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.
제4권4호
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The
$UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the$UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at$1400^{\circ}C$ for fire clay and chamotte refractories containing high content of$SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free$SiO_2$ and/or$SiO_2$ bonded to$Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced$SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for$UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas. -
Dielectric properties of
$Pb(Mg_{1/3}Nb_{2/3})O_{3}-PbTiO_{3}$ , ceramics prepared by the columbite precursor method have been investigated as a function of the sintering temperature in the range of 1000∼$1250^{\circ}C$ . The$Pb(Mg_{1/3}Nb_{2/3})O_{3}-PbTiO_{3}$ ceramics show typical relaxor ferroelectric behavior. As the sintering temperature increased, the dielectric constant increased and the phase transition temperature shifted to lower temperature. The TCK(temperature coefficient of dielectric constant) and VRK (variation rate of dielectric constant) increased with increasing sintering temperature. The$Pb(Mg_{1/3}Nb_{2/3})O_{3}-PbTiO_{3}$ compositions sintered at$1250^{\circ}C$ appear to be suitable for ferroelectric bolometer. -
In wet powder processing of alumina, a number of organic molecules such as dispersant and binder are used to produce the flow behavior and properties requisite for shape forming. In this study, interparticle forces of alumina particles suspended in aqueous media were controlled by suspension pH, poly (methacrylic acid) (PMAA, used as dispersant) and poly (vinyl alcohol) (PVA, used as binder). The combined adsorption isotherms of the dispersant and binder additives on alumina were determined by total organic carbon analyzer, while the adsorption of dispersant was differentiated from binder in the mixed additive system by ultraviolet spectroscopy. The electrokinetic behavior of alumina suspensions were then correlated with the adsorption characteristics of dispersant and binder onto alumina particles. It was found that the isoelectric (
$pH_{iep}$ ) of alumina shifted from pH 8.9${\pm}$ 0.1 to acidic pH as PMAA concentration increased, while PVA adsorption did not affect the$pH_{iep}$ but caused a decrease in the near surface potential. -
The effect of aliovalent dopants,
$ Nb_2O_5$ and MnO, on the phase stability of 12 mol% ceria partially-stabilized zirconia (Ce-TZP) polycrystals was studied. Both dopants (MnO and$ Nb_2O_5$ ) significantly increased the stability of the tetragonal zirconia phase (Mb temperature lower than liquid nitrogen temperature). The enhancement of the stability of the tetragonal phase in Ce-TZP doped with 1 mol% of Mno(Ce-TZP/MnO) andCe-TZP doped with 1 mol% of$ Nb_2O_5$ (Ce-TZP/$ Nb_2O_5$ ) were explained by the significant reduction of the driving force, -${\Delta}$ Gchem, for the tetragonal-to-mono-clinic phase transformation caused by the addition of MnO and$ Nb_2O_5$ . The enhanced stability of the tetragonal phase in the Ce-TZP and Al2O3 composite (Ce-TZP/$Al_2O_3$ ) is believed to be caused by smaller grain size, moderate reduction in the chemical driving force and increase in the strain energy barrier to the transformation. Mechanical properties of the Ce-TZP and the Ce-TZP/$Al_2O_3$ with (i) the same grain size and (ii) the same Mb temperature were examined by measuring stress-strain behavior in 3 point bending. The Ce-TZP/$Al_2O_3$ composite doped with 1.3w% MnO (Ce-TZP/$Al_2O_3$ /MnO), which had the same grain size as the Ce-TZP and De-TZP/$Al_2O_3$ showed more transformation plasticity than either the Ce-TZP or the Ce-TZP/$Al_2O_3$ composite. The Ce-TZP wihch had the same Mb temperature as that of the Ce-TZP/$Al_2O_3$ /MnO did not show any transformation plasticity. -
Carbothermal reduction has been one of the important processes for the production of ceramic raw materials such as silicon carbide, silicon nitride, boron carbide, etc. The process has also been one of several trials for the recovery of ZnO from ZnO-containing waste. It usually involves two consecutive steps: the evolution of Zn vapor and its oxidation with air. In this study a ZnO-containing raw material is reduced by carbon at
$1250^{\circ}C$ and the evolved Zn vapor is oxidized with air, resulting in fine powders of ZnO. computer programs, THERMO and PYROSIM developed by MINTEK, are used to simulate the process thermodynamically and the results are compared with the experimental results. It is shown that the ZnO-containing raw material can be reduced and can form fine ZnO with the yield as high as 98.7% under a proper condition. Based on these results, a process is engineered for the production of ZnO in a rotary kiln at a rate of 3 tons/day. The produced ZnO powders show properties suitable to the usual applications in ceramic industries with a purity of > 95wt% and an average particle size of ∼3${\mu}m$ . -
American Society for Testing and Materials (ASTM) standard test method PS 070-97 has been created for measuring fracture toughness of advanced ceramics. PS 070-97 includes three test methods which use beams in bending: chevron notch (CNB), single-edged precracked beam (SEPB), and surface crack in flexure (SCF). Supporting data has been collected through several Versailles Advanced Materials and Standards round robins. This paper discusses the evolution of the standard including the rationale for the choice of the three methods and the specifications in the standard. Progress on Standard Reference material 2100 which will have certified values of fracture toughness is presented.
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Mixed oxide compounds of potential usefulness for fibre coatings (hexagonal celsian,
$BaAl_2Si_2O_8$ and lanthanum hexaluminate,$LaAl_{11}O_{18}$ ) or for matrix materials (yttrium aluminium garnet,$Y_3Al_5O_{12}$ ) were prepared by hybrid sol-gel synthesis and their thermal crystallisation was monitored by thermal analysis, X-ray diffraction and multinuclear solid state MAS NMR. All the gels convert to the crystalline phase below about$12200^{\circ}C$ , via amorphous intermediates in which the Al shows and NMR resonance at 36-38 ppm sometimes ascribed to Al in 5-fold coordination. Additional information about the structural changes during thermal treatment was provided by$^{29}Si$ ,$^{137}Ba$ and$^{89}Y$ MAS NMR spectroscopy, showing that the feldspar framework of celsian begins to be established by about$500^{\circ}C$ but the Ba is still moving into its polyhedral lattice sites about$400^{\circ}C$ after the sluggish onset of crystallization. Lanthanum hexaluminate and YAG crystallise sharply at 1230 and$930^{\circ}C$ respectively, the former via$\gamma-Al_2O_3$ , the latter via$YAlO_3$ . Yttrium moves into the garnet lattice sites less than$100^{\circ}C$ after crystallisation. -
R-curve, of three kinds of silicon nitride-based ceramics were measured, using single edge notched beam (SENB) method at room and at elevated temperatures, up to
$1200^{\circ}C$ . Stable fraacture was seen on ceramic materials with SENB specimens if the machined notch is deep enough, even though the crack resistance did not increase with crack length. Hot pressed silicon nitride did not show the rising R-curve behavior at room temperature, but it showed some rising at$1000^{\circ}C$ and above. Si3N4 reinforced with SiC whiskers showed no rising behavior at room and elevated temperatures, as it has smaller grain size, compare to the monolithic specimen. Gas pressure sintered silicon nitride had very large and elongated grains, and it showed rising R-curve even at room temperature. However, it showed some creep behavior at$1200^{\circ}C$ and the calculated R-curve on this condition did not show a good result. We cannot apply this technique on this condition for obtaining the R-curve. -
Kim, Hyun-Min;Takadama, Hiroaki;Miyaji, Fumiaki;Kokubo, Tadashi;Nishiguchi, Shigeru;Nakamura, Takashi 336
Bioactive titanium metal can be prepared by simple 5M-NaOH treatment and subsuquent heat treatment at$600^{\circ}C$ to form an amorphous sodium titanate on its surface. In the present study, mechanism of apatite formation on the titanium metal was investigated by examining its surface compositional and structural changes in a simulated body fluid. The apatite formation on the metal was found to proceed in the sequence of 1)$Na^+$ ion release from the sodium titanate to form hydrated titania abundant in Ti-OH groups, 2) early and selective binding of calcium ions with the Ti-OH groups to form a calcium titanate, and 3) late binding of phosphate ions to make apatite nucleation and growth. This indicates that Ti-OH groups do not directly induce the apatite nucleation, but via formation of a calcium titanate. -
Failure mechanisms were investigated for the two layer thermal barrier coatings consisting of NiCrAlY bond coat and
$ZrO_2$ -8wt.%$Y_2O_3$ ceramic coating during cyclic oxidation.$Al_2O_3$ developed at the ceramic coating/bond coat interface first, followed by the Cr/Ni rich oxides such as$NiCr_2O_4$ and$Ni(Al, Cr)_2O_4$ during cyclic oxidation. It was observed that the spalling of ceramic coatings took place primarily within the NiCrAlY bond coat oxidation products or at the interface between the bond coat oxidation products and zirconia based ceramic coating or the bond coat. It was also observed that the fracture within these oxidation products occurred with the formation of$Ni(Cr, Al)_2O_4$ spinel or Cr/Ni rich oxides. It was therefore concluded that the formation of these oxides was a life-limiting event for the thermal barrier coatings. -
Thermal shock resistance of
$Al_2O_3$ - and Fe-$Al_2TiO_5$ -based Castable Refractories was studied using a central heating technique. Ring type specimens, 10mm thick and 20 and 100mm inner and outer diameters, respectively, were rapidly heated on the internal surface of the centre hole using a high power electrical heating element. The temperature field was measured experimentally and modelled using finite element analysis (FEA). The thermal stress field was also modelled using FEA. A radial notch was introduced to the ring specimens to enable calculation of the thermal stress intensity factors (SIF). A special LVDT device was incorporated in the thermal shock tester to monitor crack mouth opening displacement (COD). The thermal shock fracture initiation and crack propagation behaviour of the castable refractories were ascertained using the COD measurements and the fracture mechanics analysis data. -
Dense
$ Pb(Zr, Ti)O_3(PZT)/Al_2O_3$ nanocomposites were prepared by the 28 GHz microwave heating method and conventional electric furnace sintering. Electrical and mechanical properties of the composites were investigated. The fracture strength of the PZT composites with 0.1vol%$Al_2O_3$ was significantly improved in both sintering methods. Smaller grain size and effective reinforcement of the PZT matrix by the second phase were considered to be responsible for the excellent fracture strength. Planar electromechanical coupling factor Kp of the composites sintered by 28GHz microwave heating was higher than that of the materical prepared by the conventional route. It seemed that the control of the reaction between PZT and$Al_2O_3$ by the microwave rapid sintering resulted in the high piezoelectric properties. -
Hertzian crack suppression phenomena and relatively high damage tolerance were investigated in hard/soft silicon nitride (
$Si_3N_4$ ) bilayers. Coarse$\alpha}-Si_3N_4$ powder was wsed for the hard coating layer and fine$\alpha}-Si_3N_4$ powder was used for the soft substrate layer. The two layers were designed with a strong interface. Hertzian indentation was used to investigate contact fracture and damage tolerance property. Hertzian crack suppression has occurred with increasing applied load and decreasing coating thickness. The crack suppression contributed strength improvement, especially in the bilayers with thinner coatings. Ultimately, the combination of hard coating with soft but tough underlayer improved the damage tolerance of brittle$Si_3N_4$ ceramics. -
Alumina/mica and spinel/mica composites were fabricated by sintering of compacts containing 20 mass% fluoromica (
$KMg_3AlSi_3O-{10}F_2$ ) glass and alumina or spinel. In both composites, mica precipitated as plate-like crystals at temperatures lower than$1300^{\circ}C$ and melted at$1300^{\circ}C$ to$1400^{\circ}C$ . In alumina/mica composites, alumina and glass reacted to produce spinel, and the densification progressed by the solution-precipitation of alumina. Consequently, the glass composition changed and the mica did not precipitate at temperatures higher than$1400^{\circ}C$ . However, mica precipitated after a reheating process. In spinel/mica composites, the glass composition did not change. After the mica phase melted, it recrystallized during slow cooling. The relative density reached the maximum at$1500^{\circ}C$ for alumina/mica and at$1300^{\circ}C$ spinel/mica composites, and decreased at further high temperatures. -
The work aims to evaluate the necessary physical properties of Abrasion Resistant Pavers designed for high volume pedestrian and road vehicle traffic and their influence on the selection of raw materials and ceramic processes. The pavers' specifications such as high strength and ware resistance demand a careful clay preparation, slow drying, slow firing and a balanced chemical and mineralogical composition. Therefore, developing abrasion Resistant Pavers in existing modern brickmaking plants, which are designed primarily for making bricks and pavers for domestic applications, has become a challenge for manufacturers and ceramic professionals. The significance of quality control and research and development in the production of these high class pavers is also emphasised in this work through the investigation of a paver that exhibits shrinkage cracking.
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Using calcium-phosphate-powder targets with the Ca/P ratios of 1.0-1.67, hydroxyapatite (
$Ca_{10}(PO_4)_6(OH)_2$ , HAp) thin films with 4-7㎛ thickness were prepared on titanium metal plates by r.f. magnetron sputtering, followed an annealing at$200^{\circ}C$ for 24 hr under a high water vapor pressure using an autoclave. All the specimens were systematically characterized by XRD, FT-IR, SEM and EDS analyses. The post-annealed films were confirmed to be a nonstoichiometric oxyhydroxyapatite by XRD and FT-IR measurements. -
Wear behaviors of unidirectionally oriented
$Si_3N_{4w)/Si_3N_4$ composites, sintered at different temperatures with different alignments of whiskers, have been studied in parallel and perpendicular sliding directions with respect to the orientation of the whiskers by using a ball-on-disk reciprocating sliding apparatus. The results show that wear rate in parallel direction is much greater than that in perpendicular direction. With decreasing alignment of the whiskers, the wear rate decreases in parallel sliding direction and increases in perpendicular direction. With increasing sintering temperature, the wear rate increases obviously in both parallel and perpendicular directions. -
titanate and a silicon carbide/zirconium diboride particulate composite have each been blended with thermoplastic of aqueous binders and extruded. The green extrudates have diameters ranging between 50 and 150 ㎛ and polyethylene-base 150
${\mu}m$ diameter fibers can be drawn down at elevated temperature to approximately 40${\mu}m$ diameter. Hollow fibers with 150${\mu}m$ outer and 90${\mu}m$ inner diameter can also be fabricated. Green fibers have been processed into chopped fiber felts for use as gas distributors/current collectors in an experimental solid oxide fuel cell (SOFC) and the first attempts at producing simple textile structures have been successful. The fibers, tubes and felts have been successfully debound and sintered and characterization of the sintered PSZ fibers, for example, has revealed a density in excess of 99% and tensile failure stresses up to 1.0 GPa for 78${\mu}m$ diameter fibers. -
The formation of titanium diboride (
$TiB_2$ ) via the reduction of$TiO_2$ with boric oxide and carbon was studied in a partially reducing atmosphere of argon mixed with 4 vol.%H2. The effect of reaction time, temperature, partial pressure of nitrogen and$TiO_2/B_2_O3$ stoichiometric ratio on the reducibility of oxides has been studied. The phases formed were analysed by using X-ray rowder diffraction and scanning sosctron microscopic techniques. In this paper, we also investigated the presence of$CaC_2$ as a reducing agent on the reducibility of oxide mixtures and on the Ti-B-C-Ca-O phase equilibria. The morphology of$TiB_2$ formed in the presence of$CaC_2$ is compared with the microstructure of$TiB_2$ formed as a consequence of carbothermic reduction. The observed variation in$TiB_2$ crystals formed is also explained. -
$Pb_{1-x}Sr_x(Mg-{1}2}W_{1}2})O_3$ $ ceramics for application in the microwave frequency range were investigated by dielectric constant and X-ray diffraction measurements. The dielectric constant curves showed two concentration dependent characteristics in the$ region. As the Sr constant further increases to x=0.3 the dielectric curve levels off. In the concentration range between x=0.4 and x=1 in which dielectric constant dependence on temperature is negligible, it decreases and Qf value increases in the microwave frequency with increasing Sr. The temperature coefficient ($Pb(Mg-{1}2}W_{1}2})O_3$ -rich$${\tau}_{\varepsilon} $ ) of the dielectric constant changes from the negative to positive value between x=0.9 and x=1. The dielectric constant, Qf and$\tau\varepsilon$ are correlated with tolerance factor(t). From the X-ray diffraction results for$0.1{\le}x{\le}1$ the cell parameter is found to decrease as x increases and B-site ordering is observed in all the composition ranges.