Alumina mechanical properties

Keywords Porous alumina Mechanical properties freeze casting pore biocompatibility... 

The gel-based products have traditionally been the most expensive and highest performance activated alumina products. They have very good mechanical properties, high surface area, and their purity and ganima-aluniina stmcture make them somewhat resistant to thermal degradation. On the other hand, they are the most difficult to manufacture and disposal of by-product salts can present an environmental problem. 

Note The principal reinforcement, with respect to quantity, is glass fibers, but many other types are used (cotton, rayon, polyester/TP, nylon, aluminum, etc.). Of very limited use because of their cost and processing difficulty are whishers (single crystals of alumina, silicon carbide, copper, or others), which have superior mechanical properties. 

Attempts have been made to improve the mechanical properties of these cements by adding reinforcing fillers (Lawrence Smith, 1973 Brown Combe, 1973 Barton et al, 1975). Lawrence Smith (1973) examined alumina, stainless steel fibre, zinc silicate and zinc phosphate. The most effective filler was found to be alumina powder. When added to zinc oxide powder in a 3 2 ratio, compressive strength was increased by 80 % and tensile strength by 100 % (cements were mixed at a powder/liquid ratio of 2 1). Because of the dilution of the zinc oxide, setting time (at 37 °C) was increased by about 100%. As far as is known, this invention has not been exploited commercially. 

As a result, several inorganic compounds have found application in this field, and alumina trihydrate, A1(0H)-, is now by far the highest volume flame retardant (3). Its use, however, is limited to those polymers which can tolerate the exceptionally high loadings required to be effective, without seriously affecting the mechanical properties of the substrate (7 ). 

Most of the adsorbents used in the adsorption process are also useful to catalysis, because they can act as solid catalysts or their supports. The basic function of catalyst supports, usually porous adsorbents, is to keep the catalytically active phase in a highly dispersed state. It is obvious that the methods of preparation and characterization of adsorbents and catalysts are very similar or identical. The physical structure of catalysts is investigated by means of both adsorption methods and various instrumental techniques derived for estimating their porosity and surface area. Factors such as surface area, distribution of pore volumes, pore sizes, stability, and mechanical properties of materials used are also very important in both processes—adsorption and catalysis. Activated carbons, silica, and alumina species as well as natural amorphous aluminosilicates and zeolites are widely used as either catalyst supports or heterogeneous catalysts. From the above, the following conclusions can be easily drawn (Dabrowski, 2001) ... 

In this chapter, we describe the synthesis and characterisation of the microstructure and properties of layered-graded alumina-matrix composites through liquid infiltration. This approach is relatively simple and offers excellent control over the depth of the graded layer. The presence of a graded dispersion of reinforced particles in the alumina matrix has a profound influence on the physical and mechanical properties of the composites. An overview of the infiltration kinetics and the use of the infiltration process as a new philosophy for tailoring novel graded ceramic systems are also presented. 

Table 5.1 Mechanical properties of graded mullite/alumina...

Marple, B.R. Green, D.J. (1991) Mullite/alumina particulate composites by infiltration processing III, Mechanical properties. J. Am. Ceram. Soc. 74, 2453-2459. 

Pratapa, S. Low, I.M. (1998) Infiltration-processed functionally-graded AT/alumina-zirconia composites II, Mechanical properties. J. Mater Sci. 33, 3047-3053. 

Travitzky, N.A. Shlayen, A. (1998) Microstructure and Mechanical Properties of Alumina/Cu-O. Material Science and Engineering, A224, 154—160. 

Sekino, T., Niihara, K., Fabrication and mechanical properties of fine-tungsten-dispersed alumina-based composites, J. Mater. Sci., 1997, 32(15) 3943. 

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