The potential for using a silicon–carbon system as a new eutectic fixed point for thermocouple calibration

Abstract

Five Si-SiC eutectic fixed-point cells were constructed for use in thermocouple thermometry. Two cells were made from a silicon and carbon mixture within a graphite crucible; the other three were made from pure silicon. The first broke after 12 melt-freeze cycles due to weaknesses in the crucible; the other four, made with a modified crucible that was thicker and shorter than the first type, were more resistant to failure. The second, subjected to various furnace settings, was able to withstand up to 36 cycles. The third, subjected to only the furnace setting of 5 • C above and below the transition temperature, was able to withstand 56 cycles. The fourth was rapidly cooled in an unpowered furnace from 600 • C, then removed from the furnace at 300 • C and allowed to cool to room temperature. With this repeated treatment, the cell broke after only 25 cycles. The fifth was treated gently with a slow rate of 1 • C min −1 through both melting and freezing, and 2 • C min −1 to 3 • C min −1 when cooling. This cell was successfully tested through 80 melt-freeze cycles without any mechanical failure. The melting point of the five Si-SiC cells based on its maximum drift agreed within 1.2 • C.

Temperature determination of the Si–SiC eutectic fixed point using thermocouples

“…The thicknesses of the crucible and the thermometer well were 7 mm and 10 mm, respectively. We fabricated the crucibles thicker and shorter than usual graphite crucibles to make them more robust and efficient when using a smaller mass of filling material [2]. The volume of the space between the thermocouple well and the crucible, which would be filled with silicon powder, was calculated to be 11.8 cm 3 .…”

“…The high-purity graphite crucible was used as a carbon source, due to the fact that the amount of carbon to meet a eutectic composition was not that much [4,5]. In the previous work [2], we used a silicon-carbon mixture (silicon powder mixed with 0.7% carbon) and pure silicon powder as the starting material, and we found no significant differences in the result.…”

“…The transition point was then determined by calculating the zero point of the second derivative of the curve. This second method used has been discussed previously [2]. In each process of fabrication and measurement of the transition point of the Si-SiC cells, the atmosphere inside the cells was composed of a mixture of argon and hydrogen gas (0.5% by volume) maintained at a pressure slightly above ambient pressure.…”

“…The mechanical robustness and the thermal behaviour of Si-SiC cells have been investigated previously at KRISS. A well-prepared cell showed good short-term repeatability within 0.03 °C, and was tested successfully through 80 melt-freeze cycles for periods longer than 360 h at temperatures above 1400 °C without any mechanical failure [2]. However, that study did not include the transition temperature or the uncertainty of the Si-SiC eutectic point.…”

“…In this paper, we report on the determination of the transition temperature of the Si-SiC eutectic fixed point. Each of the Temperature determination of the Si-SiC eutectic fixed point using thermocouples Suherlan 1,2,3 , Yong-Gyoo Kim 1,2 , Wukchul Joung 1 and Inseok Yang 1 three Si-SiC cells used was made from pure silicon powder within a graphite crucible. After fabrication, a type S thermocouple (designated as KSTC) was used to measure the first five plateaus of each cell as a preliminary test to investigate their melting-freezing plateau behaviour.…”