Multilayer Thermal Absorber Coating for High-Temperature Durability
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Solution Overview
Problem
Existing thermal absorber coatings degrade due to corrosion, substrate diffusion, and thermal cycles, limiting their usability and operational temperature range.
Innovation Solution
A multilayer thermal absorber coating composition comprising titanium, aluminium, nitrogen, and at least one of silicon, yttrium, cerium, or chromium, deposited in a specific nanostructure configuration to enhance durability and optical performance, with a top layer providing inertness and antireflection properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing thermal absorber coatings are used, then they provide good solar absorbance and thermal emission properties, but they degrade due to corrosion, substrate diffusion, and thermal cycles, limiting their lifetime and operational temperature range
Solution Approach 1:
The coating is divided into multiple functional layers: a bottom layer (TiAlSiNx) providing adhesion and diffusion barrier, intermediate layers for optical optimization, and a top layer (TiO2 or SiO2) providing corrosion protection. This segmentation allows each layer to specialize in one function, resolving the contradiction between maintaining optical performance and resisting degradation.
Solution Approach 2:
The patent uses composite material structures combining different materials with complementary properties: TiAlSiNx provides hardness and adhesion, TiN/TiO2 layers provide optical selectivity, and SiO2/TiO2 top layers provide corrosion resistance. This composite approach enables the coating to simultaneously achieve high reliability, good optical properties, and resistance to harmful environmental factors.
2Use of energy by moving object
If multilayer optical stacks are used to achieve high solar absorbance (α > 92%) and low thermal emittance (ε < 10%), then optical performance is improved, but the coating structure becomes more complex and more susceptible to degradation
Solution Approach 1:
Different regions of the coating have different properties optimized for their specific functions: the bottom layers have high nitrogen content for adhesion and diffusion barrier, intermediate layers have optimized stoichiometry for optical interference, and the top layer has high oxygen content for corrosion protection. This local quality optimization achieves high solar absorbance without requiring excessive layer complexity.
Solution Approach 2:
The patent optimizes specific parameters such as nitrogen content (x in TiAlSiNx), layer thicknesses (50-500 nm range), and stoichiometric ratios to achieve the desired optical performance. By carefully controlling these parameters during deposition, high solar absorbance is achieved with a manageable number of layers, reducing overall structural complexity.
3Temperature
If the coating is exposed to high temperatures (up to 600°C) for extended periods, then thermal energy harvesting is improved, but the coating undergoes decolouration and adherence loss due to thermal cycles
Solution Approach 1:
The coating structure includes a diffusion barrier layer (TiAlSiNx) deposited beforehand to prevent substrate elements from diffusing into the coating during thermal exposure. The top protective layer (TiO2/SiO2) is also deposited in advance to shield the underlying layers from thermal degradation and oxidation, cushioning against the harmful effects of high-temperature operation.
Solution Approach 2:
The TiAlSiNx bottom layer acts as an intermediary between the substrate and the optical layers, providing a stable foundation that resists thermal expansion mismatch and prevents copper diffusion. This intermediary layer protects the entire coating structure from thermal cycling damage while allowing the coating to operate at elevated temperatures.
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 coating achieves extended lifetime of over 20 years at high temperatures (up to 600°C) with maintained optical performance and thermal stability, resisting decolouration and adherence loss through 20,000 thermal cycles.
Implementation Method 1
thermal absorber coatings... have a wide potential application due to their high solar absorbance in combination with a low thermal emittance at operation temperatures
Implementation Method 2
elements from a substrate material, especially in the case of copper substrates, diffuse into the coating causing again the decolouration
Data Source
AI summary
The invention relates to a method for providing a thermal absorber, which can be used in solar thermal collectors. The method comprises a step of depositing on a substrate (220) a first layer (230) having a composition that comprises titanium, aluminium, nitrogen, and one of following elements: silicon, yttrium, cerium, and chromium.