Heating sequence and hydrogen evolution in alloyed aluminium powders

Abstract

The results reported here, showing the effect of a non-continuous degassing sequence on the Al-20Si-3Cu-1 Mg powder, are a complement of previous work concerning the continuous degassing of the same powder. The degassing experiments were carried out, under high vacuum, in the temperature range 20 to 550 °C in a horizontal furnace heated at a uniform heating rate of 2.5 °C min⁻¹. The partial pressures of the released gases were monitored and analysed during the heating phase by a computerized Edwards EQ80F residual gas analyser (RGA). RGA measurements indicate that water and hydrogen are the main degassing products. A complete degassing can only be achieved if the sample is heated up to a temperature where the chemical reactions are finished in the applied time. Thermodynamical equations alone are not enough to explain the kinetics of degassing of aluminium powders. The diffusion of aluminium through its surface oxide layer (Al₂O₃), described by the self-diffusion of aluminium, can explain to a large extent the kinetics of degassing aluminium powders.