EXPERIMENTAL STUDY OF THE APPLICABILITY OF SOLID OXIDE ELECTROLYTE TO DETERMINE THE LOWER LIMIT OF OXYGEN CONTROL IN SODIUM

Solid oxide electrolyte based on zirconium dioxide stabilized with calcium oxide or yttrium oxide is the most studied. It’s currently widely used to control oxygen in gas, in the metallurgical industry production of steel, non-ferrous metals, operation of nuclear power plants with a heavy coolant, and therefore it’s interest to use it to control the oxygen content in alkaline coolants, for example, in sodium. Sodium is an extremely reducing agent for metal oxides. There are practically no literature data on the limiting value of the partial oxygen pressure and temperature for an electrolyte based on zirconium dioxide stabilized with yttrium oxide. This work presents experimental studies of the applicability of solid polycrystalline oxide electrolyte 0.85ZrO2•0.15Y2O3 for determining the oxygen content in sodium at a temperature of (400 ± 5) °C. Studies of the electrolyte 0.85ZrO2•0.15Y2O3 were carried out in the working section, which is a galvanic concentration cell (GCC). The electrolyte in the form of a pellet with a diameter of 4 mm and a length of 5-7 mm is hermetically inserted into an insulator made of alumina-magnesia spinel with the addition of magnesium oxide, which is reinforced with EI-852 steel. The reference electrode was placed in an insulator made of magnesia-alumina spinel with the addition of magnesium oxide and was hermetically sealed from the environment by a sealed lead. A weighed portion of sodium was placed in a small tank made of nickel. To change the concentration of oxygen in sodium, weighed portions of a deoxidizer were introduced into it. Lithium was used as a deoxidizer. EMF of GCC was measured by a ph-meter - ionometer “Expert 001” combined with a computer. The kinetics of the change in the each lithium sample input EMF of the GCC is presented. The weighed portions of lithium were injected until the EMF of the GCC changes with the last injection of the subsequent weighed portion. This value of the EMF of the GCC will be the limit of the applicability of a solid electrolyte to control and dose oxygen into sodium. From the measured value of the EMF GCC obtained after introducing weighed portions of lithium, the lower limit of applicability of the electrolyte was calculated from the partial pressure of oxygen over sodium and the lower limit of applicability of the electrolyte was determined from the oxygen content in sodium using the Nodena formula for the oxygen solubility in sodium. It is shown that the lower limit of applicability of solid polycrystalline oxide electrolyte 0.85ZrO2•0.15Y2O3 for monitoring the oxygen content in sodium at a temperature of (400 ± 5) °C is ~7•10-5 ppm, and for the partial pressure of oxygen over sodium - 4.6•10-59 Pa.