Loss in Cathode Life Resulting from the Shutdown and Restart of Potlines at Aluminum Smelters

Abstract

Cathode damage due to cooling resulting from the shutdown and restart of cells is commonly recognized in the primary aluminum industry. Cooling cells to ambient temperature results in the freezing of bath and metal in cells and causes irreversible and non-repairable damage to the carbon cathode lining. Cooling ultimately causes the formation of numerous cooling cracks on the surface of cathode blocks and in the seams between blocks. The cracks are caused because the strain setup by thermal gradients in the cooling cathode lining exceeds the strain capacity of the sodium saturated cathode. Carbon cathode behaves as an elastoplastic material under stress. Sodium intercalated between carbon layers changes the properties of carbon cathode blocks causing them to become less elastic and more brittle. The loss in potlife due to the shutdown of potlines can be substantially different at smelters depending on the specific circumstances.