Treatment In Hydrogen Atmosphere Research Articles

Quantifying Carbon Active Sites Chemisorbing Hydrogen on Oxygen Containing Activated Carbons during Heat Treatment in Hydrogen Atmosphere.

Carbon edge sites have been widely studied because of their importance in surface reactivity and electronic properties. The surface chemistry of the carbon edge sites is relevant to various reactions, and carbon active sites are key topics in many applications. Temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) techniques are used to clarify the fate of oxygen atoms present as CO-yielding functional groups on the activated carbon during heat treatment in hydrogen with an argon balance atmosphere. It has been elucidated that CO is decomposed, H2O is released by a reduction reaction with atmospheric H2, and CO2 is evolved by secondary reactions from the CO-yielding functional groups during TPR. Atmospheric H2 consumption during TPR is observed and its rate is characterized. The amounts of carbon active sites are quantified by determining the amount of H2 chemisorbed onto the carbon surfaces. Finally, it is quantitatively determined that the active sites that chemisorb hydrogen are generated after the decomposition of CO and CO2 caused by secondary reactions between ca. 700 and 1100 K from the CO-yielding functional groups. The origin of these CO-yielding functional groups is generally attributed to phenol/ether groups. In addition to these oxygen-containing functional group decompositions, some free sites on the edge sites are activated for H2 chemisorption by heat treatment between ca. 700 and 1100 K.

Improving Oxidation Resistance of Low Fe-Si Alloys by Preheating Treatment

In this work, attempts have been made to improve the oxidation resistance of Fe-Si alloys with 0.5, 1.0 and 2.0 mass pct Si by a preheating treatment, which was carried out at 1073 K for 24 hours in high purity hydrogen atmosphere. Compared with pure Fe and untreated Fe-Si alloys, the oxidation resistance of the preheated Fe-Si alloys at 673 K in O2 is drastically increased, in the case of 2 mass pct Si by two orders of magnitude. The improvement is attributed to a uniform, dense and continuous 25 nm pure SiO2 layer formed on the alloy surface during the preheating treatment in hydrogen atmosphere hindering the diffusion of Fe and O.

Design of hydroxylated MnO2 nano-bricks for high-performance supercapacitors

High surface area 3D architecture of H–MnO2 nano bricks (NBs) on Cu substrate is developed by employing controlled electrodeposition of Mn on Cu substrate followed by high-temperature thermal treatment in hydrogen atmosphere. The electrochemical activity of the H–MnO2 NBs as a supercapacitor electrode material shows high specific and areal capacitance of 1410 F/g and 295 mF/cm2, respectively along with high cycling stability (only 5% loss of initial specific capacitance after 3000 cycles at a current density of 2.5 A/g). This electrode exhibits an excellent energy density of 22.51 Wh/kg and a power density of 20.44 kW/kg, even at a high current density of 100 A/g. The excellent electrochemical performance of the H–MnO2 NBs as supercapacitor electrode is due to the active material's enhanced electron and ion conductivity, which is due to the presence of hydroxyl groups on the MnO2 NBs surface.

Stability of nanocrystalline Ce-Gd mixed oxide on Al2O3 support

In various technological applications (solid oxide fuel cells, heterogeneous catalysis) ceria based mixed oxides are in contact with alumina used as support or additive. It is thus important to gain knowledge on the possible interactions between the mixed oxide and the alumina at temperatures and atmospheres, corresponding to real processing or working conditions. In this work, structure and chemical stability of Ce0.5Gd0.5O1.75 nanoparticles supported on a high surface γ-Al2O3 were studied in oxidizing and reducing atmosphere by XRD, TEM, SEM-EDS, STEM-EDS, Raman spectroscopy and H2-TPR. Application of a reverse microemulsion method enabled the synthesis of highly Gd-doped, homogeneous ceria particles with mean size ∼2 nm, ideal for the studies on effect of the interaction with Al2O3 support on chemical and structural stability od doped ceria. Poor tolerance of Ce0.5Gd0.5O1.75 nanoparticles to sintering is greatly improved by their dispersion on a high surface alumina support. In oxidizing atmosphere the particles were chemically stable on the alumina up to 1100 °C, undergoing little sintering with increase of the mean crystallite size to 7 nm. In hydrogen atmosphere, the stability is limited by complex, chemical interaction between Gd doped ceria and Al2O3 support, which has been studied in detail for the first time. Ce0.5Gd0.5O1.75 nanoparticles started to spread over the support at 600 °C into a nanometer thick amorphous layer, and at 900 °C crystallized into a mixed (Gd,Ce)4Al2O9 aluminate. The (Gd,Ce)4Al2O9 aluminate, which is an intermediate phase at the low ceria/alumina molar ratio used, decomposed at 1000 °C into tetragonal CeAlO3 and hexagonal GdAlO3. When deposited on Al2O3, Ce0.5Gd0.5O1.75 nanoparticles showed much improved reducibility, especially in low-temperature range (300–600 °C). This effect is further enhanced by the spreading of ceria over Al2O3 occurring during treatment in hydrogen atmosphere at elevated temperature.The nanocrystalline Ce-Gd-O/Al2O3 system prepared by the impregnation with an aqueous solution of Ce and Gd nitrates appeared to be chemically inhomogeneous and less stable in both oxidizing and reducing atmospheres.d

Essential role of treatment in hydrogen atmosphere on creation of ferromagnetic order in carbon incorporated TiO2 nanocomposite

Carbon incorporated TiO2 nanocomposite powders were synthesized by a facile thermal co-decomposition of a mixture of titanium tetrachloride (TiCl4) and sucrose (C12H22O11) as a source of carbon ions. The crystalline structures were studied by x-ray diffraction (XRD) method through the Rietveld refinement technique of analysis. It was found that the samples consist of anatase (A) and rutile (R) with a small amount of brookite (B). It was noticed that the incorporation of C ions in TiO2 lattice enhanced the A to R transformation through creation of oxygen (O)-vacancies. It was concluded that the incorporated small-size C ion-species might occupy interstitial positions in the lattice of host TiO2. Such incorporation should create O-vacancies due to the re-distribution of static charges of ions. The optical properties were investigated by the diffuse reflection spectroscopy (DRS) method. The C-ions incorporation red-shifted the optical band gap, while the hydrogenation of the samples blue-shifted the band gap according to Moss-Burstein effect. Annealing the samples in H2-atmosphere could create O-vacancies, increase carrier concentration, and toss the incorporated in the interstitial C ion-species to occupy the O-vacancies (CO). The possible creation of FM behavior due to CO ions mutual interaction depends on their average separation (RC–C) that was estimated to explain the obtained ferromagnetic (FM) results. The FM properties were observed only with hydrogenated samples that incorporated by ∼1% C. The effective magnetic moment was evaluated to be 1.24 μB/C, which was attributed to the magnetic moment of C2p in addition to some contributions to O-vacancies. This study showed the critical importance of hydrogenation processes to create FM properties in C-incorporated TiO2 nanocomposites.

Hydrogen annealed ZnO:B film grown by LPCVD technique as TCO for enhancing conversion efficiency of a-Si:H/μc-Si:H tandem solar cells

The ZnO:B (BZO) films with different boron doping levels have been prepared by low pressure chemical vapor deposition (LPCVD) technique. The electrical and optical properties of the BZO films have been systematically investigated through a post annealing treatment in hydrogen atmosphere, as well as in vacuum for comparison. It is found that conductivity of BZO films, especially with a low boron doping level, can be enhanced significantly after annealing in hydrogen, and moreover, the total transmittance (TT) and haze factor of the H2-annealed BZO films were still almost unchanged simultaneously, which were attributed to phenomena of an increase in carrier mobility with an almost constant of free carrier concentration. The conversion efficiency of a-Si:H/μc-Si:H tandem solar cell incorporating H2-annealed lowly doped BZO film as front electrode was confirmed to be improved remarkably by 1.10% due to the enhancement of TT and haze factor, as compared to that using an as-grown heavily doped BZO film as front electrode. The results indicate that H2-annealing is a quite attractive and alternative technique to optimize properties of BZO film as TCO for further enhancing conversion efficiency of a-Si:H/μc-Si:H tandem solar cells.

Fabrication of Porous Ni by Freeze Drying and Hydrogen Reduction of NiO/Camphene Slurry

In order to fabricate the porous Mo with controlled pore characteristics, unique processing by using powder as the source and camphene as the sublimable material is introduced. Camphene-based 15 vol% slurries, prepared by milling at with a small amount of dispersant, were frozen at . Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at , and sintered at for 1 h. After heat treatment in hydrogen atmosphere, powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores due to the difference in the camphene growth rate during freezing process. The size of small pores was decreased with increase in sintering temperature, while that of large pores was unchanged. The results are strongly suggested that the porous metal with required pore characteristics can be successfully fabricated by freeze-drying process using metal oxide powders.

Fabricating Metal@N-Doped Carbon Catalysts via a Thermal Method

Nanoparticles (NPs) encapsulated with carbon material have been proven particularly successful for improving their stability; however, this carbon-coating strategy is a compromise between activity and stability because these carbon shells also reduce, even deactivate, the activity of the catalyst by blocking active sites. Herein, we report a procedure to effectively remove the carbon layer without affecting particle morphology, which enhances the surface exposure of the nanoparticles and their catalytic activity while retaining their stability. The heat treatment, such as reduction in hydrogen atmosphere or calcination in air atmosphere, could destroy the defective carbon-surrounded Ru NPs through making the methanation or oxidation reaction occur on the carbon material surface. More importantly, the heat treatment in air atmosphere at low temperature exhibited higher power to corrode the defective carbon-surrounded Ru NPs in comparison with the heat treatment in hydrogen atmosphere. We anticipate that th...

Development of Room-Temperature Ferromagnetism in Nanocomposite CdO Codoped with Al and Gd: Treatment in Hydrogen Atmosphere

Cadmium oxide codoped with Al and Gd ion powders was synthesised by thermal codecomposition of a mixture of complexes of cadmium acetate dihydrate, gadolinium acetate hydrate, and aluminum nitrate nonahydrate. The mass ratio of Al/Cd was fixed while the mass ratio of Gd/Cd varied systematically. The purpose of the present study is to synthesise and study the transparent conducting oxide (TCO) CdO powder having room-temperature ferromagnetic (RT-FM) properties. To realize that purpose, the synthesised Al/Gd-codoped CdO powder was annealed under hydrogen gas with certain conditions. The X-ray diffraction (XRD) method confirmed the formation of a single nanocrystalline structure; thus, both Al/Gd ions were incorporated into CdO lattice forming solid solutions. Magnetic measurements revealed that some of the doped CdO powders gained paramagnetic (PM) properties where the susceptibility increases with increasing dopant Gd content; the measured effective magnetic moment of dopant Gd3+ was around 8 μB. Furthermore, the magnetic energy of the created RT-FM of the codoped CdO samples by hydrogenation was found to be dependent on the Gd% doping level. For hydrogenated CdO powder doped with 3% Gd, the coercivity (Hc) was 195.9 Oe, the remanence (Mr) was 0.77 memu/g, the saturation magnetisation (Ms) was 5.05 memu/g, and the energy product (Um) was 150.6 merg/g. Thus, the possibility of production of TCO CdO with RT-FM, where magnetic characteristics can be tailored by doping and post treatment under H2 gas, was proven. Thus, a new potential candidate to be used as a dilute magnetic semiconductor (DMS) was successfully synthesised.

Effect of heat treatment on the microstructure and properties of Ni based soft magnetic alloy.

A Ni-based alloy was heat treated by changing the temperature and ambient atmosphere of the heat treatment. Morphology, crystal structure, and physical performance of the Ni-based alloy were characterized via SEM, XRD, TEM, and PPMS. Results show that due to the heat treatment process, the grain growth of the Ni-based alloy and the removal of impurities and defects are promoted. Both the orientation and stress caused by rolling are reduced. The permeability and saturation magnetization of the alloy are improved. The hysteresis loss and coercivity are decreased. Higher heat treatment temperature leads to increased improvement of permeability and saturation magnetization. Heat treatment in hydrogen is more conducive to the removal of impurities. At the same temperature, the magnetic performance of the heat-treated alloy in hydrogen is better than that of an alloy with heat treatment in vacuum. The Ni-based alloy shows an excellent magnetic performance on 1,373 K heat treatment in hydrogen atmosphere. In this process, the µm , Bs , Pu , and Hc of the obtained alloy are 427 mHm-1 , 509 mT, 0.866 Jm-3 , and 0.514 Am-1 , respectively. At the same time, the resistivity of alloy decreases and its thermal conductivity increases in response to heat treatment.

Porous W-Ni Alloys Synthesized from Camphene/WO3-NiO Slurry by Freeze Drying and Heat Treatment in Hydrogen Atmosphere

The present study demonstrates the effect of raw powder on the pore structure of porous W-Ni prepared by freeze drying of camphene-based slurries and sintering process. The reduction behavior of WO3 and WO3-NiO powders is analyzed by a temperature programmed reduction method in Ar-10% H2 atmosphere. After heat treatment in hydrogen atmosphere, WO3-NiO powder mixture is completely converted to metallic W without any reaction phases. Camphene slurries with oxide powders are frozen at −30 oC, and pores in the frozen specimens are generated by sublimation of the camphene during drying in air. The green bodies are hydrogen-reduced at 800 °C and sintered at 1000 °C for 1 h. The sintered samples show large and aligned parallel pores to the camphene growth direction, and small pores in the internal wall of large pores. The strut between large pores, prepared from pure WO3 powder, consists of very fine particles with partially necking between the particles. In contrast, the strut densification is clearly observed in the Ni-added W sample due to the enhanced mass transport in activation sintering.

The structural features of the amorphous C14 HfNiAl Laves phase

Purpose: In order to clarify whether amorphization occurs in the pseudo-binary C14 HfNi0.6Al1.4 Laves phase a detailed investigation of the effect of hydrogen treatment on it phase-structural state has been studied. This type of compounds is of interest due to their high possibility to hydrogen absorption as Laves phase structures and as Hf-Ni alloys. Design/methodology/approach: We used a combination of hydrogen treatment and grinding methods for studying of the processes of controlled structure formation. High temperature transformations of the HfNi0.6Al1.4 alloy were pointed out by means of XRD analysis. Findings: By combination of two amorphization methods and high temperature measurements we have observed a phase structural transformation of the HfNi0.6Al1.4 alloy, which could be presented as: HfNi0.6Al1.4(cryst.) + H2 ® HfNi0.6Al1.4 (nanocryst.) + HfNi0.6Al1.4 (amorphous) + H2 ® HfH2 (amorphous) + AlH3 (amorphous) + Ni. Ferromagnetic- like properties of the pseudo-binary HfNi0.6Al1.4 Laves phase was found. Research limitations/implications: Complex research of HfNi0.6Al1.4 alloy revealed various structure features depending on phase content, thermodynamic parameters and conditions of hydrogen treatment. Obtained results suppose that further studies of structure and physical properties of Hf-Ni-Al alloys will allow to find the methods to control the producing of materials with desired properties. Practical implications: Using of hydrogen treatment is effective to produce Al-based alloys with improved magnetic properties. Originality/value: Treatment in hydrogen atmosphere allows improving the glass-forming ability in Hf-Ni-Al alloys.

Oxygen vacancies mediated ferromagnetism in hydrogenated Zn0.9Co0.1O film

Zn0.9Co0.1O films were prepared by pulsed laser deposition and followed by annealing treatment in hydrogen atmosphere. Both samples show ferromagnetic behavior and saturated ferromagnetic magnetization was significantly increased by five times after the hydrogenation treatment. Co ions in both samples have been confirmed to be bivalent as substituents. Moreover, hydrogenation did not change the ZnO wurtzite structure and no segregation of Co, Co oxides or any other secondary phases were detected. Furthermore, the Co 2p3/2 peaks shift to lower energy level after hydrogenation, excluding the formation of Co-H-Co complexes. The structural characterizations clearly confirmed that the increment of oxygen vacancies was due to the hydrogenation treatment. These results indicate that the oxygen vacancies play a crucial role in mediating the ferromagnetism in Zn0.9Co0.1O film.

Effect of annealing and hydrogen plasma treatment on the luminescence and persistent photoconductivity of polycrystalline ZnO films

Photoluminescence (PL) and electrical properties of boron doped zinc oxide (ZnO) thin films, deposited by metalorganic chemical vapour deposition on a glass substrate, were investigated. The effects of annealing in air, as well as the influence of the radiofrequency—plasma treatment in hydrogen atmosphere, on the PL and electrical conductivity of the ZnO films were studied. A correlation between photoluminescence and electrical properties during annealing was observed. Hydrogen plasma treatment causes an increase in the carrier mobility and concentration and results in a very intensive near band edge emission (NBE). It was found that defects responsible for the dramatic increase in the intensity of NBE band in the hydrogen-treated ZnO films are hydrogen-related complexes formed near or at the surface of the samples. The intensity of NBE in hydrogen-treated samples decreases after aging in the dark, and, conversely, the NBE intensity increases under UV light illumination. This effect is fully reversible and depends on the gas atmosphere during the UV exposure and subsequent aging. It was proposed that the NBE band in the ZnO films annealed in the air and treated in hydrogen plasma emerges due to O-H complexes forming at zinc vacancy sites, n(O-H)-VZn.

Powder Forming Process from Machined Titanium Chips via Heat Treatment in Hydrogen Atmosphere

Powder Forming Process from Machined Titanium Chips via Heat Treatment in Hydrogen Atmosphere

Rapid hydrogenation of amorphous TiO2 to produce efficient H-doped anatase for photocatalytic water splitting

Hydrogen-doped anatase titanium dioxide (H:TiO2) thin films were synthesized by a mild annealing in hydrogen atmosphere of amorphous TiO2 thin films deposited on ITO by RF-magnetron sputtering. Two kinds of TiO2 electrodes (amorphous and anatase) were tested for the H-doping in different annealing conditions, but H-doped anatase was obtained exclusively by a rapid heat treatment in hydrogen atmosphere of amorphous TiO2 at 300°C. Instead, anatase thin films required enforced annealing conditions to incorporate H, leading to an undesirable conversion to rutile. XPS analysis reveals that in H-doped anatase thin films H atoms are bonded to O. DFT calculations, performed to investigate the density of states, predict a slight band-gap narrowing, in agreement with spectroscopic evidence. Photoelectrochemical measurements on H:TiO2 showed an elevated current density of 0.99mA/cm2 at 1.23V vs. RHE in oxygen evolution reaction, revealing better performance than pure anatase TiO2. This enhancement in catalytic activity is accounted to the effect of dangling bonds passivation performed by highly reactive H atoms, which reduce the density of carrier recombination centers. The used method for the conversion of amorphous TiO2 thin film in H:doped anatase TiO2 can be extended to amorphous TiO2 prepared by various techniques.

Nonlinear optical properties of silver nanoparticles prepared in Ag doped borate glasses

Nonlinear properties of Li2B4O7:Ag borate glasses with “Li2B4O7:Ag nanoparticles” interface region formed by thermal treatment in hydrogen atmosphere and in vacuum are investigated. From the results of plasmon absorption and normalized transmission measurements in Z-scan regime it was ascertained that “Li2B4O7:AgNPs” interface region changes the character of nonlinear refraction of Li2B4O7:Ag glass from negative to positive, and, due to plasmon resonance, increases significantly its nonlinear properties. In particular, the observed growth of nonlinear refractive index n2 is more than four orders of magnitude.

Surface Treatment of the Activated Carbon on Capacitive Deionization

The capacitive deionization (CDI) which has huge interest as an energy efficient and eco-friendly desalination process, is an electrochemically water purification technology using electro-static adsorption/desorption of ions on the charged electrode. Activated carbons are commonly used for an electrode material due to its high surface area. The surface condition of activated carbon is a remarkable point on the CDI process that repeats reversible adsorption and desorption of ions on the interface between the carbon electrode and the saline electrolyte. In this experiment, we investigated the effect of surface treatment of activated carbons on CDI performance by two kinds of commercial activated carbons which were Maxsorb-III and P-60 with a surface area of 3000, 1800m2g-1, respectively. Each activated carbon was treated by two different methods. One was to remove the surface functional groups by heat treatment in hydrogen atmosphere. Another way was to introduce the oxygen functional groups on the surface by H2O2 treatment. The characteristics such as the specific surface area and chemical states of carbon surface were evaluated by N2 adsorption isotherm and FT-IR analysis. The specific capacitance was examined using cyclic voltammetry in saline or acid electrolyte. Unit-cell CDI performances were tested and compared in a view point of surface functional groups of activated carbons

Accelerated formation of sodium depletion layer on soda lime glass surface by corona discharge treatment in hydrogen atmosphere

Formation of a sodium depletion layer on a soda lime glass surface was accelerated efficiently using a corona discharge treatment in H2 atmosphere. One origin of such acceleration was the preferential generation of H+ with a larger mobility at an anode needle end with a lower applied voltage than that in air. The second origin was the applied voltage across the glass plate during the corona discharge treatment, which was estimated theoretically as 2.7 times higher than that in air. These two effects doubled the depletion layer thickness compared with that in air.

Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing

• Fe films have been grown on Si(0 0 1) substrates and subsequently hydrogenated. • As deposited films present soft magnetic character and a strong magnetic texture. • Structural and magnetic properties can be tuned via hydrogenation treatments. • Ferromagnetic/semiconductor interfaces might be manipulated via hydrogenation. In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(0 0 1) substrates by RF sputtering have been investigated using 57 Fe conversion electron Mössbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing.