Cordierite body

Abstract

A ceramic comprising predominately a cordierite-type phase approximating the stoichiometry Mg₂Al₄Si₅O₁₈ and having a coefficient of thermal expansion (25-800° C.) of greater than 4×10⁻⁷/° C. and less than 13×10⁻⁷/° C. and a permeability and a pore size distribution which satisfy the relation 2.108 (permeability)+18.511 (total pore volume)+0.1863 (percentage of total pore volume comprised of pores between 4 and 40 micrometers)>24.6. The ceramic is suitable in the fabrication of cellular, wall-flow, diesel particulate filters having a pressure drop in kPa that at an artificial carbon soot loading of 5 grams/liter and a flow rate of 26 scfm is less than 8.9-0.035 (number of cells per square inch)+300 (cell wall thickness in inches), a bulk filter density of at least 0.60 g/cm³ and a volumetric heat capacity of at least 0.67 J cm⁻³ K⁻¹ as measured at 500° C.

Description

[0001]This application claims the benefit of U.S. Provisional Application Nos. 60 / 208,529, filed Jun. 1, 2000, entitled “Cordierite Body and Method of Making the Same”, and 60 / 234,684, filed Sep. 22, 2000, entitled “Cordierite Body”, both by Beall et al.BACKGROUND OF THE INVENTION[0002]The present invention relates to cordierite bodies of high permeability and tailored microstructure suitable for use as diesel particulate filters in applications where a low pressure drop across the length of the filter is required.[0003]Recently, much interest has been directed towards the diesel engine due to its efficiency, durability and economical aspects. However, diesel emissions have come under attack both in the United States and Europe, for their harmful effects on the environment and on humans. As such, stricter environmental regulations will require diesel engines to be held to the same standards as gasoline engines. Therefore, diesel engine manufacturers and emission-control companies ar...

AI Technical Summary

Benefits of technology

[0013]The instant invention is founded upon the discovery of a cordierite structure possessing high permeability and a microstructure with a unique combination of porosity and pore size distribution which is especially useful in the fabrication of diesel particulate filters which possess high thermal durability coupled with a low pressure drop along the length of the filter such that there exists a low back pressure against the engine, resulting in a more efficient engine.

Problems solved by technology

However, diesel emissions have come under attack both in the United States and Europe, for their harmful effects on the environment and on humans.

One of the biggest challenges in lowering diesel emissions is controlling the levels of diesel particulate material present in the diesel exhaust stream.

As the layer of soot collects on the surfaces of the inlet channels of the diesel particulate filter, the lower permeability of the soot layer causes a gradual rise in the back pressure of the filter against the engine, causing the engine to work harder.

During an uncontrolled regeneration, the combustion of the soot (a reaction which is already highly exothermic) may produce temperature spikes which would exceed the melting point of the cordierite, and can thermally shock and crack, or even melt, the filter.

However, if temperatures during uncontrolled regenerations are sufficiently high, the ash may eventually sinter to the filter or even react with the filter resulting in partial melting.

A significant problem associated with conventional cordierite diesel particulate filters is susceptibility to damage during regeneration of the filter under uncontrolled conditions that promote unusually high temperatures.

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