THE LANTHANIDE RARE EARTHS

last update 01 oct 08

* The lanthanide rare earths occupy a "side row" off of row 6 of the periodic table. The lanthanide rare earths are not necessarily rare; a good part of the list is more common than tin, it's just that their properties are so similar that they are hard to identify and extract.

The element yttrium is something of an oddity, since as far as its position in the periodic table goes, it's a transition metal. However, it is directly above the "side row" of the lanthanide rare earths in column 3 of the periodic table, and not very surprisingly yttrium's chemical behavior is very much like that of the lanthanide rare earths. Since yttrium is also often found in nature in ores with a strong association with lanthanide rare earths. it is generally referred to as a rare earth -- though this is doubly inexact, because it's twice as common as lead.

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   YTTRIUM / Y / 39

   A soft, silvery-white metal, stable in air because it forms a 
   protective oxide layer.  It react with water to release 
   hydrogen gas.  Only one isotope is found in nature, Y<89/39>; 
   it is stable.

     atomic weight:       88.90585
     abundance:           28th
     density:             4.469 g/cc
     melting point:       1,522 C
     boiling point:       5,338 C
     valence:             3
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   LANTHANUM / La / 57 

   A cheese-soft, silvery-white reactive metal.  The primary isotope
   is La<138/57>, making up 99.9% of accumulations found in nature.
   The remainder is La<138/57>, which is just barely radioactive, with
   a half-life of 100 billion years.

     atomic weight:       138.055
     abundance:           28th 
     density:             6.145 g/cc
     melting point:       918 C      
     boiling point:       3,464 C
     valence:             3
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   CERIUM / Ce / 58 

   A gray, highly reactive metal.  Four isotopes are found in nature:

     Ce<140/58> / 88.5%
     Ce<142/58> / 11%
     Ce<138/58> /  0.3%
     Ce<136/58> /  0.2%.

   All are stable, except Ce<142/58>, which has a half-life of about
   5E^16 years, longer than the age of the Universe.

     atomic weight:       140.116
     abundance:           25th 
     density:             6,770 g/cc
     melting point:       798 C      
     boiling point:       3,443 C
     valence:             3 4
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   PRASEODYMIUM / Pr / 59 

   A soft, malleable, silvery, reactive metal.  It has one stable
   isotope, Pr<141/59>; all the unstable isotopes are highly
   radioactive, with the longest-lived, Pr<143/59>, having a half-life
   of only 13.57 days.

     atomic weight:       140.90765
     abundance:           39th 
     density:             6.773 g/cc
     melting point:       931 C      
     boiling point:       3,520 C
     valence:             3
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   NEODYMIUM / Nd / 60

   A bright silvery-white, moderately reactive metal.  It is almost as
   common as copper.  There are seven isotopes found in nature:

      Nd<152/60> / 27%
      Nd<144/60> / 24%
      Nd<146/60> / 17%
      Nd<143/60> / 12% 
      Nd<145/60> /  8% 
      Nd<148/60> /  6% 
      Nd<150/60> /  6% 

   All are stable, except for Nd<144/60>, with a half-life of 2E15
   years, and Nd<150/60>, with a half-life of 1.1E19 years.

     atomic weight:       144.24
     abundance:           26th 
     density:             7.008 g/cc
     melting point:       1,021 C      
     boiling point:       3,074 C
     valence:             3
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   PROMETHIUM / Pm / 61

   Unlike the other lanthanide rare earths, promethium is inherently
   radioactive and essentially not found in nature.  There are several
   dozen known isotopes, the most stable being Pm<145/61> with a 
   half-life of 17.7 years (though some sources claim 2.6 years).

     atomic weight:        145
     abundance:            negligible
     density:              7.22 g/cc
     melting point:        1,042 C      
     boiling point:       ~3,000 C
     valence:              3
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   SAMARIUM / Sm / 62 

   A silvery-white metal that will form an oxide layer in moist 
   air.  It will burn if heated to 150 degrees Celsius.  Seven 
   isotopes are found in nature:

     Sm<152/62> / 27%
     Sm<154/62> / 23%
     Sm<147/62> / 15%
     Sm<149/62> / 14%
     Sm<148/62> / 11%
     Sm<150/62> /  7%
     Sm<144/62> /  3%

   Sm<149/62> and Sm<148/62> are both unstable with half-lived of
   more than 10^15 years, while Sm<147/62> is unstable with a half
   life of about 10^11 years.  The other four isotopes in the list
   are stable.

     atomic weight:        150.36
     abundance:            40th
     density:              7.52 g/cc
     melting point:        1,074 C      
     boiling point:        1,794 C
     valence:              2 3
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   EUROPIUM / Eu / 63

   A soft, silvery metal, the most reactive of the lanthanides; it
   will burn spontaneously in air at 180 degrees Celsius.  Two
   isotopes are found in nature:

     Eu<153/63> / 52% 
     Eu<151/63> / 48%.

   Both are stable.

     atomic weight:       151.965
     abundance:           50th
     density:             5.244 g/cc
     melting point:       822 C      
     boiling point:       1,527 C
     valence:             2 3
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   GADOLINIUM / Gd / 64

   A soft, shiny, silvery, moderately reactive metal.  There are seven
   naturally occurring isotopes, including:

     Gd<158/64> / 25% 
     Gd<160/64> / 22%
     Gd<156/64> / 20.4%
     Gd<157/64> / 15.6%
     Gd<155/64> / 15%
     Gd<154/64> / 2%
     Gd<152/64> / 0.2%

   All are stable except for Gd<152/64>, though it has a very long
   halflife of 1.1E14 years.

     atomic weight:       157.25
     abundance:           41st
     density:             7.9 g/cc
     melting point:       1,313 C      
     boiling point:       3,273 C
     valence:             3
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   TERBIUM / Tb / 65

   A cheese-soft silvery metal, it is slow to oxidize in air but 
   will react at a moderate rate in water.  The only isotope 
   found in nature is Tb<159/65>, which is stable.

     atomic weight:       158.92534
     abundance:           57th
     density:             8.23 g/cc
     melting point:       1,356 C      
     boiling point:       3,230 C
     valence:             3 4
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   DYSPROSIUM / Dy / 66

   A bright, silvery metal that oxidizes slowly in air, reacts with
   cold water, and dissolves quickly in acid.  Seven isotopes occur
   in nature:

     Dy<164/66> / 28%
     Dy<162/66> / 26.5%
     Dy<163/66> / 25%
     Dy<161/66> / 19%
     Dy<160/66> /  2.5%
     Dy<158/66> /  0.1%
     Dy<156/66> /  0.06%

   All are stable.

     atomic weight:       162.50
     abundance:           42nd
     density:             8.55 g/cc
     melting point:       1,412 C      
     boiling point:       2,567 C
     valence:             3
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   HOLMIUM / Ho / 67

   A bright, soft, silvery metal that is slowly attacked by oxygen or
   water, and dissolves in acids.  All holmium found in nature is the
   isotope Ho<165/67>.

     atomic weight:       164.93032
     abundance:           56th
     density:             8.795 g/cc
     melting point:       1,470 C      
     boiling point:       2,700 C
     valence:             3
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   ERBIUM / Er / 68

   A bright, silvery metal that is slowly attacked by oxygen or water,
   and dissolves in acids.  Six isotopes are found in nature:

      Er<166/68> / 33.5%
      Er<168/68> / 27%
      Er<167/68> / 23%
      Er<170/68> / 15%
      Er<164/68> /  1.5%
      Er<162/68> /  0.1%

   All are stable.

     atomic weight:       167.26
     abundance:           44th
     density:             9.1 g/cc
     melting point:       1,529 C      
     boiling point:       2,868 C
     valence:             3
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   THULIUM / Tm / 69

   A bright, cheese soft, silvery metal that is slowly tarnishes in
   air and reacts with water.  All thulium found in nature is the
   stable isotope Th<169/69>.

     atomic weight:       168.93421
     abundance:           61st
     density:             9.321 g/cc
     melting point:       1,545 C      
     boiling point:       1,950 C
     valence:             3
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   YTTERBIUM / Yb / 70

   A soft, silvery-white metal that is slowly tarnishes in air to form
   a protective oxide layer, but dissolves easily in acids.  Seven
   isotopes are found in nature:

     Yb<174/70> / 32%
     Yb<172/70> / 22%
     Yb<173/70> / 16%
     Yb<171/70> / 14.5%
     Yb<176/70> / 12.5%
     Yb<170/70> /  3%
     Yb<168/70> /  0.1%

   All are stable.

     atomic weight:       173.04
     abundance:           43rd
     density:             6.965 g/cc
     melting point:       819 C      
     boiling point:       1,196 C
     valence:             2 3
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   LUTETIUM / Lu / 71

   A silvery-white metal, resistant to corrosion and the hardest of
   the rare earths.  Technically, it is actually part of the
   transition metal series, but its properties are close enough to
   those of the other lanthanide rare earths to permit it to be
   included with them.  Two isotopes are found in nature:  stable
   Lu<175/71> at 97.5% and radioactive Lu<176/71> at 2.5%, with a
   half-life of 20 billion years.

     atomic weight:       174.967
     abundance:           60th
     density:             9.841 g/cc
     melting point:       1,663 C
     boiling point:       3,402 C
     valence:             3
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The lanthanide rare earths in general have niche uses; levels of production range from:

A few tens of thousands of tonnes a year for cerium and a little over ten thousand tonnes a year for lanthanum.
A hundred to a few hundreds of tonnes a year for yttrium, samarium, europium, gadolinium, dysprosium, and erbium.
Tens of tonnes a year for terbium, holmium, thulium, ytterbium, and lutetium.

Applications of the lanthanides include:

Magnetic alloys. Neodymium is used as a component to high-quality magnetic alloys, such as "NIB": neodymium, iron, and boron. Samarium-cobalt alloys used to be used for this purpose, but they have been largely replaced by NIB -- except for high-temperature applications, since samarium-cobalt alloy retains its magnetism at higher temperatures.
Dysprosium and holmium are used as minor components of magnetic alloys, Yttrium-indium-garnet (YIG) is used in a number of electronic applications, such as magnetic recording heads and filter components in microwave systems. Gadolinium is also used in mag-tape heads.
Additives to ceramics and glass. Praesodymium oxide gives a yellow coloring to glass, while neodymium oxide gives a deep purple coloring. Cerium oxide added to glass screens out ultraviolet, while samarium oxide and erbium oxide will screen out infrared. Yttrium oxide (Y2O3) is used in ruggedized glass, often for camera lenses.
TV display phosphors and components of "lasing mixtures" in lasers. Europium is used as a red phosphor element; neodymium is commonly used in lasers; and yttrium-aluminum-garnet (YAG) crystals are used in high-powered lasers.

Yttrium is used in a number of alloys, conferring various properties such as improved casting ability, finer grain, and heat resistance, depending on the alloy. Cerium oxide is a common component of catalytic systems, making it the most widely used of the lanthanides. Dysprosium is used in high-intensity halide lamps. Gadolinium has an unusually strong capability to absorb neutrons and so it is used in the control rods of nuclear reactor cores. Promethium is very radioactive and its only use is as a radiation source. Terbium, thulium, ytterbium, and lutetium are rare -- lutetium is the most expensive of all metals -- and only used in small amounts in some very specialized applications; other lanthanide rare earths are used in their place whenever possible.