Terbium (Tb)

Introduction

Terbium is a chemical element with the atomic number 65 in the periodic table. It’s one of the least plentiful rare-earth metals that occur in Earth’s crust. Located between the elements gadolinium and dysprosium, terbium is classified as a member of the lanthanide series of the periodic table. This rare-earth metal has three valence electrons and is mainly used in phosphors. 

Fact Box

Chemical and Physical Properties of Terbium

The symbol in the periodic table of elements: Tb 

Atomic number: 65

Atomic weight (mass): 158.925 g.mol-1

Group number: Lanthanides

Period: 6 (f-block)

Color: Silvery-gray

Physical state: Solid at 20°C

Half-life: From 0.94(+33−22) milliseconds to 180 years

Electronegativity according to Pauling: 1.2

Density: 8.23 g.cm-3

Melting point: 1359°C, 2478°F, 1632 K

Boiling point: 3230°C, 5846°F, 3503 K

Van der Waals radius: Unknown

Ionic radius: Unknown

Isotopes: 36

Most characteristic isotope: 159Tb

Electronic shell: [Xe]4f96s2

The energy of the first ionization: 563.5 kJ.mol-1

The energy of the second ionization: 1109.6 kJ.mol-1

Discovery date: In 1843 by Carl Gustav Mosander

With the periodic table symbol Tb, atomic number 65, atomic mass of 158.925 g.mol-1, and electron configuration [Xe]4f96s2, terbium is a soft, ductile, malleable, silvery-gray metal that can be dented with any hard object. It reaches its boiling point at 3230°C, 5846°F, 3503 K, while the melting point is achieved at X1359°C, 2478°F, 1632 K. This member of the lanthanides family of elements has an electronegativity of 1.2 according to Pauling, whereas the atomic radius according to van der Waals is unknown. 

Terbium is a highly reactive chemical. When exposed to high temperatures, terbium metal reacts with many elements, especially with carbon, arsenic, and silicon. Compared to the other lanthanides, element 65 can maintain a relatively stable electron configuration upon exposure to air. 

Element 65 occurs in three different structural modifications (crystal allotropes). When exposed to a temperature below -54.15oC/-65.47oF/219 K, Tb adopts ferromagnetic properties that become antiferromagnetic if the temperature rises above the aforementioned temperature. Terbium metal is a very strong paramagnet above −43°C/−46°F/230 K.                      

How Was Terbium Discovered?

Familiar with the fact that the rare-earth elements almost always occur within the same type of ore, the Swedish chemist Carl Gustav Mosander (1797 – 1858) attempted to study the mineral gadolinite. He was intrigued to perform new experiments on this particular mineral after the discovery of the Finnish chemist and physicist Johan Gadolin (1760 – 1852). Namely, in 1794 the Finnish scientist had succeeded in tracing the element yttrium as an impurity in the substance labeled as yttria (yttrium oxide, Y2O3.) that was contained in the yttrium mineral. 

By using ammonium hydroxide, Mosander precipitated fractions of different basicity from the yttria mineral sample. In these fractions, the Swedish chemist detected two previously unknown differently colored substances that he labeled as erbia (a rose pink erbium oxide) and terbia (a yellow-colored terbium oxide). 

How Did Terbium Get Its Name?

The discoverer of terbium, Carl Gustav Mosander, named the new element 65 terbium after the village of Ytterby in Sweden, where the mineral source of this chemical element was obtained from. 

Where Can You Find Terbium?

Terbium has an occurrence of approximately 1.2 mg/kg in Earth’s crust. It can often be traced together with other rare-earth elements in mineral ores, such as monazite (reddish-brown phosphate), xenotime (phosphate mineral), bastnasite (three carbonate fluoride mineral), cerite, and euxenite (brownish-black mineral). 

The pure form of terbium metal is prepared by a metallothermic reduction of the anhydrous fluoride with calcium metal. 

The largest terbium ore mines in the world are located in the United States, India, Sri Lanka, Brazil, and Australia. For commercial purposes, terbium is mainly obtained from the ion-adsorption clays of Southern China by ion exchange, solvent extraction, electrolysis, or reduction. 

Terbium in Everyday Life

Element 65 is one of the rarest earth metals which is also difficult to be isolated from the mineral ores. For this reason, the terbium extraction process from the minerals is very expensive. The high cost of this substance also limits its everyday use. 

The following are some of the instances where the practical terbium application can be observed:

• One of the main applications of terbium is in phosphors. The strong green luminescence emitted by Tb 3+ ions is used in color phosphors which are applied in trichromatic lighting and color TV tubes; 
• Just like europium, terbium is also used in the phosphors that are applied as security inks of the Euro banknotes. Tb ions allow easier detection of counterfeit banknotes;
• The green emission of terbium compounds is widely used in biological and medical research since it can be detected long after the fluorescence of biological molecules has decayed away. For this reason, terbium compounds are often used as biological probes to signal certain changes within the cellular and metabolic processes of the human body, as well as for early detection and treatment of diseases such as cancer;
• The bright colors of the cell phone displays are produced by small quantities of rare-earth elements, including yttrium, terbium, and dysprosium;
• Terfenol-d is a terbium-dysprosium-iron magnetostrictive alloy used for underwater acoustic devices in naval sonar systems, as well as the new generations of fuel injectors applied in diesel engines;
• Element 65 is used to dope calcium fluoride, calcium tungstate, and strontium molybdate;
• Sodium terbium borate is used in electronic equipment with silicon-based semiconductors (i.e. solid-state devices), including transistors, capacitors, low-energy light bulbs, and mercury lamps. In addition, terbium together with zirconium dioxide (ZrO2) is also widely used as a crystal stabilizer of fuel cells that operate at elevated temperatures.

How Dangerous Is Terbium?

Terbium is not classified as a toxic element. However, exposure to the metal dust particles of terbium may lead to irritation of the eyes and lungs. Terbium compounds can lead to increased irritation of the skin and eyes, as well as to some symptoms of terbium toxicity if ingested. 

Environmental Effects of Terbium

The naturally occurring element 65 is not labeled as an environmental hazard. However, the industrial waste derived from the production of items that include terbium is always a potential pollutant to the environment. 

Isotopes of Terbium

There are 36 radioactive isotopes of terbium. The pure, elemental form of element 65 is composed of one stable isotope, 159Tb. Having a half-life of 180 years, terbium-158 is the most stable form of this chemical element. 

Most of the terbium isotopes have a half-life between less than 24 seconds and 6.907 days before they undergo a beta decay process into Gd (gadolinium) or Dy (dysprosium) isotopes. 

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life [n 4]	Decay mode [n 5]	Daughter isotope [n 6][n 7]	Spin and parity [n 8][n 4]	Natural abundance (mole fraction)
	Excitation energy[n 4]							Normal proportion	Range of variation
135Tb	65	70		0.94(+33−22) ms			(7/2−)
136Tb	65	71	135.96138(64)#	0.2# s
137Tb	65	72	136.95598(64)#	600# ms			11/2−#
138Tb	65	73	137.95316(43)#	800# ms [>200 ns]	β+	138Gd
					p	137Gd
139Tb	65	74	138.94829(32)#	1.6(2) s	β+	139Gd	11/2−#
140Tb	65	75	139.94581(86)	2.4(2) s	β+ (99.74%)	140Gd	5
					β+, p (.26%)	139Eu
141Tb	65	76	140.94145(11)	3.5(2) s	β+	141Gd	(5/2−)
142Tb	65	77	141.93874(32)#	597(17) ms	β+	142Gd	1+
					β+, p	141Eu
143Tb	65	78	142.93512(6)	12(1) s	β+	143Gd	(11/2−)
144Tb	65	79	143.93305(3)	~1 s	β+	144Gd	1+
					β+, p (rare)	143Eu
145Tb	65	80	144.92927(6)	20# min	β+	145Gd	(3/2+)
146Tb	65	81	145.92725(5)	8(4) s	β+	146Gd	1+
147Tb	65	82	146.924045(13)	1.64(3) h	β+	147Gd	1/2+#
148Tb	65	83	147.924272(15)	60(1) min	β+	148Gd	2−
149Tb	65	84	148.923246(5)	4.118(25) h	β+ (83.3%)	149Gd	1/2+
					α (16.7%)	145Eu
150Tb	65	85	149.923660(8)	3.48(16) h	β+ (99.95%)	150Gd	(2−)
					α (.05%)	146Eu
151Tb	65	86	150.923103(5)	17.609(1) h	β+ (99.99%)	151Gd	1/2(+)
					α (.0095%)	147Eu
152Tb	65	87	151.92407(4)	17.5(1) h	β+	152Gd	2−
					α (7×10−7%)	148Eu
153Tb	65	88	152.923435(5)	2.34(1) d	β+	153Gd	5/2+
154Tb	65	89	153.92468(5)	21.5(4) h	β+ (99.9%)	154Gd	0(+#)
					β− (.1%)	154Dy
155Tb	65	90	154.923505(13)	5.32(6) d	EC	155Gd	3/2+
156Tb	65	91	155.924747(5)	5.35(10) d	β+	156Gd	3−
					β− (rare)	156Dy
157Tb	65	92	156.9240246(27)	71(7) y	EC	157Gd	3/2+
158Tb	65	93	157.9254131(28)	180(11) y	β+ (83.4%)	158Gd	3−
					β− (16.6%)	158Dy
159Tb[n 9]	65	94	158.9253468(27)	Stable			3/2+	1.0000
160Tb	65	95	159.9271676(27)	72.3(2) d	β−	160Dy	3−
161Tb[n 9]	65	96	160.9275699(28)	6.906(19) d	β−	161Dy	3/2+
162Tb	65	97	161.92949(4)	7.60(15) min	β−	162Dy	1−
163Tb	65	98	162.930648(5)	19.5(3) min	β−	163Dy	3/2+
164Tb	65	99	163.93335(11)	3.0(1) min	β−	164Dy	(5+)
165Tb	65	100	164.93488(21)#	2.11(10) min	β−	165mDy	3/2+#
166Tb	65	101	165.93799(11)	25.6(22) s	β−	166Dy
167Tb	65	102	166.94005(43)#	19.4(27) s	β−	167Dy	3/2+#
168Tb	65	103	167.94364(54)#	8.2(13) s	β−	168Dy	4−#
169Tb	65	104	168.94622(64)#	2# s	β−	169Dy	3/2+#
170Tb	65	105	169.95025(75)#	3# s	β−	170Dy
171Tb	65	106	170.95330(86)#	500# ms	β−	171Dy	3/2+#

Source: Wikipedia

List of Terbium Compounds

As a part of a compound, terbium typically adopts the oxidation state of +3. However, it can also occur in the oxidation states +1, +2, and +4. It mostly forms chlorides, iodides, bromides, and fluorides. 

This chemical element has a hexagonal close-packed structure and three crystal allomorphs:

• The α-phase (a close-packed hexagonal with a = 3.6055 Å and c = 5.6966 Å at room temperature);
• The β-phase (with a = 3.605 Å, b = 6.244 Å, and c = 5.706 Å at 77 K/−196 °C/−321 °F);
• The γ-phase (a body-centred cubic with a = 4.07 Å at 1,289 °C/2,352 °F). 

Terbium is an electropositive element. It oxidizes when exposed to water, most acids (such as sulfuric acid), and in the presence of all of the halogens. Tb3+ ions emit a strong green luminescence when excited.

The following are the most commonly prepared terbium compounds:

 

• Terbium gallium garnet
• Terbium silicide
• Terbium(III,IV) oxide
• Terbium(III) bromide
• Terbium(III) chloride
• Terbium(III) fluoride
• Terbium(III) hydroxide
• Terbium(III) iodide
• Terbium(III) nitrate
• Terbium(III) oxide
• Terbium(IV) fluoride
• Terbium(IV) oxide
  

5 Interesting Facts and Explanations

1. Terbium is not the only element that the Swedish chemist Carl Gustaf Mosander had discovered. Namely, this distinguished researcher is also credited for the discovery of two other rare-earth elements (lanthanoids) – lanthanum and erbium.
2. The place Ytterby in Sweden is a village located on the Swedish island of Resarö, in Vaxholm Municipality in the Stockholm archipelago. Being rich with feldspar and gadolinite ores, even eight of the periodic table elements were discovered in this small miner village. In the world of science, Ytterby is also known as “the village of the four elements”, since there are four chemical elements discovered at the location and named after it. Those are the elements yttrium (Y), erbium (Er), terbium (Tb), and ytterbium (Yb). 
3. The other four elements discovered in the mines near Ytterby are named after a Scandinavian location, chemist, or mythological concept: scandium (Sc, named after a subregion in Northern Europe), holmium (Ho, named after Stockholm), thulium (Tm, named after Thule, a mythic analogue of Scandinavia), and gadolinium (Gd, named after the Finnish chemist Johan Gadolin). 
4. According to the modern chemical calculations, a gadolinite sample typically contains extremely high concentrations of several rare-earth elements: yttrium = 16%; thulium = 5%; ytterbium = 3%; terbium = 2%, and dysprosium = 2%. 
5. Despite being labeled as a rare element, terbium occurs more commonly than some widely used metals like silver and mercury.