Publications

Extended information is provided about 19F MAS NMR and XPS spectroscopic data on 11 ternary fluorido-zirconates (Li2ZrF6, Rb2ZrF6, Cs2ZrF6, Na3ZrF7, (NH4)3ZrF7, K3ZrF7, Li4ZrF8, K2ZrF6, Na5Zr2F13, Na7Zr6F31, and (NH4)2ZrF6), which display different coordination numbers of the zirconium atom as well as different modes of fluorine atom bonding. XPS data show that binding energies on fluorine 1s electrons are sensitive to its coordination properties (ionic, terminal or bridging coordination mode) while the binding energies of zirconium orbitals are not sensitive to its coordination properties (six-, seven- or eightfold coordination). 19F chemical shifts correlate with the ionic radii of counter cations along the series Li2ZrF6, Rb2ZrF6, Cs2ZrF6 and K3ZrF7, (NH4)3ZrF7 and Na3ZrF7. This reflects the polarizability properties and shielding potential of the cations surrounding the fluorine atoms. Additionally, calculations of NMR parameters for the compounds were also carried out using the CASTEP DFT code. The correlation between the experimental isotropic chemical shifts and calculated isotropic chemical shieldings established for the studied compounds allows us to predict the 19F NMR spectrum of crystalline compounds with good accuracy. A unique technique of low temperature 19F MAS NMR experiments combined with CASTEP calculation on (NH4)2ZrF6 enabled the assignment of all 12 crystallographically non-equivalent fluorine atoms to NMR signals.

In situ high temperature NMR spectroscopy was used to characterize the NaF-ScF3 melt over a wide range of compositions. 19F, 23Na, and 45Sc NMR spectra were acquired in NaF-ScF3 melts of up to 70 mol% of ScF3. The interpretation of all experimental results obtained in situ in the melt is significantly enhanced by the contribution of Molecular Dynamics (MD) calculations. A new interatomic potential for the molten NaF-ScF3 system was developed by using a Polarizable Ion Model (PIM). The potential parameters were obtained by force-fitting to density functional theory (DFT) reference data. MD simulations were combined with further DFT calculations to determine NMR chemical shifts for 19F, 23Na, and 45Sc. The agreement between the experimental NMR data and the corresponding calculated data from our applied computational protocol indicated the polymerization and network formation in the melt. Additionally, the density and the electrical conductivity in the molten state were calculated from the statistical analysis of ionic trajectories obtained through MD simulations.

Reaction of lithium oxide with neodymium chloride was studied in LiCl, LiCl–KCl and NaCl–KCl based melts at various O2– : Nd3+ mole ratios. The effect of the experimental conditions on the degree and rate of neodymium precipitation, phase composition of the solid reaction products was investigated. Size of the particles in the precipitates formed at various conditions was determined to assess the feasibility of subsequent separation of the solids from the technological melts.

The review is devoted to overview of the current status on some radiochemical studies and their technological applications in Russian Federation. Multiple

The corrosion resistance of Haynes 230, Hastelloy S and X high-temperature alloys and Hastelloy N, B-3, G-35, C-2000 corrosion-resistant alloys was investigated in a wide temperature range (450–650 °C) in fused KCl-AlCl 3 mixtures. It was found that the mechanisms of corrosion of high-temperature alloys and corrosion-resistant alloys in KCl-AlCl 3 based melts are different. At a critical temperature phase structure of the high-temperature alloys changes after contact with chloroaluminate melts resulting in formation of intermetallic or carbon-containing phases along the grain boundaries that result in increasing strength of the alloys but initiate intense intergranular corrosion. The structural changes in most of the corrosion-resistant alloys take place at higher temperatures but they also can cause structural changes in the materials. It was shown that both types of alloys undergo intergranular corrosion up to the critical conditions. Formation of different secondary phases was detected and their influence on the corrosion processes mechanism is analyzed.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Fused chlorides can be used in technologies of nuclear fuel reprocessing and as a working media for molten salt nuclear fast reactors (MSNFR). However, application of such technologies is limited by the problem of finding suitable corrosion resistant materials stable in contact with molten salts. Existing corrosion-resistant alloys are typically manufactured for application in aggressive aqueous-based media, whereas high-temperature alloys are mostly designed for application in aerospace industry where the mechanical strength under extreme conditions is required. On the basis of the comprehensive studies of corrosion resistance of different kinds of stainless steels and various nickel-based superalloys we concluded that a new alloy with «nickel – chromium - molybdenum» matrix is needed for molten chlorides application. In the present work the results of the new alloy fabrication process and detailed examination of the alloy’s properties are presented. The required levels of the basic component contents were determined on the basis of thermodynamic calculations (Thermocalc Software AB was used to simulate the phase content of new alloy) and previously obtained experimental data on metals and alloys corrosion in molten chlorides and sensibility of these materials to intergranular corrosion. Carbon content in the material should be maintained at a minimal level. The influence of other elements presence in the γ-phase austenite matrix was analyzed. The alloy of the required composition was cast in a vacuum induction furnace. A special 4-stage refining casting procedure was developed to provide the required carbon content. The obtained ingot was hot rolled into a strip. Mechanical and thermophysical properties, susceptibility to intergranular corrosion of the new nickel alloy with a low carbon content in «as received» conditions were investigated. The obtained results correlate well with the data for typical nickel-based superalloys with austenite structure. In a special series of experiments thermodynamic stability of the fabricated alloy was studied. No formation of carbide phases was observed. Phase structure of the excessive intermetallic phases was characterized. The constructed «time – temperature – precipitation» diagram allowed to determine maximal temperature and time of alloy’s operation in contact with molten salts. Corrosion resistance of the material was studied in molten KCl-AlCl 3 electrolytes at 450–650 °C. Chloroaluminates are prospective media for the second loop of MSNFR and acidic KCl-AlCl 3 electrolytes have extremely high aggressive properties among other chloride mixtures. To create the worst possible conditions for the alloy, the electrolytes containing excess aluminum chloride were selected for the present investigation. Time of exposure varied from 6 to 1000 h. The samples were tested in «as received» conditions as well as after typical technological manipulations (bending, welding, heat treatment, etc .). Metallographic analysis showed that the alloy was subjected to slow frontal corrosion up to 550 ºC (Figure). Experimentally determined corrosion rates were below 50μm/year. The surface of the corroded samples was slightly depleted in chromium. Formation of secondary phases was not observed. Excessive sigma phases along the grain boundaries were formed after 100 h exposure at 650 ºC in the surface layer and after 400 h in the bulk of the material. Formation of the secondary phases in the surface layer is caused by selective chromium leaching and degradation of nickel-based solid solution. Prolonged contact of the material with the high-temperature melt leads to unavoidable decomposition of thermodynamically metastable nickel-based austenite. Such behavior correlates very well with the constructed «time – temperature – precipitation» diagram. Using the alloy at such temperatures (650 o C and above) becomes undesirable due to possible development of integranular corrosion. Tests performed on welded and bent samples showed that their corrosion rates were higher that could be explained by changes in the structure of the alloy caused by high temperatures (in case of welds) and increased amounts of defects. Figure. Microstructure of the new alloy after 100 h exposure in KCl–AlCl 3 melt at 450 (a, b); 550 (c, d) and 650 °С (e, f). Figure 1

A novel method of aluminium-based master alloy manufacturing using high-temperature exchange processes between aluminium and halides of various rare-earth metals (Ce, Nd, Gd) was proposed. Samples with REE content from 1 to 10 wt. % were synthesised. The yields in excess of 90, 86, and 80% were achieved for Al–Ce, Al–Nd, and Al–Gd alloys, respectively. Microstructure of the alloys consisted of a metal matrix of aluminium in which intermetallic compounds were distributed. Mechanical properties of synthesised master alloys were determined.

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No abstract is provided for this article.

The temperatures of appearance and degradation of short-range and long-range ordering in VDM® Alloy C-4 (UNS 2.4610/N06455) are determined with the he