Hydrogen Plasma Metal Reaction Research Articles

Influences of adding Y2Ti2O7 and HfH1.98 nanoparticles on the microstructure and mechanical properties of oxide dispersion strengthen steels

Adding Y2O3 will make Al-containing oxide dispersion strengthened (ODS) steels produce coarse Y-Al-O particles, which deteriorates their mechanical properties. Herein, Y2Ti2O7 nanoparticles and Hf hydride nanoparticles (NPs) were successfully prepared by hydrogen plasma-metal reaction (HPMR) method and added together in the Fe-Cr-Al ODS steel to replace the traditional Y2O3 NPs. The microstructure of matrix and oxide in ODS steels has been characterized by scanning transmission electron microscopy (STEM) and high resolution transmission electron microscopy (HRTEM). The oxide NPs in FHYT-0.6 (Fe-14Cr-4.5Al-2 W-0.35HfH1.98–0.6Y2Ti2O7, wt%) are made of Y2Ti2O7 (semi-coherent with the matrix and about 10 nm) and HfO2 (incoherent with the matrix and about 26 nm). The size of oxide dispersoid in FHYT-0.6 is reduced to 8.8 nm and the number density is greatly increased to 9.4 × 1023 m−3 compared with FTYT-0.6 (Fe-14Cr-4.5Al-2 W-0.35Ti-0.6Y2Ti2O7, wt%) and FTY-0.6 (Fe-14Cr-4.5Al-2 W-0.35Ti-0.6Y2O3, wt%). The tensile strength at room temperature of FHYT-0.6 is 1194 MPa, which is 24.1 and 14.1% higher than the FTY-0.6 and FTYT-0.6, respectively. Our work has proved that the mechanical properties of the alloy can be significantly improved by adding Y2Ti2O7 and HfH1.98 NPs, which provides a new idea for manufacturing high-performance ODS steels.

Al and Zr addition to improve the hydrogen storage kinetics of Mg-based nanocomposites: Synergistic effects of multiphase nanocatalysts

Solid-state hydrogen storage is regarded as the key technology to develop commercial application of hydrogen energy, and Mg added with high efficiency catalysts is a promising candidate to break through the barrier of hydrogen storage materials. Herein, Mg−Al and Mg−Al−Zr nanocomposites have been prepared by adding the single-metal (Al) and bimetal (Al, Zr) into Mg nanoparticles by the hydrogen plasma-metal reaction (HPMR) method. The two kinds of nanocomposites have an approximate size of 100 nm. With the expansion of the plasma current, the content of Al and Zr in Mg−Al−Zr nanocomposites increases gradually, and the addition of Al and Zr conspicuously accelerates the kinetics of hydrogen absorption and desorption of Mg. Compared with the nanocomposites with the single-metal (Al), the addition of bimetal (Al, Zr) can further enhance the hydrogen absorption kinetics of Mg, and the content of Zr has a positive effect on the reduction of activation energy (Ea). The Ea of Mg88.3Al7.6Zr4.1 for hydrogen absorption is 68.6 kJ/mol, which is significantly lower than that of Mg92.6Al7.4 (80.6 kJ/mol) and other two Mg−Al−Zr nanocomposites with low Al and Zr (70.7 and 69.8 kJ/mol, respectively). Both the nanostructure of Mg and the synergistic catalytic effects of active “catalytic sites” and H “diffusion channels” provided by the multiphase nanocatalysts of MgAl and AlZr3 contribute to the reduction of Ea. This work provides guidance for the development of Mg-based hydrogen storage materials with high catalytic efficiency.

Constructing yolk-shell Co@void@PPy nanocomposites with tunable dielectric properties toward efficient microwave absorption

The cobalt-based absorbing materials with core-shell structure have been widely investigated and developed in the microwave absorption territory, but their shortcomings such as relatively high density and weak dielectric loss limit their practical applications. In this work, taking the modification of microstructure and coating material as the cut-in point, we fabricated the Co@void@polypyrrole (PPy) nanocomposites (NCs) with yolk-shell structure and conductive polymer PPy coating via an integration of hydrogen plasma-metal reaction (HPMR), in-situ SiO2/PPy coating and SiO2-etching approaches. The Co@void@PPy with a PPy layer thickness of 7.6 nm exhibits the optimal microwave absorption performance. The minimum reflection loss (RL) value comes up to −28.4 dB at 1.4 mm, and the corresponding effective absorption bandwidth (EAB, RL≤ −10 dB) is 5.7 GHz. The optimal EAB is 7.2 GHz with a thickness of only 1.6 mm, where the RLmin is −23.4 dB. Such excellent dielectric loss property and attenuation ability is closely related to the PPy coating and the yolk-shell structure, which give rise to abundant interfaces between PPy and Co core and greatly promote multiple scattering and interface polarization. Accordingly, the yolk-shell structured Co@void@PPy NCs can be a competent candidate in the region of high-performance absorbers.

Synergistic effects of yolk-shell and nanopore architectures on the microwave absorption performance of Co@void@C nanocomposites

Due to deficiencies of poor dielectric loss and narrow absorption bandwidth, how to improve the performance of cobalt-based absorbers remains a challenge in the field of microwave absorption materials. In this work, a convenient and efficient strategy combining hydrogen plasma-metal reaction (HPMR) and chemical dealloying has been developed for the fabrication of nanoporous Co@void@C nanocomposites (NCs). The performance exhibits apparent enhancement owing to the synergistic effects of yolk-shell and nanopore architectures. The minimum reflection loss (RLmin) value reaches −19.5 dB at the thickness of 1.6 mm and the effective absorption bandwidth (EAB, RL ≤ −10 dB) goes up to 6.8 GHz at the thickness of 1.9 mm. For comparison, the porous Co@C NCs with only nanopore architecture have a narrow EAB of 2.6 GHz and Co@void@C NCs with only yolk-shell architecture cannot effectively absorb the incident microwave (RL > −10 dB) within 2–18 GHz. The novel Co-based absorber with yolk-shell and nanopore architectures possesses great potential for the application in microwave absorption field.

Microporous Co1−xFex@C nanoparticles: Strong wideband microwave absorbers for reflection loss less than −20 dB

For advanced microwave absorption materials, the bandwidth of reflection loss (RL) ≤ −20 dB is becoming more and more important due to their applications under some extreme occasions where most of the electromagnetic signals must be absorbed. Herein, in-situ carbon-coated Co-Fe-Al precursor nanoparticles (NPs) were prepared by hydrogen plasma metal reaction (HPMR), and then microporous Co1−xFex@C NPs with an average particle size of about 50 nm were successfully prepared by chemical dealloying. They exhibit a distinct core-shell structure with an amorphous carbon shell of approximately 3 nm and a Co1−xFex alloy core containing micropores of 1.1 nm. As the amount of Fe in the microporous Co1−xFex@C NPs increases from 2.1 wt% to 12.0 wt%, the saturation magnetization gradually enlarges from 82.6 to 92.4 emu g−1 whereas the coercive force only decreases slightly. The Co0.98Fe0.02@C sample shows the widest bandwidth (RL ≤ −10 dB) of 11.3 GHz, and surprisingly the bandwidth corresponding to the RL below −20 dB reaches 6.0 GHz, far superior to other Co-based absorbers. Meanwhile, its minimum RL (RLmin) value reaches −102.3 dB with a thickness of 1.8 mm. As the content of Fe increases to 12.0 wt%, the absorption bandwidth (RL ≤ −20 dB) of Co0.88Fe0.12@C sample decreases to 5.7 GHz while its RLmin value strengthens to −133.7 dB. Both the two samples added with Fe exhibit much wider absorption bandwidth (RL ≤ −20 dB) compared with Co@C NPs without Fe addition. The excellent absorption properties are mainly attributed to the facts that microporous morphology promotes the interfacial and dipole polarization, and Fe addition enhances the magnetic resonance. The Co1−xFex@C NPs may pave a new way for designing effective broadband absorbers for RL ≤ −20 dB to meet the high-performance requirements.

Bead-like cobalt nanoparticles coated with dielectric SiO2 and carbon shells for high-performance microwave absorber

The development of high-efficiency microwave absorption materials with both strong absorption intensity and wide absorption bandwidth is still a significant challenge. In this work, the bead-like cobalt nanoparticles of 50 nm with strong magnetic loss capability are prepared by hydrogen plasma-metal reaction. To further regulate the dielectric parameters, the carbon, SiO2, and SiO2/carbon shells are coated on the bead-like cobalt cores by in-situ polymerization of silica and phenolic resin to obtain the Co@C, Co@SiO2, and Co@SiO2@C nanocomposites, respectively. The Co@SiO2@C nanocomposite possesses the best electromagnetic wave (EMW) absorption performances among the samples. At the thickness of only 1.7 mm, the minimum reflection loss (RL) value of −39.6 dB at 13.5 GHz and the effective absorption bandwidth (EAB) of 7.6 GHz for RL < −10 dB are simultaneously obtained. Surprisingly, the absorption bandwidth (RL < −20 dB) is as wide as 14.2 GHz (3.8–18 GHz) with the thickness of 1.3–5.0 mm. The excellent microwave absorption performances are ascribed to the strong magnetic loss of the bead-like Co, the synergistic effect between multiple components, as well as the multiple polarization and multiple scattering induced by core–shell structure. As a consequence, the Co@SiO2@C nanocomposite can serve as an ideal candidate for high-performance microwave absorption.

Microwave absorption properties of microporous CoNi@(NiO-CoO) nanoparticles through dealloying

CoNi alloy is an important absorber and it can combine characteristics of transition metals Co and Ni with various advantages of strong magnetic loss, low cost and easy morphology control. The microporous CoNi@(CoO-NiO) nanoparticles (NPs) of about 45 nm are obtained by using hydrogen plasma metal reaction (HPMR) and dealloying methods. The Al element in Al9Co2, Al70Co15Ni15 and Al14Co3Ni3 phases can be dealloyed by NaOH at 323 K. The CoNi surface would oxidize to CoO and NiO, leading to the core@shell structure. The CoNi@(CoO-NiO)-paraffin wax composite displays high microwave absorption performance with minimum reflection loss (RL) of −38.1 dB at matching thickness of 5.0 mm. The effective absorption bandwidth (RL < −10 dB, at thickness of 2.0 mm) is 5.9 GHz. The RL values below −10 dB cover frequencies of 4.6–18.0 GHz with thickness ranging from 2.0 to 5.0 mm. The effective permittivity modification for a mixture of air and microporous CoNi host, and the large interfacial polarization relaxation of the CoNi@(CoO-NiO) structure contribute much to the enhanced microwave absorption performances.

Electrode based on nanoporous (Co-Ni)@(CoO,NiO) nanocomposites with ultrahigh capacitance after activation

This work introduces a two-step method to fabricate nanoporous (Co-Ni)@(CoO,NiO) nanocomposites with different Ni/Co ratios (2:1, 1:1 and 1:2) by using hydrogen plasma-metal reaction (HPMR) and chemical dealloying techniques. These nanocomposites with average diameters of 43, 44 and 52 nm are nearly-spherical in shape and contain many micropores. The electrode based on the nanocomposite with Co/Ni ratio of 1:1 exhibits the highest initial specific capacitance of 676 F/g at 1A/g and the best rate capability (77% retention at 10 A/g). The subsequent cycling process continuously activates the electrodes based on these nanocomposites, and remarkably enhances their capacitance. The electrode with Co/Ni ratio of 1:1 achieves the highest capacitance of 2051 F/g at 1 A/g after 1000 cycles. The high pseudocapacitive performance of the (Co-Ni)@(CoO,NiO) nanocomposites is mainly attributed to the nanoporous structure which facilitates fast electron/ion transport, the existence of Co-Ni core which serves as an efficient channel for electron conduction to the current collector, and the continuous activation with formation of electrochemically active materials. This specific nanoporous nanocomposite opens a new way to develop the high performance supercapacitor.

Influences of different hydride nanoparticles on microstructure and mechanical properties of 14Cr[sbnd]3Al ferritic ODS steels

In order to suppress the formation of large Y-Al-O particles in the Al-containing oxide dispersion strengthened (ODS) steels, spherical Zr/Hf hydride nanoparticles (NPs) of 21 ± 6 nm and 16 ± 4 nm were prepared by the hydrogen plasma metal reaction (HPMR) method and added as raw particles to produce the ODS Fe-14Cr-3Al-2 W-0.35Y2O3 steels using mechanical alloying (MA) and hot isostatic pressing (HIP). Zr/Hf hydride NPs gave rise to the formation of fine complex oxide NPs, Y4Zr3O12 of 14.2 ± 8.1 nm and Y2Hf2O7 of 9.1 ± 6.9 nm. These oxide NPs were semi-coherent with the matrix, (43¯2¯)Y4Zr3O12//(D = 2.57 × 10−17m2/s)α-Fe, and (D = 1.54 × 10−17m2/s)Y2Hf2O7//(D = 6.25 × 10−12m2/s)α-Fe. With the increasing atomic number of IVB group element (from Ti to Hf), the addition of its hydride NPs can create finer complex oxide nanoparticles in the Al-containing ODS steels and bring about higher mechanical properties. The tensile strength of the 14Cr3Al ODS steel added with 0.1 wt% Hf hydride NPs exhibited a tensile strength of 1067 MPa at 25 °C and 284 MPa at 700 °C, higher than those ODS steels added with 0.1 wt% Zr/Ti hydride NPs. Furthermore, the ODS steel added with Hf hydride showed a large uniform elongation of 11.5% at 25 °C. The addition of Hf hydride NPs is promising to develop high performance Al-containing ODS steels.

Recoverable Ni2Al3 nanoparticles and their catalytic effects on Mg-based nanocomposite during hydrogen absorption and desorption cycling

The Mg-3.9 wt% Ni2Al3 nanocomposite is produced by hydrogen plasma-metal reaction method. The particle size of Mg is in range of 40–160 nm with an average size of 90 nm. The Ni2Al3 nanoparticles (NPs) of about 9 nm uniformly disperse on the surface of Mg NPs and in situ transform to Mg2NiH0.3 and Al after hydrogen absorption process. Surprisingly, the Mg2NiH0.3 and Al can recover to the initial state of Ni2Al3 after hydrogenation/dehydrogenation cycle. The Mg-Ni2Al3 nanocomposite shows enhanced hydrogen sorption rate and storage capacity. It can quickly uptake 6.4 wt% H2 within only 10 min at 573 K, and release 6.1 wt% H2 within 10 min at 623 K. The apparent activation energies for hydrogenation and dehydrogenation are calculated to be 55.4 and 115.7 kJ mol−1 H2. The enhanced hydrogen storage performances of the Mg-Ni2Al3 nanocomposite are attributed to both the nanostructure of Mg and the catalytic effects of Ni2Al3 NPs.

Synergistic catalytic effects of the Ni and V nanoparticles on the hydrogen storage properties of Mg-Ni-V nanocomposite

The Mg-5.0 wt%Ni-2.3 wt%V nanocomposite has been produced through reducing NiCl2 with the Mg-V nanoparticles (NPs) prepared by hydrogen plasma metal reaction (HPMR) approach. The in situ formed Ni and V particles of about 15 nm uniformly decorate on the surface of Mg NPs. The Ni NPs transform into Mg2Ni while the V NPs remain unchanged after first hydrogen absorption and desorption cycle at 673 K. They show synergistic catalytic effects on the hydrogen storage properties of Mg-Ni-V nanocomposite. The nanocomposite can absorb 4.6 wt% H2 within 30 min at 473 K and desorb 5.2 wt% H2 within 10 min at 623 K. The activation energies of hydrogenation/dehydrogenation processes are decreased to 52.8 and 85.1 kJ per mol H2, lower than those of the Mg-5.4 wt%Ni nanocomposite of 63.2 and 89.3 kJ per mol H2. The enhanced hydrogen storage performances of the Mg-Ni-V nanocomposite are mainly attributed to the synergistic catalytic effects of the Mg2Ni and V catalysts, and the nanosize effect of Mg NPs on the decrease of the hydrogen diffusion distance.

High coercive Zn-bonded Sm-Fe-N magnets prepared using fine Zn particles with low oxygen content

To improve the coercivity of Zn-bonded Sm-Fe-N magnets, fine Zn particles with low oxygen content were fabricated by the hydrogen plasma-metal reaction (HPMR), and Zn-bonded Sm-Fe-N magnets were prepared using the Zn particles. The primary and secondary average Zn particle sizes were 0.23 and 0.93 μm, respectively, and the oxygen content was 0.068 wt%. The oxygen content in the Zn-bonded Sm-Fe-N magnets prepared using the Zn particles also decreased, and the coercivity and energy products of the 15 wt% Zn-bonded Sm-Fe-N magnets were 2.66 MA·m−1 and 53.1 kJ·m−3, respectively, at room temperature. The 10 wt% Zn-bonded Sm-Fe-N magnet was also a high coercivity value of 2.41 MA·m−1, and the energy product was 56.1 kJ·m−3. The coercivity strongly depended on the oxygen content rather than the particle size of Zn, and decreasing the oxygen content in the starting material improved the magnetic properties of Zn-bonded Sm-Fe-N magnets. The coercivity of the 15 wt% Zn magnet measured at 180 and 200 °C was 1.23 and 1.10 MA·m−1, respectively, and the temperature coefficient of coercivity was −0.32%·°C−1.

Improved kinetics of nanoparticle-decorated Mg-Ti-Zr nanocomposite for hydrogen storage at moderate temperatures

The hydrogenation kinetics of Mg can be improved by mixing with Ti hydrides catalytic additives. But the dehydrogenation kinetics of Mg is still not acceptable in the practical application cases. To address this dilemma, Zr hydride is introduced into the Mg-Ti system. The Mg-TiH1.971-TiH1.5-ZrH1.66 nanocomposite is synthesized by hydrogen plasma-metal reaction (HPMR) method and activation process at 673 K. The synthesized nanocomposite presents the special surficial decorated nanostructure, that is the surfaces of Mg nanoparticles (NPs) of about 130 nm are uniformly embedded with the spherical TiH1.971-TiH1.5-ZrH1.66 NPs (20 nm). It is demonstrated that the decorated TiH1.971-TiH1.5-ZrH1.66 NPs can act as a combining catalytic effect in improving the hydrogen sorption kinetics of Mg at moderate temperatures. The decorated TiH1.971-TiH1.5-ZrH1.66 NPs has a pioneer (de)hydrogenation effect, causing the H concentration difference from the surface and inner core of Mg, favorably for the following hydrogen sorption of Mg. Particularly, the dehydrogenation kinetics is significantly enhanced as the result of the introduction of Zr hydride NPs. The Mg-TiH1.971-TiH1.5-ZrH1.66 nanocomposite can efficiently uptake 4.2 wt % H2 within 5 min at 473 K and 3.0 wt % H2 in 5 min at 373 K, and release hydrogen at 573 K and reach a value of 2.7 wt % in 5 min. Even at 473 K the Mg-TiH1.971-TiH1.5-ZrH1.66 nanocomposite can quickly release 1.0 wt % H2 in 10 min.

Heat Modeling and Material Development of Mg-Based Nanomaterials Combined with Solid Oxide Fuel Cell for Stationary Energy Storage

Mg-based materials have been investigated as hydrogen storage materials, especially for possible onboard storage in fuel cell vehicles for decades. Recently, with the development of large-scale fuel cell technologies, the development of Mg-based materials as stationary storage to supply hydrogen to fuel-cell components and provide electricity and heat is becoming increasingly promising. In this work, numerical analysis of heat balance management for stationary solid oxide fuel cell (SOFC) systems combined with MgH2 materials based on a carbon-neutral design concept was performed. Waste heat from the SOFC is supplied to hydrogen desorption as endothermic heat for the MgH2 materials. The net efficiency of this model achieves 82% lower heating value (LHV), and the efficiency of electrical power output becomes 68.6% in minimizing heat output per total energy output when all available heat of waste gas and system is supplied to warm up the storage. For the development of Mg-based hydrogen storage materials, various nano-processing techniques have been widely applied to synthesize Mg-based materials with small particle and crystallite sizes, resulting in good hydrogen storage kinetics, but poor thermal conductivity. Here, three kinds of Mg-based materials were investigated and compared: 325 mesh Mg powers, 300 nm Mg nanoparticles synthesized by hydrogen plasma metal reaction, and Mg50Co50 metastable alloy with body-centered cubic structure. Based on the overall performances of hydrogen capacity, absorption kinetics and thermal conductivity of the materials, the Mg nanoparticle sample by plasma synthesis is the most promising material for this potential application. The findings in this paper may shed light on a new energy conversion and utilization technology on MgH2-SOFC combined concept.

High hydrogen desorption properties of Mg-based nanocomposite at moderate temperatures: The effects of multiple catalysts in situ formed by adding nickel sulfides/graphene

Nickel sulfides decorated reduced graphene oxide (rGO) has been produced by co-reducing Ni2+ and graphene oxide (GO), and is subsequently ball milled with Mg nanoparticles (NPs) produced by hydrogen plasma metal reaction (HPMR). The nickel sulfides of about 800 nm completely in situ change to MgS, Mg2Ni and Ni multiple catalysts after first hydrogenation/dehydrogenation process at 673 K. The Mg-5wt%NiS/rGO nanocomposite shows the highest hydrogen desorption kinetics and capacity properties, and the catalytic effect order of the additives is NiS/rGO, NiS and rGO. At 573 K, the Mg-NiS/rGO nanocomposite can quickly desorb 3.7 wt% H2 in 10 min and 4.5 wt% H2 in 60 min. The apparent hydrogen absorption and desorption activation energies of the Mg-5wt%NiS/rGO nanocomposite are decreased to 44.47 and 63.02 kJ mol−1, smaller than those of the Mg-5wt%rGO and Mg-5wt%NiS samples. The best hydrogen desorption properties of the Mg-5wt%NiS/rGO nanocomposite can be explained by the synergistic catalytic effects of the highly dispersed MgS, Mg2Ni and Ni catalysts on the rGO sheets, and the more nucleation sites between the catalysts, rGO sheets and Mg matrix.

Pseudocapacitance of nanoporous Ni@NiO nanoparticles on Ni foam substrate: Influence of the annealing temperature

Nanoporous Ni nanoparticles (NPs) have been successfully prepared by a facile two-step process, hydrogen plasma-metal reaction (HPMR) and chemical dealloying. Via the subsequent passivation at room temperature, an oxide layer is generated outside the Ni NPs as the result of surface oxidation. The passivated Ni@NiO NPs of 48 nm exhibit a highly porous structure with pore volume of 0.812 cm3/g. The NPs are subsequently annealed at different temperatures to adjust the content of Ni and NiO. With the increase of the annealing temperature from 423 to 573 K, the particle size increases from 54 to 61 nm and the pore volume decreases from 0.432 to 0.02 cm3/g. The specific capacitance (SC) of the Ni@NiO NPs decreases with the increasing annealing temperature, and the passivated sample with a large pore volume and low resistance has the highest SC of 641 F/g at a charge–discharge current density of 1 A/g. The passivated sample also shows an energy density of 25.95 W h/kg, a power density of 2.7 kW/kg, and good stable specific capacitance retention of 73% after 1000 cycles. The charge–discharge mechanism is discussed in terms of pore architecture and core@shell structure.

Synergic catalytic effect of Ti hydride and Nb nanoparticles for improving hydrogenation and dehydrogenation kinetics of Mg-based nanocomposite

The Mg-9.3wt% (TiH1.971-TiH)−0.7wt%Nb nanocomposite has been synthesized by hydrogen plasma-metal reaction (HPMR) approach to enhance the hydrogen sorption kinetics of Mg at moderate temperatures by providing nanosizing effect of increasing H “diffusion channels” and adding transition metallic catalysts. The Mg nanoparticles (NPs) were in hexagonal shape range from 50 to 350nm and the average size of the NPs was 177nm. The small spherical TiH1.971, TiH and Nb NPs of about 25nm uniformly decorated on the surface of the big Mg NPs. The Mg-TiH1.971-TiH-Nb nanocomposite could quickly absorb 5.6wt%H2 within 5min at 573K and 4.5wt%H2 within 5min at 523K, whereas the pure Mg prepared by HPMR could only absorb 4 and 1.5wt%H2 at the same temperatures. TiH1.971, TiH and Nb NPs transformed into TiH2 and NbH during hydrogenation and recovered after dehydrogenation process. The apparent activation energies of the nanocomposite for hydrogenation and dehydrogenation were 45.0 and 50.7kJmol−1, which are much smaller than those of pure Mg NPs, 123.8 and 127.7kJmol−1. The improved sorption kinetics of the Mg-based nanocomposite at moderate temperatures and the small activation energy can be interpreted by the nanostructure of Mg and the synergic catalytic effects of Ti hydrides and Nb NPs.

Influences of ultrasonic irradiation on the morphology and structure of nanoporous Co nanoparticles during chemical dealloying

The Co-61.8wt% Al nanoparticles of 45 nm were prepared by hydrogen plasma-metal reaction (HPMR) method. The nanoparticles display core shell structure with Al13Co4 and CoAl core and aluminum oxide shell (about 2nm). Under ultrasonic irradiation, nanoporous fcc-Co nanoparticles were produced successfully by chemically dealloying the Co-Al nanoparticles at room temperature, whereas, without ultrasonic irradiation CoAl phase could hardly react with sodium hydroxide solution. At 323K the Co-Al nanoparticles could be dealloyed to fcc-Co and hcp-Co phases even without ultrasonic irradiation. The surface area of the dealloyed nanoparticles under ultrasonic irradiation was larger than that of the dealloyed sample without ultrasonic irradiation at the same temperature. It is believed that the microjet and shock-wave induced by ultrasonic irradiation give rise to particles size reduction, interparticle collision and surface cleaning, and accelerate the dealloying process and the phase transformation.

Microporous Ni@NiO nanoparticles prepared by chemically dealloying Al3Ni2@Al nanoparticles as a high microwave absorption material

The Al3Ni2@Al nanoparticles (NPs) were prepared from Ni45Al55 master alloy by hydrogen plasma-metal reaction method, and were subsequently dealloyed to produce porous Ni@NiO NPs of 36nm. The pore size ranges from 0.7 to 1.6nm, leading to large specific surface area of 69.5m2/g and big pore volume of 0.507cc/g. The saturation magnetization (MS) and coercivity (HC) of the microporous Ni@NiO NPs are 11.5emu/g and 5.2Oe. They exhibit high microwave absorption performance with a minimum reflection coefficient (RC) of −86.9dB and an absorption bandwidth of 2.6GHz (RC≤−10dB) at thickness of 4.5mm. The enhanced microwave absorption properties are attributed to the synergistic effect of the magnetic Ni core and dielectric NiO shell, and the micropore architecture. The NPs with micropore morphology and core/shell structure open a new way to modify the microwave absorption performance.

TiAl₃-TiN Composite Nanoparticles Produced by Hydrogen Plasma-Metal Reaction: Synthesis, Passivation, and Characterization.

TiAl3 and TiN composite nanoparticles were continuously synthesized from Ti–48Al master alloy by hydrogen plasma-metal reaction in a N2, H2 and Ar atmosphere. The phase, morphology, and size of the nanoparticles were studied by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and evolved gas analysis (EGA) were used to analyze the surface phase constitution and oxygen content of the nanoparticles. The as-synthesized nanopowders were mainly composed of nearly spherical TiAl3 and tetragonal TiN phases, with a mean diameter of ~42 nm and mass fractions of 49.1% and 24.3%, respectively. Passivation in the atmosphere of Ar and O2 for 24 h at room temperature led to the formation of amorphous Al2O3 shells on the TiAl3 particle surface, with a mean thickness of ~5.0 nm and a mass fraction of ~23.5%, as well as TiO2 with a mass fraction of ~3.2%.