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The standard molar Gibbs free energy of formation of PbO Oxygen concentration-cell measurements at low temperatures
O-85 .I. Chem. Thermo&namics 1984, 16, 781-792
The standard molar formation of PbO
Gibbs
free
Oxygen concentration-cell at low temperatures M.
energy
of
measurements
J. BANNISTER
Advanced Materials Laboratory, 506 Lorimer Street, Fisherman’s
CSIRO Division of Materials Bend, Victoria, Australia
(Received 13 December 1983: in revised.form
6 March
Science,
1984)
The thermodynamic equilibrium: Pb(l) + $0,(g) = PbO(s), has been studied between 645 and 977 K by e.m.f. measurements on the solid-electrolyte oxygen concentration cell: Pb(l)lPbO(s)lZrO, + Y,O,lair. {Pt +(U,,,, Sc,,,,)O,,,} powders were used instead of porous Pt as the air electrode to ensure its low-temperature reversibility.
1. Introduction The equilibrium: Pb(1) + *O,(g) = PbO(s),
(1)
has been studied several times’1-5’ using e.m.f. measurements with solid-electrolyte oxygen concentration cells. With one exception, (3) the cell measurements gave standard molar Gibbs free energies of formation less negative than those in the JANAF tables’@ (figure 1). The discrepancy increased at low temperatures, although in only one case(4) did it exceed the likely errors in the JANAF values. The lowest temperature for which experimental results have been reported is 673 K.‘5’ Previous cell measurements used either (metal + metal oxide), e.g. (Ni + NiO),“* 3,4) or (Cu + Cu,O),“’ or O,(g),“’ or air,“’ at the reference electrode. With (metal + metal oxide) references, uncertainties in the thermodynamic values for the reference oxide have to be included in the final results. Gaseous references with porous platinum electrodes can become unreliable below 900 K.“’ We have found that finely divided porous mixtures of Pt and non-stoichiometricoxide solid solutions of the type (U, M)O,,,, where M is SC or Y, are much better than porous platinum as electrodes on stabilized-zirconia solid electrolytes, particularly at low temperatures. (8-10’ They enable an air reference electrode to operate reversibly and accurately down to temperatures approaching 600 K.“” A cell with an air? reference electrode of this type has been used to redetermine the t In this paper 002l-9614/84/080787
do,,
air) = 21.23 kPa; +06
%02.00/O
R = 8.31441 J’K
‘.mol-‘;
F = 9.648456x
,i: 1984 Academic
IO4 C,mol
Press Inc. (London)
’ Limited
788
M. J. BANNISTER
T/K FIGURE 1. Standard molar Gibbs free energy change A,C;;, for the reaction: Pb(l)+tO,(g) = PbO(s). 0, JANAF data.‘@ From e.m.f. measurements: 1, to 720 to 1070 K;“’ 2, to 772 to 1160 K;“’ 3, to 748 to 1130 K;13’ 4, to 923 to 1152 K;‘+ 5, to 673 to 1160 K.-l
thermodynamic properties of {Pb(l) + PbO(s)} at temperatures down to 645 K, well below the minimum temperature of previous work.
2. Experimental The cell used in this study is shown in figure 2. A bath f of Pb(1) saturated with oxygen was held in a closed end tube k made of (chromium + alumina) cermet. The cermet was not attacked by Pb(1) or PbO(s) over the experimental temperature range, in agreement with Jacob and Jeffes.w N,(g) containing mass fraction about 1 x 10m5 of 0, was bubbled into the upper part of the bath through the four-bore alumina tube d to stir the molten lead and to ensure that it was saturated with oxygen. The oxygen potential of the molten lead was measured using an SIRO, Sensor”“l’ (Ceramic Oxide Fabricators Pty. Ltd., Australia), comprising a solid electrolyte pellet j sealed by a eutectic welding operation into the end of alumina tube e. The solid electrolyte pellet contained 50 mass per cent of (ZrO,),,,,(Y,O,),,,, and 50 mass per cent of alumina, the alumina being present to ensure a close thermal-
A,G;(PbO)
FROM
E.M.F.
789
MEASUREMENTS
n
--f
m
.-h
g I
1 k
---
j
FIGURE 2. Cell assembly. a, Thermocouple; b, alumina tube; c. rubber stopper; d, four-bore gas-inlet tube; e, alumina tube body of SIRO, Sensor; f, molten lead; g, thermocouple junction; h, (Pt + 13 mass per cent of Rh) disk; i, {Pt+(U,,,,Sc,,,,)O,,,) reference electrode; j, solid electrolyte pellet of SIRO, Sensor; k. (Cr + Al,O,) cermet tube; I, Pt wire; m, thermocouple; n, alumina gas-outlet tube.
expansion match between pellet j and the tube e. The rear face of the pellet was provided with an electrode i of 25 mass per cent of PtO, and 75 mass per cent of (U 0.3&0.62)02 *xFO applied as a paste in triethylene glycol and then fired at 873 K to convert the PtO, to Pt. Electrical contact to this electrode was made by a (Pt + 13 mass per cent of Rh) disk h and the bead g of Pt-to-(Pt + 13 mass per cent of Rh) thermocouple a mounted in a four-bore alumina tube, down which reference air was supplied to the electrode i. The Pt leg of the internal thermocouple served as the positive cell lead. The electrical circuit of the cell was completed through the lead bath and across the wall of cermet tube k to Pt wire 1 which was bound tightly around tube k and supported within the insulating alumina tube b. Separate experiments showed that the resistance across the cermet wall was small compared with the total cell resistance, and did not affect the e.m.f. measurements. The cell e.m.f. was fed to a high input-impedance (about 1 x 10” 0) low outputimpedance amplifier with a gain of 1, and thence to a potentiometric recorder and a
790
M. J. BANNISTER
digital voltmeter (Doric type 410A). The temperature was measured with the internal thermocouple a connected to a digital thermometer (Doric type 415A) calibrated to 0.1 K using a d.c. source. The similar external thermocouple m was used to verify that the temperature gradient in the cell was small, the indicated temperature difference between thermocouples being less than 1 K above 750 K and reaching 2.8 K at 646 K. The lead used in the experiments was Analytical-Reagent grade, with a purity better than 99.98 mass per cent, obtained from B.D.H. Ltd., England. The following preliminary experiments were carried out to check the performance of the cell. Firstly, it was heated to 973 K and held for several days, during which time the gas bubbling through the bath was alternated several times between N, and (50 moles per cent of CO + 50 moles per cent of CO,). A steady e.m.f., reproducible to within 1 mV and, for the (CO + CO,) mixture close to the value predicted using the JANAF tables,“*’ was eventually achieved after each change, demonstrating that the cell responded to variations in the oxygen potential of the lead. Further experiments with bubbling N, showed that stable e.m.f.‘s were obtained after 24 h at constant temperature, whereas holding times of only 2 to 3 h, as used by others,“’ invariably gave e.m.f.‘s which, although drifting only slowly with time, were several mV low. No electrochemical titrations were carried out with the cell. The cell was finally reheated to 977 K and held in bubbling N, for 120 h to ensure that the bath was saturated with oxygen. Measurements were then made between 645 and 977 K, the temperature being varied step-wise in a random fashion to avoid any error in the slope of the e.m.f. E against T curve that might be caused by the sequence of collection. Both the temperature and the cell e.m.f. were measured to fO.l K and fO.1 mV after a holding time of 24 to 72 h at each temperature. During the final 7 h of each isothermal period the temperature and the cell e.m.f. were recorded continuously; the temperature was stable to within + 1 K and the e.m.f. varied less than f0.5 mV. The e.m.f. fluctuations were correlated in both amplitude and period with the small fluctuations in temperature.
3. Results and discussion The experimental temperatures and potentials are given in table 1. Comparison with a calibrated thermocouple suggests that the temperatures were accurate to within f0.5 K. A linear least-squares analysis of the results gives, for the cell: PWWWWr02
+Y20,1airlPtl(U,,,,Sc,.,2)02
ix7
the expression: EymV
= 1140.15-0.5566(T/K)&0.81,
(645 to 977 K),
(2)
where the error quoted is the standard deviation from the straight line. This equation yields for the standard molar Gibbs free energy change for reaction (1): ArGk/(kJ.mol-‘)
= -220.01+0.10091(T/K)f0.16.
(3)
The PbO(s) is assumed to have changed from yellow to red below its normal
A,G;(PbO)
791
FROM E.M.F. MEASUREMENTS
‘TABLE I. Experimental values of the cell temperature T and potential E, together with values of the standard molar Gibbs free energy change A,Gi and the third-law standard molar enthalpy of reaction A,H;(298.15 K) for the reaction: Pb(l)+ &O,(g) = PbO(s). The runs are listed in chronological order. each run representing the same cell equilibrated at a new temperature Run no.
T K
1
977.0 976.7 857.7 645.7 645.2 796.6 959.5
2 3 4 5 6 7
E A,Gk mViiiT&F 595.6 595.5 663.2 779.7 780.0 691.6 605.7
- 121.28
-121.26 -133.55 -154.65
ArHL(298.15 K) kJ.mol-’ -222.03 -221.98 -222.45 -222.13
Run no. 8 9 10 11
- 154.71
-222.13
12
- 139.19 -123.12
-222.56 -222.13
13 14
T
E
k-
mV
774.4 888.1 701.5 823.6 910.8 739.3 673.1
709.8 646.1 750.9 682.7 633.4 729.2 764.5
A,H:(298.15 K) kJ.mol-’ -142.00 - 130.45
- 149.46 - 137.09 -128.15 - 145.52 - 151.90
- 222.53 - 222.38 - 222.62 -222.57 - 222.34 - 222.50 -222.17
transition temperature of 762 K; (6) however, no positive identification was carried out. The experimental values of A,Gk for reaction (1) are compared in figure 3 with JANAF values.‘@ The agreement is excellent, being well within the standard deviation of f 160 J. mol-’ obtained in the present work, even at the lowest temperatures used. Such accuracy is attributed to the system having been allowed adequate time to achieve equilibrium, and to the use of a reference electrode which
FIGURE 3. Standard molar Gibbs free energy change A,G; for the reaction: Pb(l)+ to,(g) = PbO(s). 0. JANAF:“” x, present study; the numbers indicate the order in which the results were collected.
792
M. J. BANNISTER
is reversible to oxygen at low temperatures. Short equilibration times and poorly reversible reference electrodes both lead to e.m.f.‘s which are too low and to values of A,Gk(PbO, s) reported before”.2.4.s’ which are not sufficiently negative. Table 1 also lists values of the standard molar enthalpy of reaction, calculated from the experimental results by the third-law method using JANAF thermal functions.(6*‘2’ The mean value of -(222.3 ?0.2) kJ. mol-’ agrees closely with the second-law estimate of - (222.4 f 0.3) kJ. mol r obtained using JANAF heat capacities@, 12) to correct to 298.15 K. Both agree with the JANAF valuet6’ of -(222.36f0.63) kJ.mol-‘. The author thanks Mr R. C. Wotherspoon for collecting most of the experimental results, and Drs S. P. S. Badwal, J. Drennan, and H. G. Scott for reviewing the manuscript. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. IO.
II. 12.
Alcock, C. B.; Belford, T. N. Trans. Faraday Sot. 1964,60, 822. Charette, G. G.; Flengas, S. N. J. Elecrrochem. Sot. 1968, 115, 796. Jacob. K. T.: Jeffes. J. H. E. Trans. Inst. Min. Met. 1971. 80. C32. Iwase: M.; Fujimura, K.; Mori, T. Trans. Jpn Inst. Me!. ‘IWk, 19, 377. Sugimoto, E.; Kuwata, S.; Kozuka, 2. J. Jpn Inst. Met. 1980, 44, 644. Chase, M. W.; Curnutt, J. L.; Hu. A. T.; Prophet, H.; Syverud. A. N.; Walker, L. C. J. Phys. Chem. Ref. Data 1974, 3, 31 I. Anthony, A.-M.; Baumard, J. F.; Corish, J. Zirconia-83, Stutrgarl. Second International Conferencr on the Science and Technology of Zirconia. Stuttgart, FRG, 21 to 23 June 1983. Paper Dl2. Badwal, S. P. S. J. Electroanai. Chem. 1983, 146, 425. Badwal, S. P. S. J. Eleclroanal. Chem. 1984, 161, 75. Badwal, S. P. S.; Bannister, M. J.; Garrett. W. G. Zirconia-83, Stuttgart. Second International Conference on the Science and Technology of Zirconia. Stuttgart, FRG. 21 to 23 June 1983. Paper D7. Bannister, M. J.; Garrett, W. G.; Johnston, K. A.; McKinnon. N. A.; Stringer. R. K.; Kanost. H. S. Materials Science Monographs 1980, 6. 211. Stull, D. R.; Prophet, H. JANAF Thermomechanical Tables, Second Edition, NSRDS-NBS 37. United States Department of Commerce, National Bureau of Standards. 1971.
The standard molar formation of PbO
Gibbs
free
Oxygen concentration-cell at low temperatures M.
energy
of
measurements
J. BANNISTER
Advanced Materials Laboratory, 506 Lorimer Street, Fisherman’s
CSIRO Division of Materials Bend, Victoria, Australia
(Received 13 December 1983: in revised.form
6 March
Science,
1984)
The thermodynamic equilibrium: Pb(l) + $0,(g) = PbO(s), has been studied between 645 and 977 K by e.m.f. measurements on the solid-electrolyte oxygen concentration cell: Pb(l)lPbO(s)lZrO, + Y,O,lair. {Pt +(U,,,, Sc,,,,)O,,,} powders were used instead of porous Pt as the air electrode to ensure its low-temperature reversibility.
1. Introduction The equilibrium: Pb(1) + *O,(g) = PbO(s),
(1)
has been studied several times’1-5’ using e.m.f. measurements with solid-electrolyte oxygen concentration cells. With one exception, (3) the cell measurements gave standard molar Gibbs free energies of formation less negative than those in the JANAF tables’@ (figure 1). The discrepancy increased at low temperatures, although in only one case(4) did it exceed the likely errors in the JANAF values. The lowest temperature for which experimental results have been reported is 673 K.‘5’ Previous cell measurements used either (metal + metal oxide), e.g. (Ni + NiO),“* 3,4) or (Cu + Cu,O),“’ or O,(g),“’ or air,“’ at the reference electrode. With (metal + metal oxide) references, uncertainties in the thermodynamic values for the reference oxide have to be included in the final results. Gaseous references with porous platinum electrodes can become unreliable below 900 K.“’ We have found that finely divided porous mixtures of Pt and non-stoichiometricoxide solid solutions of the type (U, M)O,,,, where M is SC or Y, are much better than porous platinum as electrodes on stabilized-zirconia solid electrolytes, particularly at low temperatures. (8-10’ They enable an air reference electrode to operate reversibly and accurately down to temperatures approaching 600 K.“” A cell with an air? reference electrode of this type has been used to redetermine the t In this paper 002l-9614/84/080787
do,,
air) = 21.23 kPa; +06
%02.00/O
R = 8.31441 J’K
‘.mol-‘;
F = 9.648456x
,i: 1984 Academic
IO4 C,mol
Press Inc. (London)
’ Limited
788
M. J. BANNISTER
T/K FIGURE 1. Standard molar Gibbs free energy change A,C;;, for the reaction: Pb(l)+tO,(g) = PbO(s). 0, JANAF data.‘@ From e.m.f. measurements: 1, to 720 to 1070 K;“’ 2, to 772 to 1160 K;“’ 3, to 748 to 1130 K;13’ 4, to 923 to 1152 K;‘+ 5, to 673 to 1160 K.-l
thermodynamic properties of {Pb(l) + PbO(s)} at temperatures down to 645 K, well below the minimum temperature of previous work.
2. Experimental The cell used in this study is shown in figure 2. A bath f of Pb(1) saturated with oxygen was held in a closed end tube k made of (chromium + alumina) cermet. The cermet was not attacked by Pb(1) or PbO(s) over the experimental temperature range, in agreement with Jacob and Jeffes.w N,(g) containing mass fraction about 1 x 10m5 of 0, was bubbled into the upper part of the bath through the four-bore alumina tube d to stir the molten lead and to ensure that it was saturated with oxygen. The oxygen potential of the molten lead was measured using an SIRO, Sensor”“l’ (Ceramic Oxide Fabricators Pty. Ltd., Australia), comprising a solid electrolyte pellet j sealed by a eutectic welding operation into the end of alumina tube e. The solid electrolyte pellet contained 50 mass per cent of (ZrO,),,,,(Y,O,),,,, and 50 mass per cent of alumina, the alumina being present to ensure a close thermal-
A,G;(PbO)
FROM
E.M.F.
789
MEASUREMENTS
n
--f
m
.-h
g I
1 k
---
j
FIGURE 2. Cell assembly. a, Thermocouple; b, alumina tube; c. rubber stopper; d, four-bore gas-inlet tube; e, alumina tube body of SIRO, Sensor; f, molten lead; g, thermocouple junction; h, (Pt + 13 mass per cent of Rh) disk; i, {Pt+(U,,,,Sc,,,,)O,,,) reference electrode; j, solid electrolyte pellet of SIRO, Sensor; k. (Cr + Al,O,) cermet tube; I, Pt wire; m, thermocouple; n, alumina gas-outlet tube.
expansion match between pellet j and the tube e. The rear face of the pellet was provided with an electrode i of 25 mass per cent of PtO, and 75 mass per cent of (U 0.3&0.62)02 *xFO applied as a paste in triethylene glycol and then fired at 873 K to convert the PtO, to Pt. Electrical contact to this electrode was made by a (Pt + 13 mass per cent of Rh) disk h and the bead g of Pt-to-(Pt + 13 mass per cent of Rh) thermocouple a mounted in a four-bore alumina tube, down which reference air was supplied to the electrode i. The Pt leg of the internal thermocouple served as the positive cell lead. The electrical circuit of the cell was completed through the lead bath and across the wall of cermet tube k to Pt wire 1 which was bound tightly around tube k and supported within the insulating alumina tube b. Separate experiments showed that the resistance across the cermet wall was small compared with the total cell resistance, and did not affect the e.m.f. measurements. The cell e.m.f. was fed to a high input-impedance (about 1 x 10” 0) low outputimpedance amplifier with a gain of 1, and thence to a potentiometric recorder and a
790
M. J. BANNISTER
digital voltmeter (Doric type 410A). The temperature was measured with the internal thermocouple a connected to a digital thermometer (Doric type 415A) calibrated to 0.1 K using a d.c. source. The similar external thermocouple m was used to verify that the temperature gradient in the cell was small, the indicated temperature difference between thermocouples being less than 1 K above 750 K and reaching 2.8 K at 646 K. The lead used in the experiments was Analytical-Reagent grade, with a purity better than 99.98 mass per cent, obtained from B.D.H. Ltd., England. The following preliminary experiments were carried out to check the performance of the cell. Firstly, it was heated to 973 K and held for several days, during which time the gas bubbling through the bath was alternated several times between N, and (50 moles per cent of CO + 50 moles per cent of CO,). A steady e.m.f., reproducible to within 1 mV and, for the (CO + CO,) mixture close to the value predicted using the JANAF tables,“*’ was eventually achieved after each change, demonstrating that the cell responded to variations in the oxygen potential of the lead. Further experiments with bubbling N, showed that stable e.m.f.‘s were obtained after 24 h at constant temperature, whereas holding times of only 2 to 3 h, as used by others,“’ invariably gave e.m.f.‘s which, although drifting only slowly with time, were several mV low. No electrochemical titrations were carried out with the cell. The cell was finally reheated to 977 K and held in bubbling N, for 120 h to ensure that the bath was saturated with oxygen. Measurements were then made between 645 and 977 K, the temperature being varied step-wise in a random fashion to avoid any error in the slope of the e.m.f. E against T curve that might be caused by the sequence of collection. Both the temperature and the cell e.m.f. were measured to fO.l K and fO.1 mV after a holding time of 24 to 72 h at each temperature. During the final 7 h of each isothermal period the temperature and the cell e.m.f. were recorded continuously; the temperature was stable to within + 1 K and the e.m.f. varied less than f0.5 mV. The e.m.f. fluctuations were correlated in both amplitude and period with the small fluctuations in temperature.
3. Results and discussion The experimental temperatures and potentials are given in table 1. Comparison with a calibrated thermocouple suggests that the temperatures were accurate to within f0.5 K. A linear least-squares analysis of the results gives, for the cell: PWWWWr02
+Y20,1airlPtl(U,,,,Sc,.,2)02
ix7
the expression: EymV
= 1140.15-0.5566(T/K)&0.81,
(645 to 977 K),
(2)
where the error quoted is the standard deviation from the straight line. This equation yields for the standard molar Gibbs free energy change for reaction (1): ArGk/(kJ.mol-‘)
= -220.01+0.10091(T/K)f0.16.
(3)
The PbO(s) is assumed to have changed from yellow to red below its normal
A,G;(PbO)
791
FROM E.M.F. MEASUREMENTS
‘TABLE I. Experimental values of the cell temperature T and potential E, together with values of the standard molar Gibbs free energy change A,Gi and the third-law standard molar enthalpy of reaction A,H;(298.15 K) for the reaction: Pb(l)+ &O,(g) = PbO(s). The runs are listed in chronological order. each run representing the same cell equilibrated at a new temperature Run no.
T K
1
977.0 976.7 857.7 645.7 645.2 796.6 959.5
2 3 4 5 6 7
E A,Gk mViiiT&F 595.6 595.5 663.2 779.7 780.0 691.6 605.7
- 121.28
-121.26 -133.55 -154.65
ArHL(298.15 K) kJ.mol-’ -222.03 -221.98 -222.45 -222.13
Run no. 8 9 10 11
- 154.71
-222.13
12
- 139.19 -123.12
-222.56 -222.13
13 14
T
E
k-
mV
774.4 888.1 701.5 823.6 910.8 739.3 673.1
709.8 646.1 750.9 682.7 633.4 729.2 764.5
A,H:(298.15 K) kJ.mol-’ -142.00 - 130.45
- 149.46 - 137.09 -128.15 - 145.52 - 151.90
- 222.53 - 222.38 - 222.62 -222.57 - 222.34 - 222.50 -222.17
transition temperature of 762 K; (6) however, no positive identification was carried out. The experimental values of A,Gk for reaction (1) are compared in figure 3 with JANAF values.‘@ The agreement is excellent, being well within the standard deviation of f 160 J. mol-’ obtained in the present work, even at the lowest temperatures used. Such accuracy is attributed to the system having been allowed adequate time to achieve equilibrium, and to the use of a reference electrode which
FIGURE 3. Standard molar Gibbs free energy change A,G; for the reaction: Pb(l)+ to,(g) = PbO(s). 0. JANAF:“” x, present study; the numbers indicate the order in which the results were collected.
792
M. J. BANNISTER
is reversible to oxygen at low temperatures. Short equilibration times and poorly reversible reference electrodes both lead to e.m.f.‘s which are too low and to values of A,Gk(PbO, s) reported before”.2.4.s’ which are not sufficiently negative. Table 1 also lists values of the standard molar enthalpy of reaction, calculated from the experimental results by the third-law method using JANAF thermal functions.(6*‘2’ The mean value of -(222.3 ?0.2) kJ. mol-’ agrees closely with the second-law estimate of - (222.4 f 0.3) kJ. mol r obtained using JANAF heat capacities@, 12) to correct to 298.15 K. Both agree with the JANAF valuet6’ of -(222.36f0.63) kJ.mol-‘. The author thanks Mr R. C. Wotherspoon for collecting most of the experimental results, and Drs S. P. S. Badwal, J. Drennan, and H. G. Scott for reviewing the manuscript. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. IO.
II. 12.
Alcock, C. B.; Belford, T. N. Trans. Faraday Sot. 1964,60, 822. Charette, G. G.; Flengas, S. N. J. Elecrrochem. Sot. 1968, 115, 796. Jacob. K. T.: Jeffes. J. H. E. Trans. Inst. Min. Met. 1971. 80. C32. Iwase: M.; Fujimura, K.; Mori, T. Trans. Jpn Inst. Me!. ‘IWk, 19, 377. Sugimoto, E.; Kuwata, S.; Kozuka, 2. J. Jpn Inst. Met. 1980, 44, 644. Chase, M. W.; Curnutt, J. L.; Hu. A. T.; Prophet, H.; Syverud. A. N.; Walker, L. C. J. Phys. Chem. Ref. Data 1974, 3, 31 I. Anthony, A.-M.; Baumard, J. F.; Corish, J. Zirconia-83, Stutrgarl. Second International Conferencr on the Science and Technology of Zirconia. Stuttgart, FRG, 21 to 23 June 1983. Paper Dl2. Badwal, S. P. S. J. Electroanai. Chem. 1983, 146, 425. Badwal, S. P. S. J. Eleclroanal. Chem. 1984, 161, 75. Badwal, S. P. S.; Bannister, M. J.; Garrett. W. G. Zirconia-83, Stuttgart. Second International Conference on the Science and Technology of Zirconia. Stuttgart, FRG. 21 to 23 June 1983. Paper D7. Bannister, M. J.; Garrett, W. G.; Johnston, K. A.; McKinnon. N. A.; Stringer. R. K.; Kanost. H. S. Materials Science Monographs 1980, 6. 211. Stull, D. R.; Prophet, H. JANAF Thermomechanical Tables, Second Edition, NSRDS-NBS 37. United States Department of Commerce, National Bureau of Standards. 1971.