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Crystal nucleation in Pd-Si alloysA study of the crystal phase nucleation in undercooled droplets of Pd-Si alloys with composition near the Pd(84.5)Si(15.5) eutectic composition is reported. Molten droplets are released at the top of a drop tube and solidify (to either a crystalline or glassy state) during descent. This provides a containerless (and nearly gravity free) environment so that nucleation due to container walls or vibrations is eliminated. It is found that crystallization, due to homogeneous nucleation, is bypassed in droplets of 1 mm diameter when cooled at 760 K/sec. From this an upper limit of the homogeneous nucleation rate is estimated. Results are compared with a previously published study of nucleation in 0.06 mm to 0.33 mm diameter droplets, which indicated that nucleation results from heterogeneous surface nucleation and that the number of these nuclei is dependent on the atmosphere in the drop tube.
Document ID
19830062042
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Drehman, A. J.
(Harvard Univ. Cambridge, MA, United States)
Turnbull, D.
(Harvard University Cambridge, MA, United States)
Date Acquired
August 11, 2013
Publication Date
January 1, 1982
Subject Category
Astronautics (General)
Meeting Information
Meeting: Materials processing in the reduced gravity environment of space; Annual Meeting
Location: Boston, MA
Start Date: November 16, 1981
End Date: November 18, 1981
Sponsors: NASA
Accession Number
83A43260
Funding Number(s)
CONTRACT_GRANT: NAS8-32691
Distribution Limits
Public
Copyright
Other

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