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.
The thermoelectric inhomogeneity as a function of position along wires is one the significant uncertainty of measurement using thermocouples. Here we report development of an electrical annealing system for thermoelectric inhomogeneity treatment. Two inhomogeneous type-S thermocouples, which had the inhomogeneity greater than 0.04%emf, are successfully recovered using the system. An improvement on thermocouple performance as large as 0.28 °C (at temperature of 1000 °C) can be obtained using the system. This article provides detailed information and may help the reader to obtain a quick grasp about the system.
The temperature of the Si-SiC eutectic fixed point for use in thermocouple thermometry has been determined. Three Si-SiC cells were fabricated from pure silicon powder within separate graphite crucibles. Each of the three cells was cycled through 17 melt-freeze cycles and subjected to temperatures above 1400 °C for a period of approximately 73 h, and none showed any sign of mechanical failure. The melting transition was measured using three types of thermocouple: one type S, one type B, and two Pt/Pd thermocouples calibrated at the fixed points of Ag, Cu, Fe-C, Co-C, and Pd (only for type B). The transition temperature, measured using the type S and two Pt/Pd thermocouples, was (1410.0 ± 0.8) °C with k = 2. However, the measurement uncertainty using the type B thermocouple was as large as 1.5 °C (k = 2) due to the inhomogeneity of the thermocouple. The repeatability of the three Si-SiC cells was calculated to be 0.3 °C, and the extremes of the temperature measurement differed by 0.8 °C.
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