Hydrogen gas dissolves very easily in liquid Al metals, but does not dissolve in solid AL. So during solidification (liquid AL solidifies into a solid phase), hydrogen gas which initially dissolves becomes insoluble to the solid phase, and forms bubbles of gas that escape in the solid phase.
H2 gas released in the castings results in defects in the castings, in the form of holes evenly distributed throughout the castings to form a circle whose diameter is between 0.01 mm to 1.5 mm. Degaser tablets (Degastab) are made to remove H2 gas in aluminum melt, so as to reduce H2 gas to a minimum to produce clean liquid Aluminum.
Available in two types, namely Nitrogen Base Degasser (Degastab SF1000) and Cl Base Degasser (Degastab SF2000).