ORDINARY CHEMISTRY AND NUCLEAR CHEMISTRY - BASIC COMPARISON AND TUTORIALS

An atom consists of a nucleus that is made of positively charged protons and neutral neutrons, and electrons surrounding it, as we outlined above. Two entirely different types of chemistry stem from this structure.

One is concerned with the nucleus and the other with how electrons behave. The former is “nuclear chemistry,” with “radiochemistry” as its important sub-discipline. The latter is the ordinary “chemistry.”

The basic reason for this division is that the nuclear forces binding protons and neutrons in the nucleus are enormously stronger than the electrostatic force binding the electrons to the nucleus. When one applies a force to a substance and induces a change, a certain amount of energy may be expended or gained.

Hence, an energy change always accompanies a change in substance. “Energy” is often used as a measure of a change in science, particularly in chemistry.

In terms of energy, then, a nuclear reaction (change in general) is greater by several orders of magnitude (typically a million times) than a typical chemical reaction, as the nuclear reaction involves changes in protons/neutrons in the nucleus while chemical reactions involve changes in electrons.

Therefore, ordinary chemical reactions would not be able to cause a change in nucleus (i.e., nuclear reaction). As a result, it is quite safe to deal with nuclear chemistry as separate from “ordinary” chemistry.

As a corollary, all isotopes that belong to an element, though they have different atomic masses, can be assumed to behave (approximately) the same chemically. However, isotopes behave very differently in terms of nuclear reactions.

It is now obvious that principles governing nuclear reactions are quite different from those operating in the ordinary chemical reactions.

SURFACE LAYERS CHARACTERIZATION METHODS BASIC AND TUTORIALS

Numerous surface analytical techniques that can be used for the characterization of surface layers are commercially available (Buckley, 1981; Bhushan, 1996).

The metallurgical properties (grain structure) of the deformed layer can be determined by sectioning the surface and examining the cross section by a high magnification optical microscope or a scanning electron microscope (SEM).

Microcrystalline structure and dislocation density can be studied by preparing thin samples (a few hundred nm thick) of the cross section and examining them with a transmission electron microscope (TEM). The crystalline structure of a surface layer can also be studied by X-ray, high-energy or low-energy electron diffraction techniques.

An elemental analysis of a surface layer can be performed by an X-ray energy dispersive analyzer (X-REDA) available with most SEMs, an Auger electron spectroscope (AES), an electron probe microanalyzer (EPMA), an ion scattering spectrometer (ISS), a Rutherford backscattering spectrometer (RBS), or by X-ray fluorescence (XRF). The chemical analysis can be performed using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS).

The thickness of the layers can be measured by depth-profiling a surface, while simultaneously conducting surface analysis. The thickness and severity of deformed layer can be measured by measuring residual stresses in the surface.

The chemical analysis of adsorbed organic layers can be conducted by using surface analytical tools, such as mass spectrometry, Fourier transform infrared spectroscopy (FTIR), Raman scattering, nuclear magnetic resonance (NMR) and XPS. The most commonly used techniques for the measurement of organic layer (including lubricant) thickness are depth profiling using XPS and ellipsometry.