• Journal of Powder Materials
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• v.17 no.1
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• pp.29-35
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• 2010

We produced cylindrical porous TiNi bodies by Self-propagating High-temperature Synthesis (SHS) process, varying the heating schedule prior to ignition of a loose preform compact made from (Ti+Ni) powder mixture. To investigate the effect of the heating schedule on the behaviour of combustion wave propagation and the structure of porous TiNi shape-memory alloy (SMA) body, change of temperature in the compact during SHS process was measured as a function of time and used for determining combustion temperature and combustion wave velocity. Microstructure of produced porous TiNi SMA body was observed and the results were discussed with the combustion characteristics. From the results it was concluded that the final average pore size could be controlled either by the combustion wave velocity or by the average temperature of the preform compact prior to ignition.

• Journal of Power Electronics
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• v.18 no.1
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• pp.81-91
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• 2018

This paper proposes a double line voltage synthesis (DLVS) strategy for three-to-five phase direct matrix converters. In the proposed strategy, the input and expected output voltages are divided into 6 segments and 10 segments, respectively. In addition, in order to obtain the maximum voltage transfer ratio (VTR), the input line voltages and "source key" should be selected reasonably according to different combinations of input and output segments. Then, the corresponding duty ratios are calculated to determine the switch sequences in different segment combinations. The output voltages and currents are still sinusoidal and symmetrical with little lower order harmonics under unbalanced or distorted input voltages by using this strategy. In addition, the common mode voltage (CMV) can be suppressed by rearranging some of the switching states. This strategy is analyzed and studied by a simulation model established in MATLAB/Simulink and an experimental platform, which is controlled by a DSP and FPGA. Simulation and experimental results verify the feasibility and validity of the proposed DLVS strategy.

• Current Applied Physics
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• v.18 no.11
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• pp.1410-1414
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• 2018

Magnetic nanoparticles (MNP) have attracted considerable interest in many fields of research and applied science due to their impressive properties. In the past, especially biomedical problems have promoted the development of MNPs. For technical applications e.g. wastewater treatment and absorption of electromagnetic waves, the existing synthesis approaches are too expensive and/or the producible quantities are too low. In this work we present a method for simple preparation of size-controlled magnetic iron oxide nanoparticles by electroerosion dispersion (EED) of carbon steel in water. We describe the synthesis method, the laboratory installation and discuss the structural, chemical and electromagnetic properties of the synthetized EED powders as well as their applicability for microwave absorption compared to other available ferrite powders.

• Clean Technology
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• v.26 no.4
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• pp.251-256
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• 2020

The biocompatibility and plasmonic properties of Au nanoparticles make them useful for photothermal therapy, drug delivery, imaging, and many other fields. This study demonstrated a novel, facile, economic, and green synthetic method to produce gold nanoparticles. Gold nanoparticles (AuNPs) with spherical and triangular shapes were effectively synthesized using only Schisandra chenesis fruit extract as the capping and reducing agent. The shape of the AuNPs could be engineered simply by adjusting the molar concentration of HAuCl4 in the reaction mixture. The as-synthesized AuNPs were characterized using UV-VIS spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), and energy dispersive X-ray analysis (EDXA). This study revealed that by using the HAuCl4 concentration in the AuNP synthesis, the shape and size of the AuNPs could be controlled by the concentration of HAuCl4 and Schisandra chinensis fruit extract as a surfactant. The as-synthesized AuNPs samples had sufficient colloidal stability without noticeable aggregation and showed the predominant growth of the (111) plane of face-centered cubic gold during the crystal growth. The catalytic efficiency of the AuNPs synthesized using Schisandra chenesis fruit extract was examined by monitoring the catalytic reduction of 4-nitrophenol to 4-aminophenol using Ultraviolet-visible spectroscopy (UV-Vis spectroscopy). The synthesized AuNPs showed good catalytic activity to reduce 4-nitrophenol to 4-aminophenol, revealing their practical usefulness.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.153-160
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• 2022

ZnO nanosheets have been used for many devices and antibacterial materials with wide bandgap and high crystallinity. Among the many methods for synthesizing ZnO nanostructures, we report the synthesis of ZnO/Zn(OH)₂ nanosheets using the ionic layer epitaxy method, which is a newly-developed bottom-up technique that allows the shape and thickness of ZnO/Zn(OH)₂ nanosheets to be controlled by temperature and time of synthesis. Results were analyzed by scanning electron microscopy and atomic force microscopy. The physical and chemical information and structural characteristics of ZnO/Zn(OH)2 nanosheets were compared by X-ray photoelectron spectroscopy and X-ray diffraction patterns after various post-treatment processes. The crystallinity of the ZnO/Zn(OH)₂ nanosheets was confirmed using scanning transmission electron microscopy. This study presents details of the control of the size and thickness of synthesized ZnO/Zn(OH)₂ nanosheets with atomic layers.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.437-446
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• 2014

The dihydroxylation reaction of allylic amines is a facile and useful synthetic method to obtain amino diol structures that are widely found in lots of biologically important natural products. This review will focus on the recent methods of both substrate-controlled and ligand-controlled dihydroxylation reactions of acyclic allylic amines. In addition, several applications of the diastereoselective dihydroxylation methods to asymmetric syntheses of natural products are presented.

• Textile Coloration and Finishing
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• v.22 no.2
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• pp.123-131
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• 2010

Shape and size controlled synthesis of gold particles has been studied by using wet-chemical method. When ${AuCl_4}^-$ in aqueous $HAuCl_4$ precursor was reduced using $Na_2SO_3$ as a reducing agent, mixtures of spherical, triangular and hexagonal particles were prepared in a few minutes. It was found that the shape selective oxidative etching by ${AuCl_4}^-\;+\;Cl^-$ anions and crystal growth took place simultaneously. As the ${AuCl_4}^-$ and $Cl^-$ concentration increased, yields of large triangular and hexagonal plate type particles increased, while the spherical particles decreased in most cases. Possible etching and growth mechanisms are discussed.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.3.1-3.1
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• 2011

Nanoengineered materials with advanced architectures are critical building blocks to modulate conventional material properties or amplify interface behavior for enhanced device performance. While several techniques exist for creating one dimensional heterostructures, electrospinning has emerged as a versatile, scalable, and cost-effective method to synthesize ultra-long nanofibers with controlled diameter (a few nanometres to several micrometres) and composition. In addition, different morphologies (e.g., nano-webs, beaded or smooth cylindrical fibers, and nanoribbons) and structures (e.g., core-.shell, hollow, branched, helical and porous structures) can be readily obtained by controlling different processing parameters. Although various nanofibers including polymers, carbon, ceramics and metals have been synthesized using direct electrospinning or through post-spinning processes, limited works were reported on the compound semiconducting nanofibers because of incompatibility of precursors. In this work, we combined electrospinning and galvanic displacement reaction to demonstrate cost-effective high throughput fabrication of ultra-long hollow semiconducting chalcogen and chalcogenide nanofibers. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions, morphology, and crystal structures, providing a large material database to tune electrode potentials, thereby imparting control over the composition and shape of the nanostructures that evolved during galvanic displacement reaction.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.210-214
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• 2007

Silicon nanoparticles are widely studied as a material with great potential for wide applications. For application to present industry, it should be easy to control the characteristics of nanoparticle including the size and structure. In this paper, we investigated the formation of Si nanoparticle using pulse plasma technology. Plasma technology is already quite common in device industry and the size of nanoparticle can be easily controlled according to plasma pulse duration. An inductively-coupled plasma chamber with RF power (13.56 MHz) was used with DC-biased grid $(-200\sim+200\;V)$ installed above the substrate. In order to measure the shape and size of nanoparticle, TEM was used. It was found that the size of nanoparticles can be controlled well with the plasma pulse duration and the collection efficiency is increased with the use of either negative or positive DC-bias.

• Journal of Powder Materials
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• v.19 no.5
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• pp.367-372
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• 2012

Single crystalline Cu nanowires with controlled diameters and aspect ratios have been synthesized using electrochemical deposition within confined nanochannels of a porous anodic aluminium oxide(AAO) template. The diameters of nano-sized cylindrical pores in AAO template were adjusted by controlling the anodization conditions. Cu nanowires with diameters of approximately 38, 99, 274 nm were synthesized by the electrodeposition using the AAO templates. The crystal structure, morphology and microstructure of the Cu nanowires were systematically investigated using XRD, FE-SEM, TEM and SAED. Investigation results revealed that the Cu nanowires had the controlled diameter, high aspect ratio and single crystalline nature.