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.