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Full Paper
published : vol. 127, no.5, May 2019
Yukio HINATSU and Yoshihiro DOI
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The phase transition of Sm3TaO7 with orthorhombic fluorite-related structure was investigated. Solid solutions (Sm1−xNdx)3TaO7 and (Sm1−xEux)3TaO7 were prepared, and their structures at room temperature are well described with the space group C2221. The phase transition temperature for (Sm1−xNdx)3TaO7 decreases from 1340 K with increasing Nd concentration, while that for (Sm1−xEux)3TaO7 increases with Eu concentration. However, both of these solid solutions show the same trend, i.e., with decreasing average rare earth radii, the phase transition temperature of (Sm1−xLnx)3TaO7 (Ln = Nd, Eu) increases. This trend is the same as that observed for Ln3MO7 (M = Mo, Ru, Re, Os, or Ir). That is, the phase transition occurs with lattice contraction. Above the transition temperature, crystal structures for (Sm1−xLnx)3TaO7 (Ln = Nd, Eu) are well described with space group Pnma.
Full Paper
published : vol. 127, no.5, May 2019
Li LONGBIAO
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This paper reports on an investigation of time-dependent proportional limit stress of carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs). The temperature-dependent material parameters are considered to determine the proportional limit stress. The effects of the fiber volume fraction, interface properties and matrix fracture energy on the time-dependent proportional limit stress and interface debonding of C/SiC composite are discussed. The temperature-dependent proportional limit stress increases with the fiber volume fraction, interface shear stress, interface debonded energy and matrix fracture energy. The fiber/matrix interface debonded length increases as the oxidation time increases, leading to a decrease in the proportional limit stress. The experimental time-dependent proportional limit stresses of C/SiC composites corresponding to different oxidation times are predicted.
Full Paper
published : vol. 127, no.5, May 2019
Ying REN, Xiaoduo HOU and Guifeng ZHANG
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For the first time, Ni–ZrO2 nanocomposite coatings have been successfully co-electrodeposited by varying the concentration of ZrO2 particles in the bath. For this, to prevent agglomeration of ZrO2 nanoparticles in the plating bath and enhance the mass fraction of nano-particles in the composite coatings, the effects of surfactants and ZrO2 content on the Ni–ZrO2 nanocomposite coatings have been investigated. It was shown that the ZrO2 fraction and the microhardness of the composite coatings are improved by using less than 20 g L−1 ZrO2 and adding anionic and cationic surfactants, respectively. A high concentration of nanoparticles can cause agglomeration, which affects the Orowan strengthening effect. The addition of a cationic surfactant increases the charge on the ZrO2, migrates faster toward the cathode, and aids improvement of the ZrO2 nanoparticle fraction. In contrast, the anionic surfactant, due to its dispersion and ZrO2 fraction with a small increase, enhances the Orowan strengthening, which limits the plastic deformation of the coating and increases the improvement in coating hardness. Furthermore, the microhardness of the Ni–ZrO2 composite coating is further increased after a high-temperature annealing process up to a maximum temperature of 900°C, which results from the oxidation of nickel and the dispersion of ZrO2 nanoparticles.
Full Paper
published : vol. 127, no.5, May 2019
Iori HIMOTO, Seiji YAMASHITA and Hideki KITA
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The fracture mechanism and reliability of typical dense ceramics can be statistically analyzed using a Weibull distribution as a basis for device design. However, it is not understood if the Weibull distribution can even be applied to highly porous ceramics. In this study, porous Siliconized Silicon Carbide (Si–SiC) ceramics with anisotropic three-dimensional network structures in a porosity range of 71–92% were fabricated and subjected to a fracture analysis using the results of three-point bending tests. Observations of fracture behavior during the bending tests were conducted using a high-speed camera, image analysis of stress distribution, and observation of crack distribution inside the partially damaged specimens using X-ray computed tomography. The results indicate non-linear behavior with multiple peaks in the load–displacement curves. In this regard, the fracture mechanism of the porous Si–SiC ceramics was intrinsically different from the brittle fracture of dense ceramics and did not appear to be based on the weakest-link model. However, the Weibull distribution was found to be applicable to the bending strength of the porous ceramics with a confidence coefficient of 0.90. This was because although strain and cracks were generated sporadically during loading, the catastrophic fracture of the porous Si–SiC ceramic specimens occurred with a macroscopic crack opening at the bottom of the test specimens, almost the same as a Mode I crack opening in dense ceramics. Furthermore, graded three-layer structures can be formed integrally using the proposed novel replication method with uniaxial pressing, taking the plateau of the stress–strain curve of the template polyurethane foam into account, providing a kind of damage tolerance owing to the sporadic generation and sequential propagation of cracks, manifested as the multiple peaks shown in the load–displacement curves.
Full Paper
published : vol. 127, no.5, May 2019
Hirofumi TSUKASAKI
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The ferroelectric state in a simple-perovskite mixed-oxide system (1 − x)Na0.5Bi0.5TiO3xBaTiO3 (NBT–xBT) for 0.30 ≤ x ≤ 1.0 was investigated primarily via in situ transmission electron microscopy observation. Dielectric permittivity measurements reveal that the NBT–xBT samples for 0.30 ≤ x < 0.80 exhibited hysteresis with a temperature width of approximately 20–50°C. This result suggests that a successive phase transition was present and that the ferroelectric state at room temperature was not a simple tetragonal symmetry. In situ transmission electron microscopes observation reveals that the ferroelectric state in the BT-rich end had an MC-type monoclinic symmetry with 〈201〉C polarization vectors in {100}C planes. The ferroelectric MC state was characterized by a 79° (pseudo 90°) domain with a (110)C twin structure and 180° domain. Thus, the continuous change at room temperature from the ferroelectric tetragonal state in BT for x = 1.0 to the monoclinic MC state for x = 0.30 can be explained by the introduction of a 〈100〉C component perpendicular to the original [001]C polarization vector in the tetragonal system.
Full Paper
published : vol. 127, no.5, May 2019
Tengfei DENG, Baijun YAN and Fangjun YANG
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The model used to predict the liquid viscosity value of clay based ceramics was determined in this study. The viscosity values of liquid phases in clay based ceramic were measured precisely in a closed tube furnace by rotating the spindle in the melts at high temperature. The chemical compositions of the glassy phases in the ceramics were analyzed. The glassy phases were prepared by the pure chemicals after the analysis. The viscosity values of the melts followed Arrhenius assumption. Four different models were applied to calculate the viscosity values of melts in the present study. The predicted results of Urbain model and Riboud model were far away from the experimental results. However, the calculated results of Shaw model (SW model), used to predict the viscosity value of lava), and Modification of Shaw model (M-SW model) were found to be much closer to the experimental results but were still with some deviations. The calculated viscosity values of M-SW model were smaller than the experimental results. On the other hand, M-SW was a reliable predictor of viscosity values of liquid phases in clay based ceramics after modification. The modification of M-SW considered “FeO” as network-modifier and got rid of a part of excess Al2O3. The assumptions of SW model and M-SW model limited the accuracy of the prediction results of liquid viscosity values in the clay based ceramics. More experiments were needed to revise the slope intercept data of K2O and “FeO”.
Full Paper
published : vol. 127, no.5, May 2019
Cong WANG, Weiwei CHEN, Anze SHUI, Jianqiao LI, Wei TIAN, Juan MA, Bin DU and Satoshi TANAKA
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In this study, the foam ceramics based on ceramic tile polishing waste (CTPW) were successfully prepared by a simple solid phase sintering method. The CTPW was used as the main raw material, SiC inside CTPW as the foam agent and (NH4)6Mo7O24 as the sintering additive. Effects of the amounts addition of (NH4)6Mo7O24 (0–6 wt %) and sintering temperature (1080–1200°C) on the sintering properties, structural evolution, phase composition and mechanical properties have been investigated. During the sintering process, the SiC inside CTPW could react with oxygen and then produce the gases such as CO and CO2, which caused a closed-pore structure. After adding (NH4)6Mo7O24 and increasing the sintering temperature, a better porous structure with suitable pore size and high compressive strength could be obtained. It was found that the foam ceramics doped with 2 wt % (NH4)6Mo7O24 and sintered at 1200°C for 30 min showed excellent properties: a low bulk density (0.362 g/cm3), the appropriate pore size (0.94 mm), a uniform pore size distribution and a very high compressive strength (8.16 MPa).
Note
published : vol. 127, no.5, May 2019
Masaki KAKIAGE, Mao YOSHIDA and Hidehiko KOBAYASHI
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Hydroxyapatite having nanometer/micrometer-size pores was formed from the olive oil/amorphous calcium phosphate (ACP)-poly(vinyl alcohol) (PVA) gel emulsion. An ACP-PVA gel was prepared by a freeze-thaw process to form an interconnected nanoporous structure. An emulsion templating method was used to form micrometer-size pores. Nanometer/micrometer-size pores were formed from the olive oil/ACP-PVA gel emulsion. The blending of oils (olive oil/squalane) resulted in the formation of bimodal nanometer/micrometer-size pores.
Technical Report
published : vol. 127, no.5, May 2019
Yoshiki SUGIMOTO, Kimiyasu SATO and Yuji HOTTA
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Production and utilization of carbon fibers (CFs) and CF reinforced plastic composites have been greatly widespread because of their distinguished properties. Although recycling of post-consumer CFs is required, recycled CFs often suffer from surface defects which diminish their quality. This article presents a process that create ceramic thin layers on the CF surfaces. CFs covered with α-Si3N4 and β-SiC layers were prepared readily and they were characterized by significantly improved oxidation resistivity. The method would be available to recuperate properties of the recycled CFs and might convert the post-consumer CFs into value-added products.
The 72th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 126, no.10, October 2018
Kotaro FUJII and Masatomo YASHIMA
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This article provides the first critical review on the discovery and development of BaNdInO4. Exploring a new structure family of ionic conductors is an important task to develop ceramic ionic conductors. Since some A2BO4 compositions exhibit high oxide-ion conductivities, we investigated ABCO4 compositions to explore new oxide-ion conductors with A/B/C cation-ordered structures. Here A, B and C are cations [ionic radii: r(A) ≥ r(B) ≥ r(C)]. In 2014, we discovered a new material BaNdInO4 which belongs to a new structure family of perovskite-related structures. This BaNdInO4-type structure (monoclinic, P21/c) consists of alternative stacking of the A rare earth oxide unit and perovskite unit with a b c tilt system. We also discovered new materials BaRInO4 (R = Sm, Y, Ho, Er, Yb) having the BaNdInO4-type structure, and report their lattice parameters and anisotropic chemical expansion. Electrical conductivity of BaNdInO4 was higher than those of BaRInO4 (R = Sm, Y, Er). Oxide-ion conduction was dominant for BaNdInO4 in the P(O2) region from 3.8 × 10−22 to 5.5 × 10−9 atm at 858°C. Oxide-ion conductivities of Ba1.1Nd0.9InO3.95, BaSr0.1Nd0.9InO3.95 and BaCa0.2Nd0.8InO3.9 were higher than that of BaNdInO4. Structure analyses of Ba1.1Nd0.9InO3.95 and BaSr0.1Nd0.9InO3.95 indicated that the excess Ba and doped Sr cations were partially substituted for Nd cation and that there existed oxygen vacancies, leading to the increase of the carrier concentration and higher oxide-ion conductivity. Following the discovery of BaNdInO4, BaRScO4 (R = Nd, Eu, Y, Yb) and SrYbInO4 were reported as new ABCO4 materials. BaYScO4 and BaYbScO4 have the BaNdInO4-type structure. BaNdScO4 and BaEuScO4 crystallize into the space group Cmcm, which has a higher symmetry than P21/c for BaNdInO4. SrYbInO4 is the first example of pure oxide-ion conductors with CaFe2O4-type structure. Further investigations of ABCO4 compositions and BaNdInO4 related materials will lead to development of materials science and solid state ionics.
Full Paper
published : vol. 126, no.10, October 2018
Jang-Hoon HA, Sujin LEE, Syed Zaighum Abbas BUKHARI, Jongman LEE, In-Hyuck SONG, Seung Jun LEE and Jaeho CHOI
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Porous ceramic membranes have received increasing attention for decades. Due to their excellent thermal and chemical properties. Because their pore sizes of as-sintered silicon carbide supports are within the microfiltration range, silicon carbide membranes have been actively investigated by many researchers and industries. For example, silicon carbide supports by themselves (average pore size of 1–10 µm) and microfiltration layer-coated silicon carbide supports (average pore size of 0.1–1 µm) can be easily prepared. However, there is insufficient data concerning the combination of ultrafiltration layer-coated silicon carbide supports (average pore size of below 0.1 µm). Therefore, the authors first prepared typical microfiltration layer-coated silicon carbide supports, and then deposited ultrafiltration layers on them. Furthermore, the authors characterized the membrane properties of the ultrafiltration layer-coated silicon carbide supports. In addition, the possibility of reducing the average pore size of microfiltration layer-coated silicon carbide supports below 0.1 µm was investigated, and improving the water permeability of ultrafiltration layer-coated silicon carbide supports by controlling processing conditions such as the heat-treatment temperature, dip-coating conditions, and composition of the alumina coating slurry was explored.
Full Paper
published : vol. 126, no.10, October 2018
Yoshiteru ITAGAKI, Jian CUI, Naoto ITO, Hiromichi AONO and Hidenori YAHIRO
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Samaria-doped ceria, (SmO1.5)0.2(CeO2)0.8 (SDC), containing nickel (Ni) was prepared as the anode of solid oxide fuel cell fueled with 6% ammonia (NH3). The Ni-free SDC powders prepared by the reverse co-precipitation method exhibited poor catalytic activities for NH3 decomposition in 6% NH3/Ar. Impregnation of Ni onto the SDC powders significantly enhanced its catalytic activity. The catalytic activity was highest at 10 wt % Ni–SDC, but it decreased with an increase in the Ni content. Contrary to expectation, the anodic performances were similar between 10 and 40 wt % of Ni loading and the highest maximum power densities were 98.8 and 96.5 mW·cm−2 at 900°C, respectively. Impedance analysis of the anodes revealed that the anodic performance was rate-controlled by the similar process in 4%H2 fuel and that was electrochemical oxidation and diffusion processes.