The maximum equilibrium solubility of hydrogen at a partial pressure of 1 atm in liquid magnesium is 26 cm^3 per 100g. This drops to 18cm^3 per 100g upon solidification. The density of Mg (liquid and solid) is 1.74 g/cm^3.
(a) what would be the gas porosity (volume of dihydrogen/total volume) of the Mg casting if the liquid saturated with hydrogen at 1 atm were allowed to solidify?
(b) what partial pressure of hydrogen should be maintained over the melt if a pore free casting is required?