Hot Trap Research Articles

(Invited) Small Polarons and Surface Defects in Metal Oxide Photocatalysts Studied Using Xuv Reflection-Absorption Spectroscopy

In photocatalytic transition metal oxides, the surface electronic structure and carrier kinetics are complicated by charge trapping at defects as well as by carrier self-trapping as small polarons. These processes are unique to the material interface, where surface carrier dynamics deviate from bulk behavior due to the presence of surface defect states, undercoordination, or interface bonding. This talk will highlight the ability to directly visualize these processes with surface sensitivity, chemical state resolution, and ultrafast time resolution using extreme ultraviolet (XUV) reflection-absorption spectroscopy. This method measures element-specific, core-to-valence spectra analogous to x-ray absorption, but with the added benefits of surface sensitivity and ultrafast time resolution. Using this method, we investigate surface trapping and recombination in α-Fe2O3 and TiO2 as two prototypical metal oxide photocatalysts. In α-Fe2O3, we observe ultrafast polaron formation with a rate that is three times slower than observed in bulk. Kinetic analysis reveals that this is a result of increased lattice relaxation energy for polaron formation at a surface, and we show that these rates can be rationally tuned by surface molecular functionalization. In contrast, in photoexcited TiO2 we observe that hot holes trap as small polarons at oxygen vacancy defects in approximately 50 fs, and hot electrons couple to polar optical phonons leading to vibrational coherence and large polaron formation in approximately 1 ps. These findings provide examples of the unique opportunities enabled by XUV spectroscopy for understanding surface electron dynamics in photocatalytic systems.

Au–Ag bimetallic nanoparticles decorated silicon nanowires with fixed and dynamic hot spots for ultrasensitive 3D SERS sensing

Abstract Three-dimensional (3D) SERS substrates have being intensively investigated since they can afford substantial hot spots and trap targets exponentially, silicon nanowires (SiNWs) array is a promising candidate due to its facile preparation. Most often, the SiNWs based substrates were decorated with pure Ag or Au nanoparticles (NPs), Au–Ag bimetallic NPs (BMNPs) with superior plasmonic properties and stabilities are rarely studied for the fabrication of SiNWs based SERS substrates. In this work, we reported a facile method to fabricate Au-Ag BMNPs decorated SiNWs as 3D SERS substrates, the effects of Au-Ag BMNPs scale and composition ratios on SERS performance were well investigated through experiments and theoretical simulations. The vertically aligned SiNWs coated with dense Au-Ag BMNPs further improved the sensitivity by forming fixed and dynamic hot spots, and the detection limit of R6G on SiNWs-AuAg can be as low as 10-12 M by using a portable Raman spectroscopy. Meanwhile, the prepared 3D SERS substrate showed a higher SERS enhancement factor (EF) and oxidation resistance ability due to the synergistic effect of Au and Ag atoms in Au–Ag BMNPs. Considering the facile fabrication process and excellent performances, the prepared 3D SERS substrate can be potentially applied for ultrasensitive detection of trace analytes.

Preparation of extremely low nitrogen concentration lithium by Fe-5at.%Ti alloy hot trap

Abstract In the lithium loop of IFMIF (International Fusion Materials Irradiation Facility), the target value of the nitrogen concentration in lithium flow is designed to be 99.9999 %), it was contaminated by nitrogen as an impurity of the cover gas. Therefore, the hot trap experimental pot sealed was placed in a vacuum exhaust glove box. In order to minimize nitrogen contamination, lithium sampling for nitrogen concentration measurement was carried out by scraping out lithium in a solid state. Then, nitrogen concentration was determined by the ammonia conversion method. As a result of the hot trap experiment under the above conditions, the nitrogen concentration in lithium was reduced from 43 to 10 wt.ppm by immersing Fe-5at.%Ti grains (∼160 μm) at 509 ℃ after 192 h, from 62 to 9.8 wt.ppm at 550 ℃ after 168 h, and from 65 to 9.9 wt.ppm at 557 ℃ after 144 h.

Numerical investigation of hydrogen isotope retention by an yttrium pebble-bed from flowing liquid lithium

Ensuring a secure and reliable execution of the International Fusion Materials Irradiation Facility (IFMIF) and the DEMO-Oriented Neutron Source (DONES) requires their liquid lithium loops to be purified from hydrogen isotopes which are generated during operation. For this purpose, an yttrium pebble-bed will serve as a hydrogen hot trap. Former intentions to predict the retention behavior of an yttrium pebble-bed are based on the consideration of the trap as a black box with a predetermined trap efficiency. Disregarding the internal physical mechanisms of the gettering process these models are built on simplified assumptions and should be extended to allow reliable trap designs for IFMIF/DONES. Therefore, a detailed numerical model describing the hydrogen transport from flowing liquid lithium into an yttrium pebble-bed has been developed from scratch within the scope of this work. It enables simulating the hydrogen retention process into an arbitrarily dimensioned getter bed for the low concentration regime by solving a system of differential equations with a finite-difference approach. The model is used to calculate the time evolution of the hydrogen concentrations in a simplified loop system which is connected in line with an yttrium pebble-bed. Special focus is placed on the observation of a case relevant for IFMIF/DONES considering a constant generation of tritium in the loop. Simulation results reveal that the trap efficiency decreases with time and that lower system temperatures significantly improve the trap efficiency. It is found that for heavier pebble-beds the tritium inventory build-up in the lithium is slowed down more efficiently. These findings are of great importance for the design of the hot traps for IFMIF/DONES. To demonstrate the reliability of the model experimental data of a previous deuterium retention experiment are successfully reproduced.

Application of the Perturbed-Chain SAFT to Phase Equilibria in the Fischer–Tropsch Synthesis

As an alternative route to produce liquid fuels, Fischer–Tropsch synthesis (FTS) has received considerable attention. Phase equilibria have been one of the key issues in the design and operation of not only an FTS reactor, but also relevant downstream processing, e.g., stepwise condensation of FTS products, wastewater treatment, and the recovery of α-olefins. These issues are extremely complex due to a wide spectrum of FTS products and the presence of noncondensable gas, nonpolar components, associating components, and highly polar components. To address these issues, the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) was evaluated using phase equilibrium data of binary and ternary mixtures containing water, alcohols, hydrocarbons, and noncondensable gases. The parameter values are available via a three-step parametrization strategy established in our previous work [Zheng et al. Ind. Eng. Chem. Res. 2018, 57, 3014]. A couple of popular benchmark models, namely the Soave–Redlich–Kwong (SRK) EoS with the modified Huron–Vidal second-order mixing rule (SRK/MHV2) and the predictive SRK (PSRK) EoS, were selected for comparison to put the performance of the PC-SAFT EoS into perspective. It was found that the PC-SAFT EoS gives reliable correlations/predictions in all the studied cases, whereas the other two models fail to do so. The three models were also employed to simulate hot and cold traps where the stepwise condensation of the reactor effluent occurs. It was found that all three models yield satisfactory results for the paraffin distribution of the liquid stream leaving the hot trap, while the SRK/MHV2 and PSRK models are less accurate for the olefin distribution, particularly at high temperature. It was also found that all three models are capable of predicting the composition of the two liquid streams (namely organic and aqueous) leaving the cold trap except that the SRK/MHV2 model fails to accurately reproduce the distribution of alcohols in the two liquid streams. This study advocates the practical use of the PC-SAFT EoS by its application to a complex, industrially important FTS process and a comprehensive evaluation, together with the two popular benchmark models.

Comparative Study of Cryogenic Versus Room-Temperature Proton Irradiation of N-Channel CCDs and Subsequent Annealing

Two PLATO Teledyne-e2v CCD280 have been proton irradiated: one whilst operating at cold and the other unbiased at room temperature. We report on differences in the postirradiation hot pixel population, trap species, and charge transfer inefficiency (CTI), including after annealing. We demonstrate once more that proton irradiation performed at the charge-coupled device temperature of operation can show significant differences to the traditional room-temperature irradiation. The cold-irradiated detector shows a factor 2 greater radiation induced increase in dark current and a factor 3 to 4 greater increase in hot pixel numbers, however, the parallel CTI measured in the PLATO operating conditions is a factor 1.5 lower. Using the trap pumping technique, we provide distributions of radiation-induced trap release time constants at different temperatures, which can be used to identify the type of defects and estimate CTI in other operating conditions.

In situ and downstream sulfidation reactivity of PbO and ZnO during pyrolysis and hydrogenation of a high–sulfur lignite

Economical valorization of low quality, high sulfur feedstocks is an important challenge. Most of the valorization processes start from pyrolysis, with a significant amount of evolution of sulfur containing compounds. This study addresses in situ and downstream sulfur capture ability of lead oxide (PbO) in comparison to zinc oxide (ZnO) during the pyrolysis of high–sulfur Tuncbilek lignite. In order to assess the role of hydrogen in sulfur capture, hydrogenation experiments were also performed. Sulfidation reaction thermodynamics of PbO and ZnO was compared to most commonly used metal oxides for sulfur capture i.e., FeO, MnO, and CaO. The equilibrium conversions indicated superior performance of PbO and ZnO towards sulfidation reactions at high temperatures. Thermodynamic superiority of PbO sulfidation encouraged us to investigate the PbO as a new sulfur sorbent for hot gas desulfurization. The experimental verification of the high temperature sulfidation ability of PbO and ZnO was performed using high–sulfur Tuncbilek lignite under semibatch conditions. The final compounds formed after each process were observed by X-ray diffractometer (XRD) and Diffuse Reflectance Infrared Fourier Transformation Spectroscopy (DRIFTS). Experiments revealed that PbO can be promising candidate as hot gas sulfur trap during pyrolysis and hydrogenation processes, while ZnO can hold up sulfur only in the presence of hydrogen. Furthermore, both PbO and ZnO show the superior sulfur capture performance in the presence of hydrogen when they were used as adsorbents located after the reactor (downstream) at ambient conditions.

Effects of experimental operations on the Fischer-Tropsch product distribution

The present study provides insight into the effect of experimental operations on the Fischer-Tropsch synthesis (FTS) product distribution by combining experimental and theoretical analyses of the process. Experimental errors originated from GC data processing and product collecting conditions are addressed here based on the experimental data obtained using commercial iron-based catalyst in a tubular fixed-bed reactor. A corrected area normalization method, which is a combination of the area normalization and simulated distillation, is proved to be an accurate and convenient method for FTS heavy oil chromatogram quantification. The flash loss from the hot trap and the cold trap is found to be negligible under the normal operating conditions. However, water may be condensed remarkably in the hot trap at low temperature and wrapped by wax. In addition, the selectivity of the high-carbon-number alcohols will be seriously underestimated at low temperature of the hot trap. The FTS product distributions under a wide range of reaction conditions are exhibited.

Purification of liquid metal systems with sodium coolant from oxygen using getters

For increasing the safety and economic parameters of nuclear power stations (NPSs) with sodium coolant, it was decided to install all systems contacting radioactive sodium, including purification systems of circuit I, in the reactor vessel. The performance and capacity of cold traps (CTs) (conventional element of coolant purification systems) in these conditions are limited by their volume. It was proposed to use hot traps (HTs) in circuit I for coolant purification from oxygen. It was demonstrated that, at rated parameters of the installation when the temperature of the coolant streamlining the getter (gas absorber) is equal to 550°С, the hot trap can provide the required coolant purity. In shutdown modes at 250–300°С, the performance of the hot trap is reduced by four orders of magnitude. Possible HT operation regimes for shutdown modes and while reaching rated parameters were proposed and analyzed. Basic attention was paid to purification modes at power rise after commissioning and accidental contamination of the coolant when the initial oxygen concentration in it reached 25 mln–1. It was demonstrated that the efficiency of purification systems can be increased using HTs with the getter in the form of a foil or granules. The possibility of implementing the “fast purification” mode in which the coolant is purified simultaneously with passing over from the shutdown mode to the rated parameters was substantiated.

Removal of low-concentration deuterium from fluidized Li loop for IFMIF

It is important to control the concentration of hydrogen isotopes as impurities included in Li by Y hot trap for the International Fusion Materials Irradiation Facility (IFMIF). Impurities limit goals in IFMIF are determined as <10wppm for D, and <1wppm for T to realize safety and stability of Li flow. In order to demonstrate the effective operation of Y hot trap and give actual proof based on experimental data, an experimental study is performed under Li fluidized conditions simulating IFMIF. D recovery down to 10wppm is demonstrated under fluidized Li conditions, where only D is included in Li. In addition, since there is possibility in that N in Li contaminates Y surfaces, influence of N included in Li is investigated to clarify recovery performance of Y hot trap. It was proved that Y hot trap can work effectively even in real IFMIF conditions to achieve the goal of Li purity limit necessary for its operation.

Nitrogen Hot Trap Design and Manufactures for Lithium Test Loop in IFMIF/EVEDA Project

Nitrogen Hot Trap Design and Manufactures for Lithium Test Loop in IFMIF/EVEDA Project

RAMI assessment for IFMIF lithium facility

A RAMI (reliability, availability, maintainability and inspectability) assessment performed on the IFMIF (International Fusion Materials Irradiation Facility) Lithium Facility (LF) is presented. Given the high availability requirements for the IFMIF plant, a target requirement of 94% availability has been attributed to the LF and its feasibility verified for the proposed system design. The LF performance for the foreseen operation mission has been investigated by the mean of failure mode, effect and criticality analysis (FMECA) and reliability block diagrams (RBDs). The first assessment performed on the base of the present design did not satisfy the above target requirement. Then, possible optimizations in design solutions and maintenance policy have been investigated. The RBD analysis shows that with some improvements the LF could be able to comply with the availability target requested, as the obtained mean availability for 10 years of simulation is of 93.4% and the inherent availability more than 99%. The reliability to operate the LF without failure during the yearly scheduled operation time is about 64%. Most critical components in terms of impact on LF reliability and availability, are: (i) the Li loop Target Section (back plate) and electro-magnetic pumps for the main loop, (ii) the getter beds of the hydrogen hot trap and the electromagnetic pump for the impurity control system.

Impurity diffusion in a harmonic potential and nonhomogeneous temperature

We propose different ways of manipulating the dispersion of impurities along a semiconductor layer during heat treatment. The impurities undergo a random walk assisted by a nonlinear harmonic potential and nonhomogeneous temperature. Depending on the strength of a hot spot, trap potential, impurity density and standard deviation of the hot spot, the impurities diffuse away from the central region and pile up around the peripheral region of the semiconductor layer. Furthermore, the numerical result depicts that the internal field at high doping level can be of sufficient strength to cause the broadening of the impurity profile.

Chemical Analysis of Hydrogen Isotopes Dissolved in Li and Y for Hot Trap of IFMIF Target Loop

IFMIF-EVEDA progresses in Japan as one of the EU-Japan Broader Approach Activities. The research is performed to decide whether or not IFMIF is constructed after some uncertainties included in the design are clarified. One of the uncertainties included in the Li purification process is to prove experimentally the removal of 1 weight ppm (wppm) T and 10 wppm D from flowing Li for safety.Our research group is experimentally investigating the recovery of hydrogen isotopes including T not only in static Li but also in fluidized Li. In the past study, hydrofluoric acid (HF) treatment of Y is successful in removing oxide inevitably formed on its surfaces. The recovery of hydrogen isotopes including T less than 1 wppm is successfully proved with use of the HF-treated Y at 300°C, which is the IFMIF hot-trap temperature. Mass-transfer rates of hydrogen isotopes in the liquid Li and Y under stirred conditions were determined.In addition, we developed a way to determine an amount of D or T dissolved in Li and Y by using a dissolution method. The quantitative D analysis is performed by using techniques of HNO3 solution for Y and H2O one for Li. The distribution coefficient between Li and Y is determined as a function of temperature and contact time.

Lifus (lithium for fusion) 6 loop design and construction

The Lifus 3 loop was designed and constructed in 2001/2002 in ENEA, to evaluate the corrosion behaviour of Fusion reference structural materials, and in particular AISI 316 and Eurofer, in flowing lithium environment. To fully accomplish the experimental program originally foreseen for Lifus 3 and not respected it was decided in 2010 to build a new experimental facility, simplified from the hydraulic point of view, capable of performing the set of tests required by the IFMIF community. The operating parameters of this loop, named Lifus 6 [1], are: isothermal loop with operating temperature of 350°C, maximum velocity in the test section of about 16m/s, cold trap continuously operated to remove carbon and oxygen impurities, hot trap operated in batch to remove nitrogen ones. An integral measurement of impurities is made on line by using a resistivity meter.The Lifus 6 loop design is presented in the paper.

Irregularities in Product Distribution of Fischer–Tropsch Synthesis Due to Experimental Artifact

Experimental product distribution of Fischer–Tropsch synthesis frequently presents notable deviations from the typical double-α Anderson–Schulz–Flory pattern: bump or dip around the breaking carbon number, positive or negative deviation for heavy hydrocarbons. These irregularities were studied experimentally in a fixed-bed reactor over an industrial Fe/Mn catalyst, and theoretically by a product separation model based on Aspen Plus software. First, it was found that the unsteady state of reaction condition or improper gas chromatograph procedure could lead to deviation for heavy hydrocarbon distribution. Second, the bump near the breaking carbon number could be attributed to the accumulation of water in hot trap, which leads to an inaccurate measurement of the wax amount. This irregularity can be eliminated by selecting either a higher temperature or a lower pressure of the hot trap. Third, vaporization or flash loss of the oil sample during product collection could result in dip in light hydrocarbon dist...

Analysis of hydrogen isotopes absorption between liquid lithium and yttrium under dynamic conditions

The use of D–Li stripping reaction to generate multiple neutron is expected in the International Fusion Materials Irradiated Facility (IFMIF). Tritium generated by its side reaction needs to be recovered from liquid Li for safety. Y hot trap is expected as an effective purification system to recover tritium from the liquid Li loop. In IFMIF, since liquid Li circulates in a loop, it is important to trace tritium behavior in Y and liquid Li under dynamic conditions. In this study, the authors investigate the effectiveness of tritium recovery from liquid Li under dynamic conditions of Y hot trap. Hydrogen absorption in Li instead of tritium is investigated under dynamically fluidized conditions by stirring liquid Li with an arbitrary rotational rate. The experimental results prove that the hydrogen absorption rate from liquid Li to Y is independent of the rotational rate. This means that the rate-determining step is hydrogen diffusion in Y.

Hydrogen Recovery from Liquid Li with Y Hot Trap

Materials to compose a fusion reactor chamber are subjected to neutron irradiation. International Fusion Materials Irradiated Facility (IFMIF) will be used to analyze how neutron damage affects material durability. The material is irradiated by high-intensity neutron beam, which is generated by the D-Li stripping reaction. Tritium (T) generated by by-pass reaction needs to be recovered from liquid Li for safety. Recovery of tritium by an yttrium (Y) hot trap is one of the ways to recover T from liquid Li in IFMIF. Therefore, it is necessary to analyze the behavior of T in the liquid Li. In this study, the authors measured H2 absorption rates under stirred conditions of liquid Li and analyzed the effect of hydrogen absorption rate of Y by elevating temperature from 250 ◦ C to 400 ◦ C to establish the way to recover T from liquid Li with the Y hot trap in IFMIF. Judging from the comparison, we considered the rate-determining step is H diffusion in Y. Mass transfer coefficients at each temperature were determined by fitting the results between calculation and experiment.

Tritium removal by Y hot trap for purification of IFMIF Li target

The use of Li is expected for a flowing target in the International Fusion Materials Irradiation Facility (IFMIF) for high-intensity neutron generation. Tritium (T) of by-product is removed by a Y hot trap placed in a by-path position of the flowing Li target. Since the equilibrium pressure of hydrogen isotopes is extremely low, the removal rate of H isotopes is affected by coexisting other impurities such as N, C and O dissolved in Li. In the present study, the removal rate of H isotopes in Li is experimentally investigated under the three different methods or conditions: (i) measuring gravimetrically in a static Li + Y system with the supply of low-concentration H 2 in Ar purge, (ii) counting the change of T radioactivity in a static Li + Y system after neutron irradiation and (iii) measuring the change of the H 2 concentration in a stirred Li + Y system with the supply of low-concentration H 2 in Ar purge. There was no corrosive action in the Li–Y interface observed after contact at 500 °C for 100 h. The present results are extended to design a Y hot trap for the IFMIF–EVEDA Li loop in order to remove H isotopes less than a specified concentration.

Latest design of liquid lithium target in IFMIF

This paper describes the latest design of liquid lithium (Li) target system in International Fusion Materials Irradiation Facility (IFMIF). IFMIF is an accelerator-driven intense neutron source for fusion reactor materials testing. Two 40 MeV deuteron beams with a total current of 250 mA strikes a liquid Li target circulating in a Li loop. The Li target is to provide a stable Li jet at a speed of 10–20 m/s to handle an averaged heat flux of 1 GW/m 2. A concaved Li flow is applied to avoid Li boiling. A cold trap and two kinds of hot trap are applied to control impurities (T, 7Be, C, O, N) below permissible levels. A back wall made of RAFM is located in the most severe region of neutron irradiation (50 dpa/year). System availability requires more than 95% during plant lifetime. EVEDA tasks including Li loop are now being performed under the Broader Approach.