R. N. Vasin

Rietveld texture analysis from synchrotron diffraction images. I. Calibration and basic analysis

Synchrotron X-ray diffraction images are increasingly used to characterize not only structural and microstructural features of polycrystalline materials, but also crystal preferred orientation distributions. Diffraction data can be analyzed quantitatively and efficiently with the Rietveld method and here the detailed procedure is reported from the experiment to the calibration of the two-dimensional detector and full analysis of the sample. In particular, we emphasize the advantage of doing the calibration inside the Rietveld least-squares fitting instead of a preliminary graphical calibration. Then the procedure is described to quantify crystal preferred orientations with the Rietveld method implemented in software Materials Analysis Using Diffraction. The process is illustrated for a US nickel coin, a 75 at.% copper 25 at.% nickel alloy with face-centered cubic structure and a strong cube texture.

Rietveld texture analysis from synchrotron diffraction images. II. Complex multiphase materials and diamond anvil cell experiments

© International Centre for Diffraction Data 2014. Synchrotron X-ray diffraction images are increasingly used to characterize crystallographic preferred orientation distributions (texture) of fine-grained polyphase materials. Diffraction images can be analyzed quantitatively with the Rietveld method as implemented in the software package Materials Analysis Using Diffraction. Here we describe the analysis procedure for diffraction images collected with high energy X-rays for a complex, multiphase shale, and for those collected in situ in diamond anvil cells at high pressure and anisotropic stress.

Investigation of the structure and properties of quartz in the α-β transition range by neutron diffraction and mechanical spectroscopy

The paper reports on the results of complex investigations into the physical properties of synthetic quartz single crystals and quartz powders in the temperature range of the α-β transition with the use of neutron diffraction and mechanical spectroscopy. The crystal structure of quartz powders with different average sizes of grains is determined in the temperature range up to 620°C and in the α-β transition temperature range. The temperature dependences of the internal friction and the resonant frequency for quartz samples in the vicinity of the phase transition temperature are obtained upon excitation of vibrations in the planes parallel and perpendicular to the Z axis of the quartz crystal. The temperatures at the maxima of the internal friction in the range 560–620°C are determined. The assumptions regarding the possible reasons for the shift of the phase transition temperature are made. It is revealed that the internal friction is characterized by a maximum that is observed in the vicinity of 350°C and is not related to the structural transformations in quartz.

Acoustic emission of quasi-isotropic rock samples initiated by temperature gradients

The influence of temperature gradients and heating rate on crack formation in quasi-isotropic samples of marble and sandstone is studied using acoustic emission records. The behavior of velocities and attenuation of elastic waves in the samples is also examined. The crystallographic textures of marble and sandstone are measured by the neutron diffraction method, and it is shown that temperature gradients of up to 52°C/cm do not lead to a change in the textures. It is established that the temperature dependence of acoustic activity in the sandstone samples strongly depends on the internal heating rate. The maximum acoustic activity of the sandstone samples was observed at maximum temperature gradients in the samples. The temperature dependence of acoustic activity in marble differs significantly from that in sandstone. Maximums of acoustic activity in the marble samples are observed at temperatures of 30–60 and higher than 200°C. A decrease in acoustic activity was recorded in the interval between these temperatures. Such behavior suggests a predominant role of the surface structure and the concentration of surface defects in the process of crack formation in marble. During cooling, all samples demonstrate similar behavior: maximum acoustic activity is observed at the switching-off of the heating element and the emission activities of different samples are comparable in intensity.

Investigation of thermal and deformation properties of quartzite in a temperature range of polymorphous α-β transition by neutron diffraction and acoustic emission methods

The results of combined application of the neutron diffraction and acoustic emission methods for investigation of the physical properties of synthetic quartz and natural quartzite in a temperature range of α-β transition are given. In experiments, the quartzite sample was exposed to heating and uniaxial compression. Changes of the lattice spacings in quartzite were measured in a temperature range 540–620°C. On the basis of these measurements, the inner inner stresses are evaluated and found to exceed the applied stresses by several times. It is found that after the phase transition is finished, short bursts of acoustic emission (AE) occur which are two orders of magnitude more intense than the acoustic emissions produced by thermal cracking of the sample while the sample is heating up to the transition temperatures. An assumption is made that the anomalous behavior of the physical properties of quartz-containing rocks under relatively low pressures near the transition temperature can cause the formation of strong concentrators of local stresses comparable with the breaking point of the material, thereby initiating microcracking.

On the use of a composite moderator at the IBR-2 reactor: Advantages for the neutron-diffraction texture analysis of rocks

A unique cold moderator based on a mixture of mesitylene and m-xylene is developed for the IBR-2 pulsed reactor. If combined with a standard warm-water moderator, it provides a high neutron flux in a wide wavelength range. The advantages of the use of this composite moderator in neutron-diffraction texture analysis are discussed using the example of a sample of slate (formed from five minerals) studied using the SKAT diffractometer. The diffraction data obtained in experiments with warm-water and composite moderators are compared.

Application of neutron stress diffractometry for the study of residual stress and texture in industrial metal products processed in various ways

Residual stress and texture in industrial metal products, processed in different ways, are investigated by means of high-resolution neutron diffraction. The samples are pipe sections made of 30KhN2MFA steel, which are parts of precision machinery and operate under complex loading conditions. The products are manufactured using various methods of plastic deformation, namely, rotary forging and drawing on a mandrel. The results of comparative analysis of the distributions of residual stress and microstrain throughout the wall thickness for all samples are presented. Additionally, neutron texture experiments are performed; based on their results, pole figures are calculated and the crystallographic texture characteristics are evaluated.

Peculiarities of quasi-longitudinal elastic wave propagation through the interface between isotropic and anisotropic media: Theoretical and experimental study

The peculiarities of elastic wave propagation in a bilayer medium are studied theoretically and experimentally. One (isotropic) layer was an acrylic glass plate, and the other (anisotropic) was a quartz single-crystal. In experiments, the elastic waves were generated by a piezoelectric transmitter and received by a piezoelectric transducer contacting the surface of the model medium. The propagation time of a quasi-longitudinal wave was determined using high-order statistics. In the general case, the incident elastic waves are split at the interface between the layers: beams undergo double reflection and triple refraction. The measured dependences of the propagation times of quasi-longitudinal split waves on the angles of refraction are in satisfactory agreement with the calculated ones. The calculation was performed by solving the Christoffel equation with allowance for the boundary conditions.

Possible influence of polymorphic transitions in minerals (according to the quartz example) on seismotectonic processes in the lithosphere

The thermally activated physical processes essential for earthquake source physics and the formation of mylonite layers and deep shear zones are examined. The possibility of the influence of polymorphic (structural) phase transitions in the rock-forming minerals on the geodynamic effects is discussed. On the basis of experimental data, the deformation-strength and elastic properties of stratum containing quartz in the region of the α-β transition in quartz are studied as an example. It is shown that the α-β transition in quartz corresponds in a number of ways to the observed features specific to the physical properties of substance in connection with seismic processes.

Similar Quartz Crystallographic Textures in Rocks of Continental Earth's Crust (by Neutron Diffraction Data): III. Relation of Quartz Texture Types with Means and Conditions of Texture Formation

Examples of different rocks collected in different regions of the continental earth’s crust are presented. Groups of quartz crystallographic textures of the same type are selected for these rocks. The relationship between the types of textures and the physical means and conditions of their formation is analyzed. The effect of the α-β phase transition in quartz on the texture transformations in rocks is considered.