ORNL-1816 - the Molten Salt Energy Technologies Web Site

Oxidation and Oxidation Protection
H. lnouye J. H. Coobs
Metallurgy Division
Temporary cycling tests from 150OOF to room
temperature in air have been performedon Hastelloy
8 and other nickel-molybdenum base alloys to
determine the behavior to be expected in a NaK-to-
air heat exchanger such as will be required for
aircraft reactor application. The severest operating
condition that could exist would be a thermal
cycle from operating temperature (15OOOF) to room
temperature under stresses caused by high-velocity
air.
The cycling tests of Hastelloy B were evaluated
by daily visual examination of the test piece which
had beenthrougha heating cycle of 17 hr at 15OOOF
and then cooling to room temperature in the furnace.
Weight changes were also measured daily. In
conjunction with these tests, identically prepared
specimens were tested at a constant temperature
of 15OOOF. The results of these initial tests are
shown in Table 7.2 and in Fig. 7.1.
The results presented in Table 7.2 show that
the loss of metal from the Hastelloy B specimen
through oxide spalling was prevented by the use
of platings. In general, aluminum and aluminum
plus nickel are considered to be unsatisfactory
platings, however, because of spalling of the
protective coating.
Several other alloys have been tested for oxi-
dation at 15OOOF for comparison with Hastelloy B
and to determine whether they need oxidation
protection during elevated-temperature mechanical
and corrosion tests. The results of the tests are
shown in Fig. 7.2.
PERIOD ENDING DECEMBER 10, 7954
At a constant elevated temperature in air, nickel-
molybdenum alloys of intermediate compositions
form a protective coating of NiMoO,. Upon cooling,
regardless of the rate, the coating will spalll vigor-
ously at temperatures between 440 and :23OoF.’
Experimental evidence shows that this spalling
may be due to a change in the crystalline structure
of the NiMoO, coating.
Radiator Fabrication
P. Patriarca K. W. Reber
R. E. Clausing G. M. Slaughter
Metal I urgy D i vi sion
J. M. Cisar
Aircraft Reactor Engineering Division
R. L. Heestand
Pratt & Whitney Aircraft
A series of test specimens of Hastelloy B radi-
ators has been fabricated for use in evaluciting the
ability of Hastelloy B to withstand thermal shock
and oxidation. A specimen that includes approxi-
mately 3 in. of Inconel-clad copper fins spaced
15 fins per inch is illustrated in Fig. 7.3.
The 20 tube-to-header joints were inert-arc
welded by using the semiautomatic welding equip-
ment described previously.* The manifolds were
manually inert-arc welded, and the assembly was
brazed to effect the tube-to-fin joints and the
l
J. W. Spretnak and R. Speiser, Protection of Molybdenum
Against Corrosion ut High Temperatures,
Ohio State University Research Foundation Status
Report No. 8.
2P. Patriarca et al., ANP uar. Prog. Rep. June 10,
1954, ORNL-1729, Fig. 6.5, ~$6.
Surface Condition
Aluminum spray + 0.0370 Spalled