• 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.

• 폴리머
• /
• 제37권4호
• /
• pp.507-512
• /
• 2013

수분산 폴리우레탄(waterborne polyurethane; WPU)의 물리화학적/전기적 특성을 개선하기 위하여 그래핀에 이소시아네이트기를 도입하고 in-situ 방법으로 폴리우레탄을 중합하여 그래핀/WPU 나노 복합체를 제조하였다. 본 연구의 접근 방법으로 그래핀을 2 wt%까지 그래핀/WPU 나노 복합체에 도입하면 기존 WPU에 비해 인장강도가 57%, 전기전도도는 약 $10^2$배 정도 향상되는 결과를 얻었다. 또한 단순 블렌드 방법으로 만든 그래핀/WPU 복합체와 비교하였을 때, in-situ 중합 방법으로 제조된 복합체가 상대적으로 우수한 기계적 물성과 전기 전도도를 가졌다. 이것은 전자현미경을 이용한 복합체 단면의 형태학적 분석으로부터 이소시아네이트기가 개질된 그래핀(iGO)이 in-situ 중합 방법에 기인한 WPU 매트릭스와의 공유결합과 수소결합을 통하여 균일하게 분산되었기 때문이다.

• 한국세라믹학회지
• /
• 제51권5호
• /
• pp.386-391
• /
• 2014

Silicon nitride ($Si_3N_4$) is regarded as one of the most promising materials for high temperature structural applications due to its excellent mechanical properties at both room and elevated temperatures. However, one high-temperature $Si_3N_4$ material intended for use in radomes has a relatively high dielectric constant of 7.9 - 8.2 at 8 - 10 GHz. In order to reduce the dielectric constant of the $Si_3N_4$, an in-situ reaction process was used to fabricate $Si_3N_4-SiO_2$-BN composites. In the present study, an in-situ reaction between $B_2O_3$ and $Si_3N_4$, with or without addition of BN in the starting powder mixture, was used to form the composite. The in-situ reaction process resulted in the uniform distribution of the constituents making up the composite ceramic, and resulted in good flexural strength and dielectric constant. The composite was produced by pressure-less sintering and hot-pressing at $1650^{\circ}C$ in a nitrogen atmosphere. Microstructure, flexural strength, and dielectric properties of the composites were evaluated with respect to their compositions and sintering processes. The highest flexural strength (193 MPa) and lowest dielectric constant (5.4) was obtained for the hot-pressed composites. The strength of these $Si_3N_4-SiO_2$-BN composites decreased with increasing BN content.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
• /
• pp.67-70
• /
• 2000

Mechanical properties of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites fabricated by the reaction squeeze casting were compared with those of (15%$AI_20_3{\cdot}SiO_2$)/Al composites. Intermetallic compound formed by reaction between molten aluminum and reinforcing powder was uniformly distributed in the Al matrix. These intermetallic compounds were identified as $Al_3$NI using EDS and X-ray diffraction analysis. Microhardness and flexural strength of hybrid composites were higher than that of (15%$AI_20_3{\cdot}SiO_2$)/Al Composite. In-Situ fracture tests were Conducted on (15%$AI_20_3{\cdot}SiO_2$)/Al Composites and (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites to identify the microfracture process. It was identified from the in-situ fracture test of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al composites, microcracks were initiated mainly at the short fiber / matrix interfaces. As the loading was continued, the crack propagated mainly along the separated interfacial regions and the well developed shear bands. It was identified from the in-situ fracture test of (10%$AI_20_3{\cdot}SiO_2$+5%Ni)/Al hybrid composites, microcracks were initiated mainly by the short fiber/matrix interfacial debonding. The crack proceeded mainly through the intermetallic compound clusters

• 대한금속재료학회지
• /
• 제46권6호
• /
• pp.382-389
• /
• 2008

To manufacture Al MMCs, in-situ melt mixing process is used because it is free from contamination, and it makes reinforcements homogeneously dispersed. Large eddy simulation method is used to find the optimum melt mixing condition. At the Re 3000, the most suitable mixing is occurred between Al-Ti and Al- B melts. The in-situ formed $TiB_2$ particles has the size varying from 40 nm to 130 nm, due to the increase of cooling rate, and exhibits a homogeneous dispersion. And the interface between reinforcement and matrix is clean. Both hardness and Young's modulus of this composite are improved with increasing the cooling rate.

• Carbon letters
• /
• 제14권4호
• /
• pp.251-254
• /
• 2013

In this study, poly(amic acid) was prepared via a polycondensation reaction of 3,3'-dihydroxybenzidine and pyromellitic dianhydride in an N-methyl-2-pyrrolidone solution; reduced graphene oxide/polybenzoxazole (r-GO/PBO) composite films, which significantly increased the electrical conductivity, were successfully fabricated. GO was prepared from graphite using Brodie's method. The GO was used as nanofillers for the preparation of r-GO/PBO composites through an in situ polymerization. The addition of 50 wt% GO led to a significant increase in the electrical conductivity of the composite films by more than sixteen orders of magnitude compared with that of pure PBO films as a result of the electrical percolation networks in the r-GO during the thermal treatment at various temperatures within the films.

• Carbon letters
• /
• 제13권4호
• /
• pp.230-235
• /
• 2012

In this study, reduced graphene oxide/polyimide (r-GO/PI) composite films, which showed significant enhancement in their electrical conductivity, were successfully fabricated. GO was prepared from graphite using a modified Hummers method. The GO was used as a nanofiller material for the preparation of r-GO/PI composites by in-situ polymerization. An addition of 20 wt% of GO led to a significant decrease in the volume resistivity of composite films by less than nine orders of magnitude compared to that of pure PI films due to the electrical percolation networks of reduced GO created during imidization within the films. A tensile test indicated that the Young's modulus of the r-GO/PI composite film containing 20 wt% GO increased drastically from 2.3 GPa to 4.4 GPa, which was an improvement of approximately 84% compared to that of pure PI film. In addition, the corresponding tensile strength was found to have decreased only by 12%, from 113 MPa to 99 MPa.

• 대한기계학회논문집A
• /
• 제38권6호
• /
• pp.629-636
• /
• 2014

비정질합금이 가지고 있는 우수한 기계적 성질과 화학적 특성을 부품소재에 표면개질을 목적으로 고속화염 용사법으로 대면적 코팅층을 형성하였고 내열성이 높은 자융성합금과 초경합금 성분들을 적절히 혼합하여 비정질기지 복합재료를 제조하여 코팅들의 미세조직 관찰과 나노인덴테이션을 이용한 미세표면의 기계적 거동을 분석하였다. 각 코팅층의 미세조직을 관찰한 결과, 단일상 비정질 코팅에는 미용융 입자와 lamellae 영역이 존재하고 자융성합금이 고용된 복합재에는 in-situ $Cr_2Ni_3$ 석출물, 자융성합금과 초경합금성분이 함께 혼합된 코팅층은 석출물과 ex-situ WC 강화입자가 공존하였다. 이들 미세표면의 기계적 거동은 제 2 상이 고용된 비정질 기지 복합재의 코팅층의 기계적 특성이 전체적으로 향상되었다.

• 한국의류학회지
• /
• 제23권2호
• /
• pp.326-334
• /
• 1999

Polyaniline(PAn)-nylon 6 composite fabrics were prepared by immersing the nylon 6 fabrics in 100% distilled aniline for specified diffusion time and drawn out. Then the excess aniline on the fabric surface was blotted and successive polymerization was initiate by immersing them into oxidant and dopant solution for in situ polymerization of polyaniline. Consequently highly conductive PAn-nylon 6 composite fabrics could be obtained and the conductivity reaches as high as 10-2 S/cm. The maximum conductivity was obtained when the fabric was immersed in 100% aniline at 4$0^{\circ}C$ for 3hours and polymerization was proceeded in 0.25M ammonium peroxydisulfate solution at 5$^{\circ}C$ for 1hour.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2001년도 춘계학술대회 논문집
• /
• pp.443-450
• /
• 2001

This paper shows the reduction effect of tile earthquake-induced liquefaction potential of soils that improved by Vibro-Replacement Stone Columns. The Vibro-Replacement Stone Columns method transforms soft cohesive soils into a composite mass of compacted granular or crushed stone columns by using vibrating equipment and water jets. This study investigated and analyzed the behavior of the stone columns and composite ground using the results of in situ test and measurement at the job-site. This paper shows the evaluation of the earthquake-induced liquefaction potential of soils using in situ test. There are different types of in situ test used in the evaluation the liquefaction potential. In the particular study the Standard penetration test, and Cone penetration test were used. The N value of Standard Penetration test has been used all over for a very long time. The evaluation of the liquefaction of soil was performed using the worldwide renewed Cone penetration test