SYNTHESIS OF NANOSIZED NIOBIUM PENTOXIDE FILMS FOR CREATING A CRYOGENIC GYROSCOPE ROTOR

A rotor coated by niobium is used for creating a cryogenic gyroscope. It is necessary to protect the coating from interaction with the environment (oxygen) that to extend the service life of the device. The protective coatings must have high dielectric characteristics, which can be achieved by electrochemical oxidation of niobium. The goal of this study is to determine optimal conditions for synthesis of nanoscale films of niobium pentoxide. Oxidation of niobium was carried out using an AUTOLAB PGSTAT 20 potentiostat with the GPES software package (version 4.4) at a temperature of 573 K using galvano- and potentiostatic electrolysis modes. The NaNO3-KNO3 (46 wt.% NaNO3, 54 wt.% KNO3) eutectic melt and 1% H3PO4 solution were used as electrolytes. A molybdenum rod served as the cathode, and a rolled niobium plate served as the anode. X-ray phase analysis was carried out on a DRON-2.0 diffractometer with Cu-Kα radiation. To study the microstructure, a Thixomet image analysis system was used, including an Observer.D1m optical microscope from Carl Zeiss with a video camera. The thickness and optical roughness of the films were measured by spectroscopic ellipsometry. It has been established that the oxide films obtained in the NaNO3-KNO3 eutectic melt with a galvanostatic mode were inhomogeneous and had many defects. The films obtained in a 1% H3PO4 solution with utilization the same mode had uncoated round areas according to the data of metallographic studies. Dense and defect-free films were obtained using the potentiostatic mode of electrolysis in 1% H3PO4 solution at a potential of 30 V and exposition time 120 min. The electrical insulating properties of niobium pentoxide films were studied by electrochemical impedance spectroscopy. It has been determined that the optimal mode of niobium oxidation is the potentiostatic mode of electrolysis at a potential of 90 V relatively to the molybdenum cathode.