Elemental base heterogeneous-homogeneous

INAA is well suited to study homogeneity of small samples because of its dynamic range of elemental sensitivity. The technique allows for the use of small solid samples, with the smallest usable sample size in the range of 0.5 mg to i mg as determined by handling and blank considerations. The INAA analytical procedure is well understood and characterized with mathematical relationships. Its analytical uncertainties can be sufficiently controlled and can be well determined for a particular procedure. This allows the calculation of the contribution of material heterogeneity to the uncertainty budget based on experimental data. 

The word "matter" describes everything that has physical existence, i.e. has mass and takes up space. However, the make up of matter allows it to be separated into categories. The two main classes of matter are pure substance and mixture. Each of these classes can also be divided into smaller categories such as element, compound, homogeneous mixture or heterogeneous mixture based on composition. 

The fractal concept is based on the assumption of reproduction of the general elements of structure of porous materials at all levels—from microscopic to macroscopic ones. This assumption is valid for numerous macroporous materials, while it is too difficult to check its validity for microporous ones. However, based on general thermodynamic considerations, one may assume that fractal concepts also apply to some of microporous materials. As it is shown below, the main condition of the applicability of the fractal approach to microporous materials consists in their homogeneity. However, one has to take into account that this strict analysis does not allow the assumption of homogeneity of any microporous system, not least, because the subsystem micropore-wall of micropore is obviously heterogeneous. Therefore, the fractal concept is probably not applicable to very narrow micropores (ultramicropores, according to Dubinin s classification). 

Synthesis of nitrides of group III-VI elements and nitride-based composite materials by SHS (CS) nitriding of ferroalloys have been studied in Chapter 7. Phenomenon of phase formation during SHS (CS) nitriding of ferroalloys has been discovered. High catalytic activity of the composites is determined by combination of heterogeneous and homogeneous catalyses. 

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