Thermal Treatment In Vacuum Research Articles

Ultrahigh Thermal Robustness of High‐Entropy Spectrally Selective Absorbers for Next‐Generation Concentrated Solar Power System

AbstractSpectrally selective absorbers (SSAs) are a critical component in concentrated solar power (CSP) systems, as they maximize sunlight absorption while suppressing heat radiative loss. Despite various SSAs being demonstrated, the challenges remain on the limitations of thermal instability at elevated operating temperatures especially above 650 °C due to component oxidation and diffusion in the absorption layer. To address these challenges, herein a high‐entropy strategy is resorted. By utilizing high‐entropy nitride film as an absorption layer, a double‐layer SSA is prepared by a facile magnetron sputtering method. High‐entropy engineering intensifies and complicates the localized electronic bands, concurrently exhibiting relatively flat bands around the Fermi level, which can significantly enhance 3d interband transition. The resultant SSA delivers the desired spectral selectivity (α/ɛ82 °C = 92.7%/8.4%). Benefitting from the high‐entropy effect, the SSA maintains outstanding optical properties (α/ɛ82 °C = 93.3%/9.4%) even after a 750 °C vacuum thermal treatment for 120 h. Under 1 kW m−2 simulated illumination, the surface temperature of the absorber can easily rise to 95.3 °C, suggesting its remarkable solar‐thermal performance. Furthermore, its effectiveness in parabolic trough collectors (PTCs) is validated. All these competitive performances make the high‐entropy SSA a potentially promising candidate for PTCs.

Vacuum Thermal Treatment for Achieving Macroscale Superlubricity by Nanodiamond and Hexagonal Boron Nitride on H‐DLC Film Surfaces in Dry Nitrogen

Vacuum Thermal Treatment for Achieving Macroscale Superlubricity by Nanodiamond and Hexagonal Boron Nitride on H‐DLC Film Surfaces in Dry Nitrogen

Highly efficient regeneration of VOCs-saturated activated carbon by vacuum-thermal treatment

The substantial energy consumption and carbon loss associated with conventional thermal regeneration of activated carbon (AC) pose significant constraints on the advancement of deactivated AC recycling. Here, a vacuum-thermal process was applied to regenerate AC saturated with VOCs. Results showed that desorption efficiency under vacuum conditions (99 % at 200 °C) was significantly higher than that in air and nitrogen (85.2 % and 86.4 %, respectively). The adsorption capacities of different AC samples were maintained at 74.2 %, 97.8 %, 90.9 %, and 96.4 % after seven regeneration cycles, respectively. Pore structure analysis showed that vacuum-thermal regeneration caused less damage to the AC pore structure compared to the air and nitrogen. In addition, micropores were shown to be most conducive to the adsorption of VOCs, while mesopores larger than 4 nm are conducive to desorption. The larger the saturated vapor pressure of the VOCs, the larger the driving force it is subjected to, and the easier it is to desorption. Density field theory (DFT) calculations showed that the higher the binding energy between VOCs and AC surface, the more stable the adsorption system, making it more difficult to regenerate the adsorbent. This work provides insight into the development of an economical and environmentally friendly regeneration route for AC adsorption.

Morphological and chemical changes in nuclear graphite target under vacuum and high-temperature conditions

Nuclear-grade graphite is a high-efficiency material, widely used for vacuum applications in nuclear reactors and accelerators as targets facing particle beams. In these contexts, graphite is often exposed to extreme thermal stresses altering its physical and chemical properties. The thermal-induced release of volatile contaminants from targets and the damage of structural components are critical issues that can affect the safety and operation efficiency of beamline facilities. Here, we provide for the first time a detailed picture of the chemical and morphological changes occurring in a nuclear-grade graphite target, obtained through Electrical Discharge Machining (EDM), when exposed in vacuum to high temperatures. The radial temperature gradient induced by the impact of a pulsed energetic (MeV- GeV range) focused particle beams was reproduced by cyclically heating, in the 1300–1800 K temperature range, a disc-shaped graphite target in a vacuum setup. An accurate surface and in-depth chemical analysis of the graphite target was obtained thanks to the high sensitivity (ppm/ppb) of the Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) technique. The chemical maps clearly show the presence of several metal oxides and impurities in the surface and subsurface regions of the untreated sample. Such contaminants were removed because of the thermal treatment in vacuum more or less efficiently, as demonstrated by Thermogravimetric analysis (TGA), X-ray Photoelectron Spectroscopy (XPS), and ToF-SIMS. However, Raman spectroscopy and SEM-EDS revealed that the high-temperature treatment induces a decrease in the crystallite size of the graphite as well as changes in the target surface porosity with the appearance of microvoids, leading the graphite target to be more prone to the breakage.

Enhancing CdSe/ZnS Quantum-Dot Light-Emitting Diode Performance: The Impact of Thermal Treatment Atmospheres on Fabrication Processes

We explored the thermal treatment impact on the performance of quantum-dot light-emitting diodes (QLEDs). The QLEDs comprised multiple layers: a 2.2-μm thick epoxy buffer layer; a bottom cathode composed of 12-nm MoOx/10-nm Ag/12-nm MoOx; a 20-nm ZnO electron transporting layer (ETL); a 10-nm CdSe/ZnS quantum dot light emission layer (EML); a 40-nm 4,4′,4″-Tris(carbazol-9-yl) triphenylamine hole transporting layer; a 10-nm WOx hole injection layer; and a 100-nm Ag top anode. We applied thermal treatments to the cathode, ETL, and EML separately to assess their effects on the QLEDs. Additionally, we evaluated the impact of the thermal treatment atmosphere. Vacuum thermal treatment on the cathode and EML resulted in minor improvements in QLED performance, whereas treatment of the ETL led to a decline in performance. In contrast, air thermal treatment on the cathode and EML decreased QLED performance but significantly improved it by 15% in current efficiency when applied to the ETL. The performance differences attributable to the thermal treatment atmosphere are likely due to ligand removal and oxidation processes, facilitated by thermal energy and oxygen. Our study highlights that air thermal treatment on the ETL substantially improves QLED performance, offering crucial insights into the significance of thermal treatment in QLED development.

Optimization of Ammonia Nitrogen Removal and Recovery from Raw Liquid Dairy Manure Using Vacuum Thermal Stripping and Acid Absorption Process: A Modeling Approach Using Response Surface Methodology

Dairy manure adds a substantial amount of nitrogen to wastewater due to its high levels of associated nutrients. Removal and recovery of ammonia nitrogen (NH3-N) from raw liquid dairy manure (RLDM) is greatly valued. This study was focused on the vacuum thermal stripping–acid absorption (VTS-AA) process for NH3-N from RLDM, followed by modeling and optimization. Using the response surface methodology (RSM)-based central composite design (CCD) approach, the critical operational parameters of the vacuum thermal stripping process, including temperature (50–70 °C), pH (9–11), vacuum pressure (35–55 kPa), and treatment time (60–90 min), were optimized. With the specified parameters set at temperature 69.9 °C, pH 10.5, vacuum pressure 53.5 kPa, and treatment time 64.2 min, the NH3-N removal efficiency attained was 98.58 ± 1.05%, aligning closely with the model prediction. Furthermore, the recovered ammonium sulfate ((NH4)2SO4) closely matched their commercial counterparts, confirming the effectiveness of the VTS-AA process in recovering NH3-N from RLDM. The distinct advantage of the employed technology lies in the concurrent energy demand reduction achieved by introducing a vacuum system. These findings contribute valuable insights into the practical implementation of the VTS-AA process for treating raw dairy manure, particularly in large-scale operational contexts.

Effect of thermal modification on axial compression properties and hardness of laminated bamboo

Vacuum thermal modification is an environmentally friendly method to improve the durability and reduce insect infestation of bamboo, which has the advantages of preventing deformation, preventing oxidation of the bamboo surface, and uniformity of thermal conductivity compared to previous studies that used mediums such as nitrogen, air, or oil for heating. This study thermally modified laminated bamboo materials for 1 to 5 h under vacuum conditions ranging from 170 to 230 °C and evaluated their microstructure, surface hardness, water absorption, and axial compression mechanical properties. The results showed that compared with untreated laminated bamboo timber, the colour gradually deepened as the temperature and time of heat treatment increased, while the equilibrium moisture content of heat-treated laminated bamboo timber was reduced by about 4–27% and the density by about 11–18%. This phenomenon indicates that the cell walls of laminated bamboo become denser with increasing temperature, which leads to a significant decrease in the hygroscopicity of laminated bamboo. The dimensional stability of the material was improved. Regarding the macroscopic axial compression test, the results showed that the thermal modification treatment significantly increased the axial compression strength of laminated bamboo, and this improvement in mechanical properties was inversely related to the heat treatment temperature. In addition, through the nanoindentation test, we found that the laminated bamboo's surface hardness and modulus of elasticity showed an inflexion point when the treatment temperature reached 210 °C, indicating that the material properties changed significantly in this temperature range. Investigating the response mechanism between the temperature and time of vacuum thermal heat treatment and the mechanical properties of bamboo will contribute to the development or optimization of the thermal modification process, leading to materials with excellent properties and broadening the application areas.

High Performance Nitrogen-Doped Hierarchical Nanostructured Carbon Electrode for Vanadium Redox Flow Batteries

In recent years, we have seen an impressive progress in the deployment of renewable energy sources, and in particular of photovoltaics and wind turbines. However, renewable energies have some well-known drawbacks due to their intermittent nature and direct usage of the electricity generated would destabilize the grid. To overcome these problems large scale energy storage systems have drawn great attention in the last few years both from the academic and industrial world. Redox flow batteries (RFB) are emerging as one more promising electrochemical energy storage technologies. Notably, the Vanadium redox flow battery (VRFB) is currently the most widespread technology as it allows for the implementation of strategies to recover the capacity decay induced by ion cross-over. Despite the many advantages, VRFBs have long suffered from low power density, mainly caused by the usage of electrodes which are not optimized for this application. The use of heteroatom dopants, such as nitrogen, phosphor, and boron, is currently the most common method to enhance the performance of carbon electrodes. Nitrogen has been extensively studied as a catalyzer for Vanadium redox reactions, showing exceptional boosts in performance in several works. In a previous work we developed a two-step process based on a plasma enhanced nano-aerosol jet deposition source and a vacuum thermal treatment. Starting from a gas precursor we deposited a nanostructured carbonaceous material on a commercially available substrate, this process allows to increase the current density to 400 mAcm-2 with an energy efficiency of 80%, that is, 4 times greater than the commercial reference. The two-steps process permits a fine tuning of the properties and structure of the material leading to an exceptionally high surface area and a defect rich structure. The advantage of this process is that nitrogen can be added easily during the deposition phase by using a N2-C2H2 mixture, without the need for any other processing steps. In this work we aim to further increase the performance of our nanostructured electrode by adding nitrogen functionalities to the carbon nanostructure, thus combining the effects of an incredibly high surface area with the excellent catalytic properties of nitrogen. The morphology and chemistry of the synthesized material is analyzed by different techniques such as SEM, Raman spectroscopy, XPS, BET analysis. Nitrogen doping was confirmed by XPS analysis, in particular a high amount of graphitic nitrogen, which is considered to be the most active towards vanadium ions, is present. Moreover, BET analysis shows an incredibly high surface area, up to 756 m2/g. The properties of the material are then correlated to the electrochemical properties by testing the material in increasingly complex setups, starting from a three-electrode setup, then in symmetric cell and finally in a full-cell setup. The kinetic activity of the material is studied by cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammetry showed an impressive activity of the electrodes towards the active species, especially towards the V2+/V3+ couple where a peak-to-peak separation of 65 mV was obtained, which is among the lowest reported in literature. These results were confirmed by EIS, from which the reaction rate constants were calculated following the method proposed by Stimming et al. [1] The addition of nitrogen led to an order of magnitude increase of the reaction rate with respect to the un-doped material. The performance enhancement was then validated by the test in symmetric cell. Polarization curves show a significant decrease in the overpotential, especially in V2+/V3+. Thus, we propose a vertically integrated process, from the synthesis of the material to the final application, which is able to deliver a comprehensive overview on the material properties, its electrochemical performance and the correlation between the two.[1] Friedl, J., Bauer, C. M., Rinaldi, A., & Stimming, U. (2013). Electron transfer kinetics of the VO2+/VO2+–Reaction on multi-walled carbon nanotubes. Carbon, 63, 228-239.

A functional coating with mechanoluminescent properties for sensing cavitation erosion and early warning of protection failure

Protective materials coated on the surface of fluid machinery are often used to slow down the damage caused by cavitation. Once the protective material fails, there is no real-time monitoring to predict, which will directly threaten the safe operation of the equipment. In this work, we designed a functional SrAl2O4: Eu2+, Dy3+ coating by atmospheric plasma spraying (APS), which can sense the impact of bubble implosion and realize the early warning of the failure of anti-cavitation erosion polyurethane (PU) coating. It is found that the luminescent properties of the functional coatings are easily affected by lattice defects, amorphous phase and valence state of europium ions. The functional coating is more sensitive to the perception of micro-jets and shock waves after vacuum thermal reduction treatment, and can distinguish the difference in stress by the brightness of the light. More importantly, when the surface polyurethane coating is removed by cavitation erosion (CE) down to 0.1 mm, this functional coating emits light to warn the polyurethane coating of impending failure. Therefore, this work provided a solution for sensing CE and predicting when the protection would fail.

Development and Scale-up of High Performance Electrodes for Vanadium Redox Flow Batteries

Vanadium redox flow battery (VRFB) is a promising technology for energy storage because of its independent energy to power ratio and long cycle life. However, VRFB commercialization is still hindered by some technological issues, among which the limited power density. This results in increased cell area and system costs.In order to tackle this issue is fundamental to boost the sluggish electrode kinetic. In the literature different wet processes, such as acid treatments, have been widely employed to add catalytic functionalities to commercial carbon electrodes [1,2]. Also plasma etching or plasma doping have been adopted for the improvement of electrode performance [3]. Recently, the introduction of heteroatoms is becoming one of the most common method to enhance the catalytic activity of carbon electrodes. Zhao et al. [21] performed thermal treatment of graphite felt combined with electrochemical deposition of Bismuth nanoparticles, obtaining 80% energy efficiency at 600 mA cm-2. Li et al. [22] developed a hierarchical nitrogen doped electrode, reaching 76.8% energy efficiency at 400 mA cm-2.In this work it is proposed a prototypal deposition method, called NanoJeD. It is a high throughput, dry and easily scalable process starting from gas phase. It consists in radiofrequency (RF) plasma operating in dusty mode, through which a non-flammable mixture of Acetylene and Argon is fluxed and the RF plasma ignites the decomposition and clasterization of the Acetylene. The former nanoparticles, following the gas streamline are dragged to a high aspect ratio orifice and ejected in a low-pressure chamber where a substrate is placed. Kinetic energy of the nanoparticles ejected in the chamber defines their impact energy with the substrate and the consequent collection mechanism. Subsequently, a vacuum thermal treatment is performed and this two-steps process allows a fine tuning of the material properties and the formation of a carbon allotropes with catalytic peculiarities known as Carbon Nano Onions (CNOs).Deposited CNOs were firstly characterized with Raman spectroscopy, Scanning Electrode Microscopy (SEM) and Transmission Electrode Microscopy (TEM). Electrochemical characterization was performed in a three-electrode setup with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CNOs exploit their unique properties: high conductivity, high chemical-mechanical stability, and catalytic activity towards redox reactions. The peculiarities of CNO reside in the edge of graphene sheet, which is ascertained to share a higher catalytic activity with respect to the basal plane of the same graphene sheet [6].Afterwards CNOs were deposited on a commercial carbon paper electrode, Sigracet® SGL 39 AA (nominal thickness of ∼290 μm), that was tested in 4 cm2 symmetric cell with Nafion® 211, permitting to evaluate the effect of CNOs on both positive and negative electrode. Subsequently, full cell test at different current densities was performed in cycles with fixed cut-off voltages (1-1.65 V), obtaining an energy efficiency of 81% and 74% at 400 mA cm-2 and 600 mA cm-2, respectively. The corresponding electrolyte utilization was 70% and 59%. Moreover, electrode stability has been evaluated during 1’000 cycles operation.Finally, the process has been scaled-up permitting to obtain a 100 cm2 electrode. The corresponding full cell test with Nafion® 212 resulted in 75% energy efficiency at 0.3 A cm-2.

Temperature Dependence of 3С-SiC Growth During Rapid Vacuum Thermal Silicon Treatment

The paper presents the results of a study of the structure, phase composition, and growth kinetics of silicon carbide epitaxial layers on silicon substrates during their rapid vacuum thermal treatment. Transmission electron microscopy revealed the formation of layers of the cubic polytype SiC (3C-SiC) on silicon during carbidization in the temperature range of 1000–1300 °C. It was found that the formation of SiC layers proceeds in two stages, characterized by different activation energies. In the lower temperature range from 1000 to 1150 °C, the activation energy of the SiC growth process is Ea = 0.67 eV, while in the temperature range from 1150 to 1300 °C, the activation energy increases by almost an order of magnitude (Ea = 6.3 eV), which indicates a change in the limiting physical process. It has been established that the type of conductivity and the orientation of the substrate affect the thickness of the formed SiC layers. In this case, the greatest thickness of silicon carbide layers is achieved on silicon substrates with (111) orientation of p-type conductivity.

The Experimental Study on the Mechanical Properties of Fiber-Reinforced Metal Laminates Using an Innovative Heat-Solid Integrated Forming Technology

In the forming process of fiber-reinforced metal laminates (FMLs) product, the exploratory compound forming technology, including hot stamping of aluminum alloy and laying process of fiber prepreg which is named HFQ-FMLs was proposed to solve the puzzles such as weak rigidity, low strength and integration deformation with large difficulty, and the feasibility and mechanical properties of the innovative forming process were studied. Firstly, based on the modified metal volume fraction formula, the theoretical values of the mechanical properties of the HFQ-FMLs plates were calculated. Compared with the experimental results, the minimum error is 1%, proving that the HFQ-FMLs technology scheme is feasible. Secondly, three kinds of metal sheets with different heat treatments and specimens by HFQ-FMLs were carried out for the tensile tests, the mechanical properties distributions were demonstrated, and the influence regularity of the strain rate and rolling direction on the stress analysis was considered at the same time. As can be seen from the distribution of yield strength and tensile strength, the yield stress of metal sheets obtained by HFQ-FMLs technology along the 45° is superior to the raw material and can increase by 46% under strain rate = 0.01 s−1. While, because the vacuum thermal curing treatment makes the aluminum alloy happen double aging, the metal sheet strength dropped, and the jointing strength between the metal and fiber prepreg became weak too, which made the strength limit of the new material improve weakly. Thirdly, the fractured style of the FMLs under different conditions was studied qualitatively. It is helpful to achieve the development rule of defects, optimize the craft route, and avoid deformation failure.

Preparation of 82Se thin films with trigonal hexagonal crystal structure for in-beam nuclear structure experiments

We report a novel approach in producing and characterizing enriched isotopic selenium-82 (82Se) thin films with trigonal hexagonal crystal structure (t-82Se), the most thermodynamically stable form of the element. The obtained t-82Se thin films are used as targets in accelerator based nuclear structure experiments. Several 82Se thin films with thicknesses around 5 mg/cm2 (10.4 μm) were deposited on 5 mg/cm2 (3 μm) tantalum (Ta) foils by vacuum evaporation-condensation method. The condensed 82Se films exhibit unstable amorphous structure (a-82Se), therefore were converted to t-82Se by means of an appropriate vacuum heat treatment developed in the target laboratory of IFIN-HH. After the thermal treatment, the microstructure, morphology and composition of the 82Se films were evaluated before and after the vacuum thermal treatment using Fourier Transform Raman Spectroscopy (FT-Raman), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) techniques. Furthermore, an in-beam γ-spectroscopy experiment performed at the 9-MV tandem accelerator of IFIN-HH confirmed that the thermally treated t-82Se films possess high durability and high purity with no detectable contamination and no mass loss.

Effects of Accelerated Aging on Thermal, Mechanical and Shape Memory Properties of Cyanate-Based Shape Memory Polymer: III Vacuum Thermal Cycling.

Shape memory polymers (SMPs) with intelligent deformability have shown great potential in the field of aerospace, and the research on their adaptability to space environments has far-reaching significance. Chemically cross-linked cyanate-based SMPs (SMCR) with excellent resistance to vacuum thermal cycling were obtained by adding polyethylene glycol (PEG) with linear polymer chains to the cyanate cross-linked network. The low reactivity of PEG overcame the shortcomings of high brittleness and poor deformability while endowing cyanate resin with excellent shape memory properties. The SMCR with a glass transition temperature of 205.8 °C exhibited good stability after vacuum thermal cycling. The SMCR maintained a stable morphology and chemical composition after repeated high-low temperature cycle treatments. The SMCR matrix was purified by vacuum thermal cycling, which resulted in an increase in its initial thermal decomposition temperature by 10-17 °C. The continuous vacuum high and low temperature relaxation of the vacuum thermal cycling increased the cross-linking degree of the SMCR, which improved the mechanical properties and thermodynamic properties of SMCR: the tensile strength of SMCR was increased by about 14.5%, the average elastic modulus was greater than 1.83 GPa, and the glass transition temperature increased by 5-10 °C. Furthermore, the shape memory properties of SMCR after vacuum thermal cycling treatment were well maintained due to the stable triazine ring formed by the cross-linking of cyanate resin. This revealed that our developed SMCR had good resistance to vacuum thermal cycling and thus may be a good candidate for aerospace engineering.

Argon and Other Defects in Amorphous SiO2 Coatings for Gravitational-Wave Detectors

Amorphous SiO2 thin films are one of the two components of the highly reflective mirror coatings of gravitational-wave detectors. For this study, layers of amorphous SiO2 on crystalline Si substrates were produced by ion-beam sputtering (IBS), using accelerated neutralized argon ions as sputtering particles, as is the case for the actual mirror coatings of gravitational-wave detectors. The aim of this study is to investigate the possible presence of various defects in the materials in order to improve the coating quality. We provide evidence that, due to the synthesis method, about 0.2 wt.% of Ar is present in the coatings, and it can be released by means of thermal treatments, starting around 400 °C. The time and temperature to obtain the total release of Ar increases with the coating thickness; for a thickness of 100 nm, all argon is released below 600 °C, while an isotherm of one hour at 900 °C is necessary for a coating 5 μm thick. Besides the Ar atoms left from the synthesis, other defects, such as Si clusters and silicon dangling bonds, are present in the coatings. The concentration of both of them is strongly reduced by thermal treatments either in vacuum or in air. The overall thickness of the coating is slightly increased after thermal treatments, as witnessed by the change of the period of interference fringes.

Effect of carbon-tin oxides vacuum thermal treatment on performance of lithium-ion batteries

Effect of carbon-tin oxides vacuum thermal treatment on performance of lithium-ion batteries

Porosity Formation in Thin Welded Joints of Al-MG-LI Alloys.

This work is about the study of the correlation of pore formation in welded joints of Al–MG–LI alloy with zirconium additives with the state of the base metal, thermal vacuum treatment, and welding technologies MIG and EBW. Metallographic analysis has been carried out, the phase composition of the alloy and weld metal has been investigated, and thermal cycles of welding have been calculated, allowing to estimate the residence time of metal in the alloying zone and weld metal in the liquid state. The nature of the allocation of strengthening fine-dispersed phases in the welded joints of the alloy has been determined. The regularity and character of pore formation in welded joints depending on the applicable thermal vacuum treatment (TVT) and welding technology have been revealed. It was established that TVT with subsequent hardening and aging has no effect on the phase composition of the alloy. However, this type of treatment contributes to the formation of a more homogeneous and uniform nature of the separation of fine-dispersed strengthening phases. It was revealed that the MIG technology (metal with and without TVT) is characterized by a large length of the fusion zone, the high residence time of metal in the fusion zone and weld metal in the liquid state, and the formation of pores. Phase formation in the temperature range of the beginning and end of the alloy crystallization occurs not only in the weld at the final stage of crystallization but also in the fusion zone, which may induce pore formation, whereas EBW welding shows the opposite trend and no pores. It was found that EBW technology prevents pore formation and makes it possible to obtain welded joints of 1420 Al alloys of the required quality.

Sample preparation induced phase transitions in solution deposited copper selenide thin films.

Thin films of CuSe were deposited onto GaAs substrate. XRD showed that the as-deposited films were of the Klockmannite (CuSe – P63/mmc 194) phase with lattice parameters a0 = b0 = 0.3939 nm, c0 = 1.7250 nm; however, electron diffraction in the TEM surprisingly indicated the β-Cu2−xSe phase (Cu1.95Se – R3̄m 166) with lattice parameters a0 = b0 = 0.412 nm, c0 = 2.045 nm. The discrepancy originated from the specimen preparation method, where the energy of the focused ion beam resulted in loss of selenium which drives a phase transition to β-Cu2−xSe in this system. The same phase transition was observed also upon thermal treatment in vacuum, as well as when the 200 keV electron beam was focused on a powder sample in the TEM. The initial phase can be controlled to some extent by changing the composition of the reactants in solution, resulting in thin films of the cubic α-Cu2−xSe (Cu1.95Se – Fm3̄m) phase co-existing together with the β-Cu2−xSe phase.

Purification of Hydrogen from CO with Cu/ZSM-5 Adsorbents.

The transition to a hydrogen economy requires the development of cost-effective methods for purifying hydrogen from CO. In this study, we explore the possibilities of Cu/ZSM-5 as an adsorbent for this purpose. Samples obtained by cation exchange from aqueous solution (AE) and solid-state exchange with CuCl (SE) were characterized by in situ EPR and FTIR, H2-TPR, CO-TPD, etc. The AE samples possess mainly isolated Cu2+ cations not adsorbing CO. Reduction generates Cu+ sites demonstrating different affinity to CO, with the strongest centres desorbing CO at about 350 °C. The SE samples have about twice higher Cu/Al ratios, as one H+ is exchanged with one Cu+ cation. Although some of the introduced Cu+ sites are oxidized to Cu2+ upon contact with air, they easily recover their original oxidation state after thermal treatment in vacuum or under inert gas stream. In addition, these Cu+ centres regenerate at relatively low temperatures. It is important that water does not block the CO adsorption sites because of the formation of Cu+(CO)(H2O)x complexes. Dynamic adsorption studies show that Cu/ZSM-5 selectively adsorbs CO in the presence of hydrogen. The results indicate that the SE samples are very perspective materials for purification of H2 from CO.

Thermal-Vacuum Method for Obtaining Nanodispersed Zirconium Dioxide

An energy-efficient thermal-vacuum method for continuous production of nanodispersed powder of amorphous zirconium dioxide from zirconium hydroxide has been developed. This approach is based on a principle of creating an aerodynamic flow with an initial powder-like material in the cavity of the heating element of a thermal-vacuum installation. In this way, short-term contacts of particles of zirconium hydroxide with the inner surface of the heating element made in the form of the winding helical are created. As a result, the crushing of the particles is carried out due to the high thermal stresses in the particles contacted. This process is aggravated by the presence of residual moisture in the original powdery material. Transformations of the zirconium hydroxide in the process of thermal-vacuum treatment have been investigated. Amorphous dioxide has been obtained. The study of structural composition of the material in the initial state and processed in a thermal-vacuum installation was carried out using X-ray analysis and scanning microscopy. Experimental data on the structural-phase composition of the original material and data on the closest structural prototypes of crystalline-impurity compounds are presented. They are also given data on the volume of crystal cells and estimates of the molar concentration of the components. A mass spectrometric assessment of the elemental composition of the obtained zirconium dioxide is given. Thermal-vacuum method allows toobtain highly dispersed zirconium dioxide in its amorphous state directly from zirconium hydroxide without using liquid media and, moreover, in a short time – within 15...20 s.