Selective Absorber Coating With Diffusion Barrier Layers
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Solution Overview
Problem
Existing absorber coatings for parabolic collectors face challenges in maintaining high absorption and low emission while enduring elevated operating temperatures, leading to reduced longevity and increased costs due to diffusion of substrate materials into the infrared reflection layer, which impairs their performance.
Innovation Solution
A radiation-selective absorber coating with at least two barrier layers, where the second barrier layer is a SiOx compound, effectively prevents thermal diffusion from the substrate, and a third barrier layer between the infrared reflection and absorption layers enhances thermal stability, allowing for higher operating temperatures and improved durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the operating temperature of the absorber coating is increased to achieve higher energy efficiency, then the energy conversion efficiency is improved, but the lifetime of the coating decreases due to ageing and diffusion processes
Solution Approach 1:
The coating is divided into multiple functional layers including a cermet absorption layer, an infrared reflection layer, and multiple barrier layers (oxide layer, diffusion barrier layer, protective layer). This segmentation allows each layer to perform its specific function while protecting against thermal degradation at elevated operating temperatures.
Solution Approach 2:
A diffusion barrier layer consisting of metal oxide is introduced between the substrate and the infrared reflection layer to prevent direct diffusion of substrate materials into the reflection layer. This intermediary layer acts as a barrier to atomic diffusion while allowing the system to operate at higher temperatures.
2Device complexity
If a single barrier layer is used to prevent diffusion, then the structure is simple, but the protection against thermal diffusion is insufficient at elevated temperatures
Solution Approach 1:
The barrier system is segmented into multiple layers with different functions: an oxide layer providing initial protection, a diffusion barrier layer of metal oxide specifically designed to block atomic diffusion, and an outer protective layer. This multi-layer segmentation provides superior diffusion protection compared to a single layer while maintaining structural organization.
Solution Approach 2:
The barrier system uses composite material structures combining different oxide layers and metal oxide layers with complementary properties. The combination of these materials creates a synergistic effect that provides enhanced thermal stability and diffusion protection.
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 solution achieves high absorption (>95.5%) and low emission (<0.95%), enabling efficient energy conversion and prolonged economic operation of parabolic collectors, allowing for the use of inexpensive heat carrier media like water and reducing energy consumption for pump operation.
Implementation Method 1
at least two barrier layers, of which the second barrier layer consists of a SiOx compound, are arranged between the absorber tube and the layer which reflects in the infrared region
Implementation Method 2
at least one layer which reflects in the infrared region
Implementation Method 3
at least one absorption layer arranged above the reflecting layer
Data Source
AI summary
The radiation-selective absorber coating (20) has two barrier layers (24a, 24b), an IR-reflecting layer (21) arranged thereon, an absorption layer (22) arranged above the IR-reflecting (21) and an antireflection layer (23) over the absorption layer (22). The absorber tube (13) is a steel tube (1) with the radiation-selective absorber coating (20) applied to the outside thereof. In the process of coating the absorber tube (13) a first oxide barrier layer (24a) is applied to a steel tube by thermal oxidation; a second barrier layer (24b) is then applied by physical gas phase deposition of silicon with supply of oxygen; the IR-reflecting layer (21) is then applied by gas phase deposition of gold, silver, platinum or copper; the absorption layer (22) is then applied by deposition of aluminum and molybdenum; and a final antireflection layer (23) is applied by deposition of silicon with supply of oxygen.