RARE -- CHAPTER 4 -- INSIDE A SINGLE ROCK

CHAPTER 4 – INSIDE A SINGLE ROCK

This chapter relates stories of how the rare earth elements yttrium, praseodymium, and neodymium were discovered.  Isolation and subsequent discovery and identification of new rare earth elements is further complicated by the fact that these elements have very similar physical and chemical properties which make it hard to separate and differentiate them from each other.  A good example of this is the case of praseodymium and neodymium.  Carl Mosander discovered the substance didymium not realizing that it is actually a mixture of the simpler substances praseodymium and neodymium intimately bound to each other.  The author features the spectroscope as the predominant tool that scientists used to discover and identify new elements.

·         Because the physical and chemical properties of the rare earth elements are very similar, it is difficult to separate them from a mixture.

·         They also exist bound to carbon and oxygen.

·         Concentrated acids and bases are necessary to extract individual pure samples of each.

·         Yttrium was the first of the 17 REE to be discovered:

·         Johan Gadolin (from Finland) first isolated and identified yttrium from a black rock sample taken from a feldspar quarry in Ytterby, Sweden andsent to him by Carl Axel Arrhenius.

·         The same ytterbite mineral from which Gadolin extracted the oxide of yttrium also contained beryllium, an element that was not discovered till 5 years later. Beryllium is deemed vital to US national security for its use in fighter jets and drones.

·         Gadolinium was later named in honor of Gadolin. Gadoolinium is used in the memory-storage components of hard drives.

·         Discovery of praseodymium and neodymium:

o   Carl Gustaf Mosander discovered the substance didymium in a metal oxide sample in 1841 and mistakenly believed that it is its own element. About 15 years after Mosander’s death, Carl Auer von Welsbach discovered that didymium is actually a mixture of two different elements which he named praseodymium (“green dymium”) and neodymium.

·         Uses of didymium (mixture of two elements):

o   Because of its ability to selectively block light components, didymium found use as an additive to blacksmith goggles used by glass workers to filter intense flashes of light during the smithing process.

o   In the US during World War I, didymium metal was used to dope lenses used in transmitters which allowed them to conceal the “dits” and “dahs” of Morse code without using a special viewing filter.

o   At present, didymium is used by oil refineries as a catalyst in petroleum cracking (reducing long chain hydrocarbons to shorter chains).

·         Mosander also discovered lanthanum, erbium, and terbium.

·         Important tool for detecting and identifying new elements:  The spectroscope was instrumental in scientists’ efforts to discover new elements and identify others.  In its simplest form used by early discoverers of new elements, it consists of a tube with a prism inside.  When substances are heated to very high temperatures, they emit thermal radiation that can then be viewed through a spectroscope and resolved as individual lines of different frequencies.  This unique set of colored lines can then be used as a signature or fingerprint for each individual element:

o   Hydrogen’s emission spectrum consists of 4 lines, purple, blue, green-blue, and red.

o   Indium’s spectrum consists of two lines, a light blue and a dark blue line.

o   Iron and phosphorus on the other hand have very complex spectra consisting of dozens of lines.