• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.709-714
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• 2003

Eu doped $Y_2$ $O_3$ nanoparticles were prepared with the solvothermal synthesis using the ethyleneglycol solvent at 20$0^{\circ}C$ for 3-5 h and then annealed in air at 1000-140$0^{\circ}C$ for 2-4 h. The X-ray diffraction pattern of annealed crystals at 100$0^{\circ}C$ for 2 h could be indexed as pure cubic cell of $Y_2$ $O_3$ phase with lattice parameters a=10.5856 $\AA$ which is very close to the reported data (JCPDS Card File, 41-1105 a=10.6041 $\AA$). Average size of prepared phosphor particles have about 100 nm, which were spherical morphology. The phosphor particle sizes decreased and the emission intensity increased at the annealing temperature. Though PL spectrum analysis, the 3% Eu doped $Y_{2-x}$ $O_3$:E $u_{x}$ $^{3+}$(x=0.06) phosphor showed the excitation spectrum at 250 nm wavelength and the maximum emission spectrum at 611 nm wavelength.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.95-101
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• 1997

Using aluminum powder with average particle size of 22.1 $\mu$m, aluminum compact made by Pressureless Powder Packing Method showed 52% green density. The activation energy of aluminum oxidation was cal-culated from the weight change of TG, and it was varied in the range of 16~64 kJ/mol. It was found from the variation of the activation energy and the observation of the microstructure that oxidation was de-pendent on the destruction of oxide film and the melt-out of aluminum. Aluminum compact was reaction-bonded at 1000~140$0^{\circ}C$ for 4~60hrs, and oxidation was dependent on temperature rather than time. Reac-tion-bonded aluminum oxide at 140$0^{\circ}C$ for 60hrs showed 92% oxidation percent. It was sintered at 1$600^{\circ}C$ for 15hrs and the sintered body showed 62% relative density.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.429-435
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• 2009

In this study, we investigated microstructure and the CO gas sensing properties of Ag-CuO-$SnO_2$ thin films prepared by co-evaporation and subsequently thermal oxidation at air atmosphere. The sensitivity of a Cu-Sn films, thermally oxidized at $600^{\circ}C$, is strongly affected by the amount of Cu. At Cu:7 wt%-Sn:93 wt%, the film exhibited a maximum sensitivity of ${\sim}2.3$ to CO gas of 1000 ppm at $300^{\circ}C$. In contrast, the sensitivity of a Sn-Ag film did not change significantly with the amount of Ag. An enhanced sensitivity of ${\sim}3.7$ was observed in the film with a composition of Ag:3 wt%-Cu:4 wt%-Sn:93 wt%, when thermally oxidized at $600^{\circ}C$. In addition, this thin film shows a response time of ${\sim}80$ sec and a recovery time of ${\sim}450$ sec to 1000 ppm CO gas. The results demonstrate that the CO sensitivity of the Ag-CuO-$SnO_2$ thin films may be closely associated with coexistence of $SnO_2$ and SnO phase, decrease in average particle size, and a porous microstructure. We also suggest that co-evaporation and followed by thermal oxidation is a very simple and effective method to prepare oxide gas sensor thin films.

• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.156-161
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• 2014

Gallium oxide ($Ga_2O_3$) powders were synthesized using a precipitation method and a polymerized complex method. TG-DSC, SEM, and XRD were performed to investigate the phase and morphology of the $Ga_2O_3$. In situ high-temperature XRD analysis revealed the crystal structure of $Ga_2O_3$ at different temperatures. The $Ga_2O_3$ obtained using the precipitation method and polymerized complex method were generally spherical-shaped particles and their average particle size was approximately 80 nm and $1{\mu}m$, respectively. The crystal structure of the $Ga_2O_3$ prepared by the precipitation method was changed from rhombohedral to monoclinic at $700^{\circ}C$, while monoclinic $Ga_2O_3$ was obtained directly from the precursor by the polymerized complex method.

• Asian-Australasian Journal of Animal Sciences
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• v.5 no.2
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• pp.295-301
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• 1992

Eight crop residues : 1, sorghum (Sorqhum bicolor) straw, 2, maize (Zea mays) straw, 3, cotton (Gossypium Sp.) straw, 4, sunflower (Helianthus Sp.) straw, 5, cotton (Gossypium Sp.) seed hulls, 6, groundnut (Archais hypogaea) hulls, 7, maize (Zea mays) cobs, 8, sugarcane (Saccharum officinarum) bagasse and two forest grasses 9, Heteropogan contortus dry grass and 10, Sehima nervosum dry grass were subjected to three physical processing 1, chopping (2-3 cm) 2, grinding (8 mm sieve) and 3, pelleting (10 mm die holes). The processed material was fed ad lib. Along with 250 g of concentrate mixture per head per day to 6 adult local goats and 16 adult Nellore rams in ten digestion experiments and finally assessed the nutritive value of the processed roughages by difference method. Grinding increased bulk density by 32.4 (cotton seed hulls, CSH) to 88.1% (Sehima dry grass) while pelleting of ground material increased bulk density by 53.9 (maize cobs) to 235.8% (maize straw). The average particle size ranged from $584.1/^U$ (sorghum straw) to $1467/^U$ (CSH). Modulus of uniformity ranged from 2:5:3 (sorghum straw) to 7:2:1 (CSH) while modulus of fineness ranged from 3.4 (sorghum straw) to 5.4 (CSH). Molasses absorbability was highest with cotton seed hulls and least with maize cobs. Pelleting increased DM intake of the residues except cotton seed hulls compared to grinding. Grinding of chopped material/unprocessed material increased DM intake on sorghum straw and cotton seed hulls. Sheep consumed more DM compared to goats on all the residues except sorghum and sunflower straws. Pelleting increased nutritive value of all the residues compared to grinding and chopping. However, no difference was observed in the nutritive value due to grinding and chopping. Goats performed better compared to sheep in utilizing the fibrous residues.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.807-810
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• 2002

$GdPO_4$:Tb phosphor particles with spherical shape and high photoluminescence were prepared by spray pyrolysis. The brightness of prepared $GdPO_4$:Tb under the vacuum ultraviolet(VUV) illumination was comparable with that of the commercial $Zn_2SiO_4$:Mn phosphor particles. The photoluminescence spectra of $GdPO_4$:Tb phosphor particles had maximum peak at 547 nm, and the sharp peaks at 480 nm, 580 nm, and 620 nm. The spherical morphology of prepared $GdPO_4$:Tb particles was completely maintained even after the posttreatment up to 1100 $^{\circ}C$. When the posttreatment temperature was over 1100 $^{\circ}C$, the particles did not have the spherical shape anymore. The average particle size of $GdPO_4$:Tb phosphor particles prepared by using $(NH_4)_2HPO_4$ was changed from 0.5 to 1.9 ${\mu}m$ and its effect on the PL intensity was investigated. It was found that the optimized $GdPO_4$:Tb particles have a good excitation spectrum comparable to that of the commercial $Zn_2SiO_4$:Mn phosphor particles under the VUV illumination from 140 to 220 nm. We concluded that the $GdPO_4$:Tb phosphor particles with spherical shape prepared by spray pyrolysis is a promising candidate for a green-emitting PDP phosphor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.2049-2054
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• 2013

Recently, magnesium hydroxide ($Mg(OH)_2$) has many applications in various field, due to its outstanding characteristics such as a nontoxic, noncorrosive and thermal stable properties. In this study, different shapes of flower and flake type magnesium hydroxide were synthesized by precipitation method at room temperature using $MgSO_4$, $MgCl_2$ and $Mg(NO_3)_2$ as magnesium sources, NaOH and $NH_3$ as alkaline sources. Influence of synthesis on the morphological characteristics, sizes and shapes of magnesium hydroxide particles, was investigated, such as different precursors and parameters. The shape of magnesium hydroxide depend on magnesium and alkali sources. Average size of flower particle had about $1{\mu}m$, and flake had about 20 ~ 50 nm. The synthesised magnesium hydroxide groups were characterized by XRD, FE-SEM, FT-IR, EDS, PSA and TG.

• Journal of the Korean Applied Science and Technology
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• v.22 no.4
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• pp.306-314
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• 2005

In this study, spherical $pre-BaTiO_3$ particles are prepared by gelation and aging process in autoclave without catalysts. The (Ba-Ti) gel used as a starting material was prepared by aging mixtures of titanyl acylate with barium acetate aqueous solution([glacial acetic acid (AcOH)]/[titanium isopropoxide (TIP)] 4, [barium acetate]/[TIP] 1) at $45^{\circ}C$ for 48hrs. XRD and SEM results for the (Ba-Ti) gel sample at aging process showed that the gel was formed via aggregation of the fine particles. It seems to be the primary particles of bulk (Ba-Ti) gel amorphous, but the spatial arrangement of barium and titanium in the (Ba-Ti) gel is similar to that in crystalline $BaTiO_3$ particles. From XRD and FT-IR. spectroscopy analysis it was found that the crystal structure of the prepared particles continuously transformed from amorphous to tetragonal as the calcination temperature increased, and crystallized spherical cubic and tetragonal $BaTiO_3$ powder obtained at the very low calcination temperature between $500^{\circ}C$ and $900^{\circ}C$ after 1hrs of heat treatment respectively. According to BET analysis result, final particle have pore structure of ink bottle shape which is produced by aggregation of fine spherical particles with surface area of $280m^2/g$ and average pore size of 130nm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.483-487
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• 2014

In this study, joining methods with SiC powder as the joining adhesives were studied in order to avoid the residual stresses coming from CTE (Coefficient of Thermal Expansion) mismatch between substrate and joining layer. The shear strength and microstructure of joined material between SiC substrates are investigated. The commercial Hexoloy-SA (Saint-Gobain Ceramics, USA) used in this work as substrate material. The fine ${\beta}$-SiC nano-powder which the average particle size is below 30 nm, $Al_2O_3$, $Y_2O_3$, and $SiO_2$ were used as joining adhesives. The specimens were joined with 20MPa and $1400-1900^{\circ}C$ by hot pressing in argon atmosphere. The shear test was performed to investigate the bonding strength. The cross-section of the joint was characterized by using an optical microscope and scanning electron microscopy (SEM).

• International Journal of Highway Engineering
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• v.12 no.2
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• pp.115-121
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• 2010

To evaluate the engineering characteristics of aggregate base materials, cyclic triaxial, CBR and permeability tests were performed for 15 samples. The CBR values of aggregate base materials have wide range from 32 to 110(average 81) and the amount of swelling in submerged conditions has below 0.04mm. The Modulus of aggregate base materials were significantly affected by volumetric stress, linear volumetric model was best for fitting. The modulus of aggregate base materials were determined within range of 100MPa~600MPa, 80~270 and 0.1~0.6 for model coefficient $k_1$ and $k_2$ respectively. The empirical correlation model was suggested that prediction the modulus from the basic properties obtained from particle size distribution test and compaction test. The coefficient of determination of the proposed correlation model was 0.423 for model coefficient $k_1$, 0.920 for model coefficient $k_2$ and 0.872 for modulus with stress level.