Transport of beryllium in beryllium dichloride vapour

Abstract

Experiments on the transport of beryllium in beryllium dichloride vapour at about 1 × 10^–4 atmospheres have been made in the temperature range from 1250 to 1500 K. The transport can well be interpreted as resulting from the reaction Be(s)+ BeCl₂(g)= 2BeCl(g)(1) and agrees with that extrapolated from previous transport experiments by Greenbaum, Arin, Wong and Farber between 1570 and 1725 K. A third law analysis of all the experiments leads to ΔH^°_f298, BeCl(g)= 1.7±0.7 kcal/mol.

This interpretation of the transport experiments can, however, not be reconciled with mass spectroscopic equilibrium measurements by Hildenbrand and Theard which led to ΔH^°_f298, BeCl(g)= 13.1 + 2.2 kcal/mol.

Second law analysis of the transport experiments interpreted as resulting from Be(s)+ BeCl₂(g)=(BeCl)₂(g)(2) is much less satisfactory than that from (1) and their third law analysis according to (2) with a reasonably estimated entropy for (BeCl)₂(g), leads to a well defined enthalpy of reaction 2 (=±1.2), but to an enthalpy of dimerisation of about –90 kcal, which is much more negative than one can expect.