Author: Mevlüt Karabulut
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Category :
Languages : en
Pages : 0
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"The atomic structure, glass forming and crystallization characteristics, and the chemical durability of vitreous binary iron phosphates of approximate batch composition 40Fe2O3-60P2O5 (mol%) and those containing up to 40 wt% of one or more common nuclear waste components such as Na2O, CS2O, SrO, UO2, or Bi2O3 have been investigated. The analytical tools used are Fe-57 Mössbauer, x-ray absorption, x-ray photoelectron, and Raman spectroscopies, high energy x-ray and neutron diffraction techniques, differential thermal analysis (DTA), and the product consistancy test (ASTM C-1285-94). The excellent chemical durability of iron phosphate glasses containing nuclear waste components is indicated by dissolution rates (at 90 °C in distilled water) as low as 10−10 to 10−11 g/cm2/min. When melted in air at 1100 to 1200°C, these iron phosphate melts reach a redox equilibria corresponding to a Fe(II)/Fe(III) ratio less than 0.51. The Fe(II) content increases with increasing melting temperature and when melted in reducing atmospheres. However, the glass forming ability of the melts decreases when the Fe(II)/Fe(III) ratio exceeds ca. 0.67. Both species of iron ions are coordinated with 5 to 5.5 near neighbor oxygen ions. The phosphorous-oxygen network is dominated by (P2O-- )4− dimer units. The iron-oxygen coordination and the phosphorous-oxygen network do not appreciably depend on the type or the concentration of the waste elements. The waste ions, which are situated outside the second shell coordination environment of iron and phosphorus ions, are not a major influence on the chemistry of the iron-oxygen-phosphorus host matrix. Therefore the addition of waste components does not cause major changes in properties such as the chemical durability of the iron phosphate host matrix. Vitreous iron phosphate host matrices appear to be a low cost and effective alternative to borosilicate glasses for vitrifying selected nuclear wastes"--Abstract, leaf iv
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Category :
Languages : en
Pages : 5
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Certain high level wastes (HLW) in the U.S. contain components such as phosphates, heavy metals, and halides which make them poorly suited for disposal in borosilicate glasses. Iron phosphate glasses appear to be a technically feasible alternative to borosilicate glasses for vitrifying these HLWs. The iron phosphate glasses mentioned above and their nuclear wasteforms are relatively new, so little is known about their atomic structure, redox equilibria, structure-property relationships, and crystallization products and characteristics. The objective of this research is to gain such information for the binary iron-phosphate glasses as well as iron phosphate wasteforms so that a comprehensive scientific assessment can be made of their usefulness in nuclear waste disposal.
Author:
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Category :
Languages : en
Pages : 34
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Objectives of this project are to: (1) investigate the glass composition and processing conditions that yield optimum properties for iron phosphate glasses for vitrifying radioactive waste, (2) determine the atomic structure of iron phosphate glasses and the structure-property relationships, (3) determine how the physical and structural properties of iron phosphate glasses are affected by the addition of simulated high level nuclear waste components, and (4) investigate the process and products of devitrification of iron phosphate waste forms. The glass forming ability of about 125 iron phosphate melts has been investigated in different oxidizing to reducing atmospheres using various iron oxide raw materials such as Fe2O3, FeO, Fe3O4, and FeC2O4 2H2O. The chemical durability, redox equilibria between Fe(II) and Fe(III), crystallization behavior and structural features for these glasses and their crystalline forms have been investigated using a variety of techniques including Mossbauer spectroscopy, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Extended x-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analysis, differential thermal and thermogravimetric analysis (DTA/TGA), and X-ray and neutron diffraction.
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ISBN:
Category :
Languages : en
Pages : 4
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Certain high level wastes (HLW) in the US contain components such as phosphates, heavy metals, and halides which make them poorly suited for disposal in borosilicate glasses. Iron phosphate glasses appear to be a technically feasible alternative to borosilicate glasses for vitrifying these HLWs. The iron phosphate glasses mentioned above and their nuclear wasteforms are relatively new, so little is known about their atomic structure, redox equilibria, structure-property relationships, and crystallization products and characteristics. The objective of this research is to gain such information for the binary iron-phosphate glasses as well as iron phosphate wasteforms so that a comprehensive scientific assessment can be made of their usefulness in nuclear waste disposal. This report summarizes the work undertaken and completed in the first 20 months of a three year project. Approximately 250 samples, binary iron phosphate glasses and iron phosphate glasses containing one or two common nuclear waste components such as UO2, Na2O, Bi2O3, Cs2O, SrO, and MoO3, have been prepared. Weight loss has been used to measure the chemical durability and the redox equilibria between Fe(II) and Fe(III) has been investigated using Moessbauer spectroscopy. The atomic structure has been investigated using a variety of techniques including Mossbauer, Raman, X-ray absorption (XAS), and X-ray photoelectron (XPS) spectroscopies and neutron/high energy X-ray scattering. Glass forming and crystallization characteristics have been investigated using differential thermal analysis (DTA). In addition, information necessary for glass manufacturing such as suitable refractories and Joule heating parameters also have been obtained.
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Category :
Languages : en
Pages : 5
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As mentioned above, the overall goal of this research project was to collect the scientific information essential to develop iron phosphate glass based nuclear wasteforms. The specific objectives of the project were: (1) Investigate the structure of binary iron phosphate glasses and it's dependence on the composition and melting atmosphere: Understand atomic arrangements and nature of the bonding. Establish structure-property relationships. Determine the compositions and melting conditions which optimize the critical properties of the base glass. (2) Understand the structure of iron phosphate wasteforms and it's dependence on the composition and melting atmosphere: Investigate how the waste elements are bonded and coordinated within the glass structure. Establish structure-property relationships for the waste glasses. Determine the compositions and melting atmosphere for which the critical properties of the waste forms would be optimum. (3) Determine the role(s) played by the valence states of iron ions and it's dependence on the composition and melting atmosphere: Understand the different roles of iron(II) and iron(III) ions in determining the critical properties of the base glass and the waste forms. Investigate how the iron valence and its significance depend on the composition and melting atmosphere. (4) Investigate glass forming and crystallization processes of the iron phosphate glasses and their waste forms: Understand the dependence of the glass forming and crystallization characteristics on overall glass composition and valence states of iron ions. Identify the products of devitrification and investigate the critical properties of these crystalline compounds which may adversely affect the chemical and physical properties of the waste forms.
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Category : Dissertation abstracts
Languages : en
Pages : 848
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Author:
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Category :
Languages : en
Pages : 12
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Because of their unusually good chemical durability, iron phosphate glasses are a natural candidate for a nuclear waste disposal glass. We have studied the effects of UO2 high-level waste on the structure of iron phosphate glasses with both neutron and high-energy x-ray diffraction using the GLAD instrument of the Intense Pulsed Neutron Source and the 1-BM bending magnet beamline of the Advanced Photon Source, respectively. The results of neutron scattering, which is mostly sensitive to correlations involving light atoms i.e. O-O, Fe-O and P-O, suggest the main structural features of the base glass are largely unaffected by the addition of UO2. The nearest-neighbor P-O, Fe-O and O-O peaks remain at the same position in real space and their intensities scale approximately with concentration. These findings are consistent with the earlier results of Raman scattering and EXAFS on the Fe-K edge wherein both cases the spectra remain similar to the base glass. High-energy x-ray scattering which is sensitive to correlations involving the heavier atoms and thus complements the neutron measurements, is also consistent with uranium occupying interstitial sites in the relatively undisturbed base glass structure. However, important questions remain as to the precise local structure and oxidation state of uranium in these glasses.
Author: Jincheng Bai
Publisher:
ISBN:
Category :
Languages : en
Pages : 190
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"The development of glasses to immobilize nuclear wastes requires a detailed understanding of how composition affects the critical properties required to design wasteforms, including thermal stability and chemical durability. Those properties depend on the molecular-level structures of the glasses. The principal objective of this research was to develop a comprehensive understanding of the composition-structure-property relationships, including the effects of processing conditions, for glasses in the alkali-molybdenum-iron-phosphate systems that could then be used to inform the development of wasteforms of interest to the US Department of Energy. The molecular-level structures of the alkali molybdenum iron phosphate glasses were analyzed by high-pressure liquid chromatography, Raman spectroscopy, and Mössbauer spectroscopy. Alkali ions (Cs+ and Na+) are associated with both phosphate and molybdate anionic species, and the polymerization of the phosphate network with increasing MoO3 content correlates with the formation of isolated Mo6+O6 octahedra in the Mo-rich glasses. The coordination environment of iron is affected both by the addition of large Cs+ ions into glass structure and by the reduction of Fe3+ to Fe2+; the latter is sensitive to the choice of oxidizing or reducing raw materials. Mo5+ ions are incorporated in highly distorted Mo5+O5 octahedral sites, which are associated with crosslinked Mo5+OPO4 structural units that affect properties like molar volume and the glass transition temperature. The dissolution kinetics are sensitive to iron contents, with the most durable glasses having the highest iron contents and smallest phosphate anions. Glasses with isolated Mo6+O6 octahedra in their structures are less chemically durable"--Abstract, page iv.
Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 846
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Author:
Publisher: DIANE Publishing
ISBN: 142234567X
Category :
Languages : en
Pages : 279
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