Total scattering atomic pair distribution function: new methodology for nanostructure determination

The conventional X-ray diffraction (XRD) methods probe for the presence of long-range order towards a solution of the average crystal structure. Experimentally, structural information about long-range, periodic atomic ordering is reflected in the Bragg scattering while local atomic structural deviations from the average structure mainly affect the diffuse scattering intensities. In order to obtain structural information about both average and local atomic structures, a technique that takes in account both Bragg and diffuse scattering needs to be employed, such as the total scattering atomic pair distribution function (PDF) technique. This article introduces a PDF-based methodology that can be applied to extract precise structural information about nanoparticles such as the size of the crystalline core region, the degree of crystallinity, the atomic structure of the core region, local bonding, and the degree of the internal disorder, as a function of the nanoparticle diameter. This article sheds light on a new PDF-based methodology that can yield precise quantitative structural information about small nanocrystals from XRD data, and also describes the essential aspects of this proposed methodology as well as its great potential. This method is generally applicable to the characterisation of the nanoscale solid, many of which may exhibit complex disordered structure.     

Soot oxidation kinetics under pressurized conditions

The oxidation kinetics, under different pressures, of soot samples obtained from different liquid fuels and two standards (a commercial black carbon sample and a reference diesel soot) was studied. Soot samples were generated in a flat-flame, premixed burner under heavily-sooting conditions and captured on a water-cooled stabilization plate located above the burner surface. The collected soot was oxidized using a high-pressure thermogravimetric analyzer (HTGA). TGA operation was optimized to reduce mass transfer effects by adjusting the oxidizer flow rate and initial sample mass. Further corrections for mass transfer were accomplished by computing the effectiveness factors for intraparticle, interparticle, and external mass transfer. Two pressures were evaluated (1 and 10 atm) and O₂ concentration was varied between 10 and 21%.     

CONTROLLED AGGREGATION OF POLYMER LATICES PART 3. INFLUENCE OF TEMPERATURE AND SURFACE CHEMISTRY

ABSTRACT

The possibility of obtaining narrowly dispersed particles through the controlled aggregation of polymer latices has been investigated. Concentrated polystyrene, poly(styrene-co-acrylic acid) and poly(styrene-co-butadiene-co-acrylic acid) latices were aggregated through the addition cationic surfactant under stirring. The method under investigation was proven to be effective in obtaining 5-15 urn particles with a narrow size distribution and a strong control of the average size. The aggregation properties of polymer latices were related to their chemical nature (chemical structure of the polymer and surface chemistry); the trends observed were explained through calculations of the fundamental forces involved in this process. Important differences were found between the aggregation of the latices that contain acrylic acid as a comonomer and those without acrylic acid. Narrow size distributions, with geometric standard deviations between 1.2–1.35 were obtained only for the latices containing acrylic acid. It was shown that on the surface of these particles there is a hairy layer formed by the polyacrylic acid chains. The thickness of this layer is dependent on the chemical environment and temperature. Its presence was demonstrated by capillary viscometry and electrophoretic mobility measurements.     

Effect of unsaturation in bicarboxylic acid dopants for solid‐state synthesis of polyaniline

Conjugation in the polymeric backbone leads to an electrical conducting nature for conducting polymers, and organic acids can be used as dopants to manipulate the electroactive behaviour. The present investigation deals with the effect of unsaturation in bicarboxylic acid dopant structures on the properties of polyaniline (PAni). PAni was synthesized via solvent‐free solid‐state polymerization. Oxalic acid, fumaric acid and trans,trans‐muconic acid containing 0, 1 and 2 double bonds, respectively, in their molecular structures were used as dopants. Fine particles directionally agglomerate to form nanowires. The use of a conjugated dopant results in highly crystalline PAni. With an increase in the number of double bonds in the dopant structure, the conductivity at room temperature increases, whereas the activation energy, hopping range, optical band gap and supercapacitive performance reduce. The inter‐chain hopping is expected to be favoured by the presence of unsaturation, and even more by conjugation in the dopant structure. © 2016 Society of Chemical Industry     

MnO/C core-shell nanorods as high capacity anode materials for lithium-ion batteries

MnO/C core-shell nanorods were synthesized by an in situ reduction method using MnO₂ nanowires as precursor and block copolymer F127 as carbon source. Field emission scanning electron microscopy and transmission electron microscopy analysis indicated that a thin carbon layer was coated on the surfaces of the individual MnO nanorods. The electrochemical properties were evaluated by cyclic voltammetry and galvanostatic charge-discharge techniques. The as-prepared MnO/C core-shell nanorods exhibit a higher specific capacity than MnO microparticles as anode material for lithium ion batteries.     

表面纳米化技术制备梯度纳米结构金属材料的研究进展

多数工程结构材料的失效都是从表面的薄弱环节开始发生或者传导,从而引起材料的性能下降,使用寿命缩短.受生物材料的梯度结构启发,近年来开发了多种表面纳米化技术,成功在工程材料表面制备了晶粒尺寸从表层纳米尺度连续变化到内部宏观尺度的梯度纳米结构,强化和保护了材料表面,有效地解决了上述问题.结合国内外表面纳米化的研究结果,综述了金属材料梯度纳米材料的研究进展.首先,介绍了梯度塑性变形、物理化学沉积等表面纳米化加工技术的最新进展.其次,对梯度等轴纳米晶、梯度纳米层片和梯度纳米孪晶等多种表面纳米化材料的微观结构进行了归纳,并对最新发展的梯度纳米结构材料表层晶粒的晶体学取向等微观信息表征方法进行了系统地阐述.随后,总结了梯度纳米结构对工程材料的表面强度、塑性、强-塑匹配、加工硬化、疲劳、耐磨、腐蚀和热稳定性等性能的影响.最后展望了表面纳米化技术制备梯度纳米结构金属材料的发展趋势及工程应用所面临的挑战.     

3D打印Ti-6Al-4V钛合金表面纳米孔洞制备技术

目的 通过3D打印技术制得钛合金,并构建出微米级多孔粗糙表面,再通过阳极氧化表面处理技术在微米级多孔粗糙表面构建出纳米级结构.方法 首先,通过高压水处理与酸蚀处理相结合的方法,对3D打印钛合金表面进行前处理,去除不良结合的球形粉末颗粒,降低3D打印钛合金表面的粗糙度及各向异性.然后,通过阳极氧化处理,在3D打印钛合金表面制备出具有纳米级孔洞的TiO2类骨膜层.结果 3D打印钛合金表面存在较大的各向异性,导致后续的电化学过程中电场放电不均匀,形成的TiO2类骨膜层稳定性差,而阳极氧化的前处理方法可有效解决这些问题.此外,纳米多孔结构抑制了阳极氧化处理中不稳定放电现象的发生,保证了膜层表面颜色的均匀性,且使膜层与钛或钛合金结合牢固,可在3D打印钛合金表面构建纳米级膜层结构.结论 该工艺方法制备的3D打印钛合金表面膜层的成膜速率和稳定性较好,膜层呈三维网状结构,大孔内附有小孔.该结构有利于细胞在其表面更好地粘附、分化和增殖,是理想的医用植入材料.     

不对称金纳米结构的光致热增强效应的调控研究

提出了一种产生光致热增强效应的不对称的人工金 纳米结构,建立了物理模型并进行了计算。采用离散偶极近似(DDA)方法计算水介质环境中 该结构及其不对称性改变后对吸收光谱及近区电磁场分布的影响,进而 利用傅里叶热传导定律数值模拟了该结构产生的热增强效应。结果表明:改变纳米结构的不 对称程度会明显影响结 构的光谱吸收位置、线型和峰值强度;同时,通过调节纳米结构的不对称性也可以有效地将 磁场能转化为热能,并 在结构周围形成高度限定的局域热增强现象。本文提出的纳米结构可在较大的近红外波段范 围内调控温度,可作为纳米尺度 下精确控制光致热效应的温度和设计热等离子纳米器件之参考。     

Fe82Nb6B12合金表面纳米多孔结构的形成及电催化析氢性能的研究

目的增加条带表面积,提高电催化析氢活性。方法采用真空激冷装置制备Fe_(82)Nb_6B_(12)前驱体条带,通过控制铜辊转速得到α-Fe纳米晶/非晶双相结构。利用α-Fe纳米晶与非晶基体在0.5 mol/L H_2SO_4溶液中腐蚀性能的差异,通过脱合金法得到非晶纳米多孔结构。使用XRD、DSC、SEM、EDS等表征手段以及电化学测试方法,研究铜辊转速、脱合金时间对物相、成分、形貌及电催化析氢性能的影响。结果 1kr/min样品完全晶化,2~3 kr/min样品为α-Fe纳米晶/非晶双相合金,且随着铜辊转速增大,前驱体条带中α-Fe纳米晶含量减少。脱合金后成功制备了非晶纳米多孔结构,铜辊转速越大,孔径越小,比表面积越小。4 kr/min样品为非晶态,脱合金后没有得到多孔结构。2 kr/min多孔结构的析氢性能最好,在电流密度为10 mA/cm~2时的过电位为220 mV,塔菲尔斜率为105 mV/dec。结论采用甩带法可以制备具有α-Fe纳米晶/非晶双相结构的Fe_(82)Nb_6B_(12)合金。通过α-Fe纳米晶的选择性腐蚀,在条带表面得到纳米多孔结构,条带比表面积显著改善,从而提高了其析氢性能。     

An overview on novel thermal barrier coatings

Thermal barrier coatings (TBCs) offer the potential to significantly improve efficiencies of aero engines as well as stationary gas turbines for power generation. On internally cooled turbine parts, temperature gradients of the order of 100-150℃ can be achieved. TBCs, typically consisting of an yttrium stabilized zirconia top coat and a metallic bond coat deposited onto a superalloy substrate, are mainly used to extend lifetime. Further efficiency improvements require TBCs being an integral part of the component which requires reliable and predictable TBC performance. TBCs produced by electron beam physical vapor deposition (EbPVD) or plasma spray (PS) deposition are favored for high performance applications. The paper highlights critical R&D needs for advanced TBC systems with a special focus on reduced thermal conductivity and life prediction needs. To further enhance the efficiency of gas turbines, higher temperature and a longer lifetime of the coating are needed for the next generation of TBCs. This paper presents the development of new materials, new deposition technologies, and new concept for application as novel TBCs. This paper summarizes the basic properties of conventional thermal barrier coatings. Based on our own investigation, we reviewed the progress on materials and technologies of novel thermal barrier coatings. Except yttria stabilized zirconia, other materials such as lanthanum zirconate and rare earth oxides are also promising materials for thermal barrier coatings. Nanostructure thermal barrier coating is presented as a new concept. This paper also summarizes the technologies for depositing the thermal barrier coatings.