• 한국세라믹학회지
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• 제34권8호
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• pp.854-860
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• 1997

The tribological property of ceramics is very important for use in seal rings, pump parts, thread guides and mechanical seal, etc. In the present study, which RBSC/graphite composites were manufactured by adding graphite powders with different particle sizes to mixtures of SiC powder, metallic silicon, carbon black and alumina, effects on the tribological property of each RBSC/graphite composite was investigated in accordance with the particle size of the added graphite powder. The water absorption, the bending strength and the resistance for the friction and wear were measured, and the crystalline phase and the microstructure were respectively examined by using XRD and SEM. In case that the particle size of the graphite powder was fine(2${\mu}{\textrm}{m}$), the formation of $\beta$-SiC was accelerated, thereby making the increase of the bending strength and the decrease of the water absorption, but no improvement for the tribological properties. Furthermore, in case that the particle size of the graphite powder was some large(88~149${\mu}{\textrm}{m}$), the formation of $\beta$-SiC was not accelerated, to thereby make the decrease of the bending strength and the increase of the water absorption, but the improvement for the tribological property of only the composite having the graphite powder of 20 vol%. In addition, in case that the particle size distribution of the graphite powder was large (under 53 ${\mu}{\textrm}{m}$), there was no improvement for every properties. However, the composites, which the graphite powder with the particle size of 53~88 ${\mu}{\textrm}{m}$ was added in 10~15 vol%, had the most increased resistance for the friction and wear which show the worn out amount of 0.4~0.6$\times$10-3 $\textrm{cm}^2$, and the value of the bending strength is 380~520 kg/$\textrm{cm}^2$.

• Bulletin of the Korean Chemical Society
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• 제31권1호
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• pp.47-51
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• 2010

A powder, containing 80 percent of blue cobalt aluminate $(CoAl_2O_4)$ crystallites, was synthesized at $210 ^{\circ}C$ using a (metal nitrate-malonic acid-ammonium hydroxide-ammonium nitrate) system. The optimal amount of concentrated ammonia water and initial decomposition temperature were determined for the blue $CoAl_2O_4$ crystallites preparation. Three $CoAl_2O_4$ precursor pastes, corresponding to the various amounts of concentrated ammonia water, were prepared by evaporating the initial solutions in an electric furnace fixed at $80 ^{\circ}C$ under a vacuum of 25 torr. The initial solution was used to dissolve the starting materials. The powder with the maximum content (80%) of blue $CoAl_2O_4$ crystallites was prepared when the prepared precursor was decomposed at $210 ^{\circ}C$. The blue $CoAl_2O_4$ crystallite content in the prepared sample decreased with increasing initial decomposition temperature. For 0.2 mole of the $Al^{3+}$ ion, the chemical compositions of the precursor corresponded to molar ratios of 0.4, 1.40, 2.56 and 2.00 for the $Co^{2+}$ ion, malonic acid, ammonia and ammonium nitrate per mole of the $Al^{3+}$ ion, respectively. The blue $CoAl_2O_4$ crystallite content in the sample decreased with the amount of ammonia deviated from the optimal value. The characteristics of the powders were examined using X-ray diffraction, optical microscopy, Fourier transformation infrared spectroscopy and the Brunauer-Emmett-Teller technique.

• 한국재료학회지
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• 제23권2호
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• pp.135-142
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• 2013

The Ti-6Al-4V extra low interstitial (ELI) alloy has been widely used as an orthopedic implant material because of its excellent mechanical properties and biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity of the Al and V elements. Therefore, non-toxic biomaterials with a low elastic modulus need to be developed. A high energy mechanical milling (HEMM) process is introduced to improve the effect of sintering. Rapid sintering of spark plasma sintering (SPS) under pressure was used to make an ultra fine grain of Ti-25 wt.%Nb-7 wt.%Zr-10 wt.%Mo-(10 wt.%CPP) composites with bio-attractive elements for increasing strength. These composites were fabricated by SPS at $1000^{\circ}C$ at 60 MPa using HEMM powders. During the sintering process, $CaTiO_3$, TixOy, and CaO were formed because of the reaction between Ti and CPP. The effects of CPP content on the physical and mechanical properties of the sintered Ti-Nb-Zr-Mo-CPP composites were investigated. The biocompatibility and corrosion resistance of the Ti-Nb-Zr-Mo alloys were improved by the addition of CPP.

• 한국분말재료학회지
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• 제25권5호
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• pp.408-414
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• 2018

This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are $1{\pm}0.5%$ for all three specimens. Microstructural analysis confirms the formation of second carbide phases of $W_2C$, $Co_6W_6C$, and $Cr_7C_3$ owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of $W_2C$ phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the $Cr_3C_2-20CrNi$ coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of $Cr_3C_2-20NiCr$, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide-binder and binder-binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.

• 한국세라믹학회지
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• 제38권5호
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• pp.405-411
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• 2001

Compacts of a mixture of fine $\alpha$-Si$_3$N$_4$powders, 6% $Y_2$O$_3$and 1% $Al_2$O$_3$were attrition milled time on phase and microstructural development in silicon nitride ceramics. The sintered surface and the interior showed different behaviors in phase and microstructral developments. Increased oxygen content with increased milling time of powder mixture leads to the formation of Si$_2$$N_2$O phase at temperatures as low as 155$0^{\circ}C$. Si$_2$$N_2$O is stable in the interior of the samples but unstable in the surface region of the specimen sintered at higher temperature. This results in a duplex structure where the interior consists of Si$_2$$N_2$O grains dispersed in $\beta$-Si$_3$N$_4$matrix and a surface which contains only $\beta$-Si$_3$N$_4$. The alpha to beta phase transformation and the microstructural development are shown to be influenced by the formation and decomposition of the Si$_2$$N_2$O.

• 한국세라믹학회지
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• 제36권1호
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• pp.7-14
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• 1999

SHS 마이크로파를 이용하여 티타늄, 지르코니움과 보론분말을 혼합하여 TiZrB2 고용체를 합성된 분말의 분말특성과 소결체의 소결특성을 연구하였다. 합성 중 온도 profile 결과 연소온도와 연소속도는 Zr의 몰비가 증가함에 따라 증가 하였으며, Ti0.2Zr0.8B2조서에서 연소온도와 연소속도는 285$0^{\circ}C$, 14.6m/sec로 최고값을 얻었다. 190$0^{\circ}C$에서 30 MPa의 압력으로 60분간 고온가압소결한 TiZrB2고용체는 TiB2와 ZrB2로 상분리가 최고값을 얻었다. 190$0^{\circ}C$에서 30MPa의 압력으로 60분간 고압가압소결한 TiZrB2 고용체는 TiB2와 ZrB2로 상분리가 일어나 복합체가 형성되었으며, Ti0.8Zr0.2B2에서 가장 좋은 물성값을 나타내었는데 상대밀도, 꺽임강도, 파괴인성 및 경도는 각각 99%, 680MPa, 7.3MPam1/2, 2750Kg/$ extrm{mm}^2$이었다.

• 한국세라믹학회지
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• 제43권12호
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• pp.781-787
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• 2006

NiO-coated YSZ powder was prepared using heterogeneous precipitation of Ni hydroxides on YSZ particle surface and high energy milling. The powders were characterized by TG/DTA, XRD, XPS, and SEM. Amorphous Ni precipitate completely decomposed into NiO at $500^{\circ}C$ and the growth of NiO crystallites was constrained by the core particles. Nanocrystalline NiO-coated YSZ core-shell structure powder could be obtained after calcination at $800^{\circ}C$ for 2 h. A core-shell powder compact, due to high sinterability, showed a near theoretical density at $1350^{\circ}C$. After reduction at $900^{\circ}C$, interpenetrating Ni-YSZ microstructure with very uniformly distributed fine Ni and YSZ grains and pores was observed. In contrast, the mechanically mixed oxide sample showed less uniform distribution of pores and larger discontinuous We particles as compared with the core-shell samples.

• 한국세라믹학회지
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• 제27권8호
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• pp.991-1003
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• 1990

A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent, various types of metal hydroxides were obtained by single precipitation(series A) and co-precipitation(series B) method at the pH condition between 7 and 11. Fine Al2O3-ZrO2 powders were prepared at optimum calcination condition and the effects of ZrO2 on microstructures and mechanical properties of Al2O3 were investigated. The composition of Al2O3/ZrO2 composites wax fixed as Al2O3-15 v/o ZrO2(＋3m/o Y2O3). ZrO2 limited the grain growth of Al2O3 and increased grain size homogeneity of Al2O3 more effectively than MgO.Flexural strength values in Al2O3 and Al2O3/ZrO2 composites were 340-430 MPa and 540-820 MPa, respectively, and the effect of strength improvement showed 20-50% by adding ZrO2 to Al2O3. Fracture toughness of Al2O3/ZrO2 composites was improved by stress-induced phase transformation of tetragonal ZrO2 and toughening effect by microcrack was not observed. Also, ZrO2 particles located at Al2O3 grain junction contributed to toughening, while spherical ZrO2 particles located within Al2O3 grain did not contribute to toughening. Weibull moduli of Al2O3 ceramics and Al2O3/ZrO2 composites of series A and series B were 4.34, 5.17 and 9.06, respectively. Above 0.5 of failure probability, strength values in Al2O3 ceramics and Al2O3/ZrO3 composites of series A and series B were above 400 MPa, 700 MPa and 650 MPa, respectively.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.791-795
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• 2016

The effects of $TiO_2$ addition on the electrical insulation of AlN ceramics with 1 wt% $Y_2O_3$ as a sintering aid have been investigated. Some of $TiO_2$ has reacted with AlN powders and transformed to fine TiN particles during sintering, which was uniformly dispersed along grain boundaries of AlN. At a high electrical field (500 V/mm), the resistivity of AlN ceramics with $TiO_2$ addition of 0.2 wt% increased about 1000 times from $3{\times}10^{10}{\Omega}cm$ to $3.1{\times}10^{13}{\Omega}cm$. Based on the impedance spectroscopy measurement, it was found that $TiO_2$ addition increased dramatically electrical resistivity of AlN grains much more than that of grain boundaries. Thus, $TiO_2$ was believed to dissolve inside AlN grains to suppress ionic conduction of Al vacancies. This suppressed ionic conduction by Ti incorporation into AlN grains seems to contribute to more electrically insulating AlN ceramics.

• 자원리싸이클링
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• 제16권6호
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• pp.10-19
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• 2007

폐리튬이온전지의 리싸이클링을 위하여 폐전지의 기계적 처리에 의한 Co의 농축과 습식처리에 의한 Co의 회수기술이 개발되었다. 전 연구에서는 폐전지 리싸이클링의 부가가치를 향상시키기 위하여 Co 농축 침출액으로부터 양극활물질을 재합성하는 공정으로 citrate precursor combustion법을 제안하고 가능성을 확인하였다. 기존의 전극제조 공정에서는 활물질인 $LiCoO_2$와 첨가제인 탄소의 비중 및 크기 차이로 균일한 혼합이 이루어지지 않으므로 충방전 용량이 이론용량에 비하여 매우 낮고 또한 싸이클이 반복될수록 용량이 크게 감소하는 경향을 보였다. 본 연구에서는 합성된 $LiCoO_2$ 전극특성을 향상시키는 일환으로 합성공정의 개선을 통하여 초미립 $LiCoO_2$을 합성하였으며, 탄소 첨가시 혼합법의 개선에 의하여 우수한 충방전 특성을 갖는 리튬전지용 양극을 개발하였다.