Thermochromatography

The transeinsteinium actinides, fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr), are not available in weighable (> ng) quantities, so these elements are unknown in the condensed bulk phase and only a few studies of their physicochemical behavior have been reported. Neutral atoms of Fm have been studied by atomic beam magnetic resonance 47). Thermochromatography on titanium and molybdenum columns has been employed to characterize some metallic state properties of Fm and Md 61). This article will not deal with the preparation of these transeinsteinium metals. 

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... 

For the experimental investigation of volatile transactinide compounds two different types of chromatographic separations have been developed, thermochromatography and isothermal chromatography. Sometimes also combinations of the two have been applied. The basic principles of thermochromatography and isothermal chromatography are explained in Figure 7. 

Fig. 7. Upper panel temperature profiles employed in thermochromatography and isothermal chromatography lower panel deposition peak and integral chromatogram resulting from thermochromatography and isothermal chromatography, respectively.

Eichler, B. Domanov, V.P. "Thermochromatographie tragerfreier Kernreaktions-produkte als Chloride". In Joint Institute for Nuclear Research Report, PI 2-7775, Dubna, (1974). 

Thermochromatography was also applied to investigate the volatility of Rf and Hf bromides [9], These experiments yielded evidence that Rf bromide is more volatile than Hf bromide, and also more volatile than Rf chloride. 

Top Schematic of the early thermochromatography experiment with Db in a brominating atmosphere (Br2+BBr3). 

For over 20 years, 263Sg with a half-life of 0.9 s was the longest-lived known Sg isotope. In addition to the minute production rates, this short half-life effectively prevented a chemical identification of Sg. In 1992 S. Timokhin et al. from Dubna studied the chemical identification of Sg as a volatile oxychloride making use of an on-line thermochromatography method [25], This claim was substantiated by ancillary experiments [26, 27] and further studies of the behavior of homologues elements Mo and W [28], Shortly thereafter, an international collaboration of chemists conducted on-line... 

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].

From this experiment it appears that the interaction of element 112 with an Au or Pd surface is much weaker than for Hg. The obtained enthalpies of adsorption were -A//a°(Hg) > 75 kJ/mol and -A//a°(element 112) < 55 kJ/mol. Such a vastly different chemical behavior as in the present case of element 112 compared to its lighter homologue Hg has not been observed for any of the lighter transactinides so far and might reflect the predicted inertness and enhanced volatility due to relativistic effects. Obviously, in a next step, the enthalpy of adsorption of element 112 on Au surfaces has to be measured experimentally. This can be done with a cryo thermochromatography detector containing Au coated detectors. The temperature in the gradient should start at room temperature and reach down to the adsorption temperature of Rn, which should be still above the temperature of liquid N2. 

The thermochromatography of trace amounts of a number of elements including Po, Am and Cf in their elemental states was studied. The deposition temperatures suggest the existence of different types of intersection between the adsorbate atoms and the Ti surface. The technique is presented as having practical analytical applications. 

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