• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.295-295
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• 2013

Supercapacitors with higher energy and power density are attracting growing attention for their wide range of potential applications such as portable electronic equipments, hybrid vehicle and cellular devices. In various classes of materials for supercapacitors, the redox pseudocapacitive materials such as conducting polymers and metal oxides have been most widely studied recently. The nanostructuring of the electrode surface has also been focused on since it can provide large surface area and consequently easy diffusion of ions in the capacitors. Among the active materials, in this work, we have used polyaniline (PANi) and manganese oxide ($MnO_2$). PANi is one of the promising electrode and active materials due to its desirable properties such as high electrochemical activity, high doping level and stability. $MnO_2$ is also widely studied material for supercapacitors since it is relatively cheap and environmentally friendly. In this work, we fabricated PANi hollow nanospheres by polymerizing aniline monomers on the polystyrene (PS) nanospheres and then dissolving the inner PS spheres. This nanostructuring of the PANi surface can provide large surface area and hence easy diffusion of electrolyte ions. We also incorporated $MnO_2$ nanoparticles into the PANi hollow nanospheres and investigated its electrochemical properties. It is expected that the combination of these two active materials with slightly different working potential windows show synergetic effects such as broader working potential range and enhanced specific capacitance.

• Advances in materials Research
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• v.9 no.1
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• pp.15-32
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• 2020

In this article, an analytical solution is presented for the steady-state axisymmetric thermal stress distributions in a composite hollow cylinder. The cylinder is composed of two isotropic and anisotropic materials which is subjected to the thermal boundary conditions of convective as well as radiative heating and cooling on the inner and outer surfaces, respectively. The solution of the temperature is obtained by means of Bessel functions and the thermal stresses are developed using Potential functions of displacement. Numerical results are derived for a cylinder which is similar to a gas turbine combustor and showed that the maximum temperature and thermal stresses (radial, hoop, axial) occurred in the middle point of cylinder and the values of thermal stresses in anisotropic cylinder are more than the isotropic cylinder. It is worthy to note that the values of the thermal conditions which estimated in this research, not to be presented in any other papers but these values are very accurate in calculation.

• Advances in Computational Design
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• v.3 no.3
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• pp.303-318
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• 2018

This article presents a semi-analytical solution for an exponentially graded piezoelectric hollow sphere. The sphere interacts with electric displacement, elastic deformations, electric potentials, magneto-thermo-elasticity, and hygrothermal influences. The hollow sphere may be standing under both mechanical and electric potentials. Electro-magneto-elastic behavior of magnetic field vector can be described in the hollow sphere. All material, thermal and magnetic properties of hollow sphere are supposed to be graded in radial direction. A semi-analytical technique is improved to deduce all fields in which different boundary conditions for radial stress and electric potential are presented. Numerical examples for radial displacement, radial and hoop stresses, and electric potential are investigated. The influence of many parameters is studied. It is seen that the gradation of all material, thermal and magnetic properties has particular effectiveness in many applications of modern technology.

• Journal of Sensor Science and Technology
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• v.33 no.5
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• pp.242-247
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• 2024

Pure and 0.3 wt% Au-doped In₂O₃ hollow spheres were synthesized via ultrasonic spray pyrolysis of droplets containing an In-source and sucrose in air and their gas sensing characteristics to 1 ppm ethanol, 1 ppm toluene, 1 ppm xylene, 2 ppm nitrogen dioxide (NO₂), and 30 ppm carbon monoxide (CO) were measured at 400 - 450℃. The pure In₂O₃ hollow spheres exhibited relatively low gas responses and sluggish recovery kinetics. In contrast, the doping of Au into In₂O₃ hollow spheres significantly increased the gas response (S= resistance ratio) to 1 ppm ethanol (S= 20.6) at 400℃ with low cross-responses (S = 1.3-8.8) to other interference gases. Furthermore, the hollow spherical morphology of In₂O₃ provides a large surface area and facilitates rapid gas diffusion, resulting in fast response and recovery times. The sensor exhibited excellent performance with a low detection limit of 1.6 ppb. These findings indicate that the Au-In₂O₃ hollow spheres are promising candidates for advanced ethanol-sensing applications, particularly in breath-alcohol monitoring for ignition interlock devices.

• Membrane Journal
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• v.15 no.2
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• pp.147-156
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• 2005

It is well-known that polyethersulfone (PES) has high $CO_2$ selectivity over $N_2\;(or\;CH_4)$ and excellent pressure resistance of $CO_2$ plasticization among muy commercialized engineering plastics[1-4]. Asymmetric PES hollow fiber membranes for flue gas separation were developed by dry-wet spinning technique. The dope solution consists of PES, NMP and acetone. Water and water/NMP mixtures are used in outer and inner coagulants, respectively. Gas permeation rate (i.e., permeance) and $CO_2/N_2$ selectivity were measured with pure gas, respectively and the micro-structure of hollow fiber membranes was characterized by scanning electron microscopy. The effects of polymer concentration, ratio of NMP to acetone, length of air gap, evaporation condition and silicone coating were investigated on the $CO_2/N_2$ separation properties of the hollow fibers. Optimized PES hollow fiber membranes exhibited high permeance of $25\~50$ GPU and $CO_2/N_2$ selectivity of $30\~40$ at room temperature and have the apparent skin layer thickness of about $0.1\;{\mu}m$. The developed PES hollow fiber membranes, would be a good candidate suitable for the flue gas separation process.

• Korean Journal of Materials Research
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• v.3 no.3
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• pp.300-309
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• 1993

Abstract In this work. gasification of graphite cores from nickel-coated graphite composite powders was carried out to munufacture the hollow nickel metal powders which can be used as a raw materials for porous nickel metal strips. Graphite cores were gasified by $H_2O-H_2$ mixture gases at the temperature between $800^{\circ}C$ and $900^{\circ}C$ and nearly all removed from the composite powders within 1 hour. The hollow nickel metal powders prepared from 82.2wt. % Ni-17.8wt. % C composite powders which have the graphite cores of 21${\mu}$m average size were pressed and sintered at $1150^{\circ}C$ for 1 hour in vacuum furnace. The porosities of green and sintered compacts were 45% and 30%. respectively, and pores were distributed very homogeneously in the sintered compact. It was confirmed that pore distribution and porosity in porous materials can be easily controlled by using hollow powders as a raw materials.

• Journal of mucopolysaccharidosis and rare diseases
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• v.1 no.1
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• pp.5-14
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• 2015

This paper addresses the state of arts of microneedles for the transdermal drug delivery applications. Microneedles can be classified based on materials and shapes. For the materials, microneedles could be made of ceramics, metals and polymers. The shape of the microneedles can be classified into solid and hollow microneedles. Methods of transdermal drug delivery based on microneedle patch are discussed, and various fabrication methods of microneedle patches are introduced.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1920-1933
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• 2006

Piezoelectric materials produce an electric field by deformation, and deform when subjected to an electric field. The coupling nature of piezoelectric materials has acquired wide applications in electric-mechanical and electric devices, including electric-mechanical actuators, sensors and structures. In this paper, a hollow sphere composed of a radially polarized spherically anisotropic piezoelectric material, e.g., PZT_5 or (Pb) (CoW) $TiO_3$ under internal or external uniform pressure and a constant potential difference between its inner and outer surfaces or combination of these loadings has been studied. Electrodes attached to the inner and outer surfaces of the sphere induce the potential difference. The governing equilibrium equations in radially polarized form are shown to reduce to a coupled system of second-order ordinary differential equations for the radial displacement and electric potential field. These differential equations are solved analytically for seven different sets of boundary conditions. The stress and the electric potential distributions in the sphere are discussed in detail for two piezoceramics, namely PZT _5 and (Pb) (CoW) $TiO_3$. It is shown that the hoop stresses in hollow sphere composed of these materials can be made virtually uniform across the thickness of the sphere by applying an appropriate set of boundary conditions.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.471-473
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• 2006

An object of the present study is to provide a hollow fiber membrane humidifier capable of improving the humidification efficiency while lowering the pressure loss, and is suitably usable for PEMFC(Polymer Electrolyte Membrane Fuel Cell). The performance of PEMFC is decisively dependent on the humidity of the electrolyte membrane(fluorinated membrane) and a humidifier plays an important role in moisturizing electrolyte membrane. Especially this humidifier is adaptable for lower price to promote the commercialization of fuel cell vehicles and is passive type to be power free and to be volumetrically optimized. In this research, we propose the substitutes for the expensive fluorinated materials and the optimum dry-jet wet spinning conditions of hollow fiber membrane to get the fuel cell humidifier. In addition to that we established the standard method of evaluating the moisturizing performance of the humidifier of various materials.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.6
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• pp.1-6
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• 2010

Aluminum rear lower arm is designed for luxury sedan and manufactured by hollow sand casting in the present study. Here we present the relationship between local microstructure and coupon tensile test in the rear lower arm. The characteristics of the local tensile deformation are supposed to be dependent upon Si distribution and DAS (dendrite arm spacing). Si distribution affects the yield strength and DAS affects the elongation of local area in the part, respectively.