... ore is heated in a pressure vessel along with a sodium hydroxide solution at a temperature of 150 to 200 °C. At ... liquid is cooled, and then seeded with fine-grained aluminium hydroxide. The gibbsite is usually converted into aluminium oxide, Al2O3, by ... the Hall–Héroult process, heating ore along with elemental sodium or potassium in a vacuum made elemental aluminium. The method ...