• 한국세라믹학회지
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• 제31권12호
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• pp.1513-1520
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• 1994

Mechanical properties of hot-pressed SiC whisker/Al2O3 composites were strongly dependent on the granular characteristics of mixed powder, which were controlled by co-dispersion condition, the existence of steric barrier on whisker surface, and granulating method, etc. Heat-treatment of SiC whiskers at $700^{\circ}C$ for 1 hr in air was very effective both for achieving dispersion stability of whiskers with PVA adsorption and for obtaining excellent mechanical properties of resulting composites. It is believed from the fractography of composites prepared with various whisker dispersion conditions that the most common fracture origin of Al2O3 agglomerate could be attributed to whisker clusters arising due to flocculation. Further improvement of mechanical properties of composites were achieved by hot pressing green tapes prepared by Doctor-blade process, which promoted two-dimensional random alignment of whiskers.

• 한국분말재료학회지
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• 제10권3호
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• pp.168-171
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• 2003

Interpenetrating phase composites of $TiB_2$-Cu system were produced via Spark-Plasma Sintering (SPS) oi nanocomposite powders. Under simultaneous action of pressure, temperature and electric current titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a fine-grained skeleton. Increasing SPS-temperature and he]ding time promote densification due to local melting of copper matrix When copper melting is avoided the compacts contain 17-20% porosity but titanium diboride skeleton is still formed representing the feature of SPS . High degree of densification and formation of titanium diboride network result in increased hardness of high-temperature SPS-compacts.

• 자원리싸이클링
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• 제11권4호
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• pp.3-10
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• 2002

핵연료 원료인 $UO_2$ 분말을 사용해 원자로에서 연소된 사용후 핵연료 소결체를 모의 제조하여 1회 산화ㆍ환원처리하여 분말로 만든 후, 건ㆍ습식 attrition 분쇄에 따른 분말의 특성 및 소결성을 조사하였다. 분쇄에 의한 분말의 평균입자크기는 건식분쇄의 경우에는 1 $mu extrm{m}$ 이하인 미분말이 쉽게 생성되었으나, 습식분쇄에서는 그 이상의 분말만이 생성되었다. 그리고 분쇄분말의 비표면적은 건식분쇄한 경우가 습식분쇄한 경우 보다 높았다. 분말의 미세구조는 건식분쇄에 의해서는 느슨한 응집체가 형성되었으며, 습식분쇄 분말은 압분성이 낮은 불규칙적이고 각진 입자형태를 나타내었다. 건식분쇄에 의해서 압분체 밀도는 크게 증가하며 소결체 요구 조건을 만족하는 이론밀도의 95%이상이 되고 평균 결정립 크기가 8 $\mu\textrm{m}$이상인 소결체를 얻을 수 있었다.

• 한국분말재료학회지
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• 제10권6호
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• pp.443-447
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• 2003

Nano-sized $TiB_2$ was in situ synthesized in copper matrix through self-propagating high temperature synthesis (SHS) with high-energy ball milled Ti-B-Cu elemental mixtures as powder precursors. The size of $TiB_2$ particles in the product of SHS reaction decreases with time of preliminary mechanical treatment ranging from 1 in untreated mixture to 0.1 in mixtures milled for 3 min. Subsequent mechanical treatment of the product of SHS reaction allowed the $TiB_2$ particles to be reduced down to 30-50 nm. Microstructural change of $TiB_2$-Cu nanocomposite during spark plasma sintering (SPS) was also investigated. Under simultaneous action of pressure, temperature and electric current, titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a interpenetrating phase composite with a fine-grained skeleton.

• 한국세라믹학회지
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• 제28권4호
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• pp.315-323
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• 1991

The preparation of zirconium carbide powders by the halogenide process of ZrCl4-C-Mg system (1:1:2, molar ratio) was studied between 300。 and 120$0^{\circ}C$ under Ar gas flow (200 mι/min). The formation mechanism and kinetics of zirconium carbide and characteristics of the synthesized powder were examined by TG-DTA, XRD, SEM and PSA. 1) The formation mechanism of zirconium carbide were as follows, above 30$0^{\circ}C$ ZrCl4(S)+Mg(s)longrightarrowZrCl2(s)+MgCl2(s) above 40$0^{\circ}C$ ZrCl2(S)+Mg(s)longrightarrowZr(s)+MgCl2(s) above 50$0^{\circ}C$ Zr(s)+C(s)longrightarrowZrC(s) 2) The apparent activation energy of the reduction-carbonization at temperature of 800$^{\circ}$to 100$0^{\circ}C$ was 11.9 kcal/mol. 3) The lattice parameter and the crystallite size of ZrC which was produced from the mixture powder of ZrCl4, C and Mg (1:1:2, molar ratio) at 100$0^{\circ}C$ for 1 h were 4.700A and 180A, respectively. 4) The powders obtained from the mixture powder of ZrCl4, C and Mg(1:1:2, molar ratio) at 100$0^{\circ}C$ for 1 h were agglomerate with the average size of about 13${\mu}{\textrm}{m}$ in SEM micrograph.

• 한국분말재료학회지
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• 제19권1호
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• pp.13-18
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• 2012

This study has been performed on the full density sintering of Fe nanopowder and the surface hardening by plasma ion nitriding. The Fe sintered part was fabricated by pressureless sintering of the Fe nanopowder at $700^{\circ}C$ in which the nanopowder agglomerates were controlled to have 0.5-5 ${\mu}m$ sized agglomerates with 150 nm Fe nanopowders. The green compact with 46% theoretical density(T.D.) showed a homogeneous microstructure with fine pores below 1 ${\mu}m$. After sintering, the powder compact underwent full densification process with above 98%T.D. and uniform nanoscale microstructure. This enhanced sintering is thought to be basically due to the homogeneous microstructure in the green compact in which the large pores are removed by wet-milling. Plasma ion nitriding of the sintered part resulted in the formation of ${\gamma}$'-$Fe_4N$ equilibrium phase with about 12 ${\mu}m$ thickness, leading to the surface hardening of the sintered Fe part. The surface hardness was remarkably increased from 176 $H_v$ for the matrix to 365 $H_v$.

• Journal of information and communication convergence engineering
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• 제7권1호
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• pp.72-77
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• 2009

Three different procedures for adding Pd compounds to $SnO_2$ particles have been investigated. These processes are: (1) coprecipitation; (2) dried powder impregnation; and (3) calcined powder impregnation. The microstructures of $SnO_2$ particles have been analyzed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). In the coprecipitaion method, the process does not restrain the growth of $SnO_2$ particles and it forms huge agglomerates. In the dried powder impregnation method, the process restrains the growth of $SnO_2$ particles and the surfaces of the agglomerates have many minute pores. In the calcined powder impregnation method, the process restrains the growth of $SnO_2$ particles further and the agglomerates have a lot more minute pores. The sensitivity ($S=R_{air}/R_{gas}$) of the $SnO_2$ gas sensor made by the calcined powder impregnation process shows the highest value (S = 21.5 at 5350 ppm of $C_3H_8$) and the sensor also indicates the lowest operating temperature of around $410^{\circ}C$. It is believed that the best result is caused by the plenty of minute pores at the surface of the microstructure and by the catalyst Pd that is dispersed at the surface rather than the inside of the agglomerate. Schematic models of Pd distribution in and on the three different $SnO_2$ particles are presented.

• Applied Microscopy
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• 제32권4호
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• pp.311-317
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• 2002

입자 크기에 따라 상전이 경로가 달라지며 매우 큰 응집체로 존재하는 gibbsite 분말과 같은 재료의 정량적인 전이 구조 분석의 전제로서 입자 크기가 선택적인 TEM 시편의 준비가 절실히 요구된다. 입자 크기 선택성을 실현한 TEM 시편 준비의 방법론을 확립하기 위한 방안으로서 본 실험이 전개되었다. 약 1 wt%의 gibbsite 원료 분말을 에탄올 용매에 혼합 한 뒤, ball-milling에 의해 조분쇄 처리를 하고 증류수에 1 : 19의 비로 희석된 분산 조제, Darvan C, 0.25 vol%의 첨가와 함께 ultrasonic 처리를 하여 gibbsite suspension을 만들었다. 제조된 gibbsite suspension의 누적 농도 변화 관찰에 의한 침강 시간의 조정 후 정적 침강 분리에 의해 nm 크기별로 분리된 TEM 시편을 만들 수가 있었다. 시편의 전체적인 양상은 SEM으로 관찰하였고 개개 입자들의 morphology 는 TEM으로 분석하였다. 또한, 공정 과정 중의 상변화 가능성을 검토하기 위해 XRD 분석을 실시하였다.

• 한국세라믹학회지
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• 제25권5호
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• pp.473-478
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• 1988

In order to obtain the high purity $\beta$-SiC powder that possesses the excellent sinterability and is close to the spherical shape, the carbon black was mixed into the composition of Si(OC2H5)4-H2O-NH3-C2H5OH which the monodispersed spherical fine particles is formed the hydrolysis of Ethylsilicate and the mixture was carbonized under an argon atmosphere. Particle shpae, size and the yield of $\beta$-SiC powder were investigated according to the molar ratio of carbon/alkoxide and variations of reaction temperature and reaction time. The results of this study are as follow ; 1) The yield of $\beta$-SiC gained from the reaction for one hour at 150$0^{\circ}C$ almost got near 100% and the particle size of $\beta$-SiC from the reaction for 15 hrs at 150$0^{\circ}C$ was 0.2${\mu}{\textrm}{m}$ on the average and close to the spherical shape agglomerate state. 2) When the molar ratio carbon/alkoxide is over 3.1 and the reaction occurs at 145$0^{\circ}C$ for 5hrs, the carbon content has not an effect on the kind of crystal of product.

• 한국분말재료학회지
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• 제11권4호
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• pp.294-300
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• 2004

This study for preparation of aluminum nitride (AlN) with high purity was carried out by self-propagating high-temperature synthesis method in two different systems, $Al-N_{2}$ and $Al-N_{2}$-AlN, with the change of nitrogen gas pressure and dilution factor. On the occasion of $Al-N_{2}$ system, unreacted aluminum was detected in the product in spite of high nitrogen pressure, 10 MPa, This may be caused by obstructing nitrogen gas flow to inner part of molten and agglomerate of aluminum, formed in pre-heating zone. In $Al-N_{2}$-AlN system, AlN with a purity of 95% or ever can be prepared in the condition of $f_{Dil}\geq0.5$, $P_{N_{2}}\geq$ 1 MPa, and the purity can be elevated to 98% over in the condition of $f_{Dil}$ = 0.7 and $P_{N_{2}}$ = 10 MPa.