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将高温煤沥青和浸溃荆沥青在92MPa下炭化,在2500℃下对所得沥青炭进行石墨化处理;测试了所得沥青炭的体积密度、开孔率、比表面积(SBET);利用扫描电子显微镜(SEM)观察了所得沥青炭的显微结构;利用X射线衍射方法(XRD)检测了所得沥青炭石墨化处理后的石墨化度;测试了所得沥青炭的氧化性能;测试了沥青炭试样的比热容、导热系数、热扩散率和线膨胀系数。结果表明:在92MPa下,两种沥青炭有着相近的密度和开孔率;浸渍剂沥青炭的SBEt高于高温煤沥青炭;浸渍荆沥青炭为流线型结构,高温煤沥青炭为镶嵌型和域型并存的结构;流线型结构沥青炭石墨化度较高;高温煤沥青炭的抗氧化性能要好于浸溃荆沥青炭;随着沥青炭石墨化程度的增大,比热客、导热系数、热扩散率都增大,而线膨胀系数减小。 相似文献
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以水性中间相沥青(AMP)为前驱体,阳离子表面活性剂(CTAB)为结构导向剂,通过控制AMP的凝胶化和自组装过程,采用溶胶-凝胶法来制备介孔沥青炭微球。利用SEM、HRTEM、SAXRD、FT-IR等分析手段,对产物的形貌及结构进行表征,并研究了介孔沥青炭微球的形成机理和电化学性能。结果表明:在制备介孔沥青炭微球的过程中,CTAB与离子化的AMP可通过S+I-静电力作用形成凝胶球,经炭化后得到介孔沥青炭微球。当CTAB/AMP=1.2时(CTAB为2 g),炭化后得到的介孔炭微球之间界面明显,表面光滑,球体粒径为300~500 nm,当增加CTAB胶束在溶液中的浓度时,炭化产物中得到纳米炭棒。所得介孔沥青炭微球C-AMP1.2-800有序度差、石墨化度低,球体为乱层石墨结构,其在50 mV.s-1下的比电容为103.5 F/g。 相似文献
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以商业化的Kapton型聚酰亚胺为前驱体制备炭膜,采用容量法研究了不同炭化温度制备的炭膜CO2吸附和扩散行为,并利用Sips模型对实验数据进行拟合,DA方程计算炭膜的孔结构参数,Fick扩散模型求取CO2在炭膜内的扩散系数,采用XRD分析探讨了炭膜的炭结构。结果表明,炭膜孔结构随着热解炭化温度的提高,孔径收缩,且当炭化温度从600℃升高到800℃,炭膜的微孔体积随炭化温度的升高而增大,而800℃以后,微孔体积随炭化温度的升高而下降。CO2在不同炭膜中的扩散系数约为1.04×10-13~8.56×10-12m2·s-1,在实验测定的压力范围内扩散系数随着平衡压力的增大呈现出先增大后减小的规律。 相似文献
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High temperature oxidation resistance of Y2O3 modified ZrB2-SiC coating for carbon/carbon composites
Hanchun Ma Qiang Miao Wenping Liang Yangyang Liu Hao Lin Hairui Ma Shiwei Zuo Lin Xue 《Ceramics International》2021,47(5):6728-6735
To protect carbon/carbon (C/C) composites from oxidation at high temperature, Y2O3 modified ZrB2-SiC coating was fabricated on C/C composites by atmospheric plasma spraying. The microstructure and chemical composition of the coatings were characterized by SEM, EDS, and XRD. Experiment results showed that the coating with 10 wt% Y2O3 presented a relatively compact surface without evident holes and cracks. No peeling off occurred on the interface between the coating and substrate. The ZSY10 coating underwent oxidation at 1450 °C for 10 h with a mass loss of 5.77%, while that of ZS coating was as high as 16.79%. The existence of Y2O3 played an important role in inhibiting the phase transition of ZrO2, thus avoiding the cracks caused by the volume expansion of the coating. Meanwhile, Y2SiO5 and ZrSiO4 had a similar coefficient of thermal expansion (CTE), which could relieve the thermal stress inside the coating. The ceramic phases Y2SiO5, Y2Si2O7 and ZrSiO4 with high thermal stability and low oxygen permeability reduced the volatilization of SiO2. 相似文献
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Min Zhang Xiaoyan Zhang Xiwei Qi Hongen Zhu Ying Li Yaohang Gu 《Ceramics International》2018,44(17):21269-21276
A lead–free multiferroic ceramic 0.7BiFeO3–0.3BaTiO3 showed strong ferroelectric and piezoelectric properties, but weak magnetic and magnetoelectric properties. We herein expected that the electrical and magnetic properties of 0.7BiFeO3–0.3BaTiO3 ceramics could be enhanced by introducing LaFeO3. (0.7–x) BiFeO3–0.3BaTiO3–xLaFeO3 (x?=?0–0.2) were synthesized by solid-state reaction. All the ceramics formed a perovskite structure, and a morphotropic phase boundary (MPB) between rhombohedral and orthorhombic phases formed at x?=?0.025. The ceramics with MPB composition had high unipolar strain (Smax = 0.14%), piezoelectricity (d33 = 223 pC/N, d33 * = 350?pm/V), ferroelectricity (Pr = 25.67 mC/cm2) and magnetoelectricity (aME = 466.6?mV/cm·Oe), which can be attributed to addition of La ions. The improved phase angle also demonstrated augmentation of ferroelectricity on the microscopic view. The ferromagnetism was evidently improved after LaFeO3 doping, and the remanent magnetization Mr increased from 0.0207 to 0.0622?emu/g with rising x from 0 to 0.075. In conclusion, with strong magnetoelectric properties, the prepared ceramics may be applicable as promising lead–free multiferroic ceramic materials for novel electronic devices. 相似文献
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La doping effects on intergrowth Bi2WO6–Bi3TiNbO9 ferroelectric ceramics were studied by X-ray diffraction, electron probe microanalysis and dielectric spectroscopy. It was found that the La3+ distribution, ferroelectric phase transition and dielectric relaxation behavior are apparently affected by La doping. With increasing La3+ content, the site of dopant ion varies, the grain growth of Bi5TiNbWO15 is restrained, the Curie temperature is reduced and broadened. Furthermore, two dielectric relaxation loss peaks were observed both in temperature and frequency spectra. The calculated relaxation parameters revealed the oxygen vacancy related to the relaxation process. 相似文献
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This article studies estimation and asymptotic properties of Threshold Quantile Autoregressive processes. In particular, we show the consistency of the threshold and slope parameter estimators for each quantile and regime, and derive the asymptotic normality of the slope parameter estimators. A Monte Carlo experiment shows that the standard ordinary least squares estimation method is not able to detect important nonlinearities produced in the quantile process. The empirical study concentrates on modelling the dynamics of the conditional distribution of unemployment growth after the second world war. The results show evidence of important heterogeneity associated with unemployment and strong asymmetric persistence of unemployment growth in the higher quantiles. 相似文献
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《Ceramics International》2023,49(5):8022-8031
During aluminium production, the molten metal will always contain varying amounts of impurities, e.g., non-metallic inclusions, and for high-quality products removing such inclusions is essential. This can be achieved by filtration using ceramic foam filters (CFFs). However, these filters are highly brittle materials subjected to strong mechanical and thermo-mechanical stresses during transport and operation, which occasionally leads to failure of the filter material. In the present study, the compression strength of five different Al2O3-based CFFs was measured at room temperature and elevated temperature (compressed at 730 °C), as well as while submerged in molten aluminium with varying melt compositions (pure aluminium and an aluminium-magnesium alloy). The compression strengths at room temperature were established to be in the range of 1.19–2.09 MPa depending on the filter type tested. In the case of the CFFs compressed at elevated temperature, a reduction in compression strength in the range of 9.2–58.6% was established to exist depending on filter type and heating duration, except in three of the filter/duration-combinations tested. Compression of CFF samples submerged in molten aluminium led to an even further reduction in compression strength in the range of 42.6–69.4% depending on filter type and duration of exposure. With an exposure time of only 5 min, no difference in compression strength was observed between the two aluminium melts. 相似文献