Papers by Keyword: Al₂TiO₅

Abstract: Aluminum titanate (AT) ultrafine powder with high productivity ratio was prepared via hydrolytic sol-gel (HSG) method at 1250 °C, using aluminum nitrate (Al (NO₃)₃·9H₂O) and titanium tetrachloride (TiCl₄) as precursors, ethanol as solvent through solvothermal treatment process. Water required for hydrolysis reaction was supplied by the crystal water of aluminum nitrate itself. The effect of process parameters including filling ratio, solvothermal temperature and soaking time on the synthesis of AT powder was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The cause of low temperature synthesis of AT was investigated. The result showed that excessive or insufficient filling ratio, too high or low solvothermal temperature, too long soaking time was not beneficial for the preparation of AT. The optimized ultrafine AT powder appeared at the decomposition temperature of 1250 °C with average particle size less than 1μm at a relatively high productivity ratio of 98 % with filling ratios of 60 %, solvothermal temperatures of 130 °C and soaking time of 30 min. The refinement of particles in the AT xerogel through solvothermal treatment process, and increasing reactivity of precursor, plays the key role in the low temperature synthesis of AT.

Abstract: The incorporation of nano-size TiO2 particles can significantly enhance the microstructure and mechanic properties of Al2O3 coating. Phase transformation from mainly stable α-Al2O3 and anatase-TiO2 in the powders to predominant metastable γ-Al2O3 and rutile-TiO2 in the coatings was observed. Reaction between Al2O3 and TiO2 phase also occurred producing new phase Al2TiO5 phase. Microstructural investigation showed that well separated TiO2 lamellas were homogeneously dispersed between Al2O3 lamellas. It was found that the plasma-sprayed composite coating possessed better wear resistance than that of monolithic Al2O3 coating. The addition of TiO2 was found to improve friction coefficient, wear resistance and fracture toughness.

Abstract: In the present paper, Al2TiO5-Al2O3 composites with 10, 20, 40, 60, 80, and 90 Vol. % of Al2O3 respectively were prepared by the sintering of Al2TiO5 and Al2O3 powers. The thermal expansion ratio was measured and the quenching-strength method was used to study the thermal shock-resistance performance. The thermal expansion ratio was found to increase from zero for the sample with 10-20Vol.%Al2O3 to that of 0.007% as the content of Al2O3 increased . The results of quenching-strength test showed that the residual strength of Al2TiO5-Al2O3 composites decreased with increasing of Al2O3 content and the thermal shock cycles. The Al2TiO5/Al2O3 composite with 20Vol.% Al2O3 remained a strength of 33.4MPa after three cycles and exhibited good thermal shock-resistance performance.

Abstract: The low thermal expansion (α25-1100oC = 0.05 ~ 1.6 × 10–6/K) of Al2TiO5 ceramics are apparently due to a combination of grain boundary micro cracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. During the reheating run, the individual crystallites expanded at low temperature; thus, the solid volume of the specimen expanded into the micro cracks, where as the macroscopic dimensions remained almost unchanged. As a result, the material expanded very little. The micro cracks closed at higher temperatures. This result is closely related to relatively steeper thermal expansion curves.

Abstract: In the present paper, magnesium dititanate (MgTi2O5, M2T) was introduced into aluminum titanate (Al2TiO5, AT) to form AT-M2T solid solution so that the thermal shock resistance of Al2TiO5 could be kept still good while without any decomposition. The effect of MgTi2O5 addition on thermal shock resistance of Al2TiO5 was investigated. The experimental results showed that the thermal shock resistance of Al2TiO5 began to decrease when a little amount of MgTi2O5 was added and then rose with the continuous addition of MgTi2O5, even overrunning that of pure Al2TiO5 when 30mol% MgTi2O5 was contained. It was found that fine solid solution was formed between Al2TiO5 and MgTi2O5, which enhanced the thermal shock resistance of Al2TiO5.

Abstract: High temperature structural ceramics based on Al2TiO5-ZrTiO4 (ZAT) having excellent thermal-shock-resistance were synthesized by a reaction sintering. The ZAT ceramics sintered at 1600oC had a negative thermal expansions up to 1000oC and a much lower thermal expansion coefficient (0.3 ~ 1.3 x 10-6 /K) than that of polycrystalline Al2TiO5 (1.5 x 10-6 /K). These low thermal expansion are apparently due to a combination of microcracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. The microstructural degradation of the composites after various thermal treatment for high temperature applications were analyzed by scanning electron microscopy, X-ray diffraction, ultrasonic and dilatometer.

Abstract: Alumina (Al2O3)-aluminium titanate (Al2TiO5) composites present higher toughness than alumina materials but rather low strength due to microcracking. Laminates in which a flaw tolerant material is located between high strength layers is one way to overcome this problem. In this work, the fracture behaviour of a laminated structure constituted by five layers, where low residual stresses are expected, is studied. In this system, external and central layers of monophase alumina with high strength were combined with intermediate layers of alumina with 10vol.% of aluminium titanate. In the monophase alumina layers, an additional "in situ" formed layer of about 200 µm, constituted by large (@10µm) grains was found, close to the composite layers. The laminated structure presented semistable behaviour during SENVB tests for conditions in which stable crack propagation is not predicted for small grain sized alumina materials. Toughening mechanisms related to thermal expansion mismatch between matrix and second phase in the composite layers and crack bridging in the large grain sized alumina layer were identified.

Abstract: The mechanical properties of directionally solidified two-phase eutectics can be superior to that of either constituent alone due to the strong constraining effects of the interlocking microstructure. The present work focuses on the failure mechanisms that occur in Al2O3-Al2TiO5 composites fabricated by directional solidification. Two compositions rich in alumina have been considered. The constituents were the same in both materials, primary Al2O3 dendrites surrounded by a TiO2-containing phase, with different morphological and size characteristics. The dendrites in the material containing the smallest amount of Al2O3 were short and highly interpenetrated by the secondary phase whereas those of the material with the highest Al2O3 content were long and much less interpenetrated. The mechanical behaviour in bending was determined by these microstructural differences because the load bearing phase in these directionally solidified materials in the system Al2O3-Al2TiO5 are the Al2O3 dendrites.