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wrought plate used as base material. Further at-
tempts are also being made to secure high-purity
niobium powder from commercial sources.
Two companies were contacted for information on
high-vacuum furnaces capable of temperatures of
2100OC for sintering niobium and other materials.
Literature and quotations have been received and
are being evaluated.
Three specimens of lnconel-clad niobium have
been machined to slightly larger than creep speci-
men dimensions and are to be undercut and edge-
protected as described previously. l4 They will be
creep tested in an inert atmosphere. Both highly
purified argon and liquid sodium show promise as
creep-test environments for unclad niobium. Iden-
tical specimens will be run in each environment at
1500°F, and the results will be compared Data on
weight and hardness change will also be corre-
I ated.
LOW-CONDUCTIVITY GAMMA-RAY
SHIELDING MATERIAL
J. H. Gobs J. P. Page
Conductivity data received from a commercial
supplier of cemented carbide bodies, correlated
with data obtained at ORNL, indicate the thermal
conductivity of tungsten carbide to be approxi-
mately 0.125 cal/sec-°C*cm. This value, coupled
with the "inertness" on hot pressing, makes tung-
sten carbide the most promising base material for
a low-conductivity gamma-ray shield.
Constantan was chosen as a binder for the tung-
sten carbide because of its low thermal conduc-
"J. P. Pogc, H. Inouye, and V. Kolba, ANP Quat.
Prog. Rep. March 10, ORNL-2061 p 161.
PERIOD ENDlNG JUNE 10, 1956
tivity (0.06 cal/sec*°Can), its low liquidus tem-
perature ( 122OoC), which minimizes hot-pressing
difficulties, its low cost, and its brazeability.
Further, the elemental copper and nickel powders
from which it is prepared are readily available.
Six tungsten carbide-constantan thermal-conduc-
tivity specimens, as described in Table 3.3.9, have
been hot pressed and finished to size. The varia-
tion of thermal conductivity with composition
should become evident upon evaluation of these
specimens. The composition showing the lowest
conductivity will be chosen for use as the gamma
shield around the ART pump shafts.
Three cold-pressed and sintered EO, thermal-
conductivity specimens, with densities of 3.09,
3.52, and 4.41 g/cm, respectively, were machined
to Battelle Memorial Institute specifications for
thermal-conductivity determination at that installa-
tion. These pieces will be tested in a helium
atmosphere to simulate service conditions.
L IT H I U M-M AG N E S I UM ALL 0 Y S
R. E. McDonald C. F. Leitten, Jr.
Work continued on the 20% Li-80% Mg alloy for
use as shielding material. Corrosion of the alloy
in air and in water was found to be severe. Freshly
cleaned specimens gained 0.088 mg/cm2 during 6
hr of exposure in air. Another specimen tested for
various times in boiling water was found to have
lost 0.292 mg/cm2 in the first 2 min of exposure,
which amounted to 90% of the weight lost during
the entire 15-min test. The decrease in rate of
weight loss may be attributed to the depletion of
lithium at the surface, since no protective film
could be detected. Pure magnesium tested in
boiling water for IS min showed a weight loss of
TABLE 3.3.9. DATA ON TUNGSTEN CARBIDE-CONSTANTAN THERMAL-CONDUCTIVITY SPECIMENS
Code No.
Density Composition (wt X) Composition (~01%) Porosity
(s/cm3) wc Con stantan wc Constantan (%I
12-0 11.53 57 43 42 56 2
12-7 11.63 71 29 53 38 9
12-14 1 1.60 85 15 64 19 17
12-19 11.55 94 6 68 7 25
13-5 12.96 79 21 65 30 5
13-15 12.67 93 7 75 10 15
173