Diffusion

Diffusion

In virtually all solid state reactions and transformation, matter moves; that is, atoms 

and/or molecules are transported to and from the reaction site. Often in the solid state 

that motion is by a random process, and such random processes are termed diffusive 

processes. Early in Chapter 5 on diffusion in solids the form for a variety of diffusion 

equations are compared,and it is observed that seemingly unrelated phenomena are gov- 

erned by equations with the same form,namely there is a flux in response to a force.That 

flux (with units of amount/area · time) can be matter, heat, charge, energy, and so on. 

Even the famous Schroedinger equation of quantum mechanics (see Chapter 9) has the 

form of a diffusion equation.Although only mass diffusion is covered in Chapter 5,heat 

transport, for example, involves the solution of similar equations. 

In the field ofmass diffusion many treatments deal purely with the underlying physics 

that enable random matter transport, while other approaches deal exclusively with the 

mathematics of solving the differential diffusion equations. In Chapter 5 both areas are 

addressed. In addition another fundamental tenet in materials science is introduced, 

namely the random walk problem. While applied strictly to diffusion in this chapter, the 

random walk problem yields insight into how random processes can yield simple under- 

standable results precisely because of the assumed randomness of the system. This is a 

powerful idea that helps hone the intuition of a materials scientist who must often deal 

with seemingly unsolvable problems involving randomness and complexity. In the field 

of electronic materials diffusion plays a central role that includes the transport of 

dopants,other point defects (vacancies and impurities,and electronic carrier diffusion in 

electronic and optical devices.

Ramon A. Carmona C.

C.I 17646653

CRF

http://media.wiley.com/product_data/excerpt/71/04716959/0471695971.pdf

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