Interdiffusion in Thallium Amalgams

Abstract

The interdiffusion coefficient of thallium in thallium amalgams was measured by the capillary reservoir technique. At 25" C the values of 106D in cm2 sec-I a t 0. 00365, 0.0536, 0.0895, 0.148, 0.188, 0.283, 0.323, and 0.404 mole fraction thallium were 1. 08, 1.37, 1.50, 1.37, 1.14,0.83, 0.95, and 1.11 respectively with standard deviations in 10-S(cm2 sec-I) of 0. 03, 0.06, 0.09, 0.10, 0.09, 0.08, 0.08, and 0.11 respectively. The minimum in the value of D a t 0.288 mole fraction thallium shows that the compound T12HgS plays a significant role in the diffusion process.Values of a In a/a In N for the thallium and for the compound were used to explain the dependence of D on the concentration.This study of diffusion in thallium amalgams was undertaken because this unusual system is liquid a t room temperature from 0 t o 42 wt% thallium and because accurate thermodynamic data are available from the classic work of Richards and Daniels (1) on thallium amalgam concentration cells. For the concentration range 0.137-0.160 wt% thallium, von Wogau (2) reports that a t 11.0-12.0' C the diffusion coefficient of thallium is 1.03 )( cm2 sec-I; and, for the concentration range 0.00216 to 0.00287 wt% thallium, Furnam and Cooper (3), from polarographic measurements a t 25' C, found that the diffusion coefficient was 0.99 X cm2 sec-l. Stromberg (4), from polarographic measurements -on a 1 0 4 wtyo amalgam, deduced a value of I.60X lov5 cm2 sec-l.The experimental method used was based on that employed by Anderson and Saddington (5) with the modification that a chemical rather than a radiochemical method of analysis was used. Fick's second law of diffusion for a one-dimensional system states that where c is the concentration of the diffusing species, t is the time, and D is the diffusion coefficient with dimensions of area per unit of time. Consider a capillary of length I, with one end closed, having an initial concentration Ci uniform throughout. Let the capillary be immersed in so large a volume of solution of composition C, that a t infinite time when diffusion is complete and the composition within the capillary and outside the capillary is the same the composition is still C,. The solution of equation [I] for time t under these circumstances is where C,, is the average composition of the solution in the capillary a t time t. The series on the right side of equation [2] is rapidly convergent.In the derivation of equation [2] from equation [I] it was assumed that the diffusion coefficient is independent of the concentration. When the difference in concentrations of the two solutions is small, it may be assumed that the diffusion coefficient is constant. In this present work a chemical method of analysis was used t o evaluate the terms on the left-hand side of equation [2] with the result that in both the numerator and the denomi-

Review Selected properties of simple amalgams

“…Some investigations of significantly concentrated amalgams showed extremes in the DM-composition dependence. The minimum of DT~ is observed for a composition close to T12Hg5 [107] and for D K at KHg2 [108]. Unquestionably these facts are proof of the existence of such ICs in liquid phases.…”

The Measurement of Diffusion Coefficients in Binary Liquid Metals with a Concentration Cell

“…Thermodynamic data (2) reveal that negative deviations from Raoult's law exist for this system. Diffusion coefficients have been measured as a function of composition for two other systems which show negative deviations from Raoult's law, Hg-T1 (12) and Bi-Ph (13). In both cases a maximum exists.…”

“…For the range 0.25 < NK < 0.35, Bonilla et al report much higher values than were found in the present investigation. Diffusion coefficients over a wide range of compositions have been reported for the following binary liquid metal systems; Hg-T1 (12), Bi-Sn (I3), In-Sn (14,15,16), Bi-Pb (13,17,18), Zn-Hg (19), Pb-Sn (13), and Na-Pb (20). With the exception of one investigation, Pb-Bi (i3), in no case did the diffusion coefficients vary by more than a factor of 2.2 over the composition range.…”

The Activities and Activity Coefficients of Tin and Indium in Their Amalgams at High Temperature

“…However, indium amalgam can be ~egarded as a simple mixture of indium and mercury rather than InxHgy as we pointed out. Smallman (23), Halder (24), and Fotley (25)(26)(27) reported that T12Hg5 was formed in a simple mixture of thallium and mercury and the amount of T12Hg5 varied with the temperature and concentration of thallium amalgam. Namely, all metal atoms in an amalgam do not always exist as MxHgy.…”