In an aluminum smelting plant, aluminum is produced by passing high levels of electrical current through alumina dissolved in a sodium-aluminum-fluoride electrolytic bath. The electricity flows from a carbon anode through the alumina solution, and out through the carbon cathode and through the lining of the pot. As the alumina (aluminum oxide) is converted to elemental aluminum, the carbon reacts with oxygen (creating CO2 gas), and 99.7% pure aluminum falls to the bottom of the pot to be periodically siphoned off.
The smelting of aluminum occurs at 800 C / 1475 F, while the melting point of aluminum is 660 C / 1190 F. As a result, the molten aluminum contains excess thermal energy as it is drawn from the smelting pot. This excess energy is sometimes used to melt supplementary recycled aluminum before the metal is poured into the ingot molds. The addition of this supplemental aluminum cools the stream, therefore an accurate, real-time stream temperature is essential for optimal efficiency.
Hot metal temperature may be confirmed by measuring the stream temperature as it flows from one vessel to another, or while free falling from a trough. While these measurements often may be made using an immersion thermocouple, an infrared thermometer is more effective and efficient when measuring in locations that are fast-flowing. In these locations, the use of thermocouples is often problematic due to the highly corrosive nature of aluminum.