Density, thermal expansion of stainless steel and interfacial properties of UO2-stainless steel above 1690 K

The sessile drop method was used for the determination of the density in liquid state. The results for stainless steel 1.4970 using uranium dioxide as substrate material in the temperature range 1690 K (liquidus temperature T1)<T< 2120 K are rho=6.82 X 103-10.25 X 10-1(T-T1)kg/m3, and α=1.50 X 10-4K-1. Below 1690 K the linear thermal expansion is given by Δl/l0=0.00204 + 7.110 X 10-6T + 7.734 X 10-9T2. Using the same method but not correlated with the density measurements the following interfacial properties of the system UO2-stainless steel have been determined: surface energy of liquid steel γsub(LV) = 1.19-0.57 X 10-3(T-T1)J/m2 and interfacial energy of liquid steel against UO2 γsub(SL) = 1.57-2.01 X 10-3(T-T1)J/m2, the results yield a contact angle theta = 00 at T = 2515 K. Using literature data for the compressibility of liquid UO2, an estimate of the surface energy of UO2 in liquid state was performed. The estimated value at the melting point is: γsub(LV)=0.522 J/m2. The mean value of the experimental data given by several authors is 0.513 +- 0.085 J/m2. The estimated temperature dependence of the surface energy of liquid UO2 is given by dγsub(LV)/dT=-0.19 X 10-3J/m2. (Auth.)