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1.
LiNi1/3Co1/3Mn1/3O2 cathode materials have been coated with Al2O3 nano-particles using sol-gel processing to improve its electrochemical properties. The X-ray diffraction (XRD) pattern of the as-prepared Al2O3 nano-particles was indexed to the cubic structure of the γ-Al2O3 phase and had an average size of ∼4 nm. The XRD showed that the structure of LiNi1/3Co1/3Mn1/3O2 was not affected by the Al2O3 coating. However, the Al2O3 coatings on LiNi1/3Co1/3Mn1/3O2 improved the cyclic life performance and rate capability without decreasing its initial discharge capacity. These electrochemical properties were also compared with those of LiAlO2-coated LiNi1/3Co1/3Mn1/3O2 cathode material. The electrochemical impedance spectroscopy (EIS) was studied to understand the enhanced electrochemical properties of the Al2O3-coated LiNi1/3Co1/3Mn1/3O2 compared to uncoated LiNi1/3Co1/3Mn1/3O2. 相似文献
2.
Haiyi Peng Haishen Ren Mingzhao Dang Yi Zhang Xiaogang Yao Huixing Lin 《Ceramics International》2018,44(6):6527-6532
Ca0.9La0.067TiO3 (abbreviated as CLT) ceramics doped with different amount of Al2O3 were prepared via the solid state reaction method. The anti-reduction mechanism of Ti4+ in CLT ceramics was carefully investigated. X-ray diffraction (XRD) was used to analyze the phase composition and lattice structure. Meanwhile, the Rietveld method was taken to calculate the lattice parameters. X-ray photoelectron spectroscopy (XPS) was employed to study the valence variation of Ti ions in CLT ceramics without and with Al2O3. The results showed that Al3+ substituted for Ti4+ to form solid solution and the solid solubility limit of Al3+ is near 1.11 mol%. Furthermore, the reduction of Ti4+ in CLT ceramics was restrained by acceptor doping process and the Q × f values of CLT ceramics were improved significantly. The CLT ceramic doped with 1.11 mol% Al2O3 exhibited good microwave dielectric properties: εr = 141, Q × f = 6848 GHz, τf = 576 ppm/°C. 相似文献
3.
The deposition of Al2O3 on LiCoO2 electrodes using a low-temperature atomic layer deposition has been investigated. Scanning electron microscopy confirms that Al2O3 films can be homogeneously deposited on LiCoO2 particles of porous electrodes at 120 °C. The results of X-ray photoelectron spectroscopy show that the Al2O3 preferentially deposits on the LiCoO2. Furthermore, the results of cycling stability tests show that the cells with Al2O3-coated LiCoO2 electrodes have enhanced performance. 相似文献
4.
This paper introduces a simplified method for low-temperature pressureless sintering of Al2O3-Ni-SiC nanocermets in air environment. In this method, a thin and continuous Ni shell was coated on the surface of Al2O3 particles using electroless deposition method. The composite powders were subsequently compressed to prepare bulk specimens. By preventing the ceramic particles from direct contact during the densification of green specimens, sintering temperature of cermet materials was reduced from that of Al2O3 (>?1400?°C) to the range of Ni solid-phase sintering temperature. Furthermore, dissolution of a low amount of phosphorus in the composition of Ni coatings caused the further decrease of the sintering temperature to 800?°C. At such low temperatures, pressureless sintering of the cermets in the air environment was successfully performed instead of the common hot pressing process in a reducing atmosphere. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD) characterizations indicated that the microstructure of such sintered samples consists of a continuous Ni network surrounding Al2O3 grains, without any structural defects or Ni oxidation. Furthermore, mechanical properties of the cermet materials were improved through reinforcement of the continuous Ni network by different amounts of SiC nanoparticles. The results showed that Al2O3-Ni-5?wt% SiC nanocermets sintered at 800?°C obtain the highest compressive strength of 242.5?MPa, hardness of 56.8 RA, and the lowest wear weight loss of 0.04?mg/m. 相似文献
5.
Yuping Wang Xinhong Liu Xiaoyu Chen Yubin Wen Quanli Jia 《Ceramics International》2018,44(7):7883-7890
Evolutions of phase composition and microstructure of commercial Al2O3 gel in different heat treatment conditions (temperature, atmosphere and additives) were investigated. There was almost no effect of atmosphere and carbon additive on phase evolution of Al2O3 gel during heating, γ-Al2O3 formed at 800?°C, γ-Al2O3 and minor θ-Al2O3 co-existed at 1000 °C, and single phase of ɑ-Al2O3 occurred at heating temperature ≥1200?°C. Atmosphere and carbon had great effects on morphology and crystal size of Al2O3 particles. Crystal size of spherical-shape Al2O3 particles was 10–20?nm after heating at 800–1000?°C in air, afterwards, they rapidly grew into micro or macro scale when temperature was above 1200?°C, and sintering phenomena of worm-like Al2O3 particles were observed. In the presence of carbon, spherical-shape Al2O3 particles grew slightly from 10 to 20?nm to 50–60?nm with the temperature increasing from 800?°C to 1500?°C in reducing atmosphere, carbon inclusions in Al2O3 grain boundaries triggered a steric hindrance of Al2O3 particles growth. Al2O3 gel had a high reactive ability and could react with microsilica to form nano mullite crystals at relatively lower temperature. 相似文献
6.
Guilherme T. Araújo Thiago S. Brito Douglas F. Souza Alysson M.A. Silva Eduardo H.M. Nunes Manuel Houmard 《Ceramics International》2018,44(1):580-587
In this work we successfully obtained freeze-cast alumina (Al2O3) and magnesium aluminate spinel (MgAl2O4) samples. Camphene was used as the freezing vehicle in this study. The specimens prepared herein were examined by Archimedes tests, scanning electron microscopy, and X-ray powder diffraction. Cold crushing tests were also carried out at room temperature. It was observed that the pore structure of Al2O3 samples can be tailored by changing the solid loading and freezing rate; the higher the solid loading and freezing rate, the finer the pore structure of the freeze-cast sample. MgAl2O4-based specimens were fabricated by keeping the solid loading in the starting slurry at 30 vol% and using liquid nitrogen as the cooling agent. The material obtained from a 60 Al2O3?40 MgO slurry showed a spinel amount of about 90%, an expressive total porosity (63 ± 3%), and a significant cold crushing strength (58 ± 6 MPa). In addition, this material exhibited the finest pore structure among the composition studied herein, showing a mean pore size of about 4 µm. 相似文献
7.
The Vickers hardness of dense Al2O3-cubic BN (cBN) composites prepared by spark plasma sintering under a moderate pressure of 100 MPa at 1200-1600 °C was investigated at indentation loads of 0.098-19.6 N. The BN grains in the Al2O3-BN composite prepared at 1300 °C showed no transformation from the cBN to hBN phase, and the hardness was 59 GPa at 0.098 N. The hardness of the Al2O3 matrix in the Al2O3-BN composites containing 10-30 vol% cBN prepared at 1300-1400 °C was around 25 GPa at 0.098 N, which was higher than monolithic Al2O3 bodies prepared at the same temperatures. The hardness of the Al2O3 matrix in the Al2O3-BN composites decreased with increasing sintering temperature. The increase in the hardness of the Al2O3 matrix may be due to the decrease in the size of Al2O3 grains in the Al2O3-BN composites owing to the addition of cBN particles and the decrease in sintering temperature. The Meyer exponents of the monolithic Al2O3 bodies and Al2O3-BN composites were 1.90-1.94 independent of cBN content. 相似文献
8.
In-Jin Shon Song-Lee DuIn-Yong Ko Tae-Wan KimJung-Mann Doh Jin-Kook YoonSang-Whan Park 《Ceramics International》2011,37(4):1353-1357
Nanopowders of 5.33Fe0.37Cr0.16Al0.4Si0.07 and Al2O3 were synthesized from Fe2O3, Cr, Si, and Al powders by high-energy ball milling. A high-density nanocrystalline 5.33Fe0.37Cr0.16Al0.4Si0.07-Al2O3 composite was consolidated by a high-frequency, induction-heated sintering (HFIHS) method within three minutes from mechanically synthesized powders of Al2O3 and 5.33Fe0.37Cr0.16Al0.4Si0.07. The advantage of this process is that it allows very quick densification to near theoretical density and prohibits grain growth in nano-structured materials. The average grain sizes of Al2O3 and 5.33Fe0.37Cr0.16Al0.4Si0.07 were 99 nm and 14 nm, respectively. 相似文献
9.
Al2O3 doped multi-walled carbon nanotubes (MWCNT) were synthesized as a conducting additive in alumina–epoxy terminated poly(dimethylsiloxane) (ETDS). The addition of Al2O3 doped MWCNT improved the thermal conductivity of the composites, which was a function of the Al2O3 loading. The mechanisms underlying this enhanced conductivity were examined in the context of the Hashin–Shtrikman (HS) boundaries and interconnectivity. The measured thermal conductivity revealed more enhanced thermal conductivity than expected by analytical predictions at a fixed micro Al2O3 concentration. Further analytical investigations showed that the addition of Al2O3 doped MWCNT affected the interconnectivity between the conducting particles because of their high aspect ratios. Overall, Al2O3 doped MWCNT may be useful for establishing three-dimensional heat conducting percolating networks in a matrix that affect the thermal conductivity of a composite. 相似文献
10.
Ba4Nd9.33Ti18O54·x wt%Al2O3 (BNT-A) ceramics (x=0, 0.5, 1.0, 1.5, 2.0, 2.5) were prepared by the conventional solid state reaction. The effects of Al2O3 on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 (BNT) ceramics were investigated. X-ray diffraction and backscatter electronic images showed that the Al2O3 additive gave rise to a second phase BaAl2Ti5O14 (BAT). The formation mechanism and grain growth of the BAT phase were first discussed. Dielectric property test revealed that the Al2O3 additive had improved the dielectric properties of the BNT ceramics: increased the Q×f value from 8270 to 12,180 GHz and decreased the τf value from 53.4 to 11.2 ppm/°C. A BNT-A ceramic with excellent dielectric properties: εr=70.2, Q×f=12,180 GHz, τf=20 ppm/°C was obtained with 2.0 wt% Al2O3 added after sintering at 1320 °C for 4 h. 相似文献
11.
Qingliang Shan Qian Feng Jianbao Hu Xiangyu Zhang Xihai Jin Yanmei Kan Haijun Zhou Hongda Wang Shaoming Dong 《Ceramics International》2018,44(4):4009-4015
The influence of Al2O3 addition on the oxidation behavior of Si-B-C ceramics at 1200 °C in O2/H2O (40/60) atmosphere was studied. Results showed that Al2O3 was enriched in the oxidized layer, and impeded the crystallization of oxide (cristobalite) during cooling. Denser oxidized layer and less weigh change were observed. Infrared spectra indicated that the addition of Al2O3 could weaken the tendency of bridged oxygen atoms (Si-O-Si, Si-O-Al) to become non-bridged oxygen atoms (Si-O-H) and enhance the degree of interconnection of the structural units. The above phenomenon was attributed to the fact that the bridging oxygen bond between Al and Si was not broken but protonated. The protonated bridging oxygen (Al-O(H)-Si) still acts as a linkage in the glass network, which results in higher viscosity of the aluminosilicates melt and lower reaction activity with steam, thereby significantly improving the oxidation resistance of Si-B-C in O2/H2O atmosphere. 相似文献
12.
Ling Wang Ce Gao Lei Dai Huizhu Zhou Yuehua Li Wei Meng Zhangxing He R.V. Kumar 《Ceramics International》2018,44(8):8983-8991
New Al3+ ion conducting solid electrolytes (Al0.2Zr0.8)4/3.8NbP3O12-xF2x(0?≤x?≤?0.4) with Nasicon-structure are successfully prepared by solid state reaction method. The influences of the doped F- content on the properties of the (Al0.2Zr0.8)4/3.8NbP3O12-xF2x samples are investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results show that F- doping can effectively improve the sinterability and the total conductivity of the (Al0.2Zr0.8)4/3.8NbP3O12-xF2x samples. Among the solids series, (Al0.2Zr0.8)4/3.8NbP3O11.7F0.6 shows the highest conductivity of 1.53?×?10?3 S?cm?1at 500?°C, which is approximately 7.9 times higher than that of the undoped (Al0.2Zr0.8)4/3.8NbP3O12. The ion transference number of the samples is higher than 0.99 at 300–700?°C. On the basis of the promising properties, a mixed-potential type NH3 sensor based on (Al0.2Zr0.8)4/3.8NbP3O11.7F0.6 electrolyte and In2O3 sensing electrode has been developed. The sensing performance of the sensor is evaluated. The mixed-potential type sensor can work at relatively low temperatures of 200–350?°C and an excellent sensitivity of 99.71?mV/decade at 250?°C is obtained. The sensor also displays excellent stability and reproducibility, accompanied by low cross-sensitivities to CO2, CH4 and H2. 相似文献
13.
The effect of particle size of MgO and Al2O3 on the spinel formation associated with permanent linear change on reheating (PLCR) and microstructure of Al2O3–MgAl2O4–C refractory is investigated as a function of heating cycle at 1600 °C with 2 h holding at each cycle. It was found that rate of spinel formation and associated volume expansion is very much dependent on the reactivity and particle size of the reactant. When the reactants are very fine and reactive there is considerable amount of spinel formation, whereas coarser reactants with lower reactivity show negligible formation of spinel phase and associated expansion. Magnesia and alumina with moderate reactivity develops optimum PLCR of the refractory. It continuously increases with the number of heating cycles. The SEM photomicrographs show that in Al2O3–MgAl2O4–C refractory the spinel phase is formed in between the calcined bauxite grain and the EDX analysis indicates that the spinel phase formed is stoichiometric in nature. 相似文献
14.
George Ting-Kuo Fey P. Muralidharan Cheng-Zhang Lu Yung-Da Cho 《Electrochimica acta》2006,51(23):4850-4858
An enhanced electrochemical performance LiCoO2 cathode was synthesized by coating with various wt.% of La2O3 to the LiCoO2 particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La2O3-coated LiCoO2 revealed that the coating did not affect the crystal structure, α-NaFeO2, of the cathode material compared to pristine LiCoO2. TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about ∼15 nm. XPS data illustrated that the presence of two different environmental O 1s ions corresponds to the surface-coated La2O3 and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La2O3 on LiCoO2 improved cycle stability (284 cycles) by a factor of ∼7 times over the pristine LiCoO2 cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at ∼464 K was significantly smaller for the La2O3-coated cathode material and recognized its high thermal stability. 相似文献
15.
Synthesis, electrochemical, and structural properties of LiNi0.8Co0.15Al0.05O2 cathodes prepared by TiO2 nanoparticles coating on a Ni0.8Co0.15Al0.05(OH)2 precursor have been investigated by the variation of coating concentration and annealing temperature. TiO2-coated cathodes showed that Ti elements were distributed throughout the particles. Among the coated cathodes, the 0.6 wt% TiO2-coated cathode prepared by annealing at 750 °C for 20 h exhibited the highest reversible capacity of 176 mAh g−1 and capacity retention of 92% after 40 cycles at a rate of 1C (=190 mA g−1). On the other hand, an uncoated cathode showed a reversible first discharge capacity of 186 mAh g−1 and the same capacity retention value to the TiO2-coated sample at a 1C rate. However, under a 1C rate cycling at 60 °C for 30 cycles, the uncoated sample showed a reversible capacity of 40 mAh g−1, while a TiO2-coated one showed 71 mAh g−1. This significant improvement of the coated sample was due to the formation of a possible solid solution between TiO2 and LiNi0.8Co0.15Al0.05O2. This effect was more evident upon annealing the charged sample while increasing the annealing temperature, and at 400 °C, the coated one showed a more suppressed formation of the NiO phase from the spinel LiNi2O4 phase than the uncoated sample. 相似文献
16.
Gui-Fang Xu Qin-Qin Liu Juan Yang Xiu-Juan Sun Xiao-Nong Cheng 《Ceramics International》2009,35(8):3131-3134
The Sc2W3O12-type negative thermal expansion material attracts an extensive interest because of its thermodynamic stability and great chemical flexibility. In this paper, nanostructured Sc2W3O12-type negative thermal expansion material Al2W2MoO12 was synthesized by a convenient method, the stearic acid method. The thermodynamic property of the precursor was studied by thermogravimetric and differential scanning calorimetric methods. The structure and the size of the resulted products were characterized by powder X-ray diffraction and transmission electron microscopy, respectively. The negative thermal expansion property was studied by high temperature powder X-ray diffraction. Results show that nanostructured Al2W2MoO12 powders with average size about 10 nm were first synthesized here by the stearic acid method and the nanoparticles would be rearranged to form large rods by prolonging the heat-treatment time. The obtained nanoparticles exhibited negative thermal expansion property in the temperature range of 20–600 °C. 相似文献
17.
Zhaoyue Liu Kai Pan Meijia Wang Jinghong Li Yubai Bai Tiejin Li 《Electrochimica acta》2005,50(13):2583-2589
A novel Al2O3-coated SnO2/TiO2 composite electrode has been applied to the dye-sensitized solar cell. In such an electrode, two kinds of energy barriers (SnO2/TiO2 and TiO2/Al2O3) were designed to suppress the recombination processes of the photo-generated electrons and holes. After the SnO2 was modified by colloid TiO2, the photoelectric conversion efficiency of the SnO2/TiO2 composite cell increased to 2.08% by a factor of 2.8 comparing with that of the SnO2 cell. The Al2O3 layer on the SnO2/TiO2 composite electrode further suppressed the generation of the dark current, resulting in 37% improvement in device performance comparing with the SnO2/TiO2 cell. 相似文献
18.
M. Kaneeda H. Iizuka T. Hiratsuka N. Shinotsuka M. Arai 《Applied catalysis. B, Environmental》2009,90(3-4):564-569
The present work has been undertaken to tailor Pt/Al2O3 catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al2O3 catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al2O3 catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al2O3 catalysts by the Pd addition. The Pd-modified Pt/Al2O3 catalysts should be a promising one for NO oxidation of practical interest. 相似文献
19.
Iana A. Minich Oleg I. Silyukov Liliia D. Kulish Irina A. Zvereva 《Ceramics International》2019,45(2):2704-2709
A protonated form of the n?=?4 layered bismuth containing perovskite-like titanate K2.5Bi2.5Ti4O13 belonging to Ruddlesden-Popper phases was prepared via ion exchange reaction of interlayer K+ with protons. Its composition was investigated by TG ICP and EDX analysis was found to be H2K0.5Bi2.5Ti4O13·H2O. The thermal behavior of the obtained phase was investigated by STA coupled with mass-spectrometry, the structural changes, happening with the sample during heating, were examined by XRD. It was shown that the as-prepared hydrated phase undergoes two-stage dehydration at low temperatures (up to 160?°C). The further heating leads to the gradual decomposition and crystallization of new phases, notably Bi2Ti2O7, Bi4Ti3O12 and Bi2Ti4O11. The morphology of the as-prepared sample and samples after heat treatment was examined using SEM. 相似文献
20.
Kunlun Chen Peng Song Chao Li Ying Zhou Xuan He Xiao Yu Jiansheng Lu 《Ceramics International》2018,44(12):13727-13735
Al2O3-TiO2-MgO ceramic alternant layer coatings were prepared by atmospheric plasma spraying and heat treated at 600, 700, 800, 900, and 1000?°C. The influence of heat treatment on microhardness, fracture toughness, and the structural evolution of the coatings on steel were investigated. Heat treatment promoted alternant layer interdiffusion within ceramic coatings, which could result a transformation from a lamellar morphology to mutual pinning. The interfacial diffusion between the bond coating and substrate was clearly demonstrated after heat treatment at different temperatures. Heat treatment also significantly affected the evolution of the hardness and fracture toughness. Temperature strongly affected the microhardness of the specimens, and the hardness arrived to the highest value at 1000?°C. The formation of a new Mg2Al6Ti7O25 phase and alternant layer mutual pinning were beneficial to hardness improvement, and heat treatment also significantly improved fracture toughness. 相似文献