Point defects physical properties affected

Point defect populations profoundly affect both the physical and chemical properties of materials. In order to describe these consequences a simple and self-consistent set of symbols is required. The most widely employed system is the Kroger-Vink notation. Using this formalism, it is possible to incorporate defect formation into chemical equations and hence use the powerful methods of chemical thermodynamics to treat defect equilibria. 

The microstmcture and imperfection content of coatings produced by atomistic deposition processes can be varied over a very wide range to produce stmctures and properties similar to or totally different from bulk processed materials. In the latter case, the deposited materials may have high intrinsic stress, high point-defect concentration, extremely fine grain size, oriented microstmcture, metastable phases, incorporated impurities, and macro-and microporosity. AH of these may affect the physical, chemical, and mechanical properties of the coating. 

Note that "b" in this diagram is the same as that in 3.1.8. Because edge and volume defects propagate throughout the lattice, they affect the physical properties of the solid, whereas it is the point defects that affect the chemical properties of the solid. These latter properties include electrical and resistive, optical and reactivity properties of solids. Thus, we can now classify directs in solids as ... 

As with metals, ceramic crystals are not perfect. They can contain all of the same types of defects previously described in Sections 1.1.3-1.1.5. What is unique about ceramic crystals, particularly oxide ceramics, is that the concentration of point defects, such as vacancies and interstitials, is not only determined not only by temperature, pressure, and composition, but can be influenced greatly by the concentration of gaseous species in which they come in contact (e.g., gaseous oxygen). The concentration of gaseous species affects the crystal structure, which in turn can affect physical properties such... 

In addition to mechanical properties, other physical properties of polycrystaUine materials, such as electrical and thermal conduction, are also affected by microstmcture. Although polycrystals are mechanicaUy superior to single crystals, they have inferior transport properties. Point defects (vacancies, impurities) and extended defects (grain boundaries) scatter electrons and phonons, shortening their mean free paths. Owing to... 

It is important to study point defects because they mediate mass transport properties, as will be discussed in Chapter 6. Although the inhuence of point defects on physical and chemical properhes is well founded, relahvely little has been reported concerning their affect on the mechanical behavior of solids. A mechanical force applied over a... 

Radiation-induced point defects are usually preferred over thermal point defects (obtained by quench-in from some higher temperature and freeze-in these point defects) for studying their effects on the physical and mechanical behavior of ceramics. Radiation affects mechanical properties by way of changes in strength. 

There are several different kinds of defects in crystals. Depending on the type and number of defects in any volume of crystal (that is, the type and density of defects), the physical and chemical properties of the crystal may be altered from the properties of the perfect crystalline form. Defects can be separated on the basis of whether they affect a single point, a line of points, or a plane of points. For simplicity s sake, we will assume that we are considering an atomic crystal, but all crystals—atomic, ionic, molecular—exhibit most of the defects discussed here. 

Field failures may seem to be completely different from painting problems, but they may be connected to a greater extent than we realize. An excellent source of information in this area is Ref. 20. The author points out that for a coating to fad, it must be stressed. How it responds to this stress depends on the physical and mechanical properties of the coating and its interface with the substrate. These, in turn, depend on the chemistry of the coating and the degree of cure, but may also be affected by the apphcation process, defects in the coating, or repairs to defects. Let us consider some field fadures. 

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