• 대한기계학회논문집A
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• 제24권3호
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• pp.735-742
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• 2000

Densification behaviors of mixed metal powder under high temperature were investigated. Experimental data of mixed copper and tool steel powder with various volume fractions of Cu powder were obtained under hot isostatic pressing and hot pressing. By mixing the creep potentials of McMeeking and co-workers and of Abouaf and co-workers originally for pure powder, the mixed creep potentials with various volume fractions of Cu powder were employed in the constitutive models. The constitutive equations were implemented into a finite element program (ABAQUS) to compare with experimental data for densification of mixed powder under hot isostatic pressing and hot pressing. Finite element calculations by using the creep potentials of Abouaf and co-workers agreed reasonably well with experimental data, however, those by McMeeking and co-workers underestimate experimental data as observed in the case of pure metal powders.

• 한국세라믹학회지
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• 제31권3호
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• pp.337-345
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• 1994

The reaction-sintered alumina and zirconia-alumina ceramics having low firing shrinkage were prepared from the Al/Al2O3 or Al/ZrO2(Ca-PSZ) powder mixtures via the attrition milling. And in this milling process the effect of the characteristics of used powders was investigated. Attrition milling was much more effective in reducing the particle size of ceramic/metal mixed powders than ball milling. Powder mixtures of flake-type Al with coarse alumina was much more effectively comminuted by the attrition milling than the mixtures of globular-type Al with coarse alumina powders. And coarse alumina than fine alumina was much more beneficial in cutting and reducing the ductile Al particles. In the contrary to Al/Al2O3 powder mixtures, Al/ZrO2 powder mixtures was not effectively comminutd. But whether using the alumina ball media or attrition milled with Al2O3 powder rather than Al, the milling efficiency was much more increased.

• 한국재료학회지
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• 제14권4호
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• pp.293-299
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• 2004

Transition metal ions doped $TiO_2$ nanostructured powders were prepared with simply heating aqueous $TiOCl_2$ solutions, contained various metal ions (Ni, Al, Fe, Zr, and Nb) of 1.47 mol% added as metal-chlorides, at $100^{\circ}C$ for 4 hrs by homogeneous precipitation process under suppressing conditions of water vaporization. The characterizations for prepared $TiO_2$ powders were carried out to observe doping of metal ions, their concentrations and microstructures using XRD, UV-VIS (DRS), XPS, SEM, TEM and ICP. Also, photo-oxidative abilities were evaluated by decomposition of 4-chlorophenol (4CP) under ultraviolet light irradiations. No secondary oxide phases were formed in all the $VTiO_2$ powders, showing doping with various transition metal ions. When adding ions ($Ni^{2+}$ or$ Al^{3+ }$ and $Zr^{4+}$ ) having valance states or ionic radii greatly different from those of $Ti^{4+}$ , the $TiO_2$ powders of mixed anatase and rutile phases were formed, whereas in the case of additions of $^Fe{3+ }$ and $Nb^{ 5+}$ as well as no addition of metal ion the powders with pure rutile phase alone were formed. Among the prepared $TiO_2$ powders, Ni$^{2+}$ doped $TiO_2$ powders, containing a small amount of anatase phase, showed excellent photo-oxidative ability in 4CP decomposition because of relative decreases in electron-hole recombination and poisoning of $TiO_2$ surface during the photoreaction.n.

• 한국세라믹학회지
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• 제27권5호
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• pp.625-630
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• 1990

Cordierite powders were prepared from Si(OC2H5)4, Al(OC3H7i)3 and Mg(OC2H5)2 by the sol-gel method. Two different methods were applied for producing fine and homogeneous powders. One is that Si(OC2H5)4 with a lowr rate of hydrolysis was partially hydrolyzed and then Al(OC3H7i)3 and Mg(OC2H5)2 were mixed and reacted. The other is based on the simultaneous hydrolysis of these metal alkoxides using i-C4H9OH which retards the rate of hydrolysis of Al(OC3H7i)3 and Mg(OC2H5)2. It was confirmed that ifne and homogeneous powders were obtained from both methods. Also these powders were calcined at four different temperatures during two hours. X-ray diffraction patterns show only ${\mu}$-cordierite phase at 1000$^{\circ}C$, ${\mu}$-cordierite and ${\alpha}$-cordierite phases at 1100-1200$^{\circ}C$ and ${\alpha}$-cordierite phase at 1300$^{\circ}C$ respectively.

• 한국전기전자재료학회논문지
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• 제25권8호
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• pp.651-656
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• 2012

A study on capacitive characteristics of stylus pen for touch panel are progressed in this paper. Also the main factors for capacitive sensitivity are studied. Namely, highly sensitive stylus pen which can be applied to capacitive touch panel are studied based on the analysis of materials and process conditions regardless of pattern shapes. Stylus pen was made of PDMS(Poly-Di-Methyl-Siloxane) and conductive metal powders which does not damage the touch panel surface. We tried to get the advantages of both the properties of soft PDMS and conductive metal powders. We found that potential difference of capacitance change with conductivity of the composite materials(PDMS + metal powders) it implies that during touch process, large voltage difference can be caused by the high conductive materials of stylus pen. Stylus pen made by PDMS with mixed with Ag powders which has large conductivity shows more capacitance change of 1 pF than PDMS with other materials of Ni or C powders.

• Progress in Superconductivity
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• 제1권2호
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• pp.120-124
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• 2000

Ni-13%Cr and Ni-70%Cu alloy tapes were prepared by using high purity metal powders as starting materials. The Ni-13%Cr and the Ni-70%Cu mixtures were isostatically pressed, sintered, rolled and texture-annealed. SEM EDS analysis showed that copper and nickel atoms were completely mixed, while the alloying between the chromium powders and the nickel powders was incomplete. In spite of incomplete alloying between nickel and chromium powders, sharp cube-texture was developed for the Ni-13%Cr tape as well as the Ni-70%Cu tape.

• 한국분말재료학회지
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• 제13권5호
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• pp.351-359
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• 2006

Ni based($Ni_{57}Zr_{20}Ti_{18}Si_2Sn_3$) bulk metallic glass(BMG) powders were produced by a gas atomization process, and ductile Cu powders were mixed using a spray drying process. The Ni-based amorphous powder and Cu mixed Ni composite powders were compacted by a spark plasma sintering (SPS) processes into cylindrical shape. The relative density varied with the used SPS mold materials such as graphite, hardened steel and WC-Co hard metal. The relative density increased from 87% to 98% when the sintering temperature increased up to $460^{\circ}C$ in the WC-Co hard metal mold.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.395-399
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• 1999

MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.

• 소성∙가공
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• 제27권1호
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• pp.5-11
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• 2018

Direct energy deposition (DED) technique uses a laser heat source to deposit a metal layer on a substrate. Many researchers have used the DED technique to study the hardfacing of molds and dies. The aim of this study is to obtain high surface hardness and a sound bonding between the AISI M4 deposits and a substrate utilizing a mixed powder that contains M4 and AISI P21 powders. To prevent interfacial cracks between the M4 deposits and the substrate, the mixed powder is pre-deposited onto a JIS S45C substrate, before the deposition of M4 powders. Interfacial defects occurring between the deposits and substrate and changes in the microhardness of the intermediate layer were examined. Observations of the cross-sections of deposited specimens revealed that the interfacial cracks appeared in samples with one and two mixed layers regardless of the mixture ratio. However, the crack was removed by increasing the mixture ratio and the number of intermediate layers. Meanwhile, the microhardness in the mixed layer was found to decrease with increasing ratio of P21 powder in the mixture and that in the upper region of the deposited layers was approximately 800 HV, which was attributed to various alloying elements in the M4 powder.

• 한국분말재료학회지
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• 제15권4호
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• pp.285-291
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• 2008

Fe based ($Fe_{68.2}C_{5.9}Si_{3.5}B_{6.7}P_{9.6}Cr_{2.1}Mo_{2.0}Al_{2.0}$) amorphous powder were produced by a gas atomization process, and then ductile Cu powder fabricated by the electric explosion of wire(EEW) were mixed in the liquid (methanol) consecutively. The Fe-based amorphous - nanometallic Cu composite powders were compacted by a spark plasma sintering (SPS) processes. The nano-sized Cu powders of ${\sim}\;nm$200 produced by EEW in the methanol were mixed and well coated with the atomized Fe amorphous powders through the simple drying process on the hot plate. The relative density of the compacts obtained by the SPS showed over 98% and its hardness was also found to reach over 1100 Hv.