Gas thermochromatography

As early as 1970, gas chemical experiments with Db were performed in a chlorinating atmosphere [24]. These studies applied the gas thermochromatography technique see Experimental Techniques . They indicated that the deposition... 

In the gas-phase chromatography experiments, the measure of volatility is assumed to be either a deposition temperature in a thermochromatography column or the temperature in an (isothermal) column at which 50% (T50%) of the desired product (50% chemical yield ) are passing through the gas chromatography column [8]. The values are then correlated with the adsorption enthalpies (AHads). The latter is then related to the sublimation enthalpy (AHsub), a property of the macro-amount using some models, see... 

GAS CHEMICAL STUDIES WITH SEABORGIUM 4.2.1 Thermochromatography of oxychlorides... 

Oxides and oxide hydroxides of Tc and Re are typically formed in an O2/H2O containing gas phase. They were extensively studied, mostly using the method of thermochromatography [56-67]. The technique has also been applied to develop Tc and Re generator systems for nuclear medical applications [68,69]. In their works, M. Schadel et al. [70] and R. Eichler et al. [53] studied the oxide and the oxide hydroxide chemistry of trace amounts of Re in an 02/H20-containing system with respect to its suitability for a first gas chemical identification of Bh. They investigated the behavior... 

Thermochromatography of oxides and oxide hydroxides. In thermochromatography experiments three different processes can be distinguished, reflected in the deposition peaks B, C, and D in Figure 17, depending on the pretreatment of the column surface and the oxidation potential of the carrier gas. These are ... 

The volatilization and deposition of carrier-free radionuclides of the elements Re, Os, Ir, Mo, Tc, and Ru in a thermochromatography column were studied using air as a carrier gas [83]. The columns were filled with quartz powder (200 fim). Os was completely volatilized and adsorbed at -40 °C. The deduced enthalpy of adsorption on the quartz surface was -A//a°(OsO4)=50 5 kJ/mol. Ru was deposited at much higher temperatures around 400 °C and identified as Ru03. Later, in different online TC experiments consistently values for -A//a°(0s04) between 39 and 41 kJ/mol were determined [79, 85, 96]. 

Fig. 23. Thermochromatography of 106Ru in 02 gas (20 ml/min) in an empty quartz column. The solid line represents the temperature profile in the column. Two different Ru zones were observed after completion of the experiment (for details see text). Some of the Ru was not volatilized at the starting position. The dashed lines indicates the modeled deposition zone of a species transported by mobile adsorption with -Af/a0(RuO4)=54 kJ/mol. Figure reproduced from [92].

The activation method requires the use of high-puiity targets, in order to exclude the influence of other nuclear reactions. Chemical procedures may be applied to separate the reaction products and to identify their atomic number Z. If short-lived radionuclides are to be measured, fast separation methods are required, for instance on-line separation in a gas stream that passes a temperature gradient (thermochromatography). In the case of half-lives of the order of milliseconds or less, however, only physical methods are applicable, in particular separation by a sequence of electric and magnetic fields. Stable or long-lived products may be determined by use of mass spectrometry, provided sufficient masses are available. 

Thermochromatography using a quartz column is applied for separation of volatile compounds (section 12.3). Aerosols may be injected for transportation of the radionuclides and a reactive gas (e.g. CI2) may be added to form special compounds or to investigate the chemical behaviour of the radionuclides, in particular radionuclides of heavy elements. 

Clear interseparation of the lanthanoids or actinoids by gas chromatography of inorganic compounds is a challenge to experimental techniques. Thermochromatography does not have adequate resolving power for the separations, but the method proved very useful for adsorption studies of tracer metals. Hiibener [77] was the first to realize the difficult experiments with some lanthanoids and the actinoids... 

Adapted from Radiokhimiya, 16(5), Zvaral, EichlerB, Belov VZ, ZvarovaTS, Korotkin YuS, Sha-laevskii MR, Shchegolev VA, Hussonnois M, Gas chromatography and thermochromatography in the study of transuranium elements, 720-727, 1974, with permission of Akademizdat Nauka Publishers. 

Reproduced (adjusted) from Nuclear Instruments and Methods, 174(3), Hickmann U, Greulich N, Trautmann N, Gaggeler H, Gaggeler-Koch H, Eichler B, Herrmann G, Rapid continuous radiochemical separations by thermochromatography in connection with a gas-jet recoil system, 507-513, 1980, with permission from Elsevier. 

In thermochromatography the zone continuously moves to even lower temperature, though with decreasing linear speed. Then the temperature-dependent expanding and compression forces may not be in equilibrium at each point, for example, when the carrier gas flows very fast and the temperature profile is steep. Nevertheless, the authors of Refs. [15,16] almost straightforwardly applied the formulae derived for the width of the chromathermographic zone in filled columns to the TC zones in open columns. To obtain a formula for the steady dispersion a-, they... 

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