Niobium Data Sheets:
C-103 Physical Properties
Density 0.320 lbs./cu. in. or 8.85
grms./cu. cm.
Melting Point 2350 ± 50°C - 4260 ± 90°F
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Thermal Expansion
The linear coefficient of thermal expansion for
C-103 in the temperature ranges of room temperature
to -2200°F is listed in Table 1. For
design consideration over a given duty cycle (heat-up
rate) a value of 4.0 x10 -6 is normally used.
Thermal Conductivity 
Themal conductivity is of prime consideration
in applications which require a “heat sink” to
meet design requirements. As C-103 has a thermal
conductivity superior to super-alloys, it is often
to one’s advantage to use Niobium, even if the
design temperature is below 2200°F. The thermal
conductivity for C-103 at various temperatures
is as shown at right.
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| Table 2
shows thermal conductivity of various metals, alloys
and compounds over a temperature range span from
room temperature to 4400°F. Although super alloys
are not plotted on the graph, the values range from
approximately 5 BTU's/hr. -ft -°F at room temperature
to approximately 16 at 1700 °F. 70 60 50 40 TZM
C-129Y W |
Enthalpy Temperature*°F BTU/lb. 1610 103 2017
145 2390 184 *Reference 32F
Specific Heat 0.082 BTU/°F/lb.
Emissivity
Emissive power is the ratio of the rate of loss of
heat per unit of a surface at a given temperature to
the rate of loss of heat per unit area of a black body
at the same temperature and with the same surroundings.
The values of emissive powers range from 1.0 for lampblack
down to 0.02 for polished silver. Radiation is a direct
function of the emissivity times the temperature differential
to the fourth power. Extensive emissivity tests have
been conducted on bare Niobium and coated Niobium. Most
tests have been made in a vacuum of 10 -6 mm Hg. However,
similar results are obtained when tested in argon. Emissivity
factors for Niobium on smooth surfaces which were knurled
to increase the surface area showed no difference in
emissivity. Table 4 shows the emissivity of C-103 with
a modified aluminide coating. Testing of silicides show
that the emissivity is approx. .85 at 2700°F and
.65 at 3000°F. Most designs will conservatively
use an emissivity factor of 0.8 up to 2700°F and
0.6 from 2700°F to 3000°F. Emissivity values
for
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