Aluminum Titanate Compositions for Diesel Particulate Filters

Abstract

ABSTRACT Compositions in the mixed strontium/calcium feldspar ([Sr/Ca]O . Al 2 O 3. 2SiO 2 ) - aluminum titanate (Al 2 O 3. TiO 2 ) system have been investigated as alternative materials for the diesel particulate filter (DPF) application. A key attribute of these compositions is their low coefficient of thermal expansion (CTE). Samples have been prepared with porosities of >50% having average pore sizes of between 12 and 16µm. The superior thermal shock resistance, increased resistance to ash attack, and high volumetric heat capacity of these materials, coupled with monolithic fabrication, provide certain advantages over currently available silicon carbide products. In addition, based on testing done so far aluminum titanate-based filters have demonstrated chemical durability and comparable pressure drop (both bare and catalyzed) to current, commercially available, silicon carbide products. INTRODUCTION Diesel particulate matter (PM) emissions pose serious health concerns and are under environmental regulation. Diesel filter after-treatment technology is currently used to remediate PM emissions. SiC and cordierite filters are two of the most viable solutions available for use today. Cordierite has a low coefficient of thermal expansion and can survive thermal shock in this application, but cordierite is limited by its low heat capacity. It is also susceptible to ash reaction during exceedingly high temperature applications [1]. SiC, on the other hand, has a lower thermal shock resistance and thus needs to be segmented. The segmentation increases manufacturing costs and is a concern because of potential mechanical integrity issues. Other issues with SiC have been reported recently and solutions have been implemented [2-3]. An alternate DPF candidate is a novel Aluminum Titanate (AT) ceramic oxide composite. The composition is highly refractory with a melting temperature exceeding 1500°C. The high heat capacity of the composition is an attribute that is beneficial for thermal management and allows the filter regeneration temperature to be low. Although the intrinsic coefficient of thermal expansion of aluminum titanate is quite high (CTE = >9*10