Solid solution of aluminum oxide in rutile titanium dioxide

Slepetys, Richard A.; Vaughan, Philip A.

doi:10.1021/j100727a010

Cited by 96 publications

(55 citation statements)

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“…The results ͑plotted as solid diamonds in Fig. 4͒ clearly do not support that notion; the EDS results are more in line with the literature data 34,35 confirming the latter. There is thus little doubt that Al dissolves in TiO 2 .…”

Section: Reaction 5 Is Consistent With the Results Of Yan And Rhodessupporting

confidence: 43%

Oxidation of Ti[sub n+1]AlX[sub n] (n=1-3 and X=C, N)

Barsoum

2001

J. Electrochem. Soc.

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In this, Part I of a two-part study, a generalized model for the oxidation of the ternary compounds, Ti nϩ1 AlX n , where n ϭ 1-3 and X is carbon and/or nitrogen, is proposed. In all cases, the oxidation products in the 800-1100°C temperature range are rutile TiO 2 , in which some Al is dissolved, i.e., (Ti 1Ϫy Al y )O 2Ϫy/2 , where y Ͻ 0.05 and Al 2 O 3 . The oxidation occurs by the inward diffusion of oxygen and the outward diffusion of Al 3ϩ and Ti 4ϩ ions through the (Ti 1Ϫy Al y )O 2Ϫy/2 layer. The C and N atoms are presumed to diffuse through the reaction layers and oxidize. The basic premises of the model are that the subjection of the (Ti 1Ϫy Al y )O 2Ϫy/2 layer to an oxygen chemical potential gradient results in its demixing, with the Al 3ϩ dissolving into the rutile at the low oxygen partial pressure and its precipitation as Al 2 O 3 at the high partial pressure side. If extensive, the demixing results in the formation of layers of porosity, through which the Al 3ϩ ions cannot diffuse but the O 2Ϫ ions can. The resulting microstructures can be highly striated where three layers; an Al 2 O 3 -rich layer, an (Ti 1Ϫy Al y )O 2Ϫy/2 -rich layer, and a porous layer repeat numerous times. Comparison with previously published results on the oxidation of Ti 3 SiC 2 leaves little doubt that dissolution of the Al in the reaction layer enhances the oxidation kinetics. This is most probably accomplished by an increase in the oxygen vacancy concentration. The fact that the oxide scales are not fully dense is also believed to play an important role in enhancing the oxidation kinetics.At this time, it is well established that the ternary carbides and nitrides with the general formula M nϩ1 AX n with n ϭ 1-3, where M is an early transition metal, A is an A group element, and X is C and/or N, are structurally related. 1-7 This family of compounds possesses an unusual set of properties. 7-17 With Vickers hardness values in the range of 2-5 GPa, they are anomalously soft compared to typical binary transition metal carbides and nitrides. They are also good thermal and electrical conductors and readily machinable with regular high speed tool steels, hacksaw, or band saw, without the need for either cooling or lubrication.Recently, a reactive hot-pressing route was employed to fabricate, for the first time, fully dense, predominantly single phase, samples of Ti 2 AlC, 15 Ti 2 AlN 0.5 C 0.5 , 15 Ti 3 AlC 2 , 16 and Ti 4 AlN 3 . 17 A more thorough description of the microstructures and stoichiometries tested is presented in the accompanying paper. 18 These phases are characterized by a relatively low density ͑Ϸ4.5 g/cm 3 ͒, high Young's moduli ͑200-325 GPa͒, and moderate thermal expansion coefficients ͑8 to 10 ϫ 10 Ϫ6 K Ϫ1 ͒. 15-17 All these ternaries go through a brittle to plastic transition around Ϸ1050°C. They are also thermal shock resistant and damage tolerant. 16,17 The combination of relatively low density, high stiffness, and plasticity at higher temperatures renders these ternaries potential materials for high tempera...

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Section: Reaction 5 Is Consistent With the Results Of Yan And Rhodessupporting

confidence: 43%

Oxidation of Ti[sub n+1]AlX[sub n] (n=1-3 and X=C, N)

Barsoum

2001

J. Electrochem. Soc.

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“…We observed a slight increase for both lattice parameters. In contrary, two detailed works on the solid solution of alumina in rutile reported a small shrinkage when the rutile lattice incorporates Al 3+ [25,26]. However, long termed annealed samples were investigated in these studies, which might be the reason for the observed difference.…”

Section: Resultsmentioning

confidence: 87%

Melt synthesis of Al2TiO5 containing composites and reinvestigation of the phase diagram Al2O3–TiO2 by powder X-ray diffraction

2006

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Recently the fabrication of ceramics starting from the appropriate melts of the educts has attracted increasing attention due to the easy shaping of work pieces and other advantages compared to powder sintering methods. We focused our interest on aluminum titanate (β-Al 2 TiO 5 ) based ceramics which are interesting for high temperature applications due to the low thermal expansion coefficient. For this purpose we have investigated the titania-rich side of the Al 2 O 3 -TiO 2 system (up to 50 mol% titania) under rapid cooling conditions with respect to the phase formation. By powder X-ray diffraction we could prove the solely formation of the known phases rutile and β-Al 2 TiO 5 in agreement with the equilibrium phase diagram. Furthermore, powder pattern fitting has revealed the formation of solid solutions for both compounds.

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“…XRD data suggests that Al ions dissolve substitutionally in the TiO 2 lattice because of the similar ionic radius to Ti [26], then oxygen vacancies are expected to generate [27] and the defect equation with charge conservation can be written as:…”

Section: Resultsmentioning

confidence: 99%