• Journal of the Korean Vacuum Society
• /
• v.5 no.4
• /
• pp.327-332
• /
• 1996

In this study, the effects of $WSi_x$, thickness and fluorine concentration in tungsten polycide gate structure on gate oxide were investigated. As $WSi_x$, thickness increases, gate oxide thickness increases with fluorine incorporation in gate oxide, and time-to-breakdown($T_{BD,50%}$) of oxide decreases. The stress change with $WSi_x$ thickness was also examined. But it is understood that the dominant factor to degrade gate oxide properties is not the stress but the fluorine, incorporated during $WSi_x$ deposition, diffused into $WSiO_2$ after heat treatment. In order to understand the effect of fluorine diffusion into oxidem fluorine ion implanted gates were compared. The thickness variation and $T_{BD,50%}$ of gate oxide is saturated over 600 $\AA$ thickness of $WSi_x$. The TEM and SIMS studies show the microstructure less than 600 $\AA$ thickness is dense and flat in surface. However, over 600$\AA$, the microstructure of $WSi_x$ is divided into two parts: upper porous phase with rugged surface and lower dense phase with smmoth interface. And this upper phase is transformed into oxygen rich crystalline phase after annealing, and the fluorine is captured in this layer. Therefore, the fluorine diffusion into the gate oxide is saturated.

• Korean Journal of Materials Research
• /
• v.26 no.8
• /
• pp.449-453
• /
• 2016

$HA(hydroxyapatite)/{\beta}-TCP$ (tricalcium phosphate) biomaterial (BCP; biphasic calcium phosphate) is widely used as bone cement or scaffolds material due to its superior biocompatibility. Furthermore, $NH_4HCO_3$ as a space holder (SH) has been used to evaluate feasibility assessment of porous structured BCP as bone scaffolds. In this study, using a spark plasma sintering (SPS) process at 393K and 1373K under 20MPa load, porous $HA/{\beta}-TCP$ biomaterials were successfully fabricated using $HA/{\beta}-TCP$ powders with 10~30 wt% SH, TiH2 as a foaming agent, and MgO powder as a binder. The effect of SH content on the pore size and distribution of the BCP biomaterial was observed by scanning electron microscopy (SEM) and a microfocus X-ray computer tomography system (SMX-225CT). The microstructure observations revealed that the volume fraction of the pores increased with increasing SH content and that rough pores were successfully fabricated by adding SH. Accordingly, the cell viabilities of BCP biomaterials were improved with increasing SH content. And, good biological properties were shown after assessment using Hanks balanced salt solution (HBSS).

• Korean Journal of Materials Research
• /
• v.23 no.9
• /
• pp.510-516
• /
• 2013

Fly ash is one of the aluminosilicate sources used for the synthesis of geopolymers. The particle size distribution of fly ash and the content of unburned carbon residue are known to affect the compressive strength of geopolymers. In this study, the effects of particle size and unburned carbon content of fly ash on the compressive strength of geopolymers have been studied over a compositional range in geopolymer gels. Unburned carbon was effectively separated in the $-46{\mu}m$ fraction using an air classifier and the fixed carbon content declined from 3.04 wt% to 0.06 wt%. The mean particle size ($d_{50}$) decreased from $22.17{\mu}m$ to $10.79{\mu}m$. Size separation of fly ash by air classification resulted in reduced particle size and carbon residue content with a collateral increase in reactivity with alkali activators. Geopolymers produced from carbon-free ash, which was separated by air classification, developed up to 50 % higher compressive strength compared to geopolymers synthesized from raw ash. It was presumed that porous carbon particles hinder geopolymerization by trapping vitreous spheres in the pores of carbon particles and allowing them to remain intact in spite of alkaline attack. The microstructure of the geopolymers did not vary considerably with compressive strength, but the highest connectivity of the geopolymer gel network was achieved when the Si/Al ratio of the geopolymer gel was 5.0.

• Journal of the Korean Institute of Gas
• /
• v.24 no.5
• /
• pp.39-46
• /
• 2020

This paper is considered about centerline segregation of API 5L steel used in pipeline. Mn/S, Nb and C were known as segregated elements in the centerline of pipe thickness. The Mn usually was accompanied by S consisting of long viscous shape. Microstructure of the centerline was composed of MnS and Nb/Ti indusions including oxide. The segregation effect in centerline region was analyzed by OM, SEM/EDS and micro Vickers hardness. The Mn, Nb and C are retarded elements in transformation from austenite to ferrite or martensite. These elements could derive a bainitic microstructure as a kind of martensite, which is different from difference and element segregation between in matrix and centerline derived from steel melting and heat treatment.

• Journal of Powder Materials
• /
• v.11 no.6 s.47
• /
• pp.493-502
• /
• 2004

In this study, nano-sized indium oxide powder with the average particle size below 100 nm is fab-ricated from the indium chloride solution by the spray pyrolysis process. The effects of the reaction temperature, the concentration of raw material solution and the inlet speed of solution on the properties of powder were studied. As the reaction temperature increased from 850 to $1000^{\circ}C$, the average particle size of produced powder increased from 30 to 100 nm, and microstructure became more solid, the particle size distribution was more irregular, the intensity of a XRD peak increased and specific surface area decreased. As the indium concentration of the raw material solution increased from 40 to 350 g/l, the average particle size of the powder gradually increased from 20 to 60 nm, yet the particle size distribution appeared more irregular, the intensity of a XRD peak increased and spe-cific surface area decreased. As the inlet speed of solution increased from 2 to 5 cc/min., the average particle size of the powder decreased and the particle size distribution became more homogeneous. In case of the inlet speed of 10 cc/min, the average particle size was larger and the particle size distribution was much irregular compared with the inlet speed of 5 cc/min. As the inlet speed of solution was 50 cc/min, the average particle size was smaller and microstructure of the powder was less solid compared with the inlet speed of 10 cc/min. The intensity of a XRD peak and the variation of specific area of the powder had the same tendency with the variation of the average par-ticle size.

• Journal of Powder Materials
• /
• v.22 no.2
• /
• pp.111-115
• /
• 2015

This study investigates the microstructure and thermal shock properties of polycrystalline diamond compact (PDC) produced by the high-temperature, high-pressure (HPHT) process. The diamond used for the investigation features a $12{\sim}22{\mu}m$- and $8{\sim}16{\mu}m$-sized main particles, and $1{\sim}2{\mu}m$-sized filler particles. The filler particle ratio is adjusted up to 5~31% to produce a mixed particle, and then the tap density is measured. The measurement finds that as the filler particle ratio increases, the tap density value continuously increases, but at 23% or greater, it reduces by a small margin. The mixed particle described above undergoes an HPHT sintering process. Observation of PDC microstructures reveals that the filler particle ratio with high tap density value increases direct bonding among diamond particles, Co distribution becomes even, and the Co and W fraction also decreases. The produced PDC undergoes thermal shock tests with two temperature conditions of 820 and 830, and the results reveals that PDC with smaller filler particle ratio and low tap density value easily produces cracks, while PDC with high tap density value that contributes in increased direct bonding along with the higher diamond content results in improved thermal shock properties.

• Journal of Powder Materials
• /
• v.18 no.1
• /
• pp.41-48
• /
• 2011

As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr)$TiO_3$ powder. Porous (Ba,Sr)$TiO_3$ ceramics were prepared by pressureless sintering at $1350^{\circ}C$ for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr)$TiO_3$ ceramics were investigated. The porosity of porous (Ba,Sr)$TiO_3$ ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from $7.51\;{\mu}m$ to $5.96\;{\mu}m$ with increasing carbon black contents. PTCR jump of the (Ba,Sr)$TiO_3$ ceramics prepared by adding carbon black was more than $10^5$, and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr)$TiO_3$ ceramics prepared by adding 40 vol% carbon black showed an excellent value of $9.68{\times}10^5$, which was above two times higher than that in (Ba,Sr)$TiO_3$ ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr)$TiO_3$ ceramics. It was considered that carbon black is an effective additive for preparing porous $BaTiO_3$ based ceramics. It is believed that newly prepared (Ba,Sr)$TiO_3$ cermics can be used for PTC thermistor.

• Korean Journal of Food Science and Technology
• /
• v.22 no.2
• /
• pp.192-198
• /
• 1990

Texture, losses of total solids and proteins o) soybeans were studied during cooking at $100-135^{\circ}C$. The textural changes were measured using the puncture probe with an Instron Universal Testing Machine, and changes in microstructure of beans were observed with scanning electron microscopy during the cooking. The major effect observed was a breakdown of the cell walls and appearance of the protein bodies with soaking process. As the cooking time at $100^{\circ}C$ is longer, the separation of cells and changes in cell shape could be seen in the sample. The greater amounts of soluble solids were leached out with longer coo king time from the beans.

• Journal of Powder Materials
• /
• v.24 no.3
• /
• pp.202-209
• /
• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.11
• /
• pp.124-129
• /
• 2017

In this study, we report characteristics of friction stir welding (FSW) technique applied to Al-6005-T6 extruded sheets, which is a common material for railway car bodies. With the welding speed fixed at 300 mm/min, the revolution per minute (RPM) of the rotating tool was varied from 600 to 1800 RPM, with the aim at evaluating the resultant microstructure and mechanical behaviors. Comparison is also made with the conventional Metal Inert Gas (MIG) welding technique. Unlike MIG, no micro-voids were observed for FSW specimens. Hardness measurement revealed that the increased heat input by increasing RPM results in widened heat affected zone (HAZ) and decreased hardness for HAZ due to grain coarsening. Hardness results for the nugget do no show difference. During tensile tests, specimens fractured at HAZ, and increasing rpm led to decrease of the yield stress and tensile stress for the selected RPM range, which is considered to be due to the grain coarsening for HAZ.