The Al-H (Aluminium-Hydrogen) system

In a search of the literature through 1989, no phase diagram for the Al--H system was found. What was available consisted of T-X diagrams representing the maximum observed hydrogen solubility in solid and liquid Al, mostly at atmospheric pressure and one P-X plot showing one decomposition isotherm. Because the solubility of H in solid (Al) is less than in liquid Al, the phase diagram should contain a eutectic-type reaction near the melting point of Al, 660.452 deg C. The lowering of the Al melting point by approx 2 deg C as a result of H absorption has been observed, but only at a H sub 2 pressure of 100 MPa. The (Al)/(Al) + H sub 2 and the L/L + H sub 2 boundaries were obtained, which are the assessed analytical approximations for the maximum observed H solubility in solid and liquid Al up to a pressure of 0.1 MPa. Thus the dashed lines do not necessarily demarcate the boundaries of equilibrium phases. The compositions along the melting point line for the curves representing the solid and liquid regions-were obtained and have the values X = 1.164 x 10 exp --6 and X = 1.179 x 10 exp --5 , respectively, where X = H/Al is the atomic ratio. The corresponding values in atomic percent are given.