• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.368-369
• /
• 2006

By means of magnetic pulsed compaction and sintering of weakly aggregated alumina based nanopowders the jet forming nozzle samples for the hydroabrasive cutting were fabricated. The ceramics was obtained from pure alumina, as well as from alumina, doped by $TiO_2$, MgO and AlMg. It was shown that the samples sintered from AlMg doped $Al_2O_3$ powder have the best mechanical properties and structural characteristics: relative density ${\sim}0.97$, channel microhardness. - 18-20 GPa, channel surface roughness ${\sim}0.7\;{\mu}m$, average crystallite size ${\sim}1\;{\mu}m$.

• 한국세라믹학회지
• /
• 제50권6호
• /
• pp.410-415
• /
• 2013

$ZrB_2$-SiC ceramics are fabricated via hot pressing with different ratios of submicron or nano-sized SiC in a $ZrB_2$-20 vol%SiC system, in order to examine the effect of the SiC size ratio on the microstructures and physical properties, such as thermal conductivity, hardness, and flexural strength, of $ZrB_2$-SiC ceramics. Five different $ZrB_2$-SiC ceramics ($ZrB_2$-20 vol%[(1-x)SiC + xnanoSiC] where x = 0.0, 0.2, 0.5, 0.8, 1.0) are prepared in this study. The mean SiC particle sizes in the sintered bodies are highly dependent on the ratio of nano-sized SiC. The thermal conductivities of the $ZrB_2$-SiC ceramics increase with the ratio of nano-sized SiC, which is consistent with the percolation behavior. In addition, the $ZrB_2$-SiC ceramics with smaller mean SiC particle sizes exhibit enhanced mechanical properties, such as hardness and flexural strength, which can be explained using the Hall-Petch relation.

• 한국세라믹학회지
• /
• 제52권1호
• /
• pp.61-65
• /
• 2015

The effect of Sr addition on the flexural strength of bulk SiOC ceramics was investigated in polymer-derived SiOC ceramics prepared by conventional hot pressing. Crack-free, dense SiOC discs with a 30 mm diameter were successfully fabricated from commercially available polysiloxane with 1 mol% strontium isopropoxide derived Sr as an additive. Agglomerates formed after the pyrolysis of polysiloxane led to the formation of domain-like structures. The flexural strength of bulk SiOC was strongly dependent on the domain size formed and Sr addition. Both the minimization of the agglomerate size in the starting powders by milling after pyrolysis and the addition of Sr, which reinforces the SiOC structure, are efficient ways to improve the flexural strength of bulk SiOC ceramics. The typical flexural strength of bulk Sr-doped SiOC ceramics fabricated from submicron-sized SiOC powders was ~209 MPa.

• 한국세라믹학회지
• /
• 제53권3호
• /
• pp.332-337
• /
• 2016

As a case study on yttria stabilized zirconia ceramics, the sintering characteristics of submicron powders and the granulation prepared by two-fluid spray drying of submicron particles were investigated. As-received powders of yttria stabilized zirconia particles were reduced to a uniform size of less than about 200 nm by repeated milling. Granulation size obtained by the two-fluid spray drying was affected by the organic matter and the primary particle size. Sintering behavior such as porosity, water absorption ratio, density, and transparency was influenced by processing conditions of the powder, and the discontinuous interfaces in a green body were reduced.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1994년도 하계학술대회 논문집 C
• /
• pp.1271-1273
• /
• 1994

In the field of the optics, precise machine, semiconducting processing, the micro-positioning actuators are required for the control of position in the submicron range. In this study, PNN-PZN-PZT ceramics were fabricated by solid state reaction. The structural, dielectric and electric properties were investigated for sintering condition. The specimen sintered for 1hr at 1,150($^{\circ}C$), had the highest density and dielectric contant.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1996년도 하계학술대회 논문집 C
• /
• pp.1508-1511
• /
• 1996

In the fields of the optics, precise machine, semiconducting processing, the micro-positioning actuators are required for the control of position in submicron range. In this study, dielectric properties of 0.5PNN-(0.5-x)PZN-xPZT system ceramics with different PZT mole ratio were investigated. As the amount of PZT incerases, curie temperature was increased. The maximum of dielectric and piezoelectric constant was shown at 0.3 mole ratio of PZT amount. As a results, we have found that the structrue of ceramics with PZT 0.3 mole was morphotropic phase boundary.

• 한국재료학회지
• /
• 제29권4호
• /
• pp.264-270
• /
• 2019

As a case study on aspect ratio behavior, Kaolin, zeolite, $TiO_2$, pozzolan and diatomaceous earth minerals are investigated using wet milling with 0.3 pai media. The grinding process using small media of 0.3 pai is suitable for current work processing applications. Primary particles with average particle size distribution D50, ${\sim}6{\mu}m$ are shifted to submicron size, D50 ${\sim}0.6{\mu}m$, after grinding. Grinding of particles is characterized by various size parameters such as sphericity as geometric shape, equivalent diameter, and average particle size distribution. Herein, we systematically provide an overview of factors affecting the primary particle size reduction. Energy consumption for grinding is determined using classical grinding laws, including Rittinger's and Kick's laws. Submicron size is obtained at maximum frictional shear stress. Alterations in properties of wettability, heat resistance, thermal conductivity, and adhesion increase with increasing particle surface area. In the comparison of the aspect ratio of the submicron powder, the air heat conductivity and the total heat release amount increase 68 % and 2 times, respectively.

• 한국세라믹학회지
• /
• 제51권5호
• /
• pp.380-385
• /
• 2014

Clay-based membranes with submicron pore size were successfully prepared by a simple pressing process using low-cost starting materials(e.g., kaolin (K), bentonite (B), talc (T), and sodium borate). The green bodies were sintered at $1000^{\circ}C$ for 2 h in air. The effect of clay-mineral composition on the flexural strength of clay-based membranes was investigated. The porosity of the clay-based membranes could be controlled within the range of 34 - 42% by adjusting the starting composition. The flexural strength of the low-cost membranes depended on both the porosity and the ${\alpha}$-quartz content. In turn, the porosity and ${\alpha}$-quartz content were affected by the (B+T) /(K+B+T) ratio. The plot of strength relative to this ratio, showed a maximum when the ratio was 0.4. The typical flexural strength of these clay-based membranes (with ratio 0.4) was 28 MPa at 34% porosity.

• 한국분말재료학회지
• /
• 제19권5호
• /
• pp.379-384
• /
• 2012

This paper reports the microstructures and thermal conductivities of $ZrB_2$-SiC composite ceramics with size and amount of SiC. We fabricated sintered bodies of $ZrB_2$-x vol.% SiC (x=10, 20, 30) with submicron and nanosized SiC densified by spark plasma sintering. Microstructure retained the initial powder size of especially SiC, except the agglomeration of nanosized SiC. For sintered bodies, thermal conductivities were examined. The observed thermal conductivity values are 40~60 W/mK, which is slightly lower than the reported values. The relation between microstructural parameter and thermal conductivity was also discussed.

• 한국수소및신에너지학회논문집
• /
• 제28권6호
• /
• pp.663-668
• /
• 2017

SOFC anode fabricated core-shell using machano-fusion method using core with submicron size Ni, nano size YSZ for shell. Using prepared core-shell, depending on the thickness of the shell, we studied how the characteristics of sintering and SOFC cell change by sintering the anode. The Ni-YSZ core-shell has a Ni core of 0.5 to $1.2{\mu}m$ over 2 to 7 YSZ of 15 to 20 nm is, and as the high speed mixing time increases, the YSZ number increases and the shell thickness becomes uniform increased. When the fuel electrode is manufactured with core-shell, it has superior sintering property, has grain of uniform size compared with the one synthesized by general mixing, the falling path is short, the conductors (electrons and ions) connection is excellent, the electrical conductivity has become excellent. The thicker the shell, the lower the electrical conductivity. When the thickness of shell ranged from 46 to 139 nm and 61 to 81 nm, the performance was the highest and the ASR was the smallest.