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1.
《Ceramics International》2017,43(2):2143-2149
Graphene has been successfully fabricated by a novel method, using graphite powder and NMP (N-Methyl Pyrrolidone) as the raw materials based on the principles of liquidoid exfoliation and mechanical milling. SEM, TEM and Raman spectrum were utilized to characterize the morphology of the homemade graphene, illustrating the few defects and rare layers were endowed in this study. Afterwards, the homemade and commercial graphene were doped into Al2O3 powder with the mass ratio of 0%, 1%, 2%, and 3% to reinforce the mechanical properties of the matrix. The composites were processed at 1600 °C, pressure of 30 MPa and soaking time of 1 h by vacuum hot pressing. The test results illustrated the bending strength and fracture toughness tended to be intensive at first and subdued afterwards, achieving the optimal performance of 625.4±18.2 MPa and 6.07±0.22 MPa m1/2 at 2 wt% prepared graphene additive, and the commercial grapheme owned the best heighten effect in 3 wt% graphene/Al2O3 composites. Compared to the blank Al2O3 sintered samples, the graphene/Al2O3 specimens (both prepared and commercial additive) behaved evident increase in mechanical properties, even upon 30% enhanced in fracture toughness and bending strength generally by the prepared grapheme. Moreover, the prepared graphene had better improvement effect than commercial graphene in enhancing mechanical properties of Al2O3 ceramic. 相似文献
2.
《Ceramics International》2016,42(7):8620-8626
In this work a 19.58Li2O·11.10ZrO2·69.32SiO2 (mol%) glass–ceramic matrix was prepared and milled in order to determine its coefficient of thermal expansion (CTE) and to study how it is influenced by the addition of nanosized Al2O3 particles (1–5 vol%) and submicrometric Al2O3 particles (5 vol%). Comminution studies from the LZS parent glass frit showed that a powder with an adequate particle size (3.5 µm) is achieved after 120 min of dry milling followed by a second step of 60 h wet milling. The obtained LZS glass–ceramic samples (fired at 900 °C/30 min) showed an average relative density of ∼98% with zirconium silicate and lithium disilicate as main crystalline phases. Prepared composites with 1, 2.5 and 5 vol% of nanosized Al2O3 and 5 vol% submicrometric Al2O3 showed average relative densities varying from 97% to 94% as the alumina content increased. The formation of β-spodumene in the obtained composites leads to reduce the CTEs, whose values ranged from 9.5 to 4.4×10−6 °C−1. Composites with 5% nanosized alumina showed a CTE lower than that of the equivalent formulation with submicrometric alumina. 相似文献
3.
《Carbon》2013
Reduced graphene oxide (rGO) tethered with maghemite (γ-Fe2O3) was synthesized using a novel modified sol–gel process, where sodium dodecylbenzenesulfonate was introduced into the suspension to prevent the undesirable formation of an iron oxide 3D network. Thus, nearly monodispersed and homogeneously distributed γ-Fe2O3 magnetic nanoparticles could be obtained on surface of graphene sheets. The utilized thermal treatment process did not require a reducing agent for reduction of graphene oxide. The morphology and structure of the composites were investigated using various characterization techniques. As-prepared rGO/Fe2O3 composites were utilized as anodes for half lithium ion cells. The 40 wt.%-rGO/Fe2O3 composite exhibited high reversible capacity of 690 mA h g−1 at current density of 500 mA g−1 and good stability for over 100 cycles, in contrast with that of the pure-Fe2O3 nanoparticles which demonstrated rapid degradation to 224 mA h g−1 after 50 cycles. Furthermore, the composite showed good rate capability of 280 mA h g−1 at 10C (∼10,000 mA g−1). These characteristics could be mainly attributed to both the use of an effective binder, poly(acrylic acid) (PAA), and the specific hybrid structures that prevent agglomeration of nanoparticles and provide buffering spaces needed for volume changes of nanoparticles during insertion/extraction of Li ions. 相似文献
4.
《Ceramics International》2017,43(15):12154-12161
We fabricated CuO/Al2O3 green compacts from plate-like Al2O3 and granular CuO powders by multi-press forming and investigated the alumina orientation using Lotgering's method. The results showed that Al2O3 particles preferentially aligned perpendicular to the pressure direction and the orientation degree increased as the forming pressure was increased. We proposed a model describing the movement of the alumina particles to explain the pressure effect on their orientation. The orientation calculation was in good agreement with those by Lotgering's method. Furthermore, we prepared the CuAlO2 compacts by regular or spark plasma sintering (SPS). However, the compacts sintered by SPS exhibited higher orientation degree and density than those produced by regular sintering. The electrical conductivity values of the orientation-controlled compacts sintered by SPS reached 770 S m−1 at 928 K, which was close to that of CuAlO2 single crystal. The power factor of the CuAlO2 compacts with highest orientation degree is as high as 5.95 × 10−5 W m−1 K−1 at 928 K. Therefore, we can conclude that orientation control is an effective method to enhance the thermoelectric performance of compact polycrystalline CuAlO2 bulks. 相似文献
5.
《Carbon》2014
Direct growth of graphene on Al2O3 film is successfully achieved assisted with NiAl2O4 film on a SiO2 substrate by chemical vapor deposition at 800 °C. The Ni particles are first uniformly separated out on the substrate, and play an important role in capturing carbon atoms and accelerating the nucleation to grow high quality graphene rooting on insulating Al2O3 film. The thickness of graphene films can be tuned from two layers to few layers (<10) by changing growth time. The continuous graphene films exhibit extremely excellent electrical transport properties with a sheet resistance of down to 18.5 Ω sq−1. The graphene/Ni/Al2O3/SiO2 is used as the counter electrode of dye sensitized solar cell which achieves a photovoltaic efficiency of 7.62%. 相似文献
6.
《Journal of the European Ceramic Society》2017,37(1):213-221
This paper proposes a new strategy to design the high-performance Al2O3/Mo self-lubricated composites with excellent practical value and durability. The relationships among the relevant structural parameters, interfacial compositions, mechanical and thermal properties of the materials were analyzed. Results show that the apparent toughness, bending strength and work of fracture of the optimal Al2O3/Mo-Al2O3 laminated materials could reach 8.1 MPa m1/2, 634 MPa and 330 J m−2. Moreover, the new-developed materials exhibited a good self-lubricating property on every surface and thermal shock resistance. The friction coefficients of all the surfaces can be as low as 0.45 at 800 °C, and the retention rates of strength and toughness after thermal shock between 25 °C and 1000 °C for 50 cycles could reach 98.8% and 85.3%, respectively. The new strategy is based on a combination strong interfacial bonding and with accelerated formation of a reasonable residual stress and enhanced grain-interlocking among particles during fatigue. 相似文献
7.
《Ceramics International》2017,43(9):7153-7158
In this work, Yb3+ was selected to replace the Y3+ in yttrium aluminum garnet (YAG) in order to reduce its thermal conductivity under high temperature. A series of (Y1-xYbx)3Al5O12 (x=0, 0.1, 0.2, 0.3, 0.4) ceramics were prepared by solid-state reaction at 1600 °C for 10 h. The microstructure, thermophysical properties and phase stability under high temperature were investigated. The results showed that all the Yb doped (Y1-xYbx)3Al5O12 ceramics were comprised of a single garnet-type Y3Al5O12 phase. The thermal conductivities of (Y1-xYbx)3Al5O12 ceramics firstly decreased and subsequently increased with Yb ions concentration rising from room temperature to 1200 °C. (Y0.7Yb0.3)3Al5O12 had the lowest thermal conductivity among investigated specimens, which was about 1.62 W m−1 K−1 at 1000 °C, around 30% lower than that of pure YAG (2.3 W m−1 K−1, 1000 °C). Yb had almost no effect on the coefficients of thermal expansion (CTEs) of (Y1-xYbx)3Al5O12 ceramics and the CTE was approximate 10.7×10−6 K−1 at 1200 °C. In addition, (Y0.7Yb0.3)3Al5O12 ceramic remained good phase stability when heating from room temperature to 1450 °C. 相似文献
8.
《Journal of the European Ceramic Society》2007,27(8-9):2967-2971
The effects of slow-cooling and annealing conditions on dielectric loss, thermal conductivity and microstructure of AlN ceramics were investigated. Y2O3 from 0.5 to 1.25 mol% at 0.25% increments was added as a sintering additive to AlN powder and pressureless sintering was carried out at 1900 °C for 2 h in a nitrogen flowing atmosphere. To improve the properties, AlN samples were slow-cooled at a rate of 1 °C min−1 from 1900 to 1750 °C, subsequently cooled to 970 °C at a rate of 10 °C min−1 and then annealed at the same temperature for 4 h. AlN and YAG (5Al2O3/3Y2O3) were the only identified phases from XRD. AlN doped with 0.5 and 0.75 mol% Y2O3 had a low loss of <2.0 × 10−3 and a high thermal conductivity of >160 W m−1 °C−1. 相似文献
9.
《Carbon》2014
Porous iron oxide (Fe2O3) nanorods anchored on nitrogen-doped graphene sheets (NGr) were synthesized by a one-step hydrothermal route. After a simple microwave treatment, the iron oxide and graphene composite (NGr-I-M) exhibits excellent electrochemical performances as an anode for lithium ion battery (LIB). A high reversible capacity of 1016 mAh g−1 can be reached at 0.1 A g−1. When NGr-I-M electrode was further coated by 2 ALD cycles of ultrathin Al2O3 film, the first cycle Coulombic efficiency (CE), rate performance and cycling stability of the coated electrode can be greatly improved. A stable capacity of 508 mAh g−1 can be achieved at 2 A g−1 for 200 cycles, and an impressive capacity of 249 mAh g−1 at 20 A g−1 can be maintained without capacity fading for 2000 cycles. The excellent electrochemical performance can be attributed to the synergy of porous iron oxide structures, nitrogen-doped graphene framework, and ultrathin Al2O3 film coating. These results highlight the importance of a rational design of electrode materials improving ionic and electron transports, and potential of using ALD ultrathin coatings to mitigate capacity fading for ultrafast and long-life battery electrodes. 相似文献
10.
《Journal of the European Ceramic Society》2017,37(6):2491-2499
The key requirements for a successful thermal and environmental barrier coating (T/EBC) material include stability in high temperature water vapor, low Young's modulus, close thermal expansion coefficient (TEC) with mullite, low thermal conductivity and weak mechanical anisotropy. The current prime candidates for top coat are ytterbium silicates (Yb2SiO5 and Yb2Si2O7). A major weakness of these two silicates is the severe anisotropy in mechanical properties and thermal expansion that would lead to cracking of the coating. Thus, searching for new materials with weak mechanical and thermal anisotropy is of signification. In this work, the crystal structure, mechanical and thermal properties of a promising T/EBC candidate, Yb4Al2O9, are investigated theoretically and experimentally. Good ductility, low shear deformation resistance, low Young's modulus (151 GPa) and low thermal conductivity (0.78 W m−1 K−1) is underpinned by heterogeneous bonding characteristic and distortion of the structure. Close TEC (6.27 × 10−6 K−1) with mullite and weak mechanical anisotropy highlight the suitability of Yb4Al2O9 as a prospective T/EBC. 相似文献
11.
《Ceramics International》2017,43(8):6232-6238
Uniform Nb2O5 nanospheres/surface-modified graphene (SMG) composites for anode materials in lithium ion batteries were synthesized by hydrothermal method. The microstructure and morphology of composites were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscope techniques. The experimental results showed that Nb2O5 nanospheres were tightly and uniformly grown on the surface of SMG nanosheets. Nb2O5 nanospheres/SMG composites exhibited an impressive reversible capacity of 404.6 mA h g−1 at the current density of 40 mA g−1 after 100 cycles, and an excellent rate capacity of 345.5 mA h g−1 at the current density of 400 mA g−1. 相似文献
12.
《Ceramics International》2016,42(14):15634-15642
Sb2O3/reduced graphene oxide (RGO) composites were prepared through a facile microwave-assisted reduction of graphite oxide in SbCl3 precursor solution, and investigated as anode material for sodium-ion batteries (SIBs). The experimental results show that a maximum specific capacity of 503 mA h g−1 is achieved after 50 galvanostatic charge/discharge cycles at a current density of 100 mA g−1 by optimizing the RGO content in the composites and an excellent rate performance is also obtained due to the synergistic effect between Sb2O3 and RGO. The high capacity, superior rate capability and excellent cycling performance of Sb2O3/RGO composites demonstrate their excellent sodium-ion storage ability and show their great potential as electrode materials for SIBs. 相似文献
13.
《Ceramics International》2017,43(8):6554-6562
In order to improve the electrochemical performance of lithium titanium oxide, Li4Ti5O12 (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173 mA h g−1 at 0.1 C and a well maintained capacity of 65 mA h g−1 even at 20 C. The energy density of 14 Wh kg−1 at a power density of 2700 W kg−1 was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4 A g−1. This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels. 相似文献
14.
《Journal of the European Ceramic Society》2017,37(13):3909-3915
Highly porous Ca3Co4O9 thermoelectric oxide ceramics for high-temperature application were fabricated by sol–gel synthesis and subsequent conventional sintering. Growth mechanism of misfit-layered Ca3Co4O9 phase, from sol–gel synthesis educts and upcoming intermediates, was characterized by in-situ X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations. The Ca3Co4O9 ceramic exhibits a relative density of 67.7%. Thermoelectric properties were measured from 373 K to 1073 K. At 1073 K a power factor of 2.46 μW cm−1 K−2, a very low heat conductivity of 0.63 W m−1 K−1 and entropy conductivity of 0.61 mW m−1 K−2 were achieved. The maintained figure of merit ZT of 0.4 from sol–gel synthesized Ca3Co4O9 is the highest obtained from conventional, non-doped Ca3Co4O9. The high porosity and consequently reduced thermal conductivity leads to a high ZT value. 相似文献
15.
《Ceramics International》2016,42(10):12097-12104
In this work, cross-linked graphene aerogel (CL-GA) and its composite with Fe2O3 nanoparticles (NPs) were synthesized through a one-step hydrothermal procedure by using p-phenylenediamine (PPD). Structural characterizations revealed that in the preparation of the composite PPD acts as a cross-liker and provides high surface area by decreasing restacking of graphene sheets and functions as nitrogen source simultaneously. The electrochemical characteristics of the nanocomposite were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS) and Fast Fourier transform continues cyclic voltammetry (FFTCCV). The results show that cross-linked graphene aerogel/Fe2O3 (CL-GA/Fe2O3) nanocomposite displays enhanced supercapacitive performance, where it has capacitance of 445 at 1 A g−1, high energy density of 63 W h Kg−1, and 89% capacitance retention after 5000 cycles in 3 M KOH. Presence of PPD considerably improved supercapacitive performance of nanocomposite as a result it could be promising material in synthesis of efficient graphene/metal oxide-based electrode material for high performance supercapacitors. 相似文献
16.
《Carbon》2013
Graphene was prepared using liquid phase exfoliation and dispersed in an alumina matrix using an ultrasonication and powder processing route. Al2O3–graphene composites with up to 5 vol% content were densified (>99%) using SPS. The fracture toughness of the material increased by 40% with the addition of only 0.8 vol% graphene. However for higher graphene contents the improvement in fracture toughness was limited. Graphene changed the mechanism of crack propagation for the alumina matrix from inter-granular to trans-granular. The formation of an inter-connecting graphene network promoted easy fracture for concentration ⩾2 vol%. Elastic modulus remained nearly constant for up to 2 vol% and decreased significantly for 5 vol% due to the formation of the inter-connecting graphene network. Fracture toughness measured with the indentation and chevron notch methods were consistent up to 2 vol% and at 5 vol% the percolating network of graphene resulted in easy crack propagation with significant discrepancy between the results for the two methods. 相似文献
17.
《Carbon》2013
The composites of V2O3–ordered mesoporous carbon (V2O3–OMC) were synthesized and used as anode materials for Li-ion intercalation. These materials exhibited large reversible capacity, high rate performance and excellent cycling stability. For instance, a reversible capacity of V2O3–OMC composites was 536 mA h g−1 after 180 cycles at a current density of 0.1 A g−1. The high electrochemical performance of the V2O3–OMC composites is attributed to the anchoring of nanoparticles on mesoporous carbon for improving the electrochemical active of V2O3 particles for energy storage applications in high performance lithium-ion batteries. 相似文献
18.
《Journal of the European Ceramic Society》2017,37(9):3131-3136
Thermal insulation applications have long required materials with low thermal conductivity, and one example is yttria (Y2O3)-stabilized zirconia (ZrO2) (YSZ) as thermal barrier coatings used in gas turbine engines. Although porosity has been a route to the low thermal conductivity of YSZ coatings, nonporous and conformal coating of YSZ thin films with low thermal conductivity may find a great impact on various thermal insulation applications in nanostructured materials and nanoscale devices. Here, we report on measurements of the thermal conductivity of atomic layer deposition-grown, nonporous YSZ thin films of thickness down to 35 nm using time-domain thermoreflectance. We find that the measured thermal conductivities are 1.35–1.5 W m−1 K−1 and do not strongly vary with film thickness. Without any reduction in thermal conductivity associated with porosity, the conductivities we report approach the minimum, amorphous limit, 1.25 W m−1 K−1, predicted by the minimum thermal conductivity model. 相似文献
19.
《Journal of the European Ceramic Society》2006,26(4-5):703-710
Thermal diffusivity, a, and thermal conductivity, κ, between room temperature and 600 K were investigated for SiC composites containing 0–50 mass% of Tyranno® SiAlC (SA) fibre (mean length: 394 μm) hot-pressed at 1800 °C for 30 min under a pressure of 31 MPa. The monolithic SiC specimen possessed κ of 32.1 W m−1 K−1 at room temperature; no significant changes were found for the SiC composite containing ≤20 mass% of SA fibre addition. However, further increases in the amount of SA fibre to 50 mass% improved κ to a maximum of 56.3 W m−1 K−1. The value of a for the SiC composite containing 40 mass% of SA fibre was 0.185 cm2 s−1 at room temperature and decreased to 0.120 cm2 s−1 at 600 K. In addition, SiC composites using 40 mass% of SA fibre with a carbon interface of approximately 100 nm were fabricated. The effect of this interface on a and κ was marginal. 相似文献
20.
《Carbon》2014
A transparent, gas barrier film comprised of poly(vinyl alcohol) (PVA) and graphene oxide (GO) is synthesized through combined methods of solution blending and isothermal recrystallization. The recrystallized PVA/GO film with only 0.07 vol% GO gives an O2 transmission rate <0.005 cc m−2 day−1 and an O2 permeability <5.0 × 10−20 cm3 cm cm−2 Pa−1 s−1; hence, it is far superior to other blend polymer/inorganic composites. The excellent O2 barrier properties are attributed to a unique hybrid of PVA crystals and GO sheets. PVA crystals form around the GO during isothermal recrystallization, indicating that a GO sheet can act as a nucleating agent. The newly formed PVA crystals fill in the spaces between the GO sheets, and together they become ultra-large impermeable regions, which can prevent the passage of O2. The hybrid film has potential applications in flexible electronics, pharmaceuticals, and food packaging. 相似文献