Porous Ceramic Filters with Polymer Barrier Coatings
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Ceramic honeycomb filters used in diesel exhaust applications face challenges with increased thermal expansion and reduced gas permeability due to catalyst and washcoat applications, which can lead to structural damage and high pressure drops, especially in microcracked materials like aluminum titanates.
Innovation Solution
A thermally crosslinkable polymer formulation is applied to ceramic supports before washcoating, selectively blocking microcracks and micropores to maintain low thermal expansion and high gas permeability, using a method that involves applying a polymer solution, heating to dry and crosslink, and then removing the polymer to restore gas flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If catalyst and washcoat coatings are applied to ceramic filter walls, then emissions control performance is improved, but thermal expansion increases and gas permeability decreases
Solution Approach 1:
A polymer pre-coating is applied to the ceramic filter walls before catalyst and washcoat coatings. This pre-coating selectively fills microcracks and micropores, creating a barrier that prevents subsequent catalyst and washcoat materials from penetrating into the ceramic structure. By performing this protective action in advance, the ceramic maintains its low thermal expansion properties while still allowing emissions control coatings to be applied on the surface.
Solution Approach 2:
The polymer pre-coating is selectively distributed to fill only the microcracks and micropores of the ceramic structure, leaving the macroscopic pore structure intact. This localized filling approach prevents thermal expansion increases caused by coating penetration into microcracks, while maintaining gas permeability through the larger pores necessary for exhaust flow.
2Reliability
If catalyst and washcoat coatings are applied to ceramic filter walls, then emissions control performance is improved, but gas permeability decreases causing high pressure drops
Solution Approach 1:
The polymer pre-coating is applied before catalyst and washcoat coatings to selectively occupy microcracks and micropores. This preliminary action prevents coating materials from blocking the macroscopic pore structure, thereby maintaining high gas permeability and low pressure drops while still enabling emissions control functionality through surface coatings.
Solution Approach 2:
The polymer pre-coating selectively fills only the microcracks and micropores (local regions), leaving the macroscopic pore network intact. This selective local modification prevents coating penetration into harmful micro-defects while preserving the gas flow pathways necessary for high permeability and low pressure drop performance.
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
This approach reduces thermal expansion coefficients and pressure drops, allowing for high catalyst loadings while maintaining low CTE and gas permeability, thus enhancing the durability and performance of ceramic filters.
Implementation Method 1
a pre-coating or passivation step is used to improve the properties of the catalyzed substrates, by reducing catalyst and/or support coating diffusion into the fine pores, microchannels (necks interconnecting individual pores), and microcrack structure of the substrates
Implementation Method 2
heating to dry and crosslink, and then removing the polymer to restore gas flow
Data Source
AI summary
Porous ceramic catalyst supports or filters to be provided with catalyst coatings via oxide washcoating processes are pre-coated with cross-linked polymer barrier layers to prevent washcoat nanoparticle intrusion into the microcracked and/or microporous surfaces of the ceramics, the barrier coatings being formed by thermally cross-linking hydrocarbon polymers that are vaporizable at moderate washcoat stabilization or catalyst activation temperatures and that preferentially block the micropore/microchannel pore volume of the article.