Anodic oxides physical properties

There are many types of silicon oxides such as thermal oxide, CVD oxide, native oxide, and anodized oxide. Only native oxide and anodic oxide are directly relevant in the context of this book. Anodic oxide film, which is involved in most of the electrochemical processes on silicon electrodes, has not been systematically understood, partly due to its lack of application in mainstream electronic device fabrication, and partly due to the great diversity of conditions under which anodic oxide can be formed. On the other hand, thermal oxide, due to its importance in silicon technology, has been investigated in extremely fine detail. This chapter will cover some aspects of thermal oxide such as growth kinetics and physical, electrical, and chemical properties. The data on anodic oxide will then be described relative to those of thermal oxide. 

FIGURE 3.22. The physical, electrical, and chemical properties of anodic oxides relative to thermal oxides. Data from Table 3.2. 

A. Grosman, M. Chamarro, V. Morazzani, C. Ortega, S. Rigo, J. Siejka, and H. J. von Bardeleben, Study of anodic oxidation of porous silicon Relation between growth and physical properties, /. Lumin. 57, 13, 1993. 

For perovskites that are used in high-temperature applications, such as solid oxide fuel cells that operate above 800°C or so, thermal expansion becomes an important physical property, as mismatch of the thermal expansion of the cell components, cathode, electrolyte and anode, will cause early cell failure. The magnitude of the thermal expansion of many perovskites is rooted in the thermal behaviour of the BXg octahedra and is associated with octahedral tilt, distortion and the bonding between the B-cation and the surrounding anions. These are all susceptible to modification as the temperature rises and can contribute to anomalies in thermal expansion characteristics. 

Mogensen, M., lindegaard, T., and Hansen, U. R. (1994). Physical properties of mixed conductor solid oxide fuel-cell anodes of doped CeOz- J Electrochem. Soc. 141 2122-2128. 

Two parts are treated one is the physical and chemical features of materials of molten carbonate fuel cells (MCFCs), and the other is performance analysis with a 100 cm class single cell. The characteristics of the fuel cell are determined by the electrolyte. The chemical and physical properties of the electrolyte with respect to gas solubility, ionic conductivity, dissolution of cathode material, corrosion, and electrolyte loss in the real cell are introduced. The reactirm characteristics of hydrogen oxidation in molten carbonates and materials for the anode of the MCFC are reviewed. The kinetics of the oxygen reduction reaction in the molten carbonates and state of the art of cathode materials are also described. Based on the reaction kinetics of electrodes, a performance analysis of MCFCs is introduced. The performance analysis has importance with respect to the increase in performance through material development and the extension of cell life by cell development. Conventional as well as relatively new analysis methods are introduced. 

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