NdFeB Magnet Corrosion Resistance via Parylene Polysulfone Coating
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Solution Overview
Problem
NdFeB magnets used in implantable medical devices, such as CSF shunts, face demagnetization or reverse magnetization in strong external magnetic fields like those found in MRI scanners, and suffer from corrosion issues, particularly when exposed to aqueous saline solutions, leading to potential failure and the need for surgical replacement.
Innovation Solution
A corrosion-resistant barrier is created by vapor-depositing a fluorinated parylene conformal coating with a melting point of at least 430°C and low moisture vapor transmission, followed by a polysulfone thermoplastic overlayer on NdFeB magnets, providing a continuous protection against corrosion and maintaining magnetic strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If NdFeB magnets are used to provide high magnetic strength, then magnetic performance is improved, but corrosion resistance deteriorates when exposed to aqueous saline solutions
Solution Approach 1:
The patent applies a multi-layer composite coating system consisting of a fluorinated parylene conformal coating as the base layer and a polysulfone thermoplastic as the overlayer. This composite structure provides both corrosion protection and mechanical durability while maintaining the magnetic properties of the underlying NdFeB magnet, resolving the contradiction between magnetic strength and corrosion resistance.
Solution Approach 2:
The fluorinated parylene conformal coating forms a thin film barrier that conforms to the magnet surface, providing continuous corrosion protection. The polysulfone thermoplastic overlayer adds a protective shell that enhances mechanical resistance. Together, these flexible protective layers shield the magnet from corrosive saline environments without compromising magnetic performance.
2Reliability
If protective coatings such as plating or powder coatings are applied to improve corrosion resistance, then corrosion protection is enhanced, but the coating may be breached within 24 hours in aqueous saline solution
Solution Approach 1:
The patent specifies precise parameter requirements for the coating materials: the fluorinated parylene must have a melting point of at least 430°C and moisture vapor transmission less than 0.5 g-mm/m2/day at 90% RH and 37°C. The polysulfone overlayer provides additional thermal and chemical stability. These controlled parameters ensure the coating system maintains integrity in saline environments, preventing the breaching issue observed with conventional coatings.
3Stability of the object's composition
If samarium cobalt magnetic materials are used to resist demagnetization in strong magnetic fields, then magnetic stability is improved, but corrosion resistance is poor
Solution Approach 1:
The patent uses NdFeB magnets with high intrinsic coercivity (Hci) to achieve magnetic stability comparable to or exceeding samarium cobalt materials. The multi-layer composite coating system (fluorinated parylene + polysulfone) then provides the corrosion protection that samarium cobalt lacks, allowing the use of superior magnetic materials without sacrificing corrosion resistance.
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 coated magnets exhibit no visible corrosion after immersion in saline solutions and retain full magnetic strength, even in high-temperature saline environments, effectively resisting demagnetization and corrosion, thus reducing the need for surgical replacement.
Implementation Method 1
vapor depositing upon an NdFeB magnet a layer or layers of a fluorinated parylene conformal coating
Implementation Method 2
a moisture vapor transmission less than about 0.5 g-mm/m2/day at 90% RH and 37° C.
Implementation Method 3
applying molten polysulfone over the conformal coating
Data Source
AI summary
A magnetic article with a corrosion resistant barrier formed from a poly (tetrafluoro-p-xylene) conformal coating or from a parylene conformal coating having a melting point of at least about 430° C. and a moisture vapor transmission less than about 0.5 g-mm/m2/day at 90% RH and 37° C., the conformal coating being covered with a polysulfone thermoplastic overlayer.