共查询到20条相似文献,搜索用时 31 毫秒
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Synthesis of nanosized tungsten carbide from phenol formaldehyde resin coated precursors 总被引:1,自引:0,他引:1
Nanosized tungsten carbide was synthesized from phenol formaldehyde resin (PF) coated tungsten precursors.The process has three steps in which nanosized tungsten particles were first coated with PF,then the precursors were carburized at 950℃,and finally the carburized powders were treated in flowing wet hydrogen atmosphere at 940℃ to remove the uncombined carbon.The obtained powders were characterizedusing X-ray diffraction analysis (XRD),field-emission scanning electron microscopy (FESEM),small angle X-ray scattering (SAXS),andcombustion-gas-volume method.The results indicated that single-phase WC could be synthesized using excessive PF as carburizer at a muchlower temperature compared with using mixed carbon black.After wet hydrogen treating,the mean size of the obtained WC particles was 94.5nm and the total carbon content was 6.18 wt.%. 相似文献
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Research on the quantitative analysis of subsurface defects for non-destructive testing by lock-in thermography 总被引:1,自引:0,他引:1
This paper describes the quantitative analysis of the boundary, location and depth of subsurface defects by lock-in thermography. The phase difference between defective areas and non-defective areas illustrates the qualitative analysis of the boundary and the location of the subsurface defect. In order to accurately estimate the size, location and depth of the defects, the phase is normalised, the heat transfer partial differential equation (PDE) model is used to filter the noise of normalised phase image and the differential normalised phase profile is employed to determine the boundary and location of the defect. The profile of the differential normalised phase distribution has maximum, minimum and zero points that help to quantitatively determine the boundary and location of the subsurface defect. An artificial neural network (ANN) is proposed to determine the depth of the subsurface defect. Experimental results for a steel plate, a carbon fibre-reinforced polymer (CFRP) sheet-foam sandwich, and honeycomb structure composites with artificial subsurface defects show good agreement with the actual values. 相似文献
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Renaldas Raišutis Rymantas Kažys Egidijus Žukauskas Liudas Mažeika Alfonsas Vladišauskas 《NDT & E International》2010,43(5):416-424
One of the most important parts of gliders is a lightweight longeron reinforcement made of carbon fibre reinforced plastic (CFRP) rods. During manufacturing, in order to build the arbitrary spar profile, these small diameter (few millimetres) rods are glued together into epoxy filled matrix. Still, defects present in the rods, such as break of fibres, multiple delaminations due to lack of bonding and reduction in density affect construction strength markedly and are extremely complicated to eliminate. Therefore, appropriate non-destructive testing techniques intended for carbon fibre rods should be applied prior to gluing them together.The aim of the present paper is to analyse development possibilities of NDT technique based on application of ultrasonic guided waves and intended for CFRP rods that are used for aerospace applications and are defective with multiple delaminations.The regularities of ultrasonic guided wave propagation in a defective CFRP circular-shape rod with multiple delaminations have been investigated using 3D numerical simulations, finite difference and finite element models. The corresponding experiments have been conducted as well. Based on leaky wave suppression over a defective region due to the weak vertical component of particle displacements, the mechanism of guided wave interaction with the region of multiple delaminations is explained from the ultrasonic NDT viewpoint. 相似文献
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Anders From Rolf Sandstrm 《International Journal of Refractory Metals and Hard Materials》1996,14(5-6):393-405
A method for the quantitative assessment of the degree of clustering in dispersions of small particles has been developed. Clusters are defined as the areas where particle to particle distance is shorter than a pre-selected distance called interaction distance. The method gives the number of clusters per unit area (density) as a function of the interaction distance. Implementation on modern image analysis system shows that the time of analysis is relatively short. In order to increase the understanding of the resulting cluster density function a series of tests on computer generated particle dispersions has been done. Algorithms for the generation of both isotropic random dispersions, i.e. clumping and random clustered dispersions are given. The method of analysis was tested on two specimens of WC-10% Co cemented carbide alloys. The microstructure on polished specimen surface consisted of clustered particles of uncombined carbon. This clustering was quantified. 相似文献
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Transient thermography was employed in the inspection of defects in various aircraft composite panels. Three different categories of defects were investigated in the laboratory; notches on aluminium alloy panels under carbon or boron composite patching, a simulation of delamination on a boron composite patch, and fibre breakout on carbon composites. In all situations, the defects were artificially created. After detecting the defects, quantitative analysis concerning the contrast of the detected defects was carried out. Finally, information about the size of the artificial delaminated panel in relation to transient time was also performed. 相似文献
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推导了恒定激光脉冲激励作用下的焊点瞬态热平衡方程,及基于极限温差反问题识别的缺陷尺寸及热阻解析求解方法;通过建立空洞缺陷焊点数字化模型,对恒定激光脉冲激励过程进行了热分析仿真,得到了焊点温差、热阻及缺陷尺寸之间的演化规律;通过制备虚焊缺陷焊点试验样本,实施了不同温度参数组合下的热试验,并对热试验后的焊点缺陷演化情况进行红外测温分析.试验结果表明,热试验过程中的焊点缺陷演化机理具有与金属材料蠕变曲线相似的变化规律,缺陷尺寸呈现先增大、后减小及再增大的变化行为,有助于完善和补充焊点的热试验理论. 相似文献
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The difference of physicochemical properties among minerals in Baotou rare earth tailings is not significant,which leads to a great difficulty in separation of minerals.In this article,the process of magnetizing roast and low-intensity magnetic separation was used to recover iron.Effect of calcination temperature,holding time and carbon/oxygen ratio on roasting efficiency was investigated.The parameters evaluating magnetizing roast efficiency and theoretical value were determined.X-ray diffraction(XRD)analysis was used to investigate the conversion of Fe phase after roasting.The results show that the best magnetizing roast conditions are calcination temperature of 650℃,holding time of 2.5 h,and carbon/oxygen molar ratio of 3.85.The best magnetization rate is 2.36,which is close to the theoretical value of 2.33.Based on experiments of low-intensity magnetic separation under different intensities,the best current intensity is 2.0 A to obtain the best separation results.Under the best condition,the concentrate grade of iron is 45.45% and the recovery of iron is 68.36%.Most of rare earth,fluorine,and phosphorus are enriched in the magnetic separation tailings.The XRD analysis shows that Fe exists in Fe2O3 before roasting and exists in Fe3O4after roasting. 相似文献
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This paper proposes a method of lossless micromagnetic detection in the geomagnetic field for detecting traces of carbon impurity defects in crystalline silicon. The magnetization tests show that crystalline silicon is a diamagnetic substance with a stronger relative permeability than carbon. Micromagnetic decay theory is gained according to the energy decay. When the geomagnetic field penetrates through the materials, the apparent magnetic susceptibility can be calculated and subsequently used to project the images. The resulting image clearly showed the location of the defects. Test results are proved by the metallographic phase and spectral analysis. New method and ideas are provided for effective detection of trace carbon impurity defects in the crystalline silicon. 相似文献
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以东安513型汽油发动机整机为例,基于ANSYS有限元分析软件对其进行流体场、瞬态温度场以及瞬态结构场的多物理场双向耦合研究,实现了对发动机实际工况下的有限元分析。研究了发动机整机在实际工况下的受力以及密封情况,并对现有发动机组合结构存在的密封缺陷进行优化调整。文中详细阐述了在分析过程中涉及到的关键技术和要点,并最终获得了发动机整机实际工作状态下的多个结果云图。根据分析结果云图可以发现,发动机在热载荷、螺栓预紧力以及爆破压力的共同影响下,会使整机发生一定的形变,这种变形会影响其工作状况下的密封性能。通过对分析结果的研究,最终选择调整螺栓预紧力的大小和分布来提高发动机密封性能。 相似文献
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Fourteen test sites were established in the tropical humid atmosphere of the Yucatán Peninsula and the Mexican Caribbean area. In each environment sulfur dioxide and chloride deposition rates were measured and the corrosion rates of flat plate samples (low carbon steel, copper and zinc) determined. In selected locations open helix samples of copper, and low carbon steel were also tested. In two typical test sites (a rural-urban and a marine-coastal) the time-of wetness and temperature were registered, then their influence on the metallic corrosion rates discussed. The obtained data were used for classification of atmospheric aggressivity, according to ISO 9223. It was observed that the aggressivity categories of marine coastal zones are C5, the highest one, while the rural and rural-urban sites classify as C2, C3 and C4. No appreciable difference in category classification is observed, when flat plates or open helix samples are used. 相似文献
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大气等离子喷涂的YSZ纳米热障涂层的微观结构 总被引:12,自引:0,他引:12
采用YSZ(8%Y2O3-Zr02,质量分数)纳米粉末,经大气等离子喷涂(APS)方法制备得YSZ纳米热降涂层(TBC).喷涂前的粉末额粒直径为30—50nm,晶粒尺寸约12nm.对涂层的分析结果表明:YSZ纳米涂层平均晶粒尺寸在20—30nm,有个别粗晶直径达200—300nm.涂层由立方相c—ZrO2和四方相t′—ZrO2组成,t′相内存在畴结构.涂层内孔洞细小弥散,多呈闭合式.TEM下可见位错缠结和富层错的板条带结构. 相似文献
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《Synthetic Metals》2001,125(2):231-238
Quantitative characterization of nano-sized spaces by STM techniques was discussed. Nano-sized spaces were introduced by oxidation; either oxygen plasma on perfect graphite structure or air oxidation on the surface of carbon spheres with highly disordered structure. By the irradiation of oxygen plasma at room temperature, nano-sized structural defects (missing carbon atoms, vacancies) were introduced in graphite layer plane. The increase in input power led to the increases in both density and size of defects, but that in irradiation time with a constant power resulted mostly in the increase of defect density, a little effect on the size of defects. By the oxidation of carbon spheres with disordered structure in static air at 400°C, spaces in the size range of 0.5–1.35 nm increased, though large spaces with the size of >2.2 nm were formed. The characterization of nano-sized spaces by STM with the aid of image processing and statistical analysis was shown to be effective. 相似文献
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针对TC4激光选区熔化成形件内部缺陷射线检测及定量尺寸评价,通过CR检测方法研究TC4人工缺陷(气孔、熔合不良)试样射线检测灵敏度及最小缺陷可检能力,利用显微CT定量分析缺陷尺寸、三维形貌及空间分布,并对比两种成像方法对于缺陷尺寸计量的差异。结果表明:CR检测方法能够检出?0.4 mm的模拟气孔、?0.8 mm×0.3 mm熔合不良缺陷,而显微CT具有更高的检测灵敏度,适用于微小气孔的缺陷检测、尺寸评价及定量分析,可检出?0.3 mm的模拟气孔缺陷;人工缺陷设计/实物尺寸偏差范围≤10%,并且随着缺陷设计尺寸的增大,缺陷实际打印三维形貌越不规则。 相似文献
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《Acta Materialia》2007,55(15):5269-5279
Researchers are claiming that the feasibility of space elevator cable is now realistic, thanks to carbon nanotube technology, proposing its realization within a decade. However, the current view of basing the design of the megacable on the theoretical strength of a single carbon nanotube is naïve, as has recently been emphasized. In this paper the role of thermodynamically unavoidable atomistic defects with different size and shape is quantified on brittle fracture, fatigue and elasticity, for nanotubes and nanotube bundles. Nonasymptotic regimes, elastic plasticity, rough cracks, finite domains and size effects are also discussed. The results are compared with atomistic simulations and nanotensile tests of carbon nanotubes. Key simple formulas for the design of a flaw-tolerant space elevator megacable are reported, suggesting that it would need a taper ratio (for uniform stress) of about two orders of magnitude larger than currently proposed. 相似文献
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相变-扩散钎焊是作者提出的一种将相变超塑性扩散焊与扩散钎焊结合起来的新型复合工艺,它具有所需温度循环次数少(与相变超塑性扩散焊相比)、高温停留时间短但扩散效率高(与扩散钎焊相比)、改善热影响区组织(与弧焊和扩散钎焊相比)等优点。针对其典型接头的界面接合形貌及缺陷,采用扫描电镜及能谱仪进行了分析。结果表明,界面接合良好,未观察到片状夹杂物、气孔及未焊合。而缺陷具有如下主要特点:存在于距离界面内部有一定距离的残留中间层内,并不在界面上;并非夹杂而是孔洞;尺寸远小于晶粒尺寸;稀疏且错落排列。分析认为该孔洞是由母材溶解到中间层中带来的碳还原母材与中间层氧化物所产生的CO气孔。 相似文献