共查询到18条相似文献,搜索用时 93 毫秒
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利用平面冲击波技术,对溶胶-凝胶法制备的锐钛矿型TiO2粉体和干凝胶进行冲击实验,采用X射线衍射(XRD)、透射电镜(SEM)和激光粒度分析仪(LPSA)等手段对冲击前后的TiO2粉体和干凝胶进行表征。结果表明:冲击波的高温作用能够实现亚稳态的锐钛矿型TiO2向稳定态的金红石型TiO2转变,并且冲击波直接作用于干凝胶时更容易获得稳定态的金红石型TiO2;冲击波的瞬时性可以抑制TiO2晶粒的长大,实现晶粒纳米化;冲击波的高压作用可以有效控制由于溶胶-凝胶法导致的粉体团聚现象。 相似文献
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采用柱面冲击波回收装置,通过炸药爆轰产生的冲击波作用于Pb4O3、ZrO2和TiO2混合物粉体以合成PZT95/5粉体。通过对回收粉体进行的X射线衍射(XRD)分析,并结合冲击波理论,从实验和理论两个方面探讨了PZT粉体的合成机理和过程。结果表明,PZT的合成反应与Pb3O4的分解反应几乎同时进行,由于冲击波的特殊性,系统的温度和压力能同时满足Pb3O4分解和PZT合成的反应热力学条件,由Pb3O4分解的PbO一旦形成,就立刻与ZrO2、TiO2等氧化物反应生成PZT;冲击波合成PZT粉体属于特殊的固相反应,物质的扩散速度和反应速度大大提高。 相似文献
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研究了冲击波对PZT-95/5压电陶瓷的活化改性作用,对PZT-95/5粉末及块状材料进行动态冲击波加载。实验表明:在合适的条件下,冲击波作用可提高样品的密度ρ,压电应变常数d33,介电常数ε,降低介电耗损系数tg δ%。通过对样品进行X射线衍射,扫描电镜SEM、透射电镜TEM和X射线光电子能谱XPS等微观测试分析,揭示了冲击波改性的机理主要是:晶粒细化,晶界破坏,孔隙增多,缺陷增多,相变产生等,从而达到对样品改性的作用。 相似文献
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We theoretically show that H atoms can be chemically adsorbed onto the surface of the Si-C heterofullerene- based nanotubes. The adsorbing energy of the H atom on Si-C heterofullerene-based nanotubes is in the range of 4.28-5.66 eV without any barrier for the H atom to approach to the Si-C heterofullerene-based nanotubes. The band-gap of Si-C heterofullerene-based nanotubes can be dramatically modified by introducing dopant states, i.e., there is a transition from semiconductor to conductor of the Si-C heterofullerene-based nanotubes induced by the adsorption of the H atom. These results actually open a way to tune electronic properties of heterofullerene-based nanotubes and thus may propose an efficient pathway for band structure engineering. 相似文献
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含冲击波流场干涉图的图像处理方法研究 总被引:2,自引:1,他引:1
本文研究了含冲击波流场干涉图的图像处理方法,它包括干涉条纹的快束细化算法,冲击波波阵面的提取算法和时间序列冲击波波阵面的配准算法.根据这些算法,在PC-VISION 100图像处理机上开发了应用软件.实验结果表明,该方法可用于定量计算冲击波的传播速度和压力分布,增加了流场干涉图的用途. 相似文献
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A.T. Raghavender Damir Pajic Kreso Zadro Tomislav Milekovic P. Venkateshwar Rao K.M. Jadhav D. Ravinder 《Journal of magnetism and magnetic materials》2007
Nanocrystalline Al-doped nickel ferrite powders have been synthesized by sol–gel auto-ignition method and the effect of non-magnetic aluminum content on the structural and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with inverse spinel structure. The calculated grain sizes from XRD data have been verified using transmission electron microscopy (TEM). TEM photographs show that the powders consist of nanometer-sized grains. It was observed that the characteristic grain size decreases from 29 to 6 nm as the non-magnetic Al content increases, which was attributed to the influence of non-magnetic Al concentration on the grain size. Magnetic hysteresis loops were measured at room temperature with a maximum applied magnetic field of ≈1 T. As aluminum content increases, the measured magnetic hysteresis curves become more and more narrow and the saturation magnetization and remanent magnetization both decreased. The reduction of magnetization compared to bulk is a consequence of spin non-collinearity. Further reduction of magnetization with increase of aluminum content is caused by non-magnetic Al3+ ions and weakened interaction between sublattices. This, as well as the decrease in hysteresis was understood in terms of the decrease in particle size. 相似文献
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Cryomilled eutectic aluminum–12% silicon powder was sintered using spark plasma sintering (SPS) to create bulk compacts. The cryomilling serves to break up and disperse the eutectic phase in the powder to create a well-distributed Si phase throughout the matrix and to modify the morphology of the Si phase from plate-like to spherical, whilst refining the aluminium grain size to the nanometric level. The effects of different sintering times and temperatures using SPS on the densification of the powder, the aluminium grain size evolution, the growth of the Si phase and the morphology change of the Si phase were investigated. The compacts were analysed using X-ray diffraction, scanning electron microscopy and optical microscopy. The initial stages of densification appear to be highly dependent on the yield strength of the powder. An estimate of the temperature gradient seen in the powder bed was made and calculated to be near 200?°C at the highest point. The Al and Si phase growth was investigated and it was observed that the Si coarsening rate is increased due to the increased volume of grain boundaries. As the Si coarsens, any pinning effect on the Al grains is lost, resulting in a highly unstable microstructure that coarsens rapidly. 相似文献
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Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250 °C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange. 相似文献
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《Current Applied Physics》2009,9(4):777-782
Fe–Si alloys are of significant commercial and academic interests, due to the large diversity of their physical properties. In practice, alloy powders are unsuitable because of their hardness, poor compactibility and resulting excessive tool wear. Therefore the powder mixture route is suitable as alloying technique. The properties of the Fe–Si sintered materials depend strongly on the influence of the element Si and content of it, which influence mainly the compactibility and the sintering behaviour as well as sintering parameters such as the optimum temperature. In this study, Cr–Mo prealloyed steel powders with different Si contents were prepared by powder mixture route. Mixed powders compacted under pressing pressure of 600 MPa, and then sintered at 1120 and 1250 °C. It was found out that in Si alloyed Cr–Mo steels sintered at higher temperatures such as 1250 °C, an intermediate liquid phase appeared and caused extreme shrinkage and distortion, but strongly accelerated sintering and had a beneficial effect also on homogenization. 相似文献
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Al-0.5%Cu-1%Si thin films deposited onto oxidized Si substrates were subjected to both wafer curvature and in situ transmission electron microscopy thermal cycling experiments between room temperature and 450°C. The evolution of precipitates was monitored during cycling. Chemical analysis revealed that the precipitates are pure Si. Their average size increased from 80?nm in the as-deposited state to 300?nm after thermal cycling. The Si precipitates serve as anchoring points for dislocations and grain boundaries. Direct evidence for pipe-diffusion ripening was found in the vicinity of a dissolving precipitate. Real-time measurement of the radius of the precipitate allowed us to estimate the coefficient of pipe diffusion of Si in Al at this temperature. As expected, this coefficient is several orders of magnitude larger than the volume diffusion coefficient. The impact of precipitate ripening on the mechanical behavior of these alloyed Al films will also be discussed. 相似文献
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The nucleation and growth of Si has been investigated by TEM in a series of high purity melt spun Al–5Si (wt%)-based alloys with a trace addition of Fe and Sr. In the as-melt-spun condition, some twinned Si particles were found to form directly from the liquid along the grain boundary. The addition of Sr into Al–5Si-based alloys promotes the twinning of Si particles on the grain boundary and the formation of Si precipitates in the α-Al matrix. The majority of plate-shaped and truncated pyramid-shaped Si precipitates were also found to nucleate and grow along {111}α-Al planes from supersaturated solid solution in the α-Al matrix. In contrast, controlled slow cooling decreased the amount of Si precipitates, while the size of the Si precipitates increased. The orientation relationship between these Si precipitates and the α-Al matrix still remained cube to cube. The β-Al5FeSi intermetallic was also observed, depending on subsequent controlled cooling. 相似文献
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D. He J.Y. Wang E.J. Mittemeijer 《Applied Physics A: Materials Science & Processing》2005,80(3):501-509
Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/Si and Si/Al bilayers was studied upon annealing at 250 °C by X-ray diffraction and Auger electron spectroscopy. The Al/a-Si bilayers and a-Si/Al bilayers were prepared by sputter deposition on single-crystal silicon wafers with a silicon-oxide film on top. During the isothermal annealing a layer-exchange process occurred in both types of bilayers. A continuous polycrystalline silicon (poly-Si) film was formed within, and thereby gradually replacing, the initial Al metal layer. The sublayer sequence in the original bilayer influenced the speed of the poly-Si formation and the layer-exchange process. After annealing, the Al fiber texture in the as-deposited bilayers had become stronger, the Al crystallites had grown laterally, and the macrostress in the Al layer had been released. The amorphous Si layer had crystallized into an aggregate of nanocrystals with {111} planes parallel to the surface, with a crystallite size of about 15–25 nm. An extensive analysis of the Gibbs energy change due to annealing showed that the layer exchange may be promoted by the release of elastic energy and grain growth for the Al phase. PACS 05.70.Jk; 61.43.Dq; 68.35.Rh; 61.72.Cc; 68.55.Jk 相似文献
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S. N. Kulkov 《Russian Physics Journal》2004,47(9):954-963
The special features of the structure and phase composition of nanocrystalline zirconia-based powders subjected to shock-wave treatment are studied. The investigations show that zirconia with small amounts of yttria and/or alumina is in nanocrystalline and quasi-amorphous states representing a nonequilibrium solid solution of ZrO2 (Y, Al) and that an increase in the monoclinic phase abundance is associated with a reduction in the critical size of tetragonal crystallites due to an accumulation of lattice microdistortions. The monoclinic phase in powders with yttria and alumina additions is not formed even with shock compression at pressures up to 20 GPa. This is attributed to the fact that the resultant lattice microdistortion level is inadequate to destabilize the nanocrystalline tetragonal phase. Relaxation of microdistortions on annealing causes the critical size of tetragonal crystallites to increase. As this takes place, the monoclinic phase is converted into the tetragonal one.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 61–70, September, 2004. 相似文献