ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPOR7
transfer to occclr. As may be seen in Table 6.12,
hydrogen and the unsaturated oxygen ions are most
important for the hydroxides of potassium, rubidium,
and cesium.
Furthermore, these computations provide the first
estimate of the thermal stability of the alkali-metal
hydroxides (other than LiOH). These estimates
confirm the frequently made assumption that the
alkali-metal hydroxides are by far the most thermally
stable hydrogen-containing liquids known.
It must be emphasized that these computations
are given as a progress report in a continuing in-
vestigation. Thus, many of the values obtained,
such as the standard free energies of formation, do
not in themselves provide direct information about
hydroxide corrosion, but they are essential values
for any theoretical investigations of corrosion.
Experimental Studies (with M. E. Steidlitz, MetaI-
lurgy Division). An investigation is under way to
determine experimentally whether a significant
amount of hydrogen is liberated when NaOH is
heated to 900°C in an inert environment. The pre-
liminary method being tested is to use a pair of
automatic Toepler pumps to concentrate any gaseous
products liberated from the hydroxide. The col-
lected gas is analyzed with a mass spectrometer.
The most difficult aspect of this research has been
the endeavor to provide an inert container for the
NaOH, which reacts with all metals studied at
900°C (including the most noble metals) to pro-
duce hydrogen. It reacts strongly with nearly all
teromics except magnesium oxide. Unfortunately,
nonporous crucibles of pure MgO are not available
because of the difficulty in sintering this material.
Ordinary Mg0 crucibles, which usually contain a
small amount of binder such as silica, break down
due to attack on the binder. The problem was
solved by machining out large single crystals of
pure magnesium oxide prepared by the Ceramics
Group.
In the experiments which have been performed
to date, appreciable quantities of hydrogen have
been found in addition to much ,larger quantities of
water. However, there was evidence of contamina-
tion by organic material and the hydrogen may have
come from this source. These studiesare continuing,
13H. J. Buttram et ai., ANP Qum. Prog. Rep. J7mp 10,
1954, ORNL-1729, p 63.
108
CHEMICAL STUDIES OF CORROSION
F. Kertesz
Materials Chemistry Division
Effect sf Temperature on Corrosion of
Inconel and Type 316 Stainless Steel
H. J. Uuttram R. E. Meadows
N. V. Smith
Materials Chemistry Division
The effect of temperature on the corrosion of
lnconel by molten fluorides in static tests, as
indicated by the extent of void formation observed
and by chromium concentration of the melt, was
discussed in a previous report.13 In those studies
there was some evidence that a maximum in the
corrosion could be observed at 800 to 900°C and
that both void formation and chromium concentration
in the melt were less at 1000°C than at 800°C.
While it is possible to rationalize the decreased
void formation on the basis that a high rate of dif-
fusion for chromium in the metal may minimize the
formation of voids, the decreased chromium con-
centration in the melt is, hawever, more difficult
to explain.
During the past quarter NaZrF, and NaF-ZrF,-UF,
(53.5-40-6.5 mole %) were tested in type 316 stain-
less steel under static and nearly isothermal con-
ditions for 100 hr at 100°C intervals over the range
600 to 1000"C, as a check of the findings with
Inconel. Metallographic examination of the cap-
sules exposed at 600°C revealed light intergranular
penetration up to 1 mil in depth. At 1000°C the
attack was still light, but one isolated case of
intergranular penetration to a depth of 18 mils WQS
noted. When the chromium concentration of the
melt was plotted against test temperature for the
NaZrF,, [I slight maximum in the curve appeared
between 800 and 900°C; a similar plot for the UF,-
bearing mixture shows a plateau between 700 to
1000°C. However, more chromium appeared in
solution in the NaZrF, samples than in the UF,-
bearing mixtures. The tendency toward less cor-
rosion at 1000°C than at 800°C never appears to
be pronounced, but it has been sufficiently persistent
in these tests to require explanation.
A plausible explanation can be evolved in the
following manner. ?he NaZrF, melt which has
been used in these experiments gave rise to ab-
normally high chromium concentrations (1000 ppm)
compared with equilibrium values (200 ppm) ob-
tairred in measurements carried out with carefully