Neodymium iron boron magnet
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| Names | |
|---|---|
| IUPAC name
N/A
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| Other names
Neodymium magnet, neo-magnet
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| Properties | |
| Nd2Fe14B + various trace materials | |
| Molar mass | 1081.15 g/mol |
| Appearance | Metallic gray alloy |
| Odor | Odorless |
| Density | 7.4 g/cm3 |
| Insoluble | |
| Solubility | Insoluble in organic solvents |
| Hazards | |
| Related compounds | |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
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.
Contents
Properties
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.
Chemical
The alloy inside the magnets is primarily composed of macroscopic M2Fe14B grains, surrounded by a M-rich matrix layer (~90% M), where M typically represents Nd but can also include other rare-earth elements such as Gd, Ce, and Pr due to the lack of effect of rare-earth impurities on magnetic strength and thus loose manufacturing purity controls. 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
Magnetism
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 °C.
Cylindrical magnets are often recommended for beginners.
Availability
Almost all rare-earth permanent magnets are made of this material. Larger-size magnets can be found in hard disk drives as a quarter-arc section of magnetic material in one corner. Smaller sizes can be bought as novelty magnetic toys, found in earbuds, or bought online.
Projects
Extracting neodymium from magnets
This project is difficult for the home chemist. Witness the epic that is The trouble with Neodymium thread.
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 moisture and 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.
