Aluminum oxide grain growth

Figure 24.22 Reprinted from Kaysser, W.A., Sprissler, M., Handworker, C.A., and Blendell, J.E. (1987) Effect of a liquid phase on the morphology of grain growth in alumina, J. Am. Ceram. Soc. 70 339. With permission from Blackwell Publishing and the American Ceramic Society. See also R. D. Monahan, R.D. and Halloran, J.W. (1979) Single-crystal boundary migration in hot-pressed aluminum oxide, J. Am. Ceram. Soc. 62, 564.

Adding carbon or carbon-containing compounds such as aluminum carbide, SiC or related compounds to remove any boron oxide layers from the boron carbide particle surface. This in turn will increase the surface energy and inhibit exaggerated grain growth due to evaporation-condensation [382]. 

Pentacene (Fig. 25.3) is a typically studied small molecular material since the charge transport properties were reported to be excellent (Farchioni and Grosso, 2001). As its important feature, pentacene can form the well-ordered thin film on oxidized silicon. The study shows that the smallest stable island consists of four molecules in monolayer films (Ruiz et al., 2003). The single-crystal grain can be achieved under appropriate growth conditions (Meyer zu Heringdorf et al., 2001). It also can be deposited on aluminum oxide and metal. Brinkmann et al. have shown that pentacene can be deposited onto polymer film (Brinkmann et al., 2003). 

Fine flakes of A1 immediately form an oxide layer (AI2O3). When this powder is used to make sintered alloys, the oxide is retained as a dispersoid. This oxide prevents grain growth as well as dislocation motion, thus producing a high strength, high creep resistant sintered aluminum powder (SAP) alloy. 

The microstructures of ceramic matrices grown from two different classes of alloys have been reported. The external growth surface of ceramic matrices grown from an Al-Si-Mg alloy in the absence of a reinforcement was covered by a thin ( 1- to 4-gm) layer of MgO that sometimes contained up to 5% MgAl204 [33]. The external MgO layer typically was separated from the interconnected A1203 matrix by a thin aluminum alloy (1- to 3-gm) layer. Only rarely was an A1203 grain found in direct contact with the external oxide layer. Within the bulk of the composite, the metallic channels typically were 3 to 8 /tm in width. 

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