• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.419-430
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• 1992

Fabrication possibility of low-shrinkage alumina without oxidation and wetting agent was presented on the basis of observation about oxidation behavior, microstructure and physical characteristics of such reaction agents free Al2O3-Al system. The composition less than Al 10w/o where Al can act as a sintering agent for Al2O3 was excluded. Under the condition of present experiments oxidation of Al2O3-Al system was dependent not on holding time but mainly on oxidation temperature. In thes case of Al powder not comminuted effectively during powder mixing of Al2O3-Al, columnar structure which would act as a hindrance to the densification during sintering developed more during oxidation with higher Al contents, and which made the fabrication of low-shrinkage Al2O3 ceramics impossible. If Al powder was comminuted effectively due to co-mixed Al2O3 characteristics, densification was improved because of no columnar structure and made the fabrication of sintered body with -2.7% dimensional change and 81% relative density possible. As a result, it is possible to fabricate dense low-shrinkage Al2O3 ceramics without oxidation and wetting agent under conditions such as smaller particle size of Al, Al contents below 50v/o, higher green density of Al2O3-Al compact and the use of Al2O3 powder used for high-density ceramics.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.241-245
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• 2016

The purpose of this study was to investigate the bloating mechanism of artificial lightweight aggregates with different sizes (ESA, effective surface area). Aggregates were produced using hard clay, stone sludge, and a bloating agent in order to observe the effect of the gradation of the artificial lightweight aggregates. Kerosene and amorphous carbon were used as bloating agent. The particle size of the produced aggregate ranged from 3 mm to 9 mm. With regard to the amount of bloating agent to be used, 2 ~ 6 parts by weight were used. The specific gravity, absorption rate, and the type of aggregates produced by rapid sintering at $1075{\sim}1200^{\circ}C$ were determined. Microstructures were observed. When ESA had a value of 1 or below, kerosene, which has a high burning rate, was found to be advantageous for use as a bloating agent. When ESA had a value of 1 or above, carbon, which has a relatively low burning rate was found to be an advantageous bloating agent. It is thought that kerosene is more advantageous, as ESA decreases, for the production of aggregates having low water absorption rate.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1247-1253
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• 1997

Sinter-active yttria powders were prepared by a solution precipitation with using a self-decomposing precipitation agent NH2CONH2(urea). The cold-pressed powders can be sintered to full density and the microstructure of grains less than 200 nm at a temperature as low as 120$0^{\circ}C$. The activity of the yttria powder has been controlled by varying nucleation conditions during precipitation and by minimizing formation of aggregates. The type of precursor is decisive in preparation of a sinter-active oxide powder, and urea is desirable as a precipitation agent for an active yttrium oxide powder.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.444-452
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• 2000

Dense composites of titanium matrix and Al2O3 matrix with reinforcements of carbon or titanium carbide fibers were successfully fabricated by high-pressure self-combustion sintering method or combustion reacton under 30 MPa of uniaxial pressure with an aid of external heating in vaccum. It was found that the fibers were uniformly distributed in the matrix, and aligned in a phase perpendicular to the pressure axis. As a moel ratio of Ti/C or reaction time increased, the density of Ti-matrix composite increased Micro pores around fibers could be removed by using clean carbon fibers without sizing agent on their surface. The evolution of carbide fibers from carbon fibers was observed. The composition of the various phases around fibers were analyzed.

• Korean Journal of Materials Research
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• v.30 no.2
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• pp.93-98
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• 2020

Effective control of the heat generated from electronics and semiconductor devices requires a high thermal conductivity and a low thermal expansion coefficient appropriate for devices or modules. A method of reducing the thermal expansion coefficient of Cu has been suggested wherein a ceramic filler having a low thermal expansion coefficient is applied to Cu, which has high thermal conductivity. In this study, using pressureless sintering rather than costly pressure sintering, a polymer solution synthesis method was used to make nano-sized Cu powder for application to Cu matrix with an AlN filler. Due to the low sinterability, the sintered Cu prepared from commercial Cu powder included large pores inside the sintered bodies. A sintered Cu body with Zn, as a liquid phase sintering agent, was prepared by the polymer solution synthesis method for exclusion of pores, which affect thermal conductivity and thermal expansion. The pressureless sintered Cu bodies including Zn showed higher thermal conductivity (180 W/m·K) and lower thermal expansion coefficient (15.8×10^-6/℃) than did the monolithic synthesized Cu sintered body.

• Journal of Powder Materials
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• v.9 no.4
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• pp.235-244
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• 2002

The effects of residual impurities on solid state sintering of the powder injection molded (PIMed) W-15wt%Cu nanocomposite powder were investigated. The W-Cu nanocomposite powder was produced by the mech-ano-chemical process consisting of high energy ball-milling and hydrogen reduction of W blue powder-cuO mixture. Solid state sintering of the powder compacts was conducted at $1050^{\circ}C$ for 2~10 h in hydrogen atmosphere. The den-sification of PIM specimen was slightly larger than that of PM(conventional PM specimen), being due to fast coalescence of aggregate in the PIM. The only difference between PIM and PM specimens was the amount of residual impurities. The carbon as a strong reduction agent effectively reduced residual W oxide in the PIM specimen. The $H_2O$ formed by $H_2$ reduction of oxide disintegrated W-Cu aggregates during removal process, on the contrary to this, micropore volume rapidly decreased due to coalescence of the disintegrated W-Cu aggregates during evolution of CO.It can be concluded that the higher densification was due to the earlier occurred Cu phase spreading that was induced by effective removal of residual oxides by carbon.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.200-210
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• 2009

It is necessary to minimize the mismatch of sintering shrinkage between dielectric ceramic and Ni inner electrode layers for the purpose of developing the ultra high-capacity multi layered ceramic condenser(MLCC). Thus, low temperature sintering of dielectric $BaTiO_3$ ceramic should be precedently investigated. In this work, the influence of the milling condition on sintering behavior and electrical properties of $BaTiO_3$ ceramics was investigated in the $BaTiO_3$(BT)-Mg-Dy-Mn-Ba system with borosilicate glass as a sintering agent. As milling time increased, specific surface area(SSA) of the powder increased linearly, while both sinterability and dielectric property were found to be drastically decreased with an increasing SSA. It was also revealed that the sinterability of the excessively milled $BaTiO_3$ ceramics could be recovered by increasing Ba content, rather than increasing glass addition. These results suggest that the sintering behavior of $BaTiO_3$ ceramics under the high SSA was more strongly dependent on the transient liquid phase caused by Ba addition, than the liquid phase from additional glass.

• Journal of Powder Materials
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• v.30 no.5
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• pp.394-401
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• 2023

Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is considered to be one of the promising solid-state electrolytes owing to its excellent chemical and thermal stability, wide potential range (~5.0 V), and high ionic conductivity (~10^-4 S/cm). LATP powders are typically prepared via the sol-gel method by adding and mixing nitrate or alkoxide precursors with chelating agents. Here, the thermal properties, crystallinity, density, particle size, and distribution of LATP powders based on chelating agents (citric acid, acetylacetone, EDTA) are compared to find the optimal conditions for densely sintered LATP with high purity. In addition, the three types of LATP powders are utilized to prepare sintered solid electrolytes and observe the microstructure changes during the sintering process. The pyrolysis onset temperature and crystallization temperature of the powder samples are in the order AC-LATP > CA-LATP > ED-LATP, and the LATP powder utilizing citric acid exhibits the highest purity, as no secondary phase other than LiTi₂PO₄ phase is observed. LATP with citric acid and acetylacetone has a value close to the theoretical density (2.8 g/cm³) after sintering. In comparison, LATP with EDTA has a low sintered density (2.2 g/cm³) because of the generation of many pores after sintering.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.368-373
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• 2015

Porous alumina ceramics with two different pore sizes were fabricated using hollow microspheres as the pore-forming agent. The relative density, total porosity, and microstructure of the obtained alumina ceramics were studied. It was found that the total porosity of sintered samples with different amounts of hollow microsphere content, from 2.0 to 4.0 wt%, was 69.3-75.6%. The interconnected and spherical cell morphology was obtained with 3.0 wt% hollow microsphere content. The resulting ceramics consist of a hierarchical structure with large-sized cells, and small-sized pores in the cell walls. Moreover, the compressive strength of the sintered samples varied from 8.3-11.5 MPa, corresponding to hollow microsphere contents of 2.0-4.0 wt%.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.586-591
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• 2012

$Zr_2WP_2O_{12}$ powder, which has a negative thermal expansion coefficient, was synthesized by a solid-state reaction with $ZrO_2$, $WO_3$ and $NH_4H_2PO_4$ as the starting materials. The synthesis behavior was dependent on the solvent media used in the wet mixing process. The $Zr_2WP_2O_{12}$ powder prepared with a solvent consisting of D. I. water was fully crystallized at $1200^{\circ}C$, showing a sub-micron particle size. According to the results obtained from a thermal analysis, a $ZrP_2O_7$ was synthesized at a low temperature of $310^{\circ}C$, after which it was reacted with $WO_3$ at $1200^{\circ}C$. A new sintering additive, $Al(OH)_3$, was applied for the densification of the $Zr_2WP_2O_{12}$ powders. The cold isostatically pressed samples were densified with 1 wt% $Al(OH)_3$ additive or more at $1200^{\circ}C$ for 4 h. The main densification mechanism was liquid-phase sintering due to the liquid which resulted from the reaction with amorphous or unstable $Al_2O_3$ and $WO_3$. The densified $Zr_2WP_2O_{12}$ ceramics showed a relative density of 90% and a negative thermal expansion coefficient of $-3.4{\times}10^{-6}/^{\circ}C$. When using ${\alpha}-Al_2O_3$ as the sintering agent, densification was not observed at $1200^{\circ}C$.