Terbium
History

Swedish chemist Carl Gustaf Mosander discovered terbium in 1843. He detected it as an impurity in yttrium oxide, Y O, then known as yttria. Yttrium, erbium, and terbium are all named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques.

Mosander first separated yttria into three fractions, all named for the ore: yttria, erbia, and terbia. "Terbia" was originally the fraction that contained the pink color, due to the element now known as erbium. "Erbia", the oxide containing what is now known as terbium, originally was the fraction that was yellow or dark orange in solution. The insoluble oxide of this element was noted to be tinged brown, and soluble oxides after combustion were noted to be colorless. Until the advent of spectral analysis, arguments went back and forth as to whether erbia even existed. Spectral analysis by Marc Delafontaine allowed the separate elements and their oxides to be identified, but in his publications, the names of erbium and terbium were switched, following a brief period where terbium was renamed "mosandrum", after Mosander. The names have remained switched ever since.

The early years of preparing terbium (as terbium oxide) were difficult. Metal oxides from gadolinite and samarskite were dissolved in nitric acid, and the solution was further separated using oxalic acid and potassium sulfate. There was great difficulty in separating erbia from terbia; in 1881, it was noted that there was no satisfactory method to separate the two. By 1914, different solvents had been used to separate terbium from its host minerals, but the process of separating terbium from its neighbor elements - gadolinium and dysprosium - was described as "tedious" but possible. Modern terbium extraction methods are based on the liquid–liquid extraction process developed by Werner Fischer et al., in 1937.
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