Aluminum Interlayer Coatings for Selective Alkaline Stripping
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Solution Overview
Problem
Existing wet-chemical stripping methods using oxidation agents like KMnO4 attack both the coating and substrate, requiring precise timing to avoid substrate damage, are non-selective, and necessitate additional masking and mechanical treatments, especially for substrates with varying coating thickness and complex geometries.
Innovation Solution
A method involving an aqueous alkaline solution with 30-50 wt.% NaOH at 80-160 °C, utilizing a metallic or wurtzite aluminum nitride interlayer deposited via PVD, which acts as a 'predetermined breaking point' for selective stripping without substrate damage, and optionally using a sacrificial anode to prevent cobalt leaching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If oxidation agents like KMnO4 are used for wet-chemical stripping, then the coating can be dissolved, but the substrate surface is also attacked and damaged
Solution Approach 1:
The coating system is segmented into two functional layers: a strippable interlayer containing aluminum and a protective top layer. The interlayer serves as a predetermined breaking point that dissolves selectively in alkaline solution, while the substrate remains protected. This segmentation allows the coating to be stripped without damaging the substrate.
Solution Approach 2:
The strippable interlayer acts as an intermediary between the coating and the substrate. It is specifically designed to be attacked by alkaline stripping solutions while the substrate is protected. This intermediary layer absorbs the harmful chemical attack, preventing direct contact between the stripping agent and the substrate.
2Productivity
If the substrate remains in the stripping solution for a long time to ensure complete coating dissolution, then the coating is completely stripped, but the substrate surface is heavily damaged
Solution Approach 1:
A strippable interlayer is deposited on the substrate surface before applying the protective coating. This preliminary action creates a predetermined breaking point that controls the stripping process. The interlayer dissolves first, automatically stopping the stripping action before the substrate is damaged, eliminating the need for precise timing control.
3Ease of manufacture
If non-coated surfaces are exposed to the chemical stripping solution, then the stripping process is simple, but the non-coated surfaces are attacked and damaged
Solution Approach 1:
The strippable interlayer provides universal protection for the substrate across all surfaces. Whether a surface is coated or non-coated, the interlayer serves as a protective barrier against chemical attack. This eliminates the need for selective masking of non-coated areas, as the interlayer uniformly protects the entire substrate surface.
4Object-affected harmful factors
If masking materials are applied to protect non-coated areas, then the substrate is protected from chemical attack, but additional working steps and costs are incurred
Solution Approach 1:
The strippable interlayer provides self-service protection for the substrate. It automatically protects non-coated areas from chemical attack without requiring external masking materials or additional protective measures. The interlayer serves its protective function inherently, eliminating the need for complex masking processes.
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
Enables rapid, selective stripping of coatings without substrate damage, eliminating the need for masking and mechanical treatment, and effectively handles substrates with complex geometries and varying coating thickness.
Implementation Method 1
the coating is dissolved from the substrate by introducing the coated substrate in the aqueous, alkaline solution
Implementation Method 2
a strippable substrate is manufactured by depositing a coating comprising aluminum directly on the substrate surface to be stripped
Implementation Method 3
the disadvantage of using oxidation agents, such as KMnO4, is that not only the coating but also the substrate is attacked by the chemical solution
Data Source
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AI summary
Method for stripping a coating from a coated surface of a substrate, wherein the coating is stripped in an aqueous alkaline solution, characterized in that the method comprises following steps: - preparing the coated substrate to be decoated by providing the substrate with a strippable coating by depositing a coating comprising one or more layers, wherein one layer comprising aluminum is deposited directly on the substrate surface to be decoated and - introducting the substrate to be decoated in the aqueous alkaline solution, thereby conducting a chemical stripping of the coating from the substrate, whereas the aqueous alkaline solution comprises NaOH in a concentration in weight percentage from 30wt.% to 50wt.%.