Details

Autor(en) / Beteiligte

• CASTELLO, P
• RICCI, E
• PASSERONE, A
• COSTA, P

Titel

Oxygen mass transfer at liquid-metal-vapour interfaces under a low total pressure

Ist Teil von

• Journal of materials science, 1994-12, Vol.29 (23), p.6104-6114

Ort / Verlag

Heidelberg: Springer

Erscheinungsjahr

1994

Quelle

SpringerLINK Contemporary (Konsortium Baden-Württemberg)

Beschreibungen/Notizen

• The problem of O exchange at the interface between a gas and a liquid metal is treated for systems under a "vacuum" (Knudsen regime, pressures < 1 Pa) where, due to the large mean free path of gas molecules in a vacuum, transport processes in the gas phase have no influence on the total interphase mass exchange, which is controlled by interface phenomena and by O partition equilibrium inside the liquid. Owing to the double contribution of molecular O sub 2 and volatile oxides to the O flux from the surface, non-equilibrium steady-state conditions can be established, in which no variations in the composition of the two phases occur with time, as the result of opposite O exchanges. The total O and metal evaporation rates are evaluated as a function of the overall thermodynamic driving forces, and an account of the transport kinetics is given by using appropriate coefficients. A steady-state saturation degree s sub r is defined which relates the O activity in the liquid metal to the O pressure imposed and to the vapour pressures of volatile oxides. When metals able to form volatile oxides are considered, pressures of molecular O sub 2 higher than those defined under equilibrium conditions have to be imposed in the experimental set-up in order to obtain a certain saturation degree, as a consequence of the condensation of the oxide vapours on the reactor walls. Effective oxidation parameters are determined, which define the conditions leading the liquid to a definite steady-state composition under a "vacuum" when it is out of equilibrium. The effective value of the O pressure which corresponds to the complete O saturation of the metal, P sub O2,s exp E , is evaluated at different temperatures for the systems Si-O and Al-O. The results are represented as curves of log P sub O2,s exp E vs. T, which separate different oxidation regimes; these results agree well with other experimental data.