Chemistry update

[Fred56]

Reports

In Situ Determination of the Nanoscale Chemistry and Behavior of Solid-Liquid Systems

Santhana K. Eswaramoorthy,1 James M. Howe,1* Govindarajan Muralidharan2

 

Many fundamental questions in crystal-growth behavior remain unanswered because of the difficulties encountered in simultaneously observing phases and determining elemental concentrations and redistributions while crystals nucleate and grow at the nanoscale. We show that these obstacles can be overcome by performing energy-dispersive x-ray spectroscopy on partially molten Al-Si-Cu-Mg alloy particles during in situ heating in a transmission electron microscope. Using this technique, we were able to (i) determine that the aluminum and silicon concentrations change in a complementary and symmetric manner about the solid-liquid interface as a function of temperature; (ii) directly measure the solid- and liquid-phase compositions at equilibrium and in highly undercooled conditions for quantitative comparison with thermodynamic calculations of the liquidus and solidus phase boundaries; and (iii) provide direct evidence for homogeneous nucleation of the aluminum-rich solid.

 

1 Department of Materials Science and Engineering, University of Virginia, 140 Chemistry Drive, Charlottesville, VA 22904–4745, USA.

2 Materials Science and Technology Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831–6132, USA.

 

* To whom correspondence should be addressed. E-mail: jh9s@virginia.edu

 

-Science 30 November 2007:

Vol. 318. no. 5855, pp. 1437 - 1440

DOI: 10.1126/science.1146511