• Journal of the Korea Institute of Building Construction
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• v.4 no.3
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• pp.93-100
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• 2004

In recent years, it has widely been studied on the light-weight composites for the purpose of the large space and thermal insulation of building structures. The purpose of this study is to evaluate the properties of light-weight composites made by binders as cement, resin and polymer cement slurry. The concrete composites are prepared with various conditions such as polymer-cement ratio, void-filling ratio, type of resin, filler content and light-weight aggregate content, tested for thermal conductivity. From the test results, the thermal conductivity of concrete composites with the binder of cement tends to decrease with increasing polymer-cement ratio, and to increase with increasing void-filling ratio. The thermal conductivity of concrete composites with the binder of resin are markedly affected by the light-weight aggregate content, type of resin and filler content. The composites made by polymer-modified concrete and polymer cement slurry have a good thermal insulation property. From the this study, we can recommend the proper mix proportions for thermal insulation Panel or concrete. Expecially. the thermal conductivity of concrete composites made by polyurethane resin is almost the same as that of the conventional expanded polystyrene resin.

• Journal of the Korean Applied Science and Technology
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• v.33 no.1
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• pp.92-99
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• 2016

Polyurethane resin used to leather coat was synthesized by the addition reaction of PPG and PTMG with different mole ratios. Physical characteristics of the synthesized polyurethane resin were measured by the SEM, FT-IR and the UTM. Increasing mole ratio of PTMG having four methylene groups caused the increase of abrasion resistance and tensile strength. The elongation was decreased. As we measured the solvent(toluene) resistance of poly urethane resin, it was found the there were no effect of PTMG mole ratios on the phyhsical properties of the resin. The viscosity was increased by ratio of PTMG mole ratio.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.31-38
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• 2018

The effects of polymer-binder ratio and metakaolin content on the properties of ultrarapid-hardening polymer-modified concretes using metakaolin are examined. As a result, regardless of the metakaolin content, the flexural, compressive and adhesion in tension strength of the ultrarapid-hardening polymer-modified concretes tend to increase with increasing polymer-binder ratio. Regardless of the polymer-binder ratio, the strengths of the ultrarapid-hardening polymer-modified concretes increase with increasing metakaolin content, and reaches a maximum at metakaolin content of 5%. The water absorption, carbonation depth and resistance of chloride ion penetration of the ultrarapid-hardening polymer-modified concretes decrease with increasing polymer-binder ratio. The resistance of freezing and thawing improvement is attributed to the improved bond between cement hydrates and aggregates because of the incorporation of polymer dispersion.

• Journal of the Korean Magnetics Society
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• v.6 no.5
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• pp.334-339
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• 1996

In order to investigate the influence of the magnetic paticle size and its properties on the particulate magnetic material, we evaluated the dispersion of magnetic particles and the electromagnetic properties in magnetic tape made from the magnetic paints by use of each magnetic particles witch were different from particle size and its propertis. The dispersion of magnetic particles depends on the surface chemical properties rather than particle size. As particle size is smaller, the packing ratio of magnetic particle and the magnetic flux density in tape increase. The output levels in playing back of tape incerase in wide frequency range from 315 Hz to 10 kHz and the noises decrease. It is very important to choose the size, the shape, the surface chemical properties and the magnetic properties of the magnetic particle in producing the high quality magnetic tape.

• Journal of Adhesion and Interface
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• v.9 no.1
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• pp.3-8
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• 2008

Self-sensing was evaluated for carbon nanofiber (CNF)/epoxy composites with two different aspect ratios via electro-micromechanical technique and wettability test. Volumetric electrical resistance was measured to evaluate the comparative dispersion degree indirectly and it decreased due to the increase of electric contacts with increasing CNF concentration. The dispersion degree was evaluated indirectly by calculating coefficient of variation (COV) of volumetric electrical resistance. The CNF type A with a high aspect ratio showed better self-sensing than the case of CNF type B with a short aspect ratio. The CNF type B/epoxy composite showed little self-sensing at a concentration higher than 2 vol% probably due to poor dispersion. The apparent modulus of CNF type B was higher than that of CNF type A due to the orientation effect and the high surface area. The thermodynamic work of adhesion was consistent with the result of apparent modulus.

• Economic and Environmental Geology
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• v.27 no.4
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• pp.387-396
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• 1994

Mineralogical and geochemical studies on gold-bearing quartz veins and wallrock from the Mugeug mine were carried out in order to investigate the variation of mineralogical composition and the geochemical behavior of elements with distance from the gold-bearing quartz veins. Gold-bearing quartz veins occur in early Cretaceous medium- to coarse-grained biotite granite. The unaltered wallrock is composed mainly of quartz, plagioclase, orthoclase, microcline, biotite and hornblende with accessory minerals of sphene and apatite. Mineralogical changes in altered wallrock around the gold-bearing quartz veins were observed as follows; 1) biotite and hornblende altered into chlorite, and next to sericite, 2) plagioclase, orthoclase and microcline altered into sericite, and 3) calcite and quartz introduced into wallrock. Contents of $K_2O$, Rb, Cs, Au, As and Sb in altered wallrock increase, whereas those of $Na_2O$, CaO, Ba, and Sr decrease with proximity to the gold-bearing quartz veins. The loss on ignition also increases with the increase of alteration mineral. The width of primary dispersion increases in order $Au=SiO_2<As=Cs=Rb<K_2O=Sb$ and $MnO<Na_2O=CaO=Ba<Sr$. The sericitization index, $K_2O/(K_2O+Na_2O)$, is an important indicator to interpret the degree of alteration at the Mugeug mine, which is more than 0.8 in strongly and moderately altered granite, 0.5~0.8 in wea altered granite, and less than 0.5 in unaltered granite. Alteration indices for major and trace elements, and the ratio of Rb/Sr are also useful to discriminate alteration zones.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

• Composites Research
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• v.36 no.3
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• pp.180-185
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• 2023

This paper investigates the impact of fiber dispersion on the internal structure and mechanical strength of SiC_f/SiC composites manufactured using spread SiC fibers. The fiber volume ratio of the specimen to which spread SiC fiber was applied decreased by 9%p compared to the non-spread specimen, and the resin slurry impregnated between the fibers more smoothly, resulting in minimal matrix porosity. In order to compare the fiber dispersion of each specimen, a method was proposed to quantify and evaluate the separation distance between fibers in composite materials. The results showed that the distance between fibers in the spread specimen increased by 2.23 ㎛ compared to the non-spread specimen, with a significant 42.6% increase in the distance between fiber surfaces. Furthermore, the 3pt bending test demonstrated a 49.3% higher flexural strength in the spread specimen, accompanied by a more uniform deviation in test data. These findings highlight the significant influence of SiC fiber dispersion on achieving uniform densification of the SiC_f/SiC matrix and increasing mechanical strength.

• Journal of Powder Materials
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• v.5 no.2
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• pp.122-128
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• 1998

NiAl based ODS (Oxide Dispersion Strengthened) intermetallic alloys have been produced by mechanical alloying (MA) process and consolidated by hot extrusion. Subsequent thermomechanical treatments have been applied to induce secondary recrystallization in an attempt to improve creep resistance in this material. The creep behavior of secondary recrystallized MA NiAl has been investigated and compared with those of as-extruded condition. Minimum creep rate were shown to be approximately two orders of magnitude lower than that in as-extruded condition. The improvement in creep resistance is believed due to the grain coarsening, restricting of dispersoid coarsening as well as increase in grain aspect ratio. Creep threshold stress behavior, below which no measurable creep rate can be detected, has been discussed on the basis of particle-dislocation interaction theory. The threshold stress becomes negligible after secondary recrystallization in MA NiAl, presumably due to dispersoid coarsening and a decrease in grain boundary area during secondary recrystallization.

• Journal of Astronomy and Space Sciences
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• v.20 no.1
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• pp.63-82
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• 2003

Using the Schwarzschild's linear programming technique, we obtained the general solutions of the collisionless Bolzmann equation describing the spherical galaxy in dynamical equilibrium. From this calculation we have confirmed the existence of isotropic spherical galaxies obeying a de Vaucouleurs'law which includes a dark halo. The flattening profile of the velocity dispersion curve seen in the elliptical galaxies can be explained as the increase of mass to light ratio in this dark matter. The space density distribution of this dark matter shows that the core radius of the dark matter is smaller than the effective radius of the galaxy.