Hot Nitric Acid Research Articles

Studies on the Corrosion Performance of CP-Ti and Zr-4 in Hot Nitric Acid with Formaldehyde for Aqueous Reprocessing Applications

Studies on the Corrosion Performance of CP-Ti and Zr-4 in Hot Nitric Acid with Formaldehyde for Aqueous Reprocessing Applications

Synergistic Improvement in Ductility and Hot Nitric Acid Corrosion Resistance of LPBF Ti-6Al-4V Alloy via Hot Isostatic Pressing

Synergistic Improvement in Ductility and Hot Nitric Acid Corrosion Resistance of LPBF Ti-6Al-4V Alloy via Hot Isostatic Pressing

Electrochemical Surface Nanostructuring of Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 Metallic Glass for Improved Pitting Corrosion Resistance

Ti‐based bulk metallic glasses are envisioned for human implant applications. Yet, while their elevated Cu content is essential for a high glass‐forming ability, it poses biocompatibility issues, necessitating a reduction in near‐surface regions. To address this, surface treatments that simultaneously generate protective and bioactive states, based on nanostructured Ti and Zr‐oxide layers are proposed. An electrochemical pseudo‐dealloying process using the bulk glass‐forming Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 alloy is defined. Melt‐spun ribbons are immersed in hot concentrated nitric acid solution, monitoring the anodic polarization behavior. From the current density transient measurements, together with surface studies (field‐emission scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy), the surface reactions are described. This nanostructuring process is divided into three stages: passivation, Cu dissolution, and slow oxide growth, leading to homogenous nanoporous and ligament structures. By tuning the applied potential, the pore and ligament sizes, and thickness values are adjusted. According to X‐ray photoelectron spectroscopy, these nanoporous structures are Ti and Zr‐oxides rich in hydrous and nonhydrous states. In a simulated physiological solution, for those treated glassy alloy samples, complete suppression of chloride‐induced pitting corrosion in the anodic regime of water stability is achieved. This high corrosion resistance is similar to that of clinically used cp‐Ti.

Exploring the impact of Al alloying on microstructure and hot nitric acid corrosion resistance of Ti-xAl (x=0, 1, 2, 3, 4, 5) alloys

Enhancing the corrosion resistance of titanium alloys in hot nitric acid environments is imperative for advancing spent fuel reprocessing. Here, we explored the impact of Al alloying on microstructure and corrosion resistance of Ti-Al alloys via experimental assessments and theoretical computations. Results indicated that Al alloying induced a comparable Widmanstatten structure and increased hardness. Electrochemical findings demonstrated the optimal corrosion resistance for the alloy with 4 wt% Al. DFT computation presented the highest WF and the lowest EF for Ti-4Al alloy, indicative of superior thermodynamic stability. Eventually, a mechanistic understanding of Al alloying on nitric acid corrosion resistance was proposed.

Effect of chloride ion on the corrosion behavior of SiN stainless steel in concentrated hot nitric acid media

The effect of Cl− on the corrosion behavior of SiN stainless steel (SS) in simulating spent fuel reprocessing environment was systematically investigated. The results indicated that both cathodic and anodic behaviors of SiN SS were altered and multiple current peaks were observed as Cl− concentration increased. Meanwhile, there existed a critical Cl− concentration beyond which SiN SS transitioned from passive state to active dissolution state. Furthermore, a formulation for multiple current peaks was put forward based on mixed potential theory, and the corrosion mechanism in hot nitric acid with various Cl− concentrations was proposed involving the competitive adsorption of ions.

Effect of oxidizing ions on the corrosion behavior of SiN stainless steel in high-temperature nitric acid solution

The oxidizing ions, abundantly existing in spent fuel reprocessing process, play a vital role in the corrosion behavior of stainless steels due to the inherently high electrode potential. However, the systematic research on the effect of these ions on the corrosion mechanism of stainless steels in high-temperature nitric acid media is rarely reported. Herein, the electrochemical behavior and the passive film characteristics of SiN stainless steel in hot nitric acid solution containing different ions with various concentrations were investigated. The oxidizing Cr6+, V5+ and Ce4+ affected both the anodic and the cathodic reactions, while the non-oxidizing Fe3+ only changed the cathodic reactions. Meanwhile, the passive film characteristics of SiN stainless steel are partly altered with the change in ion concentration, and the passive film primarily consisted of Fe2O3, Cr2O3, Cr(OH)3 and silicate. The existence of silicate with high chemical stability improved the protection of passive film, displaying a high resistance to intergranular corrosion in the transpassive domain. In addition, a critical concentration phenomenon was observed in nitric acid with oxidizing ions, and the deposition theory was proposed to reveal the mechanism of critical concentration phenomenon.

Hydrothermally Enhanced Tungsten-Tungsten Bronze (W-MxWO3) Electrodes for Pseudocapacitive Energy Storage

Hexagonal tungsten bronzes (h-MxWO3) are an emergent class of pseudocapacitive energy storage material: a metastable phase arranged in a hexagonal crystal structure that enhances the oxide’s rapid intercalation mechanism with impressive capacitances of over 200 F/g and excellent cyclability figures reported. A symmetrical pseudocapacitive device composed of h-MxWO3 electrodes negates the need for expensive and problematic rare minerals such as cobalt and lithium instead using low-cost tungsten whilst offering more efficient high-rate energy storage than commercial lithium-ion batteries.Hexagonal tungsten bronze has shown some promising capacitances in literature in conventional electrode configurations, i.e. composite structures with binder support materials which increase electrode mass impacting specific capacitance. If the bronze was instead grown directly upon a current-collecting substrate, this would negate the need for additional electrode components, with the entire electrode mass participating in storing charge. The present work explores this concept of a novel binder-free electrode design where the nanostructured tungsten-bronze (active material) is grown directly upon a tungsten-based substrate (current collector). This simple design offers potentially higher specific capacitances than conventionally fabricated electrodes.Nanostructured W/h-MxWO3 electrodes were fabricated in a twostep process. Firstly, tungsten foil was oxidised in hot nitric acid, forming a seed layer of monoclinic-WO3. A second step saw the hexagonal bronze deposited upon substrates through a hydrothermal dehydration reaction of sodium tungstate (Na2WO4) where the effect of the directing agent (NaCl, Na2SO4, (NH4)2SO4& Rb2SO4) on the deposited nanostructure was investigated. To assess the benefit of the acid pretreatment step, vis-à-vis a pristine untreated tungsten foil, the hydrothermal reaction was completed upon both a pristine tungsten foil and an acid treated foil. The nanostructured surface deposited from the hydrothermal reaction was characterised by SEM, and the crystal phase identified by XRD. The electrochemical behaviour was analysed using a Biologic SP-300 potentiostat in a 3-electrode cell: as-synthesised foils employed as working electrode; Pt Wire as counter electrode; a saturated calomel electrode (SCE) as reference; and 0.5M H2SO4 as electrolyte. The performance of devices fabricated from two symmetrical as-synthesised electrodes was also characterised using both the potentiostat and a NEWARE battery cycling test system in a two-electrode cell configuration.XRD analysis confirmed that hexagonal-tungsten bronzes were successfully deposited upon substrates irrespective of the substrate pretreatment. The acid pretreatment generally resulted in larger masses of bronze being deposited upon the substrate, but this did not necessarily translate to superior electrochemical performance. The choice of directing agent present in hydrothermal synthesis drastically altered the nature of the deposited layer as may be seen in the provided figure of as-synthesised electrodes (figure b-d). Sodium directed samples formed powder-like deposits (figure b), ammonium sulphate produced larger colloidal bronze layers (figure c) and rubidium sulphate developed glossy smooth sheets (figure d). Additionally, the ratio of tungstate ions (WO4 2-) to directing agent cations (M+) was identified as being critical to obtaining the hexagonal phase. The mechanical stability of the deposited bronze proved problematic, with the layer prone to delamination and disintegration from a variety of mechanisms. A bespoke electrode holder, device testing apparatus and handling procedure was therefore developed to enable repeatable electrode characterization.The cyclic voltammetry response of the hydrothermally deposited layers was typical of an intercalation system, though an initial pseudocapacitive behaviour deteriorated to a battery-like response at sweeprates above 20 mV/s. Galvanostatic charge-discharge testing displayed a significant pseudocapacitive response over limited potential windows; moving beyond these limits produced steep non-linear curves indicating a departure from pseudocapacitive charge transfer processes. The charging at current densities above 1 A/g occurred over rapid time scales showing the electrodes’ suitability for high power applications. Preliminary 3-electrode capacitance results are encouraging with specific capacitances of over 100 Fg-1 by dry mass. The tunnelated M+ ion in the bronze is found to greatly influence the electrochemical performance of the electrode.This work reports the first example of hexagonal tungsten bronze being successfully grown directly on tungsten substrates for application as energy storage electrodes. The binder free electrodes were found to deliver promising performance characteristics in both 3-electrode analysis and in a two-electrode symmetrical device. The performance so far is hampered by the mechanical fragility of the electrode structures, while scale-up of the manufacturing process may prove challenging. The observed mechanism of deposition of hexagonal tungsten bronze from solution to substrate is of interest for future work, as is the significance of tunnelated M+ cations to the hexagonal bronze (h-MxWO3) structure, stability, and electrode performance (figure a). Figure 1

Increasing the oxygen-containing functional groups of oxidized multi-walled carbon nanotubes to improve high-rate-partial-state-of-charge performance.

Multi-walled carbon nanotubes (MWCNTs) with different oxygen functional groups were prepared from hot nitric acid reflux treatment. The acid-treated MWCNTs (a-MWCNTs) were introduced to negative active materials (NAMs) of lead-acid batteries (LABs) and the high-rate-partial-state-of-charge (HRPSoC) performance of the LABs was evaluated. A-MWCNTs with high quantities of carboxylic (COO−) and carbonyl (C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O) functional groups significantly improve the lead sulfate (PbSO4) reduction to lead (Pb) and thereby improve HRPSoC cycle life. The addition of a-MWCNTs to NAMs is helpful for the formation of larger crystals of ternary lead sulfate (3BS). The improved LABs performance is due to the formation of a sponge crisscrossed rod-like structure at the negative plate in the presence of a-MWCNTs. This unique channels structure is conducive to the diffusion of the electrolyte into the negative plate and delays the PbSO4 accumulation during HRPSoC cycles. The HRPSoC cycle life with a-MWCNTs is significantly prolonged up to the longest cycles of 39 580 from 19 712. In conclusion, oxygen-containing groups on the a-MWCNTs showed significant influence on the curing process and forming process and then improved HRPSoC performance.

Understanding the impurity gettering effect of polysilicon/oxide passivating contact structures through experiment and simulation

Polysilicon/oxide (poly-Si/SiOx) passivating contacts are a promising technology for the next-generation of high-efficiency silicon solar cells. The structure can be realised by a range of fabrication techniques, which can induce very different impurity gettering effects during the formation process. Understanding the different gettering effects will enable tailored solutions to optimise the gettering efficiency in device fabrication. This paper demonstrates a method to separately quantify the impact of each component on the overall gettering effect of the poly-Si/SiOx passivating contact structures. These components consist of the heavily doped poly-Si layer, in terms of its gettering strength; the SiOx interlayer, regarding its potential blocking effect for slowing down the diffusion of impurities; and the dopant in-diffused surface regions of the silicon wafer bulk directly below the SiOx interlayer, which may have a small additional gettering effect due to heavy doping. Phosphorus in-situ doped poly-Si layers from plasma-enhanced chemical vapour deposition (PECVD), coupled with SiOx interlayers from different growth techniques, were used to demonstrate the method. The experimental and simulation results confirm that the heavily doped poly-Si layer acts as the main gettering sink and the presence of different SiOx interlayers determines the overall gettering rate. For the ultrathin SiOx interlayers studied in this work, which have a similar thickness but different stoichiometry, a standard thermally grown SiOx demonstrates the strongest blocking effect, followed by a chemically grown SiOx from hot nitric acid, and a thermal SiOx of a reduced stoichiometry (grown in a pure nitrogen ambient) demonstrates practically no blocking effect.

Ti Ta Nb clads produced by electron beam surface alloying in regular air at atmospheric pressure: Fabrication, structure, and properties

In this study, the non-vacuum electron beam (EB) technology was used to clad commercially pure (CP-) Ti with Ta and Nb. The microstructure of the samples was characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The cladded layers were 1.7–2.7 mm thick and had a dense defect-free structure. Compositional inhomogeneity caused by dendritic liquation was observed in the cladded layers. High cooling rates during non-vacuum EB cladding led to the formation of the α’, α”, β, and ω metastable phases in the samples. The nanoscale ω phase was found in the regions with a high amount of Ta and Nb. Due to the increase in the Nb and Ta content, the microstructure of the samples was refined, and the microhardness increased from 330 HV to 400 HV. The impact toughness of the materials with cladded layers remained at a sufficiently high level (180–250 J/cm2). Corrosion tests carried out in hot nitric acid revealed that the addition of 15% Ta and 11.3% Nb to Ti decreased the corrosion rate from 0.104 mm/year to 0.004 mm/year, which was related to an increase in the fraction of Ta and Nb oxides in the oxide film. The produced materials can be recommended as a relatively cheap alternative for nuclear waste recycling when a hot solution of nitric acid is used.

(Invited) On the Intergranular Corrosion in Non-stationary Conditions: Experimental Approach and Modeling by Cellular Automata

Intergranular corrosion can affect stainless steels even if they are in a non-sensitized state. This is the case when the corrosive medium is particularly oxidizing such as in hot and concentrated nitric acid [1]. Intergranular corrosion is characterized by the formation of triangular grooves at the level of the grain boundaries. Their progression leads to the detachment of grains with a certain periodicity. This corrosion type is quite well described and modeled by different techniques when the medium remains the same [2-3]. Nevertheless, the medium may vary in some industrial chemical processes. Therefore, this work has investigated the impact of non-stationary conditions on the evolution of the intergranular corrosion.The intergranular corrosion kinetics of a 310L stainless steel was first studied in nitric acid with different levels of VO2 + concentrations in stationary conditions. Then non-stationary experiments were performed by varying the concentration of VO2 + as a function of time by periods. The corrosion kinetics was characterized by the evolution of the mass loss of the samples and of the geometry of the grooves (angle and depth) optically measured on cross sections.Numerical simulations were also performed by cellular automata [3]. A hexagonal close-packed (HCP) grid was chosen for the simulations. A realistic 3D granular structure of the stainless steel was modeled with a Voronoi algorithm. Two corrosion probabilities (for the grains and the grain boundaries) were adequately chosen for driving the time evolution in each conditions. These probabilities were kept constant in stationary conditions and varied with time by periods in non-stationary conditions. The simulated mass loss and the surface morphology reflects the same pattern of the experiments.In stationary conditions, the corrosion reaches a steady state after a transient period corresponding to the detachment of the first layer of grains: the corrosion rate and the specific surface in contact with the solution (increased by the formation of grooves) becomes constant. The characteristics of the steady state are directly dependent on the concentration of VO2 +. In non-stationary conditions, it appears that the characteristics of the intergranular corrosion (mass loss and geometry of the grooves) at a given period are influenced by the characteristics reached after the previous period (in other chemical conditions). This influence is only transient during a time corresponding approximately to the duration necessary to the consumption of a layer of grains.[1] Fauvet, P., Corrosion issues in nuclear fuel reprocessing plants. Nuclear corrosion science and engineering. D. Feron, Woodhead Publishing. 22 (2012) 679-728.[2] B.Gwinner et al., Towards a reliable determination of the intergranular corrosion rate of austenitic stainless steel in oxidizing media. Corrosion Science 107 (2016) 60-75.[3] D.Di Caprio et al., 3D cellular automata simulations of intra and intergranular corrosion. Corrosion Science 112 (2016) 438-450.

Comparison of different types of interfacial oxides on hole-selective p+-poly-Si passivated contacts for high-efficiency c-Si solar cells

We present a systematic study of highly boron (B)-doped poly-silicon (p+-poly-Si) and ultrathin silicon oxide (SiOx) bi-layer structure, also named as p-TOPCon, as the hole-selective passivated contact on n-type c-Si wafer, where the SiOx layer is made with three methods of hot nitric acid oxidation SiOx (NAOS-SiOx), plasma-assisted nitrous-oxide (N2O) gas oxidation (PANO-SiOx), and thermal oxidation (Thermal-SiOx). We demonstrate that the SiOx has a strong influence on the passivation quality. The best result is achieved using the Thermal-SiOx, while the NAOS-SiOx is slightly inferior, but better than the PANO-SiOx. The p+-poly-Si/SiOx structures with the three SiOx layers achieve the optimized passivation quality at different annealing temperatures of 820 °C for the NAOS-SiOx, 880 °C for the PANO-SiOx, and 930 °C for the Thermal-SiOx. The other potential factors affecting the passivation quality are also studied. The most important observation is that the optimized p-TOPCon structures with the three SiOx layers have a similar B diffusion profile, which penetrates into the c-Si wafer about 50 nm with B concentration decreasing to ~1 × 1018 cm−3. However, the overall p+-poly-Si/SiOx is still much poorer than n+-poly-Si/SiOx in terms the passivation quality. The comparison of the τeff versus carrier injection intensity spectra suggests that the B–O complex is the passivation killer possibly, and the approaches to improve the p-TOPCon are searching the other elements to reduce the B–O defects. In addition, contact resistivity (ρc) measurements show that the Thermal-SiOx leads a higher ρc than the others, but its value is still low enough for high-efficiency solar cells.

Recovering Metals from Aqueous Solutions by Biosorption onto Hydrolyzed Olive Cake

Olive cake obtained as a by-product from the olive oil industry has been evaluated as biosorbent of heavy metals from aqueous solutions in batch and continuous systems (fixed-bed columns). First, a complete study of effect of hydrothermal treatment with water on biosorption capacity of resulting solid was performed. Results showed that the values of biosorption capacity increased when the particle size of material decreased and the temperature of treatment increased. Then, hydrolyzed olive cake was treated by common chemicals (hot water, nitric acid, and sodium hydroxide) and the impact of chemical treatment was analyzed. The results were well reproduced by Langmuir and Freundlich isotherm models, getting maximum experimental biosorption capacities that changed between 42.34 mg/g obtained for the solid material modified by NaOH and 14.27 mg/g obtained for the solid material modified by nitric acid. Finally, laboratory tests in fixed-bed columns were performed with four different heavy metals and at three different inlet concentrations. The biosorption capacity increased from 2.83 mg/g (Cr), 4.51 mg/g (Cu), 12.30 mg/g (Pb), and 4.10 mg/g (Zn) to 3.08 mg/g (Cr), 5.17 mg/g (Cu), 13.21 mg/g (Pb), and 5.51 mg/g (Zn) when the concentration of metal ions increased, from 50 mg/L to 200 mg/L, respectively. Also, the experimental data obtained was successfully correlated with the Thomas, Yoon–Nelson, and dose–response models.

Impact of Fe(III) on the Autocatalytic Processes of Corrosion of Stainless Steels in Concentrated Nitric Acid

This study takes place in the industrial context of the spent nuclear fuel reprocessing plants, in which hot and concentrated nitric acid is used in the process to dissolve nuclear fuel. This imply a high oxidative solution, due to nitric acid but also to species resulting from the dissolution of the fuel and/or the equipment. Especially where there is stagnant solution in which different nitrogenous species can accumulate, causing the autocatalytic reduction reactions of nitric acid. These mechanisms can be responsible of the corrosion processes of the equipment. Then, in order to have resistant equipment to this acidic and oxidizing medium, stainless steels were chosen. The purpose of this work is to investigate the corrosion mechanisms of stainless steels in such aggressive medium. Particularly, it was established that the presence of Fe(III) (corrosion product) accelerates the corrosion of stainless steels, due to the rise of the cathodic reactions [1, 2]. Thus, this work was focused on the specific impact of Fe(III) on the corrosion processes, including autocatalytic reduction reactions of nitric acid. Indeed, it was not clear if this acceleration of the cathodic processes was induced by a direct reduction of Fe(III) to Fe(II) at the surface of the material or if it was an indirect impact of Fe(III) by a catalyse of the nitric acid reduction process (involving reduced species of nitric acid such as HNO2, NO2 and NO) (Figure 1). In order to investigate this point, we coupled stationary electrochemical techniques (chronoamperometry, steady-state polarisation curves) or dynamic electrochemical techniques (electrochemical impedance spectroscopy) with local analytical techniques (RAMAN microspectroscopy, Scanning ElectroChemical Microscope). These studies were completed with the analysis of the gaseous products of the reactions (NO2 and NO production) by mass and IR spectroscopies. It was shown that the direct reduction of Fe(III) to Fe(II) at the surface of stainless steel has a minor contribution to the corrosion. Thus, the role of Fe(III) is essentially related to its catalytic effect on the nitric acid reduction reaction (Figure 1). From the different measurements performed, the following mechanism of interaction of Fe(III) with the nitric acid reduction was proposed (Figure 1) and the kinetic constants of some elementary steps were determined. [1] Fauvet, P., et al. (2008). "Corrosion mechanisms of austenitic stainless steels in nitric media used in reprocessing plants." Journal of Nuclear Materials 375(1): 52. [2] Fauvet, P. (2012). Corrosion issues in nuclear fuel reprocessing plants. Nuclear corrosion science and engineering. D. Feron, Woodhead Publishing. 22: 679-728. [3] Lange, R., Phénomènes de couplage acier 304L – platinoïdes dans les milieux de dissolution des combustibles usés. 2012, UNIVERSITÉ PIERRE ET MARIE CURIE. p. 174. Figure 1

Hot nitric acid diffusion in fluoroelastomer composite and its degradation

Fluoroelastomers (FKM) are vital sealing materials in acidic environment and their failure can cause severe safety problems. Therefore, investigation of the degradation behavior and mechanism of FKM materials is of great significant. Herein, we investigate a diffusion model of an acidic solution into an FKM composite and its degradation behavior upon immersion in hot nitric acid solution. The results indicate that the diffusion process of the HNO3 solution into the FKM composite conforms to the Fick diffusion model at a low concentration of nitric acid solution. Besides, the concentration of HNO3 solution affects the diffusion process of solvent molecules and the dissolution process of the filler particles to some extent. SEM showed that the surface topography of the FKM was significantly altered after it was immersed in HNO3 solution. The structural and chemical changes of the FKM were studied using ATR-FTIR, SEM-EDS and MAS NMR, which demonstrated the occurrence of decrosslinking via hydrolysis of the crosslinks and backbone cleavage by dehydrofluorination. This was also manifested by the decrease in crosslinking degree and mechanical properties. The present study is helpful for revealing the chemical changes in FKM in hot HNO3 solution.

Small-scale cook-off experiments and models of ammonium nitrate

ABSTRACTWe have completed a series of small-scale cook-off experiments of ammonium nitrate (AN) prills in our Sandia Instrumented Thermal Ignition test at nominal packing densities of about 0.8 g/cm3. We increased the boundary temperature of our aluminum confinement cylinder from room temperature to a prescribed set-point temperature in 10 min. Our set-point temperature ranged from 508 to 538 K. The external temperature of the confining cylinder was held at the set-point temperature until ignition. We used type K thermocouples to measure temperatures associated with several polymorphic phase changes as well as melting and boiling. As the AN boiled, our thermocouples were destroyed by corrosion, which may have been caused by reaction of hot nitric acid (HNO3) with nickel to form nickel nitrate, Ni(NO3)2. Videos of the corroding thermocouples showed a green solution that was similar to the color of Ni(NO3)2. We found that ignition was imminent as the AN boiling point was exceeded. Ignition of the AN prills was modeled by solving the energy equation with an energy source due to desorption of moisture and decomposition of AN to form equilibrium products. A Boussinesq approximation was used in conjunction with the momentum equation to model flow of the liquid AN. We found that the prediction of ignition was not sensitive to small perturbations in the latent enthalpies.

Separate Crystallization of Lanthanide Oxalates and Calcium Oxalates from Nitric Acid Solutions

The separation of lanthanides from calcium compounds in the form of oxalates from hot nitric acid solutions of Ln(NO3)3 and Ca(NO3)2 with the insertion of oxalic acid and a Ln2(C2O4)3 · nH2O crystal seed was studied by mass-spectrometric, atomic emission, microscopic, X-ray diffraction, and fluorescence analyses. The produced single-phase precipitate was found to contain an isomorphic impurity of La–Sm oxalates, while calcium oxalate remained in the hot nitric acid solution (95°С) saturated with oxalic acid. This facile and efficient method provides Ln2(C2O4)3 · nH2O (n = 9.5 mol) in one step in a 80.1 rel. % yield, with the major phase being at least 99.4 wt %. The unit cell parameters were determined for the crystals of the isomorphic lanthanide oxalate mixture: a = 11.243(2) A, b = 9.591(2) A, c = 10.306(2) A; α = γ = 90°, β = 114.12(1)°; Z = 2; V = 1013.7(5) A3.

Synthesis, characterization and solubility of mixed zirconium-cerium molybdate precipitates

ABSTRACT The reaction between fission products Mo(VI) and Zr(IV) in hot nitric acid solution during the spent fuel dissolution process leads to the formation of hydrated zirconium molybdate precipitate. This solid can include other metallic cations at the 4th oxidation state (+ IV) inside the crystal such as Pu(IV). Precipitations in the inactive surrogate system of mixed zirconium-cerium molybdates Mo-Zr(IV)-Ce(IV) were performed all over the cerium molar percentage scale from 0 to 100%, Ce(IV) being used as a surrogate of Pu(IV). The crystal structures were identified from powder X-ray diffraction patterns and complementary investigations by SEM and elemental analyses were carried out. The solid composition pointed out two phases that are ZrMo2O7(OH)2(H2O)2 and Ce3Mo6O24(H2O)4. Each of these compounds was proved being a solid solution within which the ZrIV and CeIV atoms can substitute each other. Moreover, the influence of the cerium molar fraction on the precipitate solubility was investigated and showed a strong evolution of solubility not only with the nature of the precipitate and the Ce content, but also with the nitric acid concentration.

Optimization of the Sample Preparation Procedure for the Determination of Trace Elements in Auricularia auricula by Inductively Coupled Plasma-Optical Emission Spectrometry

ABSTRACTThis study aimed to develop a precise and accurate method of sample preparation of Auricularia auricula for inductively coupled plasma-optical emission spectrometry-based trace element determination and to compare concentrations of seven trace elements (Mg, Fe, Mn, Zn, Ni, Cr, Sr) in six A. auricula samples belonging to three varieties with two cultivation substrates. Five sample preparation procedures, microwave-assisted digestion, nitric acid digestion with hot plate heating, nitric acid and perchloric acid digestion with hot plate heating, nitric acid digestion with ash content, and aqua regia digestion with ash content, were compared. The performance of the procedures was determined based on the precision and accuracy of the results and the limits of detection of the elements. The best results, with limits of detection of 0.60–6.60 ng · mL−1 and recoveries for spiked samples between 93.80 and 105.00%, were found using nitric acid digestion with ash content. Six A. auricula samples were analyzed using the proposed procedure. Among the tested elements, the concentration of Fe was highest in all six A. auricula samples up to a maximum concentration of 284.83 µg · g−1. The concentrations of Mn, Cu, and Ni increased in mixed stands (basswood, birch, and mongolica) compared with pine sawdust cultivation.

The kinetics of transpassive dissolution chemistry of stainless steels in nitric acid: The impact of Si

Atomic emission spectroelectrochemistry was used to monitor the elemental dissolution of two stainless steels during transpassive polarization. A 304LN stainless steel (X2 CrNiN 18-10) was compared with a 3.5 wt% Si rich stainless steel (X1 CrNiSi 18-15-4) so as to elucidate the effect of Si on the dissolution mechanism. The enrichment in Si shifted the cathodic reaction to lower potentials explaining that in hot and concentrated nitric acid containing oxidizing species, 304LN SS corrodes more rapidly due to the transpassive break of passivity, while the 3.5 wt% Si SS remains passive. However, when polarized into the transpassive domain, preferential grain boundary corrosion was observed for the 304LN but not for the 3.5 wt% Si SS, despite having similar current densities. Congruent alloy dissolution was observed in the transpassive domain with the stoichiometry of Fe(III), Cr(VI) and Ni(II) yielding a faradaic yield of 100% at early times. For longer times, with the 304LN, the faradaic yield drop to 70% indicative of intergranular dissolution in which the cations released in the intergranular space were not detected by the ICP-AES. Transmission electron microscopy coupled with energy dispersive spectroscopy showed that the interface of the 3.5 wt% Si SS enriches in Cr during a polarization in the transpassive domain of the steel. No similar enrichment was detected for the 304LN.