• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.39-43
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• 1997

Effects of B$_2$O$_3$ addition in the Li$_2$O-MgO-MgF$_2$-SiO$_2$g1ass system were investigated in order to make glass-ceramics for low temperature firing substrate. Base glass was made by melting at 145$0^{\circ}C$ . This glass was analyzed by THA and DTA to settle nucleation and crystallization temperature. After crystallization. crystal phase and microstructure were absorvated by XRD and SEM. Glass powders were made by water swelling method. Average particle size was 5.44${\mu}{\textrm}{m}$

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.5
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• pp.595-605
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• 2000

Dental ceramics have good aesthetics, biocompatibility, low thermal conductivity, abrasion resistance, and color stability. However poor resistance to fracture and shrinkage during firing process have been limiting factors in their use, particularly in multiunit ceramic restorations. A new method for making all-ceramic crowns that have high strength and low processing shrinkage has been developed and is referred to as the Vita In-Ceram method. This study was performed to investigate the effect of $CeO_2$ addition in borosilicate glasses on the strength of alumina-glass composites. Porous alumina compacts were prepared by slip casting and sintered at $1,100^{\circ}C$ for 2 hours. Dense composites were made by infiltration of molten glass into partially sintered alumina at $1,140^{\circ}C$ for 4 hours. Specimens were polished sequentially from #800 to #2000 diamond disk. and the final surface finishing on the tensile side was received an additional polishing sequence through $1{\mu}m$ diamond paste. Biaxial flexure test was conducted by using ball-on-three-ball method at a crosshead speed of 0.5mm/min. To examine the microstructural aspect of crack propagation in the alumina-glass composites, Vickers-produced indentation crack was made on the tensile surface at a load of 98.0 N and dwell time of 15 sec, and the radial crack patterns were examined by an optical microscope and a scanning electron microscope. The results obtained were summarized as follows; 1. The porosity rates of partially sintered alumina decreased with the rising of firing temperature. 2. The maximum biaxial flexure strength of 423.5MPa in alumina-glass composites was obtained with an addition of 3 mol% $CeO_2$ in glass composition and strength values showed the aspect of decrease with the increase of $CeO_2$ content. 3 The biaxial flexure strength values of alumina-glass composites were decreased with rising the firing temperature. 4. Observation of the fracture surfaces of alumina-glass composites indicated that the enhancement of strength in alumina-glass composites was due to the frictional or geometrical inter-locking of rough fracture surfaces and ligamentary bridging by intact islands of materials left behind the fracture front.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.3
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• pp.37-43
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• 1999

Co-firing incompatibility between the low temperature sinterable Glass/ceramic and Ag-thick film was studied. The dielectric material, which has been developed for microwave frequency applications, consists of $SiO_2-TiO_2-Bi_2O_3$-$Bi_2O_3$-RO system(RO:BaO -CaO-SrO) crystallizable glass and $Al_2O_3$as a ceramic filler. The large camber in the sintered specimen and cracks at the Ag-film under the influence of the camber occurred due to the difference of densification rate between the ceramic sheet and the Ag-film $B_2O_3$addition to the Glass/ceramic mixture reduced the severe camber. The cambers decreased with increasing the $B_2O_3$ content, and completely disappeared with 14 vol% $B_2O_3$addition. With additions of $B_2O_3$, $\varepsilon_{r}$ decreased abruptly, Q$\times$f value increased largely and the $\tau_f$ value of the material quickly shifted to positive one.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1245-1252
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• 1996

The charcteristics for the copper-contained spinel ferrites such as NiCu-and ZnCu ferrites with various copper content are investigated in this study which can provide a explanation for the behavior of copper in sintering at a low temperatuer. The bulk density and the grain size for these sintered ferrites were increased with the larger amount of copper in compositions. In microstructure of copper-contained spinel ferrites copper exists in the grain boundary which is sintering process. Electrical resistivity and frequency range with maximum Q-facor of NiCu-or ZnCu ferrites were decreased as increasing of copper content in ferrite composition.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1566-1571
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• 2009

The discharge electrodes in ac PDP are coated with dielectric layer, and transparent MgO thin films are deposited on the dielectric layer. The main role of the MgO thin films in ac PDP is to protect the dielectric layer from sputtering by ion bombardment in the glow-discharge plasma. An additional important role of the MgO thin film is the high secondary electron emission coefficient which leads the low firing voltage and low cost of the PDP. In this paper, we investigated the relations of the crystal orientation about deposition thickness, deposition rate, temperature of substrate, and distance between the MgO tablet and the substrate. Additionally, we investigated the discharge characteristics of the AC PDP using nano-powder MgO tablet

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.131-136
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• 2004

The ongoing developmental studies on the application of hydrogen peroxide for propulsion are briefly reviewed. A detailed design-study of a laboratory scale facility of a hydrogen peroxide mono-propellant engine of 100-N thrust is presented. For the preparation of concentrated hydrogen peroxide, a distillation facility has been realized. Results of water analogy tests are presented. Initial firings using the concentrated hydrogen peroxide were not successful. Low environmental temperature, low contact area of the catalyst pack, and contamination in the hydrogen peroxide were considered to be the reasons. Addressing the first two points resulted in successful firing of the rocket engine.

• Journal of Information Display
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• v.7 no.1
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• pp.25-29
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• 2006

By the voltage threshold (Vt) close-curve measurement method, the changes in the discharge characteristics such as a firing voltage and IR emission among the three electrodes were examined relative to the low or high panel temperature ranging from -10 to $80^{\circ}$. The variation in the panel temperature was found significantly influence the surface discharge between the MgO surfaces rather than the plate gap discharge between the MgO and phosphor layers. Based on this experimental observation, a modified reset waveform that alleviates the surface discharge during a ramp-up and -down period was deeloped. By adopting the proposed reset waveform, a stable address discharge could be obtained irrespective of the panel temperature variation.

• Transactions on Electrical and Electronic Materials
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• v.4 no.2
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• pp.20-23
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• 2003

Piezoelectric powder with the composition of PbTiO$_3$-PbZrO$_3$-Pb(Mn$\_$1/3/Nb$\_$2/3/)O$_3$ and small particle size of 0.3 $\mu\textrm{m}$ was investigated for low-temperature firing of PZT thick films. PbTiO$_3$-PbZrO$_3$-Pb(Mn$\_$1/3/Nb$\_$2/3)O$_3$ ceramics showed dense microstructure and superior piezoelectric properties, electromechanical coupling factor (k$\_$p/) of 0.501 and piezoelectric constant (d$\_$33/) of 224. The PZT paste was made of the powder and organic vehicles, and screen-printed on Pt(450nm)/YSZ(110nm)/SiO$_2$(300nm)/Si substrates and fired at 800∼900$^{\circ}C$. Any interface reaction between the PZT thick film and the bottom electrode was not observed in the PZT thick films. The PZT thick film fired at 800$^{\circ}C$ showed moderate electrical properties, the remanent polarization(p$\_$r/) of 16.0 ${\mu}$C/$\textrm{cm}^2$, the coercive field(E$\_$c/) of 36.7 ㎸/cm, and dielectric constant ($\varepsilon$$\_$r/) of 531. Low-temperature sinterable piezoelectric composition and high activity of fine particles reduced the sintering temperature of the thick film. This PZT thick film could be utilized for piezoelectric microactuators or microsensors that require Si micromachining technology.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.255-258
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• 2002

Liquid rocket engines using liquefied natural gas (LNG) or methane as a fuel is known to have several good characteristics, such as high specific impulse compared to other hydrocarbon fuels, environment-friendly exhaust gas, low production cost, and re-usability with low soot generation in the cooling channel. In this study, experimental combustion chambers capable of using LNC and $CH_{4}$ are being researched through experimental firing tests, and within easy range of eyes' inspection, there are the periodical existence of soot or discoloration in the chamber wall surface. This result means that mixture ratio of oxidizer and fuel fluctuates periodically between outer-row injectors in the mixing head in the circumferential direction. Therefore, based on this phenomenon, the variation of mixture ratio near the chamber wall caused by the spill pattern of a shear coaxial injector was analyzed quantitatively and the thermal heat flux Into the cooling channel is modified. Then, the calculated and modified results are compared with the measured ones.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.3
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• pp.87-99
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• 1991

The effect of oven firing on the color stability and surface texture of extrinsic stains used characterization and color modification of metal cermic restoration were studied by comparing different temperatures and techniques. They were autoglaze technique, applied glaze technique, two step low-fusing glaze technique and one step low-fusing glaze technique. Autoglaze technique and applied glaze technique were air-fired to manufacturer's recommended temperature. Two step low-fusing glaze technique is separated staining and overglazing. Thin slurry of stain powder were air-fired to $1500^{\circ}F$, Overglaze powder powder was then mixed with seam medium and air-fired to $170^{\circ}F$. One step low-fusing glaze technique is combined staining and overglazing. Thin slurry of stain and glaze powder were air-fired to $170^{\circ}F$. The obtained results were as fellows. 1. Slightly significant color differences by colorimeter were found between different stain application and fusion techniques(P<0.05). 2. Two step low-fusing glaze method showed the most rough surface, especially ceramco orage stain(P<0.05). 3. Surface roughness increased gradually in order of autoglaze, applied glaze, one step low-fusing glaze but they were not significantly different(P<0.05). 4. When two step low-fusing glaze was applied, both color measurement and surface texture were sinificantly different from other groups(P<0.05).