Oxidation Behavior of Mo-Si-B Alloys in Wet Air Page: 4 of 9
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The mass change of Alloys 1, 2, and 3 are
shown in Figure 2. The initial mass loss of
each alloy was approximately independent
of the test temperature and moisture content
of the atmosphere. The average initial mass
losses for Alloys 1, 2, and 3 were 1.6, 7.6,
and 51 mg/cm2, respectively.
Measurements were average values based
on four samples each of Alloys 1 and 2, and
upon three samples each of Alloy 3. The
magnitude of these initial losses varied
according to the Mo content of the alloys.
Alloys 1 and 2, which both contain the
oxidation resistant T1 phase, are similar.
The higher overall Mo content of Alloy 2
(88.6 wt%) compared to Alloy 1 (84.0
wt%) contributed to a five-fold increase in
initial mass loss. Alloy 3 contains 94.6 wt%
Mo, and this contributed to a thirty-fold
increase in initial mass loss compared to
The estimated rate constants indicated the
tendency for all alloys to undergo either a
small steady state mass gain or mass loss.
The small steady state changes observed,
typically less than 5 x 10-3 mg/cm2/hr, were
not statistically significant based on the
uncertainty in the individual mass
measurements. However, these data
indicated that after the initial mass loss due
to the volatilization of MoO3, all three alloys
formed stable oxide layers that protected
each alloy from rapid mass gain or loss. Of
particular interest is the formation of a
protective scale on Alloy 3, which contains
a significant volume fraction of Mo metal.
The oxidized samples were carefully
analyzed by x-ray diffraction (XRD) to
identify scale phases. These results are
shown in Figure 3. For clarity of the
+1100 C, 600C water; SD = 0.11
A- +1 C, 40C water; SD = 0.04 i
-K-1100 *C, 20 *C water; SD = 0.12
-E-1100 C, Dry Air; SD = 0.31-
--1000 C, 400C water; SD = 0.18
-1000*C, Dry Air; SD = 0.23
0 50 100 150 200 250 300
- I' I~
50 100 150
200 250 300
- 1100 C, 60 C Water; SD = 5.66
-$-1100 C, 40 C Water; SD = 37.8
-k-1100 C, 20 C Water; SD = 7.96
-a-1100 C, Dry Air; SD = 3.50
--1000 C, 40C Water; SD = 11.7
$B1000 C, Dry Air; SD = 10.2
0 50 100 150
200 250 300
Figure 2: Mass change at 10000 and 1100 C in dry and wet
air for (A) Alloy 1, (B) Alloy 2, and (C) Alloy 3. The pooled
standard deviation for each run condition is indicated in the
graph legend as SD, and this gives an indication of the
uncertainty in the measurements.
- +1100 C, 60 C Water; SD = 0.35
B -8-1100*C, 40 C Water; SD = 1.3
--1100*C, 20 C Water; SD = 0.56
-E$1100*C, Dry Air; SD = 0.42
-G- 1000 C, 40 C Water; SD = 0.80
- E$1000 C, Dry air; SD = 1.58
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Kramer, M.; Thom, A.; Degirmen, O.; Behrani, V. & Akinc, M. Oxidation Behavior of Mo-Si-B Alloys in Wet Air, report, April 22, 2002; Iowa. (digital.library.unt.edu/ark:/67531/metadc742667/m1/4/: accessed May 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.