Comparing the Influence of Additives on Reaction Sintering, Microstructure and Properties of solid- state and Sol_Gel-Drived Aluminum Titanate in Aqueous Solution

Aluminium titanate (AT), Al2TiO5 is an excellent thermal shocker resistant ceramic which has a pseudo brookite structure [1].AT exists in two allotropic forms α and ß and the low temperature phase is ß Al2TiO5. AT is a well known ceramic mostly recommended for the most structural applications such as a catalyst carriers, thermal insulation liners in internal combustion engines and filters in the metallurgical and glass industries [2]. However, AT has two major problems limiting its wider application [3], such as decomposition to alumina and titania in the range of 800 to 1280°C and spontaneous micro cracking due to the thermal expansion anisotropy in the sintered ceramics which ultimately result in poor mechanical strength. Micro cracks are found to develop predominately above the critical sintered grain size of 1.5 μm and therefore fine grained microstructure is necessary [4]. Additives such as Al2O3, MgO, SiO2 and ZrO2 are employed in the AT precursor to suppress decomposition of the phases[5].Another approach is to control the sintered grain size to below1.5 μm, for which nanosize starting particle size is a possibility. Also, in some cases sintering aids and grain growth inhibitors are used [6].AT ceramic has many potential applications, such as thermal protection layers in internal combustion engines, kiln furniture and pouring spouts for foundry applications, due to its low thermal expansion coefficient (CTE: 0.2×10-6 to 1×10-6 K), low thermal conductivity (0.9–1.5W/m/K), and high thermal shock resistance (about 500W/m) [7].AT is also recognized as a second phase material for improving the thermo-mechanical properties like thermal shock resistance, toughness, and flaw tolerance behaviour of many ceramic matrix composites[8].It has been traditionally obtained by conventional communication of crystalline powders that are fired at temperature above 1300 °C. The advantages of this method are low cost and none aggregation of powders, but it also has some drawbacks, because of the low purity, homogeneity and large particle size [9]. Chemical techniques such as sol-gel, co-precipitation and combustion have also been reported for obtaining fine-grained AT, because by using these techniques one can control the initial particle size as well as the low temperature needed for densification. [3]. among solution methods, there are some advantages such as: simplicity, economic cost, high separation efficiency (> 95 %) and by-product recycling [10]. No detailed work has been reported in the synthesis and sintering features of aluminium titanate by aqueous sol–gel methods involving TiCl4 and Al (NO3)3. 9H2O precursors with other additives such as magnesium nitrate salt. There fore we report a novel approach for the synthesis of submicron AT containing average particle of size ~800nm. In this work tow procedure (solid-state and sol-gel synthesis) are compared. The low- temperature formation of Al2TiO5 is possibly due to the nature of the starting sol-gel reaction mixture. The effects of precursors on the AT phase formation evolution of particle size, sintering behaviour, and microstructural features are studied and discussed for the both pf the procedures