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Über dieses Buch

As is often the case, the preface is the last task to be finished during the preparation of a large volume such as you are now holding. The first task, obtaining approval for a symposium on the industrial applications, now seems a long time ago. The idea orginated with John Stevens, probably in 1982, from his observation of papers dealing with industrial applications of the Mossbauer effect appearing in the Mossbauer Effect Reference and Data Journal. His initial suggestion for a symposium entitled "Industrial Applications of the Mossbauer Effect" to be held at a national meeting of the American Chemical Society eventually led to the symposium at the International Chemical Congress of Pacific Basin Societies which met in Honolulu, Hawaii in December 1984. This volume is the result of the symposium at the above mentioned Congress, but is not actually the 'proceedings' of the symposium because this volume does not contain all of the over one hundred Mossbauer effect papers that were pre­ sented at the symposium. Rather it contains a selection of papers that the or­ ganizing committee for the symposium deemed most appropriate for a volume devoted to industrial applications of the Mossbauer effect. The final volume also contains six chapters that were not a part of the symposium but which are closely related to the topic. There is another difference from many proceedings.

Inhaltsverzeichnis

Frontmatter

Introduction

Chapter 1. The Dozen Uniquenesses of the Mössbauer Effect

The Mössbauer effect is a unique method.

Uli Gonser

Chapter 2. Metal Research of Industrial Significance by Mössbauer Spectroscopy

In 1970 Lyle Schwartz [1] read a paper to the l0th Annual Symposium of Physics and Non-Destructive Testing in Chicago.

T. E. Cranshaw

Techniques and General Applications

Chapter 3. Mössbauer Spectroscopy in Physical Metallurgy

In materials science, three discoveries had a great impact on our Society, that is, on its understanding of science and technology. The first of these, dislocations, has just had its 50th anniversary. Dislocations were discovered by Orowan [1], Polanyi [2], and Taylor [3]. With the concept of dislocations we are able to get a better insight into the nature of metals, in particular their mechanical properties and their plastic deformation behavior. Second,in the early fifties Welker [4] discovered the electrical properties of III-V Compounds. They play a dominating role in the semiconductor and microelectronic industries. Third, also in the middle of the Century, amorphous metals were discovered and, in the following years more and more technological applications were found for them. Although the great significance of these three discoveries has been well recognized, they have not been honored by the Nobel Prize, the highest award for achievement in natural science. In our opinion the reason for this unfortunate omission is the fact that, for the chemist, these discoveries invoke too much physics and, for the physicist, the materials are too dirty.

U. Gonser, M. Ackermann, H.-J. Bauer, N. Blaes, S. M. Fries, R. Gaa, H.-G. Wagner

Chapter 4. Industrial Applications of Mössbauer Spectroscopy to Microcrystals

Microcrystalline materials with crystallite dimensions in the ränge 5–1OOnm are very common on the earth. For example, sediments often contain microcrystals of clay minerals, iron oxides and iron oxyhydroxides. Moreover, rapidly cooled lavas may also contain microcrystalline minerals. Even in biological samples microcrystals are common. The iron storage proteins of animals contain microcrystals of iron oxyhydroxides. Because clays are commonly used for manufacturing ceramics and building materials, such samples may also be microcrystalline. Fly ash, which is another example of a microcrystalline material is used, for example, as an additive to concrete.

Steen Mørup

Chapter 5. Conversion Electron Mössbauer Scattering. A Technique for Structural Microanalysis of Thin Films and Subsurface Regions in Materials

Within the past few years, conversion electron Mössbauer spectroscopy, CEMS, has been used increasingly for structural analysis of thin films and subsurface regions in solids. Because of its attractive probing depth, ranging from first atomic layers on the surface to about lμm below the surface, and because of its high sensitivity, which in most favorable cases enables studies of films as thin as 1 to 100ng/cm2, i.e., 1013-10l5at/cm2, CEMS has established itself as a sensitive depth-selective method for materials characterization in different areas of high-technology and related basic research. Various problems currently investigated with the help of CEMS include surface physics and chemistry, studies of thin films and inter- faces, magnetism, metallurgy, catalysis, materials fatigue, corrosion, ion implantation, radiation damage, and plasma-wall interaction. Experimental aspects of CEMS and its applications were discussed in several earlier reviews [1–7] and a complete list of references until November 1982 can be found in the “Conversion Electron Mössbauer Spectroscopy Handbook” [8].

J. A. Sawicki

Chapter 6. Surface Phase Analysis by Depth-Selective Conversion Electron Mössbauer Spectroscopy

Depth-selective iron-57 conversion electron Mössbauer spectroscopy, DCEMS, is a rapidly developing technique for the nondestructive investigation of iron-57 containing surface layers of materials [1], The potential of DCEMS lies in the unique possibility of studying, to a certain extent and resolution, local physical properties as a function of depth below the surface, without relying on destructive and possibly disturbing methods such as etching or sputtering off surface layers. In DCEMS, electrons emerging from the surface of a Mössbauer absorber are detected by means of an electron spectrometer of several percent energy resolution, and Mössbauer electron backscattering spectra are obtained at various selected electron energies. Mono-energetic conversion electrons are emitted after the deexcitation of Mössbauer nuclei (e.g., 7.3keV K-conversion electrons in the case of iron- 57), and their energy loss is related to their depth of origin below the surface of the Mössbauer absorber. In this way, information on the depth dependence of local physical parameters can be obtained, DCEMS can, in principle, be applied to any sample of fundamental or technological interest which contains a sufficient amount of iron-57.

K. Saneyoshi, K. Debusmann, W. Keune, R. A. Brand, D. Liljequist

Chapter 7. Rapid Mössbauer-Based Methods for Applications in the Coal and Steel Industries

Conventional Mössbauer spectroscopy is not suited for routine quality- control applications in industry because of the long sample turn-around times and relatively sophisticated nature of the technique and its interpretation. Moreover, because quality-control applications tend to involve repetitive determinations of the same quantity, the füll power of the technique is generally not necessary. It appears that Mössbauer spectroscopy is perhaps 1overqualified1 for industrial applications on the shop floor. As a result, simpler and more rapid Mössbauer techniques have been proposed and developed for such applications.

F. E. Huggins, G. P. Huffman, G. R. Dunmyre

Applications to Steel and Steel Alloys

Chapter 8. Mössbauer Spectroscopy in Steel Industry

This review article is not intended to be an alternative to the numerous excellent articles written by various research workers and in particular to these written by Huffman and Huggins, who have pioneered the utilization of the Mössbauer spectroscopy to the steel industry. It is rather intended to draw the attention of research workers in this field and related fields to the exciting and most practical commercial utilization of the technique in the industry by consolidating a number of studies related to the steel industry reported in the literature. It is very likely that the survey of the literature is not complete. Only a few examples from the published work have been chosen more because of the biased interest of the author.

K. R. P. M. Rao

Chapter 9. Mössbauer Investigation of High-Manganese Steels

Austenitic high-manganese steels containing from 16 to 36 weight percent manganese and from 0.01 to 0.75 weight percent carbon were investigated by Mössbauer spectroscopy in both hot-rolled and cold-rolled conditions. Spectra were obtained over the temperature ränge 10 to 295K in the transmission mode and at room temperature in the X-ray re-emission mode. In the hot-rolled condition, the steels were primarily antiferromagnetic y-phase austenite, and exhibited Neel temperatures ranging from 234 to 460K. After cold reduction, varying degrees of transformation to the nonmagnetic hcp e-phase were observed, the resistance of the austenite to mechanically induced transformation increased with increasing manganese and carbon content. Steels that exhibited relatively small amounts of the e-phase after cold reduction showed continuous work hardening with increasing cold reduction. Steels that exhibited large amounts of e-phase formation during cold reduction exhibited rapid work hardening followed by Saturation. No magnetic a-phase material was observed by Mössbauer spectroscopy, in agreement with the very small changes observed in magnetic susceptibility.

G. P. Huffman, Chiaki Ouchi

Chapter 10. The Application of Mössbauer Spectroscopy to Iron-Aluminum Alloys and Industrial Aluminum Samples

The use of aluminum in manufacturing is expanding and in many areas there is a move to replace iron based alloys by aluminum based alloys. The merits of iron versus aluminum based alloys in packaging will not be commented on here. Rather the discussion will center on the application of iron-57 Mössbauer spectroscopy of the study of iron-aluminum alloys and as a probe for investigating the nature of the aluminum used in the manufacturing industry, because all commercial aluminum contains iron as an impurity. The form in which the iron is incorporated into the aluminum depends upon the nature of the other contaminants and, in some cases, upon the treatment that the metal received in processing.

Thomas Birchall, Dave Hodgson, Harish D. Merchant

Chapter 11. Mössbauer Investigation of ALFe and ALFeSi Phases in Specially Produced Aluminum Alloys and in Industrial Aluminum

This paper is a summary of the Mössbauer investigations done in the framework of a project supported by the Ministry of Culture and Education of Hungary and by the ALUTERV-FKI. The aim of the project is to study industrial aluminum with respect to the precipitation and transformation processes of the various phases formed by iron, an unwanted alloying element which, unfortunately, is a constant impurity in aluminum.

Sàndor Nagy, Attila Vértes, Zoltàn Homonnay, Lajos Murgàs, Tibor Turmezey, Agnes Griger, Jòzsef Lakner

Chapter 12. Sulfidation-Induced Changes in Iron-Aluminum and Iron-Silicon Alloys

By using X-ray phase and microanalysis, optical and scanning electron microscopy and Mössbauer spectroscopy, we investigated the influence of sulfidation of iron-aluminum alloys containing 0.8 and 3 weight percent aluminum and a iron-3 weight percent Silicon. We find that the near-surface zone of the metallic core is enriched in the solute element and in the case of iron-silicon alloy it contains an admixture of the Fe3Si phase. A mechanism is proposed in order to account for the enrichment.

S. M. Dubiel, Z. Żurek, M. Przybylski

Chapter 13. Hyperfine Fields in Fe-Ni-X Alloys and their Application to a Study of Tempering of 9Ni Steel

Hyperfine magnetic field perturbations due to the solutes in Fe-Ni-X alloys were systematized, and interpreted with a model of linear response of hyperfine magnetic fields to magnetic moments. The effects of solutes on the iron-57 hyperfine magnetic field were used for chemical analysis of the austenite formed in 9Ni steel during tempering. Diffusion kinetics of the nickel and X solutes were found to play an important role in the formation of the austenite particles.

B. Fultz, J. W. Morris

Chapter 14. Surface Characterization of Nitrogen Implanted Carbon- and Alloy-Steels: A Review and Recent Results

Ion implantation, consisting of the direct injection of energetic ions into the subsurface region of materials, has been utilized in recent years to improve the technological properties of metallic surfaces. Many experimental studies as well as industrial applications have established in particular the specific advantages of nitrogen implication with respect to conventional nitriding methods. These include, in particular, the possibility limit of impurities in the matrix, prevent dimensional changes of treated specimens, and ensure clean and well controlledn process conditions. Furthermore, it has been found that thermally nitrided stells may be improved in their surface properties by additional nitrogen implantation. The subject has been recently reviewed [1–11].

G. Principi, S. Lo Russo, C. Tosello

Chapter 15. Studies of the Phosphatization of Steel and its Corrosion Products

The reaction of phosphoric acid with steel is a basic process in many technological procedures. A typical example is the pretreatment of steel surfaces for the application of coatings. The aim of the treatment is to clean the surface, to produce a homogeneousr tight, and smooth cover and to provide a reliable adhesion between the steel substrate and the coating. This example points out that the phase composition of the layer formed is of great interest, and that reactions with residues on the surface, such as oxides and corrosion products, have to be considered, too. The same holds for phosphate layers formed in order to modify the mechanical or corrosion behavior of steel surfaces. Because of the electrolytic character of these processes, in addition to the usual reaction parameters, such as temperature, concentration, and time, the electrochemical potential of the sample has to be controlled during the reaction. In these examples, diluted phosphoric acid, phosphate solutions, and mixed solutions are used. Solutions of higher concentration are used as “rust transformers”. An example for the use of concentrated phosphoric acid is its application for the removal of rust from vessels, tubes, etc. If the corrosion products to be removed are contaminated, as for instance in nuclear power plants, a minimum quantity of the reagent needed for the treatment is desired.

W. Meisel

Chapter 16. Conversion Electron Mössbauer Studies of the Corrosion Products Formed on the Steel Surface in Atmospheres Containing HCl, H2S, and S02

Conversion electron Mossbauer spectrometry, CEMS, was applied to the analyses of the steel surface corroded and the corrosion products formed in HCl, H2S, and S02 environments. In an HCl environment, FeCl2•2H20 and FeCl2•4H20 was formed at the initial stage and transformed into γ-FeOOH if the relative humidity was high and ß-FeOOH if it was low. The exposure to an H2S atmosphere resulted in the formation of paramagnetic FeSl-x, as fine particles at the initial stage, coarse ferromagnetic FeSl-x particles at the intermediate stage, and finally the surface was sulfided to Fe3S4. In a combined S02 air atmosphere, the formation of FeSO4•H20 and FeS04•4H20 as the initial and γ-Fe00H as the final corrosion product could be confirmed. The Utility of CEMS for the corrosion study was demonstrated.

Yusuke Ujihira, Arimichi Handa, Masanori Fujinami

Applications to Amorphous Alloys and Glasses

Chapter 17. Transition Metal Substitution in Fe7 5TM5 B2 0 Amorphous Alloys. Effect on Structure, Thermal Stability, and Structural Relaxation

A series of amorphous alloys of Fe80B20, with a constant amount of transition metal substitution and the nominal composition Fe75TM5B20, have been obtained by the “melt-spinning” technique. Differential scanning calorimetry, resistivity, small angle x-ray scattering measurements, and Mössbauer spectroscopy have been utilized to study the substitution-induced modification of the behavior, in both the amorphous and annealed states, of the temperature and enthalpy of crystallization, the activation energy for crystallization, the electrical resistivity, the local magnetic and electronic properties, and the structural homogeneity. The effects of substitution on the electronic structure and hyperfine field at the iron atoms are also discussed.

P. Matteazzi, G. Cocco, G. Le Caer, G. Riontino

Chapter 18. Mössbauer Investigations of Magnetic Interactions and Crystallization Behavior of the Amorphous Alloy Fe7 2 Ni4 Mo6 B1 6 Si2

Metallic glasses, produced by rapid quenching of metallic melts have emerged as an important class of materials with unusual combinations of desired properties. Further, many of the unique characteristics arise due to their amorphous structure. Study of the amorphous State is of great current interest as evidenced by the publications of books and the proceedings of international conferences on this subject [1–3]. One of the features of these alloys is that they can be prepared with a variety of compositions with a number of elements, providing a method to alter or modify their magnetic, mechanical, electrical, and corrosion behavior. The alloys constitute a large range of material containing from two to as many as five elements. They behave as very soft magnetic materials, exhibit exceptional hardness, high tensile strengths, and almost zero thermal expansion in certain instances. Some of them show marked resistance to corrosion. Such combinations of properties and in particular the existence of ferromagnetism in these alloys, a property earlier thought to be impossible in non-crystalline materials, have made them potential and competitive candidates in a wide range of applications. Recent developments include their suitability in large and electronic-size transformers, in motors, in mechanical applications such as brazing filler materials, as transducers and as potential catalysts.

R. Jagannathan, T. G. N. Babu, B. B. Prasad, A. K. Bhatnagar, V. R. V. Ramanan

Chapter 19. The Fitting Method for Mössbauer Spectra of Amorphous Alloys and an Investigation of their Properties and Structure

Over the past several years, the amorphous alloys have been of scientific and technological interest and have been extensively investigated. In particular, much attention has been devoted to ferromagnetic metallic glasses. For investigation of the magnetic anisotropy or the structural relaxation and crystallization during annealing Mossbauer spectroscopy is known to be a suitable widely used technique. A number of results have reported that, for many amorphous alloys, the structural relaxation below the crystallization temperature increases the average magnetic hyperfine field [1–3] and that the crystallization pattern above the crystallization temperature varies for amorphous alloys, such as Fe-P [4], Fe-B [5,6], and Fe-B-Si [2,7], and Fe-B-Si-C [3,8,9]. Another interesting Mossbauer result has reported that, despite the large demagnetizing effect which would favor the moments lying in the ribbon plane, out-of-plane anisotropy is observed for various amorphous alloys when measured at low temperature [10,11] or when the alloys are annealed at higher temperature [1,12–16].

Zuxiong Xu, Ruzhang Ma, Jueyun Ping

Chapter 20. Mössbauer Effect Study of the Cluster Distribution in the Spin Glass θ-Me0.35V2O5 (Me=Fe, A1)

Mössbauer data for the Vanadium oxide bronzes, 0-Fe0.35V2O5 and 0-A10.26Fe0.09V2O5 reveal a randomly oriented spin arrangement with only weak indirect exchange interaction possibly stimulating a spin-glass like order. Below 18K the onset of magnetic order shows up as a broadened magnetic hyperfine patterns. Two sextets are observed below 6K. The Mössbauer spectra can be fit assuming superparamagnetic relaxation of a Cluster magnetization. Our relaxation model is appropriate for a flipping of the hyperfine field into a reversed direction. From the resolved spectra, it is apparent that Clusters with different relaxation frequencies of 4.0 and 0.9MHz and different hyperfine fields of 45.0 and 38.5 Tesla are present. The Cluster distribution function was derived from the temperature dependence of the relative intensity of the doublets.

H. Lass, J. Pebler

Chapter 21. Application of Mössbauer Effect on the Crystallization of Several Glasses

The structural change of glass from a non-crystalline State to a poly- crystalline State caused by controlled crystallization is a very important and interesting phenomenon both from the scientific and industrial point of view. Crystallized glasses are extensively utilized in many industrial fields such as mechanical, electrical, and nuclear engineering because of their ultra low thermal expansion and high mechanical strength [1,2]. Crystallization of glasses is generally known to proceed by two steps, nucleation and crystal growth. The crystallized glasses are known to consist of many crystalline particles mixed into the remaining glass phase. Because of this, crystallized glasses are still regarded as non-crystalline, and are called glass-ceramics [1,2]. As for the crystallization of glasses, several techniques [3–8] have so far been utilized to study glass ceramics. Differential thermal analysis [4–6] and differential scanning calorimetry [7] are known to be very useful. Mössbauer studies on the crystallization of glasses [9–11] have also been performed, and the method proved to be extremely useful for the structural study of borate [12–15], borosilicate [16,17], phosphate [18,19], borophosphate [20], germanate [21,22], zinc Chloride [23], and zirconium tetrafluoride [24] glasses. Structural studies of glasses by Mössbauer spectroscopy and NMR have been reviewed by Müller-Warmuth and Eckert [25].

Nishida Tetsuaki, Yoshimasa Takashima

Chapter 22. Application of Iron-57 Mössbauer Spectroscopy to the Characterization of Silicate Glasses Used for High Temperature Incinerated Low-Level Radioactive Waste Products

Above seventy glass samples with the general compositions (84-y- x)SiO2•xFe2O3•yA12O38M O•8M21O and (84-y-x)SiO2•xFe2O2•yA12O3•8M O•8M21O, where MH is calcium, magnesium, or barium and M’ is lithium or potassium and with y either zero or equal to x and with x + y up to 30, have been investigated by means of iron-57 Mössbauer spectroscopy at room temperature. The spectra of the iron(III) glasses are composed of a weak broad iron(II) doublet, arising from a wide spread in local environment, and two iron(III) doublets attributed to ions in essentially octahedral and tetrahedral positions. The variations of the iron(II) to iron(IH) ratio, the iron(III) site occupancy and the hyperfine interactions are determined as a function of the composition x and y, and for a particular composition, as a function of the preparation conditions. The results are discussed in terms of the structural and chemical properties of the glass network. The crystalline phase, which segregates when the total amount of iron and aluminum exceeds a certain limiting value, is characterized by both its hyperfine parameters and X-ray diffraction patterns. The influence of the composition and quenching mode upon the crystallization process is determined. The iron(II) glasses were prepared in an argon atomsphere which results in high iron(II) concentrations. The structure of these glasses is different in that much more iron and aluminum may be incorporated and that iron(III) ions seem to be situated in the larger holes with a coordination number of six or higher. The iron(II) hyperfine parameters exhibit a broad distribution which is accounted for by fitting the absorption envelope with a sum of five quadrupole doublets. The coordination of the iron(II) cations is discussed and the Variation of the Mössbauer parameters with the composition is investigated.

E. De Grave, P. Van Iseghem

Applications to Coal, Minerals, and Mineral Processing

Chapter 23. Mössbauer Analysis of Q-Basic Oxygen Process Slags

The Q-Basic Oxygen Process (Q-BOP) is one of a number of alternate oxygen steelmaking processes that can be utilized to refine the so-called hot metal or carbon-saturated liquid iron produced in the conventional blast furnace. In the steelmaking process, the carbon and other dissolved impurities in the hot metal are oxidized by blowing oxygen into the bath. The oxidation products separate from the liquid steel as gases (e.g., carbon monoxide) or by partitioning as oxides into the slag layer on the top of the liquid steel. In the Q-BOP, the oxygen, as well as burnt lime that forms the slag, is blown through the hot metal from underneath in contrast to other major steelmaking processes such as the open hearth, electric-arc furnace, and the BOF (also known as BOP or LD), in which oxygen is blown into the hot metal from above.

F. E. Huggins, G. P. Huffman

Chapter 24. Slag Attack of Firebrick in a Tin Smelting Furnace

A combined tin-119 and iron-57 Mössbauer study has been made of the slag and an aluminosilicate hearthbrick taken from a reverberatory tin furnace. Three distinct tin(II) glassy phases were observed, one of which also contains iron(II) and appears to be the phase responsible for the attack on the furnace hearth. Some SnO2 was also found to have penetrated 4cm past the reaction zone in the brick, presumably by vapor transport.

Pamela McNamara, John D. Cashion, Mary S. J. Gani

Chapter 25. Mössbauer Effect Study of Decreptation Phenomena in Iron Ores

Hematite, α-Fe2O3, was one of the first iron Compounds studied by Mössbauer spectroscopy and the study of its properties as well as its participation in the formation of the other minerals have been object of several such investigations. Brazil has one of the world’s largest mineral deposits of hematitic iron among which, the compact hematite, is the subject of the present investigation.

Joice Terra, Elisa B. Saitovitch, Jacques Danon, Nilce G. Souza

Chapter 26. Coal Treatment and Desulfurization

Pyrite, an impurity commonly found in coal, will react with air to form sulfur oxides, which are poisonous to humans and can cause severe damage to industrial equipment. Because of the relatively high percentage of pyrite found in many coals, it is necessary to treat coal to satisfy environmental regulations. Mössbauer spectroscopy can be effectively used to monitor the pyrite and other iron sulfides through various coal treatment processes.Mechanical treatment of coal, such as froth flotation and float-sink Separation, is today the most commonly used procedure. For pulverized coal, it is possible to use magnetic desulfurization in which pyrite is transformed into pyrrhotite. This enhances the magnetic susceptibility of the inorganic sulfur containing material.Other treatment processes include several chemical methods and biological leaching, which still needs development, but is very promising. One of the chemical methods is the Meyer’s process, TWR, and is perhaps the best because it recycles the chemical, it does not require fine crushing of the coal, and sulfur removal is very efficient.

H. Pollak, J. G. Stevens

Chapter 27. Iron Phases in Brown Coal Ashes

Iron-57 Mössbauer spectroscopy has been used in three areas of analysis of precipitator ash and deposits resulting from the combustion of Victorian brown coals. The principal iron-containing constituents identified in the samples were two mixed oxides (calcium aluminoferrite and magnesioaluminum ferrite). The changes occurring in some of the phases by altering the combustion conditions and during wet agglomeration are described. This work is aimed at developing a systematic description of relative phase stabilities for different flyash compositions, based on chemical analysis of the coal.

J. D. Cashion, L. Joan Brown, A. L. Ottrey

Chapter 28. Mössbauer Spectroscopy as a Tool for Studying Hydrometallurgical Treatments of Copper-Iron-Sulfides

Chalcopyrite, CuFeS2, is by far the most abundant copper-bearing mineral, and forms the basis of the major copper deposits currently being exploited. In flotation concentrates chalcopyrite is often accompanied by one or more of the following minerals; bornite, Cu5FeS4, pyrite, FeS2, pyrrhotite, Fe1-xS, or hematite, α-Fe2O3. Present copper extraction technology relies on smelting of concentrates, which is polluting and energy inefficient, and substantial effort has been directed towards hydrometallurgical treatment of copper concentrates [1,2].

Stuart A. Fysh

Chapter 29. Mössbauer Effect Study of the Thermal Reactions of Phosphate Minerals from Christmas Island Fertilizer Rocks

Phosphate rock from Christmas Island is processed for agricultural purposes by sulfuric acid treatment, which converts it into soluble superphosphate. The presence of iron in the ore can interfere with this reaction. A Mössbauer effect study undertaken to identify the crystallographic environment of the iron in these rocks has focussed on crandallite, millisite, and goethite, the principal impurity components. A combination of Mössbauer spectroscopy, thermal analysis, and X-ray diffraction has been used to follow the structural course of the iron throughout the thermal reactions of these phosphate rocks, providing information about the initial State of iron in these minerals and the final environment of the iron in the calcined phosphate ores.

I. W. M. Brown, J. E. Davies

Chapter 30. Mössbauer Studies of Thermal Reaction Mechanisms in Hydrous Iron Layer Silicates

To shed light on mechanistic aspects of the thermal reactions of industrially important clay minerals such as kaolinite and Serpentine, Mössbauer studies have been made of analogous iron-containing minerals. The relatively rare iron layer-lattice silicates amesite, cronstedtite and berthierine form a series structurally related to Serpentine, and containing various substitutions of iron(II) and iron(III) in both octahedral and tetrahedral sites. Comparative Mössbauer studies of the thermal reactions of these minerals in both oxidizing and reducing conditions have been used to identify trends in the thermal stability of the various aspects of the thermal decomposition mechanisms of the related economic minerals.

K. J. D. MacKenzie, M. E. Bowden, R. M. Berezowski

Chapter 31. A Study of the Initially-Formed Hydrolysis Species and Intermediate Polymers and their Role in Determining the Product Iron Oxides Formed in the Weathering of Iron

Iron oxides and hydrous oxides (oxyhydroxides and hydroxides) are ubiquitous in soils and weathered iron-containing material. In the weathering process iron is initially released to form aquated iron(II) and/or iron(III) ions in Solution. Under appropriate pH and redox conditions aquated iron(II) is readily oxidized to form iron(III) ions which may then lose proton(s) to form FeOH2+ and/or Fe(OH)+2 species as well as the dimer, Fe2(OH)24+. The true nature of these species are probably [Fe4+(H2O)6]3+, [Fe(H2O)5 OH)]2+, [Fe(H2O)4 (OH)2] , and [(H2O)4 Fe(OH)2 Fe(H2O)4]4+, respectively, but they are usually abbreviated to the former. Such species have been identified in Solution by spectrophotometric and Potentiometrie methods [1–9], and by magnetic methods [10]. However, in other than very acidic Solution, hydrolysis continues beyond these simple products and based upon ultracentrifuge analyses [11] large polymers form. Pathways for polymer formation have been suggested by Dousma and deBruyn [7]. With time, and a continued supply of monomeric species such polymers continue to grow and ultimately yield precipitates of iron oxides or hydrous oxides, [12,13] the nature of which can vary depending on the conditions in the hydrolyzing medium. Factors influencing the product distribution include pH, temperature, iron concentration, rate of hydrolysis and the nature and concentration of other solutes [12]. Possible pathways for the formation of the product iron oxides and hydrous oxides are shown in Figure 1 and the general characteristics of these oxides [14] are presented in Table I. In some cases previous workers have used the term iron oxides to include collectively both the oxides and hydrous oxides [14]. For simplicity this approach will be adopted here.

James H. Johnston, David G. Lewis

Chapter 32. The Oxidation of Hydroxycarbonate Green Rusts

Green rusts are elusive Compounds. These hydroxy salts are members of the pyroaurite group. Their structure consists of brucitic layers containing the cations that carry a net positive Charge in alternation with anion plus water containing interlayers. The brucitic layers can contain both iron(II) and iron(III). Their structure and the presence of substantial amounts of iron(II) in them renders the green rusts highly susceptible to rapid oxidation and breakdown. This is probably one of the main factors that has so far prevented their identification in natural systems, should they exist there (e.g. in soils, where their presence has been long suspected). The formation of green rusts as intermediate phases during the corrosion of iron has also been indicated [1,2]. Positive identification of such a phase as a corrosion product has, however, been effected in only one case [3]. It is nevertheless conceivable that green rusts are much more frequently formed in the course of corrosion processes than is hitherto known.

Enver Murad, Reginald M. Taylor

Chapter 33. Metal Adsorption by Activated Carbon

Iron-57 and gold-197 Mössbauer spectra have been taken of activated carbon loaded from aqueous Fe2(SO4)3 and KAu(CN)2 Solutions, respectively. The iron-57 spectra for six different samples of activated carbons exhibited considerable variations, showing more than one active site as well as differ ent sites for the inherent iron, The spectra did not resemble those known previously for either Fe2(SO4)3 or intercalated species. In contrast, the gold-197 parameters agreed very closely with those for KAu(CN)2, consistent with the gold being adsorbed as either Au(CN)-2 or KAu(CN)2 solutions, resprectively. The iron-57 spectra for six different samples of activated carbons exhibited considerable variations, showing more than one active site as well as different sites for the inherent iron. The spectra did not resemble those known previously for either Fe2(SO4)3 or intercalated species. In contrast, the gold-197 parameters agreed very closely with thos for KAu(CN)2, consistent with the gold being adsorbed as either Au(CN)2 or KAu(CN)2.

J. D. Cashion, D. J. Cookson, L. J. Brown, D. G. Howard

Applications to Catalytic Materials

Chapter 34. Mössbauer Spectroscopy of Iron and Iron Alloy Fischer-Tropsch Catalysts

Mössbauer spectroscopy is an excellent technique for in situ investigations of iron-containing catalysts, because of the high penetrating power of the y-radiation and the high sensitivity of the spectral parameters to the chemical State and the local environment of the Mössbauer atom. Applications of Mössbauer spectroscopy in the field of catalysis up to 1980 have extensively been reviewed by Dumesic and Topsøe [1], and by Topsøe, Dumesic, and Mørfrup [2]. Here we will review Mössbauer investigations of iron and iron alloy Fischer-Tropsch catalysts, carried out at the Interuniversitair Reactor Instituut at Delft.

A. M. van der Kraan, J. W. Niemantsverdriet

Chapter 35. Mössbauer Effect Characterization of Silica Supported Rhodium-Iron Catalysts

Silica supported rhodium-iron catalysts were characterized with iron-57 Mössbauer spectra indicated that iron in the catalysts existed as iron(0) in the rhodium-iron alloy and iron(III) stabilized through the metal-support interaction. A part of iron(III) combined the rhodium-iron alloy and the silica as an anchor. The iron(III) to iron(0) ratio and Mössbauer effect parameters were found to depend on the iron to rhodium ratio in the catalysts. Their dependences correspond to the change of the catalytic properties of rhodium-iron catalysts with the iron content. A schematic model for the surface structure of the rhodium-iron catalysts is proposed. The Mössbauer spectra of rhodium-iron catalysts with various metal loading supported this model.

Yoshitaka Minai, Takeshi Tominaga, Takakazu Fukushima, Masaru Ichikawa

Chapter 36. The Application of Mössbauer Spectroscopy to Metallic, Bimetallic, and Mixed Metal Oxide Catalysts

The ability of Mössbauer spectroscopy to examine authentic solid catalysts in their working gaseous environments has conveyed a special power to the technique for the characterization of heterogeneous catalysts. The application of Mössbauer spectroscopy in this particular field has been comprehensively reviewed on two occasions in the recent past [1,2] and in this article of restricted length only a few systems have been selected, mainly from work reported since the last reviews, to demonstrate the suitability of Mössbauer spectroscopy for the study of solid catalysts and to illustrate its Potential power in the examination of metallic, bimetallic, and mixed metal oxide catalysts

Frank J. Berry

Chapter 37. Influence of Promoters on the Physical Properties of Iron Zeolite Catalysts

In addition to classical Fischer-Tropsch, F-T, gasoline production, many new efforts in technology are being directed towards production of basic hydrocarbons, because of the need of an alternative source for oil and gas. The main components of F-T catalysts usually are iron or cobalt. Promoters present, in general, simultaneously influence the chemisorption of the reactants, promote the formation of the primary complex, and improve rates of all carbon monoxide reactions.

Friedrich Schmidt

Chapter 38. Application of Mössbauer Emission Spectroscopy to the Study of Cobalt-Molybdenum Hydrodesulfurization Catalysts

The need for reducing sulfur pollution has made hydrodesulfurization an important catalytic process for removing sulfur from oil fractions. Hydrodesulfurization, HDS, is commonly carried out by passing oil, together with hydrogen, over a sulfided catalyst consisting of cobalt and molybdenum supported on a high surface area alumina. In this way the sulfur is removed as H2S. For many years the structure of HDS catalysts has been the subject of extensive research efforts. Nevertheless, until recently, the nature of the catalytically active phase has been a subject of great controversy [1–5]. The first investigation of HDS catalysts using Mössbauer spectroscopy was published in 1975 [6]. In this study part of the cobalt atoms in the catalysts were replaced by iron-57 atoms in order to allow absorption spectra to be obtained. In subsequent investigations the catalysts have been doped with cobalt-57 and used as sources in Mössbauer emission studies [7-14]. Catalysts in which all the cobalt has been replaced by iron have also been studied [9,12].

Steen Mørup, Bjerne S. Clausen, Henrik Topsøe

Chapter 39. Applications of the Mössbauer Effect in Electrolysis

During electrolysis ions are removed from the electrolytic Solution as the electrolytic processes occur at the electrode-electrolyte interfaces. The processes are heterogeneous reactions accompanied by the transfer of electric Charge across the interface. As a consequence of these generally complicated multistep cathodic and anodic reactions, neutral atoms or molecules are formed on the electrode surfaces. Recently Mössbauer spectroscopy has been successfully applied to the study of these products not only under ex situ, but also under in situ conditions.

A. Vèrtes, I. Czakò-Nagy, M. L. Varsànyi

Miscellaneous Applications

Chapter 40. Role of Tin Complexes in Bonding Silver to Glass: Mössbauer Studies

The nature of the tin surface complex formed during the sensitization of glass in a silver mirror-making process has been studied by tin-119 Mössbauer spectroscopy. The tin is found to be in the 4+ oxidation State which eliminates proposed bonding mechanisms based upon simple acid/base or ligand ex- change reactions, and confirms a mechanism based on oxidation of the tin(II) ions upon bonding to Silicon atoms on the glass surface. Further, the isomer shift of the tin complex is consistent with tin bonding to several hydroxide groups, in agreement with the oxidation reaction model. Although Auger electron spectral surface analyses show that the tin complex covers less than a monolayer of the glass surface, useful Mössbauer data are obtained by both transmission and backscatter, conversion electron, Mössbauer techniques. This is possible in part because of careful sample preparation but also due to effective surface areas of the glass slides which are significantly larger than that corresponding to perfectly flat surfaces.

T. M. Thomas, D. L. Williamson, D. P. Rainville

Chapter 41. Use of Mössbauer Spectroscopy in the Study of IV–VI Semiconductors

The IV–VI semiconductor group has received much attention over the last 15 years because it may be used in several different types of technological applications, such as optoelectronic devices like photovoltaic detectors and tunable infrared diode lasers, and in thermoelectric energy conversion, The technological properties of this group are directly related to both their fundamental properties and their methods of synthesis. For instance, some pseudobinary semiconductors, such as Pb1-x SnxTe, have a composition-dependent energy gap which, according to the proposal of Dimmock [1], has a band model which can be made arbitrarily small by varying the stoichiometry, i.e., the lead to tin ratio, as shown in Figure 1. However, the commonly used single crystal growth methods from the melt induce a significant concentration gradient along the growth axis.

Ida Ortalli, Vincenzo Fano

Chapter 42. The Mössbauer Characterization of Multilayered Films with Artificial Superstructures

Artificially structured metallic superlattices have attracted much attention in recent years [1]. Artificial superstructures can be fabricated, not only from similar elements that form solid solutions but also by combining elements with considerably different atomic radii. A very interesting example of the latter case is the multilayer consisting of iron and magnesium, because these are mutually insoluble elements even in the liquid State. As will be described below, the present authors have confirmed that artificial periodicities with very short wavelengths can be constructed in iron-magnesium multilayers [2].

Teruya Shinjo, Toshio Takada

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