Nucleation Statistics of Nb and Zr Under Various Drop Tube Processing Conditions
A series of undercooling experiments using pure metal samples of niobium and zirconium were performed using the MSFC 105 meter drop tube, and for zirconium using both electromagnetic and elctrostatic levitation in the laboratory. The results from a large number of experiments allowed nucleation frequencies to be measured, following the suggestion of Skripov. Using the nucleation frequencies, the nucleation probability distributions and the cumulative distributions, the critical free energy of nucleation and the magnitude of the pre-exponential in the classical nucleation equation were determined. The results for the pre-exponential and critical free energy for zirconium ranged from 10^8 to 10^13 and 15 kT to 24 kT respectively. Higher purity zirconium stock was observed to cause significant shifts in the undercoolings to higher values. For niobium the values were 10^31 and 73 kT for the pre-exponential and the critical free energy, respectively.
Curator: Tom Rathz/UAH tom.rathz@msfc.nasa.gov
Principal Investigator: William Hofmeister/Vanderbilt hof@vuse.vanderbilt.edu