Paulus Bronsveld

A study of amorphous, quasi crystalline and crystalline Al-Fe alloys by Mössbauer-effect and diffraction techniques

Abstract Amorphous Al 6 Fe, icosahedral Al-Fe and crystalline Al m Fe have been investigated by X-ray diffraction, electron diffraction and Mossbauer-effect measurements. The results show that the type and number of iron nearest neighbors is very similar in all three alloys. It is suggested that one possible explanation for the spread in Electric Field Gradient magnitudes can be the existence of holes in the aluminum network.

Twinning in θ Alumina Investigated with High Resolution Transmission Electron Microscopy

θ alumina obtained by dehydration of boehmite at about 1200°C for 3 h was investigated by HRTEM. The major characteristics of the microstructure are the multiple twinned lamellae arranged along the [001] direction. The width of these lamellae changes from half a θ alumina unit cell to several unit cells. The lamellae were observed either to form ledges along the [100] direction or to be terminated within the twinned lamellae. Polytypism resulting from repetitive twinning has been found leading to a variety of periodic arrays having a repeat along the c axis of n × 0.59 nm. The polytype with n = 2 was determined by electron diffraction to have an orthorhombic structure.

TEM study of Ti-N and Cr-N precipitate formation in iron alloys

The formation of precipitates of Ti and Cr nitrides in cold-rolled Fe + Ni(4at%) Ti(2at%) and Fe + Ni(4at%) + Cr(3at%) after a pre-nitriding step was investigated by Mossbauer spectroscopy (MS) and transmission electron microscopy (TEM). From MS data we conclude that initially most of the Ti and Cr were atomically dispersed. Using TEM and high-resolution TEM (HRTEM), we found that the Baker-Nutting (B-N) orientation relationship (OR) holds for platelets one to two interatomic distances thick, producing streaking around the (200) reflections, while for thicker pre- cipitates the Nishiyama-Wasserman (N-W) OR is more favorable. We also observed a transient phase, Cr2N, the formation of which was possible due to the relatively low nitriding temperature, a low nitriding potential, and the presence of Cr inclusions of relatively large initial size.

Single crystal X-ray diffraction of the quasi crystal Al6CuLi3

Abstract Results of a single crystal X-ray diffraction study of the quasi crystal Al 6 CuLi 3 are presented. The positions of the reflections are accurately determined, and found to be in accordance with the icosahedral point group symmetry in very good approximation. The six reciprocal axes could uniquely be assigned, and a length of 0.4203 A -1 is determined. The intensities also show the icosahedral point symmetry, but a higher symmetry, for example a 6D hypercubic space group, could not be detected in the diffraction pattern.

Quasi-crystals studied with convergent beam electron diffraction☆

Abstract Chill-cast Al6CuLi3 was studied together with roller-quenched Al4Mn and melt-spun Al7Mn2. With convergent beam electron diffraction it was established that Al6CuLi3 and Al4Mn exhibited a pentagon as the dominant Kikuchi band pattern while Al7Mn2 showed a decagon. The quasi-crystalline m 3 5 and the crystalline Im3 structures seem to occur simultaneously.

On the alleged breakdown of the Kirchhoff theory in the case of diffraction and interference by a two-dimensional array

The application of a two-dimensional diffraction array to the measurement of wire-cloth screens has been treated by Chapman and Butland (see ibid., vol.10, p.621 (1977)). Here the interference-diffraction pattern of such an array is analyzed in the Kirchhoff approximation according to the Babinet principle. It is shown that the confusion arising from the indistinguishableness of the diffraction patterns of the two complementary arrays does not involve a breakdown in the Kirchhoff theory.