Praseodymium: a metal that generates cold

How praseodymium was discovered and where it’s used

Praseodymi­um is a soft, duc­tile and mal­leable met­al of a sil­very col­or, and one of the lan­thanide el­e­ments. Praseodymi­um is chem­i­cal­ly ac­tive, and be­comes cov­ered with a green ox­ide film in air. It is en­coun­tered with oth­er rare-earth met­als in na­ture, and is the fourth most abun­dant lan­thanide. Its con­tent in the earth’s crust is 9.1 g/t. Praseodymi­um can be found in the min­er­als mon­azite and bast­nae­site.

How praseodymi­um was dis­cov­ered

In 1841, the Swedish doc­tor and chemist Carl Gus­tav Mosander dis­cov­ered the “new el­e­ment Didymi­um” (from the Greek δίδυμος — twin), with prop­er­ties that were very sim­i­lar to lan­thanum – hence the name of the el­e­ment. Sci­en­tists at the time be­lieved that didymi­um was a mix­ture of two or more el­e­ments. In 1885, the Aus­tri­an chemist Carl Auer von Wels­bach dis­solved dou­ble am­mo­ni­um ni­trates of didymi­um in ni­tric acid, and then car­ried out frac­tion­al crys­tal­liza­tion. It turned out that didymi­um re­al­ly was a mix­ture of two new el­e­ments. One of these el­e­ments formed bright green ox­ides. The sci­en­tist called this el­e­ment “praseodymi­um” (from the Greek πράσιος, light green and δίδυμος, twin). The sec­ond el­e­ment was neodymi­um (from the Greek νέος, new and δίδυμος, twin).

Where praseodymi­um is used

There are not so many spheres for the ap­pli­ca­tion of praseodymi­um

Like its more abun­dant neigh­bors in the lan­thanide group, praseodymi­um is used to turn glass a char­ac­ter­is­tic light green col­or. The first glass of this kind was man­u­fac­tured at Moser Glass­works in Karlovy Vary, in the present-day Czech Re­pub­lic. In the 1920s, Leo Moser, the son of the fac­to­ry’s founder, de­vel­oped glass on the ba­sis of praseodymi­um – Prasemit. Ad­di­tion­al­ly, praseodymi­um com­pounds are used to col­or ce­ram­ics yel­low.

Praseodymi­um, like neodymi­um which was dis­cov­ered along with it, is used to make pow­er­ful mag­nets and es­pe­cial­ly strong al­loys for air­craft en­gines. Praseodymi­um also found an ap­pli­ca­tion in the film in­dus­try: it is present in the car­bon arc lights used in film pro­jec­tors and stu­dio light­ing.

In chem­istry, a sol­id so­lu­tion of praseodymi­um ox­ide and ce­ria or ce­ria-zir­co­nia is used as an ox­i­da­tion cat­a­lyst. How­ev­er, the most in­ter­est­ing prop­er­ties are dis­played by sil­i­cate crys­tals doped with praseodymi­um ions, and also the in­ter­metal­lic com­pound PrNi₅. Sil­i­cate crys­tals doped with praseodymi­um can slow down light to a few hun­dred me­ters per sec­ond!

PrNi₅ has mag­ne­tocaloric prop­er­ties, which means it can change the tem­per­a­ture un­der the im­pact of a mag­net­ic field. This ef­fect in sci­ence makes it pos­si­ble to ap­proach record low tem­per­a­tures – sev­er­al hun­dredths of a de­gree of ab­so­lute zero on the Kelvin Scale, or -273.15 °С.

Sources:

  • Paul Par­sons, Gail Dixon — The Pe­ri­od­ic Ta­ble A vis­ual guide to the el­e­ments (p.140);
  • Wikipedia.Praseodymi­um.
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