A thermodynamic study of iron in reduced rutile

Grey, Ian E.; Li, C.; Reid, Allen F.

doi:10.1016/0022-4596(74)90106-6

Cited by 19 publications

(4 citation statements)

References 12 publications

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“…The interval Ti 3 O 5 to TiO 2 is relevant in illmenite smelting. Later studies were to attain better resolutions and to measure oxygen potentials (see Porter, 1965;Zador, 1968;Suzuki and Sambongi, 1972;Merritt et al, 1973;Grey et al, 1974b;Kowalski et al, 1995: Fig. 3.14).…”

Section: Ti 3 O 5 -Tio 2 Binarymentioning

confidence: 99%

“…Its inclusion leads to a series of short, parallel solid-solution series, certain members of which are in equilibrium with metallic iron at high temperatures. Grey et al (1974b) measured the compositions of three-phase assemblages in this part of the system at 1200°C, and the invariant oxygen fugacities stabilizing them (see Den Hoed, 1993: pp. 152-153).…”

Section: Magnéli Phasesmentioning

confidence: 99%

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Oxidation and Reduction of Iron-Titanium Oxides in Chemical Looping Combustion: A Phase-Chemical Description

Hoed

Luckos

2011

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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Section: Ti 3 O 5 -Tio 2 Binarymentioning

confidence: 99%

Section: Magnéli Phasesmentioning

confidence: 99%

Oxidation and Reduction of Iron-Titanium Oxides in Chemical Looping Combustion: A Phase-Chemical Description

Hoed

Luckos

2011

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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“…crystals containing {121} c.s. planes from th a t of stoichiometric rutile, A^f(Tin0 2n_1), and compared it to calculated values derived from the experimental results recorded by M erritt & Hyde (1973) and Grey et al (1974).…”

Section: 3mentioning

confidence: 99%

Energy calculations for planar faults in reduced rutile (TiO ₂ )

Aizawa

Iguchi

Tilley

1984

Proc. R. Soc. Lond. A

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Calculations have been made of the energetics of reduced rutile (TiO 2 ) crystals containing ( a ) an isolated {132} c. s. plane, ( b ) an ordered array of {132} c. s. planes corresponding to an oxide of composition Ti 20 O 39 , ( c ) a vacancy disc lying on {132} planes and ( d ) an ordered array of vacancy discs lying on {132} planes, which gives the crystal a composition of Ti 20 O 39 . The calculations were made by using the polarizable point ion shell model, and by taking the electronic polarizabilities of the ions involved into account. The results show that the c. s. planes are preferred to vacancy discs, and that this is largely due to the electronic polarization energy terms. The enthalpy of formation of an isolated {132} c. s. plane in rutile was calculated. A comparison with an estimate of the enthalpy of formation of the vacancy disc suggests that vacancy discs will be converted into c. s. planes in real crystals and will not exist as discrete defects. The change of the energy terms as the polarizabilities of the ions varied was also calculated to quantify the relation between preferred defect structure and dielectric constant. It was found that a change in dielectric constant did not have a significant effect upon the stability of vacancy discs, but did have a large effect on the energetics of c. s. planes, which suggests that c. s. planes are only favoured in crystals of high dielectric constant. It is shown that electronic polarizability is of importance in stabilizing {132} c. s. planes and that the polarizability of the O 2 ─ ions, in particular, is of great significance.

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“…Above 1050°C, it is thermodynamically possible to reduce rutile further to Ti3O5. At 1200°C, the Magnéli phases incorporate iron from 1.2 at.% when n=8, to 0.8% for M3O5 (Grey, Li and Reid, 1974).…”

Section: Ti3o5-tio2 Boundary and Magnéli Phases (Tino2n-1)mentioning

confidence: 99%

Pre-Oxidation of New Zealand Ironsand - Where does the Titanium go?

Bjareborn

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The interplay between iron- and titanium oxides has been studied, for a better understanding of how different amounts of titanium affects iron ore, for relevance in downstream ironmaking processes. The oxidation of NZ ironsand as well as synthetic titanomagnetite (TTM) of three different compositions has been studied in air up to 1320°C. In-situ monitoring of mass gain and thermal response during oxidation (TGA-DSC), as well as ex-situ analysis of crystals phases (powder XRD) and microstructure (SEM) of samples after quenching from select oxidation temperature at deliberate time intervals. Crystal phases in the samples were mapped spatially using SEM- EBSD, and chemical composition using (SEM-EDS). This has enabled a detailed evaluation of the relationship between the growth of specific crystals and their relative chemical compositions. Characterization of NZ ironsand revealed an overall homogenous ore body with a majority (90%) of homogenous (TTM) particles. However, a distribution of compositions was found between particles, with regards to Ti (0-42%), Al (1-5%) and Mg (1-4%). Approximately 1% of particles where homogeneous titano-hematite (TTH) particles of significantly higher Ti content, and 10% of particles where partially oxidised two-phase particles, containing both TTM and TTH. The two-phase particles showed higher Ti content in the TTH phase and higher Al- and Mg content in the TTM phase. Isothermal oxidation of Ironsand pellets at 960 °C,1100 °C and 1310°C, found that pseudobrookite (PSB) was formed within 3 min of oxidation time at these temperatures and that the amount of PSB formed decreased with increasing temperature in the range. Development of SEM-EBSD analysis enabled spatial mapping of crystal phases within the samples, showing that PSB formation was occurring preferentially at locations of higher Ti -content, such as two-phase and TTH particles.Temperature and Ti- content significantly affects the resulting phases and morphology after oxidation. To isolate and elaborate on the effects of Ti content, the use of synthetically prepared single- phase TTM samples, where each sample is homogeneous in composition was proposed. A novel synthesis methodology for producing such single-phase TTM samples was developed, where thermal decomposition of ferrous oxalate mixed with rutile nano powder, in a controlled atmosphere, at 1200°C produced samples with Ti/(Ti+Fe) = 8, 15 and 20%, in a reduced time frame. TGA-DSC analysis of synthetic samples revealed four distinct oxidation events, associated with distinct oxidation mechanisms and temperatures, and the effects of Ti content on them. The first (~350°C) related to gradual transformation to titanomaghemite (TMH), which manifested as a shortening of the lattice parameter (a). The second (~550°C) related to partial formation of TTH, and was preferential towards higher Ti samples, with more Ti in the TTH phase. The third (~660°C) related to the formation of PSB, and was also preferential to higher Ti samples, driving the segregation of Fe and Ti further. The fourth (~720°C) was related to oxidation of the remaining (Ti poor) TTM phase to TTH. The third and fourth events showed considerable overlap, due to the sequential nature of the phase changes (TTM → TTH → PSB). Isothermal experiments with synthetic TTM samples were done at 500°C, 960°C, 1100°C and 1310°C. The gradual formation of TMH at 500°C was monitored through measurements of the lattice parameter (a) which was shown to decrease linearly with oxidation degree (z) for all three sample compositions, with a steeper slope with increased titanium content. At higher temperatures (960°C, 1100°C and 1310°C) the formation of TTH and PSB was monitored. The amount of PSB increased with increasing Ti content but decreased with increasing temperature. The synthetic samples of similar composition formed more PSB than ironsand, indicating that other cations in ironsand depresses the formation of PSB.The morphology of samples showed small, finely dispersed, lamellar features at 960 °C, and larger elongated globular features at the higher temperatures (1100°C and 1310°C), reaching ~5 μm after 15 min oxidation at 1310 °C. The reaction progressed through the samples in a shrinking core fashion. Progression of reaction fronts varied with temperature and composition. At 960 °C TTH primarily formed at grain boundaries, and then progressing along parallel crystal planes. At 1100°C and 1310°C, reaction fronts were less ordered with broader features. A clear (10-20 μm) gap between two distinct reaction fronts was observed for high Ti samples, illustrating the sequential oxidation (TTM → TTH → PSB).In general, increasing Ti-content promotes oxidation, and segregation of Fe -Ti, both at high and low temperatures. Increasing the oxidation temperature decreases the amount of PSB formed and thus the Fe- Ti segregation. This was found in ironsand and subsequently validated using synthetic TTM samples.

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A thermodynamic study of iron in reduced rutile

Cited by 19 publications

References 12 publications

Oxidation and Reduction of Iron-Titanium Oxides in Chemical Looping Combustion: A Phase-Chemical Description

Oxidation and Reduction of Iron-Titanium Oxides in Chemical Looping Combustion: A Phase-Chemical Description

Energy calculations for planar faults in reduced rutile (TiO ₂ )

Pre-Oxidation of New Zealand Ironsand - Where does the Titanium go?

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A thermodynamic study of iron in reduced rutile

Cited by 19 publications

References 12 publications

Oxidation and Reduction of Iron-Titanium Oxides in Chemical Looping Combustion: A Phase-Chemical Description

Oxidation and Reduction of Iron-Titanium Oxides in Chemical Looping Combustion: A Phase-Chemical Description

Energy calculations for planar faults in reduced rutile (TiO 2 )

Pre-Oxidation of New Zealand Ironsand - Where does the Titanium go?

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Energy calculations for planar faults in reduced rutile (TiO ₂ )