Electric relaxation of superparamagnetic Gd-doped lead molybdato-tungstates Ceram. Int. (IF 3.057) Pub Date : 2018-11-17 Z. Kukuła, M. Maciejkowicz, E. Tomaszewicz, S. Pawlus, M. Oboz, T. Groń, M. Guzik
Tetragonal, scheelite-type Pb1-3x□xGd2x(MoO4)1-3x(WO4)3x materials (x = 0.0455, 0.0839, 0.1154, 0.1430, 0.1667 and 0.1774, where □ denotes vacancies) synthesized via solid state reaction route were magnetically and electrically examined. The ac and dc magnetic measurements as well as the Brillouin fitting procedure showed paramagnetic state with characteristic superparamagnetic-like behaviour and a spin-only contribution to the paramagnetic moment. Broadband dielectric spectroscopy studies exhibited existence in the loss spectra the faster and slower relaxation processes with various time scales for the gadolinium-poorer samples with the x vacancy parameter up to 0.1154. For samples with higher Gd content, i.e. when x > 0.1154, no signs of any relaxation processes was observed. This phenomenon has been explained by a smaller number of structural and spin defects as opposed to the samples poorer in gadolinium ions.
HF/HCl Acid Resistance Mechanisms of Alumina Ceramics in the Al2O3-MgO-CaO-SiO2-Y2O3 system Ceram. Int. (IF 3.057) Pub Date : 2018-11-17 Tingting Wu, Jian Zhou, Bolin Wu
Silicon compounds in raw materials are the main reason for the low HF/HCl acid resistance of alumina ceramics. Y2O3 can improve the acid resistance of alumina ceramics. This work aimed to reveal the mechanisms of the effects of Y2O3 on the form of Si and the durability of the ceramic. An experiment on a high-temperature reaction between Y3Al5O12 and a polycrystalline alumina ceramic was designed. The effect of corrosion time on the acid solubility of the alumina ceramic was investigated. The results show that Si can dissolve in Y3Al5O12 to generate solid solutions, impeding the generation of Si-containing compounds with bad acid resistance, and decreasing the content of amorphous Si. The acid solubility of the ceramic was only 0.95%, even when the corrosion time was extended to 60 times the industry standard. This revelation of the acid resistance mechanisms can provide a new idea for designing corrosion-resistant ceramics.
Temperature-driven phase transitions and enhanced piezoelectric responses in Ba(Ti0.92Sn0.08)O3 lead-free ceramic Ceram. Int. (IF 3.057) Pub Date : 2018-11-17 Lingcan Qin, Changrong Zhou, Qingning Li, Ling Yang, Jiwen Xu, Guohua Chen, Changlai Yuan, Guanghui Rao
Ferroelectric phases coexistence or transition is an important strategy on generating high piezoelectricity. Here, the temperature-induced phase structural evolution correlated with small signal piezoelectric response d33, bias-field piezoelectric activity dmax 33(E), unipolar and bipolar strain piezoelectric outputs d⁎ 33 in Ba(Ti0.92Sn0.08)O3 (BTS0.08) ceramic was investigated in details. Temperature-driven successive phase transitions from rhombohedral(R) to orthorhombic(O), tetragonal(T), finally to cubic(C) phases took place around 14 °C, 38 °C and 61 °C, respectively. The highest d33 value of 675 pC/N is achieved in the T-C phase transition. However, the O-T phase boundary gives the highest dmax 33 = 1170 pm/V, bipolar d⁎ 33 = 822 pm/V and unipolar d⁎ 33 = 1318 pm/V. The temperature-driven phase transition exhibits large enhancements in piezoelectric property comparable to that of composition-induced phase boundary. These features suggest an effective method to design high-performance piezoelectrics by tailoring the types of phase boundary.
Complex Structural Contribution of the Morphotropic Phase Boundary in Na0.5Bi0.5TiO3 - CaTiO3 system Ceram. Int. (IF 3.057) Pub Date : 2018-11-17 Roy Roukos, Sara Abou Dargham, Jimmy Romanos, Fatima Barakat, Denis Chaumont
The correlation between structure and dielectric properties of lead-free (1-x)Na0.5Bi0.5TiO3 - xCaTiO3 ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09 ≤ x < 0.15 was identified where rhombohedral and orthorhombic symmetries coexist at room temperature. The fraction of orthorhombic phase increases gradually with x in the MPB region. Dielectric measurements reveal that the relative permittivity increase with addition of Ca2+. This behavior is unusual with this kind of doping. A thermal hysteresis occurred only in the MPB composition which varies in a non-monotonically manner with x, detected by dielectric properties. This phenomenon is related to the crystalline microstructure by a linear relationship between the fraction of each phase and dielectric properties, and, more precisely, to the strong interaction between rhombohedral and orthorhombic phases.
Porous magnetic carbon nanofibers (P-CNF/Fe) for low-frequency electromagnetic wave absorption synthesized by electrospinning Ceram. Int. (IF 3.057) Pub Date : 2018-11-17 Xiaodan Zuo, Pan Xu, Chongyang Zhang, Mengzhu Li, Xiangyu Jiang, Xigui Yue
The recent criteria to evaluate electromagnetic wave absorber include low density, strong absorbency, wide absorption bandwidth and thin absorber thickness, but its performance at low frequencies is always ignored. In this paper, the porous magnetic carbon nanofibers (P-CNF/Fe) for high-efficient electromagnetic wave absorption at low frequencies were fabricated by electrospinning followed by stabilization and carbonization. With the introduction of porous nanostructure, the permittivity of carbon nanofibers was decreased at low frequency and the impedance matching of permittivity and permeability was realized. The electromagnetic absorbing properties were investigated in detail. The minimum reflection coefficient reaches −44.86 dB at 4.42 GHz, and the widest effective absorption bandwidth (EAB) in the frequency was 3.28 range from 12.96 to 16.24 GHz. Consequently, considering the EM wave absorption performance, P-CNF/Fe synthesized in this work can be a promising candidate in the field of EM wave attenuation.
Magnetic properties of magnetite-based nano-glass-ceramics obtained from a Fe-rich scale and borosilicate glass wastes Ceram. Int. (IF 3.057) Pub Date : 2018-11-15 Tales Gonçalves Avancini, Marcelo Tramontin Souza, Antonio Pedro Novaes de Oliveira, Sabrina Arcaro, Annelise Kopp Alves
Magnetite-based glass-ceramic is a special composite material composed by magnetic nanocrystals embedded in a vitreous matrix. In this work, it was developed magnetic glass-ceramics based on borosilicate glass wastes and, for the first time, by using iron-rich scale (a waste from the metallurgical industry). Different compositions were established with increasing scale contents (20, 30, 45 wt.%). Raw materials were melted (1550 °C/4 h) and later cast in a preheated steel mold at 400 °C. Then, the obtained samples were heat-treated at 700 °C/ 30 min. The sample with 45 wt.% scale also was heated at 800 °C and 900 °C/ 30 min, in order to promote more crystallization. The obtained glass-ceramics properties were investigated using X-ray diffraction (XRD), Raman spectroscopy, vibrating-sample magnetometer (VSM), Mössbauer spectroscopy and transmission electron microscopy (TEM). Magnetite nanocrystals (average size in the 40 to 64 nm range) in the glass-ceramics were evidenced by TEM images and Mössbauer spectrum. VSM analysis revealed that the obtained ferrimagnetic glass–ceramic with composition of 45 wt.% scale annealed at 800 °C/ 30 min, improved the magnetic saturation (Ms), reaching 42 emu/ g. Results indicated a great potential of this magnetic-based glass-ceramics for being applied in many applications, such as the biomedical engineering field, in magnetic devices, magnetic resonance imaging contrast agents, hyperthermia, waste sorbent, and microwave devices.
Tungsten doped M-phase VO2 mesoporous nanocrystals with enhanced comprehensive thermochromic properties for smart windows Ceram. Int. (IF 3.057) Pub Date : 2018-11-15 Bin Li, Shouqin Tian, Haizheng Tao, Xiujian Zhao
The phase transition temperature (~ 68 °C) of M-VO2 film can be lowered significantly by tungsten (W) doping into the crystal lattice of VO2 due to the reduction of the strength of V-V pair interaction. However, W doping was always coupled with a serious weakening of luminous transmittance and solar modulation efficiency because W dopants can increase the electron concentration of VO2 film. Herein, the simultaneous introduction of W dopants and mesopores into M-VO2 nanocrystals was employed to prepare VO2 film. Interestingly, the obtained 0.4 at% W-doped mesoporous VO2 nanocrystals based composite films exhibited enhanced comprehensive thermochromic performance with excellent solar modulation efficiency (ΔTsol= 11.4%), suitable luminous transmittance (Tlum= 61.6%) and low phase transition temperature around 43 °C, much lower than 65.3 °C of undoped VO2. It was demonstrated that the lower phase transition temperature of VO2 can be primarily attributed to abundant lattice distortion after W doping, whereas the mesoporous structure can facilitate the uniform distribution of W dopants in VO2 nanocrystals, enhance the luminous transmittance and guarantee enough VO2 nanocrystals in the composite film to keep relatively high solar modulation efficiency. Therefore, this work can provide a new way to balance the three important parameters for the thermochromic performance of VO2 film (ΔTsol, Tlum and Tc) and probably promote the application of VO2 nanocrystals in the energy efficient windows.
Influence of the ceramic powder morphology and forming conditions on the optical transmittance of YAG:Yb ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 F.F. Malyavin, V.A. Tarala, S.V. Kuznetsov, A.A. Kravtsov, I.S. Chikulina, M.S. Shama, E.V. Medyanik, V.S. Ziryanov, E.A. Evtushenko, D.S. Vakalov, V.A. Lapin, D.S. Kuleshov, L.V. Tarala, L.M. Mitrofanenko
The influence of the dispersity and morphology of ceramic powders on the characteristics of green bodies and the optical transmittance of YAG:Yb (20 at.%) ceramics was considered. The effect of the specific surface area on the relative density of compacts was studied. An increase in the specific surface area from 1.45 to 12.38 m2/g led to a decrease in the relative density of green body compacts from 52 to 38% under the fixed uniaxial pressure of 50 MPa. An increase in the uniaxial pressing value up to 150 MPa provided a maximum increase of the optical transmission of ceramics. However, an increase in the specific surface area and uniaxial pressure led to the appearance of macrodefects in ceramic samples. Cold isostatic pressing at 200 MPa after uniaxial pressing at 50 MPa resulted in an increase of optical transparency and the elimination of the macrodefect formation in ceramics. Dispersity and morphology of ceramic powders have a significant effect on the optical transparency of ceramics. Forming conditions had insignificant influence on optical characteristics. Highly transparent YAG:Yb ceramics with 80% transmittance were developed.
Effect of Ti combined with Si and C on mechanical performance and oxidation resistance of SiC castables for plasma gasifier Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Ding Chen, Huazhi Gu, Ao Huang, Yanwen Deng
Gaseous products released during the oxidation of SiC at 1700 °C lead to serious degradation of SiC castables. Ti combined with Si and carbon black are added to improve the mechanical behavior and oxidation resistance of SiC castables in this study. The mechanical behavior, isothermal oxidation, microstructure, and thermodynamic analysis are used to evaluate the properties of SiC castables. The result shows that SiC castables with more Ti exhibit better degradation resistance at high temperature oxidation atmosphere. The preferential oxidation of metal Ti to TiO2 reduces the oxidizing gases and increases the content of SiO (g) in the matrix, which is beneficial for the generation of SiC fibers; in turn, this reinforces the mechanical behavior. In addition, a certain amount of TiO2 dissolves into SiO2 glass following the decrease in viscosity. TiO2 is not only more difficult to volatilize than SiO2, but also can decrease the viscosity of SiO2 glass to improve the mobility of the liquid, which is good for healing the pores on the surface and protecting the inner SiC from being oxidized; this improves the mechanical properties and oxidation resistance.
Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3 Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Mitang Wang, Long Fang, Mei Li, Ao Li, Xiaowei Zhang, Yanhong Hu, Zhaogang Liu, Ruhil Dongol
The effect of Y2O3 on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO-30B2O3–10SiO2 glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies Eg calculated by using both Kissinger and Moynihan model decrease from 668 kJ/mol to 573 kJ/mol for Kissinger model, and 682 kJ/mol to 587 kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6 mol%. And the glass crystallization kinetics parameters, crystallization activation energy Ec and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58 kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6 mol% yttrium oxide into 60ZnO-30B2O3–10SiO2 glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO-30B2O3–10SiO2 glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893 K and 993 K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO-30B2O3–10SiO2 glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.
Facile synthesis of thin coating C/ZnO composites with strong electromagnetic wave absorption Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Dongchao Wei, Yujie Qi, Senhao Lv, Guimei Shi, Yuxiang Dai, Yang Qi
C/ZnO composites with increased electromagnetic (EM) wave absorbing features have been synthesized through a simple one-pot hydrothermal process and subsequent high temperature carbonization under the protection of argon. The results depict that the maximum absorption of C/ZnO composites synthesized with the optimal molar ratio of zinc acetate to glucose is –50.43 dB at 15.77 GHz. The 1.16-mm-thick coating shows a wide effective absorption bandwidth (3.52 GHz) of EM wave (RL≤−10 dB). The thin coating thickness of the C/ZnO composites is desirable for decreasing the absorber weight in EM wave absorption. And there are no other reagents used throughout the synthesis process except for the green glucose and zinc acetate. Thus, C/ZnO composites would be highly promising lightweight EM wave absorbing materials.
Fabrication of complex shaped ceramics parts with surface-oxidized Si3N4 powder via digital light processing based stereolithography method Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Rong-Ji huang, Qiang-Guo Jiang, Hai-Dong Wu, Yan-Hui Li, Wen-Yong Liu, Xin-Xin Lu, Shang-Hua Wu
Si3N4 ceramic is difficultly fabricated by digital light processing (DLP) based stereolithography method, due to a large refractive index difference between Si3N4 powder and resin. In this paper, a surface oxidation approach of Si3N4 powder for improving cure depth is proposed. The results showed that, the amorphous SiO2 layer was uniformly attached onto the surface of Si3N4 powder by surface oxidation, and the absorbance of Si3N4 powder decreased as increasing oxidation degree. Moreover, the cure depth of the suspension significantly increased because of a smaller absorbance and a refractive index difference at the interface between oxidized Si3N4 powder and resin. At the exposure energy of 500 mJ/cm2, the cure depth of the raw Si3N4 powder was 34 μm. After oxidizing at 1150 °C and 1200 °C for 1 h, the cure depth effectively increased to 42 μm and 51 μm, respectively. Finally, the complex-shaped Si3N4 parts were successfully fabricated using surface-oxidized Si3N4 powder via DLP method.
Comprehensive characterization of CIGS absorber layers grown by one-step sputtering process Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Jae Cheol Park, Mowafak Al-Jassim, Seung Wook Shin, Jin Hyeok Kim, Tae Won Kim
We have demonstrated that the use of a one-step sputtering process allowed for the fabrication of copper indium gallium diselenide (CIGS) thin films by RF magnetron sputtering without an additional selenization process. The CIGS thin films deposited at different substrate temperatures were synthesized on soda-lime glass (SLG) substrates using a single quaternary CIGS target. The film composition ratios of ([Cu]/[In]+[Ga]), ([Ga]/[In]+[Ga]), and ([Se]/[Cu]+[In]+[Ga]) were almost consistent with those of the sputtering target. X-ray diffraction (XRD) and Raman results showed that the crystallinity of the CIGS thin films was gradually improved as substrate temperatures increased. Transmission electron microscopy (TEM) showed that the films grown at 600 °C have a columnar structure with the grain size of ~100 nm. In addition, for the CIGS films grown at 600 °C, TEM-EDX analysis revealed that the synchronized fluctuation of the Cu and Se signals was observed in the direction of the film depth, while the In and Ga signals were constant. As a result, the CIGS solar cell made using the film showed a degraded cell efficiency of 2.5%, which might be have been caused by not only Cu-rich and Se-poor compositions but the locally unstable composition in the CIGS films fabricated by one-step sputtering.
Non-linear changes of performances caused by introduction of chloride ions into Er3+-doped fluorozirconate glass Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Longfei Zhang, Qihua Zhu, Yiguang Jiang, Zaiyang Wang, Xinqiang Yuan, Haonan Li, Hao Chang, Sujie Cui, Lin Wang, Long Zhang
The effect of chloride ions on the properties of Er3+-doped fluorozirconate glass is systematically studied. We first observed a nonlinear mutation of the glass-forming abilities and fluorescence properties of glass when 1 mol% fluoride ions were replaced by chloride ions. The results differed from previous reports. In order to explain this special phenomenon, we investigated the changes of the structure and the Judd-Ofelt theory of glass before and after halogen anion substitution. The results indicate that part of the fluorozirconium octahedral network was destroyed and transformed into a chain structure due to the bridging chlorine atoms, of which the electronegativity is lower than F-. With the increase of Cl-, the glass-forming abilities gradually recovered due to the decrease of the liquid's temperature. Therefore, a non-linear mutation of the glass-forming abilities was exhibited. Furthermore, the predictor χ, the ratio between the Judd–Ofelt parameters Ω4 and Ω6, and the reduction in phonon density caused a mutation on the fluorescence properties of glass, such as the intensity and lifetime. This research could provide a new reference for the anion modification of fluoride glass.
Higher permittivity of Ni-doped Lead Zirconate Titanate, Pb[(Zr0.52Ti0.48)(1-x) Nix]O3, ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Nitu Kumari, Shagun Monga, Mohd. Arif, Neeraj Sharma, Arun Singh, Vinay Gupta, Paula M. Vilarinho, R.S. Katiyar
The paper reports highest obtained dielectric constant for Ni-doped Lead Zirconate Titanate [PZT, Pb(Zr0.52Ti0.48)O3] ceramics. The Ni-doped PZT ceramic pellets were prepared via conventional solid-state reaction method with Ni content chosen in the range 0–20 at.%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to investigatethe crystal structure of the prepared ceramics. The X-ray diffraction analysis indicated that the ceramic pellets had crystallized into tetragonal perovskite structure. A minute displacement of XRD peaks was detected in the diffraction spectra of Ni-doped PZT which when examined by size-strain plot (SSP) method revealed presence of homogenous strain that decreased with increase in concentration of Ni. In FTIR the maximum absorption at 597 cm−1, 608 cm−1, 611 cm−1, 605 and 613 cm−1 for Ni = 0, 5, 10, 15 and 20 at.%, respectively, confirmed the formation of perovskite structure in all the compositions and the slight shift suggests decrease in cell size on doping. The values of dielectric constant (ε′) & tanδ as a function of frequency and temperature were measured for the prepared ceramics and it revealed highest ever reported dielectric constant for Ni - doped PZT with Ni = 5 at.%. The dielectric variation with temperature exhibited a diffused type ferroelectric–paraelectric phase transition for the doped samples. Also, the maximum dielectric constant value (εʹmax) decreased with an increase in doping concentration of Ni while the phase transition temperature increased with increase in doping concentration. The estimated activation energy of different compositions was found to increase from 0.057 to 0.068 eV for x = 0.00 to x = 0.20 in ferroelectric phase. The piezoelectric, ferroelectric and magnetic properties were also investigated.
Ultraviolet electroluminescence from nanostructural SnO2-based heterojunction with high-pressure synthesized Li-doped ZnO as a hole source Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Rui Deng, Jinliang Zhao, Duanyi Zhang, Jieming Qin, Bin Yao, Jing Song, Dayong Jiang, Yongfeng Li
We report an ultraviolet (UV) electroluminescence (EL) in n-SnO2/p-ZnO heterojunction light-emitting diodes with the nanostructural SnO2 as an n-type layer and the Li-doped ZnO (ZnO:Li) synthesized by high-temperature high-pressure (HTHP) method as a high hole concentration p-type layer. Two kinds of SnO2 nanostructures including nanobelts (NBs) and nanowires (NWs) were used to fabricate n-type layers in the heterojunctions. The two heterojunctions with different SnO2 nanostructures demonstrate different light-emission feature in EL measurements. The SnO2 NBs/p-ZnO heterojunction shows a blue emission band centered at 416 nm under forward-bias voltage. A strong UV emission peak located at 391 nm was observed for the SnO2 NWs/p-ZnO heterojunction. Photoluminescence (PL) spectra indicate that the difference in EL is attributed to morphology-dependent light-emission feature in nanostructural SnO2 layer. Our results suggest that the nanostructural SnO2/ZnO:Li heterojunction is a potential and promising system in the UV optoelectronic field.
Effect of Ta addition on the microstructures and mechanical properties of in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Hong-Yu Yang, Zheng Wang, Shi-Li Shu, Jian-Bang Lu
In this work, in situ bi-phase (TiB2-TiCxNy)/(Ni-Ta) cermets were fabricated via a combined combustion synthesis and hot-pressing (CSHP) method in a Ni-Ti-BN-B4C-Ta system. The effects of Ta addition on the reaction process, phase constituents, microstructures and mechanical properties of the (TiB2-TiCxNy)/(Ni-Ta) cermets were studied. Ta is shown to dilute the system and lead to a small number of intermediate phases (Ni20Ti3B6 and Ni3Ti) that are retained in the products. Furthermore, the addition of Ta can markedly refine the ceramic particles and decrease the size and quantity of voids. The evaluation of the mechanical properties revealed that an increase in the Ta content resulted in increases in the compression strength (σUCS) and hardness and that the fracture strain (εf) increased first and then decreased. The cermet with the optimal addition of 5 wt.% Ta possessed the best mechanical properties without decreasing the value of εf (2.9%). The addition of 5 wt.% Ta resulted in a compressive strength of 3.37 GPa and the highest hardness of 1909 Hv, which is an increase of ~16% and ~22%, respectively, compared to cermets without added Ta.
Oxidation behavior of carbon/carbon-boron nitride composites fabricated by additives and chemical vapor infiltration Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Peng Xiao, Zeyan Liu, Zhi chao Li, Bengu Zhang, Zhuan Li, Yang Li
Carbon/carbon-boron nitride (C/C-BN) composites were manufactured by adding hexagonal boron nitride (h-BN) powders into carbon fiber preform and a subsequent chemical vapor infiltration (CVI) process for deposition of pyrolytic carbon (PyC). Microstructure and oxidation behavior of carbon/carbon composites with 9 vol% h-BN (C/C-BN9) were studied in comparison to carbon/carbon (C/C) composites. Results showed that with the addition of h-BN powders, a regenerative laminar (ReL) PyC with higher texture was achieved. Note that the introduction of h-BN powder make great contributes to graphitization degree of PyC, leading to larger oxidation activation energy. Moreover, under an air atmosphere, h-BN started to oxidize above 800℃, and generated molten boron oxide (B2O3) which prohibited oxygen diffusion by filling in pores, cracks and other defects. As these reason mentioned above, after oxidation test under an air atmosphere, mass losses of C/C-BN9 composites were lower than that of C/C composites at all test temperature (600–900 °C), indicating that the oxidation resistance of C/C-BN9 composites is better than that of C/C composites.
Antibacterial efficiency of alkali-free bio-glasses incorporating ZnO and/or SrO as therapeutic agents Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 A.C. Popa, H.R. Fernandes, M. Necsulescu, C. Luculescu, M. Cioangher, V. Dumitru, B.W. Stuart, D.M. Grant, J.M.F. Ferreira, G.E. Stan
A series of seven alkali-free silica-based bioactive glasses (SBG) with ZnO and/or SrO additives (in concentrations of 0 – 12 mol%) were synthesized by melt-quenching, aiming to delineate a candidate formulation possessing (i) a coefficient of thermal expansion (CTE) similar to the one of titanium (Ti) and its medical grade super-alloys (crucial for the future development of mechanically adherent implant-type SBG coatings) and (ii) antibacterial efficiency, while (iii) conserving a good cytocompatibility. The SBGs powders were multi-parametrically evaluated by X-ray diffraction, Fourier transform infrared and micro-Raman spectroscopy, dilatometry, inductively coupled plasma mass spectrometry, antibacterial (against Staphylococcus aureus and Escherichia coli strains) suspension inhibition and agar diffusion tests, and human mesenchymal stem cells cytocompatibility assays. The results showed that the coupled incorporation of zinc and strontium ions into the parent glass composition has a combinatorial and additive benefit. In particular, the “Z6S4” formulation (mol%: SiO2—38.49, CaO—32.07, P2O5—5.61, MgO—13.24, CaF2—0.59, ZnO—6.0, SrO—4.0) conferred strong antimicrobial activity against both types of strains, minimal cytotoxicity combined with good stem cells viability and proliferation, and a CTE (~8.7 × 10−6 × ºC−1) matching well those of the Ti-based implant materials.
Hydrothermal synthesis and characterization of In2O3-ZnGa2O4 nanocomposites and their application in IGZO ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-11-16 Yang Liu, Yu Zhang, Chen Qiu, Chao Qi, Benshuang Sun, Xueyun Zeng, Jinpeng Zhu, Yongchun Shu, Jilin He
Poly-crystalline In2O3-ZnGa2O4 nanocomposites were successfully synthesized by hydrothermal method with a mixed solution of In, Ga and Zn nitrates with equal mole ratio (In: Ga: Zn=1: 1: 1) and the ammonia was used as the precipitant. The effects of hydrothermal temperature and pH value of the mixed solution on the properties of the nanocomposites were investigated. The microstructure of the prepared In2O3-ZnGa2O4 nanocomposites was characterized by SEM and TEM, respectively. The growth mechanisms of In2O3-ZnGa2O4 nanocomposites were also preliminarily discussed in this study. Results reveal that the IGZO ceramics prepared by In2O3-ZnGa2O4 nanocomposites own a high relative density of 99.5% and low resistivity of 1.2 mΩ·cm, which can be applied to the preparation of IGZO thin film with superior performance.
Hexagonal boron nitride nanosheet/carbon nanocomposite as a high-performance cathode material towards aqueous asymmetric supercapacitors Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Xiuyan Jiao, Ting You, Fang Dai, Panpan Zhang, Tianli Li, Feng Yu, Lu Hu, Liwen Ding, Lei Zhang, Zubiao Wen, Yuping Wu
The two-dimensional hexagonal boron nitride (h-BN) has garnered tremendous interest due to its unique mechanical, thermal and electronic properties. However, the application of h-BN has been restricted as electrode materials for supercapacitors because of its wide band gap and rather low conductivity. Herein, a carbon-modified hexagonal boron nitride nanosheet (h-BN/C) nanocomposite is prepared through a facile and scalable solid-state reaction. Interestingly, the h-BN/C nanocomposite as cathode material exhibits a pair of distinct and reversible redox peaks in 2 M KOH aqueous electrolyte. Because of the enhanced electrical conductivity derived from the modified carbon and the increased specific surface area, the h-BN/C nanocomposite presents a high specific capacitance of 250 F g-1 at the current density of 0.5 A g-1. More importantly, the fabricated aqueous asymmetric supercapacitor with the h-BN/C as cathode and activated carbon as anode displays an operating voltage of 1.45 V, an energy density of 17 Wh kg-1 at a power density of 245 W kg-1, and high stability up to 1000 cycles. Therefore, h-BN/C nanocomposite would promisingly be a cathode material for aqueous asymmetric supercapacitors.
Effect of BaO on the phase composition and properties of aluminates for Ba-W cathodes Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Jinglin Li, Weihua Zhao, Jianjun Wei, Yongbao Feng, Xiaoyun Li, Tai Qiu
In this study, we prepared (4.8+x)BaO·CaO·2Al2O3(0≤x≤1.6) aluminates by calcining the precursors under static air at 1500 °C for 120 min. The precursor powders were prepared using a liquid phase co-precipitation method. The effects of the molar content of BaO on the phase composition (before and after melting), melting properties, environmental stability, evaporation, and emission properties of the aluminates was investigated systematically The results showed that the phase of the aluminates completely transformed from Ba5CaAl4O12 to Ba3CaAl2O7 with an increase in the BaO content. After melting, the phase changed from Ba5CaAl4O12 to a mixed phase of Ba5CaAl4O12 and Ba3CaAl2O7. In the high-temperature molten state, the aluminates were in the ionic state, which generated a relatively low-energy Ba5CaAl4O12 phase during cooling crystallization. With every 0.4 mol increase in the BaO content, the initial melting temperature of the aluminates decreased by 10–20 ℃, while the environmental stability deteriorated gradually. When the aluminates reacted with H2O and CO2 in the air, the original phase still existed and the characteristic peaks gradually broadened, but with the formation of Ca(OH)2, CaCO3, and BaCO3. At 1050 °C, with an increase in the BaO content, the evaporation rate of the Ba-W cathodes increased and the emission current density first increased and then decreased. The main components of the Ba-W cathode evaporation were Ba and BaO. At n(BaO):n(CaO):n(Al2O3)=6:1:2, the Ba-W cathode showed the best emission performance, and its pulse emission current density at 1050 °C was as high as 35.31 A/cm2.
Synthesis and structural characterization of ceria nanoparticle agglomerates with shape inherited from an oxalate precursor Ceram. Int. (IF 3.057) Pub Date : 2018-11-15 D.V. Maslennikov, A.A. Matvienko, S.A. Chizhik, A.A. Sidelnikov
In this work, cerium dioxide nanoparticles (CeNPs) were synthesized by thermal decomposition of cerium oxalate decahydrate Ce2(C2O4)3∙10H2O. Although a large amount of water was removed along with CO2, the product of decomposition retained the shape of the precursor crystal, i.e. a pseudomorph formed. The Ce2(C2O4)3∙10H2O precursor crystals were of plate-like shape; this shape was inherited by CeO2 formed upon decomposition of the precursor. CeO2 plates with a thickness of less than 15 µm were transparent to visible light. X-ray diffraction analysis, transmission electron microscopy and specific surface area measurements indicated that the plates consisted of CeNPs 4–6 nm in size. The influence of the annealing temperature on the growth of crystallites of the pseudomorph was studied. Fast coarsening of the crystallites started at a temperature of 500 °C.
The external and internal influences on the tuning of the properties of perovskites: an overview Ceram. Int. (IF 3.057) Pub Date : 2018-11-15 Aslam Hossain, Sanjay Roy, K. Sakthipandi
Perovskite-type materials become multipurpose class of compounds based on systematic studies of structure and numerous properties. Further the variation of properties can be tuned by adding or substitution of second anionic species such as halide, nitride, hydride etc. The different charges, covalencies, sizes, and new modes of local coordination offer convenient ways to further control carrier doping, magnetism, conductivity, and even chemical reactivity. This review aims to discuss the different effects of hypothetical and experimental methods that can modify the properties of perovskites for suitable device applications. This review will provide a clear idea to experienced researchers about the different methods adopted to tune the properties of perovskite. A brief description of comprehensive modification procedures will enable an understanding of alternative ways of tuning the properties of perovskite.
CdO-Ag-ZnO nanocomposites with hierarchically porous structure for effective VOCs gas-sensing properties Ceram. Int. (IF 3.057) Pub Date : 2018-11-15 Xinxin Xing, Yue Yang, Zhiyong Yan, Ying Hu, Tong Zou, Zidong Wang, Yude Wang
In this work, CdO-Ag-ZnO nanocomposites with hierarchically porous structure and large surface area were successfully fabricated by solution combustion synthesis (SCS) method. Crystalline structure, morphology, surface chemical states and specific surface area were investigated by XRD, SEM, TEM, XPS and BET techniques, respectively. Sensors fabricated from CdO-Ag-ZnO nanocomposites were made based on indirect heating method, which showed superior sensing properties in detecting different concentration of volatile organic compounds (VOCs). In contrast with singular ZnO, gas-sensing experiment results reveal that the addition of CdO and Ag effectively decreases optimum working temperature, increases gas response value and shortens response and recovery time. What’s more, other gas-sensing properties including repeatability, sensitivity and long-term stability are also discussed in this research. Particularly, gas sensor based on 10 mol% CdO-Ag-ZnO shows modest gas-sensing performance to VOCs at the operating temperature of 200 oC, and its gas response values are 198.63, 156.07, 53.04, 64.23, 183.65to 100 ppm formaldehyde, ethanol, acetone, methanol and isopropanol, respectively, indicating it a promising candidate in detecting VOCs. Superior sensing property is mainly ascribed to large specific surface area, special porous surface morphology, unique combination of nanocomposites and good catalytic ability of metallic Ag.
Enhanced Blue-light emission on Cd0.9-xZn0.1CrxS(0 ≤ x ≤0.05) quantum dots Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 I. Devadoss, P. Sakthivel, S. Muthukumaran, N. Sudhakar
Zn, Cr dual doped CdS quantum dots (QDs) have been synthesized using co-precipitation method at room temperature without any capping agent. The prepared samples were analyzed by x-ray diffraction (XRD), Transmission electron microscopic (TEM) study, Scanning electron microscopic (SEM) study, Energy Dispersive X-ray (EDX) spectra, UV-Visible absorption &transmission spectra, Fourier Transform Infra-Red (FTIR) spectra and Photoluminescence studies (PL). All the samples were exhibited cubic structure and they confirmed that the presence of Cr did not alter the original structure. TEM study and SEM study revealed the structure and morphology of the particles. Crystallite size was reduced for the addition of Cr and it was ranged as ~2 nm. As large number of small particles aggregated on the surface, agglomeration was received on surface morphological study. EDX spectra confirmed the occurrence of doped elements in CdS as per the targeted ratio. In UV-visible absorption study, Cr doping caused blue shift on absorption peaks. UV-visible Transmittance peaks intensity was reduced as a function of Cr doping. Optical energy band gap value was slightly increased for the addition Cr. High intense blue light emission and red shifted red emission were received on PL study for the Cr, Zn dual doped CdS QDs. Since these materials offered better optical and luminescent properties, shall be suitable for the opto-electronic device applications.
Enhanced electrochemical performance of layered Li-rich cathode materials for lithium ion batteries via Aluminum and Boron dual-doping Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Zhongdong Peng, Kunchang Mu, Yanbing Cao, Lian Xu, Ke Du, Guorong Hu
Lithium-rich layer oxides can possess satisfactory specific capacity but suffer from severe voltage attenuation and poor cycle stability. In this work, Al-B dual-doping technique is introduced to modify Li-rich layered oxide cathode materials. Cross-section scanning electron microscopy, Energy Disperse Spectroscopy and X-ray photoelectron spectroscopy results confirm that Al and B successfully doped into the interior of the bulk Li1.2Ni0.2MnO2 particles, and the High-resolution transmission electron microscopy and X-ray diffraction Rietveld refinement results reveal that the c-axis distance of LMR-AB increases. The Al-B co-doped sample shows greatly enhanced electrochemical performance. Specifically, it exhibits of a discharge capacity of 120 mAh g-1 at 5C and a capacity retention of 89.12% after 100 cycles at 1C. The voltage decay is also greatly alleviated. The enhanced electrochemical performance of LMR-AB is due to the synergistic effects bought by the Al-B dual-doping, where increase of c-axis distance decreases Li+ intercalation/deintercalation barrier. B3+ doping into the tetrahedral site block the migration of TM ions and Al3+ act as pillars in the octahedral site, stabilizing the structure and suppressing the phase transition during cycling.
Enhanced piezoelectric, electrocaloric and energy storage properties at high temperature in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Xiangjian Wang, Hongcheng Gao, Xihong Hao, Xiaojie Lou
The piezoelectric, electrocaloric and energy storage properties were systemically investigated in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics from room temperature to high temperature region. These ceramics can be poled completely to obtain large piezoelectric coefficient (104–153 pC/N) at low electric field of ~30 kV/cm. The piezoelectric property shows good thermal stability due to high depolarization temperature (Td). For BNKT20, a large low electric field-induced strain of 0.36% is obtained at 120 °C under 50 kV/cm, the corresponding normalized strain coefficient is up to 720 pm/V，which is larger than other BNT-based ceramics at high temperature region. The electrocaloric properties of these ceramics are studied via indirect and direct methods. Large EC value (~1.08 K) in BNKT20 ceramic is obtained at 50 kV/cm using indirect calculation. Above 100 °C, the dielectric energy storage density and efficiency of BNKT20 is still up to ~0.85 J/cm3 and 0.75, respectively. The BNKTx ceramics may become promising candidates in the fields of actuators, electrocaloric cooling and energy storage at high temperature region.
Dissolution behaviour of Al2O3 in mould fluxes with low SiO2 content Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Zhirong Li, Boran Jia, Yabing Zhang, Shengping He, Qiangqiang Wang, Qian Wang
A kinetic model of the dissolution of Al2O3 into mould fluxes with low SiO2 content was established, and the restrictive step of the dissolution process was investigated by employing a rotating cylinder method. Then, the effects of the relative moving speed between the Al2O3 sample and the flux as well as the effects of the temperature and composition on the dissolution rate of Al2O3 were analysed. The results showed that the dissolution of Al2O3 is controlled by the diffusion in the product layer. The dissolution rate increases with the increase in the relative moving speed and temperature. The activation energy of the dissolution of Al2O3 into mould fluxes A-1, A-2, and B were 150.8 kJ·mol−1, 156.1 kJ·mol−1, and 131.4 kJ·mol−1, respectively. The dissolution accelerates with increasing (CaO+BaO)/(Al2O3+SiO2) ratio and Na2O, Li2O, B2O3, and F− contents. The result of the analysis of the Al2O3/flux interface by scanning electron microscopy–energy dispersive X-ray spectroscopy showed that a product layer was formed in the dissolution process, with interfacial products BaO·6Al2O3 and BaO·2CaO·4Al2O3.
Densification rate and mechanical properties of carbon/carbon composites with layer-designed preform Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Lu Xuefeng, Zhang Jie, Qian Kun
In this work, carbon fiber needle-punching preforms were designed into two structure according to the density change along the thickness direction. One structure is designed to two layers with low-density layer and high-density layer, and the other is to three layers with low-density exterior layer and high-density interior layer. Then the effect of the preform with different structure on the densification rate and compressive properties of C/C composites was investigated. The results show that both two designed preforms can effectively avoid surface blocking, and lead to the faster densification rate of C/C composites during the chemical vapor infiltration processes. These results are attributable to the change of pore size distribution and pyrocarbon thickness, which was caused by fiber architecture designs. Meanwhile, these structural changes can improve the compressive strength of C/C composites, especially for the three-layer preforms. When the density of preforms is 0.45 g/cm3, C/C composites with three-layer preform has the highest compressive strength. The damage of most C/C composites with two and three-layer preforms is caused by shear or delamination failure, while that of C/C composites with common preforms usually caused by matrix collapse. Cracks in C/C composites with two and three-layer preforms always happened on the low-density layer, and consequently ceased or changed propagation direction in the interface between two layers.
Synthesis of Y2BaCuO5 nano-whiskers by a solution blow spinning technique and their successful introduction into single-grain, YBCO bulk superconductors Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Maycon Rotta, Devendra K. Namburi, Yunhua Shi, Alexsander L. Pessoa, Claudio L. Carvalho, John H. Durrell, David A. Cardwell, Rafael Zadorosny
The ability of single grain Y-Ba-Cu-O (YBCO) bulk superconductors to trap large magnetic fields is due generally to the presence of embedded, non-superconducting Y2BaCuO5 (Y-211) phase particles, in optimum amount, in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix, which increases flux pinning and, hence, critical current density of the bulk material. The presence of smaller particles of Y-211 could be expected to improve further the superconducting properties of single grain, bulk YBCO samples, although the smallest Y-211 particles that have been engineered to date within the bulk microstructure are around 800 nm in size. It is extremely challenging to reduce the Y-211 particle size any further due to problems of particle agglomeration that originate, inevitably, from the effects of surface energy and reactivity at relatively high processing temperatures. In this work, we report a novel approach to the fabrication of Y-211 pinning centres in bulk YBCO superconductors in the form of nano-whiskers manufactured by a solution blow spinning technique. The Y-211 nano-whiskers, of which 62% were smaller than 500 nm, were added to the YBCO precursor powders to produce a single grain bulk sample by the buffer-aided top-seeded melt growth (BA-TSMG) processing technique. The resulting YBCO single grain, of diameter 20 mm, was able to trap a magnetic field of 0.63 T at 77 K with an associated critical current density of 3.9 ×104 A/cm2 in self-field. The results of this study demonstrate clearly that the use of Y-211 nano-whiskers is a promising route for enhancing flux pinning in bulk YBCO single-grains, which is potentially significant for the development of high field engineering applications.
Solvent dependent morphological modification of micro-nano assembled Mn2O3/NiO composites for high performance supercapacitor applications Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 M. Karuppaiah, P. Sakthivel, S. Asaithambi, R. Murugan, G.Anandha babu, R. Yuvakkumar, G. Ravi
The different attractive morphologies of micro-nano assembled sphere, pseudo sphere, rock candy and cube-like Mn2O3/NiO composites were synthesized by the facile solvothermal method through varying the solvents and their volume ratio. The structural, morphological and compositional properties of synthesized samples were investigated by using powder X-ray diffraction (XRD), FE-SEM, EDS and XPS. The TG/DTA results confirmed the transformation of MnCO3/NiCO3 to Mn2O3/NiO structures. XRD results revealed that the synthesized samples exhibited the body-centred cubic of Mn2O3 and face-centred cubic of NiO. FESEM images depicted the formation of different micro-nano assembled morphologies. XPS study confirmed the presence of manganese, nickel and oxygen elements and their oxidation states. Pseudocapacitance properties of Mn2O3/NiO electrodes were evaluated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy using 1 M KOH electrolyte solution. The specific capacitance values of all the synthesized samples were calculated and the morphology of rock candy like Mn2O3/NiO composite exhibited superior properties of high specific capacitance of 566.21 Fg−1 at a current density of 0.5 Ag−1, better rate capability of 63.25% and good cycling stability of 87.42% capacitance retention even after 1000 cycles. From these results, the well morphological ordered Mn2O3/NiO composites may be preferred as the future electrode materials for electrochemical supercapacitor energy storage devices.
Reaction synthesis of spark plasma sintered MoSi2-B4C coatings for oxidation protection of Nb alloy Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Ping Zhang, Chenglong Chen, Zheng Chen, Xuanru Ren, Chengjin Shen, Peizhong Feng
MoSi2-B4C coatings with different B4C contents were prepared on Nb alloy by spark plasma sintering (SPS) process. Powder mixtures of Mo, Si and B4C were used as the coating starting materials. Besides MoSi2 and B4C phases, small amounts of SiC and MoB are also found in the coatings because of the reactions of Mo, Si and B4C powders during sintering. Compared with single MoSi2 coating, the MoSi2-B4C coatings show better oxidation resistance at 1450℃, and dense B2O3-SiO2 oxide scales form after 100 h oxidation. The B4C or MoB in the MoSi2-B4C coatings can serve as the B donor for the formation of B2O3. A slight degradation in the microstructure of the MoSi2-B4C coatings after oxidation is observed, which can be attributed to the presence of an NbB layer in the inter-diffusion zone of the coatings that retards the inward diffusion of Si from the coating into the substrate alloy. The microstructure development and oxidation behavior of the MoSi2-B4C coatings have been discussed.
Effect of Cr-doping on the physicochemical properties of blue TiO2 and its application in dye-sensitized solar cells via low-temperature fabrication process Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Sami Bin Humam, Huy Hao Nguyen, Chhabilal Regmi, Gobinda Gyawali, Bhupendra Joshi, Soo Wohn Lee
Cr-doped blue TiO2 (Cr-BTiO2) nanoparticles were fabricated at room temperature using lithium-ethylenediamine (Li-EDA) as reducing agent. The addition of Li-EDA promotes the selective reduction of the rutile phase of TiO2 into the amorphous phase keeping anatase phase unaltered. Hence, the phase-selective reduction of TiO2 leads to the formation of blue TiO2 nanoparticles. Synthesized samples were characterized by equipment fitted with modern technology. The shifting of (101) peak to a lower angle (2θ) in Cr-BTiO2 in X-ray diffraction (XRD) pattern suggests the successful doping of chromium into TiO2 lattices. In Raman spectra, the shifting of the active Eg peak of Cr-BTiO2 nanoparticles to higher wavenumber also suggests the successful substitution of Ti by Cr. The blue TiO2 and Cr-BTiO2 show increased absorption of light in the visible region compared to TiO2 (P25). The modified TiO2 samples have improved electron-hole separation tendency as predicted by the photoluminescence spectra (PL). Also, doping of Cr- into TiO2 lattice results the formation of oxygen vacancy as detected by X-ray photoelectron spectroscopy (XPS). Among all samples, Cr-BTiO2 demonstrated improvement in Jsc and overall incident photon to current conversion efficiency. Therefore, the synthetic effect is thus responsible for the enhancement in efficiency of Cr-BTiO2 towards the dye-sensitized solar cell (DSSC) by 2.5 and 1.5 times higher than the P25 and blue TiO2, respectively.
3D microstructure model and thermal shock failure mechanism of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Yuan Shuowei, Yang Zichun, Chen Guobing
In this study, an efficient method was proposed to establish 3D microstructure model of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles and its failure mechanism under thermal shock was studied based on the established microstructure model. The proposed modeling method based on modified 3D Voronoi tessellation method and “precise shrinkage ratio method” was able to establish 3D geometric model of a SiC ceramic refractory with SiC high volume fraction particles more quickly than usual methods. The modified 3D Voronoi tessellation method generated Voronoi polyhedrons (VPs) limited in finite space perfectly. The proposed “precise shrinkage ratio method” achieved a precise volume fraction of SiC particles in the established microstructure model. The crack initiation and propagation under thermal shock were calculated by employing the extended finite element method (XFEM) on the established microstructure model. The results showed the failure mode on micro-scale clearly and efforts of interface strength on the failure mode were also explored. The proposed modeling method was especially suitable for establishing 3D microstructure models of ceramic composites or isotropic metal-ceramic particle composites with high volume fraction particles and extended the use of VPs.
Effects of Amino Groups on Dispersibility of Silicon Nitride Powder in Aqueous Media Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Ben Qiu, MengXing Li, BaoSong Xu, PengFei Liu, Qi Chen, BingJie Xu, Zhao Han
Silicon nitride (Si3N4) powders were subjected to amination modification by grafting γ-aminopropyltriethoxysilane (APTES) via a direct blending method in solution. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the hydroxyl groups present on the surface of Si3N4 powder particles interacted with the silanols groups of APTES to combine through covalent bonding. Thermogravimetric analysis (TGA) suggested that the grafting of APTES on Si3N4 powder surface was successful with grafting content reaching up to 7%. Compared to native Si3N4, the surface hydrophilicity of amino Si3N4 powder was enhanced and dispersibility was improved. Overall, these findings indicated the promising aspects of amination modification and future potential use in environmental protection by using water instead of organic solvents during Si3N4 ceramic formation process.
Surface strengthening aluminum alloy by in-situ TiC-TiB2 composite coating Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Fang Yang, Qian Qin, Tao Shi, Cunguang Chen, Zhimeng Guo
An integration technology was employed to prepare TiC-TiB2 strengthening coating on aluminum alloys, with the combination of Self-propagating high-temperature synthesis (SHS) and Vacuum-expendable pattern casting (VEPC). During the VEPC process, the Ti-C-B4C-TP SHS reaction was ignited by molten Al alloy, resulting in the simultaneous obtainment of TiC-TiB2 SHS coating with the cast Al alloy. Specifically, Teflon (PTFE) as reaction promoter was introduced into the SHS system to guarantee the reaction to be ignited successfully. With 3.8 wt.% PTFE addition, homogeneous and dense TiC-TiB2 coating microstructure was obtained. Compared to the matrix, the hardness of the surface coating increased from 80 HB to 284 HB. And, the weight loss decreased from 533 mg to 52 mg at load of 20 N, indicating the significant improvement of wear resistance. In addition, a comprehensive bonding strength of 160 MPa was achieved. The proposed method for preparing hard coating on Al alloys broadens their industry application, where higher hardness and better wear resistance are required.
The thermal shock resistance prediction of porous ceramic sandwich structures with temperature-dependent material properties Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Z. Li, K.F. Wang, B.L. Wang, S.L. Guo
A general numerical model to predict the thermal shock resistance of porous ceramic sandwich (PCS) structures with temperature-dependent material properties is developed. Knowledge of the temperature distribution and associated thermal stress in PCS panel is determined by the finite element method of coupled thermoelasticity. The present work considers the hot/cold shock induced center/edge cracks and measures the time-varied thermal stress intensity factors at the crack tip area. The roles of crack length, relative density of foam core, thermal shock load and geometric parameters of the PCS structures are examined. Moreover, fracture failure analysis of the whole PCS structures is carried out and crack propagation manners are detected. The thermal shock resistance curves of the structures are provided and the critical thermal shock temperatures are estimated for any selected characteristic materials. Results reveal that the thermal shock resistance of the PCS structures will be dramatically underestimated with the ignorance of temperature-dependent material properties. The analysis model of this paper provides a rapid prediction of thermal shock behavior of PCS structures at arbitrary temperatures.
Unlocking the nature of the co-doping effect on the ionic conductivity of CeO2-based electrolyte Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Meina Chen, Huiying Gao, Lei Zhang, Yan Xuan, Junfeng Ren, Meng Ni, Zijing Lin
Doped CeO2 is a very promising electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). To further improve the performance of the CeO2-based electrolyte, co-doping two different elements into CeO2 is a feasible method, however the co-doping effect on the ionic conductivity is not well understood and whether it is synergistic or average is even controversial. In order to gain a fundamental understanding of the co-doping effect, the microscopic properties of co-doped CeO2 are calculated using the DFT+U method. Density of states, band structures, oxygen vacancy formation energies, defect association energies, and oxygen vacancy migration energies are systematically calculated for In3+, Sm3+ single-doped and co-doped CeO2. Based on our calculations, we find that the coexistence of the two doped ions in the local structures of the doped CeO2 can suppress the reduction of Ce4+ to Ce3+, which is beneficial for the decrease of the internal short circuit current of the CeO2-based electrolyte. For In3+ and Sm3+ co-doped CeO2, when the distance between the two doped ions is the first nearest neighbor, the co-doping effect is average. However, when the distance between the two doped ions extends to the second nearest neighbor, the availability of the free oxygen vacancies is synergistically enhanced. Therefore whether the co-doping effect on the ionic conductivity is average or synergistic is highly dependent on the local structures of the co-doped CeO2 which are difficult to control in experiments, offering a reasonable explanation for controversial experimental results. Our work provides a new atomistic level insight into the co-doping effect in CeO2 which would be helpful for high performance electrolyte development.
Spark plasma sintering of Al-doped ZrB2–SiC composite Ceram. Int. (IF 3.057) Pub Date : 2018-11-14 Babak Mohammadpour, Zohre Ahmadi, Mohammadreza Shokouhimehr, Mehdi Shahedi Asl
This research presents the influence of Al addition on microstructure and mechanical behavior of ZrB2–SiC ultra-high temperature ceramic matrix composite (UHTCMC) fabricated by spark plasma sintering (SPS). A 2.5 wt% Al-doped ZrB2–20 vol% SiC UHTCMC was produced by SPS method at 1900 °C under a pressure of 40 MPa for 7 min. The microstructural and phase analysis of the composite showed that aluminum-containing compounds were formed in-situ during the SPS as a result of chemical reactions between Al and surface oxide films of the raw materials (i.e. ZrO2 and SiO2 on the surfaces of ZrB2 and SiC particles, respectively). The Al dopant was completely consumed and converted to the intermetallic Al3Zr and Al4Si compounds as well as Al2O3 and Al2SiO5. A relative density of 99.8%, a hardness (HV5) of 21.5 GPa and a fracture toughness (indentation method) of 6.3 MPa.m1/2 were estimated for the Al-doped ZrB2–SiC composite. Crack bridging, branching, and deflection were identified as the main toughening mechanisms.
Crystallization, microstructure and dielectric properties of the SrO-BaO-Nb2O5-Al2O3-SiO2 based glass ceramics added with ZrO2 Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Shaohui Liu, Jiao Wang, Jun Ding, Haoshan Hao, Limin Zhao, Siyi Xia
The SrO-BaO-Nb2O5-Al2O3-SiO2 (SBN-AS) based glass ceramics with different ZrO2 content were synthesized via the glass melting process and temperature controlled crystallization. The influences of adding different amounts of ZrO2 on the microstructure, crystallization and dielectric properties of SBN-AS based glass ceramics were investigated. Among the studied SBN-AS based glass ceramics with different ZrO2 content, the dielectric constant of the SBN-AS based glass ceramics increases from108.9 to 135.9 with the ZrO2 content when the ZrO2 is lower than 0.5 mol% and then decreases when higher than 1.0 mol%. The breakdown strength of the SBN-AS based glass ceramics first gradually increases from 1111.2 to 1129.4kV/cm with the ZrO2 content and then increases quickly from 1291.6 to 1377.7kV/cm when the ZrO2 content is higher than 1.0mol%. For the 1.0 mol% of ZrO2 content added, the maximum value of energy storage density for the resulting glass-ceramic is 8.9 J/cm3, which is about 113% greater than that of the SBN-AS based glass ceramic without ZrO2 addition. The enhanced energy storage density could be attributed to a few ZrO2 content added into the SBN-AS based glass ceramics as nucleating agents at and excess content ZrO2 as network agents.
Microstructures and properties of amorphous, polycrystalline, and Mn+1AXn-phase Ti–Al–N films synthesized from an Mn+1AXn-phase Ti2AlN compound target Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Teng Fei Zhang, Qixun Xia, Zhixin Wan, Qi Min Wang, Kwang Ho Kim
In this study, the microstructures and properties of amorphous, polycrystalline, and Mn+1AXn (MAX)-phase Ti–Al–N thin films deposited from an MAX-phase Ti2AlN target by magnetron sputtering were studied. The phase structures of the films were altered by varying the deposition parameters and cathode power supply. The effects of the different phase structures on the mechanical, tribological, and nanowear properties of the Ti–Al–N films were systematically investigated. Compared to those of the amorphous and polycrystalline Ti–Al–N thin films, the MAX-phase Ti2AlN film exhibited higher hardness and toughness owing to its unique nanolaminated structure. In addition, the MAX-phase film exhibited a better wear resistance in ball-on-disk and nanowear tests, than those of the other two phases owing to its higher toughness, hardness, and H/E values.
Microstructure evolution and growth behavior of rod-shaped ZrB2 in situ preparation of ZrB2-SiC composite powders Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Yuehua Lin, Jinghang Liu, Shaolei Song, Jingbo Liu, Sajid Bashir, Yun Guo, Qiang Zhen
The microstructure evolution of rod-shaped ZrB2 in situ synthesis of ZrB2-SiC composite powder was studied under different heat treatment. TG-DSC, XRD, SEM, EDS, TEM, and HRTEM were used to describe the preparation, phase composition and morphology of rod-shaped ZrB2. As a result, tiny ZrB2 rod grew out of the liquid phase and adopts a layered growth process. As the rod grew in the longitudinal and transverse directions, the surrounding liquid phase was consumed, and the adjacent rods began to grow in parallel or cross grow to form multiple structures.
INFLUENCE OF DEPOSITION PARAMETERS ON THE STRUCTURE AND MICROSTRUCTURE OF Bi12TiO20 FILMS OBTAINED BY PULSED LASER DEPOSITION Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 L.F. Gorup, V. Bouquet, S. Députier, V. Dorcet, M. Guilloux-Viry, I.M.G. Santos, A.A. Silva, A.E. Nogueira, A.M. Kubo, E. Longo, E.R. Camargo
The structure, morphology and surface roughness of Bi12TiO20 (BTO) thin films grown on R-sapphire by pulsed laser deposition (PLD) were studied at different substrate temperatures, target-substrate distances, oxygen pressures and laser-pulse repetition rates. Although the substrate temperature seems to be the most important experimental parameter, the gas pressure and the target–substrate distance played important role on the phase formed and film thickness, with a significant effect of the laser-pulse repetition rate on the films thickness and preferred orientation of the deposited film. Single-phase γ-Bi12TiO20 was obtained on substrates at 650 °C, while several BTO metastable phases were observed in films deposited on substrates at temperatures between 500 and 600 °C. By the first time, thin films of pure and textured δ-Bi12TiO20 were successfully growth on substrates at 450 °C. When annealed, all the films deposited at lower temperatures resulted in the thermodynamically stable γ-Bi12TiO20.
Preparation and characterization of the three-dimensional network mullite porous fibrous materials by pressure and freeze-casting method Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Fei He, Wenjie Li, Liang Zhou, Lijuan Yang, Hongbo Zhao, Xiaodong He
Porous fibrous materials (PFMs) with three-dimensional networks were prepared by mullite fibers as skeleton and silica sols as binder via pressure and freeze-casting method. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) were used to investigate the microstructures, phase and porous characteristics. The density of PFMs can be controlled by adjusting the pressure and sintering during the synthetic process. With the increase of density, the mechanical and thermal conduction properties were increased due to densification of fibers. Based on their lightweight and low thermal conductivity, the PFMs can be used in the field of high temperature thermal insulation.
Effect of B4C on co-sintering of SiC ceramic membrane Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Jingxiong Liu, Chao Tian, Hanning Xiao, Wenming Guo, Pengzhao Gao, Jianjun Liang
A SiC ceramic membrane was successfully fabricated at 2200 °C by a co-sintering process through the addition of B4C powder. The support and membrane with a pore size of 34.92μm and 9.93 μm were prepared with coarse SiC powder (~120 μm) and spheroidized SiC powder (~22 μm), respectively. The interface between the support and membrane was distinct and particles were closely bonded to each other. The addition of 1.5 wt% B4C can decrease the sintering temperature of support from 2350 °C to 2200 °C, which had a good match with that of membrane. The mechanism for promoting the sintering of support is that B4C dissolved into the SiC lattice and increased the crystal defects. The bending strength of the support and the membrane was 38.77 MPa and 32.15 MPa, respectively. The nitrogen gas flux and gas permeability of the SiC ceramic membrane was 19406 m3/m2·h·bar and 5.817×10–12 m2.
Iron molybdate and manganese dioxide microrods as a hybrid structure for high-performance supercapacitor applications Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Aqib Muzaffar, M. Basheer Ahamed
FeMoO4@MnO2 microrod binary hybrid structure is synthesized by a simple two-step hydrothermal method. The phase formation and morphology of FeMoO4@MnO2 were analyzed using X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) respectively. High-resolution transmission electron microscopy (HRTEM) analysis of the sample confirms its microrod morphology and polycrystalline natuer. The electrochemical measurements revealed the supercapacitive behavior by encompassing both double layered capacitance as well as pseudocapacitance at lower and higher scan rates respectively. A symmetric fabrication method was employed using FeMoO4@MnO2 as both negative and positive electrode for electrochemical analysis. The symmetric supercapacitor cell yields a specific capacitance of 839.29 F g−1 at a current density of 1 A g−1 in addition to higher cyclic stability and performance. The sandwiched symmetric supercapacitor device displays a high specific energy density of 56.95 W h kg−1 at a power density of 418.46 W kg−1. In addition to that, the device showed a promising capacity retention of 87% with an efficiency 80% of after 10000 cycles. The electrochemical results show that FeMoO4@MnO2 could present itself as a promising electrode material for the next generation supercapacitors applications.
Tuning of Optical and Antibacterial Characteristics of ZnO thin films: Role of Ce Content Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Zohra Nazir Kayani, Sonia Sahar, Saira Riaz, Shahzad Naseem
The properties of Ce-doped ZnO (CZO) thin films synthesized through sol-gel dip coating processing were evaluated. Five thin films were synthesized by increasing Ce percentage between 1–5 at. wt. %. The XRD study put forward that Ce doped ZnO displayed hexagonal wurtzite ZnO structure and Ce ions are embedded in the ZnO lattice successfully. Results showed that the crystallite size decreased, as the percentage of Ce in the ZnO increased. The lattice volume of the thin film was distorted in the presence of Ce. Broadening and shrinking of the band gap took place under different Ce doping concentrations due to generation of defects and appearance of secondary phase. All thin film has shown antibacterial activity.
Crystal structure and microwave dielectric properties of Li4Mg3[Ti1-x(Mg1/3Ta2/3)x]2O9 (x=0–0.4) ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 C.F. Xing, H.T. Wu
A series of Li4Mg3[Ti1-x(Mg1/3Ta2/3)x]2O9 (LMT1-x(MT)x) (x=0–0.4) ceramics were prepared via the traditional solid-state method. The effects of the substitution of (Mg1/3Ta2/3)4+ on the sintering characteristic, crystal structure, phase composition and dielectric properties of Li4Mg3Ti2O9 ceramics were investigated for the first time. The analysis of the X-ray diffraction pattern indicated that the pure cubic Li4Mg3Ti2O9 phase could be formed in the whole composition range of 0≤x≤0.4. Dense and homogeneous microstructures of LMT1-x(MT)x ceramics sintered at 1400–1550 °C could be revealed from the scanning electric microscope. The optimum microwave dielectric properties, with a permittivity 15.77, a quality factor 160,575 GHz (at 8.38 GHz) and a τf value 0 ppm/°C, were achieved in the Li4Mg3[Ti0.8(Mg1/3Ta2/3)0.2]2O9 ceramic sintered at 1550 °C.
Magnetic phase separation in polycrystalline Pr0.5–xBixSr0.5MnO3 (x ≤ 0.15) Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 A. Krichene, W. Boujelben, S. Mukherjee, N.A. Shah, P.S. Solanki
In this paper, magnetic phase coexistence and magnetotransport properties of Pr0.5–xBixSr0.5MnO3 (x ≤ 0.15) samples have been studied. Our specimens demonstrate complicated magnetic properties through the presence of several transitions as a function of temperature. With increase in bismuth content, a spin–glass–like–state appears at low temperatures and long–range charge ordering can be observed for x = 0.15. Magnetization and resistivity seems to be sensitive to magnetic field cycling, testifying the presence of training effect. Both, magnetic phase separation phenomenon and 6 s² lone pair electrons of Bi3+ ions, play a key role in the governance of the physical response of studied specimens.
Preparation and performance of ultrafine grained WC-10Co alloys with added La2O3 Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Jianfeng Li, Jigui Cheng, Bangzheng Wei, Pengqi Chen
La2O3/WC-10Co mixed-powders with different amounts of La2O3 were prepared by ball milling. Then, the powders were pressed and consolidated by microwave sintering. The microstructure and mechanical properties of the La2O3/WC-10Co alloys with different La2O3 contents were investigated. The experimental results show that addition of an appropriate amount of La2O3 can suppress WC grain growth and narrow the grain size distribution. With the addition of a small amount of La2O3, the nanosize La2O3 particles mainly distribute at the interfaces between the WC and Co phases. However, excessive addition of La2O3 leads to aggregation, forming large particles with a size of approximately 200 nm. Two types of interface relationships were observed between the La2O3 and WC phases in the samples. One is that of the well-coherent interface, and the other is that of the poorly coherent interface where structural disorder is found in the 1–3 nm wide region between the La2O3 and WC phases. However, this structural disorder does not occur in the interfaces between Co and La2O3 phases. Addition of a minor amount of La2O3 into the alloys has less effect on the relative density of the La2O3/WC-10Co alloys. Regarding the mechanical properties, when the La2O3 content is 0.8 wt.% (the mass ratio of La2O3 in Co), the Rockwell hardness and fracture toughness of the La2O3/WC-10Co alloys reach 91.8 HRA and 13.44 MPa∙m1/2, respectively. The transverse rupture strength (TRS) has a maximum value of 2359 MPa when the La2O3 content is 1.2 wt.%.
Effect of growth temperature on Catalyst free hydrothermal Synthesis of crystalline SnO2 micro-sheets Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Sajad Hussain, Jolly Jacob, Nadia Riaz, Khalid Mahmood, Adnan Ali, Nasir Amin, Ghulam Nabi, M. Isa, Mian H.R. Mahmood
In this work, We have successfully grown the crystalline Tin Oxide (SnO2) micro-sheets by hydrothermal technique without using any catalyst. We also able to controlled the thickness of grown sheets by modulating the growth temperature and have reported the thickest micro-sheets (5μm thick) for the first time. X-ray diffraction (XRD) studies confirm the tetragonal crystalline structure of grown SnO2 and particle size was found to be increased from 2–15 nm as the synthesis temperature increased from 50–250 °C. SEM images have shown the micro-sheets like morphology of synthesized samples and the thickness of sheets increased from 1.4–5.1±0.01 μm as the growth temperature increased from 150–250 °C respectively. Raman spectroscopy measurements showed a dominant peak at 639 cm−1 which is related to A1g mode of SnO2. The intensity of A1g mode increased with growth temperature supporting the XRD results that the crystal structure of grown SnO2 sheets improved with increasing growth temperature. Furthermore, the degree of crystanality, calculated from Raman data, increased to 68% at growth temperature 250 °C. The analysis of UV–Visible data demonstrated that increasing temperature from 150℃ to 250℃ causes the shift in the optical absorption edge from 280–290 mm respectively.
Fabrication and characterization of Li4SiO4 pebbles by extrusion spherodization technique: Effects of three different binders Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 G. Jaya Rao, R. Mazumder, D. Dixit, C. Ghoroi, S. Bhattacharyya, P. Chaudhuri
The present report demonstrates the effects of three different binders on fabrication of Li4SiO4 pebbles by extrusion-spherodization technique. It is found that the nature of binders, concentrations and moisture content have significant effect on the density, sphericity, grain size and crush load of the Li4SiO4 pebbles. Different viscosity grade binders namely PVA, PVP and guargum have been explored for the fabrication of pebbles. XRD, FESEM, BET, Inverse gas chromatography, pebble crush load tester are used to study different properties. It has been observed that the pebbles fabricated with 6 wt% PVP show the desired properties [appreciable density (85%), smaller grain size (<8 µm), good sphericity (0.98) and notable crush load (17 N)] when compared with the other two binders. Surface energy and microstructure of the green aggregates provide some comprehensive information for achieving desired properties in PVP derived pebbles. The effects of the sintering temperature on the different properties have also been studied.
Development of MgO:TiO2 thin films for gas sensor applications Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Buse Cömert Sertel, Nihan Akin Sonmez, Meltem Donmez Kaya, Suleyman Ozcelik
In this study, structural, morphological and optical properties, and gas sensor performance of magnesium oxide (MgO) doped titanium dioxide (TiO2) thin films were investigated in detail. Gas sensor metallic patterns were fabricated on Si substrate using traditional photolithographic technique. MgO doped TiO2 thin films were deposited on formed Pt electrode surface by confocal sputtering (co-sputtering) system as the active layer. Thin film characterizations were realized by using secondary ion mass spectrospocy (SIMS), atomic force microscope (AFM) and UV–Vis Spectrometer (UV-Vis). Gas sensing measurements were performed by gas sensing test system against methane gas at working temperature of 300 °C. To evaluate deposition and thermal annealing effects on the sensing performance, sensors were tested under gas. The sensitivity and response/recovery time of gas sensors were measured in 1000 ppm. MgO doped TiO2 based sensor at substrate temperature of 100 °C has high sensitivity and short response/recovery time.
Aloe peel-derived honeycomb-like bio-based carbon with controllable morphology and its superior electrochemical properties for new energy devices Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Ziqi Wang, Sining Yun, Xiaodong Wang, Chen Wang, Yiming Si, Yangliang Zhang, Hongfei Xu
In this study, aloe peel-derived honeycomb-like porous carbons (AP-HC) are controllably prepared by combining simple hydrothermal carbonization with chemical activation. A morphology transformation from the spherical structure (AP-SC) to the honeycomb-like structure (AP-HC) is achieved for biomass-derived carbon materials and is accompanied by an increase in the specific surface area from 13 m2 g−1 to 1286 m2 g−1. The AP-HC as a counter electrode (CE) for dye-sensitized solar cells (DSSCs) exhibits remarkable catalytic activity for I3- ion reduction and a high power conversion efficiency (PCE) of 6.92% that matches the Pt-based DSSC's performance (7.19%). As a working electrode in supercapacitors (SCs), a high specific capacitance of 264 F g−1 at 0.5 A g−1 is achieved in a three-electrode system. Additionally, a high retention rate of ∼77.45% (ranging from 0.5−30.0 A g−1) and superior cycling performance (91% capacitance retention after 5,000 cycles) are also demonstrated. This study provides an efficient strategy for fabricating morphology-controllable porous bio-based carbon with higher specific surface area (1286 m2 g−1) that exhibits significant potential for new energy devices.
β-SiAlON ceramic membranes modified with SiO2 nanoparticles with high rejection rate in oil-water emulsion separation Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Dong-Shuai Zhang, Hamidreza Abadikhah, Jun-Wei Wang, Lu-Yuan Hao, Xin Xu, Simeon Agathopoulos
Porous ceramic membranes with high mechanical strength are suitable for oil-water emulsion separation. Nonetheless, it is difficult to prepare ceramic membranes with a small pore size and a good antifouling ability. In this work, SiO2 nanoparticles were used to modify β-SiAlON ceramic membranes, which were successfully utilized to remove small oil droplets from oil-water emulsion. The modified membranes displayed a narrow pore size (the average pore size decreased from 1.05 μm, in the unmodified membrane, to 0.65 μm), and gas and water fluxes which are suitable for oil-water separation. Oil rejection rate was always higher than 90% under various pressures (1.0 − 2.0 bar) and flow velocities (1.0 − 3.0 L·min−1) tested, which is considerably higher (60%) than the rejection rate of the unmodified membrane (which was 39.8%). Moreover, the modified membranes exhibited a good antifouling ability, since flux declined by only 7.0% after three recoveries via a simple ultrasonic treatment, over a total running period of 10 h. Accordingly, the produced membranes can be qualified for further consideration in oily wastewater treatment.
Microscopic wear study of the sintered diamond trepanning drill during machining alumina armor ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Lei Zheng, Wendong Wei, Xianglong Dong, Chen Zhang, Yong Zeng, Chunwei Zhang, Haixiang Huan
High purity engineering ceramics have been increasingly used for constituting novel lightweight ceramic composite armors along with various FRP materials. In the assembly process of ceramic composite armors, a large number of hole processing is required. Usually, diamond trepanning drills are preferentially adopted for machining relatively large holes of engineering ceramics. However, during drilling high purity armor engineering ceramics, the diamond tools are usually worn considerably due to their high dynamic compression strength and high hardness. In this study, taking the high purity alumina armor ceramics (99 wt% Al2O3) as machining object, the comprehensive wear features of the sintered diamond trepanning drill have been intensively studied through SEM examinations, including the microscopic wear morphologies of diamond grains and matrix binding agent, the diamond abrasion mechanism, the wear disfigurations of the drill labial surface and the drill slipping mechanism. According to the discussed results, the wear process of the diamond grains at the matrix labial surface can be divided into three stages: intact crystal, slight wear and severe wear stages. The quicksand phenomenon occurrence around the diamond grains is the typical feature of the matrix binding agent wear. The normal grinding of the drill can be interrupted by the severe inner-trumpet-shape wear and the cutting-groove wear of the drill labial surface. In most situations, only the slight inner-trumpet-shape wear occurs for the drill, which does not affect the normal drilling operation. The drill slipping is mainly attributed to the fact that most exposed diamond grains at the drill labial surface have been rubbed down into a polished planar shape and totally blunted. The results achieved in this study can provide helpful references for the performance improvement design of the sintered diamond trepanning drill.
Engineering Bi2S3/BiOI p-n heterojunction to sensitize TiO2 nanotube arrays photoelectrodes for highly efficient solar cells and photocatalysts Ceram. Int. (IF 3.057) Pub Date : 2018-11-13 Qingyao Wang, Zhiyuan Liu, Hao Feng, Rencheng Jin, Shaohua Zhang, Shanmin Gao
To significantly improve the solar harvesting and electron transportation, Bi2S3/BiOI p-n heterojunctions were successfully formed on the surface of TiO2 nanotube arrays (TiO2 NTs/Bi2S3-BiOI) by a simple solvothermal method, and the morphology, composition and photoelectrochemical property of the TiO2 NTs/Bi2S3-BiOI were investigated by adjusting the concentration ratio of sulphur/iodonium. TiO2 NTs/Bi2S3-BiOI nanosheets and nanorods were prepared, and the self-assembled microflowers were also observed. The results indicated that flower-like TiO2 NTs/Bi2S3-BiOI showed high visible light absorption, photocurrent density and rapid photoelectrocatalytic removal of organic dyes and Cr(VI). The growth and photocatalytic mechanism were proposed to illuminate the high photoelectrochemical performances. The excellent photoelectrochemical activities drive the TiO2 NTs/Bi2S3/BiOI being superior environmental and energy materials in the applications of wastewater purification and solar cells.
Fabrication and tribological properties of a self-lubricating wear-resistant coating based on structural coupling Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 Hang Zhao, Yu-feng Liu, Bin Xu, Yan-jun Lu, Chao-lan Zhou, Xiao-yu Wu, Jian-jun Li
To improve the traditional laser cladding self-lubricating coating technique, a new type of self-lubricating composite coating is proposed in this study. This novel structural-coupling self-lubricating wear-resistant coating (SSWC) is fabricated on stainless steel using a laser cladding + vacuum pressure thermal-diffusion welding (VPTW) process. The coating has an interlaced-stripe structure from an organic combination of separated wear-resistant units (WUs) and self-lubricating units (SUs), which are prepared using NiCrSiB powder and Cu-coated graphite composite powder, respectively. The WUs have a microstructure consisting of a Ni-rich γ- (Ni, Fe) matrix and Cr-rich carbide and boride precipitates, and the SUs primarily consist of Cu matrix and graphite. Distinctive microstructures determine the obvious increase in the hardness of the WUs compared to the substrate and the decrease in the hardness of the SUs. As a result, microhardness with alternating softness and hardness occurs on the surface of the SSWC. The tribological properties of the SSWC are evaluated through the reciprocating friction and wear test compared with the as-received substrate, NiCrSiB coating and Cu-G coating at room temperature. The results exhibit considerably better antifriction properties of the SSWC compared to other wear specimens. This property can be attributed to the positive role of the SUs contained in the SSWC, which have a self-lubricating property and promote the formation of tribofilm with a lubricity and protection on the worn surface of WUs by sliding action. The wear mechanism of SUs is mainly abrasive wear. In contrast, the main wear mechanism of WUs varies with the sliding time: abrasive wear at the initial stage that shifts to delamination wear and abrasive wear after long-term sliding due to the generation of tribofilm. Additionally, a synergistic relationship between the WUs and SUs was observed during the wear process, which can lead to the specific tribological properties of the SSWC.
Synthesis of a cubic Ti(BCN) advanced ceramic by a solid-gas mechanochemical reaction Ceram. Int. (IF 3.057) Pub Date : 2018-11-12 E. Chicardi, C. García-Garrido, A.M. Beltrán, M.J. Sayagués, F.J. Gotor
In this work, a titanium boron carbonitride advanced ceramic was successfully synthesised by a solid-gas mechanochemical reaction in a planetary ball mill from a mixture of elemental Ti, B, and C under nitrogen atmosphere. This material, with a general formula of Ti(BCN), exhibits a face-centred cubic structure (NaCl type) that is analogous to Ti(CN). This phase was gradually formed with sufficient milling time as a result of diffusional processes, which were permitted by the reduction of the energy in the system caused by the decrease in the spinning rate of the planetary ball mill. In contrast, under more energetic milling conditions, a mechanically induced self-sustaining reaction (MSR) took place, leading to the formation of a TiB2-Ti(CN) ceramic composite. The microstructural characterisation revealed that Ti(BCN) was composed of ceramic particles constituted of misoriented nanocrystalline domains. B, C and N were optimally distributed in the Ti(BCN) phase. The TiB2-Ti(CN) ceramic composite was composed of micrometric and nanometric particles homogeneously distributed. Additionally, the nitrogen content obtained for Ti(BCN) was higher than for the Ti(CN) phase in the composite material.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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