Technetium oxide

Diamine chelate complexes are more stable than the monodentate amine heterocycles and, therefore, can be studied under physiological conditions. The imidazole complexes are unstable in aqueous solution and decompose rapidly to technetium oxide hydrate. Six-membered ring chelates are significantly less stable than five-membered ones. Lesser flexibility of the ligand, such as 1.2-diamino-cyclohexane, parallels somewhat lower stability of the complex [53] ... 

Table 4 presents the calculated results of the effective charges on technetium atoms in technetium compounds, arrived at by using various theoretical approximations. In technetium compounds with M-M bonds and formal technetium oxidation states 2.0 + and lower, Zeff is less than 1.0 +, whatever the... 

It might be noted that there are several forms of technetium oxides. Their formula depends on the oxidation state ofTc ions an example is NH TcO. ... 

The temperature of the furnace is slowly raised to 350-450° over a period of 30 min then the furnace is held at this temperature in order to convert the lower technetium oxides to ditechnetium heptaoxide. This oxidizing period varies from sample to sample but is usually complete in about 30 min. The protective tube is now partially withdrawn from the furnace thus exposing the sealed tube holding the product. This produces a cold region at one end of the sealed tube into which the sample sublimes. The furnace is then allowed to cool to 230°. The clay plug is removed, and the protective tube is now pushed through the furnace to provide a cold region (at the opposite end of the product tube) into which the oxide sublimes. The furnace temperature is maintained at 230°. The time required for the final sublimation is ca. 

Some hazardous metals such as chromium (Cr) and radioactive fission products such as technetium (Tc) exhibit exactly opposite solubility characteristics as compared to the metals discussed above. These metals in higher oxidation states, e.g., chromates (Cr ) and pertechnetate (Tc ), are more soluble than their counterparts, e.g., chromium and technetium oxide (Cr and Tc " "). Chromium is a hazardous metal and technetium ( Tc) is a radioactive isotope. As we shall see in Chapters 16 and 17, one way to reduce their dispersibility is to reduce their solubility in ground water and reduce them into their lower oxidation state, and then encapsulate them in the phosphate ceramic. Thus, the reduction approach is also useful in stabilization of hazardous metal oxides of high oxidation states. Because of these reasons, a good understanding of the reduction mechanism of oxides... 

Behavior of Technetium and Ruthenium A pilot plant test was conducted to study the behavior of technetium and ruthenium in the uranium calcination process. The U0- product from these tests was used i subsequent fluorination studies. The UNH feed was spiked with xc (as ammonium pertechnetate) and nonradioac-tive ruthenium (as ruthenium nitrate), and then denitrated under normal run conditions. As expected, most of the technetium was found in the UO product as technetium oxide. Over half of the ruthenium (RuO )° was volatilized and found in the condensate from the off-gas. 

Dry distillation and gas phase separation of technetium oxides from oxides of rhenium, osmium, iridium, and ruthenium by temperature-programmed gas chromatography using O2 as reactive gas was reported [109]. Furthermore, the separation of technetium chloride (TeCU) from volatile chlorides of numerous elements by thermo-chromatography combined with complex formation was investigated. The separation tube had a temperature gradient from 600 to 25 °C and was coated with KCl, CsCI, NaCl, and BaClj [HOj. 

J cO.i was identified from the mass spectra as a significant vapor species, present in substantial concentrations, when undefined technetium oxide material was exposed to low pressures of oxygen and heated to 900 °C [36]. 

Technetium oxide tetrafluoride like the pentafluoride is formed as a by-product of TcFf, in the lluorination of technetium metal [59,78,79]. TCOF4 forms two phases that may be separated from TcFs and from one another by vacuum sublimation. One phase of TcOF forms blue needles, has a chain structure, and is isostructural with its rhenium analogue. The other modification is a more volatile green compound of tri-meric structure [78,79]. 

In the reaction of technetium metal with chlorine trifluoridc at 650 °C, the mixed oxide fluoride chloride molecules TCOF2CI and TCOFO2 were recently identified by mass spectrometry, in addition to already known technetium oxide fluorides and oxide chlorides [87],... 

Technetium oxide trichloride, TCOCI3, was obtained by reaction of technetium dioxide in a chlorine stream at 30f)-35() °C. The brown, slightly volatile product can be sublimed at about. 500 "C in vacuum. TcOCls shows a strong band in the IR at 1017 cm, which can be attributed to the metal-oxygen stretehing mode. Tlie compound is readily hydrolyzed and disproportionates [.30.98.99] ... 

Technetium oxide tetrachloride. TcOCU, was separated from the mixture of the oxide chlorides, which are produced upon ehlorination of technetium metal at 300 °C. by trap-to-trap distillation in vacuum in the dark. Pure TcOCU is a purple crystalline solid that forms large crystals and melts at 35 °C. It is stable at room temperature if kept out of the light, but decomposes rapidly to TCOCI3 even at -78 "C, if left in sunlight or artificial fluorescent light. The chlorine produced in the photochemical reaction... 

Recently, the existence of gaseous technetium trioxide bromide. TcO.iBr, and trioxide iodide. TcOiI, was established mass spcctromctrically by heating an undefined technetium oxide, probably TCO2. in a Knudsen cell up to 800 C, through which the reactive gases Bi 2.12, and O2 were flowed. The Tc()3Br formation was found to be more facile than that of TCO3I. Both vapor species are stable to at least 700 =C [108]. 

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