Heavy Rare Earths

• Dysprosium in Terfenol-D, is used to produce sonar sensors, positioning actuators, active noise and vibration cancellation, seismic waves, and tool machining.
• A dysprosium additive to neodymium-iron-boron magnets increases the operating temperature range for use in hybrid and electric vehicles.
• Dysprosium phosphide (DyP) is a semiconductor used in laser diodes and high power, high-frequency applications.
• Dysprosium oxide in a cermet is used in nuclear reactor control rods to control the fission process.
• Dysprosium-165 is injected into joints in the body to treat rheumatoid arthritis.
• Radiation badges to detect and monitor radiation exposure.
• Coating compact disks (CD) for digital data, music, and video storage.

Dysprosium was discovered by French chemist Paul Émile Lecoq de Boisbaudran in 1886. Working with an impure holmia, Lecoq de Boisbaudran used fractional crystallisation to separate the impure holmia using ammonium hydroxide, followed by additional separations using potassium sulfate. After multiple fractionations, four “earths” precipitated in the following order: terbium, dysprosium, holmium, and erbium. Three of the elements had previously been discovered. In discovering dysprosium, Lecoq de Boisbaudran noted that he had very little material to work with and confided in Professor Georges Urbain that most of his fractional crystallisations had been prepared on a marble fireplace slab at his residence in Cognac, France. Dysprosium is named after the Greek word, dusprositos (δυσπροσιτός), meaning difficult to approach or get at, in reference to the painstaking number of fractional crystallisations needed to make the precipitate.

Large resources of dysprosium in xenotime and monazite are available worldwide in ancient and recent placer deposits, uranium ores, and weathered clay deposits (ion-adsorption ore). It occurs in the Earth’s crust at an average concentration of 3 parts per million(ppm). Xenotime is enriched in dysprosium oxide and contains 8% to 9% of the rare-earth oxide (REO) content. Monazite-(Ce), which is more abundant in the Earth’s’ crust than xenotime, has dysprosium oxide contents of 0.2% to 0.9% of the REO content.

Hastings’ Yangibana Project contains an average of around 50ppm Dy2O3, which is higher than the average concentration in the earth’s crust.

Used as a dopant in calcium fluoride, calcium tungstate, and strontium molybdate, materials that are used in solid-state devices, and as a crystal stabilizer of fuel cells which operate at elevated temperatures, together with ZrO2.

Used in alloys and in the production of electronic devices. As a component of Terfenol-D, terbium is used in actuators, in naval sonar systems, sensors, in the SoundBug device (its first commercial application), and other magnetomechanical devices. Terfenol-D is a terbium alloy that expands or contracts in the presence of a magnetic field. It has the highest magnetostriction of any alloy.

Used in green phosphors in fluorescent lamps and color TV tubes. Sodium terbium borate is used in solid state devices. The brilliant fluorescence allows terbium to be used as a probe in biochemistry, where it somewhat resembles calcium in its behavior. Terbium “green” phosphors (which fluoresce a brilliant lemon-yellow) are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide the trichromatic lighting technology which is by far the largest consumer of the world’s terbium supply. Trichromatic lighting provides much higher light output for a given amount of electrical energy than does incandescent lighting.

Used to detect endospores, as it acts as an assay of dipicolinic acid based on photoluminescence

Terbium was first isolated in 1843 by the Swedish chemist Carl Mosander at Stockholm. He had already investigated cerium oxide and separated a new element from it, lanthanum, and now he focussed his attention on yttrium, discovered in 1794, because he thought this too might harbour another element. In fact Mosander was able to obtain two other metal oxides from it: terbium oxide (yellow) and erbium oxide (rose pink) and these he announced in 1843. This was not the end of the story, however, because later that century these too yielded other rare earth elements (aka lanthanoids). Today these elements are easily separated by a process known as liquid-liquid extraction.

Along with other rare earth elements, terbium can be found in minerals, including cerite and gadolinite. The element can be extracted from monazite, in which it is present to the extent of 0.03 percent; from euxenite, a complex oxide containing 1 percent or more of terbia; and xenotime.

Recent advances ion-exchange techniques for separating the rare earth elements have enabled the isolation of terbium. One method for producing the rare earth metal is by reducing the anhydrous chloride or fluoride with calcium, although other methods of isolation are available. Vacuum remelting can remove calcium and tantalum impurities.