XRD investigation on structural aspects of Indium melting

During melting of polycrystalline Indium the structure of solid and liquid phases have been investigated by X-ray diffractometry (XRD) in I-g conditions. At melting point a re-orientation of crystalline grains occurs in the solid phase. The texture change, unusually rapid for a thermally activated process, is attributed to an abnormal increase of vacancy concentration. This explanation is in agreement with the observed shifts of XRD peaks towards lower angles. As a consequence of the texture change, the lattice planes facing the first formed liquid are (002) and (101) planes, i.e. those planes allocating Ist and 2nd neighbours around a given atom with shell radii very close to the mean distance of nearest neighbours in liquid as obtained from the radial distribution function (RDF). Convective motions in the liquid can be eliminated by repeating in mu -g the same XRD measurements. To get the best experimental conditions it is discussed the possibility to use thin oxide films grown on the external surface of samples as containers during melting. Present investigators have successfully tested this technique in the experiment ES 311 A-B carried out during the mission SPACELAB-1.