Latent-Heat Storage Microcapsules with Ceramic Shell
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Solution Overview
Problem
Existing methods for producing PCM microcapsules face challenges in achieving sufficient shell thickness for cyclic strength and maintaining the composition of the PCM, leading to issues with heat storage density, conductivity, and operational temperature stability at high temperatures.
Innovation Solution
A process involving chemical conversion coating treatment, followed by the deposition of hydroxide aluminum and subsequent heat treatment in an oxidizing atmosphere to form a thick Al oxide film, ensuring the cyclic strength of the capsule without altering the PCM composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a metal coating film is formed by electroplating to encapsulate PCM, then the capsule can be micronized, but the heat resistance is low and the coating film tears at high temperature causing PCM leakage
Solution Approach 1:
The invention changes the material parameter of the coating film from metal to ceramic, and changes the formation method parameter from electroplating to suspension firing. This allows the capsule to maintain micronized size while achieving high heat resistance, as ceramic coatings can withstand temperatures up to 1600°C without deforming or tearing like metal coatings
Solution Approach 2:
The invention creates a composite structure with a PCM core and ceramic coating shell. The ceramic coating (e.g., Al2O3, SiO2, TiO2) provides high heat resistance and chemical stability, while the PCM core maintains its latent heat storage function. This composite approach resolves the contradiction by combining materials with complementary properties
2Ease of manufacture
If water-soluble PCM materials are used for microencapsulation, then the encapsulation process is simplified, but use under high temperature harsh environment with corrosion is extremely difficult
Solution Approach 1:
The invention changes the temperature parameter to enable high-temperature processing (suspension firing at 800-1600°C), which transforms the coating material from a simple organic layer to a robust ceramic shell. This high-temperature treatment simultaneously achieves encapsulation and imparts excellent corrosion resistance, resolving the contradiction between manufacturing ease and environmental durability
Solution Approach 2:
The invention converts the potential harm of high-temperature processing (which could degrade water-soluble PCMs) into a benefit by using it to form a protective ceramic coating. The suspension firing process creates a heat-resistant barrier that protects the PCM from corrosion in harsh environments, turning a thermal challenge into a protective mechanism
3Reliability
If separate molding of outer shell and internal storage body is performed, then heat resistance and corrosion resistance are improved, but the capsule size must be large and microencapsulation is practically impossible
Solution Approach 1:
The invention merges the shell formation and PCM encapsulation processes into a single suspension firing step. The PCM particles are suspended in a ceramic slurry, and upon firing, the ceramic forms a coating directly on the PCM surface. This combined approach eliminates the need for separate shell molding and assembly, enabling microencapsulation while maintaining heat and corrosion resistance
Solution Approach 2:
The PCM particles themselves serve as the core around which the ceramic coating forms automatically during suspension firing. The process is self-organizing, with the coating naturally depositing on and adhering to the PCM surface without requiring separate assembly steps. This self-service mechanism enables precise microencapsulation at small scales
4Strength
If thick shell is formed to ensure cyclic strength, then capsule durability is improved, but the composition of PCM changes leading to reduced heat storage density
Solution Approach 1:
The invention changes the coating material from metal or organic polymer to ceramic with high melting point and low reactivity. This allows formation of a sufficiently thick coating (several micrometers) for mechanical strength and cyclic durability without the coating material mixing with or degrading the PCM composition, thereby preserving heat storage density
Solution Approach 2:
The invention uses a thin layer of ceramic coating that provides sufficient protective function without excessive thickness. The coating is optimized to be just thick enough to provide mechanical strength and chemical protection, avoiding unnecessary material that would displace PCM and reduce heat storage capacity
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 process results in a latent heat storage body microcapsule with enhanced heat storage density, conductivity, and stability across multiple heat storage cycles, capable of operating at relatively high temperatures without composition changes.
Implementation Method 1
forming a primary coating film by chemical conversion coating treatment of a surface of a core particle
Implementation Method 2
forming a secondary coating film by treating the core particle after the first step in a solution comprising Al ions such that hydroxide of aluminum is deposited on the surface of the primary coating film
Implementation Method 3
forming an Al oxide film on the surface of the core particle by heat treating the secondary coating film in an oxidizing atmosphere
Data Source
AI summary
In the present invention, after a primary coating film is formed by boehmite treatment of the surface of a core particle in a solution comprising Al ions, a secondary coating film is formed by cooling the solution to the supersaturation temperature of the Al ions to cause deposition of a hydroxide of aluminum on the surface of the primary coating film, and an Al oxide film is formed on the surface of the core particle by heat treating the secondary coating film in an oxidizing atmosphere. Consequently, the shell is thickened by the amount of secondary coating film formed, so that the cyclic strength of the capsule can be secured and the composition change of the PCM in the production process is remarkably suppressed.