Solar Absorber Coating Composition for Adhesion and Thermal Stability
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Solution Overview
Problem
Existing solar heating systems face challenges with coatings that fail to meet requirements for high solar absorbance, low thermal emissivity, thermal stability, and corrosion resistance, particularly at elevated temperatures, and often have poor adhesion properties.
Innovation Solution
A sol-gel based coating method using a ceria nitrate sol with manganese ferrite black spinel dispersed in CeO2, combined with organic additives for improved adhesion, applied via coil coating on aluminum substrates, achieving high solar absorbance and thermal stability through specific processing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sol-gel type coatings are used for solar heating, then chemical stability and thermal stability are improved, but adhesion properties deteriorate
Solution Approach 1:
The patent uses a composite coating system consisting of an inorganic sol-gel layer (providing thermal stability) combined with an organic binder layer (providing adhesion). The organic binder contains specific functional groups that chemically bond to both the inorganic oxide layer and the metal substrate, creating a multi-layer composite structure that combines the advantages of both material types.
Solution Approach 2:
The organic binder acts as an intermediary layer between the inorganic sol-gel coating and the metal substrate. This intermediate layer provides chemical bonding groups that facilitate adhesion to the metal while also bonding to the inorganic oxide layer, thus mediating the interface between materials with poor direct adhesion.
2Strength
If conventional black paints with organic binder are used, then adhesion properties are improved, but thermal stability deteriorates
Solution Approach 1:
The patent creates a composite system where an inorganic sol-gel layer (thermally stable) is combined with an organic binder layer (adhesive). The organic binder contains functional groups that provide adhesion while the inorganic layer provides thermal stability, creating a multi-functional composite coating.
Solution Approach 2:
The patent modifies the organic binder by incorporating specific functional groups (carboxyl, hydroxyl, amino groups) that can chemically interact with both the inorganic oxide and metal substrate. This chemical modification changes the bonding parameters of the organic binder to achieve both adhesion and thermal resistance.
3Use of energy by moving object
If high solar absorbance is achieved through black coatings, then solar absorption is improved, but thermal emissivity increases
Solution Approach 1:
The patent applies different properties to different layers of the coating: the inorganic sol-gel layer is designed with low thermal emissivity to reduce heat loss, while the overall coating structure maintains high solar absorbance. This spatial differentiation of properties allows simultaneous optimization of both solar absorption and thermal retention.
Solution Approach 2:
The composite structure combines materials with complementary optical properties: the inorganic oxide layer provides low thermal emissivity in the infrared range, while the overall coating composition (including organic binder and pigment) maintains high absorption in the solar spectrum, achieving selective optical properties.
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 demonstrates excellent adhesion, thermal stability, and corrosion resistance, with enhanced solar absorption and reflectivity properties, meeting industrial-scale requirements for solar heating systems.
Implementation Method 1
High solar absorbance (0,28 - 2,5 μm), a ≥ 95%
Implementation Method 2
Low thermal emissivity (2,5 - 50 μm), e ≤ 0,1
Data Source
AI summary
Method for making an absorber coating for solar heating and a coating as such to be applied on a metal substrate, in particular a coating to be applied on a thin aluminium metal sheet. The coating is of the sol-gel type based on a metal oxide precursor where pigment particles are intimately mixed into the precursor followed by application of the mixed sol lacquer on the substrate and thereafter reaction in humid air at a required temperature to obtain the sol-gel coating. The precursor may preferably be a CeO2 (NO3) based sol with preferably 20 % CeO2 having a particle size of 10- 20 nm and a pH of 1,5. Further the pigment may be a manganese ferrite black spinel, Mn3Cu2FeO8.