A reference sample of sepiolite and products of its comminution by vibrating dry-milling have been studied using X-ray diffraction (XRD) line-broadening analysis, complementary field emission scanning electron microscopy (FESEM) images and surface area measurements. The apparent crystallite sizes determined via XRD are in agreement with observations on FESEM images. The sepiolite aggregates consist of lath-shaped agglutinations of prisms and pinacoids elongated along [001], each lath including several crystallites in that direction. The surface area magnitudes are in the range of previous experimental measurements of other sepiolites. The results obtained show the effectiveness of vibro-milling as the procedure to use for the comminution of sepiolite.

Due to the great technological importance of the microstructure of kaolinite, characterizing its evolution during dry milling of kaolin and analyzing the microstructural information obtained from different methods were the main aims of this work. The microstructural alteration of kaolinite is evaluated by X-ray diffraction and electron microscopy methods, comparing the results obtained and analyzing the correlations between them. The Warren-Averbach and Voigt-function methods of X-ray diffraction microstructural analysis have been applied successfully to the study of the effects of two different, vibrating-cup dry-milling configurations in the microstructure of kaolinite from the reflections corresponding to (001) diffracting planes. The crystallite-size estimates obtained from the two methods correlate well. Field emission scanning electron microscopy measurements of kaolinite particle thickness are in good agreement with the crystallite size estimated by the two methods. The Warren-Averbach method also provided estimates of the contribution to line broadening. Vibrating-cup milling has been proved to be a more efficient method of strain comminution of kaolinites than other milling techniques, reaching extensive microstructural degradation within seconds.

Chromite grains in ores from the Great Dyke, Zimbabwe, exhibit varying degrees of shearing when viewed by optical microscopy. High resolution diffraction data revealed that line broadening from powder samples of sheared chromites is largely due to two or more spinel phases with slightly different cell parameters, the number of phases increasing with the degree of shearing. The dominant or “parent” phase, with parameters ranging from 8.3123(2) to 8.2676(2) Å, constitutes 57% to 76% of most samples. The cell parameters of secondary phases are generally less than that of the parent phase by δa/a0 in the range −1.3 to −4.0×10−3, the difference again tending to increase with shearing. Most reflections for the parent phase are relatively sharp whereas those for the secondary phases exhibit line broadening that could be analyzed in terms of crystallike (domain) size and rms strain. The crystallite diameters, assuming spherical particles, are relatively large for the parent phases [260(2)–100(5) nm], while those for the secondary phases range from 165(70) to 70(25) nm. The rms strain is not large for any sample and is negligible or small for the unsheared and weakly sheared material. The microstrain in secondary phases is greater than that in the parent phase and tends to increase with shearing, the maximum rms strain being 1.6(3)×10−3. Two new forms of chromite in highly sheared material are reported, one with a slight (0.33%) tetragonal distortion and the other with a cell parameter of 17.561(2) Å, greater than that of normal spinel chromites by a factor of about 3/√2, and a lowering of symmetry from Fd3¯m to Fm3¯m. Changes in chemical composition, indicated by a range in cell parameter, are attributed to tectonics that affected much of the Great Dyke. The strain is partitioned between failure by brittle deformation of the chromite grains and stress-induced cation migration leading to cells with slightly different composition.

Two different approaches for studying sample’s contributions to diffraction-line broadening are analyzed by applying them to several nickel hydroxide samples. Both are based in the refinement of powder diffraction data but differ in the microstructural model used. The first one consists in the refinement of the powder diffraction pattern using the FAULTS program, a modification of DIFFaX, which assigns peak broadening mainly to the presence of stacking faults and treats finite size effects by convolution with a Voigt function. The second method makes use of the program FULLPROF, which allows the use of linear combinations of spherical harmonics to model peak broadening coming from anisotropic size effects. The complementary use of transmission electron microscopy has allowed us to evaluate the best approach for the Ni(OH)2 case. In addition, peak shifts, corresponding to reflections 10l (l≠0) were observed in defective nickel hydroxide samples that can be directly correlated with the degree of faulting.

A comparison of different methods of X-ray diffraction analysis for the determination of crystallite size and microstrain; namely, line profile analysis, Rietveld refinement, and three approaches based on the variance method, is presented. The analyses have been applied to data collected on a ceria sample prepared by the IUCr Commission on Powder Diffraction. In the variance method, split Pearson VII, the Voigt function, and its approximation pseudo-Voigt function were fitted to X-ray diffraction line profiles. Based on the fitting results, the variances of line profiles were calculated and then the crystallite size and root mean square strain were obtained from variance coefficients. A SS plot of Langford as well as a Fourier analysis and Rietveld refinement have been carried out. The average crystallite size and microstrain were determined. The values of area-weighted domain size determined from the variance method are in agreement with those obtained from line profile analysis within a single (largest) standard uncertainty, and the volume-weighted domain sizes derived from the SS plot, Fourier size distribution, and Rietveld refinement agree within a single standard uncertainty. The results of rms strain calculated from variance and Pearson VII shape function and those from Rietveld refinements fall within a single esd. However, the variance method in conjunction with pseudo-Voigt and Voigt functions produce rms strains substantially larger than those determined from line profile analysis and Rietveld refinements.

We analyze time series scans of the solar limb performed by the spectrometer SUMER on-board the SoHO satellite. The analyzed dataset consists of observations obtained in the C III 977 Å line. After applying the standard SUMER data reduction procedure, we perform a one line Gaussian fit to the profiles to obtain different parameters for each pixel within the scans. Studying the variations of the line width from the disk to the limb and off-limb we find that it increases off-limb and shows a peak at $\sim15\prime\prime above the limb. We suggest that this increase is due to the random directions of several spicules found along the line of sight.