• Journal of the Korean Ceramic Society
• /
• v.40 no.8
• /
• pp.777-783
• /
• 2003

The mechanical properties of B$_4$C/Al composites normally depend on the species and quantity of reaction products between B$_4$C and Al and then the control of reaction products is necessary to make desirable composites for lightweight advanced or armor materials. TiB$_2$ is chemically inert with aluminum and has a lower contact angle (85$^{\circ}$ at 100$0^{\circ}C$) to liquid aluminum than B$_4$C. Thus, TiB$_2$ coating on B$_4$C may lower infiltration temperature of aluminum when the B$_4$C/Al composites is fabricated by infiltration process. In this study, the effects of TiB$_2$ on the microstructure and mechanical properties of the B$_4$C/Al composites have been investigated. TiB$_2$ coated B$_4$C powder was prepared using the sol-gel technique. It was found that the B$_4$C surface is homogeneously covered with TiB$_2$ having a particles size of 20-50 nm. While the B$_4$C/Al composites prepared by infiltration after TiB$_2$ coating had 17 wt% of unreacted Al, on the other hand, the B$_4$C/Al composites without coating included 14 wt% of Al. As a result, the composites infiltrated after the coating showed higher fracture toughness and lower hardness. This strongly suggests that TiB$_2$ not only lowers the infiltration temperature, but also inhibits the reaction between B$_4$C and Al.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.17 no.3
• /
• pp.121-127
• /
• 2007

We have applied mechanical alloying (MA) to get $Mg_2Si$ thermoelectric material with nano-sized grains. An optimal milling and heat treatment conditions to obtain the single phase of $Mg_2Si$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Mg_{66.7}Si_{33.3}$ MA samples ball-milled for $20{\sim}180\;hrs$ exhibit two broad exothermic heat releases around $220^{\circ}C$ and $570^{\circ}C$. On the other hand, MA sample ball-milled far 260 hrs exhibits only a sharp exothermic peak at $230^{\circ}C$ Single phase Mg2Si powder can be obtained by MA of $Mg_{66.7}Si_{33.3}$ mixture for 60 hours and subsequently heated up to $620^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $800{\sim}900^{\circ}C$ under 50 MPa. The shrinkage of sintering sample during SPS was significant at about $200^{\circ}C$. All compact bodies have a high relative density above 94% with metallic glare on the surface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.851-856
• /
• 2003

We have investigated the material and electrical properties of $Bi_{4-x}La_xTi_3O_{12}$ (BLT) ferroelectric thin film for ferroelectric nonvolatile memory applications of capacitor type and single transistor type. The 120nm thick BLT films were deposited on $Pt/Ti/SiO_2/Si$ and $SiO_2/Nitride/SiO_2$ (ONO) substrates by the sol-gel spin coating method and were annealed at $700^{\circ}C$. It was observed that the crystallographic orientation of BLT thin films were strongly affected by the excess Bi content and the intermediate rapid thermal annealing (RTA) treatment conditions regardeless of two type substrates. However, the surface microstructure and roughness of BLT films showed dependence of two different type substrates with orientation of (111) plane and amorphous phase. As increase excess Bi content, the crystallographic orientation of the BLT films varied drastically in BLT films and exhibited well-crystallized phase. Also, the conversion of crystallographic orientation at intermediate RTA temperature of above $450^{\circ}C$ started to be observed in BLT thin films with above excess 6.5% Bi content and the rms roughness of films is decreased. We found that the electrical properties of BLT films such as the P-V hysteresis loop and leakage current were effectively modulated by the crystallographic orientations change of thin films.

• Journal of the Korean Ceramic Society
• /
• v.40 no.6
• /
• pp.577-582
• /
• 2003

BaTiO$_3$ fine powders were synthesized by hydrothermal process from peroxo-coprecipitate precursors. The peroxo-coprecipitates were obtained by addition of the BaCl$_2$, TiCl$_4$, and $H_2O$$_2$ aqueous solution to an ammonium solution. Hydrothermal reaction was conducted at various reaction temperatures, times and pH ranges. Unlike the conventional hydrothermal synthesis which needs highly alkaline condition over pH 13 with KOH or NaOH, the present method offered well-developed crystalline (perovskite) BaTiO$_3$ powders synthesized below pH 12 with use of ammonium solution. It was found that the phase-pure fine powders were formed at temperatures as low as 11$0^{\circ}C$ and the properties of the powders synthesized over 13$0^{\circ}C$ were almost same regardless of the reaction time. BET surface area of the prepared powder was as high as 76 $m^2$/g and the calculated particle (particulate) size was below 20 nm. The ultrafine particulates formed weak agglomerates. The microstructure and dielectric properties of BaTiO$_3$ ceramics sintered at the temperature range of 1150~125$0^{\circ}C$ were evaluated.

• Journal of the Korea Concrete Institute
• /
• v.19 no.3
• /
• pp.333-339
• /
• 2007

The purpose of this study was to enhance bond performance between recycled PET (polyethylene telephthalat) fiber and cement composites through hydrophilic treatment using maleic anhydride grafted polypropylene(mPP). The mPP with various concentration of 0%, 5%, 10%, 15% and 20% to determine effect on bond behavior of recycled PET fiber were applied as experimental variables. Dog bone shaped specimens according to JCI SF-8 was applied to evaluate the bond strength and pullout energy. The results showed increased bond strength and pullout energy as concentration of mPP. Concentration of 15% mPP showed the most effective results while 20% showed reduced performance results. Because 15% mPP ensures perfect coating while 20% makes thick coating area that resulted in crack propagation and consequent separation of PET fiber and coated area during pullout load occurred. Enhancement mechanism of bond performance of recycled PET fiber and cement composites with each concentration of mPP could be conformed through investigation of microstructure of fiber surface.

• Journal of the Microelectronics and Packaging Society
• /
• v.12 no.3 s.36
• /
• pp.253-258
• /
• 2005

Characteristics of electroplated Ni films such as grain size, resistivity, solder wetting angle, and growth rate of intermetallic compound were evaluated as a function of electroplating current density. With increasing the electroplating current density from $5\;mA/cm^2 $ to $40\;mA/cm^2 $, the nodule size on the Ni film surface decreased, grain refinement occurred, and resistivity increased from $7.37\mu\Omega-cm$ to $9.13\mu\Omega-cm$. Compared with Ni film processed at $40\;mA/cm^2 $, Ni films electroplated at $5\;mA/cm^2 $ and $10\;mA/cm^2 $ exhibited low resistivity, dense microstructure, and slow growth rate of intermetallic compound. Ni films electroplated at $5\;mA/cm^2 $ and $10\;mA/cm^2 $ are more suitable for Ni UBM application than that fabricated at $40\;mA/cm^2 $.

• Journal of the Microelectronics and Packaging Society
• /
• v.13 no.1 s.38
• /
• pp.1-5
• /
• 2006

We prepared 80 nm-thick TiSix on each 70 nm-thick amorphous silicon and polysilicon substrate using an RF sputtering with $TiSi_2$ target. TiSix composite silicide layers were stabilized by rapid thermal annealing(RTA) of $800^{\circ}C$ for 20 seconds. Line width of $0.5{\mu}m$ patterns were embodied by photolithography and dry etching process, then each additional annealing process at $750^{\circ}C\;and\;850^{\circ}C$ for 3 hours was executed. We investigated the change of sheet resistance with a four-point probe, and cross sectional microstructure with a field emission scanning electron microscope(FE-SEM) and transmission electron microscope(TEM), respectively. We observe an abrupt change of resistivity and voids at the silicide surface due to interdiffusion of silicide and composite titanium silicide in the amorphous substrates with additional $850^{\circ}C$ annealing. Our result implies that the electrical resistance of composite titanium silicide may be tunned by employing appropriate substrates and annealing condition.

• Korean Journal of Plant Taxonomy
• /
• v.43 no.3
• /
• pp.208-222
• /
• 2013

In this paper, we conducted the taxonomic study of the tribe Epilobieae Endl. and concluded that a total of nine taxa, including one Chamerion (Raf.) Raf. ex Holub and eight Epilobium L., exist in Korea. Although C. angustifolium subsp. angustifolium has been placed traditionally either in Epilobium or Chamaenerion, it can be clearly distinguished from the species of Epilobium by having alternate leaves, slightly zygomorphic flowers, non-clefted petals, and equal length of 8 stamens, supporting the recognition of genus Chamerion. All but one species of Epilobium, E. platystigmatosum, was investigated for the surface of seeds using scanning electron microscope (SEM). The seed sculpture of Korean Epilobium can be classified into three types, i.e., papillose, reticulate, and ridged. E. ciliatum subsp. ciliatum is the only species Epilobium, which has the ridged seed sculpture. E. amurense subsp. cephalostigma can be distinguished from conspecific E. amurense subsp. amurense based on leaf shape, trichome shape and distribution, size and habit. Both E. fastigiatoramosum and E. palustre have entire leaf margins, but they can be distinguished based on leaf shape, stigma, and seed sculpture; the former has elongated elliptic leaves, capitate stigma, ridged seed sculpture, whereas the latter one has elongated lanceolate leaves, club-shaped stigma, and reticulate seed sculpture. Finally, we report the first record of E. platystigmatosum in Korea, and further comparative study including conspecific populations from Japan and China can clarify the occurrence of this taxon in Korea.

• Korean journal of food and cookery science
• /
• v.3 no.2
• /
• pp.9-16
• /
• 1987

This study was designed to determine the amino acid composition and to investigate microstructure by scanning electron micrographs of silkworm larvae protein and modified silkworm larvae protein concentrate. The results were as follows: 1, The protein contents of soybean and silkworm larvae protein concentrate were 70.3% and 84.1%, respectively. 2. In general, the essential amino acid content of silkworm larvae protein concentrate were higher than soybean protein concentrate as well as FAO provisional scoring pattern. Silkworm larvae protein concentrate was especially high in lysine and methionine indicating that it could be a good supplemental source for cereals and beans. Succinylation and acetylation resulted in no difference in most amino acid content. 3. The scanning electron microscopic observations revealed that silkworm larvae protein concentrate had smooth surface topography while defatted silkworm larvae flour showed different shapes and sizes with relatively rough surfaces. Acylated silkworm larvae protein concentrate exhibited less cellularity and denser than protein concentrate. However, succinylated silkworm larvae protein concentrate showed especially good texture indicating that it could increase the functional properties of silkworm larvae protein concentrate.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.27 no.6
• /
• pp.319-326
• /
• 2017

In this study, a lightweight geopolymer was prepared using by slag discharged from IGCC (Integrated Gasification Combined Cycle) power plant and its physical properties, the density and compressive strength, were analyzed as a function of the concentration of alkali activators, W/S ratio and aging times. Also the possibility of applying it to lightweight materials by adding Si sludge as a foaming agent to the geopolymerg was investigated. In particular, a complex composition of alkali activator and a pre-curing process were applied to improve the strength properties of lightweight geopolymers. While the compressive strength of the lightweight geopolymer using a single activator was 9.5 MPa, the specimen made with a complex composition of alkali activator had compressive strength of 2~5 times higher. In addition, the lightweight geopolymer with pre-curing process showed a compressive strength value of 18~48 % higher than that of specimen made with no precuring process. In this study, by using a complex activator and a pre-curing process. the maximum compressive strength of lightweight geopolymer was obtained as 40 MPa (The specimen was aged for 3 days and had density of $1.83g/cm^3$), which is comparable to cement concrete. By analyzing the crystal phase and microstructure of geopolymers obtained in this study using by XRD and SEM, respectively, it was confirmed that the flower-bud-like zeolite crystal was homogeneously distributed on the surface of the C-S-H gel (sodium silicate hydrate gel) in the geopolymer.