PREWETTING PHASE-DIAGRAM OF MERCURY ON SAPPHIRE

Optical reflectivity experiments on fluid mercury against an optically transparent sapphire window at high temperatures and pressures close to the liquid-vapour critical point (T-c = 1478 degrees C, p(c)=1673 b ar, rho(c)=5.8 g cm(-3)) reveal clearly the existence of a prewetting transition of mercury on the sapphire substrate. The prewetting line i ntersects the coexistence curve at the prewetting temperature T-omega= 1310 degrees C, and terminates at the prewetting critical temperature T-p omega(c)=1468degrees>C and prewetting critical pressure P-p omega( c) = 1586 bar lying close to the bulk critical point. The interrelatio n between the metal-non-metal is discussed.