SiC Honeycomb Coating Material Crack Suppression
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Solution Overview
Problem
Existing coating materials for silicon carbide-based honeycomb structures face issues with cracking during drying and heat treatment due to differences in thermal expansion coefficients and high costs associated with refractory ceramic fibers, as well as concerns regarding water resistance and chemical resistance.
Innovation Solution
A coating material comprising 20-75% ceramic powder with 55-95% silicon carbide and 5-30% silicon dioxide, along with additional ceramic powders like cordierite and alumina, and hollow particles, which have a specific particle size distribution and thermal expansion coefficient matching that of the honeycomb structure, to minimize cracking and enhance thermal shock resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating material containing 30% by mass of RCF (Refractory Ceramic Fiber) is used, then sink marks and coating failure are suppressed, but the cost increases and thermal shock resistance deteriorates due to larger difference in thermal expansion coefficient
Solution Approach 1:
The patent changes the particle size parameters of the ceramic powder, specifically setting D90/D10 ratio between 5-50, D10 at 50 μm or less, and D90 at 4 μm or more. This parameter optimization allows the coating material to achieve proper flowability and packing density without requiring expensive RCF additives, thereby reducing cost while maintaining coating quality and suppressing sink marks.
Solution Approach 2:
The patent replaces expensive RCF (Refractory Ceramic Fiber) with conventional ceramic powders that are cheaper and readily available. By optimizing the particle size distribution of these conventional powders, the invention achieves the same coating quality improvement without the high cost associated with RCF-containing materials.
2Reliability
If a coating material containing 30% by mass of RCF is used, then sink marks and coating failure are suppressed, but thermal shock resistance deteriorates due to larger difference in thermal expansion coefficient
Solution Approach 1:
The patent optimizes the particle size parameters (D90/D10 ratio of 5-50, D10 ≤50 μm, D90 ≥4 μm) to achieve proper coating density and thermal expansion characteristics. This parameter optimization enables the use of conventional ceramic powders with thermal expansion coefficients closer to the substrate, thereby improving thermal shock resistance while maintaining coating quality.
Solution Approach 2:
The patent uses conventional ceramic powders that have more similar thermal expansion properties to the substrate compared to RCF. By optimizing their particle size distribution, the coating achieves homogeneous thermal expansion behavior with the substrate, reducing thermal stress and improving thermal shock resistance.
3Manufacturing precision
If drying temperature is set at 100° C., then drying cracks are suppressed, but water resistance and chemical resistance deteriorate due to reversible water adsorption and desorption of colloidal silica
Solution Approach 1:
The patent changes the drying temperature parameter from the conventional 100° C. to a higher temperature range (typically 150-200° C. or more). This temperature increase ensures complete evaporation of water and proper condensation of colloidal silica, forming a cross-linked gel structure that provides both crack suppression during drying and excellent water/chemical resistance in the final coating.
4Reliability
If coating material does not contain color developing components (SiC, TiO2), then laser marking cannot be performed, but this would maintain chemical and heat treatment resistance
Solution Approach 1:
The patent incorporates color developing components such as SiC (silicon carbide) or TiO2 (titanium dioxide) into the coating material formulation. These components have specific optical properties that enable laser marking when irradiated, while also providing chemical and heat treatment resistance. The particle size optimization (D90/D10 ratio of 5-50) ensures these components are properly distributed and functional.
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
Effectively suppresses cracking during drying and heat treatment, improves thermal shock resistance, and reduces costs by utilizing grinding scraps, while maintaining chemical and water resistance.
Implementation Method 1
a ratio of a thermal expansion coefficient after drying the coating material at 600° C. for 30 minutes to a thermal expansion coefficient of the silicon carbide honeycomb structure is from 0.8 to 1.1
Implementation Method 2
there is concern about thermal shock resistance
Implementation Method 3
the colloidal silica used as the inorganic adhesive is in a state of allowing reversible water adsorption and desorption
Data Source
AI summary
A coating material for a silicon carbide-based honeycomb structure, the coating material including from 20 to 75% by mass of ceramic powder (A), the ceramic powder (A) including from 55 to 95% by mass of silicon carbide and from 5 to 30% by mass of silicon dioxide as chemical components.