Neodymium

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Neodymium is a lanthanide with the symbol Nd and atomic number 60. Also classified as a rare earth metal, it is a silvery solid that tarnishes quickly in air and will completely corrode to a pink oxide powder if stored improperly. Its most common use is in high-strength neodymium magnets. As a tripositive ion, neodymium has unusually narrow absorption bands and will undergo color changes depending on the light source.

Properties

Physical properties

Neodymium is a silvery metal that is about as dense as tin. Older samples that have been exposed to air show corrosion, which will appear bluish. Although the metal is known for its use in powerful magnets, it is only slightly paramagnetic and cannot be lifted by a neodymium magnet. It may be possible to observe the magnetism by placing a small piece on a styrofoam block and allowing it to move toward a magnet.

Neodymium salts undergo large and dramatic color changes under different light sources. Under incandescent light or sunlight, which consist of continuous spectra, neodymium salts generally appear pink or purple. Fluorescent lighting consists of only a few specific energies of light which do not match the absorption bands of neodymium salts, thus causing the compounds to appear colorless. Holmium compounds will undergo similar color changes.

Chemical properties

Neodymium metal is rather reactive, and a centimeter-sized sample will corrode within a year on exposure to air. Thus, the metal must be stored under oil or in an ampoule filled with argon. The metal reacts only slowly with water, but reacts vigorously with acids and the halogens to form neodymium salts. Most neodymium salts are soluble in water except for the fluoride and oxalate. Neodymium oxide and hydroxide are insoluble in water, but will absorb carbon dioxide from the air to form neodymium carbonate. All three of these compounds are insoluble in water, but will readily dissolve in acids.

Neodymium sulfate is notable for its inverse solubility curve, which causes the salt to precipitate at high temperatures. It is nearly impossible to redissolve after being precipitated. The double sulfate of potassium and neodymium is less soluble than neodymium sulfate itself. Different preparations of neodymium sulfate have given different colors, possibly due to the formation of acid and basic sulfates.

Most lanthanides do not form complexes easily, but there is evidence for a possible chloride complex.

Availability

Pure neodymium metal can be bought from Metallium. It is sold as 5 and 50 gram sizes, as well as rods, ampoules, and coins.

Preparation

The most common source of neodymium is neodymium magnets. It's difficult, however, to extract the neodymium from the magnets, and a procedure to produce pure neodymium metal from neodymium fluoride with either calcium or lithium as the reductor is still in development.

Projects

  • Color changing crystals
  • Color changing glass
  • Extracting neodymium from magnets

Safety

Storage

Neodymium metal must be stored away from air and water. Ampouling the metal is a viable long-term storage solution. Storing the metal under mineral oil is an ideal short-term solution, but air will still diffuse through the oil anyway. Unlike europium, the reaction with water is not violent.

Toxicity

Neodymium compounds do not appear to be very toxic. They act similarly to calcium ions within the body. However, research on the toxicity neodymium compounds is not complete, and they should be handled with general safety precautions in place.

Flammability

Neodymium is somewhat flammable and may spark when struck. Powdered neodymium may ignite very easily. Class D fire extinguishers should be used against neodymium fires. Water may aggravate a neodymium fire and should never be used.

References

Relevant Sciencemadness threads