The compatibility of alumina ceramics with liquid sodium

Single Crystal and Sintered Alumina Corrosion in Liquid Sodium

“…The IGC is particularly damaging since once initiated over a depth of several grains, rows of grains could become detached, leading to large weight loss or even to the complete disintegration of the specimen over a relatively short time. According to Kano and Mayer [6][7], trace impurities in ceramic such as silica (SiO2) play a major role in its occurrence: silica is said to segregate at grain boundaries and to preferentially react with liquid metal or with dissolved oxygen, according to the following thermodynamically possible reactions (free enthalpies from [8]): Kinetics is fast above 300 °C [9]. Sodium silicate (Na2SiO3) forms probably a liquid phase at the grain boundary and is highly soluble in liquid sodium.…”

“…The available literature data suggest that the reaction kinetics of these thermodynamically more stable oxides is low. Jung [9] observed the formation of sodium aluminate layer, with a colored (blackened) alumina zone underneath, on high density and high purity alumina specimen immersed in static condition at 900 °C in oxygen saturated sodium, conditions that are extremely severe. The thickness of the sodium aluminate layer appeared to increase with increasing test duration (400 µm -100 h).…”

“…The apparent 'dissolution' reaction is then characterized by weight loss, as measured by Kano [6] and should then present a receding interface. Jung [9] observed the formation of thick sodium aluminate layer, either because the volume of the test capsule was small so that the liquid metal got quickly saturated in dissolved sodium aluminate oxide, or because the conditions were extremely severe both in temperature and in oxygen content, or for both reasons. Lastly, sodium may reduce the oxide substrate because of its high reducing oxygen potential, leading to the formation of metal (Al) as well as to the formation of point defects, also known as colored centers or 'F' centers ( • according to the Kröger & Vink notation).…”

“…Lastly, sodium may reduce the oxide substrate because of its high reducing oxygen potential, leading to the formation of metal (Al) as well as to the formation of point defects, also known as colored centers or 'F' centers ( • according to the Kröger & Vink notation). This blackened surface layer presents a thickness that increases with temperature and exposure time [9], but only a small fraction of the vacancies are involved. Heat treatment of the specimen (800 °C -2 h) after the sodium test corresponds to the re-oxidation: weight gain appears indeed as negligible [9].…”

“…This blackened surface layer presents a thickness that increases with temperature and exposure time [9], but only a small fraction of the vacancies are involved. Heat treatment of the specimen (800 °C -2 h) after the sodium test corresponds to the re-oxidation: weight gain appears indeed as negligible [9]. However, if its effect on the mechanical properties is unknown, its effect on the electrical properties is an increase of the electronic conduction.…”