Triple-points of low melting substances and their use in cryogenic work

The fusion curves of xenon, krypton, and argon

“…remaining 74 data points in this table and the {s(fcc) + ' + g} triple-point selected by Staveley et al [31] (i.e., p 0 = 72.999 kPa, T 0 = 115.772 K) we obtain as parameters in the Simon equation (2), for the fusion of the lower pressure fcc-solid, a = (266.627 ± 0.061) MPa and c = (1.4951 ± 0.0001), with a correlation coefficient exceeding 0.9999, and AAD less than three per cent. By applying the same procedure as that described above for xenon and using the experimental information provided by Jephcoat and Besedin [8] and by Boehler et al [9], we arrived at the values of the parameters in equation (2) for the hcp-solid form: a = (7947 ± 331) MPa, c = (6.4594 ± 0.1374), with T 0 = (2310 ± 10) K, and p 0 = (23130 ± 840) MPa as coordinates of the plausible {s(fcc) + s(hcp) + '} triple-point of krypton.…”

“…The extrapolation to higher temperatures and pressures of the first form of the equation so obtained showed that it also fits the two experimental points due to Jephcoat and Besedin [8] and those measured by Boehler et al [9] at temperatures up to about 2800 K. This observation led us to include the 16 points at the lower temperatures reported in reference [9] and the two points mentioned in reference [8] to obtain a second, better, approach to the fusion curve equation of the fcc-solid phase of xenon. In the resulting Simon equation (2), for the fcc-solid phase fusion curve, where p 0 = 81.675 kPa, T 0 = 161.404 K are the coordinates of the low-pressure {s(fcc) + ' + g} triple-point [31], the parameters are a = (259.351 ± 2.059) MPa, c = (1.4905 ± 0.0029). The correlation coefficient (r) of this fitting is 0.997, and the average absolute deviation (AAD) for the 70 experimental points used in this fitting is less than 8%.…”

“…For the {s(fcc) + ' + g} triple-point pressure where it is necessary to establish the lower pressure forms of equation (2), we have taken the values analysed by the criteria and selected by Staveley et al [31].…”

“…The experimental values registered in the literature and included in table 3 have been used in the calculations. By using the {s(fcc) + ' + g} triple-point pressure given in reference [31], p 0 = 68.898 kPa, and the corresponding value of temperature (T 0 = 83.8058 K, which is a fixed point in ITS-90) we obtain the parameters for the fcc-solid phase fusion curve: a = (224.471 ± 3.191) MPa and c = (1.5354 ± 0.0044), with AAD of 2% and a correlation coefficient above 0.999, for the 269 experimental points involved in the adjustment. Due to the fuzzy nature of the intersection of the fcc and hcp-fusion curves, as shown in figure 2 of reference [9], only the eight measurements made by Boehler et al [9] and the two points from Jephcoat and Besedin [8] at the higher pressures of their measurements were considered to estimate the parameters in the argon hcp-fusion curve.…”

“…(2); the dash-dotted line (-Á-) is for the melting of the hcp-solid as calculated from equation (2); the dashed lines (---) indicate the possible limits of the fcc and hcp-solid phases. The symbols are: ., reference [31]; Â, reference [32]; M, reference [33]; h, reference [34]; N, reference [35]; +, reference [8]; s, reference [9];…”