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  • Co-doping for significantly improved thermoelectric figure of merit in p-type Bi1-2xMgxPbxCuSeO oxyselenides ☆
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Yazhou Sun, Cencen Zhang, Chengming Cao, Jianxin Fu, Liangming Peng

    The microstructure, oxidation state and thermoelectric transport properties of Mg and Pb co-doped p-type Bi1-2xMgxPbxCuSeO oxyselenides have been investigated. Pure single BiCuSeO phase are obtained for all the samples without preferential growth in the crystallites. X-ray photoelectron spectroscopy (XPS) results indicate that both Mg and Pb dopants are in the 2+ oxidation state whereas other than the expected Bi3+, higher-oxidation-state Bi ions also exist in both the pristine and doped BiCuSeO compounds. The Mg and Pb co-doping yields a remarkable enhancement in the electrical conductivity coupled with a moderate Seebeck coefficient. A pronounced increment in power factor is achieved from 2.54 μWcm−1K−2 for the pristine BiCuSeO to 11.1 μWcm−1K−2 for Bi0.88Mg0.06Pb0.06CuSeO at 750 K. In addition to increasing the power factor, Mg and Pb co-doping reduces the lattice thermal conductivity owing to the dopant-induced point defect scattering of phonon. The combination of optimized power factor and intrinsically low lattice thermal conductivity results in a high ZT Z T of 1.19 at 750 K for Bi0.88Mg0.06Pb0.06CuSeO, which is about 3.1 times as large as that for the pristine BiCuSeO.

    更新日期:2017-09-20
  • The reduced reversible phase transition field of lead‒free Bi‒based ceramic composites by adding nonergodic relaxor
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Thi Hinh Dinh, Vu Diem Ngoc Tran, Thi Thao Nguyen, Quyen Thi Ngoc Hoang, Hyoung–Su Han, Jae–Shin Lee

    This study investigated the microstructure, dielectric, ferroelectric, and strain properties of lead‒free 0.995Bi1/2(Na0.82K0.18)1/2TiO3–0.005BaZrO3/0.98Bi1/2(Na0.78K0.22)1/2TiO3–0.02LaFeO3 (BNKT18BZ/BNKT22LF) ceramic composites. We found that the required electric field for trigging the phase transition from ergodic relaxor (ER) to ferroelectric of BNKT18BZ/BNKT22LF ceramic composites can be effectively decreased by adding BNKT18BZ as nonergodic relaxor (NER) with changes of three different stabilized regions and the highest Susable peak points as a function of the applied electric field. The highest d33⁎ value of 690 pm/V was obtained at 4 kV/mm for 0.3 weight BNKT18BZ fraction ceramic composites. This value was higher than 636 pm/V of BNKT22LF ceramics under an applied electric field of 5 kV/mm.

    更新日期:2017-09-20
  • Magnetic and ferroelectric properties of Aurivillius phase Bi7Fe3Ti3O21 and their doped films
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    D.P. Song, J. Yang, Y.X. Wang, X.B. Zhu

    Thin films of Bi7Fe3Ti3O21, Bi7Fe2CoTi3O21, and Bi6.15Sm0.85Fe2CoTi3O21 are prepared on Pt/Ti/SiO2/Si (100) substrates by using a chemical solution deposition route and the magnetic and ferroelectric properties are investigated. Thin film of Bi7Fe3Ti3O21 shows robust ferroelectric polarization loop compared with ceramics, signal crystal and thin films reported before. The room-temperature ferromagnetism is clearly observed in the films of Bi7Fe2CoTi3O21 and Bi6.15Sm0.85Fe2CoTi3O21, while the Bi7Fe3Ti3O21 film shows the paramagnetic behavior at room temperature. The Co-doped sample exhibits a high remnant magnetization Mr of 2.67 emu/cm3 and remnant polarization Pr of 19.2 μC/cm2. The ferromagnetism can be ascribed to the spin canting of Fe- and Co-based sublattices via the Dzyaloshinskii-Moriya interaction and the ferrimagnetic ordering of transition metals. The improvement of the Pr and Mr are discussed in terms of growth grain size, reduce grain boundary, and the variation of intergrain connectivity caused by Co- and Sm-doping.

    更新日期:2017-09-20
  • MD-based design of SiC/graphene nanocomposites towards better mechanical performance
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    M. Barfmal, A. Montazeri

    In this study, molecular dynamics (MD) simulation has been implemented to explore the main parameters affecting the reinforcing role of graphene in ceramic-based composites. Due to the importance of silicon carbide in industrial applications, this ceramic has been considered as the matrix material. Uniaxial tensile test is employed to analyze the mechanical behavior of this type of nanocomposites. Accordingly, the stress-strain curve can be achieved for each sample from which different mechanical properties including Young's modulus, ultimate tensile strength, failure strain, and fracture toughness can be achieved. This is followed by investigation of the reinforcing role of graphene at different temperatures. In the present work, single layer graphene sheet (SLGS) and its double layer counterpart has been utilized as the reinforcing agent at two different volume fractions (VFs) of 3 and 5%. Results show that increasing the VF of SLGS up to 5%, causes an enhancement in the Young modulus by 31.7%. Additionally, it is found that increasing the number of graphene layers has a detrimental effect on the mechanical behavior of mentioned nanocomposite samples. This is attributed to the interlayer sliding occurred between graphene layers due to the weak van der Waals interactions operating between them. Finally, the dominant mechanism of the fracture toughness of these nanocomposites is systematically studied through various case studies.

    更新日期:2017-09-20
  • Effect of ball sizes on synthesis of OsB2 powders by mechanical alloying
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Canhui Zou, Ying Long, Xin Zheng, Hua-Tay Lin, Fenglin Zhang

    In present study, OsB2 powders were synthesized by mechanical alloying (MA) using high energy ball milling technique. Milling balls with different sizes (6.5 mm, 9.5 mm, 11.5 mm, and mixture of 3 ball sizes) were used with other milling parameters unchanged. The effects of ball sizes on synthesis process of the OsB2 powders were studied. Phase identification, morphology and particle size of the mixed powders synthesized by balls with different sizes under different milling time were performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. Results show that the main phase of the as-synthesized powders are ReB2-type hexagonal OsB2 obtained for the four groups of milling balls with different sizes. But the synthesis efficiency of OsB2 powders increases with the decrease of ball sizes. With ball diameter of 6.35 mm (the smallest size), the main phase in the as-synthesized powder is ReB2-type hexagonal OsB2, whereas mixture of hexagonal and orthogonal OsB2 powders are obtained with other three groups of balls. The different in synthesis efficiency and phase composition of the powders could be attributed to the varied total energy generated during the collision process and the surface area of the balls with different ball sizes.

    更新日期:2017-09-20
  • Localization induced by pressure in pyrochlore Bi2Ir2O7
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Wei Liu, Hui Han, Langsheng Ling, Long Ma, Li Pi, Lei Zhang, Yuheng Zhang

    In this work, the resistivity and magnetization of Bi2Ir2O7 are investigated under hydrostatic pressure. At ambient pressure, the resistivity of Bi2Ir2O7 exhibits a metallic behavior with the decrease of temperature. When the pressure is applied, a metal-insulator phase transition at low temperature is induced under a pressure of ∼ 0.48 GPa. The metal-insulator phase transition temperature (TMI)(TMI) increases linearly with pressure as <img height="15" border="0" style="vertical-align:bottom" width="156" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0272884217320540-si0014.gif">dTMI/dP=3.4±0.3K/GPa. The temperature dependence of resistivity [ρ(T)][ρ(T)] in the pressure-induced insulating phase exhibits a thermal activation behavior (ρ=ρ0eΔE/kBT)(ρ=ρ0eΔE/kBT), where the thermal activation energy (ΔE)(ΔE) increases monotonously with the pressure. Meanwhile, the magnetization is enhanced by the pressure, which indicates an enhancement of magnetic ordering. The results suggest that localization occurs due to the magnetic ordering induced by the pressure, which confirms the magnetic-electronic coupling in Bi2Ir2O7

    更新日期:2017-09-19
  • Performance investigation of resin bonded ferro-silicon nitride- corundum refractories after creep at 1300 °C
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Haixia Qin, Yong Li, Menglong Long, Wendong Xue, Peng Jiang, Guisheng Yao, Xiuming Jin

    Novel tempered resin bonded ferro-silicon nitride-corundum refractories containing 0 wt.%, 15 wt.% and 25 wt.% ferro-silicon nitride were prepared respectively. Creep tests were performed under a load of 0.2 MPa at a temperature of 1300 °C for 50 hours in air. The results showed that creep performance was significantly improved by the addition of ferro-silicon nitride. Ferro-silicon nitride-corundum containing 15 wt.% ferro-silicon nitride initially presented a steady-state stage and was able to remain stable from the beginning of the holding time until 50 hours of creep testing. All the specimens exhibited cold crushing strength more than 100 MPa both before and after creep testing. Phase composition and microstructure were analyzed following the creep experiments. The results showed that Si2N2O and O’-sialon crystals formed in situ during creep testing, in addition to the conversion of α-Si3N4 to β-Si3N4. Liquid Fe3Si from the ferro-silicon nitride component accelerated the formation of the O’-sialon and prolonged the growth of β-Si3N4, which improved the creep performance significantly. Fe3Si liquid migrated into the pores, and some Fe3Si coexisted with residual carbon from the resin, which filled a part of pores and protected the specimens from severe oxidation.

    更新日期:2017-09-19
  • Fast and easy synthesis of novel Strontium apatite nanostructured phase: Structure, spectroscopy, and dielectric analysis
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Reem AL-Wafi, Rashida Jafer, I.S. Yahia, Attieh A. Al-Ghamdi, Maryam A. Al-ghamdi, A.M. El-Naggar

    A simple and fast synthesis method of hydroxyapatite (Ca10(PO4)6(OH)2 (HAp) is presented in this study. By using fast microwave/hydrothermal synthesis technique, different concentrations of strontium doped HAp nanorods titled as (0.03, 0.06, 12, 0.24, 0.48) were prepared. The as-prepared Sr-doped HAp was characterized for its structure and morphology using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Spectroscopic properties were also enquired through Raman and Fourier transform infrared (FTIR) spectroscopy. The morphological studies by scanning electron microscopy showed the effective synthesis of HAp nanorods with different sizes. In addition, the dielectric properties of Sr-doped HAp were also studied by using dielectric impedance spectroscopy technique. Raman and FTIR study show an agreement with no shift in the peaks at the increasing concentrations of Sr in all Sr-HAp samples. PO4 peak was clearly seen in Raman and the basic HAp structure was revealed in all FTIR results at various concentrations of Sr. The study has been proved that mixing of diverse concentrations of Sr to the HAp matrix, can affect the degree of crystallinity of the synthesized samples. The crystallite sizes of pure HAp and with different concentrations of Sr dopped HAp were found to be 12 and 27 nm. Moreover, doping of HAp with different concentration of Sr also affect the dielectric properties of the studied samples. This newly synthesized Sr-doped HAp can be applied in different biological applications such as bone and teeth cement engineering.

    更新日期:2017-09-19
  • Effect of particle size on dry sliding wear behaviour of sillimanite reinforced aluminium matrix composites
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-19
    Sandeep Sharma, Tarun Nanda, O.P. Pandey

    Present work describes the development of Al-Si/sillimanite reinforced composites via stir casting route. Sillimanite is abundant mineral available in coastal regions of India and has not been explored much as reinforced mineral for the development of composites. In the present work, dry sliding wear behaviour of LM30 aluminium alloy reinforced with sillimanite has been investigated. Composites reinforced with sillimanite in different weight percentage (3–18 weight percentage) and particle size range (fine: 1–20 µm, medium: 32–50 µm, and coarse: 75–106 µm) were prepared. Microstructural studies revealed uniform distribution of sillimanite particles in the matrix of composites. Nanoindentation taken at different phases indicated good bonding between reinforced particles and matrix. Fine particles (1–20 µm) reinforced composites containing 15 wt.% sillimanite exhibited higher wear resistance which is 55% more compared to base LM30 alloy. Beyond this reinforcement level, wear resistance deteriorated because of agglomeration of the fine particles. Analysis of wear track and debris revealed that at low applied loads, abrasive wear was predominant whereas at higher applied loads, adhesive wear was dominating factor.

    更新日期:2017-09-19
  • Anisotropy measurments of a cuboid of nanostructured hydrothermally-prepared Bi0.45Sb1.55Te3
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Ankam Bhaskar, Hsin-Chang Lai, Yen-Liang Liu, Chia-Jyi Liu

    A cuboid of p-type Bi0.45Sb1.55Te3 is fabricated using hydrothermal synthesis followed by consolidation using cold pressing and evacuated-and-encapsulated sintering in a Pyrex ampoule. Powder x-ray diffraction, electrical resistivity, thermopower, and thermal conductivity measurements are performed on three different faces of the cuboid, one face perpendicular to the press direction and the other two faces parallel to the press direction. Both the electrical resistivity and thermal conductivity are anisotropic, while the thermopower is nearly isotropic. According to the x-ray diffraction patterns, there are more ab planes oriented within the two faces of the cuboid parallel to the press direction than that of the face perpendicular to the press direction. As a result, the power factor and dimensionless thermoelectric figure of merit zT for the former are larger than for the latter. The magnitude of zT at 300 K for the two faces parallel to the press direction is 1.59 and 1.49, respectively. The magnitude of zT at 300 K for the face perpendicular to the press direction is 1.11.

    更新日期:2017-09-19
  • Catalyst-free growth of multi-shaped SiC nanofibers on carbon fibers at elevated temperatures
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Jixiang Dai, Jianjun Sha, Zhaofu Zhang, Junqi Shao, Yufei Zu, Mingkai Lei

    Large quantities of multi-shaped SiC nanofibers were successfully synthesized on carbon fibers at elevated temperatures via a catalyst-free chemical vapor reaction method. FE-SEM and TEM investigations revealed that all SiC nanofibers grew along the [111] crystal orientation. The diameters of SiC nanofibers were in the range of 100–400 nm. The length of nanofibers was about several hundreds of micrometers. The vapor-solid mechanism was applied to understand the growth of the multi-shaped SiC nanofibers. The change in morphological shape of SiC nanofibers could be attributed to the temperature-dependent growth kinetics, which strongly associated with the partial pressure of SiO.

    更新日期:2017-09-19
  • A comprehensive analysis of the influence of resistive coupled microwave sintering on the optical, thermal and hardness properties of infrared transparent yttria-magnesia composites
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    C.T. Mathew, Jijimon K. Thomas, Y.V. Swapna, Jacob Koshy, Sam Solomon

    A novel resistive coupled microwave sintering strategy was developed to sinter yttria-magnesia nanocomposite synthesized by a combustion technique to a density greater than 99% of the theoretical density. A substantial reduction in the sintering temperature and soaking duration were observed in the resistive coupled microwave sintering. The new method yielded pellets with average grain size ~0.15 µm which showed a better transmittance of 82.8% in the mid infrared range and an improved hardness of 10.81 GPa compared to the pellets sintered via resistive heating and susceptor assisted microwave heating. The enhanced hardness and transmittance properties achieved by resistive coupled microwave sintering without affecting the thermal properties is a remarkable result which can be used effectively in fabricating high quality futuristic infrared transparent windows and domes for strategic defence and space missions.

    更新日期:2017-09-19
  • The impact of Yb and Co on structural, magnetic, electrical and photocatalytic behavior of nanocrystallinemultiferroic BiFeO3 particles
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Sajjad Ahmad, Muhammad Azhar Khan, Mansoor Sarfraz, Aziz ur Rehman, Muhammad FarooqWarsi, Imran Shakir

    The nanocrystalline particles of BiFO3,co-doped with ytterbium and cobalt Bi1-xYbxCoyFe1-yO3 (BYCFO) were fabricated via micro-emulsion method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant. The dopant contents were kept x= 0.00, 0.025, 0.05, 0.075, 0.1, 0.125 and y = 0.00, 0.05, 0.1, 0.15, 0.2, 0.25 for six different compositions. The BYCFO-nanoparticles were investigated for structure, electric, dielectric, magnetic and photocatalytic properties. The X-ray diffraction (XRD) analysis confirmed the normal growth habitat Rhombohedral (R3c) phase on inclusion of ytterbium and cobalt ions as it is observed in undoped BiFeO3 multiferroic. However further doping of Yb+3 and Co+3 ions (x= 0.125, y= 0.25) resulted in some extra peaks, that is attributed to the formation of extra phase. The vibrating sample magnetometer recorded saturated magnetization (Ms) 0.385 emu/g with remanent magnetization (Mr) 0.13 emu/g for a coercivity of 405 Oe which is higher than the undoped BiFeO3.The substitution of Yb+3 and Co+3 ions improved the canting angle and optimally aligned the sub lattices in ferromagnetic order.The grain size was found in the range of 20–24 nm which is less than spiral spin modulation (≈62 nm).The entire dielectric parameters showed smooth decreasing trend in low range frequency but at higher frequency (1.98 GHz) resonance peaks appeared in the spectra. The insulating character was also enhanced up to 16.42×1010 Ω cm−1, with increase in doping concentrations. The optical band gap was measured 1.5 eV which was lower than the undoped BiFeO3 (2.15 eV). The photocatalytic performance of co doped ceramic (Bi0.875Yb0.125Co 0.25Fe0.75O3) was monitored using the textile dye Congo red. Approximately 28% of initial concentration (0.5 ppm) was degraded by 200 mg of ceramics in 42 minutes under visible light irradiation. Being magnetic in nature, the Bi1-xYbxCoyFe1-yO3 particles could be separated by conventional magnetic bar.

    更新日期:2017-09-19
  • Carbothermal synthesis of micron-sized β-Si3N4 with tailored morphology
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Si-Yuan Sun, Zhao-Bo Tian, Jie Zhang, Ke-Xin Chen, Zhi-peng Xie

    Micron-sized β-Si3N4 powders with tailored morphology were successfully synthesized by carbothermal reduction–nitridation (CRN) strategy. β-Si3N4 granules with low aspect ratios were prepared with 10 mol% of CaO additive and the size of particles could be regulated by altering N2 pressures. β-Si3N4 particles with high aspect ratios were synthesized when the content of CaO was less than 5%. Increasing content of additive could reduce the diameter of β-Si3N4 granules. More significantly, the underlying growth mechanism of the β-Si3N4 was tentatively put forward.

    更新日期:2017-09-19
  • CNTs@C@Bi2Se3 composite as an improved-performance anode for lithium ion batteries
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Rencheng Jin, Mingwei Sun, Guihua Li

    Bi2Se3 with layered structure has been considered as a promising host for Li ion batteries due to its high electrical conductivity. However, the disadvantages such as dissolution loss of selenium species and the large volume expansion extremely hinder its practical application. Here, the electrochemical performance is improved by synthesizing CNTs@C@Bi2Se3 nanocomposites. The electrochemical measurements results indicate that the CNTs@C@Bi2Se3 delivers high rate capacity (222 mAh g−1 at 2000 mA g−1) and long-term cycle stability (243 mAh g−1 after 300th cycles at 1000 mA g−1). Moreover, the electrochemical reaction mechanism is proposed based on the ex situ HRTEM technique.

    更新日期:2017-09-19
  • Hot Corrosion Behavior of ZrB2-HfB2 Solid Solutions in KCl and K2SO4 at 1500 °C
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Steven J. Sitler, Krishnan S. Raja, Indrajit Charit

    Novel electrode coating materials are needed for coal-fired magnetohydrodynamic (MHD) direct-current extraction power plants. Addition of potassium salt to increase the conductivity of coal plasma combined with high temperature render the service conditions extremely arduous. Therefore, the electrode coating materials must possess certain properties including high-temperature corrosion resistance, high-temperature oxidation resistance, and adequate electrical conductivity. In this work, those very properties of three different compositions of transition metal diboride solid solutions of HfB2-ZrB2 are studied. Two main approaches of oxidation mitigation methods were employed: adding chemical dopants, such as Hf and La, and performing pre-anodization on the samples to create a protective oxide coating. Thermogravimetric experiments were run at different partial pressures of oxygen to determine the high-temperature oxidation resistance of these boride ceramics. In addition, two different salt coatings (KCl and K2SO4) were applied to the surface of the samples to test their hot corrosion resistance. High-temperature polarization resistance tests were also conducted to measure the electrical resistivity. The addition of lanthanum aided in long term oxidation and corrosion protection, with a parabolic rate constant, Kp = 1.33 × 10-5 kg2/m4•s, a 40% improvement over the sample without the addition of lanthanum under the same conditions. Anodization, however, proved disadvantageous when combined with either lanthanum or a corrosive environment.

    更新日期:2017-09-19
  • Thermoelectric Characterization of Multi-walled Carbon Nanotube/ Sodium Cobalt Oxide Prepared by a Low-cost Flame Sintering Technique
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Chutima Oopathump, On-Uma Kheowan, Anek Charoenphakdee, Adul Harnwunggmoung, Siwaporn M. Smith, Christopher B. Smith

    Multi-walled carbon nanotubes/sodium cobalt oxide (MWCNTs/NaxCoO2) composites were successfully obtained via a flame sintering method. Such sintering is accountable for a surface densification that can preserve the MWCNTs entity within the composites. Raman spectroscopy confirmed the presence of MWCNTs in the composites, with NaxCoO2 being present as a single phase (γ) as revealed by X-ray diffraction. EDX results suggested non-uniform distribution of MWCNTs within the NaxCoO2 material, although their presence resulted in increased electrical conductivity through enhancements in charge mobility. The effect of MWCNTs addition on the thermoelectric performance of NaxCoO2 was examined. Addition of MWCNTs results in increased levels of phonon scattering in the composites, leading to decreased thermal conductivity. Although Seebeck coefficients decreased due to an increase in charge density, the thermoelectric efficiency of the composites reported as ZT values was enhanced in comparison to those in material without added MWCNTs, with optimum conditions found in composites derived from 0.25 wt.%MWCNTs/NaxCoO2 (with ZT enhancement by ca. 60% at 398 K).

    更新日期:2017-09-19
  • Flux synthesis and chemical stability of Nd and Ce co-doped (Gd1-xNdx)2(Zr1-xCex)2O7 (0≤ x ≤1) pyrochlore ceramics for nuclear waste forms
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Jin Wang, Junxia Wang, Yibing Zhang, Yuxiang Li, Yuancheng Teng, Zhe Wang, Hongbin Tan

    A series of Nd and Ce co-doped (Gd1-xNdx)2(Zr1-xCex)2O7 (0≤x≤1) pyrochlores were synthesized by flux method at 900–1000 °C using nitrates as starting materials and a small amount of NaF as fluxing agent. The influences of contents of Nd/Ce, fluxing agent and reaction temperature on the phase structure of the pyrochlores were systematically investigated by X-ray diffraction (XRD) and Raman spectroscopy (Raman). The chemical stability of Nd and Ce co-doped pyrochlore bulk ceramics was also evaluated. XRD and Raman results showed that the crystalline phase of (Gd1-xNdx)2(Zr1-xCex)2O7 (0≤x≤1) pyrochlores always remained a single disordered defect-fluorite structure for any x value. XRD, Raman spectrum and SEM-EDX results revealed that the Nd and Ce could be co-doped at the A-site and B-site of the Gd2Zr2O7 pyrochlore structure, respectively. The normalized release rates of Gd, Zr, Nd and Ce in (Gd1-xNdx)2(Zr1-xCex)2O7 pyrochlore bulk ceramics (x=0.25, 0.5 and 0.75) remained relatively constant in a low value below 10−4 g·m−2·d−1 at 90°C for 7 days, exhibiting superior chemical stability.

    更新日期:2017-09-19
  • Matricial inclusion of AlN and Al2O3 Al 2 O 3 nanoparticles in C/C composites from aqueous growth and ceramization at the pre-densified stage
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Nicolas Martin, Hervé Plaisantin, Patrick Weisbecker, Jean-Marc Leyssale, René Pailler

    We report on a successful attempt to introduce Al2O3 Al 2 O 3 and AlN nanoparticles in the matrix of a C/C composite via (i) aqueous synthesis of AlOOH nanoparticles in a predensified C/C composite preform, (ii) ceramization of AlOOH into either Al2O3 Al 2 O 3 or AlN, and (iii) final pyrocarbon densification. We show that we were able to synthesize a uniform and thin layer of high aspect ratio (nanoneedle) AlOOH particles at the surface of pyrocarbon coated fibers. This morphology was conserved upon transformation to alumina, however, coalescence into larger compact grains (thus discontinuous) was observed after nitridation. Nevertheless, the ceramic introduction did not alter the microstructure of the resulting composite after full densification. While most of the ceramic/carbon interfaces showed a parallel arrangement of graphene layers at the surface of the ceramic particles, characteristic of weak bonding, a carbon/AlN interface showed a perpendicular arrangement, suggesting strong covalent bonding.

    更新日期:2017-09-19
  • Powder Preparation and High Infrared Performance of NaLaS2 Transparent Ceramics
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Huanyong Li, Ping Li, Jiahao Zhang, Leiyuan Tian, Heqing Li, Jingli zhao, Fa Luo

    NaLaS2 powders with various Na/La molar ratios were prepared via a gas-solid reaction method where NaF nanocrystal was used as the sodium source, and CS2 served as the sulfurizing agent. The effective sulfurization parameters were designed based on the thermodynamic properties of the precursor obtained via the reverse coprecipitation way. The phase compositions and morphologies of sulfide powders depended strongly on NaF amount. The powder with a molar ratio of Na/La=1.3 was selected for sintering NaLaS2 ceramic via hot-pressing process under vacuum due to its highest phase purity and lowest oxidesulfide, fluorosulfide impurities level. As-sintered NaLaS2 ceramic exhibited a consolidated microstructure, a minor amount of oxysulfide impurities and high 8~14μm mean transmissivity with the maximum transmittance up to 67.5% at 9μm. Contrasting study proves that NaLaS2 ceramic has the tendency to possess the better IR performance and antioxidation capacity than γ-La2S3 and CaLa2S4 ceramics.

    更新日期:2017-09-19
  • Structural and Electromagnetic Evaluations of YIG Rare Earth Doped (Gd, Pr, Ho,Yb) Nanoferrites For High Frequency Applications
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Majid Niaz Akhtar, M. Yousaf, S.N. Khan, M.S. Nazir, Mukhtar Ahmad, Muhammad Azhar Khan

    Multiple rare earth metal cations (Gd, Yb, Ho and Pr)were doped in yttrium iron garnet (YIG) nanocrystalline ferrites. Following five samples i.e. YIG (Y3Fe5O12), Gd doped YIG (Y2.8Gd0.2Fe5O12), Pr doped YIG (Y2.8Pr0.2Fe5O12), Ho doped YIG (Y2.8Ho0.2Fe5O12) and Yb doped YIG (Y2.8Yb0.2Fe5O12) were prepared using sol-gel auto-combustion synthesis route. The samples were characterized via XRD, FTIR, SEM and VSM whereas VNA was also used to evaluate these samples for high frequency applications. XRD analysis confirms the peaks of garnet ferrites which show cubic phase structure for all YIG doped samples. The lattice constant in all the substituted garnet nanoferrites initially increased and then consequently decreased as the doping increased except for Pr-substituted YIG nanoferrites. This is due to the greater ionic radii of Pr as compared to other doped YIG nanoferrites. FTIR was used to find out the garnet phase in all the substituted YIG nanoferrites. The morphological features of the garnet nanoferrites were observed using the SEM images. High frequency measurements such as permittivity, permeability, dielectric losses, ac conductivity, electric modulus and Q factor of YIG and doped YIG nanoferrites were measured using VNA. Saturation magnetization, remanence, coercivity, squareness ratio, Bohr magneton and magneto crystalline anisotropy were measured from the magnetic hysteresis loops recorded by VSM. Pr-doped YIG show better dielectric and magnetic properties with lower losses at higher frequency suggest the use of these garnet nanoferrites for microwave high frequency devices and applications.

    更新日期:2017-09-19
  • Fabrication of SiCf/SiC and Integrated Assemblies for Nuclear Reactor Applications
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Amit Siddharth Sharma, Pipit Fitriani, Dang-Hyok Yoon

    This study examined the processing feasibility of electrophoretic deposition (EPD), as an effective matrix infiltration method, in conjunction with hot-pressing to fabricate dense and tough SiCf/SiC materials. Flat and tubular specimens were fabricated by hot pressing at 1750°C and 20 MPa after infiltrating a SiC-based matrix phase into Tyranno® SA3 SiC fabrics, which can be used as the core structural components for the next generation fission reactors and as blanket materials for future fusion reactors. For the tubular specimens, two types of preforms were compared: filament wound and jelly-rolled with different woven structures. The incorporation of SiC green tapes between the successive layers of SiC fabrics allowed better control over the composite density and pore distribution. The macro-architecture of the composites was optimized in terms of the slurry composition, sintering additives, and phase evolution. Fractography revealed considerable debonding at the SiCfiber-PyCcoating interface and fiber pull-out with pronounced tail extension behavior when tested in flexure. Joining of the flat-tube and flat-flat SiCf/SiC was performed using a range of filler systems; the structures integrated using the Ti-based MAX fillers at 1750°C and 3.5 MPa for 1–2 h soaking time are discussed.

    更新日期:2017-09-19
  • MAGNESIUM-DOPED ZIRCON-TYPE RARE-EARTH ORTHOVANADATES: STRUCTURAL AND ELECTRICAL CHARACTERIZATION
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    T.H. Gayathri, A.A. Yaremchenko, J. Macías, P. Abhilash, S. Ananthakumar

    Undoped LnVO4 and magnesium-doped Ln0.95V0.95Mg0.10O4-δ (Ln = Pr, Sm, Gd, Dy and Er) orthovanadates were synthesized by solid state reaction method and characterized by XRD, SEM/EDS, electrical conductivity measurements in controlled atmospheres, and modified e.m.f. technique for determination of oxygen-ion transference numbers. XRD analysis showed the formation of phase-pure materials with tetragonal zircon-type structure and a decrease in lattice parameters with a decrease of ionic radius of rare-earth cations. Trace amounts of MgO and Mg-V-O phases revealed by SEM/EDS suggest that the solid solubility limit of magnesium cations in LnVO4 lattice is somewhat lower than the nominal doping level, and that magnesium substitutes preferentially into the vanadium sublattice. LnVO4 and Ln0.95V0.95Mg0.10O4-δ orthovanadates show semiconducting behavior under oxidizing conditions at 450–950 °C and are predominantly oxygen-ionic conductors, except PrVO4 that shows mixed conductivity. In the LnVO4 series, electrical conductivity is the highest for PrVO4 and SmVO4 (~4×10−4 S/cm at 800 °C) and decreases with increasing atomic number of rare-earth cation for the other compositions. Additions of magnesium results in a drop of electrical conductivity, by 1.5–2 times for most of compositions. Interstitial oxygen diffusion is discussed as a prevailing mechanism of ionic transport in undoped LnVO4, whilst acceptor-type magnesium doping suppresses the formation of interstitial oxygen ions. Humidity has a rather negligible impact on the electrical properties of substituted ceramics, indicating only minor (if any) protonic contribution to the total electrical transport of the studied orthovanadates.

    更新日期:2017-09-19
  • Effect of temperature and heating rate on the sintering performance of SiC-Al2O3-Dy2O3 and SiC-Al2O3-Yb2O3 systems
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    S. Ribeiro, L.A. Gênova, G.C. Ribeiro, M.R. Oliveira, A.H.A. Bressiani

    Samples of SiC+10vol.%(Al2O3+Dy2O3) and SiC+10vol.%(Al2O3+Yb2O3) mixtures were obtained by cold isostatic pressing and sintered for one hour in a dilatometer at 1800°C and 1900°C, applying heating rates of 10, 20 and 30 °C/min. The results of the complete sintering cycle indicated that the heating rates do not significantly influence the shrinkage, but that temperature and total sintering time may be relevant factors. The compacts sintered at 1900°C shrank on average 9% more than those sintered at 1800°C, and it was found that the sintering time can be reduced by 40 to 50% at faster heating rates. The maximum shrinkage rates occurred at temperatures lower than those of the sintering thresholds for the two mixtures, two temperatures and three heating rates. It was also found that after formation of the liquid, the mechanisms of particle rearrangement and solution-precipitation were not as fast as reported in the literature, even at high heating rates, for example 30 °C/min, but they are responsible for much of the shrinkage occurring throughout the sintering cycle.

    更新日期:2017-09-19
  • Synthesis of anatase nano wire and its application as a functional top layer for alumina membrane
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    M.F. Zawrah, R.M. Kattab, L.G. Girgis, E.E. El Shereefy, S.E. Abo Sawan

    Nowadays, the structural and functional deficiencies of ceramic membranes prepared by conventional approaches are of particular research of interest. In the present work, ceramic membrane was fabricated by constructing hierarchically structured separation layer on a porous alumina substrate. This layer was TiO2 nano wires which synthesized by hydrothermal method followed by calcination at 550 °C to obtain the active anatase form. The synthesized TiO2 nano wire was characterized by XRD, SEM, EDAX, TEM and UV-vis spectroscopy. The antibacterial activity of the synthesized TiO2 nano powder was investigated against Escherichia coli bacteria by zone of inhibition test. To fabricate the ceramic membrane, the synthesized nano wire was sprayed on a porous sintered alumina substrate fabricated by gel-casting technique. Microstructure of TiO2/alumina ceramic membrane was investigated by SEM. XRD results revealed that the as-synthesized material at 200 °C was Na-titanate which transformed into H-titanate when neutralized with acid. After calcination at 550 °C, the formed phase was anatase nano wire. As indicated from TEM images, H-titanate long wires with 5–200 nm diameter and 5–25 µm length were obtained. After calcination, linear anatase nano wires with 10–50 nm thickness, 1–2 µm length and aspect ratio about 100 were detected. The TiO2 nano wires exhibited bacterial activity toward E. coli with zone of inhibition equal 15mm. Moreover, the fabricated alumina membrane had ideal microstructure which consists of three layers having gradual pore size and thickness. These layers were alumina support, interface layer, and TiO2 nano wire layer.

    更新日期:2017-09-19
  • Synthesis and electrochemical properties of LiVP2O7/C as novel cathode material for lithium ion batteries
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Huayi Yu, Zhi Su, Lei Wang

    Monoclinic LiVP2O7/C was successfully synthesized by the sol-gel method using citric acid as both the carbon source and reducing agent. The structure and morphology of the sample were investigated. TEM image showed that the surface of sample was covered with a thin carbon layer. Charge-discharge testing revealed that the LiVP2O7/C sample with carbon content of 6.63 wt% prepared at 800 °C exhibited the best initial discharge capacity of 102.3 mAh·g−1, 96.2% of which was retained after 50 cycles. The experimental results indicate that the sol-gel method and carbon coating not only provide a facile and practical approach, but are beneficial to the electrochemical properties of the LiVP2O7/C cathode material.

    更新日期:2017-09-19
  • Transient Liquid Phase Bonding of Copper and Ceramic Al2O3 by Al/Ni Nano Multilayers
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-18
    Zhongmin Long, Bo Dai, Shijie Tan, Yong Wang, Xianhua Wei

    Transient liquid phase (TLP) diffusion bonding has been achieved for the dissimilar joining of ceramic Al2O3 and copper using Al/Ni multilayers as interlayers at low temperature. The freestanding Al/Ni nano-multilayers were deposited by direct current magnetron sputtering and their properties were studied by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy (SEM). The joining experiments were carried out at 550, 650 and 750 °C for a holding time of 30 min without extra pressure under nitrogen protection. The interfacial microstructure and microstructural characterization of the diffusion welded joints were investigated by SEM, energy dispersive X-ray spectroscopy and element mapping. The effectiveness of different temperatures for the mechanical properties of the joints was evaluated by shear strength. In the present work, an AuSn solder was added to expand the surface contact of the welding. The results show that the applications of Ni/Al multilayers and the AuSn solder reduce the bonding temperature and improve the joining quality.

    更新日期:2017-09-19
  • Influence of Magnesium Aluminate Spinel Powder Content on Cement Clinker Corrosion and Adherence Properties of Lightweight Periclase-Spinel Refractories
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-17
    Sanbao Ma, Wen Yan, Stefan Schafföner, Xiaoli Lin, Nan Li, Yaojie Zhai, Xijun Liu, Linlin Xu

    The effect of the amount of magnesium aluminate spinel powder (MASP) in lightweight periclase-spinel refractories on the cement clinker corrosion and adherence properties was investigated by the static crucible test and sandwich test. The results showed that MASP addition significantly affected the cement clinker corrosion resistance and adherence properties although it had little effect on the apparent porosity and pore size of refractories. The spinel in the refractories reacted with the cement clinker rather than periclase to generate the glass phase. Its amount and viscosity increased from 0 to 13 wt% MASP addition in refractories, which brought the benefit to the adherence strength. However, the excessive glass phase deteriorated the corrosion and penetration resistances of refractories as MASP was added up to 19 wt%. So, the addition amount from 9 to 13 wt% MASP into periclase-spinel refractories balanced the cement clinker resistance and adherence strength.

    更新日期:2017-09-19
  • Microstructure, Dielectric and Piezoelectric Properties of 0–3 Lead Free Barium Zirconate Titanate Ceramic-Portland Fly Ash Cement Composites
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-17
    Phakin Chomyen, Rumporn Potong, Rattiyakorn Rianyoi, Athipong Ngamjarurojana, Prinya Chindaprasirt, Arnon Chaipanich

    Piezoelectric ceramic – Portland cement composites have been developed for sensor application in concrete structures to overcome the acoustic matching problem that may occur for piezoelectric ceramic or polymers with concrete. Pozzolanic materials such as fly ash are commonly used in concrete to enhance durability. The objectives of this research were to investigate the effects of fly ash addition on the physical properties, dielectric properties and piezoelectric properties of 0–3 barium zirconate titanate ceramic– Portland cement composites. The results showed that the dielectric constant of these composites decreased when the fly ash content in the composite increases. However, the piezoelectric coefficient (d33) value of BZT–PC composite with fly ash 10% by volume was found to be similar to that of BZT–PC composites.

    更新日期:2017-09-19
  • Effect of rare-earth doping in CeO2 matrix: Correlations with structure, catalytic and visible light photocatalytic properties
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-17
    Kushal Singh, Kundan Kumar, Saurabh Srivastava, Anirban Chowdhury

    The nanoparticles involving LaxCe1−x O2–δ system (x = 0.1, 0.2 and 0.5) with various rare earth La3+-doping levels were successfully synthesized and characterized for their structural, catalytic and photocatalytic properties. The structural characterizations (via X-ray diffraction, high-resolution transmission electron microscopy, Raman spectroscopy) confirmed the presence of phase-pure catalyst nanoparticles with desired target stoichiometry; induced lattice strains were correlated with various doping amounts. Raman spectroscopy results illustrated the effect of progressively higher La-doping with increasing peak asymmetry, broadening and shifting of the key peaks to lower energies. The 10% La-doped ceria catalysts depicted superior catalytic reduction and visible light photocatalytic (for the degradation of methylene blue) properties along with promising oxygen storage capacity values. Our results suggest that low (≤20%) doping of the rare-earth metal is sufficient for maintaining a balance between catalytic properties and overall deformation (strain, vacancy etc) in the fluorite CeO2 lattice.

    更新日期:2017-09-19
  • Erosion Mechanism of YAG:Ce3+ Phosphor in Bismuth Borate Glasses
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-17
    Libin Xia, Xinyu Ye, Hongyuan Ge, Yaochun Qiang, Qinghui Xiao, Qian Zhang, Zhifang Tong

    The poor thermal stability of current commercial white light emitting diodes (WLED) fabricated using a blue chip, a yellow YAG:Ce3+ phosphor (YAG) and resins, restricts their application in fields where long service time and high power lighting systems are required. Incorporating YAG into glass offers a possible way to resolve the problem by removing the organic resins in LED encapsulation. In the present study, YAG glass-ceramics with bismuth borate glass matrices were prepared using a rapid melt quenching technique. The YAG erosion mechanism was investigated for the first time in various glass matrix compositions at different co-sintering temperatures. The results demonstrate that neither B2O3 nor Bi2O3 individually erodes YAG particles, but the mixtures of B2O3 and Bi2O3 binary glass systems react with YAG and dissolve it almost completely or generate YAl3(BO3)4 (abbreviated as YAB), and they even erode as-produced YAB again under certain conditions. The production of YAB particles increases with the increase of the nBi/nB ratio at a lower temperature (680 °C), while it first increases and then decreases at a higher temperature (800 °C). The maximum production of YAB can be obtained at the co-sintering temperature of 680°C with an nBi/nB ratio of 55:45 or at 760 °C with an nBi/nB ratio of 35:65. The intermediate Bi4B2O9 phase is found during the transformation of YAG into YAB. A simple but efficient approach is proposed to prevent YAG erosion and increase the luminous properties of YAG glass ceramics to a great extent by simply adding Ca2+ into bismuth borate glass matrices. The degree of YAG erosion decreases with increasing Ca2+ concentration until an impurity phase appears when the Ca2+ concentration exceeds 20 mol%. The combination of good white light emission and suitable quantum efficiency as well as higher thermal stability makes the as-prepared YAG glass-ceramics equipped with a blue chip a possible alternative to commercial WLED.

    更新日期:2017-09-19
  • Improving Mullite-Silicon Carbide Refractory in Coke Dry Quenching using Aluminum Nitride Whiskers Formed In Situ
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Meijie Zhang, Cangjuan Han, Kangxiang Ni, Huazhi Gu, Ao Huang, Zhijun Shao

    The formation conditions and their influence on the properties of mullite-SiC refractory were studied by adding metallic Al powder to the raw materials to form AlN whiskers in a coke dry quenching furnace. The results show that the AlN whiskers were formed in situ and interacted to form networks in the matrix when the metallic Al powder was added into the mullite-SiC refractory after heat treatment above 850 °C for 8 h under nitrogen flow. The whiskers grew lengthwise as the firing temperature increased and the cold modulus of rupture, cold crushing strength, and hot modulus of rupture increased. The amount and particle size of the metallic Al powder also affected the properties of the refractory. The optimum amount of Al powder addition was determined to be 6 wt%, which provided the highest strength and excellent toughness after heat treatment at 1000 °C for 8 h under nitrogen. Reducing the particle size of the metallic Al powder could promote formation of the AlN whiskers and improve the strength of the refractory.

    更新日期:2017-09-15
  • A facile method for the preparation of ceramic beads with hierarchical porosity
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Vassiliki Chalkia, Eleni Marathoniti, Vassilis N. Stathopoulos

    In this work a phase inversion method is effectively applied towards the formation of technical ceramics such as mm sized yttria stabilized zirconia beads. For the first time yttria stabilized zirconia spherical beads of uniform mm size diameter and hierarchical porosity are prepared by a simple one pot method utilizing phase inversion and templating synthesis. Solvent exchange and subsequent thermal treatment developed an open porous network of radial hierarchical porosity. Multimodal pore size distribution ranging within 3 orders of magnitude was identified and porosity values up to 74% were measured.

    更新日期:2017-09-15
  • Dielectric response and alternating current conductivity in (Co,Ni)Al2O4 nano-spinel
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Harshit Agarwal, T.P. Yadav, O.N. Srivastava, M.A. Shaz

    The dielectric behavior and alternating current conduction mechanism of nanocrystalline (Co,Ni)Al2O4 aluminate spinel have been investigated over a broad frequency range (1KHz to 1 MHz) for different temperatures i.e. 50°C to 90°C. The low cost and environmental friendly method has been used to developed the nanocrystalline (Co,Ni)Al2O4 spinel phase. The formation of homogeneous single phase of nanocrystalline (Co,Ni)Al2O4 spinel has been confirmed by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The dielectric response and alternating current conductivity have been observed by inductance, capacitance and resistance bridge which confirms traditional dielectric behavior of (Co,Ni)Al2O4. The frequency dependent complex dielectric impedance behavior has also been explored. The activation energy of (Co,Ni)Al2O4 has been found nearly 0.3eV-0.1 eV b/w the frequency range 1KHz to 1 MHz. The alternating current conduction mechanism reveals the signature of correlated barrier hopping by following the power law where the maximum barrier length has been found 144 ± 0.25 MeV. This alternating current conduction also follows the Meyer-Neldel rule in the low frequency region.

    更新日期:2017-09-15
  • Dye-adsorption properties of WO3 nanorods grown by citric acid assisted hydrothermal methods
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Soo-Min Park, Chunghee Nam

    Dye-adsorbing tungsten trioxide (WO3) powders were prepared by a simple wet chemical hydrothermal method at 120 °C. In order to study the effect of specific surface area on the dye-adsorption properties, various morphologies of WO3 powders were synthesized using different concentrations of a structure-directing agent (citric acid). The morphology, structure, specific surface area, and adsorption characteristics of the synthesized WO3 powders were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller (BET) method, and UV-Vis adsorption spectroscopy, respectively. The BET measurements showed different surface area values for the samples prepared at different concentrations of citric acid, and the adsorption capacity increased as the surface area increased. WO3 nanorods synthesized using 0.2 mol of citric acid showed the largest surface area of 81.5 m3/g and the highest adsorption capacity of 57.6 mg/g at a pH of 7.0.

    更新日期:2017-09-15
  • Na+-solidification behavior of SiO2-Al2O3-CaO-MgO (10 wt.%) ceramics prepared from red mud
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Dejian Pei, Yu Li, Daqiang Cang
    更新日期:2017-09-15
  • Development of a carbon-coated reticulated porous alumina material with tailored structural properties for potential radar-absorption applications
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Jang-Hoon Ha, Sujin Lee, Jae Ryung Choi, Jongman Lee, In-Hyuck Song, Seung Jun Lee, Jaeho Choi

    Porous ceramics have attracted research interest because of their high levels of thermal and chemical stability. Reticulated porous ceramics have been fabricated for several decades. However, insufficient data exists regarding the radar-absorption properties of reticulated porous ceramics. Therefore, the authors investigated the feasibility of using reticulated porous ceramics, prepared using alumina, as a platform for a radar-absorbing coating-material, such as carbon. The experimental data were used to determine whether carbon-coated reticulated porous alumina could be effectively prepared while maintaining an acceptable compressive strength by controlling the processing conditions. The structural properties and radar-absorption properties of the carbon-coated reticulated porous alumina material were examined using scanning electron microscopy (SEM), mercury porosimetry, and a network analyzer. The compressive strengths of the reticulated porous alumina specimens could be tailored by controlling the sintering temperature and the pore density of the polyurethane foams. The reflection loss of the reticulated porous alumina specimen with a thickness of 18.40 mm, coated with a carbon slurry with a carbon content of 10 wt. %, was calculated as approaching −40 dB at 10.0 GHz.

    更新日期:2017-09-15
  • Tailorable radio-frequency negative permittivity of titanium nitride sintered with different oxidation pretreatments
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    Guohua Fan, Peitao Xie, Zhongyang Wang, Yunpeng Qu, Zidong Zhang, Yao Liu, Runhua Fan

    Titanium nitride (TiN) with high-temperature plasmonic property can be a promising candidate for metamaterials at radio-frequency region.In this paper, pure TiN powders were pretreated by a facile oxidation process. The introduced titanium oxide was in favor of sintering of TiN, and further controlled the dielectric properties of TiN bulks. The radio-frequency (10MHz-1GHz) permittivity spectra of the obtained samples were investigated in detail. Negative permittivity was achieved using TiN based ceramic and it was tailorable by the oxidation temperatures of powders before sintering. The negative permittivity induced by plasma oscillations of conductive electrons was analyzed by Drude model. Interestingly, the zero-crossing points of permittivity from negative to positive were depend on the porous microstructure and weakly conductive titanium oxynitride, as well as the scattering effect by grain boundaries and impurity atoms. The conduction loss is dominant in determining the high dielectric loss. The realization of tunable negative permittivity using TiN gives a new and simple method to achieve negative electromagnetic parameters in single-phase materials.

    更新日期:2017-09-15
  • The Role of CaO Additive on Sintering of Aluminum Nitride Ceramics
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-15
    A.L. Molisani, H. Goldenstein, H.N. Yoshimura

    AlN with 0.5 to 8 wt.% CaO was pressureless sintered between 1100 °C and 1800°C. The results of density, second-phases, microstructure, and weight loss were used to identify the possible mechanisms that may cause a significant delay on the densification of AlN with CaO additive. It was observed that the additive content is the main parameter controlling the densification behavior during liquid phase sintering (LPS) of AlN with CaO. The positive effects of increasing the CaO content were associated with the decrease in the temperature of liquid-phase formation and the increase of the liquid-phase fraction during sintering. The negative effects were associated with the high viscosity of the liquid-phase below 1600°C, the formation of large pores, and the gas entrapment in closed pores. The balance between positive and negative effects results in an intermediate additive content (around 2 wt.% CaO), which is best to promote densification of AlN at a temperature as low as 1650°C.

    更新日期:2017-09-15
  • Optical and structural properties of arc melted Ce or Pr –doped Y2O3 transparent ceramics
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Andrzej Kruk

    This article presents the influence of praseodymium or cerium ions on physicochemical properties of yttrium oxide. Pure yttrium oxide and yttrium oxide doped with Ce or Pr ions powders were obtained by arc plasma synthesis. As a result of arc plasma synthesis, transparent, dense, uniform samples were obtained. To examine the microstructure and morphology of the powders and samples X-ray diffraction and scanning electron microscopy were used. X-ray studies have shown the incorporation of additives in the crystal lattice of yttrium oxide. In the present research work, Raman and FT-IR spectra of arc melted Ce or Pr –doped Y2O3 ceramics were reported. The optical and optical-magnetic properties were investigated for application as an optical insulator. Optical properties of the bulk samples were conducted from 200 to 1100 nm. The in-line transmittances of ceramics exceed 35% from the visible band to the near infrared band. The results of measuring Faraday effect indicated that additives significance improve Verdet constant (>130 deg/Tcm).

    更新日期:2017-09-15
  • Preparation of ZrCN−TiCN solid solutions by spark plasma sintering
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Ying Li, Hirokazu Katsui, Takashi Goto

    ZrCN–TiCN solid solutions were consolidated by spark plasma sintering (SPS) using ZrC and TiCN powders at 1573–2373 K for 300 s. ZrCN–TiCN solid solutions were densified to relative densities of 96−99% at temperatures above 2073 K. When sintered below 1973 K, the sintered bodies were composed of two phases, Zr-rich and Ti-rich solid-solution phases, whereas a ZrCN–TiCN solid solution in a single phase was obtained above 2073 K. With increasing the sintering temperature, the lattice parameters of the ZrCN–TiCN solid solution decreased and increased at Zr-rich and Ti-rich compositions, respectively. The ZrCN–TiCN solid solution exhibited a Vickers hardness (HV) of 23 GPa and a fracture toughness (KIC) of 3.5 MPa m1/2.

    更新日期:2017-09-15
  • Intermediate temperature fuel cell durability of Eu-doped SrCeO3-SrZrO3 solid solution/ NaCl-KCl composite electrolyte
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Ruijuan Shi, Junlong Liu, Hongtao Wang, Fufang Wu, Hui Miao

    A SrCe0.7Zr0.2Eu0.1O3-α (SCZE-SG) electrolyte was successfully fabricated by a sol-gel method using Eu2O3, Sr(C2H3O2)2·1/2H2O, (NH4)2Ce(NO3)6 and Zr(NO3)4·5H2O as raw materials and was subsequently reacted with NaCl/KCl. The obtained materials were characterized by XRD and SEM techniques. XRD results showed that SCZE-SG and NaCl/KCl did not chemically react. The SEM images revealed that the particle size of SCZE-SG is uniform, and NaCl/KCl is coated on the surface of SCZE-SG, acting as a binder in SrCe0.7Zr0.2Eu0.1O3-α-NaCl-KCl (SCZE-SG-NK). The oxide ion and protonic conduction of SCZE-SG was studied using gas concentration cells, and the results indicate that the durability of the fuel cell based on SCZE-SG-NK exhibits excellent cell performance with a maximum power output density of approximately 0.58 W·cm−2 during a 40-h operation at 700 °C.

    更新日期:2017-09-15
  • Dielectric Properties of CoCrFeO4 Nano-powder Prepared by Solution Self Combustion Synthesis
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    A.K. Sijo, Dimple P. Dutta, M. Roy

    The structural and dielectric properties of CoCrFeO4 nanoparticles synthesized via solution combustion technique have been studied. The phase purity of the product has been ascertained via powder XRD analysis. The morphology and size of the ferrite has been studied using TEM and the particles size matches well with that obtained from XRD. The dielectric studies done on the samples indicate that dielectric constant and dielectric loss tangent decrease with increase in frequency which can be attributed to space charge polarization. The dielectric loss vs. frequency curves recorded as a function of temperature show secondary maxima with a minimum in the negative side which shifts to the lower frequency side with increase in temperature. This helps in elucidating the conduction behaviour in these cobalt chromium ferrite particles.

    更新日期:2017-09-15
  • Low temperature fired Ln2Zr3(MoO4)9 (Ln=Sm, Nd) microwave dielectric ceramics
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Weiqiong Liu, Ruzhong Zuo

    A series of new microwave dielectric ceramics Ln2Zr3(MoO4)9 (Ln=Sm (SZM), Nd (NZM)) was successfully fabricated by a standard solid-state reaction method. The X-ray diffraction and Rietveld refinement results demonstrate that pure-phase SZM and NZM ceramics belong to the hexagonal system with a space group R3(_) 3 ( _ ) c. Scanning electron microscopy results reveal dense and homogeneous microstructures of these two ceramics as sintered at their respective optimum sintering temperature. Furthermore, the SZM and NZM ceramics sintered at 875 °C for 4 h and 850 °C for 4 h possess excellent microwave dielectric properties of dielectric permittivity εr ~ 11.0, quality factor Qxf ~ 74,012 GHz (10.6 GHz), and temperature coefficient of resonance frequency τf ~ −45.3 ppm/°C, and εr ~ 10.8, Qxf ~ 58,942 GHz (10.5 GHz), and τf ~ −40.9 ppm/°C, respectively. These experimental results show great potentials for applications of low temperature co-fired ceramic technology.

    更新日期:2017-09-14
  • Effects of sintering temperature and composition on dielectric, ferroelectric, and magnetoelectric properties of BaTiO3–BiFeO3 solid solutions
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Min Zhang, Xiaoyan Zhang, Xiwei Qi, Ying Li, Li Bao, Yaohang Gu

    A series of (1–x)BaTiO3–xBiFeO3 ( (1–x)BT–xBFO) multiferroic ceramics with the composition of x from 0 to 0.07 have been synthesized. The effects of the sintering temperature and composition on the crystal structure, microstructure, dielectric, ferroelectric, and magnetoelectric properties of the ceramics were investigated. With an increase of BFO content, the phase structure of the as prepared ceramics changed from tetragonal to cubic at a threshold value of x = 0.03. The region of the morphotropic phase boundary lies in the composition of x from 0.03 to 0.05, in which the tetragonal and cubic phase coexist. The dielectric constants have been greatly increased from 812 for pure BaTiO3 to 2667 of the composition 0.96BT–0.04BFO at the 10 kHz, which have been improved about 328%. The ceramics with the composition of x = 0.04 exhibited excellent ferroelectric characteristics, in which the remnant polarization Pr is 16.74 μC/cm2. The maximum magnetoelectric coefficient is 298.8 mV/cm·Oe for the material with x = 0.04 at 900 kHz and 1 kOe.

    更新日期:2017-09-14
  • Structural evolution, magnetization enhancement, and ferroelectric properties of Er3+-doped SmFeO3
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Xiaoxiong Wang, Jing Yu, Jun-cheng Zhang, Xu Yan, Chao Song, Yunze Long, Keqing Ruan, Xiaoguang Li

    The effects of Er3+ ion doping on the lattice structure, magnetism, and ferroelectric properties of SmFeO3 were investigated by X-ray diffraction (XRD), magnetic characterization, and ferroelectricity characterization. The results show that the lattice constant was reduced and the distortion became more significant after doping. Both the magnetic susceptibility and saturation magnetization were significantly enhanced, and the system was transformed from hard magnetic system to soft magnetic system. The electric polarization was also decreased with the doping.

    更新日期:2017-09-14
  • Study of critical behavior using the field dependence of magnetic entropy change in La0.7Sr0.3Mn1-xCuxO3 (x=0.02 and 0.04)
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    P.T. Phong, L.T.T. Ngan, L.V. Bau, P.H. Nam, P.H. Linh, N.V. Dang, In Ja Lee

    We report the magnetic properties and critical behavior of La0.7Sr0.3Mn1-xCuxO3 (x=0.02 and 0.04) perovskite manganites. Results of temperature-dependent magnetization show that the Curie temperature decreases from 360 K (x=0.02) to 356 K (x=0.03) with increasing Cu content. Field dependence of isothermal entropy change data is used to estimate the critical exponents, and the results satisfied the requirements of the scaling law. Calculated critical exponents are β=0.4641, γ=1.1623, and δ=3.546 for x=0.02, and β=0.4486, γ=1.2024, and δ=3.6805 for x=0.04. These results indicate that La0.7Sr0.3Mn1-xCuxO3 can be characterized by long-range mean-field behavior. Thus, the field dependence of magnetic entropy change can be effectively used in studying the critical behavior of magnetic materials.

    更新日期:2017-09-14
  • Cross-linking behavior and dielectric properties of SiCN precursor
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Xue Guo, Yurun Feng, Yu Liu, Xiao Lin, Yujun Zhang, Hongyu Gong

    The SiCN precursor was prepared by cross-linking process using polysilazane (PSZ) as raw materials. The cross-linking behavior and dielectric properties of SiCN precursor were analyzed. The results indicated that the main reactions during cross-linking process were double bond addition reaction, hydrosilylation reaction, dehydrogenation coupling reaction and transamination reaction. The SiCN precursor was made up of Si-C-N network structure and the main chemical bonds were Si-C, Si-N and C-C. The appropriate cross-linking temperature of SiCN precursor was 600 °C. Furthermore, the increasing content and crystallization degree of free carbon could improve the dielectric properties of SiCN precursor.

    更新日期:2017-09-14
  • Characterization of Calcination Temperature on a Ni-Substituted Lanthanum -Strontium-Zirconate Pyrochlore
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Daniel J. Haynes, Dushyant Shekhawat, David A. Berry, John Zondlo, Amitava Roy, James J. Spivey

    A lanthanum strontium zirconate pyrochlore material was substituted with Ni, and the effect of calcination temperature on important catalytic properties was evaluated. The introduction of the Ni into the pyrochlore decreased the BET surface as compared to non-Ni containing materials due to enhanced sintering. The presence of Ni dispersed in the precursor material produced oxygen vacancies which improved solid state diffusion of the pyrochlore cations, and lowered the onset of crystallization by almost 100 °C compared to the baseline material without Ni. Furthermore, only a small amount of Ni was found to be soluble in the structure up to 1000 °C, at which point almost no Ni occupies lattice positions in the pyrochlore crystal structure. The Ni was found to exsolve to the surface and grain boundary regions of the pyrochlore and reside on the surface as NiO. Heating to temperatures greater than 800 °C also led to the formation of a La2ZrNiO6 perovskite phase. Surface composition, as measured by XPS, showed a decrease in Ni concentration at the surface as the calcination temperature was increased. This was likely due to the formation of larger Ni particles with increasing temperature, as well as the migration of the Ni into the bulk through the formation of the La2ZrNiO6 phase. Temperature programmed reduction results showed that increasing the calcination temperature resulted in particle growth of the NiO and a weaker interaction with the pyrochlore surface, which made the NiO more reducible at lower temperatures. Multiple reduction-oxidation TPR/TPO cycles showed that the results were not reproducible from cycle-to-cycle for the lowest calcination temperature material (700 °C) due to an amorphous La-Zr-O phase initially present. However, materials calcined at all other temperatures showed an almost identical TPR/TPR profiles after the second cycle.

    更新日期:2017-09-14
  • Zirconia based feedstocks: influence of particle surface modification on the rheological properties
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    M.C. Auscher, R. Fulchiron, N. Fougerouse, T. Périé, P. Cassagnau

    Controlling the particle-matrix interface of filled systems is generally an essential challenge for reaching target characteristics. Herein, a simple method is described to characterize and optimize the filler surface chemistry in the case of zirconia feedstocks using stearic acid (SA) as a surfactant. Our technique involves contact angle measurements by the sessile drop method between water and thermally treated zirconia powders mixed with SA. It is shown that this is a powerful way to determine the optimum additive concentration and processing parameters. In addition, the effect of coated particles on the dynamic rheological behavior of the molten feedstock is investigated. Furthermore, the kinetics of the hydrophobization of the powder surface induced by esterification between the fatty acid and the adsorbed hydroxyls at the powder surface has been accurately followed.

    更新日期:2017-09-14
  • Recycling of spent Cu-based oxygen carriers into high-strength ceramic proppants
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Frantisek Kukurugya, Jef Bergmans, Ruben Snellings, Jeroen Spooren

    Chemical-looping combustion (CLC) technology can play a significant role in decreasing costs for CO2 capturing in the future. The technology relies on the use of an oxygen carrier (OC) material, which becomes a solid waste material after it is deactivated. The aim of this study was to verify the possibility to produce high-strength ceramic proppants from a spent Cu-based OC, consisting mainly of α-Al2O3 and a minor content of CuAl2O4. Experiments were carried out with both pure α-Al2O3 and a spent Cu-based OC delivered from a pilot CLC plant. Milling, granulation and sintering were the main process steps developed in the study. The results clearly demonstrated the technical feasibility to use a Cu-based spent OC as a raw material for producing high-strength ceramic proppants. After milling for 1 min., granulation and sintering at 1400 °C, ceramic particles with a compressive strength >100 MPa and a sphericity of 0.9 were obtained. Further increasing the sintering temperature to 1600 °C enabled to reach compressive strengths >150 MPa. At this sintering temperature the CuAl2O4 melted and separated from the solid ceramic spheres.

    更新日期:2017-09-14
  • The Cross-Disciplinary Emergence of 3D Printed Bioceramic Scaffolds in Orthopedic Bioengineering
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Hossein E. Jazayeri, Martin Rodriguez-Romero, Mehdi Razavi, Mohammadreza Tahriri, Karan Ganjawalla, Morteza Rasoulianboroujeni, Mohammad H. Malekoshoaraie, Kimia Khoshroo, Lobat Tayebi

    Over the past several decades, the implementation of bioceramics in orthopedic bioengineering has become increasingly profound. The resemblance of the material to bone histomorphology makes them favorable to use in tissue engineering schemes, in addition to the evidence that they exhibit osteoconductivity and that many manifest the appropriate mechanical strength. Moreover, the strategy to use the 3D bioprinting technique holds the potential to consistently manufacture commercializable scaffolds, tailored for diverse clinical applications with physicochemical property-dependent biodegradation rates, and usher in a new era of effective hard tissue fabrication. This review is the first of its kind in that it has thoroughly compiled the most recent studies on 3D printing of bioceramic scaffolds to treat bone defects and anomalies. Manuscripts were mostly chosen from the last decade, highlighting the novelty of the approach to regenerative orthopedic bioengineering via ceramic-based 3DP technologies. Likewise, in addition to the materials perspective present in the body of this work, tissue engineering scaffold requirements were explained as well as the incorporation of drug delivery schemes for localized drug administration and cargo release rates in pre-clinical studies.

    更新日期:2017-09-14
  • Nanograined Al2O3-ZrO2 (Y2O3) ceramics through pressureless sintering of powders with different degrees of crystallinity
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Xiqing Xu, Jiachen Liu, Mengmeng Zhuang, Anran Guo, Haiyan Du, Feng Hou

    In this work, Al2O3-ZrO2 (Y2O3) nanoceramics were prepared via pressureless sintering of powders with different degrees of crystallinity. It was demonstrated that, the crystallization of amorphous phase in starting powders highly enhanced the densification during sintering. When the crystal content was 25 vol%, the powders exhibited better sinterability than other powders, and they could be sintered into bulk nanoceramics with relative densities higher than 98% at 1400 °C and 1500 °C. The superior sinterability of C25 powders was due to the crystallization of amorphous phase promoted by the as-existed nanocrystalline powders as nucleation seeds. The obtained nanoceramic exhibited homogenously distributed ZrO2 and Al2O3 particles with grain size of about 450 nm, and displayed excellent mechanical property with Vickers hardness of 15.3 GPa, fracture toughness of 5.2 MPa·m1/2, and flexure strength of 1190 MPa. This work may provide new guidance for optimization in preparing bulk nanoceramics by managing the crystallinity of starting powders.

    更新日期:2017-09-14
  • Optimization of the tape casting slurries for high-quality zirconia substrates
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-14
    Qizheng Dong, Tianbin Zhu, Zhipeng Xie, Yao Han, Di An

    A cheap and environmental friendly non-aqueous tape casting process for preparing high density ZrO2 ceramic substrates was explored. A binary solvent mixture of ethanol and ethyl acetate -based formula was developed by using castor oil, polyvinyl butyral and dibutyl phthalate as the dispersant, binder and plasticizer, respectively. The influence of dispersant content, binder content and solid loading on the rheological properties of ZrO2 slurries was firstly investigated. It was found that the optimized formulation for dispersant, binder and solid loading was 1 wt.%, 4 wt.% and 60 wt.%, respectively. The flat, flexible and uniform green tapes with a thickness of 200~280 μm and high-quality including high bulk density, uniform pore distribution and low porosity were obtained. After drying and debinding, the green sheets were sintered at 1480℃ for 1 h, where the ZrO2 ceramics with a relative dense of 98% and a dielectric constant being 32 can be achieved. The sintered samples could satisfy the use requirement of the fingerprint identification cover plate.

    更新日期:2017-09-14
  • Characterization of plasma electrolytic oxidation coating on low carbon steel prepared from silicate electrolyte with Al nanoparticles
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-13
    Wenbin Yang, Weimin Liu, Zhenjun Peng, Baixing Liu, Jun Liang

    The plasma electrolytic oxidation (PEO) coatings were prepared on low carbon steel from silicate electrolyte without and with Al nanoparticles, respectively. The structure, composition, anti-wear and anti-corrosion properties of the PEO coatings were investigated. The results indicated that the Al nanoparticles in the silicate electrolyte turned into alumina during the PEO process and reduced the amount of iron oxides in the coating. The PEO coating prepared from silicate electrolyte with Al nanoparticles showed enhanced wear resistance due to the formation of alumina. Furthermore, the coating was characterized by sealed pores on the surface, different from the open pores on the surface of PEO coating prepared from silicate electrolyte without Al nanoparticles. The modified structure and the changed composition of PEO coating by introducing Al nanoparticles in the electrolyte significantly improved the corrosion resistance of the coating, demonstrated by the electrochemical corrosion and salt spray tests.

    更新日期:2017-09-13
  • Sintering behavior and microstructural evolution of the monodispersed β-gallium oxide micro-particles with different morphology and size
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-13
    Jing-Jing Shan, Chen-Hui Li, Jia-Min Wu, Jiang-An Liu, An-Nan Chen, Yu-Sheng Shi

    In this paper, the sintering behavior and microstructural evolution of as-prepared monodispersed β-Ga2O3 micro-ellipsoid particles (E-G), β-Ga2O3 micro-rods particles (R-G) and as-received commercial β-Ga2O3 particles (C-G) were investigated. The XRD analysis showed that the main peak (−202) of E-G and R-G ceramics sintered at elevated temperature, ascribed to the lowest surface energy of the (−202) crystal surface. The in-situ high temperature optical dilatometer analysis revealed that, compared with C-G, the monodispersed E-G and R-G had higher sintering activity with a more uniform particle size and a smaller aspect ratio and the densification temperature of as-prepared β-Ga2O3 was reduced by over 100 °C. The highest density of E-G, R-G and C-G ceramics were 5.96 g/cm3 sintered at 1400 °C, 5.98 g/cm3 sintered at 1450 °C and 5.89 g/cm3 sintered at 1550 °C, respectively. Differential densification and subsequent separation of the pores from the boundaries led to the lower density of C-G ceramics. Due to a higher sintering activity, E-G and R-G ceramics had larger grains than those of C-G ceramics sintered at the same temperature. Furthermore, the sintering temperature had an important effect on the microstructure and weight losses of sintered Ga2O3 ceramics. Finally, the high-density target obtained using Ga2O3 particles with uniform size as the raw materials exhibited promising industrial applications for optoelectronic devices.

    更新日期:2017-09-13
  • Molecular dynamics simulations for responses of nanotwinned diamond films under nanoindentation
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-13
    Cheng Huang, Xianghe Peng, Bo Yang, Yinbo Zhao, Henggao Xiang, Xiang Chen, Qibin Li, Tao Fu

    We performed molecular dynamics (MD) simulations for the responses of single crystal (SC) and nanotwinned (nt) diamond films under nanoindentation, respectively, aimed to uncover the effects of twin boundary (TB) and twin thickness (δ) on hardness (H) and the corresponding deformation mechanisms. We found the Hall-Petch type relationship between H and δ. We also found that the inelastic deformation of SC-diamond under indentation could mainly be attributed to the nucleation and propagation of <110>{111} dislocation loops. It showed that dislocation blockage and pile up at the TBs may induce additional hardening of the nt-diamond, while the softening of the material could be attributed to: (i) the formation and movement of the dislocation loops parallel with the surface, and (ii) the breakage of TBs, which may serve as new sites for dislocations nucleation.

    更新日期:2017-09-13
  • Analysis of granule fracture under biaxial compression
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-12
    Hiroshi Satone, Kenji Iimura, Tsubasa Teraoka, Taisuke Hanafusa, Shuhei Hisatani, Masashi Nishiwaki, Michitaka Suzuki

    In this study, the mechanism of granule fracture under biaxial compression was investigated through both experimental and simulation methods. The results of the experiment indicate that the fracture behavior differs depending on the number of compressional axes. The fracture load under the biaxial condition is smaller than that under the uniaxial condition because in the latter, the compressed granule can be deformed planarly, whereas in the former, the compressed granule can be deformed into only one axial direction that is not compressed. To investigate this phenomenon in detail, finite-element method (FEM) analysis was used to analyze the tensile stress inside granules. The results of the FEM simulation indicate that the dominant factor in fracture phenomenon is tensile stress at the center of granules. From these results, it will be possible to theoretically predict, without any complicated experiments, the likelihood of fracture in granules.

    更新日期:2017-09-12
  • Synthesis of boron and nitrogen-doped expanded graphite as efficient reinforcement for Al2O3-C refractories
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-12
    Qinghu Wang, Yawei Li, Ning Liao, Xiaofeng Xu, Shaobai Sang, Yibiao Xu, Guanghui Wang, Mithun Nath

    Boron and nitrogen doped expanded graphite (B-doped EG & N-doped EG) were synthesized for the first time by annealing the mixtures, obtained from the suspensions of expanded graphite (EG) with boric acid and urea, respectively. Afterwards, the doped EG were introduced into Al2O3-C refractories by partially replacing the graphite flake. Synthesized materials were characterized using SEM-EDS, XPS, XRD, TG-DSC and Raman Spectroscopy. Also, evaluation of various mechanical properties and oxidation resistance tests were conducted. Boron (B) and Nitrogen (N) were successfully introduced into the C skeleton via different C-B bonds (B4C, B-sub-C and BC2O) and C-N bonds (pyridine-N, amino-N and graphitic-N) respectively, maintaining the hexagonal graphitic lattice and lower reactivity. Compared to as-received EG, the B-doped EG and N-doped EG remained relatively intact structure in Al2O3-C refractories at high temperature due to their less defects and lower reactivity. Addition of B-doped EG and N-doped EG into Al2O3-C refractories showed improved mechanical properties such as modulus of rupture (CMOR), force, displacement and thermal shock resistance. Besides, the Al2O3-C specimens containing B-doped EG and N-doped EG exhibited significantly better oxidation resistance, which further promote the reinforcement effect of doped EG in Al2O3-C refractories during actual service condition.

    更新日期:2017-09-12
  • The influence of silica nanoparticles addition on the physical, mechanical, thermo-mechanical as well as microstructure of Mag-Dol refractory composites
    Ceram. Int. (IF 2.986) Pub Date : 2017-09-12
    Hassan Gheisari Dehsheikh, Salman Ghasemi-Kahrizsangi

    The high hydration potential of CaO and MgO phases restricted the application of Mag-Dol refractory composites. In this study, the impact of nano-silica (SiO2) addition on the physical, mechanical, thermo-mechanical as well as microstructure of Mag-Dol refractory composites is investigated. Mag-Dol compositions were prepared by using calcined dolomite and magnesite particles (micron, 0–1, 1–3, 3–5, and 5–8 mm), liquid resin, and 0, 0.5, 1, 1.5, 2, and 2.5 wt% nano SiO2 as additives. Specimens were heated up to 1650◦C for the 3 h soaking period. Fired specimens were characterized by physical (apparent porosity, bulk density, and hydration resistance), mechanical (cold crushing strength), and thermo-mechanical (flexural strength at 1200◦C) measurements. XRD and SEM/EDS analysis were done to study phases and microstructure analysis of the fired samples, respectively. Results showed that by adding up to 2.5 wt% nano-SiO2, due to the formation of CaO.MgO.2SiO2 (Diopside), 2CaO.MgO.2SiO2 (Akermanite), and CaO.MgO.SiO2 (Monticellite) phases, physical and mechanical properties were enhanced. But the highest flexural strength value is achieved for 1 wt% nano-SiO2 containing sample.

    更新日期:2017-09-12
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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