Hollow Metal Research Articles

Effects of volume fraction and diameter of hollow spheres on acoustic properties of Metallic-Hollow-Sphere/Polyurethane (MHSP) acoustic composites

Metallic hollow spheres and polyurethane resin are excellent sound insulation and sound absorption materials. In this study, the surface modified 316L stainless steel hollow spheres were added into polyurethane by casting method. The influence of the volume fraction and diameter of the hollow spheres on the sound insulation and sound absorption performance of the Metallic-Hollow-Sphere/Polyurethane (MHSP) acoustic composites was investigated by impedance tube method and the relevant acoustic mechanism was discussed. When the volume fraction of hollow spheres is 45% and the diameter is 2.5 mm, composite has the best sound insulation performance. And when the volume fraction of hollow spheres is 60% and the diameter is 2.5 mm, composite has the best sound absorption performance. Due to the mass effect, damping effect, change of acoustic impedance and multiple interface of composites, sound waves will reflect, refract and scatter many times in the process of propagation, thus losing lots of sound energy to improve the sound insulation performance. The sound absorption mechanism of MHSP is that the friction, viscosity and reflection of sound waves in the pores of polyurethane, cavities of the hollow spheres and interfaces will cause the loss of sound energy and turn it into heat energy.

Mechanical and Wear Properties of 42CrMo Steel by Plasma Nitriding assisted Hollow Cathode Ion Source

Plasma nitriding is a plasma-activated thermochemical method widely used to increase the fatigue strength, hardness and wear resistance of low-alloy steels. In this work, a new structure consisting of a hollow cathode metal plate can produce a hollow cathode discharge and heat the workpiece by radiation. This principle is used to perform hollow cathode source plasma nitriding (HCSPN). Herein, 42CrMo steels were treated by conventional plasma nitriding (CPN) and HCSPN treatments. The 42CrMo steels were nitrided at 525 °C for 6 h in NH3 atmosphere. The mechanical and dry wear properties were measured by nano-indentation, Vickers micro-indentation and ball-on-disk tribometer, respectively. The H3/E⁎2 ratio was 0.0274 GPa (H=11.51 GPa and E⁎=235.84 GPa) for the CPN sample and 0.0276 GPa (H=10.87 GPa and E⁎=215.54 GPa) for the HCSPN sample. Compared with the untreated 42CrMn steel, all the nitrided samples possess increased fracture toughness. Because the workpiece was not used as a discharge cathode, this HCSPN treatment overcame the disadvantages of the conventional CPN treatment. Additionally, results showed that the surface of the HCSPN sample was smoother than that of the CPN sample, and its tribological performance was better.

Preparation of hollow metal-organic frameworks via epitaxial protection and selective etching.

Hollow metal-organic frameworks (MOFs) with only a shell may be used for efficient catalysis. In this work, a general sequential synthesis was employed to successfully create Hf-based hollow MOFs, such as UiO-66, MOF-808, and PCN-223. Etchants including monocarboxylic acids and H2O are required to remove the interior of the MOFs to form hollow structures, while the different stability of the interior and surface of the MOFs partly resulting from surface epitaxy protection was responsible for the selective etching. With these insights, scale-up of hollow octahedral UiO-66 was realized. This work paves a way to rationally design hollow MOFs.

Numerical analysis of the effective properties of inhomogeneously polarized porous piezoelectric ceramics with ni-doped pore walls taking into account the influence of volume fractions of metal and pores

The paper considers a porous piezoelectric composite with metal layers deposited on the interface between the piezoelectric and vacuum phases. Such metal layers can be added technologically to improve the mechanical and electromechanical properties of the composite. To find the effective moduli, we designed a simple representative cubic volume of a unit cell consisting of a piezoelectric matrix with a compound spherical pore in its center. In turn, the compound pore includes the pore itself and a hollow metal sphere on its surface. The composite's three phases were all modeled as piezoelectric materials. The conducting interface layer was modeled as a piezoelectric material with very high dielectric constants, small piezoelectric moduli, and elastic properties of the employed metal, while the vacuum pore was modeled as a piezoelectric material with marginal moduli. The mathematical formulation of boundary value homogenization problems with full contact conditions on the interface boundaries, based on the Hill energy criterion, was described. By solving nine boundary value problems of electroelasticity with different boundary conditions for displacements and electric potential by the finite element method, a complete set of effective moduli of the piezoelectric composite is determined. The importance of considering the inhomogeneous polarization due to the presence of pores and metallic inclusions was discussed. An approximate method was proposed for determining the inhomogeneous polarization field in a piezoceramic matrix, based on a preliminary solution of the electrostatic problem for dielectrics and locating the element coordinate systems rotated along the polarization vector. The paper describes the results of computational experiments for a piezocomposite consisting of PZT-5H piezoceramic matrix, pores, and nickel layers on the pore surfaces. Comparisons between the effective properties of this composite with different volume fractions of metal and the conventional porous piezocomposite were provided, depending on the porosity and taking into account the inhomogeneous polarization. Significant differences were observed for some piezomoduli and dielectric constants, which are promising for various practical applications of the considered composites in piezoactuators using the phenomenon of the transverse piezoelectric effect.

Влияния условий горения разряда на распределения параметров плазмы, генерируемой в несамостоятельном тлеющем разряде внутри полого катода

The parameters of the plasma of a non-self-sustaining glow discharge generated inside a metal hollow cathode 300 mm long and 25 mm in inner diameter are investigated. A feature of this system is the additional injection of electrons from the auxiliary discharge plasma, formed by a plasma source with a combined heated and hollow cathode «PINK». The dependences and combustion modes of a non-self-sustaining glow discharge are presented and described at a pressure in the range (0.06 ÷ 1.4) Pa and a combustion voltage (70 ÷ 300) V. Studies of plasma parameters using double Langmuir probes have shown that this discharge system provides generation nitrogen plasma inside the hollow cathode with inhomogeneity from ± 12 to ± 63%.

Facile fabrication of carbon-coated spinel nickel–cobalt–sulfide hollow spheres to achieve high-performance supercapacitors

This paper presents a simple method to prepare carbon-coated spinel nickel–cobalt–sulfide metal hollow spheres with excellent electrochemical properties.

Design of Hollow Nanocapsules and their Applications in Biomedical Imaging

Different nanocarrier systems owing to their nano size, increased surface area and unique electrical and magnetic properties are employed for biomedical applications. Among the various nanocarrier systems, hollow nanocapsules are one of the most interesting carrier systems for thier use in bioimaging and biomedical applications. The unique properties of hollow nanocapsules make them suitable for use in bioimaging. In this article hollow nanocpsules have been classified into four classes based on thier composition: (i) liposomes, (ii) polmersomes and other polymeric hollow nanocapsules, (iii) metallic hollow nanocapsules and (iv) others. The formation and design of these hollow nanocapsules and their diagnostic and therapeutic applications using different agents/imaging probes and imaging modalities is discussed briefly. Hollow nanocapsules have revolutionized the field of biomedical imaging.

All-solid-state asymmetric supercapacitor with MWCNT-based hollow NiCo2O4 positive electrode and porous Cu2WS4 negative electrode

To develop a high-performance supercapacitor, synergy between the positive and negative electrodes is essential. On the positive side, saturation is achieved in exploring novel materials, whereas on the negative side, there are extremely limited options. In this study, we propose a novel combination of hollow metal oxide positive and porous metal sulfide negative electrodes incorporated with MWCNTs to achieve advanced supercapacitors. We have rationally designed hierarchical hollow spheres of NiCo2O4, as positive electrodes, by carefully tuning the reaction and annealing parameters. We propose a novel material, i.e., porous Cu2WS4, which has never, to the best of our knowledge, been explored as negative electrodes for supercapacitors. Even though both the materials showed reasonably good electrochemical performance, to further improve their output, they were clubbed with MWCNTs to form composites. The strategy of incorporating MWCNTs worked well and the electrochemical properties were significantly improved. Both the composite electrodes exhibited an ultrahigh specific capacitance of 2240 and 1420 F g−1, respectively. The fabricated solid-state asymmetric supercapacitor exhibited remarkably high specific capacity and energy density 116 mAh g−1 and 87 Wh kg−1, respectively, at 1 A g−1. The device was also perfect in terms of power, coulombic efficiency and cycling stability for >10,000 cycles with ~88% capacity retention. The observed results pave a modern way of optimizing electrode materials and combining them to achieve high-performance hybrid supercapacitors for large scale integrated energy-storage systems.

High-performance hybrid supercapacitors based on MOF-derived hollow ternary chalcogenides

In-situ growth of hybrid nanostructures composed of hollow transition metal chalcogenides has attracted increasing attention for the fabrication of high-performance hybrid supercapacitors (HSCs). Herein, we report the binder-free design of hierarchical ternary Cu(Co-Ni)2S4 nanotubes on nickel foam (Cu(Co-Ni)2S4 NTs/Ni foam) using synchronous etching and multi-ion doping enabled metal-organic framework (MOF) precursors. The MOF-derived hollow structured Cu(Co-Ni)2S4 NTs/Ni foam electrode unveils an excellent battery-type redox kinetics with highest areal and specific capacities of Qac: 382.1 µAh/cm2 and Qsc:181.9 mAh/g, respectively at a current density of 2 mA/cm2 with good cycling stability in 1 M KOH electrolyte. With the large electroactive area and superior electrochemical conductivity, the hierarchical composite electrode offers much space to grasp huge volume of charges, thus enabling an excellent energy storage performance. By integrating battery-type Cu(Co-Ni)2S4 NTs/Ni foam as a positive electrode with porous carbon as a capacitive-type electrode, a prototype HSC device is assembled. Along with high energy and power densities of 0.27 mWh/cm2 and 21.75 mW/cm2, the fabricated prototype device retains excellent cyclability with an energy efficiency of 95.8%. Capitalizing high energy storage properties of HSC, an assembled self-powered station consisting of HSC and solar cell further illustrates its practical applicability for renewable energy applications.

Hydrogen production by methane steam reforming using metallic nickel hollow fiber membranes

The metallic nickel hollow fiber membranes (NHFMs) consisting of a dense skin layer integrated on porous nickel substrate were fabricated in a single extrusion step by using a 90 wt% NMP-H2O solution and water as the respective internal and external coagulants during the spinning process. The resultant asymmetric Ni hollow fibers by sintering were directly applied to hydrogen production from methane steam reforming (MSR), where the porous internal surface functioned as a catalyst bed for MSR reactions, and the external dense skin layer served as the membrane for hydrogen extraction from the reaction products. The effects of the feed composition in terms of steam-to-methane ratio (H2O/CH4) and methane concentration; the operational parameters including temperature, space velocity, and the sweep gas flow rate on the performance of the hollow fibers were investigated. The results reveal that the reaction operational temperature should be above 800 °C and the H2O/CH4 ratio controlled around 3 so as to achieve both high methane conversion and high H2 production rate. When operated at 1000 °C and 25,937 h−1 methane space velocity, the maximum H2 production rate reached 50.84 mmol m−2 s−1 while the methane conversion reached at 98.58%. In order to produce pure hydrogen, steam may be used as the sweep fluid instead of inert gases such as nitrogen to prevent the dilution of the permeated gaseous hydrogen. The prepared asymmetric NHFMs also demonstrate high chemical stability in the reformate gases and high resistance to carbon deposition at above 800 °C, and thus may be a promising way of cost-effective hydrogen production by MSR at high temperatures.

Performance of Composite Metal Foam Armors against Various Threat Sizes

The ballistic capabilities of composite metal foam (CMF) armors were experimentally tested against a 14.5 × 114 mm B32 armor-piercing incendiary (API) and compared to various sizes of armor-piercing (AP) ballistic threats, ranging from a 7.62 to 12.7 mm. Three different arrangements of layered hard armors were designed and manufactured using ceramic faceplates (in one layer, two layers or multiple tiles), a combination of ceramic and steel face sheets, with a single-layered CMF core, and a thin aluminum backing. The performance of various CMF armor designs against the 14.5 mm rounds are compared to each other and to the performance of the rolled homogeneous armor standard to identify the most efficient design for further investigations. The percentage of kinetic energy absorbed by the CMF layer in various armor arrangements and in tests against various threat sizes was calculated and compared. It appears that the larger the threat size, the more efficient the CMF layer will be due to a greater number of hollow metal spheres that are engaged in absorbing the impact energy. The results from this study will help to model and predict the performance of CMF armors against various threat sizes and impact energies.

Controllable SnO2/ZnO@PPy hollow nanotubes prepared by electrospinning technology used as anode for lithium ion battery

The one-dimensional hollow nanostructure can effectively decrease the diffusion distance of lithium ions and alleviate the volume change of SnO2 during cycling. In this work, SnO2/ZnO hollow nanotubes were obtained from two different molecular weights of Polyvinylpyrrolidone (PVP) by combining electrospinning technology and heat treatment. Mechanism studies indicated the hollow nanotubes with different morphology could be controllable by varying the molecular weight of PVP. SnO2/ZnO nanotubes with high molecular weight PVP as precursor (SnO2/ZnO–H) had smaller diameter and denser structure, which as anode showed better stability and capacity in electrochemical test. The conductivity and stability of SnO2/ZnO–H were further improved after coated with Polypyrrole (PPy) by the in-situ polymerization. The reversible capacity of the batteries was improved, and the volume expansion of the metal oxide was restrained during charging and discharging. The SnO2/ZnO@PPy anode exhibited a high discharge capacity of 626.1 mA h g−1 of 0.2C after 100 cycles, showing an outstanding stability. Therefore, controllable hollow metal oxide nanotubes structures could be obtained via different the molecular weights of precursor polymer. And the hollow nanotubes after coating by PPy as anode materials exhibited the excellent electrochemical performance. This research provided an idea in further design and optimization of anode microstructure for lithium-ion batteries.

Surface Modification of Pb1 – xSnxSe Films during Plasma Treatment Near the Sputtering Threshold

The processes of the plasma sputtering of epitaxial lead-tin selenide films near the sputtering threshold are studied. Pb1 – xSnxSe films (x = 0.03, 0.07) with a thickness of 0.5–2 microns are grown by molecular-beam epitaxy on CaF2/Si(111) substrates. The films are plasma treated with radio-frequency high-density low-pressure inductively coupled argon plasma with an ion energy of 20–25 eV at typical process times of 60–360 s. As a result of plasma treatment for a prolonged period, the formation of hollow metal particles of nano- and submicron sizes is observed on the surface. Using scanning electron microscopy methods, it is shown that the lateral dimensions of the obtained structures, their shape and surface density vary over wide ranges and significantly depend on the time of plasma sputtering. The features of plasma sputtering for the studied films and films of a binary compound of lead selenide are compared.

STUDY OF THE DEFORMED STATE CONNECTION OF THE PISTON WITH THE ROD OF THE UNREGULATED PISTON PUMP

The technological processes of cold rolling of precision workpieces and ring parts, rolling of pipes, rolling of piston-connecting rod axial-rotor piston pump, which are a kind of processing of metals by pressure and contain changes in the shape of workpieces according to performing relative to the axis of the workpiece radial rotational motion. The workpiece can remain stationary or rotate. It is shown that by means of technological process of rolling of pipes, unrolling of preparations various hollow axisymmetric metal products receive, the specified processes are combined by the mechanism of deformation, namely: at them two deformations of compression and one - tension are realized. This mechanical deformation scheme creates favorable conditions for plastic deformation, because intercrystalline displacements are difficult, leading to the violation of mechanical bonds, and plastic deformation occurs mainly due to intracrystalline displacements. It is shown that in the process of connecting the piston-connecting rod in compliance with the process parameters (output supply pressure, feed rate, leaving time) the value of the specified gap either exceeds the maximum value or decreases to the value at which the next operation of the piston-connecting rod spell. The deformed state in the technological operation of rolling the piston-connecting rod pair at different stages of shape change is studied, the process control mechanism is revealed, which prevents the defect in the form of deviation from the regulated gap after rolling between the piston and the connecting rod. The used resource of plasticity at different stages of rolling is calculated, the deformability of the piston workpiece in the rolling process is estimated.

Rational Fabrication and Improved Lithium Ion Battery Performances of Carbon Nanofibers Incorporated with α-Fe2O3 Hollow Nanoballs

The present results contribute a facile route to prepare carbon nanofibers hybrided with hollow metal oxide nanoparticles under the assistance of Kirkendall effect. α‒Fe2O3 hollow nanoball incorporated carbon nanofibers (denoted as FOCNFs) are rationally fabricated by using electrospun composite carbon nanofibers (CNFs) as the precursors. The hollow nanoparticles are 69.8 nm in the average size with the shell thickness of 14 nm. The composite nanofibers are hierarchically porous. The mesopores are in the range of 2 ‒ 10 nm and center at 3.7 nm. The micropores center at 0.5 nm with the micropore volume of 0.02 cm3·g−1. Time dependant morphology evolutions confirm that the formation of α‒Fe2O3 hollow nanoballs is promoted by the nanoscale Kirkendall effect due to the migration difference between oxygen molecules and Fe3+ cations in the solid. This route is also successfully extended to fabricate hollow Co3O4 and NiO nanoparticles incorporated carbon nanofibers. FOCNFs exhibit improved lithium ion battery performances with enhanced capacity, rate capability and long-term cycling stability. The optimized sample of FOCNFs‒30 delivers a high initial capacitance of 1903.8 mAh·g-1 at 100 mA·g-1. A reversible capacity of 601.2 mAh·g-1 sustains at 0.1 C after 300 charge-discharge cycles. The improved electrochemical performances of FOCNFs stem from coupling the characteristics of α-Fe2O3 nanoballs and porous nanofibrous carbon matrix.

Enabling improved cycling stability of hollow SnO2/C composite anode for lithium-ion battery by constructing a built-in porous carbon support

Owing to the cooperative effect of well-defined interior voids and conductive and flexible carbon coating, the hollow nanostructural SnO2/C composites exhibit significantly improved electrochemical performance over their pure nanostructured SnO2 counterparts, and hence attracts increasing research interests. However, the potential collapse of SnO2 inwards interior voids and subsequent agglomeration will diminish the cycling stability of hollow SnO2/C composites and hence needs to be further improved. Herein, to reduce the excess void space and block agglomeration of the SnO2 inwards interior voids, a cubic hollow SnO2/C composite with a built-in porous carbon support yolk has been designed and constructed successfully. As a result, thus as-constructed composite with a novel architecture displays significantly improved cycling stability as comparison to the similar hollow SnO2@C composite without a built-in porous carbon, delivering 788 and 588 mAh g−1 at 200 and 1000 mA g−1 after 550 and even 900 cycles, respectively. The results obtained here could pave the way for properly improving the cycling stability of other hollow metal oxides/carbon composites for advanced lithium-ion battery anodes.

Engineering hollow porous platinum-silver double-shelled nanocages for efficient electro-oxidation of methanol

Direct methanol fuel cell technology requires high-performance electrocatalysts for practical utilization at the commercial scale. A novel, high-efficiency electrocatalyst composed of hollow porous platinum-silver double-shelled nanocages (Pt-Ag DSNCs) for the electro-oxidation of methanol (EOM) is demonstrated. The Pt-Ag DSNCs were synthesized with a facile one-pot self-template mechanism with the assistance of N, N-Methylenebisacrylamide (MBAA). The double shells can be precisely controlled by regulating the feeding amount of MBAA and the Pt/Ag ratio. The hollow MBAA-based metal polymer acts as a nano-reactor and nucleation site for the deposition of PtAg alloy on its inner (exposed to AgCl nanoparticles) and outer (exposed to bulk solution) sides. To our knowledge, this is the first report of a direct one-pot synthesis of Pt-Ag double-shelled nanocages. Combining a unique double-shelled structure and an optimized bimetallic chemical composition, the Pt-Ag DSNCs (optimized Pt/Ag ratio is 3/1) show more than a two-fold improvement in specific activity and greater stability towards the EOM compared with a commercial Pt catalyst. Density functional theory (DFT) studies demonstrate the introduction of Ag is important for the improvement of EOM performance. The facile synthetic strategy and competitive EOM performance endow Pt-Ag DSNCs with great application potential in direct methanol fuel cells.

Design and Implementation of Van de Graaff Generator

The paper proposes a design and implementation of Van de Graaff generator whose output voltage is 80.28 KV. To calculate the generated output voltage we have use the sphere gap method. A Van de Graaff generator is an electrostatic generator as it works on a principle of electrostatics. A Van de Graaff generator is used to generate a high DC voltage. It was first developed by Robert Jemison Van de Graaff in 1929, in USA and carries his name along 1931. This generator uses a moving belt to build up very high voltages on a hollow metal globe which is located on top of the generator. The potential difference that is developed in modern Van de Graaff generator reach about 5 megavolts. A Van de Graaff generator that we design and built that is intended to be used in schools and colleges for teaching the basics principles of Electrostatics and Electromagnetics as well as many other applications. Nowadays many schools and colleges laboratories and many museums use this type of generators for electrostatics demonstrations.

Facile Tuning and Refractive Index Sensitivity of Localized Surface Plasmon Resonance Inflection Points in Hollow Silver Nanoshells

Hollow metal nanostructures are fascinating because of their unique and surrounding environment-sensitive localized surface plasmon resonances (LSPRs). Herein, we have investigated the hollow silver nanoshell (HSN) sensitivity of different inner core radii and shell thicknesses with respect to change in surrounding medium refractive index. Also, we have shown that the extinction peak of HSNs can be fine-tuned in the visible region as well as biological windows by manipulating the size parameters. Moreover, an enhancement in refractive index sensitivity of 133 to 283 nm/RIU can be achieved in the biological windows by thick hollow silver nanoshells in comparison to thin ones. To achieve a comprehensive study, the sensitivity of homogeneous LSPR extinction inflection points with change in refractive index is also investigated. A consistent improvement in bulk refractive index sensitivity of 36% and 15% is predicted with thick and thin shell layers, respectively. Finally, thick HSNs showed higher refractive index sensitivity when compared with thin ones. Moreover, we envision the idea of more than one molecule detection by tracking the curvature changes. Therefore, we provide a deeper insight into the refractive index sensitivity of homogeneous LSPR inflection points for their use in LSPR-based sensors.

Investigation of the Extinction Spectra of a Plasmonic Noble-Metal Hollow Nanocube

In this work, a hollow cubic nanostructure based on noble metals of silver and gold is studied. The extinction spectra of the plasmonic hollow cube are numerically calculated via the finite-difference time-domain method. A two-peak feature is witnessed in the extinction spectra, and the electric fields at the two resonance wavelengths are computed, indicating two different electromagnetic modes. The resonance wavelengths, the full widths at half maximum, and the peak intensities are also determined from the extinction spectra. In the calculations, the structural parameters of the hollow nanocube are systematically varied, including the cubic size, the thickness of the metallic wall, the geometric ratio of the cube, and the dielectric constants of the inner and outer surrounding media. With changing the structural parameters, the trends revealed in the simulated extinction spectra highlight a great tunability in the plasmonic resonances. Based on the results shown in this work, it is suggested that the proposed metallic hollow nanocube be implemented in designs of plasmonic devices.