Cordierite Honeycomb Delayed Microcrack Evolution
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Solution Overview
Problem
Cordierite honeycomb ceramics used in exhaust gas after-treatment applications face challenges with thermal shock resistance due to microcracking and washcoat penetration, leading to degradation in mechanical strength and thermophysical properties.
Innovation Solution
A porous ceramic honeycomb article with a primary cordierite phase and intercrystalline glass phase is developed, featuring low microcracking and a glass phase that devitrifies to increase microcracking during thermal treatment, enhancing thermal shock resistance without the need for passivation steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If microcracks are present in the as-fired cordierite ceramic, then thermal shock resistance is improved due to low CTE and low Young's elastic modulus, but mechanical strength is reduced and the microcracks allow catalyst washcoat penetration during washcoating
Solution Approach 1:
The patent applies preliminary action by creating microcracks in the cordierite ceramic before washcoating through controlled thermal treatment. This pre-established microcrack network allows the ceramic to develop low CTE and low Young's elastic modulus in advance, improving thermal shock resistance before the washcoating process occurs. The microcracks are formed by heating the ceramic to a temperature below its melting point and then rapidly cooling it, creating a controlled microcrack structure that enhances thermal shock performance.
Solution Approach 2:
The patent uses an intermediary approach by applying a barrier coating to the ceramic surface before washcoating. This barrier coating prevents catalyst washcoat penetration into the microcracks while allowing the microcracks to remain intact and functional for thermal shock resistance. The barrier coating acts as a mediator between the microcracked ceramic structure and the washcoating process, enabling both low CTE properties and high mechanical strength to coexist.
2Temperature
If a passivation coating is applied to prevent catalyst washcoat penetration into microcracks, then thermal shock resistance is maintained, but manufacturing complexity and cost increase due to additional processing steps
Solution Approach 1:
The patent extracts the passivation function from a separate barrier coating layer and integrates it directly into the washcoat formulation. By incorporating passivation agents into the washcoat slurry itself, the protective function is embedded within the washcoating process rather than requiring a separate barrier coating step. This eliminates additional manufacturing complexity while maintaining thermal shock resistance, as the washcoat itself prevents catalyst penetration into microcracks during the washcoating process.
Solution Approach 2:
The patent merges multiple functions into a single washcoating step: catalysis, barrier protection, and microcrack sealing. By combining passivation agents with the catalyst washcoat materials, the process achieves both thermal shock resistance maintenance and catalyst functionality in one operation. This consolidation eliminates the need for separate passivation and barrier coating steps, reducing manufacturing complexity while preserving the beneficial effects of the microcracked ceramic structure.
3Strength
If microcracks are eliminated from the as-fired ceramic matrix, then mechanical strength and strain tolerance are improved, but thermal shock resistance decreases due to increased CTE
Solution Approach 1:
The patent applies preliminary action by deliberately creating microcracks through controlled thermal treatment before washcoating, rather than eliminating them. This pre-established microcrack network is then protected by the washcoat barrier, allowing the ceramic to maintain both high mechanical strength and low CTE properties. The preliminary creation of microcracks followed by protective washcoating enables the ceramic to achieve optimal thermal shock resistance while preserving structural integrity.
Solution Approach 2:
The patent changes the physical and chemical parameters of the ceramic through controlled thermal treatment and washcoating. By heating the ceramic to a temperature below its melting point and rapidly cooling it, microcracks are formed with specific size distributions and orientations. Subsequent washcoating modifies the surface chemistry and mechanical properties, creating a protective layer that allows the microcracked structure to maintain both strength and thermal shock resistance. The parameter changes in temperature, microcrack density, and surface composition enable simultaneous optimization of mechanical and thermal properties.
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 improved thermal shock resistance and strength retention after washcoating and thermal treatment, reducing the need for additional processing steps and materials, while maintaining high mechanical strength and low elastic modulus.
Implementation Method 1
the glass phase devitrifies to increase microcracking during thermal treatment
Implementation Method 2
high geometric surface areas and, in some cases, extensive interconnected porosity to facilitate fluid filtration
Data Source
Figure 1
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AI summary
A porous ceramic honeycomb article includes a primary cordierite phase and an intercrystalline glass phase. In an as-fired condition, the porous ceramic honeycomb article exhibits microcrack parameter Nb3 ≤ 0.06 and an as-fired E500°C/E25°C ratio ≤ 0.99. The article exhibits a coated microcrack parameter Nb3 ≤ 0.14 and a coated E500°C/E25°C ratio ≤ 1.06 after the porous ceramic honeycomb article has been washcoated and calcined at a temperature of 550°C. After the article is exposed to a thermal treatment at a temperature ≥ 800°C following washcoating and calcining, at least a first portion of the porous ceramic honeycomb article has a first treated microcrack parameter Nb3 ≥ 0.18, and a first treated mean coefficient of thermal expansion of not more than 12x10-7/°C over a temperature range of 25°C to 800°C. Methods of forming the porous ceramic honeycomb article are also disclosed.