• 한국결정성장학회지
• /
• 제23권1호
• /
• pp.27-30
• /
• 2013

Catalyst-free graphene nano-sheets without substrates have been synthesized using fullerene and a high direct current (dc) pulse in the spark plasma sintering (SPS) process. Graphene nano-sheets were synthesized directly in the gas phase of carbon atoms which are generated from fullerene at a temperature of $600^{\circ}C$. Characterization has been carried out by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).

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

• 한국분말재료학회지
• /
• 제7권3호
• /
• pp.149-153
• /
• 2000

In this study, the fabrication of $Al_2O_3$/5vol.%Cu nanocomposite and its mechanical property were discussed. The nanocomposite powders were produced by high energy ball milling of $Al_2O_3$ and Cu elemental powders. The ball-milled powders were sintered with Pulse Electric Current Sintering (PECS) facility. The relative densities of specimens sintered at $1200^{\circ}C$ and $1250^{\circ}C$ after soaking process at $900^{\circ}C$ were 96% and over 97%, respectively. The sintered microstructures were composed of $Al_2O_3$ matrix and the nano-sized Cu particles distributed on grain boundaries of $Al_2O_3$ matrix. The nanocomposite exhibited the enhanced fracture toughness compared with general monolithic $Al_2O_3$. The toughness increase was explained by the crack deflection and bridging by dispersed Cu particles.

• 한국재료학회지
• /
• 제11권5호
• /
• pp.378-384
• /
• 2001

본 연구에서는 기계적 합금화 공정을 통하여 평균 10nm의 크기를 가지는 결정립으로 이루어지는 나노구조 Fe-Co 합금분말을 제조하였으며 제조된 합금분말을 PECS 공정으로 소결하여 벌크의 나노구조 Fe-Co 연자성 합금을 제조하고자 하였다. PECS 공정은 소결온도를 700, 800, 900과 100$0^{\circ}C$로 변화시키고 유지시간을 0에서 16분가지 변화시켜주며 수행하였다. PECS 공정의 나노구조 소결체 제조에 관한 효율성을 평가하였으며 소결온도와 유지시간의 변화에 따른 소결밀도와 미세구조의 변화를 관찰하여 최적의 소결조건을 찾고자하였다. 또한 각 소결조건에서 제조된 소결체들의 보자력과 포화자화값을 측정하여 자성특성을 평가하였다.

• 한국재료학회지
• /
• 제12권8호
• /
• pp.656-660
• /
• 2002

It was investigated that $Al_2$$O_3$/Cu nanocomposite powder could be optimally prepared by dispersion and reduction of Cu oxide, and suitably consolidated by employing pulse electric current sintering (PECS) process. $\alpha$-$Al_2$$O_3$ and CuO powders were used as elemental powders. In order to obtain $Al_2$O$_3$ embedded by finely and homogeneously dispersed CuO particles, the elemental powders were high energy ball milled at the rotating speed of 900 rpm, with the milling time varying up to 10 h. The milled powders were heat treated at $350^{\circ}C$ in H$_2$ atmosphere for 30 min to reduce CuO into Cu. The reduced powders were subsequently sintered by employing PECS process. The composites sintered at $1250^{\circ}C$ for 5 min showed the relative density of above 98%. The fracture toughness of the $Al_2$$O_3$/Cu nanocomposite was as high as 4.9MPa.$m^{1}$2//, being 1.3 times the value of pure $Al_2$$O_3$ sintered under the same condition.

• 한국재료학회지
• /
• 제10권9호
• /
• pp.642-647
• /
• 2000

Ni-36at.%Al을 함유하는 나도 결정립의 NiAl 합금이 기계적 합금화법에 의해 제조되었다. 제조된 분말은 방전 플라즈마 소결법에 의해 만들어졌다. 상변테에 영향을 주는 인자는 냉각속도와 열처리 시간의 조건으로 논의되었다. 소결체의 상변태 거동은 시차 열분석(DSC)과 X-선 회절(XRD) 분석법에 의해 조사되었다. 미세구조는 주사전자현미경(SEM)으로 관찰되었다. 마르텐사이트 격사상수와 체적 분율은 X-선 회절분석법 중 직접비교법에 의해 계산되었다.

• 대한금속재료학회지
• /
• 제48권4호
• /
• pp.369-375
• /
• 2010

Ti-6Al-4V ELI alloy, which is commonly used as a biomaterial, is associated with a high elastic modulus and poor biocompatibility. This alloy presents a variety of problems on several areas. Therefore, the development of good non-toxic biocompatible biomaterials with a low elastic modulus is necessary. Particularly, hydroxyapatite (HA) is an attractive material for human tissue implantation. This material is widely used as artificial bone due to its good biocompatibility and similar composition to human bone. Many scientists have studied the fabrication of HA as a biomaterial. However, applications of bulk HA compact are hindered by the low strength of HA when it is sintered. Therefore, HA has been coated on Ti or Ti alloy to facilitate good bonding between tissue and the HA surface. However, there are many problems when doing this, such as the low bonding strength between HA and Ti due to the different thermal expansion coefficients and mechanical properties. In this study, a Ti-HA composite with a porous surface was successfully fabricated by pulse current activated sintering (PCAS) and a subsequent leaching process.