Experimental Investigation of the Cr3C2–C Peritectic Fixed Point

Abstract

The Cr3C2–C (1,826°C) peritectic point was investigated for its performance as a high-temperature fixed point. Dependence on the impurity content was observed, although it was less severe for the higher of the two equilibrium temperatures obtained with the same cell, the Cr3C2–C peritectic point, than for the lower, the Cr7C3–Cr3C2 eutectic point. Thermal history had an effect on the melting plateau duration, but not on the point-of-inflection temperature nor on the melting range. The melting rate had no apparent effect. The repeatability evaluated as the standard deviation of the repeated melting plateaux within a day was 20 mK for the Cr3C2–C peritectic point, while for the Cr7C3–Cr3C2 eutectic point, this was 210 mK. For both the Cr3C2–C peritectic and the Cr7C3–Cr3C2 eutectic, the freezing plateaux often showed deep supercools, which made them unsuitable for use. The observed good repeatability shows the peritectic-point performance to be comparable to the best MC-eutectic high-temperature fixed points investigated so far. The insensitivity to thermal history constitutes an important and practical advantage. The low price of chromium is a clear benefit as compared to Pt–C (1,738°C) or Ru–C (1,953°C) eutectic points, the M–C eutectic points in this temperature range.