Henryrsquo;s Law vaporization studies and thermodynamics of einsteiniumhyphen;253 metal dissolved in ytterbium

摘要

The cohesive energy of metallic einsteinium determines whether einsteinium is a trivalent or divalent metal. The enthalpy of sublimation, a measure of the cohesive energy, is calculated from the partial pressures of einsteinium over an alloy. The partial pressure of253Es has been measured over the range 470ndash;870 K, using combined target and mass spectrometric Knudsen effusion techniques. An alloy was prepared with einsteinium dissolved in a ytterbium solvent to produce a very dilute solution. Partial pressure measurements on the alloy were amenable to the experimental technique and a data analysis using a Henryrsquo;s law treatment of the data. Vapor pressure data are combined with an estimated crystal entropyS0298and Dgr;C0pfor ytterbium, to produce enthalpy, entropy, and free energy functions from 298 to 1300 K. The vapor pressure of einsteinium in a dilute einsteiniumndash;ytterbium alloy is described by the equation logthinsp;P(atm)=minus;(6815plusmn;216)/T+2.576plusmn;0.337, from which we calculate for the enthalpy of sublimation of pure einsteinium Dgr;H0298(second law)=31.76 kcal/mol. The value of the enthalpy of sublimation is consistent with the conclusion that Es is a divalent metal.