Small Angle X-ray Scattering Study of Precipitation Kinetics in Al-Zn-Mg-Cu Alloys

The evolution of microstructure parameters （precipitate size and volume fraction） for two types of Al-Zn-Mg-Cu alloys （7075 and 7055） during aging has been studied by synchrotron-radiation small angle X-ray scattering （SAXS）.The results show that the precipitates are only a few nanorneters for both alloys ageing even at higher temperature of 160℃ for 72 h （4.44 and 5.82 nm, respectively）. The maximum of the precipitate volume fraction increases with in creasing Zn content and is about 0.023-0.028 and 0.052-0.054, respectively. The coarsening of precipitate is consistent with LSW （Lifshitz-Slyozov-Wagner） model even at the initial stage where volume fraction is still varying.The activation energy of coarsening regime has been determined to be about 1.22±0.02 eV and 1.25±0.02 eV for alloys 7075 and 7055, respectively.

Growth Kinetics of Nanocrystals and Nanorods by Employing Small-angle X-ray Scattering (SAXS) and Other Techniques

In this article, we report the results of our detailed investigations of the growth kinetics of zero-dimensional nanocrystals as well as one-dimensional nanorods by the combined use of small angel X-ray scattering （SAXS）, transmission electron microscopy （TEM） along with other physical techniques. The study includes growth kinetics of gold nanocrystals formed by the reduction of HAuCl4 by tetrakis（hydroxymethyl） phosphonium chloride in aqueous solution, of CdSe nanocrystals formed by the reaction of cadmium stearate and selenium under solvothermal conditions, and of ZnO nanorods formed by the reaction of zinc acetate with sodium hydroxide under solvothermal conditions in the absence and presence of capping agents. The growth of gold nanocrystals does not follow the diffusion-limited Ostwald ripening, and instead follows a Sigmoidal rate curve. The heat change associated with the growth determined by isothermal titration calorimetry is about 10 kcal·mol^-1 per I nm increase in the diameter of the nanocrystals. In the case of CdSe nanocrystals also, the growth mechanism deviates from diffusion-limited growth and follows a combined model containing both diffusion and surface reaction terms. Our study of the growth kinetics of uncapped and poly（vinyl pyrollidone） （PVP）-capped ZnO nanorods has yielded interesting insights. We observe small nanocrystals next to the ZnO nanorods after a lapse of time in addition to periodic focusing and defocusing of the width of the length distribution. These observations lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence on the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening. The PVP-capped nanorods, however, show a time dependence, which is best described by a combination of diffusion （L^3） and surface reaction （L^2） terms.

Scanning Microfocus Small Angle X-ray Scattering Study of the Avian Eggshell

Synchrotron microfocus small angle X-ray scattering was used to investigate the nanostructure and microscopic variation of eggshells. It uses a microbeam allowing the ability to probe interactions between the organic and inorganic components at nanometer level and is ideal for mapping over small areas to obtain a detailed analysis of structural variations. Thin sections of eggshells were scanned from the shell membrane （inner） to the cuticle （outer） surface. The data collected was used to produce two-dimensional maps showing microscopic changes within the different layers of the eggshell. The structural alterations ap- parently could have implications at the macroscopic level of the resulting eggshell. As the organic matrix is embedded within the eggshell this may contribute to the variations observed in calcite crystal form and texture, Structural information obtained about a biomaterial at different length scales is important in relating the structure to its functional properties. This knowledge and the principles behind the formation of biomaterials could be used in the attempt of bioengineering new systems.

Characteristics of AOT Microemulsion Structure: a Small Angle X-ray Scattering Study

The method of synchrotron radiation small-angle X-ray scattering (SR-SAXS) has been used to obtain structural information on the system of bis (2-ethylhexyl) sulfosuccinate (AOT)/H2O/isooctane. By using the Guinier plot (Ln I (q) versus q(2)) on the data sets in a defined small q range (0.03-0.06 Angstrom (-1)), the gyration radius at different water/surfactant molar ratio, W-0, was obtained. With the increase of W-0, the gyration radius (R-g) increased at the range of 23.2 similar to 52.7 Angstrom.

Probing Nanoscale Morphology of PS/PMMA/CdS &PS/PVC/CdS Polymeric Nanocomposites through Small Angle X-Ray Scattering Analysis

Polymeric nanocomposites of PS/PMMA/CdS and PS/PVC/CdS samples have been synthesized through dispersion solution casting technique. The nanoparrticles of CdS were prepared by simple chemical method using CdCl2 and H2S gas produced from thiourea. The nanoscale morphology of the prepared polymeric nanocomposite samples is probed through small angle X-ray scattering (SAXS). The SAXS study reveals that CdS nanoparticles take place at voids position in the respective plymer blend matrix and exhibit their nano nature with very little tendency to agglomerates.

Nano-scale pore distribution characterisation of coal using small angle X-ray scattering

In the process of coal seam fracturing with liquid nitrogen(LN_(2)),the change of coal pore structure has an important influence on the efficiency of coalbed methane(CBM)extraction.The nano-scale pore size distribution(PSD)in coal particles before and after freezing with LN_(2) are experimentally studied in this work.Coal samples are collected from four coal mines,where coal and gas outburst accidents have occurred.Small angle X-ray scattering technology(SAXS)and scanning electron microscopy(SEM)are used to study the pore structure changes of coal samples quantitatively and qualitatively.It is found that the scattering intensity of coal samples increases after freezing.The PSD of all samples significantly changes in the range of 0.8–7 nm,showing new pore spaces in 0.8–4 nm and fewer pores in the 4–7 nm range.Both the pore fractal dimension and the radius of gyration of coal samples increase after freezing and are mainly affected by the changes in pores and the anisotropy of the coal matrix.Crack expansion and pore connections are observed in the surface structure of the coal sample using SEM.This study provides a better understanding of the nano-scale mechanism of coal seam fracturing with LN_(2) for the prevention of coal and gas outbursts.

Small angle X-ray scattering of the colloidal crystal

The monodisperse polystyrene spheres are assembled into the colloidal crystal on the glass substrate by vertical deposition method, which is aimed at the so-called photonic crystal applications. The structural information of the bulk colloidal crystal is crucial for understanding the crystal growth mechanism and devel- oping the various applications of colloidal crystal. Small-angle X-ray scattering （SAXS） technique was used to obtain the bulk structure of the colloidal crystal at Beamline lW2A of BSRF. It is found that the SAXS pattern is sensitive to the relative orientation between the colloidal sample and the incident X-ray direction. The crystal lattice was well distinguished and determined by the SAXS data.

DETERMINATION OF SIZE DISTRIBUTION OF THE CRYSTALLINE PARTICLE IN AGED METALLIC GLASS BY SMALL ANGLE X-RAY SCATTERING

Ⅰ. INTRODUCTIONAlthough many authors have investigated the structure of annealed metallic glass by means of small angle X-ray scattering (SAXS), there has been no report in which size distribution of the crystalline particle in aged metallic glass is determined. Determining size distribution of the crystalline particle will be beneficial to understanding the nucleation and growth process of the crystalline particle. In this note, size distribution of the crystalline parti-

DETERMINATION OF THE SHAPE AND DIMENSION OF PRECIPITATE FROM AGED Lc4 ALUMINIUM ALLOY BY SMALL ANGLE X-RAY SCATTERING

Small angle X-ray scattering (SAXS) is extensively used for determining the dimension of a particle, but rarely used for determining its shape. The difficulty is that it needs to do extensive calculations. In addition, it can only be carried out for the mono-dispersion system. In re cent years, Reuther et al. succeeded in determining the shape and dimension of the particle of a polymer gel.

Characterization of the nanopore structures of PAN-based carbon fiber precursors by small angle X-ray scattering

The nanopore structures in precursors Four carbon-fiber precursors are prepared. They are crucial to the performance of PAN-based carbon fibers are bath-fed filaments （A）, water-washing filaments （B） hot-stretching filaments （C） and drying-densification filaments （D）. Synchrotron radiation small angle X-ray scattering is used to probe and compare the nanopore structures of the four fibers. The nanopore size, discrete volume distribution, nanopore orientation degree along the fiber axis and the porosity are obtained. The results demonstrate that the nanopores are mainly formed in the water-washing stage. During the processes of the subsequent production technologies, the slenderness ratio of nanopores and their orientation degree along the fiber axis increase further and simultaneously, the porosity decreases. These results are helpful for improving the performance of the final carbon fibers.

Influence of energy bandwidth of pink beam on small angle X-ray scattering

Background Compared with the traditional monochromatic synchrotron radiation beam,a pink beam is a quasimonochromatic beam which can be obtained by screening a harmonic of the undulator.The energy bandwidth(E/E)of a pink beam is about 10−2.Despite the intensity gain from the quasi-monochromatic beam,the decrease in the energy resolution will lead the collected data to be smeared.Purpose To study the influence of the energy bandwidth on the small angle X-ray scattering(SAXS)by experiments and verify the feasibility of SAXS with a pink beam.Method Firstly,the influence of different energy bandwidths on SAXS has been studied by simulation and experiment.Then,TEM tests have been performed and compared with the experimental results.Result It has been shown that the scattering curves deviate slightly from the traditional monochromatic ones.This deviation does not influence the data processing for the maximum deviation of the results is just less than 2%.In return,the gain in the intensity(one to two orders of magnitude)makes the pink beam very important for the time-resolved SAXS.Further,the results of TEM and SAXS have shown an excellent agreement.Conclusion Thiswork proves that the pink beam could be used for SAXS directly without a desmearing procedure.Benefiting from the increase in the beam intensity,the exposure time can be greatly shortened,thus enhancing the utilization efficiency of the synchrotron radiation.

Stability of the Dividing Distribution Function Method for ParticleSize Distribution Analysis in Small Angle X－Ray Scattering

The Dividing Distribution Function (DDF) method is one of the methods by which the particle size distribution of ultrafine powder can be evaluated from its small angle X-ray scattering data. In this paper, the stability of the solution obtained from DDF method has been investigated through optimizing the coefficient matrix, introducing a damping factor and a least square treatment. All calculations were accomplished with a microcomputer. It was shown that the average deviations of the size distribution obtained are not larger than the assigned random errors to the scattering intensities as long as the corresponding requirements are satisfied.

Microstructural characterization of polycrystalline materials by synchrotron X-rays

Third generation synchrotron X-rays provide an unprecedented opportu- nity for microstructural characterization of many engineering materials as well as natural materials. This article demonstrates the usage of three techniques for the study of structural materials： differential-aperture X-ray microscopy （DAXM）, three-dimensional X- ray diffraction （3DXRD）, and simultaneous wide angle/small angle X-ray scattering （WAXS/SAXS）. DAXM is able to measure the 3D grain structure in polycrystalline materials with high spatial and angular resolution. In a deformed material, streaked diffraction peaks can be used to analyze local dislocation content in individual grains. Compared to DAXM, 3DXRD is able to map grains in bulk materials more quickly at the expense of spatial resolution. It is very useful for studying evolving microstructures when the materials are under deformation. WAXS/SAXS is suitable for studying materials with inhomogeneous structure, such as precipitate strengthened alloys. Structural informa- tion revealed by WAXS and SAXS can be combined for a deeper insight into material behavior. Future development and applications of these three techniques will also be discussed.

Properties,Morphology and Structure of BPDA/PPD/TFMB Polyimide Fibers

The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） backbone.The best strength and modulus of BPDA/PPD/TFMB polyimide（PI） fiber（diamine molar ratio of PPD/TFMB= 90/10） were 1.60 and 90 GPa,respectively,which was over two times that of BPDA/PPD PI fiber.SEM image showed that the cross-section of fibers at each stage was round and voids free.Besides,the ＂skin-core＂ and microfibrillar structure were not observed.The thermal properties of PI fibers were also investigated.The results showed that the fibers owned excellent thermal stability,moreover,the structural homogeneity of fibers were significantly improved by heat-drawn stage.The T g values were found to be around 300 °C by dynamic mechanical analysis（DMA）.Wide angle X-ray diffraction（WAXD） and small angle X-ray scattering（SAXS） experiments indicated that the order degree of longitudinal and lateral stacks,the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.

利用小角X射线散射技术研究改性处理对苎麻/热固性聚乳酸复合材料界面特性和分形特征的影响

以苎麻为增强体,以热固性聚乳酸（Polylactic acid,PLA）为基体,采用模压成型工艺制成了苎麻/PLA复合材料,并对复合材料进行碱、碱-偶联剂改性处理;应用小角X射线散射（SAXS）方法研究不同改性处理对苎麻/PLA复合材料界面特性与分形特征的影响,并对改性前后的复合材料弯曲性能进行了测试,宏观反映了改性处理对复合材料界面特性和分形特征等微观结构的影响.结果表明：散射曲线不遵守Porod定理,形成负偏离,说明苎麻与PLA间存在界面层,界面层厚度在22.70-26.42nm范围内;碱、碱-偶联剂处理后,界面层厚度减小,苎麻与PLA结合的更紧密;苎麻/PLA复合材料具有表面分形特征,碱、碱-偶联剂处理后,表面分形维数提高,复合材料精细结构增多,表面变得更加粗糙,起到了良好的应力传递作用,使得复合材料的弯曲强度有所提高.

多孔材料孔界面分形结构小角度X射线散射实验

简要介绍了用X射线小角散射分析技术测定多孔固体材料中孔界面分形维数的理论,同时报道了应用这一理论对多种炭素材料和水泥石材料中孔界面分形维数的测定结果。结果表明,所有试样中孔界面均具有分形结构特征。

硅粉水泥石中微孔界面分形结构实验研究

采用X射线小角散射(SAXS)技术,对硅粉水泥石中微孔孔界面分形结构进行实验研究.结果表明,硅粉水泥石中微孔界面不具有分明的边界,而是有一个2nm左右的电子密度缓变的过渡层;微孔界面具有分形结构特征,分形维数与3接近,说明其孔界面是非常粗糙的;水胶比、硅粉含量对孔界面分形维数具有显著的影响,笔者根据实验结果,从微观的角度进行了探讨性的解释.

Determination of Average Wall Thickness of Mesoporous Silica

Small Angle X-ray Scattering (SAXS) experiment using Synchrotron Radiation as X-ray source was used to determine the average wall thickness of mesoporous silica prepared by condensation of tetraethylorthosilicate (TEOS) using non-ionic alkylpolyethyleneoxide (AEO(9)) surfactant as templates. The results agreed with that of high-resolution TEM (HRTEM) measurement.