Decomposition Of Aluminium Titanate Research Articles

Development of dense Al2O3–TiO2 ceramic composites by the glass-infiltration of porous substrates prepared from mechanical alloyed powders

In this work bio-composites were obtained by infiltrating porous alumina–titania (Al2O3–TiO2) substrates with a lanthania-rich (La2O3) glass. Al2O3–TiO2 substrates were fabricated using high-energy milled powder mixtures of two different compositions with molar ratios of 3:1 and 1:1, uniaxial compaction under 100 MPa and sintering at 1300 °C - 2 h or 1400 °C - 2 h. The high energy milling process of the powders resulted in homogeneous, extremely fine mixtures. For comparison, as-received Al2O3 and TiO2 powders were also mixed at a proportion of 3:1 and sintered at 1600 °C - 2 h. The sintered substrates presented α-Al2O3 and β-Al2TiO5 (aluminium titanate) as crystal phases and relative densities ranging between 65.5 ± 2% and 69.4 ± 1.2% of the theoretical density. These porous substrates were infiltrated with a lanthania containing glass at a temperature of 1140°C-2h. The resulting ceramic composites exhibited high density, varying between 94 to 99% of the theoretical density, Vickers hardness ranging between 895 ± 14 HV and 1036 ± 33 HV, fracture strength ranging between 218 ± 28 MPa and 254 ± 18 MPa and a fracture toughness (KC) higher than 2.6 MPam1/2. Phase analysis of the infiltrated substrates by X-ray diffraction indicated the decomposition of aluminium titanate into alumina and titania besides the formation of lanthanum borosilicate, LaBSiO5. In addition, all compositions studied presented non-cytotoxic behaviour and low chemical solubility, inferior to 75 μg/cm2.

Influence of Feedstock Powder Modification by Heat Treatments on the Properties of APS-Sprayed Al2O3-40% TiO2 Coatings

The formation and decomposition of aluminum titanate (Al2TiO5, tialite) in feedstock powders and coatings of the binary Al2O3-TiO2 system are so far poorly understood. A commercial fused and crushed Al2O3-40%TiO2 powder was selected as the feedstock for the experimental series presented in this paper, as the composition is close to that of Al2TiO5. Part of that powder was heat-treated in air at 1150 and 1500 °C in order to modify the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including EDS of metallographically prepared cross sections. Only a maximum content of about 45 wt.% Al2TiO5 was possible to obtain with the heat treatment at 1500 °C due to inhomogeneous distribution of Al and Ti in the original powder. Coatings were prepared by plasma spraying using a TriplexPro-210 (Oerlikon Metco) with Ar-H2 and Ar-He plasma gas mixtures at plasma power levels of 41 and 48 kW. Coatings were studied by XRD, SEM including EDS linescans of metallographically prepared cross sections, and microhardness HV1. With the exception of the powder heat-treated at 1500 °C an Al2TiO5-Ti3O5 (tialite–anosovite) solid solution Al2−xTi1+xO5 instead of Al2TiO5 existed in the initial powder and the coatings.

Phase Formation in the Region of laser Irradiation of Al2O3–TiO2–Y2O3 Oxide Eutectic Mixtures

The phase formation processes in the zone of directional laser irradiation of compacted Al2O3–TiO2–Y2O3 mixtures have been investigated. It has been established that the formed ceramic material (track) has a complex structure. Its surface layer contains α-Al2O3 as the main phase and Y2Ti2O7 inter layers. With increase in the distance from the surface of the track, the content of α-Al2O3 decreases, and the content of Y2Ti2O7 increases. The volume layers of the track contain Y2Ti2O7 as the main phase and inclusions of Y3Al5O12. The absence of Al2TiO5 or its small content is explained by the decomposition of aluminum titanate into Al2O3 and TiO2 under the conditions of rapid cooling of eutectic melt. Released titanium oxide takes part in the formation of the Y2Ti2O7 phase.

Nano- and micrometre additions of SiO2, ZrO2 and TiO2 in fine grained alumina refractory ceramics for improved thermal shock performance

The present contribution investigates the influence of micro-metre- as well as nano-metre-additions of zirconia (ZrO2), titania (TiO2), silica (SiO2) and magnesia (MgO) into alumina-rich fine grained ceramic materials for refractory applications. Slip casted samples in the system alumina–zirconia–titania (AZT), alumina–zirconia–titania–silica (AZTS) and alumina–zirconia–titania–magnesia (AZTM) were sintered and the physical as well as mechanical properties were investigated as fired and after thermal shock treatments. The generation of a micro-crack network after sintering due to the formation of phases with different thermal expansion coefficients and the formation and decomposition of aluminium titanate (Al2TiO5) before and after thermal shock exposure leads to higher strengths after thermal shock attack.

Preparation of Alumina Ceramics with Uniformly Dispersed Micropores

Submicron micropores were uniformly dispersed in an alumina ceramic matrix by using the volume shrinkage accompanied by the decomposition of aluminum titanate (AT) into corundum and rutile. The methodology for the fabrication of the pore-dispersed alumina includes (1) homogeneous mixing of 2-8wt% TiO2 with alumina, (2) densification of AT-dispersed alumina, and (3) decomposition of AT into corundum and rutile with the formation of micropores. Such micropores are considered to release the residual thermal strain and to deflect cracks propagating in the alumina matrix.

Thermal and mechanical properties of aluminumtitanate-mullite composites (part 1)

The thermal expansion, thermal stability and bending strength of aluminumtitanate (AT)-mullite composites prepared from synthesized AT, Newzealand kaolin and aluminum hydroxide were investigated. The results obtained are summarized as follows; (1) The average linear thermal expansion coefficient from 100° to 1100°C increased slightly with increasing amount of AT up to 50wt%, and decreased with further increase in the amount of AT, approaching to be value of fired AT. The average linear thermal expansion coefficients from 1100° to 1400°C in heating and from 1400°C to the turning point in the cooling stage increased monotonously with increasing AT content. (2) The degree of thermal expansion hysteresis decreased with decreasing amount of AT. (3) The bending strength of the composites containing 10-30wt% AT was the highest, and decreased with further increase in the amount of AT. (4) The decomposition of AT in the composites was restrained almost completely.

Thermal and Mechanical Properties of Aluminumtitanate-Mullite Composites (Part 1)

The thermal expansion, thermal stability and bending strength of aluminumtitanate (AT)-mullite composites prepared from synthesized AT, Newzealand kaolin and aluminum hydroxide were investigated. The results obtained are summarized as follows; (1) The average linear thermal expansion coefficient from 100° to 1100°C increased slightly with increasing amount of AT up to 50wt%, and decreased with further increase in the amount of AT, approaching to be value of fired AT. The average linear thermal expansion coefficients from 1100° to 1400°C in heating and from 1400°C to the turning point in the cooling stage increased monotonously with increasing AT content. (2) The degree of thermal expansion hysteresis decreased with decreasing amount of AT. (3) The bending strength of the composites containing 10-30wt% AT was the highest, and decreased with further increase in the amount of AT. (4) The decomposition of AT in the composites was restrained almost completely.