Neutron Diffraction Methods Research Articles

Crystal structure, hydrogen bonds and thermal transformations of superprotonic conductor Cs6(SO4)3(H3PO4)4.

Crystals of Cs6(SO4)3(H3PO4)4 belong to the family of alkali metal acid salts that show a high protonic conductivity at relatively low temperatures. Such properties make superprotonic crystals an excellent choice for the study of the influence of the hydrogen subsystem on the physicochemical properties and promising materials for energy-efficient technologies. Single crystals of Cs6(SO4)3(H3PO4)4 were studied by neutron diffraction methods, optical polarization microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Neutron diffraction studies made it possible to determine the positions of all the atoms with high accuracy, including the H atom on a hydrogen bond characterized by a single-minimum potential, to confirm the chemical composition of the Cs6(SO4)3(H3PO4)4 crystals and their cubic symmetry in low- and high-temperature phases, and to draw conclusions about the three-dimensional system of hydrogen bonds, which is fundamentally different in comparison with other superprotonic compounds. Based on the experimental data obtained, crystal transformations with temperature changes are reported, and the stability of the chemical composition is shown.

Morphology and composition of Goldeye (Hiodontidae; Hiodon alosoides) otoliths

We provide up-to-date morphological and compositional data on otoliths of the osteoglossomorph Goldeye (Hiodon alosoides). Using computed tomography (CT) X-ray, we documented the location of each of the three pairs of otoliths (lapilli, sagittae, and asterisci) in relation to the swim bladder, which extended forward in close proximity to the sagittae and asterisci. The lappili were the largest otoliths in terms of surface area and volume, but the sagittae were highly modified, appearing spiral in shape when viewed dorsally, with a surface area to volume ratio more than double that of the lapilli. Using scanning electron microscopy, the surface of each otolith was viewable in great detail, and small otoconia (~10.5 μm diameter) were observed on each, but were most numerous on the sagittae. On scanning electron micrographs, the sagittae appeared to be bi-lobed, with asymmetrical lobes each oriented in the same general direction. Using neutron and X-ray diffraction methods, we found three polymorphs of calcium carbonate crystals (aragonite, vaterite, and calcite), sometimes all within the same otolith. However, in general, lapilli and sagittae were composed predominately of aragonite whereas asterisci were composed chiefly of vaterite. With these results, we provide information on a unique species, whose inclusion in future studies would benefit our understanding of fish hearing, fish evolution, and fisheries ecology.

The crystal and magnetic structure of nanostructured manganite La0.53Sr0.47MnO3 at high pressure

The crystal and magnetic structure of the nanostructured manganite La0.53Sr0.47MnO3 has been studied using the neutron diffraction method in the pressure range 0–5.5 GPa and the temperature range 15–300 K. At ambient pressure, the ferromagnetic ordering in the studied compound is formed below T ≈ 335 K. With an increase of the pressure above 2.1 GPa and cooling below T < 250 K, an A-type antiferromagnetic phase appears, which coexists with the initial ferromagnetic one. Further increase of the pressure leads to the growth of the volume fraction of the antiferromagnetic phase, while the ferromagnetic ordering is gradually suppressed. The structural origins of the pressure-induced magnetic phase separation in the nanostructured manganites are discussed.

Neutron diffraction study of samples of fuel element claddings made of austenitic steel

The paper presents the results of investigation of the performance of industrial fuel elements operating in the active zone of a fast–neutron reactor BN-600. As a continuation of previous works, we have studied fuel elements made of austenitic steel EK-164 after their irradiation under a maximal dose of 72.3 dpa at temperatures ranging from 370 to 628 °C. As in the earlier work on studying spent fuel elements fabricated from standard steel ChS-68, neutron-diffraction method was used that demonstrates a number of advantages over traditional methods, in particular, it is the least-exposing workers to radiation hazards and most suitable for studying bulk irradiated materials. Based on the experience gained, some quite typical microstructure distortions arisen under irradiation were revealed, changes in the density and type of dislocations depending on the dose and temperature were determined, and the dominant role of temperature at high doses of fast neutrons was confirmed. The behavior of EK-164 steel samples selected from different series is shown to depend on their initial structural state.

Direct air capture of CO2 via crystal engineering.

This article presents a perspective view of the topic of direct air capture (DAC) of carbon dioxide and its role in mitigating climate change, focusing on a promising approach to DAC involving crystal engineering of metal–organic and hydrogen-bonded frameworks. The structures of these crystalline materials can be easily elucidated using X-ray and neutron diffraction methods, thereby allowing for systematic structure–property relationships studies, and precise tuning of their DAC performance.

Konturni metod u određivanju aksijalnih rezidualnih napona kod hladno ekstrudiranih čeličnih šipki

Residual stresses in cold extruded parts play an important role in both component lifetime and succeeding in manufacturing performance. When a cold extruded part is used directly, the lifetime of the part depends on the residual stresses induced during cold extrusion. On the other hand, if the part is exposed to post operations such as machining, residual stresses may cause distortions. Despite their importance, there are only a few residual stress measurement methods to assess axial residual stresses in full cylindrical thick components of massive forming. As high-energy X-ray and neutron diffraction methods are less available and considerably expensive, the contour method may be an alternative providing the accurate assessment of residual stresses without requiring specialized facilities. In the present work, residual stresses in cold extruded rods are determined via the contour method for various extrusion ratios. The finite element analyses for the same conditions are also carried out to provide the comparison to the contour method. The results indicate that the contour method can be a valuable candidate for the measurement of axial residual stresses in cold extruded thick components.

Нейтронографическое исследование кинетики низкотемпературного распада мартенсита среднеуглеродистой стали

It is found that the low-temperature decomposition of martensite in quenched medium-carbon steel occurs in two stages. In the first stage, the rate of decomposition is higher than that in the subsequent stage. Application of the neutron diffraction method allows the identification of two stages of transformation in the first stage of martensite decomposition. It is shown that the first stage is associated predominantly with carbon segregation at dislocations, and the second, with the outdiffusion of carbon from the supersaturated solid solution with the formation of dispersed particles of metastable carbides. It is shown that the change in the concentration of carbon and, accordingly, the degree of tetragonal lattice of martensite at aging and low tempering occurs to a certain limit, independent of the cooling rate during quenching and tempering temperature. This is due to the establishment of a relative equilibrium between a supersaturated solid solution and fine particles of metastable iron carbide. It is found that the determining process, which leads to a change in the microhardness the low-temperature decomposition, is the out diffusion of carbon from the supersaturated solid solution.

Magnetic Structure of Inorganic–Organic Hybrid (C6H5CH2CH2NH3)2MnCl4 Using Magnetic Space Group Concept

Previously, we reported that inorganic–organic hybrid (C6H5CH2CH2NH3)2MnCl4 (Mn-PEA) is antiferromagnetic below 44 K by using magnetic susceptibility and neutron diffraction measurements. Generally, when an antiferromagnetic system is investigated by the neutron diffraction method, half-integer forbidden peaks, which indicate an enlargement of the magnetic cell compared to the chemical cell, should be present. However, in the case of the title compound, integer forbidden peaks are observed, suggesting that the size of the magnetic cell is the same as that of the chemical cell. This phenomenon was until now only theoretically predicted. During our former study, using an irreducible representation method, we suggested that four spin arrangements could be possible candidates and a magnetic cell and chemical cell should coincide. Recently, a magnetic structure analysis employing a magnetic space group has been developed. To confirm our former result by the representation method, in this work we employed a magnetic space group concept, and from this analysis, we show that the magnetic cell must coincide with the nuclear cell because only the Black–White 1 group (equi-translation or same translation group) is possible.

Structure of As-Se glasses by neutron diffraction with isotope substitution.

The method of neutron diffraction with selenium isotope substitution is used to measure the structure of glassy As0.30Se0.70, As0.35Se0.65, and As0.40Se0.60. The method delivers three difference functions for each sample in which the As-As, As-Se, or Se-Se correlations are eliminated. The measured coordination numbers are consistent with the "8-N" rule and show that the As0.30Se0.70 network is chemically ordered, a composition near to which there is a minimum in the fragility index and a boundary to the intermediate phase. Chemical ordering in glassy As0.35Se0.65 and As0.40Se0.60 is, however, broken by the appearance of As-As bonds, the fraction of which increases with the arsenic content of the glass. For the As0.40Se0.60 material, a substantial fraction of As-As and Se-Se defect pairs (∼11%) is frozen into the network structure on glass formation.

Study of Through-Thickness Stress Distribution in Steel Double-V Butt Weld

Through-thickness stress distribution in 32 mm thick ferritic steel plates welded with double-V groove was studied using neutron diffraction and finite element methods. The stress distribution is close to the symmetrical with respect to the weld centerline and not symmetrical with respect to the weld mid-thickness. The peak longitudinal stress (530 MPa) is located in the first half of the weld thickness, where the groove was filled first. The region of maximum compressive transverse stresses (–400 MPa) is located in the second half of the plate thickness. Post weld heat treatment reduces maximum tensile stresses down to ∼200 MPa. The position of maxima and minima of transverse residual stresses obtained by finite element methods are in agreement with the results of measurement by the neutron diffraction method. However, at some locations, the calculated values are approximately 300 MPa higher than the experimental ones.

Study on residual stress distribution of 2024-T3 and 7075-T6 aluminum dissimilar friction stir welded joints

Friction stir welding (FSW) can weld 2024-T3 and 7075-T6 aluminum parts into one integral aircraft assembly. In order to perform the integrity assessment of the dissimilar welded structure, the first thing is to identify its residual stress distribution. In this paper, 2024 and 7075 dissimilar aluminum plates were welded by FSW, and the residual stress profiles of the dissimilar welded specimen were measured by the neutron diffraction method. A three-dimensional finite element model was used to calculate and compare the residual stress distributions of different welding parameters. Microstructure characteristics in different FSWed zones were studied by the electron backscattered diffraction (EBSD) method. It is shown that the longitudinal residual stress of 7075 side is higher than that of 2024 side, and the maximum residual stress decreases from the top scan line to the bottom scan line. The transverse and the normal residual stresses are tensile in 7075 side, while that of 2024 side is compressive. The numerical simulation results agree with the neutron diffraction measurements. The KAM map of the thermo-mechanical affected zone shows larger local plastic deformation than that of the stirred zone, which leads the longitudinal residual stress has the “double peak” shape.

Lattice Parameter of Cementite Phase in Pearlite Structure

The lattice parameter of cementite in a pearlite structure was measured using the in situ heating neutron diffraction method. The lattice parameters of the cementite phase of the b- and c- axes in the pearlite structure were smaller than those in the martensite structure and Reed’s results [3]. The lattice parameter of the a-axis in the pearlite structure was almost equal to that in the martensite structure and Reed’s results [3]. The thermal and misfit strains, caused by the differences between the thermal expansion rate and lattice parameter of the cementite and ferrite phases, should affect the lattice parameter of cementite in the pearlite structure.

Investigation into the influence of carbon nanotubes addition on residual stresses and mechanical properties in the CNTs@SiCp/Mg-6Zn hybrid composite using neutron diffraction method

An interfacial CNT-(Mg-6Zn) layer was introduced between SiC particle and Mg-6Zn matrix by a novel method in aim to reduce the excessive thermal residual stresses between SiC particles and matrix. The CNTs were synthesized via CVD on the SiC surfaces, and CNTs kept on the surfaces of SiC particles in the composite during fabrication process. The influence of the interfacial CNT-(Mg-6Zn) layer on the microstructure, the mechanical properties and the Type II thermal residual stresses of composite were investigated with neutron diffraction method. Compared with mono-SiCp reinforced Mg-6Zn composite, the CNTs@SiCp/Mg-6Zn composite presents superior mechanical properties. The E, YTS, UTS and elongation are increased by 9.6%, 14%, 20%, 18.2% respectively. The residual stress of Mg in CNTs@SiCp/Mg-6Zn (35 MPa) is less than half of that (74 MPa) in SiCp/Mg-6Zn composite. Digital image correlation (DIC) investigation indicates that the additional CNTs enhances the bonding strength between SiCp and Mg matrix. The interface layer could release the thermal residual stresses in the composite in two ways: firstly, the gap of the coefficient of thermal expansion (CTE) between the SiCp and the Mg matrix is reduced; secondly, the thermal diffusivity of the composite is declined, leading to lower cooling rate of the as-cast composite in which a portion of residual stresses are released. This work highlights the influence of the interfacial CNT-(Mg-6Zn) layer on the Type II residual stresses and the mechanical properties of the CNTs@SiCp/Mg-6Zn composite.

Neutron Diffraction Analysis of Residual Strain in High-Pressure Die Cast A383 Engine Blocks

The residual strains in three high-pressure die cast A383 engine blocks were measured using neutron diffraction. Residual strains and stresses can be generated during high-pressure die casting process due to high thermal gradients and may cause fatigue failure or dimensional distortion. Neutron diffraction can measure the residual strain distributions deep inside castings with complex geometries, because neutrons can penetrate substantially more material than x-rays. In the present work, the residual strains (in the axial and hoop directions) along the whole cylinder bridge of high-pressure die cast A383 engine blocks in as-cast and heat-treated conditions were measured by neutron diffraction methods. The effect of heat treatment on the distribution and magnitude of residual strains was also investigated. The results indicate that the residual strain in the cylinder bridge is tensile in both the axial and hoop components for both the as-cast and the heat-treated engine blocks. The residual strain in the hoop direction is bigger in magnitude than the residual strain in the axial direction. Heat treatment significantly relaxes the residual strain in the axial direction but only slightly relaxes the residual strain in the hoop direction.

Phase transitions, molecular dynamics and structural properties of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid

Recently, ionic liquids are very promising substances mentioned in electrochemistry as electrolytes in supercapacitors. Due to the fact the operation conditions for supercapacitors require low temperatures, an important issue is an investigation of melting behavior of ionic liquid applied as an electrolyte. In the presented work, we report the experimental studies of the melting behavior of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI); for this purpose the methods of dielectric spectroscopy (DS) and differential scanning calorimetry (DSC) in wide temperature ranges were applied. To investigate the structural properties of the system the temperature-controlled WAXS and Neutron Diffraction methods were adopted. The measurements of the complex permittivity of the studied EMIM TFSI allowed us to determine the relaxation of the system in wide temperature range from 140 K to 300 K. The results obtained from DSC and DS indicate that the ionic liquid on the heating process undergoes two phase transitions: solid-solid transition at temperature 230 K and the melting transition at 257 K, wherein the melting process is not homogeneous. Based on the structural studies results, performed in the temperatures range 10 K – room temperature, it was shown that in the temperature range 10 K–230 K EMIM TFSI forms a crystal monoclinic structure where the rotation motions of molecular groups are observed. At the higher temperature up to the melting temperature the crystal structure is undefined and the rotational motions of molecular groups are changed.

Non-Destructive and Micro-Invasive Techniques for Characterizing the Ancient Roman Mosaic Fragments

The color characteristics, vibration spectra, phase and mineral composition, internal structural organization of several fragments of the ancient Roman mosaics from the Roman Mosaic Museum, Constanta, Romania were studied by non-destructive (Chromatic analysis, Neutron Diffraction, Neutron Tomography) and micro-invasive techniques (Optical Microscopy, X-ray Diffraction, Field Emission Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy, Raman Spectroscopy, Wavelength Dispersion X-ray Fluorescence). These investigations were performed in order to characterize the original Roman mosaic fragments. The major and minor phase components of the studied mosaic fragments were determined, the crystal structure of the main phases was analyzed, and their three-dimension spatial arrangement was reconstructed. The similar composition of the major phases of all mosaic fragments can indicate a generic recipe for making mosaic elements, but minor phases were presumably added for coloring of mosaic pieces. Some degradation areas inside the volume of the mosaic fragments were found by means of neutron diffraction and neutron tomography methods. These degradation areas are probably related to the formation of iron hydroxides during chemical interactions of mosaic fragments with the sea and urban polluted atmosphere.

Deep Neural Network Enabled Space Group Identification in EBSD.

Electron backscatter diffraction (EBSD) is one of the primary tools in materials development and analysis. The technique can perform simultaneous analyses at multiple length scales, providing local sub-micron information mapped globally to centimeter scale. Recently, a series of technological revolutions simultaneously increased diffraction pattern quality and collection rate. After collection, current EBSD pattern indexing techniques (whether Hough-based or dictionary pattern matching based) are capable of reliably differentiating between a "user selected" set of phases, if those phases contain sufficiently different crystal structures. EBSD is currently less well suited for the problem of phase identification where the phases in the sample are unknown. A pattern analysis technique capable of phase identification, utilizing the information-rich diffraction patterns potentially coupled with other data, such as EDS-derived chemistry, would enable EBSD to become a high-throughput technique replacing many slower (X-ray diffraction) or more expensive (neutron diffraction) methods. We utilize a machine learning technique to develop a general methodology for the space group classification of diffraction patterns; this is demonstrated within the $\lpar 4/m\comma \;\bar{3}\comma \;\;2/m\rpar$ point group. We evaluate the machine learning algorithm's performance in real-world situations using materials outside the training set, simultaneously elucidating the role of atomic scattering factors, orientation, and pattern quality on classification accuracy.

Study of Residual Stresses and Microstructural Changes in Charpy Test Specimens Reconstituted by Various Welding Techniques

Changes in the reactor pressure vessel (RPV) material properties due to neutron irradiation are monitored by means of surveillance specimen programs, which are used for realistic evaluation of the RPVs’ lifetime. Due to a limited number of surveillance specimens, the evaluation of reconstitution methods by various welding techniques after Charpy impact tests is of great importance. Time-of-flight (TOF) neutron diffraction method was used to determine the residual stress distributions and microstructural changes in Charpy specimens welded by arc stud, electron, and laser beam welding techniques. The lowest level of the residual stress in weld seams regions was found for the specimen welded by electron beam with optimal parameters as compared to other techniques. At the same time, this specimen exhibits the maximal level of microstrain, which points to high dislocation density in the material. The corresponding contributions to the yield strength due to various strengthening mechanisms were estimated.

The Influence of Powder Milling on Properties of SPS Compacted FeAl.

The Fe-28 at.% Al alloy was studied in this article. The aim was to describe the influence of gas atomized powder pre-milling before SPS (Spark Plasma Sintering) sintering on the structure and properties of the bulk materials. The initial powder was milled for 0.5, 1, and 8 h. It was proven that 1 h milling leads to the change in size and morphology of the particles, B2→A2 phase transformation, and to the contamination with the material from a milling vessel. Powder materials were compacted by the SPS process at 900, 1000, and 1100 °C. The differences between the bulk materials were tested by LM, SEM, and TEM microscopy, XRD, and neutron diffraction methods. It was proven that, although the structures of initial powder (B2) and milled powder (A2) were different, both provide after-sintering material with the same structure (D03) with similar structural parameters. Higher hardness and improved ductility of the material sintered from the milled powder are likely caused by the change in chemical composition during the milling process.

Non-invasive characterization of ancient Indonesian Kris through neutron methods

This study focuses on a non-invasive characterization of a set of ancient kris by means of neutron imaging and diffraction methods. The kris (or keris) is an elongated dagger or short sword distinctive of Malaysia and Indonesia. Its complex structure results from the combination of several layers of iron, steel and sometimes iron–nickel alloy welded together in an intricate pattern that is brought out on the polished surface of the blade through the use of an etchant. Based on the tomographic analysis, four different structural arrangements were identified for the first time. Complementarily, the average quality of the ferrous materials used to produce the four kris was evaluated via time-of-flight neutron diffraction analysis. New details about the manufacturing process of a still little studied class of artefacts were derived from our investigation.