Cryolitic vein XPS imaging from an industrial grade carbon

Aluminium carbide formation and subsequent dissolution is a generally accepted mechanism to explain the cathode wear in the Hall-Heroult industry. Carbide formation is thought to occur inside the cathode pores. Being dependent upon cathodic current density, it is believed to be an electrochemical process. It is also associated with the presence of cryolitic bath species involved in the dissolution of the carbide layer and thus enabling further carbide formation. X-Ray Photoelectron Spectroscopy imaging has the capacity to illustrate both the species chemistry and the spatial localization of such species. However, spectroscopic imaging requires long acquisition time. The value of mathematical treatment becomes obvious when applying multivariate data analysis on raw data. Principal Component Analysis (PCA) can substantially reduce the collection time without reducing the analysis quality of the data. In the current work, the C 1s photoelectron region was imaged and aluminium carbide (Al4C3), aluminium oxycarbide (Al4O4C and Al2OC), and graphite (C) were spatially tracked within the first millimetres under the cathode block surface. Preliminary work on differentiating between cryolite (Na3AlF6), alumina (Al2O3), and Al4C3 in the Al 2p narrow scan regions was conducted. More generally, the XPS analysis enabled further investigation of the chemical species present in bath penetrated veins of the carbon cathode. (C) 2013 Elsevier B.V. All rights reserved.