Mullite-aluminum titanate body and method for making same

Abstract

This invention relates to a mullite-aluminum titanate body having a low coefficient of thermal expansion of less than 15×10−7 C−1, a high porosity of at least 38% by volume, a median pore diameter of at least 8 microns, and a narrow pore size distribution as characterized by the relation (d50-d10) / d50 being less than 0.50 corresponding to a high degree of interconnected porosity. The inventive ceramic body also contains at least 0.10% by weight metal oxide, the metal being either yttrium, calcium, bismuth, a lanthanide metal or combinations of thereof. The inventive ceramic body is particularly useful as a wall-flow filter for diesel exhaust. A method of fabrication is provided where the sintering temperature is between 1375°-1550° C.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to a mullite-aluminum titanate ceramic body that has improved properties for use in high temperature applications and a method for making the same. [0002] Porous refractory ceramics have long been used as particulate filters in hot gas or corrosive environments such as advanced coal-based gas turbine cycles, municipal and industrial waste incinerators, and diesel or natural-gas engine exhaust systems. For such applications, ceramic particulate filters must possess chemical inertness, thermal shock resistance, high filtration efficiency, low pressure drop, and adequate strength. In particular, a diesel particulate filter (DPF) ideally combines low CTE (for thermal shock resistance), low pressure drop (for engine efficiency), high filtration efficiency (for removal of most particles from the exhaust stream), high strength (to survive handling, canning, and vibration in use), and low cost. [0003] Candidate materials for D...

AI Technical Summary

Benefits of technology

[0008] MAT ceramic bodies of the present invention offer low thermal expansion, high thermal shock resistance, a narrow pore size distribution and greater interconnectivity of the porosity, and are fabricated at lower sintering temperatures of between 1375° C.-1550° C. by using a metal oxide sintering additive in the raw material batch. The metal oxide is added in an amount of at least 0.10% by weight, in some applications between 0.10%-5.0% by weight, the oxide relating to a metal selected from the group consisting of yttrium, bismuth, calcium, lanthanide metals, and combinations thereof.

Problems solved by technology

However, the relatively low volumetric heat capacity (approximately 2.8 J cm−3 ° C.-−1 at 800K) and low thermal conductivity of cordierite can result in unacceptably high temperatures during operation when the filters are regenerated under certain conditions.

Further, obtaining a well-interconnected pore microstructure in cordierite filters, in combination with low porosity required for high thermal mass, has been a challenge.

However, silicon carbide is relatively expensive.

Furthermore, the high coefficient of thermal expansion requires silicon carbide filters to be fabricated as cement-bonded segments, adding to manufacturing cost and raising concerns about their long-term thermo-mechanical durability.

However, in the manufacture of MAT bodies sintering temperatures greater than 1600° C. are often required to achieve sufficient grain growth for microcracking and low thermal expansion.

Such high heating temperatures add cost to manufacturing and final product.

Nonetheless, such methods often result in a strong sensitivity of the physical properties, including CTE, porosity, or pore size, to the firing temperature, which is undesirable for manufacturability.

Also, desired properties for DPF use are not expected to be achieved.

Further, many methods for making aluminum titanate-based bodies require the use of pre-reacted aluminum titanate and / or mullite powders, which also increase the manufacturing cost.

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