Analytical techniques Mossbauer spectroscopy

Mossbauer spectroscopy is an analytical technique that, in archaeological ceramic studies, provides information on the condition and characteristics of the compounds of iron in pottery. Using the technique makes it possible to determine the relative amounts of the different (ferrous and ferric) ions of iron and hence to ascertain the firing conditions of the pottery at the time it was made. The technique involves irradiating a sample of pottery with gamma rays and then assessing the amount of radiation absorbed by the nuclei of the ions of iron within the pottery (Feathers et al. 1998 Bearat and Pradell 1997). 

The Mossbauer effect has been used as an analytical tool to characterize the diffrent iron-bearing minerals in coal. It has been pointed out that by the use of low-temperature measurements (in the presence of a large external magnetic field) and treatment of the coal samples, all the iron-bearing minerals can be identified correctly. The use of Mossbauer spectroscopy as a quantitative analytical tool presents several experimental difficulties. It is recommended that this spectroscopy be used as a complement to and not as a substitute for the standard techniques. 

Hawthorne et al. (1991) used a wide variety of analytical techniques (EMPA, TGA, powder XRD and IR, single crystal XRD, Mossbauer spectroscopy, Si MAS-NMR, EXAFS/XANES spectroscopies and HRTEM) to determine the stmcture of a-decay damaged titanite. The metamictization process was proposed to begin with the formation of isolated defects caused by a-particles and amorphous domains caused by a-recoil tracks which, with increasing dose, overlapped to produce the metamict state. Fe" was reduced to Fe with increasing a-decay dose. In a set of annealing experiments of... 

In this chapter we shall consider the various techniques which have been used for observation of the Mbssbauer effect, together with methods of source and absorber preparation and computer techniques for data analysis. Some of the advantages and limitations of Mossbauer spectroscopy will become apparent during the discussion of these problems. References to more recent development will be found in the review by J. R. De Voe and J. J. Spijkerman in Analytical Chemistry, 1970, 42, 366R, and in Spectroscopic Properties of Inorganic and Organometallic Compounds published annually by the Chemical Society (London). 

In carrying out calculations for multi-site mixing such as this, you can either use equation (15.10) directly, or work through the problem stepwise and ion by ion as with (15.8) the two methods are equivalent. Further details are given by Powell (1977). It is possible using analytic techniques such as X-ray diffraction, Mossbauer spectroscopy and infra-red, Raman and UV-visible spectroscopy to analyze for the concentration of different ions on specific crystal sites. Thus the activities, configurational entropies, and other such properties of solid solutions can often be calculated. This provides detailed information on the stability and structure of crystalline solutions. 

This book is about Mossbauer spectroscopy. We might wonder how it can be applied to study surfece layers a few nanometers thick. A surface analytical technique needs to meet two important requirements (i) it should be sensitive, that is, it should be able to detect a small number of atoms (while a cubic centimeter of solid material contains roughly substitute 10 atoms, a square centimeter of the same material contains a much smaller number of atoms, approximately 10 atoms), and (ii) it should be specific, that is, it should be able to separate the contributions of the surface from those of the bulk. 

In this chapter, the aim is to identify and quantify the iron mineral phases present in South African coal fractions by the use of Mossbauer spectroscopy, in conjunction with various other analytical techniques. Because the atomic weight of the carbon content in coal is low, Mossbauer spectroscopy is a convenient, and to a certain degree unique, analytical tool in the identification of iron-bearing minerals in coal with iron contents as low as 1%. With an understanding of the iron mineral phases present in the as-mined coal, the fete of these minerals during transportation, weathering, oxidation, and combustion or gasification can be better understood. 

Several surface-sensitive techniques can provide details about bonding in amorphous materials. Such information complements structural analyses obtained by traditional bulk analytical techniques like Raman and infrared spectroscopy, solid state nuclear magnetic resonance spectroscopy, and Mossbauer spectroscopy. 

It is impossible to comprehensively discuss all non-vibrational in situ techniques with a potential application to oxidation catalysts within this chapter. Therefore, we have selected only those methods for a more detailed presentation which have seen a widespread application so far and/or offer unique opportunities for understanding the functioning of real catalysts. For more specific in situ methods, such as the microscopy techniques mentioned above, Mossbauer spectroscopy which is restricted to the viewing of elements only, or thermo-analytical studies using an oscillating microbalance reactor,the reader is referred to the respective reviews. 

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