MEASURING SENSOR FOR OXYGEN CONCENTRATION FOR MOLTEN METAL

PURPOSE:To obtain the excellent oxygen concentration measuring sensor having a film which is not cracked or exfoliated even when being immersed in the molten metal, by applying a mixture of powdered metal fluoride with a binder to the outer-peripheral surface of a solid electrolyte element which has oxygen ion conductivity. CONSTITUTION:The standard electrode materials (Ni+NiO, Mo+MoO3, etc.) 3 of the sensor which are immersed in the molten metal to constitute an oxygen concentration cell are filled up in the inside of the element 1 of solid electrolyte (ZrO2, etc.) having oxygen ion conductivity, and on the outer-peripheral surface of the element 1 the film 2 for improving the wetting property of the molten metal with the element 1 is formed by applying a slurry composed of metal fluoride, such as MgF2 and CaF2, which is hardly soluble in water, of Al2O3 particles and of an organic binder and by drying with contact of a finger at a room temperature and later at the temperature of 130 deg.C for twenty-four hous. A coating agent is composed, for instance, of 50wt% of Al2O3, 5- 18wt% of MgF2, 0-5wt% of CaF2 and water. When the element thus prepared is immersed directly in the molten metal, the fluoride thereof turns an oxide immediately and reacts to Al2O3 simultaneously, thus forming a firm combined layer. In this way, the sensor free from exfoliation and the like is obtained.