Application of Flame Jet Spray Technique to Manufacture of Oxygen Sensor

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As a method of direct measurement of oxygen content in molten metal and oxygen partial pressure in Atmosphere, the electorochemical method by use of solid electorolyte is well known. The principle of this method is based on an oxygen concentration cell, as shown in Equation (1). This cell is composed of a reference electrode of known oxygen potential, a solid electrolyte which is an oxygen ion conductor, and an electrode with unknown oxygen potential.The unknown oxygen partial pressure, Po_2, is then calculated by the EMF (E) represented by Equation (2). To facilitate the handling of the existing oxygen sensor and to reduce its cost, improved response character and mass-production are essential. To meet these demands, a new type of miniaturized oxygen concentration cell has been developed, using a spraying technique.The new oxygen concentration cell utilizes Fe/FeO coating as the reference electrode, and stabilized zirconia coating as the solid electrolyte. The solid electrolyte are the thermal sprayed one layer on the substrate. During the development stage, the shape of the substrate and the coating thickness were investigated to improve the measurement accuracy which is influenced by spalling of the coating due to thermal shock or by a leakage of oxygen gas. The thickness of Fe/FeO coating as the reference electrode is a leading factor to determine the senor properties. The test performance has revealed that the oxygen sensor made by the thermal spray technique, is in the same performance level as the conventional tubular type cell.