Selective Absorber Coating With Barrier Layers for High-Temperature Stability
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Solution Overview
Problem
Conventional absorber coatings for solar collectors face challenges in maintaining high absorptivity and low emissivity at elevated temperatures due to degradation and diffusion issues, leading to reduced durability and efficiency.
Innovation Solution
A radiation-selective absorber coating is developed with a cermet layer of aluminum oxide and molybdenum as the second barrier layer, along with an adhesion-improving molybdenum layer and a thermally produced oxide first barrier layer, which enhances adhesion and stability, allowing for higher operating temperatures without compromising absorption and reflection properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional absorber coating with molybdenum reflection layer and cermet absorption layer is used, then high absorptivity and low emissivity are achieved, but the coating shows poor adhesion and layer destruction at elevated temperatures
Solution Approach 1:
The coating is divided into multiple functional layers: a substrate, a diffusion barrier layer preventing metal oxidation, a cermet absorption layer for solar energy absorption, and a protective top layer. This segmentation allows each layer to optimize its specific function while maintaining overall coating integrity at high temperatures.
Solution Approach 2:
A diffusion barrier layer composed of aluminum oxide and molybdenum oxide is introduced as an intermediary between the metal substrate and the cermet absorption layer. This barrier layer prevents direct diffusion and adhesion failure between layers, thereby improving overall coating stability and preventing layer destruction at elevated temperatures.
2Productivity
If the operating temperature is increased to improve energy conversion efficiency, then higher energy yield is achieved, but the absorber coating degrades and loses its absorption and reflection properties
Solution Approach 1:
The coating composition is optimized with specific ratios of aluminum oxide (40-70 wt%) and molybdenum oxide (30-60 wt%) in the diffusion barrier layer, along with controlled thickness parameters (barrier layer: 5-20 μm, absorption layer: 2-10 μm). These parameter changes enable the coating to maintain its optical and structural properties at elevated operating temperatures up to 400°C, thereby improving energy conversion efficiency without compromising durability.
3Reliability
If a diffusion barrier layer is added to improve temperature stability, then layer adhesion is improved, but the device complexity increases
Solution Approach 1:
The diffusion barrier layer combines multiple protective functions into a single integrated layer: it acts as a diffusion barrier preventing metal oxidation, provides thermal stability, and enhances adhesion between the substrate and absorption layer. This merging of functions reduces the need for multiple separate layers, thereby limiting the increase in device complexity while achieving improved temperature stability.
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 high absorption (>95.5%) and low emissivity (<9%) at 400°C, maintaining performance even after accelerated aging, enabling efficient energy conversion and extending the service life of solar collectors, allowing for higher operating temperatures and cost-effective operation.
Implementation Method 1
a first barrier layer of thermally produced oxide and a second barrier layer of cermet material, disposed above the first barrier layer
Implementation Method 2
the first barrier layer of thermally produced oxide
Implementation Method 3
a high degree of absorption in the solar spectrum range
Implementation Method 4
a layer which reflects in the infrared range
Data Source
Figure 1
Figure 2
AI summary
The coating (20) has an absorption layer (22) arranged over a layer (21) reflecting in infrared range. An anti-reflection layer (23) is arranged on the absorption layer, and the layer reflecting in infrared range is arranged on two barrier layers (24a, 24b) that are arranged over each other. One of the barrier layers is made of thermally generated oxide such as chromite oxide. The other barrier layer is made of a cermet material that is comprised of elements such as aluminum oxide, silicon oxide, nickel oxide, chromium oxide, molybdenum, nickel, tungsten and vanadium.