Depth-profiling of phase composition and preferred orientation in a graded alumina/mullite/aluminium-titanate hybrid using X-ray and synchrotron radiation diffraction

X-ray diffraction (XRD), grazing-incidence synchrotron radiation diffraction (GISRD) and multi-wavelength synchrotron radiation diffraction (MWSRD) have been successfully used for near-surface depth profiling of phase composition and texture in a functionally-graded alumina/mullite/aluminium-titanate hybrid prepared by an infiltration process. Depth profiling of near-surface information both in the nanometer and micrometer scale has been done by (a) varying the X-ray wavelength, (b) varying the grazing-incidence angle, and (c) gradual polishing of the sample surface with diamond lap. Results show a distinct gradation in the phase abundance near the surface of the hybrid sample. The distribution of mullite near the surface is highly textured and shows a distinct depth-dependent gradation in preferred grain-orientation. The unique but powerful capability of XRD, GISRD and MWSRD as complementary tools for depth profiling the near-surface region of graded materials has been demonstrated in this work.     

On the fundamental imaging-depth limit in two-photon microscopy

We have analyzed how the maximal imaging depth of two-photon microscopy in scattering samples depends on properties of the sample and the imaging system. We find that the imaging depth increases with increasing numerical aperture and staining inhomogeneity and with decreasing excitation-pulse duration and scattering anisotropy factor, but is ultimately limited by near-surface fluorescence with slight improvements possible using special detection strategies.     

Plane analysis for functionally graded magneto-electro-elastic materials via the symplectic framework

By introducing the displacements, electric potential, magnetic potential and their dual counterparts as state variables, a symplectic analysis framework is established in the Hamiltonian system to solve the plane problem of functionally graded magneto-electro-elastic materials. The material properties are assumed to vary along the length direction in an identical exponential form. The method of separation of variables along with the eigenfunction expansion technique is employed to reduce the original problem to the eigenvalue/eigensolution analysis. The particular eigensolutions corresponding to eigenvalues of zero and –α are given, which while bearing definite physical interpretations exhibit some unique characteristics. A numerical example is presented to show the influence of material inhomogeneity on the β-group solutions of the problem.     

Texture studies using neutron diffraction

Various aspects of the application of neutron scattering methods to texture studies are reviewed. The neutron method is compared with other methods of texture measurement and techniques of neutron diffraction registration of texture are discussed.Examples are presented of the use of neutron scattering for texture examination in materials having various grain sizes and degrees of structural inhomogeneity. It is also demonstrated that the information about texture can be used in the discussion of the deformation and recrystallization processes in metals.Neutron diffraction results are shown to be helpful in the examination of the influence of texture on the anisotropy of physical properties in materials. The possibility of neutron diffraction measurements of magnetic texture is reported. Finally the accuracy of texture measurements using the neutron method is discussed.On leave from Academy of Mining and Metallurgy, Cracow, Poland.     

Irregularities of crystallographic orientation and residual stresses in the crossed-lamellar shell as a natural functionally graded material

The microstructures of different groups of molluscs are characterized by preferential orientations of crystallites (texture), leading to a significant anisotropy of the physical properties of the shells. A complementary characteristic, usually neglected, is the distribution of the residual stresses existing within the shell wall. By means of X-ray diffraction, we study the distribution of stresses with thickness in the shell wall of the gastropod Conus marmoreus, which has a microstructure of the crossed-lamellar type. The results revealed an extraordinary texture inhomogeneity and the existence of tensional residual stresses along the shell thickness, the origins of which are unknown. Some of the observed changes in textural parameters and stresses coincide with the transitions between shell layers, although other features are of unknown origin. Our results provide insight into the microstructural regularities that govern the mesoscale construction of shells, such as that of C. marmoreus.     

孔结构对泡沫混凝土性能的影响与控制技术

泡沫混凝土是我国水泥基建筑材料的重要组成部分,分析了孔结构的分类及其对泡沫混凝土的强度、耐久性、保温系数等宏观性能的影响,发现泡沫混凝土的宏观性能与孔结构密切相关。总结了泡沫混凝土孔结构的控制技术,发现水灰比、矿物掺合料等的加入都会影响孔的形成。在此基础上,提出加强对建立孔结构与宏观性能之间的理论模型、孔结构与宏观性能间关系的适用范围、孔的定量控制等方面的研究。     

Use of 3He++ in RBS analysis of CMT and related epilayers

The advantages of using a beam of ³He⁺⁺ extracted from conventional accelerator equipment for RBS analysis of CMT - related materials are described. Results obtained on an epilayer of HgTe grown on a CdTe substrate are compared with results of ⁴He⁺ beam RBS. The improved mass resolution combined with the lower energy loss rate of the ³He beam on penetration provides a much enhanced profiling depth both for Hg in the near-surface region and for diffusion effects at the interface. The method should extend to other heavy-element materials.     

Laser surface melting of mild steel with submicronic titanium carbide powders

Surface alloys are of great interest for improving the mechanical and/or chemical properties of the near-surface region of metallic materials. A new method is described to produce surface alloys under laser irradiation using submicronic powders suspended in a polymeric mixture. By this process, Fe-TiC composite surface alloys were achieved on mild steel; they exhibited increased hardness, the value of which may be varied by controlling the TiC fraction incorporated.     

Orientation-dependent function for properties of polycrystals and its applications

Polycrystals are aggregates of numerous tiny crystallites whose orientation distributions are described by the orientation distribution function (ODF). Since crystal lattices are anisotropic, the properties of polycrystals depend on the ODF. The texture coefficients, which can be measured by X-ray diffraction, are the expanded coefficients of the ODF under the Wigner D-function bases. The texture coefficients contain the information of crystalline orientation distributions and crystal symmetries on polycrystals. Herein an orientation-dependent function is introduced to present the properties of polycrystals. A general expression of the orientation-dependent function for polycrystals is given. The general expression with the texture coefficients can be widely used to determine the properties of polycrystals. As applications of the general expression, the direction-dependent function, the elastic strain energy, and the yield function for anisotropic cubic polycrystals are given in simple and explicit forms.     

Three-dimensional distribution of polymorphs and magnesium in a calcified underwater attachment system by diffraction tomography

Biological materials display complicated three-dimensional hierarchical structures. Determining these structures is essential in understanding the link between material design and properties. Herein, we show how diffraction tomography can be used to determine the relative placement of the calcium carbonate polymorphs calcite and aragonite in the highly mineralized holdfast system of the bivalve Anomia simplex. In addition to high fidelity and non-destructive mapping of polymorphs, we use detailed analysis of X-ray diffraction peak positions in reconstructed powder diffraction data to determine the local degree of Mg substitution in the calcite phase. These data show how diffraction tomography can provide detailed multi-length scale information on complex materials in general and of biomineralized tissues in particular.     

Crystallographic Texture in Ceramics and Metals

Preferred crystallographic orientation, or texture, occurs almost universally, both in natural and man-made systems. Many components and devices in electronic and magnetic systems are fabricated from materials that have crystallographic texture. With the rapidly increasing use of thin film technology, where sharp axisymmetric crystallographic texture normal to the film plane is frequently observed, the occurrence and impact of texture are rising. Thin film applications in which the texture of the material plays a key role in determining properties and performance are broad: complex oxides in random access memory devices, ZnO thin film resonators for cell phone applications, metallic alloys in magnetic recording media, and Al and Cu interconnects in integrated circuits are but a few examples. Texture is established during the synthesis or post-synthesis heat treatment of a material and thus has a strong dependence upon processing history. Accurate measurement of texture is not simple and a variety of tools and approaches are being actively employed in texture studies. X-ray, neutron and electron diffraction based techniques are practiced around the world at varying levels of complexity with regard to equipment and analysis methods. Despite the well-documented existence of these varied approaches, many reported texture measurements on electronic materials are based solely on the relative intensities of conventional θ-2θ x-ray diffraction peaks, which typically yield inaccurate results. NIST has developed quantitative texture measurement techniques that employ equipment commonly available in most industrial and academic settings. A number of examples of texture measurement in ceramic and metal systems will be presented, taken from the historical development and application of these techniques at NIST over the past 7 years.     

On-line determination of texture-dependent materials properties

Macroscopic properties of polycrystalline materials may strongly depend on crystal orientation distribution, i.e., the texture of the material. This applies to all kinds of crystallographically anisotropic volume and boundary properties. The necessary texture parameters can be determined from a low number of intensity values measured with a fixed-angle, X-ray texture analyzer which is particularly suited for on-line determination. Alternatively, the texture-property relationship can be used to calculate the texture parameters from property measurement in different sample direction. On-line measurement of the texture can also be used as an indicator for other materials properties such as recrystallization or fatigue.     

Competing Striped Structures in La2CuO4+y

High temperature superconductivity emerges in unique materials, like cuprates, that belong to the class of heterostructures at atomic limit, made of a superlattice of superconducting atomic layers intercalated by spacer layers. The physical properties of a strongly correlated electronic system, emerge from the competition between different phases with a resulting inhomogeneity from nanoscale to micron scale. Here, we focus on the spatial arrangements of two types of structural defects in the cuprate La₂CuO_4+y : (i) the local lattice distortions in the CuO₂ active layers and (ii) the lattice distortions around the charged chemical dopants in the spacer layers. We use a new advanced microscopy method: scanning nano X-ray diffraction (nXRD). We show here that local lattice distortions form incommensurate nanoscale ripples spatially anticorrelated with puddles of self-organized chemical dopants in the spacer layers.     

Die Welt ist keine Scheibe

The world is not flat: from field ion microscopy to atom probe tomography Atom probe tomography has gained considerable importance in the past couple of years due to the steadily increasing demands on the capabilities of analytical tools for nanotechnology. Presently available preparation and instrumental methods allow the application of atom probe tomography also for technically relevant specimens. This affords a unique analytical approach for a quantitative and highly sensitive characterization of the chemical content of materials; by combining these features with the three dimensional registration of the elemental distributions, atomic spatial resolution can be achieved both laterally and in‐depth. For this reason, atom probe tomography is very well suited for the determination of the composition and morphology of crystalline and amorphous materials and nanostructures, and may have an enormous impact on research and development in various areas of material sciences. The first part of this contribution on modern atom probe tomography illustrates the evolution of the technique from its beginnings in the 1950s to the presently available commercial instruments. In the course of this overview, the basic physical and instrumental concepts will briefly be outlined. The second part will concentrate on the presentation of selected, current applications; these examples will serve also to emphasize some of the limitations of atom probe tomography.     

Evaluating the Inhomogeneity of Thermocouples Using a Pressure-Controlled Water Heat Pipe

There exists various research reports concerning the evaluation methods for the measurement uncertainty due to inhomogeneity of thermocouples; however, the universal method is still waiting to be established. This article considers the evaluation methods for the measurement uncertainty due to inhomogeneity of thermocouples based on comparison between results of two measurement methods. The first method is to estimate the uncertainty from the immersion characteristics of a thermocouple within a fixed-point furnace during its realization. The second method is to estimate the uncertainty from the immersion characteristics of a thermocouple within a heat-pipe furnace with a long uniform region. A pressure-controlled water heat-pipe furnace with an immersion depth of 1000?mm is developed to enable this work. It overcomes the technical difficulties that existed in applying conventional sealed heat pipes to such applications. From the immersion characteristics of a thermocouple measured by the above two methods, we have introduced three measurement parameters. Estimating the measurement uncertainty due to the inhomogeneity from our measurement results as examples is discussed.     

Design-based stereology to quantify structural properties of artificial and natural snow using thin sections

The quantification of the structural properties of snow is traditionally based on model-based stereology. Model-based stereology requires assumptions about the shape of the investigated structure. Here, we show how the density, specific surface area, and grain boundary area can be measured using a design-based method, where no assumptions about structural properties are necessary. The stereological results were also compared to X-ray tomography to control the accuracy of the method. The specific surface area calculated with the stereological method was 19.8 ± 12.3% smaller than with X-ray tomography. For the density, the stereological method gave results that were 11.7 ± 12.1% larger than X-ray tomography. The statistical analysis of the estimates confirmed that the stereological method and the sampling used are accurate. This stereological method was successfully tested on artificially produced ice beads but also on several snow types. Combining stereology and polarisation microscopy provides a good estimate of grain boundary areas in ice beads and in natural snow, with some limitations.     

Emerging X-ray imaging technologies for energy materials

With the growing need for sustainable energy technologies, advanced characterization methods become more and more critical for optimizing energy materials and understanding their operation mechanisms. In this review, we focus on the synchrotron-based X-ray imaging technologies and the associated applications in gaining fundamental insights into the physical/chemical properties and reaction mechanisms of energy materials. We will discuss a few major X-ray imaging technologies, including X-ray projection imaging, transmission X-ray microscopy, scanning transmission X-ray microscopy, tender and soft X-ray imaging, and coherent diffraction imaging. Researchers can choose from various X-ray imaging techniques with different working principles based on research goals and sample specifications. With the X-ray imaging techniques, we can obtain the morphology, phase, lattice and strain information of energy materials in both 2D and 3D in an intuitive way. In addition, with the high-penetration X-rays and the high-brilliance synchrotron sources, operando/in-situ experiments can be designed to track the qualitative and quantitative changes of the samples during operation. We expect this review can broaden readers’ view on X-ray imaging techniques and inspire new ideas and possibilities in energy materials research.     

高强IF钢板沿厚度方向的织构和显微组织

利用X射线三维取向分布函数(ODF)方法和金相方法分别对加磷强化的高强IF钢沿厚度方向织构和显微组织的不均匀性及其变化规律进行了研究。结果表明:该高强IF钢板厚度中心层的γ纤维织构强度及体积分数最高,其次为1/4厚度层,最弱为表层;钢板的显微组织则由表层大小不均匀的晶粒逐渐转变为中心层大小非常均匀的等轴晶粒;这种织构和显微组织沿厚度方向的不均匀现象是由于在轧制过程中钢板的变形不均匀性所造成的。     

Effect of crystallization time on the physico-chemical and catalytic properties of the hierarchical porous materials

A series of hierarchical porous materials were prepared by a dual template method. The effect of different crystallization time on the channel architecture, morphology, acid performance of the hierarchical porous materials was investigated. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, nitrogen adsorption and ²⁷Al nuclear magnetic resonance were performed to obtain information on the physico-chemical properties of the materials. It was shown that the change in crystallization time could influence the structure/texture and surface acid properties of the hierarchical porous materials. In addition, alkylation of phenol with tert-butanol reaction was carried out to investigate the catalytic performance of the hierarchical porous materials. The results showed that the catalytic activity of the hierarchical porous materials and the selectivity to the bulkly product 2,4-di-tert-butyl-phenol decreased with processing time.