E.m.f. measurements on cells of the type, Na|iq/Na+(glass)/Na-Hgnq have been made on sodium amalgams (mainly in the 1 to 20 atom % sodium region) at 350°to 400°C. The determined activity coefficient on Na can be expressed by the equation, log7n= = -yn®-+ ya.4¿ xNo+('4.7-0.027T) X Na This equation can be used for calculating thermodynamic properties from 5°to 400°C. for liquid sodium amalgams containing up to 40 atom % sodium.ThE THERMODYNAMIC properties of the sodiummercury system have been investigated by several methods in the past, both at room temperature and at elevated temperatures. The data at the lower temperature were from e.m.f. measurements of liquid amalgams containing up to 0.05 mole fraction sodium (2, 5, 6). At higher temperatures, the data were obtained from e.m.f. and vapor pressure measurements. The e.m.f. data were obtained at 300°and 375°C. on amalgams ranging from 0.34 to 0.91 mole fraction Na, while the vapor pressure data were obtained at 300°, 335°, and 375°C. on amalgams ranging from 0.038 to 0.489 mole fraction Na. At the higher temperature, Hauffe (3) has combined his e.m.f. data of amalgams in the sodium-rich region with the vapor pressure data of Bent and Hildebrand (1) on more dilute amalgams to obtain the activity of sodium over the entire composition range at 375°C. The vapor pressure data at 375°C. were represented by only one experimental observation in the dilute concentration region. Thus, accurate temperature coefficients could not be calculated, and the data could not be used for calculating entropies and other thermodynamic functions in the dilute region. To obtain data necessary for these calculations, the e.m.f. method was applied to a study on the sodium-mercury system in the mercury-rich region at elevated temperatures. Cells of the type Na^/borosilicate glass (Na+)/Na-Hgliq were used.

The chemical and electrochemical characteristics of sodium amalgam galvanic cells were studied. A static electrode cell, contained in a stainless steel pressure vessel, was operated at temperatures from 477 to 510°C. under 140 to 180 psig argon cover gas pressure. A molten eutectic mixture of sodium salts was used as the electrolyte. Current densities as high as 200 ma./sq. cm. were achieved without appreciable electrode polarization. A flowing electrode cell with a tubular electrode matrix was designed, built, and tested. In this cell the anode and the cathode compartments were supplied with continuous streams of concentrated and dilute amalgam, respectively. A complete thermally regenerative system (a flowing electrode cell coupled with a regeneration loop) was successfully operated for a period of 1200 hrs. at a cell temperature of about 490°C.'T'he application of thermally regenerative fuel cells for the conversion A of heat into electrical energy has been discussed recently (9). Thermally regenerative systems using liquid metal electrodes and fused salt electrolytes appear to be particularly promising because energy losses through electrode polarization and electrolyte resistance can be much 1 Work performed under company-sponsored, independent research and development program.

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