Showing papers in "Journal of Korean Society for Atmospheric Environment in 1993"

Simulation of Encapsulation Process for BGA Type Semi-conducting Microchip

Abstract: The encapsulation process for semi-conductor chips is mainly affected by the thermal and rheological characteristics of EMC encapsulants. In this research, encapsulation processes for the BGA (Ball Grid Array) type chip were simulated after investigating the thermal and rheological characteriseics of EMC. The values of parameters involved in Kamal and Cross equations which were used in C-Mold were acquired by making regressions on the thermal and rheological data performed by DSC and RMS respectively. The simulation and experimental results showed that the dynamic characteristics of melt-front have good agreements with those of real short shot process.

Fabrication of Al Nano Powders by Pulsed Wire Evaporation (PWE) Method

Abstract: Nano-sized Al powders were synthesized by the Pulsed Wire Evaporation (PWE) method. The wire, which was fed continuously into a chamber filled with Ar gas, was exploded into nano powders by high pulsed current and voltage. After the nano powders were synthesized, they were classified by sizes using cyclone and various kinds of filters. We passivated the powder surface with a thin oxide layer to stabilize at room temperature. The size and shape of the nano powders were investigated by TEM. XRD was conducted for phase analysis and grain size determination. XPS and BET analyses were conducted for the investigation of the oxide layer on the Al powder and specific surface area, respectively. From the TEM observation, it was found that the Al nano powder was spherical shape of 80 - 120 nm diameter with the thickness of the oxide layer of 2 -3 nm. The Al phase was crystalline with FCC structure, on the other hand the oxide layer was an amorphous state.

Appropriate Environmental Sphere of Application for Unpainted Weathering Steel

Abstract: The current study was carried out to establish the appropriate environmental sphere of application for unpainted weathering steel as civil structures, such as bridge structures, general construction, electric posts, guide rails, etc. As such, based on existing guideline for acceptable flying marine salt concentrations, the suitability of 4 selected locations was investigated in relation to environmental factors, including the direction and velocity of the wind, rainfall, humidity, and temperature. The results for the flying marine salt concentrations, considering the character of the selected locations, were as follows: the maximum and minimum flying marine salt concentrations measured by the gauge method at the selected locations #1, #2, #3, and #4 were 0.046 and 0.094, 0.08 and 0.131, 0.050 and 0.08, and 0.021 and 0.051 mg-NaCl/dm(2)/day, respectively. The concentrations of flying marine salt at locations #3 and #4 were lower than 0.1 mg-NaCl/dm(2)/day, indicating that the application of unpainted weathering steel was possible in these positions. However, the maximum concentration of flying marine salt at location #2 was 0.131 mg-NaCl/dm(2)/day. Accordingly, the current results revealed that locations #3, and #4, which were farther than 1000 m from the sea coast, were appropriate environments for the use of unpainted weathering steel, whereas location #2, which was less than 1000 m from the sea coast was found to be an unsafe environment for the use of unpainted weathering steel.

Heavy Metal Adsorption Characteristics of Zeolite Synthesized from Fly Ash

Abstract: Heavy metal adsorption by zeolite synthesized from fly ash was investigated. Approximately 90% of the lead and copper ions originally present in the solution were adsorbed onto the adsorbent within about 30 min after the start of the adsorption and an equilibrium was reached within 2 h. The favorable pH region was from 5 to 6. The maximum adsorption capacities obtained using the Langmuir model were about 1.29 mmole/g for lead and 1.16 mmole/g for copper. The capacity for lead removal by the synthesized zeolite was dependent on the ligand type and concentration. In a binary adsorption system, the influence of copper ions on the lead ion adsorption was small, yet the copper ion adsorption was significantly decreased when lead ions were present.

Amphiphilic Polyurethane-co-polystyrene Network Films Containing Silver Nanoparticles

Abstract: Yellow transparent polyurethane-co-polystyrene films containing silver nanoparticles could be synthesized. Silver nanoparticles and transparent polymer film making up nanocomposite films were formed simultaneously through radical initiated polymerization of amphiphilic urethane acrylate, nonionomer (UAN)/styrene/silver nitrate mixtures. Size of silver nanoparticle could be controlled by varying weight ratio of styrene in UAN/styrene mixtures and chain length of PEO and PPO segment in UAN chain, which are much easier process compared to the synthetic process of nanoparticles using amphiphilic block copolymers. Formation of silver nanoparticles and change of nanoparticle size could be conformed by transmission electron microscopy and characteristic UV absorbance spectra. Tensile modulus and glass transition temperature of polyurethane-co-polystyrene films were drastically increased at 0.45 wt% of silver nanoparticles embedded at their matrix, indicating that silver nanoparticles embedded at polymer films can act as an inorganic nanofiller for improving mechanical property.

Properties of Metal Supported Porous Carbon and Bactericidal Effects

Abstract: The studies on physicochemical properties and bactericidal effects of the Ag, Cd and Cu-treated activated carbons are carried out. According to the adsorption studies, it is confirmed that all of the metal-treated activated carbons have micropore structure rather than mesopore structure. The surface areas of the treated carbon obtained from BET equation are in the range of 741 ~ 1112, 1104 ~ 1418 and 1084 ~ 1361 m(2)/g for Ag-AC, Cd-AC and Cu-AC, respectively. Upon the micropore volumes obtained from αs-plot, decrease of micropore volume is dependant on the contents of treated-metal except Ag. From the SEM study, it is observed that much of micropores in activated carbon are blocked by window blocking effect of metals after the treatment. Combining the information obtained from the studies on adsorption isotherms, specific surface area, and micropore volume, it is recognized that Ag shows different behavior from other metals. It is postulated that the differences in adsorption properties among the metals are mainly due to different blocking effects. And the effects depend on the way of distribution, the shape of metal particles, and the pattern of aggregates. Finally, bactericidal effects of metal treated activated carbon against Escherichia coli are discussed. Comparing the effects among the metals employed, the highest effects are obtained from Cd, while the lowest effects are obtained from Cu. Antibacterial activity becomes higher with the increase of the amount of metal treated. From the shake flask test, the optimum concentrations of metals are known to be 0.4 mole for Ag, 0.1 mole for Cd, and 0.6 mole for Cu, respectively.

Synthesis and Application of Fly Ash-Derived Zeolites for Pyrolysis of Polyolefins

Abstract: Fly ash-derived zeolites were synthesized by hydrothermal treatment of fly ash in NaOH solution. The effects of synthesis conditions including NaOH concentration and reaction time on the mineralogical structure of the zeolites were investigated and the effects of these fly ash-derived zeolites on the pyrolysis behaviors of low density polyethylene and polypropylene were delineated in terms of the recovery and simulated boiling point distribution of the liquid pyrolysis products. It appeared that the fly ash-derived zeolites were not so much effective for LDPE pyrolysis, but slightly effective for PP pyrolysis.

PtRu Nanoparticle Electrocatalysts Prepared by Various Synthetic Methods for Use in Direct Methanol Fuel Cells

Abstract: The synthesis and characterization of carbon-supported PtRu nanoparticles were carried out by impregnation and colloidal methods and products were compared with commercial carbon-supported PtRu. To confirm the characteristics of the synthesized PtRu nanoparticles, TEM (and EDX), XRD, and electrochemical analysis were performed to evaluate alloy formation, surface structure, chemical composition of the nanoparticles, and the electrocatalytic activity for methanol oxidation. The impregnation method was relatively easy and straightforward but the average particle size was in excess of 3 nm and the size distribution was broad. However, colloidal methods involved more complicated procedures and required a heat treatment to increase activity, resulting in an average particle size of up to 2.2 - 2.3 mn. The heating conditions used, to achieve a higher catalytic activity, were investigated. A simpler nanoparticle synthetic method that results in a small particle size and high activity without a heat treatment would be desirable.

In-Digester Demethylation Kinetics for VOC/TRS Formation During the Kraft Pulping of Loblolly Pine

Abstract: The objective of this study was to examine the reaction kinetics of demethylation and VOC/TRS formation during the kraft pulping process. The methyl mercaptan and dimethyl sulfide were taken into account as the major compounds for TRS, and methanol for the major VOC. On the basis of H-factor process variable, the kinetic analysis was conducted using the mechanistic assumptions of two parallel competing reaction and bimolecular-type second order reaction. Demethylation appeared to be proportional to the degree of delignification. The rate constants of the demethylation showed as high a value in the order of ten as the delignification rate constants. Sulfidity has a significant impact on both demethylation and delignification. Higher sulfidity-dependency was observed in demethylation rates. The VOC formation rate was highly proportional to the effective alkali charge in the kraft process, whereas TRS formation to sulfidity. VOC formation rate appeared to be about seven times higher than TRS formation at a lower level of sulfidity, but the difference between them increasingly decreased with increasing sulfidity. These results suggest that higher effective alkali charge at a given level of sulfidity should be instrumental to minimize the TRS formation during the kraft pulping.

Protein Microarrays and Chips

Abstract: Recent development of protein microarrays and protein chips is allowing high-throughput analysis of proteins and/or molecules interacting with proteins. Powerful new technologies have currently been reported, which range from synthetic peptide arrays to whole cell protein arrays. Protein chips have been used in various applications for detecting interactions between enzyme-substrate, synthetic molecules-protein and different kinds of protein-protein. Such studies demonstrated that protein chips can be used to examine the functions of thousands of proteins in parallel in a single experiment. This review describes the development of protein microarrays and their potential applications in biological research, medicine and diagnostics.

Synthesis and LCST Behavior of Thermosensitive Poly (N-isopropylacrylamide)-Clay Nanocomposites

Abstract: Thermosensitive polymer-clay nanocomposites were prepared via organically modified claypoly(N-isopropylacrylamide) (PNIPAM) nanocomposites. Nanocomposites containing a 5 wt% of montmorillonite exhibited a lower critical solution temperature (LCST) similar to the unmodified PNIPAM hydrogel, and similar phenomena with a large thermal volumetric change and transition kinetics compared to conventional PNIPAM gels. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) suggested that the clay minerals in the nanocomposite were partially exfoliated in a dried state and mostly exfoliated in a swollen state.