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mary of paper to be presented at American Nuclear Society Symposium on
"Vapor It üsition Techniques for Fabrication of Fuels and Refractory Metal
Tubing" in San Francisco, California, November 30 to December 3, 1964.
.
CONF-654-9
A
.
TECHNIQUES FOR DEPOSITION AND SYSTEMATIC STUDY OF
PROPERTIES OF PYROLYTIC CARBUIN ON CERAMIC
FUEL PARTICIES*
MASTER
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:
AUG 1 3 1964
EXT-
R. L. Beatty, J. L. Cook, and
F. L. Carlsen, Jr.**
Metals and Ceramics Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee
.
4. RT1
Techniques have been developed for fluidized-bed coating of carbide
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and oxide fuel particles with pyrolytic carbon at temperatures to 2000 C
under precisely controlled conditions. Systematic studies of the effects
of deposition conditions on coating properties were accomplished using
either Sic or graphite resistance-heated furnaces. The particles were
coated in graphite tubes 3/4 in. or l in. I.D., with 30° included-angle
nozzles and the heating elements and gas-entrance ports of the nozzles
were positioned so as to minimize the variation of temperature in the
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beds. Temperature control was based upon calibrations of tube temperature
(monitored during operation) with measurements of the true bed temperature.
Detailed evaluation of the coated particles included coatins density
TË
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measurements, electron microscopy and diffraction, and determination of
*
such crystallographic parameters as interlayer spacing, Co, apparent
crystallite size, Ic, and preferred orientation by x-ray diffraction.
115
*Research sponsored by the U. S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
**Sponsored by W. 0. Harms, member ANS.
-LEGAL NOTICE
Q
MOT FOR PUBLIC RELEASE - OFFICIAL
DISTRIBUTION MAY BE MADE. OFFICIAL
REQUESTS MAY BE FILLED. REPORT
CONTAINS NOTHING OF PATENT INTEREST
PROCEDURES ON FILE IN RECEMMS.
SECTION

24
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Terjerature of applicacion is a dominant coating variable in
that it aifects -... measurable properties of the coatings. For
example, the apparent crystallite size increases and the strength
decreases with increasing coatină temperature. Coating density
passes through a minimum in the intermediate temperature range.
Another major variable, though not an independent one, is deposition
rate.
This rate is contro led by the temperature of the fluid bed,
the temperature of the fluidizing gas, tine hydrocarbon gas flow rate,
and the setioce area of the charge being coated.
The importance of methane partiai pressure and average deposi-
tion rate on the properties of coatings applied at 1400 C is shown
in Fig. 1. In these experiments, the fuel particles consisted of
dense uranium dicarbide, 150-2504 in diameter, and the average
coating thickness was 50u. The total flow rate of methane plus
helium (760 cm3/min), initial charge size (10 6), and volume of car-
bon deposited were held constant. The inside diameter of the re-
action vessel was 3/4 in. Density was measured by a helium pycnometer
-
technique and values of C. and L, were determined by refined x-ray.
diffractometer methods. Preferred orientation was evaluated by the
technique described by Bacon
on coatings stripped from small
graphite disks included in the fluid-bed coating runs after the
method used by Bokros." In this technique a pole figure is derived
Ko
in the form of the integrated intensity, I(6), of the (002)
reflection as a function of the inclination angle, ø, relative to
the normal of the deposition plane. This functional relationship
is approximated by cosy, where the anisotropy parameter, M, is

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DEPOZITION RATE (u/hr)
50 100
' COATING DENSITY I
A CRYSTALLITE SIZE, Lc.
A ANISOTROPY PARAME
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COATING DENSITY (g/cm3)
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INTER LAYER SPACING, CA (A)
CRYSTALLITE SIZE, LE (A)
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M1 (0oz / Cox = M+1)
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500
1000
50
100 200
METHANE PARTIAL PRESSURE (mm)
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Effect of Methane Partial Pressure on Properties of 50.4-thick Pyrolytic Carboil Coatings
Deposited on Spheridal Uranium Carbide Particles in a Fluidized Bed at 1400°C.
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Higure 1. Effect of Methane Partial Pressure or Properties of 50-4- thick
Pyrolytic Cazdon Coatings Deposited on Spheroidal Uranium Carbide
Particles in a Fluiäized Bed at 1400°C.
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related to the Bacon anisotropy factor, Coz/ooxs by 0oz/Cox = M + 1.
It is of interest to note that coniitions which gave a minimum in
density and in Lc yielded a coating with maximum anisotropy, and
that essentially random orientation was obtained at average deposi-
tion rates greater than about 30u/hr.
Electron diffraction and transmission microscopy studies
showed that the as-deposited coatings consisted 01 turbostratically
stacked monolayers having the hexagonal graphite structure with a
basal-plane crystallite size, La, of approximately 100 A. LOW
density dieposits contained microvcids approximately 100 A in diameter
and the density of the microvoids increased as the coating density
decreased.
There was no significant change in I, with density.
i
1. Carlsen, F. L., Jr., et al., "Development of Fueled Graphite Con-
taining Pyrolytic-Carbon Coated Carbide Particles for Nonpurged,
Gas-Cooled Reactor Systems." (To be published in Nuclear Science
and Engineering.)
2. Cools, J. L., et al., ÜCR Program semiann. Frogr. kept. Mar. 31,
1963, ORNL-3523, pp. 103-06.
3. Bacon, G. E., J. Appl. Chem. 6, 77-81 (1956).
4. Bokros, J. C., Private Communic tion.
5. Stiegler, J. O., et al., An Electrin Optical Study of Structural
Features of pyrolytic Carbons, ORNL-IM-863 (in press).
Features of jyro
ytic Carbons, ORNL-T
****
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DATE FILMED
1/ 1865
.
11
-LEGAL NOTICE
The report was prepared M M sacows of Government sponsored work. Metters the United
Satos, nor the Commission, nor any person acting on ball of the Coundon:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or wefulness of the tutormation contained to me report, ur that the we
of my tabormation, apparatus, method, or process dlaclavad to the report may not Infringe
privately owned rights; or
B. Ammos y Mantuities of the rompect to the we of, or for d ecorating from the
undang tuloration, appuntu, method, or process dlachend to the report.
As wood la the abovo, "pernou actug au bohall of the conteston" Includes my a-
ploym or contractor of the Commington, or aployee of mucha contractor, to the ocent that
much employee of contractor of the Companiesdon, or anployw dl woch contractor preparea,
diewentualns, or provide recome to my hotormation part to his employment of contract
with the Commiston, or wo employment with me contractor.
-
END
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