• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.9-14
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• 1986

$\beta$-SiC bonded SiC bodies were prepared from various conditions such as several compositions of(Si+C)/$\alpha$ -SiC ratio and different firing schedules and were respectively investigated compressive strength MOR and mi-crostructure. One firing schedule which produced the specimens that had $\beta$-SiC neck form with the highest strength was selected and experimented by each firing temperature. results obtained are as follows : 1) The amount of (Si+C) for th highest MOR of SiC-(Si+C) sintered body is 20wt% 2) By adding 20wt% content of (Si+C) and heating up to 1, 500 with soaking 3hrs respectively at 1,150$^{\circ}C$ 1,250$^{\circ}C$ 1,350$^{\circ}C$ and 1,400$^{\circ}C$ the highest MOR of fired specimen was resulted and its microstructure of ma-trix was composed of close $\beta$-SiC neck. 3) Microstructure of $\beta$-SiC were different greatly from each other by firing time and/or quantity of adding mix-ture and it was confirmed that they were composed of neck particle-like and heterogeneous texture. 4)$\beta$-SiC synthesis proceed rapidly at the temperature between 1,250$^{\circ}C$ and 1,350$^{\circ}C$ 5) All of the properties of 85 SiC-20(Si+C) specimen improved according to increasing temperature above 1,350$^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.374-386
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• 2019

A process for nitrogen doping of TiO₂ ceramics was developed, whereby polycrystalline titania particles were prepared at 450-1000℃ with variation of the firing schedule under N₂ atmosphere. The effect of nitrogen doping on the polycrystallites was investigated by X-ray diffraction (XRD) and Raman analysis. The microstructure of the TiO₂ ceramics changed with variation of the firing temperature and the firing atmosphere (N₂ or O₂). The microstructural changes in the nitrogen-doped TiO₂ ceramics were closely related to changes in the Raman spectra. Within the evaluated temperature range, the nitrogen-doped titania ceramics comprised anatase and/or rutile phases, similar to those of titania ceramics fired in air. Infiltration of nitrogen gas into the titania ceramics was analyzed by Raman spectroscopy and XRD analysis, showing a considerable change in the profiles of the N₂-doped TiO₂ ceramics compared with those of the TiO₂ ceramics fired under O₂ atmosphere. The nitrogen doping in the anatase phase may produce active sites for photocatalysis in the visible and ultraviolet regions.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.394-398
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• 2019

In this paper, the joining characteristics of GDC-LSM ceramics with Crofer 22 APU metal alloys was investigated at different brazing temperatures and holding times by reactive air brazing. Brazing was performed using Ag-10 wt% CuO filler, at three different temperatures (1000, 1050, and 1100℃ for 30 minutes) as well as for three different holding times (10, 30, and 60 minutes at 1050℃). The interfacial microstructures were examined by scanning electron microscopy and the joining strengths were assessed by measuring shear strengths at room temperature. The results show that with increasing brazing temperature and holding time, joint microstructure changed obviously and shear strength was decreased. Shear strength varied from a maximum of 100±6 MPa to a minimum of 18±5 MPa, depending on the brazing conditions. These changes were attributed to an increase in the thickness of the oxide layer at the filler/metal alloy interface.

• Journal of Powder Materials
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• v.21 no.6
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• pp.415-421
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• 2014

W-10vol.%ZrC composites reinforced by micrometric and nanosized ZrC particles were prepared by hot-pressing of 25 MPa for 2 h at $1900^{\circ}C$. The effect of ZrC particle size on microstructure and mechanical properties at room temperature and elevated temperatures was investigated by X-ray diffraction analysis, scanning electron microscope and transmission electron microscope observations and the flexural strength test of the W-ZrC composite. Microstructural analysis of the W-ZrC composite revealed that nanosized ZrC particles were homogeneously dispersed in the W matrix inhibiting W grain growth compared to W specimen with micrometric ZrC particle. As a result, its flexural strength was significantly improved. The flexural strength at room temperature for W-ZrC composite using nanosized ZrC particle being 740 MPa increased by around 2 times than that of specimen using micrometric ZrC particle which was 377 MPa. The maximum strength of 935 MPa was tested at $1200^{\circ}C$ on the W composite specimen containing nanosized ZrC particle.

• Journal of the Korean Ceramic Society
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• v.38 no.3
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• pp.218-224
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• 2001

Yttria-stabilized zirconia (YSZ) films were deposited with varying temperatures of ZrCl$_4$between 250~55$0^{\circ}C$ with YCl$_3$and the substrate at 100$0^{\circ}C$. Nanoamperes per square centimeter of the electric current were measured in the reactor during deposition and the current increased with increasing evaporation temperature of ZrCl$_4$. The zirconia nanometer size clusters were captured on the grid membrane near the substrate during the CVD process and observed by transmission electron microscopy (TEM). The deposition rate decreased with increasing evaporation temperature of ZrCl$_4$. A cauliflower-shaped structure was developed at 25$0^{\circ}C$ then gradually changed to a faceted-grain structure above 35$0^{\circ}C$. Dependence of the growth rate and the morphological evolution on the evaporation temperature of ZrCl$_4$was approached by the charged cluster model.

• Journal of the Korean Ceramic Society
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• v.42 no.1
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• pp.33-36
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• 2005

Effect of heating rate was studied on consolidation of the low-temperature-sinterable PMN-PT-BT powder by varying the heating rate from 5, 10, to $20^{circ}C/min$. Slow rate of $5^{circ}C/min$ showed more homogeneous microstructure than high rate of 10 or $20^{circ}C/min$ due to low PbO (m.p. $886^{circ}C$) evaporation at 850^{circ}C$. It showed sintered density of $7.93 g/cm^{3}$, room temperature dielectric constant of 15300, and dissipation factor of $0.92\%$.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.809-816
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• 1995

Ti1-xAlxN films were successfully deposited on high speed steel and silicon wafer by plasma-assisted chemical vapor deposition using a TiCl4/AlCl3/N2/Ar/H2 gas mixture. Plasma process enabled N2 gas to nitride AlCl3, which is not possible in sense of thermodynamics. XPS analyses revealed that the deposited layer contained Al-N bond as well as Ti-N bond. Ti1-xAlxN films were polycrystalline and had single phase, B1-NaCl structure of TiN. Interplanar distance, d200, of (200) crystal plane of Ti1-xAlxN was, however, decreased with Al content, x. Al incorporation into TiN caused the grain size to be finer and changed strong (200) preferred orientation of TiN to random oriented microstructure. Those microstructural changes with Al addition resulted in the increase of micro-hardness of Ti1-xAlxN film up to 2800Kg/$\textrm{mm}^2$ compared with 1400Kg/$\textrm{mm}^2$ of TiN.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.83-91
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• 1996

Monolithic AlN and AlN-W composites were fabricated by pressure-less sintering at 190$0^{\circ}C$ under nitrogen atmosphere and the influences of tungsten phase on the microstructure and mechanical properties were investi-gated. In the fabrication of sintered specimen no additive was used. And monolithic AlN showed substantial grain growth and low relative density. AlN-W composites were fully densified and grain growths of matrix were inhibited. The densification behavior of composites were inferred to be achieved through the liquid phase sintering process such as particle-rearrangement and solutino-reprecipitation. Also the oxid phases which is expected to form liquid phases duringsintering process were detected by XRD analysis. As the tungsten volume content increases fracture strength was decreased and fracture toughness was increased. It was suppo-sed that the strength decrease of composites with tungsten content was due to existence of interface phases. The subcritical crack growth behavior was observed from the stress-strain curve of composites. The effect of the secondary phase and interface phases on toughness in crease were studied through observation of crack propagation path and the influence of residual stress on crack propagation was investigated by X-ray residual stress measurement. In the result of residual stress measurement the compressive stress of matrix in composi-test was increased with tungsten volume content and the compressive stress distribution of matrix must have contributed to the inhibition of crack propagation.

• Journal of the Korean Ceramic Society
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• v.35 no.1
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• pp.66-78
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• 1998

the microstructure and mechanical properties of seeded and ball-milled dry gels prepared by boehmite sol-gel method were discussed. The densification of seeded gels was improved with increasing seed content namely the number of seed The number of seed was 1.09, 3.35, 5.72${\times}$1012/cm3 boehmite when seeded with 1, 3, 5wt% respectively The ball milled gel contained about 0.5wt% seed and the number of seed was 4.72${\times}$1012/cm3 boehmite. The sintered density of 5wt% seeded gel was below 80% when sintered at 1300$^{\circ}C$ for 1h. On the other hand that of ball milled gel was very improved and reached to 97% In the case of 3wt% seeded gels the density over 97% was attained when sintered at 1500$^{\circ}C$for 1h. and the grain of the sintered body was several micrometers in size. However the sintered body of ball milled gel showed grain size of submicrometer when sintered at 1300$^{\circ}C$ for 1h. And this specimen showed highest harness value of 1900kg/mm2 The fracture toughness increased with increasing sintering temperature. The sintered body of ball milled gel showed the largest grain size and the highest fracture toughness without regard to sint-ering temperature.

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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• pp.338-342
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• 2007

Porous silicon nitride ceramics were prepared by SHS (Self-Propagating High Temperature Synthesis) from silicon powder, silicon nitride powder and pore-forming precursor. The microstructure, porosity and the flexural strength of the porous silicon nitride ceramics were varied according to the Si/Si3N4 ratio, size and amount of the pore-forming precursors. Some sample exhibited as high flexural strength as $162{\pm}24\;MPa$. The high strength is considered to result from the fine pore size and the strong bonding amoung the silicon nitride particles.