Journal of the Ceramic Society of Japan

Cover

Released: June 01, 2017

p.H6-1

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Preface

Released: June 01, 2017

p.P6-1-P6-3

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Electrical and mechanical properties of glass and glass-ceramic electrolytes in the system Li₃BO₃–Li₂SO₄

Masahiro TATSUMISAGO, Ryohei TAKANO, Masashi NOSE, Kenji NAGAO, Atsutaka KATO, Atsushi SAKUDA, Kiyoharu TADANAGA, Akitoshi HAYASHI

Released: June 01, 2017

p.433-437

Low-melting oxide glasses are promising as electrolytes for all-solid-state lithium rechargeable batteries. Glasses in the pseudobinary system Li₃BO₃–Li₂SO₄ were prepared by a mechanochemical technique. Raman spectra revealed that the glasses contained no macroanions which form networks but consisted only of Li⁺ ions and two discrete ortho-oxoanions, BO₃³⁻ and SO₄²⁻. The density and molar volume increased and elastic moduli decreased with an increase in the Li₂SO₄ content in the glasses. The heat treatment of the Li₃BO₃–Li₂SO₄ glasses at around 300°C brought about the crystallization to form ion conducting glass-ceramics. Electrical conductivities of the glasses and glass-ceramics in this system were maximized with the mixing of Li₃BO₃ and Li₂SO₄. The conductivities were higher in the glass-ceramics of the compositions with small amounts of Li₂SO₄, ranging from 3 × 10⁻⁶ to 1 × 10⁻⁵ S cm⁻¹ at room temperature, compared to the corresponding glasses. This conductivity enhancement by the heat treatment is probably due to the precipitation of solid solutions with a high temperature Li₃BO₃ phase.

Lifetime-based measurement of mechanical load using mechanical-quenching of CaZnOS:Cu

Dong TU, Chao-Nan XU

Released: June 01, 2017

[Advance Publication] Released: April 07, 2017

p.438-440

The response characteristics of mechanical-quenching (MQ) are discussed and the influencing factors on MQ measurement such as the loading stress, loading rates and loading cycles are analyzed. Moreover, as an evaluation factor, the lifetime is introduced to measure the MQ change, which is proportional to the applied load and is inversely proportional to the loading rate. While the MQ measurement during the multiple loading cycles, the decay lifetime kept stable, indicating that the lifetime can be used for quantitative nondestructive evaluation especially for the multiple loading cycles.

Indirect measurements of electrocaloric effect in ferroelectric thin films by positive-up-negative-down method

Shogo MATSUO, Tomoaki YAMADA, Takafumi KAMO, Hiroshi FUNAKUBO, Masahito YOSHINO, Takanori NAGASAKI

Released: June 01, 2017

p.441-444

Positive-up-negative-down (PUND) polarization measurement was employed to indirectly estimate the electrocaloric (EC) effect in ferroelectric films. By subtracting the conductive component from the observed charge profile, the polarization values at various electric fields and temperatures were precisely determined. The estimated EC effect for an epitaxial Ba_0.3Sr_0.7O₃ thin film fabricated on SrRuO₃/SrTiO₃ (001) substrate showed the largest temperature change at around the ferroelectric-paraelectric phase transition temperature, which agrees with the theoretical prediction. On the other hand, the EC effect estimated by the conventional hysteresis loop measurement showed different peaking temperature from the theoretical prediction. The deviation became larger with lowering the measurement frequency. The observed results indicate the importance of precise evaluation of polarization for the examined temperature-electric field space.

Evaluation of oxygen vacancies in ZnO single crystals and powders by micro-Raman spectroscopy

Hiroaki FUKUSHIMA, Hiroshi UCHIDA, Hiroshi FUNAKUBO, Takashi KATODA, Ken NISHIDA

Released: June 01, 2017

p.445-448

Investigations of defects are important to understand the properties of zinc oxide (ZnO), especially oxygen vacancies, which are intrinsic defects that are easily generated during crystal growth or device processing. In this study, we evaluate the oxygen vacancies in ZnO single crystals and powders using micro-Raman spectroscopy. Reducing ZnO in a hydrogen atmosphere at 400–600°C for 30–240 min changes the amount of oxygen vacancies. Raman spectroscopy reveals a slight shift and a decrease in the E₂(high) phonon mode, which is related to the oxide ion vibration. The peak position of the E₂(high) mode shifts toward a lower frequency and the peak intensity decreases as the oxygen vacancies increase. This behavior can be explained by the existence of oxygen vacancies in ZnO. Because the E₂(high) peak shift and the intensity are scaled in accordance with the amount of oxygen vacancies, these correlations offer a simple and useful probe to evaluate oxygen vacancies in ZnO.

High-temperature property of flexible polyvinylidene fluoride/(Na_0.5K_0.5)NbO₃ vibration energy harvester

Norihisa MATSUBARA, Teruaki FUCHIGAMI, Ken-ichi KAKIMOTO

Released: June 01, 2017

p.449-453

Flexible polyvinylidene fluoride/(Na_0.5K_0.5)NbO₃ (PVDF/NKN) composite harvester was first characterized at high temperature. The origin of high flexibility is the unique structure assembled by alternately stacking four-sheets and three-fabrics (4-3 harvester). The 4-3 harvester was fabricated by uniformly dispersing piezoelectric NKN particles within a PVDF-sheet and a PVDF-fabric layer. Electric power-output of the 4-3 harvester was measured by using a custom-designed apparatus in the temperature range from 25 to 150°C and was compared with that of PVDF/BaTiO₃ (BT) harvester. The PVDF/NKN 4-3 harvesters and PVDF/BT 4-3 harvesters showed significantly different temperature dependences in the temperature range from 25 to 150°C. Electric power-output obtained at 25°C by applying an oscillation at 75 Hz in the thickness direction for the PVDF/NKN 4-3 harvesters and PVDF/BT 4-3 harvesters were 5.7 and 3.5 nW/cm² per an amplitude, respectively. In particular, at temperature above 130°C, the PVDF/NKN 4-3 harvester showed a stable output performance from 3.3 to 3.8 nW/cm², whereas the PVDF/BT 4-3 harvester demonstrated no electric power-output. Thus, the harvester composed of high T_C piezoelectric particles such as NKN is suitable as a vibration energy harvester operated under high-temperature environment.

Hydrothermal synthesis of lead-free perovskite (Bi_1/2K_1/2)(Zr_xTi₁₋_x)O₃ powders

Makoto ITO, Manabu HAGIWARA, Shinobu FUJIHARA

Released: June 01, 2017

p.454-457

We developed a hydrothermal synthesis method for lead-free perovskite (Bi_1/2K_1/2)(Zr_xTi₁₋_x)O₃ (BKZT) powders. Single-phase BKZT powders with various nominal Zr contents as high as x = 0.10 were obtained using amorphous hydrous oxide (Zr_xTi₁₋_x)O_2·nH₂O precursors prepared by the hydrolysis of Zr- and Ti-alkoxides, whereas a reaction using a mixture of crystalline TiO₂ and ZrO₂ powders did not provide single-phase BKZT. Elemental analysis revealed that the Zr contents of the obtained BKZT powders were slightly higher than the nominal values. The powders had fine particle sizes smaller than 300 nm and were stable against a high-temperature heat treatment at 1000°C. These observations suggest that the hydrothermally derived powders are suitable for use in fabricating bulk BKZT ceramics via sintering.

Orientation change with substrate type and composition in (100)/(001)-oriented epitaxial tetragonal Pb(Zr_xTi₁₋_x)O₃ films

Daichi ICHINOSE, Takaaki NAKASHIMA, Yoshitaka EHARA, Takahiro OIKAWA, Takao SHIMIZU, Osami SAKATA, Tomoaki YAMADA, Hiroshi FUNAKUBO

Released: June 01, 2017

p.458-462

Tetragonal 30-nm thick Pb(Zr_xTi₁₋_x)O₃ films were grown epitaxially on (100) KTaO₃ and (100) SrTiO₃ single crystal substrates by pulsed metal organic chemical vapor deposition. High temperature X-ray diffraction (XRD) reciprocal space mapping showed that Pb(Zr_xTi₁₋_x)O₃ thin films of different compositions have a misfit strain that may not be apparent from room temperature XRD measurements. The misfit strain depends on the combination of the substrate and film composition. The misfit strain revealed by high temperature XRD measurements showed good agreement with previous theoretical predictions, even for relaxed films had except for an anomalous Pb(Zr_0.45Ti_0.55)O₃ film, perfect (100) orientation was obtained for PbTiO₃ on (100)-KTaO₃ substrates with in-plane tensile and compressive strain. A mixture of (100) and (001) orientations was found for Pb(Zr_xTi₁₋_x)O₃ thin films with x = 0.22 and 0.30. On (100)-SrTiO₃ substrates, however, the (001) orientation was obtained for Pb(Zr_xTi₁₋_x)O₃ thin films grown with x = 0–0.45. These results reveal the importance of accounting for misfit strain at the growth temperature rather than at room temperature. Anomalous Pb(Zr_0.45Ti_0.55)O₃ films grown on KTaO₃ had a perfect (001) orientation, despite having a small misfit strain at the growth temperature owing to relaxation. The lower degree of tetragonality of the crystal structure may contribute to the perfect (001) orientation in these films.

Enhanced polarization properties of ferroelectric (Bi_1/2Na_1/2)TiO₃–Ba(Mg_1/3Nb_2/3)O₃ single crystals grown under high-pressure oxygen atmosphere

Kohei MAKISUMI, Yuuki KITANAKA, Yuji NOGUCHI, Masaru MIYAYAMA

Released: June 01, 2017

p.463-467

Single crystals of (Bi_1/2Na_1/2)TiO₃–Ba(Mg_1/3Nb_2/3)O₃ [(1 − x)BNT–xBMN] with x = 4% were grown by the flux method (Po₂ = 0.02 MPa) and the high-Po₂ top-seeded solution growth method (Po₂ = 0.9 MPa) and their crystal structures and properties are investigated along the pseudocubic [001] direction. The crystal grown at a higher Po₂ of 0.9 MPa exhibits a well saturated polarization hysteresis, showing that the rhombohedral phase with x = 4% has a spontaneous polarization (P_s) of 48.5 µC/cm² (P_s parallel to the pseudocubic [111] direction). The superior properties obtained for the crystal (Po₂ = 0.9 MPa) are discussed in terms of domain clamping and depolarization associated with oxygen vacancies.

Relation between nonlinearity and semiconducting characteristics of SrCoO₃ additive in ZnO varistors sintered in a reducing atmosphere

Yoshiko HIGASHI, Eiichi KOGA

Released: June 01, 2017

p.468-471

Air-sintered SrCoO₃ is strongly reduced at 1020°C in P_O2 = 1.6 × 10⁻⁹ MPa and then post-annealed at various temperatures in air. The conductive and structural characteristics are examined, comparing them with those of air-sintered. Although annealing in a reducing atmosphere breaks down SrCoO₃ to several compounds, SrCoO₃ is re-synthesized by post-annealing above 800°C. When post-annealed at 1000°C, the oxidation state of SrCoO₃ is believed to be the same higher level as that of sintered in air. The result shows that, enhancement of p-type carriers in SrCoO₃ at grain boundaries leads to nonlinearity improvement of SrCoO₃-doped ZnO varistors sintered in reducing atmospheres.

Synthesis of Li₂SiO₃ using novel water-assisted solid state reaction method

Mizuki WATANABE, Jun INOI, Sun Woog KIM, Tatsuro KANEKO, Ayano TODA, Mineo SATO, Kazuyoshi UEMATSU, Kenji TODA, Junko KOIDE, Masako TODA, Emiko KAWAKAMI, Yoshiaki KUDO, Takaki MASAKI, Dae Ho YOON

Released: June 01, 2017

p.472-475

Single phase of orthorhombic Li₂SiO₃ was synthesized via a novel soft-chemical synthesis method, water assisted solid state reaction method at 343–353 K for 60 min. The crystal structure of the samples was characterized by X-ray diffraction (XRD) analysis. The scanning electron microscope (SEM) observation revealed that the estimated size of the particles is 50–200 nm. The XRD patterns and SEM images were compared to those of samples by a conventional solid state method at 1173 K for 4 h.

An optical method for evaluating the degradation mechanism of a developing RuO₂ thick film resistor element for power modules

Yoshinobu NAKAMURA, Yuki KITANAKA, Masaru MIYAYAMA, Takeshi ITO, Koichi URANO, Kiyoshi TANAKA, Tomohiko NAKAJIMA, Tetsuo TSUCHIYA

Released: June 01, 2017

p.476-481

We devised a simple and noninvasive method for evaluating the spacial distribution of local electron densities of a thick-film RuO₂-based chip resistor using UV–VIS-IR reflectance microscopy. After a long-term durability test for 874 h under an elevated temperature of 623 K, RuO₂ resistors were thermally damaged, and their resistance became more than 10% higher. We identified the thermally damaged region by this new method and found that the thermal degradation is mainly due to an increase in the resistance between the Ag electrode and the RuO₂ resistor film.

Effects of mixing Al₂O₃ particles with tin-doped indium oxide particles on the properties of aerosol-deposited thin films

Yutaka HASEGAWA, Yuuki SATO, Shinzo YOSHIKADO

Released: June 01, 2017

p.482-486

Tin-doped indium oxide (ITO) thin films are a key material for optical devices due to their high electrical conductivity and high optical transparency. Thin films were formed on glass and polyvinylchloride substrates by aerosol deposition (AD) using aerosol mixtures of ITO and A₂O₃ (AO) particles; X-ray diffraction measurements indicated that the composite thin films comprised AO and ITO. The thickness of the film increased with increasing AO volume and reached the maximum value at approximately 50 vol %, giving a film thickness that was approximately 10 times that of a thin film deposited using only ITO particles. This study revealed that the amount of ITO particles required to generate ITO films using AD is about 20 times less than that required to fabricate ITO films of the same thickness and resistivity using conventional approaches. The resistivities of films deposited using an aerosol with 33.3 vol % ITO or more were similar to that of ITO thin film. The absorption coefficients in the visible region for ITO thin films deposited by AD were approximately 40% smaller than that of commercially available ITO thin films.

Electrical conductivity of Sr₂MgMoO_6−δ for solid oxide fuel cell anodes

Kazuya SASAKI, Kiyoto SHIN-MURA

Released: June 01, 2017

p.487-493

A high purity powder of Sr₂MgMoO_6−δ (SMM) was synthesized by a solid-state reaction under atmosphere-controlled conditions. The powder was sintered at a relatively low temperature (1200°C) to prepare compacts with high grain boundary density. SMM is a promising anode material for solid oxide fuel cells and hence, the samples were characterized under conditions relevant to this application. The electrical conductivity values of SMM under various oxygen partial pressures (p_O2 = 10⁻¹⁵–10^4.3 Pa) over the temperature range of 300–850°C were measured by AC impedance spectroscopy. The grain boundary resistivity and bulk resistivity exhibited different oxygen-partial-pressure-dependent behavior. Electron conduction is proposed as the primary mechanism for electrical conductivity in the bulk of the sintered body of SMM under both low and high oxygen partial pressures. Electron conduction and oxygen ion conduction were found to be the primary mechanisms for electrical conductivity at the grain boundary of SMM under low and high oxygen partial pressures, respectively.

Electrochemical performance of a newly-designed all-solid-state Li ion battery with a LiNi_1/3Co_1/3Mn_1/3O₂–LiVO₃ mono-particle layered cathode and a lamellar LiVO₃ anode

Taigo ONODERA, Jun KAWAJI, Akira SATO, Takefumi OKUMURA

Released: June 01, 2017

p.494-499

All-solid-state Li ion battery (ASS-LIB) with a LiNi_1/3Co_1/3Mn_1/3O₂–LiVO₃ mono-particle layered (NCMLVO-MPL) cathode was newly developed by blade coating method with a mixture of NCM and deliquescent-LiVO₃ (LVO). The electrode was fabricated by coating the aqueous slurry containing the LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) particles and the liquefied LVO on the Al foil and drying it at low temperature below 150°C. By controlling the gap of blade coater, we successfully fabricated “mono-particle layered structure”, where NCM particles are highly dispersed in the LVO matrix and the thickness was almost same as the diameter of the particles. The ASS-LIB with the NCMLVO-MPL cathode exhibited high discharge retention of 84% after 50 cycles. In the MPL structure, the well-dispersed NCM mono-particles functioned as the ion and electron conductive path in the direction perpendicular to the electrode, which kept charge–discharge capacity during the cycle test. Moreover, the all-solid-state Li ion battery incorporated with the NCMLVO-MPL composite cathode and a lamellar LVO anode was designed, also exhibiting high discharge retention of 92% after 50 cycles.

Hydrothermal synthesis and characterization of visible-light-driven Cl-doped Bi₂WO₆ nanoplate photocatalyst

Anukorn PHURUANGRAT, Phattranit DUMRONGROJTHANATH, Titipun THONGTEM, Somchai THONGTEM

Released: June 01, 2017

p.500-503

Pure Bi₂WO₆ and Cl-doped Bi₂WO₆ nanoplates were successfully synthesized by hydrothermal method. The characteristic results revealed the presence of orthorhombic Bi₂WO₆ products with 200–300 nm square-like nanoplates and anionic Cl incorporated in the Bi₂WO₆ lattice. In this research, the photocatalytic activity of Cl-doped Bi₂WO₆ nanoplates was tested through the degradation of Rhodamine B under visible light irradiation. The 3 wt % Cl-doped Bi₂WO₆ exhibited higher photocatalytic activity for degradation of Rhodamine B than other Bi₂WO₆ photocatalysts.

Effects of particle size of Al(OH)₃ on the properties of porous purging materials

Qingheng WANG, Yuanbing LI, Shujing LI, Ruoyu CHEN, Ruofei XIANG, Nana XU

Released: June 01, 2017

p.504-508

Porous purging plug is promising in the course of steel-making especially for producing the pure steel. Five designed castables containing the same aggregates and different matrixes were fabricated successfully. Air permeability tests, microstructural characterization and grey incidence analysis were carried out to analyze the particle size of aluminum hydroxide [Al(OH)₃] effects on the properties of porous purging materials. According to the attained results, the smaller particle size of Al(OH)₃ seemed to be suitable to improve the properties of such materials, as it induced the formation of connected pores and hot modulus of rupture changed slightly. When the particle size was 36.1 µm, the air permeability could reach 13.4 µm². Moreover, the grey incidence analysis matched to the experimental observations, attesting the smaller particle sizes (10–20 µm) were helpful for enhancing the air permeability while the bigger particle sizes (≥100 µm) had the opposite effects.

Fabrication of dense Si₃N₄ ceramics via coating amorphous Si₃N₄ nano-powders by sodium reduction in liquid ammonia

Qi WANG, Mei YANG, Jiusan XIAO, Hongmin ZHU

Released: June 01, 2017

p.509-512

Commercial Si₃N₄ powders coated with 0–30% amorphous Si₃N₄ nano-powders were fabricated successfully. Amorphous Si₃N₄ nano-powders coating were prepared through the reduction of silicon tetrachloride (SiCl₄) by sodium in liquid ammonia at −45°C. Dense Si₃N₄ ceramics with 97.2% relative density of theoretic value were obtained from Si₃N₄ micro-powders coated with 30% nano-powders sintered by spark plasma sintering at 1500°C without sintering additives.

Hydrothermal synthesis and characterization of visible-light-driven 0–3 wt % Br-doped Bi₂MoO₆ photocatalysts

Anukorn PHURUANGRAT, Phattranit DUMRONGROJTHANATH, Titipun THONGTEM, Somchai THONGTEM

Released: June 01, 2017

p.513-515

0–3 wt % Br-doped Bi₂MoO₆ samples as visible-light-driven photocatalysts were successfully synthesized by hydrothermal method. The Br-doped Bi₂MoO₆ samples were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. In this research, the as-synthesized samples were specified as the orthorhombic Bi₂MoO₆ phase with very high crystalline degree. The 3 wt % Br-doped Bi₂MoO₆ sample shows the best photocatalytic degradation of rhodamine B and its photocatalytic performance follows the first order kinetics model under visible light irradiation.

Synthesis of SiC layer on metal silicon from SiO by a chemical vapor deposition process

Norihiro MURAKAWA, Tomonori IIZUKA, Masanori EGUCHI, Kohei TATSUMI

Released: June 01, 2017

p.516-519

A new process for forming an SiC layer is proposed in which a surface of metal silicon is exposed to gaseous SiO and a gaseous carbon compound at around 1400°C, thereby an SiC layer is formed substantially only on the surface of metal silicon. The resulting SiC layer is of crystalline cubic SiC and a few tens µm in thickness. We consider that the carbon of the SiC layer derives from the gaseous carbon compound and the gaseous SiO promotes the formation of the SiC layer, therefore this process for forming the SiC layer can be defined as one of chemical vapor deposition processes.

Preparation and proton conductivity of ultrafine Y-doped BaZrO₃ ceramics

Du YUANSHENG, Xia JINFENG, Nian HONGQIANG, Zhou GUOHONG, Jiang DANYU, Li QIANG

Released: June 01, 2017

p.520-523

Y-doped BaZrO₃ powders prepared by high-temperature solid state reactions often suffer the disadvantage of serious aggregation. In order to eliminate this disadvantage, planet-mill and sand-mill processing methods were employed. The results of particle-size determination and scanning electron microscopy images confirm that sand milling can efficiently eliminate the aggregation and produce ultrafine and well-dispersed Y-doped BaZrO₃ powders. Starting from powders treated by sand milling, completely densified Y-doped BaZrO₃ ceramics can be fabricated by sintering at a low temperature of 1640°C for 15 h. Y-doped BaZrO₃ ceramics sintered from powders treated by sand-mill for 5 h possess an ultrafine crystal size and a higher density and proton conductivity compared to those treated for 2 h.

Kinetics of reactive diffusion between solid La₂GeO₅ and gases [GeO + 1/2O₂]

Hiroki BANNO, Ryoya KATO, Toru ASAKA, Abid BERGHOUT, Emilie BÉCHADE, Olivier MASSON, Jenny JOUIN, Philippe THOMAS, Koichiro FUKUDA

Released: June 01, 2017

p.524-527

We successfully prepared the polycrystalline lanthanum germanate oxyapatite (LGO) by the reactive diffusion between solid La₂GeO₅ and gases [GeO + 1/2O₂] during isothermal heating at 1573–1723 K for 2–50 h. The reaction products were investigated by polarizing-microscopy for microtexture characterization, Raman spectroscopy for phase identification, and X-ray diffractometry for determination of the {00l}_LGO texture fractions. The LGO polycrystals were highly c*-axis-oriented, and hence the Lotgering factor f₀₀_l ranged, regardless of annealing temperatures, between 0.94 and 0.99. The thickness (l/m) of LGO layer steadily increased with the increase of annealing time (t/s) in accordance with a parabolic relationship of l = [exp(−1.502 × 10⁴/T − 5.233)] × t^1/2. The growth of LGO layer was predominantly controlled by volume diffusion of GeO₂ component, with the activation energy being ca. 125 kJ mol⁻¹.

Anode-supported SOFC with thin film of proton-conducting BaCe_0.8Y_0.2O_3−α by electrophoretic deposition

Yoshiteru ITAGAKI, Yuga YAMAMOTO, Hiromichi AONO, Hidenori YAHIRO

Released: June 01, 2017

p.528-532

Anode-supported solid oxide fuel cells with a thin layer of proton conducting BaCe_0.8Y_0.2O_3−α (BCY) were fabricated by electrophoretic deposition technique using an organic suspension. BCY green films were formed on a graphite-added NiO–BCY substrate. By the classification of particle size distribution by the suitable period of sedimentation yielded a crack-free green film. Sintering of the crack-free green film at 1450°C yielded a dense layer of BCY with the thickness of about 9.2 ± 0.3 µm after sintering at 1450°C. The BCY thin film on the NiO–BCY substrate exhibited conductivity of 1.6 × 10⁻² S·cm⁻¹ at 600°C and its activation energy was 0.35 eV. The anode-supported single cell with the BCY thin film resulted in the maximum power density of 74.2 mW·cm⁻² at 600°C.

Carbonation of a concrete using a large amount of blast furnace slag powder

Shigeyoshi MIYAHARA, Eiji OWAKI, Masataka OGINO, Etsuo SAKAI

Released: June 01, 2017

p.533-538

Pastes of a low-carbon concrete in which ground-granulated blast-furnace slag was hardened by activators were subjected to accelerated carbonation to investigate the changes in the pore structure and composition of hydrates. The carbonation rate was more strongly correlated with Ca/(Si + Al) of calcium silicate hydrates (C–S–H) than with Ca/Si, with the rate being higher with a decrease in Ca/(Si + Al). Carbonation reduced the porosity but increased large-diameter pores, and a mixture with a higher carbonation rate showed more significant coarsening of pores. It was also found that different reactions occurred in different region of the paste. A mechanism was suggested whereby C–S–H in the inner products is strongly affected by carbonation to decompose to an amorphous silica gel, with the released Ca transferring out of the grains to form CaCO₃. In the outer products, the Ca/Si of C–S–H was reduced by carbonation similarly to the inner products, but the decomposition did not proceed to a silica gel as long as Ca(OH)₂ remained to be present.

Synthesis and characterization of spherical alumina nanoparticles by spray pyrolysis using radiofrequency plasma

Shigehiro ARITA, Nobuyoshi AOYAGI, Kenji OHSHITA, Yasuhiro TSUBOTA, Takashi OGIHARA

Released: June 01, 2017

p.539-542

Alumina nanoparticles were directly synthesized by spray pyrolysis using radiofrequency (RF) plasma. The mist that was generated from the aqueous solution of aluminum nitrate by using an ultrasonic vibrator was continuously pyrolyzed in the RF plasma. Scanning-electron-microscope and transmission-electron-microscope images showed that as-prepared alumina nanoparticles exhibited spherical morphology with non-aggregation. The particle size and geometrical standard deviation of the alumina nanopowders obtained at 3000°C were 80 nm and 1.41, respectively. The average particle size of the alumina nanopowders decreased with increasing pyrolysis temperature. The average particle size and particle size distribution of the alumina nanopowders were independent of the concentration. X-ray diffraction revealed that as-prepared alumina nanopowders were crystallized to γ-alumina. The crystallinity of the as-prepared alumina nanopowders increased with increasing pyrolysis temperature. BET revealed that the specific surface area (SSA) increased with increasing pyrolysis temperature. The as-prepared alumina nanopowders had a high SSA of 100 m²/g at 3,000°C.