Solar Absorber Coating With Oxide Diffusion Barrier Layer
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Solution Overview
Problem
Existing radiation-selective absorber coatings on metal substrates face issues with diffusion of elements and gases through the substrate, leading to reduced performance and vacuum loss in solar concentrating thermal systems, particularly due to the porous nature of sputtered diffusion barrier layers.
Innovation Solution
A diffusion barrier layer comprising oxidized components of the metal substrate, such as iron oxide and chromium oxide, is formed on the polished substrate surface, which prevents substrate-to-coating diffusion and enhances coating adherence, with a thickness between 50 and 200 nm, and is created through a tempering process in air at 400 to 600°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sputtered diffusion barrier layer is used, then the substrate is protected from diffusion, but the layer has a porous structure reducing its effectiveness
Solution Approach 1:
The invention changes the formation parameters of the diffusion barrier layer by using oxidation processes at elevated temperatures (400-600°C) to transform the layer structure from porous to dense and adherent, thereby resolving the contradiction between diffusion protection and structural integrity
Solution Approach 2:
The invention employs oxidation (using oxygen or oxygen-containing atmospheres) to convert the metal substrate surface into a stable oxide layer that serves as an effective diffusion barrier, eliminating the porosity problem inherent in sputtered layers
2Strength
If the metal surface is polished to reduce roughness, then coating adherence is improved, but the diffusion barrier effectiveness is reduced due to porous structure
Solution Approach 1:
The invention changes the surface treatment parameters by combining polishing with subsequent oxidation heat treatment, transforming the surface morphology and chemical composition to achieve both good adherence and effective diffusion blocking simultaneously
3Temperature
If operating temperatures are increased for solar concentrating systems, then energy efficiency is improved, but diffusion processes increase causing performance degradation
Solution Approach 1:
The invention applies preliminary oxidation treatment to the substrate surface before coating deposition, creating a stable, dense oxide layer that prevents high-temperature diffusion processes from degrading the coating performance, thus enabling reliable operation 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 oxide diffusion barrier effectively reduces substrate diffusion and gas transport, improving the adherence and performance of the absorber coating, maintaining vacuum integrity and enhancing solar energy absorption efficiency.
Implementation Method 1
The oxide layer forms a diffusion barrier layer between the absorber coating and the substrate. It prevents or reduces transport and diffusion processes involving transport from the substrate
Implementation Method 2
A diffusion barrier layer comprising oxidized components of the metal substrate, such as iron oxide and chromium oxide, is formed on the polished substrate surface, with a thickness between 50 and 200 nm, and is created through a tempering process in air at 400 to 600°C
Data Source
AI summary
The absorber pipe for solar thermal applications consists of a metal pipe and a radiation-selective absorber coating applied to the outer surface of the metal pipe. The radiation-selective absorber coating consists of, in sequence from the outer surface toward an exterior: a diffusion barrier layer, a metallic reflective layer a cermet layer, and an anti-reflective layer. The diffusion barrier layer is an oxide layer on the outer surface of the preferably steel or stainless steel pipe which is formed by an oxidation process during tempering and which includes oxidized components of the metal pipe. The tempering is preferably performed in air in an oven at a temperature of 400 to 600° C. for 0.5 to 2 hours.