“The hexagonal-rhombohedral Ti2O3 phase in the Ti-O system extends from 32.5 to 34.5% oxygen b.w., with the exact composition of Ti2O3 nearly in the middle of the phase. Seven samples of different composition within that phase were made, and the lattice constants (a and c) and the density of each sample were determined.
The plots of the constants against the composition of the samples revealed a deviation from Vegard’s rule when approaching the exact composition of Ti2O3. The lattice constants of this compound, obtained by graphical interpolation were; a25 = 5.148 Å, c25 = 13.636 Å, and c/a = 2.649 (or a25 = 5.435 Å with the interstitial angle α = 56.676 deg. in the rhombohedral lattice). The interpolation density of this compound at 25.0°C was 4.589 g/cm3.
The linear thermal expansion coefficients along the a and c axes were calculated from the variation of the lattice constants with temperature. There was gradual change of these coefficients with composition.
The lattice perfection of the seven samples was determined from the volume of the unit cell, the chemical molecular weight (computed from the formula Ti2Ox) and the density of the sample It was found that on the left side of the Ti2O3 phase there was an excess of Ti metal (extractable by hydrofluoric acid under hydrogen evolution from the phase), partially located in interstitial positions (up to 1.02%).
On the right half of the phase, there was oxygen in excess (in interstitial positions), the amount increasing toward the right border of the phase (up to 1.57%).
The lattice a constants decreased with increasing titanium content and increased with increasing excess oxygen content in the solid solution. The lattice c constant greatly increased with increasing excess titanium content and decreased with the excess of oxygen.
The number of interstitial atoms as plotted against the chemical composition of the samples gave a straight line, passing through the number zero within the limits of error, meaning that the lattice is sound at that composition.
The excess oxygen charges (negative) on the right side of the phase are compensated by tetravalent titanium ions.
It was found that the range of homogeneity of the TiO2 phase extends from TiO1.989 to TiO2.006. The lattice constants (tetragonal a and c constants), and the densities were determined for seven samples of different color within the range of homogeneity prepared under different oxygen equilibrium pressures.
The lattice constants obtained by graphical extrapolation were; a25 = 4.5937 Å, c25 = 2.9619 Å, and c/a =0.64478. The intrapolated macroscopic density at 25.0°C was 4.2441 g/cm3.
The linear thermal expansion coefficients along the a and c axes were: αa = 6.88 x 10-6, αc = 9.91 x 10-6.
The lattice perfection of the samples was determined. It was found that on the left side of the phase there were oxygen vacant sites (up to 2.06%). On the oxygen side, there was an excess of oxygen, probably in interstitial positions, which increased with increasing oxygen content toward the border of the phase (1. 20%).
The lattice a constant increased with increasing oxygen content by a parabolic relation (positive deviation from Vagard’s rule).
The lattice c constant decreased with increasing oxygen content by a parabolic relation (negative deviation from Vagard's rule).
The number of oxygen vacant sites as plotted against the composition of the samples gave a straight line, passing through the number zero within the limits of error, meaning that the lattice at that composition is sound.
From the plots of the equilibrium oxygen pressure against the composition of the samples, it was found that the dissociation pressure of TiO2 at 1400°C is approximately 2/3 of the atmospheric pressure”—Abstract, pages i-iii.
Schlechten, A. W.
Straumanis, Martin E., 1898-1973
James, William Joseph
Materials Science and Engineering
Ph. D. in Metallurgical Engineering
National Science Foundation (U.S.)
U. S. Atomic Energy Commission
Missouri School of Mines and Metallurgy
x, 172 pages
© 1959 Tatsuhiko Ejima, All rights reserved.
Dissertation - Open Access
Titanium alloys -- Thermal properties
Titanium -- Thermal properties
Titanium alloys -- Metallurgy
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Ejima, Tatsuhiko, "Imperfections within Ti₂O₃ and TiO₂ phases in the titanium-oxygen system" (1959). Doctoral Dissertations. 974.