Article
Nanoscience & Nanotechnology
Lihong Liu, Koji Morita
Summary: By using a simple one step spark-plasma-sintering (SPS) process to form a fine-grained Al2O3 layer on MgAl2O4, transparent MgAl2O4/Al2O3 laminated composites with an in-line transmission higher than 40% and a hardness of 29.1 GPa can be obtained. This composite structure demonstrates better mechanical properties compared to traditional monolithic materials.
SCRIPTA MATERIALIA
(2021)
Article
Materials Science, Ceramics
Aref Basiri, Amir Hossein Nassajpour-Esfahani, Mohammad Reza Haftbaradaran-Esfahani, Amir Alhaji, Ali Shafyei
Summary: This study investigated the granulation process of magnesium aluminate spinel powders using spray freeze drying method. The optimal amount of binder was found to be 3%, and the ideal solid load was determined to be 35 wt%, resulting in granules of 10-50 μm in size. Powder granulation increased density by approximately 20% and improved the in-line transmission for the IR range by over 15%.
CERAMICS INTERNATIONAL
(2022)
Article
Materials Science, Ceramics
Barak Ratzker, Roni Shrem, Inbar Ayalon, Avry Shirakov, Zeev Burshtein, Sergey Kalabukhov, Nitzan Maman, Vladimir Ezersky, Amiel Ishaaya, Ehud Galun, Nachum Frage
Summary: This study utilized spark plasma sintering (SPS) to fabricate transparent Co2+:MgAl2O4 saturable absorbers for laser passive Q-switching. Doping and densification of MgAl2O4 powders were achieved using coprecipitation and high-pressure SPS (HPSPS) methods. The presence of LiF as a sintering additive negatively affected the optical properties, while HPSPS without LiF resulted in highly transparent Co2+:MgAl2O4 ceramics. The fabricated samples demonstrated saturable absorption at a wavelength of approximately 1.5 μm, with ground-state and excited cross-sections of 3.5 x 10(-19) and 0.8x10(-19) cm(2) respectively.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2022)
Article
Materials Science, Ceramics
Jinghua Wu, Yong Lin, Chunfeng Hu, Salvatore Grasso, Danyang Zhu, Jiang Li, A. Katz-Demyanitcz, Adrian Goldstein
Summary: Ultra-fast high-temperature sintering (UHS) is a simple method to produce small transparent MgAl2O4 spinel parts. By using highly sinter active raw-material based on nano spheroidal particles with a narrow pore size distribution, fast densification can be achieved within 80 seconds at approximately 2200 degrees C. The resulting pellets have a thickness of 0.5 mm, an inline transmittance of T similar to 60% (wavelength = 1.1 mu m), and a Vickers hardness of 13.2 GPa.
CERAMICS INTERNATIONAL
(2023)
Article
Materials Science, Ceramics
Vojtech Necina, Willi Pabst
Summary: Sinter-forging is a shaping and densification technique that can be utilized for preparation of transparent ceramics with smaller pore size and higher in-line transmittance compared to conventional SPS.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2021)
Article
Materials Science, Ceramics
Lihong Liu, Koji Morita
Summary: A high hardness and wide band transparency were achieved in MgAl2O4/Al2O3 laminated composites fabricated by a one-step spark-plasma-sintering method. The optimized sintering conditions resulted in smaller grain sizes and higher densities of both the MgAl2O4 and Al2O3 phases, leading to improved mechanical properties and transparency.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2022)
Article
Materials Science, Ceramics
Nasrin Heidari, Fatemeh Davar, Amir Alhaji
Summary: In this project, magnesia-alumina composite granules were prepared using the spray drying method and then sintered at temperatures of 1400 degrees C to 1500 degrees C by spark plasma sintering without using any sintering aids. The study focused on the effects of sintering temperature on the phase evolution, density, fracture toughness, and light transmission properties of the samples. Results showed that the sample sintered at 1400 degrees C had better transparency and higher density, hardness, and fracture toughness compared to the sample sintered at 1500 degrees C.
CERAMICS INTERNATIONAL
(2022)
Article
Materials Science, Ceramics
Vaclav Pouchly, Ali Talimian, Jaroslav Kastyl, Martin Chvila, Erik Scasnovic, Ana M. Betlran, Juan G. Lozano, Dusan Galusek
Summary: The effects of LiOH doping and different SPS schedules on densification behavior and final transparency of polycrystalline magnesium aluminate spinel were investigated. Slow heating rate was optimal for undoped spinel with the highest transmittance, while fast heating rate was beneficial for LiOH-doped spinel with reduced carbon contamination.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Ceramics
Ji-Hwoan Lee, Byung-Nam Kim, Byung-Koog Jang
Summary: The transparent Y2O3 ceramics were fabricated using a two-step pressure and heating profile, which improved shrinkage behavior and achieved sufficient density without excessive coarsening. As a result, the normalized real in-line transmittance was 80.6% at 1100 nm, close to the theoretical transmittance of 81.6%. The two-step SPS profile proved to be advantageous in manufacturing ceramics with transparency and densification.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2021)
Article
Materials Science, Ceramics
L. Zarazua-Villalobos, G. Fantozzi, G. Bonnefont, L. Tellez-Jurado, H. Balmori-Ramirez
Summary: Transparent magnesium aluminate spinel was obtained through one-step spark plasma reaction-sintering (SPRS) using different precursor powders. The HT450 and HT850 powders showed better sinterability and transparency, likely due to the higher reactivity of their precursor particles.
CERAMICS INTERNATIONAL
(2022)
Article
Materials Science, Ceramics
Ahmed A. M. El-Amir, Shufeng Li, Mahmoud Abdelgawad, Emad M. M. Ewais
Summary: c-zirconia ceramic composites were successfully synthesized by SPS technique with MA addition, resulting in improved stability and strength. The SPS sintering process led to dense compacts with refined microstructure and superior compaction resistance, showing great potential for high-tech engineering applications.
JOURNAL OF THE KOREAN CERAMIC SOCIETY
(2021)
Article
Engineering, Electrical & Electronic
Madireddy Buchi Suresh, Papiya Biswas, Bhaskar Prasad Saha, Roy Johnson
Summary: Transparent MgAl2O4 spinel ceramic parts were successfully fabricated using the slip casting process and achieved near theoretical optical transmission through air sintering and hot isostatic press (HIP) treatments. The material exhibited large grain size, promising dielectric and AC conductivity properties, making it a potential candidate for high-frequency dielectric applications and high-temperature broad frequency range optical devices.
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS
(2023)
Article
Materials Science, Ceramics
Sawao Honda, Yuki Ogihara, Akio Ikesue, Yan Lin Aung, Shinobu Hashomoto, Yuji Iwamoto
Summary: The microstructure and mechanical properties of high-translucency polycrystalline spinel ceramics (MgAl2O4) were studied. Different sintering conditions were used to prepare various polycrystalline spinel ceramics, which were compared with single-crystal spinel and sapphire. Polycrystalline spinel with smaller grain size, fabricated without sintering aids, exhibited higher bending strength than single-crystal spinel. The fracture toughness of polycrystalline spinel without sintering aids was also higher than that of spinel with sintering aids. By minimizing the size of voids, high transmission and good mechanical properties can be achieved in polycrystalline spinel without sintering aids.
JOURNAL OF ASIAN CERAMIC SOCIETIES
(2023)
Article
Materials Science, Ceramics
Andre A. Bernardes, Andre L. da Silva, Jefferson Bettini, Jair C. C. Freitas, Ricardo H. R. Castro, Douglas Gouvea
Summary: Interface segregation plays a crucial role in the properties of nanocrystalline ceramics. This study investigates the spatial distribution of Li+ dopants in magnesium aluminate spinel nanoparticles and reveals a clear correlation between the microstructure of the nanoparticles and the distribution of Li+.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Multidisciplinary
Surendra Peddarasi, Debasish Sarkar
Summary: This research explores the mechanochemical effect of vibrating ball milling and planetary micro-milling processes on the synthesis and sintering of MgAl2O4 spinel. The use of micro-milling in ethanol solvent aids in achieving pure phase and optimum grain size, leading to the development of nanoscale particles and dense ceramics.
MATERIALS CHEMISTRY AND PHYSICS
(2021)
Article
Materials Science, Multidisciplinary
Hiroshi Masuda, Koji Morita, Tomoharu Tokunaga, Takahisa Yamamoto, Hidehiro Yoshida
Summary: Understanding the defect physics is crucial for comprehending the impact of electric fields and/or currents on enhanced ionic diffusion during flash sintering of ceramics. This study examined conventionally sintered yttria-stabilized zirconia and investigated the mechanical properties of flashed and non-flashed samples. The results showed rate-dependent and time-dependent mechanical behaviors, attributed to the presence of stress-induced and thermally activated recoverable motions of point defects induced by the flash process.
Article
Materials Science, Ceramics
Lihong Liu, Koji Morita
Summary: A high hardness and wide band transparency were achieved in MgAl2O4/Al2O3 laminated composites fabricated by a one-step spark-plasma-sintering method. The optimized sintering conditions resulted in smaller grain sizes and higher densities of both the MgAl2O4 and Al2O3 phases, leading to improved mechanical properties and transparency.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2022)
Article
Materials Science, Ceramics
Shunsuke Kayukawa, Yutaro Katsuyama, Ayu Kodaira, Tomoharu Tokunaga, Koji Morita, Atsutomo Nakamura, Kimitaka Higuchi, Takahisa Yamamoto
Summary: Thermally healed Vickers microcracks perpendicular to the (001) surface of cubic zirconia single crystals were studied using scanning transmission electron microscopy. The orientation relationship of areas with healed microcracks was restored to that of the original single crystal, but pores remained where the original microcrack was located. Isolated pore formation occurred through dislocation recovery and diffusion bonding via surface diffusion. Once isolated pores were formed, the total pore volume did not significantly change with increasing healing temperature, although pore sizes increased and the number of pores decreased. Ostwald ripening became pronounced in pore microstructure evolution when pore elimination was dominated by lattice diffusion after complete crystallographic restoration to a single crystal.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Ceramics
Kohta Nambu, Taisuke Kitaoka, Koji Morita, Kohei Soga, Tomoharu Tokunaga, Takahisa Yamamoto, Hiroshi Masuda, Hidehiro Yoshida
Summary: In this study, flash joining experiments were conducted using an AC field on 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) bodies. The necessary conditions for achieving almost complete self-joining of Y-TZP bodies were clarified. By applying an AC field at specific conditions, successful joining with 92% of the flexural strength of the as-sintered Y-TZP body was achieved.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Ceramics
Yuta Aoki, Hiroshi Masuda, Hidehiro Yoshida
Summary: A fine eutectic microstructure was obtained in an Al2O3-GdAlO3 (GAP) composite through local melting and rapid solidification during a flash event. The flash event was induced by applying a 1 kV/cm AC field at a frequency of 1 kHz to a calcined Al2O3-GAP body at a furnace temperature of 1400 degrees C. The resulting structure had rodlike GAP phases in the Al2O3 matrix with an interphase spacing of approximately 170 nm, comparable to previous studies on Al2O3-GAP eutectic materials. Flash events and subsequent rapid cooling can facilitate the formation of fine eutectic ceramics with a lower furnace temperature and shorter processing time.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Ceramics
Ryo Nakamura, Hiroshi Masuda, Hidehiro Yoshida
Summary: This study investigates the local mechanical responses near single grain boundaries of oxide ceramics through nanoindentation. Contrary to traditional strengthening theories, the study found negligible variations in hardness among grain interiors, grain boundary vicinities, and grain boundaries. However, transmission electron microscopy observation revealed the presence of dislocation pileups at grain boundaries. Therefore, single grain boundaries make limited contributions to the mechanical properties of oxide ceramics.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Ceramics
Ayano Nakamoto, Kohta Nambu, Hiroshi Masuda, Hidehiro Yoshida
Summary: Undoped Y2O3 polycrystals were densified by flash sintering under DC or AC electric field with varying holding times up to 60 min. The chemical bonding state and crystal structure were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. DC flash sintering with longer holding times (>= 30 min) resulted in blackening in cathodic regions, indicating the electrode-dependent introduction of neutral oxygen vacancies. The Y 3d3/2 and Y 3d5/2 binding energies decreased with increasing holding time in both DC- and AC-flash-sintered Y2O3 specimens, regardless of polarity, indicating that positively charged oxygen vacancies were introduced by the flash sintering in an electrode-independent manner, even under DC electric field. XRD analysis revealed short-range structural fluctuations in flash-sintered specimens with longer holding times. These electrode-dependent and independent point defect generations under electric fields may be related to the enhanced atomic diffusion during flash sintering.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Multidisciplinary
Shoma Takahashi, Koji Morita, Kohta Nambu, Daisuke Terada, Kiyoshi Kobayashi, Tomoharu Tokunaga, Takahisa Yamamoto
Summary: The effect of initial grain size on microcrack healing behavior under DC electric field in 8 mol% Y2O3-stabilized cubic ZrO2 (8Y-CSZ) polycrystals was studied. The healing behavior was found to be strongly dependent on the initial grain size, with faster healing observed in fine-grained 8Y-CSZ compared to coarse-grained 8Y-CSZ. The enhanced healing phenomena observed under the flash event cannot be solely attributed to thermal effects, but also to nonthermal effects caused by the flash event. Grain boundaries were found to play an important role in the flash event, and the flash healing was accelerated through field/current-enhanced diffusional processes, especially through the grain boundary diffusivity of the cations.
ADVANCED ENGINEERING MATERIALS
(2023)
Article
Materials Science, Ceramics
Shintaro Kawabata, Shoma Takahashi, Kohta Nambu, Koji Morita
Summary: The effect of the flash event (FE) on microcrack healing behavior in 8 mol% yttria-stabilized zirconia was investigated under different electric field conditions and healing temperatures. The healing rate increased with crack length, indicating that external energy stored as crack surface energy played a role in driving the crack healing. The healing rate was significantly accelerated by the FE treatment under the AC electric field compared to the DC field, suggesting that nonthermal effects contributed to the enhanced healing behavior.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Ceramics
Michiyuki Yoshida, Mitsuki Hada, Osamu Sakurada, Koji Morita
Summary: Transparent tetragonal zirconia (3YTZ) was obtained by sinter forging nanoparticles at 950°C under an applied stress of 200 MPa. The initial compact made by gel-casting had a densely packed structure of nanoparticles. The resulting dense sample had a grain size of approximately 47 nm. The in-line transmittance of a 0.9 mm-thick sample was 28% at a wavelength of 640 nm, representing 37% of the theoretical value. The sample with the best transparency in this study had a slight whitish appearance. This study demonstrated the effectiveness of combining nanoparticle gel-casting with external pressure to lower the sintering temperature for obtaining transparent tetragonal zirconia.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2023)
Article
Materials Science, Multidisciplinary
Apurv Dash, Koji Morita, Luca Balice, Robert Muecke, Olivier Guillon
Summary: This article demonstrates the enhanced plasticity of gadolinium-doped ceria (GDC) ceramics under mild and strong AC electric current, in terms of steady state creep rate under both compressive and tensile loading. A current density of 25 and 200 mA mm(-2) is used for the creep deformation, and the creep rate increases by up to two orders of magnitude under electric current. The stress exponent remains unchanged for creep experiments at 1200 °C with and without electric current, suggesting a grain boundary sliding (GBS) mechanism of plastic deformation in both cases. The field-enhanced creep rate is attributed to the interaction of space-charge layer and the electric field resulting in enhanced GBS. A higher current density results in enhanced ductility of GDC even when the Joule heating effect is compensated by reducing the furnace temperature.
ADVANCED ENGINEERING MATERIALS
(2023)
Article
Physics, Applied
Hiroshi Masuda, Daiki Tamao, Hidehiro Yoshida
Summary: Recent experiments have reported the effects of external electric fields on phonon-associated phenomena in ZrO2 ceramics, such as phase transformation and diffusion. This study used density-functional perturbation theory to examine the effects of external direct current (DC) electric fields on phonon vibration properties in a tetragonal ZrO2 unit cell. The results showed that the field sensitivities of phonon characteristics exhibited significant orientation dependence, and optical phonons showed considerable field sensitivities near the Brillouin zone boundaries. In contrast, transversal acoustic phonons demonstrated a softening trend with increasing field strengths, indicating the potential phase transformation under strong external electric fields.
APPLIED PHYSICS LETTERS
(2023)
Article
Materials Science, Ceramics
Daichi Morikawa, Kohta Nambu, Koji Morita, Hidehiro Yoshida, Kohei Soga
Summary: The impact of electric field/current on creep deformation in fine-grained 8 mol% Y2O3 stabilized cubic ZrO2 was investigated under direct and alternative current conditions. The acceleration effect caused by electric fields/currents, which cannot be explained by the increase in sample temperature due to Joule heating, is more significant in AC than in DC conditions. The deformation mechanism changes from diffusional creep to grain boundary sliding (GBS) under DC and AC, indicating that the athermal effect of electric field/current enhances GBS and its rate controlling process of cation diffusivity, especially in AC.
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
(2023)
Article
Multidisciplinary Sciences
Koji Matsui, Kohei Hosoi, Bin Feng, Hidehiro Yoshida, Yuichi Ikuhara
Summary: The attainment of both high strength and toughness is the ultimate goal for most structural materials. Although ceramic materials have high strength and good chemical stability, they suffer from low toughness. Y-TZP-based ceramic materials with toughnesses exceeding 20 MPa m(1/2) and strengths over 1,200 MPa have been developed by reducing the phase stability of tetragonal zirconia through tailoring microstructure and chemistry, which can further advance the design and application of ceramic-based structural materials.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2023)
