National University of Science and Technology "MISIS" (MISiS)

V. I. Moskvitin, Professor, e-mail: vmoskvitin@mail.ru

D. A. Popov, Post-Graduate Student

S. V. Makhov, Senior Researcher of a Chair of Non-ferrous Metals and Gold

Zirconium is widely used as a modifier for aluminum and its alloys. The effect is already apparent at concentrations of zirconium, the order of hundredths part of a percent. Modifiers are addicted into the metal in the form of ligatures. The highest rates in obtaining ligatures has aluminothermic method of zirconium reduction from fluozirconate potassium or sodium. However, this way is expensive because of high cost and fluorozirconate scarcity. The cheapest and most accessible of the zirconium compounds is zirconium oxide. Its solubility in cryolite is only 2.3% at 1050 ^oC. To reduce the process temperature redundance of aluminum fluoride and potassium chloride was addicted in the salt system. A thermodynamic assessment of the possible occurrence of the reaction of ZrO₂ with components of the molten salt is performed. It is shown, that in the system is formed potassium hexafluorozirconate (K₂ZrF₆). Incrising the temperature, the probability of fluoridation of oxide zirconium with fluoride of aluminum with formation K₂ZrF₆ sharply increases. For its acknowledgement there are performed X-ray researches of salt melt samples on the DRON-diffractometer. The process of obtainning a ligature by aluminothermic reduction of zirconium from fluorozirconate of alkaline metal proceeds on reaction:

3K₂ZrF₆ + 4Al = 3Zr + 2K₃AlF₆ + 2AlF₃.

Reduced zirconium reacts with aluminum with formation intermetallide Al₃Zr. Solubility ZrO₂ with temperature increase grows in salt system NaF – AlF₃ – KCl. Thermodynamic calculation is carried out. There is a thermodynamic calculation of equilibrium concentration fluorozirconates of alkaline metals and it is maximum thermodynamic possible extraction of zirconium in a ligature at various temperatures of aluminothermic zirconium reduction. It is shown, that zirconium extraction from the molten salt is increasing by reducing the temperature. It can reach 90–93% at 800 ^oC. Thermodynamic calculation of expected sizes of extraction of zirconium in a ligature is carried out at various temperatures of aluminothermic zirconium reduction.

1. Posypayko V. I., Alekseeva E. A. Diagrammy plavkosti solevykh sistem (Fusibility curves of the salt systems). Moscow : Metallurgiya, 1977. 415 p.

2. Korshunov B. G., Safonov V. V., Drobot D. V. Diagrammy plavkosti galogenidnykh sistem perekhodnykh elementov (Fusibility curves of the halide systems of the transitional elements). Moscow : Metallurgiya, 1977. 248 p.

3. Napalkov V. I., Makhov S. V. Legirovanie i modifitsirovanie alyuminiya i magniya (Alloying and modification of aluminium and magnesium). Moscow : MISiS, 2002. 375 p.

4. Morachevskiy A. G., Sladkov I. B. Termodinamicheskie raschety v metallurgii (Thermodynamic calculations in metallurgy). Moscow : Metallurgiya, 1985. 137 p.

5. Ruzinov L. P., Gulyanitskiy B. S. Ravnovesnye prevrashcheniya metallurgicheskikh reaktsiy (Balanced transformations of metallurgical reactions). Moscow : Metallurgiya, 1975. 416 p.

6. Hansen M., Anderko K. Struktury dvoynykh splavov (Structures of double alloys). Moscow : Metallurgizdat, 1962. 608 p.