Aluminium hydroxide surface modification

Many surface modifications are used with aluminium hydroxide, which responds to both silane and fatty acid treatments. Special proprietary silane coatings seem to be preferred for polypropylene applications [99]. Despite the production being water based, the preference seems to be for dry coating procedures. 

Alumina. Alumina (aluminium oxide) (Figure 3.3) can be synthesised to the same degree of purity and specification as silica gel by a series of non-uniform dehydration processes of various crystalline modifications of aluminium hydroxide [51]. Furthermore, the reaction conditions can be adjusted to produce aluminium oxide with either an acidic, basic or neutral surface it can be used with or without a binder and the use in the latter form is more common than with silica. 

Our results indicated that the presence of titanium intti alunt i induce changes in texture and surface properties of the carrier. Results of Table 1 indicatei hat coprecipitation of both titania and aluminium hydroxides produce solids with higho sui ce area than pure yalumina synthesized under the same conditions. This increase in surface area with increase in TIO2 loading in the 0-lS wt% HO2 is aoctmfianied i) a ermtinuous decrease in pore size distribution, ii) modification of ZPC toward lower pH values and iii) a simultaneous increase in surface acidity. 

C. M. Liauw, G. C. Lees, and S. J. Hurst, The effect of filler surface modification on the mechanical properties of aluminium hydroxide filled polypropylene. Plastics Additives and Compounding, 24 (1995), 249-60. 

After 5 days of aging treatment, grain boundaries appeared on SEM micrographs. Surface modifications is assumed to be due to formation of volatile aluminium hydroxides, as expected by themodynamic modelUng [9], As the corrosion phenomenon remains limited to the surface, it is not affecting the stability of the foam in the bulk. As a proof, mechanical resistance of alumina foams is kept constant before and after aging the compressive crash strength of 10 ppi alumina foams with 85% apparent porosity has been measured at 2 MPa. 

The same considerations apply to the surfaces of the many crystalline modifications of aluminium oxide (Boehm 1966). Besides a-A Os (corundum) there are at least eight oxides mostly classed under the term of Y-AI2O3 (cf. Ginsberg et al. 1957). Some of these forms may be non-stoechiometric oxide-hydroxides. 

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