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Download fileFluoridation of HfO2
journal contribution
posted on 05.03.2021, 17:07 authored by Steven Flynn, Chi Zhang, Kent J. Griffith, Jiahong Shen, Christopher Wolverton, Vinayak P. Dravid, Kenneth R. PoeppelmeierFluoridation of HfO2 was
carried out with three commonly
used solid-state fluoridation agents: PVDF, PTFE, and NH4HF2. Clear and reproducible differences are observed in
the reaction products of the fluoropolymer reagents and NH4HF2 with the latter more readily reacting in air. Strong
evidence of distinct, previously
unreported hafnium oxyfluoride phases is produced by both reactions,
and efforts to isolate them were successful for the air-NH4HF2 reaction. Synchrotron XRD, 19F NMR, and
elemental analysis were employed to characterize the phase-pure material
which appears to be analogous to known Zr–O–F phases
with anion-deficient α-UO3 structures such as Zr7O9F10. Comparison with the hydrolysis
of β-HfF4 under identical conditions depicts that
the NH4HF2 route produces the oxyfluoride with
greater selectivity and at lower temperatures. Thermodynamic calculations
were employed to explain this result. Potential reaction pathways
for the NH4HF2 fluoridation of HfO2 are discussed.