Title : Q & A (MAGNET AND MAGNETISM)
Contain:
Contain:
- NdFeB (Neodymium-Iron-Boron) -- The most powerful 'rare-earth' permanent magnet composition known to mankind, and our specialty. This formulation is relatively modern, and first became commercially available in 1984. NdFeB magnets have the highest B, Br, and BHmax of any magnet formula, and also have very high Hc (see below for definitions). They are however very brittle, hard to machine, and sensitive to corrosion and high temperatures. Useful in the home, workshop, pickup truck, laboratory, wind turbine, starship and more. We carry both new and surplus stock in many sizes and shapes.In almost all magnet applications, NdFeB are the best choice for incredible strength and coercivity at a reasonable price! In power generation applications, NdFeB magnets can be expected to give 4-5 times the power output of ceramic magnet.
- Ferrite (Ceramic) -- Also known as 'hard ceramic' magnets, this material is made from Strontium or Barium Ferrite. It was developed in the 1960s as a low-cost and more powerful alternative to AlNiCo and steel magnets. Less expensive than NdFeB magnets, but still very powerful and resistant to demagnetization. Useful everywhere. We carry both new and surplus in multiple shapes and sizes. Ferrite magnets are lower in power (B, Br, BHmax) compared to other formulations, and are very brittle. However, they have very high Hc and good Tc (see below), and are quite corrosion-resistant. A very cost-effective choice.
- AlNiCo (Aluminum-Nickel-Cobalt) for medium strength and excellent machinability. Developed in the 1940s and still in use today. They perform much better than plain steel, but are much weaker in strength (lower B, Br and BHmax) and must be carefully stored since they are prone to demagnetization. Contact with a NdFeB magnet can easily reverse or destroy the field of an AlNiCo magnet.
- SmCo (Samarium Cobalt)-- for high power and resistance to high temperatures and corrosion. Developed in the 1970s, these were the first so-called 'rare earth' magnets. They are almost as powerful as NdFeB magnets, and far more powerful than all the others (high B and Br). They are the most expensive magnet formulation, and usually only used where resistance to high temperatures (high Tc) and corrosion are needed. Also very brittle and hard to machine.
- Bonded (flexible)-- magnets are a rubberized formulation often seen on refrigerators and magnetic signs. Though they may be manufactured from any magnet formulation when powerdered and mixed with rubberizer, the result is always less powerful than a traditional sintered magnet of any formula. Used only where unusal and difficult shapes are needed.
How does temperature affect the behavior of a
permanent magnet?
Curie Temperature (Tc): This is the temperature at
which a magnet material loses it's strength, permanently. Another useful number
(if available) is Tmax, the recommended maximum operating temperature. Above
Tmax (around 266 deg. F for most NdFeB magnets) a magnet will start ot lose its
power, and at Tc all power is lost. If you need strong magnets that can be used
at high temperatures, consider using Samarium Cobalt (SmCo) magnets.
Will magnets corrode if used outdoors?
NdFeB magnets are susceptible to corrosion. The 'Fe'
in the name stands for Iron, and it rusts! Many of our magnets come with a
Nickel, Zinc, Gold or Epoxy coating to protect them from moisture. If the
coating is damaged (frequently the case with surplus magnets) the magnet could
rust if exposed to water or humidity. If this is a concern to you, you can
easily add another layer of protection by dipping the magnet in epoxy or
plastic coating.
Conclusion: The best magnet is NdFeb type followed
by Ferrite and others. As long my project does not need so much output power
therefore the ferrite magnet is the suitable one to be included for the
project. Instead, the magnets also will be coated with suitable material too.
The material that will be used will be discussed later on.
ref: http://wondermagnet.com/magfaq.html
