Study of the Effect of Temperature on the Process of Preliminary Incorporation of Zirconium and Titanium Oxides into the Crystal Lattice of Alumina
Abstract Generated abstract
This study examines how preliminary heat treatment temperature affects the incorporation of zirconium and titanium oxides into alumina-based charges, a factor considered important for the homogeneity and quality of alloyed corundums. Mixtures containing alumina with small additions of zirconium oxide or titanium oxide, and a ternary alumina, zirconium oxide, titanium oxide composition, were fired for one hour at temperatures from room temperature to 1000°C and evaluated by visible-region spectrophotometry using reflection coefficients. The results indicate that solid-phase interaction of zirconium and titanium oxides with alumina begins at about 400°C, while the main structural restructuring of the material is practically completed in the 800 to 900°C range.
Full Text
STUDY OF THE EFFECT OF TEMPERATURE ON THE PROCESS OF PRELIMINARY INCORPORATION OF ZIRCONIUM AND TITANIUM OXIDES INTO THE CRYSTAL LATTICE OF ALUMINA
V. M. VITYUGIN, V. V. KOYAIN, G. S. FROLOVA,
N. I. PODDUBNYAK, A. V. SOKOLOV
(Presented by the scientific seminar of the Department of General Chemical Technology)
It is known from the literature [1–3] that TiO₂ dissolves in Al₂O₃ at 1573°K only within the range of 0.25–0.30 mol%. Moreover, when TiO₂ is introduced as an additive during heating, a substitutional solid solution is formed, which is due to the closeness of the ionic radii of Al³⁺ (0.57 Å) and Ti⁴⁺ (0.64 Å). Then, at high temperatures, Ti⁴⁺ gradually transforms into Ti³⁺. This transition is accompanied by deformation of the Al₂O₃ lattice owing to the considerably larger ionic radius of Ti³⁺ (0.98 Å) than that of Ti⁴⁺. Since the ionic radii of Al³⁺ and Ti³⁺ differ considerably from each other, upon cooling of the melt the substitutional solid solution must transform into an interstitial solid solution.
As for the Al₂O₃—ZrO₂ system, a number of authors [4–6] present its phase diagram and establish that no chemical compounds are formed in this system.
From melts lying above the liquidus curve on the Al₂O₃ side, Seville [7] found a new modification, which is customarily called E—Al₂O₃. Its stability region lies at temperatures above 1930°. The new phase is formed from melts of composition 99% Al₂O₃ and 1% ZrO₂.
One of the factors affecting the quality of alloyed corundums is the homogeneity of the initial charge. This can be achieved by preliminary heat treatment, as a result of which the additive is incorporated into the crystal lattice of alumina [8]. This incorporation takes place at temperatures significantly below the melting temperature of the charge.
To establish the temperature at which interaction of the oxides with alumina begins, heat treatment was carried out on charges of the following composition:
99% alumina and 1% titanium oxide;
99% alumina and 1% zirconium oxide;
68% alumina, 30% zirconium oxide, and 2% titanium oxide.
The products obtained were studied on an SF-10 spectrophotometer in the visible region of electromagnetic radiation.
The experimental results are given in Table 1.
Thus, on the basis of the experiments performed it may be concluded that the interaction of zirconium and titanium oxides in the solid phase begins already at a temperature of 400°. In practice, however, complete restructuring of the material structure occurs in the temperature range from 800 to 900°C.
Table 1
Results of the study of SF-10 batches
\((\mathrm{Al_2O_3}+\mathrm{ZrO_2};\ \mathrm{Al_2O_3}+\mathrm{TiO_2};\ \mathrm{Al_2O_3}+\mathrm{ZrO_2}+\mathrm{TiO_2})\),
fired for 1 hour at various temperatures
| Heat-treatment temperature, °C | Reflection coefficient, % for batch: 99% \(\mathrm{Al_2O_3}\) + 1% \(\mathrm{ZrO_2}\) | Reflection coefficient, % for batch: 99% \(\mathrm{Al_2O_3}\) + 1% \(\mathrm{TiO_2}\) | Reflection coefficient, % for batch: 68% \(\mathrm{Al_2O_3}\) + 30% \(\mathrm{ZrO_2}\) + 2% \(\mathrm{TiO_2}\) |
|---|---|---|---|
| 20 | 77 | 62 | 45 |
| 400 | 83.5 | 70 | 50 |
| 500 | 84 | 81 | 70 |
| 600 | 84 | 81 | 80 |
| 700 | 84 | 81 | 80 |
| 800 | 84.5 | 82.5 | 82 |
| 900 | 84.5 | 82.5 | 82 |
| 1000 | 84.5 | 82.5 | 82 |
LITERATURE
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- Report on contractual research topic 189/68. Improvement of the Technology for the Production of Chromic Corundum. Tomsk, 1970.