PREWETTING PHENOMENA IN MERCURY-VAPOR

We review recent work on the acoustic characteristics of mercury in mo lybdenum and niobium cells at high temperatures (to 1900 K) and high p ressures (to 180 MPa) and report some further experimental progress. T he sound velocity, and the transmitted and reflected signals have been observed simultaneously. Apparent first-order phase transitions appea r in the vapor region of the mercury phase diagram. The corresponding transition curve (for Mo) meets the bulk liquid-gas coexistence curve tangentially at (T-0, P-0)congruent to(1250 K, 30 MPa) and terminates above 1860 K and 183 MPa. The data provide strong evidence that the ob servations represent prewetting transitions, bounded below by a wettin g transition at(T-W, P-W)drop(T-0, P-0) and above by prewetting critic al points which lie well above the bulk critical point (T-c congruent to 1764 K, P-c congruent to 167 MPa). (C) 1998 Elsevier Science B.V. A ll rights reserved.