Description: The application of Rietveld texture analysis (RTA) to time-of-flight (TOF) neutron diffraction data allows complex materials with many diffraction peaks to be investigated, for example, rocks composed of different minerals. At the recently upgraded SKAT texture diffractometer at the JINR in Dubna (Russia), which provides three alternative multidetector systems, resolution and accessible range of lattice d spacings can be adapted to sample requirements. In order to infer the optimum experimental setup and the reliability of texture estimates from complicated TOF patterns, the influence of counting statistics and various spectral resolutions on texture deconvolution was investigated. Comparing the results obtained at different resolutions and from different sections of the d patterns indicates that the textures of a four-phase sample can be determined, but using a section at small d spacings with a larger number of peak overlaps leads to smoother textures. A complex seven-phase sample shows orientation differences in addition to the smoothing effect. Weak textures and textures of the minor rock constituents are inaccurate owing to multiple peak overlaps. Consequently, good resolution is essential for RTA on such samples. Grid thinning tests confirmed that no more than 150 diffraction spectra are needed to characterize the texture of a monomineralic sample, and approximately 350 spectra are sufficient for a four-phase sample. The irregular grid point arrangement caused by the SKAT geometry has no negative consequences.

Description: Dependent on the ‘intrinsic’ effects on the crystal lattice of the rock constituents and the diminishing ‘extrinsic’ effects of pores and microcracks, elastic wave velocity versus pressure trends in cracked rocks are characterized by non-linear velocity increase at low pressure. At high pressure the ‘extrinsic’ influence vanishes and the velocity increase becomes approximately linear. Usually, the transition between non-linear and linear behaviour, the ‘crack closure pressure’, is not accessible in an experiment, because actual equipment is limited to lower pressure. For this reason, several model functions for describing velocity—pressure trends were proposed in the literature to extrapolate low-pressure P-wave velocity measurements to high pressures and, in part, to evaluate the ‘intrinsic’ velocity—pressure trend from low-pressure data. Knowing the ‘intrinsic’ velocity trend is of particular importance for the quantification of the crack influence at low pressure, at high pressure, the ‘intrinsic’ trend describes the velocity trend as a whole sufficiently well. Checking frequently used model functions for suitability led to the conclusion that all relations are unsuitable for the extrapolation and, if applicable, the estimation of the ‘intrinsic’ velocity trend. However, it can be shown that the ‘intrinsic’ parameters determined by means of a suitable model function, the zero pressure velocity and the pressure gradient depend on maximum experimental pressure in a non-linear way. Our approach intends to obtain better estimates of particular parameters from observed non-linear behaviour. A converging exponential function is used to approximate particular trends, assuming that the point of convergence of the function represents a better estimate of the zero pressure velocity and the pressure gradient, respectively. Whether the refined ‘intrinsic’ velocity trend meets the ‘true intrinsic’ velocity trend within acceptable errors cannot be proven directly due to missing experimental data at very high pressure. We, therefore, conclude that our approach cannot ensure absolutely certain ‘intrinsic’ velocity trends, however, it can be shown that the optimized trends approximate the ‘true intrinsic’ velocity trend better as all the other relations do.