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.

Small-angle X-ray scattering investigation of aging behavior of Al-Cu-Mg-Ag alloys using synchrotron radiation

The aging behavior of Al-Cu-Mg-Ag alloys with high Cu/Mg was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) using synchrotron radiation. TEM study reveals that the major strengthening phases of the alloy after aging at 160?C for 10 h are Ω and less θ′. SAXS study shows that the scattering patterns are composed of several concentric circles at the beginning of aging process, which is replaced by the butterfly-wings scattering patterns with the increase of aging time. The butterfly-wings scattering patterns are composed of several branches. The angles between the branches are roughly equal to that between the habit planes of precipitates. The evolution of Guinier radius with aging time indicates the good coarsening resistance of the precipitates. The evolution of integrated intensity is consistent with the classical two-step precipitation process.

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.

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.

Small Angle X-ray Scattering Study of PS Conformation in Tetrahydrofuran Solvent with Gas Anti-solvent

Small angle X-ray scattering (SAXS) was used to study the effect of dissolved CO2 on the conformation of polystyrene (PS) in PS/tetrahydrofuran(THF) solution at 308.15 K and at pressures up to 3 MPa. The cloud pressure and the expansion curve of the solution were also determined. The dependence of the conformation on pressure was discussed.

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.

Investigation of the topological shape of bovine serum albumin in solution by small-angle x-ray scattering at Beijing synchrotron radiation facility

This paper reports that at a newly constructed small-angle x-ray scattering station of Beijing Synchrotron Radia- tion Facility, the topological shape of ligand-free bovine serum albumin in solution has been investigated. An appropriate scattering curve is obtained and the calculated value of the gyration radius is 31.2~=t=0.25 ~_ （11=0.1 nm） which is co- incident with other ones＇ results. It finds that the low-resolution structure models obtained by making use of ab initio reconstruction methods are fitting the crystal structure of human serum albumin very well. All of these results perform the potential of the beamline to apply to structural biology studies. The characteristics, the defects, and the improving measures of the station in future are also discussed.

Modification of Classical SPM for Slightly Rough Surface Scattering with Low Grazing Angle Incidence

Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classical perturbation method at grazing angle is overcome for the vertical polarization at a rough Neumann boundary of infinite extent. The derivation of the formulae and the numerical results show that the backscattering cross section depends on the grazing angle to the fourth power for both Neumann and Dirichlet boundary conditions with low grazing angle incidence. Our results can reduce to that of the classical small perturbation method by neglecting the Neumann and Dirichlet boundary conditions.

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.

空化处理油酸钠体系一水硬铝石聚团行为

通过小角激光散射法研究了空化处理(HC)油酸钠体系一水硬铝石聚团行为。结果表明:短时间(<15 min)空化处理没有改变油酸钠化学性质,但导致了纳米气泡的生成;絮体粒径随油酸钠浓度、空化强度、空化时间的增加而逐渐增大,随搅拌转速、搅拌时间的增加而先减小后增大,最大为31.278μm,最小为15.628μm;絮体质量分形维数随油酸钠浓度、搅拌转速、搅拌时间的增加而先增大后减小,随空化强度、空化时间的增加而逐渐减小,最大为1.912,最小为1.692;空化处理油酸钠溶液没有改变絮体性质总体变化规律,但导致絮体粒径相对增大、质量分形维数相对减小;空化溶液中纳米气泡桥联诱导形成大而松散的絮体,促使颗粒聚集过程向有限扩散集团凝聚转变。总体而言,纳米气泡越多,絮体性质变化越明显。

X-射线小角散射法测定钢铁及合金中析出相的粒度

对钢铁及合金中各种不同粒度析出相的电解提取和化学分离方法、X-射线小角散射法测定析出相粉末的测定条件进行了研究,优选了各种测定参数,从而建立了钢铁及合金中多种析出相粒度分布分析方法。该方法被广泛应用于各种高温合金、中低合金钢、微合金化钢中碳化物、金属间化合物的粒度尺寸分布的测定。结果发现,随着回火温度的增加,低合金钢中的M3C相的数量增加,但粒度变化不大,当回火温度升至700℃时,M3C相分解而使平均粒度增加;在含铬的中低合金钢中,析出的M23C6相的粒度随时效温度的增加而增加,而MC相的粒度无明显变化;在一类高温合金中,800℃时γ′的粒度随时效时间的增加而增加,另一类高温合金富铬相α-Cr的粒度明显要比其他的析出相颗粒要粗,平均粒度达390 nm。

纳米粒子粒径评估及测试方法的比较

本文介绍了透射电镜综合分析—分散法测定纳米粒子粒径的方法,并将此法与X射线小角散射法及透射电镜暗场法测粒径进行了实验与分析的比较。认为采用X射线小角散射法与透射电镜综合分析—分散法相结合测定评估纳米粒子粒径可以以较快的速度得到准确的结果、综合的信息。

页岩和煤岩的孔隙结构差异及其天然气运移机理

页岩和煤岩作为非常规天然气储层,其孔隙结构控制着天然气的赋存状态与运移机理。为了定量表征两种储层孔隙结构特征及其差异,借助小角中子散射技术、高压压汞法、气体吸附法和场发射扫描电镜观察对下志留统龙马溪组和上二叠统龙潭组过成熟页岩以及上石炭统本溪组煤岩的储集性和孔隙结构进行对比分析,明确了页岩与煤岩的孔隙结构差异及其成因,并研究了甲烷在其储层中的赋存和运移机理。研究结果表明:①煤岩主要储集空间集中在小于5 nm的孔径范围内,其中甲烷赋存状态以吸附气为主,页岩中大于5 nm的孔径范围是主要的游离气储集空间;②基于小角中子散射与高压压汞实验结果的差异特征可以用于评价孔隙连通性,且本研究中煤岩的孔隙连通性要优于页岩;③重复压汞法显示高压对于过成熟的页岩和煤岩不会导致样品产生新的裂缝。结论认为,煤岩储层微孔中的吸附气解吸成为游离气是煤层气开发的关键,页岩储层中页岩气从基质储集空间运移到天然裂缝或人工裂缝中受孔隙连通性的控制;增加页岩中诱导裂缝,有效连通诱导缝和天然裂缝并且提高有机孔隙网络与外部的连通性是提高页岩气采收率的关键,该认识为后续两类非常规油气储层的科学评价提供了重要理论支撑。