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ORNL P
1260
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1.0
1.25 L4 LE
MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
Феүi Jно

0.581 - AIC - OFFICIAL
JUN 24 1968
THE DECOMPOSITION RATES OF CERIA IN VACUUM
BETWEEN 1100 AND 1700*
CESTI PRICES
OENLAIC-OFFICIAL
NOT
RELEASE - OFFICIAL
H.C. $1.00 ; MN 50
-
Coi
vuot tu .
"
-
"
Henry Inouye
Metals and Ceramics Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee
wemasompa 2: JURIS 'ON FILE IN RECEIVING
SECTION.
Ceria exists as a single nonstoichiometric phase between Ce02.00
and Ce01.72 at temperatures above 665°C. Retireen these composition limits
the oxygen dissociation pressure decreases in several orders of magnitude.
For example, at 1169°C the dissociation pressure oi Ce01.98 is approximately
10-8 atm and decreases to 10-17 atm at Ce0-.12. (ref 1)
Although the above data predict that ceria compositions near Ce02.00
will decompose in vacuums of the order of 10-20 atm, the kinetics of the
decomposition are not known. The purpose ci this study was to measure the
decomposition rates between 1100 and 1200 °C at pressures of approximately
10 -20 atm and from the i’esults to estimate the rates for temperatures as

high as 1700°C.
RELEASED FOR ANNOUNCEMENT
PROCEDURE
IN NUCLEAR SCIENCE ABSTRACTS
The ceria was supplied as pellets 0.250 in. in diameter and 0.20 in.
1
long which weighed approximately 0.76 g each. The sample was placed on a
platinum pan which was in turn suspended irom one arm of a Sartorius micro-
balance. The pellet was brought to temperature at a system pressure of
0.3 to 0.5 torr of air to avoid premature decomposition. While heating
to the test temperature, the pellet lost weight but stabilized at a con-
stan value after a few hours at temperature. This weight was taken as
the starting weight of the specimen.
ORAL - AEC - OFFICIAL
*Research sponsored by the U.S. Atomic Energy Commission under contract
with the Union Carbide Corporation.
ORN! - AIC - OFFICIAL
ay naman ang arawer management options
The test commenced upon decreasing the pressure. Within 15 min of
activating the diffusion pumps the pressure was lowered from approximately
0.3 to 10-5 torr and was in the low 10-6 torr after filling a liquid
O!!!1 - AIC - OFFICIAL
nitrogen cold trap and 1 hr of operation. The specimen weight change was
continuously recorded ană could be read within +10 ug. After this high
vacuum exposure, the specimen was reoxidized with air by increasing the
system pressure to between 0.3 ana 2.5 torr.
RESULTS
The weight losses recorded for three separate pellets at 1100, 1150,
and 1200°C and in vacuums from 1 x 10-7 to 2 x 10-6 torr (1.3 x 10-20 to
:
2.6 x 10-9 atm) are shown in Fig. 1. The test at 1200°C was repeated by
reexposing the oxidized pellet used for the initial run to the high vacuum.
The reproducibility in this test was excellent (solid circles). These
curves show that the decomposition rates of ceria increase with temperature
but decrease with time. As these tests progressed, an unidentified
brownish deposit developed in the cooler parts of the furnace. This obser-
vation, plus the fact that the pellet weight was not restored to its original
value upon reoxidation in 0.3 torr air, indicates that some vaporization
occurred under the test conditions.
The de composition rates can be expressed by equations in which the
weight change is a function of time to an exponent. The exponent, n, was
determined to be 0.45, 0.49, and 0.60 at 1100, 1150, and 1200°C, respectively,
with an average value of 0.51. Therefore, the rate equation can be written 8.3:
Aw = kt2/2,
Tri viisi-ir-irido
where
OXYL-AI-OPFICIAL
Aw = weight loss (ug• cm“?)
t = exposure time (hr)
k = decomposition ratr, constant ligocm- hr-/2)
Plots of Aw vs t1/2 were straight lines with slopes of k as shown in Fig. 2.
From a log k vs 1/t plot, k values for several temperatures were estimated
and are tabuiated in Table 1.
CONCLUSIONS
The present results show that the decomposition rates of ceria in
vacuums are proportional to t1/2 and increase exponentially rith temperature:
OKNL - AEC - OFFICIAL
RETERENCES
ORHE-AEC - OFFICIAL
2D.J.M. Bevan and J. Kordis, "Mixed Oxides of the Type Moz (Fluorite) – M203.
I: Oxygen Dissociation Pressures and Phase Relationships in the System CeO2-Ce203
at High Temperatures," I. Inorg. Ivucl. Chem. 26(9), 1509–1523 (1964).
ORNI – AEC - OFFICIAL
torr.
1700
1500
1400
1300
1200
1150
1100
(°C)
Temperature
& In vacuums of approximately 10-6
Ceria at Various Tenperatures
Table I. The Decomposition Bates of
105
2850
204
690
123
63
Rate Constant - k
lugaroom-2.n-1/2*
20
OkiXl-AEC-OFFICIA!
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FIGURE LEGENDS
ORHL-AEC - OFFICIAL
Figure 1.
The Thermal Stability of Cerium Oxides in Vacuums of
10-6 to 0.3 Torr.
Figure 2. The Decomposition Rates of Ceria from 1100 to 1200°C.
ONL - AEC - OFFICIAL
.
UNCLASSIFIED
ORNL-DWG 64-11477
(x10

ههههههههههههههه
1100 °C
Assistastaas saskaras
200 ug/cm2 AT 125 hr
**
0.020
bonbondow Ad
1150 °C
22.000
d
ed 'Ammindesberg
WEIGHT CHANGE (149/cm2) :
0.3 torr AIR ADDED
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soome noooooooooo
yen
1200 °C
ocorotonpost
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0
10
20
30
0.3 torr AIR ADDED T
40 50 60 70 80
TIME (hr)
90
|
UNCLASSIFIED
ORNL-DWG 64-11476

p
lasma memandangan, mandarina matat
1100 °C
andan sonra da desta tend
Santos
k=-20
M
_692902600200
1150 °C
WEIGHT CHANGE (p g/cm2)
k=-63
co 1200
cm
oporoordanoqonood
k=-123
1
2
3
4
5
6
7
8
9
figal

END
LA
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DATE FILMED
5 / 12 /66







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