We have measured the rate of diffusion of aqueous CuSO₄ into pure water across a free liquid interface both on the ground and in 'microgravity' aboard the STS-43 mission of the Space Shuttle. Because both experiments were carried out under isothermal conditions with the CuSO₄ solution on the bottom and the pure water on the top, there was no obvious source of buoyancy. Moreover, the expected decrease in the diffusion coefficient due to hydrostatic pressure diffusion of CuSO₄ was two orders of magnitude less than the experimental error, which was 3-4 percent. Thus, within this error, our experiments show that there is not effect of gravity on diffusion in the case of a gravitationally stabilized, isothermal liquid. This is in contrast to the results obtained by others using melts under non-isothermal conditions where effects as large as 10 percent have been reported.

Date Published: 12 July 1996
PDF: 3 pages
Proc. SPIE 2809, Space Processing of Materials, (12 July 1996); doi: 10.1117/12.244336

Published in SPIE Proceedings Vol. 2809:
Space Processing of Materials
Narayanan Ramachandran, Editor(s)