排序方式: 共有33条查询结果,搜索用时 15 毫秒
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Lau Cher Hon Cervini Raoul Clarke Stephen R. Markovic Milena Ginic Matisons Janis G. Hawkins Stephen C. Huynh Chi P. Simon George P. 《Journal of nanoparticle research》2008,10(1):77-85
Nanosized powders of Ti-Nb oxide core-shell nanocrystals with atomic ratios of Nb/Ti = 0.11, 0.25, and 0.38 have been prepared
by two preparation routes. The first route was co-precipitation, followed by␣annealing, using NbCl5 as a source of Nb. The second route was coating of pure TiO2 nanocrystals by Nb-isopropoxide in liquid medium, followed by impregnation of the Nb into the nanoparticles by annealing.
Both methods yielded anatase nanocrystals with a Nb-rich shell and a core, which had much lower Nb loadings. The anatase structure
solid solution (with Nb incorporated) was stable under annealing up to 760°C. The particle size remained within the nanometric
scale (<50 nm) under heat-treatment up to 760°C. It has been shown that the fabricated powders can be redispersed in aqueous media
by simple ultrasound treatment, resulting in nanosized dispersions. Using a variety of analytical techniques, including depth
profiling of single nanocrystallites by AES combined with sputtering by Ar ions, the mechanism of the core-shell structure
creation was studied. It is proposed that the formation of the core-shell structure is governed by solubility limitations
in the co-precipitation route and by solubility and diffusion limitations in the coating-incorporation route. 相似文献
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分散有ZnS:Mn2+纳米超微粒的有机薄膜的制备和光学性质 总被引:1,自引:1,他引:0
近年来,半导体超微粒的合成及光物理性质研究已成为活跃的领域.由于量子尺寸效应引起的量子点能级结构的变化及其光学性质已经作了大量研究[1-4].1993年,Bhar-gava首次报导了化学反应合成的ZnS Mn超微粒的光学性质[5],掺杂半导体纳米材料的出现,为纳米科学的研究开辟了新的领域. 相似文献
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为了使激光冲击强化技术能较好地应用于TC6钛合金的发动机叶片,对TC6钛合金进行试验研究。通过X射线衍射仪、透射电子显微镜等测试技术分析了不同参数下TC6钛合金的微观组织变化,用显微硬度计和残余应力测试仪分别表征表层硬度和残余应力变化,并测试材料冲击后的振动高周疲劳性能。试验结果表明:激光冲击材料后表面组织得到明显细化,随着冲击次数的增加,先后出现了高密度位错、位错胞、亚晶和纳米晶。性能方面,表面硬度在冲击一次即可提高19%,硬度影响深度达到700 m;与此同时表面残余应力最高达到-608.5 MPa,在500 m深度上仍具有-100 MPa左右的应力存在。经三次冲击后,标准疲劳试片的疲劳极限提高近20%。 相似文献
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L. M. Babkov T. V. Bezrodnaya G. A. Puchkovskaya K. E. Uspenskii V. V. Shimanovaskaya 《Journal of Structural Chemistry》2008,49(3):517-523
This contribution provides the theoretical background for the structure-determining role of hydrogen bonding in the formation of a near-surface layer of titania nanocrystallites, previously revealed by the authors in the investigation of IR experimental spectra of two-component solid mixtures of nanocrystalline titanium dioxide with benzophenone or 4-pentyl-4′-cyanobiphenyl. DFT calculations (B3LYP) in 6-31+G(d) basis set is used to simulate the structure and IR spectra of free molecules of water, 4-pentyl-4′-cyanobiphenyl, benzophenone and their H-complexes formed in the near-surface layers of titania nanocrystallites due to presence of water adsorbed on their surfaces. Using the results of simulation and analysis of IR spectrum bands corresponding to stretching vibrations of polar bonds O-H, C=O, C≡N, the formation mechanism of near-surface layers of titania nanocrystallites in the considered heterogeneous two-component systems is theoretically substantiated: they are formed by hydrogen-bonded complexes involving components of the mixture and water. 相似文献
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微波水热法合成硅酸钇纳米晶 总被引:3,自引:0,他引:3
以硝酸钇、硅酸钠和氢氧化钠为主要原料,采用一种新方法-微波水热法可控合成了硅酸钇纳米晶.研究了起始溶液配比,合成温度及退火温度对硅酸钇的影响.采用X射线衍射仪(XRD)和透射电子显微镜(TEM)对粉体进行了表征.结果表明:随着合成温度的升高,Y_2SiO_5的含量增加.低温退火处理有助于提高硅酸钇微晶的结晶程度.选不同配比的溶液体系,经微波水热150 ℃作用10 min后,得到的前驱体于900 ℃下保温2 h,最终可获颗粒尺寸分别为400~600 nm、200~400 nm和400~600 nm的Y_2SiO_5、Y_(4.67)(SiO_4)_3O和Y_2Si_2O_7三种晶型的纳米晶,且其晶型最佳. 相似文献
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(ZrO2)1-x(Yb2O3)x (x=0.07, 0.09, 0.11) nanocrystallites were hydrothermally prepared in basic media by using co-precipitated Zr(OH)4 and Yb(OH)3 as precursor. The nanocrystallites have small particle sizes of 5.8~7.5 nm, narrow size distribution, less agglomeration and high sinterability. The oxide-ionic conduction properties of the prepared ceramics were investigated by means of AC impedance spectroscope, oxygen concentration cell at 600~1 000 ℃. The results show that the ceramic with x=0.09 is superior to the ceramics with x=0.07 and 0.11 in oxide-ionic conduction. 相似文献
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氧化锌纳米微晶的顺磁共振特性 总被引:16,自引:0,他引:16
半导体纳米微粒是制备新一代电子器件的理想材料[1,2].电子自旋共振谱(ESR)是研究纳米微晶表面电子自旋构象和表面结构的一种有效方法.体相ZnO是一种抗磁性物质,通常观察不到顺磁共振信号(ESR).有关ZnO纳米微晶电子顺磁共振特性研究还未见文献报导.本文ZnO纳米微晶是用微乳法制备的:这样就制成了纳米尺度的具有表面包覆的ZnO微粒有机溶胶.这里表面活性剂起着“空间位阻”作用,一方面防止成胶过程中粒子间的聚合,使胶粒均匀细小;另一方面,包覆能减少微粒表面缺陷,使粒子性质变得十分稳定.将上述制得的ZnO纳米微粒… 相似文献
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Cathodoluminescence (CL) spectra for the Si nanocrystallites embedded in a matrix of silicon oxide films are measured at room temperature. The CL spectra consist of two principal bands whose peak energies are in a near-infrared (NIR) region (<1.6 eV) and in a blue region (2.6 eV), respectively. The spectral feature of the NIR CL band is similar to the corresponding PL spectra. The strong correlation between the presence of Si nanocrystallites and the formation of the NIR CL band are found as well as the PL spectrum. The peak energy of the blue CL band is slightly lower than that of the luminescence band originating from oxygen vacancies (≡Si–Si≡) in SiO2. Therefore, the blue CL band is considered to come from Sin clusters with n3 in the oxide matrix. Under irradiation of electron beams, degradation of the intensity is observed for both the CL bands but the decay characteristics are different. 相似文献