Defects interfacial

Interfacial defects are boundaries that have two dimensions and normally separate regions of the materials that have different crystal structures and/or crystallographic orientations. These imperfections include external surfaces, grain boundaries, phase boundaries, twin boundaries, and stacking faults. 

In spite of this disordered arrangement of atoms and lack of regular bonding along grain boundaries, a polycrystalline material is still very strong cohesive forces within and across the boundary are present. Furthermore, the density of a polycrystalline specimen is virtually identical to that of a single crystal of the same material. 

Phase boundaries exist in multiphase materials (Section 9.3), in which a different phase exists on each side of the boundary furthermore, each of the constituent phases has its own distinctive physical and/or chemical characteristics. As we shall see in subsequent chapters, phase boundaries play an important role in determining the mechanical characteristics of some multiphase metal alloys. 

A catalyst is a substance that speeds up the rate of a chemical reaction without participating in the reaction itself (i.e., it is not consumed). One type of catalyst exists as a solid reactant molecules in a gas or liquid phase are adsorbed onto the catalytic surface, at which point some type of interaction occurs that promotes an increase in their chemical reactivity rate. 

One important use of catalysts is in catalytic converters on automobiles, which reduce the emission of exhaust gas pollutants such as carbon monoxide (CO), nitrogen oxides (NO., where x is variable), and unburned hydrocarbons. (See the chapter-opening diagrams and photograph for this chapter.) Air is introduced into the exhaust emissions from the automobile engine this mixture of gases then passes over the catalyst, which on its surface adsorbs molecules of CO, NO , and O2. The NO dissociates into N and O atoms, whereas the O2 dissociates into its atomic species. Pairs of nitrogen atoms combine to form N2 molecules, and carbon monoxide is oxidized to form 

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To evaluate the rate coefficient in terms of the interfacial defect concentrations, it is thus necessary to evaluate Ci (8 ) and Ci (L ), utilizing one aspect of the interfacial zone equilibrium approximation. At thermal equilibrium... 

Wang R.S., Gu Q.L., Ling C.C., and Ong H.C. (2008) Studies of oxide / ZnO near-interfacial defects by photoluminescence and deep level transient spectroscopy Appl. Phys. Lett. 92 042105. 

This chapter has argued for the critical role of interfacial defects in solids. We have favored an artificial classification into three primary types of interfacial defects, namely, surfaces, stacking faults and twins, and grain boundaries. In each of these cases, it has been argued that a continuum description of the energetics of such... 

The discussion will be rounded out by our taking stock of microstructural evolution as seen from the more traditional metallurgical viewpoint. In particular, grain growth will be taken up from a theoretical perspective. This discussion should be seen as a continuation of those given in the previous chapter since the attempt to understand these phenomena rests heavily on a synthetic understanding of point, line and interfacial defects in concert. Our contention will be that despite the exertion of Herculean efforts, a number of key difficulties remain. 

The role of the a-c interface in Ion Beam Induced Epitaxial Crystallization (IBIEC) is demonstrated in Fig. 10.11, which shows that the regrowth rate is orientation dependent. The data shows that the rate is much lower (almost by a factor of 4) for (111) substrates relative to (100) substrates. These results suggest that the same interfacial defects that are responsible for thermal regrowth also are important in IBIEC, with the role of the ion beam being that of changing the average defect concentration. 

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