Comments pubs.acs.org/cm
Comment on “Chemical-Composition-Dependent Metastability of Tetragonal ZrO2 in Sol−Gel-Derived Films under Different Calcination Conditions”
I
n the mentioned paper, Chang and Doong1 used these equations in order to estimate the volume fractions of the tetragonal (Xt) and monoclinic phases (Xm) It(101) Xt = It(101) + Im(111) + Im( 1̅ 11)
(1)
Xm = 1 − Xt
(2)
Im(111) + Im( 1̅ 11) Im(111) + Im( 1̅ 11) + Ic,t(111)
Tyagi et al. used the net peak area of the characteristic peak of tetragonal phase (at 2θ = 30.5°) and monoclinic phase (at 2θ = 24.2, 28.4, 31.6, 34.1°) calculated using software, and measured the percent composition of each phase by the following procedure
∑ (hw)monoclinic ∑ (hw)monoclinic and tetragonal © 2012 American Chemical Society
[(peak area)tetragonal] ∑ (peak area)tetragonal and monoclinic
%tetragonal =
(6)
× 100
%monoclinic =
∑ (peak area)monoclinic ∑ (peak area)tetragonal and monoclinic × 100
(7)
In this manuscript, we are going to explain method of calculating the volume fractions of monoclinic and tetragonal phases that proposed by Toraya et al.11 published by the journal of American ceramic society in 1984. In the discussed paper, it has been related that in X-ray powder diffractometer geometry, the intensity of reflection hkl, H(hkl), from the surface of a thick slab of crystal powder can be calculated by p ⎛ 1 + cos2 2θ cos2 2θM ⎞ |F(hkl)|2 ⎟ H(hkl) = K ⎜ 2 μ⎝ sin θ sin 2θ ⎠ U
(3)
(8)
For the monoclinic-tetragonal zirconia system, they defined the integrated intensity ratio, Xm, by
The primary calibration curves first obtained by Duwez and Odell,5 Adam and Cox,6 and Whitney.7 Garvie and Nicholson8 developed a linear calibration curve for phase analysis in partially stabilized zirconia based on X-ray diffraction techniques using the “polymorph method” and corrected the intensities in eq 3 for Lorentz polarization factors to improve the accuracy. In further research, Porter and Heuer9 and Fillit et al.10 corrected the intensities for structure factor that caused to reach more precision. Toraya et al.11 and Evans et al.12 performed experimental work to obtain a calibration curve that showed high accuracy and coincidence with experimental data. As related by ref 11, the assumed linearity considered by some previous authors is not strictly correct and the deviation from linearity should be taken into account. Su et al.13 used a different procedure to calculate these volume fractions based on three characteristic peaks (2θ = 28 and 31° for monoclinic phase and 2θ = 30° for tetragonal phase). They obtained the percent composition of each phase from the Gaussian area hw, where h and w are the height and the half-width of X-ray diffraction of the characteristic peaks. %monoclinic =
(5)
14
Where It(101) is the XRD integrated peak intensity of the (101)t plane of tetragonal phase and Im(111) and Im(11̅ 1) are the XRD integrated peak intensity of the (111)m and (1̅11)m planes of the monoclinic phase, respectively. They referred these equations to papers of Štefanić and Musić,2 but in that paper, the authors used a different procedure to calculate volume fractions of tetragonal and monoclinic phases. Unfortunately, some authors such as Pushpal Ghosh et al.3,4 used the wrong procedure published by ref 1 to calculate these volume fractions. Utilization of the X-ray powder diffraction (XRD) for quantitative analysis of two or three phase zirconia mixtures have been studied in several publications. In the tetragonalmonoclinic and cubic-monoclinic two-phase zirconia systems, the following term containing intensities of two phases always has been used in the analysis Xm =
∑ (hw)tetragonal ∑ (hw)monoclinic and tetragonal
%tetragonal =
Xm =
Im(111) + Im( 1̅ 11) Im(111) + Im( 1̅ 11) + It(101)
(9)
Where, subscripts m and t represent the monoclinic and tetragonal phases, respectively. They assert that Xm can be expressed with Xm =
νm[Hm( 1̅ 11) + Hm(111)] νm[Hm( 1̅ 11) + Hm(111) + (1 − νm)Ht(101)] (10)
Where, νm is the volume fraction of monoclinic phase. After solving eq 10 for νm, the following equation has been obtained PX m 1 + (P − 1)X m
(11)
Ht(101) Hm( 1̅ 11) + Hm(111)
(12)
νm =
That P is P=
Received: July 10, 2012 Revised: September 30, 2012 Published: October 11, 2012
(4) 4268
dx.doi.org/10.1021/cm301930m | Chem. Mater. 2012, 24, 4268−4269
Chemistry of Materials
Comments
The value of P calculated from theoretical values is 1.34. Its value obtained by their experimental work was 1.311 ± 0.004. So the empirical equation will be νm =
1.311X m 1 + 0.311X m
Table 1. Volume Fraction of Tetragonal Phase Calculated Based on Figure 1 νt calcd using eq 1 νt calcd using eq 13 νt calcd using eq 6
(13)
The authors mentioned that the empirical equation is better to use instead of theoretical one. Thus the Xm and Xt are not the volume fractions of monoclinic and tetragonal phases, as addressed by the authors in refs 1, 3, and 4, and it is necessary to perform subsequent calculation using eq 13 in order to measure the volume fractions with high accuracy. Zirconium oxide is an important ceramic material and has a lot of applications because of unique features of its various phases. Catalytic activity of tetragonal zirconia as well as its higher surface hardness and smoothness than monoclinic zirconia, caused to increase interest in synthesizing tetragonal phase.14 Knowing phase composition in the tetragonalmonoclinic two phase zirconia is of the importance in many applications of this material. It can easily be measured with high accuracy by utilization the X-ray powder diffraction (XRD) as well as using Raman spectroscopy. The Raman spectroscopy gives better results compared with XRD when the amount of monoclinic phase in the tetragonal-monoclinic binary systems is almost low.15 Figure 1 shows XRD pattern of pure zirconia powder synthesized by Zirconium oxychloride as the initial salt via
Figure 1a
Figure 1b
0.401 0.338 0.321
0.357 0.298 0.297
catalytic performance, surface hardness, etc. Furthermore, it is clear that there is a good agreement between the values measured by eqs 13 and 6 (see Table 1). In eq 6, the peak area must be calculated using related softwares while eq 13 is simpler to use and has fewer calculations. So the model proposed by ref 11 can be a simple and almost accurate model in order to calculate the percent composition of tetragonal-monoclinic binary systems.
Peyman Khajavi Ali Akbar Babaluo*
■
Nanostructure Material Research Center (NMRC), Sahand University of Technology, Tabriz, Islamic Republic of Iran.
AUTHOR INFORMATION
Corresponding Author
*Tel: +98-412-3459081. Fax: +98-412-3444355. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Chang, S.; Doong, R. Chem. Mater. 2005, 17, 4837. (2) Štefanić, G.; Musić, S. Croat. Chem. Acta 2002, 75, 727. (3) Ghosh, P.; Priolkar, K. R.; Patra, A. J. Phys. Chem. C 2007, 111, 571. (4) Ghosh, P.; Patra, A. Langmuir 2006, 22, 6321. (5) Duwez, P.; Odell, F. J. Am. Ceram. Soc. 1949, 32, 180. (6) Adam, J.; Cox, B. J. Nucl. Energy, Part A 1959, 11, 31. (7) Whitney, E. D. Trans. Faraday Soc. 1965, 61, 1991. (8) Garvie, R. C.; Nicholson, P. S. J. Am. Ceram. Soc. 1972, 55, 303. (9) Porter, D. L.; Heuer, A. H. J. Am. Ceram. Soc. 1979, 62 (No. 5− 6), 298. (10) Fillit, R.; Homerin, P.; Schafer, J.; Bruyas, H.; Thevenot, F. J. Mater. Sci. 1987, 22, 3566. (11) Toraya, H.; Yoshimura, M.; Somiya, S. J. Am. Ceram. Soc. 1984, 67, C−119. (12) Evans, P. A.; Stevens, R.; Binner, J. G. P. Br Ceram. trans. J. 1984, 83, 39. (13) Su, C.; Li, J.; He, D.; Cheng, Z.; Zhu, Q. Appl. Catal., A 2000, 202, 81. (14) Tyagi, B.; Sidhpuria, K.; Shaik, B.; Jasra, R. V. Ind. Eng. Chem. Res. 2006, 45, 8643. (15) Kim, B. K.; Hahn, J. W.; Han, K. R. J. Mater. Sci. Lett. 1997, 16, 669. (16) Tahmasebpour, M.; Babaluo, A. A.; Razavi Aghjeh, M. K. J. Eur. Ceram. Soc. 2008, 28, 773.
Figure 1. XRD pattern of pure zirconia powder synthesized by Zirconium oxychloride calcined at (a) 750 °C, (b) 800 °C in the region 2θ = 20−40°.
polyacrylamide gel method16 calcined at 750 and 800 °C. As a case study, the volume fraction of tetragonal phase is calculated as presented in Table 1. As can be seen, νt calculated for samples a and b using eq 13 are 0.338 and 0.298, whereas its value measured by eq 1 is 0.401 and 0.357. Because of the importance of the volume fraction of tetragonal phase in the zirconia powder synthesis, calculating tetragonal phase fraction with high accuracy results in exact evaluating of the final material properties such as 4269
dx.doi.org/10.1021/cm301930m | Chem. Mater. 2012, 24, 4268−4269
