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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Ceramic Society
Journal Basic Information
Journal DOI :
The Korean Ceramic Society
Editor in Chief :
Volume & Issues
Volume 31, Issue 12 - Dec 1994
Volume 31, Issue 11 - Nov 1994
Volume 31, Issue 10 - Oct 1994
Volume 31, Issue 9 - Sep 1994
Volume 31, Issue 8 - Aug 1994
Volume 31, Issue 7 - Jul 1994
Volume 31, Issue 6 - Jun 1994
Volume 31, Issue 5 - May 1994
Volume 31, Issue 4 - Apr 1994
Volume 31, Issue 3 - Mar 1994
Volume 31, Issue 2 - Feb 1994
Volume 31, Issue 1 - Jan 1994
Selecting the target year
Preparation of Monodispersed, Sheperical Al2O3 and Mg-doped Al2O3 Powder and Sintering Characterization of These Powders
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 1~10
Monodispersed alumina and Mg-doped alumina fine particles were prepared by controlled hydrolysis of alkoxides. Aluminium alkoxide and magnesium alkoxide were dissolved into complex solvent which was composed of hydrophobic n-octanol and hydrophilic acetonitrile. Hydroxypropyl cellulose(HPC) was used as a dispersant for the alumina particles. The size of these prepared powders was approximately 0.3
. In the case of sintering above 100
, most of these prepared powders were transformed to
-alumina. The relative density of the sintered body of these prepared powders at 1
was 98%. The sintered body of the Mg-doped alumina powder had more uniform grain size than that of the undoped alumina podwer.
Design of Ferrite Composite Microwave Absorber
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 11~16
The impedance matching solution map is not a sufficient method for designing the broad-band absorber because of its difficulty to get numerical data about practical band-width. Therefore, we develope a new method to design the broad-band absorber. The complex permeability limits, which is necessary for designing the broad-band absorber in C-X band (4 GHz~12.4 GHz) were investigated and application was also examined. The complex permeability limits represent the frequency dependence of the complex permeability at a practical frequency band. These complex permeability limits can be used effectively to design broad-band single-layered absorber because they offer numerical data about the band-width in the case of various dielectric loss tangent, practical frequency bands and permitted reflection losses of an absorber.
Microstructures and Densification Behaviors of
Composites Fabricated by a Surface-induced Coating
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 17~24
Al2O3-ZrO2(ZTA) composites were fabricated by a surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2O3. The fabricated composites were characterized by a uniform spatial distribution of the dispersed ZrO2 phase and by the absence of large ZrO2 grains throughout the Al2O3 matrix. The fracture toughness (KIC) and the bending strength of ZTA composites sintered at 1
, respectively, were 5.6 MPa.m1/2 (for 20 wt% ZrO2) and 600 MPa (for 15wt% ZrO2). The fraction of tetragonal ZrO2 phase decreases as the total content of ZrO2, suggesting that both the stress-induced tlongrightarrowm transformation and the microcrack nucleation contribute to the toughening of the ZTA composites fabricated by the surface-induced coating.
Preparation, Wear Resistance and Mechanical Properties of W-Ti-C-N Based Hard Materials
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 25~30
W-Ti-C-N based multiphase hard materials have been prepared from WC/TiN powder mixture. By sintering at and above 190
, the two phases of powder mixture has transformed into intermixed W, W2C and Ti(C, N) phases. For the temperature range between 180
, the sintered or hot pressed samples show maximum density and hardness. The seems that metallic W grains enhance the fracture toughness of materials. The wear resistance of the material is found to increase with increasing hardness.
Preparation of Alumina Ceramics by Pressureless Powder Packing Forming Method: (I) Development of Pressureless Powders Packing Forming Method and Characterization of Green Body
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 31~38
To overcome the demerit of conventional forming method, new forming method, pressureless powder packing forming method, was investigated. This technique is performed by powder packing followed by the infiltration of binder solution. Various alumina powders were used as starting materials and the powders showing good packing condition through powder packing experiment were chosen. The green densities prepared by this new forming method with these powders were lower than those of specimens by pressing method, but, nearly same density was obtained in case of green body prepared with the powders having high packing density. The distribution of binder in a green body was homogeneous and it was possible to a complex shape form by this forming method.
Crystal Growth of
and the Effect pf Crucible Type and Atmosphere
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 39~46
LiTaO3 single crystals were growth without cracking using Pt-Rh crucible and Ir crucible. The starting composition to get the melt of congruent melting composition, which has been dependent upon the experimental procedure, was taken after fixing the total growing process by the result of preliminary experiments. The Rh contamination from the Pt-Rh crucible was to be neglected if the crystal had been grown under inert atmosphere, which resulted in the crystal color being slightly yellow. This color was decolored after 24 hour's annealing at 1200℃ under air atmosphere. The optimum conditions for the crystal growing and the diameter control were so dependent upon the crucible material in spite of using the crucible of the same size. The liquid-solid interface of LiTaO3 crystal of 1" diameter has been flat if the rotation speed was 45rpm.
Basic Studies On Uljin Pottery Stones
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 47~54
The fundamental studies for exploit natural resources was investigated on Uljin pottery stones that estimated the amount of mineral deposits at 350 million tons. The results obtained are as follows; In the chemical composition of Uljin pottery stones the amount of Al2O3 are a little compared with other pottery stones and that of Na2O and K2O are a large. Fe2O3 content is lower than 0.3 wt%, thus whiteness of its is 83. The major minerals composition of Uljin pottery stones are quartz and feldspar mineral. The refractoriness (SK) of its is 14. Lattice constants of quartz in Uljin pottery stones are 4.8865
in a-axis and 5.3852
in c-axis. Lattice constants were expanded by HCl treatment and sintering. Microstructures of Uljin pottery stones are linked up with the crystal particles under 10 microns in size.
Preparation of High Permeability Mn-Zn Ferrites by the Wet Method
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 55~61
Mn-Zn ferrite powder was obtained by wet method that was to be coprecipitated the metal ions of Fe2+, Mn2+ and Zn2+ with alkali solution. The target composition of the ferrite powder was 52 mol% Fe2O3, 24 mol% MnO, and 24 mol% ZnO, that was based on the region of high permeability. And the other ferrite powder was prepared by the dry method that was to be mixed the metal oxides as the above chemical composition. The wet method was compared with dry method for the powder properties and the electromagnetic characteristics of sintered cores. The synthesized powder by wet method was smaller particle size, narrower particle distribution, and higher purity than that of dry method. The initial permeability of sintered sample prepared by the wet method was 14000~28000, on the other side, 9000~15500 in case of the dry method.
A Study on the S-block Structure in Hexagonal Ferrites
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 62~68
It is compared the structures of the S-block in the Ba-Co-Zn Y-type hexagonal ferrites (Ba2Co2-xZnxFe12O22, x=0~2) and the Co-Zn spinel ferrites (Co1-xZnxFe2O4, x=0~1) expressed by a hexagonal axis system (space group R3m). The structures have been refined with a Rietveld analysis of the powder X-ray diffraction pattern with high precision (Rwp<0.13, RI<0.03). The overal dimension of the S-block is slightly different from the 1/3 of a hexagonal spinel unit cell as follow: 1.6~2.0% longer c-axis, 1.3~1.6% shorter a-axis and about 1% smaller volume. Upto Zn:Co=1:1 in the Ba-Co-Zn Y-type hexagonal ferrites, the zinc substitute primarily the tetrahedral sites in the S-block. Beyond that the zinc seems to go into the T-block as well.
Application of Sol-Gel Coating Process in Pressureless Sintering of Si3N4 and Their Properties
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 69~73
Si3N4 ceramics could be densified above 3.2g/㎤ with pressureless sintering at below 178
by coating Si3N4 and Y2O3 powder with an alumina sol. Substitution a portion of Al2O3 with AlN improved densification. Additional milling of the coated powder in large improvement in bending strength greater than 800 MPa (4-point).
Reliability Improvement of Thin Oxide by Double Deposition of Silicon
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 74~78
Degradation of thin oxide by doped poly-Si and its improvement were studied. The gate oxide can be degraded by phosphorous in poly-Si doped POCl3. The degradation is increased with the decrement of sheet resistance and poly-Si thickness. Oxide failures of amorphous-Si are higher than those of poly-Si. In-situ double deposition of amorphous-Si, 54
/30 nm, and poly-Si, 6
/220 nm, forms the mismatch structure of grain boundary between amorphous-Si and poly-Si, and suppresses the excess phosphorous on oxide surface by the mismatch structure. The control of phosphorous through grain boundary improves the oxide reliability.
Hydrolysis of Aluminum Nitride Powder
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 79~87
Aluminum nitride was hydrolyzed in contact with water, evolving the reaction heat of 172 cal/g within 12 hours to form alumina trihydrates. At 4
>, amorphous alumina hydrate was easily produced by the spontaneous breaks of AlN particle at the beginning of the hydrolysis process, while bayerite was formed by the dissolution-recrystallization processes of amorphous alumina hydrate at the temperature between 4
, and pseudo-boehmite was generated on the surface of AlN particle by the condensation process of the corresponding phase at 6
<. The longer the hydrolysis timje or the higher the value of pH in solution, the more the bayerite phase was produced. However, pseudo-boehmite was easily generated under the following favorable conditions; when the hydrolysis reaction occured rapidly at the beginning and when the absorption of OH radical on the surface of AlN particle was disturbed by ethyl alcohol in a solution. However, aluminum nitride was hardly hydrolyzed in a solution of pH 2.0
Effects of Gas Flow Variables on the Crystal Growth of Diamond in Hot Filament-Assisted CVD
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 88~96
Hot filament-assisted CVD was carried out to deposit diamond films on Si(100) substrate at 90
using a 1% CH4-H2 mixture gas. Deposition was made at various conditions of mass flow rate of the feed gas (30~1000 sccm), pressure (2.5~300 Torr), and filament-substrate distance (4~15 mm), and the deposited films were characterized by SEM, XRD, and Raman spectroscopy. As the flow rate increases, the growth rate also increased but the crystallinity of the film was degraded. A longer filament-substrate distance simply caused both the growth rate and the crystallinity to become poorer. On the other hand, the pressure variation resulted in a maximum growth rate of 2.6
/hr at 10 Torr and the best film quality around 50 Torr, exhibiting an optimum condition. The observed trends were interpreted in terms of the flow velocity-dependent pyrolysis reaction efficiency and mass transport through the boundary layer.
Influence by Preheat-Treatment on Raw Coke in Fabrication of Carbon Solids
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 97~103
The influence of ground petroleum coke, preheat-treated at temperatures ranged of 150~35
, was studied. It has been found that the coke powder preheat-treated at the temperature of 175
has been spherical-shaped in grinding and have showed the highest strength and density in sintering. The coke powder was also the best for the binding force and the (H/C) values showed 0.45 at the above temperature.
Fibers by Sol-Gel Process and Their Phase Characterization by Raman Microprobe
Journal of the Korean Ceramic Society, volume 31, issue 1, 1994, Pages 104~114
ZrO2 fibers were fabricated by means of the Sol-Gel process using Zr(O-nC3H7)4-H2O-C2H5OH-HNO3 solution as a starting material. The optimum experimental parameters such as molar ratio of starting materials, concentration, temperature, viscosity, the amounts of stabilizer and the pH of solution were determined. The experimentally determined optimum variables which produce good ZrO2 fibers were used to manufacture the Y2O3-and CaO-ZrO2 fibers. The amounts of Y2O3 and CaO were varied within the range from 1.5~5 mol% and 3~15 mol% respectively. The phase transformation and microstructural evolution of the fabricated ZrO2 gel fibers were investigated after heat treatments up to 120
by X-ray diffraction, Raman microprobe spectroscopy, SEM, and specific surface area and pore volume measurements. From the analysis of X-ray diffraction and Raman spectra, the phase of heat treated Y2O3-and CaO partially stabilized ZrO2 gel fibers(Y2O3:2.5~3 mol%, CaO:6~9 mol%) were identified as a tetragonal phase up to 100
. The maximum tensile strength of 2.5Y2O3-97.5ZrO2 and 6CaO-94ZrO2 (in mol%) fibers heat treated at 100
for 1 hr was found be 1.3~2 GPa with diameters of 10~20