Here - PMOD/WRC

Comparing curves 5 and 6 shows that the graphite holder
does not improve the uniformity.
Another holder we used was a 3 mm thick CC tube of
150 mm length rapped with 4 layers of graphite cloth.
Such a holder, in distinction from the graphite one,
improves the uniformity, which is shown on Fig.3.
Temperature Difference, C
Figure 2. Temperature distributions measured by thermocouple
at T=1500 o C for BB3500YY with a graphite holder
Temperature Difference, C
40
20
0
-20
-40
-60
-80
-100
20
0
-20
-40
-60
-80
1. All baffles+felt
2. No outer baffles
3. No inner baffles
4. No felt
5. Hot rings at rear end
6. Hot rings+graphite holder
-100 -80 -60 -40 -20 0 20 40 60 80 100 120 140
Distance from Holder centre, mm
1. Hot ring s. CC tube
2. Hot ring s. No tube
3. Hot ring s. CC tube+cloth
4. No tube
5. CC tube+cloth
6. NEW heater. CC tube+cloth
-100
-120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120
Distance from Holder centre, m m
Figure 3. Temperature distributions measured by thermocouple
at T=1500 o C for BB3500YY with a CC-tube holder
Distribution measured first for the arrangement with
some high resistance rings at the rear end of the cell
position but without any holder (curve 2), then for the
same arrangement but with the CC-tube (curve 1), and
then with the tube wrapped in the cloth (curve 3).
Comparison of the curves shows that the cloth has more
significant effect than the tube itself. Curves 4 and 5
represent distributions measured without and with the tube
wrapped with cloth respectively but for arrangement with
low resistance rings around the rear end of the cell position.
Finally a new set of rings was arranged, which showed (in
combination with CC holder) the uniformity (curve 6)
within 5 degrees along the distance of 110 mm.
Temperature uniformity at 2500 o C
Two radiation thermometers were used for temperature
distribution measurement at higher temperatures. One of
them, narrow-beam fiber radiation thermometer looked
through the rear channel of the furnace to a blind baffle
placed at the rear end of the CC-tube holder and used for
furnace temperature control. The second thermometer
looked through the front opening to a movable target
inside the holder. The target was a 10 mm length graphite
tube with soot-blackened bottom at one end and 5 mm
aperture at another one.
At the beginning the target was placed inside the CC
tube near its front end, the furnace was brought to the
desired temperature of 2500 °C, and the temperature of the
target was measured by means of the second radiation
thermometer. Then the furnace was brought to the
temperature of 1500 o C, the target was pushed by an
alumina rod to be moved by one step of 10 to 20 mm, the
furnace was brought back to the temperature of 2500 °C
and the second point of the temperature distribution
measurement was taken. This was repeated to cover the
length of the CC tube.
As a test of the validity of this method, the temperature
distribution was measured at 1500 o C and was compared
with measurement with the thermocouple with the same
furnace arrangement. Both methods agreed within one
degree. Then the method was applied to measure the
temperature distribution at 2500 o C. The measurements
showed that the hottest point was just in the center of the
CC tube and temperature gradually decreased towards its
ends. The central 40 mm and 80 mm parts of the tube were
uniform within 2 and 5 degrees respectively.
Work with eutectics cell
The NMIJ Re-C cell of 45 mm length, 24 mm outer
diameter and 3 mm aperture cavity was heated in
BB3500YY furnace to observe melting and freezing
plateaus. The same cell was then used for observing the
plateaus in VR10-A23 furnace [6], which has operation
temperature limited to 2500 o C. The former showed better
melting plateau shapes.
BB3500YY was used for filling one Re-C and one
TiC-C cells. The Re-C cell was compared with a similar
one but filled in VR10-A10 furnace (vertical variant of
VR10-A23). The TiC-C cell was compared with a cell
manufactured by VNIIOFI. The results of these
comparisons will be presented in the paper.
References
[1] Yamada Y., Advances in High-temperature Standards above
1000 o C, MAPAN - Journal of Metrology Society of India, v.20,
No 2, 2005, pp.183-191.
[2] Sapritsky, V., Ogarev, S., Khlevnoy, B., Samoylov, M., and
Khromchenko, V., Metrologia 40 (2003), S128-S131. 2003
[3] N. Sasajima, M. K. Sakharov, B. B. Khlevnoy, Y. Yamada, M.
L. Samoylov, S. A. Ogarev, P. Bloembergen and V. I. Sapritsky.
'A comparison of Re-C and TiC-C eutectic fixed-point cells
among VNIIOFI, NMIJ and BIPM'. in 9th International
Symposium on Temperature and Thermal Measurements in
Industry and Science (TEMPMEKO). 2004. Dubrovnik.
[4] Woolliams E., Khlevnoy B., Sakharov M., Samoylov M.,
Sapritsky V., Investigation of TiC-C and ZrC-C eutectic
fixed-point blackbodies., Submitted to Metrologia.
[5] Sapritsky V. and others, Applied Optics, 36, 5403-5408, 1997.
[6] Y. Yamada, N. Sasajima, H. Gomi, and T. Sugai, in
Temperature: Its Measurement and Control in Science and
Industry, 7 (Ripple et al ed.), AIP Conference Proceedings,
Melville, New York (2003) 965-990.
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