Surface engineering definition

In the majority of mechanical applications of materials, their surfaces experience contact with another material and take the external load before the bulk of the material is influenced. In some cases, surface interactions influence the bulk (e.g., propagation of cracks dislocations or point defects from the surface in depth). In many cases, only the outermost surface layer is affected by the surface contact with no detectable changes in the bulk of the material. This is like a storm that is frightening and destructive on the ocean surface, but does not have any influence on deep-water life. We are primarily concerned in this review with that kind of interaction. The surface layer thickness affected by external mechanical forces ranges from nanometers to microns. Thus, in our case, the definition of surface is different from the one used by surface scientists, that is, physicists and chemists. We introduce here an engineering definition of surface the outermost layer of the material that can be influenced by physical and/or chemical interaction with other surfaces and/or the environment. In this chapter, we consider only mechanical effects, but both mechanical and chemical interactions are possible and their synergy can lead to mechanochemical alteration of a material surface. 

Electrostatic and EDL forces are found to play a very important role in a variety of systems in science and engineering. It would be useful to consider a specific example in order to understand these phenomena. Let us take a surface with positive charge that is suspended in a solution containing positive and negative ions. There will be a definite surface potential, /0, which decreases to a value zero as one moves away into solution (Figure 7.5). 

General Remarks—Definition of a Chemical Engineer—DiflFerence between Applied Chemistry, Chemical Engineering, and Chemical Technology—Effect of Time, Space, and Surface on Chemical Operations... 

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