Variable range hopping conduction in fully dense calcium cobalt oxide textured ceramics Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 Nidhi Puri, Ram P. Tandon, Ajit K. Mahapatro
Low temperature synthesis of pure phase TaB2 powders and its oxidation protection modification behaviors for Si-based ceramic coating in dynamic oxidation environments Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 Xuanru Ren, Lifeng Wang, Peizhong Feng, Ping Zhang, LiTong Guo, Xiaojun Sun, Hongsheng Mo, Ziyu Li
To reveal the generation mechanisms of the Ta-Si-O glass ceramics layer in dynamic oxidation environments, a 40 wt%TaB2-SiC coating was prepared by liquid phase sintering method. To obtain pure phase TaB2 powders at lower temperature (1500 °C), excessive B2O3 powders were added in raw materials to eliminate the TaC byproduct phase. The hexagonal pure phase TaB2 powders own average particle size of about 386 nm. During the TGA dynamic oxidation tests, after the modification of 40 wt% TaB2, the initial weight loss temperature of the sample delayed by about 48%, while the weight loss percentage and rate in fastest weight loss zone decreased by about 61% and 53%, respectively. During oxidation, the generated Ta-oxides were peeled and carried away by the formed fluid SiO2 glass layer to form “Ta-oxides halation” at first, which results the dissolution of Ta-oxides in the SiO2 glass, thus forming the Ta-Si-O glass ceramics with dendritic structure. With the spread of the SiO2 glass layer and growth of the Ta-Si-O dendrite, the Ta-Si-O glass ceramics gradually cover on the surface of the SiO2 glass layer, forming the structure of Ta-Si-O/SiO2 double glass layer that is capable of sealing and arresting of microcracks.
Tailoring Interfacial Interaction through Glass Fusion in Glass/Zinc-Hydroxyapatite Composite Coatings on Glass-Infiltrated Zirconia Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 Kumaresan Sakthiabirami, Van Thi Vu, Ji Won Kim, Jin Ho Kang, Kyoung Jun Jang, Gye Jeong Oh, John G. Fisher, Kwi Dug Yun, Hyun Pil Lim, Sang Won Park
In the current study, the biocompatibility and mechanical characteristics of glass-infiltrated zirconia were improved via a simple composite coating made of Zn-doped hydroxyapatite (ZnHA) ceramic and a silicate-based glass. During thermal treatment, significant reaction and crystallization occurred and some of the ZnHA was transformed into β-tricalcium phosphate, calcium oxide phosphate, and calcium zirconium oxide. Moreover, the glass crystallised into a sodium calcium aluminium silicate phase. The mechanical properties were investigated and the results indicated that the amount of glass in the composite and in the glass-infiltrated zirconia layer strongly affected the flexural strength and adhesion of the coating layer. The composite coatings on the glass-infiltrated zirconia displayed better mechanical properties than the pure ZnHA coating due to the newly formed crystalline phases. Murine pre-osteoblastic (MC3T3-E1) cells adhered to and spread well on the composite coating surfaces. The cell viability results revealed that the glass/ZnHA composites demonstrated a superior bioactivity of osteoblast cells compared to uncoated zirconia. These results show that the glass/ZnHA composites on the glass-infiltrated zirconia structure are suitable for use as hard tissue implant coatings due to their morphological and mechanical stability and enhanced bioactivity to pre-osteoblastic cells.
Ionic conduction and dielectric properties of yttrium doped LiZr2(PO4)3 obtained by a Pechini-type polymerizable complex route Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 C.R. Mariappan, P. Kumar, A. Kumar, S. Indris, H. Ehrenberg, G.V. Prakash, R. Jose
We report on the ion transport properties of Li1+xZr2-xYx(PO4)3 (0.05 ≤ x ≤ 0.2) NASICON type nanocrystalline compounds prepared through a Pechini-type polymerizable complex method. Structural properties were characterized by means of powder X-ray diffraction, Raman spectroscopy and electron microscopy with selected area electron diffraction. Impedance spectroscopy was utilised to investigate the lithium ion transport properties. Y3+ doped LiZr2(PO4)3 compounds showed stabilized rhombohedral structure with enhanced total ionic conductivity at 30 °C from 2.87 × 10−7 S cm−1 to 0.65 × 10−5 S cm−1 for x=0.05 to 0.20 respectively. The activation energies of Li1+xZr2-xYx(PO4)3 show a decreasing trend from 0.45 eV to 0.35 eV with increasing x from 0.05 to 0.2. The total conductivity of these compounds is thermally activated, with activation energies and pre-exponential factors following the Meyer-Neldel rule. The tanδ peak position shift to the high-frequency side with increasing yttrium content. Scaling in AC conductivity spectra shows that the electrical relaxation mechanisms are independent of temperature.
Electrical characterization of BaTiO3 and Ba0.77Ca0.23TiO3 ceramics synthesized by the proteic sol–gel method Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 D.V. Sampaio, M.S. Silva, N.R.S. Souza, J.C.A. Santos, M.V.S. Rezende, R.S. Silva
In this work, we introduce a simple, low-cost, and ecofriendly method for producing barium titanate (BaTiO3–BT) and barium calcium titanate (Ba0.77Ca0.23TiO3–BCT) powders. The synthesis was performed by using a proteic sol–gel route which use coconut water in the polymerization step of the metallic precursor. We investigated the effects of the processing parameters with the density, microstructure, and (di)electric properties as sample quality indicators. The sintered ceramics exhibit single crystalline phase, relative density of 95%, a homogeneous microstructure, and an average grain size of 4 μm. The respective dielectric constants of 1200 (BT) and 700 (BCT), measured at room temperature, and the activation energy values for the conductive process are according to those reported in the literature for conventionally prepared ceramics.
Hydrothermal-assisted synthesis of surface aluminum-doped LiCoO2 nanobricks for high-rate lithium-ion batteries Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Shuai Hu, Chunhui Wang, Ling Zhou, Xifeng Zeng, Li Shao, Jun Zhou, Chunxian Zhou, Chenghuan Huang, Xiaoming Xi, Lishan Yang
Effects of strontium/lanthanum co-doping on the dielectric properties of CaCu3Ti4O12 prepared by reactive sintering Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Rodrigo Espinoza-González, Samuel Hevia, Álvaro Adrian
The extremely high dielectric constant of the cubic perovskite CaCu3Ti4O12 (CCTO) has attracted increasing attention for a variety of capacitive elements in microelectronic device applications. In this research, the influence of Sr and La replacing Ca and Cu, respectively, to simultaneously controlling the intrinsic properties of grain boundaries in a co-doped CCTO ceramic has been investigated. The preparation was done using high purity compounds milled and mixed by mechano-synthesis and further consolidated by reactive sintering without calcination. Characterization by XRD confirmed the formation of single-phase CCTO ceramic and a residual amount CaTiO3. The microstructure and composition analyzed by SEM/EDX showed a smaller grain size for the co-doped CCTO. Impedance measurements indicated the smallest dielectric loss for the co-doped ceramics compare to pure and single-doped CCTO, while reaching a higher dielectric permittivity than single-doped ceramics. The CCTO-SrLa sample also showed high thermal stability of the dielectric permittivity between 100 and 470 K, and the lowest loss between 200 and 300 K. This behavior was attributed to the lower bulk resistance exhibited by the co-doped sample.
Reduction Kinetics of Undoped and Aluminum Titanate (Al2TiO5) Doped NiO-YSZ Solid Oxide Fuel Cell Anodes Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Madisen McCleary, Roberta Amendola
Undoped and 1–10 wt.% aluminum titanate, Al2TiO5, (ALT) doped nickel oxide/yttria-stabilized zirconia (NiO/YSZ) anode materials were kinetically evaluated during isothermal (800 °C) H2 reduction (5% H2–95% N2 and pure H2 gas). It was found that the two parameter Avrami-Erofe’ev model (AEn) was the most successful in representing reduction kinetics. The reduction mechanisms have been identified as the formation and growth of nuclei and is maintained after aluminum titanate, Al2TiO5, (ALT) doping and when the H2 concentration in the gas flow is increased. ALT doped samples result in the formation of NiAl2O4; which, when present in sufficient amounts, slowly reduces causing a shift of the model from the experimental data. This phenomenon has been correlated, through microstructural evaluation, to the formation of Ni nanoparticles. In all investigated cases, the reduction kinetics of the system was accelerated when the H2 concentration was increased from 5% to 100%.
Investigation of thermoluminescence and kinetic parameters of gamma ray exposed LiF: Sm3+, Eu3+ Nanophosphors for Dosimetric applications Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Arun Kumar, A.K. Sharma, R. Dogra, M. Manhas, Sandeep Sharma, Ravi Kumar
Thermoluminescence (TL) properties of LiF: Sm3+ (0.05 mol%) co-doped with Eu3+ (0.02, 0.04, 0.06, 0.08 mol %) nanophosphor for the applications of TL dosimetry have been studied. The nanophosphors have been synthesized by chemical co-precipitation method at 8 pH value. The phase purity of the prepared samples has been confirmed by using X-ray diffraction (XRD) data. The XRD peaks broadening revealed the formation of the nanostructure, complemented by the TEM image. For TL studies, the samples have been irradiated with gamma rays using 6°Co source in the irradiation dose range of 0.1kGy to 30kGy. In gamma exposed samples, the TL glow curve consists of single glow peak at 410 K and three shoulder peaks at 475 K, 550 K and 632 K. The dosimetry properties such as the effects of exposure doses, heating rates and fading characteristics have also been studied. The kinetic parameters such as activation energy (E), the frequency factors (s) and order of kinetic (b) of the glow curves have also been calculated by using Chen's peak shape method. The linear behavior of TL intensity with radiation doses and low fading shows that the LiF: Sm3+, Eu3+ Nanophosphor is a potential candidate for dosimetry applications.
Processing, properties and applications of highly porous geopolymers: a review Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Chengying Bai, Paolo Colombo
Geopolymers, possessing a semi-crystalline three-dimensional inorganic network generated by the dissolution and reaction of a solid alumino-silicate source with an activating solution, have attracted increasing attention from both academia and industry because of their unique and favorable characteristics. This review deals with the synthesis, characterization and potential applications of porous geopolymers, realized through different processing routes. Firstly, the processing approaches are divided into five categories: (i) Direct foaming, (ii) Replica method, (iii) Sacrificial filler method, (iv) Additive manufacturing, and (v) Other methods. Their microstructure, porosity and properties are compared and discussed in relation also to the different processing routes. This review highlights the fact that porous geopolymers are promising low-cost candidates for technologically significant applications such as catalyst supports or membranes, filtration of liquid or gases, adsorption and insulation. This review aims at summarizing the main published results and fostering further investigations into developing innovative ways to generate components with improved properties.
Rectangular shaped zinc oxide nanoparticles: Green synthesis by Stevia and its biomedical efficiency Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Mehrdad Khatami, Hajar Q. Alijani, Hossein Heli, Iraj Sharifi
Fabrication and characterization of nanostructured hydroxyapatite coating on Mg-based alloy by high-velocity oxygen fuel spraying Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Marzieh Mardali, Hamidreza Salimijazi, Fathallah Karimzadeh, Berengere J.C. Luthringer-Feyerabend, Carsten Blawert, Sheyda Labbaf
Magnesium alloys are currently being investigated in orthopedic applications due to their biodegradability and mechanical properties. However, sometimes these benefits are limited by their high corrosion rate in the physiological environment before healing of damaged bones. A large number of recent researches in this field have been dedicated to the control of magnesium corrosion rate by surface protection using new and advanced coatings. In this work, hydroxyapatite powders were coated on the anodized Mg-based alloy substrates by using high velocity oxy-fuel (HVOF) spraying. Increasing of the bioactivity and reduction of the released hydrogen gas during corrosion of the substrate were two main objects of this work. Phase formations were characterized by X-ray diffraction (XRD). It was found that around 96% of the phases formed were hydroxyapatite. The amounts of hydrogen gas released during magnesium corrosion tests in the simulated body fluid (SBF) were measured to evaluate the corrosion resistance of the coated samples. Hydroxyapatite (HA) coating reduced the hydrogen evolution from 100 per cm2 ml to about 15 per cm2 ml after 29 h of immersion.
A novel oxidation protective SiC-ZrB2-ZrSi2 coating with mosaic structure for carbon/carbon composites Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Lei Zhou, Qiangang Fu, Caixia Huo, Yu Wang, Mingde Tong
An oxidation protective SiC-ZrB2-ZrSi2 coating with mosaic structure was designed to improve the oxidation resistance of carbon/carbon composites by a combined method of hydrothermal electrophoretic deposition and pack cementation. The phase composition, microstructure, thermal shock resistance and oxidation protective ability of the coating were investigated. Results show that the as-prepared SiC-ZrB2-ZrSi2 coating was dense and crack-free. After 50 thermal cycles between 1773 K and room temperature, the weight gain of the coated samples was 15.2 g m−2. The weight loss of the coated samples was only 15.6 g m−2 after oxidation in air at 1773 K for 580 h. The good thermal shock resistance and oxidation protective ability of the coated samples were attributed to the synergetic effect of the glass layer protection, compressive stress restraint and pinning role of ZrSiO4 inlaid phase.
Optimization of mechanical and tribological properties of carbon fabric/resin composites via controlling ZnO nanorods morphology Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Dan Luo, Jie Fei, Chao Zhang, Hejun Li, Lijie Zhang, Jianfeng Huang
The multi-scale reinforcements of ZnO nanorods/carbon fabric with different morphologies were obtained using a simple water bath method via controlling the concentration of growth solution for a new application in wet friction materials. The ZnO nanorods/carbon fabric were characterized via X-ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectra. As a result, the ZnO nanorods/carbon fabric/resin composite (sample CP3) possesses the maximum bending and tensile strength of 62.7 MPa and 170.0 MPa, which increases by 40.2% and 59.1% compared with that of bare carbon fabric/resin composite due to the best mechanical interlocking and chemical adhesion at the interfacial region of the composite. Meanwhile, the wear rate of the sample CP3 decreases obviously by 81.5% together with stable friction coefficient under various friction condition. From view point of material design, it is necessary to control the morphologies of ZnO nanorods to optimize mechanical and tribological properties of ZnO nanorods/carbon fabric/resin composites.
Enhanced mechanical properties of 3 mol% Y2O3 stabilized tetragonal ZrO2 incorporating tourmaline particles Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Yanjun Song, Dongbin Zhu, Jinsheng Liang, Xiaoxu Zhang
The current study reports on the improvement of mechanical properties of 3 mol% Y2O3 stabilized tetragonal ZrO2 (3Y-TZP) by introduction of tourmaline through ball milling and subsequent densification by pressureless sintering at 800, 1200, 1300, 1400 °C. Findings demonstrate that no matter which sintering temperature the 3Y-TZP ceramic containing 2 wt% tourmaline reach a maximum value in flexural strength and fracture toughness as compared to other composite ceramics. As the tourmaline content is 2 wt% and the sintering temperature is 1300 °C, the flexural strength and fracture toughness of the composite ceramics are the highest, increases of 36.2% and 36.6% over plain 3Y-TZP ceramic respectively. The unique microstructure was systematically investigated through X-ray diffraction, scanning electron microscopy, energy dispersive spectrum, and flourier transform-infrared. The strengthening and toughening mechanism of tourmaline in 3Y-TZP ceramic were also discussed.
Magnetocaloric effect in La1-xSrxCoO3 undergoing a second-order phase transition Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Phan The Long, T.V. Manh, T.A. Ho, Q.V. Dong, P. Zhang, S.C. Yu
We have prepared rhombohedral La1-xSrxCoO3-δ (x = 0.2–0.5) compounds with a mass density ρ ≈ 5.5 g/cm3. Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (ΔSm) and relative cooling power (RCP), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the ΔSm magnitude is maximum (ΔSmax) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field (H) magnitude and Sr content (x). For H = 50 kOe, |ΔSmax| can be tuned in the range of 1.6~2.7 J/kg·K, corresponding to RCP values of 89~141 J/kg. Among the studied La1-xSrxCoO3-δ samples, the samples with x = 0.3–0.5 have the largest |ΔSmax| values. If combining these samples as MC blocks in refrigeration application, the working temperature range of a cooling device could range from 204 to ~280 K, with |ΔSmax| stable at ~2.6 J/kg·K and RCP ≈ 198 J/kg. We have also assessed the phase-transition type and magnetic order and found La1-xSrxCoO3-δ undergoing a second-order phase transition. Magnetic order tends to change from the long-range type to the short-range one when x varies from 0.2 to 0.5. This is in good agreement with the results obtained from the analysis of critical behavior.
A study on the wetting behavior of liquid iron on forsterite, mullite, spinel and quasi-corundum substrates Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Hyun Sik Park, Youngjae Kim, Sookyung Kim, Taehee Yoon, Yelim Kim, Yongsug Chung
Wetting characteristics of liquid iron on magnesia, alumina and silica mixture substrates were studied by sessile drop experiments. Chromium-free forsterite, mullite, spinel and quasi-corundum phases were selected as alternative refractories in MgO-Al2O3-SiO2. Morphological changes of molten electrolytic iron on the oxide substrates were investigated via apparent contact angle measurements. The results showed that the wetting behavior was significantly influenced by FeO compounds that were formed via oxidation of the liquid iron. Morphologies of the reacted layer were studied by Scanning Electron Microscope (SEM)/EDX analysis. The ternary phases FeO-MgO-SiO2 and FeO-Al2O3-SiO2 improved the wetting of liquid iron on the forsterite and mullite substrates by providing liquid phases at solid (refractory)–liquid (iron) interfaces. However, corrosion by liquid iron was significantly inhibited at spinel phase which did not feature FeO based compounds at the interface. Quasi-corundum (10MgO-25SiO2–65Al2O3) showed a much enhanced resistance to liquid iron compared to forsterite or mullite refractories.
Performance of Si3N4/(W, Ti)C graded ceramic tool in high-speed turning Iron-based superalloys Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Xianhua Tian, Jun Zhao, Xinya Wang, Haifeng Yang, Zhongbin Wang
A Si3N4/(W, Ti)C graded nano-composite ceramic tool was fabricated and its performance in high speed turning iron-based alloys GH2132 was investigated compared with homogeneous and commercial ceramic tools. The chip morphology, cutting forces, cutting temperature, tool life and failure mechanisms and machined surface roughness were recorded and analyzed. The results showed that with the increasing cutting speed the resultant cutting force shows a tendency to first increase and then decrease while the cutting temperature increases gradually. Straight continuous chips, bending continuous chips, twist continuous chips and snarled chips form in turn. Saw-tooth chips tend to form when the cutting speed is more than 200 m/min. The graded tool shows longer tool life especially at the cutting speed of 150 and 200 m/min compared with the homogenous and commercial ceramic tools. Tool failure modes mainly include grooving on the rake face, notching on the flank face, abrasion and adhesion. The grooving on the rake face tends to decrease while notching on the flank face tends to increase as cutting speed increases. Surface roughness of the machined iron-based super-alloys is relatively high due to the serious adhesion. Better surface roughness can be got using the graded tool.
Effects of chemical etching on structure and properties of Y0.5Gd0.5Ba2Cu3O7-z coated conductors Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 M.J. Wang, W.T. Wang, L. Liu, F. Scurti, Y.D. Xia, B.L. Huo, X. Yang, Y. Zhao
Corrosion resistance is a crucial property to achieve successful superconducting joints of Y0.5Gd0.5Ba2Cu3O7-z (YGdBCO) coated conductors (CCs). Cu and Ag metallic layers need to be fully removed from the area of conductor to be joint to allow for a superconducting path across the joint. Therefore, when using a wet etching process to remove the metallic layers, the joint performance can be significantly influenced by the etching conditions. The effects of chemical etching with ammonia water and hydrogen peroxide mixture on crystal structure, surface microstructure and critical current (Ic) of YGdBCO CCs were systematically investigated. We found the set of etching parameters that does not affect conductor performance, leaving the Ic of the YGdBCO conductor unchanged upon etching. However, when the etching conditions are not optimal, decrease in Ic was found and the underlying reasons driving the degradation were investigated. Raman spectroscopy and XRD analysis indicated that the reduced Ic is mainly due to oxygen deficiency in the YGdBCO crystal lattice.
Influence of Na & F doping on microstructures, optical and magnetic properties of ZnO films synthesized by sol-gel method Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Huan Yuan, Ming Xu
Undoped, Na-doped, and Na-F codoped ZnO films were synthesized using sol-gel method. Na+ and F+ ions were used as two different dopants that yielded a synergistic doping effect. This effect was measurable using XRD, accompanied by a redshift in the optical bandgap from 3.284 to 3.261 eV in ZnO, ZnO-F, and ZnO-Na-F thin films, respectively. We then studied the resulting photoluminescent changes, which were attributed to O-related defects. Ferromagnetism measurements revealed that magnetic orderings decreased significantly with F doping. However, increased Na doping enhanced the oxygen-vacancy mediated ferromagnetic state.
Preparation of high strength porous mullite ceramics via combined foam-gelcasting and microwave heating Ceram. Int. (IF 2.986) Pub Date : 2018-05-26 Lei Han, Xiangong Deng, Faliang Li, Liang Huang, Yuantao Pei, Longhao Dong, Saisai Li, Quanli Jia, Haijun Zhang, Shaowei Zhang
Porous mullite ceramics with improved mechanical strength were fabricated by using a combined foam-gelcasting and microwave firing method at 1373–1523 K for 30 min. The porous mullite prepared at 1373 K contained 76.6% porosity, and exhibited flexural and compressive strength values as high as respectively 3.8 and 15.2 MPa. Moreover, its thermal conductivity still remained as low as 0.269 W/(m K). These values were comparable or even superior to those of porous mullite ceramics prepared previously via conventional heating at much higher temperatures (1573–1873 K), indicating that it is more beneficial to use microwave heating instead of conventional heating to make high quality porous mullite ceramics at a much lowered temperature.
Enhanced energy storage properties of BaO-K2O-Nb2O5-SiO2 glass ceramics obtained through microwave crystallization Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 Jia Tian, Shujian Wang, Ke Yang, Jingran Liu, Jiwei Zhai, Bo Shen
BaO-K2O-Nb2O5-SiO2 (BKNS) glass ceramics were prepared by microwave crystallization of transparent glass matrices and the effects of microwave treatment temperature on their dielectric performances, phase structure, microstructure and breakdown strength (BDS) were investigated systematically. X-ray diffraction results suggested that microwave treatment had no significant influence on the type of precipitated phases. The microstructure of the glass ceramics was remarkably optimized via microwave treatment. The dielectric constant and breakdown strength of microwave-treated samples were significantly improved as compared with conventional-heated samples at the same temperature. The maximum theoretical energy storage density of microwave-treatment samples at 750 °C reached 12.7 J/cm3, which was larger than that of the conventional-heated samples (8.6 J/cm3).
Template-Free Rapid Sonochemical Synthesis of Spherical α-MnO2 Nanoparticles for High-Energy Supercapacitor Electrode Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 S. Sankar, Akbar I. Inamdar, Hyunsik Im, Sejoon Lee, Deuk Young Kim
Novel self-reinforcing ZrO2–SiO2 aerogels with high mechanical strength and ultralow thermal conductivity Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Xianbo Hou, Rubing Zhang, Baolin Wang
Novel self-reinforcing ZrO2–SiO2 aerogels with high mechanical strength and ultralow thermal conductivity are fabricated by impregnating hydrolyzed ZrO2–SiO2 sol into wet gel matrix and drying. The ZrO2–SiO2 sol fills the macropores and defects of ZrO2–SiO2 aerogel matrix generating during the gelation process, which contributes to the improvement of the mechanical properties of the ZrO2–SiO2 aerogel matrix. The mechanical and thermal properties of the as-prepared ZrO2–SiO2 aerogel are investigated and discussed. The results show that the mechanical strength of the self-reinforcing aerogels obviously increases from 0.51 to 3.11 MPa with the increase of impregnation times, while the thermal conductivity of the aerogels slightly increases from 0.0235 to 0.0306 W·m−1K−1. The novel self-reinforcing ZrO2–SiO2 aerogel could have interesting applications in aerospace and energy because of its outstanding mechanical and thermal properties.
Synthesis and characterization of reaction-bonded calcium alumino-titanate-bauxite-SiC composite refractories in a reducing atmosphere Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Jianwei Chen, Huizhong Zhao, Jun Yu, Han Zhang, Zhengkun Li, Jiaqin Zhang
To take full advantage of the excellent properties of CA6 present in calcium alumino-titanate (CAT) and reduce the formation of the low melting point phase (anorthite), CAT-bauxite-SiC composite refractories were fabricated under buried sintering in order to achieve low thermal expansion, superior high-temperature performance, and increased alkali resistance. Furthermore, the corrosion mechanism of K vapor was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that CA6 present in CAT can be partially retained and the hot strength of CAT-bauxite-SiC composites slowly decreases when the amount of CAT added is less than 21.6 wt%. The cold strength and bulk density decrease with the CAT content, and the residual ratio of MOR firstly decreases and subsequently increases with the CAT content. For the specimens with CAT additions, 43.2 wt% CAT results in the highest volume expansion at high temperatures. It is proposed that the corrosion mechanism of CAT aggregates under buried sintering is as follows: 1) K vapors penetrate into the CAT with high CA6 content through the lamellar CA6 gap and deposit on the inner regions of CAT; and 2) K vapors react with corundum and anorthite present in CAT and cause the microstructural destruction of CAT due to a decrease in the amount of the Al2O3-CaO-SiO2 liquid phase in the CAT. The alkali resistance of the CAT-bauxite-SiC composites decreases as the CAT content increases, which is attributed to poor sintering densification and high apparent porosity.
Bandgap engineering of Gd0.8Ca0.2BaCo2O5+δ double perovskite for photocatalysis applications Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Rong Zhang, Shanshan Hu, Chunhua Lu, Zhongzi Xu
To design the material rationally, we predict the effect of oxygen vacancy on the material bandgap and electron state density based on the first principle density functional theory. Crystal structure, electronic properties, as well as the oxidation and reduction states of Gd0.8Ca0.2BaCo2O5+δ oxides were studied by GGA-PBE+U calculation. By changing one oxygen atom in the Gd-O0.5 plane of supercell, Gd0.8Ca0.2BaCo2O5.25 and Gd0.8Ca0.2BaCo2O5.75 were created. And they show half-metallic and metallic properties respectively, which is related to the strong electronic correlations for 3d orbitals of Co. Calculation results of partial density of states suggest that O-2p and Co-3d orbits have a great effect on the band gap of Gd0.8Ca0.2BaCo2O5.5, and the location of cobalt may be an active site. Besides, Gd0.8Ca0.2BaCo2O5+δ were prepared and annealed in atmosphere to regulate the oxygen vacancy content. Hence, a deep and systematic study on Gd0.8Ca0.2BaCo2O5+δ was conducted based on theoretical calculations and experiments, including crystal structure, electron distribution and oxygen vacancy. Differing from the conventional doping modification to adjust the electronic energy band structure, this work is dedicated to synthesizing the stable and efficient materials from the theoretical design, which providing a new feasible thought for the efficient and stable material design.
MgO fumes as a potential binder for in situ spinel containing refractory castables Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 A.P. Luz, L.B. Consoni, C. Pagliosa, C.G. Aneziris, V.C. Pandolfelli
MgO is pointed out as an alternative binder for refractory materials, mainly for systems where the presence of CaO might not be desired. Selecting the most suitable magnesia source is an important step as its purity and reactivity should influence the hydration reaction, leading to binding effect or cracks. This work investigated the design of vibratable high-alumina compositions bonded with MgO fumes [which is a very fine powdered oxide (d < 3 μm) resulting from the production process of electrofused magnesia] and/or dead-burnt magnesia (d < 212 μm). Acetic and formic acids were added to the castables during their processing steps in order to adjust the density of active sites for Mg(OH)2 formation and control the crystal growth of this phase. The green mechanical strength and thermomechanical performance (cold and hot mechanical strength, thermal shock, refractoriness under load, corrosion, etc.) of designed MgO-bonded compositions were analyzed. Improved green mechanical strength and crack-free samples were obtained when adding up to 6 wt.% of MgO fumes to the refractories and processing them with aqueous solutions with 3 wt.% of formic acid. The compositions with 6 wt.% of magnesia fumes resulted in samples with flexural strength in the range of 12.0 MPa after curing at 50 °C/24 h and similar green mechanical strength (12.9 MPa) as the ones bonded with 4.0 wt.% of calcium aluminate cement after drying at 110 °C for 24 h, which highlights the great potential of this MgO source. Despite the enhanced green mechanical strength, alumina-based castables containing 6 wt.% of MgO (fumes, dead-burnt or their blend) showed low mechanical strength at intermediate temperatures and high linear expansion, as a consequence of the in situ spinel phase formation above 1200 °C. Thus, better densification, improved HMOR, thermal shock resistance and corrosion behavior were obtained for the castables prepared with less MgO fume contents.
Color-tunable properties based on complex anion substitution in Eu2+ doped Ca8Sc2(PO4)6-y(SiO4)1+y phosphor Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Fengping Ruan, Degang Deng, Hua Yu, Ming Wu, Bowen Chen, Shiqing Xu, Ruoshan Lei
We synthesized and investigated the effect of Eu2+ ions doping in a novel phosphor-silicate Ca8Sc2(PO4)6(SiO4) phosphor. The structure and photoluminescence properties were determined by X-ray powder diffraction Rietveld refinement, diffuse reflection spectra, emission-excitation spectra, decay curves and temperature dependence spectra. The phosphors showed an asymmetric broad-band blue emission (Eu2+) with peak at 470 nm. Furthermore, we presented the Ca7.96Sc2(PO4)6-y(SiO4)1+y: 0.04Eu2+ phosphors by co-substituting [Eu2+-Si4+] for [Ca2+-P5+], and different behaviors of luminescence evolution in response to structural variation were verified among the series of phosphors. The results were attributed to the presence of multi Ca2+ sites, resulting in the mixing of blue and green emissions for Eu2+ ions. The complex anion substitution of [PO4]3- by [SiO4]4- induced an increased crystal field splitting of the Eu2+ ions, which caused a decrease in emission energy from the 5d excited state to the 4 f ground state and a resultant red-shift from 470 nm to 520 nm. All the properties indicated that the Ca8Sc2(PO4)6(SiO4): Eu2+ phosphors have potential application for color-tunable WLEDs.
Synthesis of Mn-CeOx/Cordierite Catalysts Using Various Coating Materials and Pore-forming Agents for Non-methane Hydrocarbon Oxidation in Cooking Oil Fumes Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Honghong Yi, Yonghai Huang, Xiaolong Tang, Shunzheng Zhao, Fengyu Gao, Xizhou Xie, Jiangen Wang, Zhongyu Yang
Cooking oil fumes (COFs) as an important source of volatile organic compounds (VOCs) in metropolitan areas is poisonous to the environment and human health, and the removal rate of Non-methane Hydrocarbon (NMHC) in COFs was used to verify the activity of catalysts made to depurate COFs. The textural properties of cordierite are limitation to the catalyst's performance. Therefore, in this paper, coating the cordierite to improve its surface properties was investigated. The experiment results and characterization data revealed that TiO2 was a better coating material because of coating on TiO2 can improve the surface morphology better than that of Al2O3. The SEM and BET data of the materials synthesized with different content of CTAB showed that 10 wt% additive amount of pore-forming agent had a better textural properties than other additive amount of pore-forming agents. It is clear that the SBET and DV of the catalysts were significantly increased, and the catalyst exhibited smaller particle size and more developed pore structure after ultrasonic treatment which proving that ultrasound can enhance the catalyst's catalytic activity. It is obviously that the catalyst synthesized with CTAB had best pore structure and Mn4Ce1/Ti/NC-CTAB-U exhibited the best performance for catalytic combustion of NMHC with the removal rate was 93.6% at 400°C.
Ag containing polydopamine coating on a melt-derived bioactive glass-ceramic: effect on surface reactivity Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 R. Tejido-Rastrilla, G. Baldi, A.R. Boccaccini
We have synthesized a silicate bioactive glass-ceramic (BGC1) in the system SiO2-CaO-Na2O-P2O5-K2O-MgO-CaF2 which was used to fabricate pellets by powder compaction and sintering. The surface of BGC1 pellets was coated with polydopamine by using a simple immersion method. Silver nanoparticles were then deposited onto the surface of polydopamine modified pellets in order to confer antibacterial properties. The biomineralization ability was tested by soaking the samples in simulated body fluid (SBF). Results showed the successful deposition of both polydopamine and silver nanoparticles on the bioactive glass-ceramic surface. In addition, the formation of a hydroxyapatite layer (HA) on the surface of the samples after soaking them in SBF was confirmed. The kinetics of HA formation was minimally reduced by the presence of polydopamine.
Microstructure, conductivity and mechanical properties of calcia stabilized zirconia ceramics obtained from nanosized precursor and reduced graphene oxide doped precursor powders Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Olga Yu. Kurapova, Oleg V. Glumov, Ivan V. Lomakin, Sergey N. Golubev, Mikhail M. Pivovarov, Julia V. Krivolapova, Vladimir G. Konakov
In the work 12CaO-88ZrO2 (12CSZ, mol.%) ceramics was manufactured both from nanopowder, obtained via cryochemical technique, and composite precursor 12CSZ+0.25 wt.% rGO (reduced graphene oxide). Via SEM, XRD and Raman spectroscopy the detailed investigation of the effect of the precursor type and intermediate processing on the microstructure and electrical conductivity of ceramics was carried out. It was shown that rGO is completely removed during the annealing at 1550 °C for 3 hours in air with no effect on the high ionic conductivity of ceramics. The use of nanosized powder and the additional processing step results in vacuum dense solid electrolytes characterized by well-formed cubic zirconia based solid solution, thin discontinuous grain boundaries and rather high ionic conductivity. The addition of rGO leads to slight microhardness (HV) decrease comparing to ceramics manufactured from the nanosized precursor. As a result, a new technique for zirconia based solid electrolytes having both high electrical conductivity at high temperatures and sufficient mechanical properties was suggested.
Structure, mechanical properties and thermal stability of Ti1-xSixN coatings Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 Fei Pei, Yu X. Xu, Li Chen, Yong Du, Hou K. Zou
Ti1-xSixN coating is a promising candidate for wear resistant applications due to their super-hardness and high thermal stability. Here, we explored the structure, mechanical properties and thermal stability of Ti1-xSixN (x = 0, 0.13, 0.17 and 0.22) coatings with single cubic structure. Monolithically grown Si-containing Ti1-xSixN coatings, which are Si-solution in TiN for x = 0.13 and 0.17, reveal a high hardness of 39.4 ± 0.67 and 40.6 ± 0.72 GPa, respectively. Then Ti1-xSixN transforms into a nanocomposite structure consisting of cubic Ti(Si)N nanocrystallite enveloped by the amorphous SiNx tissue phase for x = 0.22, which exhibits a high hardness of 40.0 ± 0.6 GPa. However, increasing of Si content leads to a significant increase in compressive stress from −0.63 GPa for x = 0 to −3.78 GPa for x = 0.13 to −4.54 GPa for x = 0.17 to −5.51 GPa for x = 0.22. The hardness of Ti1-xSixN coatings can be maintained up to ~1000 °C due to the suppressed grain growth, and then decreases for further elevated annealing temperature, whereas the TiN coating exhibits a continuous drop in hardness towards its intrinsic value of ~21.3 GPa.
Cutting performance and wear mechanism of TiB2-B4C ceramic cutting tools in high speed turning of Ti6Al4V alloy Ceram. Int. (IF 2.986) Pub Date : 2018-05-25 Da-Wang Tan, Wei-Ming Guo, Hong-Jian Wang, Hua-Tay Lin, Cheng-Yong Wang
TiB2–20vol%B4C (TB20) and TiB2–80vol%B4C (TB80) ceramic cutting tool materials were prepared by hot pressing, and then tested in turning of Ti6Al4V alloy with various cutting parameters. The tool life and wear mechanism of TB20 and TB80 were studied and compared with a commercial grade tungsten carbide tool (WO). The results of turning showed that effective cutting length of TB20 was about one third longer than that of TB80 and WO. Among the three tools, the increment of cutting temperature measured for TB20 was the lowest as flank wear increased from 0 to 600μm. Analysis showed that dominant wear mechanism was adhesive wear in all of the three tools tested, while chipping was also observed in TB80 and temperature deterioration in WO. In addition, the TB20 exhibited a much better integrity of cutting edge after flank wear reaching 600μm, due to its higher toughness than TB80 and higher thermal resistance than WO, respectively. The adhesive layers of work-piece material on the rake and flank faces of both TB20 and TB80 were much thinner than that of WO, which suggested a lower adhesive wear rate in TiB2-B4C cutting tools. The high wear resistance of TiB2-B4C cutting tools is attributed to higher thermal resistance, higher hardness, and lower chemical affinity with titanium as compared with tungsten carbides, which makes them very promising materials for high speed machining of titanium alloys.
Luminescence enhancement of (Ca1−xMx)TiO3:Dy3+ phosphors through partial M (Mg2+/Zn2+) substitution for white-light-emitting diodes Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Jiaming Liu, Qinxue Tang, Zhu Liu, Wentao Zhang, Kehui Qiu
White-light-emitting (Ca1−xMx)TiO3:Dy3+ (M = Zn2+, Mg2+) phosphors were synthesized via combustion. The phase compositions and morphologies of the (Ca1−xMgx)TiO3:Dy3+ and (Ca1−xZnx)TiO3:Dy3+ phosphors were investigated via X-ray powder diffraction and scanning electron microscopy, respectively. The luminescence of the (Ca1−xMgx)TiO3:Dy3+ and (Ca1−xZnx)TiO3:Dy3+ phosphors was characterized using photoluminescence spectra, which indicate that the best substitution concentration of both Zn2+ ions and Mg2+ ions is 4%. Moreover, a comparison of the luminescence intensities of the (Ca.96Mg.04)TiO3:Dy3+ and (Ca.96Zn.04)TiO3:Dy3+ phosphors indicates that the Zn2+ ions could much more significantly enhance the luminescence intensity of CaTiO3:Dy3+ phosphors. These results suggest that the (Ca.96Zn.04)TiO3:Dy3+ phosphors excited by UV radiation are promising materials for white-light-emitting diodes.
Negative magnetization and exchange bias effect in Fe-doped CoCr2O4 Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 C.L. Li, T.Y. Yan, G.O. Barasa, Y.H. Li, R. Zhang, Q.S. Fu, X.H. Chen, S.L. Yuan
Polycrystalline ceramics of Co(Cr1-xFex)2O4 (0 ≤ x ≤ 0.12) were experimentally studied based on a series of temperature and time-dependent dc magnetic measurements using different magnetic field histories. Magnetization in field cooling process was continuously decreased for doping content x in the range of 0 ≤ x ≤ 0.04. Remarkable negative magnetization is observed when x reaches to 0.06 and persists up to x = 0.1. Two-sublattice model is established and competition of the two magnetic sublattices is responsible for the phenomenon. The magnetic switching effect is realized just by changing the magnitude of the applied magnetic field and double magnetocaloric effects are obtained. These unique features under low magnetic fields show attractive for application in spintronic devices due to that the magnetic state can effectively be tuned through magnetic field or temperature. Besides, the system exhibits both positive and negative exchange bias fields which are considered to be originating from the unidirectional anisotropy of exchange coupling of antiferromagnetic/ferromagnetic phases and spin reorientation of the two sublattices magnetic moments, respectively.
Surface topography and roughness of silicon carbide ceramic matrix composites Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 Shuoshuo Qu, Yadong Gong, Yuying Yang, Ming Cai, Yao Sun
The silicon carbide ceramic matrix composite (Cf/SiC) plays an important role in aeronautic and space applications due to its excellent performance. Cf/SiC consists of silicon carbide and carbon fibers. The effects of the grinding parameters on the 3D parameters of surface roughness and surface topography when grinding 2.5D needled Cf/SiC materials have rarely been investigated. The primary purpose of this paper is to fill this knowledge gap. Cf/SiC material was ground in the direction of the orthogonal surface, and the surface topography, grinding parameters and grinding mechanism were analysed through a series of experiments. The results indicated that matrix cracks, fiber fractures, fiber wear and interfacial debonding were the primary removal methods of the material. The grinding parameters exert a substantial influence on the quality of the machined surface, primarily because of the undeformed chip thickness and the length of the contact arc. In the grinding process of the 2.5D Cf/SiC material, the quality of the surface roughness and its parameters gradually improved with increasing grinding speed, whereas the feed speed and grinding depth produced the opposite effect. Based on the conclusions, the surface topography and roughness parameters of 2.5D Cf/SiC material can be predicted, which thus provides useful technical support for increasing the machining quality of 2.5D Cf/SiC material and all its composites.
Electrical conduction mechanisms in graphene nanoplatelet/yttria tetragonal zirconia composites Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 R. Poyato, J. Osuna, A. Morales-Rodríguez, Á. Gallardo-López
Yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composites with 5, 10 and 20 vol% graphene nanoplatelets (GNPs) were prepared by spark plasma sintering (SPS) and their electrical conductivity as a function of temperature was characterized. The composites exhibit anisotropic microstructures so the electrical conductivity studies were carried out in two directions: perpendicular (σ⊥) and parallel (σ||) to the SPS pressing axis. The composites with 5 and 10 GNP vol% showed high electrical anisotropy, whereas the composite with 20 GNP vol% exhibited nearly isotropic electrical behavior. σ⊥ shows metallic-type behavior in the composites with 10 and 20 vol% GNP revealing that charge transport takes place through defect-free GNPs. For the composite with 5 vol% GNP the observed semiconductor-type behavior was explained by a two dimensional variable range hopping mechanism. σ|| shows metallic-type conductivity in the composite with 20 GNP vol% and positive dσ||/dT slope in the composites with 5 and 10 GNP vol%.
Largely enhanced mechanoluminescence properties in Pr3+/Gd3+ co-doped LiNbO3 phosphors Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 Gaojian Qiu, Hua Fang, Xusheng Wang, Yanxia Li
Pr3+/Gd3+ co-doped LiNbO3 phosphors were prepared by a traditional solid-state reaction method and their structure, photoluminescence, mechanoluminescence and thermoluminescence were investigated. The results showed that the LiNbO3 phase with a rhombohedral structure and an R3c space group was successfully prepared. Mechanoluminescence intensity in nonstoichiometric LiNbO3:Pr3+ was largely increased by introducing Gd3+ ions. The optimal co-doped concentration of Gd3+ was 1 mol% and the enhanced ML intensity of LiNbO3:0.01Pr3+, 0.01Gd3+ was about 177% times compared with that of LiNbO3:0.01Pr3+. The effect of Gd3+ co-dopants on trap levels were explored through thermoluminescence curves. The enhancement of mechanoluminescence intensity was suggested to be ascribed to the regulated trap quantities caused by co-doped Gd3+ ions. Appropriate co-dopants are proved to be effective sensitizers for mechanoluminescence materials.
Effects of HfO2 Dopant on Characteristics of Li2MgTiO4-based Red Phosphors: Thermal Stability, Photoluminescence Intensity and Quantum Efficiency Improvement Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 Li-Fang Nien, Chung-Hao Chiang, Hsiau-Hsian Nien, Sheng-Yuan Chu
To produce natural and vivid color, the color rendering index of white light-emitting diodes (WLEDs) with single phosphors is usually lower than 70, which is problematic for LED applications. A commonly used method to resolve this issue is to enhance the red component of WLEDs. In the present study, Hf4+ and Mn4+ co-doped Li2MgTiO4 red phosphors are synthesized using a solid-state reaction method. When this red phosphor is excited at 397 and 468 nm, it exhibits weak reabsorption in the blue region and emits a broad and deep red emission band in the range of 640 to 750 nm, which is attributed to the 2Eg → 4A2g transition. With 5 mol% HfO2 dopant, the photoluminescence intensity is enhanced by 1.45-fold and thermal stability is increased by 7.7%. Moreover, this red phosphor was applied to a red phosphor-in-glass (RPiG) optical device with a low-melting TeO2-B2O3-ZnO-Na2O-WO3 glass system. In the RPiG melting process, Li2MgTiO4:Mn4+, Hf4+ red phosphor triggered neither a chemical reaction nor severe degradation, indicating good thermal stability. Li2MgTiO4:Mn4+, Hf4+ has potential as a red emission material for warm WLED applications.
Shape Controlled synthesis of Cu3BiS3 Nano- and microstructures by PEG assisted solvothermal method and functional properties Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 T. Manimozhi, J. Archana, K. Ramamurthi
One-dimentional Cu3BiS3 nano-and microstructures were synthesized by solvothermal route using structural directing agent poly ethylene glycol (PEG) as soft template. The effects of thiourea concentration on the morphological, structural and optical properties of Cu3BiS3 nano- and microstructures were investigated. X-ray diffraction study revealed that the synthesized Cu3BiS3 belongs to orthorhombic structure. Raman spectrum of the Cu3BiS3 exhibited its functional groups. The chemical bonding of the ions was examined by X-ray photoelectron spectroscopy. Field emission scanning electron microscope and transmission electron microscope analyses evidently showed that thiourea concentration acts as a crucial factor in tuning the morphology of Cu3BiS3 nano- and microstructures. The presence of Cu3BiS3 was confirmed by Energy Dispersive X-ray Analysis and elemental mapping. The growth mechanism of Cu3BiS3 nanostructures has been discussed. Conductivity of Cu3BiS3 measured by I-V characteristics of the nano- and microstructured film of ~2.5 µm thickness deposited on FTO substrate using electron beam evaporation method showed linear curve. The Hall measurements of the Cu3BiS3 films deposited on glass substrate were determined.
Raman scattering and infrared reflectivity study of orthorhombic/monoclinic LaTiNbO6 microwave dielectric ceramics by A/B-site substitution Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 Jian Zhang, Ruzhong Zuo
The structure origin of microwave dielectric properties in A/B-site substituted LaTiNbO6 ceramics with different crystal structures was explored by means of Raman scattering and infrared reflection spectra. Compared with the monoclinic (M) phase, the broadening of the Raman modes associated with B-O stretching and bending vibrations in the orthorhombic (O) phase was believed to be a result of the increased octahedral distortion. The Raman mode at 659 cm−1 was assigned to the stretching vibration of B-O-B and O-B-O bonds in the unique interlayer chain structure of O phase. The Raman modes of the BO6 tilting within 340~520 cm−1 suggest that different octahedral connection ways should be one of the vital reasons why M and O phases own opposite-sign temperature coefficient of resonance frequency τf. Moreover, the result of infrared reflection spectrum fitted with a four-parameter semiquantum model indicates that the dielectric response of both M and O phases would mainly originate from the A-BO6 external vibrations in the far-infrared frequency, particularly their AO8 structure units. These results would provide useful insights into the structure-property relation in the RETi(Nb,Ta)O6 (RE: rare earth) material system.
Direct and Hybrid Microwave Solid State Synthesis of CaCu3Ti4O12 Ceramic: Microstructures and Dielectric Properties Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 Guillaume Riquet, Sylvain Marinel, Yohann Breard, Christelle Harnois, Alain Pautrat
CaCu3Ti4O12 (CCTO) electroceramic possesses unusual giant dielectric permittivity up to ε =104 at low frequency range and room temperature. CCTO dielectric properties strongly depend on its microstructure therefore it is essential to pay attention to the processing techniques which impact grain size and microstructure. In this work, direct and hybrid microwave solid state synthesis was specifically designed and used for the synthesis of CCTO. The microwave process was also compared to the conventional process which involves usual infra-red heating. The structural (XRD) and microstructural (SEM) characterizations indicate that microwave synthesis is particularly efficient to get rapidly pure CCTO powder. The fully automated 915 MHz single-mode microwave cavity used for hybrid synthesis allows a perfect control of the temperature distribution and heating rate. Therefore hybrid microwave synthesis leads to a fine, mono-disperse and practically pure CCTO powder in the range of 300 – 500 nm. The advantages of the hybrid microwave heating method are discussed and compared to the conventional and direct microwave heating processes. From the powders synthesized by the different routes, dense compacts were sintered in air at 1050 °C in a conventional furnace. Microstructural characterizations reveal abnormal grain growth during sintering which levels dielectric properties. All exhibit a giant dielectric constant ε> 103 at room temperature which decreases drastically to ε =90 at 10 K. Those properties are discussed according to the well-established Internal Barrier Layer Capacitor (IBLC) model.
Enhanced dielectric properties and discharged energy density of composite films using submicron PZT particles Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 Guanliang Chen, Xiujuan Lin, Jianan Li, John G. Fisher, Yan Zhang, Shifeng Huang, Xin Cheng
Flexible dielectric composite films are highly desirable materials with potential application in capacitors due to their high energy density and discharged efficiency. However, agglomeration induced by the large surface energy of nanoparticles and their large dielectric losses are unfavorable to the improvement of energy density. Submicron lead zirconate titanate (PZT) particles have shown great potential as filler in achieving a high energy storage capacity because of their excellent dielectric properties and good dispersion. In this work, calcined PZT particles were used to prepare PZT/polyvinylidene fluoride (PVDF) composite films. The results showed that composite films of high quality could be obtained even with high contents of submicron PZT particles. The introduction of PZT particles significantly improved the dielectric performance of composite films compared with that of the pristine PVDF film. The discharged energy density of composite films with 10 vol% PZT particles achieved 6.41 J/cm3 at 250 kV/mm. A high efficiency of 87.25% was obtained at 50 kV/mm. These findings confirm the feasibility of PZT particles as inorganic filler in composite films for energy storage applications.
Yttrium doped cobalt ferrite nanoparticles: Study of dielectric relaxation and charge carrier dynamics Ceram. Int. (IF 2.986) Pub Date : 2018-05-24 S. Chakrabarty, M. Pal, A. Dutta
We report the effect of yttrium (Y) doping on structural, optical properties and conductivity relaxation behavior of cobalt ferrite (CFO) nanoparticles prepared via citrate auto-ignition route. Microstructural analysis using XRD study confirms the growth of single phase nanocrystalline CFO, HRTEM images delineate faults in the crystal stacking sequence. UV–vis absorption spectra show a blue shift for optical band gaps of the doped samples. Impedance spectroscopy suggests that both grain and grain boundaries contribute to the conduction process. A universal power law dependence of the conductivity spectra has been observed. Scaling of the conductivity spectra resulted the conduction mechanism to be independent of composition and temperature. Stretched behavior of the dielectric response has been elucidated by Harviliak-Negami (H.N.) model based functions. Defects in the crystal structure played important role on the overall transport properties of the system.
In-vitro formation and growth kinetics of apatite on a new light-cured composite calcium phosphate cement Ceram. Int. (IF 2.986) Pub Date : 2018-05-23 Nafise Elahpour, Sayed Mahmood Rabiee, Mohammad Hossein Ebrahimzadeh, Ali Moradi
Calcium phosphate cements are used as synthetic bone grafts with several advantages such as biocompatibility, osteoconductivity, and moldability. In this study, the synthesis of a biocement starting from calcium hydroxide (Ca(OH)2) and Monocalcium Phosphate Monohydrate (MCPM) was investigated. A 6 wt% Na2HPO4 aqueous solution along with a modified polymeric resin (RIVA(SDI)®) were adopted as the variable liquid phase in self- and light-cure cement groups. XRD analysis and FTIR spectroscopy were used to study the phase composition. The composite microstructure was characterized by scanning electron microscopy (SEM) and the degradation rates were measured by atomic absorption spectroscopy (AAS) analysis. In addition, the effect of soaking time of the cement in simulated body fluid (SBF) on the final phase and morphology was studied. The results showed that soaking the composite in SBF has a significant influence in phase transformation into hydroxyapatite, but following a slower kinetic in light-cured composite cements. Evidences of crosslinking reactions in light-cured cements were observable, which at the same time can legitimize slower apatite formation and faster biodegradation of these composite cements.
In-situ observation of oxygen mobility and abnormal lattice expansion in ceria during flash sintering Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Shikhar Krishn Jha, Harry Charalambous, Han Wang, Xin Li Phuah, Christopher Meade, John Okasinski, Haiyan Wang, Thomas Tsakalakos
Flash sintering has been shown to be an effective method of sintering for many types of ceramics. However, the characteristics of flash sintering for each type of ceramic varies. When ionically conducting ceramics are sintered under a DC electric field, a strong dependence of densification with respect to position is observed. Microstructural analysis of the effect of electric field on oxygen ion conductors shows non-stoichiometry (oxygen deficiency) at the cathode which continues to build up over time under flash. In oxygen ion conductors, dominant charge carriers during flash are oxygen ions and the final density of the specimen is related to the availability of oxygen. This effect is no longer evident when using an AC power supply. Thus, use of AC instead of DC electric field is preferable for flash sintering of ionically conducting ceramics.
Microstructure and properties of a graphene platelets toughened boron carbide composite ceramic by spark plasma sintering Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Mingdan Chen, Zengbin Yin, Juntang Yuan, Weiwei Xu, Jiadong Ye, Shiyu Yan
A kind of B4C/SiC composite ceramic toughened by graphene platelets and Al was fabricated by spark plasma sintering. The effects of graphene platelets and Al on densification, microstructure and mechanical properties were studied. The sintering temperature was decreased about 125–300℃ with the addition of 3–10 wt.% Al. Al can also improve fracture toughness but decrease hardness. The B4C/SiC composite ceramic with 3 wt.%Al and 1.5 wt.% graphene platelets sintered at 1825℃ for 5 min had the optimal performances. It was fully densified, and the Vickers hardness and fracture toughness were 30.09±0.39 GPa and 5.88±0.49 MPa·m1/2, respectively. The fracture toughness was 25.6% higher than that of the composite without graphene platelets. The toughening mechanism of graphene platelets was also studied. Pulling-out of graphene platelets, crack deflection, bridging and branching contributed to the toughness enhancement of the B4C-based ceramic.
Facile synthesis of monetite nanoparticles from basic raw materials Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Marie Švecová, Vilém Bartůněk
Nanosized calcium phosphate phase – monetite was synthetized at room temperature by simple one-pot method using only basic raw materials: concentrated phosphoric acid, calcium hydroxide suspended in water and ethanol for crystallisation and purification purposes. Synthetized rod-shaped nanocrystals were characterised by XRD, SEM-EDS, TEM, and Raman spectroscopy. This simple approach may be utilised for large-scale synthesis of nanosized monetite for various applications, including biomedical and purification technologies.
Electrophoretic deposition of titania nanostructured coatings with different porous patterns Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Morteza Farrokhi-Rad
Titania nanostructured coatings with different porous patterns were fabricated by electrophoretic deposition (EPD) in isopropanolic suspension including different concentrations of carbon active (CA) or carbon black (CB) particles as the porogen additives. Finer and negatively charged CA particles were electrostatically adsorbed on the coarser and positively charged titania particles and formed CA-titania particles. While, finer and positively charged titania particles were electrostatically adsorbed on the coarser and negatively charged CB particles to form titania-CB particles. Both CA-titania and titania-CB particles had the net positive surface charge and so cathodic EPD was applicable. EPD was carried out at optimized conditions of 60 V and 10 s. Thermogravimetry (TG) analysis showed that CA and CB burn out between 450–600°C. The higher the carbon content in the suspension the higher was their content in the coating. The coatings were characterized by SEM, AFM, adhesion strength and bioactivity tests. Even coatings with interconnected fine pores and low roughnesses were obtained after the heat treatment of CA-titania coatings. While, rough coatings with coarse and isolated pores were obtained after the heat treatment of titania-CB coatings. The porosity of coating increased as the carbon content increased in the suspension. The hydroxyapatite layer grew on the coatings after their soaking in simulated body fluid for 1week at 37.5±1.5°C.
One-step synthesis of in-situ carbon-containing calcium aluminate cement as binders for refractory castables Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Guoqing Xiao, Shoulei Yang, Donghai Ding, Yun Ren, Lihua Lv, Pan Yang, Xing Hou, Jianying Gao
In-situ carbon-containing calcium aluminate cement (CCAC) was synthesized through carbon-bed sintering with calcium citrate tetrahydrate and Al2O3 as raw materials. The synthesized product was characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and infrared carbon–sulfur analysis. The results show that after sintering at 1500 °C for 4 h, the phase compositions of the product approached that of the commercial cement Secar71. The in-situ carbons in the product had partially graphitized domains and porous structures, were uniformly embedded in calcium aluminate, and the carbon content of the product was 1.45%. The floating ratios and oxidation ratios of the CCAC were lower than those of carbon back/Secar71 (S71CB) composite powders, implying that the water dispersion and oxidation resistance of CCAC were improved. Furthermore, the cold crushing strength (CCS), and cold modulus of rupture (CMOR) of the corundum-based castables bonded with CCAC, and S71CB, respectively, were compared. The CCS and CMOR values of the castables bonded with CCAC after being fired at 1100 °C for 3 h are higher by 20% and 21%, respectively, than those of the castables bonded with S71CB, suggesting that CCAC can be applied as a promising binder for the refractory castables.
Bioactive glasses – when glass science and technology meet regenerative medicine ☆ Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Francesco Baino
Over the millennia, men have continuously potentiated their abilities through developing and applying new materials and technologies. A number of metallic, ceramic and polymeric implants have been experimented as “spare parts” to restore lost functions or organs in the body. Till the 1960s, the selection of potentially suitable prosthetic materials was based on the criterion of maximum biological and biochemical inertness in contact with body fluids. Fifty years ago, the invention of the first bioactive glass, which was able to create a strong bond with living bone, radically changed this concept and paved the way for the advent of the modern era of biomaterials science. Since then, a number of bioactive glass-based products, such as small solid blocks, fine particles, granules, porous scaffolds and injectable putties, have been implanted in millions of patients primarily to repair bone and dental defects. Over the last decade, bioactive glasses have also shown promise in highly fascinating, emerging applications that involve angiogenesis (e.g. wound healing), interfacial hard-soft tissue engineering and controlled drug delivery. This review offers the reader a “guided tour” in the field of bioactive glass science and technology, also highlighting the future challenges to be met by materials scientists, bioengineers and clinicians to further exploit the benefits associated to these ever-surprising materials, which were unthinkable when research began.
Structural, microstructural and electrochemical studies on LiMn2-x(GdAl)xO4 with spinel structure as cathode material for Li-ion batteries Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 A. Venkateswara Rao, B. Ranjith Kumar, S.D. Ramarao
Gd and Al co-doped LiMn2-x(GdAl)xO4 (x = 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) materials with spinel structure were synthesized by sol-gel method. Powder X-ray diffraction results confirm the formation of cubic spinel structure and average particle sizes are found to be between 80–110 nm from FE-SEM and TEM analysis. Decrease in peak potential difference as a function of doping in Cyclic Voltammetry results establishes enhancement in Li+ intercalation and de-intercalation. Electrochemical Impedance Spectroscopy (EIS) results showed that accumulation of charges on electrode has improved with doping over pristine samples. At a doping of x = 0.02 charge transfer resistance values were found to be least. First cycle charge-discharge profiles for LiMn1.96(GdAl)0.02O4 shows 139.2 mAh/g discharge capacity over other doped derivatives and pure LiMn2O4 (119.6 mAh/g) in aqueous Li2SO4 electrolyte. Doping of x = 0.02 exhibit good cycling performance with only a total 4% capacity loss after 30 cycles.
Enhancement of thermal, mechanical, ignition and damping response of magnesium using nano-ceria particles Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Milli Suchita Kujur, Vyasaraj Manakari, Gururaj Parande, Khin Sandar Tun, Ashis Mallick, Manoj Gupta
Magnesium (Mg)-based nanocomposites owing to their low density and biocompatibility are being targeted for transportation and biomedical sectors. In order to support a sustainable environment, the prime aim of this study was to develop non-toxic magnesium-based nanocomposites for a wide spectrum of applications. To support this objective, cerium oxide nanoparticles (0.5 vol%, 1 vol%, and 1.5 vol%) reinforced Mg composites are developed in this study using blend-press-sinter powder metallurgy technique. The microstructural studies exhibited limited amounts of porosity in Mg and Mg-CeO2 samples (< 1%). Increasing presence of CeO2 nanoparticles (up to 1.5 vol%) led to a progressive increase in microhardness, dimensional stability, damping capacity and ignition resistance of magnesium. The compressive strengths increased with the increasing addition of the nanoparticles with a significant enhancement in the fracture strain (up to ~48%). Superior energy absorption was observed for all the composite samples prior to compressive fracture. Further, enhancement in thermal, mechanical and damping characteristics of pure Mg is correlated with microstructural changes due to the presence of the CeO2 nanoparticles.
High-temperature mechanical properties of NextelTM 610 fiber reinforced silica matrix composites Ceram. Int. (IF 2.986) Pub Date : 2018-05-22 Ru Jiang, Lingwei Yang, Haitao Liu, Xun Sun, Haifeng Cheng
Novel NextelTM 610 fiber reinforced silica (N610f/SiO2) composites were fabricated via sol-gel process at a sintering temperature range of 800-1200 °C. The sintering-temperature dependent microstructures and mechanical properties of the N610f/SiO2 composites were investigated comprehensively by X-ray diffraction, nanoindentation, three-point bending etc. The results suggested a thermally stable NextelTM 610 fiber whose properties were barely degraded after the harsh sol-gel process. A phase transition in the silica matrix was observed at a critical sintering temperature of 1200 °C, which led to a significant increase in the Young's modulus and hardness. Due to the weak fiber/matrix interfacial interaction, the 800 °C and 1000 °C fabricated N610f/SiO2 composites exhibited quasi-ductile fracture behaviors. Specially, the latter possessed the highest flexural strength of ≈164.5 MPa among current SiO2-matrix composites reinforced by fibers. The higher sintering-temperature at 1200 °C intensified the SiO2 matrix, but strengthened the interface, thus resulting in a brittle fracture behavior of the N610f/SiO2 composite. Finally, the mechanical properties of this novel composite presented good thermal stability at high temperatures up to 1000 °C.
Surface structural and solar absorptance features of nitrate-based copper-cobalt oxides composite coatings: Experimental studies and molecular dynamic simulation Ceram. Int. (IF 2.986) Pub Date : 2018-05-21 Amun Amri, Ahmad Fadli, Zhong-Tao Jiang, Chun-Yang Yin, M. Mahbubur Rahman, Hantarto Widjaja, Syamsu Herman, Silvia Reni Yenti, M. Miftahul Munir, Gadang Priyotomo, M. Iqbal, Neni Frimayanti
The copper and cobalt oxides composites coatings on aluminum substrates have been successfully synthesized via sol-gel method using nitrate-based sol precursors. The composites were characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and UV-Vis-NIR spectrophotometry. The sol-gel reactions were discussed and Molecular Dynamics (MD) simulation was integrated into the study to predict molecules assembly properties. The XRD analyses revealed that the CuO and the Co3O4 composites were formed after the annealing process with the average difference of the calculated lattice parameters compared to ICDDs was 1.17%. The surface electronic structure was mainly consisted of tetrahedral Cu(I), octahedral Cu(II), tetrahedral Co(II), octahedral Co(III) as well as surface, sub-surface and lattice oxygen O−. The XRD, XPS and MD simulation results showed that there was minimal (or possibly non-existing) indication of copper-cobalt mixed phase oxides formations. FESEM and AFM surveys revealed that the coating had a porous surface composed of interlinked nanoparticles in the range of ~10 to ~40 nm. UV-Vis-NIR reflectance spectra showed that the sol precursors concentration and the dip-drying cycle significantly influenced the absorptance value with optimum absorptance (α) of 88.7% exhibited by coating synthesized using sol concentration of 0.1 M and 10 dip-drying cycles. High absorptance value and simplicity in the synthesis process render the coatings to be very promising candidates for solar selective absorber (SSA) applications.
Effect of Zinc precursor ratio on morphology and luminescent properties of ZnO nanoparticles synthesized in CTAB medium Ceram. Int. (IF 2.986) Pub Date : 2018-05-21 C. Amirthavalli, A. Manikandan, A.A.M. Prince
In this study, the effect of precursor ratio on structural, morphology and luminescent properties of zinc oxide (ZnO) nanoparticles (NPs) prepared by cationic surfactant-assisted method was studied. ZnO NPs were prepared at room temperature by increasing Zn2+: CTAB mole ratio. The pristine ZnO samples showed phase-purity (without need for calcination) as shown by X-ray diffractograms (XRD). Nitrogen adsorption − desorption analysis showed that the samples exhibit Type III isotherm and H3 hysteresis with mesoporosity. The triangular- to quadrilateral-shaped morphological evolution of the ZnO NPs with increasing concentrations of zinc ions was confirmed by SEM and TEM images of the samples. The UV-Vis-DRS studies showed blue-shifted λmax (band gap) in all the ZnO samples which indicated their nanostructured nature. The photoluminescence spectra of these ZnO samples show emissions in UV and visible regions. The mechanism of formation of nanostructured ZnO was suggested based on the model reported for mesoporous silica synthesized in CTAB medium.
Nanostructured CeO2 for selective-sensing and smart photocatalytic applications Ceram. Int. (IF 2.986) Pub Date : 2018-05-21 K. Negi, M. Kumar, G. Singh, S. Chauhan, M.S. Chauhan
Well crystalline CeO2 nanoparticles have been successfully synthesized via solution combustion synthesis (SCS) using (NH4)2[Ce(NO3)6] and C4H6O6 as oxidizer and fuel. The structural characteristics of as-synthesized material were investigated in terms of FESEM, HRTEM, EDS, XRD, FTIR and UV-Vis spectroscopy techniques. The surface area of synthesized CeO2 nanoscale material was obtained from BET plot. Results showed a pure, well-crystallized, flake-like mesoporous material to be formed with crystallite size of 18.86 nm. The focus of this study was to investigate the application of as-synthesized CeO2 nanomaterial for sensing and photocatalytic degradation of picric acid (PA) in its aqueous solution. It was found to be highly selective for PA detection in aqueous solution when compared with other aromatic compounds. Detection limit (0.52 µM) for PA when compared with earlier studies was found to be much better. In addition, 0.05 gm of as-synthesized CeO2 is found to be optimum amount ensuring maximum catalytic photodegradation of 10 ppm PA in aqueous solution. These experimental findings point out that as-synthesized CeO2 nanomaterial can be efficiently used as an effective chemical sensor and photocatalyst.
Synthesis and Investigation of environmental protection and Earth-abundant Kesterite Cu2MgxZn1-xSn(S,Se)4 thin films for Solar Cells Ceram. Int. (IF 2.986) Pub Date : 2018-05-21 Yu Zhang, Dongyue Jiang, Yingrui Sui, Yanjie Wu, Zhanwu Wang, Lili Yang, Fengyou Wang, Shiquan Lv, Bin Yao
We have synthesized Cu2MgxZn1–xSn(S,Se)4 (0≤x≤0.6) thin films by a facile sol-gel method, and studied the influence of Mg concentration on the crystal structure, surface morphology and photoelectric performance of Cu2MgxZn1–xSn(S,Se)4 thin films systematically. It was shown that the smaller Zn2+ in Kesterite phase Cu2ZnSn(S,Se)4 will be replaced by larger Mg2+, forming uniform pure phase Cu2MgxZn1–xSn(S,Se)4. The band gap of Cu2MgxZn1–xSn(S,Se)4 films can be adjusted from 1.12 to 0.88 eV as the x value changes from 0 to 0.6. Furthermore, the Cu2MgxZn1–xSn(S,Se)4 thin films with large grain size, smooth surface and less grain boundaries was obtained at an optimized condition of x=0.2. The carrier concentration of Cu2MgxZn1–xSn(S,Se)4 thin film reaches the maximum 6.47×1018 cm−3 at x=0.2, which is a potential material to be the absorption layer of high efficiency solar cells.
Carbon Fiber Reinforced Ceramic Matrix Composites with an Oxidation Resistant Boron Nitride Interface Coating Ceram. Int. (IF 2.986) Pub Date : 2018-05-21 Samuel J. Frueh, Timothy P. Coons, Justin W. Reutenauer, Rebecca Gottlieb, Michael A. Kmetz, Steven L. Suib
Toughening a ceramic in a ceramic matrix composite (CMC) depends on an ability of the composite to tolerate an accumulation of matrix cracks. When the reinforcement phase is carbon fiber, these cracks leave the fiber susceptible to destructive oxidation by ingress of air during high temperature exposure. Generally, a graphitic carbon interface coating is applied to carbon fibers because it provides for a weak bond between fiber and matrix that is required to promote toughening. This investigation seeks to utilize a BN coating instead of a C coating in order to promote oxidation resistance. Like graphitic carbon, BN is soft and easily cleavable. Preliminary observations that C/BN/SiC CMC's using Toray T300 carbon fibers were highly brittle and of low strength lead to a requirement of heat treating the fibers prior to the CVD of BN for toughened composites to be fabricated. It is likely heat treating removed reactive functionalities from the fiber surface to yield a weakly adhered and compliant interface.
Crystal structure and multiferroic behavior of perovskite YFeO3 Ceram. Int. (IF 2.986) Pub Date : 2018-05-21 O. Rosales-González, F. Sánchez-De Jesús, C.A. Cortés-Escobedo, A.M. Bolarín-Miró
We present a study of multiferroic properties of YFeO3 synthesized by means of high-energy ball milling assisted by annealing at low temperature. Fe2O3 and Y2O3 powders were mixed in a stoichiometric ratio, milled for 5 h, pressed and annealed at temperature from 773 to 1073 K. X-ray diffraction (XRD) analysis confirmed the formation of single-phase orthorhombic structure. Magnetic hysteresis loops, at room temperature, from vibrating sample magnetometry show the transition from ferromagnetic order to G-antiferromagnetic order, related to the transformation from amorphous to crystalline orthorhombic single phase. The value of Néel temperature of single phase YFeO3 was obtained at 595 K, lower than previously reported. Dielectric behavior at room temperature of YFeO3 single-phase sample shows a direct dependence with frequency of both dielectric constant and dielectric loss, in good agreement with Maxwell-Wagner effect. A fit made using Cole-Cole equation shows that the Low Temperature Dielectric Relaxation, LTDR, corresponds to a Debye-type relaxation. Finally, it was found that AC conductivity (σAC) increases linearly with frequency. All results show that YFeO3 synthesized by high-energy ball milling assisted with annealing possess a multiferroic behavior.
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