Cordierite Ceramic Filters with Controlled Pore Structure
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Solution Overview
Problem
Cordierite ceramic filters with high porosity and coarse pore sizes face challenges in achieving a balance between thermal shock resistance and mechanical strength, as high porosity tends to reduce strength and microcracking lowers thermal shock performance, making them unsuitable for diesel engine exhaust systems.
Innovation Solution
Cordierite ceramic honeycombs with controlled median pore sizes and mean coefficients of thermal expansion, achieving porosities of 64-80% and specific CTE ranges, which enhance modulus of rupture strength and thermal shock resistance while maintaining low pressure drop and filtration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high porosity and coarse pore sizes are increased to reduce pressure drop and accommodate NOx catalyst/adsorber, then filtration efficiency and catalyst capacity improve, but mechanical strength decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the coefficient of thermal expansion (CTE) within specific ranges (5-15×10^-7/°C) and median pore diameters (10-45 μm) to achieve optimal balance between porosity (64-80%) and mechanical strength. This systematic parameter optimization allows the ceramic to maintain both high catalyst capacity and sufficient structural integrity
Solution Approach 2:
The patent utilizes composite material design by combining cordierite ceramic with specific pore structure characteristics and catalyst layers. The multi-functional composite structure integrates the ceramic substrate, porous walls for catalyst support, and controlled pore networks to simultaneously achieve high porosity, adequate strength, and effective NOx treatment
2Reliability
If very low CTE is pursued to increase thermal shock resistance, then thermal shock resistance improves, but microcracking increases which lowers strength
Solution Approach 1:
The patent resolves this contradiction through precise parameter control of the coefficient of thermal expansion, specifying a range of 5-15×10^-7/°C that balances thermal shock resistance with mechanical strength. This optimized CTE range prevents excessive microcracking while maintaining adequate thermal shock performance in the harsh exhaust environment
Solution Approach 2:
The patent references and builds upon established cordierite ceramic compositions while introducing specific modifications to achieve the target CTE range and pore structure, effectively copying successful material systems and adapting them for optimal performance in diesel exhaust filtration applications
3Reliability
If high porosity cordierite ceramics with extensive microcracking are produced to achieve very low CTE, then thermal shock resistance improves, but modulus of rupture strength becomes insufficient for practical use
Solution Approach 1:
The patent applies parameter changes by controlling the CTE within 5-15×10^-7/°C and median pore diameter within 10-45 μm ranges, achieving a balance point where thermal shock resistance is sufficient without inducing excessive microcracking that would compromise modulus of rupture strength below practical thresholds
Solution Approach 2:
The patent implements local quality control by maintaining different pore size distributions in different regions of the ceramic structure, with coarse pores (10-45 μm) strategically distributed to provide thermal shock resistance while preserving local structural integrity and adequate strength in load-bearing regions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides cordierite ceramic filters with improved mechanical strength and thermal shock resistance, ensuring effective filtration and catalyst retention in diesel engine exhaust systems with reduced pressure drop and increased durability.
Implementation Method 1
Porous cordierite ceramic filters of the wall-flow type have been utilized for the removal of particles in the exhaust stream
Implementation Method 2
very low CTE has often been pursued as a means for increasing thermal shock resistance (TSR)
Implementation Method 3
cordierite, being a low-cost material, in combination with offering a low coefficient of thermal expansion (CTE)
Data Source
AI summary
Cordierite ceramic articles with high volume percent porosities of at least 64% but less than 80% have controlled median pore sizes and mean coefficients of thermal expansion that impart substantially improved modulus of rupture strengths (MOR) and thermal shock resistance (TSR) to the ceramic articles.