Interaction of Yttria and Molybdenum with UFn gas (n = 4,6) at high temperatures
Tez Türü: Doktora
Tezin Yürütüldüğü Kurum: University of Florida, Amerika Birleşik Devletleri
Tez Danışmanı: Samim Anghaie
Tezin Onay Tarihi: 1992
Tezin Dili: İngilizce
Desteklendiği Program: Diğer
Özet:
The
work focuses on the characterization of reaction layers formed when yttria (Y2O3)
is subjected to UF6 gas firstly at 900 oC, and secondly to
UF4 gas at 1377 oC and 1477oC. Experiments were conducted under inert atmosphere
(Ar) with resistive and inductive heating respectively. Two and three consecutive layers were
observed and characterized using SEM-EDS, XRD, EMP respectively. The chemical
reactions of yttria with UF(n=4,6) vapours alongside the phase
boundaries were described. Static weight change analyses was also performed. The
velocities of moving boundaries were calculated using layer thicknesses
observed under optical microscopy. The
inner layer was composed of YOF whereas outer layer was a mixture of YF3
and UO2 following the
reaction of yttria with UF6.
In UF4 case, inner layer was again YOF, but an intermediate compact
layer of UO2 formed additionally.
The outer layer was a mixture of a eutectic matrix (YUF7 - YU10F3)
in which UO2 dendrites were dispersed throughout. Center layer
controlled inward diffusion of Uranium
and Fluorine and back diffusion of oxygen and yttrium. The reaction of yttria with liquid UF4
was much more intensive and all sample was consumed in a very short time when
dipped in liquid UF4. It was
concluded that although a stable oxide thermodynamically, yttria was not a
proper material for space power applications; however Molybdenum metal was
resistant to uranium gases under space conditions even at temperatures
exceeding 2000 oC.