Hydrogen Reduction Process Research Articles

Preparation of a ZnO Nanostructure as the Anode Material Using RF Magnetron Sputtering System.

In this study, a four-inch zinc oxide (ZnO) nanostructure was synthesized using radio frequency (RF) magnetron sputtering to maximize the electrochemical performance of the anode material of a lithium-ion battery. All materials were grown on cleaned p-type silicon (100) wafers with a deposited copper layer inserted at the stage. The chamber of the RF magnetron sputtering system was injected with argon and oxygen gas for the growth of the ZnO films. A hydrogen (H2) reduction process was performed in a plasma enhanced chemical vapor deposition (PECVD) chamber to synthesize the ZnO nanostructure (ZnO NS) through modification of the surface structure of a ZnO film. Field emission scanning electron microscopy and atomic force microscopy were performed to confirm the surface and structural properties of the synthesized ZnO NS, and cyclic voltammetry was used to examine the electrochemical characteristics of the ZnO NS. Based on the Hall measurement, the ZnO NS subjected to H2 reduction had a higher electron mobility and lower resistivity than the ZnO film. The ZnO NS that was subjected to H2 reduction for 5 min and 10 min had average roughness of 3.117 nm and 3.418 nm, respectively.

Magnetic modulation of core@shell MoS2-based flower-like multicomponent nanocomposites to improve microwave attenuation

Nanocomposites with a three-dimensional (3D) flower-like geometrical morphology were considered as excellent microwave absorbers (MAs) because of the numerous effective sites for the multiple reflections of electromagnetic (EM) wave. Herein, for optimizing the EM matching characteristic and taking full advantage of interface polarization, a strategy of magnetic modulation was proposed to further improve the EM wave absorption performances (EMWAPs) of MoS2-based nanocomposites. We adopted a simple hydrothermal route and a combined method of hydrothermal treatment/hydrogen reduction to synthesize core@shell CoFe2O4@MoS2 and CoFe@MoO2/MoS2 flower-like nanocomposites, respectively. The obtained results indicated that the hydrogen reduction effectively improved their magnetic properties and magnetic loss capabilities, and their 3D flower-like geometrical morphologies were well maintained during the hydrogen reduction process. The obtained core@shell CoFe@MoO2/MoS2 flower-like nanocomposites presented the extraordinary comprehensive EMWAPs including the optimal reflection loss value of −54.83 dB with the matching thicknesses (dm) value of 2.05 mm and effective absorption bandwidth value of 6.40 GHz with the dm value of 2.59 mm, which were evidently superior to the properties of CoFe2O4@MoS2. Therefore, the findings provided an effective pathway to further improve EMWAPs of MoS2-based core@shell nanocomposites and the as-prepared core@shell CoFe@MoO2/MoS2 flower-like nanocomposites could be utilized as the novel high-efficient MAs.

Fabrication of Ultra-Fine-Grained W-TiC Alloys by a Simple Ball-Milling and Hydrogen Reduction Method

In this paper, a simple method to fulfill the ideal microstructural design of particle reinforced tungsten (W) alloys with promising mechanical properties is presented. W-0.5 wt.% TiC powders with core-shell (TiC/W) structure are prepared by ball-milling and controlled hydrogen reduction processes. TEM observation demonstrates that the nano TiC particles are well coated by tungsten. The W-TiC powders are sintered by spark plasma sintering (SPS) under 1600 °C. The sintered microstructures are characterized by FESEM and TEM. It is found that the W-0.5TiC alloys obtain an ultra-fine-sized tungsten grain of approximately 0.7 μm. The TiC particles with the original nano sizes are uniformly distributed both in tungsten grain interiors and at tungsten grain boundaries with a high number density. No large agglomerates of TiC particles are detected in the microstructure. The average diameter of the TiC particles in the tungsten matrix is approximately 47.1 nm. The mechanical tests of W-0.5 TiC alloy show a significantly high microhardness and bending fracture strength of 785 Hv0.2 and 1132.7 MPa, respectively, which are higher than the values obtained in previous works. These results indicate that the methods used in our work are very promising to fabricate particle-dispersion-strengthened tungsten-based alloys with high performances.

Electrospinning fabrication and enhanced microwave absorption properties of nickel porous nanofibers

One-dimensional Ni porous nanofibers (Ni PNFs) were prepared through a facile electrospinning followed by hydrogen reduction process, and their electromagnetic characteristics and microwave absorbing properties were investigated. Benefiting from the unique microstructure, three-dimensional conductive network and multiple attenuation forms, Ni PNFs exhibit remarkably increased dielectric loss capacity and improved impedance matching level relative to Ni nanoparticles. Consequently, Ni PNFs offer a significantly enhanced microwave absorption property with a minimum reflection loss (RL) of −40.4 dB at a relatively low filling ratio of 30 wt% and an effective absorption bandwidth (RL<−10 dB) of 4.6 GHz (8−12.6 GHz). Our results demonstrate that the microstructure and morphology of materials have considerable influence on their electromagnetic performances and the as-obtained Ni PNFs can be a promising candidate for lightweight and high-efficiency microwave absorption or electromagnetic shielding.

Effect of pore characteristics on hydrogen reduction kinetics based on a novel analysis approach combined model-fitting and iso-conversion

Carbon reductant used in metallurgy industry is a considerable source of carbon dioxide emissions. Growing concerns over greenhouse effect have urgently prompted research in the application of hydrogen energy as an alternative. However, some basic kinetic problems in the hydrogen reduction process have not been clarified and resolved yet, such as the activation energy fluctuations caused by neglect of pore characteristics, along with the overly subjective division of the whole reaction process to analyze rate limiting mechanisms. In this study, a novel approach for acquiring instantaneous activation energy is proposed that is able to identify the activation energy at every reaction moment and thereby provide a quantitative basis for kinetics segmentation and rate-limiting mechanism determination. Moreover, due to the space requirements, the activation energy for the reaction stage controlled by nucleation and nuclei growth has a strong correlation with specific surface area. Whereas the restriction mechanisms of chemical reaction and diffusion are closely related to the average pore size. These results reveal that the different pore characteristics and changes in value have a direct influence on the corresponding rate limiting mechanisms and restriction degrees.

A Continuous Hydrogen Reduction Process for the Production of Water on the Moon

A Continuous Hydrogen Reduction Process for the Production of Water on the Moon

Preparation of black-titanium dioxide nanotubes by thermal decomposition of sodium borohydride

Titanium dioxide is a very attractive material in catalysis. Although the titanium dioxide exhibits superior proper-ties in ultra violet radiation, activity of the catalyst can be improved by some modifications specially for daylight radiation. Titanium dioxide was colored by thermal decomposition of sodium borohydride at 400 0C. The gray colored nanotube-titanium dioxide obtained where the molar ratio of titanium dioxide to sodium borohydride, 1.2 and 0.6. The black nanotube-titanium dioxide was prepared by making the ratio 0.3. While heterogeneous dispersion observed after coloring of commercial titanium dioxide, all photocatalysts prepared from nanotube-titanium dioxide were perfectly homogeneous after coloring. Structural properties of photocatalysts analysed by using XRD, BET and SEM. The nanotube form of titanium dioxide prepared by hydrothermal method. The nanotube photocatalysts are anatase and have high surface area. The activities of colored nanotubes investigated according to these structural properties. Photocatalysts could not be colored homogeneously with the hydrogen reduction process but efficient reduction and coloration obtained with sodium borohydride. The visible region activities of photocatalysts increased by coloring with sodium borohydride compared to coloring by hydrogen. While the surface structure is important, all prepared nanotube-titanium photocatalysts exhibited more efficient color removal yield with regard to commercial one. More active catalysts prepared for absorption of daylight energy and 98.4 % color removal yield from 30 ppm methylene blue solution obtained with black nanotube-titanium dioxide photocatalyst.

Kinetics of synthesizing process for obtaining iron nanopowder by chemical-metallurgical method under isothermal conditions

In this work the kinetics of synthesizing process of metallic iron nanopowder by hydrogen reduction from α-FeOOH hydroxide under isothermal conditions were studied. α-FeOOH nanopowder was prepared in advance by chemical deposition from aqueous solutions of iron nitrate Fe(NO3)3 (10 wt. %) and alkali NaOH (10 wt. %) at room temperature, pH = 11, under the condition of continuous stirring. The hydrogen reduction process of α-FeOOH nanopowder under isothermal conditions was carried out in a tube furnace in the temperature range from 390 to 470 °C. The study of the crystal structure and composition of the powders was performed by X-ray phase analysis. The specific surface area S of the samples was measured using BET method by low-temperature nitrogen adsorption. The average particle size D of powders was determined via the measured S value. The size characteristics and morphology of the particles were investigated by transmission and scanning electron microscopes. The calculation of the kinetic parameters of the hydrogen reduction process of α-FeOOH under isothermal conditions was carried out by the Gray-Weddington model and Arrhenius equation. It is shown that the rate constant of reduction at 470 °C is approximately 2.2 times higher than in the case at 390 °C. The effective activation energy of synthesizing process of iron nanopowder by hydrogen reduction from α-FeOOH was ~38 kJ/mol, which indicates a mixed reaction mode. In this case, the kinetics overall process is limited by both the kinetics of the chemical reaction and the kinetics of diffusion, respectively, an expedient way to accelerate the process by increasing the temperature or eliminate the diffusion layer of the reduction product by intensive mixing. It is show that Fe nanoparticles obtained by hydrogen reduction of its hydroxide at 410 °C, corresponding to the maximum specific rate of the reduction process, are mainly irregular in shape, evenly distributed, the size of which ranges from several dozens to 100 nm with an average value of 75 nm.

Ceria supported platinum catalyst for CO oxidation reaction: Importance of metallic active species ― Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

Ceria supported platinum catalyst has now been widely studied due to its excellent activity for CO oxidation. However, the electron state of active metal center is still an open question. In this work, a ceria nanorod support was prepared and platinum (Pt) with 0.9 at% was deposited using an impregnation method to obtain Pt/CeO2 catalyst. With the help of “light-off” experiment and temperature-programmed reduction under CO (CO-TPR) test, the conclusion is proposed that the process of hydrogen reduction can enhance the activity of CO oxidation reaction for the generation of optimal active Pt site. An innovative near-situ X-ray absorption fine structure (XAFS) technique was used to investigate the chemical state of central Pt atom during the reaction process, clearly demonstrating that the high oxidized state of Pt does harm to the activity for CO oxidation while the relatively reductive Pt exhibits high activity, and the different oxidized state and chemical environment of Pt during every process has been identified. Furthermore, the activity of our Pt/CeO2 catalyst is superior to that of most of the previous reports about CO catalytic oxidation by Pt based catalyst. Moreover, the optimal active species (Pt–O4) have been identified after hydrogen reduction, which could be a possible key strategy to control the oxidation of Pt.

MOF-derived Co/CoO particles prepared by low temperature reduction for microwave absorption

Ameliorating the absorption capability and thickness of microwave-absorbing materials is still a formidable challenge. Herein, novel nanoporous Co particles are synthesized successfully via the thermal decomposition of Co-based zeolitic imidazolate framework (ZIF-67) and subsequent hydrogen reduction process at relatively low temperatures. Through controlling passivation process, the nanoporous Co/CoO particles are generated as a result of the surface oxidation of Co particles. The crystalline size of Co/CoO particles ranges from 15.1 to 27.7 nm. The Co/CoO sample reduced at 200 ℃ exhibits the highest microwave absorption intensity with a minimum reflection loss (RL) value of −87.2 dB at a matching thickness of merely 1.0 mm, whose effective absorption bandwidth (EAB) for RL ≤ −10 dB is 6.2 GHz. The absorption bandwidth of Co/CoO increases with the increasing reduction temperature, but the matching thickness gets larger. Co/CoO reduced at 300 ℃ possesses extremely broad EAB of 8.2 GHz at a thickness of 1.5 mm. Notably, such superior microwave absorbing properties are attributed to the facts that nanoporous structure can adjust the effective permittivity of the material, and CoO improves the impedance match by promoting dipolar polarization and interfacial polarization processes. The nanoporous Co/CoO particles with strong absorption ability and ultrathin thickness demonstrate a potential application in the electromagnetic wave absorbing field.

KINETICS OF SYNTHESIZING PROCESS OF MICRON NICKEL POWDER BY HYDROGEN REDUCTION FROM OXIDE COMPOUND UNDER NON-ISOTHERMAL CONDITIONS

In this work the kinetics of the process of obtaining micron nickel powder by hydrogen reduction of the oxide compound under non-isothermal conditions were studied. The hydrogen reduction process of micron NiO powder with hydrogen under non-isothermal conditions was carried out in the linear heating mode at a rate of 10°C/ min in the temperature range of 20-450°C. The study of crystal structure and composition of the powder samples was performed by XRD phase analysis. The specific surface area S of the powders was measured using BET method by low-temperature nitrogen adsorption. The average particle size D of powder samples was determined via the measured S value. The size and shape of the particles were investigated by scanning electron microscopic method. The calculation of kinetic parameters of the reduction process of nickel oxide in nonisothermal conditions was carried out by the differential-difference method using the data of thermogravimetric analysis and the equation for non-isothermal kinetics. It was revealed that the hydrogen reduction process of micron NiO powder in non-isothermia occurs in the temperature range of 270-335°C with a maximum specific rate of 9.667·10-8 kg/s recorded at 316°C. The dependence of the degree of conversion during reduction process was determined by mathematical statistics method and can be well described by the expression y=0.0001e0.0168·x with the coefficient of determination R2=0.9739. The activation energy of hydrogen reduction processes of the micron NiO powder under non-isothermal conditions was found to be ~43 kJ/mol, which indicates a mixed reaction mode. In this mode, a rational way to accelerate the process is both increasing the temperature and eliminating the diffusion layer of the reduction product by intensive mixing. It is shown that an increase in temperature to 316ºС can effectively increase the rate of the overall process of hydrogen reduction of micron NiO powder while guaranteeing the quality of the reduction product. The obtained micron Ni particles are highly porous material, while the Ni particles are collected in large porous aggregates up to 10 μm in size.

Кінетика процесу водневого відновлення нанопорошка оксиду нікелю при неізотермічних умовах

In this work the kinetics of the hydrogen reduction process of nickel oxide nanopowder in non-isothermal conditions were studied. NiO nanopowder was prepared in advance by thermal decomposition at 300°C of nickel hydroxide Ni(OH)2. Ni(OH)2 nanopowder was prepared by chemical deposition from aqueous solutions of nickel nitrate Ni(NO3)2 (10 wt. %) and alkali NaOH (10 wt. %) at room temperature, pH=9, under the condition of continuous stirring. The hydrogen reduction process of NiO nanopowder in non-isothermal conditions was carried out in the linear heating mode at a rate of 5°C/min in the temperature range 25–400°C. The study of the crystal structure and composition of the powder samples was performed by X-ray phase analysis. The specific surface area S of the powders was measured using BET method by low-temperature nitrogen adsorption. The average particle size D of powder samples was determined via the measured S value. The size and shape of the particles were investigated by scanning electron microscopic method. The calculation of kinetic parameters of the reduction process of nickel oxide in non-isothermal conditions was carried out by the differential-difference method using the data of thermogravimetric analysis and the equation for non-isothermal kinetics. It was revealed that the hydrogen reduction process of NiO nanopowder in non-isothermal conditions occurs in the temperature range 240–300°С with a maximum specific rate of 13,045•10-8 kg/s recorded at 280°С. The activation energy for the reduction process of NiO nanopowder was estimated at ~59 kJ/mol, which confirms the kinetic mode of limiting the process. It is shown that an increase in temperature to 280 °С can effectively increase the rate of the overall hydrogen reduction process of NiO nanopowder while guaranteeing the quality of the reduction product. The obtained Ni nanoparticles mainly have a rounded shape, their size ranges from 40–80 nm. Keywords: kinetics, nickel, nanopowder, hydrogen reduction, non-isothermal conditions, activation energy.

Hydrogen reduction behavior of W/Y2O3 powder synthesized by ultrasonic spray pyrolysis

In this study, hydrogen reduction behavior of W/Y2O3 powder was investigated. Phase transformation of WO3/Y2O3 powder was observed during the hydrogen reduction process in the temperature range of 400–800 °C for up to 5 h. The reduction behavior was investigated by the morphology images and the x-ray diffraction (XRD) patterns of the reduced powders at each step. The reduction of WO3/Y2O3 powder was started from the outer region of powder, and the crack was occurred at outer region due to the transformation, which was able to be explained by crackling core model. The particle size of W/Y2O3 decreased due to the addition of Y2O3 particle compared to that of W powder. The activation energy of WO3/Y2O3 powder was calculated via temperature programmed reduction (TPR) analysis, and WO3/Y2O3 and WO3 powder had a difference in activation energy calculated from first peaks in TPR analysis. The addition of Y2O3 particle affected the reduction behavior, especially reduction of WO3 phase to WOx (2 ≤ x < 3) phases.

Influence of the Corrosiveness of a Medium on the Ratio of the Cathodic Protection Current to the Ultimate Diffusion Current for KH70 Pipe Steel

We study the dependence of the ratio of the cathodic protection current to the ultimate diffusion current for Kh70 steel within the range of protective polarization potentials (-0.75)–(-1.05) V (relative to the silver-chloride reference electrode) standardized by the DSTU 4219 in media with different degrees of corrosiveness. It is shown that, within the рН range 5.6–9.6, as the potential shifts to more negative values, the ratio $$ {j}_{\mathrm{c}.\mathrm{p}.}/{j}_{{\mathrm{O}}_2} $$ increases from 0.5 to 138. It was discovered that, for the identical protective polarization potentials in a section of the gas main, the corrosion rate in a defect of the protective coating of steel may not only decrease but also activate the process of hydrogen reduction. It is reasonable to determine a value of the ratio $$ {j}_{\mathrm{c}.\mathrm{p}.}/{j}_{{\mathrm{O}}_2} $$ above which the process of decomposition of soil electrolytes is accelerated and the hydrogenation of the pipe wall in a defect of the coating becomes possible for every medium and take into account this value both in the design of the cathodic protection and in the process of monitoring in the course of operation to prevent stress-corrosion cracking.

Fabrication of superhydrophobic copper metal nanowire surfaces with high thermal conductivity

Copper is an important practical metal with a high thermal conductivity that is widely used as a heat exchanger material. However, a liquid film often forms on the Cu surface through water vapor condensation, causing a large resistance to heat transfer. To address this issue, a superhydrophobic Cu metal nanowire surface is developed herein via Cu anodizing in a KOH electrolyte to form Cu(OH)2 nanowires, followed by hydrogen reduction at an elevated temperature and the application of a wet organic coating. The hydrogen treatment reduces the hydroxide to the metal while maintaining the nanowire morphology. The superhydrophobic Cu metal nanowire surface exhibits effective removal of water droplets formed through water vapor condensation. Furthermore, the metal nanowire surface exhibits highly improved heat transfer compared with the Cu(OH)2 nanowire surface. Therefore, the combined process of anodizing and hydrogen reduction is a simple approach that forms an effective superhydrophobic Cu surface with high thermal conductivity.

MAIN CHARACTERISTICS OF SYNTHESIZING PROCESSES OF MAGNETITE AND IRON NANOPOWDERS BY HYDROGEN REDUCTION FROM HYDROXIDE COMPOUND

Purpose. Study of the main characteristics of synthesizing processes of magnetite and iron nanopowders by hydrogen reduction from hydroxide compound (α-FeOOH). Materials and methods. α-FeOOH hydroxide nanopowder was obtained by chemical precipitation from aqueous solutions of iron (III) nitrate Fe(NO3)3 (10 wt. %) and alkali NaOH (10 wt. %) at room temperature, pH = 11, under the condition of continuous stirring. Synthesizing processes of Fe3O4 and Fe nanopowders by hydrogen reduction of hydroxide α-FeOOH were carried out in a tubular furnace SNOL 0.2/1250. The study of the crystal structure as well as the composition of the powder samples was performed by X-ray phase analysis. The size and morphology of nanopowder particles were investigated by scanning and transmission electron microscopes. The specific surface area of the powders was measured by using BET method by low-temperature nitrogen adsorption. The average size of the powders articles was determined via the measured value of specific surface area. Results. It has been established that the optimal temperatures corresponding to the values of the maximum specific rate for carrying out the synthesizing processes of Fe3O4 and Fe nanopowders by hydrogen reduction are 340 and 500 °C, respectively. The resulting products are nanopowders of pure Fe3O4 and Fe after being through hydrogen reduction process for 2 hours. It was shown that Fe3O4 nanoparticles consist of particles with indefinite shape, which are prone to the formation of flakes. They have a nanometer size (about tens of nm) and are in a sintered state with connections to several neighboring particles by isthmuses. Fe nanoparticles are mainly rounded and spherical, up to one hundred nm in size and distributed separately. Originality. For the first time, the optimal temperatures have been established for synthesizing processes of Fe3O4 and Fe nanopowders by hydrogen reduction from hydroxide compound. Practical value. The research results will serve as a basis for the synthesis of nanopowders based on Fe3O4 and Fe, guarantee the acceleration of processes, ensure the necessary properties of nanopowders and can be used for various fields of science, technology, ecology and oth.

Synthesis and Densification of Nano-Sized W Powders Prepared by Hydrogen Reduction of Ball-Milled WO3 Powders

The synthesis and consolidation of nano-sized W powders are attempted with the combination process of hydrogen reduction of ball-milled WO₃ powder and spark plasma sintering. The reduction behavior of WO₃ is analyzed by temperature-programmed reduction. The reaction peaks for reduction of WO₃ are observed in the temperature range of 590-782 °C. XRD and TEM analysis reveals that oxide powder is changed to metallic W with an average particle size of 100 nm by hydrogen reduction at 900 °C for 1 h. The densified specimen by spark plasma sintering at 1700 °C under an applied pressure of 50 MPa using nano-sized W powder shows increased relative density compared with that using micron-sized W powder. The results suggested that the W bulk with increased relative density fine microstructure can be fabricated by spark plasma sintering of hydrogen-reduced WO₃ powder, more effectively.

Application Of Rf (13.56 MHz) Arc Discharge For Plasma Chemical Conversion Of Volatile Fluorides

The report discusses the use of a new type of plasma source of hydrogen plasma based on a RF (13.56 MHz) arc discharge of atmospheric pressure between two electrodes. This discharge was used for hydrogen reduction of the tetrafluorides of silicon, boron and molybdenum. As a result of the studies, the main regularities of the hydrogen reduction process were established and the main synthesized products were determined. Samples of carbides of silicon, boron and molybdenum were prepared.

Fabrication of ultrafine W-Cu composite powders and its sintering behavior

Ultrafine W-Cu composite powders with various copper (Cu) contents (5, 20 and 40 wt.%) have been fabricated by a method consisting of a carbothermic pre-reduction step and a subsequent hydrogen reduction step. After roasting the mixture of ammonium tungstate ((NH4)10[H2W12O42]·xH2O) and copper nitrate trihydrate (Cu(NO3)2·3H2O), the mixture of CuWO4 and CuO (or WO3) was obtained. Subsequently, this mixture was pre-reduced by insufficient carbon black to generate the products containing W, Cu and a small amount of WO2 which was further reduced to W in the following hydrogen reduction process. Thus, the ultrafine W-Cu composite powders were successfully produced. After sintering the green compacts made of these powders at 1100 ℃, 1150 ℃, 1200 ℃ and 1250 ℃, respectively, the microstructure, relative densities, electric conductivity and thermal conductivity of the sintered alloys were measured. The experimental results indicated that the higher the sintering temperature is, the better the performance of alloys will be.

Seeded growth synthesis of W nanoparticles in reduction process of WO2 by hydrogen

In this study, a seeded growth strategy was employed to prepare W nanoparticles (NPs) with controlled sizes through the growth of W nanoseeds via chemical vapor transport in hydrogen reduction process of WO2. It was found that the formation of sufficient dispersed W nuclei and the chemical vapor transport of W source (WO2(OH)2) were the two most crucial issues for the synthesis of W NPs. In the hydrogen reduction of WO2, it was hard to produce W NPs due to the difficulty of forming sufficient stable dispersed W nuclei. However, when WO2 contained different amounts of pre-fabricated W nanoseeds (25 nm, 12 mass% - 40 mass%) were used as raw materials, W NPs with the average sizes ranged from 35 nm to 180 nm can be successfully synthesized. The presence of W nanoseeds can promote the hydrogen reduction of WO2 and noticeably decrease the activated energy from 173.3 kJ/mol to 95.5–112.0 kJ/mol. The mechanisms of chemical vapor transport, nucleation, growth and reduction kinetics in the reduction of WO2 by hydrogen were investigated in detail. This method has a great potential for the industrial production of W NPs.