Aluminum- Oxygen- Zirconium

Phase diagram, Crystallographic and Thermodynamic Data

Younes Sina

In principle it is possible to dope crystals in two different ways:

1) Doping of an existing crystal

2) Growing the crystal from the normal constituents plus the desired amount of the foreign atoms

1) Doping of an existing crystal

There are 3 ways to introduce foreign atoms into an existing crystal:

1) Bringing the crystal into contact with another phase which contains the desired foreign atoms. This then enter the crystal by solid state diffusion.

2) Bombarding the crystal with appropriate ions

3) Nuclear transmutation

There are no ternary phases in the Al-O-Zr system. Monoclinic αZrO2 practically does notdissolve Al2O3. According to [1964Alp] the solubility of ZrO2 in Al2O3 is 0.83 mol%.[2000Jer] found that it is even smaller (0.008 mol% ZrO2).

Al2O3-ZrO2

Fig. Zr-083—System ZrO2-Al2O3, showing a new phase, e-Al2O3 (Al2O3:ZrO2, 99:1 wt%).G. Cevales, Ber. Dtsch. Keram. Ges., 45 [5] 216-219 (1968). Starting materials were reagent-grade ZrO2 and Al2O3 (purity 99.88%) which had been heated to 1350°C for 15 h. Mixtures were formulated at 5% intervals and additionally at 0.2% intervals in the regions 55 to 59% Al2O3 and 95 to 100% Al2O3. Ground mixtures with <70 wt% ZrO2 were melted in W crucibles in a vacuum furnace. Mixtures with >70 wt% ZrO2

were heated in an electric arc furnace. The melting temperatures were measured with a calibrated optical pyrometer, and observations were made on two series of compositions, one for heating and one for cooling. The composition Al2O3:ZrO2 (99.1 wt%), when fused in the arc furnace and quenched in H2O, yielded a new phase, e-Al2O3. The phase was indexed on a hexagonal unit cell but with several low-angle peaks unaccounted for. The new phase was verified by high-temperature X-ray diffractometry, using an IR strip furnace and optical pyrometry. However, the high-temperature X-ray pattern reproduced is not convincing. The solubility of Al2O3 in ZrO2 was not studied because of the more general problem of the stabilization of tetragonal ZrO2. For a version of the system in an Ar atmosphere, see Fig. Zr-084. The polymorphism of pure ZrO2 is shown in Figs. Zr-042 and Zr-043.

0 20 40 60 80 100

1600

1800

2000

2200

2400

2600

Mol %

T, o C

ZrO2 Al2 O3

Liquid

ZrO2 + Liq.

-Al2 O3

1960o

1930o

-Al2 O3 + Liq.

(61.7%)1710o10o

Al2 O3 + ZrO2

Fig. Zr-083

Al2O3-ZrO2

Fig. Zr-085—System ZrO2-Al2O3 (calculated).P. Doerner, L. J. Gauckler, H. Krieg, H. L. Lukas, G. Petzow, and J. Weiss, CALPHAD: Comput. Coupling Phase Diagrams Thermochem., 3 [4] 241-257 (1979).

The program used is for the calculation of condensed phase fields.1,2 The strategy for the calculation is outlined in[3]All thermodynamic data used are taken from the JANAF tables [4]. For ZrO2 only a monoclinic and a tetragonal modification were included. In the case of the latter, the data were modified in such a manner as to yield the correct melting point. Both solid phases are treated as purely stoichiometric.The mixing entropy of the liquid phase is described as an ideal mixture of molar units of AlO1.5 and ZrO2; therefore, only mixing of cation units is modeled. For the diagram, the results have been transformed into the molar units Al2O3 and ZrO2.The whole composition range is covered. The temperature range of the calculation is 1527° to 2727°C. The pressure is not included as a variable in the program (normal conditions in air are simulated).The corresponding experimental diagram in Fig. Zr-084 is reproduced reasonably well especially if one takes into account that only ideal mixing for the liquid phase was used and no higher terms were introduced.

1. B. Zimmermann; Ph.D. Dissertation. University of Stuttgart, Stuttgart, Germany, 1976.2. L. J. Gauckler, H. L. Lukas, E. Th. Henig, and G. Petzow, CALPHAD: Comput. Coupling Phase Diagrams Thermochem., 2 [4] 349-356 (1978).3. H. L. Lukas, J. Weiss, and E. Th. Henig, CALPHAD: Comput. Coupling Phase Diagrams Thermochem., 6 [3] 229-251 (1982).4. D. R. Stull and H. Prophet; "JANAF Thermochemical Tables, 2nd ed.", Natl. Stand. Ref. Data Ser. (U. S., Natl. Bur. Stand.), Rep. No. NSRDS-NBS 37, National Bureau of Standards, U. S. Department of Commerce; Washington, D.C., 1141 pp. (1971).

Fig. Zr-085

0 20 40 60 80 100 1600

1800

2000

2200

2400

2600

Mol %

T, o C

ZrO2 Al2 O3

Liquid

1845o

Al2O3-ZrO2

Fig. Zr-086—System ZrO2-Al2O3. Binary phase relations under He atmosphere.G. R. Fischer, L. J. Manfredo, R. N. McNally, and R. C. Doman, J. Mater. Sci., 16 [12] 3447-3451 (1981).

Approximately 20 samples were examined to determine liquidus temperature in situ using high-temperature X-ray diffraction. Starting materials were coprecipitated from mixed metal chloride solutions using NH4OH. The resultant gel was stirred, dried in air, and then calcined to 1000°C. Chemical analysis of the resultant powders resulted in a maximum absolute error of ±1 wt% ZrO2. (All reported ZrO2 values include a relative 1.8 wt% HfO2). Semiquantitative spectrographic analysis for trace impurities indicated generally <1000 ppm total impurities with no detectable chlorine in any sample.A second set of samples were prepared by solid state reaction synthesis of "reagent-grade" oxides for determination of the eutectic composition through microstructural examination of fused samples. For liquidus studies, the coprecipitated mixtures were ground to smaller than 325 mesh and mixed with xylene for application to the 5-mm Ta-foil strip heater substrate. Approximately 0.05-g samples were used. High-temperature X-ray diffraction studies were performed using a wide-angle goniometer with a detector panel, and equipped with a modified commercial high-temperature attachment. All studies used Ni-filtered CuKa radiation, with an atmosphere of purified helium maintained to prevent oxidation of the sample holders. Temperature measurement was performed optically, matching the apparent brightness of the Ta holder with the pyrometer filament. Accuracy was assured by calibration curves established using known melting points of Pt, Au, and the end-member oxides and was said to be ±20°C. Melting was determined through observance of the disappearance of characteristic diffraction lines as the sample temperature was increased step-wise. The eutectic composition, 42.5 ±1 wt% (61.8 mol%) ZrO2, was confirmed by optical microscopy on polished sections of samples surrounding the apparent liquidus minimum composition. These samples were fused in an induction furnace.

Fig. Zr-086

0 20 40 60 80 100 1800

2000

2200

2400

2600

2800

Mol %

T, o C

Al2 O3ZrO2

Liquid

(61.8%)1910o10o

Al2O3-ZrO2 Fig. Zr-087—System ZrO2-1/2(Al2O3). Calculated. F ss, T ss, and M ss = cubic, tetragonal, and monoclinic ZrO2 solid solutions; Crn = corundum (Al2O3).R. G. J. Ball, M. A. Mignanelli, T. I. Barry, and J. A. Gisby, J. Nucl. Mater., 201, 238-249 (1993).

Models were developed in this paper for phase equilibria of oxides subject to reactions between nuclear reactor core debris and concrete. Calculations were performed using thermodynamic and phase equilibria data from the literature. The optimized description of crystalline and liuqid phases obtained was then used to predict phase relationships in higher-order systems.The optimization programs used included one reported in Ref. [1]. The reference value for the Gibbs energy of a phase that was used was the weighted sum of the enthalpies of its constituent elements in their standard states at 25°C. The temperature dependence of the Gibbs energy is expressed in an equation that includes experimental enthalpy, entropy, and heat capacity data. For solution phases, the Gibbs energy mixing is included using an associated solution model.2 Thermodynamic data were obtained by critically assessing the results in Refs. [3-11]. 1. H. L. Lukas, E. Th. Henig, and B. Zimmermann, CALPHAD: Comput. Coupling Phase Diagrams Thermochem., 1 [3] 225-236 (1977).2. F. Sommer, Z. Metallkd., 73 [2] 72-76 (1982).3. M. W. Chase, Jr., C. A. Davies, J. R. Downey, Jr., D. J. Frurip, R. A. McDonald, and A. N. Syverud, J. Phys. Chem. Ref. Data, Suppl., 14 [1] 927-1856 (1985).4. I. Ansara and B. Sundman, "The Scientific Group Thermodata Europe"; pp. 154-158 in Proc. Int. CODATA Conf., 10th (Computing, Handling and Dissemination of Data), 1986. Edited by P. S. Glaeser, Elsevier Science B.V., Amsterdam, Netherlands, 1987.5. E. H. P. Cordfunke and R. J. M. Konings; Thermochemical Data for Reactor Materials and Fission Products, 695 pp. North-Holland, Amsterdam, Netherlands, 1990.6. M. H. Rand, R. J. Ackermann, F. Groenvold, F. L. Oetting, and A. Pattoret, Rev. Int. Hautes Temp. Refract., 15 [4] 355-365 (1978).7. J. D. Cox, D. D. Wagman, and V. A. Medvedev; CODATA Key Values for Thermodynamics, 271 pp. Hemisphere Publishing, Bristol, Pennsylvania, 1989.8. D. D. Wagman, W. H. Evans, V. B. Parker, R. H. Schumm, I. Halow, S. M. Bailey, K. L. Churney, and R. L. Nuttall, J. Phys. Chem. Ref. Data, Suppl., 11 [2] 1-392 (1982).9. V. P. Glushko, L. V. Gurvich, I. V. Veyts, C. B. Alcock, G. A. Bergman, G. A. Khachkuruzov, V. A. Medvedev, and V. S. Yungman; Thermodynamic Properties of Individual Substances: A Hand Book. Hemisphere Publishing, Bristol, Pennsylvania, 1981 & 1989.10. I. Barin and O. Knacke; Thermochemical Properties of Inorganic Substances, 921 pp. Springer- Verlag, Berlin, Germany, 1973.11. L. B. Pankratz, "Thermodynamic Properties of Elements and Oxides", Bull. - U.S., Bur. Mines, Bull. No. 672, U. S. Government Printing Office; Washington, D.C., 509 pp. (1982).

Fig. Zr-087

0 20 40 60 80 100 1000

1400

1800

2200

2600

Mol %

T, o C

1/2(Al2 O 3)

ZrO2

Liquid

Crn + Liq.

F ss+ Liq.

T ss + Liq.

T ss + Crn

Crn + M ss

Al2O3-ZrO2

Fig. Zr-088—System ZrO2-Al2O3. T = tetragonal; M = monoclinic; F = fluorite-type (cubic).S. N. Lakiza and L. M. Lopato, J. Am. Ceram. Soc., 80 [4] 893-902 (1997). Powders of ZrO2 and Al2O3 (both 99.99% pure) were used to prepare specimens at 5 mol% intervals. Samples for 17 compositions were blended in an agate mortar with ethanol, pressed into pellets, and heated in Mo containers in a DTA apparatus under He to 2500°C. The investigation also used derivative thermal analysis to 3000°C with a solar furnace, X-ray powder diffraction, petrographic analysis, microstructural phase analysis, and electron microprobe X-ray analysis. 1. F. Schmid and D. J. Viechnicki, J. Mater. Sci., 5 [6] 470-473 (1970).2. J. Echigoya, Y. Takabayashi, K. Sasaki, S. Hayashi, and H. Suto, Trans. Jpn. Inst. Met., 27 [2] 102-107 (1986).3. A. V. Shevchenko, L. M. Lopato, G. I. Gerasimyuk, and V. D. Tkachenko, Izv. Akad. Nauk SSSR, Neorg. Mater., 26 [4] 839-842 (1990); Inorg. Mater. (Engl. Transl.), 26 [4] 705-708 (1990).

Fig. Zr-088

0 20 40 60 80 100

1000

1400

1800

2200

2600

Mol %

T, o C

ZrO2 Al2 O3

Liquid

Al2 O3 + Liq.

(63%)1860o

F-ZrO2

F-ZrO2 + Liq.

(20%)2260o

T-ZrO2

+ F-ZrO2

T-ZrO2 + Liq.

T-ZrO2

T-ZrO2 + Al2 O3

1150oT-ZrO2 + M-ZrO2

M-ZrO2 M-ZrO2 + Al2 O3

1170o

2370o

2710o

Al2O3-ZrO2

Fig. 11136—System ZrO2-Al2O3. T-x sections of the phase diagram for the ZrO2-AlO1.5 system. (A) Calculated T-x phase diagram; (B) calculated ToL ss curve together with the extended T ss data from Ref. 1. C ss, T ss, and M ss symbols denote cubic (fluorite-type) zirconia solid solution, tetragonal zirconia solid solution, and monoclinic zirconia solid solution, respectively.T. Wang and Z. P. Jin, J. Cent. South Univ. Technol. (Engl. Ed.), 4 [2] 108-112 (1997).

Phase relations in the quasibinary ZrO2-AlO1.5 system were assessed by means of the CALPHAD technique. The liquid phase, cubic (fluorite-type) zirconia solid solution, and tetragonal zirconia solid solution were described by a regular solution model. Monoclinic zirconia and a-AlO1.5 were treated as stoichiometric phases. A consistent set of optimized parameters were obtained to agree with the available experimental data. The assessed data for invariant equilibria in the ZrO2-AlO1.5 system are listed in the following table. —————————————————————— Composition (mol% AlO1.5) Temp. (°C)—————————————————————— C ss = Liquid + T ss 3.4 38.6 2.5 2263 Liquid = T ss + α-AlO1.5

77.9 6.3 100 1862 T ss = M ss + a-AlO1.5

1.1 0.0 100 1140—————————————————————— The calculated eutectic temperature is consistent with the results of Refs. 2-4. The calculated eutectic composition agrees well with that from Refs. 2-6 within the estimated errors.The accuracy of the phase diagram is dependent on the entire set of the experimental and thermodynamic information; further studies are needed for the equilibrium solubilities of AlO1.5 in ZrO2 phases.The results are applied to the production of highly corrosion resistant and refractory materials.

1. M. L. Balmer, F. F. Lange, and C. G. Levi, J. Am. Ceram. Soc., 77 [8] 2069-2075 (1994).2. F. Schmid and D. J. Viechnicki, J. Mater. Sci., 5 [6] 470-473 (1970).3. A. V. Shevchenko, L. M. Lopato, G. I. Gerasimyuk, and V. D. Tkachenko, Izv. Akad. Nauk SSSR, Neorg. Mater., 26 [4] 839-842 (1990); Inorg. Mater. (Engl. Transl.), 26 [4] 705-708 (1990).4. S. N. Lakiza, L. M. Lopato, and A. V. Shevchenko, Poroshk. Metall. (Kiev), 33 [9-10] 46-51 (1994); Sov. Powder Metall. Met. Ceram. (Engl. Transl.), 33 [9-10] 486-490 (1994).5. J. B. MacChesney and P. E. Rosenberg; pp. 114-165 in Phase Diagrams: Materials Science and Technology, Vol. I (Theory, Principles, and Techniques of Phase Diagrams). Edited by A. M. Alper. Academic Press, London/New York, 1970.6. I. Shindo, S. Takekawa, K. Kosuda, T. Suzuki, and Y. Kawata, Adv. Ceram, 12 [Sci. Technol. Zirconia 2] 181-189 (1984).

Fig. 11136

0 20 40 60 80 100 900

1300

1700

2100

2500

Mol %

T, o C

ZrO2 AlO1 .5

Liquid

1149o

1862o

2263o

C ss

T ss

M ss

Al2O3-ZrO2

Fig. Zr-084—System ZrO2-Al2O3 in Ar

A. M. Alper, "Interrelationship of Phase Equilibriums, Microstructure, and Properties in Fusion-Cast Ceramics"; pp. 335-369, in Sci. Ceram, Vol. 3. Edited by G. H. Stewart. Academic Press, London, United Kingdom, 1967.

Experiments were conducted in an induction furnace, with setter materials of the same compositions as the mixtures being heated. About 16 samples were melted in an Ar atmosphere, and temperature was measured with an optical pyrometer. According to Ref. 1, <1% ZrO2 goes into solid solution in a-Al2O3 and up to ~7% Al2O3 can form a solid solution with ZrO2. The distribution of phases obtained was found to be related to the phase diagram and was dependent on composition and cooling rate.

1. A. M. Alper, R. N. McNally, and R. C. Doman, Am. Ceram. Soc. Bull., 43 [9] 643-643 (1964).

0 20 40 60 80 100 1600

1800

2000

2200

2400

2600

Mol %

T, o C

ZrO2 Al2 O3

Liquid

Al2 O3 ss + Liq.ZrO2 ss + Liq.

Al2 O3 ss + ZrO2 ss

Al2 O3 ssZrO2 ss

Fig. Zr-084

Zirconia was prepared by firing the coprecipitate from ZrOCl2 and AlCl3 mixed aqueous solution with ammonia. When fired above 600°C, the products were fine crystalline tetragonal zirconia of crystallite size <10 nm. In previous studies, the tetragonal phase had been assumed to be a (Zr 4+

1-x Al3+x)O2-x/2 solid solution, where x < 0.25. However, X-ray

diffraction pattern simulation and Al K-edge X-ray absorption near-edge structure (XANES) spectroscopy confirmed the present product to be a mixture of t-ZrO2 fine powder with a small amount of δ-Al2O3 of very low crystallinity, even below the expected compositional range of x < 0.25 in the a (Zr 4+

1-x Al3+x)O2-x/2 solid solution.

Shinichi Kikkawa, Akio Kijima, Ken Hirota, and Osamu YamamotoDepartment of Material Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628, Japan

Growing the crystal from the normal constituents plus the desired amount of the foreign atoms

Because of a high melting point of sapphire ( Tm=2323 K), the growth of single crystals from melt is performed in most cases using tungsten or molybdenum–tungsten crucibles in heating units (furnaces) made of sheet molybdenum. For this reason, both metals arehighly probable impurities in the final sapphire substrates. Additional impurities can pass to as-grown crystals from the initial materials.

Glow Discharge Mass Spectroscopy (GDMS) analysis of Heat Exchanger Method (HEM) sapphire showed the following typical impurities (all values in ppm):

Na 1 Si 4 Fe 0.6 Ca 2 Mg 2 Ga 2 Cr 0.2 Ni 0.3 Ti <0.3 Mn 0.5 Cu 0.1 Mo <0.5 Zn 1 Zr 1 Most of the impurities are close to the detectability limits of GDMS.

Diffusion studies coupled with doping data can also yield information about thelikely defect types present in a solid. For example, zirconia, ZrO2, as an impurityin alumina, Al2O3. The Zr4+ cations are accommodated on Al3+ sites as substitutional defects with an effective positive charge, Zr •

Al. As ZrO2 is oxygen rich compared to alumina, the extra oxygen can either be accommodated as oxygen interstitials, Oi

2’:

2 Zro2 (Al2O3)→2 Zr•Al+ 3 Oo+Oi2’

or balanced by Al3+ vacancies, V3’Al:

3 ZrO2 (Al2O3)→3 Zr•Al+ 6 Oo+ V3’

Al

Isothermal sections for the Al-O-Zr system were constructed based on diffusion couplestudies. No ternary phases have been observed.

[1977Guk, 1978Guk1, 1978Guk2, 1978Guk3

Al-O-Zr. Isothermal section at 1300°C

Isothermal sections for the Al-O- Zr system were constructed based on diffusion couplestudies. No ternary phases have been observed.

[1977Guk, 1978Guk1, 1978Guk2, 1978Guk3

Al-O-Zr. Isothermal section at 1130°C

Mahabad- Iran