• 열처리공학회지
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• 제14권1호
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• pp.1-7
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• 2001

A method to simultaneously synthesize and consolidate the silicide $NiSi_2$ and the composite $NiSi_2$-20vol.%Nb from powders of Ni, Si, and Nb was investigated. Combustion synthesis was carried out under the combined effect of an electric field and mechanical pressure. The final density of the products increased nearly linearly with the applied pressure. Highly dense $NiSi_2$ and $NiSi_2$-20vol.%Nb with relative densities of up to 97% were produced under the simultaneous application of a 60MPa pressure and a 3000A current on the reactant powders. The respective Vickers microhardness values for these materials were 6.0 and 5.8 GPa. From indentation crack measurements, the fracture toughness values for $NiSi_2$ and $NiSi_2$-20vol.%Nb were calculated to be 3.3 and 4.7 $MPa{\cdot}m^{1/2}$, respectively.

• Journal of Welding and Joining
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• 제15권4호
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• pp.166-177
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• 1997

The high strength AlZnMgCu0.5 alloy is a light metal with good age hardenability, and has a high tensile and yielding strength. Therefore, it can be used for structures requiring high speciple strength. Even though high strength AlZnMgCu alloy has good mechanical properties, it has a lot of problems in TIG and MIG welding processes. Since lots of high heat absorption is introduced into the weldment during TIG and MIG processes, the microstructural variation and hot cracks take place in heat affected zone. Therefore, the mechanical properties of high strength AlZnMgCu0.5 alloy can be degraded in weldment and heat affected zone. Welding process utilizing high density heat source such as electron beam should be developed to reduce pore and hot cracking, whichare usually accompanied by MIG and TIG welding processes. In this work, electron beam welding process were used with or without AlMg4.5Mn as filler material to avoid the degradation of mechanical properties. Mechanical and metallurgical characteristics were also studied in electron beam weldment and heat affected zone. Moreover hot cracking mechanism was also investigated.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마연구회
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• pp.85-88
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• 2003

In this study, porcelain insulator samples which have a different alumina composition were manufactured in order to test electrical and mechanical properties and make an analysis of the propagation phenomena of micro cracks on porcelain body. From XRD quantitative analysis the crystalline phases were different with alumina composition, sample C and D which have about 17wt% Corundum phase without the Cristobalite phase shows better electrical and mechanical properties than sample A and 8 which have the Cristobalite phase. In dielectrics test on porcelain samples with below 17wt% alumina composition, it was found that the amount of glass phase$(SiO_2)$have an main effect to decrease the dielectric loss$(tan{\delta})$, and the dielectric breakdown voltage of aluminous porcelain insulators was largely affected by its relative density. As a micro cracks analysis, HRS were measured, then the intensity of HRS increased with the amount of alumina composition. On the other hand, the propagation behaviors of cracks was fairly influenced by the distribution of pores.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.209-209
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• 2003

The adventages of Li alloys have attracted the attention of many research groups, many of which have investigated tin-based alloys [1-2], Despite interesting performances of these, the irreversible capacity loss systematically observed on the first cycle for these compounds is a main drawback for their use as anode materials in lithium ion cells. Not only Sn is efficient in forming alloys with Li, Si can also react with Li to form alloys with a high Li/Si ratio, like Li$\_$22/Si$\_$5/ at 400$^{\circ}C$. It corresponds to a capacity of 4200mAh/g. Electrochemical Li-Si reaction occurs between 0 and 0.3 V against Li/Li$\^$+/, so that high-energy density battery can be realized. Despite the high theoretical capacity of elements like Si, however, particles of the alloys crack and fragment due to the repeated alloying and do-alloying which occurs as cell are charged and discharged. The research groups of Muggins [3] and Besenhard [4] have proposed that the volume expansion due to the insertion of Li can be reduced in micro- and submicro-structured matrix alloys. For this reason, the research group of J.R. Dahn investigated Sn/Mo sequential sputter deposition to prepare nanocomposites [5]. In this study, we investigated the characterization and the electrochemical characteristics of sequentially sputtered Si/Mo multilayer for microbattery anode.

• 한국분말재료학회지
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• 제15권1호
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• pp.37-45
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• 2008

This article presents the challenges toward the successful consolidation of $Al_2O_3$ nanopowder using magnetic pulsed compaction (MPC). In this research the ultrafine-structured $Al_2O_3$ bulks have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were investigated. The obtained density of $Al_2O_3$ bulk prepared by the combined processes was increased with increasing MPC pressure from 0.5 to 1.25 GPa. Relatively higher hardness and fracture toughness in the MPCed specimen at 1.25 GPa were attributed to the retention of the nanostructure in the consolidated bulk without cracks. The higher fracture toughness could be attributed to the crack deflection by homogeneous distribution and the retention of nanostructure, regardless of the presence of porosities. In addition, the as consolidated $Al_2O_3$ bulk using magnetic pulsed compaction showed enhanced breakdown voltage.

• 센서학회지
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• 제15권5호
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• pp.371-377
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• 2006

Nano porous, transparent silica aerogels monoliths were prepared under ambient drying (1 atm, $270^{\circ}C$) condition by the combination of sol-gel process and surface modification with subsequent heat treatment. Three kinds of solvent, n-hexane, n-heptane and xylene, were selected in the point view of low surface tension and vapor pressure in order to restrain a formation of cracks during drying. Crack-free silica aerogels with over 93 % of porosity and below $0.14g/cm^3$ of density were obtained by solvent exchange and surface modification under atmosphere condition. Optimum solvent was confirmed n-heptane among these solvents through estimation of FT-IR, TGA, BET and SEM. Modified silica aerogel exhibited a higher porosity and pore size compare to unmodified aerogels. Hydrophobicity was also controled by C-H and H-OH bonding state in the gel structure and heat treatment over $400^{\circ}C$ effects to the hydrophobicity due to oxidation of C-H radicals.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.431-434
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• 2001

The mechanical and phase transformation of the cold isostatically pressed $\alpha$-SiC ceramic were investigated as a function of the sintering temperature. The result of phase analysis by XRD revealed 6H, 4H, 3C and phase transformation between 6H and 4H showed a sudden change over 200$0^{\circ}C$. However, the alongrightarrow$\beta$ reverse transformation did not occur to any sintering temperature. The relative density and the mechanical properties of $\alpha$-SiC ceramic was increased with increased sintering temperature. The flexural strength rapidly inclosed below 210$0^{\circ}C$ and showed the highest value of 410 MPa at 220$0^{\circ}C$. This reason is because crack was propagated through surface flaw. The fracture toughness showed the highest value of 3.3 MPa.m$_{1}$2/ at 220$0^{\circ}C$.

• 한국전기전자재료학회논문지
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• 제17권3호
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• pp.353-359
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• 2004

In this study. porcelain insulator samples which have a different alumina composition were manufactured in order to test electrical and mechanical properties and make an analysis of the propagation phenomena of micro cracks on porcelain body. From XRD quantitative analysis the crystalline phases were different with alumina composition, sample C and D which have about l7wt％ Corundum phase without the Cristobalite phase shows better electrical and mechanical properties than sample A and B which have the Cristobalite phase. In dielectrics test on porcelain samples with below l7wt％ alumina composition, it was found that the amount of glass phase(SiO$_2$) have an main effect to decrease the dielectric loss(tan$\delta$), and the dielectric breakdown voltage of aluminous porcelain insulators was largely affected by its relative density. As a micro tracks analysis, HRB were measured, then the intensity of HRB increased with the amount of alumina composition. On the other hand, the propagation behaviors of cracks was fairly influenced by the distribution of pores.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 반도체재료
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• pp.38-41
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• 2001

In this work, we have been studied the characteristics of each nitride film for the optimization of PMD(pre-metal dielectric) liner nitride process, which can applicable in the recent semiconductor manufacturing process. The deposition conditions of nitride film were splited by PO (protect overcoat) nitride, baseline, low hydrogen, high stress and low hydrogen, respectively. And also we tried to catch hold of correlation between BPSG(boro-phospho silicate glass) deposition and densification. Especially, we used FTIR area method for the analysis of density change of Si-H bonding and Si-NH-Si bonding, which decides the characteristics of nitride film. To judge whether the deposited films were safe or not, we investigated the crack generation of wafer edge after BPSG densification, and the changes of nitride film stress as a function of RF power variation.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2011년도 추계 학술논문 발표대회
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• pp.237-239
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• 2011

This study was performed to investigate the influence of curing temperature on the properties of light weight foamed concrete, manufactured on-site construction according to the various experimental factor such as temperature of material, curing temperature in air(5, 10, 20℃), curing time in air(5, 10, 15hour), and target density of hardened state(0.8, 1.2t/㎥). As a result, the influence of the curing temperature on various properties of foamed concrete is greater than curing time. When increasing temperature and time in air curing, progress of hydration is fast and compressive strength is increasing more and more. However, when considering the productivity, minimum curing time is required 15hours at 5℃, 10hours at 10℃, and 5hours at 20℃. If this condition is not required, there is some crack due to volume expansion on the surface of light weight foamed concrete.