Coating Design using Computational Codes for Steam Oxidation Conditions

摘要

Thermodynamical calculations were performed using Thermo-Calc codes to obtained equilibrium diagrams of the heterogeneous system (steel P92, Fe-30Al-6Cr coating (wt. %))|(oxide compounds)|(O_2 + H_2O gas mixture). Calculations were made for 650℃, constant water vapour pressure, equal 10~(-1) atm, and variable oxygen partial pressure from 1.10~(-20) to 1.10~(-1) atm. From obtained results indicate that in the steam gas environments the highest volatile compounds form Mo, W and Cr oxides. Formation of volatile products depends on the oxygen pressure in the O_2 + H_2O gas mixture. There is change of the principle volatile species in the Fe-Cr system, when at constant water vapour pressure, the oxygen partial pressure decrease. In such conditions there is a decrease of CrO_2(OH)_2 vapour pressure, which is accompanied by an increase of Fe(OH)_2 vapour pressure. At higher oxygen partial pressure vapour pressure of CrO_2(OH)_2 exceeds that of the most volatile aluminium species, Al(OH)_3,by many orders of magnitude.