All articles published by are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by , including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to https:///openaccess.
Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.
Editor’s Choice articles are based on recommendations by the scientific editors of journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.
Britvic 2015 Sustainable Business Report
New Preparative Approach to Purer Technetium-99 Samples—Tetramethylammonium Pertechnetate: Deep Understanding and Application of Crystal Structure, Solubility, and Its Conversion to Technetium Zero Valent Matrix
By Mikhail A. Volkov 1, * , Anton P. Novikov 1, 2, Mikhail S. Grigoriev 1, Vitaly V. Kuznetsov 1, 3, Anastasiia V. Sitanskaia 1, Elena V. Belova 1, Andrey V. Afanasiev 1, Iurii M. Nevolin 1 and Konstantin E. German 1
) makes Tc a hazardous material. Two principal ways were proposed for its disposal, namely, long-term storage and transmutation. Conversion to metal-like technetium matrices is highly desirable for both cases and for the second one the reasonably high Tc purity was important too. Tetramethylammonium pertechnetate (TMAP) was proposed here as a prospective precursor for matrix manufacture. It provided with very high decontamination factors from actinides (that is imperative for transmutation) by means of recrystallisation and it was based on the precise data on TMAP solubility and thermodynamics accomplished in the temperature range of 3–68 °C. The structure of solid pertechnetates were re-estimated with precise X-ray structure solution and compared to its Re and Cl analogues and tetrabutylammonium analogue as well. Differential thermal and evolved gas analysis in a flow of Ar–5% H
Solved ***use Sql*** I Use The Microsoft Sql Server
Gas mixture showed that the major products of thermolysis were pure metallic technetium in solid matrix, trimethylammonium, carbon dioxide, and water in gas phase. High decontamination factors have been achieved when TMAP was used as an intermediate precursor for Tc.
Technetium is a hazardous component of radioactive waste that accumulates in large quantities while nuclear energetics develops [1, 2, 3, 4, 5]. Methods for its immobilization and utilization have been developed for intermediate and low-level radioactive wastes [6, 7, 8, 9, 10, 11]. The safe handling with high-level radioactive waste implies the separation of long-lived radionuclides, their immobilization into stable matrices, and disposal of the solidified wastes into geological formations for long-term storage [12, 13, 14, 15, 16, 17, 18, 19]. An alternative way for neutralization of technetium is nuclear transmutation into stable ruthenium [20]. In both cases, metallic or metal-like matrices are considered to be the most effective [21, 22, 23]. However, the method of their production should be optimized and special procedure for improving the technetium purity should be elaborated.
One of the ways of such optimization is the use of new materials at the Tc concentration and conversion stages. These materials should provide effective separation of technetium from solutions and the possibility of its additional purification from actinides and other fission products that accompany technetium in the spent nuclear fuel reprocessing streams. As TMAP ([Me
Highest Paying Jobs In Cadillac, Mi
) is sparinglymoderately soluble in water, it is a promising material for the separation and purification of technetium. Thermodynamics of TMAP dissolution in aqueous solutions, the crystal structure of [Me
, and the possible ways of its conversion are essential for assessing the viability of the method for the treatment of technetium-containing waste. In addition to the issues of processing high-level radioactive waste, the structure of solid pertechnetates is of interest for modern inorganic chemistry. Nowadays, we see an important renaissance of pertechnetate-focused studies due to its role in spent nuclear fuel (SNF) reprocessing and being the old but still useful model for general chemistry upgrade [24, 25].
Understanding the patterns of interaction of technetium (VII) with nitrogen-containing compounds of various structures can be used to predict the behavior of radiopharmaceuticals in living organisms, calculate quantum-chemical interactions of technetium compounds, and plan further chemical studies. Weak intermolecular interactions are of particular interest from a theoretical point of view; the study of such interactions in pertechnetates and perrhenates of purines led to the discovery of a new type of chemical bond [26]. New methods for separating perrhenates and pertechnetates are based on nonvalent interactions [27, 28, 29, 30].
Transit Oriented Development By Jimena Veloz
And preliminary data on its structure and the structures of analogous compounds were described in our early works [2, 31, 32, 33]. However, TMAP crystals are sensitive to even small mechanical action provoking twinning the crystals, which led to a problem with space group attribution. It is necessary to redetermine TMAP structure using a modern equipment.
Therefore, the present study aims to measure the solubility of TMAP in water and aqueous solutions of nitric acid and to determine the thermodynamic characteristics of the dissolution process. It was also important to redetermine the crystal structure of solid TMAP and identify the major products of its thermolysis.
(4). In all these structures of tetraalkylammonium permetalates, hydrogen atoms were refined, in contrast to those previously known structures [34]. Still the structure solution quality for 3 and 4 is rather low, so it is not discussed in detail, and most attention given to its Hirshfeld surface analysis. We just mention here that the mean distances Tc–O are underestimated (see Supplementary data) that is evidently explained by liberation shortening in such a loose structure similarly to the explanation described in details in [35] for temperature effects. For comparison, similar data are provided for tetramethylammonium perrhenate crystals synthesized using a method similar to that described above. Selected bond lengths and bond angles are presented in Tables S1–S10.
Bristol's Covid Breakdown As Cases Double In A Week
Consists of tetramethylammonium cations and pertechnetate anions. The technetium atoms and two oxygen atoms occupy particular positions 4d on the mirror reflection plane and the N atoms of tetramethylammonium cations occupy particular positions 4c on the double axis. The average Tc–O distance in the pertechnetate ion is 1.678 Å, the O–Tc–O angles are close to tetrahedral. The precise data on pertechnetate anion geometry was erroneously considered as a pseudo-Jahn-Teller distorted pyramid earlier [31]. Nowadays, it is described as a slightly distorted tetrahedron.
In a crystal lattice of TMAP, every anion is surrounded by eight cations and vice versa. The salt is crystallized in the CsCl structure. The corresponding pseudocubic primitive cell has halved parameters b and c, i.e., a = 5.9320 Å, b = 6.0678 Å, c = 6.1140 Å. The distances between technetium and nitrogen atoms vary from 4.94 to 5.44 Å.
. The distances between atoms in both the salts are close to each other. The average Re–O distance in the perrhenate ion is 1.682 Å.
Pdf) Assessing Tourism Development: The Case Of Krusevo, Macedonia
According to modern ideas, the non-valence interactions are essential for the chemistry of the oxyanions of group 7 elements [36]. The interactions between tetraalkylammonium cations and pertechnetate anions affect the solubility of TMAP in aqueous solutions and its other physicochemical properties.
The analysis of intermolecular interactions in the structures of tetramethylammonium pertechnetate, perrhenate, and perchlorate was carried out on the basis of Hirshfeld surfaces that were calculated in the CrystalExplorer 17.5 program [37]. The structure of [Me
Obtained at 150 K. It was shown earlier that a temperature change in the range 150–300 K has little effect on the balance of interactions in the Hirshfeld surface analysis, provided that there are no phase transitions associated with a change in the hydrogen bond system [39].
Grant Maker Factsheet
Surface indicate the intermolecular interactions with the formation of weak hydrogen bonds C–H···O. Contributions of various types of intermolecular contacts in the Hirshfield surface are given in Table 1.
The prevalence of intermolecular contacts of O···H/H···O types with slight differences of 0.1% is characteristic for both TMAP and tetramethylammonium perrhenate. By contrast, the contribution of these interactions is lower for tetramethylammonium perchlorate (space group P 4/nmm with Z = 2, a = 8.238 ± 0.001 Å and c = 5.826 ± 0.001 Å at 210 K [38]). Probably, this is due to the smaller size of the perchlorate anion as compared with the pertechnetate and perrhenate anions.
To assess the effect of the size of the alkyl substituent, we have constructed Hirshfeld surfaces for tetrapropylammonium (TPA) and tetrabutylammonium (TBA) perrhenates, and TBA pertechnetate. Above, we considered the contribution of each type of interaction in cations and anions. Since in this case there were no disordered anions and there was one cation per anion, surfaces were constructed for all molecules in an asymmetric cell (Figure 2). In the literature, we have not found single crystal structural data for tetraethylammonium perrhenates or pertechnetates. We took the structure of tetrapropylammonium perrhenate from the work [40].
Jobs In Zimbabwe
With an
0 komentar
Posting Komentar