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41.
Shengyue Gu Shouyang Zhang Fei Liu Wei Li 《Journal of the European Ceramic Society》2018,38(15):5082-5091
Y2Hf2O7 possesses low thermal conductivity and high melting point, which make it promising for a new anti-ablation material. For evaluating the thermal stability and the potential applications of Y2Hf2O7 on anti-ablation protection of C/C composites, Y2Hf2O7 ceramic powder was synthesized by solution combustion method and Y2Hf2O7 coating was prepared on the surface of SiC coated C/C composites using SAPS. Results shown that the coating exhibits good ablation resistance under the heat flux of 2.4?MW/m2 with the linear and mass ablation rates are 0.16?μm?s?1 and ?0.028?mg?s?1, respectively, after ablation for 40?s. With the prolonging of the ablation time, the increasing thermal stress causes the increase of cracks. Moreover, the chemical erosion from SiO2 and the physical volatilization of low temperature molten products aggravate failure of the Y2Hf2O7 coating. 相似文献
42.
《Ceramics International》2020,46(8):12102-12110
Selective laser sintering was combined with reactive melt infiltration to fabricate SiSiC part, and the effects of carbon fiber (Cf) on the properties of the SLS green body, the carbonized and final SiSiC sample were investigated. Results show that the addition of an appropriate amount of Cf (1.59 wt%~2.97 wt%) can increase the bulk density and geometric precision of the sample at all stages, and improve the mechanical properties of green and carbonized samples. The main phases composed of the SiSiC composite were free Si, a-SiC, β-SiC, plus a very small amount of Al–Si alloy. With 1.59 wt% Cf addition, a relatively comprehensive favorable macro-properties of both the green sample and carbonized sample was achieved, and the homogeneous microstructure of the latter favored the decreased free Si content and increased β-SiC content of the final composite. The evolution mechanism of Cf added to the raw material is inferred to be the mutual diffusion of [C] and [Si] that occurred at the Cf/Si melt boundary leading to the formation of the siliconized Cf with relatively large diameter size (24.3 μm) and high aspect ratio (>30). Amorphous C, which derived from the pyrolysis of epoxy resin E12, undergone a dissolution-precipitation mechanism with the formation of fine-grain β-SiC. 相似文献
43.
The neutral axis depth is considered the best parameter for quantifying the moment redistribution in continuous concrete beams, as exemplified in various design codes worldwide. It is therefore important to well understand the variation of neutral axis depth against moment redistribution. This paper describes a theoretical investigation into the neutral axis depth and moment redistribution in concrete beams reinforced with fibre reinforced polymer (FRP) and steel bars. A finite element model has been developed. The model predictions are in favourable agreement with experimental results. Three types of reinforcement are considered, namely, glass fibre, carbon fibre and steel. Various levels of reinforcement ratio are used for a parametric evaluation. The results indicate that FRP reinforced concrete continuous beams exhibit significantly different response characteristics regarding the moment redistribution and variation of neutral axis depth from those of steel reinforced ones. In addition, it is found that the code recommendations are generally unsafe for calculating the permissible moment redistribution in FRP reinforced concrete beams, but the neglect of redistribution in such beams may be overconservative. 相似文献
44.
This paper presents an experimental study of low velocity impact response of carbon/epoxy asymmetrically tapered laminates. The tests are realised at energy between 10 and 30 J on two types of layup with multiple terminated plies. The type and localisation of damage are analysed using C-scan and micrographs. Then, the data is compared with the response of corresponding respective plain laminate. The effects of some tapering parameters (taper angle, drop-off disposition and configuration) on the impact damage mechanisms are also investigated. Very similar impact damage phenomena are found between tapered and plain laminates. The presence of material discontinuity due to the resin pocket affects less the damage mechanism than the structural difference between the thick and the thin sections. 相似文献
45.
《Ceramics International》2020,46(6):7888-7895
Graphite carbon nitride (g-C3N4) is an appealing metal-free photocatalyst for hydrogen evolution, but the potential has been limited by its poor visible-light absorption and unsatisfactory separation of photo-induced carriers. Herein, a facile one-pot strategy to fabricate carbon self-doped g-C3N4 composite through the calcination of dicyanamide and trace amounts of dimethylformamide is presented. The as-obtained carbon self-doped catalyst is investigated by X-ray photoelectron spectroscopy (XPS), confirming the substitution of carbon atoms in original sites of bridging nitrogen. We demonstrate that the as-prepared materials display remarkably improved visible-light absorption and optimized electronic structure under the premise of principally maintaining the tri-s-triazine based crystal framework and surface properties. Furthermore, the carbon doped g-C3N4 composite simultaneously weakens the transportation barrier of charge carriers, suppresses charge recombination and raises the separated efficiency of photoinduced holes and electrons on account of the extension of pi conjugated system. As a result, carbon self-doped g-C3N4 exhibits 4.3 times greater photocurrent density and 5.2 times higher hydrogen evolution rate compared with its bulk counterpart under visible light irradiation. 相似文献
46.
Alinda Samsuri Mohd Nor Latif Mohd Razali Shamsuddin Fairous Salleh Maratun Najiha Abu Tahari Tengku Shafazila Tengku Saharuddin Norliza Dzakaria Mohd Ambar Yarmo 《International Journal of Hydrogen Energy》2021,46(48):24831-24844
Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO3) catalyst. The composition and morphology of the reduced phases were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). The reduction progression of MoO3 catalyst was attained with different reductant types and concentration (10% H2/N2, 10% and 20% CO/N2 (%, v/v)). Two different modes of reduction process were applied. The first approach of reduction involved non-isothermal mode reduction up to 700 °C, while the second approach of reduction involved the isothermal mode reduction for 60 min at 700 °C. Hydrogen temperature programmed reduction (H2-TPR) results showed the reduction progression of three-stage reduction of MoO3 (Mo6+ → Mo5+ → Mo4+ → Mo0) with Mo5+ and Mo4+. XRD analysis confirmed the formation of Mo4O11 phase as an intermediate phase followed by MoO2 phase. After 60 min of isothermal reduction, peaks of metallic molybdenum (Mo) appeared. Whereas, FESEM analysis showed porous crater-like structure on the surface cracks of MoO2 layer which led to the growth of Mo phase. Meanwhile, the reduction of MoO3 catalyst in 10% carbon monoxide (CO) showed the formation of unstable intermediate phase of Mo9O26 at the early stage of reduction. Furthermore, by increasing 20% CO led to the carburization of MoO2 phase, resulted in the formation of Mo2C rather than the formation of metallic Mo, as confirmed by XPS analysis. Therefore, the presented study shows that hydrogen gave better reducibility due to smaller molecular size, which contributed to high diffusion rate and achieved deeper penetration into the MoO3 catalyst compared to carbon monoxide reductant. Hence, the reduction of MoO3 in carbon monoxide atmosphere promoted the formation of Mo2C which was in agreement with the thermodynamic assessment. 相似文献
47.
Koji Morita Byung-Nam Kim Hidehiro Yoshida Keijiro Hiraga Yoshio Sakka 《Journal of the European Ceramic Society》2018,38(6):2588-2595
Carbon contamination from the carbon paper/dies during spark-plasma-sintering (SPS) processing was examined in the MgAl2O4 spinel. The carbon contamination sensitively changes with the heating rate during the SPS processing. At the high heating rate of 100 °C/min, the carbon contamination having organized structures occurred over almost the entire area from the surface to deep inside the SPSed spinel disk. In contrast, at the slow heating rate of 10 °C/min, the carbon contamination having disordered structures occurred only around the surface area. The carbon phases transform into high pressure CO/CO2 gases by post-annealing in air and lead to pore formation along the grain junctions. The pore formation significantly occurs at the high heating rate due to the large amount of the contaminant carbon phases. This suggests that if once the carbon contamination was formed in the materials, it is very difficult to remove the carbon phases from the materials. 相似文献
48.
Antonio Vinci Luca Zoli Diletta Sciti 《Journal of the European Ceramic Society》2018,38(11):3767-3776
The microstructure and the oxidation resistance in air of continuous carbon fibre reinforced ZrB2–SiC ceramic composites were investigated. SiC content was varied between 5–20?vol.%, while maintaining fibre content at ~40?vol.%. Short term oxidation tests in air were carried out at 1500 and 1650?°C in a bottom-up loading furnace. The thickness, composition and microstructure of the resulting oxide scale were analysed by SEM-EDS and X-Ray diffraction. The results show that contents above 15?vol.% SiC ensure the formation of a homogeneous protective borosilicate glass that covers the entire sample and minimizes fibre burnout. The scale thickness is ~90?μm for the sample containing 5?vol.% SiC and decreases with increasing SiC content. 相似文献
49.
在45钢表面以超声波辅助脉冲电沉积制备Ni-TiN复合镀层。研究了平均阴极电流密度、脉冲占空比、超声功率和TiN粒子(平均直径20~30 nm)添加量对复合镀层的TiN粒子含量和显微硬度的影响。得到较优的工艺参数为:NiSO4ꞏ6H2O 300 g/L,NiCl2ꞏ6H2O 30 g/L,H3BO330 g/L,十二烷基硫酸钠0.3 g/L,TiN 25 g/L,pH 4.1~4.3,温度40°C,平均阴极电流密度4 A/dm2,脉冲占空比40%,脉冲频率1000 Hz,超声功率300 W,机械搅拌速率200 r/min,时间60 min。该条件下所得Ni-TiN复合镀层的TiN质量分数为8.35%,显微硬度为819 HV,表面平整、致密,晶粒尺寸均匀。 相似文献
50.
Roberto C. Dante Pablo Martín-Ramos Pedro Chamorro-Posada Dario Rutto José Vázquez-Cabo Denisse G. Dante 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(7):533-540
AbstractIn this work, a new g-C3N4-based Z-scheme with γ-Fe2O3 and β-Ag2Se both n-type semiconductors, and graphite to favor electron exchange is presented. The composite material was studied by XRD, FTIR, UV-Vis, TEM, XPS, TGA, DSC and TOF-SIMS, and the ability of this photocatalytic system to act as a photo-reductant was assessed using crystal violet (CV+) dye. Solar light driven photo-reduction of CV+ in the presence of tri-sodium citrate evidenced a synergistic enhancement of the activity of the composite toward reduction, with ~20 times higher conversion rates per unit of surface area than those of g-C3N4. Photo-oxidation experiments under Xe lamp irradiation in the presence of H2O2 also showed that the AgFeCN composite featured a higher activity (~8×) than g-C3N4. This Z-scheme may deserve further study as a photo-reductant to obtain hydrogen or hydrogenated compounds. Moreover, the use of CV+ may represent a facile procedure that can aid in the selection of new photocatalysts to be used in hydrogen production. 相似文献