Burned alumina

Aluminum sesquioxide, or a-alumina (a-Al Oj), also called calcined alumina (CA) or burned alumina in the ceramic and refractory industries, is the final product resulting from the thermal decomposition of all aluminum hydroxides. Actually, in the temperature range 1000-1250°C, the exothermic transformation of transition aluminas into a-Al Oj occurs... 

Chemical recovery ia sodium-based sulfite pulpiag is more complicated, and a large number of processes have been proposed. The most common process iavolves liquor iaciaeration under reduciag conditions to give a smelt, which is dissolved to produce a kraft-type green liquor. Sulfide is stripped from the liquor as H2S after the pH is lowered by CO2. The H2S is oxidized to sulfur ia a separate stream by reaction with SO2, and the sulfur is subsequendy burned to reform SO2. Alternatively, ia a pyrolysis process such as SCA-Bidemd, the H2S gas is burned direcdy to SO2. A rather novel approach is the Sonoco process, ia which alumina is added to the spent liquors which are then burned ia a kiln to form sodium aluminate. In anther method, used particulady ia neutral sulfite semichemical processes, fluidized-bed combustion is employed to give a mixture of sodium carbonate and sodium sulfate, which can be sold to kraft mills as makeup chemical. 

Zirconium oxide is fused with alurnina in electric-arc furnaces to make alumina—zirconia abrasive grains for use in grinding wheels, coated-abrasive disks, and belts (104) (see Abrasives). The addition of zirconia improves the shock resistance of brittle alurnina and toughens the abrasive. Most of the baddeleyite imported is used for this appHcation, as is zirconia produced by burning zirconium carbide nitride. 

The activation energy for burning from a coked zeoHte has been reported as 109 kj/mol (29) and 125 kj/mol (30 kcal/mol) has been found for coke burning from a H-Y FCC catalyst. Activation energies of 167 kJ/mol (40 kcal/mol) (24) and 159 kJ/mol (25) have been reported for the burning of carbon from a coked amorphous siUca-alumina catalyst. 

Fireclays can be dividea into plastic clays and hard flint clays they may also be classified as to alumina content. Firebricks are usually made of a blended mixture of flint clays and plastic clays which is formed, after mixing with water, to the requirea shape. Some or all of the flint clay may be replaced by highly burned or calcined clay, called... 

Troublesome amounts of C and Q acetylenes are also produced in cracking. In the butadiene and isoprene recovery processes, the acetylenes in the feed are either hydrogenated, polymerized, or extracted and burned. Acetylene hydrogenation catalyst types include palladium on alumina, and some non-noble metals. 

PVA was used as a temporary binder owing to its water solubility, excellent binding strength and clean burning characteristics. To prepare the PVA solution, 4 g of PVA were added to 100ml distillated water. The mixture was heated and stirred vigorously until all the PVA was dissolved in the water. This took about half an hour. Peptisation was done by addition of 5 ml 1M HN03 to the solution. Finally, the solution was refluxed for 4 hours. The PVA solution was used in the preparation of the zirconia-alumina sol-gel solution. The preparation of the PVA solution can be summarised as follows ... 

Several varieties of technical activated alumina were used. After three or four runs the catalyst becomes covered with a brown tar and the yield of dihydropyrane decreases. The catalyst may be regenerated by igniting it at red heat until the tar is burned off. The checkers used 8-14 mesh activated alumina from the Aluminum Ore Company of America. The catalyst was reactivated at 450° by drawing a slow stream of air through it until the tar was burned off. 

It is of interest to note that the polymer containing ZnSn(OH) does not burn in air even at 250°C and, accordingly, this composition has a temperature index of at least 50°C above that of the rubber containing ATH alone. The 01 and high temperature 01 data therefore provide substantial evidence as to the benefit of using ZnSn(OH) as a flame-retardant synergist with alumina trihydrate filler. 

A variety of material could be used as the basis for cracking catalyst, including synthetic silica-alumina, natural clay, or silica-magnesia. If these materials did not contain significant amounts of metals such as chromium or platinum that catalyzed the burning of carbon, the burning rate of the coke is independent of the base as shown in Fig. 7. 

Fig. 9. A comparison of the results computed from Eq. (12) for transitional burning (indicated by O) with the observed burning rate behavior for silica-alumina catalyst (solid curve).

The Pt current collector was first used to deposit short ( 2 pm) Pt nanoposts [37,73] into the template membrane (Fig. 21A). These Pt nanoposts anchor the alumina membrane to the Pt surface and will serve to make electrical contact to the LiMu204 nanotubes. After Pt deposition, the pores in the membrane were filled with an aqueous solution that was 0.5 M in LiNOs and 1 M in Mn(N03)2 (Fig. 21B). The excess solution was wiped from the membrane surface, and the solvent (water) was removed by heating (50°C) in vacuum for 1 hour. The assembly was then heated at 500°C in air for 5 hours. This burns away the plastic tape and also causes tubules of LiMu204 to form within the pores (Figs. 21C, 22). 

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