Whiskers alumina

Aluminate cement, 2 415-416 Aluminate ions, silica sols and, 22 394s Aluminates, 2 273-279 analysis, 2 275-276 chemical reactions, 2 273-274 dispersants, 8 710t economic aspects, 2 275 health and safety factors, 2 276 manufacture, 2 274-275 physical properties of, 2 273-274 uses of, 2 276-277 Alumina trihydrate (ATH), 2 274 in synthetic fillers, 11 314-315 Alumina whisker reinforcement, 5 574t Alumina xerogels, X-ray diffraction of, 23 78... 

Fig. 50. TG curve showing the formation of alumina whiskers during oxidation of iron-aluminum alloy in wet hydrogen (2%)/argon mixture (isothermal at 1555 °C). Sample weight 1000 mg...

Fig. 51. Schematic presentation of the course of the reaction during formation of alumina whiskers...

Fig. 52. Typical growth of alumina whiskers in an alumina crucible...

Figure 8 Alumina whisker-covered surface of a FecraIIoy -type metal monolith. The bar represents I xm. (From Ref. 77.)...

Figure 4.12. (a) TG curve showing formation of alumina whiskers in wet H2 20<,)/Ar atmosphere (72). (f>) schematic representation of reactions occurring during whisker formation (72). 

Zwinkels, M.F.M., Jaras, S.G., and Menon, P.G. (1994) Preparation of combustion catalysts by washcoating alumina-whiskers-covered metal monoliths using a sol-gel method. Proc. 6th Int. Symp. on Scientific Bases for the Preparation of Heterogeneous Catalysts, Louvain-la-Neuve, Belgium, Sep. 5-9, Vol. I, pp. 85-94. 

The coating of metallic monolith, which was more problematic than for ceramics, has been extensively studied and improved. Zwinkels et have shown that special treatment of metallic alloy generates an alumina whisker-covered surface. Those alumina whiskers act as an anchor and facilitate the stable washcoating with ceramics. 

Preparation of combustion catalysts by washcoating alumina whiskers-covered metal monoliths using a sol-gel method... 

Figure 1. Electron micrograph of the metal monolith surface, showing the alumina whiskers. The bar i---- represents 1 pm.

Roberts, J.M., Singh, J.P., and Scattergood, R.O. (2008) Microstructure and properties of alumina-whisker-reinforced tetragonal zirconia polycrystal matrix, in Ceramics Engineerir and Science Proceedings, voL 12 (7-8) (ecL J.B. Wachtman, Jr), The American Ceramic Society, Inc., Columbus, OH, pp. 1193-1200. 

The constmction material of metallic monoliths are alloys of iron, about 15-20 wL % chromium and 5 wt.% aluminium (Fecralloy). The unique feature of these alloys is the formation of a thin alumina layer (0.5 pm) on their outer surface when treated at temperatures above 850 °C [130]. Long alumina whiskers are formed at temperatures of around 900 °C and an oxidation time of greater than 12h (see Figure 10.6). This alumina layer then acts as an adhesion layer for the catalyst coating. On top of this, the alumina layer protects the alloy from corrosion, which allows the operation of ultra-thin Fecralloy foils at high temperatures. 

Figure 10.6 Alumina whiskers produced on the surface of Fecralloy by treatment in air at a temperature of 900°C for 22 h [130].

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