• 한국세라믹학회지
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• 제53권6호
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• pp.670-675
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• 2016

Calcium phosphate crystallites were prepared by wet chemical method for use in artificial bone. In order to obtain ${\beta}$-tricalcium phosphate (TCP), nano-crystalline calcium phosphate (CaP) was precipitated at $37^{\circ}C$ and at $pH5.0{\pm}0.1$ under stirring using highly active $Ca(OH)_2$ in DI water and an aqueous solution of $H_3PO_4$. The precipitated nano-crystalline CaP solution was kept at $90^{\circ}C$ for the growth of CaP crystallites. Through the growing process of CaP crystallites, we were able to obtain various sizes of rectangular CaP crystallites according to the crystal growing times. Dry nano-crystalline CaP powders at $37^{\circ}C$ were mixed with dry macro-crystalline CaP crystallites and the shaped mixture sample was fired at $1150^{\circ}C$ to make a ${\beta}-TCP$ block. Several tens of nm powders were uniformly coated on the surface, which was comprised of powders of several tens of ${\mu}m$, using a vibrator. The mixing ratio between the nanometer powders and the micrometer powders greatly affected the mechanical strength of the mixture block; the most appropriate ratio of these two materials was 50 wt% to 50 wt%. The sintered block showed improved mechanical strength, which was caused by the solid state interaction between the nano-crystalline ${\beta}-TCP$ and the macro-crystalline ${\beta}-TCP$.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2008년도 추계학술대회 초록집
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• pp.34-35
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• 2008

We investigated the effects of Pt nano electrodeposits on the corrosion of carbon substrate in an acidic solution. The electrodes for experiments were prepared by electrodepositing Pt on carbon substrate in a solution of 5 mM $H_2PtCl_6$ and 0.5 M $H_2SO_4$ using pulse deposition technique. In cyclic voltammograms for the carbon electrodes with and without Pt nano electrodeposits, total anodic current including both currents from oxygen evolution reaction and carbon corrosion increased abruptly above a critical potential. In addition, the critical potential of the carbon electrodes with Pt nano electrodeposits was lower than that of bare carbon electrode. This phenomenon was more prominent at $75^{\circ}C$ than $25^{\circ}C$. In potentiostatic experiments, the current transients and the corresponding power spectral density increased with increasing the applied potential for the electrodes. Furthermore, the current transients for the carbon electrodes with Pt nano electrodeposits were much higher than those for the bare carbon substrate. This indicates that the corrosion of carbon substrate can be highly accelerated by Pt nano electrodeposits.

• 한국분말재료학회지
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• 제14권4호
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• pp.238-244
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• 2007

The electrophoretic deposition process of Ni nano-particles in organic suspension was employed for self-repairing of heat exchanger tubes. For this purpose, Ni nano-particles prepared by levitational gas condensation method were dispersed into the solution of ethanol with the addition of dispersant Hypermer KD2. For electrophoretic deposition of Ni nano-particles on the Ni alloy specimen, constant electric fields of 20 and 100 V $cm^{-1}$ were applied to the specimen in Ni-dispersed solution. It was found that as electrophoretic deposition proceeds, the size of the pit or crack remarkably decreased due to the agglomeration of Ni nano-particles at the pit or crack. This strongly suggests that the electrophoretic mobility of the charged particles is larger for the damaged part with a higher current value rather than outer surfaces with a lower current value.

• 한국표면공학회지
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• 제40권1호
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• pp.32-38
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• 2007

Ni coating layers were formed using a newly developed electroless Ni plating solution. The properties of Ni coating layer such as internal stress, hardness, surface roughness, crystallinity, solderability and surface morphology were investigated using various tools. Results revealed that internal stress decreased with plating time and reached $40N/mm^2$ at 20 minutes of the plating time. Hardness increased with increasing P content and thickness. Surface roughness of the pad decreased with Ni and Ni/Au plating. Crystallinity decreased with increasing P content. Solderability based on wettability decreased with Ni and Ni/Au plating. Based on surface morphology, it is expected that Ni coating layer formed using a newly developed electroless Ni plating solution is lower than that formed using a commercial electroless Ni plating solution in possibility of black pad occurrence.

• 자원리싸이클링
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• 제23권6호
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• pp.22-29
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• 2014

네오디뮴 폐자석 침출액으로부터 희유금속인 네오디뮴을 회수하는 연구와 함께 네오디뮴과 같이 침출되는 철의 부가가치를 높이는 연구가 필요하다. 본 연구에서는 네오디뮴과 같이 침출되는 철의 유용자원화를 위한 기초연구로 철 나노분말을 제조하는 실험을 수행하였다. 본 연구는 $FeCl_3$ 용액을 철 분말 원료로, 분산제는 $Na_4P_2O_7$와 Polyvinylpyrrolidone를 이용하였고, 환원제로는 $NaBH_4$, 철 나노분말 핵생성 촉진제 seed로 염화팔라듐을 사용하였다. 제조한 철 나노분말을 XRD, SEM을 이용하여 분말의 형상 및 크기를 분석하였다. Fe와 $NaBH_4$의 몰 비를 1 : 5로 조절하여 철 분말을 제조하였으며, 이 때 철 분말은 구형이었으며, 입도는 약 50 ~ 100 nm 였다. 분산제 $Na_4P_2O_7$의 경우 100 mg/L에서 철 이온의 제타포텐셜이 음의 값을 가졌고, $FeCl_3$ 과 PVP와 Pd의 질량비 1 : 4 : 0.001에서 분산이 양호하고, 입도가 100 nm 인 철 나노분말을 합성하였다. 같은 반응 조건에서 폐 Nd 침출액의 Fe 이온을 pH를 조절하여 슬러리화한 후 실험을 진행한 결과, pH 9에서 구형의 철 분말을 합성할 수 있었으며, 20 L 이상의 Scale-up 공정에서는 분산제 없이 환원제로 175 nm 크기의 철 분말을 합성할 수 있었다.

• 자원리싸이클링
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• 제15권4호
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• pp.19-26
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• 2006

함은 폐재의 리싸이클링을 위한 연구의 일환으로써 Hydrazine Hydrate을 환원제로 사용하여 질산은 수용액으로부터 Ag 나노분말을 제조하기 위한 실험을 수행하였다. 이를 위해 질산은을 소정 농도로 증류수에 용해시킨 수용액에 Ag 미립자의 응집방지를 위한 분산제로써 Tamol NN8906 혹은 Tween 20을 미리 혼합한 다음 환원제인 Hydrazine Hydrate 용액을 첨가하는 방법으로 환원반응을 실시하였다. 환원반응을 통하여 제조한 Ag 미립자는 입도분석기 및 TEM 측정을 통하여 형상과 평균입도를 측정하였다. Hydrazine Hydrate에 의한 은의 환원을 위해서는 이론치의 약 2배를 첨가해 주어야 하는 것으로 나타났으며, Tamol NN8906을 분산제로 사용하여 제조한 Ag 나노분발은 매우 좁은 입도범위의 분포특성을 보여 주었다. Tween 20을 분산제로 사용한 경우의 입도 분포는 bimodal 혹은 multimodal distribution을 보였으며, 입자 모양에 있어서는 Tamol NN8906과 Tween 20이 모두 비슷하게 표면이 매끄러운 불규칙한 모양의 입자들로 구성되어 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제37회 하계학술대회 초록집
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• pp.190-190
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• 2009

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.432-434
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• 2009

Metal nano-wire arrays on Cu-coated seed layers were fabricated by aqueous solution method using sulfate bath at room temperature. The seed layers were coated on Anodic aluminum oxide (AAO) bottom substrates by electrochemical deposition technique, length and diameter of metal nano-wires were dominated by controlling the deposition parameters, such as deposition potential and time, electrolyte temperature. Anodic aluminum oxide (AAO) was used as a template to prepare highly ordered Ni, Fe, Co and Cu multilayer magnetic nano-wire arrays. This template was fabricated with two-step anodizing method, using dissimilar solutions for Al anodizing. The pore of anodic aluminum oxide templates were perfectly hexagonal arranged pore domains. The ordered Ni, Fe, Co and Cu systems nano-wire arrays were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Vibrating Sample Magnetometer (VSM). The ordered Ni, Fe, Co and Cu systems nano-wires had different preferred orientation. In addition, these nano-wires showed different magnetization properties under the electrodepositing conditions.

• 한국재료학회지
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• 제16권9호
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• pp.538-542
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• 2006

Nano-sized cobalt oxide powders were prepared by low pressure spray pyrolysis process. The precursor powders obtained by low pressure spray pyrolysis process from the spray solution with ethylene glycol had several microns size and hollow structure. The precursor powders obtained from the spray solution with optimum concentration of ethylene glycol formed the nano-sized cobalt oxide powders with regular morphology after post-treatment without milling process. On the other hand, the cobalt oxide powders obtained from the spray solution without ethylene glycol had submicron size and spherical shape before and after posttreatment. The mean size of the cobalt oxide powders formed from the spray solution with concentration of ethylene glycol of 0.7M was 180 nm after post-treatment at temperature of $800^{\circ}C$. The mean size of the powders could be controlled from several tens nanometer to micron sizes by changing the post-treatment temperatures in the preparation of cobalt oxide powders by low pressure spray pyrolysis process.

• 한국재료학회지
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• 제30권2호
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• pp.93-98
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• 2020

Effective control of the heat generated from electronics and semiconductor devices requires a high thermal conductivity and a low thermal expansion coefficient appropriate for devices or modules. A method of reducing the thermal expansion coefficient of Cu has been suggested wherein a ceramic filler having a low thermal expansion coefficient is applied to Cu, which has high thermal conductivity. In this study, using pressureless sintering rather than costly pressure sintering, a polymer solution synthesis method was used to make nano-sized Cu powder for application to Cu matrix with an AlN filler. Due to the low sinterability, the sintered Cu prepared from commercial Cu powder included large pores inside the sintered bodies. A sintered Cu body with Zn, as a liquid phase sintering agent, was prepared by the polymer solution synthesis method for exclusion of pores, which affect thermal conductivity and thermal expansion. The pressureless sintered Cu bodies including Zn showed higher thermal conductivity (180 W/m·K) and lower thermal expansion coefficient (15.8×10^-6/℃) than did the monolithic synthesized Cu sintered body.