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Category: Physics of Magnets

Parylene C and it’s Value as a Coating for Neodymium Magnets

Parylene C is an ultra-thin, pinhole-free polymer coating for Neodymium magnets that is mostly used in in automotive, military and medical applications but is gaining popularity in the consumer world as its benefits are becoming understood.

Parylene’s common generic name is Poly-para-xylylenes. It forms a plastic film when applied in a vacuum as a gas to target surfaces. It is self-initiated, un-terminated and requires no solvent nor catalyst. The two most commercially used Parylene coatings are Parylene C and Parylene N.

Parylene C is produced from a step by step process that does not include a liquid phase, thus coating will not pool in low areas, bridge across substrates, or exhibit liquid properties such as meniscus or capillary action.  Parylene is a polymer that produces a very thin layer, so is therefore economical and at the same time durable.  In addition, it’s FDA approved.

The useful combination of both electrical and physical properties gives Parylene C a low permeability to moisture and corrosive gases. Parylene C has better electric insulation, bio-stability and provides a moisture barrier.  It has thermal and UV light stability and has complete surface conformity. It’s maximum operating temperature is 680 degrees, much higher than where a magnet loses its magnetic strength. This characteristic makes it useful across the magnetic heat tolerance range.

Parylene coating can be done in room temperature as it does not affect the magnet. It is the best for coating and is medically proven. It’s the most bio-accepted coating for stents, defibrillators, pacemakers and other devices which are permanently implanted into the body. This therefore means it is FDA approved. It is used in various fields such as machinery and electronics, consumer electronics. Holiday and décor, apparel, consumer goods and toys.

For magnetic applications, the Parylene C coating can be an ideal choice when the applications may require an inert coating, weather resistance, and provides a durable alternative to more common coatings such as nickel and zinc.

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How a Neodymium Magnet is Made

A neodymium magnet also known by the acronyms NdFeB, NIB or simply Neo is a permanent magnet made from an alloy of neodymium, iron, and boron. The exact ingredients depend on the grade or strength of magnet being produced. Higher values indicate stronger magnets.

 

IT BEGINS WITH THE MIX

Preparation of materials determines the type of magnet to be produced. A combination of Cobalt and Dysprosium will result in increased intrinsic coercivity and properties improved at elevated temperatures. After selection, these elements are placed into a vacuum induction furnace where they are heated by creating electrical eddy currents. After that melted to form the alloy material. It is done in a vacuum to avoid contaminants affecting the reaction. This mixture is then cooled to form ingots before being ground into tiny grains in a jet mill. Each particle is typically only three microns in size, smaller than a cell in your body!

 

INGOTS ARE THEN PRESSED

The super-fine powder is then pressed into a mold to form a solid with a preferred magnetization direction. This technique is known as die-upsetting. Simultaneously, magnetic energy is applied to the mold. The magnetism comes from a coil wire that acts like a magnet when electrical current is passed through it. It is usually performed at temperatures as high as 725 C. The solid then goes through a second pressing whereby it’s reduced to half its original size and its magnetism induced becomes parallel to that of the magnet. When the particle structure of the magnet matches the direction of magnetism, the magnet created is referred to as an anisotropic magnet. At this stage, manufacturers can give the block more acute properties.

 

AFTER PRESSING IS SINTERING

At this point, the magnetized material is demagnetised and will be re-magnetised later in the process. The compression in this stage will result in the particles adhering to each other. The temperatures involved will be below its melting point to avoid liquefaction. This is because at this stage the material would be far too soft and crumbly to be useful. This process takes place in an oxygen-free, inert environment.

 

THEY MUST COOL

Almost there, the heated material gets rapidly cooled using a technique known as quenching. This rapid cooling process minimizes areas of poor magnetism and maximizes performance. This is the stage when the raw magnets are machined into their desired shape. Less complex materials are shaped using Electric Discharge Machine (EDM), and more complex is shaped by diamond plated cutting tools.

 

TO LOOK PRETTY, THEY GET A PLATING

The last step before the material is re-magnetised is vital. Because neodymium magnets are so hard and oxidize so quickly, making them prone to breaking and chipping, they must be coated, cleaned, dried and plated. There are many different types of coating that are used with neodymium magnets, the most common being electroplating with nickel-copper-nickel mixture, but they can be coated with other metals and even rubber or PTFE. This helps them to retain their magnetic properties even in the presence of moisture.

 

WE HAVE A MAGNET

The magnets now are almost ready but not yet fully magnetic. Their pole directions have been aligned, but their magnetism hasn’t been activated. Therefore will not attract or repel as strongly.

After the plating process, the finished material is re-magnetised by placing it inside a coil, which, when an electric current is passed through it produces a magnetic field three times stronger than the required strength of the magnet. This is such a powerful process that if the magnet is not held in place, it can be flung from the coil like a bullet. The use of an industrial magnetizer is preferred. The process of creating this magnet is intricate, and the way the magnet is formed will affect how it functions.

Our company has hundreds of magnets in stock, please search our selection for what you need or reach out to make a custom order.


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What is Neodymium?

Neodymium is the chemical element of atomic number 60, and are considered a rare earth element (belonging to the rare earth elements on the periodic table). They are thestrongest rare earth magnets available, and are permanent.

Neodymium comes from the Greek word neos, meaning new, and didymos, meaning twin. The name combined means new twin and are occasionally known as Neodymium-Iron-Boron or Nd-Fe-B or NIB. The element was discovered in 1885 by Austrian chemist Carl Auer von Welsbach, with the symbol Nd. Its atomic mass is 144.242 u ± 0.003 u and has a melting point of 1,870°F (1,021°C).

Sources of Neodymium

Neodymium cannot be found in nature as a free element. It’s found in raw ore such as monazite and bastnasite, it’s also a by-product of nuclear fission. It’s extracted via ion-exchange or solvent techniques.

Benefits of using Neodymium magnets

– Very strong permanent magnets, the strongest permanent magnets that exist today
– Highest resistance to demagnetization
Affordability: compared to other magnet types, it’s by far the most economical
– Accept large number of different coatings and coating techniques
Powerful in small sizes, can be manufactured in any N rating

Risks associated with using Neodymium

– Oxidize easily
– Can catch fire at high temperatures
Cannot be soldered
Demagnetizes under high heat (max operating temp 176°F/80°C before starting to lose strength), if heated beyond 590°F/310°C they will permanently demagnetize

Where are they used today?

You name it. You likely have one in your pocket right now.

They are currently on the Mars Exploration Rovers. We see them in Cell phones, MRI scanners, hard drives, metal detectors, televisions, geocaching, ABS sensors, wind turbines, which utilize neodymium magnets to assist in enhancing turbine power and generating electricity.They are also replacing the traditional magnets used in loudspeakers.More practically you see them on shirt collar stays, broaches, name tags, refrigerators, purse latches, kitchen cabinets, white boards, oil filters, magic tricks, and even fish tank cleaners.
 


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Does Magnet Shape Matter

The shape of the magnet can have a small effect on its strength but the real strength of the magnet comes from the mass, density and material. A more magnetic material will make a stronger magnet. Changing the shape will only let you focus a little more of that strength into a different direction or area.

A great example is a magnet in the shape of a donut. If you put something in the center of the donut, the magnetic field cancels out because the forces from all the different directions are equal, so there is no pull force. It would be as if the magnet wasn’t there. But outside the donut, it behaves like a typical magnet.

In basic terms you can’t get more magnet strength out of an object by reshaping it. A magnet has a strength based on its size and materials used, but the shape has an influence how its best used.

What you can affect thru the shape is the strength of the magnetic field. For example, if your goal is to keep 2 cabinets closed, using a flat disk magnet makes more sense than using a long cylinder. It’s not that the disk has more power, it’s that the cylinder doesn’t focus the magnetic field in a way that’s useful for that particular application.


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