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.[1][4]
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Other names
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3D model (JSmol)
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| ChEBI | |
| ChemSpider | |
| 873611 | |
PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| TcO2 | |
| Molar mass | 130.00 g/mol |
| Appearance | Black solid |
| Density | 6.9 g/cm3[1] |
| Melting point | 1,100 °C (2,010 °F; 1,370 K)[3] (sublimes) |
| Insoluble | |
| Solubility | Slightly soluble in acid (dihydrate)[2] |
| Structure | |
| Isostructural to MoO2[1] | |
| Thermochemistry | |
Gibbs free energy (ΔfG⦵)
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−305.974±3.377[clarification needed units] (dihydrate) |
| Related compounds | |
Other anions
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Technetium(IV) chloride |
Related compounds
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Technetium(VII) oxide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation
editTechnetium dioxide was first produced in 1949 by electrolyzing a solution of ammonium pertechnetate under ammonium hydroxide and this method is used for separating technetium from molybdenum and rhenium.[1][4][5] There are now more efficient ways of producing the compound, such as the reduction of ammonium pertechnetate by zinc metal and hydrochloric acid, stannous chloride, hydrazine, hydroxylamine, ascorbic acid,[4] by the hydrolysis of potassium hexachlorotechnate[3] or by the decomposition of ammonium pertechnetate at 700 °C under an inert atmosphere:[1][6][7]
- 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.[8]
Properties
editThe 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 at 450 °C.[1][3][7] If water is present, pertechnetic acid is produced by the reaction of technetium(VII) oxide with water.[6]
If technetium dioxide is treated with a base, such as sodium hydroxide, it forms the hydroxotechnetate(IV) ion, which is easily oxidized to pertechnetic acid in numerous ways, such as the reaction with alkaline hydrogen peroxide, concentrated nitric acid, bromine, or tetravalent cerium.[1][7]
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)–
3 above pH 10.9. The solubility can be affected by adding various organic ligands such as humic acid and EDTA, or by the addition of hydrochloric acid. This can be a problem if technetium(IV) oxide is released into the soil, as it will increase the solubility.[9]
If technetium dioxide is electrolyzed in acidic conditions, the following reaction occurs:
- TcO2·2H2O → TcO–
4 + 4 H+ + 3 e–
The electrode potential measured for this reaction is −837.2±10.0 kJ/mol.[2]
The molar magnetic susceptibility of TcO2·2H2O was found to be χm = 244×106[clarification needed units].[3]
References
edit- ^ a b c d e f g A. G. Sharpe; H. J. Emeléus (1968). Advances in Inorganic Chemistry and Radiochemistry. Elsevier Science. p. 21. ISBN 9780080578606.
- ^ a b J. A. Rard (1983). "Critical review of the chemistry and thermodynamics of technetium and some of its inorganic compounds and aqueous species". OSTI.GOV. U.S. Department of Energy Office of Scientific and Technical Information. doi:10.2172/5580852. OSTI 5580852. S2CID 98137163. Retrieved 4 November 2022.
- ^ a b c d C. M. Nelson; G. E. Boyd; Wm. T. Smith Jr. (1954). "Magnetochemistry of Technetium and Rhenium". Journal of the American Chemical Society. 76 (2). ACS Publications: 348–352. doi:10.1021/ja01631a009.
- ^ a b c Edward Anders (1960). "THE RADIOCHEMISTRY OF TECHNETIUM". OSTI.GOV. U.S. Department of Energy Office of Scientific and Technical Information: 8. doi:10.2172/4073069. OSTI 4073069. Retrieved 4 November 2022.
- ^ L. B. Rogers (1949). "Electroseparation of Technetium from Rhenium and Molybdenum". Journal of the American Chemical Society. 71 (4): 1507–1508. doi:10.1021/ja01172a520.
- ^ a b Bradley Covington Childs (2017). Volatile Technetium Oxides: Implications for Nuclear Waste Vitrification. UNLV Theses, Dissertations, Professional Papers, and Capstones (Thesis). doi:10.34917/10985836.
- ^ a b c Edward Andrews (1959). "Technetium and Astatine Chemistry". Annual Review of Nuclear Science. 9. Annual Reviews: 203–220. Bibcode:1959ARNPS...9..203A. doi:10.1146/annurev.ns.09.120159.001223.
- ^ Nancy J. Hess; Yuanxian Xia; Dhanpat Rai; Steven D. Conradson (2004). "Thermodynamic Model for the Solubility of TcO2·xH2O(am) in the Aqueous Tc(IV) – Na+ – Cl− – H+ – OH− – H2O System". Journal of Solution Chemistry. 33 (2): 199–226. doi:10.1023/B:JOSL.0000030285.11512.1f. S2CID 96789279.
- ^ Baohua Gu; Wenming Dong; Liyuan Liang; Nathalie A. Wall (2011). "Dissolution of Technetium(IV) Oxide by Natural and Synthetic Organic Ligands under both Reducing and Oxidizing Conditions". Environmental Science & Technology. 45 (11): 4771–4777. Bibcode:2011EnST...45.4771G. doi:10.1021/es200110y. PMID 21539349.