molybdenum ← technetium → ruthenium Mn ↑ Tc ↓ Re 43Tc Periodic table
Appearance
silvery gray metal
General properties
Name, symbol, number	technetium, Tc, 43
Element category	transition metal
Group, period, block	7, 5, d
Standard atomic weight	98(0) g·mol−1
Electron configuration	Kr 4d5 5s2
Electrons per shell	2, 8, 18, 13, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	11 g·cm−3
Melting point	2430 K, 2157 °C, 3915 °F
Boiling point	4538 K, 4265 °C, 7709 °F
Heat of fusion	33.29 kJ·mol−1
Heat of vaporization	585.2 kJ·mol−1
Specific heat capacity	(25 °C) 24.27 J·mol−1·K−1
Vapor pressure extrapolated
P/Pa 1 10 100 1 k 10 k 100 k at T/K 2727 2998 3324 3726 4234 4894
Atomic properties
Oxidation states	7, 6, 5, 4, 3,[1] 2, 1[2], -1, -3 (strongly acidic oxide)
Electronegativity	1.9 (Pauling scale)
Ionization energies	1st: 702 kJ·mol−1
	2nd: 1470 kJ·mol−1
	3rd: 2850 kJ·mol−1
Atomic radius	136 pm
Covalent radius	147±7 pm
Miscellanea
Crystal structure	hexagonal
Magnetic ordering	Paramagnetic
Thermal conductivity	(300 K) 50.6 W·m−1·K−1
Speed of sound (thin rod)	(20 °C) 16,200 m/s
CAS registry number	7440-26-8
Most stable isotopes
Main article: Isotopes of technetium
iso NA half-life DM DE (MeV) DP 95mTc syn 61 d ε - 95Mo γ 0.204, 0.582, 0.835 - IT 0.0389, e 95Tc 96Tc syn 4.3 d ε - 96Mo γ 0.778, 0.849, 0.812 - 97Tc syn 2.6×106 y ε - 97Mo 97mTc syn 90 d IT 0.965, e 97Tc 98Tc syn 4.2×106 y β− 0.4 98Ru γ 0.745, 0.652 - 99Tc trace 2.111×105 y β− 0.294 99Ru 99mTc syn 6.01 h IT 0.142, 0.002 99Tc γ 0.140 -
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Technetium (pronounced /tɛkˈniːʃɪəm/ tek-NEE-shi-əm) is the lightest chemical element with no stable isotope, making it the lightest radioactive element. It has atomic number 43 and symbol Tc. Technetium occurs in nature only in minute amounts; as a spontaneous fission product in uranium ore or by neutron capture in molybdenum ores. Nearly all technetium is produced synthetically. The chemical properties of this silvery gray, crystalline transition metal are intermediate between rhenium and manganese.

Before the element was discovered, many of its properties were predicted by Dmitri Mendeleev. Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em). In 1937 technetium (specifically the technetium-97 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek τεχνητός, meaning "artificial").

Its short-lived gamma-emitting nuclear isomer technetium-99m is used in nuclear medicine for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by-products of fission of uranium-235 in nuclear reactors and is extracted from nuclear fuel rods. No isotope of technetium has a half-life longer than 4.2 million years (technetium-98), so its detection in 1952 in red giants, which are billions of years old, helped bolster the theory that stars can produce heavier elements.

Contents 1 History 1.1 Search for element 43 1.2 Official discovery and later history 2 Characteristics 2.1 Physical 2.2 Chemical 2.2.1 Hydride and oxides 2.2.2 Sulfides, selenides, tellurides 2.2.3 Technetium clusters and organic complexes 2.3 Isotopes 3 Occurrence and production 3.1 Byproduct production of technetium-99 in fission wastes 3.2 Disposal of waste 3.3 Neutron activation of molybdenum or other pure elements 4 Applications 4.1 Nuclear medicine and biology 4.2 Industrial and chemical 5 Precautions 6 Notes 7 References 8 Bibliography 9 Further reading

[edit] History

[edit] Search for element 43

From the 1860s through 1871, there was a gap in early forms of the periodic table between molybdenum (element 42) and ruthenium (element 44). Dmitri Mendeleev predicted in 1871 that this missing element would occupy the empty place below manganese and therefore be chemically similar to manganese. Mendeleev gave it the provisional name ekamanganese, eka- from the Sanskrit words for one, because the predicted element was one place down from the known element manganese.^[3] Many early researchers, both before and after the periodic table was published, were eager to be the first to discover and name the missing element; its location in the table suggested that it should be easier to find than other undiscovered elements. It was first thought to have been found in platinum ores in 1828 and was given the name polinium, but turned out to be impure iridium. Then in 1846 the element ilmenium was claimed to have been discovered but was determined to be impure niobium. This mistake was repeated in 1847 with the "discovery" of pelopium.^[4]

In 1877, the Russian chemist Serge Kern reported discovering the missing element in platinum ore. Kern named what he thought was the new element davyum, after the noted English chemist Sir Humphry Davy, but it was determined to be a mixture of iridium, rhodium and iron. Another candidate, lucium, followed in 1896 but it was determined to be yttrium. Then in 1908 the Japanese chemist Masataka Ogawa found evidence in the mineral thorianite which he thought indicated the presence of element 43. Ogawa named the element nipponium, after Japan (which is Nippon in Japanese). In 2004 H. K Yoshihara utilized "a record of X-ray spectrum of Ogawa's nipponium sample from thorianite [which] was contained in a photographic plate preserved by his family. The spectrum was read and indicated the absence of the element 43 and the presence of the element 75 (rhenium)."^[5]

German chemists Walter Noddack, Otto Berg and Ida Tacke (later Mrs. Noddack) reported the discovery of element 75 and element 43 in 1925 and named element 43 masurium (after Masuria in eastern Prussia, now in Poland, the region where Walter Noddack's family originated).^[6] The group bombarded columbite with a beam of electrons and deduced element 43 was present by examining X-ray diffraction spectrograms.^[7] The wavelength of the X-rays produced is related to the atomic number by a formula derived by Henry Moseley in 1913. The team claimed to detect a faint X-ray signal at a wavelength produced by element 43. Later experimenters could not replicate the discovery, and in fact it was dismissed as an error for many years.^[8][9] Still, in 1933 a series of articles on the discovery of elements quoted the name masurium for element 43.^[10] In 1998 John T. Armstrong of the National Institute of Standards and Technology ran "computer simulations" of the 1925 experiments and obtained results quite close to those reported by the Noddack team. He claimed that this was further supported by work published by David Curtis of the Los Alamos National Laboratory measuring the (tiny) natural occurrence of technetium.^{[8][note 1]} However, the Noddack team's experimental results have never been reproduced, and they were unable to isolate any element 43. Debate still exists as to whether the 1925 team actually did discover element 43.^[11]

[edit] Official discovery and later history

The discovery of element 43 was finally confirmed in a December 1936 experiment at the University of Palermo in Sicily conducted by Carlo Perrier and Emilio Segrè.^[12] In mid-1936 Segrè visited the United States, first Columbia University in New York, where he had spent time the previous summer, and then the Lawrence Berkeley National Laboratory in California. He persuaded cyclotron inventor Ernest Lawrence to let him take back some discarded cyclotron parts that had become radioactive. Lawrence mailed him a molybdenum foil that had been part of the deflector in the cyclotron. Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, that the molybdenum activity was indeed Z = 43, an element not found in nature due to rapid nuclear decay. With considerable difficulty they finally succeeded in isolating three distinct decay periods (90, 80, and 50 days) that eventually turned out to be two isotopes, technetium-95 and technetium-97.^[13][14] University of Palermo officials wanted them to name their discovery "panormium", after the Latin name for Palermo, Panormus. In 1947^[13] element 43 was named after the Greek word τεχνητός, meaning "artificial", since it was the first element to be artificially produced.^[4][6] Segrè returned to Berkeley and immediately sought out Glenn T. Seaborg. They isolated the isotope technetium-99m, which is now used in some 10,000,000 medical diagnostic procedures annually.^[15]

In 1952 astronomer Paul W. Merrill in California detected the spectral signature of technetium (in particular, light with wavelength of 403.1 nm, 423.8 nm, 426.8 nm, and 429.7 nm) in light from S-type red giants.^[16] These massive stars near the end of their lives were rich in this short-lived element, meaning nuclear reactions within the stars must be producing it. This evidence was used to bolster the then-unproven theory that stars are where nucleosynthesis of the heavier elements occurs.^[14] More recently, such observations provided evidence that elements were being formed by neutron capture in the s-process.^[17]

Since its discovery, there have been many searches in terrestrial materials for natural sources of technetium. In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian Congo in extremely small quantities (about 0.2 ng/kg);^[17] there it originates as a spontaneous fission product of uranium-238. There is also evidence that the Oklo natural nuclear fission reactor produced significant amounts of technetium-99, which has since decayed to ruthenium-99.^[17]

[edit] Characteristics

[edit] Physical

Technetium is a silvery-gray radioactive metal with an appearance similar to platinum. It is commonly obtained as a gray powder.^[18] The metal form is slightly paramagnetic, meaning its magnetic dipoles align with external magnetic fields but will assume random orientations once the field is removed.^[19] The crystal structure of the metal is hexagonal close-packed. Pure metallic single-crystal technetium becomes a type-II superconductor at temperatures below 7.46 K; irregular crystals and trace impurities raise this transition temperature to 11.2 K for 99.9% pure technetium powder.^[20] Below this temperature, technetium has a very high magnetic penetration depth, the largest among the elements apart from niobium.^[21]

Atomic technetium has characteristic emission lines at 363.3 nm, 403.1 nm, 426.2 nm, 429.7 nm, and 485.3 nm.^[22]

[edit] Chemical

Technetium is placed in the seventh group of the periodic table between rhenium and manganese; as predicted by periodic law, its chemical properties are intermediate between those two elements. Of the two, technetium more closely resembles rhenium, particularly in their chemical inertness and tendency to form covalent bonds.^[23] Unlike manganese, technetium does not readily form cations. Common oxidation states of technetium include 0, +2, +4, +5, +6 and +7. Technetium dissolves in aqua regia, nitric acid, and concentrated sulfuric acid, but it is not soluble in hydrochloric acid of any concentration.^[18]

[edit] Hydride and oxides

Reaction of technetium with hydrogen produces the negatively charged hydride [TcH₉]²⁻ ion, which is isostructural with [ReH₉]²⁻. It consists of a trigonal prism with Tc atom in the center and six hydrogen atoms at the corners. Three more hydrogens make a triangle lying parallel to the base and crossing the prism in its center. Although those hydrogen atoms are not equivalent geometrically, their electronic structure is almost the same. The coordination number 9 in this complex is the highest for a technetium complex. Two hydrogen atoms in it can be replaced by sodium (Na⁺) or potassium (K⁺) ions.^[24]

The metal form of technetium slowly tarnishes in moist air.^[25] Its oxides are TcO₂ and Tc₂O₇. Under oxidizing conditions technetium(VII) will exist as the pertechnetate ion, TcO−4.^[25] Technetium will burn in oxygen when in powder form.^[19]

At temperatures 400–450 °C, technetium oxidizes to form pale-yellow heptoxide:

4 Tc + 7 O₂ → 2 Tc₂O₇

It adopts a centrosymmetric structure with two types of Tc-O bonds; their bond lengths are 167 and 184 pm, and the O-Tc-O angle is 180°.^[26]

Technetium heptoxide is the anhydride of pertechnic acid and the precursor to sodium pertechnetate:^[27]

Tc₂O₇ + 2 NaOH → 2 NaTcO₄ + H₂O

Black-colored technetium dioxide (TcO₂) can be produced by reduction of heptoxide with technetium or hydrogen.^[28]

Pertechnetic acid (HTcO₄) is produced by reacting Tc₂O₇ with water or oxidizing acids, such as nitric acid, concentrated sulfuric acid, aqua regia, or a mixture of nitric and hydrochloric acids. The resulting dark red, hygroscopic substance is a strong acid and easily donates protons.

The remaining pertechnate anion TcO₄⁻ consists of a tetrahedron with oxygens in the corners and Te atom in the center. Unlike permanganate MnO₄⁻, it is a weak oxidizing agent. Pertechnate is often used as a convenient water-soluble source of Tc isotopes, such as ^99mTc, and as a catalyst.^[29]

[edit] Sulfides, selenides, tellurides

Technetium forms various sulfides. TcS₂ is obtained by direct reaction of technetium and sulfur, and Tc₂S₇ is formed as follows:

2 HTcO₄ + 7 H₂S → Tc₂S₇ + 8 H₂O

In this reaction, technetium is not reduced, which is different from the similar reaction of manganese. Upon heating, technetium heptasulfide decomposes into disulfide and elementary sulfur:

Tc₂S₇ → 2 TcS₂ + 3 S

Analogous reactions occur with selenium and tellurium.^[30]

[edit] Technetium clusters and organic complexes

Several technetium clusters are known, including Tc₄, Tc₆, Tc₈ and Tc₁₃.^[31][32] The more stable Tc₆ and Tc₈ clusters have prism shapes where vertical pairs of Tc atoms are connected by triple bonds and the planar atoms by single bonds. Every Tc atoms makes six bonds, and the remaining valence electrons can be saturated by one axial and two µ-bridging halogen atoms such as chlorine or bromine.^[33]

Technetium forms numerous organic complexes, which are relatively well-investigated because of their importance for nuclear medicine. Technetium carbonyl (Tc₂(CO)₁₀) is a white solid.^[35] In this molecule, two technetium atoms are weakly bound to each other; each atom is surrounded by octahedra of five carbonyl ligands. The bond length between Tc atoms, 303 pm,^[36] is significantly larger than the distance between two atoms in metallic technetium (272 pm). Similar carbonyls are formed by manganese and rhenium.^[37]

An example of a technetium complex with an organic ligand is shown in the figure and is used in nuclear medicine. It has a unique Tc-O moiety oriented perpendicularly to the plane of the molecule, where the oxygen atom can be replaced by a nitrogen atom.^[38]

[edit] Isotopes

Technetium is the lowest-numbered element in the periodic table that is exclusively radioactive; the second-lightest radioactive element is promethium.^[25] A specificity of nuclear structure makes Tc nuclei, which each have 43 protons, somewhat more energetic than the isotopes of the same mass of neighboring elements with an even number of protons; this additional energy makes Tc radioactive. For isotopes lighter than the most stable isotope, technetium-98 (9843Tc), the primary decay mode is electron capture, giving molybdenum.^[39] For the heavier isotopes, the primary mode is beta emission, giving ruthenium, with the exception that technetium-100 can decay both by beta emission and electron capture.^[39][40]

Most odd-numbered elements have only one stable isotope because there is little preventing beta decay of nuclides with an odd number of nucleons to a less energetic one of the same mass. Elements with even numbers of nucleons have a major difference in stability between even-even and odd-odd nuclei because of pairing effects.^[41]

The most stable radioisotopes are ⁹⁸Tc (half-life of 4.2 Ma), ⁹⁷Tc (half-life: 2.6 Ma) and ⁹⁹Tc (half-life: 211 ka).^[39] Thirty other radioisotopes have been characterized with mass numbers ranging from 85 to 118.^[39] Most of these have half-lives that are less than an hour; the exceptions are ⁹³Tc (half-life: 2.73 hours), ⁹⁴Tc (half-life: 4.88 hours), ⁹⁵Tc (half-life: 20 hours), and ⁹⁶Tc (half-life: 4.3 days).^[42]

Technetium also has numerous meta states. Technetium-99m (^97mTc) is the most stable, with a half-life of 91 days (0.0965 MeV).^[42] This is followed by ^95mTc (half life: 61 days, 0.03 MeV), and ^99mTc (half-life: 6.01 hours, 0.142 MeV).^{[42] 99m}Tc only emits gamma rays, subsequently decaying to ⁹⁹Tc.^[42]

Technetium-99 (⁹⁹Tc) is the most common and most readily available isotope, as it is a major product of the fission of uranium-235. One gram of ⁹⁹Tc produces 6.2×10⁸ disintegrations a second (that is, 0.62 GBq/g).^[19]

[edit] Occurrence and production

Since technetium is unstable, only minute traces occur naturally in the Earth's crust as a spontaneous fission product in uranium ores. In 1999 David Curtis estimated that a kilogram of uranium contains 1 nanogram (10⁻⁹ g) of technetium.^[14][43][44] Paul W. Merrill announced that he found extraterrestrial technetium in some red giant stars (S-, M-, and N-types) that stars contain an absorption line in their spectrum indicating the presence of this element.^[18][45] This subset of red-giants are known informally as technetium stars.

[edit] Byproduct production of technetium-99 in fission wastes

In contrast with the rare natural occurrence, bulk quantities of technetium-99 are produced each year from spent nuclear fuel rods, which contain various fission products. The fission of a gram of uranium-235 in nuclear reactors yields 27 mg of technetium-99, giving technetium a fission product yield of 6.1%.^[19] Other fissile isotopes also produce similar yields of technetium, such as 4.9% from uranium-233 and 6.21% from plutonium-239.^[46]

About 49,000 TBq (78 metric tons) of technetium is estimated to have been produced in nuclear reactors between 1983 and 1994, which is by far the dominant source of terrestrial technetium.^[47][48] Only a fraction of the production is used commercially.^{[note 2]}

Technetium-99 is produced by the nuclear fission of both uranium-235 and plutonium-239. It is therefore present in radioactive waste and in the nuclear fallout of fission bomb explosions. Its decay, measured in becquerels per amount of spent fuel, is dominant at about 10⁴ to 10⁶ years after the creation of the nuclear waste.^[47]

From 1945 to 1994, an estimated 160 TBq (about 250 kg) of technetium-99 was released into the environment by atmospheric nuclear tests.^[47][49] The amount of technetium-99 from nuclear reactors released into the environment up to 1986 is on the order of 1000 TBq (about 1600 kg), primarily by nuclear fuel reprocessing; most of this was discharged into the sea. Reprocessing methods have reduced emissions since then, but as of 2005 the primary release of technetium-99 into the environment is by the Sellafield plant, which released an estimated 550 TBq (about 900 kg) from 1995–1999 into the Irish Sea.^[48] From 2000 onwards the amount has been limited by regulation to 90 TBq (about 140 kg) per year.^[50]

Discharge of technetium into the sea has resulted in some seafood containing miniscule quantities of this element. For example, European lobster and fish from west Cumbria contain about 1 Bq/kg of technetium.^{[51][52][note 3]}

[edit] Disposal of waste

The long half-life of technetium-99 and its ability to form an anionic species makes it a major concern for long-term disposal of radioactive waste. Many of the processes designed to remove fission products in reprocessing plants aim at cationic species like caesium (e.g., caesium-137) and strontium (e.g., strontium-90). Hence the pertechnetate is able to escape through these treatment processes. Current disposal options favor burial in continental, geologically stable rock. The primary danger with such a course is that the waste is likely to come into contact with water, which could leach radioactive contamination into the environment. The anionic pertechnetate and iodide do not absorb well onto the surfaces of minerals, so they are likely to be washed away. By comparison plutonium, uranium, and caesium are much more able to bind to soil particles. For this reason, the environmental chemistry of technetium is an active area of research.^[53]

An alternative disposal method, transmutation, has been demonstrated at CERN for technetium-99. This transmutation process is one in which the technetium (technetium-99 as a metal target) is bombarded with neutrons to form the short-lived technetium-100 (half life = 16 seconds) which decays by beta decay to ruthenium-100. If recovery of usable ruthenium is a goal, an extremely pure technetium target is needed; if small traces of the minor actinides such as americium and curium are present in the target, they are likely to undergo fission and form more fission products which increase the radioactivity of the irradiated target. The formation of ruthenium-106 (half-life 374 days) from the 'fresh fission' is likely to increase the activity of the final ruthenium metal, which will then require a longer cooling time after irradiation before the ruthenium can be used.^[54]

The actual production of technetium-99 from spent nuclear fuel is a long process. During fuel reprocessing, it appears in the waste liquid, which is highly radioactive. After sitting for several years, the radioactivity falls to a point where extraction of the long-lived isotopes, including technetium-99, becomes feasible. Several chemical extraction processes are then used, yielding technetium-99 metal of high purity.^[55]

[edit] Neutron activation of molybdenum or other pure elements

The metastable isotope technetium-99m is produced as a fission product from the fission of uranium or plutonium in nuclear reactors. Because used fuel is allowed to stand for several years before reprocessing, all molybdenum-99 and technetium-99m will have decayed by the time that the fission products are separated from the major actinides in conventional nuclear reprocessing. The liquid left after plutonium–uranium extraction (PUREX) contains a high concentration of technetium as TcO₄^- but almost all of this is technetium-99, not technetium-99m.^[56]

The vast majority of the technetium-99m used in medical work is produced by irradiating highly enrighed uranium targets in a reactor, extracting molybdenum-99 from the targets, and recovering the technetium-99m that is produced upon decay of molybdenum-99.^[57] Additionally, molybdenum-99 can be formed by the neutron activation of molybdenum-98.^[58] Molybdenum-99 has a half-life of 67 hours, so short-lived technetium-99m (half-life: 6 hours), which results from its decay, is being constantly produced.^[14] The technetium can then be chemically extracted from the solution by using a technetium-99m generator ("technetium cow", also occasionally called a "molybdenum cow"). By irradiating a highly-enriched uranium target to produce molybdenum-99, there is no need for the complex chemical steps which would be required to separate molybdenum from a fission product mixture. This method requires that an enriched uranium target be irradiated with neutron to form Molybdenum-99 as a fission product, then separated.^[59] A drawback of this process is that it requires targets containing uranium-235, which are subject to the security precautions of fissile materials.^[60]

Other technetium isotopes are not produced in significant quantities by fission; when needed, they are manufactured by neutron irradiation of parent isotopes (for example, technetium-97 can be made by neutron irradiation of rutherfordium-96).^[61]

[edit] Applications

[edit] Nuclear medicine and biology

Technetium-99m ("m" indicates that this is a metastable nuclear isomer) is used in radioactive isotope medical tests, for example as a radioactive tracer that medical equipment can detect in the human body.^[14] It is well suited to the role because it emits readily detectable 140 keV gamma rays, and its half-life is 6.01 hours (meaning that about 94% of it decays to technetium-99 in 24 hours).^[19] There are at least 31 commonly-used radiopharmaceuticals based on technetium-99m for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors.^[62]

Immunoscintigraphy incorporates technetium-99m into a monoclonal antibody, that is an immune system protein capable of binding to cancer cells. A few hours after injection, medical equipment is used to detect the gamma rays emitted by the technetium-99m; higher concentrations indicate where the tumors are. This technique is particularly useful for detecting hard-to-find cancers, such as those affecting the intestine. These modified antibodies are produced commercially by the German company Hoechst.^[14]

Typical quantities of technetium administered for SPECT diagnostic tests range from 10 to 30 mCi for adults.^[63][64] These doses result in radiation exposures to the patient around 10 mSv, the equivalent of about 500 chest X-ray exposures.^[65]

When technetium-99m is combined with a tin compound it binds to red blood cells and can therefore be used to map circulatory system disorders. It is commonly used to detect gastrointestinal bleeding sites. A pyrophosphate ion with technetium-99m adheres to calcium deposits in damaged heart muscle, making it useful to gauge damage after a heart attack.^[66] The sulfur colloid of technetium-99m is scavenged by the spleen, making it possible to image the structure of the spleen.^[19]

Radiation exposure due to diagnostic treatment involving technetium-99m can be kept low. Because technetium-99m has a short half-life and emits primarily a gamma ray (allowing small amounts to be easily detected), its quick decay into the far-less radioactive technetium-99 results in relatively less total radiation dose to the patient per unit of initial activity after administration. In the form administered in these medical tests (usually pertechnetate), both isotopes are quickly eliminated from the body, generally within a few days.^[66] Technetium for nuclear medicine purposes is usually extracted from technetium-99m generators, because of its short 6-hour half-life.^[67]

The longer-lived isotope technetium-95m, with a half-life of 61 days, is used as a radioactive tracer to study the movement of technetium in the environment and in plant and animal systems.^[68]

[edit] Industrial and chemical

Technetium-99 decays almost entirely by beta decay, emitting beta particles with consistent low energies and no accompanying gamma rays. Moreover, its long half-life means that this emission decreases very slowly with time. It can also be extracted to a high chemical and isotopic purity from radioactive waste. For these reasons, it is a NIST standard beta emitter, used for equipment calibration.^[69] Technetium-99 has also been proposed for use in optoelectronic devices and nanoscale nuclear batteries.^[70]

Like rhenium and palladium, technetium can serve as a catalyst. For certain reactions, for example the dehydrogenation of isopropyl alcohol, it is a far more effective catalyst than either rhenium or palladium. Of course, its radioactivity is a major problem in finding safe applications.^[71]

Under certain circumstances, a small concentration (55 ppm) of potassium pertechnetate(VII) in water protects steel from any corrosion.^[72] For this reason, pertechnetate has been used as a possible anodic corrosion inhibitor for steel, although technetium's radioactivity poses problems which limit this application to self-contained systems.^[73] While (for example) CrO₄²⁻ can also inhibit corrosion, it requires a concentration ten times as high. In one experiment, a specimen of carbon steel was kept in an aqueous solution of pertechnetate for 20 years and was still uncorroded. The mechanism by which pertechnetate prevents corrosion is not well understood, but seems to involve the reversible formation of a thin surface layer. One theory holds that the pertechnetate reacts with the steel surface to form a layer of technetium dioxide which prevents further corrosion; the same effect explains how iron powder can be used to remove pertechnetate from water. (Activated carbon can also be used for the same effect.) The effect disappears rapidly if the concentration of pertechnetate falls below the minimum concentration or if too high a concentration of other ions is added.^[74]

As noted, the radioactive nature of technetium (3 MBq per liter at the concentrations required) makes this corrosion protection impractical in almost all situations. Nevertheless, corrosion protection by pertechnetate ions was proposed (but never adopted) for use in boiling water reactors.^[74]

[edit] Precautions

Technetium plays no natural biological role and is not normally found in the human body.^[18] Technetium is produced in quantity by nuclear fission, and spreads more readily than many radionuclides. It appears to have low chemical toxicity. For example, no significant change in blood formula, body and organ weights, and food consumption could be detected for rats which ingested up to 15 µg of technetium-99 per gram of food for weeks.^[75] The radiological toxicity of technetium (per unit of mass) is a function of compound, type of radiation for the isotope in question, and the isotope's half-life.^[76]

All isotopes of technetium must be handled carefully. The most common isotope, technetium-99, is a weak beta emitter; such radiation is stopped by the walls of laboratory glassware. The primary hazard when working with technetium is inhalation of dust; such radioactive contamination in the lungs can pose a significant cancer risk. For most work, careful handling in a fume hood is sufficient; a glove box is not needed.^[77]

[edit] Notes

1. ^ "Using first-principles X-ray-emission spectral-generation algorithms developed at NIST, I simulated the X-ray spectra that would be expected for Van Assche's initial estimates of the Noddacks' residue compositions. The first results were surprisingly close to their published spectrum! Over the next couple of years, we refined our reconstruction of their analytical methods and performed more sophisticated simulations. The agreement between simulated and reported spectra improved further. Our calculation of the amount of element 43 required to produce their spectrum is quite similar to the direct measurements of natural technetium abundance in uranium ore published in 1999 by Dave Curtis and colleagues at Los Alamos. We can find no other plausible explanation for the Noddacks' data than that they did indeed detect fission "masurium."
   Armstrong, John T. (2003). "Technetium". Chemical & Engineering News. http://pubs.acs.org/cen/80th/technetium.html. 
2. ^ As of 2005, technetium-99 in the form of ammonium pertechnate is available to holders of an ORNL permit:Hammond, C. R. (2004). The Elements, in Handbook of Chemistry and Physics 81th edition. CRC press. ISBN 0849304857. 
3. ^ The anaerobic, spore-forming bacteria in the Clostridium genus are able to reduce Tc(VII) to Tc(IV). Clostridia bacteria play a role in reducing iron, manganese and uranium, thereby affecting these elements' solubility in soil and sediments. Their ability to reduce technetium may determine a large part of mobility of technetium in industrial wastes and other subsurface environments. Francis, A. J.; Dodge, C. J.; Meinken, G. E. (2002). "Biotransformation of pertechnetate by Clostridia". Radiochimica Acta 90: 791–797. doi:10.1524/ract.2002.90.9-11_2002.791. http://www.extenza-eps.com/OLD/doi/abs/10.1524/ract.2002.90.9-11_2002.791. 

[edit] References

[edit] Bibliography

• Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th ed.). New York: John Wiley & Sons, Inc.. ISBN 0-471-199957-5. 
• Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. ISBN 0198503407. 
• Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed. ed.). Oxford: Butterworth-Heinemann. ISBN 0-7506-3365-4. 
• Heiserman, David L. (1992). "Element 43: Technetium". Exploring Chemical Elements and their Compounds. TAB Books. ISBN 0-8306-3018-X. 
• Schwochau, Klaus (2000). Technetium: chemistry and radiopharmaceutical applications. Wiley-VCH. ISBN 3527294961. http://books.google.com/books?id=BHjxH8q9iukC&pg=PP1. 

[edit] Further reading

Wikimedia Commons has media related to: Technetium

Look up technetium in Wiktionary, the free dictionary.

• The radiochemical Manual, 2nd Ed, edited by B.J. Wilson, 1966.
• E.R.Scerri (2007). The Periodic Table, Its Story and Its Significance. Oxford University Press,. ISBN 0195305736. http://www.us.oup.com/us/catalog/general/subject/Chemistry/?view=usa&ci=9780195305739. 
• Radiochemistry and nuclear chemistry, Gregory Choppin, Jan-Olov Liljenzin, and Jan Rydberg, 3rd Edition, 2002, the chapter on nuclear stability (pdf) (viewed 5 January 2007)
• WebElements.com – Technetium, and EnvironmentalChemistry.com – Technetium per the guidelines at Wikipedia's WikiProject Elements (all viewed 1 December 2002)
• Nudat 2 nuclide chart from the National Nuclear Data Center, Brookhaven National Laboratory
• Nuclides and Isotopes Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989
• Chemistry in its element podcast (MP3) from the Royal Society of Chemistry's Chemistry World: Technetium

v • d • e Periodic table
H																															He
Li	Be																									B	C	N	O	F	Ne
Na	Mg																									Al	Si	P	S	Cl	Ar
K	Ca	Sc															Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y															Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Uub	Uut	Uuq	Uup	Uuh	Uus	Uuo
Alkali metals Alkaline earth metals Lanthanoids Actinoids Transition metals Other metals Metalloids Other nonmetals Halogens Noble gases