Furnace Atmosphere and Dissolved Hydrogen in Aluminium

Hydrogen solubility is much higher in liquid than in solid aluminium. Therefore, if the hydrogen concentration in liquid aluminium is too high prior to solidification, there is high risk of gas porosity formation during the solidification. In a gas or oil fired reverberatory furnace for aluminium, combustion produces large amounts of water vapour. The water vapour may react with aluminium forming aluminium oxide and hydrogen gas. This hydrogen gas is then the main source for hydrogen in molten aluminium. Measurements of both water vapour in the furnace atmosphere (combustion off-gas) and dissolved hydrogen in the melt are presented. The measurements are compared to a model for hydrogen concentration in aluminium as function of the measured water vapour concentration. It is concluded that H₂O reacts with aluminium to H₂ and Al₂O₃. 49% of this H₂ escapes from the interface to the bulk gas phase, and 51% acts as a source for dissolved hydrogen in the melt.