• 한국세라믹학회지
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• 제23권1호
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• pp.1-6
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• 1986

The shrinkage rate of solid state sintering has been theoretically derived by combining the rate equation of material transport and the net free energy change resulting from the decrease of solid-vapor interface and the increase of grain boundary during sintering. For a sinteing model an idealized situation of the spherical particles with BCC packing was taken as the initial condition and the shrinkage was assumed to occur by forming the flat circualr grain boundaries on each particle. The plotted shrinkage rates as a function of grain boundary to surface energy ratio $(gamma_g/gamma_s)$ have shown that the relative density increases linearly at the initial stage of sintering but the shrinkage rate is decreased upon further sintering due to a decrease in driving force for densificaton. It has been also shown that the densification is critically affected by the $gamma_g/gamma_s$ ratio. In order to get the complete densificatin the ratio should be less than $sqrt{3}$. Any additive or atmospheric condition causing the decrease of$_g/gamma_s$ ratio will enhance sintering.

• 융복합기술연구소 논문집
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• 제6권1호
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• pp.1-5
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• 2016

Additive manufacturing is converting a digitally designed object into a tangible three dimensional solid using an additive process where materials are applied in successive layers with no or very limited material waste. It can be distinguished form traditional manufacturing which begins with a fixed amount of raw material and removes excess to arrive at the final product. Generally there are five stages to the additive manufacturing supply chain, namely materials, systems, software, application design and production. In this paper, recent market trends and technology about additive manufacturing based on supply chain are analyzed and reviewed.

• 한국분말재료학회지
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• 제18권6호
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• pp.562-567
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• 2011

This paper reports the effect of sintering processes and additives on the microstructures and mechanical properties of $ZrB_2$-SiC composite ceramics. We fabricated sintered bodies of $ZrB_2$-20 vol.% SiC with or without sintering additive, such as C or $B_4C$, densified by spark plasma sintering as well as hot pressing. While almost full densification was achieved regardless of sintering processes or sintering additives, significant grain growth was observed in the case of spark plasma sintering, especially with $B_4C$. With sintered bodies, mechanical properties, such as flexural strength and Vickers hardness, were also examined.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.439-442
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• 2004

The effects of sintering additives on the low-temperature sintering and microwave dielectric properties of $Mg_4Nb_2O_9$ dielectric ceramics were studied. When $3{\sim}20wt%$ of $0.242Bi_2O_3-0.758V_2O_5$ was added, the sintering temperature decreased from $1100{\sim}1300^{\circ}C$ to $950^{\circ}C$ and high density was obtained. When $Mg_4Nb_2O_9$ was sintered at $950^{\circ}C$ with 10wt% of sintering additive, the microwave dielectric properties of $Q{\times}f_0\;=\;80.035GHz,\;\epsilon_r\;=\;13.3\;and\;\tau_f\;=\;-12.9\;ppm/^{\circ}C$ were obtained.

• 한국세라믹학회지
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• 제44권4호
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• pp.189-193
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• 2007

Effect of additive composition on fracture toughness of in situ-toughened $SiC-Si_3N_4$ composites was investigated for five different additive compositions. The highest toughness $(6.4MPa{\cdot}m^{1/2})\;in\;SiC-Si_3N_4$ composites investigated herein was obtained when an Y-Mg-Si-Al-O-N oxynitride glass was used as a sintering additive. The improvement in fracture toughness was produced by enhanced bridging and deflection by $Si_3N_4$ grains.

• 한국전기전자재료학회논문지
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• 제14권10호
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• pp.815-820
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• 2001

The piezoelectric properties of the PT-PZ-PNN system ceramics were investigated depending on the variati on of the grain size. The grain size was varied by sintering temperature, and additive. The effect of the grain size on the electrical, dielectric, and piezoelectric properties was studied with respect to the feasibility of the application for the piezoelectric transformer. Grain size increased as the PMW contents increased. The smaller the particle size used, the smaller the grain size obtained. Specimens are densily sintered. Dielectric and piezoelectric properties are not always improved in proportion to the grain sizes. When he particle size are fine and the grain size are increased properly with the optimum additives, the piezoelectric preperties have good values. the specimen sintered at 1200$\^{C}$ with PMW 2 mol% and MnO$\_$2/ 0.5wt% contents exhibited good piezoelectric properties for a piezoelectric transformer.

• 전기의세계
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• 제31권6호
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• pp.445-449
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• 1982

This Paper describes the influence of additive concentrations and sintering temperature on the surge protection performance in ZnO ceramic varistors. It is found from the experiments that the metal-oxide semiconductors based oi ZnO with an additive incorporation of 0.50% molx(Bi$\_$2/O$\_$3/+MnO+CoO+Cr$\_$2/O$\_$3/+2Sb$\_$2/O$\_$3/) and sintered at 1250.deg. C present excellent V-I characteristics in view of transient surge suppression. Gapless arrester element with aluminum electrodes shows also good reliability against impulse shock and marks a low voltage clamping ratio(V$\_$1KA/V$\_$1mA/<2.0) compared with the conventional SiC varistors.

• 한국세라믹학회지
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• 제21권3호
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• pp.259-265
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• 1984

As the effect of Al-powder as an additive on the sintering of $Al_2O_3$ was found satisfacotry in the range of 1350-155$0^{\circ}C$ this experiment was carried out at higher temperature(1600-180$0^{\circ}C$) at which the commerical $Al_2O_3$ body is sintered. Some phsical properties were measured and the micostructures of the specimens were observed by SEM. Although some measured physical properties of the specimens were improved through the addition of Al powder to $Al_3O_2$ powder the systematic changes in microsturces of the specmens could not be observed by SEM.

• 한국전기전자재료학회논문지
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• 제13권4호
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• pp.343-348
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• 2000

NCZF ferrites doped with B-Bi-Zn(35-25-40) glass ceramics were prepared to investigate the magnetic properties. The XRD peaks of all of samples were observed only spinel phase. As the additive increased at sintering temperature 750$^{\circ}C$ and 850$^{\circ}C$ for 3 hours, the density and shrinkage of the samples increased until 5.28 g/cm$^3$ and 20% respectively. And other samples showed constant trends having the density about 5.4g/cm$^3$. According to SEM images the growth of grain progressed rapidly at sintering temperature of 850$^{\circ}C$ for 3 hours. Increasing the additive initial permeability and complex permeability decreased. The high values of complex permeability as a function of frequency showed that NCZF doped with 3 wt%, 5wt%, samples at sintered temperature of 850$^{\circ}C$/3h and 900$^{\circ}C$/3h.

• 한국세라믹학회지
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• 제20권1호
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• pp.49-54
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• 1983

The main object of this study is to investigate the effect of Al powder as an additive on the sintering of calcined alumina comparing with that of calcined alumina alone. The degree of Al oxidation is calculated by measuring the weight increase during the firing Water absorption bulk density and compressive strength of the $Al_2O_3+Al$ system at each temperature are compared with those of $Al_2O_4$ alone. The $Al_2O_3+Al$ system shows better physical propeties than Al2O3 alone and it seems by the SEM observation that the fine oxidized Al particles(fine $Al_2O_3$ particles submicron unit) fill the interstices of the original $Al_2O_3$ par-ticles and thus result in the well-close-packed arrangement of the particles.