• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.28 no.3
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• pp.241-256
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• 2018

Objectives: This study aimed to review the characteristics of three-dimensional printing technology focusing on printing types, materials, and health hazards. We discussed the methodologies for exposure assessment on hazardous substances emitted from 3D printing through article reviews. Methods: Previous researches on 3D printing technology and exposure assessment were collected through a literature review of public reports and research articles reported up to July 2018. We mainly focused on introducing the technologies, printing materials, hazardous emissions during 3D printing, and the methodologies for evaluation. Results: 3D printing technologies can be categorized by laminating type. Fused deposition modeling(FDM) is the most widely used, and most studies have conducted exposure assessment using this type. The printing materials involved were diverse, including plastic polymer, metal, resin, and more. In the FDM types, the most commonly used material was polymers, such as acrylonitrile-butadiene-styrene(ABS) and polylactic acids(PLA). These materials are operated under high-temperature conditions, so high levels of ultrafine particles(mainly nanoparticle size) and chemical compounds such as organic compounds, aldehydes, and toxic gases were identified as being emitted during 3D printing. Conclusions: Personal desktop 3D printers are widely used and expected to be constantly distributed in the future. In particular, hazardous emissions, including nano sized particles and various thermal byproducts, can be released under operation at high temperatures, so it is important to identify the health effects by emissions from 3D printing. Furthermore, appropriate control strategies should be also considered for 3D printing technology.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.5 s.170
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• pp.103-112
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• 2005

This paper presents one-axis high precision scanning system and illustrates the design of modified $X-Y-{\theta}$ stage as a tracker using VCM and commercialized air bearings for it. The scanning system for 100nm resolution is composed of the 3-axis stage and one axis long stroke linear motor stage as a follower. In this study a previous proposed and presented structure of VCM for the fine stage is modified. The tracker has 3 DOF($X-Y-{\theta}$ motions by four VCM actuators which are located on the same plane. So 4 actuating forces are suggested and designed to create least pitch and roll motions. This article will show about the design especially about optimal design. The design focus of this fine stage is to have high acceleration to accomplish high throughput. The optimal design of maximizing acceleration is performed in restrained size. The most sensitive constraint of this optimal design is heat dissipation of coil. There are 5 design variables. Because the relationship between design variables and system parameters are quite complicated, it is very difficult to set design variables manually. Due to it, computer based optimal design procedure using MATLAB is used. Then, this paper also describes the procedures of selecting design variables for the optimal design and a mathematical formulation of the optimization problem. Based on the solution of the optimization problem, the final design of the stage is also presented. The results can be verified by MAXWELL. The designed stage has the acceleration of about 5 $m/s^{2}$ with 40kg total mass including wafer chuck and interferometer mirror. And the temperature of coil is increased $50^{\circ}C$. In addition, the tracker is controlled by high precision controller system with HP interferometer for it and linear scaler for the follower. At that time, the scanning system has high precision resolution about 5nm and scanning resolution about 40nm in 25mm/s constant speed

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1278-1282
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• 2004

수열처리법으로 nano-sized $CeO_2$ 입자를 $Al_3O_3$ 입자의 표면에 균일하게 코팅하여 $AL_2O_3/O_2$ composite 연마 입자를 제조하었다. 제조된 $Al_2O_3\CeO_2$ composite 입자의 뭍성을 TEM, XRD, zeta potential analyzer 및 particle size analyzer로 측징하였다. $Al_2O_3/CeO_2$ composite 입자와 구성된 슬러리와 비교 시료로서 $Al_2O_3$와 $CeO_2$ 입자를 혼합한 슬러리를 사용하여 thermal oxide film에 대한 연마특성을 평가하였다. 연마슬러리에 포함된 $A1_2O_3/CeO_2$ composite 입자와 $Al_2O_3$와 $CeO_2$ 혼합입자에서 나노 크기의 세리아 입자가 sub-micron 크기의 알루미나 입자의 표면에 균일하게 코팅되므로서 $Al_2O_3$ 단일 성분의 슬러리에 비해 removal rate(RR)는 106 nm/min, WIWNU는 $8\sim9%$, roughness는 $2.6{\AA}$의 향상된 연마 특성을 나타내었다. 알루미나 입자의 불규칙한 형상 때문에 $Al_2O3/CeO_2$ composite 슬러리와 $Al_2O_3$ 와 $CeO_2$ 혼합슬러리의 연마 특성이 비슷한 수준을 나타내었다.

• Advances in nano research
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• v.7 no.6
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• pp.405-417
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• 2019

This research is devoted to study post-buckling analysis of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) micro plate with cut out subjected to magnetic field and resting on elastic medium. The basic formulation of plate is based on first order shear deformation theory (FSDT) and the material properties of FG-CNTRCs are presumed to be changed through the thickness direction, and are assumed based on rule of mixture; moreover, nonlocal Eringen's theory is applied to consider the size-dependent effect. It is considered that the system is embedded in elastic medium and subjected to longitudinal magnetic field. Energy approach, domain decomposition and Rayleigh-Ritz methods in conjunction with Newton-Raphson iterative technique are employed to trace the post-buckling paths of FG-CNTRC micro cut out plate. The influence of some important parameters such as small scale effect, cut out dimension, different types of FG distributions of CNTs, volume fraction of CNTs, aspect ratio of plate, magnitude of magnetic field, elastic medium and biaxial load on the post-buckling behavior of system are calculated. With respect to results, it is concluded that the aspect ratio and length of square cut out have negative effect on post-buckling response of micro composite plate. Furthermore, existence of CNTs in system causes improvement in the post-buckling behavior of plate and different distributions of CNTs in plate have diverse response. Meanwhile, nonlocal parameter and biaxial compression load on the plate has negative effect on post-buckling response. In addition, imposing magnetic field increases the post-buckling load of the microstructure.

• Journal of Adhesion and Interface
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• v.20 no.3
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• pp.102-109
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• 2019

The material constitution of multi-layered thin film coated on the PET base film was analyzed using ATR FT-IR and pyro GC/MS combination. The cross section of the film was acquired by cracking the film after dipping in liquid nitrogen and was observed using optical microscope. Total thickness of the coated film was $70{\mu}m$ and three layers were observed. Since each layers were too thin to analyze directly except the surface layer, analyzable area of each layers were exposed by using a proper solvent and were investigated using ATR FT-IR and pyro GC/MS. Results shows that three layers were commonly consisted of urethane-acrylate copolymers. Also, inorganic and/or metal inclusions detected by XPS and SEM-EDAX were exhibited by nano size $SiO_2$ particles in layer(1) and aluminum flakes in layer(2).

• Advances in materials Research
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• v.2 no.2
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• pp.77-91
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• 2013

High quality nanoparticles of neodymium barium niobium ($NdBa_2NbO_6$) perovskites have been synthesized using an auto ignition combustion technique for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy. UV-Visible absorption and photoluminescence spectra of the samples are also recorded. The structural analysis shows that the nano powder is phase pure with the average particle size of 35 nm. The band gap determined for $NdBa_2NbO_6$ is 3.9 eV which corresponds to UV-radiation for optical inter band transition with a wavelength of 370nm. The nanopowder could be sintered to 96% of the theoretical density at $1325^{\circ}C$ for 2h. The ultrafine cuboidal nature of nanopowders with fewer degree of agglomeration improved the sinterability for compactness at relatively lower temperature and time. During the sintering process the wide band gap semiconducting behavior diminishes and the material turns to a high permittivity dielectric. The microstructure of the sintered surface was examined using scanning electron microscopy. The striking value of dielectric constant ${\varepsilon}_r=43$, loss factor tan ${\delta}=1.97{\times}10^{-4}$ and the observed band gap value make it suitable for many dielectric devices.

• Korean Journal of Materials Research
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• v.31 no.9
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• pp.481-487
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• 2021

ZnO particles are successfully synthesized at 150 ℃ for 30 min using zinc acetate as the Zn source and 1,4-butanediol as solvent using a relatively facile and convenient glycol process. The effect of ammonium hydroxide amounts on the growth behavior and the morphological evolution of ZnO particles are investigated. The prepared ZnO nanoparticle with hexagonal structure exhibits a quasi-spherical shape with an average crystallite size of approximately 30 nm. It is also demonstrated that the morphology of ZnO particles can be controlled by 1,4-butanediol with an additive of ammonium hydroxide. The morphologies of ZnO particles are changed sequentially from a quasi-spherical shape to a rod-like shape and a hexagonal rod shape with a truncated pyramidal tip, exhibiting preferential growth along the [001] direction with increasing ammonium hydroxide amounts. It is demonstrated that much higher OH^- amounts can produce a nano-tip shape grown along the [001] direction at the corners and center of the (001) top polar plane, and a flat hexagonal symmetry shape of the bottom polar plane on ZnO hexagonal prisms. The results indicate that the presence of NH⁴⁺ and OH^- ions in the solution greatly affects the growth behaviors of ZnO particles. A sharp near-band-edge (NBE) emission peak centered at 383 nm in the UV region and a weak broad peak in the visible region between 450 nm and 700 nm are shown in the PL spectra of the ZnO synthesized using the glycol process, regardless of adding ammonium hydroxide. Although the broad peak of the deep-level-emission (DLE) increases with the addition of ammonium hydroxide, it is suggested that the prominent NBE emission peaks indicate that ZnO nanoparticles with good crystallization are obtained under these conditions.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.502-510
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• 2018

In order to accumulate data to lower the friction coefficient of a press mold, tribological tests were performed before and after coating SM45C with a PVC/PO film and plasma coating (CrN, concept). The ultrasonic nanocrystal surface modification (UNSM)-treated material had a nano-size surface texture, high surface hardness, and large and deep compressive residual stress formation. Even when the load was doubled, the small amount of abrasion, small weight of the abrasion, and width and depth of the abrasion did not increase as much as those of untreated materials. A comparison of the weight change before and after the tribological test with the CrN and the concept coating material and that of the untreated material showed that the wear loss of the concept coating material and P-UNSM treated material (that is, the UNSM treated material treated with the concept coating) showed a tendency to decrease by approximately 55-75%. Concept 100N had a lower friction coefficient of about 0.6, and P-UNSM-30-100N showed almost the same curve as concept 100N and had a low coefficient of friction of about 0.6. The concept multilayer coating had a thickness of $5.32{\mu}m$. In the beginning, the coefficient of friction decreased because of the plasma coating, but it started to increase from about 250-300 s. After about 350 s, the coefficient of friction tended to approach the friction coefficient of the SM45C base metal. The SGV-280F film-attached test specimen was slightly pushed back and forth, but the SM45C base material was not exposed due to abrasion. The friction coefficient was 0.22, which was the lowest, and the tribological property was the best in this study.

• BioChip Journal
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• v.12 no.4
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• pp.332-339
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• 2018

The future neuro-prosthetic devices would be required spikes data monitoring through sub-nanoscale transistors that enables to neuroscientists and clinicals for scalable, wireless and implantable applications. This research investigates the spikes monitoring through integrated CNT front-end amplifier for neuro-prosthetic diagnosis. The proposed carbon nanotube-based architecture consists of front-end amplifier (FEA), integrate fire neuron and pseudo resistor technique that observed high electrical performance through neural activity. A pseudo resistor technique ensures large input impedance for integrated FEA by compensating the input leakage current. While carbon nanotube based FEA provides low-voltage operation with directly impacts on the power consumption and also give detector size that demonstrates fidelity of the neural signals. The observed neural activity shows amplitude of spiking in terms of action potential up to $80{\mu}V$ while local field potentials up to 40 mV by using proposed architecture. This fully integrated architecture is implemented in Analog cadence virtuoso using design kit of CNT process. The fabricated chip consumes less power consumption of $2{\mu}W$ under the supply voltage of 0.7 V. The experimental and simulated results of the integrated FEA achieves $60G{\Omega}$ of input impedance and input referred noise of $8.5nv/{\sqrt{Hz}}$ over the wide bandwidth. Moreover, measured gain of the amplifier achieves 75 dB midband from range of 1 KHz to 35 KHz. The proposed research provides refreshing neural recording data through nanotube integrated circuit and which could be beneficial for the next generation neuroscientists.

• Applied Chemistry for Engineering
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• v.30 no.1
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• pp.49-53
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• 2019

Hydrous $MnO_2$ nanowires were easily synthesized by an one-pot synthesis with a simple hydrothermal method. As prepared hydrous $MnO_2$ nanowires were characterized with scanning emission microscopy (SEM), transmit emission microscopy (TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET). They showed a good catalytic activity with the suitable nano-size of 4-5 nm and morphology. The furfuryl alcohol was selected as a substrate and the reaction was carried out in a toluene solvent at $100^{\circ}C$ under the atmospheric pressure of oxygen. The hydrous $MnO_2$ nanowire catalyst exhibited an excellent yield of furfural with the first-rate selectivity and conversion. The catalytic performance during recycle tests was also carried out and the catalyst showed a good mechanical strength with a negligible loss in the activity over five reaction cycles.