Seung Gu Kang

Microwave dielectric properties of Ca[(Li1/3Nb2/3)1−xTi3x]O3−δ ceramics with B2O3

Abstract Microwave dielectric properties of Ca[(Li 1/3 Nb 2/3 ) 1− x Ti 3 x ] O 3−δ (0.0≤ x ≤0.2) (CLNT) ceramics with B 2 O 3 were investigated. In the entire composition range, the orthorhombic single phase was detected. With increase of x from 0.0 to 0.2, dielectric constant ( K ) increased from 30 to 89, Q · f value decreased from 33,000 to 3820xa0GHz, and temperature coefficient of resonant frequencies (TCF) increased from −16 to 22.4xa0ppmxa0°C −1 , respectively. Furthermore, with addition of 1.0xa0wt.% B 2 O 3 , the sintering temperature of CLNT ceramics was reduced from 1150 to 970xa0°C without degradation of dielectric properties. Typically, K =50, Q · f =6500xa0GHz, and TCF=−7.6xa0ppmxa0°C −1 were obtained for the with CLNT ( x =0.1) specimen with 1.0xa0wt.% B 2 O 3 sintered at 940xa0°C, which is promising for application of multilayer microwave devices using Ag as internal electrode.

Growth and luminescent characteristics of ZnGa2O4 thin film phosphor prepared by radio frequency magnetron sputtering

ZnGa2O4 and doped ZnGa2O4 thin film phosphors were prepared by the rf magnetron sputtering method. Deposition parameters were controlled to characterize the deposition mechanism and structural changes. And then the relation between the structure and luminous properties was characterized. To observe the effects of the substrates, thin films were deposited on Si(100), Si(111), and indium–tin–oxide (ITO) coated glass substrates. The orientational transition was observed by varying the substrate temperature. The grain size of ZnGa2O4:Mn thin film deposited on a Si wafer was smaller than that on an ITO/glass substrate, which resulted in higher photoluminescence (PL) intensity. By heat treatment, PL intensity was increased because it eliminated the defects in films and improved the crystallinity.

Influence of Addition of Waste Glass as a Fluxing Agent on the Bloating Phenomenon of Artificial Aggregates Fabricated from Coal Bottom Ash

The artificial aggregates (AAs) were manufactured from the parent batch powders consisting of bottom ash produced at thermal power plant and dredged soil by direct sintering method at 1050~1200°C for 10min. The bloating phenomenon could be occurred in AAs due to a gas-capturing caused by large quantity of liquid formed at the specimen surface. Increasing the amount of the Na2O added enlarged the area of black core and size of the macro pores in the aggregates. The inside black core got out of the surface of the specimens sintered at 1200°C showing the rugged and cracked surface, but this morphology did not cause a water absorption to increase.

Properties of Artificial Lightweight Aggregates (ALAs) Made of Dredged Soil Mixed with Waste Catalyst Slag

The artificial lightweight aggregates (ALAs) were manufactured using dredged soil produced at thermal power plant and waste catalyst slag by direct sintering method at 1050~1250°C for 10min. The ALAs of 100% dredged soil showed the black core phenomenon even at the low sintering temperature as 1050°C and become lightened by bloating pores in black core area with sintering temperature. On the other hand, the aggregates with 100% waste catalyst slag did not showed black coring and bloating phenomenon and had the low forming ability and many cracks inside. Adding the dredged soil to the waste catalyst slag decrease the specific gravity by promoting the black coring and bloating inside. The water absorption(%) of ALAs decreased with sintering temperature. The ALAs fabricated in this study showed the specific gravity of 0.8~2.0 and water absorption of 2~16% so it could be applied to various fields such as the lightweight concrete or the field of the porous carriers for purification of a contaminated soil or water.

Impact Sound Reduction Analysis of Concrete Slab Containing Artificial Lightweight Aggregates Fabricated Using a Sewage Sludge

The artificial lightweight aggregate (ALA) was fabricated using a sewage sludge produced from a municipal wastewater, and impact sound reduction analysis for concrete slab made with the ALA was done. Specific gravity of ALA decreased with the sewage sludge content due to the gas bloating caused by melt films on the surface of ALA, which is formed easily because of low temperature melting P2O5 and modifiers, CaO, MgO and K2O contained in the sewage sludge. And water absorption of ALA increased with the sewage sludge content owing to open pores which were formed by connecting an inside pore to a surface. A specific gravity of 10mm diameter ALA was lower than that of 7mm ALA since a trapped gas could not escape from the core to the surface of ALA due to longer moving distance. The ALA containing 20 wt% sludge sintered in a electric furnace showed a specific gravity 15% lower and water absorption 50% higher than that of ALA sintered in a rotary kiln. It might be attributed to easy release of gases during the pre-heat zone (600-1000oC) in the rotary kiln, resulting in densification of ALA. Light and heavy weight floor impact sound of concrete slab made with ALA were 63-72dB and 44-76dB respectively, similar to a general concrete slab. The unit weight of concrete slab made with ALA, however, was 18% lower than that of general one owing to the lightweight of ALA, so it could be suitable to applying for high-rise building.

Properties of Artificial Aggregate for Orchid Culture Fabricated from Solid Wastes

The artificial aggregates were fabricated from several industrial wastes such as waste white clay at 1100 ∼ 1150°C/10min in a rotary kiln and its physical properties were evaluated. The water absorption, porosity and emission rate of aggregates were controlled by changing processing methods or compositions which change the microstructure of specimens. The natural aggregates showed many macro pores(120∼180 μm), high porosity, high water absorption and low unit weight compared to artificial aggregates, while a porosity of artificial aggregates whose apparent shape is more regular was higher than that of a natural aggregates. Increasing waste white clay content in aggregates enhanced bloating during sintering, so increased the absorptivity of specimens. The void contents influenced a initial water emission and the natural aggregates showed a higher void content compared to artificial one due to their irregular shape. The artificial aggregates having shell structure showed a excellent water release control ability. Especially, for after 6 days, its water emission amount was lower than that of natural aggregates. However, artificial aggregates whose shell is removed through crushing process showed deteriorated water release ability.

Microwave dielectric properties of Bi(Nb1-xTax)O4 ceramics with Cu2V2O7

Abstract Microwave dielectric properties of Bi(Nb1-xTax)O4 with 0.8 wt.% Cu2V2O7 were investigated as a function of Ta content and sintering temperature. X-ray powder diffraction patterns of the specimens sintered at 775°C for 3h showed the orthorhombic single phase throughout the entire composition range. Dielectric constant was not changed drastically, however, Qf value strongly depended on the composition and sintering temperature. The temperature coefficient of the resonant frequency (TCF) could be controlled with Ta content. Typically, K of 45, Qf of 8900 GHz and TCF of +4 ppm/°C were obtained in the Bi(Nb0.6Ta0.4)O4 specimens with 0.8 wt.% Cu2V2O7 sintered at 775°C for 3h.

Fabrication of FRP Spacers of Insulating Glass for Energy-Saving Eco-Friendly Home

The FRP(fiber reinforced plastics) spacer was fabricated to enhance the heat blocking and mechanical properties of insulating glass for energy-saving eco-friendly home. The fiber volume percent in ABS(acrylonitrile-butadiene-styrene) matrix was chosen as a main controlling factor. The various properties of FRP spaces were evaluated such as 3-point bending strength, thermal conductivity, and water absorption rate. And the aging test was performed at various temperatures for the spacer immersed in water. In conclusion, the optimum fiber volume percent, 25wt% of spacer was found that is enough for handling in construction process and appropriate for blocking the heat loss through the insulating glass window.

A Comparative Study on the Physical Properties of Artificial Aggregates Made from Acid Clay and Dredged Soil

Artificial aggregates (AAs) were manufactured from the acid clay (waste bentonite) and dredged soil produced at a thermal power plant by sintering at 600~1200°C for 10min. And those specimens were compared with respect to their bloating ability. The aggregates of acid clay had well-developed black core and uniform macro pores. The specific gravity of the AAs of acid clay increased with sintering temperature at 600~1000°C due to densification, but dramatically decreased at 1100°C, and at this temperature, the AAs showed bloating. The specific gravity and water absorption of the aggregates of dredged soil decreased with sintering temperature at 600~1000°C, indicating that the dredged soil has the ability to enlarge the sintering temperature range, favorable for the mass production process. The specific gravity of the AAs fabricated in this research ranged 0.8~2.0 and the water absorption ranged 4~26%, which was sufficient for various applications, such as functional membranes, light weight construction, smart soil, sound absorption and insulation fields etc..

Physical Properties and Microstructure of the Fly Ash Based-Geopolymer/Granule Composites

In this research, the fly ash (F/A) discharged from a thermal power plant was recycled to manufacture geopolymer containing granules instead of sand. Several types of granules using fly ash were assessed. The properties of the geopolymer/granule composites were analyzed as a function of the crystalline phase and size of the granules, as well as the molding pressure. The compressive strength and density of the geopolymer composites containing the hydrated granules fabricated by hand-tapping were 5.7 MPa and 1.47 g/cm3, respectively, while composites created by pressure molding were 15.6 MPa and 1.73 g/cm3. These results are comparative or superior to those of commercial cement bricks (8 MPa according to KS F 4004). Therefore, the geopolymer/granule composites fabricated in this study can be applied to cement bricks and can be a base for the enhancement of the recycling rate of fly ash.