DISTORTION OF CRYSTAL LATTICE IN NANOCRYSTALLINE Fe_2O_3

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Recent study of nanomaterials prepared by inert gas condensation using ultra high vacuum chamber

The ultra high vacuum chamber was developed in the Department of Nuclear Physics, University of Madras with the funding from DST, India. This UHV chamber is used to prepare nanocrystalline materials by inert gas condensation technique (IGCT). Nanocrystalline materials such as PbF₂, Mn²⁺-doped PbF₂, Sn-doped In₂O₃ (ITO), ZnO, Al₂O₃, Ag₂O, CdO, CuO, ZnSe:ZnO etc., were prepared by this technique and characterized. Results of some of these materials will be presented in this paper. In solid-state²⁰⁷Pb NMR on PbF₂ a separate signal due to the presence of grain boundary has been observed. The structural phase transition pressure during the phase transformation from the cubic phase to orthorhombic phase under high pressure shows an increase with the decrease in grain size. Presence of electronic centres in nanocrystalline PbF₂ is observed from Raman studies and the same has been confirmed by photoluminescence studies. Al₂O₃ was prepared and⁵⁶Fe ions were implanted. After implantation segregation of⁵⁶Fe ions was examined by SEM. The oxidation properties of ITO were studied by HRTEM. As against the expectation of oxide coating on individual nanograins of In-Sn alloy, ITO nanograins grew into faceted nanograins on heat treatment in air and O₂ atmosphere. The growth of ITO under O₂ atmosphere showed pentagon symmetry. The PMN was initially prepared by solid-state reaction. Further, this PMN relaxor material will be used to convert into nanocrystalline PMN by IGCT with sputtering and will be studied     

MEASUREMENT OF NON-UNIFORM RESIDUAL STRESSES BY COMBINED MOIRE INTERFEROMETRY AND HOLE-DRILLING METHOD： THEORY, EXPERIMENTAL METHOD AND APPLICATIONS

Hole-drilling method is one of the most convenient methods for engineering residual stress measurement. Combined with moiré interferometry to obtain the relaxed whole-field displacement data, hole-drilling technique can be used to solve non-uniform residual stress problems, both in-depth and in-plane. In this paper, the theory of moiré interferometry and incremental hole-drilling (MIIHD) for non-uniform residual stress measurement is introduced. Three dimensional finite element model is constructed by ABAQUS to obtain the coefficients for the residual stress calculation. An experimental system including real-time measurement, automatic data processing and residual stresses calculation is established. Two applications for non-uniform in-depth residual stress of surface nanocrystalline material and non-uniform in-plane residual stress of friction stir welding are presented. Experimental results show that MIIHD is effective for both non-uniform in-depth and in-plane residual stress measurements. The project supported by the FRAMATOME ANP     

THE RATE-INDEPENDENT CONSTITUTIVE MODELING FOR POROUS AND MULTI-PHASE NANOCRYSTALLINE MATERIAL

To determine the time-independent constitutive modeling for porous and multiphase nanocrystalline materials and understand the effects of grain size and porosity on their mechanical behavior, each phase was treated as a mixture of grain interior and grain boundary, and pores were taken as a single phase, then Budiansky's self-consistent method was used to calculate the Young's modulus of porous, possible multi-phase, nanocrystalline materials, the prediction being in good agreement with the results in the literature. Further, the established method is extended tosimulate the constitutive relations of porous and possible multi-phase nanocrystalline materials with small plastic deformation in conjunction with the secant-moduli approach and iso-strain assumption. Comparisons between the experimental grain size and porosity dependent mechanical data and the corresponding predictions using the established model show that it appears to be capable of describing the time-independent mechanical behaviors for porous and multi-phase nanocrystalline materials in a small plastic strain range. Further discussion on the modification factor, the advantages and limitations of the model developed were present.     

纳米晶钽在单向拉伸载荷下的分子动力学模拟

利用分子动力学方法模拟了纳米晶钽在单轴拉伸载荷作用下的微观结构演化情况. 结果表明纳米晶钽在塑性变形过程中可以发生从BCC到FCC, HCP结构的应力诱导相变. FCC 结构原子百分比的最大值和试样的抗拉强度成线性关系，据此可推出一个相变发生的临界应 力值. 应变率越大，相变滞后于应力越严重. 当应变达到一定值时，试样会发生晶间断裂现 象，定量分析发现纳米晶钽晶间裂纹初始形成应变不受平均晶粒尺寸的影响，而与应变率和 模拟温度有着密切的关系.     

A Spray‐Based Technique for the Production of MnS Thin Films

A spray‐based technique, originally developed for the production of semiconductor nanocrystals, is utilized for the preparation of high‐quality nanocrystalline thin films, as demonstrated with manganese sulfide. The films are formed by the use of pneumatic‐assisted thermospray or pneumatic nebulizers. Our simple, low‐cost, and low‐temperature process results in a dense and phase‐pure grain structure. The concepts and benefits of this technique are described and discussed. The film characteristics show dependence on the experimental parameters, in particular the rate of solvent vaporization. Three alternative film formation mechanisms are suggested for cases with varied experimental conditions.     

Antibacterial membranes based on chitosan and quaternary ammonium salts modified nanocrystalline cellulose

Etherification of nanocrystalline cellulose (NCC) with three kinds of quaternary ammonium salts epoxypropyltrimethylammonium chloride, N,N‐dimethyl‐N‐dodecyl‐N‐(1,2‐epoxypropyl) ammonium chloride (DMDEPAC), and N,N‐dimethyl‐N‐octadecyl‐N‐(1,2‐epoxypropyl) ammonium chloride (DMOEPAC) was successfully performed via a nucleophilic addition reaction. The synthesized DMDEPAC and DMOEPAC were characterized by nuclear magnetic resonance. The modified NCC particles, NCC epoxypropyltrimethylammonium chloride, NCC‐DMDEPAC, and NCC‐DMOEPAC, were characterized by energy dispersive spectrometer. Nanocomposite films based on chitosan (CS) containing quaternary ammonium salts modified NCC were prepared with nanoparticle loadings of 5.0, 7.5, and 10.0%, respectively. The effect of nanoparticle content on the tensile strength of composite films was studied. The results indicated that the films with 5.0% nanoparticle loading exhibited the biggest increase in tensile strength. Surface morphology, smoothness, and antibacterial properties of composite films containing 5% modified NCC were also studied. CS/NCC‐DMDEPAC‐5.0 and CS/NCC‐DMOEPAC‐5.0 displayed excellent biocidal abilities against both Gram‐positive Staphylococcus aureus (ATCC 6538) and Gram‐negative Escherichia coli O157:H7 (ATCC 43895). The bio‐based nanocomposite films with increased mechanical strength and excellent antibacterial properties show great potential as food packaging materials. Copyright © 2017 John Wiley & Sons, Ltd.     

One‐step electrodeposition of amorphous carbon films containing WO3 with high conductivity and good wettability

Tungsten trioxide‐incorporated hydrogenated amorphous carbon (WO₃/a‐C:H) films have been fabricated on a single‐crystal silicon wafer by liquid phase electrodeposition using methanol as carbon source and tungsten carbonyl as incorporated reagent. The morphology, composition and structure of the films have been investigated by SEM, XPS, Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Transmission electron microscope (TEM), respectively. The effects of WO₃ incorporation on the electrical and wetting properties were studied in detail. The characterization results showed that tungsten trioxide nanocrystalline particles with diameters in the range of 10–20 nm were homogenously embedded in the amorphous carbon films. Also, the electrical conductivity and wetting ability of the films were strongly improved due to the contribution of the tungsten trioxide. Copyright © 2010 John Wiley & Sons, Ltd.     

不同粒径尿微晶的ζ电位、自相关曲线和聚集状态

采用纳米粒度仪和透射电子显微镜(TEM)比较研究了10例尿石症患者和10例健康对照者的尿液经不同孔径滤膜(0.22、0.45、1.2、3.0、10μm)过滤后,尿微晶平均粒径(d)、粒度分布、自相关曲线、ζ电位和聚集状态的变化。随着滤膜孔径由0.22μm增至10μm,患者尿微晶的d值由162 nm增至3 227 nm,自相关曲线平滑性变差,自相关时间(Ta)由1.92 ms增至2100 ms,ζ由-2.65 mV减小至-9.21 mV,TEM显示尿微晶尺寸差异大,部分尿微晶处于聚集状态。而对照者尿微晶的d值仅由187 nm增加至1 010 nm,自相关曲线平滑,Ta由1.40 ms增加至6.67 ms,ζ平均值由-5.22 mV减小至-6.89 mV,TEM显示尿微晶均匀分散,尺寸较小。上述结果表明:尿石患者的尿液体系不稳定,其尿微晶聚集程度高,导致尿石症形成的危险性增加。     

Combustion Derived Nanocrystalline‐ZrO2 and Its Catalytic Activity for Biginelli Condensation under Microwave Irradiation

Nanocrystalline zirconium(IV) oxide (nc‐ZrO₂) possessing high surface area was synthesized by a low temperature eco‐friendly solution combustion method using a new organic fuel alanine. The powder XRD, SEM and surface area measurements were carried out for characterization of nc‐ZrO₂. The powder XRD results revealed that, the nc‐ZrO₂ has the pure tetragonal phase. The crystallite size calculated by Scherrer's formula and BET surface area were found to be ca. 53–57 nm and ca. 275 m²/g, respectively. SEM micrograph exhibited the macroporous nature of the powder. nc‐ZrO₂ has been employed as a catalyst for the solvent‐free synthesis of 3,4‐dihydro‐ pyrimidin‐2‐ones (DHPMs) by a microwave (MW) assisted one‐pot, multicomponent Biginelli condensation reaction of araldehydes, ethylacetoacetate and urea or thiourea. DHPMs are obtained in good to excellent yields (85%–96%) under this reaction condition within short interval of time (10–20 min).