Red-giant branch Red-giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass stars. Red-giant-branch stars have an inert helium core surrounded by a shell of hydrogen fusing via the CNO cycle. They are K- and M-class stars much larger and more luminous than main-sequence stars of the same temperature. Red giants were identified early in the 20th century when the use of the Hertzsprung–Russell diagram made it clear that there
Hydrogen gas porosity Hydrogen gas porosity Hydrogen gas porosity is an aluminium casting defect under the form of a porosity or void in an aluminium casting caused by a high level of hydrogen gas (H) dissolved in the aluminium at liquid phase. Because the solubility of hydrogen in solid aluminium is much smaller than in liquid aluminium, when the aluminium freezes, the dissolved hydrogen gas creates porosity in solid aluminium. Aluminum smelters and aluminum foundries want to produce high quality aluminum and shape castings with minimum porosity. This can be obtained by reducing the amount of hydrogen in the liquid aluminium alloy. Hydrogen