SUPERCOOLING OF LIQUID-METAL DROPLETS FOR X-RAY-ABSORPTION-SPECTROSCOPY INVESTIGATIONS

A sample preparation technique, suitable for x-ray-absorption measurem ents of liquid and supercooled metals is described. The method is base d on an application of the emulsion technique, consisting in a dispers ion of micrometric droplets in an inert rigid matrix. It has been appl ied to Hg and Ga resulting in a very fine average droplet size in the submicrometer range. A theoretical probabilistic model, confirmed by e xperimental data, suggests a log-normal droplet-size distribution. The supercooling capabilities of the samples are studied by means of x-ra y-absorption near-edge structure measurements showing exceptional supe rcooling rates: 153 K for Hg and no crystallization at all for Ga down to 34 K. The problem of a quantitative study of the x-ray-absorption fine structure is addressed and the nonlinearity in the absorption mea surements induced by the nonuniform thickness distribution discussed. A method to calculate the sample metal thickness distribution and to d erive the actual absorption coefficient is presented.