• Advances in nano research
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• 제2권2호
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• pp.77-88
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• 2014

Solvothermal treatment of late transition metal acetylacetonates in a novel medium composed either of pure acetophenone or acetophenone mixtures with amino alcohols offers a general approach to uniform hydrophilic metal nanoparticles with high crystallinity and low degree of aggregation. Both pure metal and mixed-metal particles can be accesses by this approach. The produced materials have been characterized by SEM-EDS, TEM, FTIR in the solid state and by Nanoparticle Tracking Analysis in solutions. The chemical mechanisms of the reactions producing nanoparticles has been followed by NMR. Carrying out the process in pure acetophenone produces palladium metal, copper metal with minor impurity of $Cu_2O$, and NiO. The synthesis starting from the mixtures of Pd and Ni acetylacetonates with up to 20 mol% of Pd, renders in minor yield the palladium-based metal alloy along with nickel oxide as the major phase. Even the synthesis starting from a mixed solution of $Cu(acac)_2$ and $Ni(acac)_2$ produces oxides as major products. The situation is improved when aminoalcohols such as 2-aminoethanol or 2-dimethylamino propanol are added to the synthesis medium. The particles in this case contain metallic elements and pairs of individual metals (not metal alloys) when produced from mixed precursor solutions in this case.

• 한국분말재료학회지
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• 제21권3호
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• pp.196-201
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• 2014

In this study, nanocrystalline Cu-Ni bulk materials with various compositions were cold compacted by a shock compaction method using a single-stage gas gun system. Since the oxide layers on powder surface disturbs bonding between powder particles during the shock compaction process, each nanopowder was hydrogen-reduced to remove the oxide layers. X-ray peak analysis shows that hydrogen reduction successfully removed the oxide layers from the nano powders. For the shock compaction process, mixed powder samples with various compositions were prepared using a roller mixer. After the shock compaction process, the density of specimens increased up to 95% of the relative density. Longitudinal cross-sections of the shock compacted specimen demonstrates that a boundary between two powders are clearly distinguished and agglomerated powder particles remained in the compacted bulk. Internal crack tended to decrease with an increase in volumetric ratio of nano Cu powders in compacted bulk, showing that nano Cu powders has a higher coherency than nano Ni powders. On the other hand, hardness results are dominated by volume fraction of the nano Ni powder. The crystalline size of the shock compacted bulk materials was greatly reduced from the initial powder crystalline size since the shock wave severely deformed the powders.

• 한국재료학회지
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• 제8권12호
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• pp.1082-1089
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• 1998

$YBa_2$$Cu_3$$O_{7-y}$ (123) 초전도체에서 은 입자의 미세분산을 얻고자 말릭산을 사용한 발화합성과 고상반응법으로 123와 123-Ag 복합 초전도분말을 제조하였다. 발화합성분말을 원료로 사용할 시 마이크론 미만의 미세한 123 분말과 은 분말의 복합체를 얻을 수 있었다. 원료로 사용된 산화은($Ag_2O$) 분말은 발화합성과정 중금속 은으로 환원되었다. 원료분말에 첨가된 금속 은에 의한 반응 물질간의 확산 촉진으로 123상이 단시간내에 생성되었고 입자성장도 촉진되었다. 발화합성법으로 제조한 시편은 기계적 혼합공정으로 제조한 시편에 비해 은 입자들은 미세하게 분산시킬 수 있어서 초전도체의 임계전류밀도가 향상되었다.

• 대한금속재료학회지
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• 제46권3호
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• pp.182-188
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• 2008

Carbon nanotubes(CNTs) have outstanding mechanical, thermal, and electrical properties. Thus, by placing nanotubes into appropriate matrix, it is postulated that the resulting composites will have enhanced properties. Cold spray can produce thick metal-based composite coatings with very high density, low oxygen content, and phase purity, which leads to excellent physical properties. In this study, we applied cold spray coating process for the consolidation of Cu/CNT composite powder. The precursor powder mixture, in which CNTs were filled into copper particles, was prepared to improve the distribution of the CNT in copper matrix. Pure copper coating was also conducted by cold spraying as a reference. Annealing heat treatment was applied to the coating to examine its effect on the properties of the composite coating. The hardness of Cu/CNT composite coating represented similar value to that of pure copper coating. It was importantly found that the electrical conductivity of the Cu/CNT composite coating significantly increased from 53% for the standard condition to almost 55% in the optimized condition, taking annealed ($500^{\circ}C/1hr$.) copper coating as a reference (100%). The thermal conductivity of Cu/CNT composite coating layer was higher than that of pure Cu coating. It was also found that the electrical and thermal conductivities of Cu/CNT composite could be improved through annealing heat treatment. The microstructural evolution of Cu/CNT coating was also investigated and related to the macroscopic properties.

• 한국환경보건학회지
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• 제27권4호
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• pp.63-71
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• 2001

PM 2.5/ samples were measured at two sites, Hadan(suburban site) and Anrak (roadside site) in Busan area. PM 2.5/ sampling was performed for 24-hour intervals by the FH9.5 particulate sampler. Aerosol samples were collected on PTFE filter. A total of 60 particulate samples were collected, dad samples were measured for Particulate mass concentration, metallic elements (Cr, Mn, Ni. Cu. Se, Fe, Pb, and Zn) and waer-soluble elements (C $l^{[-10]}$ , N $O_{3}$$^{[-10]}$ ,S $O_{4}$$^{2-}$, N $H_{4}$$^{+}$, $Ca_{2}$$^{+}$, $Mg_{2}$$^{+}$ and $^{+}$.Mass concentration in Hadan ranged 24.23~57.12 $\mu\textrm{g}$/㎥ and 60.22~72.12 $\mu\textrm{g}$/㎥m Yellow Sand Events. Major cations in Hadan and Anrak site is N $H_{4}$$^{+}$and N $a^{+}$ respectively. SO42$^{[-10]}$ was the abundant specie in the PM 2.5 fraction for Hadan site an dAnrak site. Hadan site showed igher concentration in S $O_{4}$$^{2.1}$ and N $H_{4}$ $^{+}$ In Anrak site the concentration of S $O_{4}$/sip 2-/and N $a^{+}$ was higher than other ions Prominent metallic elements were Fe and Pb in two sites. Principal component analysis showed that main source of PM 2.5 aerosol particles was non-metal related source which was resulted in relating elements as Cr, Ni, and Pb at Hadan site, Anrak site also has resulted PM2.5 aerosol paricles source, which was related its element like Zn, and Ni,. The SAS package analysis also showed that long-range transport effect at Hadan area due to Yellow Sand Event by the prevailing weaterlies.ling weaterlies.

• 한국환경보건학회지
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• 제31권4호
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• pp.301-308
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• 2005

The purpose of this study was to characterize mass concentration of $PM_{10}\;to,\;PM_{2.5}$ and metallic composition using Minivol Portable Sampler from May 2003 to May 2004 in metropolitan city, Seoul. Annual average concentration of $PM_{10}$ were $57.67({\pm}28.20)\;{\mu}g/m^3\;and\;PM_{2.5},\;were\;42.06({\pm}20.23)\;{\mu}g/m^3$. The concentration was the highest in winter because persistent thermal inversion and in spring, particulate matter concentration was high because of yellow-sand events. The average $PM_{2.5}/PM_{10}$ ratio was 0.73. This indicated $PM_{2.5}$ fraction played a significant role in air pollution. The atmospheric metallic elements in the $PM_{10},PM_{2.5}$ came different emission sources such as soil, traffic, industry and resuspended particles. The results showed that average $PM_{10}$ composition order as Fe>Zn>Pb>Cu>Mn. The metallic elements Zn and Fe were the largest composition in the $PM_{2.5}$

• 분석과학
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• 제16권2호
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• pp.143-151
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• 2003

서울시에 소재한 7개 측정점으로부터 입자상물질에 결합된 금속성분의 농도를 약 1년여 기간동안 관측하였다 (2001년 3월~2002년 5월). 본 관측자료를 토대로 공간적 요인이 금속성분의 분포특성에 어떠한 방식으로 영향을 미치는 가를 조사하였다. 이러한 분석을 위해, 변이계수, 시간적 변이성, 상관성 발생의 빈도 등과 같은 기준을 활용하였다. 본 연구 결과에 의하면, 금속성분의 농도분포가 상당히 다양한 요인들의 영향에 종속된다는 사실이 확인되었다. 특히 Fe, Mn, Pb 등의 성분들은 이질적인 지역들간에도 대단히 강한 유사성을 보이는데 반해, Cu와 같은 성분은 이러한 경향을 전혀 찾기가 어려웠다. 이러한 공간적 요인의 특성을 상세하기 설명하기 위해서는 개별 성분의 지화학적 요인을 발생/소멸현상과 연계하여 설명하는 것이 중요하다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1997년도 특별강연 및 추계학술발표 개요집
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• pp.184-193
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• 1997

Aluminium and aluminium alloys have the high electrical and heat conductivity. It gives rise to difficulties for a choice of electrodes material for their contact electric welding. This paper describes the investigations performed to solve the above problem. The purpose of this investigation was to obtain dispersion-hardening alloys by the internal oxidation method, to optimize their contents and treatment modes, to produce electrodes of these alloys and to test them. The strengthing effect of alloys with oxide particles depends on their size stability at high temperatures. Despite of the fact, that oxides are the most stable of all the non-metallic phases their coagulation takes place. Based on the early results, we chose two types of alloys, first No. 1 Cu - 0,4%Al and second No. 2 Cu - 0,2%Be for production of electrodes. These alloys had not additional alloying elements. These alloys were prepared as 1 mm plates and flake-formed 200 m thick, and also No. 1 as a powder of size 100 mkm (received from Korea). The large samples for electrodes were produced by three methods : explosive welding method, dynamic one including the explosion compression of electrode blank and the quasi-dynamic method including the high-speed compression of dense briquest and the further hot extrusion of a rod.

• 한국분말재료학회지
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• 제5권2호
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• pp.139-144
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• 1998

We have evaluated the role of Ag additions on the strength, fracture toughness, elastic modulus and resistance to thermal shock of $YBa_2Cu_3O_{7-x}$(YBCO) superconductor. Addition of 10 vol.% Ag improved strength and fracture toughness, whereas, decreased elastic modulus of YBCO. In addition, YBCO-Ag composites improved resistance to thermal shock probably due to enhanced strength, fracture toughness and thermal conductivity as a result of Ag addition. It is to be noted that YBCO-Ag made by mixing with $AgNO_3$ solution showed slightly higher strength, fracture toughness and resistance to thermal shock, compared to that made by mixing with metallic Ag powder. These improvements are believed to be due to the microstructure of more finely and uniformly distributed Ag particles.

• Journal of Welding and Joining
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• 제29권5호
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• pp.90-94
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• 2011

Ag metallic particles from nano-scale to submicron-scale are combined with organic solvent to provide fine circuits and interconnection. Ink-jet printing with Ag nano particle inks demonstrated the potentials of the new printed electronics technology. The bonding at the interface between the Ag wiring layer and the various substrates is very important. In this study, the details of interfaces in Ag wiring are investigated primarily by microstructure observation. By adjusting the materials and sintering conditions, nicely formed interfaces between Ag wiring and Cu, Au or organic substrates are achieved. In contrast, transmission electron microscope (TEM) image clearly shows interface debonding between Ag wiring and Sn substrate. Sn oxides are formed on the surface of the Sn plating. The formation of these is a root cause of the interface debonding.