NEUTRON DIFFRACTION STUDIES ON INDUSTRIAL MATERIALS

Neutron diffraction can be a valuable tool in the study of industrial materials because of a)sample size in relation to industrial scaling; b)neutron penetration through machinable metals, and consequent ease of construction of environmental chambers; c)neutron atomic contrast (e.g. scattering by Al or Si); and d)magnetic scattering possibilities. Four examples illustrating points (a)-(c) will be given in this paper. The first example involves the high temperature solid state synthesis of a zeolitic pigment, ultramarine. A dynamic diffraction study of the process is difficult since the radiation must penetrate beyond the “surface” 10 mm where excess boiling of sulphur takes place: such a study is however possible with neutron radiation. Because of the differing neutron atomic scattering lengths of Al and Si, neutron Rietveld refinement has been able to distinguish between two alternative schemes of Al,Si-site occupation on the sodalite cage. The unique and surprising result found is that ultramarine, with Si/Al ∼ 1, displays a random (non-Loewenstein) occupation of the Al,Si-sites. This prompts the question as to why most zeolites appear to be otherwise. Thus interesting (dynamic) experiments have been devised, involving both solid state and hydrothermal pathways, to investigate the kinetic aspects of zeolite synthesis. One of the exciting outcomes from this pursuit has been the construction of an autoclave cell for time-resolved neutron diffraction studies: its application to the synthesis of zeolites and autoclave-curing of cements will be described.