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1.
In order to enhance the mechanical properties of B4C without density increase, the short carbon fibers M40, M55J and T700 reinforced B4C ceramic composites were fabricated by hot-pressing process. The addition of the carbon fibers accelerates the densification of the B4C, decreases their densities, and improves their strength and toughness. The enhancement effects of the three kinds of carbon fibers were studied by investigating the density, Vickers hardness and the mechanical properties such as flexural strength, flexural modulus and fracture toughness of the composites. The fiber type has a great influence on the mechanical properties and enhancement of the short carbon fiber reinforced B4C composites. The flexible carbon fiber with high strength and low modulus such as T700 is appropriate to reinforce the B4C matrix ceramic composites. 相似文献
2.
Electrochemical and thermal properties of Co3(PO4)2- and AlPO4-coated LiNi0.8Co0.2O2 cathode materials were compared. AlPO4-coated LiNi0.8Co0.2O2 cathodes exhibited an original specific capacity of 170.8 mAh g−1 and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g−1. Co3(PO4)2-coated LiNi0.8Co0.2O2 cathodes exhibited an original specific capacity of 177.6 mAh g−1 and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co3(PO4)2 coating. The Co3(PO4)2 coating material could react with LiOH and Li2CO3 impurities during annealing to form an olivine LixCoPO4 phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni4+ ions compared to the AlPO4-coated cathode. Differential scanning calorimetry results showed Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO4-coated sample. 相似文献
3.
Ru Jiang Lingwei Yang Haitao Liu Xun Sun Haifeng Cheng 《Ceramics International》2018,44(13):15356-15361
Novel Nextel? 610 fiber reinforced silica (N610f/SiO2) composites were fabricated via sol-gel process at a sintering temperature range of 800–1200?°C. The sintering-temperature dependent microstructures and mechanical properties of the N610f/SiO2 composites were investigated comprehensively by X-ray diffraction, nanoindentation, three-point bending etc. The results suggested a thermally stable Nextel? 610 fiber whose properties were barely degraded after the harsh sol-gel process. A phase transition in the silica matrix was observed at a critical sintering temperature of 1200?°C, which led to a significant increase in the Young's modulus and hardness. Due to the weak fiber/matrix interfacial interaction, the 800?°C and 1000?°C fabricated N610f/SiO2 composites exhibited quasi-ductile fracture behaviors. Specially, the latter possessed the highest flexural strength of ≈ 164.5?MPa among current SiO2-matrix composites reinforced by fibers. The higher sintering-temperature at 1200?°C intensified the SiO2 matrix, but strengthened the interface, thus resulting in a brittle fracture behavior of the N610f/SiO2 composite. Finally, the mechanical properties of this novel composite presented good thermal stability at high temperatures up to 1000?°C. 相似文献
4.
Mehri Mashhadi Ehsan Taheri-NassajMaryam Mashhadi Vincenzo M. Sglavo 《Ceramics International》2011,37(8):3229-3235
The effects of Al addition on pressureless-sintering of B4C-TiB2 composites were studied. Different amounts of Al from 0% to 5 wt.% were added to B4C-TiB2 mixtures (containing up to 30 wt.% TiB2) and the samples were pressureless sintered at 2050 °C and 2150 °C under Ar atmosphere. Physical, microstructural and mechanical properties were analysed and correlated with TiB2 and Al additions and sintering temperature. Addition of Al to B4C-TiB2 results in increased shrinkage upon sintering and final relative density and lower porosity, the effect is being more evident when both Al and TiB2 are present. Fracture strength, elastic modulus and fracture toughness of 450 MPa, 500 GPa and 6.2 MPa.m1/2, respectively were measured. 相似文献
5.
The electrochemical properties of AlPO4-coated LiCoO2 cathodes prepared in a water or ethanol solvent were characterized with the view of stabilizing LiCoO2 at charge-cutoff voltages of 4.6 and 4.8 V. Under the influence of the AlPO4 crystallinity, the coated LiCoO2 prepared in ethanol had better capacity retention than those prepared in water. This enhancement also correlated with the improved suppression of Li-diffusivity decay in the coated cathode from the ethanol compared to that from water. In addition, the differential scanning calorimetry (DSC) results of the AlPO4 nanoparticle-coated LiCoO2 with ethanol showed an enhanced thermal stability. 相似文献
6.
以正硅酸乙酯(TEOS)为硅源,氢氟酸(HF)为催化剂,采用溶胶-凝胶法及超临界干燥技术制备了莫来石纤维增强S iO2气凝胶隔热材料,研究了HF催化剂、溶剂等制备因素对溶胶-凝胶过程的影响。结果表明,加入HF可以大大加快凝胶化过程,使凝胶时间从几小时缩短至几分钟;溶剂EtOH对凝胶化过程有明显的抑制作用,凝胶时间随其用量的增加而增加;H2O对凝胶化过程的影响比较复杂,凝胶时间随其用量的增加先减后增,转折点处水硅摩尔比为5∶1;气凝胶制备过程中加入甲酰胺可以调节凝胶内部网络结构,防止干燥时由于应力不均而开裂或破裂;适宜的原料配比(摩尔比)为:TEOS∶H2O∶HF∶EtOH∶甲酰胺=1∶(4~6)∶(0.05~0.1)∶(3~6)∶(0.3~0.5)。 相似文献
7.
Emmanuel E. Boakye Thomas S. Key Pavel Mogilevsky Samuel J. Opeka Randall Corns Randall S. Hay Michael K. Cinibulk 《Journal of the European Ceramic Society》2021,41(5):3132-3140
Solutions of YPO4 were used to precipitate YPO4 on pre-oxidized Hi-Nicalon-S SiC fibers. Tows of the coated fibers were then infiltrated with a preceramic polymer loaded with SiC particles to form mini-composites. During pyrolysis of the matrix, SiO2 and YPO4 on the fibers reacted and formed a Y2Si2O7 fiber matrix interphase. Mini-composites were exposed to steam at 1000 °C for 10, 50, and 100 h, tensile tested, and the effect of oxidation in steam on the functionality of the Y2Si2O7 fiber coating was investigated. The minicomposites oxidized at 1000 °C for 10 h retained 100 % of their unoxidized strength, and those oxidized for 50 and 100 h retained 92 % and 90 % of unoxidized strength, respectively. Strength retention and fiber pullout in both unoxidized and oxidized minicomposites suggests that the Y2Si2O7 interphase was effective in maintaining a weak fiber-matrix interface. 相似文献
8.
Jared A. StoegerCharitomeni M. Veziri Miguel PalominoAvelino Corma Nick K. KanellopoulosMichael Tsapatsis Georgios N. Karanikolos 《Microporous and mesoporous materials》2012,147(1):286-294
Continuous films comprised of highly c-oriented aluminophosphate AlPO4-5 or cobalt-substituted AlPO4-5 (CoAPO-5) were grown on porous supports and subjected to heat treatment in order to investigate the potential for membrane applications. A study in the early stages of in-plane crystalline intergrowth revealed a potential mechanism for flake-like crystal formation between the original oriented columnar crystals. Variations in metal substitution (AlPO4-5, CoAPO-5), support (glass, silicon, porous alumina), and calcination method (conventional, rapid thermal processing) were chosen to examine the conditions by which structural integrity was compromised following secondary (or tertiary) growth, resulting in reduced membrane functionality. Through the use of rapid thermal processing, the structure debilitation could be partially avoided. The membrane quality was inspected through pervaporation measurements consisting of a liquid hydrocarbon feed of n-heptane and 1,3,5-triisopropylbenzene. By investigating the effect of template removal on the oriented, columnar crystalline structure, useful insight is provided into the potential for the membranes to participate in applications such as molecular separations, catalysis, or host-guest assemblies. 相似文献
9.
Manuel Snchez-Snchez Gopinathan Sankar Luis Gmez-Hortiguela 《Microporous and mesoporous materials》2008,114(1-3):485-494
A series of high-crystalline ZnAPSO-44 samples have been successfully synthesised using cyclohexylamine as structure-directing agent, keeping a constant (Si + Zn)/(Al + P) ratio of 0.25 and systematically varying the Si/Zn ratio. Chemical analyses by ICP shows a good correlation between the heteroatom (Si and/or Zn) content of the samples and that of the initial gels. A combination of single crystal and powder X-ray diffraction techniques evidences a high crystallinity and a total purity for all samples. In addition, single crystal X-ray diffraction studies of the samples from which large crystals could be isolated, allow us to certify that either the whole or the majority of the cyclohexylamine molecules adopt a NH2- or -equatorial conformation inside of the pores. Furthermore, for the first time, 1H MAS NMR spectroscopy was used as a proof of the protonation of SDA molecules within the microporous materials, unequivocally indicating that cyclohexylamine molecules were protonated. 13C MAS NMR studies indeed corroborated such protonation state of the SDA molecules and, more importantly, allowed to detect the presence of a mixture of -equatorial and -axial conformers of cyclohexylamine in the Si-richest samples, the former being always the dominant. Based on both 13C and 29Si cross-polarization MAS NMR measurements as well as on the calculated interaction energies of the two conformers as a function of the framework composition, it is proposed that this non-described -axial conformation of cyclohexylammonium within the microporous materials was associated to the presence of SiO2 islands into the AlPO4 framework, whereas the -equatorial conformer was the only one found in the case of isolated incorporation of Si4+ (and/or Zn2+) ions. 相似文献
10.
Yue DingNiu Li Naijia GuanHonggen Wang Haibin SongShouhe Xiang 《Microporous and mesoporous materials》2012,147(1):68-72
In the family of microporous aluminophosphate, AlPO4-9 is one of the members reported first in 1982. However, its structure and characteristics have not been known up to now, and this makes it a special member. In the present work, AlPO4-9 has been synthesized using piperazine as the structure-directing agent and the mixture of H2O and EG as the solvent. Structure refinement from single crystal X-ray diffraction data shows that AlPO4-9 is a material with the composition of C2H7Al5.50NO25P6. It crystallizes in the monoclinic space group C2/c (No: 15), with a = 24.230(5) Å, b = 14.026(5) Å and c = 16.197(3) Å, β = 119.87(4)°, V = 4773(2) Å3, Z = 8. The open-framework of AlPO4-9 is built of alternating corner-sharing PO4 tetrahedra and AlO4 tetrahedra (AlO6 octahedra) to construct a curved one-dimensional 8-ring channel system running along [1 0 1]. Meanwhile, the strict alternative of PO4 tetrahedra and AlO4 tetrahedra (AlO6 octahedra) results in a negative framework in AlPO4-9. Thermal stability has been determined on a thermal analyzer and by calcination. It reveals that AlPO4-9 framework is thermally stable and has a potential to be a catalytic material. 相似文献
11.
《Journal of the European Ceramic Society》2023,43(15):6699-6717
With the advantage of high temperature resistance, low expansion, low density and excellent thermal stability, carbon fiber reinforced ceramic composites have a very wide range of applications in aerospace, military, energy, chemical industries and transportation. Short carbon fiber reinforced ceramic composites are characterized by simple processes, low manufacturing costs, short preparation times and automated production, can be used in fields such as friction materials and thermal protection system. This paper reviews the current status and recent advances in research on homogenization techniques, mechanical properties, thermal properties and frictional properties of short carbon fiber reinforce ceramic composites. Different processing routes for short carbon fiber reinforced ceramic composites, including reactive melt infiltration (RMI), hot pressing (HP), spark plasma sintering (SPS) and pressureless sintering, the advantages and drawbacks of each method are briefly discussed. The future development direction of low-cost manufacturing short carbon fiber reinforced ceramic composites is prospected. 相似文献
12.
J. P. Zhai Z. M. Li Irene L. Li H. J. Liu P. Sheng Z. K. Tang 《Journal of Porous Materials》2006,13(3):291-295
Ultra-small single-walled carbon nanotubes (SWNTs) with diameter of 0.4 nm were fabricated in the channels of AlPO4-5 crystals by pyrolyzing hydrocarbon molecules. In order to improve the structural quality of the SWNTs, we introduced Br?nsted
acid sites onto the channel walls by incorporating metal cations (Mn, Mg, Co, and Si) into AlPO4-5 framework. The Br?nsted acid sites play an important catalytic role in the carbonization of hydrocarbon molecules (tripropylamine)
in the AlPO4-5 channels, and favor the formation of SWNTs, as revealed by the significant decrease in formation energy of the nanotubes.
The experimental results agree well with the predictions of first-principles calculations. 相似文献
13.
《Journal of the European Ceramic Society》2017,37(8):2991-2996
Weak fiber/matrix interface dominates the toughening properties of ceramic matrix composites. This paper reports a novel sol-gel fabricated carbon fiber reinforced mullite matrix composite, in which the fiber/matrix interface was inherently weak in shear properties (∼25 MPa), measured in-situ by fiber push-in tests. The interface microstructure was chemically sharp, characterized by transmission electron microscopy. The outcome of the weak interface was the full trigger of the toughening mechanisms like crack deflection, etc., leading to significant enhancement of the fracture toughness of the composite (∼12 MPa√m), measured by single edged notch beam method. Finally, due to the weak fiber/matrix interface and large thermal expansion mismatch of the fiber and matrix, the high temperature fracture strength was enhanced in the temperature range from 25 to 1200 °C, which is attributed to the enhancement of the interfacial property at elevated temperatures that favors better load transfers between composite constituents. 相似文献
14.
A Ni–W loaded ETS-10/AlPO4-5/Al2O3 composite support catalyst was optimized and used in hydrodesulfurization (HDS) and hydrodearomatization (HDA) of Daqing FCC diesel feedstock. The result indicated that ETS-10 and AlPO4-5 showed positive synergism effect. The effects of operating conditions on its catalytic performance were investigated by using a 100 mL hydrotreating test unit. The catalyst showed a remarkable HDS conversion of 99.9% and a HDA conversion of 73.2%. A clean diesel product with ultra-low sulfur content (<1.0 μg/g) and very low polycyclic aromatic content (<2.0 wt.%) was obtained. 相似文献
15.
Bin Zhang Jun Xu Fengtao FanQiang Guo Xiaoqiang TongWenfu Yan Jihong YuFeng Deng Can LiRuren Xu 《Microporous and mesoporous materials》2012,147(1):212-221
The influence of water content on the crystallization of the microporous aluminophosphate AlPO4-11 was investigated by a combination of in situ UV Raman and ex situ XRD and NMR characterizations. Under high water content conditions (Al2O3:H2O = 1:20-69), an AlPO4-5 intermediated formed first and later co-existed with AlPO4-11. In the last stage of crystallization, the crystalline AlPO4-5 completely disappeared and well-crystallized AlPO4-11 was obtained. The position of the three signals observed in the 31P MAS NMR spectra of the isolated solid samples did not change during the hydrothermal treatment, suggesting that the fragments containing the P site in the junction of 6- and 4-membered rings of both AlPO4-5 and AlPO4-11 formed first and that the environments of the P sites were very similar to those in the final structure. A significant increase of Al concentration in liquid media was observed before the appearance of XRD detectable AlPO4-11. Under low water content conditions (Al2O3:H2O = 1:15), the AlPO4-11 was directly crystallized from the initial mixture. In situ Raman spectra showed that the 10-membered rings were complete by the time the transformation of octahedral Al to tetrahedral Al was finished and that the conformation of the protonated di-(i-propyl)amine changed little during the crystallization. The present study showed that the composition of the liquid phase is critical to the formation of a specific structure. 相似文献
16.
A series of short-carbon-fiber/Al2O3 composites with MgO as sintering additive were fabricated by pressureless sintering process. The effects of short carbon fiber (Csf) content on the mechanical, dielectric and microwave absorbing properties of the composite were investigated. The results show that the addition of MgO enhances the density, hardness and the flexural strength of the alumina ceramic. However, these mechanical properties of the Csf/Al2O3–MgO composite decrease with increasing Csf content. Both the real and imaginary parts of the complex permittivity increase with increasing Csf content in the frequency range of 8.2–12.4 GHz, which is attributed to the increasing electron polarization and associated polarization relaxation, respectively. When the Csf content is 0.3 wt%, the reflection loss less than −10 dB and the minimum value of −27 dB are obtained with the coating thickness being 1.4 mm. The results indicate that the Csf/Al2O3 with MgO is an excellent candidate for microwave absorbing material with favorable mechanical property. 相似文献
17.
D. Arumugam 《Electrochimica acta》2010,55(28):8709-8716
LiMn2O4 spinel cathode materials were coated with 0.5, 1.0, and 1.5 wt.% CeO2 by a polymeric process, followed by calcination at 850 °C for 6 h in air. The surface-coated LiMn2O4 cathode materials were physically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). XRD patterns of CeO2-coated LiMn2O4 revealed that the coating did not affect the crystal structure or the Fd3m space group of the cathode materials compared to uncoated LiMn2O4. The surface morphology and particle agglomeration were investigated using SEM, TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 20 nm. The XPS data illustrated that the CeO2 completely coated the surface of the LiMn2O4 core cathode materials. The galvanostatic charge and discharge of the uncoated and CeO2-coated LiMn2O4 cathode materials were measured in the potential range of 3.0-4.5 V (0.5 C rate) at 30 °C and 60 °C. Among them, the 1.0 wt.% of CeO2-coated spinel LiMn2O4 cathode satisfies the structural stability, high reversible capacity and excellent electrochemical performances of rechargeable lithium batteries. 相似文献
18.
Ran Mo Fang Ye Xiaofei Liu Qian Zhou Xiaomeng Fan Jimei Xue Pengfei Zhang Litong Zhang Laifei Cheng 《Ceramics International》2021,47(6):8191-8199
The SiCf/Si3N4 composite with low–high–low permittivity sandwich structure was designed for high-temperature electromagnetic (EM) wave absorption and mechanical stability. The SiCf/Si3N4 possessed the remarkable mechanical properties at room temperature (the flexural strength is 357 ± 16 MPa and the fracture toughness is 10.8 ± 1.7 MPa m1/2) for the strong fiber strength, moderate interface bonding strength and uniform matrix. Furthermore, the retention rate is as high as 80% at 800 °C. The A/B/C nanostructure and the sandwich meta-structure endowed the SiCf/Si3N4 with an excellent EM absorbing property at room temperature. The SiCf/Si3N4 still absorbed 75% of the incident EM waves energy in X and Ku bands when the temperature increases up to 600 °C, which is only 6% lower than that at room temperature, for the partial compensation of the decreased interfacial polarization loss for the increased conductivity loss and dipole polarization loss. 相似文献
19.
Ultra-fine ZnAl2O4 spinel hydrogel precursor synthesized from mixed salt solutions of Zn2+ and Al3+ ions using ammonium hydroxide–hexamethylenetetramine as basic media for co-precipitation was used as bonding material and sintering aid for pure alumina system. The hydrogel powder exhibited some well-defined ZnAl2O4 spinel phases at 800 °C. Alumina compacts were fabricated by incorporating small proportions of the precursor in alumina powder and firing at different temperatures (1350–1500 °C). The degree of densification was studied by measurement of fired shrinkage, apparent porosity, bulk density and cold crushing strength. Phase compositions and microstructural features of sintered samples were evaluated by XRD and SEM respectively. Addition of 0.2% hydrogel powder to alumina exhibited remarkable influence on development of high mechanical strength. The in situ formed ZnAl2O4 spinel dopant acted as a grain growth inhibitor in the alumina system. 相似文献
20.
In this paper, TiO2 was introduced into boron carbide and B4C-based ceramic composites were obtained by uniaxial hot pressing. The mechanical properties, relative density and erosion behaviour of B4C-based ceramic composites were investigated. X-ray analysis showed that the fabricated composites were composed of B4C, TiB2 and C phases. SEM technique was employed to observe the original polished surfaces and the eroded surfaces of B4C-based ceramic composites. The effect of impingement angle, impact velocity of SiC erodent particle, relative density and phase ratio on the erosion rate of B4C-based ceramic composites was determined. It was found that the erosion rate of B4C-based ceramic composites increased with increasing of impingement angle and erodent particle velocity. The relative density and phase ratio influenced the erosion rate of B4C-based ceramic composites significantly by influencing their mechanical properties. 相似文献