• Journal of Korea Foundry Society
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• v.14 no.3
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• pp.258-266
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• 1994

AC4A $Al/Al_2O_3+SiC_p$ hybrid composites were fabricated by the squeeze infiltration technique. Effect of applied pressure, volume fraction of reinforcement($Al_2O_3$ and SiC) and SiC particle size($4.5{\mu}m$, $6.5{\mu}m$ and $9.3{\mu}m$) on the solidification microstructure of the hybrid composites were examined. Mechanical properties were estimated preliminarly by fractographic observation, hardness measurement and wear test. Results show that the microstructure of the hybrid composites were quite satisfactory, namely revealing relatively uniform distribution of reinforcements and refined matrix. Some aggregation of SiC particle caused by particle pushing was observed especially in the hybrid composites containg in fine particle($4.5{\mu}m$). Refined matrix was attributed to applied pressure and increased nucleation sites with addition of reinforcements. Fractured facet also revealed finer for the hybrid composites possibly due to refined matrix. Hardness and wear resistance increased with volume fraction of reinforcements. For hybrid composites with $9.3{\mu}m$ SiC, hardness was somewhat lower and wear resistance higher than other composites.

• Carbon letters
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• v.4 no.2
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• pp.57-63
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• 2003

In polymer precursor based activated carbon, the structure of starting material is likely to have profound effect on the surface properties of end product. To investigate this aspect phenolic resins of different types were prepared using phenol, mcresol and formaldehyde as reactants and $Et_3N$ and $NH_4OH$ as catalyst. Out of these resins two resol resins PFR1 and CFR1 (prepared in excess of formaldehyde using $Et_3N$ as catalyst in the basic pH range) were used as raw materials for the preparation of activated carbons by both chemical and physical activation methods. In chemical activation process both the resins gave activated carbons with high surface areas i.e. 2384 and 2895 $m^2/g$, but pore size distribution in PFR1 resin calculated from Horvath-Kawazoe method, contributes mainly in micropore range i.e. 84.1~88.7 volume percent of pores was covered by micropores. Whereas CFR1 resin when activated with KOH for 2h time, a considerable amount (32.8%) of mesopores was introduced in activated carbon prepared. Physical activation with $CO_2$ leads to the formation of activated carbon with a wide range of surface area (503~1119 $m^2/g$) with both of these resins. The maximum pore volume percentage was obtained in 3-20 ${\AA}$ region by physical activation method.

• Carbon letters
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• v.6 no.4
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• pp.243-247
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• 2005

Plasma polymerization of allylamine subsequently after plasma pre-treatment was conducted on the activated carbon fibers (ACFs) for the immobilization of amine groups in the surface of ACFs. The change of structural properties of ACFs with respect to different polymerization conditions was investigated through BET method. The change of surface morphologies of ACFs with respect to different plasma polymerization power was also studied through AFM. It was found that the structural properties such as specific surface area and micropore volume could be optimized under certain plasma deposition conditions. It was reckoned that treatment and deposition showed adverse effect on plasma polymerization, in which the former developed the micro-structures of the ACFs and the latter tended to block the micro pores. The Fourier transform infrared spectroscopy (FTIR) revealed that the poly(allylamine) was successfully immobilized on the surface of ACFs and the amount of the deposited polymer layer was related to the plasma polymerization power. SEM results showed that the plasma deposited polymer layer were small and homogenously distributed. The size and the distribution of particles deposited were closely related to the plasma polymerization power, too.

• Journal of Pharmaceutical Investigation
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• v.21 no.3
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• pp.155-160
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• 1991

Particulate is the foreign insoluble material in injectable solution inadvertently present in a given product. Considerable efforts have been made to avoid or minimize particulate contamination by pharmaceutical manufacturers during the production of parenteral products. Particulate contamination of the parenteral products can occur mainly during the opening (cutting) the container immediately before clinical use. In this study, particulate contamination generated during the opening process of ampoules (conventional type, 1-point and color-break ampoules) was compared with that of a prefilled injectable container (prefilled syringe). The particles were examined under a microscope after filtration of the total fluids in the containers. Particles having wide range of size distribution were found from all the ampoules tested. The contamination from the I-point ampoule and colorbreak ampoule was much less than from the conventional ampoule. Glass particles generated by cutting the glass-made ampoules seemed a principal source of the particulate contamination. The glass-partiaulte contamination could be improved substantially by replacing the ampoule containers with the prefilled syringe. Prefilled syringe, which can be used without any cutting process. did not generate particulates during the use. Therefore, it was concluded that prefilled syringe is most preferable container for the small volume parenteral (SVP) fluids in terms of particulate contamination.

• Journal of Welding and Joining
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• v.11 no.2
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• pp.74-85
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• 1993

Effect of Si metal powders addition with the plasma transferred arc(PTA) overlaying process on characteristics of the alloyed layer in aluminum alloy(A5083) has been investigated. The overlaying conditions were 175-250A in plasma arc current, 500mm/min in travel speed, the 5-20g/min in powder feeding rate. Main results obtained are summarized as follows. 1)Sufficient size of molten pool on surface of base metal was required for forming an alloyed layer; in a fixed travel, the formation of alloyed layer with clear and beautiful surface depend upon the plasma arc current and powder feeding rate; the greater plasma arc current and the smaller powder feeding rate were, the better bead was formed. Optimum alloyed conditions by which an excellent alloyed bead obtained was 225A in plasma arc current. PTA process made it possible to form an alloyed layer with up to 67wt% Si. 2)Microstructure in the alloyed layer was in accord with prediction from the Al-Si phase diagram 3)The hardness of the alloyed layer increased in proportion to Si content. 4)As volume fraction of primary Si increased, the specific wearness of the alloyed layer was significantly improved. However, no further improvement was found when the volume fraction was greater than about 30%. 5)Utilizing the PTA process, a crack free alloyed layer with maximum hardness of about Hv 310 could be obtained.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.532-537
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• 2000

The purpose of this study is to determine the performance of a commercial air cleaner in removing tobacco smoke indoors. Following injection of tobacco smoke in a room, decay rates for particle concentrations were obtained far mass concentration at each point. The size distribution of the tobacco smoke particles was approximately $1.266{\mu}m$ in mass median diameter with a geometric standard deviation of 1.313. The air cleaner consisted of an electrostatic filtration unit and a fan operated at a flow rate of 5.98 CMM. The collection efficiency for $>1\;{\mu}m$ was more than 99%. Without air cleaner operation, tobacco smoke concentration ratio in room decreased to 30% of initial values within 30 minutes and with air cleaner operation, decreased to 90% of initial values in the test chamber, volume $51.27\;m^3$. Without air cleaner operation, tobacco smoke concentration ratio in room decreased to 10% of initial values within 30 minutes and with air cleaner operation, decreased to 30-70% of initial values in the test chamber, volume $149.2\;m^3$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.3
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• pp.402-409
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• 2002

Experiments were performed with double-concentric diffusion flame(DDF) in order to investigate the characteristics of soot formation and temperature distributions. The flame size and shape of the DDF are similar to those of the well-known normal co-flow diffusion flame(WF), except the formation of a tiny inverse flame near the central tube exit. A laser light extinction technique was used to measure the soot volume fractions. The temperature distributions in the flame were measured by rapid insertion of a R-type thermocouple. Soot concentrations along the flame axis of the DDF were higher than those of the NDF. However, the maximum soot volume fraction of the DDF along the periphery of the flame was lower than that of the NDF. It is mainly due to the effect of nitrogen-dilution from the inner air. Measured temperature distribution explains these trends of soot concentration. The temperature along the flame axis was also higher in DDF than that of the NDF. However, the flame temperatures at the flame front of the two flames were almost same regardless of the inner flame. This phenomenon means that the inverse flame inside the DDF did not affect on the flame structure including the temperature and soot concentration, except the region around the flame axis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.867-872
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• 2002

A high intensity acoustic test facility is constructed at Korea Aerospace Research Institute (KARI) by 2003. The reverberant chamber of the facility has a volume of 1,228 cubic meters and shall provide an acoustic environment of 152 dB over the frequency range of 25 Hz to 10,000 Hz. The facility consists of a large scaled reverberant chamber, acoustic power generation systems, gases nitrogen supply systems, and acoustic control systems. This paper describes how the basic parameters of a chamber and power generation systems are controlled to meet the requirement of the test. The volume of a reverberant chamber is controlled by the size of test objects and the reverberant characteristics of a chamber. The capacity of acoustic power generation systems is determined by the energy absorption of a chamber and the efficiency of acoustic modulators. Simple math is employed to calculate the required power of acoustic modulators. Moreover, the paper explains how the distribution of sound pressure level at low frequency is checked by analytical and numerical methods.

• Progress in Superconductivity
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• v.3 no.1
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• pp.104-110
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• 2001

Since the strand-to-strand type joint far CICC (Cable-In-Conduit Conductor) is small in size and has low DC resistance, it is expected to be useful type fur a superconducting magnet system which had a compact structure like the KSTAR (Korea Superconducting Tokamak Advanced Research) coil system. The DC resistance is changed according to the distribution patterns of strands in cables connected together in the joint. A commercial code was used for the calculation of the DC resistance. With the decrease of outer diameter of the Joint, Which means the increase of strand volume fraction in the joint, the calculated DC resistance decrease rapidly and non-lineally. The variation of resistance depends mainly on the volume fraction of solder which has higher resistivity than copper. The resistance decrease inversely with the increase of the length of the joint. The resistance increase with increase of number of triplets in each stack contacted with that of another terminal cable. In case of the strand-to-strand joint that has 62mm of outer diameter, 52mm of inner diameter, 100mm of overlap length, and four triplets in each stack, the calculated DC resistance is less than 1 n-Ohm.

• Journal of Korea Foundry Society
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• v.13 no.5
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• pp.441-449
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• 1993

SiC particulate reinforced magnesium matrix composites were fabricated by melt stirring method. The effet of several factors on mechanical properties and the efficiency of melt stirring method from the viewpoint of these properties were investigated. The tensile strength increased and the elongation decreased with decrease of the particle size or the increase of the paticulate volume fraction for pure magnesium matrix and Mg-5%Zn alloy matrix composites. A longer stirring time improved the tensile strength of these composites. The tensile strength of Mg-5%Ca alloy matrix composites which shows no uniform paticulate distribution was a little lower than that of matrix alloy. Rapid solidification rate is preferred for the improved tensile strength of these composites. The pure magnesium matrix and Mg-5%Zn alloy matrix composites have tensile strength of about 400MPa. This value agrees with the tensile strength of some magnesium matrix composites fabricated by liquid infiltration method or powder metallurgy method at the same volume fraction of reinforcements of whisker or particle. Therefore, the melt stirring method which has the advantages of simple process is considered to be efficient in fabricating magnesium matrix composites.