• 보존과학회지
• /
• 제18권
• /
• pp.33-50
• /
• 2006

영산강유역이라는 지역적 연계성을 가진 영광 군동, 무안 인평고분군, 무안 구산리고분군, 함평 국산유적에서 출토된 유물 중 백제식 묘제인 횡혈식석실분 출현 이전으로 편년되는 철기유물 6점을 선정하여 미세조직을 분석하였다. 분석 결과, 고대 영산강유역에서는 저온환원법에 의해 괴련철을 생산하는 기술이 주를 이루고 있었으며, 아울러 탄소를 제거시켜 강소재를 생산하는 기술체계가 이루어졌을 가능성도 확인되었다. 또한 강도를 필요로 하는 부위에만 담금질을 함으로써 높은 강도를 가짐과 동시에 담금질 조직이 가지는 취성을 담금질이 안된 부위에 분산시켜 철기가 깨지는 것을 방지하고 인성을 부여하는 기술이 이루어지고 있었다고 생각된다. 이러한 기술은 2세기대로 편년되는 영광 군동 출토 철부 미세구조에서 확인되고 있어 높은 기술체계를 가진 집단이 2세기 이전에 존재하고 있었고 5세기 말까지 이어졌을 가능성이 높다고 판단된다. 낮은 탄소함량의 괴련철로 철기를 제작하는 경우 성형-침탄-열처리-단타를 반복적으로 행하는 제작 공정이 이루어진 것으로 보인다.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.620-625
• /
• 2002

Considering the fuel consumption of car, a light structure of aluminum alloys is desired for car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. ill the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6N01 alloy welds. Aluminum alloy plate of 2.0mm in thickness with filler metal bar was welded by twin beam Nd:YAG laser facility (total power:5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 l/min was used. The defocusing distance is kept at 0 mm. At travel speeds of 3 to 9 m/min and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.

• 대한화학회지
• /
• 제42권6호
• /
• pp.599-606
• /
• 1998

산화물 초전도체 발견 후 많은 이론적 발전이 있었으나, 초전도 상전이를 정확히 설명하는 이론은 아직 없다 하겠다. 특히 상전이점 근처에서 발견되는 이중전이(double transition)나 다양한 자기적 상전이에 대해서는 아직 정확한 이해가 없는 상태이다. 본 논문에 서는 전자유체의 응축모델을 사용하여 초전도 전이에 있어서, 전자기체의 응축과정이 CONFINEMENT와 TRAP의 두 단계로 일어남을 알았다. 이 두 단계 전이 메카니즘은 이중전이를 잘 설명할 뿐만 아니라, 여러 형태의 초전도에서 보이는 자기적 성질, 특히 다양한 vortex structure를 보여주는 magnetic phase transition을 잘 설명할 수 있었다. 여러 종류의 초전도체들에서 공통적으로 발견되는 double transition과 다양한 magnetic phase transition을 잘 설명할 수 있는지 여부가 초전도 현상 설명의 일반이론으로 적합한지를 결정할 것이다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
• /
• pp.226-229
• /
• 2004

A stoichiometric mixture of evaporating materials for $CuAlSe_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CuAlSe_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $680^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuAlSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.24{\times}10^{16}\;cm^{-3}$ and $295\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuAlSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;=\;2.8382\;eV\;-\;(8.68{\times}10^{-4}\;eV/K)T^2/(T+155K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $CuAlSe_2$ have been estimated to be 0.2026 eV and 0.2165 eV at 10K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_5$ states of the valence band of the $CuAlSe_2$. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.

• 한국주조공학회지
• /
• 제17권2호
• /
• pp.170-179
• /
• 1997

A noble technique has been developed for fabricating in situ formed $TiC_p/Al$ composites. In this process, fairly stable TiC particles were in situ synthesized in liquid aluminum by the interfacial reaction between an Al-Ti melt and SiC, which is a comparatively unstable carbide from the view-point of thermodynamics. It is possible in the present process to generate TiC particles of nearly 1 ${\mu}m$ in diameter, even utilizing SiC of 14 ${\mu}m$ as raw material. However, the dispersion behavior of TiC particles in the matrix depends on the size of the raw material SiC. Decomposing finer SiC makes the dispersion of TiC particles more uniform and the mechanical properties of composites are improved accordingly. The structure of in situ composites and their mechanical properties are affected by the fabrication temperature and the stirring time. It has been found that the most suitable condition for fabrication should be applied depending on the size of the raw material, even if the same kinds of carbide are used. Furthermore, although Al-Ti-Si system intermetallic compounds are detected in a $TiC_p/Al-Si$ composite which is fabricated by conventional melt-stirrng method, these compounds can not be observed in a $TiC_p/Al-Si$ composite made by this in situ production method. Hence the mechanical properties of the in situ $TiC_p/Al-Si$ composite are superior to those of the conventional $TiC_p/Al-Si$ composites.

• 한국재료학회지
• /
• 제23권6호
• /
• pp.339-343
• /
• 2013

Porous Ti-systems with unidirectionally aligned channels were synthesized by freeze-drying and a heat treatment process. $TiH_2$ powder and camphene were used as the source materials of Ti and sublimable vehicles, respectively. Camphene slurries with $TiH_2$ content of 10 and 15 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$ while unidirectionally controlling the growth direction of the camphene. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was heat-treated at $1100^{\circ}C$ for 1 h in a nitrogen and air atmosphere. XRD analysis revealed that the samples composed of TiN and $TiO_2$ phase were dependent on the heat-treatment atmosphere. The sintered samples showed large pores of about 120 mm which were aligned parallel to the camphene growth direction. The internal wall of the large pores had relatively small pores with a dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry. These results suggest that a porous body with an appropriate microstructure can be successfully fabricated by freeze-drying and a controlled sintering process of a camphene/$TiH_2$ slurry.

• International Journal of Korean Welding Society
• /
• 제2권2호
• /
• pp.26-31
• /
• 2002

Considering the fuel consumption of car, a light structure of aluminum alloys is desired fer car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. In the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6NO 1 alloy welds. Aluminum alloy plate of 2.Omm in thickness with filler metal bar was welded by twin beam Nd: YAG laser facility (total power: 5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 1/min was used. The defocusing distance is kept at 0 mm. At travel speeds off 3 to 9 and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.

• 한국재료학회지
• /
• 제4권2호
• /
• pp.136-142
• /
• 1994

초청장 Si(111)기탄상에 초고진공 챔버에서 Ti을 증착하여 $TiSi_{2}$를 에피층으로 성장시켰다. 재구성된 (reconstructed) Di(111)표면에 상온에서 50$\AA$ 두께의 Ti을 증착한 후 $100^{\circ}C$간격으로 $800^{\circ}C$까지 열처리 하였다. $TiSi_{2}$박막의 구조는 전자회절 패턴 분석을 통하여 준안정상인 C49상임을 확인하였다. SEM 사진은 세가지 형태의 island를 보이고 있다. 각 island 는 단결정이며 그 구조는 서로 다른 결정학적 방향을 갖는 에피구조이다. 이러한 TiSi$_{2}$ island[112]C49 TiSi$_{2}$/[110]Si, (021) C49 $TiSi_{2}$/(111)Si의 방향관계를 가지고 있다.

• 한국재료학회지
• /
• 제25권11호
• /
• pp.602-606
• /
• 2015

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of $WO_3$ and spherical PMMA of 20 vol% were frozen at $-25^{\circ}C$ and dried for the sublimation of the camphene. The green bodies were heat-treated at $400^{\circ}C$ for 2 h to decompose the PMMA; then, sintering was carried out at $1200^{\circ}C$ in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about $400^{\circ}C$, and $WO_3$ was reduced to metallic W at $800^{\circ}C$ without any reaction phases. The sintered bodies with $WO_3$-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.

• 한국분말재료학회지
• /
• 제21권3호
• /
• pp.202-206
• /
• 2014

Leaching of MOCVD dust in the LED industry is an essential stage for hydro-metallurgical recovery of pure Ga and In. To recover Ga and In, the leaching behavior of MOCVD scrap of an LED, which contains significant amounts of Ga, In, Al and Fe in various phases, has been investigated. The leaching process must be performed effectively to maximize recovery of Ga and In metals using the most efficient lixiviant. Crystalline structure and metallic composition of the raw MOCVD dust were analyzed prior to digestion. Subsequently, various mineral acids were tested to comprehensively study and optimize the leaching parameters such as acidity, pulp density, temperature and time. The most effective leaching of Ga and In was observed for a boiling 4 M HCl solution vigorously stirred at 400 rpm. Phase transformation of GaN into gallium oxide by heat treatment also improved the leaching efficiency of Ga. Subsequently high purity Ga and In can be recovered by series of hydro processes.