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This study reports on the dissolution behavior of SrO in LiCl at varying SrO concentrations from low concentrations to excess. The amount of SrO dissolved in the molten salt and the species present upon cooling were determined. The thermal behavior of LiCl containing various concentrations of SrO was investigated. The experimental results were compared with results from the simulated results using the HSC Chemistry software package. Although the reaction of SrO with LiCl in the standard state at 650 °C has a slightly positive Gibbs free energy, SrO was found to be highly soluble in LiCl. Experimentally determined SrO concentrations were found to be considerably higher than those present in used nuclear fuel (

We have developed a liquid level measurement system using the dynamic bubbler technique. Based on our previous methodology, herein, we established a field-applicable wireless measurement system to simultaneously monitor the liquid level and density of corrosive molten salts at high temperatures. The accuracy and precision of the present technique were suitable for applications in harsh field processes. Regardless of the base pressure under the present experimental conditions, percentage differences compared with reliable reference values in the literature were less than 10% in the temperature range 773–1123 K using KNO3 as a molten salt. Our dynamic bubbler technique produces an average percentage difference ca. 5–8% with a standard deviation of less than ca. 0.04 g cm−3 between measured and literature density values in all experiments, whereas the standard deviations in all liquid level measurements were less than 0.3 mm (0.07% relative standard deviation). The present technique is an excellent alternative to many conventional liquid level and density measurement techniques used under extreme environmental conditions characteristic of common industrial processes.

We demonstrated that bromine in ethyl acetate can selectively separate metallic contents in lanthanide metal-oxide mixtures for analysis, which had been validated for uranium. This Br2-EtOAc dissolution method was applied to determine the constituents of metal and metal oxide in SIMFuel that was electrochemically reduced from oxide fuel in the molten salt. Compared with the analysis results obtained after dissolving the fuel in an acid solution, we concluded that the Br2-EtOAc method can be applied to uranium and rare earths but not to noble metals for the reduction yield determination.

A long-lived radioisotope of iodine, 129I, is a fission product and is released into our environment by spent nuclear fuel reprocessing plants or nuclear accidents. The measurements pertaining to 129I are focused on evaluating the effects of using human-made nuclear fission products as environmental tracers and for monitoring samples from various types of matrices for regulating radioactive contaminants or radioactive waste repository safety. Thermal ionization mass spectrometry (TIMS), accelerator mass spectrometry (AMS), and inductively coupled plasma mass spectrometry (ICP-MS) have been applied to analyze 129I and the isotope ratio 129I/127I from the environment and food samples. The advantages of these techniques in determination of iodine are high sensitivity, reasonable analysis time, relatively simple sample preparation process, and applicability to a large number of samples. This review describes the technical strategies for quantifying 129I with the considerations of reducing the interference and matrix effect, decreasing the limit of detection, and availability of standard materials when using TIMS, AMS, and ICP-MS.

The influence of Gd-doping level and oxygen stoichiometry on the structural properties and electrochemical reactivity of U 1−y Gd y O 2±x have been investigated. The stoichiometry of UO 2 matrices with different Gd contents was determined using the lattice parameter obtained by XRD. The extent of lattice contraction, defined by a contraction factor, was found to be dependent on the stoichiometry. The surface morphologies exhibited differences in grain size which varied with stoichiometry and its influence on the U atom diffusivity during fabrication. The differences in grain size and, hence, the density of grain boundaries was reflected in variations in electrical conductivity, with hyperstoichiometric specimens with a low number of boundaries, yielding an increase in conductivity with increasing Gd content. Cyclic voltammetry showed that a variation in Gd content had only a minor influence on the electrochemical reactivity of stoichiometric U 1−y Gd y O 2 . By contrast, the reactivity of hypostoichiometric U 1−y Gd y O 2−x and hyperstoichiometric U 1−y Gd y O 2+x increased and decreased, respectively, with increasing Gd content. The formation of Gd-O v clusters in hyperstoichiometric U 1−y Gd y O 2+x has a more marked influence on reactivity than the accompanying changes in grain size and electrical conductivity.

An in-house manufactured liquid level measurement system based on dynamic tube pressure measurements was established for high-temperature corrosive molten salts. The accuracy and precision of the present technique depend on the furnace temperature, initial base tube pressure, and tube speed. Whereas the initial base tube pressure did not influence the performance of the measurements significantly, a set value of the critical pressure level for the detection of the liquid surface was an important factor, especially in case of the higher temperature experiments. Within a temperature range of 773–1073 K using KNO 3 , our technique could obtain a measurement error of less than ca. 0.05 mm in precision. The tube speed increased from 0.25 mm s −1 to 2.00 mm s −1 , resulting in a % departure of only 1.1%, 1.3%, and 1.9% at 773 K, 973 K, and 1073 K, respectively. The measurement of travel distance instead of measuring the liquid level is useful in terms of the calibration-free process monitoring. The gravimetric calibration method was also used to determine the total mass of the liquid, where the weight versus travel distance calibration curves showed an excellent linearity with R 2 = 0.9999 under all temperature conditions.

UV–VIS spectra of uranium ions provided information not only on the electronic state of U(III)–Cl and U(IV)–Cl species, but also on the metal–ligand bonding properties. The 5f – 6d transition lines in the electronic absorption spectra of U(III) and U(IV) provided key information on the covalent bonding properties of U(III)–Cl and U(IV)–Cl complexes. The position and intensities of 5f – 6d and 5f – f5 transitions varied depending on the oxidation state and bonding properties. The 5f – 6d transitions of U(III) ion occur at a lower energy of as low as the 400–600 nm range with decreased intensity. However, U(IV) ions occur at the much higher ~ 250 nm range. The 5f – 6d / 5f – 5f intensity ratio indicated the degree of covalency. The U(III)–Cl species exhibited stronger covalent bonding than the U(IV)–Cl. This means that U(III)–Cl bonding is stronger than U(IV)–Cl species. Compared with uranium ions, Eu(II) ion showed no measurable covalent bonding under the same conditions, which means that Eu(II)–Cl bonding is predominantly ionic in nature. The bond strength (covalency) was evaluated in the order of U(III)–Cl > U(IV)–Cl ≫ Eu(II)–Cl. The reduction rate of U(IV) is ~ 4 times faster than that of the oxidation of U(III), indicating that U(III)–Cl is more stable than U(IV)–Cl species. The UV–VIS spectral analysis method may also be effective in investigating the bonding properties of neptunium and plutonium ions with chloride ligands in molten salt media.

We prepared neptunium chloride complexes electrochemically and performed spectroelectrochemical measurements of neptunium ions in LiCl–KCl eutectic melts at 450 °C, where the neptunium concentrations studied were in the range of 0.1–1 mM. We observed a highly absorbing f–d transition band of Np3+ at 383 nm, which was used to determine an formal potential of the Np4+|Np3+ redox couple (E°′ = 0.45 V vs. Ag|Ag+) with a solution of concentration as low as ~0.1 mM. This result agreed well with the value (E°′ = 0.42 V vs. Ag|Ag+) determined by cyclic voltammetry with a ~15 mM solution.

Cyclic voltammetry (CV) and chronoamperometry (CA) were employed to develop a real-time monitoring system for the pyrochemical process. These electrochemical techniques showed a good linearity of the current and the passed charges with the concentration of a solute even up to 9 wt.% in a LiCl–KCl melt, showing the potential for real application. To apply CA to the pyrochemical process, where the concentration of actinides and/or lanthanides is largely variable, the repeating chronoamperometry was designed and successfully tested at a wide range of Nd 3 + ion concentration of up to 9 wt.%.

We have measured the electronic absorption spectra of the U (III) and U (IV) ions in a LiCl–KCl eutectic melt at 450 °C to understand their spectrochemical behavior in the context of pyrochemical process of spent nuclear fuel. The UV–VIS spectra of the U (III) ion consist of two main peaks in the range of 400–600 nm which are attributable to the 5f 3 – 5f 2 6d 1 transitions. The 5f – 6 d transitions of U (III) ion occurred at lower energy as low as 400–600 nm range while that of Nd (III) and U (IV) ion occur at much higher energy over the normal UV range. For the U (III) ion, the intensities of 5f – 5f transitions are about one order of magnitude larger than the 4f – 4f transitions in lanthanides. And the 5f – 6 d transitions are about one order of magnitude smaller than in the 4f – 5 d transitions in the lanthanide ions. The electronic energy levels of the U (III), U (IV) and Nd (III) ions are estimated to understand their electronic transitions. The features of the electronic absorption spectra of U (III), Nd (III), U (IV) ions are reasonably explainable by their electronic structure. In-situ monitoring of the U (III) ↔ U (VI) redox reaction in a high temperature LiCl–KCl showed that the redox reaction is reversible.

The two-dimensional Pt submonolayers on Au(111) were used as model catalyst system to study kinetics of hydrogen oxidation reaction (HOR). The morphology of different Pt submonolayers was characterized by ex situ scanning tunneling microscopy combined with statistical image analysis. The HOR kinetics data were analyzed using Levich–Koutecky formalism and presented as a function of the mean size of Pt clusters for each Pt submonolayer. The Pt submonolayers with smaller Pt clusters were found less active for HOR. This trend is well correlated with the continuum elasticity analysis of the average active strain in Pt clusters indicating that smaller clusters have less tensile strain. The density functional theory calculations were found in agreement with our results demonstrating that the size-dependent strain in Pt clusters has significant effect on the energy of the d-band center, i.e., the Pt clusters’ activity.

Time-dependent elementary polarizations of a lithium-ion battery are quantitatively investigated below room temperature in an attempt to determine the critical factors affecting low temperature power decline. From three-electrode impedance measurements and the theoretical analysis of the phenomenological equivalent circuit, the proportional contribution of the internal resistances to the total polarization is satisfactorily analyzed as a function of the pulse discharging time. The results prove that the interfacial charge-transfer resistances of the anode (graphite) and the cathode (lithium cobalt dioxide) make the highest contributions to the low temperature power decline. On this basis, a strategy for the material design to enhance the low temperature performance is suggested with two examples of surface modification and hybridization with an electrochemical capacitor.

We have measured the electronic absorption spectra of the U(III) ion in LiCl–KCl eutectic melt at 450 °C to understand its chemical behavior in the context of pyrochemical process of spent nuclear fuel. The UV–VIS spectra of the U(III) ion consist of two main peaks in the range of 400–600 nm which are attributable to the 5f 3 –5f 2 6d 1 transitions. With the aid of UV–VIS spectroscopic tool, in-situ measurement of chemical reactions of the U(III) with oxide ion as well as neodymium oxide was successfully achieved. The U(III) ion forms insoluble uranium oxide phases by reacting with oxide ion and lanthanide oxides.

Cyclic voltammetry (CV), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to investigate the electrodeposition of Eu and Al in an LiCl–KCl eutectic melt containing Eu2+ and Al3+ at 450 °C. In order to deposit a pure Eu and Al alloy, the stoichiometrically lower concentration of Al3+ than that of Eu2+ and Al wires as a counter electrode was introduced into the bath of LiCl–KCl melt for the electrodeposition. The electrodeposition takes place at a potential more negative than −1.95 V vs. Ag|Ag+ while the deposit is oxidized at more positive potential than −1.92 V. Two new reduction peaks and an anodic peak on a W working electrode were observed at −2.39 V, −2.42 V, and −2.1 V, vs. Ag|Ag+, respectively, suggesting that the potential window of the Al system in LiCl–KCl melt can be extended to −2.43 V vs. Ag|Ag+. The EDS analysis indicated that AlEu can be deposited at the potential more negative than −2.37 V.

In situ electrochemical-scanning tunneling microcopy (EC-STM) was employed to investigate the etching dynamics of the moderately doped n-Si(1 1 1) electrode during cyclic voltammetric perturbation and at the seven different potentials including the open circuit potential (OCP) in 40% NH4F solution at pH 10, which was prepared from 40% NH4F and concentrated NH4OH solution. The etching rate was significant at OCP and showed an exponential dependence on the potential applied to the silicon substrate electrode. Although some triangular pits were generated at the Si(1 1 1) surface, at the potentials more negative than OCP the site dependence in the removal of surface silicon atoms prevailed and led to the atomically flat Si(1 1 1):H surfaces with sharply defined steps of the step height 3.1 A, where the interatomic distance of 3.8 A was observed with a three-fold symmetry. At the potentials sufficiently more positive than OCP, macroporous hole was formed to limit further in situ EC-STM study. The results were compared with in situ EC-STM studies of the etching reaction of n-Si(1 1 1):H in the aqueous solution of dilute ammonium fluoride at pH 5, 40% NH4F at pH 8, and 1 M NaOH reported in the literature.

The effect of Fe 3+ concentration on saturation magnetic flux density (Bs) of electrodeposited Co40–44Fe60–56 films was investigated. The results show that if the conditions at the electrochemical interface for nucleation/precipitation of iron(III) hydroxide (Fe(OH)3) are reached, the Bs of electrodeposited Co40–44Fe60–56 films quickly decreases as a result of the Fe(OH)3 incorporation into deposit. These conditions are discussed as a function of the solution formulation (pH) and the parameters of electrodeposition process (current density, current efficiency, diffusion layer thickness) and a simple analytical model is developed qualitatively describing the hydroxide incorporation phenomenon and resulting decrease in Bs of

The etching reactions of monohydride (MH) terminated Si(1 1 1) surface were observed in oxygen-free 40% NH4F solution by an in situ electrochemical scanning tunneling microscope. The results showed that the MH silicon steps in triangular pits played an important role in producing the ideally flat MH terminated Si(1 1 1) surface. The etching rate of MH silicon steps in the triangular pits is about 8.3 nm/min at open circuit potential which is significantly lower than the value of about 28 nm/min for terrace MH steps. The etching rate of MH terminated steps in triangular pits is 3.3–4.5 times lower than the values for MH terminated steps of the terrace edges and its etching ratio of steps over pits was maximized at −0.4 V; consequently, the staircase structure with a constant step width was produced on the Si(1 1 1) surface.

In situ electrochemical-scanning tunneling microscope (EC-STM) was employed to investigate the electrodeposition of copper at the hydrogen-terminated n-Si(1 1 1) electrode in 3 mM CuSO4 + 0.1 M H2SO4 solution. Cyclic voltammogram at the silicon electrode showed a reduction peak of copper (II) at −1.2 V versus Cu(II)/Cu (−0.59 V versus SCE) without the corresponding anodic stripping peak at the scan rate of 50 mV/s, suggesting that a Schottky junction was formed when copper ions were deposited at the surface of n-Si(1 1 1):H by electroreduction. EC-STM images of the atomically flat n-Si(1 1 1):H revealed the step-edge deposition when copper was electrodeposited well before the peak potential, but the step-edge as well as terrace deposition after it. The difference in copper electrodeposition depending on the potential applied was corroborated by SEM images of the samples electrodeposited at the two experimental conditions for long time.

The etching dynamics of a moderately doped n-Si(111):H electrode misoriented in the [112] direction in 40% NH4F aqueous solution was investigated by open circuit potential (OCP) measurement, in situ electrochemical-scanning tunneling microcopy (EC-STM), and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. It was demonstrated that OCP could be used as an in situ probe in judging that the well-defined Si(111):H surface was prepared successfully in the 40% NH4F solution. The OCP initially decreased when an oxide-covered silicon wafer was immersed into the solution, increased, and finally reached a plateau value, where the EC-STM image was observed to be composed of the atomically flat terraces with a threefold symmetry of interatomic distance 3.8 A separated by a step of 3.1 A. ATR-FTIR spectra showed that a strong and sharp peak with a full width at half-maximum of 0.94 cm-1 was observed from p-mode and a simultaneous background-like signal was observed from s-mode, suggestin...

Charge transfer through thin layers of water between an STM tip and an Au surface has been investigated by using a scanning tunneling microscopy (STM) technique at a relative humidity of 95%. The plateau currents were found to appear at separations larger than several A where the current decay stops. The polarity dependence of the electrochemical currents was not observed with STM junction between an Au tip and an Au surface, which was observed with STM junction between a Pt/Ir tip and an Au surface. The plateau currents at H 2 O saturation were measured to be 10–20% higher than those at D 2 O saturation at bias voltages above |0.4| V. The results were rationalized in terms of the electrochemical currents originating mostly from the processes of OH − (OD − ) or H 2 O (D 2 O) on the positive surface with different conductivity between H 2 O and D 2 O.

Electrochemical, in situ electrochemical scanning tunneling microscope (EC-STM), and attenuated total reflectance-FTIR (ATR-FTIR) spectroscopic methods were employed to investigate the preparation of atomically flat Si(111)-H surface in ammonium fluoride solutions. Electrochemical properties of atomically flat Si(111)-H surface were characterized by anodic oxidation and cathodic hydrogen evolution with the open circuit potential (OCP) of ca. −0.4 V in concentrated ammonium fluoride solutions. As soon as the natural oxide-covered Si(111) electrode was immersed in fluoride solutions, OCP quickly shifted to near −1 V, which was more negative than the flat band potential of silicon surface, indicating that the surface silicon oxide had to be dissolved into the solution. OCP changed to become less negative as the oxide layer was being removed from the silicon surface. In situ EC-STM data showed that the surface was changed from the initial oxidecovered silicon to atomically rough hydrogen-terminated surface and then to atomically flat hydrogenterminated surface as the OCP moved toward less negative potentials. The atomically flat Si(111)-H structure was confirmed by in situ EC-STM and ATR-FTIR data. The dependence of atomically flat Si(111)-H terrace on mis-cut angle was investigated by STM, and the results agreed with those anticipated by calculation. Further, the stability of Si(111)-H was checked by STM in ambient laboratory conditions.

The electroless deposition of copper on the hydrogen-terminated Si(111) surface was investigated by means of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, scanning tunneling microscopy (STM), and energy-dispersive spectroscopy (EDS). The hydrogen-terminated Si(111) surface prepared was stable under air atmosphere for a day or more. It was found from ATR-FTIR that two bands centered at 2000 and 2260 cm - 1 appeared after the H-Si(111) surface was immersed in 40% NH 4 F solution containing 10 mM Cu 2 + . On the other hand, STM image included the copper islands with a height of 5 nm and a diameter of 10-20 nm. The EDS data displayed the presence of copper, silicon and oxygen species. The results were rationalized in terms of the redox reaction of surface Si atoms and Cu 2 + ions in solutions, which are changed into Si(OH) x (F) y containing SiF 6 2- ions and neutral copper islands.

Electrochemical scanning tunneling microscopy was employed to study the evolution of surface morphology during electrochemical preparation of Si(111)-H from Si(111) oxide. Anodic dark current of cyclic voltammogram in 0.2M solution (pH 4.7) decreased as the number of cycles increased and remained nearly constant after the second cycle. Then, the Si(111) oxide was entirely stripped, which was followed by H termination on the Si(111) surface. Hydrides at kink and step sites were etched more rapidly than on the terrace, which remained triangle pits with [112] oriented steps where existed stable monohydride. Then, triangle pits deepened. During chronomamperometry at 0.4V anodic dark current shoulder appeared and decreased slowly, indicated the stripping of Si(111) oxide and the formation of stable (112) oriented steps with monohydride. Additionally, the etching mechanism of Si(111)-H in 0.2M solution at +0.4V was discussed.

Charge transfer through thin layers of water between a Pt/Ir tip and a gold surface has been investigated by using a scanning tunneling microscopy (STM) technique at the temperature of 21 ± 1 °C. The amount of the water layer inside the STM or an atomic force microscopy (AFM) junction was controlled by relative humidity. It was found from STM, AFM, and quartz crystal microbalance experiments that the thin water film was formed on the gold sample when relative humidity was in the range up to 80%. Charge transfer across the interfacial water layer was found to originate mostly from electron tunneling. The value of the barrier height of the electron tunneling was determined to be 0.95 eV from the current vs distance curve, which was independent of the tip−sample distance and the bias voltage. At relative humidity above 90%, the surface was covered with a thick water layer. In such a case the decay for charge transfer was strongly dependent on the bias voltage. For a low bias of 0.03 V charge transfer was sim...

Electrochemical quartz crystal oscillator and four-probe techniques were employed to investigate the changes in microrheological properties of polypyrrole (PPy) during electrochemical growth in aqueous electrolyte solutions and the four-probe resistivity with the electrochemically grown PPy films, respectively. PPy films grew elastic at the initial stage and viscoelastic at the later stage in hydrochloric acid solution, while the films remained nearly elastic in the whole range of the thickness examined (8000 Hz) in sulfuric acid solution. Usual negative temperature coefficient of resistivity (TCR) was observed from 77 to 300 K with most PPy samples, but the crossover of TCR with a broad minimum peak near 200 K was found with PPy samples prepared at 0.8 V versus SCE in both hydrochloric acid and sulfuric acid solution.

Electrochemical, differential capacitance, and in situ electrochemical scanning tunneling microscopy (EC-STM) methods are used to examine the interaction of bis(3-sulfopropyl)-disulfide (SPS) and mercaptopropylsulfonic acid (MPS) with Cu(100) surfaces both in the absence and presence of chloride. Both electrochemical and differential capacitance results are weakly perturbed by the addition of either MPS or SPS in the potential region between −0.2 and −0.5 V versus Ag/AgCl relative to the additive-free case. EC-STM images obtained from solutions of MPS alone exhibit a c(2 × 2) adlattice whereas those from SPS alone yield only the (1 × 1) structure. In the presence of Cl-, both adsorbates evince only a c(2 × 2) adlattice on the Cu(100) surface. The desorption potential of these structure is identical to that found with Cl- alone. These results show that neither MPS nor SPS adsorbs strongly on Cu(100) in the presence of Cl-.