Synthesis of Al-Zr Alloys Via ZrO 2 Aluminum-Thermal Reduction in KF-AlF 3 -Based Melts

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ZIRCONIUM dioxide is the most widely available and cheap raw material for the production of aluminum-zirconium (Al-Zr) alloys. Such alloys are used in the aerospace industry and new branches for electrical engineering, as well as in the production of special-purpose Al-Zr-based alloys with titanium, silicon, scandium, and other metals. The existing methods for creating Al-Zr alloys are not economic and do not result in the production of high-quality alloys. The dissolution of metallic zirconium in an aluminum-containing melt at temperatures ranging from 1073 K to 1273 K (800 °C to 1000 °C) is a very long process, and increasing the zirconium content in an alloy by more than 2 wt pct leads to an increase in the amount of intermetallic compounds within the alloy.[1] From the currently available methods of obtaining Al-Zr alloys, the best performance is obtained using the method of aluminum-thermal recovery of zirconium from potassium or sodium fluoro-zirconates formed in KF-ZrF4 and NaF-ZrF4 systems,[2,3] respectively. Using this method, the temperature range of extraction of zirconium from its dioxide to form the alloy is from 90 to 95 pct. However, due to the scarcity and consequent high cost of alkali fluoro-zirconates, this method has not found wide application. The data on ZrO2 solubility are necessary for the development of the technology for Al-Zr alloy synthesis PAVEL S. PERSHIN, A.A. KATAEV, and A.V. SUZDALTSEV are with the Institute of High-Temperature Electrochemistry of Ural Branch of the Russian Academy of Sciences, Akademicheskaya st., 20, Yekaterinburg, Russia 620137. Contact email: paff[email protected] A.A. FILATOV, and YU. P. ZAIKOV are with the Institute of HighTemperature Electrochemistry of Ural Branch of the Russian Academy of Sciences, and also with the Ural Federal University, Mira st, 19, Yekaterinburg, Russia 620002. Manuscript submitted November 21, 2016. Article published online April 10, 2017. 1962—VOLUME 48B, AUGUST 2017

via ZrO2 reduction in aluminum-containing melts. The concentration of zirconium in the final alloy is directly dependent on the concentration of zirconium in the molten salt, and consequently, on the solubility of zirconium dioxide in the melt. Data from the literature on the solubility of ZrO2 in molten KF-AlF3 and KF-NaF-AlF3 are limited. It is known that ZrO2 interacts with fluoride compounds; however, its solubility in these salts is low. According to Reference 4, cryolite NaF-AlF3 at 1273 K (1000 °C) dissolves only 2.2 wt pct of ZrO2. A thermodynamic assessment[1] of possible zirconium dioxide interactions with the components of molten cryolite showed the possibility of sodium hexa-fluoro-zirconate formation in the temperature region from 1073 K (800 °C) to 1323 K (1050 °C). Based on these data, the authors conclude that the solvent of both ZrO2 and Al2O3 is the AlF63 ion. Other authors[5] studied the effects of various process parameters on the extraction of zirconium when obtaining Al-Zr alloys and showed that the highest solubility of zirconium dioxide in cryo