Indium: a crying metal

Interesting facts about indium

In­di­um is a very soft met­al. If you bend a piece of in­di­um met­al, it gives a high-pitched squeak. Once you’ve heard it, you’ll nev­er for­get it. This “cry” is caused by the dis­in­te­gra­tion and re­or­ga­ni­za­tion of crys­tals in­side the met­al. This phe­nom­e­non also aris­es when you bend tin, the neigh­bor­ing el­e­ment in the pe­ri­od­ic ta­ble. In­di­um gets its name from the pur­ple-in­di­go col­or of its spec­tral line, in Latin “In­dicum”, or “in­di­go”, but the sci­en­tist who dis­cov­ered it was col­or­blind!

How in­di­um was dis­cov­ered

It was dis­cov­ered in 1863 by the Ger­man sci­en­tists Fer­di­nand Re­ich and Hi­erony­mous Richter. Re­ich was study­ing the zinc ore spha­lerite, which he hoped con­tained the re­cent­ly dis­cov­ered el­e­ment of thal­li­um. Us­ing a spec­tro­scope, he ex­am­ined a sed­i­ment which was sup­posed to show the char­ac­ter­is­tic green line of thal­li­um. Re­ich was col­or­blind, so he asked his col­league Richter to check the spec­trum for him. The sci­en­tists were amazed. In­side of a green line, Richter found a bright blue line, which had not been seen be­fore. Re­ich and Richter re­al­ized they had found a new el­e­ment, and gave it the Latin name of “In­dicum”, mean­ing “pur­ple” or “in­di­go”. Re­ich and Richter even quar­reled over who had dis­cov­ered in­di­um – Richter claimed that he was the sole dis­cov­er­er of the el­e­ment.

Richter went on to iso­late the met­al in 1864. At the World Fair in Paris in 1867, an in­di­um in­got of 0.5 kg was pre­sent­ed.

Oc­cur­rence and ap­pli­ca­tion of in­di­um

Pure met­al in­di­um can be found in na­ture, but it is main­ly pro­duced as a side prod­uct in zinc ore pro­cess­ing. Like gal­li­um, in­di­um can be ap­plied to glass, and if it is al­lowed to set­tle, it forms a mir­ror, which is re­flec­tive like a sil­ver mir­ror, but less cor­ro­sive. In­di­um is added to oth­er met­als to make hard al­loys, some of which are used in den­tistry, and in sol­der al­loys of ar­mored joints to pre­vent ther­mal fa­tigue.

The melt­ing point of in­di­um (429.7485 К or 156.5985 °C) is one of the ref­er­ence points of the ITS-90 in­ter­na­tion­al tem­per­a­ture scale, the stan­dard for de­ter­min­ing tem­per­a­ture.

In­di­um is not used in the me­tab­o­lism of liv­ing or­gan­isms, but in small dos­es its salts cause a rise in me­tab­o­lism. If you swal­low more than a few mil­ligrams of in­di­um salt, a tox­ic re­ac­tion will set in, af­fect­ing the heart, di­ges­tive tract and kid­neys. The ra­dioac­tive iso­tope In-111 ra­di­ates gam­ma ra­di­a­tion and is used in med­i­cal scans to de­tect such dis­eases as os­teomyeli­tis (an acute or chron­ic bone in­fec­tion) and de­cu­bi­tus, mak­ing it pos­si­ble to car­ry out pre­cise di­ag­no­sis and treat­ment.

This el­e­ment did not have sig­nif­i­cant ap­pli­ca­tion un­til WWII, when it was used for coat­ing bear­ings in high-per­for­mance air­craft. To­day, it is used in LCD tele­vi­sions and com­put­er mon­i­tors in the form of in­di­um tin ox­ide. It is a good con­duc­tor of elec­tric­i­ty, which can send sig­nals to in­di­vid­u­al pix­els on the screen with­out light in­ter­fer­ence from oth­er pix­els. The pro­duc­tion of in­di­um has in­creased con­sid­er­ably in re­cent decades, and Chi­na is the world’s lead­ing pro­duc­er of it. Based on cur­rent rates of con­sump­tion, sci­en­tists pre­dict that in­di­um sup­plies are only suf­fi­cient for 13 years. So that hu­man­i­ty can con­tin­ue to use tele­vi­sions, com­put­ers and smart­phones, ad­di­tion­al re­cy­cling is re­quired for the ex­trac­tion of in­di­um.


The Pe­ri­od­ic Ta­ble A vis­ual guide to the el­e­ments (p.118)