ISSN 00360236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 2, pp. 237–241. © Pleiades Publishing, Ltd., 2012. Original Russian Text © P.P. Fedorov, N.V. Il’in, 2012, published in Zhurnal Neorganicheskoi Khimii, 2012, Vol. 57, No. 2, pp. 282–286.
PHYSICAL METHODS OF INVESTIGATION
Yttrium Carbonate Thermolysis P. P. Fedorova and N. V. Il’inb a
Prokhorov Institute of General Physics, Russian Academy of Sciences, Leninskii pr. 51, Moscow, 119991 Russia email:
[email protected] b INTERTECHCORP, Moscow Representative Office, Moscow, Russia email: www.intertechcorp.ru Received December 30, 2009
Abstract—The thermal stability of carbonate precursors of yttrium oxide was studied by thermal and thermo gravimetric analyses, specifically, with evolved gas mass spectroscopy, on TA Instruments equipment. The thermolysis of Y2(CO3)3 ⋅ nH2O (n = 2.46) is a complex process and comprises several stages of elimination of water (90–285°C) and carbon dioxide. DOI: 10.1134/S0036023612020076
Dispersed yttrium oxide powders are of interest for use as precursors for manufacturing laser ceramics which are competitive with single crystals in their spectral generation properties. These powders are of interest as luminescent materials, too [1, 2]. A carbon ate process is used to prepare precursors for yttrium oxide [3–6]. Fedorov et al. [1] showed that, when yttrium is pre cipitated from nitrate solutions by a solution of ammo nium hydrocarbonate NH4HCO3, hydrated yttrium carbonate Y2(CO3)3 ⋅ nH2O is precipitated to decom pose upon heating in several stages. The final product is yttrium oxide. From dilute solutions, a new com pound precipitates in crystals. Here, our goal was to study the thermolysis of the phases synthesized in [1] in a detailed way. The study was carried out on thermoanalytical equipment pro vided by TA Instruments. EXPERIMENTAL From ammonium hydrocarbonate NH4HCO3 (pure grade) and distilled water, a solution with a con centration of 1.67 mol/L (pH 7.52) was prepared. Yttrium oxide was dissolved in dilute nitric acid to pre pare an yttrium nitrate solution. The concentration of the stock solution (as Y2O3) was 0.0432 mol/L (in run 156) or 0.022 mol/L (in run 161). To the asprepared solution, the ammonium hydrocarbonate solution was dropped (direct titration) under stirring with a mag netic stirrer. Titration was carried out in a pH range of 1.8–5.9. The thusobtained precipitates were filtered through Blue Band double paper filter and washed with distilled water. Thermogravimetric analysis and differential scan ning calorimetry were carried out on an SDT Q600 thermal analyzer. HiRes Dynamic thermogravimet ric analysis, where the heating rate varied as a function
of the process rate, was carried out on a TGA Q500 thermal analyzer. Platinum or Al2O3 crucibles were used, respectively. Heating rates were 10–20 K/min. Experiments were carried out either under air or in an argon or helium flow. RESULTS AND DISCUSSION According to Xray powder diffraction and electron microscopy [1], the sample prepared in run 156 (here after, sample 156) is a powder of yttrium carbonate Y2(CO3)3 ⋅ nH2O, which consists of spherulitic parti cles with sizes of about 10 µm, these particles in turn being composed of needlelike crystals; sample 161 is a new phase formed of nanometerthick platy microc rystals of rhombic habit. The results of thermolyzing sample 156 are shown in Figs. 1–3. One can see from these figures that the decomposition of yttrium carbonate is a complex pro cess and involves several stages. Change in the gaseous atmosphere has no substantial effect on the occur rence of the process. The weight loss value correlates with heat absorption. At least five extremes are recog nized on the DSC curve corresponding to the maximal rates of the involved reactions, at 95, 285, 550, 610, and 680°С. Of them, well defined is the peak at 610°С. The others are diffuse. Weight loss values referring to process stages are shown in Fig. 2. Weight loss ends at 750°С with the formation of cubic yttrium oxide (as found by Xray powder diffrac tion [1]). The residual weight is 56.15% of the initial weight, corresponding to the formula Y2(CO3)3 ⋅ 2.46H2O for the initial sample. According to single crystal Xray diffraction [7], some water in hydrated yttrium carbonate Y2(CO3)3 ⋅ nH2O (tengerite) is zeo lite water; as a result, n can vary from 2 to 3. According to mass spectrometry (Fig. 3), the decomposition peak at 610°С is accompanied by pulse
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FEDOROV, IL’IN Weight, %
(а)
Exo
1.5
1.0 0.3
80
60
0.5
Heat flow, W/g
Deriv. weight %/°C
100
0.2 0 0.1 –0.5
40
–1.0 200
400 Temperature, °C
800
600
0.4
(b)
90 0.8 80 0.2 70 0.1
791.14°С 53.95%
60
Deriv. weight, %/°C
0 Weight, % 100
0
40 0
200
400 Temperature, °C
600
800
Fig. 1. Differential scanning calorimetry and thermogravimetry results for yttrium carbonate hydrate sample 156: (a) SDT Q600, sample size: 15.03 mg, argon atmosphere, and heating rate: 10 K/min; and (b) TGA Q500, sample size: 10.30 mg, air atmosphere, and heating rate: 20 K/min.
evolution of carbon dioxide. In addition, there are dif fuse СО2 gas evolution peaks at 250, 550, and 680°С. The appearance of diffuse peaks on thermal curves signifies the concurrence and incompletion of some intermediate thermolysis stages. This agrees with the amorphization of yttrium carbonate upon water elim
ination [1]; the crystallization of cubic yttrium oxide is observed for the final weight loss. The approximate sequence of reactions may be described as follows: Y2(CO3)3 ⋅ 2.46H2O → Y2(CO3)3 ⋅ 2H2O + 0.46H2O, (1) Y2(CO3)3 ⋅ 2H2O → Y2(CO3)3 + 2H2O,
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Weight, %
100
2.892% 9.388%
80
18.25%
7.913% 3.487%
60
987.46°С 56.16% 40
0
200
400
600 Temperature, °C
800
1000
Fig. 2. Thermogravimetry results for yttrium carbonate hydrate sample 156: TGA Q500, HiRes Dynamic mode, argon flow, and sample size: 14.46 mg.
Ion current, mА 0.0006 Exo
Weight, %
–2.2 100 0.0004 Heat flow, W/g
–2.4 80
–2.6 0.0002
60 –2.8 44.09 40 0
200
400 Temperature, °C
600
0 800
Fig. 3. Differential scanning calorimetry, thermogravimetry, and evolved gas mass–spectrometry results for yttrium carbonate hydrate sample 156: SDT Q600, sample size: 7.35 mg, helium atmosphere, and gas flow rate: 100 mL/min, and heating rate: 10 K/min.
Y2(CO3)3 → 2YО1.1(CO3)0.40 + 2.2СО2,
(3)
Y2(CO3)3 ⋅ 2.46H2O → Y2O3 + 3СО2 + 2.46H2O. (5)
2YО1.1(CO3)0.40 → Y2O3 + 0.8СО2.
(4)
The first stage is substantially over at 95°С; the cal culated weight loss for reaction (1) is 2.0%. The sec ond stage (complete dehydration) is substantially over
The overall thermolysis reaction is as follows: RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
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FEDOROV, IL’IN Ion current, mА 0.0025 Exo
Weight, %
0.0020 100
–1
80 18.19
60
Heat flow, W/g
0.0015 –2 0.0010 –3 0.0005
44.09
40 0
0 260
400 Temperature, °C
600
800
Fig. 4. Differential scanning calorimetry, thermogravimetry, and evolved gas massspectrometry results for yttrium oxide precur sor sample 161: SDT Q600, sample size: 6.00 mg, helium atmosphere, gas flow rate: 100 mL/min, and heating rate: 10 K/min.
at 285°С. Weight loss on the basis of the initial sub stance (the sum of reactions (1) and (2)) is 10.0%, which well agrees with the experiment (Fig. 2). СО2 evolution in reaction (5) corresponds to 33.2% weight loss. The dynamics of this process was traced by mass spectrometry (Fig. 3). The process comprises a diffuse stage accompanied by gradual weight loss; a sharp stage of basic decomposition at 600–620°С; and residual gas evolution at 620–750°С. A semiquantita tive explanation is possible on the assumption of a gradual formation of yttrium oxocarbonate of compo sition YО1.1(CO3)0.40 and the decomposition of the lat ter at 600–620°С. Evidence for the formation of this compound was obtained [8] in the study of yttrium hydroxocarbonate thermolysis. The product prepared at 620–750°С is an yttrium oxide nanopowder with a noticeable amount (up to 3.5%) of adsorbed carbon dioxide. Presumably, this product has a high reactivity in diverse processes, in particular, in sintering. Comparing Figs. 1–3 to each other and to earlier data [1], we find that the major thermolysis of hydrated yttrium carbonate remains the same in vari ous atmospheres and for various sample sizes. Remember that Eqs. (1)–(4) are no more than a scheme of a complex process. When bulk (290–700 mg) samples were thermolyzed in the Qmode [1], the decomposition stage at 560°С was clearly recognized. Figure 4 displays thermoanalytical data for the car bonate precursor of yttrium oxide synthesized in run 161 [1].
There are welldefined three thermolysis stages: water elimination with the maximal profess rate at 130°С to bring about amorphization of the crystalline product [1]; an intermediate process stage with the maximal process rate at 360°С, involving СО2 evolu tion; and the final process stage at 600–650°С. At the last stage, crystallization occurs to yield cubic yttrium oxide. Weight loss values referring to the stages are shown in Fig. 4. Complete weight loss was 47.08%. Unlike earlier data gained from a bulk sample [1], this experiment reveals the intermediate decomposi tion stage. Further, an exotherm associated with crys tallization of an amorphous sample is observed. Such a process yields nanopowders when interrupted in the very beginning, as we noticed for yttrium and scan dium borates [9, 10]. The available data are insufficient for finding the formulation of sample 161. The thermal curve resem bles thermolysis of amorphous yttrium hydroxocar bonate Y2(OH)2(CO3)2 ⋅ 2H2O as described in [11], but is different. ACKNOWLEDGMENTS The authors are grateful to INTERTECHCORP (USA) for providing them with instruments and to V.K. Ivanov, A.E. Baranchikov, and S.V. Kuznetsov for fruitful discussion.
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6. N. Saito, S. I. Matsuda, and T. Ikegami, J. Am. Ceram. Soc. 81 (2), 2023 (1998). 7. R. Miyawaki, J. Kuriyama, and I. Nakai, Am. Minera log. 78, 425 (1993). 8. V. K. Ivanov, A. E. Baranchikov, A. S. Vanetsev, et al., Russ. J. Inorg. Chem. 52, 1321 (2007). 9. E. A. Tkachenko, P. P. Fedorov, S. V. Kuznetsov, et al., Russ. J. Inorg. Chem. 50, 681 (2005). 10. E. A. Tkachenko, P. P. Fedorov, S. V. Kuznetsov, et al., Neorg. Mater. 42, 207 (2006). 11. L.M. d’Assuncao, I. Giolito, and M. Ionashiro, Ther mochim. Acta. 137, 319 (1989).
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