Parylene Coated Magnets
What is Parylene coating?
Parylene is the common name of Poly-para-xylylene, and it was prepared by the researcher in University of Manchester in 1947. The parylene first applied to U.S military and aerospace industry after Union Carbide prepared parylene thin film by the deposition process. Nowadays, parylene coating are widely used in various areas due to the development of automotive vapor deposition equipment. The most common types of parylene are Parylene N and Parylene C.
Parylene on magnets have long been associated with medical and technology applications. They provide a durable coating that is resistant to corrosion, and are available in Parylene C, D and N. Several factors should be considered when exploring parylene coatings so let’s take a look at these factors when choosing parylene.
Magnets that are subjected to an environment where they are banging together or hitting or grinding against other parts, may experience scratches and chips in the coating that can cause oxidation. In some applications, doubling the thickness of the coating may help, but check your tolerances to make sure the extra thickness can be used.
The active small molecules will form a polymer film on the surface of part depends on vacuum chemical vapor deposition, and its coating properties will much better than other simple coating.
Advantages of parylene coated magnets:
Unlike the conventional coating for magnet, parylene coating is very suitable for small-size magnet.
Parylene coated magnet is free of pin holes due to the vacuum vapor deposition process. The reactive monomer will fill into the pin holes and cracks.
Parylene coating is a kind of transparent film, and no stress.
The uniformity of coating thickness is excellent.
Free of liquid phase during vapor deposition process. The magnet can avoid pre-treatment process in simple coating Unreasonable acid pickling and phosphatizing parameters often cause corrosion phenomena.
Parylene coated magnet have excellent high temperature stability.
Parylene coated magnet have outstanding moisture resistance.
Parylene is a kind of chemical resistance coating.
Biocompatibility make parylene coated magnet can be used in medical field.
parylene-coated bonded NdFeB magnets
The anisotropic parylene-coated bonded NdFeB magnets with parylene C coating on the surface of NdFeB powders are prepared by warm compaction process. The parylene C coating is characterized by focused ion beam-scanning electron microscopy (FIB-SEM) and energy dispersive X-ray Spectroscopy (EDS), revealing a parylene C film of 300–500 nm thickness on the surface of NdFeB powders. The parylene-coated NdFeB magnets show excellent magnetic properties of maximum energy product ((BH)max, 104 kJ/m3), degree of alignment (DOA, 0.476) and density (6.17 g/cm3) than non-coated NdFeB magnets (60 kJ/m3, 0.337, 5.72 g/cm3). And with the increasing thickness of parylene C coating, (BH)max and density increase first, and then decrease while DOA keeps a growing trend all the time. The parylene-coated NdFeB magnets also exhibit better corrosion resistance according electrochemical test. The mechanisms for the improvement of magnetic properties and corrosion resistance are the good lubricating property and super chemical stability of parylene C coating on the surface of NdFeB powders.
The chemical vapor deposition process of parylene coated magnet include:
Sublimation process: The solid di-para-xylylene will sublimate to gas phase under 120 deg c and vacuum
Pyrolysis process: The di-para-xylylene gas will decompose into reactive monomer after pyrolysisreaction under 650 deg c.
Deposition process: The reactive monomer will deposit on magnet after entered into deposition chamfer, then polymerized with each other.
Parylene coating properties that protect
Parylene is the generic name for members of a unique polymer series. These members (or variations of Parylene) each offer their own, slightly different, coating properties to engineers. Commercially available Parylene variants, along with their respective properties, include:
The basic member of the series, Parylene N, is poly(para-xylylene), a completely linear, highly crystalline material. Parylene N is a primary dielectric, exhibiting a very low dissipation factor, high dielectric strength, and a low dielectric constant invariant with frequency. The crevice-penetrating ability of Parylene N is second only to that of Parylene HT®.
Parylene C, the second commercially available member of the Parylene series, is produced from the same raw material (dimer) as Parylene N, modified only by the substitution of a chlorine atom for one of the aromatic hydrogens. Parylene C has a useful combination of electrical and physical properties, plus a very low permeability to moisture and corrosive gases.
Parylene D, the third member of the series, is produced from the same raw material as Parylene N, modified by the substitution of chlorine atoms for two of the aromatic hydrogens. Parylene D is similar in properties to Parylene C with the added ability to withstand slightly higher use temperatures.
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