Thickeners alumina

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 ,... 

Use anionic polymers such as polyacrylic acids cross-linked with allyl ethers of pentaerythritol or sucrose as thickeners, if a gel structure and pseudoplastic (shear-thinning) properties are desirable. Consider adding colloidal alumina to further increase the viscosity at pH 13 [ 15]. 

This reaction is used, also, to a very small extent in calico-printing. A hyposulphite of alumina is formed in the cold by adding a solution of chloride of aluminium to a sol ution of hyposulphite of soda. The result is a solution of chloride of sodium and hyposulphite of alumina. This Is thickened iu the regular manner, and printed on the fabrio. The piece is then exposed to a temperature of 212° by means of steam, when the salt is decomposed, alumina being deposited on or in the cloth. Tin s alumina so deposited dyes np with madder precisely like the alumina precipitated in the ordinary manner from the acetate. 

In the process to produce alumina (Fig. 1), bauxite is crushed and wet ground to 100-mesh, dissolved under pressure and heated in digesters with concentrated spent caustic soda solution from a previous cycle and sufficient lime and soda ash. Sodium aluminate is formed, and the dissolved silica is precipitated as sodium aluminum silicate. The undissolved residue (red mud) is separated from the alumina solution by filtration and washing and sent to recovery. Thickeners and Kelly or drum filters are used. The filtered solution of sodium aluminate is hydrolyzed to precipitate aluminum hydroxide by cooling. The precipitate is filtered from the liquor, washed, and heated to 980°C in a rotary kiln to calcine the aluminum hydroxide. 

Microsphere Formation. Because the microspheres were fabricated using a batch process, we monitored the viscosity and pH of the catalyst slurry as it aged. Figure 2 shows that the viscosity of the slurry was dependent on both the age of the slurry and the additive type. The reference formula was stable for 3 h, but the CP-alumina and pseudoboehmite formulations thickened or gelled in the same time period. A typical batch starting at pH 3.0 increased to about pH 3.3 before the onset of thickening (about 100 cP). For CP formulations, the onset of thickening may be related to the median particle size of the powder. 

We believe the effect of alumina additives on catalyst slurry viscosity is associated with the surface reactivity of the additive. OH" is a catalyst for polymerization and Si-O-Si bonding of uncondensed silanols higher pH promotes conversion to a solid phase consisting of discrete silica particles (19). Ostermaier and Elliott (15) suggest that pH be carefully controlled at a value less than 3.5, or thickening occurs in the alumina-free reference formula. 

Thickening agent Polyacrylate polymer, clay, alumina 0-10... 

Some of the voluminous literature on the oxidation and corrosion of aluminum and its alloys has a direct bearing on DMO. Pure aluminum is normally covered by an amorphous native oxide film which is partially converted to 7-alumina at the interface between the parent metal and the amorphous oxide when heated to 450°C in dry air [7-9]. This unusual behavior is explained by growth of the amorphous phase, through outward cation migration, while thickening of the 7-alumina is by epitaxial growth on the parent metal, controlled by inward oxygen diffusion. Termination... 

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