shows the effects of filler content on thermal shock resistance at c/R - 0.2 for composites of silicon nitride, silicon carbide, silica, and alumina. The thermal shock resistance of resin filled with silicon nitride increases linearly with the volume fraction. The value of the thermal shock resistance is high, especially at higher volume fraction (Vf > 40%), that is, thermal shock resistance reaches 140 K (Figure 5a). The thermal shock resistance of composite filled with silicon carbide increases rapidly with the increase of filler content, and it reaches 135 K at Vf of 40%, which is similar to the case of silicon nitride (Figure 5b). In the case of silica-filled composites there is also an increase, but above a 30% volume fraction a plateau is reached (Figure 5c). Alumina-filled composites show a decrease in thermal shock resistance with filler content, then an almost constant value starting at Vf = 20% (Figure 5d).

The effects of ceramic particles and filler content on the thermal shock behavior of toughened epoxy resins have been studied. Resins filled with stiff and strong particles, such as silicon nitride and silicon carbide, show high thermal shock resistance, and the effect of filler content is remarkable. At higher volume fractions (Vf > 40%), the thermal shock resistance of these composites reaches 140 K, whereas that of neat resin is about 90 K. The highest thermal shock resistance is obtained with silicon nitride. The thermal shock resistance of silica-filled composites also increases with increasing filler content, but above 30% of volume fraction it comes close to a certain value. On the contrary, in alumina-filled resin, the thermal shock resistance shows a decrease with increasing filler content. 

Figure 19 Effect of AI2O3 content in alumina-rich spinel on slag penetration resistance of AI2O3-spinel castables. (From Ref. 49.)...

Ko YC, Chan CF. Effect of spinel content on hot strength of alumina-spinel castables in the temperature range 1000 1500°C. J Euro Ceram Soc 1999 19 2633 2639. 

Figure 8-3 is explained as follows. With an increasing content of alumina, the intensity of silicon Ka decreases progressively below the value to be expected from Equation 7-1. The deviation is a negative absorption effect that can be calculated according to Equation 7-6. The intensity of aluminum Ka, on the other hand, behaves quite differently as the silica content increases. This intensity then increases... 

In this work, various Ru-BINAP catalysts immobilized on the phosphotungstic acid(PTA) modified alumina were prepared and the effects of the reaction variables (temperature, H2 pressure, solvent and content of triethylamine) on the catalytic performance of the prepared catalysts were investigated in the asymmetric hydrogenation of dimethyl itaconate (DMIT). 

This interpretation of the experimental data is supported by the differences observed in the deactivation patterns and carbon contents after test, since one notorious effect of Hjp is the capacity to diminish the deactivation caused by coke deposition on the active sites [21,22]. This is supposed to be due to a reaction with the coke precursors, very likely a hydrogenolysis. In pure silica-aluminas, where no source of spillover is present, no special protection against deactivation should be observed. Indeed, the silica-aluminas lose most of their activity (about 80%) before reaching the steady-state and present the highest carbon contents after catalytic test. On the other hand, in the case of the mechanical mixtures, where spillover hydrogen is continuously produced by the CoMo/Si02 phase and can migrate to the silica-alumina surface, the predicted protection effect is noticed. The relative losses of activity are much lower... 

In the aluminum electrowinning process a phenomenon called the anode effect is normally encountered when the alumina content in the electrolyte falls below 2%. The anode gets partially covered with a gas blanket and as a consequence, sparking occurs and the cell voltage fluctuates considerably due to frequent breaking and reestablishment of local contact between the anode and the electrolyte. A heavy current passes through the anode area... 

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