Double-Nitride Solar Absorber Coating for 550°C Receiver Tubes
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Solution Overview
Problem
Current cermet materials used in solar installations face limitations in chemical-structural stability and reproducibility at high temperatures, leading to reliability issues in thermodynamic solar installations, particularly with temperatures between 450 °C and 550 °C.
Innovation Solution
A double-nitride cermet material is developed, comprising a ceramic matrix with a metallic component, using reactive and non-reactive sputtering processes to create a multilayer coating with a graded or multilayer structure, ensuring high deposition rates and stability up to 570 °C, and incorporating a barrier layer to prevent chemical reactions and diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cermet materials are used in solar installations, then the coating provides good chemical-structural stability at low temperatures (below 450°C), but the stability and reliability deteriorate at high temperatures (450-550°C)
Solution Approach 1:
The patent uses a composite structure consisting of a ceramic matrix (aluminum nitride or silicon nitride) with metallic particles (tungsten, molybdenum, titanium, or zirconium) dispersed within. This cermet composite combines the high-temperature stability of ceramics with the optical absorption properties of metals, enabling reliable operation at temperatures up to 550°C while maintaining chemical-structural stability.
Solution Approach 2:
The patent modifies the optical and structural parameters of the coating by controlling particle size (1-50 nm), metallic content (5-50% by weight), and layer thickness (50-200 nm). These parameter changes optimize both the high-temperature stability and the photo-thermal performance, allowing the coating to maintain reliability across extended temperature ranges.
2Reliability
If complex multilayer structures are used to achieve ideal optical behavior, then the absorbance and emissivity properties improve, but the manufacturing complexity and deposition time increase
Solution Approach 1:
The patent employs cermet composite materials that inherently provide both high solar absorbance (α > 0.95) and low thermal emissivity (ε < 0.10) through the synergistic combination of ceramic matrix and metallic particles. This composite approach achieves ideal optical behavior without requiring complex multilayer stacking, thereby reducing manufacturing complexity.
Solution Approach 2:
The patent creates graded cermet coatings where the metallic particle concentration varies through the thickness of the layer, with higher metal content near the substrate and lower content toward the surface. This local variation in composition optimizes optical performance while maintaining a relatively simple single-layer structure, reducing manufacturing complexity compared to multiple discrete layers.
3Reliability
If thin-film or thin-layer cermet structures are used, then the optical selectivity improves, but the chemical-structural stability at high temperatures deteriorates
Solution Approach 1:
The patent uses cermet composite materials where the ceramic matrix (aluminum nitride or silicon nitride) provides high-temperature chemical-structural stability while the dispersed metallic particles (tungsten, molybdenum, titanium, or zirconium) provide high optical absorbance. This composite structure maintains both optical selectivity and stability simultaneously, overcoming the limitation of thin-film structures.
Solution Approach 2:
The patent divides the coating into distinct functional components: a ceramic matrix phase that provides structural stability and high-temperature resistance, and dispersed metallic particle phases that provide optical absorption. This segmentation of functions within a single coating layer enables simultaneous achievement of optical selectivity and chemical-structural stability at high temperatures.
4Reliability
If metallic particles of very small sizes (1-5 nm) are used in cermet materials, then the optical absorption in solar radiation range improves, but the manufacturing precision and reproducibility worsen
Solution Approach 1:
The patent optimizes the particle size parameter to a range of 1-50 nm, with preferred sizes of 5-20 nm. This parameter optimization balances optical absorption performance with manufacturing feasibility, avoiding the extreme difficulty of controlling 1-5 nm particles while maintaining high optical selectivity. The patent also controls metallic content at 5-50% by weight to ensure reproducibility.
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 provides a coating material with enhanced chemical, structural, and mechanical stability, maintaining high absorbance and low emissivity across the operating temperature range, improving the reliability and efficiency of solar installations.
Implementation Method 1
reactive and non-reactive sputtering processes to create a multilayer coating
Implementation Method 2
absorb the greatest possible amount of solar radiation concentrated thereon
Data Source
AI summary
A thin-film spectrally selective coating for receiver tube of vacuumed type for use in thermodynamic solar installations and operating both at medium temperature (up to 400 °C) and at high temperature (up to 550 °C), coating where the optically absorbing layer is a multilayer of cermet material of type: WyN-AINx or MoyN-AINx, material prepared with reactive co-sputtering technique from an Al target and a W or Mo target, process conducted under a transition regimen, under PEM (Plasma Emission Monitoring) or CVM (Cathode Voltage Monitoring) monitoring for the sole Al target, with inletting near the Al target of a N2 amount adequate for obtainment of a high-transparency, high growth rate sub-stoichiometric ceramic AIN and with inletting near the W or Mo target of a N2 amount adequate for obtainment of the sole W2N or Mo2N phase, phase very stable at high temperature, such as to make the cermet material as close as possible to the formulation W2N-AINx or Mo2N-AINx (with x comprised between 0.90 and 1.00, preferably 0.95) and, therefore, cermet material employable at least up to the temperature of 550 °C.