AljOj

Plot of pMp° - p) against p/p° (r is expressed in cm (stp)). (1) Unpromoted Fe catalyst (2) AljOj-promoted Fe catalyst (3) AI2O3-KjO-promoted Fe catalyst (4) fused copper catalyst (5) chromium oxide gel (6) silica gel. (Courtesy Brunauer, Emmett and Teller.)... 

Fig. 16.1. Ionic ceramics, (a) The rocksalt, or NoCl, structure, (b) Magnesia, MgO, has the rocksalt structure. It can be thought of as an f.c.c. packing with Mg ions in the octahedral holes. ( ) Cubic zirconia ZrOj an f.c.c. packing of Zr with O in the tetrahedral holes, (d) Alumina, AljOj a c.p.h. packing of oxygen with Al in two-thirds of the octahedral holes.

Fig. 16.6. A typical ceramic phase diagram that for alloys of SiOj with AljOj. The intermediate compound...

Copper (Cu) and zinc (Zn), when mixed, form the alloy brass. Magnesia (MgO) and alumina (AljOj) when mixed in equal proportions form spinel. Iron (Fe) and carbon (C) mix to give carbon steel. 

At the alumina plant, the bauxite ore is further crushed to the correct particle size for efficient extraction of the alumina through digestion by hot sodium hydroxide liquor. After removal of "red mud" (the insoluble part of the bauxite) and fine solids from the process liquor, aluminum trihydrate crystals are precipitated and calcined in rotary kilns or fluidized bed calciners to produce alumina (AljOj). Some alumina processes include a liquor purification step. 

Corundum (AljOj) Vegetable oil mists (except castor cashew nut, or similar irritant oils) Sucrose, Tin Oxide, Titanium Dioxide Silicoh Carbide... 

Each of these grades has a minimum aluminum content of 27 percent, expressed as AljOj, and maximum FejOj and soluble contents of 0.75 percent and 0.5 percent, respectively. 

The fluorine industry is intimately related to aluminum production. Aluminum oxide, (AljOj) is electrolyzed to metallic aluminum with a flux of sodium fuoroaluminate (Na AlF,), called cryolite - a rare mineral found in commercial quantities only in Greenland with other uses glass, enamels, and as a filler for resin-bonded grinding wheels. 

The cyano group in aromatic nitriles can be converted directly to a methyl group in vapor phase over 30% Ni-on-AljOj prereduced by hydrogen i>i situ... 

Palladium may not be preferred for dihydric aromatics. Dihydroresorcinol was obtained in 87% yield by alkaline hydrogenation of resorcinol over 5% Rh-on-C (65) and in only 50-60% yield over Pd-on-C 15). A 77% yield of the dione was obtained by alkaline hydrogenation of 3,5-dihydroxyphenylacetic acid over a 10% loading of 5% Rh-on-AljOj at 55"C and 55 psig (39a). 

For the same 300-ton inventory unit, assume the alumina (AljOj) contents of the present and new fresh catalysts are 48 wt% and 38 wt%, respectively. Sixty (60) days after the catalyst switch, the alumina content of E-cat is 43 wt%. Determine % changeover ... 

Vermilyea" has adopted a thermodynamic approach to pitting, and considers that the critical pitting potential is the potential at which the metal salt of the aggressive ion (e.g. AICI3) is in equilibrium with metal oxide (e.g. AljOj). On the basis of this theory the critical pitting potential should decrease by 0-059V per decade increase in chloride ion concentration. Vermilyea s theory successfully predicts the values of the critical potentials for Al, Mg, Fe and Ni, but in the case of Zr, Ti and Ta there are large discrepancies. 

Other 7i-type oxides areTiOj, CdO, AljOj and VjOj. For TiOj, the reaction giving the non-stoichiometry is ... 

With some alloying elements, e.g. Si and Al, the concentration of element required in the lattice to form their own oxide is so low that preferential formation of pure AljOj or SiOj, which are both highly protective, may occur. For the reaction... 

The diffusion coefficient for S in AljOj at 950°C is approximately 100 times lower than that in CrjOj. Hence, for high-temperature applications in S environments, aluminium confers a much greater degree of protection than that afforded by chromium. 

Radiochemical studies indicate that the pore base is the actual site of formation of aluminium oxide, presumably by transport of aluminium ions across the barrier-layer, although transport of oxygen ions in the opposite direction has been postulated by some authorities. The downward extension of the pore takes place by chemical solution, which may be enhanced by the heating effect of the current and the greater solution rate of the freshly formed oxide, but will also be limited by diffusion. It has been shown that the freshly formed oxide, y -AljOj, is amorphous and becomes slowly converted into a more nearly crystalline modifipation of y-AljO . 

The effect of hot water sealing is to convert anhydrous y-AljO, into the crystalline monohydrate, AljOj.HjO, which occupies a greater volume and blocks up the pores, thus preventing further absorption of dyes or contaminants. The monohydrate is also less reactive. 

Al,0,-3Hj0 hydrargillite a AljOj-SHjO bayerite b AlA-HjO bohmite c... 

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