Papers by Author: Christian Scheffzük

Abstract: Strain/stress experiments for characterization of micro- and macro-strain distribution and texture experiments were carried out on a varistor ceramic using neutron-TOF-diffraction. By a radial strain scan, residual strain has been determined on the (1010 ), (0002), (1012), and (1120 ) Bragg reflections of the hexagonal ZnO as well as on the (400) reflections of the cubic spinel Zn7Sb2O12. Residual strain values in the range of -1.5x10-4 (contraction) and 4x10-4 (dilatation) were observed for ZnO, with indications of macro-strains across the cylindrical sample and substantial micro-strains between the different phases. The texture on both phases (ZnO, Zn7Sb2O12) is characterized by a weak, non-ideal fibre texture around the cylinder axis. The results indicate that the texture pattern might coincide with the strain. To our knowledge, these are the first texture and residual strain investigations in metal oxide varistor elements and they will be discussed in detail.

Abstract: An anhydrite-dolomite rock was investigated in order to find correlations between intracrystalline strain and texture. The sample represents a composite rock, called Zuckerdolomit, occurring for instance in the central Alps. Zuckerdolomit may occasionally respond to mechanical impulses with a complete break down of its structure. Residual strain was scanned at the strain/stress diffractometer EPSILON-MDS and the crystallographic texture was obtained by neutron time-of-flight diffraction at the texture diffractometer SKAT at the pulsed neutron source IBR-2 in Dubna, Russia. Texture was additionally determined by the U-stage microscopy. The texture of the rock could be derived from the main constituents: anhydrite and dolomite. The anhydrite texture appears to be characterised by an orthorhombic symmetry. One plane of the symmetry trends parallel to the rock’s foliation plane, with basal planes subparallel to and a small circle distribution within the foliation plane. There is a subordinated small circle orientation pattern relating in 45° to the rock’s foliation plane. On the other hand, the subordinated regulation pattern of anhydrite is fixed to the orientation of the foliation plane. The determined residual strain data for anhydrite and dolomite reflect a generally opposed directed state, regarding both, compression and dilatation. Moreover, taking into account the elastic constants for both minerals, which differ approximately by the factor two, the special geomechanical behaviour of the studied Zuckerdolomit appears to be considerably determined by interactions between its residual strain and textural properties. This may be of particular importance for underground activities (mining, tunnelling etc.). The dangerous geomechanical behaviour of the rock seems to be determined by its residual straintexture relations more than so far believed (anhydrite hydration).

Abstract: This paper describes the modernized diffractometer EPSILON-MDS for strain measurements of geological samples by means of neutron diffraction with the time-of-flight method. The diffractometer is characterized by a long flight path in order to get a good spectral resolution and by a multi-detector system for efficient data acquisition.