Polysilazane Multilayer Coating for Crack-Resistant Corrosion Protection
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Solution Overview
Problem
Existing silica-based coatings formed using perhydropolysilazane are fragile and prone to cracking due to their high density and low coefficient of linear expansion, leading to reduced corrosion resistance when exposed to halogen-based corrosive gases and plasmas.
Innovation Solution
A two-step coating process involving a first coating with a density less than 2.00 g/cm³ containing unconverted substances for flexibility, followed by a second dense coating with a density of 2.00 g/cm³ or more, formed at a lower temperature to relieve stress and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silica-based coating is formed using perhydropolysilazane to achieve high corrosion resistance, then the coating density and corrosion resistance are improved, but the coating becomes fragile and prone to cracking due to low coefficient of linear expansion
Solution Approach 1:
The coating process is divided into two distinct steps: first forming a flexible coating layer with lower density (containing unconverted substances), then forming a dense silica-based coating layer on top. This segmentation allows each layer to fulfill different functions - the first layer provides flexibility and stress relief, while the second layer provides corrosion resistance.
Solution Approach 2:
The final coating structure is a composite of two different coating layers with different properties. The first coating layer contains a mixture of converted and unconverted substances providing flexibility, while the second coating layer is dense silica providing corrosion resistance. This composite structure resolves the contradiction by combining materials with complementary properties.
2Strength
If the heat treatment temperature is set to a low temperature (around 300°C) to prevent cracking, then the coating flexibility is improved, but the coating contains unconverted substances that decrease denseness and corrosion resistance
Solution Approach 1:
The heat treatment process is segmented into two distinct temperature stages: first heating at a lower temperature to form the flexible coating with unconverted substances, then heating at a higher temperature to convert the second coating to dense silica. This temporal and thermal segmentation allows each stage to achieve its specific objective without compromising the other.
Solution Approach 2:
The first coating layer is formed with unconverted substances as a preliminary step to establish flexibility and stress relief. This preliminary structure is then used as a foundation for the second coating layer, which is subsequently converted to dense silica. The preliminary action of forming a flexible base layer prevents cracking in the final dense coating.
3Strength
If a thin coating is formed to prevent cracking, then the coating flexibility is improved, but the constituent members cannot be sufficiently covered and the anticorrosion effect is reduced
Solution Approach 1:
The coating thickness is segmented into two functional layers: the first layer provides flexibility and stress relief, while the second layer provides sufficient coverage and corrosion resistance. This segmentation allows the coating to achieve both flexibility and adequate coverage without forming a single thick fragile layer.
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 method achieves a dense coating with high corrosion resistance by maintaining flexibility in the first coating and relieving stress through differential expansion, preventing cracks and ensuring effective environmental shielding.
Implementation Method 1
heating the first solution to form a first coating on the surface of the metal substrate
Implementation Method 2
conversion into silica of an unconverted substance of the first coating
Implementation Method 3
difference in coefficient of linear expansion between the second coating and the metal substrate
Implementation Method 4
stress acting on the second coating is relieved due to the difference in coefficient of linear expansion
Data Source
AI summary
The method for forming a coating of the present invention includes: a first step of applying a first solution containing a polysilazane to a surface of a metal substrate and heating the first solution to form a first coating on the surface of the metal substrate, and a second step of applying a second solution containing a polysilazane to a surface of the first coating and heating the second solution at a temperature lower than a heating temperature in the first step to form a second coating on the surface of the first coating, wherein a density of the first coating is less than 2.00 g/cm3, and a density of the second coating is 2.00 g/cm3 or more.