Technetium metal

Boyd Chemistry of Technetium. II. Preparation of Technetium metal. J. Amer. chem. Soc. 74, 1852 (1952). 

Preparation. It can be made by the irradiation of molybdenum targets with deuterium nuclei. Technetium metal may be easily prepared by reduction of NH4Tc04 (or TcC>2) with hydrogen or by electrodeposition from an NH4Tc04 solution. 

The atomic radius of technetium is by 0.02 A smaller than that of rhenium, whereas the difference of the atomic radii of technetium and manganese is almost 0.1 A. The density of the technetium metal is slightly higher than that of lead. 

Technetium metal can be electrodeposited from an acidic solution of pertechnetate using a platimun, nickel or copper cathode. Electrolysis of neutral, unbuffered solutions, alkaline solutions, and sulfuric acid solutions lower than 2 N yield a black deposit of hydrated TcOj The current efficiencies are generally poor but the deposition is reasonably quantitative. The deposition requires the application of relatively negative cathode potentials and is therefore non-selective. Polaro-graphy indicates that the overpotentials for the evolution of hydrogen on technetium are rather low hence, electrolysis from acidic media will always include concurrent discharge of hydrogen . ... 

Box recommends the addition of oxalic acid, tartaric acid or another di-carboxylic acid, to sulfuric acid for plating technetium either as a metal or oxide. On copper electrodes in 0.7 M oxalate and 0.45 M sulfuric acid, more than 99% of technetium metal is plated at 1.0-1.3 A/cm from a pertechnetate solution. However, from 0.4 M oxalate and 1.9 M sulfuric acid it is the oxide that is deposited. 

Technetium isotopes formed upon irradiation of a molybdenum target by protons with an energy of 22 MeV have been ascertained by mass spectrometry. After separation of technetium by ion exchange, the isotopes Tc (0.5 %), Tc (56.0%), Tc (17.3%) and Tc (26.7%) are detected. The sensitivity of this method is very high 5 x 10 g of technetium can be detected. Mass spectrometric determination of technetium is also described by Kukavadze et al. . Pertech-netate is reduced to technetium metal and Tc ions are produced at 1600 to 1800 °C. 

Technetium metal is grayish-silver and looks much like platinum. As with most transition elements, technetium in pure form is a noncorrosive metal. It requires only 55 ppm of technetium added to iron to transform the iron into a noncorroding alloy. Because of technetiums radioactivity, its use as an alloy metal for iron is limited so as to not expose humans to unnecessary radiation. 

Direct chlorination of powdered technetium metal gives a blue product, not TcClg by reducing the amount of oxygen contamination the amount of blue material produced can be reduced but not eliminated. Chlorination of the metal on porous pot affords a green product which resembles TcCl . Both the blue and green products are, in fact, mixtures of purple TcOCl. and colourless TCOCI3 and these compounds have been isolated pure by vacuum distilla-... 

Technetium metal does not have much commercial application. Its short-... 

Pure technetium metal may he prepared hy reducing ammonium pertech-nate, NH4TCO4, with hydrogen at high temperatures. Hydrogen reduction at about 200°C first forms the oxide, Tc02, which is reduced to Tc metal at 600 to 800°C. 

Superconductivity has been observed in technetium metal and in alloys based on technetium with additions of Pd, Os, Rh, Ru, Sn, V. Ti, Re, W,... 

Contrary to some reports,1 3 ditechnetium heptaoxide is not the only product formed when technetium metal is burned in an excess of oxygen—nor can it be purified by simple resublimation. The formation of small quantities of a second volatile compound (possibly Tc03 or HTc04) has been observed by some investigators.4 6... 

Approximately 0.3 g (3 mmol) of technetium metal, 8 9 which has previously been degassed at 900° on a vacuum line, is contained in a suitable... 

The technetium metal was obtained from K[Tc04] as described in reference 8. The K[Tc04] is available from the Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830. 

Technetium(VII) oxide is a yellow solid, crystallizing in the orthorhombic space group D2)l15-Pbca and is one of the few known transition metal oxides having a molecular structure in the solid state.10 It melts at 119.5° and boils at 310.6° It dissolves in water, forming pertechnetic acid. The pertechnetate ion is known to inhibit the corrosion of steel. TechnetiumfVII) oxide is an excellent starting material for preparing pure technetium metal. 

Technetium metal melts at 2413 20 K [45]. The melting point is near those of other elements in the same period of the periodic system, e.g., molybdenum (2893 K) or ruthenium (2723 K). Rhenium melts more than 1000° higher (3453 K) than technetium, while the melting point of manganese (1.533 K) is considerably lower. The heat of melting of technetium was estimated to be 5.5 kcal molc" [37], the entropy of fusion df5 to be 3.3 cal mole [38], the heat of sublimation at 298.15 K as 152 ... 

In view of the excellent catalytic properties of rhenium and the related platinum metals, it was expected that technetium metal and compounds of technetium would also be qualified to be specific catalysts [6. ... 

Similar studies were carried out on the aromatization of n-hexane and /i-heptane on technetium metal catalysts supported by /-Al20i. MgO, Y2O3, Si02 or activated carbon. With an increase in the content of supported technetium (1 to 5 wt%) the yield of benzene (1.5 to 17.0 wt%) for the dehydrogenation reaction of n-hexane and the yield of toluene (2.0 to 22.8 wt%) for the reaction of n-hcptanc generally increased in the temperature range from 450 to 600 °C [10]. 

The most active Tc metal catalyst was obtained at the lowest temperature used for the reduction of TCO2 to Tc metal. Die apparent activation energy for the dehydrogenation process was 13.7 kcal/mole. At 220 C 30 % of isopropyl alcohol was converted to acetone. ITie activity of the technetium metal catalyst for the dehydrogenation of isopropyl alcohol is superior to that of manganese and close to that of metallic rhenium when, however, the content of rhenium in the catalyst was 30 wt% instead of around 0.2 wt% of technetium [11]. 

In addition, the dehydrogenation of isopropyl alcohol was studied using technetium metal supported on the oxides Y2O3, Pi 407, Nd203 or Yb203. Table 8.1.A. summarizes the results,... 

The outstanding catalytic properties ol technetium metal compared to rhenium and palladium arc illustrated in Fig. 8.1.A. On the ordinate the conversion rate of isopropyl alcohol in tnl/min is plotted. According to Table 8.1.A the catalytic properties of the supporting oxides arc substantially changed by adding even small amounts of technetium. The activity of the catalysts increases with increasing wt% of technetium. In particular, the selectivity of the dehydrogenation attains 100 % [12]. 

In hydrogenation of carbon monoxide over supported catalysts of technetium metal between 270 and 500 °C in a helium flow, predominantly methane was formed. The conversion of CO into methane increased with increasing temperature. Conversion yields up to 100 vol% of CH4 were obtained over a TC/7-AI2O3 catalyst [23]. 

Technetium metal is obtained by hydrogen reduction of ammonium pertechnetatc. The initial reaction at 200-300 °C produces black technetium dioxide which prevents the loss of ammonium pertechnetatc by sublimation [1], At a temperature of 500-600 °C or, even better, 700-900 °C [2] the metal is left behind as a silver-grey spongy mass according to the reaction ... 

Heating of ammonium hexachlorotechnctate(rV) in an inert atmosphere, e.g. nitrogen, at a dull red heat, also yields technetium metal. The complex salt does not melt, but decomposes under these conditions to leave technetium metal as a fine silver-grey powder [3] ... 

Technetium metal is also clectrodeposited almost quantitatively from dilute solutions of TcOj in acidic ammonium oxalate solutions. Films up to 18 mg/cm were deposited as dense adherent coatings on copper, gold, silver, and platinum cathodes at a current density of 1.3 A/cm . At an oxalate concentration of 0.7 M. the molarity of H2SO4 required for the deposition of technetium metal varied between 0.45 M with a copper cathode and 1.90 M with a platinum cathode. At lower molarities of H2SO4 technetium was deposited as oxide (Table 9.1.A). 

The technetium metal deposits had a purity of about 99 % under optimal conditions. Technetium was deposited on the cathodes in the form of microscopic spheres and could easily be removed from the cathode when dried [6]. 

Three determinations of the melting point of technetium metal are in reasonably good agreement 2140 20 °C [13, 2200 50 °C [14], and 2162 40°C (15). The average melting point of 2167 °C is near those of neighboring elements in the same period —molybdenum (2610 °C) and ruthenium (2310 °C) —but almost 1000 °C lower than that of rhenium [14]. Ilic boiling point of technetium metal was estimated as 4900 K [16] no experimental value seems to be available. 

For an ingot of arc-melted technetium metal, weighing approximately 70 g, the immersion density was found to be 11.47 g/cm [7]. An electron-beam melted sample showed a density of 11.492 g/cm [17], The X-ray density, calculated with the lattice parameters a=2.7407 A, c=4.3980 A [18] and the nuclide mass of 98.906 g, yields... 

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