Correlation of heat treatment temperature and phase composition in nanodispersed precursors based on systems TiO 2 , ZrO
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Vol. 53, No. 6, March, 2013
CORRELATION OF HEAT TREATMENT TEMPERATURE AND PHASE COMPOSITION IN NANODISPERSED PRECURSORS BASED ON SYSTEMS TiO2, ZrO2, TiO2–Y2O3–ZrO2 V. G. Konakov,1 N. V. Borisova,1 S. N. Golubev,1 E. N. Solov’eva,1 and V. M. Ushakov1 Translated from Novye Ogneupory, No. 12, pp. 42 – 47, December, 2012.
Original article submitted May 21, 2012. Powder precursors based on the system (mol.%) 8Y2O3–(92 – X) ZrO2–XTiO2 are synthesized by a sol-gel method in a reverse coprecipitation version. The correlation of phase ratio evolution in precursors and particle dimensions within them are studied as a function of precursor heat treatment temperature. It is shown that in the temperature range 400 – 1500°C and compositions 0 £ X £ 20 the main crystal phases are cubic solid solutions. Their formation mechanism is proposed. Keywords: precursor, phase, crystallization, solid solution, crystal sizes, dispersion and structurally bonded water.
Their existence gives rise at high temperature to oxygen transfer through a solid electrolyte by a vacancy mechanism:
INTRODUCTION In practical and scientific activity fluorite-like solid solutions based on the system Y2O3–ZrO2 are used extensively as high-temperature solid electrolytes. These electrolytes are used in fuel cells, in oxygen sensors, accomplishing monitoring and control for oxygen partial pressure in gas atmospheres and oxygen ion activity in oxide melts [1], and this makes it possible to control production processes during manufacture of ferrous and nonferrous metals, glass, refractories, etc. On introducing Y2O3 into ZrO2 ions of Y3+ are built into ¢ ), and oxygen the cation sublattice instead of Zr4+ ions (YZr
O O ® 1 2 O 2 + VO•• + 2e, where OO, VO•• , and e are oxygen at a lattice site, positively charged oxygen vacancy, and electron respectively. Thus, the overall conductivity st is sum of ion sion and electron se components: st = sion + se = st (tion + te), tion + te = 1, where tion and te are transfer number of oxygen ions and electrons respectively. The maximum ionic conduction of stabilized ZrO2 (tion ³ 0.99) is observed when the concentration of an oxide-addition is close to its minimum value, required for total stabilization of the cubic fluorite-like phase. It depends to a considerable extent on conditions for preparing solid electrolyte and its microstructure, connected with its fineness, oxide-addition segregation, presence of impurities, formation of ordered microdomains, and existence of kinetically retarded phase transitions. An increase in oxide-addition concentration leads to a reduction in ionic conduction as a result of forming complex defects, consisting of associated oxygen vacancies and oxide-addition cations, and exhibiting low mobility [3]. It has been shown that presence of the best operating properties (high anionic conduction, mechanical strength, absence of cracking, connected with phase transitions during cooling) in determining oxygen partial pressure
ions, added by Y2O3, finish building the anion sublattice (OOx ). However,
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