Zone refining is a metallurgical process used for the ultra-purification of crystalline solids, particularly semiconductors. It works on the principle that impurities are more soluble in the liquid phase than in the solid phase of the material. A molten zone is passed along the length of the material; as it moves, impurities segregate into the molten zone, leaving behind a purer solid. Silicon (Si), Germanium (Ge), and Gallium (Ga) are all semiconductors that require extremely high purity for use in electronic components. Zone refining is a standard method for purifying these elements.