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  • A new design of the YIG/MTC joint brazed by bismuth-based glass
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-08
    Qianqian Chen, Tiesong Lin, Panpan Lin, Peng He, Dusan P. Sekulic, Xuan Zhao, Chonglai Jiang, Jiujie Xu, Yan Liu

    The paper uncovers an underlined mechanism of joining Yttrium Iron Garnet (YIG) and Magnesium Titanate Ceramic (MTC) with a bismuth-based glass braze. The proposed joint design has not been investigated until present. The central hypothesis is as follows. The brazed bismuth-based glass microstructure and the resulting mechanical strength of a YIG/MTC joint design support favorably a good bonding of the interface domains. The supporting evidence includes the following: (i) the bismuth-based glass features good wettability on YIG and MTC, (ii) the sequence of the coefficients of thermal expansions (YIG, bismuth-based glass, MTC) is in a favorable succession. The study reveals that the interface reactions form: (i) a lamellar phase and YBO3 whiskers at the YIG/Bi25 interface, (ii) both MgFe2O4, and Bi4Ti3O12 whiskers in addition to Zn2Ti3O8 reaction layer at the MTC/Bi25 interface, and (iii) Fe2O3 phase along the brazing seam. The mechanical integrity of joints has been studied as well.

    更新日期:2018-12-08
  • Formation mechanism of titania based opacified glaze with novel core-shell nanostructure
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-06
    Hongquan Zhan, Chuanqi Wu, Ce Deng, Xiaohong Li, Zhipeng Xie, Changan Wang, Zhi-gang Chen

    The formation mechanism of titania based opacified glaze is discussed in this paper. The glaze system composed of albite, kaolin, talc, calcite, quartz, titanium dioxide and zinc oxide is used to adjust the glaze formula and to obtain the glaze samples with better opacifying effect. The whiteness and glossiness of glaze products formed with different TiO2 contents are characterized by whiteness meter and gloss meter respectively. The structure of glaze layer is analyzed by means of SEM, TEM and EDS. The results show that the introducing of TiO2 can promote the phase separation and forms the special Si-rich/Ti-rich core-shell nanostructure. During the cooling process of the glaze, the liquid-liquid phase separation occurs and results in the formation of uniform Si-rich nanoparticles. While the Ti-containing components are enriched at the interface between the different phases and a special spherical core-shell structure is obtained around the Si-rich nanoparticles. The glaze layer is filled with the core-shell nanospheres and shows a network structure like opal. However, due to the decrease of cationic content (Ti, Zn, Ca, and Mg) in the interface between glaze and body, the network nanostructure like reverse opal would be formed. In the interaction of special opal and reverse opal structure, the opacifying effect is enhanced obviously.

    更新日期:2018-12-06
  • Microstructure and flexural strength of hafnium diboride via flash and conventional spark plasma sintering
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    D. Demirskyi, T.S. Suzuki, S. Grasso, O. Vasylkiv

    Microstructure evolution in bulk hafnium diboride ceramics prepared by spark plasma sintering in flash regime was compared with conventional spark plasma sintering. The conventional and flash spark plasma sintering resulted in ceramics with a high relative density exceeding 96 % of their theoretical density. A remarkably fine grain size distribution was noticed for the specimen prepared in the flash regime. This atypical microstructure evolution provides a possible insight into the mechanism of flash sintering for conductive bulks. The room temperature flexural strength of the hafnium diboride processed by flash SPS was 650 MPa which is 140 MPa higher than the sample produced by conventional SPS.

    更新日期:2018-12-04
  • Bioceramic scaffolds fabrication: indirect 3D printing combined with ice-templating vs. robocasting
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    J. Roleček, L. Pejchalová, F.J. Martínez-Vázquez, P. Miranda González, D. Salamon

    Ice-templating combined with indirect 3D printing is proposed as a promising method for preparation of scaffolds with multiscale porosity, including a well-defined interconnected macro-channel network. Robocasting was used as a comparative technique to produce scaffolds with comparable porosity at the introduced macroporosity and the inter-grain microporosity levels. Porosity, phase composition and mechanical stability were measured and compared for bio-scaffolds prepared by both techniques. Comparable total porosities could only be achieved in robocasting by choosing a significantly lower sintering temperature (950 °C vs. 1200 °C). The compressive strength of robocast scaffolds was significantly greater (6.5 ± 1.19 MPa vs. 2.3 ± 1.00 MPa, respectively). However, the increased level of interconnected multiscale porosity coupled to a finer grain size of ice-templated samples sintered at 1200 °C (~ 500 nm vs. 2.5 µm for robocast parts) could prove to be beneficial for the development of highly porous bioactive scaffolds with enhanced biological performance.

    更新日期:2018-12-04
  • Interactions, joining and microstructure of Sn-Ti/ZrO2 system
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    Wei Fu, Xiaoguo Song, Alberto Passerone, Shengpeng Hu, Hong Bian, Yixuan Zhao, Meirong Wang, Fabrizio Valenza

    Brazing and soldering following pre-metallization were employed to obtain reliable ZrO2/Sn-Ti/ZrO2 joints. Both the metallization and brazing depend on the wettability of ZrO2 by Sn-Ti alloys. The interfacial microstructure of joints was analyzed by SEM, XRD and TEM, and the shear strength of joints was evaluated. Good brazed joints and fully covered metallization layers, leading to good soldered joints, were obtained by the Sn-4Ti and Sn-8Ti alloys, while unsatisfactory results were obtained with Sn-1Ti and Sn-2Ti alloys owing to their limited wettability on ZrO2. Both kinds of ZrO2/Sn-Ti/ZrO2 joints possessed a β-Sn matrix with Ti6Sn5 and Ti2O3 interfacial layers. A higher Ti concentration per unit area induced the formation of a Ti11.31Sn3O10 layer along with the reduction of the Ti2O3 layer thickness at the interface in the soldered joints. All the joints exhibited a similar shear strength of 22 ~ 28 MPa and fractured through the β-Sn matrix.

    更新日期:2018-12-03
  • Transparent tetragonal-cubic zirconia composite ceramics densified by spark plasma sintering and hot isostatic pressing
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    Apurv Dash, Byung-Nam KIM, Jens Klimke, Jef Vleugels

    Targeting higher toughness transparent ceramics, tetragonal (3 mol % yttria) and cubic (8 mol % yttria) ZrO2 starting powder mixtures were densified by spark plasma sintering (SPS) in vacuum at 1100 °C and post hot isostatic pressing (HIP) in argon at 1100 °C. The influence of the ultra-fine microstructure and phase composition on the fracture resistance and light transmission in the visible and infra-red range was assessed. Of special interest was the influence of a thermal annealing step in air on the transparency of the SPS and SPS-HIP ceramics.

    更新日期:2018-12-03
  • Preparation of ZrO2 fiber modified Al2O3 membrane supports with enhanced strength and permeability
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    Weiya Zhu, Yang Liu, Kang Guan, Cheng Peng, Jianqing Wu

    In this paper, Al2O3 membrane support with both enhanced permeability and strength was fabricated by introducing zirconia fiber (ZrO2(f)). Effects of the ZrO2(f) content and sintering temperature on the open porosity, shrinkage rate, microstructure, water permeance, bending strength and pore size of the support were investigated. Results reveal that apart from fiber reinforcement, ZrO2(f) was found to promote open porosity and permeability by changing pore morphology and reducing flow resistance. However, it damages the porous structure if the sintering temperature is excessive. Compared with the un-added sample, the bending strength and water permeance of the support with a ZrO2(f) addition of 4 wt% sintered at 1550 °C increased by 261% and 52%, respectively. The modified support meets the requirement for more demanding operation conditions and may achieve the objects of miniaturizing and lightening the final products.

    更新日期:2018-12-03
  • In situ high-temperature X-Ray diffraction of hollow fiber membranes under operating conditions
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    M.P. Popov, S.F. Bychkov, N.V. Bulina, A.P. Nemudry

    Oxygen-permeable hollow fiber membranes with the composition Ba0.5Sr0.5Co0.78W0.02Fe0.2O3-δ were used to demonstrate the possibility of direct AC heating for in situ high-temperature X-Ray diffraction (HT-XRD) of the hollow fiber membranes during their operation. In situ HT-XRD measurements showed that under stationary conditions of oxygen flow through the hollow fiber membrane, the surface of the membrane from the permeate side (pO2.2) is determined by the oxygen partial pressure from the feed side (pO2.1), which allows to significantly reduce the operational requirements to the material of the hollow fiber membrane.

    更新日期:2018-12-03
  • Enhanced nucleation undercooling and surface self-nanocrystallization of Al2O3-ZrO2(Y2O3) eutectic ceramics
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-03
    Zhi-Gang Wang, Jia-Hu Ouyang, Yong-Hui Ma, Yu-Jin Wang, Ling-Yun Xie, Abdelkhalek Henniche, Zhan-Guo Liu

    This present work explores initially the feasibility of producing in-situ surface nanoeutectic Al2O3-ZrO2(Y2O3) (SNAZ) ceramics via the oxyacetylene flame remelting (OAFR) process. Singular cellular nanoeutectics consist of nanoscale lamellae, which prevail in the samples formed under different irradiation times. Ultrafine nanoeutectics are achieved by prolonging the irradiation time, and their formation mechanisms associated with eutectic refinement are proposed to obtain a better understanding on the melt thermal history and microstructural inheritance. The enhanced nucleation undercooling is the essential mechanism associated with the microstructural refinement. SNAZ formed by the OAFR-based rapid solidification seem to offer an inexpensive route to realize in-situ microstructure tailoring or surface shaping.

    更新日期:2018-12-03
  • Effect of Processing on High-Velocity Water Vapor Recession Behavior of Yb-Silicate Environmental Barrier Coatings
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-30
    Emine Bakan, Yoo Jung Sohn, Willy Kunz, Hagen Klemm, Robert Vaßen

    The purpose of this research was to investigate the corrosion behavior of the low/high Yb2SiO5 containing Yb2Si2O7 coatings under high-velocity water vapor flow. To that end, Yb2Si2O7 and Si coatings were deposited by atmospheric plasma spraying on SiC substrates. The corrosion tests were performed in the burned natural gas under atmospheric pressure, with a gas flow velocity of 100 m/s at 1200 °C for 200 h. After the test, a 25 µm thick, porous corrosion layer at the surface of the Yb2Si2O7 rich coatings was found accompanied with a mass reduction, whereas samples with Yb2SiO5 rich coatings showed mass gain indicating the greater resistance of Yb2SiO5 against water vapor. A comparison of the Yb2Si2O7 rich coatings tested in this work and Yb2Si2O7 bulk samples tested in an earlier work at the same facility revealed significantly different recession rates. Possible mechanisms responsible for this distinct behavior are discussed in the manuscript.

    更新日期:2018-12-01
  • Crystallization behavior and thermal properties of B2O3–containing MgO-Al2O3-SiO2-Li2O glass-ceramic and its wettability on Si3N4 ceramic
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Liangbo Sun, Chunfeng Liu, Jia Fang, Jie Zhang, Chengjie Lu

    B2O3-containing MgO-Al2O3-SiO2-Li2O glass-ceramics were fabricated via crystallization treatment of primal glasses for the purpose of joining Si3N4 ceramics. The effects of B2O3 content on the crystallization behavior, coefficient of thermal expansion and softening temperature of MgO-Al2O3-SiO2-Li2O-B2O3 glasses were investigated. The results reveal that the glass transition temperature and the crystallization temperature of the glasses decrease with the increasing B2O3 content. It also demonstrates that γ-spodumene solid solution is detected in the glass-ceramics after heat treatment at 735 °C and 840 °C, respectively, whereas the heat treatment at 1000 °C results in the precipitation of β/γ-spodumene coexisting phases solid solution and forsterite. Additionally, by controlling the composition and crystallization treatment, the CTEs of glass-ceramics can be matched with the Si3N4. Furthermore, contact angle measurement confirms that the glass-ceramics possess a good wettability on the Si3N4 substrate, which can be considered as the candidate materials for joining Si3N4 ceramics.

    更新日期:2018-12-01
  • Comparison of low and high pressure infiltration regimes on the density and highly porous microstructure of ceria ecoceramics made from sustainable cork templates
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Rui M. Novais, Robert C. Pullar

    Cork templates were used to produce lightweight bulk biomimetic ecoceramic (environmentally conscious ceramic) monoliths. Bulk/monolithic ceramics are vital for many applications, i.e. energy materials and fuel cells. Using simple and flexible, aqueous green-chemistry procedures, for the first time the influence of infiltration regime, number of infiltration cycles and sintering temperature on ecoceramic density and microstructure was studied. This lightweight three-dimensionally ordered macroporous (3DOM) CeO2 preserved the hexagonal cellular structure of cork, but unlike the wood, the rear cell walls were open, greatly increasing open porosity. Higher sintering temperatures (1600 instead of 1000 °C) were required to produce cm size monolithic ecoceramics mechanically strong enough to be handled. The infiltration regime and number of infiltration cycles affected density and porosity. Lower infiltration pressure led to higher porosity ecoceramics (3.3-5.7%), which may favour catalytic performance, showing the possibility of tailoring porosity and specific surface area by modifying the number of infiltration cycles.

    更新日期:2018-12-01
  • Theoretical Analysis of Experimental Densification Kinetics in Final Sintering Stage of Nano-Sized Zirconia
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Byung-Nam Kim, Tohru S. Suzuki, Koji Morita, Hidehiro Yoshida, Ji-Guang Li, Hideaki Matsubara

    The experimental densification kinetics of 7.8 mol% Y2O3-stabilized zirconia was analyzed theoretically during isothermal sintering in the final stage. By taking concurrent grain growth into account, a possible value of the grain-size exponent n was examined. The Coble’s corner-pore model recognized widely was found not to be applicable for explaining the densification kinetics. The corner-pore model of n = 4 shows a significant divergence in the kinetics at different temperatures. Microstructural observation shows that most pores are not located at grain corners and have a size comparable to the surrounding grains. The observed pore structure is similar to the diffusive model where single pore is surrounded by dense body. The diffusive model combined with theoretical sintering stress predicts n = 1 or n = 2, which shows a good consistence to the measured densification kinetics. During sintering of nano-sized powder, it is found that the densification kinetics can be explained distinctively by the diffusive single-pore model.

    更新日期:2018-12-01
  • Liquid-feed flame spray pyrolysis derived nanopowders (NPs) as a route to electrically conducting calcium aluminate (12CaO.7Al2O3) films
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Eleni Temeche, Eongyu Yi, Vazrik Keshishian, John Kieffer, Richard M. Laine

    Traditionally, C12A7 materials have been processed via solid-state reaction followed by pulsed laser deposition (PLD) or floating zone (Fz) crystallization methods at high temperature, high cost approaches to single-phase films. These techniques require a significant number of process steps to generate C12A7:e- materials that have been shown to exhibit exceptional electrical conductivities as high as 1 S/cm. We demonstrate here an effective alternative method using flame made C12A7 nanopowders (NPs) produced via liquid-feed flame spray pyrolysis (LF-FSP). Nearly fully dense, single phase, and transparent C12A7 films (< 50 μ m) can be produced by processing these NPs into green films by tape-casting, thermo-compression and then sintering to 1300 ℃ /3 h/O2. Subsequent heat treatments in 20/80 H2/N2 replaces cage trapped O2- ions forming C12A7:H- followed by UV irradiation to generate C12A7:e- with electrical conductivities of 35 mS cm-1. C12A7:e- appears to belong to a new class of transparent conducting oxides (TCOs) that may offer commercial potential on further optimization due to low materials and processing costs, environmental stability, and natural abundance when processed efficiently.

    更新日期:2018-12-01
  • Spark Plasma Sintered CaO-rich Bioglass-derived Glass-Ceramics with Different Crystallinity Ratios: a Detailed Investigation of Their Behaviour during Biological Tests in SBF
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    S. Montinaro, M. Luginina, S. Garroni, R. Orrù, F. Delogu, D. Bellucci, V. Cannillo, G. Cao

    The in-vitro behaviour of three series of dense materials with different crystallization degree and phases produced by Spark Plasma Sintering (SPS) from CaO-rich bioglass powders is investigated by soaking them up to 14 days in Simulated Body Fluid (SBF). The completely amorphous materials produced after 2 min at 730 °C display the more pronounced substrate-solution interaction. This is highly beneficial for the rapid generation (< 3 days) of an apatite layer on the substrate surface. Larger amounts of such phase are also produced during the entire immersion period. These characteristics are moderately mitigated when 80 wt.% of the glass is crystallized at 850 °C with the main formation of α-CaSiO3. Nonetheless, more severe SPS conditions (1000 °C, 20 min) lead to specimens rich of β-CaSiO3 that still retain 12 wt.% of the amorphous nature while scarcely interact with SBF. The apatite formation is correspondingly delayed (7 days) and its amount significantly decreased.

    更新日期:2018-12-01
  • Enhanced mechanical properties, thermal shock resistance and ablation resistance of Si2BC3N ceramics with nano ZrB2 addition
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Ning Liao, Dechang Jia, Zhihua Yang, Bo Niu, Yu Zhou, Yawei Li

    The mechanical properties, thermal shock resistance, and ablation resistance of nano ZrB2 modified Si2BC3N ceramics were investigated. The results show that ZrB2 stimulated microstructure evolution obviously. Therefore, the maximum strength and fracture toughness reach 559.6 MPa and 6.77 MPa·m1/2, which are improved by 61.0 % and 29.4 %, respectively. Furthermore, the residual strengths of 10 wt% ZrB2 containing composites tested at 1000 ℃ retain 363.6 MPa, which is much higher than 97.7 MPa of pristine Si2BC3N ceramics. Besides, the ablation resistance of ZrB2 modified Si2BC3N ceramics at 3000 ℃ is enhanced remarkably and the linear and mass ablation rates of ZrB2-10 are only 0.009 mm/s and 1.91 mg/s, respectively. The ablation in the ultra-high temperature zone is totally dominated by the ZrB2 component, and the thermochemical erosion is determined by the oxidation resistance of ZrB2 in the thermal affected zone.

    更新日期:2018-12-01
  • DC conductivity and AC impedance of Mn doped magnesia alumina spinel (MgAl2-2xMn2xO4) over a large temperature range
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Hongyao Jia, Wancheng Zhou, Shichang Duan, Hanyi Nan, Fa Luo, Dongmei Zhu

    MgAl2-2xMn2xO4 (MAMO) with x = 0-0.12 was synthesized in a single-phase form by solid-state reaction. XRD analysis showed that the samples had the cubic center structure of the Fd-3 m space group. Electrical properties of the samples were studied over the temperature range of 300 K~1073 K. The results showed that the DC conductivity (σDC) increased from 10-11S/cm at 300 K (MAMO, x = 0) to 10-3S/cm at 1073 K (MAMO, x = 0.12). The equivalent circuit of the complex impedance spectra suggested that the relaxation of charge carriers was of non-Debye type. The conduction was mainly caused by grain boundaries and the capacitance was mainly attributed to polarization. The complex permittivity values (ε’ and ε’’) were increased by two orders of magnitude with the increase in Mn content and temperature over the measured frequency range (1 Hz-1 MHz). Therefore, doping with Mn could be applied to modify the electrical properties of MAMO at high temperature.

    更新日期:2018-12-01
  • A robust glass-ceramic sealing material for solid oxide fuel cells: Effect of Ba3Nb10O28 phase
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Zhengwei Dong, Jianxiong Lai, Weixin Huang, Shuqi Pang, Haiyan Zhuang, Hongbing Zhan, Dian Tang, Kongfa Chen, Teng Zhang

    Crack formation at the interface between sealing glass and other cell components is one of the key issues in constraining the development of solid oxide fuel cells (SOFCs). Herein, we report our finding on tuning the mechanical and thermal properties of borosilicate glass by doping Nb2O5. We observe the formation of Ba3Nb10O28 crystalline phase in the Nb2O5-doped glass, leading to significantly enhanced crack-resistant and self-healing abilities of the glass. In addition, we demonstrate long-term thermal and chemical stability at the sealing interface between the Nb2O5-doped glass-ceramics and Y2O3-ZrO2 electrolyte after heat-treatment at 700 °C for 1000 h. The possible mechanism for the improved crack-resistant and self-healing properties is discussed.

    更新日期:2018-12-01
  • Improved thermoelectric properties of n-type Bi2S3 via grain boundaries and in-situ nanoprecipitates
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Jian Yang, Junnan Yan, Guiwu Liu, Zhongqi Shi, Guanjun Qiao

    To improve the thermoelectric properties of n-type Bi2S3 materials, a certain amount of SbCl3 were added into Bi2S3 materials by a conventional melting method combined with plasma activated sintering (PAS) process. The Bi2S3-based materials evolve from the lamellar- to particle-like structures after SbCl3 doping. The phonon scattering has strong enhancement through the increased grain boundaries and in-situ Bi2S3 nanoprecipitates, resulting in the low lattice thermal conductivity. Meanwhile, the high power factor is achieved because of the marked increase in the electrical conductivity. Hence, the synergistic effect of antimony and chlorine substitutions not only contribute to reduce the thermal conductivity but also tune the electrical transport properties, yielding a peak ZT value of ~ 0.65 at 773 K for the Bi2S3-1%SbCl3 sample.

    更新日期:2018-12-01
  • Studying the wettability of Si and eutectic Si-Zr alloy on carbon and silicon carbide by sessile drop experiments
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-12-01
    Manoj Naikade, Beate Fankhänel, Ludger Weber, Alberto Ortona, Michael Stelter, Thomas Graule

    The contact angles of two different systems, molten silicon and a eutectic Si-8 at. pct Zr alloy and their evolution over timeon vitreous carbon and polycrystalline silicon carbide (SiC) substrates were investigated at 1500°C under vacuum, as well as in argon using the sessile drop technique. The contact angle and microstructure of the liquid droplet/solid substrate interface were studied to understand fundamental features of reactive wetting as it pertains to the infiltration process of silicon and silicon alloys into carbon or C/SiC preforms. Both pure Si and theeutectic alloy showed good wettability onvitreous carbon and SiC characterized by equilibrium contact angles between 29° and 39°. Theeutectic alloy showed a higher initial contact angle and slower spreading as compared to that of pure Si. On vitreous carbon bothsilicon and the eutecticalloy formed SiC at the interface, while no reaction was observed on the SiC substrates.

    更新日期:2018-12-01
  • Systematic Investigation of Close-Packed Silica Nanospheres Monolayer under Sintering Conditions
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-29
    Sakshum Khanna, Utsav, Harsh Chaliyawala, Sagar Paneliya, Debmalya Roy, Kingsuk Mukhopadhyay, Rupak Banerjee, Indrajit Mukhopadhyay

    In this paper, we have quantified and investigated the effect of various sintering temperature on close-packed Silica Nanospheres (SNs) monolayers. SNs with diameters of 140, 175 and 220 nm were fabricated by an effective and reliable spin-coating technique. The fabricated SNs monolayers were sintered up to 1200 °C and were analyzed from FESEM to investigate in details for local and extended transformations in their structural and morphological properties. A distinct "neck-formation" was observed and was quantified with different particle size distribution as well as surface packing density. It was observed that SNs monolayer undergoes intra-particle reformation in the form of shrinkage in individual SNs and compactification of growth domains, followed by inter-particle sintering. A geometrical model was developed to determine the curvature radius and interpenetration depth thus enabling us to quantify the parameters that dominate the dynamics of the sintering process for such non-porous SNs.

    更新日期:2018-11-30
  • Graphene nanoplatelets reinforced AgCuTi composite filler for brazing SiC ceramic
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-27
    Yanyu Song, Duo Liu, Shengpeng Hu, Xiaoguo Song, Jian Cao

    Graphene nanoplatelets (GNPs) were used as reinforcement in AgCuTi filler for brazing SiC ceramic. Ti from the filler reacted with SiC ceramic to form TiC and Ti5Si3 adjacent to the SiC ceramic. According to the TEM and HRTEM results, TiC layer exhibited good lattice matching with SiC substrate. TiC particles synthesized by the reaction between Ti and GNPs in situ promoted the heterogeneous nucleation of TiCu and Cu(s,s), and contributed to the refinement of microstructure. Shear tests results indicated that the adoption of GNPs affected the joint property significantly. The TiC particles and an appropriate TiC + Ti5Si3 layer thickness both relieved the residual stress of the brazed joint and thereby increased the joint strength. The shear strength of the joint reached the maximum value of 38 MPa when using AgCuTi/GNPs (GNPs reinforced AgCuTi) composite filler containing 1% GNPs, which was ~139% higher than that of the joint brazed with AgCuTi filler.

    更新日期:2018-11-28
  • Dielectric characterization of a novel Bi2O3-Nb2O5-SiO2-Al2O3 glass-ceramic with excellent charge-discharge properties
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-27
    Jia Tian, Shujian Wang, Tao Jiang, Kaikai Chen, Jiwei Zhai, Shen Bo

    A newly designed glass-ceramic system consisting of 15Bi2O3-15Nb2O5-40SiO2-30Al2O3 was successfully prepared, which was followed by its controlled crystallization at different heating temperatures. The effects of crystallization temperature on the microstructure, phase evolution and the energy storage behaviors of the novel material were systematically investigated. A maximum theoretical energy storage density of up to 15.3 J/cm3 was found in the samples heated at 800 °C. The polarization-electric (PE) hysteresis loops of this material exhibited very good linear character and high energy efficiency. In addition, an approximate value of 25 ns for discharged period T has been obtained, which demonstrated that most of the energy stored in dielectric was released over a very short time. The maximum powder density exceeds a high value of 90 MW/cc in a 390 kV/cm electric field. Therefore, the new developed Bi2O3-Nb2O5-SiO2-Al2O3 glass-ceramic can be used as an alternative, promising high-performance electrostatic capacitor material.

    更新日期:2018-11-28
  • Investigations of nano-crystalline Sr0.5Ba0.5Nb2O6 and bulk ceramics synthesized by a polymerization method using PEG400
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-26
    Roberto Köferstein, Florian Oehler, Stefan G. Ebbinghaus

    Nano-crystalline Sr0.5Ba0.5Nb2O6 was synthesized by a one-pot method using PEG400 and citric acid. Calcination of the (Sr,Ba,Nb)-gel at 600 °C leads to Sr0.5Ba0.5Nb2O6 with a crystallite size of 24(2) nm and a specific surface area of 38.5(10) m2 g―1. Sintering up to 1325 °C leads to ceramics with globular or irregular-shaped grains and average grain sizes between 1.3 and 2.4 µm, whereas higher temperatures lead to a rod-like microstructure. The indirect allowed optical band gap varies between 3.70(5) and 3.29(5) eV. Dielectric measurements show a diffuse phase transition and weak relaxor properties. The maximum of the permittivity occurs between 116 and 147 °C. The frequency dependence of the impedance can be well described by one or two RC-circuits depending on sintering temperature. The melting temperature is determined as 1506(7) °C with ΔHf = 140(20) kJ mol―1. The average linear thermal expansion coefficient is found to be 10.5(5)⋅10―6 K―1.

    更新日期:2018-11-27
  • Composition, microstructure and electrical properties of K0.5Na0.5NbO3 ceramics fabricated by cold sintering assisted sintering
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-26
    Ma Jianzhang, Li Hanying, Wang Huajing, Lin Cong, Wu Xiao, Lin Tengfei, Zheng Xinghua, Yu xing

    In this paper, cold sintering was served as a forming method to assist the conventional sintering, which is so-called cold sintering assisted sintering (CSAS) method. Lead-free K0.5Na0.5NbO3 piezoelectric ceramics were prepared by the CSAS method, and the effects of the different procedures on the sintering behaviors and electrical properties of KNN ceramics were studied. Compared with conventional sintering (CS), cold sintering process can induce potassium-rich phase on the KNN particle surface, and remarkably increase both the green and sintering density of KNN ceramics. Meanwhile, the potassium-rich phase would transform to K4Nb6O17 second phase on the grain surface, and subsequently suppress the volatilization of potassium element. The sinterability and electrical properties were greatly improved, and KNN piezoelectric ceramics with high performance can be manufactured in a wide sintering temperature range (1055 °C-1145 °C), which proves that CSAS has the potential to be an excellent sintering technique for producing KNN based ceramics.

    更新日期:2018-11-27
  • Porous polysilazane-derived ceramic structures generated through photopolymerization-assisted solidification templating
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-26
    Richard Obmann, Sebastian Schörpf, Christian Gorsche, Robert Liska, Tobias Fey, Thomas Konegger

    A novel approach to the preparation of porous polysilazane-derived ceramics is presented, combining non-aqueous solidification templating (freeze casting) of a liquid preceramic polymer with a photo-induced thiol-ene “click” reaction at temperatures below −10 °C. Upon directional solidification of the reaction mixture consisting of the preceramic polymer, a quaternary thiol, a photoinitiator, and camphene as pore-structuring agent, low-temperature photopolymerization of the preceramic polymer was achieved by irradiation with visible light, its feasibility demonstrated by photorheology. Effects of the polymer/structuring agent ratio and the solidification rate on porosity and pore morphology were evaluated using porosimetry and tomography techniques. The structural features were set in relation to mechanical properties, showing compressive strengths up to 74 MPa at porosities between 58 % and 76 %. This new processing technique facilitates the generation of polysilazane-derived ceramics with highly tailorable pore structures, with prospective uses in processes ranging from membrane-based separation to catalysis.

    更新日期:2018-11-27
  • Giant dielectric phenomenon of Ba0.5Sr0.5TiO3/CaCu3Ti4O12 multilayers due to interfacial polarization for capacitor applications
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-24
    Lili Zhao, Ruoxin Xu, Yuxing Wei, Xiao Han, Chunxue Zhai, Zhixiang Zhang, Xiaofei Qi, Bin Cui, Jacob L. Jones

    Ba0.5Sr0.5TiO3/CaCu3Ti4O12 (BST/CCTO) multilayers with different stack sequences were deposited on LaNiO3(LNO)/SiO2/Si substrates by a sol-gel process. The dielectric properties of BST/CCTO multilayers are significantly affected by the deposition sequence, the layer thickness and the impurities, effects that are interpreted using the Maxwell-Wagner interfacial polarization model. Impurities are generated by elemental interdiffusion at the interfaces of BST/CCTO, and less at the interfaces of LNO/BST and LNO/CCTO. The dielectric permittivity of the CCTO/BST/LNO/SiO2/Si sample reaches 352,200 at 10 kHz, and stabilizes above 20,000 in the range of 100 kHz to 1 MHz. This work demonstrates an effective approach to enhance dielectric properties for film capacitor applications by constructing multilayers with specific deposition sequences and layer thicknesses.

    更新日期:2018-11-26
  • Enhancement of the electrocaloric effect over a wide temperature range in PLZT Ceramics by doping with Gd3+ and Sn4+ ions
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-24
    Biao Lu, Yingbang Yao, Xiaodong Jian, Tao Tao, Bo Liang, Q.M. Zhang, Sheng-Guo Lu

    The electrocaloric effect (ECE) in gadolinium and tin ions doped lead lanthanum zirconate titanate ceramics was investigated. Five samples with different compositions and hence different relaxor behaviors and polarization properties were prepared via a conventional solid-state reaction process. The ECE was measured directly by a high resolution thermometer from 293 K to 423 K. The results show that the ECE is mainly determined by the number of polarization states and polar-correlation strength. Furthermore, the results reveal that the temperature variation of ECE around Curie temperature is associated with the generation rate, activation energy, size and freezing temperature of polar nanoregions. As a result, Sn doped PLZT composition exhibits the best ECE, i.e., a peak ΔT > 2 K obtained at 5 MV/m, and ΔT > 1.78 K achieved in the whole temperature range measured at the same field, which are very attractive for high performance ECE devices.

    更新日期:2018-11-26
  • Microstructure and ablation properties of La2O3 modified C/C-SiC composites prepared via precursor infiltration pyrolysis
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-24
    Cunqian Fang, Xin Yang, Kejian He, Lei Chen, Guang Zeng, Anhong Shi, Qizhong Huang, Boyun Huang

    Effects of La2O3 modification on the microstructure, mechanical and ablation properties of C/C-SiC composites were investigated. Experimental results show that a new La10(SiO4)6O3 phase was generated during heat treatment process. The presence of the La-compounds, namely La2O3 and La10(SiO4)6O3, had an important impact on the structure of reinforced skeleton and the molten oxide film, and thus strongly affected the mechanical and ablation properties of the composites. Excessive La addition induced the structural damage of the reinforced skeleton, resulting in weakened mechanical and ablation properties. The C/C-SiC composites with 25.65 wt.% La2O3 addition displayed better mechanical properties and the best ablation resistance. The La10(SiO4)6O3 phase could react with molten silica to form a viscous glass during ablation. The transformation of La-compounds into La2Si2O7 can reduce the ablation of SiO2 and enhance the glass film, so as to protect the composites from further ablation.

    更新日期:2018-11-26
  • Cold spray deposition of Cr2AlC MAX phase for coatings and bond-coat layers
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-22
    T. Go, Y.J. Sohn, G. Mauer, R. Vaßen, J. Gonzalez-Julian

    Highly pure Cr2AlC powders were synthesized and deposited for the first time by cold spray technology on stainless steel substrates. The Cr2AlC coatings were relative dense, up to 91 %, and present high purity (> 98%) since only small traces of Cr2Al, Al2O3 and Cr2O3 were detected by XRD, SEM and EDX. The microstructure of the coatings is homogeneous, although some preferential orientation in the basal plane was observed by XRD pole figures. The adhesion between the coating and the substrate is strong, and compressive residual stresses up to 300 MPa in the coating were determined by XRD. Furthermore, a conventional YSZ Thermal Barrier Coating (TBCs) was deposited by Atmospheric Plasma Spray (APS) on top of the cold sprayed Cr2AlC coating in order to demonstrate the processing feasibility of Cr2AlC MAX phases as a bond-coat layer.

    更新日期:2018-11-24
  • Highly-oriented (104) polycrystalline α-Al2O3 transparent ceramics prepared by a templated grain growth method
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-22
    Qinghua Yang, Huanping Wang, Shuilin Chen, Long Zhang, Shiqing Xu

    Highly-oriented (104) polycrystalline α-Al2O3 transparent ceramics were prepared by a templated grain growth (TGG) method using A-plane single-crystal sapphire as the template. This is the first report, to best of our knowledge, on polycrystalline α-Al2O3 ceramics oriented to non-optical axes. XRD and SEM results indicate that samples with high oriented grains and high-density structure are prepared. Compared to random samples, the oriented samples exhibited an increase in the real in-line transmittance (at 650 nm) from ~23% to ~62%. Moreover, the transmission remains a high level as the wavelength shifts toward the UV range (< 300 nm). This method can be extended to other uniaxial materials without optical axes in order to produce polycrystalline ceramics with excellent optical transparency.

    更新日期:2018-11-24
  • Powder injection molding of complex-shaped aluminium nitride ceramic with high thermal conductivity
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-22
    Mingli Qin, Huifeng Lu, Haoyang Wu, Qing He, Chang Liu, Xiaodong Mu, Yuelong Wang, Baorui Jia, Xuanhui Qu

    AlN is a promising material for heat sinks and microelectronic applications because of the advantages of high theoretical thermal conductivity, high mechanical strength, good electrical insulation, low dielectric constant and low thermal expansion coefficient. However, the difficulties in shaping complex-shaped parts with a high thermal conductivity have retarded the wide applications of AlN ceramic. Herein, we design a new binder system containing resin components and adopt the powder injection molding technology to fabricate complex-shaped AlN parts. After debinding process, the special binder system would produce residual carbon, which could react with Al2O3 and result in decreasing oxygen impurity and forming the yttrium-rich aluminates. The yttrium-rich aluminates can accelerate the densification of AlN ceramic and fasten the oxygen on the triangular grain boundary, leaving the clean grain boundary beneficial for the high thermal conductivity. The as-prepared AlN parts with complex shape possess a high thermal conductivity of 248 W m-1 K-1.

    更新日期:2018-11-24
  • Effects of Grain Size and Temperature on the Energy Storage and Dielectric Tunability of Non-reducible BaTiO3-based Ceramics
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-22
    Chaoqiong Zhu, Xiaohui Wang, Qiancheng Zhao, Ziming Cai, Zhenyong Cen, Longtu Li

    BaTiO3-based ceramics with various grain sizes (136-529 nm) are prepared through a chemical coating method followed by sintering in a reducing atmosphere. Effects of grain size and temperature on electric properties, energy-storage properties, and dielectric tunability are studied via Current-Field (J-E) curves, ferroelectric hysteresis loops, Capacitance-Voltage (C-V) curves and Thermally stimulated depolarization currents (TSDC). At all temperatures, fine-grain ceramics yield a lower energy density but a higher energy efficiency under the same electric field, owing to a lower ferroelectric contribution. Meanwhile, fine-grain ceramics exhibit a higher maximum energy density due to their higher breakdown strength. Fine-grain ceramics with the grain size of 136 nm have the maximum energy density of 0.41 J/cm3 under the breakdown strength of 75 kV/cm, the corresponding efficiency is 81%. C-V curves show that fine-grain ceramics have better bias-field stability. According to TSDC results, fine-grain ceramics exhibit fewer oxygen vacancies and a higher relaxation activation energy.

    更新日期:2018-11-24
  • Large electrostrain and structural evolution in (1-x)[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-xAgNbO3 ceramics
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-22
    Pengrong Ren, Zicheng Liu, Hui Liu, Shengdong Sun, Yuhui Wan, Changbai Long, Jing Shi, Jun Chen, Gaoyang Zhao

    A lead-free system formulated as (1-x)[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-xAgNbO3 exhibits an electrostrain of 0.50 % at 80 kV/cm and a maximum d33* of 721 pm/V at 60 kV/cm for x=0.3. The incorporation of AgNbO3 shifts the relaxor-ferroelectric phase transformation temperature (TF-R) to room temperature and lowers the energy barrier of the field-induced phase transformation. Furthermore, the in-situ electric field dependent high-energy synchrotron X-ray diffraction (SXRD) technique reveals that the sample x=0.03 transforms from dominant P4bm phase to a phase mixture of R3c + P4mm at 55 kV/cm during the electric field loading, and returns to initial dominant P4bm phase at 15 kV/cm during the unloading cycle of the electric field. Furthermore, it can be demonstrated that the electric field induced-phase transition in NBTBT-3AN occurs in the whole sample, rather than in the single direction of electric field. Therefore, the electrocstrain in NBTBT-3AN is more uniform, which would be beneficial to its actuator applications.

    更新日期:2018-11-24
  • Complex mullite structures fabricated via Digital Light Processing of a preceramic polysiloxane with active alumina fillers
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-22
    Johanna Schmidt, Altan Alpay Altun, Martin Schwentenwein, Paolo Colombo

    By taking advantage of the multi-functional properties of preceramic polymers, their transformation into ceramic material at low sintering temperatures and the processing capabilities of polymer manufacturing processes, mullite components were fabricated by additive manufacturing. A photocurable silicone preceramic polymer resin containing alumina particles was shaped into complex structures via Digital Light Processing. Dense and crack-free, highly complex porous mullite ceramics were produced by firing a mixture of a commercially available photosensitive polysiloxane as the silica source, containing alumina powder as active filler, in air at a low sintering temperature (1300 °C). In particular, the developed formulations, coupled with the additive manufacturing approach, allow for precise control of the architecture of the porous ceramic components, providing better properties compared to parts with stochastic porosity.

    更新日期:2018-11-24
  • Vacancy-ordered Yttria Stabilized Zirconia as a Low-Temperature Electronic Conductor Achieved by Laser Melting
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-18
    Lu Song, Qinghua Zhang, Jing Ma, Chonglin Chen, Ben Xu, Mingke Zhu, Xing Xu, Cewen Nan, Zhijian Shen

    Laser melting is known to be capable in initiating thorough evolution in microstructure and bringing novel functional performance in metals. But realization of this potential in ceramics only reaches a preliminary stage that needs further investigation. Here we demonstrate zirconia, traditionally an insulative ceramic at low temperature, could be transformed into an electronic conductor with the conductivity on order of 10-3 S∙cm-1 at room temperature by a simple laser melting process without inducing metallic phases. Transmission electron microscopy and ab initio simulation show that oversaturated oxygen vacancies, together with their ordered metastable distribution along <001 > , were introduced during the non-equilibrium process, and result in a clear defect level significantly narrowing bandgap to less than 1 eV, leading to the considerable electronic conductivity. These results identify a strategy of utilizing this non-equilibrium method in oxide ceramics to realize some unconventional performances determined by metastable structure thoroughly altered down to atomic level.

    更新日期:2018-11-20
  • Synergistic effects of zirconium- and aluminum co-doping on the thermoelectric performance of zinc oxide
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-18
    Kiryl V. Zakharchuk, David M. Tobaldi, Xingxing Xiao, Wenjie Xie, Sergey M. Mikhalev, João F. Martins, Jorge R. Frade, Anke Weidenkaff, Andrei V. Kovalevsky

    This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous co-doping with aluminum. At 1100-1223 K mixed-doped samples demonstrated around ~2.3 times increase in ZT as compared to single-doped materials, reaching ~0.12. The simultaneous presence of aluminum and zirconium imposes a synergistic effect on electrical properties provided by their mutual effects on the solubility in ZnO crystal lattice, while also allowing a moderate decrease of the thermal conductivity due to phonon scattering effects. At 1173 K the power factor of mixed-doped Zn0.994Al0.003Zr0.003O was 2.2-2.5 times higher than for single-doped materials. Stability tests of the prepared materials under prospective operation conditions indicated that the gradual increase in both resistivity and Seebeck coefficient in mixed-doped compositions with time may partially compensate each other to maintain a relatively high power factor.

    更新日期:2018-11-20
  • Ultrashort-pulsed laser machining of dental ceramic implants
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-19
    Norbert Ackerl, Maximilian Warhanek, Johannes Gysel, Konrad Wegener

    A novel approach for machining of cylindrical hard materials and arbitrary shapes is presented. Alumina-toughened zirconia dental implants with complex geometry are manufactured with femtosecond quasi-tangential laser ablation. This rapid prototyping approach for small-scale production decreases the development-time cycle tremendously and trumps conventional approaches. Moreover, a comprehensive parameter study for radial and tangential ablation with single and multi-pulse is presented. A process achieving an ablation rate of 1 mm3 min−1 with a surface roughness Ra of 0.2 μm is introduced. The meta-stable tetragonal phase of the ceramic persists and is assessed via Raman spectroscopy. The small heat-affected zone is subsequently ablated with a radial laser process step. Hence, high-precision dental implants are producible with a mean error of smaller 5 μm over the complete contour.

    更新日期:2018-11-20
  • Thermophysical properties of the most refractory carbide Ta0.8Hf0.2C under high temperatures (2000-5000 K)
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-19
    A.I. Savvatimskiy, S.V. Onufriev, S.A. Muboyadzhyan

    We studied the carbide Ta0.81Hf0.19C0.94 in the form of a thin deposited layer (1 micron) under rapid heating (5 μs) by electric current pulse. We obtain the properties of this carbide: melting heat; specific heat, and enthalpy in the solid phase from 2000 K up to Tmelt = 4300 K, and for the first time in the liquid state up to 5000 K. We measured the temperature by high-speed radiation pyrometer calibrated against the tungsten temperature lamp. Here, we confirm the earlier obtained experimental data on the melting temperature of this compound obtained by black body model and thus, we confirm that this compound has the maximum melting temperature as against the other refractory carbides (TaC and HfC). Under fast heating, the steep increase of the specific heat of the carbide Ta0.81Hf0.19C0.94 for 400 K before melting was observed.

    更新日期:2018-11-20
  • Grain growth kinetics of 3 mol. % yttria-stabilized zirconia during flash sintering
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-19
    Ke Ren, Junbo Xia, Yiguang Wang

    Grain growth kinetics of dense 3 mol. % yttria-stabilized zirconia (3YSZ) ceramics during both DC flash sintering and conventional annealing were investigated using the grain size as a marker of microstructure evolution. The results indicated faster grain growth under greater current density. In contrast to conventionally annealed specimen, the grain boundary mobility was enhanced by almost two orders of magnitude with the applied electric current, revealing that joule heating alone was not sufficient to account for the experimental results. Instead, activation energy for grain growth decreased significantly due to electro-sintering. Systematic characterization of graded microstructure further indicated that local oxygen vacancies and specimen temperature were responsible for a grain size transition. Based on electrochemical reaction involved in flash sintering, grain size reduction at the cathode was proposed to be attributed to the local rearrangement of lattice cations and generated oxygen ions.

    更新日期:2018-11-20
  • A novel low-fired, temperature-stable, and low-cost (1−x)BaCu(B2O5)−xTiO2 microwave dielectric ceramic
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-17
    Yong-jun Gu, Li-wei Lei, Jin-liang Huang, Xing-hua Yang, Qian Li, Li-hua Li, Xin-li Li, Bok-hee Kim

    BaCu(B2O5) is a typical microwave dielectric ceramic (MDC) with a low sintering temperature, but it exhibits a large negative temperature coefficient of resonant-frequency (τf) which makes it difficult to use in wireless communications. We employ TiO2 to improve its temperature-stability of resonant-frequency, and reveal the effects of TiO2 on the densification and the microwave dielectric properties of BaCu(B2O5). Here we show that BaCu(B2O5) can be well-sintered at 825 °C with proper TiO2 additions; we find that the TiO2 grains homogeneously distribute in the boundaries of BaCu(B2O5) grains, resulting in the τf compensation of BaCu(B2O5). Enhanced temperature-stability of resonant-frequency can be achieved by increasing the content of TiO2 properly. A novel temperature-stable (1-x)BaCu(B2O5)–xTiO2 (x = 0.20) MDC (τf =-0.8 ± 3.0 ppm/°C, εr = 8.8 ± 0.36, Q×f = 28612 ± 1170 GHz) is obtained using some low-cost raw materials. Our results provide the underlying insights needed to guide the design of temperature-stable MDCs for wireless communication applications.

    更新日期:2018-11-17
  • Enhanced Energy Storage and Fast Discharge Properties of BaTiO3 Based Ceramics Modified by Bi(Mg1/2Zr1/2)O3
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-15
    Xuewen Jiang, Hua Hao, Shujun Zhang, Jiahao Lv, Minghe Cao, Zhonghua Yao, Hanxing Liu

    Lead-free (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 ((1-x)BT-xBMZ) ceramics with perovskite structure were synthesized by solid-state reaction methods. (1-x)BT-xBMZ solid solution transforms from tetragonal (x≤0.04) to pseudocubic (x≥0.08) and exhibits a dispersive dielectric behavior with respect to frequency, showing typical relaxor characteristics with BMZ increasing. The optimal energy storage density of 1.25 J cm-3 and energy efficiency of >95% are obtained at x = 0.15, with maximum dielectric breakdown strength of 185 kV cm-1 at 200 μm thickness., The energy storage density and energy efficiency of 0.85BT-0.15BMZ ceramics maintain at about 0.8 J cm-3 and 89% at 150 kV cm-1 over temperature range of 25 °C~150 °C, exhibiting good thermal stability. The pulse discharge capability of 0.85BT-0.15BMZ ceramics were measured under different electric fields, showing a short charge-discharge time of 1.3 μs. Therefore (1-x)BT-xBMZ solid solution with high energy density and efficiency, good temperature stability and fast discharge speed, is promising candidate for high power applications.

    更新日期:2018-11-16
  • Densification of thermodynamically unstable tin monoxide using cold sintering process
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-16
    Sun Hwi Bang, Thomas Herisson De Beauvoir, Clive A. Randall

    SnO is a thermodynamically unstable phase and undergoes thermal decomposition into SnO2 and Sn at a relatively low temperature when heating under ambient conditions. With the cold sintering process (CSP), SnO can be densified up to 89% of theoretical density within 100 minutes by applying uniaxial pressure of 350 MPa and transient liquid phase. 15-fold BET specific surface area reduction is observed between the ball-milled powder and the cold-sintered pellet, indicating experimental evidence of sintering. The temperature profiles of 70 – 265 °C show densification while maintaining the phase purity. Water and 2 M acetic acid solution are studied as transient liquid phases which promotes dissolution-precipitation on the particle surface and induces crystalline texture. Electrical properties of the cold sintered bulk, notably electrical conductivity and Seebeck coefficient, are measured as a function of temperature.

    更新日期:2018-11-16
  • A crystallization method for preparation of anatase-based glass-ceramic glaze
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-16
    Haiyan Zhao, Cheng Peng, Min Wu, Ming Lv, Wu Jianqing

    Developing a way to prepare effective, durable and high-temperature stable anatase-based photocatalytic ceramic is of great significance. In this work, we report a crystallization method for the preparation of anatase-based glass-ceramic glaze. The raw materials were made into frit and glazed on ceramic bodies. The glazed ceramics were sintered at 1180 °C and soaked at 700 °C. The effect of soaking temperature on the crystallization process was investigated. The photocatalytic property of the glazed tiles was evaluated by degradation of methyl orange. Experimental results show that after sintering and soaking at 700 °C, nanosized anatase grains crystallize in glaze. The crystallization of anatase nanograins is attributed to the relative high viscosity at crystallization temperature. HF etching makes more anatase grains exposed on the surface. The sample etched for 45 seconds shows the highest photocatalytic activity and the methyl orange is decomposed by about 90% after illumination for 35 h.

    更新日期:2018-11-16
  • The effect of boron substitution for aluminium on the microstructure of calcium fluoro-aluminosilicate glasses and glass-ceramics
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-14
    Siqi Zhang, Artemis Stamboulis, Wen Ni

    Calcium fluoro-aluminosilicate (4.5SiO2-3Al2O3-1.5P2O5-3CaO-2CaF2) glasses have significant applications in the medical and dental fields. However, due to the biological hazard of aluminium in the human body, this study focused on the influence of boron substitution for aluminium on the structure and properties of a series of substituted glasses and their correlated glass-ceramics. The results indicated that by increasing the amount of boron, the density of glasses and their glass-ceramics both decreased, whereas the number of bridging oxygens in the glasses increased. The glass transition temperature and the crystallization temperature remained almost unchanged for the glasses with a boron substitution of less than 25 mol%. Boron formed oxygen bridges in all glasses in the form of BO3 triangles and BO4 tetrahedra. Reducing the Al content in glasses, had an effect on the morphology and orientation of the fluorapatite crystal phase formed.

    更新日期:2018-11-15
  • Mechanical evaluations of mullite fibrous ceramics processed by filtration and in situ pyrolysis of organic precursor
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-15
    Wenjun Zhu, Anran Guo, Yunjia Xue, Junjun Zhang, Zihao Liu, Chenghao Cao, Fangfang Zhang, Jiachen Liu

    Highly porous mullite fiber-based ceramics with a three-dimensional cross structure were successfully designed and fabricated by filtration method. To address the thermal migration of silica sol, polysiloxane was introduced in the bonding system as high temperature binder to form more stable nods in the skeleton as opposed to silica sol which would migrate to the surface of fibers during the sintering process. Due to the lapped structure of mullite fibers, all products showed high porosity(74.1%~80.9%), low density(0.554g/cm3~0.608g/cm3) and relatively low thermal conductivity(<0.14mW/mK). The reaction process of in situ porolysis and fracture mechanisms were illustrated, respectively. Besides, results showed that both sintering temperature and binder content had significant influence on the microstructure and mechanical properties of the products.

    更新日期:2018-11-15
  • Isothermal phase transformations of bovine-derived hydroxyapatite/bioactive glass: a study by design of experiments
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-13
    July Andrea Rincón-López, Jennifer Andrea Hermann-Muñoz, David Andrés Fernández-Benavides, Astrid Lorena Giraldo-Betancur, Juan Manuel Alvarado-Orozco, Juan Muñoz-Saldaña

    In this work, a systematic methodology to obtain third-generation bioceramics within the Ca2SiO4-Ca3(PO4)-NaCaPO4ternary system is proposed. The synthesis of Silicocarnotite (Ca5-x(PO4)2+x(SiO4)1-x; x ≤ 0.3) (SC) and Nagelschmidtite (Ca7-xNax(PO4)2+x(SiO4)2-x; x ≤ 2) (Nagel) single phases, from mixtures of bovine-derived HAp (BHAp) and 45S5-bioactive glass (BG) as precursors was developed using design of experiments (DoE). A combination of milling and sintering processing parameters was established by statistical analysis to optimize the microstructural and mechanical properties of BHAp/BG ceramics. The optimized sintering temperature obtained with simultaneous responses was 1220 °C. Variations in BHAp/BG ratios lead to isothermal phase transformation to single crystalline phases, where 85/15 and 70/30 vol:vol ratios transformed to SC and Nagel, respectively. Finally, the proposed methodology allows a feasible composition control depending only of BHAp/BG ratio to obtain non-stoichiometric SC and Nagel phases with potential applications in bone repair.

    更新日期:2018-11-14
  • New insights into linear electrical properties of pressureless sintered SiC-MoSi2-AlN composites
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-12
    Jia-Qi Zheng, Jian Chen, Xue-Jian Liu, Zheng-Ren Huang, Jun-Jun Chen

    Highly conductive SiC-MoSi2-AlN composites were fabricated by β-SiC, AlN and MoSi2 powders with Y2O3 additive via pressureless sintering. The effect of MoSi2 content on the microstructure, mechanical and electrical properties of SiC-MoSi2-AlN composites was systematically investigated. A finer microstructure was obtained and electrical conductivity was enhanced with increasing MoSi2 content. The impedance spectroscopy and potential-current measurements were implemented to figure out the electrical conduction mechanism. The introduction of MoSi2 effectively reduced the Schottky barrier height at the grain boundary, and subsequently the U-I curves changed from nonlinear to linear electrical characteristics. The notable decrease in electrical resistivity was owing to the breakdown of grain boundaries and the formation of percolation paths. The percolation threshold was in the range of 0–5.44 vol% MoSi2, much lower than the reference value. The composites with 10 wt% MoSi2 exhibited an electrical resistivity of about 60 Ω cm, suitable for infrared source element applications.

    更新日期:2018-11-13
  • Improved microstructure of alumina ceramics prepared from DBD plasma activated powders
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-12
    Václav Pouchlý, Jozef Ráheľ, Tomáš Spusta, Martina Ilčíková, David Pavliňák, Tomáš Morávek, Karel Maca

    Submicron Al2O3 powders were activated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) plasma. The influence of the plasma treatment on the powder properties and their impact on the microstructure of dry and wet shaped ceramics were investigated. Raman and FTIR analyses of treated powders showed a substantial increase of the powder’s surface hydroxylation, surface cleaning, and the presence of adsorbed NOx originating from the DCSBD. Sintering of the dry shaped plasma treated powders did not influence sintering behavior. On the other hand, the plasma treated powder was able to form stable water suspension without any chemical stabilization aid. Slip cast samples exhibited finer pore size distribution, a higher sinterability, and a finer final microstructure. The grain size of slip casted plasma treated powder was reduced by a factor of 1.7, which facilitated a grain size of 0.68 μm at the relative density of 99.54 % t.d. obtained by pressure-less sintering.

    更新日期:2018-11-13
  • Phase and microstructure evolution in plasma sprayed Yb2Si2O7 coatings
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-10
    E. Garcia, Lee H., S. Sampath

    Yb2Si2O7 coatings were deposited on Si/SiC substrates by atmospheric plasma spray (APS). The different power and plasma chemistries used in this work produced mainly amorphous crack-free coatings with compositions shifted to lower SiO2 content with higher power and H2 flow. Differences in microstructure and thermomechanical properties (crystallization behavior, thermal expansion coefficient and thermal conductivity) of as-deposited and thermally treated coatings were directly related to the evolution from amorphous to crystalline phases. A Yb2SiO5 metastable phase was identified after thermal treatments at temperatures ~ 1000 °C that transformed to its stable isomorph at 1220 °C. This transformation, followed by the growth of the crystal cell volume, promoted the coating expansion and the “healing” of microcracks present in the amorphous as-sprayed coating.

    更新日期:2018-11-12
  • Robocasting of ceramic glass scaffolds: Sol–gel glass, new horizons
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-12
    Basam A.E. Ben-Arfa, Ana S. Neto, Ilaria E. Palamá, Isabel M. Miranda Salvado, Robert C. Pullar, José M.F. Ferreira

    This article reports the first robocasting of a sol–gel based glass ceramic scaffold. Sol–gel bioactive glass powders usually exhibit high volume fractions of meso– and micro–porosities, bad for colloidal processing as this adsorbs significant portion of the dispersing medium, affecting dispersion and flow. We circumvent these practical difficulties, to achieve pastes with particle size distributions, high solids loading and appropriate rheological properties for extrusion through fine nozzles for robocasting. Scaffolds with different macro-pore sizes (300-500 μm) with solid loadings up to 40 vol.% were robocast. The sintered (800 °C, 2 h) scaffolds exhibited compressive strength of 2.5–4.8 MPa, formed hydroxyapatite after 72 h in SBF, and had no cytotoxicity and a considerable MG63 cells viability rate. These features make the scaffolds promising candidates for tissue engineering applications and worthy for further in vivo investigations.

    更新日期:2018-11-12
  • Mechanical behaviour of carbon fibre reinforced TaC/SiC and ZrC/SiC composites up to 2100°C
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-10
    Antonio Vinci, Luca Zoli, Diletta Sciti, Jeremy Watts, Greg E. Hilmas, William G. Fahrenholtz

    The microstructure and elevated temperature mechanical properties of continuous carbon fibre reinforced ZrC and TaC composites were investigated. Silicon carbide was added to both compositions to aid sintering during hot pressing. Fibres were homogeneously distributed and no fibre degradation was observed at the interface with the ceramic matrix even after testing at 2100 °C. The flexural strength increased from 260 to 300 MPa at room temperature to ~450 MPa at 1500 °C, which was attributed to stress relaxation. At 1800 °C, the strength decreased to ~410 MPa for both samples. At 2100 °C plastic deformation resulted in lower strength at the proportional limit (210 – 320 MPa), but relatively high ultimate strength (370 – 440 MPa). The sample containing ZrC had a lower ultimate strength, but higher failure strain at 2100 °C due to the weak fibre/matrix interface that resulted in fibre-dominated composite behaviour.

    更新日期:2018-11-10
  • Thermodynamic Assessment of the Group IV, V and VI Oxides for the Design of Oxidation Resistant Multi-Principal Component Materials
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-10
    Lavina Backman, Elizabeth Opila

    Multi-principal component materials (MPCMs) are currently being investigated for use in high and ultra-high temperature environments. The design of oxidation resistant multi-component materials requires as input the oxidation behavior of each of the components. FactSage free energy minimization software and databases were used to calculate the equilibrium oxide phases and free energies of formation for the oxides of the Group IV, V and VI refractory metals, and their carbides, nitrides and borides. The results are summarized in Ellingham diagrams. Periodic trends were noted; Group IV elements form the most stable oxides with the highest melting temperatures (Tm), Group V elements form oxides with low Tm, and Group VI elements form gaseous oxide species. Oxygen diffusion data from literature for some of these oxides were also reviewed and summarized. The results are utilized to identify strategies for optimizing oxidation resistance of MPCMs for service at temperatures above 1700 °C.

    更新日期:2018-11-10
  • Improved shear strength of SiC-coated 3D C/SiC composite joints with a tailored Ti-Si-C interlayer
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-08
    Xing Zhao, Liuyang Duan, Yiguang Wang

    SiC-coated 3D C/SiC composites were successfully joined using SPS technology with a Ti-Si-C interlayer. The interface morphologies, phase composition, and mechanical properties of the joints were investigated in detail. By adjusting the joining temperature, the interlayer transitioned, in situ, from Ti-Si-C compounds to Ti3SiC2 grains without decomposition. Because of the plastic deformation behavior of Ti3SiC2 grains, the ability of the interlayer to inhibit crack propagation increased. For joints with different interlayer thickness, the distribution of thermal residual stress was calculated using finite element analysis, and the distribution was associated with the evolution of interlayer morphologies, which was eventually used to establish fracture models. Optimized bonding was achieved without erosion of carbon fibers and also without interfacial defects. Finally, a reliable joint with shear strength of 51 ± 3.0 MPa was obtained by precisely controlling the interlayer reaction and optimizing thermal residual stress.

    更新日期:2018-11-08
  • Residual Porosity and Optical Properties of Spark Plasma Sintered Transparent Polycrystalline Cerium-doped YAG
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-05
    Avital Wagner, Barak Ratzker, Sergey Kalabukhov, Maxim Sokol, Nachum Frage

    Transparent cerium-doped yttrium aluminum garnet (Ce:YAG) phosphors are promising candidates for high-power white light emitting diode applications. In the present study, Ce:YAG powder was synthesized by a co-precipitation method and highly transparent ceramics were fabricated by spark plasma sintering. The effects of temperature and pressure, as well as post-sintering treatments (annealing or hot isostatic pressing), on residual porosity were studied by electron and confocal laser microscopy. Correlation between residual porosity characteristics (pore size and volume fraction) and optical properties (in-line transmittance and photoluminescence intensity) of the luminescent transparent ceramics was established.

    更新日期:2018-11-06
  • Hot isostatically pressed Y2Ti2O7 and Gd2Ti2O7 pyrochlore glass-ceramics as potential waste forms for actinide immobilization
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-05
    Tao Wei, Yingjie Zhang, Linggen Kong, Young Jip Kim, Alan Xu, Inna Karatchevtseva, Nicholas Scales, Daniel J. Gregg
    更新日期:2018-11-06
  • High hole mobility of a semi-conductive alumina/nano-carbon ceramic composite fabricated by gel-casting and reductive sintering
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-05
    Yunzi Xin, Tomoshi Kumazawa, Masayoshi Fuji, Takashi Shirai

    Semi-conductive alumina/nano-carbon ceramic composite with high hole mobility is fabricated by gel-casting and reductive sintering. The hole mobility observed in the fabricated composite is 80-fold higher than the previously reported alumina/graphene composite. Such superior semi-conductive performance of the alumina/nano-carbon composite can be attributed to the homogenous electrically conductive path induced by nano-carbon with well-controlled graphite structure formed during fabrication process. In addition, the influence of sintering temperature on the structure of nano-carbon as well as its relation to the semi-conductive properties of composite are systemically investigated.

    更新日期:2018-11-06
  • In situ TEM observations of ion irradiation damage in boron carbide
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-05
    G. Victor, Y. Pipon, N. Moncoffre, N. Bérerd, C. Esnouf, T. Douillard, A. Gentils

    This paper presents an in situ Transmission Electron Microscopy (TEM) study of the damage formation process in ion-irradiated boron carbide used as neutron absorber for fast nuclear reactors. We focused our experiment on the damage induced by 1 MeV gold ions irradiation performed on the JANNuS-Orsay in situ dual ion beam TEM facility. The effects of the crystallographic orientation and the temperature (RT, 500 °C and 800 °C) on the ion-irradiated boron carbide structure were studied. The different steps of damage formation leading to amorphization are described. At RT, material amorphization is observed at a damage dose threshold around 7.5 displacements per atom (dpa). It is also shown that no amorphization occurred when irradiation is performed at 500 °C or 800 °C up to the highest fluence studied (3 × 1015 ions. cm-2, i.e. 7.6 dpa).

    更新日期:2018-11-06
  • Novel “Z-pins like” Vanadium rods prepared by solid phase sintering to improve ablation resistance of the C/C-ZrC-SiC composites
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-06
    Tian Tian, Wei Sun, Xiang Xiong, Yonglong Xu, Yuntian Chen, Yi Zeng, Fuqun Liu

    Novel “Z-pins like” vanadium rods (V rods) were prepared as oxide compensators to improve ablation resstance of the C/C-ZrC-SiC composites. The microstructure and anti-ablation performance were investigated. Results show that the solid phase sintering promoted the formation of a good interface between the “Z-pins like” V rods and C/C-ZrC-SiC composites, and the generation of VC and Si3V5 (anti-oxidant phases) in the “Z-pins like” V rods. The unique “Z-pins like” V rods changed the local oxidation rate, and flow regime of the formed vanadium oxide high melting point. And the liquid vanadium oxide flowed radially to the surface of the C/C-ZrC-SiC replacing SiO2 with the self-healing capability and effectivelly healed the holes and cracks. Finally, a dense and homogeneous zirconium/vanadium compound oxides film was genearated to improve the ablation resistance of C/C-ZrC-SiC without any mass and thickness reduction.

    更新日期:2018-11-06
  • 3D printing of ceramics: A review
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-11-06
    Zhangwei Chen, Ziyong Li, Junjie Li, Chengbo Liu, Changyong Liu, Yang Li, Pei Wang, He Yi, Changshi Lao, Fu Yuelong

    Along with extensive research on the three-dimensional (3D) printing of polymers and metals, 3D printing of ceramics is now the latest trend to come under the spotlight. The ability to fabricate ceramic components of arbitrarily complex shapes has been extremely challenging without 3D printing. This review focuses on the latest advances in the 3D printing of ceramics and presents the historical origins and evolution of each related technique. The main technical aspects, including feedstock properties, process control, post-treatments and energy source–material interactions, are also discussed. The technical challenges and advice about how to address these are presented. Comparisons are made between the techniques to facilitate the selection of the best ones in practical use. In addition, representative applications of the 3D printing of various types of ceramics are surveyed. Future directions are pointed out on the advancement on materials and forming mechanism for the fabrication of high-performance ceramic components.

    更新日期:2018-11-06
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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