• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.4
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• pp.225-233
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• 1997

This study is performed to establish a non-destructive evaluation method for metal matrix composite using ultrasonic technique. The specimen is made of SiC/AC8A metal matrix composite by squeeze-casting method. Three kinds or reinforced particles are prepared as 4.86, 8.09 and $11.44{\mu}m$ to investigate the effect of size on the mechanical and ultrasonic properties of metal matrix composite. In addition, four different volume fractions (14, 22.5, 27.5, 35%) of reinforced particles are prepared per each size to examine the effect of volume fraction on the ultrasonic properties. From this specimen, the availability and precision of measurement of Young's modulus are examined and the evaluation method for microstructure of metar matrix composite using the speed of sound and attenuation factor is also reviewed. The results show that the Young's modulus measured by ultrasonic method is as effective as that measured by mechanical method. It is also known that the size and volume fraction of reinforced fiber are precisely evaluated using the speed of sound and attenuation factor.

• Korean Journal of Soil Science and Fertilizer
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• v.19 no.3
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• pp.187-194
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• 1986

Present stadies were carried out to obtain fundermental data for effective management of the soils by investigating the physicochemical characteristics rubber fiber, humification grade and bearing power of peats and muck which were included in Geongdeog series, and Gimje series in Honam area. The results abtained were as follows; 1. Humification grade of peats were about 23, while that of muck soils was about 45-71 and those were higher in Gimje series than Bongnam series. 2. The organic tiers which humification grade was higher were high pH, bulk density, and contents of K, $P_2O_5$, B.S and while were low OM, T-C, T-N, Na, $SiO_2$ and rubbed fiber. 3. In peats and mucks, bulk density, pH, contents of T-N $P_2O_5$ and ash were negatively correlated with rubbed fiber and OM, CEC, T-C, PAC, C/N, C/P were positively correlated with one, while these physicochemical characteristics were oppositely correlated with humification grade. 4. Cone bearing power of each soil tiers was low in every Geongdeog series which had the thick organic tiers and showed poorly drainage and it was the highest in Gimje series which was similar to in organic soils because of its thin organic tiers.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.57 no.2
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• pp.132-136
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• 2012

Kenaf (Hibiscus cannabinus) is an annual herbaceous plant of the family Malvacease that has been planted in tropical Africa and Asia region for more than 4000 years and use as source of fiber, energy and feed stock. In this study, the physiological characters and chemical compositions of kenaf mutant variety "Jangdae" developed using gamma irradiation at the Korea Atomic Energy Research Institute (KAERI) were compared with three genetic resources (Auxu, C12, and C14-DRS). Jangdae showed the highest productivity growth rates in fresh yield, dry weight (DW) yield (leaf and stem), node number, and stem thickness. Especially, leaf DW yield of Jangdae was 1.6-3.1 times higher than that of three genetic resources. Also, stem DW yield of Jangdae was 1.6-2.1 times higher than that of three genetic resources. In the analysis of chemical composition, Jangdae showed 16.9% of crude protein content that was 0.86-0.94 times lower than three cultivars. However, Jangdae showed the highest neutral detergent fiber (NDF) contents in leaf (32.5%) and stem (75.2%). Also, acid detergent fiber (ADF) contents of stem and leaf in Jangdae were 64.4% and 33.9%, respectively. Total polyphenol and total flavonoid contents were 22.1 mg/g and 7.4 mg/g in Jangdae. Based on these results, Jangdae would have the potential to become a successful forage crop.

• Journal of Conservation Science
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• v.16 s.16
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• pp.27-38
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• 2004

This study was performed to characterize historical paper artefacts from 16th to 19th century from Chungbuk National University Museum (CNUM) in Korea. In order to know the fiber composition, surface features and fiber orientation in historic paper artefacts, LM, SEM and EDX analysis observations were applied. Based on tested results, it was concluded that Korean historic papers from 16 to 19th century were made of paper mulberry fibers called dak, which had 2.79-16.03 m of fiber lengthes and $4.5-26{\mu}m$ of lumen widthes, and they were relatively well preserved. According to EDX analysis, the examined papers differed to the contents of inorganics. High contents of S, Si, Ca, P and Al refer to use fillers, such as gypsum, clay and talc, for paper artifacts. In particular, half of samples contained some amounts of S, Cl and Fe. Since those inorganics might be potentially harmful for the paper permanency, therefore it should be considered special restoration measures from the preservation point of view.

• Resources Recycling
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• v.25 no.6
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• pp.73-81
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• 2016

Geopolymers produced from aluminosilicate materials such as metakaolin and coal ash react with alkali activators and show higher fire resistance than portland cement, due to amorphous inorganic polymer. The percentage of thermal shrinkage of geopolymers ranges from less than 0.5 % to about 3 % until $600^{\circ}C$, and reaches about 5 ~ 7 % before melting. In this study, geopolymers paste having Si/Al = 1.5 and being mixed with carbon nanofibers, silicon carbide, pyrex glass, and vermiculite, and ISO sand were studied in order to understand the compressive strength and the effects of thermal shrinkage of geopolymers. The compressive strength of geopolymers mixed by carbon nanofibers, silicon carbide, pyrex glass, or vermiculite was similar in the range from 35 to 40 MPa. The average compressive strength of a geopolymers mixed with 30 wt.% of ISO sand was lowest of 28 MPa. Thermal shrinkage of geopolymers mixed with ISO sand decreased to about 25 % of paste. This is because the aggregate particles expanded on firing and to compensate the shrinkage of paste. The densification of the geopolymer matrix and the increase of porosity by sintering at $900^{\circ}C$ were observed regardless of fillers.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.29-36
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• 2000

The shape of the polymers in the mixed alkoxide solutions of Si(OC2H5)4 and Zr(n-OC3H7)4 with various water contents (1, 2, 4, and 8 in molar ratio to alkoxide, r) and catalysts was examined by rheological measurements, and its relation with fiber drawing behavior of the solutions was described. It was found that fibers could be drawn in the viscosity range 1~100 P from the acid-catalyzed solutions with lower water contents of the molar ratio H2O/alkoxide, $r{\leq}2$. On the other hand, no fiber could be drawn from the acid-catalyzed solutions including a large amount of water($r{\geq}4$) and the base-catalyzed solutions. The relation between the intrinsic viscosity [${\eta}$] and number average molecular weight ${\bar{M}}n$, namely $[{\eta}]=K{\bar{M}}n{\alpha}$, has shown that the acid-catalyzed spinnable solution (r = 1 and 2) had linear polymers where the exponent a's were about 0.56 and 0.81, whereas non-spinnable solutions (r = 4 and 8) had three dimensional network polymers or spherical particles where the exponent a's were 0.41-0.51 and 0.35.

• Journal of the Korean Ceramic Society
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• v.42 no.12 s.283
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• pp.842-845
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• 2005

Glass composites containing ceramic fiber have been developed for Solid Oxide Fuel Cell (SOFC) seals. Effect of glass type, loading pressure and thermal cycle the leak rates of composite seals was investigated. Seal performance of two commercial glasses was compared with that of $SiO_2BaO-B_2O_3$ glass synthesized in this work. The leak rate for seals made of pyrex(R) increases from $\~0.0005\;to\;\~0.004sccm/cm$ as the gas pressure increases from 10 to 50 kPa. The soda lime silicate glass seal shows the leak rate two times higher than the one made of pyrex(R) or $SiO_2BaO-B_2O_3$ glass. The viscosity of glass at the seal test temperature is presumed to affect the leak rate of the glass seal. As the applied loading pressure increases from 0.4 to 0.8 MPa at $750^{\circ}C$, the leak rate decreases from 0.038 to 0.024 sccm/cm for composite seals. It has been found that during 50 thermal cycles between $450^{\circ}C\;to\;700^{\circ}C$ leak rates remained almost constant, ranging from 0.025 to 0.03sccm/cm. The results showed an excellent thermal cycle stability as well as sealability of the glass matrix ceramic fiber composite seals.

• Resources Recycling
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• v.4 no.1
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• pp.31-37
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• 1995

This study was to investigate the effects oi agitation speed, pulp concentration, ion concentration ill the slurry solution, printed area of the waste newspaper, immerwng time and the temperature on the defiberation process for the waste newspaper. The defikration efficiency at 50% is twice that of 16%. The efficiency is improved as two times according to elevate the agtation speed as two times in the range of 200-2WO r.p.m.. Defiberation with NaOH 1X10-'M solution has higher efficiency than that of NaOH 1 x 1 0 - M solution as 3 times at the conditions of 16%, 1200 r.p.m, and 1% pulp concentration The temperature of immersing salut~on aifects on the efficiency more than immersing time does. Increasing the printed area of newspaper decreases the velocity of defiberation. The alkaline solution is effective to defiberate and the defiberation efficiency at the same dosage of alkalinity is in the order a1 NaOH) KOH) Na,SiO, ) Na,CO, ) Ca(OH)2.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.901-908
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• 2018

Graphite is used as a sample anode active material. However, since the maximum theoretical capacity is limited to $372mA\;h\;g^{-1}$, a new anode active material is required for the development of a high capacity lithium ion battery. The maximum theoretical capacity of Si is $4200mA\;h\;g^{-1}$, which is higher than that of graphite. However, it is not suitable for direct application to the anode active material because it has a volume expansion of 400%. In order to minimize the decrease of the discharge capacity due to the volume expansion, the Si was pulverized by the dry method to reduce the mechanical stress and the volume change of the reaction phase, and the change of the volume was suppressed by coating the carbon layers to the particle size controlled Si particles. And carbon fiber is grown like a thread on the particle surface to control secondary volume expansion and improve electrical conductivity. The physical and chemical properties of the materials were measured by XRD, SEM and TEM, and their electrochemical properties were evaluated. In this study, we have investigated the synthesis method that can be used as anode active material by improving cycle characteristics of Si.

• Journal of The Korean Society of Grassland and Forage Science
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• v.4 no.2
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• pp.89-97
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• 1983

This experiment was carried out in order to study the effect of seasonal changes and location differences on the productivity of the native reed (Phragmites Communis Trinius). The samples of reed were taken at about 30-days interval from May to October, 1982, on the open field of the reclaimed land, the river bank and the tideland in Chonnam area, and measured the yield, the feed compositions and in vitro dry-matter digestibility(IVD). The results are summarized as follow: 1. Plant height was rapidly heightened in May and June, and the number of leaves rapidly increased from May to August. However, dry matter yield increased until September and gradually decreased thereafter. 2. In general, the content of crude protein and the in vitro dry matter digestibility decreased with ageing, and the content of fiber increased. 3. Considerable difference by location in the chemical composition including $SiO_2$, Ca and P was observed. 4. There was a significant negative correlation (p<0.05) between the content of crude protein and that of crude fiber. There was a significant positive correlation(p<0.05) between the in vitro dry-matter digestibility(IVD) by two-stage method and the content of crude protein, and also was a significant negative correlation(p<0.05) between the content of fiber and that of crude protein.