Technetium(IV) oxide, also known as technetium dioxide, is a chemical compound with the formula TcO₂ which forms the dihydrate, TcO₂·2H₂O, which is also known as technetium(IV) hydroxide. It is a radioactive black solid which slowly oxidizes in air.

Preparation

Technetium dioxide was first produced in 1949 by electrolyzing a solution of

ammonium pertechnetate Ammonium pertechnetate is a chemical compound with the formula NH4TcO4. It is the ammonium salt of pertechnetic acid. The most common form uses 99Tc. The compound is readily soluble in aqueous solutions forming ammonium and pertechnetate ions. ...

under

ammonium hydroxide Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although ...

and this method is used for separating technetium from

molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...

and

rhenium Rhenium is a chemical element; it has symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

. There are now more efficient ways of producing the compound, such as the reduction of ammonium pertechnetate by

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It 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 periodic tabl ...

metal and

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

stannous chloride Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula . It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in aci ...

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...

hydroxylamine Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula . The compound exists as hygroscopic colorless crystals.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Prof ...

ascorbic acid Ascorbic acid is an organic compound with formula , originally called hexuronic acid. It is a white solid, but impure samples can appear yellowish. It dissolves freely in water to give mildly acidic solutions. It is a mild reducing agent. Asco ...

, by the hydrolysis of potassium hexachlorotechnate or by the decomposition of ammonium pertechnetate at 700 °C under an inert atmosphere: :2 NH₄TcO₄ → 2 TcO₂ + 4 H₂O + N₂ All of these methods except the last lead to the formation of the dihydrate. The most modern method of producing this compound is by the reaction of ammonium pertechnetate with

sodium dithionite Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions. Structure left, 220px, Packing of sodium dithionit ...

Properties

The dihydrate dehydrates to anhydrous technetium dioxide at 300 °C, and if further heated sublime at 1,100 °C under an inert atmosphere, however, if oxygen is present, it will react with the oxygen to produce

technetium(VII) oxide Technetium(VII) oxide is the chemical compound with the formula Tc2O7. This yellow volatile solid is a rare example of a molecular binary metal oxide, the other examples being RuO4, OsO4, and the unstable Mn2O7. It adopts a centrosymmetric ...

at 450 °C. If water is present,

pertechnetic acid Pertechnetic acid (HTcO4) is a compound of technetium that is produced by reacting technetium(VII) oxide (Tc2O7) with water or reacting Tc metal or TcO2 with strong oxidizing acids, such as nitric acid, mixture of concentrated sulfuric acid wit ...

is produced by the reaction of technetium(VII) oxide with water. If technetium dioxide is treated with a base, such as

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

, it forms the hydroxotechnetate(IV) ion, which is easily oxidized to

in numerous ways, such as the reaction with alkaline

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

, concentrated

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

, or tetravalent

cerium Cerium is a chemical element; it has Chemical symbol, symbol Ce and atomic number 58. It is a hardness, soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it ...

. The solubility of technetium(IV) oxide is very low and is reported to be 3.9 μg/L. The main species when technetium dioxide is dissolved in water is TcO²⁺ at pH below 1.5, TcO(OH)⁺ pH between 1.5 and 2.5, TcO(OH)₂ pH between 2.5 and 10.9, and TcO(OH) above pH 10.9. The solubility can be affected by adding various organic ligands such as

humic acid Humic substances (HS) are colored relatively recalcitrant organic compounds naturally formed during long-term decomposition and transformation of biomass residues. The color of humic substances varies from bright yellow to light or dark brown lead ...

and

EDTA Ethylenediaminetetraacetic acid (EDTA), also called EDTA acid, is an aminopolycarboxylic acid with the formula . This white, slightly water-soluble solid is widely used to bind to iron (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-solubl ...

, or by the addition of

. This can be a problem if technetium(IV) oxide is released into the soil, as it will increase the solubility. If technetium dioxide is electrolyzed in acidic conditions, the following reaction occurs: :TcO₂·2H₂O → TcO + 4 H⁺ + 3 e^– The

electrode potential An electrode is an electrical conductor used to make contact with a nonmetallic part of a Electronic circuit, circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can c ...

measured for this reaction is kJ/mol. The molar

magnetic susceptibility In electromagnetism, the magnetic susceptibility (; denoted , chi) is a measure of how much a material will become magnetized in an applied magnetic field. It is the ratio of magnetization (magnetic moment per unit volume) to the applied magnet ...

of TcO₂·2H₂O was found to be ''χ''_m = .

References

{{Oxides Technetium compounds Oxides