Thallium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
Tl and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of ever ...
81. It is a gray
post-transition metal that is not found free in nature. When isolated, thallium resembles
tin, but discolors when exposed to air. Chemists
William Crookes and
Claude-Auguste Lamy discovered thallium independently in 1861, in residues of
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
production. Both used the newly developed method of
flame spectroscopy, in which thallium produces a notable green spectral line. Thallium, from
Greek , , meaning "green shoot" or "twig", was named by Crookes. It was isolated by both Lamy and Crookes in 1862; Lamy by electrolysis, and Crookes by precipitation and melting of the resultant powder. Crookes exhibited it as a powder precipitated by zinc at the international exhibition, which opened on 1 May that year.
Thallium tends to form the +3 and +1 oxidation states. The +3 state resembles that of the other elements in
group 13
The Group 13 network ( pl, Trzynastka, Yiddish: ''דאָס דרײַצענטל'') was a Jewish Nazi collaborationist organization in the Warsaw Ghetto during the German occupation of Poland in World War II. The rise and fall of the Group ...
(
boron,
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
,
gallium,
indium). However, the +1 state, which is far more prominent in thallium than the elements above it, recalls the chemistry of
alkali metal
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
s, and thallium(I) ions are found geologically mostly in potassium-based ores, and (when ingested) are handled in many ways like potassium ions (K
+) by ion pumps in living cells.
Commercially, thallium is produced not from potassium ores, but as a byproduct from refining of heavy-metal sulfide ores. Approximately 65% of thallium production is used in the
electronics industry, and the remainder is used in the
pharmaceutical industry and in
glass manufacturing
Glass production involves two main methods – the float glass process that produces sheet glass, and glassblowing that produces bottles and other containers. It has been done in a variety of ways during the history of glass.
Glass container ...
.
It is also used in
infrared detectors. The radioisotope thallium-201 (as the soluble chloride TlCl) is used in small amounts as an agent in a
nuclear medicine
Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...
scan, during one type of nuclear
cardiac stress test.
Soluble thallium salts (many of which are nearly tasteless) are highly
toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a sub ...
, and they were historically used in
rat poisons and
insecticides. Because of their nonselective toxicity, use of these compounds has been restricted or banned in many countries. Thallium poisoning usually results in hair loss. Because of its historic popularity as a murder weapon, thallium has gained notoriety as "the poisoner's poison" and "inheritance powder" (alongside
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
).
Characteristics
A thallium atom has 81 electrons, arranged in the electron configuration
ef
145d
106s
26p
1; of these, the three outermost electrons in the sixth shell are valence electrons. Due to the
inert pair effect, the 6s electron pair is relativistically stabilised and it is more difficult to get these involved in chemical bonding than it is for the heavier elements. Thus, very few electrons are available for metallic bonding, similar to the neighboring elements
mercury and
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
. Thallium, then, like its congeners, is a soft, highly electrically conducting metal with a low melting point, of 304 °C.
[Greenwood and Earnshaw, pp. 222–224]
A number of standard electrode potentials, depending on the reaction under study, are reported for thallium, reflecting the greatly decreased stability of the +3 oxidation state:
Thallium is the first element in group 13 where the reduction of the +3 oxidation state to the +1 oxidation state is spontaneous under standard conditions.
Since bond energies decrease down the group, with thallium, the energy released in forming two additional bonds and attaining the +3 state is not always enough to outweigh the energy needed to involve the 6s-electrons.
[Greenwood and Earnshaw, pp. 224–7] Accordingly, thallium(I) oxide and hydroxide are more basic and thallium(III) oxide and hydroxide are more acidic, showing that thallium conforms to the general rule of elements being more electropositive in their lower oxidation states.
Thallium is
malleable and
sectile
Sectility is the ability of a mineral to be cut into thin pieces with a knife. Minerals that are not sectile will be broken into rougher pieces when cut. Metals and paper are sectile.
Sectility can be used to distinguish minerals of similar appea ...
enough to be cut with a knife at room temperature. It has a metallic luster that, when exposed to air, quickly tarnishes to a bluish-gray tinge, resembling lead. It may be preserved by immersion in oil. A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. ...
is formed.
Sulfuric
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
and
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
s dissolve thallium rapidly to make the
sulfate and
nitrate salts, while
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
forms an insoluble
thallium(I) chloride
Thallium(I) chloride, also known as thallous chloride, is a chemical compound with the formula TlCl. This colourless salt is an intermediate in the isolation of thallium from its ores. Typically, an acidic solution of thallium(I) sulfate is treate ...
layer.
Isotopes
Thallium has 41
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...
s which have
atomic mass
The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&n ...
es that range from 176 to 216.
203Tl and
205Tl are the only
stable isotopes and make up nearly all of natural thallium.
204Tl is the most stable
radioisotope, with a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
of 3.78 years.
It is made by the
neutron activation
Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emit ...
of stable thallium in a
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
.
The most useful radioisotope,
201Tl (half-life 73 hours), decays by electron capture, emitting X-rays (~70–80 keV), and photons of 135 and 167 keV in 10% total abundance;
therefore, it has good imaging characteristics without an excessive patient-radiation dose. It is the most popular isotope used for thallium nuclear
cardiac stress tests.
Compounds
Thallium(III)
Thallium(III) compounds resemble the corresponding aluminium(III) compounds. They are moderately strong oxidizing agents and are usually unstable, as illustrated by the positive reduction potential for the Tl
3+/Tl couple. Some mixed-valence compounds are also known, such as Tl
4O
3 and TlCl
2, which contain both thallium(I) and thallium(III).
Thallium(III) oxide, Tl
2O
3, is a black solid which decomposes above 800 °C, forming the thallium(I) oxide and oxygen.
The simplest possible thallium compound,
thallane (TlH
3), is too unstable to exist in bulk, both due to the instability of the +3 oxidation state as well as poor overlap of the valence 6s and 6p orbitals of thallium with the 1s orbital of hydrogen. The trihalides are more stable, although they are chemically distinct from those of the lighter group 13 elements and are still the least stable in the whole group. For instance,
thallium(III) fluoride, TlF
3, has the
β-BiF3 structure rather than that of the lighter group 13 trifluorides, and does not form the complex anion in aqueous solution. The trichloride and tribromide
disproportionate
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
just above room temperature to give the monohalides, and
thallium triiodide
Thallium triiodide is a chemical compound of thallium and iodine with formula . Unlike the other thallium trihalides, which contain thallium(III), is a thallium(I) salt and contains the triiodide ion, .
An appreciation as to why Tl+ is not oxidi ...
contains the linear
triiodide anion () and is actually a thallium(I) compound.
[Greenwood and Earnshaw, p. 239] Thallium(III) sesquichalcogenides do not exist.
[Greenwood and Earnshaw, p. 254]
Thallium(I)
The
thallium(I) halides are stable. In keeping with the large size of the Tl
+ cation, the chloride and bromide have the
caesium chloride
Caesium chloride or cesium chloride is the inorganic compound with the formula Cs Cl. This colorless salt is an important source of caesium ions in a variety of niche applications. Its crystal structure forms a major structural type where each ca ...
structure, while the fluoride and iodide have distorted
sodium chloride structures. Like the analogous silver compounds, TlCl, TlBr, and TlI are
photosensitive and display poor solubility in water.
[Greenwood and Earnshaw, p. 241] The stability of thallium(I) compounds demonstrates its differences from the rest of the group: a stable
oxide,
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. ...
, and
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
are known, as are many chalcogenides.
[Greenwood and Earnshaw, pp. 246–7]
The
double salt has been shown to have hydroxyl-centred triangles of thallium, , as a recurring motif throughout its solid structure.
The metalorganic compound thallium ethoxide (TlOEt, TlOC
2H
5) is a heavy liquid (ρ , m.p. −3 °C), often used as a basic and soluble thallium source in organic and organometallic chemistry.
Organothallium compounds
Organothallium compounds tend to be thermally unstable, in concordance with the trend of decreasing thermal stability down group 13. The chemical reactivity of the Tl–C bond is also the lowest in the group, especially for ionic compounds of the type R
2TlX. Thallium forms the stable
3)2">l(CH3)2sup>+ ion in aqueous solution; like the isoelectronic
Hg(CH3)2 and
3)2">b(CH3)2sup>2+, it is linear. Trimethylthallium and triethylthallium are, like the corresponding gallium and indium compounds, flammable liquids with low melting points. Like indium, thallium
cyclopentadienyl compounds contain thallium(I), in contrast to gallium(III).
[Greenwood and Earnshaw, pp. 262–4]
History
Thallium (
Greek , , meaning "a green shoot or twig") was discovered by
William Crookes and
Claude Auguste Lamy, working independently, both using flame spectroscopy (Crookes was first to publish his findings, on March 30, 1861). The name comes from thallium's bright
green
Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a combin ...
spectral
emission lines.
After the publication of the improved method of flame spectroscopy by
Robert Bunsen and
Gustav Kirchhoff and the discovery of
caesium
Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
and
rubidium in the years 1859 to 1860, flame spectroscopy became an approved method to determine the composition of minerals and chemical products. Crookes and Lamy both started to use the new method. Crookes used it to make spectroscopic determinations for
tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...
on selenium compounds deposited in the
lead chamber of a sulfuric acid production plant near
Tilkerode in the
Harz mountains
The Harz () is a highland area in northern Germany. It has the highest elevations for that region, and its rugged terrain extends across parts of Lower Saxony, Saxony-Anhalt, and Thuringia. The name ''Harz'' derives from the Middle High Germ ...
. He had obtained the samples for his research on selenium cyanide from
August Hofmann years earlier. By 1862, Crookes was able to isolate small quantities of the new element and determine the properties of a few compounds.
Claude-Auguste Lamy used a spectrometer that was similar to Crookes' to determine the composition of a selenium-containing substance which was deposited during the production of
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
from
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
. He also noticed the new green line in the spectra and concluded that a new element was present. Lamy had received this material from the sulfuric acid plant of his friend
Frédéric Kuhlmann and this by-product was available in large quantities. Lamy started to isolate the new element from that source. The fact that Lamy was able to work ample quantities of thallium enabled him to determine the properties of several compounds and in addition he prepared a small ingot of metallic thallium which he prepared by remelting thallium he had obtained by electrolysis of thallium salts.
As both scientists discovered thallium independently and a large part of the work, especially the isolation of the metallic thallium was done by Lamy, Crookes tried to secure his own priority on the work. Lamy was awarded a medal at the International Exhibition in London 1862: ''For the discovery of a new and abundant source of thallium'' and after heavy protest Crookes also received a medal: ''thallium, for the discovery of the new element.'' The controversy between both scientists continued through 1862 and 1863. Most of the discussion ended after Crookes was elected
Fellow of the Royal Society
Fellowship of the Royal Society (FRS, ForMemRS and HonFRS) is an award granted by the judges of the Royal Society of London to individuals who have made a "substantial contribution to the improvement of natural knowledge, including mathemati ...
in June 1863.
The dominant use of thallium was the use as poison for rodents. After several accidents the use as poison was banned in the United States by
Presidential Executive Order 11643 in February 1972. In subsequent years several other countries also banned its use.
Occurrence and production
Although thallium is a modestly abundant element in the Earth's crust, with a concentration estimated to be 0.7 mg/kg,
mostly in association with
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
-based
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s in
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
s,
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
s, and
granite
Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
s, thallium is not generally economically recoverable from these sources. The major source of thallium for practical purposes is the trace amount that is found in
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
,
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
,
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, and other heavy-metal-
sulfide
Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
ores.
Thallium is found in the minerals
crookesite TlCu
7Se
4,
hutchinsonite TlPbAs
5S
9, and
lorándite TlAsS
2. Thallium also occurs as a trace element in
iron pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue gi ...
, and thallium is extracted as a by-product of roasting this mineral for the production of
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
.
Thallium can also be obtained from the
smelting
Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a c ...
of lead and zinc ores.
Manganese nodules found on the
ocean floor contain some thallium, but the collection of these nodules has been prohibitively expensive. There is also the potential for damaging the oceanic environment. In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as complexes of sulfides or selenides that primarily contain
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...
,
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
, copper, lead, and
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
. These minerals are rare, and have had no commercial importance as sources of thallium.
The
Allchar deposit in southern
North Macedonia
North Macedonia, ; sq, Maqedonia e Veriut, (Macedonia before February 2019), officially the Republic of North Macedonia,, is a country in Southeast Europe. It gained independence in 1991 as one of the successor states of Socialist Feder ...
was the only area where thallium was actively mined. This deposit still contains an estimated 500 tonnes of thallium, and it is a source for several rare thallium minerals, for example lorándite.
The
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
(USGS) estimates that the annual worldwide production of thallium is 10 metric tonnes as a by-product from the smelting of copper, zinc, and lead ores.
Thallium is either extracted from the dusts from the smelter flues or from residues such as
slag that are collected at the end of the smelting process.
The raw materials used for thallium production contain large amounts of other materials and therefore a purification is the first step. The thallium is leached either by the use of a base or sulfuric acid from the material. The thallium is precipitated several times from the solution to remove impurities. At the end it is converted to thallium sulfate and the thallium is extracted by
electrolysis on
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Pla ...
or
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
plates.
The production of thallium decreased by about 33% in the period from 1995 to 2009 – from about 15 metric
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s to about 10 tonnes. Since there are several small deposits or ores with relatively high thallium content, it would be possible to increase the production if a new application, such as a thallium-containing
high-temperature superconductor, becomes practical for widespread use outside of the laboratory.
Applications
Historic uses
The odorless and tasteless
thallium sulfate was once widely used as rat poison and ant killer. Since 1972 this use has been prohibited in the United States due to safety concerns.
Many other countries followed this example. Thallium salts were used in the treatment of
ringworm, other
skin infections and to reduce the
night sweat
Night sweats, also referred to as nocturnal hyperhidrosis (Hyperhidrosis - a medical term for excessive sweating + nocturnal - night), is the repeated occurrence of excessive sweating during sleep. The person may or may not also perspire exce ...
ing of
tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, ...
patients. This use has been limited due to their narrow
therapeutic index, and the development of improved medicines for these conditions.
Optics
Thallium(I) bromide and
thallium(I) iodide crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
s have been used as infrared optical materials, because they are harder than other common infrared optics, and because they have transmission at significantly longer wavelengths. The trade name
KRS-5 refers to this material.
Thallium(I) oxide
Thallium(I) oxide is the inorganic compound of thallium and oxygen with the formula Tl2O in which thallium is in its +1 oxidation state. It is black and produces a basic yellow solution of thallium(I) hydroxide (TlOH) when dissolved in water. I ...
has been used to manufacture glasses that have a high
index of refraction. Combined with sulfur or
selenium and arsenic, thallium has been used in the production of high-
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
glasses that have low
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
s in the range of 125 and 150 Celsius, °. These glasses have room-temperature properties that are similar to ordinary glasses and are durable, insoluble in water and have unique
refractive indices.
Electronics
Thallium(I) sulfide's
electrical conductivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
changes with exposure to
infrared light, making this compound useful in
photoresistors.
Thallium selenide has been used in
bolometers for infrared detection. Doping selenium semiconductors with thallium improves their performance, thus it is used in trace amounts in
selenium rectifier
A selenium rectifier is a type of metal rectifier, invented in 1933. They were used in power supplies for electronic equipment and in high-current battery-charger applications until they were superseded by silicon diode rectifiers in the late 19 ...
s.
Another application of thallium doping is the
sodium iodide
Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions (I ...
crystals in
gamma radiation detection devices. In these, the sodium iodide crystals are doped with a small amount of thallium to improve their efficiency as
scintillation generators. Some of the electrodes in
dissolved oxygen analyzers contain thallium.
High-temperature superconductivity
Research activity with thallium is ongoing to develop high-temperature
superconducting materials for such applications as
magnetic resonance imaging, storage of magnetic energy,
magnetic propulsion, and
electric power generation and transmission. The research in applications started after the discovery of the first
thallium barium calcium copper oxide
Thallium barium calcium copper oxide, or TBCCO (pronounced "tibco"), is a family of high-temperature superconductors having the generalized chemical formula Tl''m'' Ba2 Ca''n''−1 Cu''n'' O2''n''+''m''+2.
Tl2Ba2Ca2Cu3O10 (TBCCO-2223) was dis ...
superconductor in 1988. Thallium
cuprate superconductors have been discovered that have transition temperatures above 120 K. Some mercury-doped thallium-cuprate superconductors have transition temperatures above 130 K at ambient pressure, nearly as high as the world-record-holding mercury cuprates.
Nuclear medicine
Before the widespread application of
technetium-99m
Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medica ...
in
nuclear medicine
Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...
, the
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
isotope
thallium-201
Thallium (81Tl) has 41 isotopes with atomic masses that range from 176 to 216. 203Tl and 205Tl are the only stable isotopes and 204Tl is the most stable radioisotope with a half-life of 3.78 years. 207Tl, with a half-life of 4.77 minutes, has the ...
, with a half-life of 73 hours, was the main substance for
nuclear cardiography. The nuclide is still used for stress tests for risk stratification in patients with
coronary artery disease
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pl ...
(CAD). This isotope of thallium can be generated using a transportable generator, which is similar to the
technetium-99m generator. The generator contains
lead-201 (half-life 9.33 hours), which decays by
electron capture
Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. ...
to thallium-201. The lead-201 can be produced in a
cyclotron by the bombardment of thallium with
protons or
deuterons by the (p,3n) and (d,4n) reactions.
Thallium stress test
A thallium stress test is a form of
scintigraphy
Scintigraphy (from Latin ''scintilla'', "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue ( radiopharmaceuticals) are taken internally an ...
in which the amount of thallium in tissues correlates with tissue blood supply. Viable cardiac cells have normal
Na+/K+ ion-exchange pumps. The Tl
+ cation binds the K
+ pumps and is transported into the cells. Exercise or
dipyridamole induces widening (
vasodilation) of arteries in the body. This produces
coronary steal Coronary steal (with its symptoms termed coronary steal syndrome or cardiac steal syndrome) is a phenomenon where an alteration of circulation patterns leads to a reduction in the blood flow directed to the coronary circulation. It is caused when t ...
by areas where arteries are maximally dilated. Areas of infarct or
ischemic tissue will remain "cold". Pre- and post-stress thallium may indicate areas that will benefit from myocardial
revascularization. Redistribution indicates the existence of coronary steal and the presence of ischemic
coronary artery disease
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pl ...
.
Other uses
A mercury–thallium alloy, which forms a
eutectic at 8.5% thallium, is reported to freeze at −60 °C, some 20 °C below the freezing point of mercury. This alloy is used in thermometers and low-temperature switches.
In organic synthesis, thallium(III) salts, as thallium trinitrate or triacetate, are useful reagents for performing different transformations in aromatics, ketones and olefins, among others. Thallium is a constituent of the alloy in the
anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
plates of
magnesium seawater batteries.
Soluble thallium salts are added to
gold plating baths to increase the speed of plating and to reduce grain size within the gold layer.
A saturated solution of equal parts of thallium(I)
formate (Tl(CHO
2)) and thallium(I)
malonate (Tl(C
3H
3O
4)) in water is known as
Clerici solution
Clerici solution is an aqueous solution of equal parts of thallium formate (Tl(HCO2)) and thallium malonate (Tl(C3H3O4)). It is free-flowing and odorless. Its color fades from yellowish to colorless when diluted. At 4.25 g/cm3 at , saturated ...
. It is a mobile, odorless liquid which changes from yellowish to colorless upon reducing the concentration of the thallium salts. With a density of 4.25 g/cm
3 at 20 °C, Clerici solution is one of the heaviest aqueous solutions known. It was used in the 20th century for measuring the density of minerals by the
flotation method, but its use has discontinued due to the high toxicity and corrosiveness of the solution.
Thallium iodide is frequently used as an additive in
metal-halide lamps, often together with one or two halides of other metals. It allows optimization of the lamp temperature and color rendering, and shifts the spectral output to the green region, which is useful for underwater lighting.
Toxicity
Thallium and its compounds are extremely toxic, with numerous recorded cases of fatal thallium poisoning. The
Occupational Safety and Health Administration
The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agen ...
(OSHA) has set the legal limit (
permissible exposure limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupationa ...
) for thallium exposure in the workplace as 0.1 mg/m
2 skin exposure over an eight-hour workday. The
National Institute for Occupational Safety and Health (NIOSH) also set a
recommended exposure limit (REL) of 0.1 mg/m
2 skin exposure over an eight-hour workday. At levels of 15 mg/m
2, thallium is
immediately dangerous to life and health.
Contact with skin is dangerous, and adequate ventilation is necessary when melting this metal. Thallium(I) compounds have a high aqueous solubility and are readily absorbed through the skin, and care should be taken to avoid this route of exposure, as
cutaneous absorption can exceed the absorbed dose received by inhalation at the
permissible exposure limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupationa ...
(PEL). Exposure by inhalation cannot safely exceed 0.1 mg/m
2 in an eight-hour time-weighted average (40-hour work week). The
Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
(CDC) states, "Thallium is not classifiable as a carcinogen, and it is not suspected to be a carcinogen. It is unknown whether chronic or repeated exposure to thallium increases the risk of reproductive toxicity or developmental toxicity. Chronic high level exposure to thallium through inhalation has been reported to cause nervous system effects, such as numbness of fingers and toes." For a long time thallium compounds were readily available as rat poison. This fact and that it is water-soluble and nearly tasteless led to frequent intoxication caused by accident or criminal intent.
One of the main methods of removing thallium (both radioactive and stable) from humans is to use
Prussian blue, a material which absorbs thallium. Up to 20 grams per day of Prussian blue is fed by mouth to the patient, and it passes through their digestive system and comes out in their stool.
Hemodialysis and
hemoperfusion
Hemoperfusion or hæmoperfusion (see spelling differences) is a method of filtering the blood extracorporeally (that is, outside the body) to remove a toxin. As with other extracorporeal methods, such as hemodialysis (HD), hemofiltration (HF), ...
are also used to remove thallium from the blood serum. At later stages of the treatment, additional potassium is used to mobilize thallium from the tissues.
According to the
United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
(EPA), artificially-made sources of thallium pollution include gaseous emission of
cement factories, coal-burning power plants, and metal sewers. The main source of elevated thallium concentrations in water is the leaching of thallium from ore processing operations.
See also
*
*
Myocardial perfusion imaging
Citations
General bibliography
*
External links
Thalliumat ''
The Periodic Table of Videos'' (University of Nottingham)
Toxicity, thalliumNLM hazardous substances databank – Thallium, elemental
{{Good article
Chemical elements
Post-transition metals
1861 introductions
1861 in science
Chemical elements with hexagonal close-packed structure