Here - PMOD/WRC

these materials.
Repeatability of a single cell For each cell an average
melting temperature was determined from the four
melt/freezes obtained. The standard deviation of this
average temperature was taken as a measure for the cell
repeatability. The repeatability for all cells from all
manufacturers was better than 80 mK, and when omitting
the Pd-C cells of NPL and INM better than 40 mK.
Results
The differences from the average melting temperature for
each material are summarized as measured by both radiation
thermometers in Table 1 and Figure 2.
Table 1: Differences of cells melting point temperature
with respect to the materials average melting point
temperature, shown for both radiation thermometers
T - T average / K
Co-C
Pd-C
Pt-C
Ru-C
Re-C
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
Co-C Pd-C Pt-C Ru-C Re-C
1500 1700 1900 2100 2300 2500 2700 2900
T / K
PTB LP3
NPL
NMIJ
INM
NPL
NMIJ
INM
INM LP3
Figure 2: Differences of cells melting point temperature
with respect to the materials average inflection point
temperature. PTB LP3 in blue, and INM LP3 in red.
Discussion
T / K T / K T / K u / K, (k=1)
-0.00
0.01
-0.07
-0.07
-0.06
-0.07
-0.03
-0.01
-0.06
-0.02
0.04
0.06
0.21
0.20
0.03
0.04
0.23
0.16
0.08
0.09
-0.04
-0.06
-0.14
-0.13
0.02
0.03
-0.20
-0.15
-0.02
-0.07
NPL NMIJ INM
0.04
0.04
0.06
0.05
0.05
0.04
0.12
0.10
0.12
0.10
LP3 (PTB)
LP3 (INM)
LP3 (PTB)
LP3 (INM)
LP3 (PTB)
LP3 (INM)
LP3 (PTB)
LP3 (INM)
LP3 (PTB)
LP3 (INM)
Differences between materials From the results
presented above the cells can be split up into two groups,
one which shows an internal agreement to within ~ 200 mK
(Co-C, Pt-C and Re-C), the other showing an agreement to
within ~ 450 mK (Pd-C and Ru-C). This result reflects the
purity level of the used metals. Pd (99.99%, only NMIJ
99.999 %) and Ru (99.95 %) were not available at the same
purity level as Co (99.998 %), Pt (99.999 %) and
Re (99.999 %).
Differences in manufacture Systematic differences in
manufacture can be inferred from the distribution of melting
temperatures and from a comparison of plateau shapes. The
data do not scatter randomly around the averaged values
used in creating Table 1 and Fig 2. For all materials the cells
which showed the highest melting temperatures, smallest
melting ranges and longest plateaus were produced by the
NMIJ. Melting point depression and reduction in melting
range are properties usually understood to be related to less
pure material components. For most of the metals the
nominal purity levels, as specified, were the same for all
institutes, and if reliable, the experimental results obtained
suggest that contamination has occurred during the
manufacturing processes. This conclusion was further
investigated by studies on the effect of different methods
used for cell manufacture [5].
Conclusion
Co-C, Pd-C, Pt-C, Ru-C, and Re-C eutectic fixed-point cells
manufactured by CNAM-INM, NPL and NMIJ were
investigated by directly comparing their melting
temperatures. In order to achieve lowest uncertainties it
proved essential to use two virtually identical furnaces in a
parallel scheme, as the largest source of uncertainty was the
radiation thermometer instability. The already achievable
high level of agreement found for Co-C, Pt-C and Re-C
proves the applicability of these systems as fixed points in
thermometry. Systematic differences found in the
manufacture of the cells are indicative for further
improvements in cell construction. In future, direct
comparisons similar to the one described above will be
necessary to assess such improvements.
Acknowledgement This work was part supported by the
European Commission “GROWTH” Programme Research Project
“Novel high temperature metal-carbon eutectic fixed- points for
Radiation Thermometry, Radiometry and Thermo- couples”
(HIMERT), contract number: G6RD-CT-2000-00610. Tanaka
Kikinzoku Kogyo is acknowledged for lending the high purity
metal powder for the NMIJ Pt-C cell. The authors would like to
thank S. Schiller for technical assistance.
References
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Lowe, D., Morice, R., Sadli, M., Villananan, M., “HIMERT: a
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eutectics at temperature standards”, Proc. of Temperature:, Vol.
7, ed. Ripple, D., AIP Conf. Proc., Chicago, 2003, pp. 285-290
[2] Machin et al., A comparison of high temperature fixed-points
of Pt-C and Re-C constructed by BIPM, NMIJ and NPL,
Proceedings of Tempmeko 2004, Dubrovnik
[3] Yamada, Y., Sasajima, N., Gomi, H., Sugai, T., “High
temperature furnace systems for realising metal-carbon eutectic
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