Applications of temperature-resolved diffraction methods in thermal analysis

Fundamentals and fields of application of time- and temperature-resolved diffraction methods are presented. X-ray diffraction and neutron diffraction will be considered. Dynamic diffraction methods are increasingly applied in different fields like solid state reactions, heterogeneous catalysis and biological sciences. New methods like synchrotron radiation and position-sensitive detectors permit a considerable expansion of potential research areas. The dynamic diffraction methods are compared with the classical thermoanalytical methods thermogravimetry and DSC.     

Effect of violations of the structure and layer packing on the diffraction pattern of gibbsite and bayerite

Using the simulation method for the diffraction patterns of one-dimensionally disordered materials, the effect of different violations in the layered structure of aluminum trihydroxides (gibbsite and bayerite) on their diffraction patterns is analyzed. The features of the diffraction patterns of a disordered gibbsite sample obtained by intercalation-deintercalation of lithium salts are considered.     

Study of X-ray diffraction patterns in Langmuir-Blodgett films using the few-slits model of diffraction

Multilayer films of cadmium 22-tricosenoiate were deposited by using the Langmuir-Blodgett technique in the Z-mode of deposition. The films were then irradiated with various γ-irradiation doses. Small-angle X-ray diffraction patterns of the films before and after γ-irradiation were studied by applying the model of diffraction by a few slits. The X-ray diffraction patterns of the films before γ-irradiation show nine equidistant peaks, indicating the presence of a regular periodic structure in the film. The intensities of the even-order diffraction peaks are relatively less than those from the neighbouring odd-order peaks. This phenomenon, known as even-odd intensity oscillation, was successfully explained by this model. The position of the X-ray diffraction peaks taken for films after different γ-irradiation doses does not change, indicating that the average spacing in the film is unaffected by γ-irradiation. However, the intensity of the diffraction peaks of the film does change with γ-irradiation dose. This change can be explained by the change of electron density along the molecular chain in the layer before and after various γ-irradiation doses.     

Studies of orientation and structure of crazed matter in polystyrene. II. Electron diffraction measurements

The technique of selected area electron diffraction in the transmission electron microscope is used to examine the degree of orientation of crazed matter. The theories of electron and x-ray diffraction are compared and it is shown experimentally, by comparison with published x-ray results, that it is possible to obtain electron diffraction patterns from uncrazed polystyrene that are reasonably free of both radiation damage and multiple scattering problems. Electron diffraction patterns from crazes show a considerable degree of orientation but otherwise are very similar to those from uncrazed material, showing that crazes have no structure different from that of bulk material. Diffraction patterns are also obtained from thin films drawn to draw ratios of 4.5 and 6 at 90°C. These agree well with published x-ray results from oriented polystyrene but show less anisotropy than the craze diffraction patterns.     

Solid phases of cyclopentane: combined experimental and simulation study

The phase diagram of cyclopentane has been studied by powder neutron diffraction, providing diffraction patterns for phases I, II, and III, over a range of temperatures and pressures. The putative phase IV was not observed. The structure of the ordered phase III has been solved by single-crystal diffraction. Computational modeling reveals that there are many equienergetic ordered structures for cyclopentane within a small energy range. Molecular dynamics simulations reproduce the structures and diffraction patterns for phases I and III and also show an intermediate disordered phase, which is used to interpret phase II.     

Characterization and Application of Surface Plasmon-Enhanced Optical Diffraction from Electrodeposited Gold Nanowire Arrays

Arrays of gold nanowires formed by the process of lithographically patterned nanowire electrodeposition (LPNE) were characterized by a combination of SEM, polarized UV-visible absorption spectroscopy and optical diffraction measurements. A transverse localized surface plasmon resonance (LSPR) was observed for gold nanowire arrays with an absorption maximum (λ(max)) that varied with nanowire width. Transmission optical diffraction measurements were measured with the even and odd diffraction orders creating an alternating, out of phase sinusoidal intensity pattern characteristic of the LPNE nanowire arrays. The intensities of the even diffraction order maxima were the strongest for nanowires with a width of 115 ± 10 nm; nanowires of this width exhibit a λ(max) of 635 ± 10 nm, verifying that the transverse LSPR has enhanced the optical diffraction signal. Real time total internal reflection diffraction intensity measurements were used to monitor in situ the electrodeposition of silver monolayers onto the gold nanowire arrays.     

X-ray diffraction of protein crystal grown in a nano-liter scale droplet in a microchannel and evaluation of its applicability

We describe the technical aspects of the in-situ X-ray diffraction of a protein crystal prepared by a nanodroplet-based crystallization method. We were able to obtain diffraction patterns from a crystal grown in a capillary without any manipulation. Especially in our experimental approach, the crystals that moved to the nanodroplet interface were fixed strongly enough to carry out X-ray diffraction measurements that could be attributed to the high surface tension of the nanodroplet. The crystal was damaged by an indirect action of the X-rays because our in-situ X-ray diffraction measurement was carried out in the liquid phase without freezing the crystal; however, the obtained several diffraction patterns were of sufficiently fine quality for the crystal structure factors to be generated. We consider the technical examination presented in this paper to represent a seamless coupling of crystallization to X-ray analysis.     

A method for recording X-ray diffraction patterns of milligram quantities of particulates

A method for recording X-ray diffraction patterns of milligram quantities of particulates has been developed. The resulting diffraction patterns are similar to patterns obtained by standard methods. Application of this method to analysis of airborne particulates in the vicinity of a lead smelting operation has demonstrated the practical use of the method. Sample sizes as low as 1.1 mg have produced useful diffraction patterns.     

Application of a fast X-ray diffraction method for studies of high temperature corrosion of steel surfaces

Summary A fast X-ray diffraction method was applied in order to study in situ high temperature corrosion of steel surfaces. The measuring system for high temperature corrosion testing consists of an X-ray diffractometer, a high temperature device with programmable temperature controller and a Si(Li)-detector for measurements of energy dispersive diffraction spectra at temperatures from 20 to 1500°C. With a measuring time of 100 s per diffraction pattern a series of 300 measurements can be performed during one day. The atmosphere in the high temperature device can be controlled. The samples were heated in air at ambient pressure, recording X-ray diffraction spectra every 20°C. In addition, isothermal experiments were carried out at different temperatures. From the diffraction spectra the peak intensities, lattice plane distances and lattice parameters of the base material and the oxides were calculated as a function of temperature or time. The method allows an in situ identification of the corrosion products and a direct observation of phase transitions.     

Statistical Inference of Distribution of Crystal Size by X-Ray Powder Diffraction

We describe a method to calculate the distribution of sizes of fine crystals from pure powder-diffraction profile using a method of maximum entropy (MAXENT). We apply a Monte-Carlo technique of simulated annealing to seek a global minimum of the error surface in fitting this diffraction profile. We consider pure diffraction profile (instrument de-convoluted) of a powder specimen without lattice imperfection to a significant extent. Under these circumstances, the distribution of the pure diffraction profile can be attributed to the distribution of crystallite size. We applied this method to three cases of crystal sizes having a highly inhomogeneous distribution with certain noise-tolerance. The results agree well with synthetic data of diffraction.     

Structure of nanocrystalline particles of metallic cobalt formed during the reduction of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> oxide

X-ray diffraction is applied to investigate metallic cobalt obtained by the reduction of nanocrystalline particles of Co₃O₄. The particles of metallic cobalt have a high concentration of stacking faults, i.e., violations of the layer packing sequence ABABAB..., which is seen in X-ray diffraction patterns as anisotropic broadening of diffraction peaks. Simulation of the diffraction patterns of α-Co with a different concentration of stacking faults is carried out.     

Modeling of scattering on the residual gas in an electron diffraction experiment

The scattering on the residual gas in an electron diffraction chamber is modeled. A comparison with experimental data reveals that is this scattering that may make a major contribution to the extraneous signal inevitably present in the recorded diffraction pattern. Practical recommendations on the development of the electron diffraction apparatus design are given.     

The determination of the populations of vibrational levels of molecules from electron diffraction data

The application of modern gas-phase electron diffraction for directly determining the populations of vibrational levels is demonstrated for the molecule I₂. It is concluded that, under the conditions of the conventional electron diffraction experiment, a thermal equilibrium can reliably be assumed for a gas jet but at a temperature which can be markedly lower than that of the nozzle. The diffraction results favour a Boltzmann distribution of molecules over the vibrational states.     

Structural features of finely dispersed pseudoboehmite obtained by a sol-gel method

Simulation of diffraction patterns, radial distribution function analysis, and electron microscopy are applied to study the features of the structure of nanosized pseudoboehmite obtained by the sol-gel method. It is found to consist of plate-like particles with a thickness of one lattice constant in the [010] direction. Such a structure of the pseudoboehmite particles results in the absence of the 020 diffraction peak in the diffraction pattern.     

In-plane and out-of-plane diffraction of H2 from Ru(001)

H(2) diffraction from the Ru(001) surface has been measured for incident energies E(i) = 78-150 meV and incident angles Θ(i) = 22.1-64.1°. In-plane and out-of-plane angular distributions were measured for incidence along [110] and [100] directions. Out-of-plane diffraction channels were found to be predominant for the explored experimental conditions regardless of the incidence direction. An analysis of diffraction intensities reveals that diffraction out of the scattering plane is enhanced for high incidence angles. Diffractive transitions with wavevector change in the surface plane and transversal to the incidence direction ΔK(⊥) were observed to be favored among the out-of-plane diffractive transitions. These features could be reproduced by model calculations of diffraction intensities performed using a three-dimensional soft potential. This suggests that a kinematic effect is responsible for the large out-of-plane intensities observed in experiment, more than any other features of the six-dimensional H(2)-surface interaction potential.     

常温环境下壳聚糖诱导合成单斜羟基磷灰石纳米晶体及其结构表征

本研究采用一种简便的方法,在室温环境下合成了片状的羟基磷灰石晶体。我们采用X射线粉末衍射、ICP和红外光谱,透射电镜和选区电子衍射对获得的样品进行了表征。根据表征的结果和现有文献的支持,我们认为壳聚糖的诱导作用下形成的羟基磷灰石纳米晶体属于单斜晶系。     

In situ high-pressure x-ray diffraction study of H2O ice VII

Ice VII was examined over the entire range of its pressure stability by a suite of x-ray diffraction techniques in order to understand a number of unexplained characteristics of its high-pressure behavior. Axial and radial polycrystalline (diamond anvil cell) x-ray diffraction measurements reveal a splitting of diffraction lines accompanied by changes in sample texture and elastic anisotropy. In situ laser heating of polycrystalline samples resulted in the sharpening of diffraction peaks due to release of nonhydrostatic stresses but did not remove the splitting. Radial diffraction measurements indicate changes in strength of the material at this pressure. Taken together, these observations provide evidence for a transition in ice VII near 14 GPa involving changes in the character of the proton order/disorder. The results are consistent with previous reports of changes in phase boundaries and equation of state at this pressure. The transition can be interpreted as ferroelastic with the appearance of spontaneous strain that vanishes at the hydrogen bond symmetrization transition near 60 GPa.     

铁钼粉末冶金抗磨材料次表面亚稳相的XRD分析

在一台普通的二圆X射线衍射仪上，利用不对称布拉格反射STD（试样相对于入射线倾斜在某一角度α0，进行2θ扫描）技术与常规CBD（正常的θ/2θ偶合扫描）模式相结合的方法，对铁钼粉末冶金抗磨材料的摩擦表层、次表面层及体相的物相纵向进行了较全面分析，特别揭示了摩擦次表面层Fe-C亚稳相的存在，对材料的摩擦性能有严重影响。     

Fragmentation of an infinite ZnO2 square plane into discrete [ZnO2]2- linear units in the oxyselenide Ba2ZnO2Ag2Se2

Analysis of single crystal X-ray diffraction, neutron powder diffraction, electron diffraction and Zn-K-edge EXAFS data show that Ba2ZnO2Ag2Se2 contains unusual isolated [ZnO2]2- moieties resulting from fragmentation of a ZnO2 infinite plane placed under tension.