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MoF3 e h l o
.... ~~ .... Mo
t MoF,
This scheme allows the molybdenum to be "trapped"
in the trivalent state until the source of MoF, is
removed. Then the molybdenum i s converted to the
metal by the above rcactions, which continue to
produce the volatile MoF, at a decreasing rate
until the process is complete. Attention is now
being given to experimentally checking this hy-
pothesis with molybdenum concentrations in the
ppm range.
11.3 MASS SPECTROMETRY OF
MOLYBDENUM FLUORIDES
R. A. Strehlow J. D. Redrnan
'The volatilization behavior of molybdenum and
other fission product fluorides in the MSRE has led
to a study of molybdenum fluorides. Mass spectrometrically
derived information is of particular value
in studies involving volatilization, since, at least
in principle, the vaporizing species are analyzed
with a minimum time lapse. This gives an opportunity
to observe some transient phenomena and to
distinguish among various oxidation states and impurities
which may be present.
The work so far has been concerned with the mass
analysis of vapors from three molybdenum fluoride
samples. The first objectives were to assess
144
material purity and to establish the mass spectrometric
cracking patterns for these materials which
have not previously been subjected to mass analysis.
The three samples are designated and described
in Table 11.1.
Sample I, during an increase of temperature from
400 to 725"C, yielded first MoO,F, at the lowest
temperature. As the temperature was increased, the
peaks associated with this species decreased in
magnitude and a family of peaks attributed to
MoOF, appeared. Near the upper limit of the temperature
excursion, a mass peak family was ob.
served which is attributed to MoF, and MoF vapor
species. The large amount of volatile oxides indicated
that an oxidation-hydrolysis had occurred
and that better, or at least fresher, material was
needed. A somewhat increased amount of mass 96
was obseived from this sample, which is attributed
to orthosilicic acid (H,SiO,) rather than to the
molybdenum, since its peak height was not a constant
multiple of the other Mo' peak heights.
Sample 11, MoF,, was prepared by C. F. Weaver
and H. A. Friedman and was heated in the Knudsen
cell inlet system of the Bendix time-of-flight mass
spectrometer. 'The compourid MoQ,F was not observed,
but some MoOF, was evident (along with
the usual SiF3,2,1 ions) at teinperatuies as low as
350°C. Beginning at 275'1c, MoF,', MoF,',
MoF3+, MoF ', and MoF+ were also observed. The
It
MoF,+/MoF, peak height ratio was about unity,
indicating some MoF, as well as MoF, (or MoF,).
We have insufficient evidence to demonstrate that
MoF4 has been part of our sampled vapor. At tern-peratures
greater than 600"C, only fluoride species
were observed. The spectra for sample I1 at temperatures
of 250, 300, and 725OC are shown in
Fig. 11.1. A photograph of an oscilloscope trace of
Table 11.1. Mass Analysis of Vapors from Three Molybdenum Fluoride Somples
Sample
Nominal
Cumpusition
Source
I
I1
111
MoF Exposed to air fur D. E. LaValle, Analytical Chemistry
several years
Division
MoF Recent synthesis C. F. Weaver and H. A. Friedman,
Reactor Chemistry Division
MoF' , Recent synthesis C. F. Weaver and H. A. Friedman,
Reactor Chemistry Division