Fusion Curve and Electrical Conductivity of Molten HgCl2 and HgI2 at Elevated Pressure

Abstract

The fusion curves of HgC!, and HgI2 were measured to a pressure of 22 kbar. The melting temperature can be represented as a function of pressure by tp=to+bl P+b2P2, where tp is the melting temperature in degrees Centigrade at a pressure P in kilobars; bl and b, are constants. Values for to (deg) , bl (deg kbac l ), and b2 (deg kbac') are 276, 259; 19.8, 17.1, and -0.26, -0.41, respectively. The electrical conductivities (K) of molten HgCI, and HgI2 were measured to 805 and 620°C, respectively, at a pressure of 5.4 kbar. The electrical conductivity of HgCI,(l) was also measured from 557 to 634°C at P=20.5 kbar. At these elevated pressures K varies exponentially with liT, i.e., K~A exp-(Ek/ RT). At 5.4 kbar, A =2.13 and 0.36 (g·cm)-l; Ek=8.46±0.14 and 2.53±0.12 kcal/mole, respectively, for molten HgClz and HgI,. The behavior of HgC!,(l) and HgI 2 (l) at this elevated pressure is now typical for a strong electrolyte. This is in contrast to their behavior at ordinary pressures where HgCI, shows a maximum in its K vs T curve and HgI 2 has a negative temperature coefficient of K from the onset of melting. The conductivities of molten HgCl, and HgI2 were also examined from 3 to 20 kbar at constant T. At 600 o K, Kp~20 kbarlK P-3 kbar for HgCI, = 12.4; at 555°K this ratio for HgI2 is 1.66. Thus pressure increases the conductivity of these salts. This is attributed to a greater degree of ionic dissociation at elevated pressures.

Relative behaviour of electrical conductance for solid and molten mercuric halides

“…Darnell and McCollum pointed out that their data on molten mercuric halides [10] and molten bismuth trihalides [13] at elevated pressures tend to support the suggestion made by Grantham and Yosim [8]. Incidentally, our results (shown in Figs.…”

“…After the release of pressure, the conductance gradually increases to reach a steady-state corresponding to its value at atmosphe- ric pressure. The reversible character of conductance has also been reported by Darnell and McCollum [10] for molten HgI2. Their other finding too is in agreement with what we have observed, i.e., reduction in conductance with increasing pressure.…”

“…6. -Temperature dependence of conductance for molten HgI2 at pressures 0.1 kbar and 5.4 kbar [8], [10]. decreased when the pressure was increased from 3 kbar to 20 kbar.…”

“…has been reported [1][2][3][4][5][6][7][8][9] on molten mercuric halides relating to their electrical conductivity. Darnell and McCollum [10] have lately reported their interesting measurements of conductivity for molten HgCl2 and HgI2 at elevated pressures upto 22 kbar. A summary of their important findings is worth a mention.…”

“…-3 .1 MERCURIC CHLORIDE. -Darnell and McCollum [10] observed that an increase in pressure brings about a large increase in conductance of molten HgCl2. Figure 1 shows the results of our Fig. l. -Variation of conductance as a function of time, immediately after the release of pressure (500 bar).…”