Papers by Author: Luca Lutterotti

Abstract: We illustrate the x-ray Combined Analysis approach capabilities in characterizing silicates and phyllosilicates for samples exhibiting crystallographic textures. Two mullite composite ceramics, one elaborated under uniaxial pressure the other under centrifugation, and one uniaxially pressed montmorillonite aggregate, are studied in terms of texture, cell parameters and phase contents. Several weak texture components are present in the mullite samples, combinations of planar- and fibre-like textures. The methodology is able to take account of the amorphous silica-like matrix of the composite, and cell parameters and structure of mullite correspond to the commonly modelled used for this phase. The montmorillonite turbostratic phase is correctly reproduced with its fibre texture, eventhough minor phases are also present and modelled in the aggregate.

Abstract: One of the design goals of the neutron time-of-flight (TOF) diffractometer HIPPO (HIgh Pressure - Preferred Orientation) at LANSCE (Los Alamos Neutron Science Center) was efficient quantitative texture analysis. In this paper, the effects of the HIPPO detector geometry and layout on texture analysis, particularly the shape and dimensions of the detector panels, are investigated. An aluminum sample with a strong and asymmetric texture was used to determine the methodological limitations of various methods of quantitative texture analysis. Several algorithms for extracting the orientation distribution function (ODF) from the TOF-spectra are compared: discrete orientations at arbitrary positions, harmonic method in Rietveld codes (MAUD and GSAS) and discrete methods in MAUD. All methods provide a similar representation of the main texture component, but discrete methods have a fundamental advantage over harmonic methods in characterizing regions of the ODF with low orientation densities. For HIPPO data of the present sample, harmonic expansions beyond lmax= 12 introduce subsidiary maxima and minima, which are consistently identified as artifacts. The results of our analysis establishes HIPPO as an efficient instrument to quantitatively determine preferred orientations in relatively short measuring times, if the texture features are not exceedingly sharp (full-width at half-maximum (FWHM) in the ODF > 20-30°).