**5. Experimental procedure**

The raw materials used were reactive grade: Al2O3 (D50=0.60µm), TiO2 (D50=0.88µm), V2O5 (D50=0.60µm), MnO (D50=0.60µm), ferrosilicon (D50=0.69µm), FeTiO3 (D50=0.82µm), and, alumina ball milled 98.5%FeTiO3-1.2%SiO2 purified mineral (D50=0.88µm).

Two (2) equimolar mixtures of Al2O3 and TiO2 (56wt%Al2O3 - 44wt%TiO2) were homogeneously mixed with 3, 6 and 9 wt% of each additive using alumina jars and balls, during 6 hours. No binder has been added to the aqueous media powder mixture and it was dried out at 120°C for 24 hours. The material was crushed in an alumina mortar prior to the manufacture of samples by uniaxial die compaction at 300 MPa. Green bodies were reactive sintered at 1450°C, in air for 3 h. Heating was programmed at 5°C/min. whereas cooling at 15°C/min, in order to avoid eutectoid transformation: Al2TiO5 → Al2O3 + TiO2 (Kolomietsev et al.,1981).

X-ray diffraction (XRD) analysis has been performed on powders from crushed sintered samples, with grains below 30 µm suitable to obtain rigid specimens. The quantification of Al2TiO5 formed was determined by the internal standard method, through direct determination based on the methodology of Klug and Alexander (1954). In this study, the diffraction signals used were: Al2TiO5 (023), Al2O3 (104) and TiO2 Rutile (110)*,* which are representative of the three components of interest in the studied samples.

Reactive Sintering of Aluminum Titanate 509

**Oxygen/Metal (x) Relationship**

The XRD results showed, for aluminum titanate without additive (Fig. 4.), that the selected temperature and time are sufficient for a near 100% Al2TiO5 reaction of formation, as the most important peaks correspond to this compound with a minimum of Al2O3 and TiO2 remnants. It is important to point out that in all XRD, are represented the PDF values for all

Fig. 4. X Ray Diffraction of equimolar mixture Al2O3 and TiO2 without addition, sintered at

the constituents expected in each case, although they are not present.

) vs. Oxygen/Metal (x en MOx) for the 3d metals.

Fig. 3. Oxygen partial pressure (PO2

**6.2 Structure analysis** 

1450°C for 3 hours.

Sintered sample surfaces were carefully ceramographically prepared to minimize damage and, in some cases it was needed to chemically etch in ambient 15%HF solution for 60 s, to reveal grain boundaries. The microstructure characterization was carried out using compositional back scattered electron images (BSEI) from scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Evaluation of grain size and phases present has been performed by image analysis.

In order to quantify the stabilization of Al2TiO5, sintered samples previously thermal treated at 1100°C for 100 h. were Si internal standard XRD analyzed, as in the as-sintered condition.

To determine the type of Fe ion in solution, it was used Mössbauer Spectroscopy with the isotope iron 57Fe, in the samples with addition of ilmenite and ferrosilicon. The source used was 57Co, the Mösssbauer transition is 14.41 keV, with the excited level of nuclear spin I = 3/2 and fundamental level I = 1/2. The extent of the isomeric shift provides information on the valence of the atom to which belong the core, as the electronic layers and therefore the density of electrons in the nucleus, are sensitive to chemical bonding.

Thermal expansion analysis in the temperature range of 25 to 1000°C and 1450°C, at 5°C/min heating and cooling ramps, has been performed on selected samples with good stabilization behavior.
