Low-Microcracked Porous Ceramic Honeycombs
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Solution Overview
Problem
Porous ceramic honeycomb structures, particularly cordierite honeycombs, face challenges with microcracking that affect thermal durability and strength, leading to increased coefficient of thermal expansion and reduced thermal shock resistance, which is problematic for catalytic converters and diesel particulate filters.
Innovation Solution
Development of a substantially non-microcracked, porous cordierite ceramic honeycomb body with controlled crystal orientation and pore structure, achieving high thermal shock resistance and low coefficient of thermal expansion through specific manufacturing methods and material composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional reaction-sintered cordierite honeycombs are manufactured with large fan-like domains of radiating prismatic cordierite crystallites, then the coefficient of thermal expansion is reduced, but microcracks are produced throughout the body reducing strength and thermal shock resistance
Solution Approach 1:
The patent changes the microstructural parameters by controlling cordierite crystallite size (0.5-10 μm instead of large domains), orientation distribution (random or preferred with z-axes parallel to wall surfaces), and phase composition (≥90% cordierite). These parameter changes achieve low CTE (≤15×10−7/°C.) without microcracking, resolving the contradiction between thermal expansion control and strength maintenance.
Solution Approach 2:
Instead of using large fan-like domains that cause microcracking to achieve low CTE, the patent inverts the approach by using fine-grained cordierite crystallites with controlled orientation. This inverted microstructure achieves the same low CTE effect through statistical orientation averaging rather than through microcrack formation, thereby maintaining strength and thermal shock resistance.
2Stability of the object's composition
If the cordierite crystallites are preferentially oriented with negative-expansion z-axes aligned near the plane of the wall, then thermal expansion in axial and radial directions is reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent controls the orientation parameter of cordierite crystallites during the reaction sintering process by adjusting firing temperature (1200-1400°C), holding time (1-10 hours), and raw material particle size distribution. These parameter changes enable the crystallites to self-organize with z-axes parallel to wall surfaces, achieving low CTE through a relatively simple manufacturing process without requiring complex external alignment equipment.
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 results in honeycombs with improved thermal shock resistance, strain tolerance, and filtration efficiency, maintaining strength and thermal stability across varying temperatures, suitable for advanced catalytic converters and particulate filters.
Implementation Method 1
coefficient of thermal expansion (CTE) of the ceramic... inversely proportional to the coefficient of thermal expansion (CTE) of the ceramic
Implementation Method 2
thermal shock resistance... high thermal shock resistance
Implementation Method 3
porous honeycomb structures... porous cordierite ceramic material... high porosity and coarser pore size
Data Source
AI summary
Substantially non-microcracked, porous, cordierite ceramic honeycomb bodies are provided. Although exhibiting moderately high thermal expansion (CTE) between 7×10−7 to 16×10−7/° C. (25-800° C.), the honeycomb bodies exhibit relatively high thermal shock parameter (TSP), such as TSR≧525° C. by virtue of a high MOR/E ratio, and/or low Eratio=ERT/E1000° C. and well interconnected porosity, as witnessed by a relatively high pore connectivity factor (PCF). A method of manufacturing the honeycomb ceramic structure is also provided.