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  • Universal dielectric relaxation induced giant dielectric permittivity in Mn-doped PbZrO3 ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-15
    Hongbo Liu

    Manganese-doped lead zirconate ceramics were prepared by a conventional solid reaction method. Although the doping content varies from 5% (mole) to 20% (mole), significantly enhanced universal dielectric relaxation occurs only in 5% Mn-doped lead zirconate. The behavior cannot be properly explained by Maxwell-Wagner relaxation, which is commonly used for explaining giant dielectric permittivity in electroceramics. It is found that the enhanced giant dielectric permittivity is related to hetero-valence cation doping induced universal dielectric relaxation.

    更新日期:2019-02-15
  • Taguchi design for optimization of structural and mechanical properties of hydroxyapatite-alumina-titanium nanocomposite
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-15
    Mohsen Ebrahimi, Iman Mobasherpour, Hadi Barzegar Bafrooei, Fatemeh Shirani Bidabadi, Mojtaba Mansoorianfar, Yasin Orooji, Alireza Khataee, Changtong Mei, Esmaeil Salahi, Touradj Ebadzadeh

    The Taguchi methodology was utilized to determine the influence of three factors, namely nanostructured alumina (A) and micro-structured titanium (B) weight percents and sintering temperature (C) on the phase stability, mechanical and structural properties of hydroxyapatite (HA) composites. HA nanosized powder was synthesized via wet precipitation method. According to L9 orthogonal array, different combinations of powder mixtures were cold isostatically pressed and pressure-less sintered in a reducing atmosphere. XRD analysis confirmed the presence of HA phase and metallic Ti after sintering. Analyze of Variance (ANOVA) method was used to specify the percentage contributions of three factors. Addition of 5–10 wt% titanium contributed to increasing the decomposition of HA and the amount of open porosity by 43.07% and 55.40%, respectively and caused a decrease in the strength by 44.67%. Alumina nanoparticles consistently inhibited the grain growth but showed a negligible effect on the decomposition of HA. It also caused enhancements in the strength and toughness by 14.61 and 23.70% contributions. According to ANOVA, sintering temperature illustrated considerable effects on the properties of HA composites. It exhibited more than 56% contribution to the grain growth and decomposition of HA. Structural investigations led to a total optimum condition with a combination of 7 wt % alumina/3 wt % titanium/1150 °C.

    更新日期:2019-02-15
  • Y3Ce7Ta2O23.5 and Yb3Ce7Ta2O23.5—Two kinds of novel ceramics for thermal barrier coatings
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-15
    Wang Shi-min, Zhu Wei-wei, Zhang Hong-song, Wang Fei, Sun Debing, Yang Xian-feng, Su Zhi-he, Duan Qun-peng, Mai Wen-peng

    For the development of ceramic candidates for thermal barrier coatings, two kinds of new ceramics, Y3Ce7Ta2O23.5 and Yb3Ce7Ta2O23.5, were synthesized by sintering at 1873 K for 10 h. The obtained samples were composed of a single fluorite-type phase, and their relative densities are greater than 90%. Because of phonon scattering caused by the complex lattice, the large number of oxygen vacancies, and substituted atoms, the thermal conductivity is lower than that of 8YSZ. The coefficients of thermal expansion (CTEs) of these two products are located in the range of 10.22–12.57 × 10−6/K and 9.62–12.66 × 10−6/K, respectively, from 323 K to 1473 K, and they also exhibit excellent phase stability up to 1473 K. However, their thermal conductivities and CTEs are lower than those of RE2Ce2O7 (RE = La, Nd, or Sm).

    更新日期:2019-02-15
  • Impact of crystal structure and microstructure on electrical properties of Ho doped lead-free BCST piezoceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-15
    Chitra, Ankit Khandelwal, Rahil Gupta, Radhapiyari Laishram, K. Chandramani Singh

    Conventional solid state sintering method was used to synthesize lead-free (Ba0.91Ca0.09Sn0.07Ti0.93)O3-xHo2O3 (x = 0, 1.2,1.4,1.6,1.8 and 2.0 mol%) ceramics. The influence on electrical properties of the system as a result of the structural and microstructural changes introduced by the incorporation of rare earth Ho3+ ions has been investigated. The X-ray diffraction analysis reveals that Ho3+ ions completely diffuse into the (Ba0.91Ca0.09Sn0.07Ti0.93)O3 lattice to form a homogeneous solid solution with a pure perovskite structure having tetragonal symmetry. Evidence of Ho3+ substituting Ti4+ via the oxygen vacancy compensation mechanism exists in the range of 0–1.6 mol % Ho content, while the self-compensation mode is the preferred mechanism beyond 1.6 mol %. The average grain size exhibits a drastic reduction from 16 μm to 0.7 μm as the Ho content increases from 0 to 1.6 mol%, followed by a slight increase at higher Ho concentration. It suggests that addition of Ho3+ inhibits grain growth in the ceramics. In the composition range studied, increasing Ho3+ content produces a gradual decrease in the relative density from 93% to 81%, room temperature dielectric constant (εrt) from 3997 to 807, electromechanical coupling factor (kp) from 0.23 to 0.06, and piezoelectric charge constant (d33) from 102 to 38 pC/N. This degradation in the properties is attributed to the crystalline and microstructural changes driven by the increasing presence of Ho content in the ceramics.

    更新日期:2019-02-15
  • Superb pseudocapacitance observed from eco-friendly multi-dimensional quaternary composite electrode based on Ce and Cu oxides and sulfides
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-15
    Seong Ku Kim, Supakorn Pukird, Pitchanunt Chaiyo, Pakin Inchidjui, Garam Bae, Ha-Kyun Jung, Sun Sook Lee, Ki-Seok An

    A multi-dimensional environmentally friendly quaternary composite electrode for pseudocapacitors is synthesized through a simple one-step hydrothermal method. The quaternary composite electrode consists of cerium oxide, cerium sulfides (Ce2S3 and CeS2), and cuprous oxide, all of which are based on non-toxic transition metal elements with good natural abundances. Investigation of the microstructures has revealed the formation of nanostructures of cerium oxide and cerium sulfides with high specific capacitances on relatively conductive cuprous oxide. Due to synergistic interaction between these oxides and sulfides, the quaternary electrode exhibits exceptionally high specific capacitances ranging up to 650 F g−1. In addition, great cyclic stability is observed during 1000 cycles of repeated charging and discharging at a constant current of 10 A g−1.

    更新日期:2019-02-15
  • Influence of CAD-CAM milling on the flexural strength of Y-TZP dental ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Claudinei dos Santos, Bruno Galvão Simba, Ronaldo Reis Silva, Manuel Fellipe Rodrigues Pais Alves, Roberto Oliveira Magnago, Carlos Nelson Elias

    In this work, the influence of milling strategy and cutter wear on the flexural strength of sintered Y-TZP ceramics machined in a CAD-CAM system, was investigated. Pre-sintered Y-TZP blocks were machined with tungsten carbide (WC) milling cutters and divided into three groups: a) samples machined with New Cutting Tools (NCT); b) samples machined with End-of-life cutting tools (ELCT); and c) samples machined and subsequently polished. The samples were machined parallel and perpendicularly to the diameter of pre-sintered Y-TZP blocks aiming to evaluate the effect of the machining orientation on roughness. After cutting, the specimens were sintered at 1530 °C for 2 h and characterized. After sintering, dense Y-TZP samples presenting grain size average of 0.81 ± 0.23 μm, hardness of 1205 ± 12 HV, KIC of 7.7 ± 0.4 MPam1/2 and flexural strength of 1207 ± 199 MPa were obtained. Furthermore, the control roughness (polished surfaces) presented Ra = 0.058 ± 0.011 μm. The surface roughness of the samples was influenced by the machining methodology using NCT mills, with Ra = 0.386 ± 0.149 μm and Ra = 0.292 ± 0.105 μm for samples machined parallel and perpendicularly to the pre-sintered Y-TZP blocks, respectively. The use of ELCT led to a roughness increasing (Ra = 0.582 ± 0.183 μm for samples milled perpendicularly, and Ra = 0.919 ± 0.164 μm for samples cut parallel to the pre-sintered blocks. The flexural strength of the sintered Y-TZP decreases with use of ELCT as consequence of surface roughness increasing, resulting from wear of WC mills, which presented chippings with sizes ranging from 30 to 340 μm in the cutting edge.

    更新日期:2019-02-14
  • Effect of reactivity of silicon and magnesium on the preparation of SiCMgAl2O4 composites for immobilizing graphite
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Yuancheng Teng, Qing Wang, Lang Wu, Xiaofeng Zhao, Yuan Chen, Xue Cao, Wen Wang

    SiCMgAl2O4 ceramic has a novel application for immobilizing radioactive graphite. The interface reaction between silicon and magnesium offers a significant challenge in the synthesis of SiCMgAl2O4 composites. In this paper, the effects of silicon source, magnesium source, sintering temperature and holding time on the interface reactivity were investigated by characterizing the phase compositions, microstructures, and hardness. The results show that the reactivity of silicon and magnesium varies with silicon sources and magnesium sources which also have a great effect on the microstructure of SiCMgAl2O4 composites. Either excessive sintering temperature or excessive holding time makes SiCMgAl2O4 composites decomposed into different phases, leading to a decreased hardness value. It is found that silicon as silicon source can contribute to the formation of SiC nanowires, which is in line with VS growth mechanism of SiC. The interface reactivity of element Si and Mg, which is positively correlated with high temperature and long holding time, has a negative effect on the phase compositions and performance of SiCMgAl2O4 ceramic by pressureless sintering.

    更新日期:2019-02-14
  • Dielectric relaxations in fine-grained SrTiO3 ceramics with Cu and Nb co-doping
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Junwei Liu, Qiaoli Liu, Zepeng Nie, Sheng Nie, Dayong Lu, Pinwen Zhu

    SrTi1−3x(CuxNb2x)O3 (x = 0.05, 0.1, 0.15 and 0.2) ceramics were synthesized using a solid-state reaction method at 1400 °C in air. Their structures, valence states, conduction mechanisms and dielectric properties were investigated in detail. Fine grains and vibration modes of the samples related to the doping effects were observed. A distorted pseudo-cubic structure was confirmed by XRD and Raman spectroscopy. All ceramics exhibited a colossal dielectric constant and dielectric relaxations. The dielectric constant in the low- and high-frequency ranges for x = 0.05 and 0.1 was ascribed to the contribution of the grain boundary and grain, respectively, and the electrode polarization was significant at x = 0.15 and 0.2. The dielectric relaxation peaks obeyed the T−1/4 law at low temperature for all samples, confirming the polaron relaxation process. The electric modulus analysis confirmed that low-temperature dielectric relaxation was related to the grain response, and the electric conduction exhibited the same behavior with the dielectric relaxation. The variable-range-hopping conduction indicated a highly distorted structure and the localization of carriers in SrTi1−3x(CuxNb2x)O3, which was consistent with the XRD and Raman results. The mixed-valence structure of Cu was identified by XPS, and the polaron hopping between the mixed-valence Cu ions was supposed to be responsible for the dielectric relaxation and electric conduction.

    更新日期:2019-02-14
  • Synthesis and characterisation of Co-doped ceria-based electrolyte material for low temperature solid oxide fuel cell
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Faizah Altaf, Rida Batool, Rohama Gill, Ghazanfar Abbas, Rizwan Raza, Zohaib-ur Rehman, Muhammad Ashfaq Ahmad

    Co-doped CeO2 (Ba0.10Ga0.10Ce0.80O3–δ) was synthesized via a cost-effective co-precipitation technique, and the electrochemical properties of the solid oxide fuel cell were studied. The microstructural and surface morphological properties were investigated by XRD and SEM, respectively. The structure of the prepared material was found to be cubic fluorite with an average crystallite size of 36 nm. The ionic conductivity of the prepared BGC (Ba0.10Ga0.10Ce0.80O3–δ) electrolyte material was measured as 0.071 S cm−1. The activation energy was found to be 0.46 eV using an Arrhenius plot. The maximum power density and current density achieved were 375 mW cm−2 and 893 mA cm−2, respectively, at 650 °C with hydrogen as a fuel. This study shows that the prepared co-doped electrolyte material could be used as a potential electrolyte to lower the operating temperature of solid oxide fuel cells.

    更新日期:2019-02-14
  • The effects of Cu2+ and La3+ doping on the sintering ability of sol-gel derived high silica bioglasses
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Basam A.E. Ben–Arfa, Isabel M. Miranda Salvado, José M.F. Ferreira, Robert C. Pullar
    更新日期:2019-02-14
  • Two-step sintering of Sm2O3 doped ceria stabilized zirconia
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Shiva Bejugama, Gadwal Narendra Kumar, Ajoy Kumar Pandey

    Effect of Sm2O3 addition and two-step sintering of Ceria Stabilized Zirconia (CSZ) on microstructure and mechanical properties were investigated in the present work. Samaria doped CSZ (SmCSZ) nanopowders were prepared by co-precipitation synthesis from their respective nitrate salts. Synthesized powders were calcined at 1000 °C for 2 h and then compacted to ϕ10 mm pellets using a uniaxial hydraulic press. Single step & two-step sintering methods were used to sinter the compacted pellets. Powders and sintered pellets were characterized for phase and microstructure using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) technique. Rietveld method was used for quantification of obtained phases. The hardness of the sintered samples was evaluated by Vicker's hardness tester, and toughness was estimated by indentation fracture toughness method. Samples sintered using two-step sintering method shown optimum hardness and toughness (up to 1288 HV10 and 5.37 MPa m1/2) values compared to conventionally sintered samples because of reduced grain size.

    更新日期:2019-02-14
  • Microstructure and shear strength of ZrB2SiC/Ti6Al4V joint by TiCuZrNi with Cu foam
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Gang Wang, Zhentao Wang, Wei Wang, Rujie He, Kaixuan Gui, Caiwang Tan, Wei Cao

    In this paper, brazing behaviors between ZrB2SiC and Ti6Al4V by Cu foam interlayer were studied. The microstructure, formation mechanism, mechanical property and fracture surface of the joints were systematically studied. The results showed that the phases in the joints were α+β-Ti, TiCu, Ti2Cu, Cu(s, s), TiC, TiB2 and Ti3SiC2. An optimum shear strength reached up to 435 MPa at a brazing temperature of 910 °C and holding time of 20 min. Such a shear strength was 90 MPa higher than the one without the Cu foam. The obtained high shear strength of joint was discussed from microstructure and residual stress. With the increase of brazing time, Cu(s,s) gradually disappeared and the content of Ti2Cu intermetallic compound increased, which was harmful for the joint. Furthermore, the residual stress of joint with Cu foam was calculated to be 324 MPa, lower than the one without Cu foam interlayer.

    更新日期:2019-02-14
  • Effects of modulation periods on mechanical properties of V/VN nano-multilayers
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Tao Fu, Zijian Zhang, Xianghe Peng, Shayuan Weng, Yuhan Miao, Yinbo Zhao, Shaoyun Fu, Ning Hu

    Metal/ceramic nano-multilayers, which possess the advantages of both metal and ceramics, have attracted intensive attention. In this work, the mechanical properties of V/VN nano-multilayers with different modulation periods (λs) were investigated using molecular dynamics simulations. The relationships between the microstructures and stress-strain (σ - ε) curves during in-plane tension and out-of-plane compression were explored, and the effects of λ were discussed. It shows that: (i) three kinds of V/VN nano-multilayers with different interfacial structures have different stabilities during deformation; (ii) dislocations nucleate firstly from the interfaces, propagate on {111} planes in VN layers, and deposit on the adjacent interface, and finally shift to V layers with the increase of applied strain; (iii) the nano-multilayer with larger λ has larger elastic modulus, elastic limit and lattice integrity, and strain hardening and cracks would appear in the nano-multilayers with λ > 42.90 Å.

    更新日期:2019-02-14
  • Enhanced thermal stability of piezoelectricity in lead-free (Ba,Ca)(Ti,Zr)O3 systems through tailoring phase transition behavior
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Mengye Yin, Chao Zhou, Shuai Ren, Yanshuang Hao, Minxia Fang, Wenjia Wang, Jinghui Gao, Tianyu Ma, Lixue Zhang, Sen Yang, Xiaobing Ren

    Good thermal stability in lead-free BaTiO3 ceramics is important for their applications above room temperature. In this study, thermal stable piezoelectricity in lead-free (Ba,Ca)(Ti,Zr)O3 ceramics was enhanced by tailoring their phase transition behaviors. Comparison between (1-x)Ba(Ti0.8Zr0.2)O3-x(Ba0.65Ca0.35)TiO3 and (1-y)Ba(Ti0.8Zr0.2)O3-y(Ba0.95Ca0.05)TiO3 revealed that latter system at y = 0.80 had much better thermal stable piezoelectric coefficient than the former at x = 0.45. Both systems crystalized in tetragonal to orthorhombic phase boundary at room temperature. The phase transition temperature and degree of diffusion were adjusted by Ca and Zr ions contents and demonstrated great influence on temperature dependent dielectric permittivity, hysteresis loops, and in-situ domain structures. The improved thermal stability of (1-y)Ba(Ti0.8Zr0.2)O3-y(Ba0.95Ca0.05)TiO3 prepared at y = 0.80 was linked to its higher paraelectric to ferroelectric phase transition temperature (Tm = 115.7 °C) and less degree of diffusion (degree of diffusion constant γ = 1.35). By comparison, (1-x)Ba(Ti0.8Zr0.2)O3-x(Ba0.65Ca0.35)TiO3 prepared at x = 0.45 revealed Tm = 81.3 °C and γ = 1.65. Overall, these findings look promising for future stimulation of phase transition behaviors and design of piezoelectric materials with good thermal stabilities.

    更新日期:2019-02-14
  • Optoelectronic multifunctionality of combustion-activated fluorine-doped tin oxide films with high optical transparency
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Bon-Ryul Koo, Ju-Won Bae, Hyo-Jin Ahn

    As transparent conducting oxides (TCOs) have been widely used as a common component of many optoelectronic applications, ensuring high conductivity and transparency TCOs has become a pivotal concern. In the present study, we report developing the combustion-activated pyrolysis route of horizontal ultrasonic spray pyrolysis deposition (HUSPD) as a novel strategy to form highly transparent conducting fluorine-doped tin oxide (FTO) films. Compared to the basic route, the combustion-activated FTO films showed an attractive transparent conducting performance (figure of merit of 5.34 × 10−2 Ω−1) with a highly improved optical transparency (90.1%) due to the formation of a smooth and dense film structure to reduce light scattering on the surface, and a decrease of oxygen vacancies to broaden the optical bandgap, all of which yielded an excellent performance as compared to the previously reported studies on the FTO films. Moreover, when the combustion-activated FTO films were used as TCOs of electrochromic devices and dye-sensitized solar cells, they acquired multifunctional effects of (a) an efficient electron transfer by (200) preferred orientations of the FTO; (b) a relaxed light scattering on the interface due to smooth and dense surface morphology of the FTO films; and (c) a broad optical bandgap by decreased oxygen vacancies, resulting in an impressive improvement of both electrochromic and photovoltaic performances. Taken together, our results demonstrate that combustion-activated FTO films are an attractive technique for forming high-performance TCOs that can further be used in multifunctional optoelectronic devices.

    更新日期:2019-02-14
  • Research on the machinability of A-plane sapphire under diamond wire sawing in different sawing directions
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-14
    Ningchang Wang, Feng Jiang, Xipeng Xu, Nian Duan, Qiuling Wen, Xizhao Lu

    Due to its superior mechanical, optical and chemical properties, sapphire (α-Al2O3) is widely used in engineering, optics, medicine, and other scientific research fields. The atomic structure of sapphire gives rise to anisotropy in its mechanical properties, which affects the machinability of sapphire materials on different crystal planes. Different cutting directions will affect the wafer economy and surface quality achieved during wire sawing due to this anisotropy. In this study, the machinability of A-plane sapphire was investigated for diamond wire sawing in three different directions, following the C-plane, R-plane and M-plane. The results show that the direction following the M-plane could be the best direction for diamond wire sawing because this direction results in the minimal sawing forces, the lowest specific energy and the smallest volume of material that will need to be removed during subsequent processing. These characteristics correspond to the direction with the highest fracture strength since the material is removed by brittle machining. The force ratio for sawing in the direction of the R-plane is the smallest because this direction is associated with the minimum hardness and the lowest critical load for the transition from plastic to brittle removal of the workpiece material. The 3D height parameters show no obvious pattern among the three sawing directions. The mechanism of material removal is mainly brittle removal, with some plastic removal, and is obviously affected by the crystal orientation.

    更新日期:2019-02-14
  • New high temperature amorphous protective coatings for Mg2Si thermoelectric material
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-13
    Pawel Nieroda, Krzysztof Mars, Jolanta Nieroda, Juliusz Leszczyński, Magdalena Król, Ewa Drożdż, Piotr Jeleń, Maciej Sitarz, Andrzej Koleżyński

    Magnesium silicide is one of the most promising, inexpensive, environment friendly and low density (1.99 g cm−3) thermoelectric material. These attributes distinguish it from other well-known thermoelectric materials and therefore it is currently intensively studied. Since thermoelectric materials are used in elevated temperatures, they are prone to oxygen corrosion which results in deterioration of their properties and therefore require anticorrosion protection. The aim of the work was to develop anticorrosive coating for magnesium silicide using silane-based, amorphous coatings. High purity Mg2Si samples were prepared by self-propagating high-temperature synthesis (SHS) and hot-pressing method supported by induction heater. The structural and phase compositions of the obtained samples were examined by means of X-ray diffraction (XRD) method and chemical composition analysis by scanning electron microscopy SEM, combined with EDS method. Fourier-transform infrared spectroscopy FT-IR, Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPOx) methods were used in order to determine chemical stability of prepared samples. In final step, magnesium silicide samples were covered with selected amorphous coatings by dip-coating method and then annealed in Ar gas atmospheres in various temperatures between 400-550 °C. The obtained coatings were characterized using SEM-EDS and reflectance spectroscopy method.

    更新日期:2019-02-14
  • Effect of self-developed graphene lubricant on tribological behaviour of silicon carbide/silicon nitride interface
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-13
    Zewei Yuan, Yan He, Kai Cheng, Zhenyun Duan, Lei Wang

    The research presented in this paper aims to investigate the effectiveness of different surface roughness and lubrication conditions on the interfacial tribological properties between silicon carbide (SiC) and silicon nitride (Si3N4) ceramics, particularly for providing insight into the mechanisms of how graphene reduces the friction and wear rate. The worn groove topography and surface composition were characterised in detail with 3D laser measuring microscopy and X-ray photoelectron spectroscopy. The tribological test results on the UMT-TriboLab show that a smooth initial surface is more likely to obtain a low friction coefficient and wear rate under water lubrication. The proper initial surface roughness for SiC and Si3N4 ceramics is approximately Ra 10 nm, and it will be lower in an alcohol or graphene aqueous solution. A large load does not worsen the tribological behaviour of a Si3N4 ball sliding against a SiC disk, and it reduces the friction coefficient and wear rate. Among the five lubrication states of dry friction, dry graphene lubrication, water lubrication, graphene solution lubrication, and self-developed graphene lubrication, the self-developed graphene lubricant can exhibit an ultra-low friction coefficient of 0.009 and ultra-low wear rate of 1.69 × 10−7 mm3/N·m. The excellent tribological property of the graphene-coated ceramic surface helps the prepared lubricant to decrease the friction coefficient effectively. Furthermore, the graphene film can protect the SiC from being oxidised by water under the tribo-activated action, and therefore, lead to ultra-low wear rate under low friction condition. Alcohol improves the tribological property of the self-developed graphene lubricant, mainly because of the good wettability between graphene and ethanol. The self-developed graphene lubricant can be applied in water-lubricated ceramic bearings and motorised precision spindles.

    更新日期:2019-02-14
  • Microstructure and mechanical properties of directionally solidified Al2O3/GdAlO3 eutectic ceramic prepared with horizontal high-frequency zone melting
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-13
    Shunheng Wang, Zongfu Chu, Juncheng Liu

    Directionally solidified eutectic oxide ceramics are very promising as a next-generation structural material for ultrahigh-temperature applications, above 1600 °C, owing to their outstanding properties of high corrosion resistance, oxidation resistance, high fracture strength and toughness, and high hardness. Herein, Al2O3/GdAlO3 eutectic ceramic was prepared with horizontal high-frequency induction zone melting (HIZM), and the effects of the processing parameters on the eutectic microstructure and mechanical properties were investigated. The results indicated that the directionally solidified Al2O3/GdAlO3 eutectic ceramic was composed only of the Al2O3 phase and GdAlO3 phase penetrating mutually, and the Al2O3 phase was the substrate in which the GdAlO3 phase was embedded. As the solidification rate increased from 1 to 6 mm/h, the eutectic microstructure underwent a transformation from an irregular pattern to a relatively regular “rod” or “lamellar” pattern, and the eutectic spacing constantly decreased, reaching a minimum value of 0.5 μm. The eutectic ceramic hardness and fracture toughness at room temperature increased continuously, reaching 23.36 GPa and 3.12 MPa m1/2, which were 2.3 times and 2.5 times those of the sintered ceramic with the same composition, respectively. Compared with the samples obtained from vertical high-frequency induction zone melting, the orientation of eutectic phases along the growth direction decreased significantly, and the size uniformity of the GdAlO3 phase became poorer in the samples prepared with HIZM at the same solidification rate; nevertheless, the hardness and fracture toughness of the samples increased by 11% and 63%, respectively.

    更新日期:2019-02-14
  • Synthesis, structural, electrical and magnetic properties of Bi2Fe4-xGaxO9 (0≤x≤1.6)
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-13
    M. Ashtar, G.S. Gong, Y.X. Gao, L.M. Xu, M.A. Marwat, Y.Q. Wang, S.L. Yuan, Z.M. Tian

    We investigate the electrical and magnetic properties of the Bi2Fe4-xGaxO9 (0 ≤ x ≤ 1.6) polycrystalline samples synthesized via solid-state reaction technique. Magnetic susceptibility measurements reveal that lightly doped samples (x < 0.8) undergo successive transitions, from high-temperature paramagnetic to antiferromagnetic phase followed by a low-temperature spin-glass state while the samples with heavy doping (x > 0.8) demonstrate paramagnetic to spin-glass (SG) transition. The variation of irreversible temperature obtained from zero field cooling (ZFC) and field cooling (FC) susceptibilities versus measured magnetic field and low-temperature magnetic hysteresis (M-H) loops support the existence of spin-glass phase. The dielectric constant (Ɛr) of Bi2Fe4-xGaxO9 with Ga-dilution reveals a weak-temperature sensitivity in high-temperature range (300 K ≤ T ≤ 550 K), which is advantageous for high temperature capacitor applications and electronic devices.

    更新日期:2019-02-14
  • Critical current density and mechanical performance of MgB2 superconductors prepared with different magnesium sources
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-13
    Serap Safran

    In this study, the critical current density and mechanical performance of MgB2 superconductors prepared using different magnesium sources (Mg and MgH2 with 99.9% and 96.5% purities, respectively) were analyzed. When the samples were characterized structurally and electrically, we found that the grain sizes were about 40 nm and transition temperature was around 30 K being lower than the literature. Critical current densities of all samples were calculated using Bean's model and our calculations yielded critical current density values higher than 106 A cm−2 in self-field. The highest critical transition temperature value belongs to M800 (Mg with 99.9% purity) sample and when the critical current density and transition temperature values of this sample are considered, this sample appears to have the potential for practical use. Vicker's microhardness measurements were performed and yield stress (Y), elastic modulus (E), brittleness (Bi), ductility (D) and fracture toughness (KIC) were calculated. All samples exhibited Indentation Size Effect (ISE) and microhardness measurements were compared with some microhardness models with were compatible with ISE behavior.

    更新日期:2019-02-14
  • Strontium doping into diopside tissue engineering scaffolds
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-12
    M.R. Shahrouzifar, E. Salahinejad

    In this work, an inorganic-salt coprecipitation route was used to synthesize nanostructured diopside (CaMgSi2O6) powders without/with 2 mol% strontium substituted for calcium. A sponge replication technique was then employed on the powders to manufacture highly porous scaffolds with pore interconnectivity. The structure, bioactivity, biodegradation and cell adhesion of the samples were studied by X-ray diffraction, Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy/energy-dispersive X-ray spectroscopy, Archimedes densitometry, and inductively coupled plasma spectroscopy analyses. According to the results, the Sr-doping process improves the sinterability and apatite-formation ability of the diopside-based scaffolds, but retards their biodegradation. Mesenchymal stem cells also present better adhesion and spreading with typical cell extensions on the Sr-doped scaffold in comparison to the pure one. It is eventually concluded that strontium can be further considered as a doping agent to improve the bioactivity and biocompatibility of Mg-Ca silicate scaffolds.

    更新日期:2019-02-13
  • Resistive switching behavior and mechanism in flexible TiO2@Cf memristor crossbars
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-12
    Simin Hu, Jianling Yuea, Chao Jiang, Xiuzhi Tang, Xiaozhong Huang, Zuojuan Du, Chunqi Wang

    Fiber-based memristors are expected to be one of the most ideal candidates to the future wearable nonvolatile devices. In this work, Carbon fibers coated with rutile TiO2 nanorods (TiO2 NRs) were prepared via hydrothermal method, which were denoted as TiO2@Cf. Flexible TiO2@Cf memristor crossbar was facilely assembled on a polyimide (PI) film. This device exhibited bi-directional threshold switching behavior and a maximum ON/OFF ratio of 105. In addition, the conductance of the memristors can be continuously adjusted by consecutive sweep cycles of bias voltages. The devices also exhibit excellent endurance over 1500 cycles with a negligible shift. The carriers transport and resistance switching of the TiO2@Cf memristor crossbar were explained by the Fowler-Nordheim tunneling model. The oxygen vacancies (OV) in TiO2 drifted to the interface of TiO2/Cf by an applied electric field, thereby reducing the depletion region and enhancing the current. This work provides a profound understanding of the resistive switching behavior and the related mechanism in flexible TiO2@Cf memristor crossbars, and paves a new way for potential applications for memristors in artificial synapses and flexible devices.

    更新日期:2019-02-13
  • Influence of processing parameters on the densification and the microstructure of pure zinc oxide ceramics prepared by spark plasma sintering
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-12
    P.M. Radingoana, S. Guillemet-Fritsch, P.A. Olubambi, G. Chevallier, C. Estournès

    Due to the sensitivity of nanopowders and the challenges in controlling the grain size and the density during the sintering of ceramics, a systematic study was proposed to evaluate the densification and the microstructure of ZnO ceramics using spark plasma sintering technique. Commercially available ZnO powder was dried and sintered at various parameters (temperature (400–900 °C), pressure (250–850 MPa), atmosphere (Air/Vacuum) etc.). High pressure sintering is desirable for maintaining the nanostructure, though it brings a difficulty in obtaining a fully dense ceramic. Whereas, increasing the temperature from 600 to 900 °C results in fully densified ceramics of about 99% which shows to have big impact on the grain size. However, a high relative density of 92% is obtained at a temperature as low as 400 °C under a pressure of 850 MPa. The application of pressure during the holding time seems to lower the grain size as compared to ceramics pressed during initial stage (room temperature).

    更新日期:2019-02-13
  • Structural, photoelectrical and photoluminescence properties of Ta-doped SnO2 monocrystal films grown on MgF2 (110) substrates
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-12
    Linan He, Caina Luan, Xianjin Feng, Hongdi Xiao, Xiaokun Yang, Di Wang, Jin Ma

    Epitaxial Ta-doped SnO2 films with Ta concentrations from 0 to 8 at.% have been deposited on MgF2 (110) substrates by the metal-organic chemical vapor deposition (MOCVD) method. The effects of Ta doping on the structural, photoelectrical and photoluminescence (PL) properties of the obtained films were studied in detail. The results showed that the single crystal rutile SnO2 films were obtained and the heteroepitaxial relationship was SnO2 (110) || MgF2 (110) with SnO2 [001] || MgF2 [001]. The highest Hall mobility of 74.2 cm2 V−1 s−1 was achieved for the 5 at.% Ta-doped SnO2 film and the minimum resistivity as low as 2.5 × 10−4 Ω cm was obtained at 6 at.% of Ta-doping. In the visible region, all the obtained films had average transmittances exceeding 87%. As the Ta concentration increased from 0 to 8 at.%, the optical band gap of the films rose from 3.89 to 4.32 eV. The room temperature PL spectra of Ta-doped SnO2 films showed intense green emission, weak violet and yellow emissions. The corresponding PL mechanisms were discussed.

    更新日期:2019-02-13
  • Effect of Gd doping on structural, optical properties, photoluminescence and electrical characteristics of CdS nanoparticles for optoelectronics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-12
    Aslam Khan, Mohd. Shkir, M.A. Manthrammel, V. Ganesh, I.S. Yahia, Mukhtar Ahmed, Ahmed Mohamed El-Toni, Ali Aldalbahi, Hamid Ghaithan, S. AlFaify

    Synthesis of pure and 0.1 to 5 wt.% Gd-doped CdS nanoparticles (NPs) was achieved through a modified domestic microwave-assisted route in a short timespan at 700 W power. The formation of hexagonal CdS NPs was verified via X-ray diffraction analysis, and no structural variation was observed except for lattice variation. The size of the crystallites (D), dislocation concentration, and lattice strain were calculated, and the D was in the range of 3–6 nm. Fourier transform-Raman analysis confirmed the presence of 1LO, 2LO, and 3LO modes at 294.76, 590, and 890 cm−1, respectively, in all the synthesized nanostructures, with minute variations in their positions due to doping; however, no new mode was observed. The position of the vibration modes was red shifted compared to that of the bulk material, indicating a confinement effect. Scanning electron microscopy (SEM) mapping/energy-dispersive X-ray spectroscopy revealed homogeneous doping of Gd and the presence of all the constituents in the final products. The morphology of the synthesized materials was tested via field-emission SEM, which revealed spherical NPs with small dimensions. Additionally, high-resolution transmission electron microscopy was performed to visualize the shape and size of the prepared 0.1% Gd:CdS NPs. The energy gap was calculated using the Kubelka–Munk theory and found to be in the range of 2.31–2.41 eV. The photoluminescence emission spectra exhibited two green emission peaks at 516 ± 2 nm and 555 ± 2 nm and showed the reduction of defects with Gd doping in terms of intensity quenching. The dielectric constant ( ε ' ), loss, and alternating-current electrical properties were studied in the high-frequency range. The values of ε ' were in the range of 17–27. An enhancement of these values was observed for CdS when it was doped with Gd. The electrical conductivity exhibited frequency power law behavior.

    更新日期:2019-02-13
  • Structural Rietveld refinement and magnetic features of prosademium (Pr) doped Cu nanocrystalline spinel ferrites
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-12
    Majid Niaz Akhtar, M. Babar, S. Qamar, Zia Ur Rehman, Muhammad Azhar Khan

    Pr doped spinel nanoferrites having following composition Cu Prx Fe2-xO4 (x = 0, 0.25, 0.50, 0.75, 1.00) were synthesized using sol-gel route. Prosademium (Pr) which is a rare earth metal was doped to tailor the properties of the Cu spinel nanoferrites. Characterization tools such as FTIR, XRD, FESEM and VSM were employed to investigate the phase, absorption bands, structure, microstructure and magnetic properties. FTIR was used to see the absorption bands and force constants of the Pr doped Cu spinel nanoferrites. Crystallite size, lattice parameters, cell volume and micro strains were determined from XRD data. Bulk density, X-ray density and porosity of the Pr doped Cu spinel nanoferrites were also calculated. Rietveld refinement was applied to investigate the detailed structural parameters of the Pr doped Cu spinel nanoferrites. Unit cell software based on regression diagnostics was also used to determine the structural factors of the prepared nanoferrites. It was noticed that Cu nanoferrite showed the single-phase cubic structure whereas the Pr doped Cu ferrite depicted the orthorhombic structure respectively. FESEM show large amount of agglomerations at x = 0.00 whereas irregular shape of the particles confirms the nanosized of ferrites as well. Magnetic properties were determined from VSM which elaborated the remanence, coercivity, saturation magnetization, anisotropy constant (K), initial permeability, Bohr magneton and YK (Yafet and Kittel) angles. Magnetic saturation, coercivity, remanence and anisotropy constant were decreased with Pr concentration in Cu spinel ferrite. However, YK angles were increased with Pr doping in Cu spinel nanoferrites. Microwave frequency response was evaluated which confirm the use of these Pr doped Cu spinel nanoferrites in the range of 5.2 Ghz–9.5 GHz respectively. The properties of these Pr doped Cu spinel nanoferrites suggested their used for microwave devices, memory devices and recording media applications.

    更新日期:2019-02-13
  • Evaluation of hydrogen separation performance of Ni-BaCe0.85Fe0.15O3-δ cermet membranes
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Libin Zhuang, Jiaqi Li, Jian Xue, Zhouyang Jiang, Haihui Wang

    Adding metal phase as the electronic transport channels in mixed protonic and electronic conductors is an effective method to enhance the conductivity and hydrogen permeability. Ceramic-metal (cermet) Ni-BaCe0.85Fe0.15O3-δ (Ni-BCF8515) dual-phase membranes were successfully fabricated in this article, where BaCe0.85Fe0.15O3-δ (BCF8515) served as the protonic conductor and Ni acted as the electronic conductor. The hydrogen permeability of Ni-BCF8515 dual-phase membrane was improved apparently, reaching 0.325 mL min−1 cm−2 at 1000 °C, which is four times higher than that of the single phase BCF8515 membrane. Hydrogen permeability of Ni-BCF8515 dual-phase membrane under different hydration conditions was studied here. Moreover, Ni-BCF8515 dual-phase membrane showed stable hydrogen permeability under the reducing atmosphere for 50 h.

    更新日期:2019-02-13
  • Preparation of lightweight hollow glass microsphere ceramics by gel casting
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Junjie Ding, Feng Ye, Qiang Liu, Chunping Yang, Ye Gao

    Owing to low density, hollow glass microspheres (HGMs) float on common media such as water, ethanol, and tertiary butanol. As a result, HGMs are not suitable to prepare slurries and ceramics by gel, slip, and freeze castings. In this paper, polyacrylamide (PAM) was used as dispersant and thickener agent to prepare homogeneous HGM aqueous slurries with controlled solid loadings and subsequent lightweight HGM porous ceramics were prepared by gel casting. Effects of PAM content on the stability of aqueous slurries as well as effects of solid (i.e., HGM) loading on density, porosity, pore size distribution, and compressive strength of porous ceramics were investigated. Increasing the viscosity of the slurry resulted in HGMs with significantly lower floating rates and more stable HGM aqueous slurries. HGM porous ceramics with densities and compressive strengths of 0.127–0.219 g/cm3 and 0.74–1.71 MPa, respectively, were prepared by gel casting.

    更新日期:2019-02-13
  • Development of bone scaffold using Puntius conchonius fish scale derived hydroxyapatite: Physico-mechanical and bioactivity evaluations
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Payel Deb, Emon Barua, Ashish B. Deoghare, Sumit Das Lala

    Naturally derived Hydroxyapatite (HAp) from fish scale is finding wide applications in the development of bone scaffold to promote bone regeneration. But porous HAp scaffold is fragile in nature making it unsuitable for bone repair or replacement applications. Thus, it is essential to improve the mechanical property of HAp scaffolds while retaining the interconnected porous structure for tissue ingrowth in vivo. In this study solvent casting particulate leaching technique is used to develop novel Puntius conchonius fish scale derived HAp bone scaffold by varying the wt.% of the HAp from 60-80% in PMMA matrix. Physico-chemical, mechanical, structural and bioactive properties of the developed scaffolds are investigated. The obtained results indicate that HAp-PMMA scaffold at 70 wt. % HAp loading shows optimal properties with 7.26 ± 0.45 MPa compressive strength, 75 ± 0.8% porosity, 8.0 ± 0.68% degradation and 190 ± 11% water absorption. The obtained results of the scaffold can meet the physiological demands to guide bone regeneration. Moreover, in vitro bioactivity analysis also confirms the formation of bone like apatite in the scaffold surface after 28 days of SBF immersion. Thus, the developed scaffold has the potential to be effectively used in bone tissue engineering applications.

    更新日期:2019-02-13
  • Structural, infrared reflectivity spectra and microwave dielectric properties of the Li7Ti3O9F ceramic
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Zhiwei Zhang, Liang Fang, Huaicheng Xiang, Minyu Xu, Ying Tang, Heli Jantunen, Chunchun Li

    A cubic rock salt structured ceramic, Li7Ti3O9F, was fabricated via the conventional solid-state reaction route. The synthesis conditions, sintering characteristics, and microwave dielectric properties of Li7Ti3O9F ceramics were investigated by X-ray diffraction (XRD), thermal dilatometer, Scanning Electron Microscopy (SEM) accompanied with EDS mapping, and microwave resonant measurements. Rietveld refinement, selected area electron diffraction (SAED) pattern and high-resolution transmission electron microscopy (HRTEM) confirmed that Li7Ti3O9F adopts a cubic rock-salt structure. The ceramic sintered at 950 °C presented the optimal microwave properties of εr = 22.5, Q×f = 88,200 GHz, and τf = -24.2 ppm/oC. Moreover, good chemical compatibility with Ag was verified through cofiring at 950 °C for 2 h. These results confirm a large potential for Li7Ti3O9F ceramic to be utilized as substrates in the low temperature cofired ceramic (LTCC) technology. This work provides the possibility to exploit low-temperature-firing ceramics through solid solution between oxides and fluorides.

    更新日期:2019-02-13
  • Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Dengwei Hu, Fan Zhao, Lei Miao, Zhen Zhang, Yan Wang, Hualei Cheng, Yinfeng Han, Meijuan Tian, Hongxi Gu, Rong Ma
    更新日期:2019-02-13
  • Intermediate temperature electrochemical properties of lutetium-doped SrCeO3/SrZrO3-molten carbonate composite electrolyte
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Deqian Huang, Yan Han, Fufang Wu, Hongtao Wang

    A SrCe0.6Zr0.3Lu0.1O3-α electrolyte was synthesized via a citric-nitrate auto-combustion (CNA) method using Sr(NO3)2, Zr(NO3)4·5H2O, (NH4)2Ce(NO3)6, Lu2O3, HNO3 and citric acid as raw materials. Subsequently, it reacted with the molten carbonate salt to obtain the SrCe0.6Zr0.3Lu0.1O3-α-Li2CO3-Na2CO3 composite electrolyte. The morphology, structure, conductivity and fuel cell performance of the obtained samples were investigated. SrCe0.6Zr0.3Lu0.1O3-α is fully dense after calcinated at 1540 °C for 5 h SrCe0.6Zr0.3Lu0.1O3-α and Li2CO3-Na2CO3 combined with each other to form a homogeneous interconnected structure. The highest power density and conductivity of SrCe0.6Zr0.3Lu0.1O3-α-Li2CO3-Na2CO3 are 255 mW cm−2 and 8.6 × 10−2 S cm−1 at 600 °C, respectively.

    更新日期:2019-02-13
  • Fluoride-free synthesis and microstructure evolution of novel two-dimensional Ti3C2(OH)2 nanoribbons as high-performance anode materials for lithium-ion batteries
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Biao Zhang, Jianfeng Zhu, Pei Shi, Wenling Wu, Fen Wang

    Herein, we develop a fluoride-free hydrothermal etching approach using the small amounts of water-assisted potassium hydroxide as ingenious etching agents to produce novel two-dimensional Ti3C2(OH)2-MXene nanoribbons (Ti3C2(OH)2 NRs). The as-produced Ti3C2(OH)2 NRs possess less Al atoms, more abundant hydroxyl functional groups on their surface, and more open structure features compared with their pristine counterparts and the other etching products. Simultaneously, the resulting Ti3C2(OH)2 NRs show significantly enhanced Li ions storage capabilities with outstanding specific capacity of 143.4 mA h g−1 obtained at 100 mA g−1 after 250 cycles, excellent cycling stability, and good rate property, being significantly superior than the parent Ti3AlC2 phases and the sugarcane-like transitional etching products. The superior electrochemical properties of Ti3C2(OH)2 NRs could be ascribed to the unique nanoribbon architectures with rich hydroxyl terminal groups and few Al atoms, which facilitates the adsorption and storage of a growing number Li ions on the surface active sites of Ti3C2(OH)2 NRs and the transport of electrons and ions effectively. What's more, this study provides a simple, effective, green, and nontoxic fluoride-free etching procedure to synthesize other more MXenes nanoribbons including but not limited to Ti3C2(OH)2 NRs as promising anode candidates for advanced lithium-ion batteries.

    更新日期:2019-02-13
  • Solvent-deficient synthesis of cerium oxide: Characterization and kinetics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Saša Zeljković, Dijana Jelić, Hiraku Maruyama, Juan C. Nino

    The reaction mechanism and kinetics of CeO2 synthesis using a solvent-deficient method are investigated by simultaneous thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The decomposition process of the cerium(III) nitrate hexahydrate and ammonium bicarbonate precursor mixture with four observed stages is monitored using TGA/DSC measurements in a nonisothermal regime with heating rates of 5, 10, 15 and 20 °C min−1. The proposed mechanism indicates a complex synthesis with several parallel reactions, some of which occur at room temperature. A detailed kinetic analysis is performed using isoconversional (expanded Friedman, modified Coats-Redfern and Kissinger) and model fitting (Nth order and nucleation and growth models) methods. The first three stages are best described by the Nth order model with activation energy values of 21, 53 and 90 kJ mol−1. The last stage, during which ammonium nitrate decomposition occurs, is best fit by the nucleation and growth model and has an activation energy of 129 kJ mol−1. The proposed mechanism, supported by the kinetic analysis in our study, indicates that CeO2 has already formed before the reaction reaches 200 °C. The average crystallite size of CeO2 synthesized at 300 °C, which was calculated from the XRD measurements and observed in the SEM and TEM data, is between 10 and 20 nm.

    更新日期:2019-02-13
  • Magnetoelectric coupling in multiferroic BiFeO3 by co-doping with strontium and nickel
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    F. Pedro-García, L.G. Betancourt-Cantera, A.M. Bolarín-Miró, C.A. Cortés-Escobedo, A. Barba-Pingarrón, F. Sánchez-De Jesús

    We report the effects of the Sr2+ and Ni2+ co-doping of BiFeO3 on the crystal structure and multiferroic properties of Bi1−xSrxFe1-yNiyO3 (x = 0.05, 0.0 ≤ y ≤ 0.10, and Δy = 0.05) that is synthesized using assisted high-energy ball milling. The mixtures of Bi2O3, Fe2O3, SrO and NiO were milled for 5 h, pressed at 900 MPa, and sintered at 800 °C in order to obtain cylindrical test pieces. X-ray diffraction and Rietveld refinement elucidated the effects of Sr2+ and Ni2+ on the crystal structure. Co-doping with SrNi in suitable proportions stabilizes rhombohedral BiFeO3. High contents of Ni2+ promote the precipitation of secondary phases in the forms of NiFe2O4 and Bi25FeO40. The magnetic behavior was examined by means of vibrating sample magnetometry. The results showed a change in the magnetic order from antiferromagnetic for the undoped sample to the ferromagnetic order for the co-doped samples. This change is attributed to the modulations in the magnetic moment due to crystal structure distortions. All samples show high relative permittivity values, which were enhanced by doping with Sr2+. Ni2+ cations increase the dielectric dissipation factor; this enhancement is related to their interactions with cations of a different oxidation state, such as Fe3+, Fe2+, Ni2+, Bi3+ and Sr2+ in the crystal structure of BiFeO3. The magnetoelectric coupling that was evaluated using magnetodielectric measurements was above 4% at 1 kHz for the higher applied magnetic field of 18 kOe.

    更新日期:2019-02-13
  • Focus on the ferroelectric polarization behavior of four-layered Aurivillius multiferroic thin film
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Dongpo Song, Jie Yang, Ying Wang

    The well-saturated ferroelectric hysteresis loops with double remnant polarization up to 50 μC/cm2 were obtained in four layered Aurivillius-type multiferroic Bi5FeTi3O15 thin film. Pulsed positive-up negative-down polarization measurements demonstrate the intrinsic ferroelectric polarization, which present optimal rectangularity and polarization value. The hysteresis loops measurements with larger frequency range of 0.2–100 kHz indicate stable and ultra-fast switching speed of ferroelectric domains. Persistent retention properties were observed, and they are also independent of the applied electric field. In fatigue test an increased dielectric constant is observed along with the suppression of switchable polarization. Both of them can be restored partly to their original values via the stimulating of high electric field. The block domain switching due to the oxygen vacancies aggregated on domain walls are discussed for those characteristics. It is providing important contributions of domain wall pinning in the polarization degradation of Aurivillius-type ferroelectric films with four layers.

    更新日期:2019-02-13
  • Flexural modulus of SiC/SiC composites sintered by microwave and conventional heating
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Huiyong Yang, Mingyuan Li, Xingui Zhou, Honglei Wang, Jinshan Yu

    To deeply study the variation mechanisms of mechanical properties, flexural modulus of SiC fibers reinforced SiC matrix (SiC/SiC) composites prepared by conventional and microwave heating at 800 °C–1100 °C was discussed in detail. The elastic modulus of fibers and matrix, interface bonding strength and porosity of SiC/SiC composites were considered together to analyze the changing tendencies and differences in their flexural modulus. The elastic modulus of fiber and matrix was determined by nanoindentation technique and interface characteristics applying fiber push-out test. The porosity and microstructure examinations were characterized by mercury intrusion method, X-ray Diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, two conflicts between the changing trends of elastic modulus and chemical compositions of composite components were focused and explained. Results indicate that three factors played different roles in the flexural modulus of SiC/SiC composites and residual tensile stress in composite components led to the conflicts between their elastic modulus and chemical compositions.

    更新日期:2019-02-13
  • Mono and co-substitution of Sr2+ and Ca2+ on the structural, electrical and optical properties of barium titanate ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Tasmia Zaman, Md Khairul Islam, Md Abdur Rahman, Arman Hussain, Md Abdul Matin, Md Shamimur Rahman

    In this work, Ba0.9Sr0.1TiO3, Ba0.7Sr0.3TiO3, Ba0.5Sr0.5TiO3, Ba0.5Ca0.25Sr0.25TiO3 and Ba0.5Ca0.5TiO3 have been synthesized to evaluate the influence of mono and co-substitution of A-site dopants (Sr2+ and Ca2+) on the structural, electrical and optical properties of BaTiO3 ceramics. Sr2+ added samples showed a tetragonal structure which became slightly distorted with increasing Sr2+ concentration and finally achieved a cubic structure for x = 0.50. Ba0.5Ca0.5TiO3 also retained their tetragonality with limited solubility. Presence of second phase, CaTiO3 demonstrated the fact of restricted solubility. The concurrent effect of Sr2+ and Ca2+ didn't alter the tetragonal structure. Sr2+ substitution enhanced the apparent density as well as grain size which stimulated the domain wall motion and improved dielectric properties. However, the ferroelectric nature of Ba1-xSrxTiO3 was poor due to the redistribution of point defect at grain boundary. The optical band gap was found to be reduced from 3.48 eV to 3.28 eV with increasing Sr2+ content. Co-substitution of cations improved the electrical property significantly. The highest value of dielectric constant was found to be ∼547 for Ba0.5Ca0.25Sr0.25TiO3 ceramics. Both Ba0.5Ca0.25Sr0.25TiO3 and Ba0.5Ca0.5TiO3 had developed P-E loop having lower coercive field and moderate optical band gap energy. Co-doping with Sr2+ and Ca2+ was a good approach enhancing materials electrical as well as optical property.

    更新日期:2019-02-13
  • Correlation between crystal structure and modified microwave dielectric characteristics of Cu2+ substituted Li3Mg2NbO6 ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Gang Wang, Dainan Zhang, Fang Xu, Xin Huang, Yan Yang, Gongwen Gan, Yuanming Lai, Yiheng Rao, Cheng Liu, Jie Li, Lichuan Jin, Huaiwu Zhang

    Structural characteristics exert significant influences on microwave dielectric properties, and ion substitution is widely adopted to modify material performances by adjusting the crystal structure. In this work, low loss Li3Mg2-xCuxNbO6 (x = 0–0.04) ceramics were prepared by Cu2+ substitution. The impacts of Cu2+ substitution for Mg2+ sites on the microwave dielectric characteristics and crystal structure were discussed in detail. Rietveld refinement results implied that a single Li3Mg2NbO6 phase was formed. Additionally, a dense and homogeneous microstructure with grain sizes of 7–9 μm could be achieved, and moderate Cu2+ substitution could significantly promote the grain growth. The correlation between microwave dielectric characteristics and crystal structure was discussed by calculating some structural parameters. The εr was determined by the polarizability. The Q × f was influenced by the packing fraction. The τf value was dependent on the NbO6 octahedron distortion, and the τf value could be adjusted to near zero for x = 0.02. Typically, the Li3Mg2-xCuxNbO6 (x = 0.02) composition exhibited remarkable microwave dielectric performances: εr = 15.75, Q × f = 92,134 GHz (9.86 GHz) and τf = −2 ppm/°C, making it a promising candidate for temperature-stable millimeter-wave applications.

    更新日期:2019-02-13
  • AC susceptibility and hyperfine interactions of Mg-Ca ions co-substituted BaFe12O19 nanohexaferrites
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    M.A. Almessiere, Y. Slimani, H. Güngüneş, S. Ali, A. Baykal, I. Ercan

    Magnesium and calcium co-substituted Ba M-type nanohexaferrite (NHFs) is fabricated via sol-gel auto-combustion technique. The phase formation was proved by XRD powder pattern, FESEM and HR-TEM. Magnetic properties of Ba1-2xCaxMgxFe12O19 (x ≤ 0.1) NHFs investigated by Mossbauer Spectroscopy. The variations in line width, quadrupole splitting, isomer shift, the cation distribution of Ca2+ and Mg2+ ions and hyperfine magnetic field values were estimated. The AC magnetic susceptibility and ZFC-FC measurements were also performed for the Ba1-2xCaxMgxFe12O19 (x = 0.02 and 0.08) NHFs. The MFC-MZFC results do not show blocking temperature peak, indicating the ferrimagnetic (FM) behavior of prepared products. Different models including Neel-Arhenius (N-A), Vogel-Fulcher (V-F) and critical slowing down (CSD) were tested to evaluate the AC-magnetic susceptibility behaviors. It is demonstrated that the magnetic interactions are important for x = 0.02 NHFs.

    更新日期:2019-02-13
  • Influence of interface structure on microstructure and dielectric properties of bismuth magnesium niobate thin films
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Helei Dong, Wenfang Kang, Qiulin Tan, Lihui Zhao, Jun Tang, Junping Duan, Feng Shi, Jijun Xiong

    Bismuth magnesium niobate (Bi3/2MgNb3/2O7, BMN) thin films were prepared on bare SiO2/HR-Si and Pt/TiO2/SiO2/HR-Si substrates by using sol-gel spin coating technique followed by rapid thermal annealing process. The influence of the interface on crystalline structure and tunable dielectric properties of the two types of BMN films were investigated. It was found that the BMN films prepared on SiO2/Si substrate with a BMN/SiO2 interface structure had higher orientation and better crystallinity. The deposited BMN thin films with a BMN/SiO2 interface structure exhibited superior tunability of 52.5%, while it showed a relative small tunability value of the film with BMN/Pt interface structure. It suggests that the interface state between the films and substrates, electric field distribution, and orientation degree are responsible for the impacts on the microstructure and tunable dielectric properties of the BMN thin films.

    更新日期:2019-02-11
  • Improved ferroelectric properties in KBiFe2O5-Polymer composite film
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    M.A. Jalaja, Soma Dutta

    Composite films of KBiFe2O5 and PVA were prepared with varied weight percentage of PVA by spin coating method on platinised silicon wafer. The composite films were characterised for dielectric and ferroelectric properties in comparison to pure KBiFe2O5thick film. The frequency dependent permittivity measurement indicated a higher contribution of space charge/interfacial polarization in KBiFe2O5 thick film than that in the KBiFe2O5 -PVA composite films. The ferroelectric properties in composite films were enhanced due to the reduction in leakage current and they showed well saturated polarization hysteresis loops. The remanent polarization value in KBiFe2O5 -PVA composite film (Pr = 3.7 μC/cm2) was found to be 2.5 times higher than that of the pure KBiFe2O5 film (Pr = 1.45 μC/cm2) and with the increase in PVA percentage, the remanent polarization values also increased. The space charge dominated conduction in pure KBiFe2O5 became transformed to field assisted ionic conduction in the KBiFe2O5 composite films. The polymeric matrix in KBiFe2O5 composites helped in reducing the leakage current of pure KBiFe2O5 by four orders of magnitude and further reduced with the increase in the PVA content in composite. The composite films showed fatigue free polarization even after 108 switching cycles whereas the polarization degradation in KBiFe2O5 film was 30% around 108switching cycles.

    更新日期:2019-02-11
  • A spin-valve-system in ferromagnetic semiconductor Sr2FeMoO6/SrMoO4
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-11
    Dexin Yang, Peng Zhao, Chen Yang, Tao Yang, Yulong Chen, Dexuan Huo

    In this study, we designed a novel magnetic semiconductor Sr2FeMoO6/SrMoO4 with a sharp metal-insulator transition based on the spin-glass freezing and antiferromagnetic transition behavior, which has been confirmed by various magnetic and transport measurements. To investigate the charge transport mechanisms of the sample, the electrical resistivities have been measured over a wide range of temperatures from 400 K down to liquid helium temperatures under different magnetic fields. The typical semiconductor behavior of the sample is observed. The relatively high conduction behavior is blocked below 80 K, and thereafter into the insulator state. The Vogel-Fulcher and the Mott variable-range-hopping (VRH) law are also used to study its conduction features and the relationship between magnetic and electrical properties. The spin-glass like component around the Sr2FeMoO6 crystal is initially observed by TEM and this provides a robust evidence able to verify the results from magnetic measurements. The novel features of the metal-insulator transition shielding external magnetic effects in highly disordered Sr2FeMoO6 double perovskite is dominantly controlled by a new spin-valve-system present in the spin-glass layers. Our insights into the role of the B-site disorder, spin-glass layer around the soft ferromagnetic grains, grain boundaries, and non-magnetic second phase effects demonstrate how the static and dynamic properties of magnetic materials might be tuned by designing the composition with a high B-site cation disordered matrix ferromagnetic material.

    更新日期:2019-02-11
  • Electronic structure and optical properties of La-doped KSr2Nb5O15: A first-principles investigation
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-10
    Qian Chen, Feng Gao, Jie Xu, Shuyao Cao, Yiting Guo, Guanghua Cheng

    The electronic structure and the anisotropic optical properties of lanthanum doped in KSr2Nb5O15 (KSN-La) were investigated by the first principles calculation dependent on the density functional theory, which was then supported by experiments. With La3+ doping in the KSN lattice, the band gap of KSN-La becomes smaller and the lattice structure transforms from tetragonal to orthorhombic due to the imbalance of charge of the KSN structure affected by the La3+ doping. The analysis of the anisotropic optical properties showed that the value of optical dielectric constant along [001] direction was larger compared to [010] and [100]. The calculated dielectric properties were in good accordance to the experimental results. KSN-La presented a larger dielectric constant, provided that La3+ was able to compensate the vacancies of the A sites of KSN, which were generated during the sintering process, leading to an effective enhancement of the dielectric constant.

    更新日期:2019-02-11
  • Dielectric and structural characterization and effective piezoelectric coefficient of KDP/p-Benzoquinone ceramic composites
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-10
    M.I. Pérez-Valverde, J.J. Gervacio-Arciniega, J.M. Siqueiros, M.E. Mendoza

    A study of the interaction between an inorganic phase, KH2PO4 (KDP) and an organic phase C6H4O2 (BZQ) in composites KDP/BZQ is presented here. Studies by X-ray powder diffraction and Raman spectroscopy confirm the interaction by a variation in the volume of the unit cell and new bands identified corresponding to the formation of new hydrogen bonds between KDP and BZQ in the Raman spectra. Relaxation process and conductivity were studied using an impedance analyzer in a wide frequency range (102–106 Hz) between room temperature and 90 °C allowing seeing the dielectric character of the composites and the proton conductivity behavior. Also the effective piezoelectric coefficient was determined by piezo response microscopy; it was observed a decrement of the KDP coefficient on increasing the concentration of BZQ, probably due to the interaction between them.

    更新日期:2019-02-11
  • Oral degradation of Y-TZP ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-10
    Márcio Antônio Paraizo Borges, Marcela Rodrigues Alves, Heraldo Elias Salomão dos Santos, Marcelino José dos Anjos, Carlos Nelson Elias

    The aim of this work was to study the degradation of yttria-stabilized tetragonal zirconia (Y-TZP) directly exposed to the oral environment. Four groups of Y-TZP were tested G1: TZ-PX-242A, Zpex®; G2: TZ-PX-357, Zpex Yellow®; G3: ProtMat®, and G4: LAVA Frame®. The samples were attached to the base of temporary full dentures of patients and aged for 100 days. In this way, one surface of the samples was exposed to the oral environment. The samples (25 × 2 × 1.5 mm) were cut from noncommercial (G1 and G2) and commercially available (G3 and G4) presintered zirconia blocks. Quantitative and qualitative analyses were performed by X-ray fluorescence (XRF). Microstructural characterization was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), 3D surface roughness measurements and grain size measurements. The mechanical properties were determined by a four-point bending test. The data were analyzed by one-way ANOVA (p ≤ 0.05), Tukey's test and Weibull analysis. The results showed a tetragonal-monolithic transformation in the zirconia after oral aging. The surface roughness increased in all groups, and groups G3 and G4 showed increases in their flexural strengths.

    更新日期:2019-02-11
  • Enhance the luminescence properties of Ca14Al10Zn6O35:Ti4+ phosphor via cation vacancies engineering of Ca2+ and Zn2+
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-10
    Xianbo Wu, Longhai Liu, Mao Xia, Shengxiong Huang, Yue Zhou, Wang Hu, Zhi Zhou, Nan Zhou

    Ti4+-activated zinc calcium aluminate phosphors, owing to their excellent luminescence properties, nontoxicity, environment friendliness and low price, have a certain prospect in the field of plant cultivation. In this study, we have successfully synthesized a series of Ca14-yAl10-xZn6-zO35:xTi4+ (CAZO:Ti4+) phosphors through a high-temperature solid-state method. Furthermore, the emission spectrum of CAZO:Ti4+ located in bluish violet-emitting band, and has an emission peak at 378 nm upon the excitation of 268 nm due to the charge transfer of Ti4+-O2-. Moreover, the luminescence intensity of as-synthetized phosphors can be improved by cation vacancies engineering to compensate for charge unbalance. Especially, the luminescence intensity could be further improved when the Ca2+ vacancy is 0.35 mol or the Zn2+ vacancy is 0.275 mol. Furthermore, the X-ray powder diffraction (XRD) analysis and crystal structure are checked and confirmed that the synthesized material is pure phase. The concentration quenching mechanism, FT-IR spectra, UV–vis absorption properties, lifetimes and electron transition process of Ca14-yAl10-xZn6-zO35: xTi4+ were discussed in detail. From the above, the phosphor has a potential application for plant growth field due to its broad bluish violet emission.

    更新日期:2019-02-11
  • Porous Si3N4 ceramics prepared by aqueous gelcasting using low–toxicity DMAA system: Regulatable microstructure and properties by monomer content
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-10
    Shuang Yin, Limei Pan, Xia Fang, Yufeng Li, Yanpu Li, Yongbao Feng, Tai Qiu, Jian Yang

    In this study, the low–toxicity monomer N, N–dimethylacrylamide (DMAA), serving as both gelling agent and pore–forming agent, was adopted to fabricate porous Si3N4 ceramics with a regulatable microstructure and property by aqueous gelcasting. Results indicate that monomer content played an important role in regulating and optimizing the properties of sintered bodies. With increasing monomer content (5.94–30.69 wt%), both slurry viscosity (maximum 0.14 Pa s at 95.40 s−1) and green body strength (11.35–49.23 MPa) exhibited monotonic increasing trends, demonstrating superior mechanical properties to those obtained using the neurovirulent acrylamide (AM) gelling system. The increased monomer content not only improved porosity, but also promoted α→β–Si3N4 transformation as well as β–Si3N4 grain growth through enhancing the connectivity of interlocking pores and accelerating the vapor phase transport during liquid–phase sintering. These variations in phase composition and microstructure derived from the varied monomer content further resulted in monotonic changes in porosity (40.32–51.50%), mean pore size (0.27–0.38 μm), flexural strength (202.77–132.15 MPa), fracture toughness (2.93–2.32 MPa m1/2), dielectric constant (3.48–2.78) and loss (3.52–3.09 × 10−3) at 10 GHz for sintered bodies, displaying an excellent comprehensive properties. This study suggests a promising prospect for DMAA in preparation of high–performance porous Si3N4 ceramics by aqueous gelcasting.

    更新日期:2019-02-11
  • Dry-pressed anodized titania nanotube/CH3NH3PbI3 single crystal heterojunctions: The beneficial role of N doping
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-10
    Jelena Vujančević, Pavao Andričević, Anđelika Bjelajac, Veljko Đokić, Maja Popović, Zlatko Rakočević, Endre Horváth, Márton Kollár, Bálint Náfrádi, Andreas Schiller, Kondrad Domanski, László Forró, Vera Pavlović, Đorđe Janaćković

    Highly ordered, anodically grown TiO2 nanotubes on titanium supports were annealed in ammonia atmosphere in order to incorporate nitrogen doping (˂ 2 at.%) in the titanium oxide lattice. FESEM micrographs revealed nanotubes with an average outer diameter of 101.5 ± 1.5 nm and an average wall thickness of about 13 nm. Anatase crystals were formed inside the tubes after annealing in ammonia atmosphere for 30 min. With further annealing, rutile peaks appeared due to the thermal oxidation of the foil and rise as the duration of heat treatment was increased. The concentration and chemical nature of nitrogen in the nanotube arrays can be correlated to the optical response of dry-pressed heterojunctions of doped TiO2/CH3NH3PbI3 single crystals. The N-TiO2/perovskite heterojunction with the highest amount of interstitial nitrogen exhibited an improved photocurrent, indicating the importance of the semiconductor doping-based heterojunction optimization strategies to deliver competitive levels of halide perovskite-based optoelectronic devices to be envisioned for urban infrastructures.

    更新日期:2019-02-11
  • Preparation of Cl doped SnO powder with excellent photocatalytic property by mechanical alloying
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-08
    Baoyan Liang, Lingjie Zhang, Wangxi Zhang

    Cl-doped SnO photocatalysts were synthesized by mechanical alloying (MA) from SnCl2 and NH4HCO3. The effects of MA time on the structural characterization and photocatalytic activity of SnO powders were studied. Cl-doped SnO nanoparticles can be obtained by MA treatment after 1 h, but MA time considerably affected the crystalline size, microstrain, and photocatalytic properties of the samples. The crystalline size and specific surface area of the SnO samples gradually decreased and their microstrain increased with prolonged MA time. The peak intensity of the photoluminescence spectra of the Cl-doped SnO samples remarkably increased with prolonged MA time. Moreover, the MA samples had good photocatalytic properties. The photodegradation rate of methyl orange dye in 30 min over Cl-doped SnO nanoparticles obtained by MA for 2, 4, and 8 h was approximately 99%. Aging treatment of the SnO samples remarkably affected their phase composition, which can enhance the transformation of SnO to SnO2. The SnO2 transformation degree significantly increased with prolonged MA time through aging treatment, which also slightly deteriorated the degradation efficiency of the samples.

    更新日期:2019-02-11
  • Cation-doped bioactive ceramics: In vitro bioactivity and effect against bacteria of the oral cavity
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-08
    Renato Luiz Siqueira, Patrícia Francieli Silva Alves, Thaís da Silva Moraes, Luciana Assirati Casemiro, Sidney Nicodemos da Silva, Oscar Peitl, Carlos Henrique Gomes Martins, Edgar Dutra Zanotto

    We synthesized, using a solid-state reaction, bioactive ceramics of the SiO2CaONa2OP2O5 system doped with up to 3 mol% of Ag, Mg, Sr, Zn, and Ga, elements that were used as therapeutic agents. On evaluating the in vitro bioactivity of our crystalline samples using the ICG-TC04 method (so far only tested for glassy materials), we observed that those ceramics containing up to 0.5 mol% dopant exhibited hydroxycarbonate apatite (HCA) layer formation on their surfaces in a 24-h in vitro assay — the same time observed for Bioglass®, the material considered to be “gold standard” in terms of bioactivity. The antibacterial activity of these ceramics was confirmed against 23 oral bacteria, related to caries and endodontic infections, by employing three different methods. For the agar dilution method, using a concentration range of 0.5–24 mg/mL, various bacteria were found to be susceptible to the materials — the lowest minimum inhibitory concentration (MIC) values were achieved for the doped samples, particularly those containing Ag. In the biofilm-forming capability assay, we did not observe any viable cells after 24 h incubation. Finally, the direct contact assay confirmed that all the samples showed a stronger antibacterial effect, promoting a significant reduction in the number of viable cells after only 10 min in contact with the microorganisms. This result indicates that the tested materials have an intrinsic antibacterial activity, and do not need to be doped, except for some specific bacteria or depending on how they will be used (extracts or in direct contact). Therefore, besides easy production and in vitro bioactivity, all tested materials demonstrated a considerable antibacterial effect against representative bacteria, stimulating future studies involving their application as topical endodontic disinfectants or in dental prophylaxis procedures.

    更新日期:2019-02-11
  • Nano-sized plate-like alumina synthesis via solution combustion
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-08
    Wenqiang Liu, Xuguang Liu, Pingping Zhang, Zhiyi Wang, Xia Li, Maocong Hu

    Nano-sized plate-like alumina is an important inorganic material in catalytic, ceramic and electronic applications due to its unique two-dimensional structure and properties, while its facile synthesis is still under investigation. In this work, nano-sized alumina plate was synthesized by solution combustion method with glycine and polyvinyl alcohol as composite fuels for the first time. The calcination temperature during solution combustion process was optimized as confirmed by XRD, FT-IR, TG-DSC, Raman, 27Al MAS NMR, SEM, TEM, and N2 physisorbtion. Obtained alumina displayed special nano-sized plate morphology and porous structure. It was further adopted as support for cobalt acetate and used as catalyst for selective oxidation of cyclohexane. This work develops a facile approach to synthesize two-dimensional plate-like alumina for catalytic application.

    更新日期:2019-02-11
  • Highly dispersible carbon composited Fe3O4 nanoparticles in an aqueous solvent via normal pressure liquid reaction
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-08
    Dong Ho Chae, Jin Soon Han, Jae Rok Shin, Ji Hyun Cha, Sung-Churl Choi, Yeon-Gil Jung, Gye Seok An

    In this study, a simple fabrication of carbon composited Fe3O4 nanoparticles was carried out under reflux condition using glucose as a carbon precursor. The carbon composited Fe3O4 nanoparticles having a core-shell structure were synthesized in a low-temperature and low-pressure atmosphere instead of in an autoclave. Simple carbonization without inert gas and extra heating was complemented by adding sulfuric acid, which has an important role as a carbonization catalyst. In addition, sulfuric acid also acted as the controller of such surface properties as surface area by an etching effect. The prepared nanoparticles have uniform and continuous carbon layers, which have several functions, such as stable dispersibility and an increase of electron conductivity. carbon composited Fe3O4 nanoparticles were investigated with zeta-potential, particle size distribution, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and a vibrating sample magnetometer. The results provide clear evidence that carbon-coated Fe3O4 nanoparticles are applicable in electrochemical industrial fields.

    更新日期:2019-02-11
  • An extensive investigation on gamma-ray and neutron attenuation parameters of cobalt oxide and nickel oxide substituted bioactive glasses
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-07
    H.O. Tekin, E. Kavaz, E.E. Altunsoy, O. Kilicoglu, O. Agar, T.T. Erguzel, M.I. Sayyed

    This study aimed to investigate the gamma-ray and neutron attenuation parameters of cobalt oxide and nickel oxide substituted ten bioactive glasses. The mass attenuation coefficient ( μ / ρ ) for the selected bioactive glasses was calculated using MCNPX code in photon energy range (0.02 MeV - 20 MeV) and the results were compared with the output of WinXcom software. Other vital gamma-ray attenuation parameters such as half value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Zeff), and effective electron density (Nel) for the selected bioactive glasses were also calculated for each approach. Gamma-ray and neutron transmission factors as well as neutron effective removal cross-sections of each bioactive glass (ΣR) were also taken into consideration to underline the distinctive parameters. Additionally, exposure buildup factor (EBF) values were found with G-P fitting approach depending on the energy and penetration depths. The results points that, the lowest HVL, TVL and MFP values and the highest neutron effective removal cross-sections (ΣR) values are the characteristics of NiO-4C and CoO-4. The results indicate that the density of the material affects the photon and neutron interaction parameters. While NiO-4C has the lowest TF values for both gamma and neutron radiation, the highest ΣR values are collected from NiO-4C glass material. The gamma and neutron transmission factors (TF) of the studied bioactive glasses support the aforementioned results. The lowest Zeff values were generated for 45S5C and 45S5 ordinary glasses, while CoO-4 and NiO-4C doped glasses are having the highest values of Zeff. EBF values of the glasses were also calculated in the energy range 0.015-15 MeV up to 40 mfp. The smallest EBF values were measured for CoO-4 and NiO-4C glasses. It can be concluded that NiO-4C bioactive glass outperformed compared to other studied samples and is a promising bioactive glass for gamma-ray and neutron attenuation.

    更新日期:2019-02-08
  • Metal-organic-framework-derived In2O3 microcolumnar structures embedded with Pt nanoparticles for NO2 detection near room temperature
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-07
    Yunshi Liu, Xiupeng Liu, Yubing Wang, Rui Wang, Tong Zhang

    A novel synthesis of In2O3 porous microcolumnar structures (MCs) by a self-sacrificial template route was carried out using MIL-68. Using a modified calcination strategy, the samples could maintain the original metal organic frame work (MOF) morphology with a high gas accessibility after a slow decomposition of organic ligands. Pt nanoparticles (NPs) were loaded on the samples before or after the MOF calcination, leading to different contact states of the Pt NPs and In2O3 matrix. The gas sensing properties of the samples were systematically investigated using a dynamic testing system. Particularly, sample Pt/In2O3 MCs-1 exhibited a superior NO2 sensing performance near room temperature (Rg/Ra = 44.9 at 1 part-per-million and 5.2 at 100 parts-per-billion (ppb)). The sensor resistance could recover to its baseline even at 40 °C after purging with air without any additional treatment. This can be attributed to the chemical sensitisation of the Pt NPs as well as large contents of pores and channels for gas diffusion. The introduction of humidity in the gas mixture could remarkably decrease the sensor response and recovery times owing to the ‘wet’ NO2 adsorption mechanism. This study demonstrated a novel synthesis route of Pt-loaded In2O3 porous columnar structures and its potential applications in near-room-temperature detection of ppb-level NO2.

    更新日期:2019-02-08
  • The effect of calcination atmosphere on structural properties of Y-doped SrTiO3 perovskite anode for SOFC prepared by solid-state reaction
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-07
    E. Rosa Silva, M. Curi, J.G. Furtado, H.C. Ferraz, A.R. Secchi

    Recently Y-doped SrTiO3 (YST) perovskite has been reported as a promising alternative for Ni/YSZ cermets as anode material for solid oxide fuel cells due to its mixed, ionic and electronic conduction. In this work SrTiO3 was synthesized by solid-state reaction method, calcined, and sinterized to obtain undoped (ST), 4% (YST04) and 8% (YST08) of Y-dopant and as a heterojunction with yttria-stabilized zirconia (YST08/YSZ). The effects of calcination atmosphere and dopant concentration on formation of the perovskite and grain size distribution of the material were investigated. It was observed that calcination under Ar/5%H2 atmosphere have increased the dopant maximum concentration in the SrTiO3 cubic crystal structure when compared to inert atmosphere. When the Y solubility limit was exceeded, a pyrochlore phase Y2Ti2O7 was formed at the intergranular region due to the deficiency of oxygen vacancies, especially in the presence of inert atmosphere. TGA and DTA curves present a peak of water desorption and two overlapping peaks of SrCO3 phase change and decomposition. Ceramic microstructure was studied by SEM-EDS and the results showed that Y incorporation inhibits the grain growth in sintering step; reaching a smallest amount value of grain size in YST08/YSZ heterojunction under Ar/5%H2 atmosphere.

    更新日期:2019-02-08
  • Exploring determinants of lattice structure and high energy storage properties of Fe-doped SBN ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-07
    Han Bai, Jun Li, You Wu, Yang Hong, Kouzhong Shi, Zhongxiang Zhou
    更新日期:2019-02-08
  • Molecular group system as one energy unit
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-07
    Han Gil Na, Myung Sik Choi, Jae Hoon Bang, Wansik Oum, Sun-Woo Choi, Gyu Sam Shim, Jae Hee Cho, Hyoun Woo Kim, Changhyun Jin

    In view of the various qualifications required of materials nowadays, efforts to change the characteristics of inherent materials have continued. However, most material conversion techniques that have been used in the past, such as alloy design and doping effect, cannot overcome the limitation that properties are only added to the original characteristics of pristine materials. Therefore, herein, we introduced a new material design technique, a so-called “Molecular Group System”, which is completely different from existing methods. Since whole-set-systems are considered one-energetic-unit-system, either only the merits of the constituent elements can be emphasized or new materials completely different from the raw ones can be synthesized. In this study, block-stacking bottom-up approach was employed to form a one group system from SnO2, SnOx, Sn, and graphene powders, and a binder, using high-energy irradiation. Then, we discussed theoretical verifications such as SnO2-reduction and Sn-channeling.

    更新日期:2019-02-07
  • Nanoindentation deformation and cracking in sapphire
    Ceram. Int. (IF 3.057) Pub Date : 2019-02-07
    V. Trabadelo, S. Pathak, F. Saeidi, M. Parlinska-Wojtan, K. Wasmer

    Single crystal sapphire is an anisotropic material and its mechanical behavior depends on the crystallographic orientation. In this work, a systematic study is performed to investigate the effect of crystallographic orientation on the deformation and cracking of sapphire by means of nanoindentation using spherical indenters. It aims also at determining the physical origin of the ''pop-in" appearing in the nanoindentation curves. For that purpose, nanoindentations were performed where the load was increased until the detection of the ''pop-in", followed by direct unloading. After SEM and TEM observation of the indents, it is concluded that the deformation mechanisms of sapphire depend on the tip radius and the applied indentation stress: exclusively twin formation for the smaller 1 and 2 μm tip radii indenters and twin formation together with crack propagation for larger 10 μm tip radius spherical indenter. It was also determined that the cracks propagate preferentially in the (1012−) ''R-plane". Therefore, this study is supplement to and enrichment of existing studies on deformation and cracking behavior of sapphire under spherical nanoindentation.

    更新日期:2019-02-07
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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