• Journal of the Korean Wood Science and Technology
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• v.40 no.4
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• pp.237-243
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• 2012

Sound absorption capability and anatomical features of the organosolv pretreated Japanese larch and yellow poplar wood were estimated by stereoscopic observation and two microphone transfer function method. Sound absorption capabilities of organosolv treated wood, in the entire estimated frequency range (50~6,400 Hz), were higher than those of control specimen. Especially, the treated wood's absorption capabilities measured in the frequency range of 2~4 kHz were about two times higher than those of control specimen. By the organosolv pretreatment (at $70{\sim}120^{\circ}C$), the weight loss of wood occurred in less than 1% of total weight of wood and the porosity of wood increased slightly. In addition, it was presupposed that microstructural changes of wood occurred during organosolv pretreatment and this structural changes cause the increasing of the sound absorption capability of wood.

• Korean Journal of Food Science and Technology
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• v.47 no.6
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• pp.698-703
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• 2015

The elderly or patients with masticatory disturbance and deglutition dysfunctions, may have difficulty in chewing or biting foods with a hard texture. Thus, softening of the texture of foods using hemicellulase immobilized by the nanoencapsulation technique was examined in this study. Burdock was cut into cylindrical-shaped samples, which were immersed in distilled water and non-coated or coated enzymes for 48 h at $4^{\circ}C$. The hardness of the treated samples decreased compared to the control. Microstructural observations revealed that the cells in the non-coated burdock were destroyed after 24 h. From the point of view of enzyme activity, the initial activity of the non-coated enzymes was higher than that of the coated enzymes. However, the enzyme activity was not significantly affected by the immersion time. Therefore, it appears that the encapsulation technique for enzymes may be useful for softening the texture of foods.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.443-450
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• 2015

This paper presents an investigation of the mechanical and microstructural properties of Class F fly ash based geopolymer containing sodium sulfate as an additive. Sodium sulfate was used as an chemical additive at the dosage levels of 0, 2, 4, and 6wt% of fly ash. Sodium hydroxide and sodium silicate solutions were used to activate fly ash. The compressive strengths of geopolymer pastes were measured at the age of 28 days. The microstructures of the geopolymer pastes were examined using XRD, MIP and SEM tests. The additions of 2wt% and 4wt% sodium sulfate produced geopolymers with high strength, while increasing the dosage of levels to 6% resulted in almost no changes in strength, comparing with the control geopolymer. The optimum increase in strength was obtained with the addition of 4wt% sodium sulfate. As the amount of sodium sulfate is increased, no additional crystalline phase was detected and no change of amorphous phase indicated despite the change in the strength development. The increase in the strength was due to the change of pore size distribution in samples. As addition of sodium sulfate altered the morphologies of reactive productions and Si/Al ratios of the reaction products, the strengths were thus affected. It was found that the strengths of geopolymer were larger for lower Si/Al ratios of reaction products formed in samples. The optimal amount of sodium sulfate in the fly ash based geopolymer helps to improve mechanical properties of the geopolymer, on the other hand, the high percentage of sodium sulfate could exist as an impurity in the geopolymer and hinder the geopolymer reaction.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.251-258
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• 1995

In an effort to increase the thermoelectric figure of merit by reducing the thermal conductivity, the unidirectionally solidified n-type (Bi, Pb)-Te based alloys which form a $Bi_{2}Te_{3}-PbBi_{4}Te_{7}$eutectic lamellar structure were investigated with the microstructural control at various solidification conditions. PbBi_{4}Te_{7}$ lamellae were grown on cleavage plane(0001) of $Bi_{2}Te_{3}$ and the interlamellar spacing decreased from 10.4 $\mu \textrm{m}$to 3.2$\mu \textrm{m}$ with growth velocity variation from 1.4 \times 10^{-4}$cm/sec to $8.3 \times 10^{-4}$cm/sec. Seebeck coefficient was constant, $\mid$$\alpha$$\mid$=29 $\mu$ V/K regardless of growth direction, growth velocity and temperature gradient. Electrical conductivity showed a tendency to decrease slightly with growth velocity and it parallel to growth direction was about three times as large as perpendicular direction. The figures of merit were varied differently from Seebeck coefficients and electrical conductivities depending on the growth direction, growth velocity and temperature gradients. They showed the relative increase in case of perpendicular direction compared with parallel to growth direction. It is believed to be due to the reduction of the thermal conductivity according to decrease of the interlamellar spacing.

• Korean Journal of Materials Research
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• v.9 no.6
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• pp.577-582
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• 1999

In order to make the electroconductive $Si_3N_4$-TiN composities, the Si-Ti(N) compacts were nitrided at $1450^{\circ}C$ for 20hours, and then they were post-sintered by a gas-pressure-sintering technique at 1TEX>$1950^{\circ}C$ for 3.5 hours. As starting powders, commercial si powder of about $10\mu\textrm{m}$, two types of Ti powders of 100 and 325 mesh, and fine-sized TiN of $2.5\mu\textrm{m}$ powders were used. In the $Si_3N_4$-TiN sintered bodies used Ti powders, the relative density and fracture strength and electrical conductivity are low due to the existence of large amounts of coarse pores. However, in the $Si_3N_4$-TiN composite used TiN powder, the fracture toughness, fracture strength and electrical resistivity were $5.0MPa{\cdot}m^{1/2}$, 624MPa and $1400{\omega}cm$, respectively. The dispersion of TiN particles in the composite inhibited the growth of $Si_3N_4$ in the shape of rod and made strong strain field contrasts at the $Si_3N_4$-TiNinterfaces. It was recognized that microstructural control is required to improve the electrical conductivity and mechanical properties of $Si_3N_4$-TiN composites by dispersing TiN particles homogeneously.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.2
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• pp.121-127
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• 2024

In this study, the applicability of replacing DG(Desulfurized Gypsum) from oil refinery with CCCMs(Carbon dioxide Conversion Capture Materials) as an ALC(Auto-claved LIghtweight Concrete) raw material was examined, and basic properties of ALC was measured. The main chemical components of DG and CCCMs were CaO and SO₃, and an increase in LOI(Loss of ignition) due to mineral carbonation reaction was verified. The crystalline phases of CCCMs were CaCO₃, CaSO₄, Ca(OH)₂, and CaSO₄·2H₂O. When DG, a raw material for ALC production, was replaced with CCCMs, foaming height, pore shape, absolute dry gravity, and compressive strength results measured similar for all binders. In addition, the formation of tobermorite which is main crystalline phase of ALC was shown for all specimens in microstructural analysis.