Use of the Raman Microscope to elucidate the structure of solid salt eutectics.

 

R.W.Berg and D.H.Kerridge, Chemistry Dept, Technical University of Denmark, 2800 Lyngby, Denmark.

  The Raman microscope has proved to be a power ful technique for understanding the structures of salt eutectics solidified from their melts.

  Computer images of sections across the solidified eutectics will be shown which indicate that there is considerable structural similarity in all the binary and ternary eutectics so far examined. These structures are best described as a “conglomerate” arrangement of small, roughly rounded zones, measuring in the section between 0.5 and 5 microns across with compositions alternating between the component solid solutions.

  Thus a very considerable area of contact occurs between each of the solid solutions and this high “interphasial” area in all the eutectics so far examined is considered to be the cause of unexpectedly high electrical conductiveity of the solid eutectics found for all 14 systems so far measured [1,2]. These conductivities are about two orders of magnitude higher than the extrapolated values of the ocmponent single salts.

  This high “interphasial” area is also considered to be responsible for an additional term found in the melting enthalpy diference between solidified salt eutectics and unmelted mechanical mixtures of eutectic composition. This latter, hitherto unused, paramenter also gives the compositions of limiting solid solutions and asimpler method of determining their enthalpies of formation [3,4].

 

1.       E.I.Eweka and D.H.Kerridge, Phys Lett A 174 441 1993

2.       E.I.Eweka, Ph.D.thesis, University of Southampton, 1992

3.       M.Gaune-Escard and D.H.Kerridge, “Advances in Molten Salts”

M.Gaune-Escard Ed, p 270, Begel1 House Inc, New York, 1999, ISBN-567000-142-4

4.       D.H.Kerridge, “Proc Int G Papatheodorou Symp”, S Boghosian, V.Dracopoulos, C.G.Kontoyannis and G.A.Voyiatzis Eds, p 89, 19999, ISBN-960-7839-01-3