Transmission electron microscopy studies of nanostructured TiO2 films on various substrates

A chemical vapour deposition (CVD) synthetic route to the production of nanocrystalline titanium dioxide has been carefully investigated on various substrates. CVD was performed at a relatively low temperature of 320 °C on KCl crystal, Al foil, KBr pellet and freshly sliced MICA substrates. The influence of substrate material on film formation was studied in order to find a titanium dioxide film with good intercalation properties for an electrode in a dye-sensitized solar cell. Intercalation properties depend on average grain sizes and porosity in nanophased materials. These films were thoroughly characterized with respect to their surface morphology, crystal structure and the phase composition. Transmission electron microscopy (TEM) accompanied by selected area electron diffraction (SAED) was employed for structural characterization of TiO₂ films. The studies showed that films deposited on KCl crystal, KBr pellet and MICA are solely composed of an anatase phase whereas in the film deposited onto Al foil, the brookite phase of TiO₂ is also present. The structural parameters of anatase were determined using the Rietveld refinement of electron diffraction data. By comparison of anatase lattice parameters with their corresponding bulk values, the significant deviation in values of lattice parameters a and c in anatase phase was observed and attributed to the thin-film features. The average grain size and the grain size distribution obtained by TEM were compared for TiO₂ films deposited on different substrates.     

Dynamic recrystallization-induced flow phenomena in tungsten–tantalum (4%) [001] single-crystal rod ballistic penetrators

Deformation-flow microstructures associated with [001] W–4% Ta penetrator fragments in a rolled homogeneous steel armor target exhibit dynamic recrystallization. The equiaxed, recrystallized grain structure observed in the deformed penetrator is also associated with soft zones in corresponding microhardness maps. Microstructure evolution is also examined by transmission electron microscopy (TEM) and selected-area electron diffraction (SAED).     

Nb元素的添加对Fe-Co-2V软磁合金微观结构的影响

Fe-49Co-2V与Fe-49Co-2V-0.3Nb合金经热轧、冷轧制成带材,之后在850 ℃进行2 h退火热处理。使用透射电镜和选区电子衍射对合金微观组织结构进行观察,结果表明Nb元素的添加促进了析出相的形成,析出相为Nb与Co、Fe组成的小尺寸晶粒,不含V元素,其化学式为Co₃Nb,其中部分Co原子被替换为Fe原子。在铸态样品中同样发现了形态不同的析出相,推测可能是带材中析出相的来源。在添加Nb元素的合金中发现条纹状孪晶结构且集中于析出相附近,推测可能与合金伸长率升高及晶粒细化有关。     

A method for structure analysis of nanomaterials by electron diffraction: Phase identification and unit cell determination

We report a quick and easy method for a random selected area electron diffraction (SAED) pattern without rotating and tilting the specimen to perform phase identification and unit cell determination by combined with the XRD softwares. If your TEM is well aligned and camera length is carefully corrected, two‐dimensional (2D)‐SAED pattern can be directly transformed to 1D‐profile after the center determination of pattern, this profile is then imported to XRD analysis packages. Finally, phase identification and unit cell determination can be performed after peak search or precise peak position determined by profile fitting. Two examples, flaky‐like TiO₂ nanomaterial and TiO₂ nanotubes precipitated by the silver nanoparticles, were tested and verified for the validation of phase identification and unit cell determination using this method; the successful crystallographic analysis of one single gold nanocrystal indicates it is still validate for the nanocrystals with the smaller diffraction volume, but need two or more random tilt SAED patterns. This method could be further used in the quantitative phase analysis, structure determination and Rietveld refinement for the nanomaterials if the reliable integrated intensity can be extracted. Microsc. Res. Tech. 76:641–647, 2013. © 2013 Wiley Periodicals, Inc.     

Role of Nanocrystalline Spinel Additive on the Properties of Low Cement Castable Refractories

Hydrated magnesium aluminate gel prepared via a cost-competent sol-gel route has been found to retain nanocrystals after optimum thermal treatment. The reactive gel-derived powder incorporated to the matrix of a high alumina based refractory castable upgraded its physical properties as revealed from the laboratory scale results. The performance of sol-gel spinel is better than coprecipitated spinel and almost comparable to presintered spinel powders popularly utilized by the refractory manufacturers. Attempts have been made to evaluate and analyze the better slag corrosion and thermal shock resistance properties of spinel-bonded castable by the nanocrystalline feature of the sol gel spinel. SEM, TEM, SAED, XRD, IR, and the physical properties of selected samples have been studied to understand the characteristics of the respective refractory materials.     

石墨化花岗岩中准纳米针状石英的发现及意义

首次在新疆苏吉泉花岗岩中发现一种细长针状矿物，经高分辨电镜能谱分析其化学成分为SiO2。选区电子衍射数据分析表明其结构为α-石英。准纳米针状石英长度可达10500nm，宽度为137nm。最后，讨论了研究准纳米针状石英及针状石墨的意义。     

Effects of Multiple Strengthening Treatments on Mechanical Properties and Stability of Nanoscale Precipitated Phases in an Aluminum-Copper-Lithium Alloy

Effects of multiple strengthening treatments(i.e.aging either at three or four consecutive temperatures) on mechanical properties and stability of nanoscale precipitated phases in an AA2090 alloy have been evaluated in this research.Various tests such as hardness,tensile,electrical resistance,differential scanning calorimetric(DSC),and transmission electron microscopy(TEM) have been performed.The results show that the ultimate tensile strength(UTS) and the yield strength of the samples aged at four consecut...     

离线热处理和原位电子辐照下羟基硫酸镍纳米带结构演变的TEM研究

利用透射电子显微术,主要包括亮场像形貌观察、选区电子衍射结合运动学模拟计算和高分辨电子显微像,对水热法制备的结晶良好的Nj(SO4)0.3(OH)1.4纳米带结构和生长形态进行了表征,并结合利用在不同温度的离线热处理及原位电子辐照,对从结晶良好的Nj(SO4)0.3(OH)1.4纳米带到疏松多孔的NiO纳米带,最后到NiO纳米颗粒的结构演变进行了系统研究,得到了Nj(SO4)0.3(OH)1.4和NiO的取向关系,揭示了这一系列过程的结构演变并给出了Nj(SO4)0.3(OH)1.4的初步结构模型.     

Variation in structures and photoluminescence spectra of BaxEu1−xAl2O4 powders

Barium europium(II) aluminate (Ba_xEu_1?xAl₂O₄) powders were prepared by a solid-state reaction among barium carbonate (BaCO₃), europium oxide (Eu₂O₃), and alumina (Al₂O₃) powders at 1400 °C for 3 h under a mixed gas flow of H₂ and N₂. The powders were characterized by powder X-ray diffraction (XRD), infrared and Raman spectroscopy, and photoluminescence (PL). With increasing Ba²⁺ content in Ba_xEu_1?xAl₂O₄, the structure of Ba_xEu_1?xAl₂O₄ changed from a monoclinic (P2₁) to hexagonal (P6₃) phase. The hexagonal (P6₃22) phase was also observed between the two phases. The XRD pattern of a single Ba_0.6Eu_0.4Al₂O₄ phase, which has not been reported in the literature, was refined by the Rietveld method and its structure was confirmed by selected-area electron diffraction. With increasing x value, the emission peak in the PL spectra of Ba_xEu_1?xAl₂O₄ became weaker (x = 0–0.4) and then more intense (x = 0.6–0.98), and its position showed a blue shift from 520 to 498 nm.     

Research on precision‐calibration techniques for selected area electron diffraction patterns of pyrocarbon

The key techniques for determining orientation angle (OA) and interlayer space (d002) of pyrocarbon were investigated by analyzing selected area electron diffraction (SAED) patterns. A series of algorithms, which mainly include the five‐point center‐determined technique, the integral factor for the ellipse detection, the background subtraction operation and the Gaussian multipeak fitting algorithm, were designed for intensity sampling, data correction, and data fitting. The contribution ratio of the reflection intensity to the average d002 was considered. The algorithms were programmed and applied to evaluate SAED patterns of pyrocarbon in C/C composites by chemical vapor infiltration. Results showed that the proposed techniques can be effectively used to measure various SAED patterns, with a beam stop image or not, of pyrocarbon. The azimuthal intensities along the (002) arcs essentially obey the Gaussian distribution, although this is not obvious for the lower textural pyrocarbon. It is necessary for accurate OA to use the Gaussian multipeak fitting algorithm. Microsc. Res. Tech., 2009. © 2008 Wiley‐Liss, Inc.