Kinetic of ZrO2- and HfO2ceramic destoimetrization at contact to active metal melts


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Adhesion of Melts and Brazing of Materials - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2019, #52


Materials based on zirconium dioxide and hafnium dioxide lose oxygen when interacting with active metal melts, that is, containing elements with high affinity for oxygen, such as titanium. As a result, non-stoichiometric phases with oxygen deficiency (ZrO2-x, HfO2-x) are formed, the electroneutrality of the crystal is maintained due to the formation of farben-centers, i.e. oxygen vacancies holdштп electrons. A characteristic sign of the farben centers in the crystal structure presence is a significant darkening. Moreover, in the volume of ceramic (polycrystalline) materials the dark zone is characterized by a sufficiently strict board, it allowed to study the kinetics of its propagation directly under the experimental conditions, i.e., in contact with an active metal melt. The propagation of the oxygen-deficient zone in the volume of ZrO2- and HfO2-ceramics was studied, and the eutectic of the copper-titanium system was chosen as the active metal melt in contact with the ceramics. The experiments were carried out in vacuum, the temperatures were 900 and 1000 °C. It has been established that the dependences of the size of the dark zont on the exposure time obey the parabolic law, which is characteristic of diffusion processes. Also, an increase in temperature accelerates the spread of the dark region, and the temperature dependence for hafnium dioxide is more pronounced than for zirconium dioxide, it is consistent with published data on the mobility of oxygen anions in the materials under study. Thus, the propagation of the dark region is indeed a diffusion of farben centers. The diffusion coefficients of the farben centers were calculated; they are of the order of 10-5—10-4 cm², it corresponds to published data on the properties of ceramic materials based on zirconium dioxide and hafnium dioxide.