Two pure Ni cells for thermocouple calibration were fabricated in alumina crucibles with different internal structures to investigate their melting and freezing behaviors. One of the produced crucibles had a smooth surface, and the other was made with internal circular grooves. The melting and freezing processes of each cell were investigated in 10 melting/freezing cycles using a type B thermocouple calibrated with a standard radiation thermometer. The reproducibility of the melting point was better than that of the freezing point by a factor of more than 2, regardless of the internal shape of the crucible. The freezing temperature gradually decreased with the degree of supercooling, and the slope was observed to be about −0.08 °C. It was found that in terms of reproducibility and easiness of realization the melting point was better than the freezing point for use as a fixed temperature point. Therefore, it is proposed to use the melting point as a fixed point for thermocouple c...

中文翻译：

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内部结构不同的氧化铝坩埚中纯镍电池的熔化和冻结行为

在具有不同内部结构的氧化铝坩埚中制造了两个用于热电偶校准的纯镍电池，以研究其熔化和冻结行为。所生产的一个坩埚具有光滑的表面，而另一个则具有内部圆形凹槽。使用标准辐射温度计校准的B型热电偶，在10个融化/冻结循环中研究了每个电池的融化和冻结过程。不论坩埚的内部形状如何，熔点的再现性都比冰点的再现性高2倍以上。随着过冷度，冷冻温度逐渐降低，并且观察到该斜率约为-0.08℃。已经发现，就可再现性和容易实现而言，熔点比用作固定温度点的凝固点更好。因此，建议使用熔点作为热电偶温度的固定点。