Difference between revisions of "Neodymium iron boron magnet"

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Neodymium iron boron magnets, commonly referred to as neodymium magnets or NdFeB, NIB or Neo magnets, are magnets made from a sintered alloy of neodymium, iron, and boron. They produce the highest commercially available magnetic fields (approximately 1 tesla) and make paramagnetism and diamagnetism in materials far more visible than most other magnets. They are also a common source of neodymium because they are relatively easy to obtain from different everyday objects. Due to their high field strengths large neodymium magnets may cause damage to objects if they are allowed near ferromagnetic materials, and can break bones easily.

Chemical

The alloy inside the magnets is primarily composed of macroscopic Nd₂Fe₁₄B grains, surrounded by a Nd-rich matrix layer (~90% Nd). For amateur chemist purposes, they can be assumed to be composed entirely of Nd₂Fe₁₄B alloy, with a molar mass of 1081.2 g/mol (representing weight percentages of 26.68% Nd, 72.32% Fe, and 1.00% B).

Neodymium magnets are plated in a oxidation-resistant layer of copper, nickel, and/or gold, with possible tin and mercury additives. When this layer is broken, they will react vigorously with acids to produce corresponding neodymium and iron salts, as well as boron or boric acid depending on the acid chosen.

2 Nd₂Fe₁₄B + 35 H₂SO₄ -> 4 Nd₂(SO₄)₃ + 28 FeSO₄ + 2 H₃BO₃ + 3 SO₂ + 35 H₂

Nd₂Fe₁₄B + 34 HCl -> 2 NdCl₃ + 14 FeCl₂ + B + 34 H₂

Nd₂Fe₁₄B + 71 HNO₃ -> 2 Nd(NO₃)₃ + 14 Fe(NO₃)₃ + 20 NO + 34 H₂O + H₃BO₃ + 3 NO₂

Physical

Neodymium magnets are a dark gray, grainy sintered alloy coated with a mechanically polished, electroplated layer of protective metals such as nickel, copper, tin, and/or gold.

Magnetic

Neodymium magnets are some of the strongest commercially available magnets in existence, having an unusually high magnetic anisotropy at 7 Tesla along a single, preferred crystalline orientation. This makes them hazardous, as even at small sizes (~1/2" cube or sphere) they can exert enough force to injure the human body when attracted to another magnetic object. Most neodymium magnets on the market today have a Curie temperature (the temperature at which they lose all magnetic properties) between 310 and 340 degrees C.

Availability

Almost all rare-earth permanent magnets are made of this material.

Projects

Extracting neodymium from magnets

Is difficult for the home chemist. Witness the epic that is The trouble with Neodymium thread.

Also, *Isolation of neodymium from magnets is another good thread of information.

Handling

Safety

Neodymium is a heavy metal, and as such is toxic if ingested. Standard gloves should be safe to handle neodymium compounds with.

Storage

Neodymium magnets, if magnetized, should be stored in soft foam padding to avoid injury. When demagnetized, they are essentially a lump of metal and can be stored safely in any container. Magnets should be kept away from acidic vapors in case the protective metal plating fails.

Disposal

Neodymium magnets, if of considerable size and/or magnetic strength, should be demagnetized in an oven above their Curie temperature before disposing.

References

Relevant Sciencemadness threads

• Dissolving Neodymium Magnet in Citric Acid?
• The trouble with neodymium...
• Rare earth metals, mischmetal, etc
• Isolation of neodymium from magnets