Electronegative Elements Research Articles

Healing clays: Mineralogical and geochemical constraints on the preparation of clay–water suspension (“argillic water”)

Clays have been long taken internally due to their sorption effects and the mechanical shielding developed by sheet morphologies. The purpose of this paper is the modelling of the mentioned traditional application in terms of chemical and mineralogical budget towards the body. Four polymineralic clays potentially suitable for therapeutic use were analysed for their mineralogical and geochemical composition. Quartz is always present, as well as feldspars, whereas carbonates are more variable (from trace levels, to about 40%). The clay mineralogy is characterised by mixed layers illite–smectite, kaolinite and illite. Most chemical elements show little anomalies compared to average shale [Turekian, K.K., Wedephol, K.H., 1961. Distribution of the elements in some major units of the earth's crust. Geological Society of America Bulletin, 72, 175–192], excluding Ca that is enriched according to the carbonate occurrence. Another geochemical feature is the depletion of more electronegative elements, among which very hazardous elements may be found. For the preparation of “argillic water”, the clays were dispersed in water and three suspensions were prepared to test the effect of settling time (5 min, 1 h, and 24 h). After the settling, the supernatant was centrifuged to analyse the solution and the particulate. The grinding of clays (a common practice for industrial uses) sensibly reduce the mineralogical selectivity of settling, nevertheless, quartz and feldspars are depleted during settling and phyllosilicates are enriched or fluctuate when the starting value is high; the carbonate content increases or decrease within a narrow interval. The grinding procedure minimises the different behaviour of clay minerals dispersed in water because the clay assemblage of suspended particulate does not show significant trends; only illite shows a slightly decrease. The solute composition is dominated by Na > Si > Ca > K > Mg. The comparison of the 4 clays indicates that the sample richest in mixed layers shows the highest content of many trace elements in solution. The variations of solution chemistry indicate that the less soluble elements decrease with the time of settling (e.g. Fe, Al, Mn): the elements hosted in organic matter or sulphides and soluble in oxidative media, increase with time (V, Mo, Sb, As). Many other elements are rather constant or at very low concentrations. The occurrence of sorptive minerals tends to hide these trends mainly during the first hour of settling. The chemical input to the body was calculated adding the amount of element in solution to the extractable amount from the digestion of particulates. The latter is based on the simulated digestion of clays taken from the literature. A critical point is the definition of a threshold that discriminates between useful and excessive ingestion of chemical elements. Since no reference models are available, the limit for drinking water was used. Considering that adults drink 2 l of water, the maximum daily dose for water was transformed into the amount of each chemical element considered by the law and compared with the amount available from the preparation of “argillic water”. Based on these results, the settling of clays can be tuned in order to emphasise the desired composition or to minimise side effects.

A First-Principles Investigation of LiNH2 as a Hydrogen-Storage Material: Effects of Substitutions of K and Mg for Li

Li-N-H compounds hold promise as novel hydrogen-storage materials with high gravimetric hydrogen densities. Because the dehydriding reaction caused by the decomposition of LiNH(2) requires a higher temperature than desired, much effort has been devoted to the destabilization of LiNH(2) to decrease the decomposition temperature. In particular, there has been recent experimental evidence for lowering the temperature by partial substitution of Li by Mg. However, the reason is not clear. In this study, we have employed density functional theory to investigate LiNH(2) and partially Li-substituted systems aiming to understand the effects of the substitution on the destabilization of the NH(2) species. K, a more electropositive element, and Mg, a more electronegative element, have been chosen as two probes to illustrate the effects. We have focused on the investigation of effects of substitutions on the N-H bond strength that is regarded as a qualitative indicator of the decomposition temperature. We have found that in both cases the N-H bonds are weakened, in particular, the Mg substitute appears to be more effective in the destabilization of the NH(2). The relative strength of the metal-N ionic bonding has been found to be a key factor to explain the effects of the substitutes. These have been discussed in detail in terms of Wannier function analyses.

A Hybrid Poly(ethylene oxide)/ Poly(vinylidene fluoride)/TiO2 Nanoparticle Solid‐State Redox Electrolyte for Dye‐Sensitized Nanocrystalline Solar Cells

AbstractHigh‐efficiency all‐solid‐state dye‐sensitized nanocrystalline solar cells have been fabricated using a poly(ethylene oxide)/poly(vinylidene fluoride) (PEO/PVDF)/TiO2‐nanoparticle polymer redox electrolyte, which yields an overall energy‐conversion efficiency of about 4.8 % under irradiation by white light (65.2 mW cm–2). The introduction of PVDF (which contains the highly electronegative element fluorine) and TiO2 nanoparticles into the PEO electrolyte increases the ionic conductivity (by about two orders of magnitude) and effectively reduces the recombination rate at the interface of the TiO2 and the solid‐state electrolyte, thus enhancing the performance of the solar cell.

Bonding configuration and electrical properties of nitrogen and fluorine incorporated SiOC:H thin film prepared by plasma enhanced chemical vapor deposition

In this study, the organosilicate glass (OSG) incorporated with nitrogen and fluorine (N-F:OSG) was investigated by examining the bonding configuration, refraction index, modulus, permittivity and breakdown field strength. The results of Fourier transform infrared spectroscopy show that Si–O, Si–C, Si–N, and Si–F are the major bonding in the N-F:OSG films. The XPS analysis shows that the Si 2p, F 1s, and N 1s core levels of the N-F:OSG film shifts to higher binding energy due to the neighborhood bonding of higher electronegative elements. For electrical properties, the permittivity and breakdown stress of the N-F:OSG are comparable with the OSG film accompanied with superior mechanical hardness to the OSG film.

Basis Set Requirements for Sulfur Compounds in Density Functional Theory: a Comparison between Correlation-Consistent, Polarized-Consistent, and Pople-Type Basis Sets

We have investigated the SX (X = first- or second-row atom), SO2, and SO3 molecules employing the correlation-consistent (cc), the recently developed polarization-consistent (pc), and three Pople-type basis sets, in conjunction with the B3LYP functional. The results confirmed that the aug-pc basis sets represent a great contribution in terms of cost-benefits. In the case of the B3LYP functional, when employing the aug-pc-3 and aug-pc-4 basis sets, it is possible to obtain results that are of aug-cc-pV(5+d)Z and aug-cc-pV(6+d)Z quality, respectively, at a much lower cost. The estimations obtained employing smaller members of the family are of nearly double-ζ quality and do not provide reliable results. There is no basis set of quadruple-ζ quality among the polarized-consistent basis sets, although in terms of composition, the aug-pc-3 basis set is a QZ basis set. A precise estimation of the Kohn-Sham complete basis set (CBS) limit with the aug-pc-X basis sets is too difficult for the B3LYP functional because the ∞(aug-pc-4, aug-pc-3, aug-pc-2) extrapolation gives the same results as those of the aug-pc-4 basis set. This is in contrast with the results observed for ab initio methodologies for which the largest basis sets provided the best estimation of the CBS limit. In our opinion, the closest results to the B3LYP/CBS limit are expected to be those obtained with a two-point extrapolation employing the aug-cc-pV(X+d)Z (X = 5, 6) basis sets. The results obtained with this extrapolation are very close to those predicted by the ∞(aug-pc-3, aug-pc-2, aug-pc-1) extrapolation, and that provides a cheaper but more inaccurate alternative to estimate the CBS limit. Minor problems were found for the aug-pc-X basis sets and the B3LYP functional for molecules in which sulfur is bound to a very electronegative element, such as SO, SF, SO2, and SO3. For these molecules, the cc basis sets were demonstrated to be more useful. The importance of tight d functions was observed; the total atomization energy of SO2 employing the cc-pV6Z basis set is 1 kcal/mol lower than that obtained with the aug-cc-pV(6+d)Z basis set.

First-principles study on copper-substituted lithium borohydride, (Li 1− xCu x)BH 4

Our recent analysis using the first-principles calculations for LiBH 4 [K. Miwa, N. Ohba, S. Towata, Y. Nakamori, S. Orimo, Phys. Rev. B 69 (2004) 245120], which is rather stable and desorbs hydrogen only at elevated temperatures, reveals that the charge compensation by Li + cations is a key feature for the stability of the internal bonding [BH 4] − anions. Considering this character, we have proposed the partial substitution of more electronegative elements for Li to lower the dehydriding temperature. The effect of the cation substitution is examined theoretically. We select copper as a substituent element, since the ionic radii of Cu + and Li + are almost the same but the electronegativity of Cu is larger than that of Li. Assuming the same crystal structure as orthorhombic LiBH 4, the calculations on (Li 1− x Cu x )BH 4 are performed for x = 0.25 , 0.5, 0.75, and 1. It is confirmed that the heat of formation increases with increasing the Cu content x. The optimum x is predicted to be around x = 0.3 for practical applications.

Synthesis of Fluoro Analogues of Unsaturated Fatty Acids and Corresponding Acyclic Metabolites

AbstractFor Abstract see ChemInform Abstract in Full Text.

Investigations of corrosion phenomena on gold coins with SIMS

In order to establish a new handling procedure for contaminated coins, the Coin Cabinet and the Conservation Science Department of the Kunsthistorisches Museum, Vienna, initiated a research project on corrosion effects of gold coins. By now, investigations on historic and contemporary coins included optical microscopy, scanning electron microscopy (SEM), Auger electron microscopy (AES), X-ray photoelectron microscopy (XPS), and electrochemical methods showing the distribution of pollutants. This work focuses on secondary ion mass spectrometry (SIMS) investigations merely showing the distribution of electronegative elements, such as sulfur, oxygen, and chlorine on the surface. Sulfur is highly suspected of causing the observed corrosion phenomena, and is indeed enriched near polluting splints. Since SIMS is a destructive method, the investigated samples are test coins with intentionally added impurities. These coins were manufactured in cooperation with the Austrian Mint. They were treated with potassium polysulfide (K 2S x ) for 8 h gaining a rapid corrosion of the surface. SIMS mass spectra, depth profiles, and images were done (a) at non-polluted areas, (b) near polluted areas with slight coloring, and (c) directly at polluting stains showing enrichments of sulfur and chlorine. Due to the success of these investigations further studies on historic coins are intended.

Synthesis of Fluoro Analogues of Unsaturated Fatty Acids and Corresponding Acyclic Metabolites

AbstractPolyunsaturated fatty acids, in particular arachidonic acid and its metabolites, the so‐called eicosanoids, play a major role in human health. Many of them have been involved as potent mediators for various diseases such as inflammation and asthma. Therefore, numerous modifications in the structures of these natural products have been incorporated to study the structure‐activity relationship, monitor the biosynthetic pathway and also to understand the biological activities as well as the mechanisms of action. The modifications include introduction of labelled elements, fluorine atoms, heteroelements, carbo‐ and heterocycles etc. Of all these studies, the introduction of fluorine, which has a unique role as the smallest atom in the periodic table after hydrogen and also as the most electronegative element, provided very useful information. Thus, the present microreview highlights the synthetic efforts of various research groups in the last two decades on bioactive fluorinated fatty acids and corresponding acyclic metabolites. It also presents the most relevant bioactivity data obtained from the fluorinated analogues. The data corresponding to naturally occurring fluorinated fatty acids have been added, as well as the use of fluorinated probes for some biosynthetic studies in fatty acid chemistry (desaturation and methylenation). In addition, it is important to point out that the methods and strategies which have been developed to selectively introduce a single fluorine atom, as well as CF2 or CF3 groups, on such very challenging molecules could also be of much use in many other areas of chemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Calculation of the surface binding energy for ion sputtered particles

In this paper, we consider a simple model, based on the electronegativity concept, which makes it possible to calculate the surface binding energy of any particles, sputtered from a solid surface by ion bombardment. The model contains empirical equations for calculation of “ionic” and “covalent” parts of the binding energy happened between a surface atom and its close neighbors. The model is strongly desirable in the case of the ion sputtering of any strong electronegative (C, N, O, F, Cl, etc.) or electropositive elements (alkali metals, rare earth elements) from semiconductor surfaces, when the strong ionic binding between these elements and the surface atoms can be estimated.

Oxidative Reactions and Degradations of Sugars and Polysaccharides

AbstractFor Abstract see ChemInform Abstract in Full Text.

Cesium/xenon dual beam depth profiling with TOF-SIMS: measurement and modeling of M +, MCs +, and M 2Cs 2+ yields

Using Cs + in the TOF-SIMS dual beam mode offers a semi-quantitative solution to depth profiling. Specifically, the use of these alkali ions strongly increases negative ion yields, decreases the positive ones and allows the formation of MCs + and MCs 2 + clusters. Recently, Niehuis and Grehl [Proceedings SIMS XII (2000) 49] developed a new approach consisting of co-sputtering Xe and Cs in order to control the Cs surface concentration, thus allowing the optimization of elemental and cluster ion yields. We applied that technique on different well-defined samples (e.g. Si, SiO 2 and Al 2O 3) and we monitored positive ions (e.g. Si +, Al +, CsSi +, CsAl +, CsO +, Cs 2O +, Cs 2Si +, etc.) as a function of the sputtering beam Cs concentration. First, we observed the decrease of the elemental ions due to the work function lowering, as is predicted by the tunneling model. We then studied the behavior of the MCs + and the MCs 2 + clusters. The MCs + yield exhibits a maximum at a given Cs/Xe beam concentration ratio, depending on the studied element M and also on its chemical environment (e.g. Si and SiO 2), and on the energy of the Cs beam. In other words, it is hypothesized that this yield maximum is a consequence of the competition between the varying surface Cs coverage (direct concentration effect) and the decreasing ionization probability due to that varying Cs [Phys. Rev. Lett. 50 (1983) 127; Phys. Rev. B 29 (1984) 2311; K. Wittmaack, Proceedings SIMS VIII, (1992) 91]. Simple models based on the tunneling model were applied to interpret our results. The MCs 2 + signal behaves in a very different way. As shown by Gao [Y. Gao, Y. Marie, F. Saldi, H.N. Migeon, Proc. SIMS IX, (1994) 382], these clusters are predominant for electronegative elements and increase in a monotonous way with Cs beam concentration.

Spectroscopy of excited particles sputtered by ion bombardment of Zn, Cd, and chemical compounds of these metals

The main parameters of optical emission (spectra, excitation and population efficiencies of levels, and kinetic energies) of excited particles sputtered by a beam of Ar+ ions from the surfaces of Zn, Cd, and chemical compounds of these metals with electronegative elements (O, Te, Se, and S) are studied. It is shown that, upon ion bombardment of the compounds of the metals under investigation, an additional mechanism of formation of excited particles arises in comparison with the bombardment of pure Zn and Cd. This mechanism, related to the ionicity of chemical bonds, leads to inconsistency between the yield of excited particles and the sputtering coefficient of the corresponding material. The effect of the electronic structure of a solid on the yield of excited particles and their velocity distribution is also revealed.

Cesium/xenon dual beam depth profiling with TOF-SIMS: measurement and modeling of M+, MCs+, and M2Cs2+ yields

Using Cs+ in the TOF-SIMS dual beam mode offers a semi-quantitative solution to depth profiling. Specifically, the use of these alkali ions strongly increases negative ion yields, decreases the positive ones and allows the formation of MCs+ and MCs2+ clusters. Recently, Niehuis and Grehl [Proceedings SIMS XII (2000) 49] developed a new approach consisting of co-sputtering Xe and Cs in order to control the Cs surface concentration, thus allowing the optimization of elemental and cluster ion yields. We applied that technique on different well-defined samples (e.g. Si, SiO2 and Al2O3) and we monitored positive ions (e.g. Si+, Al+, CsSi+, CsAl+, CsO+, Cs2O+, Cs2Si+, etc.) as a function of the sputtering beam Cs concentration. First, we observed the decrease of the elemental ions due to the work function lowering, as is predicted by the tunneling model. We then studied the behavior of the MCs+ and the MCs2+ clusters. The MCs+ yield exhibits a maximum at a given Cs/Xe beam concentration ratio, depending on the studied element M and also on its chemical environment (e.g. Si and SiO2), and on the energy of the Cs beam. In other words, it is hypothesized that this yield maximum is a consequence of the competition between the varying surface Cs coverage (direct concentration effect) and the decreasing ionization probability due to that varying Cs [Phys. Rev. Lett. 50 (1983) 127; Phys. Rev. B 29 (1984) 2311; K. Wittmaack, Proceedings SIMS VIII, (1992) 91]. Simple models based on the tunneling model were applied to interpret our results. The MCs2+ signal behaves in a very different way. As shown by Gao [Y. Gao, Y. Marie, F. Saldi, H.N. Migeon, Proc. SIMS IX, (1994) 382], these clusters are predominant for electronegative elements and increase in a monotonous way with Cs beam concentration.

On the appearance of induced magnetic moment of β-FeSi 2 by doping halogen or oxygen atoms

We have theoretically examined whether magnetic moment of iron atom can be induced or not when highly electronegative elements such as halogen or oxygen atoms are doped. Based on the impurity Anderson model, we evaluated the green function of d electrons. Through the analysis of green function, it is disclosed that a magnetic moment can be induced by impurity potential caused from doping elements, although intrinsic β-FeSi 2 is non-magnetic. In particular, high electronegativity of doping atoms and/or strong Coulomb repulsive interaction between conduction electrons and doped atoms easily induce magnetic moment from non-magnetic state. In the viewpoint of chemical bonding, such an induced magnetic moment appears as a result of decomposition of covalent FeSi bonds by a strong electronegative impurity potential, because the broken bonds create the unpaired 3 d electrons.

Microstructural development in equiatomic multicomponent alloys

Abstract Multicomponent alloys containing several components in equal atomic proportions have been manufactured by casting and melt spinning, and their microstructures and properties have been investigated by a combination of optical microscopy, scanning electron microscopy, electron probe microanalysis, X-ray diffractrometry and microhardness measurements. Alloys containing 16 and 20 components in equal proportions are multiphase, crystalline and brittle both as-cast and after melt spinning. A five component Fe20Cr20Mn20Ni20Co20 alloy forms a single fcc solid solution which solidifies dendritically. A wide range of other six to nine component late transition metal rich multicomponent alloys exhibit the same majority fcc primary dendritic phase, which can dissolve substantial amounts of other transition metals such as Nb, Ti and V. More electronegative elements such as Cu and Ge are less stable in the fcc dendrites and are rejected into the interdendritic regions. The total number of phases is always well below the maximum equilibrium number allowed by the Gibbs phase rule, and even further below the maximum number allowed under non-equilibrium solidification conditions. Glassy structures are not formed by casting or melt spinning of late transition metal rich multicomponent alloys, indicating that the confusion principle does not apply, and other factors are more important in promoting glass formation.

Metals and Hydrogen Bonds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ternary graphite intercalation compounds associating an alkali metal and an electronegative element or radical

Ternary graphite intercalation compounds associating an alkali metal and an electronegative element are described. The synthesis is more often realized in molten alkali metal media containing the associate electronegative element or radical in the adequate concentration. The intercalated sheets are systematically polylayered. The arrangement along c-axis and the in-plane structures are described. The physical properties of the compounds are precised.

Effect of adsorption of electronegative and electropositive elements on the surface optical anisotropy of GaAs(001)

Surface optical anisotropy of GaAs(001) is extremely sensitive to adsorption of electropositive and electronegative atoms. The oxygen-induced experimental changes of the reflectance anisotropy spectrum of the As-rich (2 × 4) surface are interpreted using ab initio calculations. We conclude that oxygen adsorption, contrary to previous beliefs, does not quench all surface-related optical transitions, but only those for which the initial state is surface-related. Alkali metal (AM) adsorption is found to induce a strong negative signal in the 3.5 eV–5 eV range, weakly dependent on surface reconstruction and AM nature, whose origin is discussed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Zintl-Klemm concept applied to cations in oxides. I. The structures of ternary aluminates.

The structures of 94 ternary aluminates are reinterpreted on the basis of the Zintl-Klemm concept and Pearson's generalized octet rule. In aluminates of highly electropositive metals such as alkali, alkaline-earth and rare-earth metals, the Al atoms form three-dimensional skeleta which can be interpreted as if the Al atoms were behaving as Zintl polyanions, adopting the structure of either main-group elements or Zintl polyanions showing the same connectivity. The O atoms are then located close to both the hypothetical two-electron bonds and the lone pairs, giving rise to a tetrahedral coordination. When more electronegative elements, such as W or Si, are present in the compound, the electron transfer towards the Al atoms does not take place. In this case, aluminium behaves as a base, transferring its electrons to the more electronegative atoms and the coordination sphere of aluminium becomes octahedral. In some compounds the Al atoms clearly show amphoteric character so that some Al atoms act as donors (bases) and hence are octahedrally coordinated, whereas others behave as acceptors (acids), adopting a tetrahedral coordination. From this it is concluded that the coordination sphere of aluminium is not a function of the ionic radius of the Al(3+) cations, but it depends on the nature of the other cations accompanying them in the structure. The networks formed by these aluminates are, in many instances, similar to those of the binary oxides of the main-group elements. For this reason, a systematic survey of these oxides is also reported. Compounds such as stuffed cristobalites and trydimites and also perovskites are examples of this new interpretation. Perovskites are then reinterpreted as a stuffed pseudo-TeO(3) structure. Other families of compounds such as silicates and phosphates are susceptible to a similar interpretation. This study provides additional examples of how cations recognize themselves in spite of being embedded in an oxygen matrix.