The Korean Journal of Ceramics
한국세라믹학회 (The Korean Ceramic Society)
- 계간
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- 1225-9381(pISSN)
과학기술표준분류
- 재료 > 세라믹재료
- 재료 > 분석/물성평가기술
Aim & Scope
The Journal of the Korean Ceramic Society is the official journal of the Korean Ceramic Society. The journal aims at the publication of original and significant results which are lasting in ceramic materials. It contains reports of original research and reviews on all aspects of ceramics and ceramics-based composites ranging from fundamentals to applications. The scope of the journal includes Basic Science of Ceramics, Classical Ceramics, Engineering Ceramics, Electronic Ceramics, and Energy Ceramics.
제5권4호
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Si3N4-TiC composites have been known as electrically conductive ceramics.
$Si_3N_4-TiC$ composites with 2 wt%$Al_2O_3$ and 4 wt%$Y_2O_3$ were hot pressed in$N_2$ environment. The mechanical properties including hardness, fracture toughness, and flexural strength and tribological properties were investigated as a function of TiC content.$Si_3N_4-40$ vol% TiC composite was hot pressed at$1,750^{\circ}C$ ,$1,800^{\circ}C$ , and$1,850^{\circ}C$ for 1, 3 and 5 hours in$N_2$ gas. Mechanical and tribolgical properties depended on microstructures, which were controlled by hte TiC content, hot press temperature, and hot press holding time. However, mechanical properties and tribological behaviors were degraded by the chemical reaction between TiC and N. The chemically reacted products such as TiCN, SiC, and$SiO_2$ were detered by the X-ray diffraction analysis. -
$Si_3N_4$ -$TiB_2$ with 2 wt%$Al_2O_3$ and 4 wt%$Y_2O_3$ additives was hot pressed in a flowing$N_2$ environment with varying$TiB_2$ content from 10 to 50 vol%. Variations of mechanical (hardness, fracture toughness, and flexual strength), and tribological properties as a function of$TiB_2$ content were investigated. As the content of$TiB_2$ increased, relative density decreased due to the chemical reaction of$TiB_2$ in$N_2$ environment. The reduction of density causes mechanical properties to be degraded with an increase of$TiB_2$ in$Si_3N_4$ . Tribological properties were dependent of microstructure as well as mechanical properties, however, they were degraded strongly by the chemical reaction of$Si_3N_4$ -$TiB_2$ during hot pressing in$N_2$ environment. SEM and TEM observations, and X-ray diffraction analysis that the chemical reaction products at the interface are TiCN, Si, and$SiO_2$ . Also, the comparison of XRD patterns of the$Si_3N_4$ -40 vol%$TiB_2$ composites hot pressed at$1,750^{\circ}C$ for 1 hour between in$N_2$ and in Ar gas was made. The XRD peaks of Si and$SiO_2$ were not found in Ar, but still a weak peak of TiCN was presented. -
Mechanical propeties of
$Y_2O_3$ -containing tetragonal$ZrO_2$ polycrystals(Y-TZP) were investigated. Several additives were used to modify the hardness fracture toughness of Y-TZP. The effects of these individual additives were discussed and their interactions were also analyzed. Each additive, such as CoO,$Fe2O3, MnO_2$ was found to deteriorate the mechanical propeties of Y-TZP when it was used singly. But the fracture toughness of Y-TZP was singnificantly improved when these additives and$Al_2O_3$ were added in combination at a certain ratio. -
Glasses in the system
$CaO-TiO_2-SiO_2-Al_2O_3-ZrO_2-B_2O_3$ were investigated to find the glass seal compositions suitable for use in the planar solid oxide fuel cell (SOFC). Glass-ceramics prepared from the glasses by one-stage heat treatment at$1,000^{\circ}C$ showed various thermal expansion coefficients (i,e.,$8.6\times10^{-6^{\circ}}C^{-1}$ to$42.7\times10^{-6^{\circ}}C^{-1}$ in the range 25-$1,000^{\circ}C$ ) due to the viscoelastic response of glass phase. The average values of contact angles between the zirconia substrate and the glass particles heated at 1,000-$1,200^{\circ}C$ were in the range of$131^{\circ}\pm4^{\circ}$ ~$137^{\circ}\pm9^{\circ}$ , indicating that the glass-ceramic was in partial non-wetting condition with the zirconia substrate. With increasing heat treatment time of glass samples from 0.5 to 24 h at$1,100^{\circ}C$ , the DC electrical conductivity of the resultant glass-ceramics decreased fromat $800^{\circ}C$ . Isothermal hold of the glass sample at$1100^{\circ}C$ for 48h resulted in diffusion of Ca, Si, and Al ions from glass phase into the zirconia substrate through the glass/zirconia bonding interface. Glass phase and diffusion of the moving ion such as$Ca^{2+}$ in glass phase is responsible for the electrical conduction in the glass-ceramics. -
An ambiguity on the correct room temperature structure of
$Bi_5Ti_3FeO_{15}$ was resolved using a combined Rietveld refinement of neutron and X-ray diffraction. The structure of this compound has been reported to have a space group of F2mm (adopting 2-fold rotation symmetry along the c-axis) or A21am. However, our diffraction, study reveals that some reflections would violate F-centering and confirm that the belong to$A2_1$ am. Out refinement with the space group of$A2_1$ am converged at$R_p=6.85%, R_wp=9.23%$ and$\chi^2$ =1.66 for an isotropic temperature model with 85 variables. The lattice constants are a=5.4677(1)$\AA$ , b=5.4396(1)$\AA$ , and c=41.2475(8)$\AA$ . In structure, Ti/Fe atoms at the oxygen octahedral sites of the perovskite unit are completely disordered, resulting in that these atoms are transparent in neutron diffraction. The octahedra of the perovskite unit are relatively displaced along the a-axis against the Bi atoms, which contribute as a major component to the spontaneous polarization of$Bi_5Ti_3FeO_{15}$ . -
Barium uranium sulfides,
$BaUS_3$ and$BaU_2B_5$ , were synthesized in a single phase by the reactin of$(Ba, UO_2)(NO_3)_2$ at Ba/U=1 and 0.5 with carbon disulfide at 1273 K for 6 h. They crystallized in orthorhombic structure with space group, Pnma. The lattice parameters a, b and c are 7.493, 10.38 and 7.238$\AA$ for$BaUS_3$ and 7.525, 8.475 and 11.858$\AA$ for$BaU_2S_5$ , respectively. The electrical conductivity of these compunds increased with increasing temperature above 200K, below which however, it was nearly temperature independent. The Hall coefficient suggested that they are n-type semiconductors. -
Highly proten-conductive elastic composites have been successfully prepared from
$H_3PO_4$ -doped silica gel and styrene-ethylene-butylene-styrene block elastic copolymer. In addition solid state electric double-layer capacitors have been fabricated using the composite as an electrolyte and activated carbon powders(ACP) hybridized with the composite as a polrizable electrode. The cyclic voltammogram of the electric double-layer capacitor fabricated demonstrated that electric charge was stored in the elecric double-layer at the interface between the polarizable electrode and the electrolyte. The value of capacitance of the capacitor was 10 F/(gram of total ACP), which was comparable to that of the capacitors using conventional liquid electrolytes. -
ZnO varistors containing cobalt, praseodymium and calcium oxides were prepared. The current-voltage charcteristics and microstructures of the specimens were investigated with respect to calcium addition and sintering temperature. The potential barrier heights and the carrier densities were estimated from C-V relations. The compatibility of Ag-Pd as an internal electrode for multilayer chip varistor was also examined.
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New glass ceramics were investigated for the application as substrates to be used in hard disk devices. The glass system to precipitate lithium di-silicate was studied so as to optimize the composition to realize very high surface flatness. The addition of small amount of several metal oxides with high valences had very drastic effects on the microstructure, because they played a role of crystallization agents, and consequently it determined surface flatness even after the polishing process. The possible mechanism changes of crystal growth due to the addition of metal oxides were discussed in relation to the final micro-texture development. The glass ceramics with very high surface flatness(Ra=7.1
$\AA$ ) was obtained by the addition of the mixture of$P-2O_5 \;and \;MoO_3$ as crystallization agents. -
Using DC faced target sputtering method we grow AIN the films on the
$Al_2O_3$ (0001) substrate with varying thickness(17$\AA$ -1000$\AA$ ). We measured x-ray diffraction(XRD) profiles by synchrotron radiation($\lambda$ =1.12839$\AA$ ) with four circle diffractometer. The full width half maximum(FWHM) of rocking curve for the AIN (0002) diffraction of the film grown at$500^{\circ}C$ was$0.029^{\circ}$ . Also, we confirmed that the stress between AIN thin film and$Al_2O_3$ (0001) substrate was reduced as increasing AIN film thickness, and the critical thickness of 400~500$\AA$ , defined as a lattice constant in the film agrees with that in a bulk without stress, was obtained. -
Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol%
$Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of$150^{\circ}C$ $250^{\circ}C$ under 4 MPa$H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the$t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the$Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8$Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$ , respectively. -
In tho XRD study of
$56ZrF_4 \cdot34BaF_2 \cdot4AIF_3 \cdot(6-x)LaF_3 \cdotxLnF_3$ glassdLn=Ce, Nd, Gd, Th), halo pattern charactarktic fo an amorphous sample appeared. When the halo peak angle ($\theta_p$ ) was converted into a wavenumber with$Qp=4\pi sinG\pi/\lambda(\lambda$ is the wavolongth of the radialion used), it was found that the Qp values varied almost liuearly with the concentration 01$LnF_3$ . The emissiou spect1.a of$Ce^{3-}$ -containing fluoride glasses nnder 273 nm excitation had a peak maximum at ea. 300 nm$(Ce^{3+}$ 5d-4f- transition). The maximal intensity of the fluorescence was observed when the$CeF_3$ , content was extremely low (ca. 1 mol%j. DTA measurement revealed tbat these fluoride glasses had two crystallization temperatures. In$56ZrF_4. 34BaF_2. 4NF_3. (6-x)LaF_3 .xNdF_3$ glasses, the actmation energies of crystallization obtained from a Kssinger plot were 1.7 and 5.0 eV for the glass with x=2, and 1.9 and 5.6 eV for the glass with x=4. -
Minute boehmite crystals with high aspect rations, which were hydrothermally synthesized from gibbsite in
$Ba(OH)_2$ solution, occluded Ba with the Ba/Al molar ratio of about 0.03 in their interlayers. Their surface areas were about 14$\m^2$ /g. The Ba-intercalated bohemite samples were partly used for producing$BaAl_{12}O){19}$ with low sinterability by externally supplementing$Ba(OH)_2$ , and for forming transient aluminas. The surface area of$BaAl_{12}O){19}$ obtained by firing at$1500^{\circ}C$ for 3 h was 5.3$\m^2$ /g, which was significantly lower than 12$\m^2$ /g of the sol-gel origin. While a mixture${\gamma}$ -alumina and BaO is known to from$BaAl_{12}O){19}$ at$1200^{\circ}C$ , solid state reaction between η-alumina transformed from the Ba-intercalated boehmite and BaO formed from$Ba(OH)_2$ deposited on the boehmite started above$1300^{\circ}C$ . This suggests that large sized$Ba^{2+}$ ion occluded in η-alumina considerably suppresses the diffusion of$Al^{3+}$ ion. The surface area of the Ba-intercalated boehmite fired at$1400^{\circ}C$ for 3h was as high as 14$\m^2$ /g indicative of its potential applicability to combustion catalysts. But it was decreased to 5.0$\m^2$ /g after firing at$1500^{\circ}C$ for 3 h, accompanied by abrupt formations of$\alpha$ -alumina and$BaAl_{12}O){19}$ as main products. The suppression of$\alpha$ -alumina formation up to$1400^{\circ}C$ also suggests the significant blocking effect of$Ba^{2+}$ ion on the diffusion of the component ions. -
Effect of high voltage screening was examined on mechanical strength of titania ceramics with two different surface roughness. Roughly finished sample showed degraded mechanical strength meaning that the introduced flaw played the role of starting point of mechanical fracture. On such sample, electrically weak parts were eliminated by applying a screening field. Mechanical strength measurement on survived parts revealed that after screening the Weibull plots bended to become a convex curve while plots at high strength region were almost the same. This result means that relatively low mechanical strength parts were eliminated by the electrical method. As a result the Weibull modulus calculated from all the data increased, demonstrating the effect of high voltage screening on titania ceramics containing fracture controlling surface flaws. Roles of the surface flaw such as a common weak spot for both failures are disscussed in relation to the electric field concentration similar to that of mechanical stress.
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Al2O3 particles were dispersed into carbon fiber reinforced epoxy composites to fabricate hybrid epoxy based composites. Interface behavior and mechanical properties of these hybrid composites were studied at room and liquid nitrogen temperature and liquid nitrogen temperature and the results were compared with the those of carbon fiber reinforced composites to investigate their applicability at room and cryogenic temperature. Young's modulus in-perpendicular to fiber direction and interlaminar shear strength at room temperature and the thermal contraction down to cryhogenic temperature were improved significantly by the addition of AL2O3 filler into the epoxy matrix. The effect of Al2O3 particle addition on mechanical properties were discussed.
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MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.
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The mechanical and electrical properties of hot-pressed and annelaed
$\beta$ -SiC+39vol.%$ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of$Al_2O_3+Y_2O_3$ (6:4 wt%). In this microstructures, no reactions and elongated$\alpha$ -SiC grains with equiaxed$ZrB_2$ grains were observed between$\beta$ -SiC and$ZrB_2$ . The properties of the$\beta$ -SiC+39vol.%$ZrB_2$ composites with 4wt%$Al_2O_3+Y_2O_3$ at R.T. are as follows: fracture toughness is 6.37 MPa.m1/2, electical resistivity is$1.51\times10^{-4}\Omega \cdot\textrm{cm}$ and the relative density is 98.6% of the theoretical density. The fracture toughness of the$\beta$ -SiC+39 vol.%$ZrB_2$ composites were weakly decreased with increasing amount of$Al_2O_3+Y_2O_3$ additives. Internal stresses due to the difference of$\beta$ -SiC and$ZrB_2$ thermal expansion coefficient and elastic modulus mismatch appeared to contribute to fracture toughening in$\beta$ -SiC+39vol.%$ZrB_2$ electroconductive ceramic composites. -
Gallium doped zinc oxide(GZO) films were deposited on soda-lime glass substrates without substrate heating
$(T_s<50^{\circ}C$ ) by dc planar magnetron sputtering using GZO ceramic oxide targe with different inert gas (Ar, or Ne). For the GZO films deposited under different total gas pressure$(P_{tot})$ , structural and electrical properties were investigated by XRD and Hall effect measurements. Crystallinity of GZO films deposited using Ar was degraded with increase in$(P_{tot})$ , suggesting that it was heavily affected by kinetic energy of sputtered Zn particles$(PA_{zn})$ arriving at substrate surface. Whereas, crystallinity of GZO films deposited at lower Ptot than 3.0 Pa using Ne gas was degraded with decrease in$(P_{tot})$ . This degradation was considered to be result of film damage caused by the bombardment of high-energy neutrals ($Ne^{\circ}$ ). On the basis of a hard sphere collision processes, the average final energy of particles (sputtered Zn,$Ar^{\circ}$ and$Ne^{\circ}$ )arriving at substrate surface were estimated. -
A two-beam polarization (TBP) interfermeter with a reflection configuration for measuring the linear electroptic coefficient is described and investigated experimentally and theoretically. It is shown that a TBP interferometer can be used for measuring the Pockels coefficient of thin film with a strong Fabry-Perot effect. The TBP interferometer technique is used to measure the effective differential linear electro-optic coefficient
$re=r_{33}-(n_0/n_0)^3r_{13}$ of lead zirconate titanate (PZT) thin film. The results are in agreement with known data. -
The synthesis of polycrystalline
$Al_2TiO_5$ ceramics with low thermal expansion by fusion in an electric arc furnance was investigated. The thermal expansion curves of$Al_2TiO_5$ ceramics were lowered because of microcracks caused by the strong thermal expansion anisotropy of the crystal axes and were accompanied by hysteresis curves. These phenomena are explained by the opening and closing of microcracks. The difference in microcracking temperatures of dilatometric cooling curves in the range of 400~$620^{\circ}C$ is caused by the difference in sintering temperature, grain size and stabilization status.