Study on the influence of X-ray tube spectral distribution on the analysis of bulk samples and thin films: Fundamental parameters method and theoretical coefficient algorithms

Knowledge of X-ray tube spectral distribution is necessary in theoretical methods of matrix correction, i.e. in both fundamental parameter (FP) methods and theoretical influence coefficient algorithms. Thus, the influence of X-ray tube distribution on the accuracy of the analysis of thin films and bulk samples is presented. The calculations are performed using experimental X-ray tube spectra taken from the literature and theoretical X-ray tube spectra evaluated by three different algorithms proposed by Pella et al. (X-Ray Spectrom. 14 (1985) 125–135), Ebel (X-Ray Spectrom. 28 (1999) 255–266), and Finkelshtein and Pavlova (X-Ray Spectrom. 28 (1999) 27–32). In this study, Fe–Cr–Ni system is selected as an example and the calculations are performed for X-ray tubes commonly applied in X-ray fluorescence analysis (XRF), i.e., Cr, Mo, Rh and W. The influence of X-ray tube spectra on FP analysis is evaluated when quantification is performed using various types of calibration samples. FP analysis of bulk samples is performed using pure-element bulk standards and multielement bulk standards similar to the analyzed material, whereas for FP analysis of thin films, the bulk and thin pure-element standards are used. For the evaluation of the influence of X-ray tube spectra on XRF analysis performed by theoretical influence coefficient methods, two algorithms for bulk samples are selected, i.e. Claisse–Quintin (Can. Spectrosc. 12 (1967) 129–134) and COLA algorithms (G.R. Lachance, Paper Presented at the International Conference on Industrial Inorganic Elemental Analysis, Metz, France, June 3, 1981) and two algorithms (constant and linear coefficients) for thin films recently proposed by Sitko (X-Ray Spectrom. 37 (2008) 265–272).     

Variation of the L X-ray fluorescence cross-sections, intensity ratios and fluorescence yields of Sm and Eu in halogen compounds

The chemical effect on the L_i (i=ι, α, β, β₁, β₂, γ) X-ray fluorescence cross-sections, the L X-ray intensity ratios and the average L shell fluorescence yields of Sm and Eu binary compounds with halogen (F, Cl and Br) were investigated. The samples were excited by 59.543 keV photons emitted from an Am-241 radioisotope source. X-rays emitted from the samples were counted by means of a Si(Li) detector, which has a resolution 155 eV at 5.9 keV. The experimental values were compared with the calculated theoretical values     

Determination of water content in silica nanopowder using wavelength-dispersive X-ray fluorescence spectrometer

A wavelength-dispersive X-ray fluorescence (WDXRF) technique that uses the scattered radiation of the X-ray tube lines and the fluorescence radiation of an element present in a powder sample is proposed as a non-destructive method for the determination of the water content in silica powder. Although direct X-ray fluorescence analysis of water using WDXRF is not adequate for the quantitative determination of water in powder, due to the very low fluorescence yield for hydrogen and oxygen, the fluorescence signal of silicon (Si) in silica powder is attenuated by water, and is shown to decrease in proportion to the water content in silica powder. In addition, it is demonstrated that the Compton- and Rayleigh-scattering of the X-ray tube lines is proportional to the water content. The coefficients of determination, R², of the linear regression equations obtained from the calibration curves for all individual scattered radiations and for the fluorescence radiation of Si were > 0.90. The sum of the peak intensities of the four scattering signals, i.e. the Rayleigh-scattered Rh K–L_2,3 and Rh K–M_2,3 lines, and Compton-scattered Rh K–L_2,3 and Rh K–M_2,3 lines, also showed fairly good linearity and sensitivity over a very wide range of water content from 0 wt.% to 61.5 wt.%. However, porosity had a significant effect on the X-ray signal at low water content, in the range from 0 wt.% to 7.5 wt.%, where the sensitivity for the silica nanopowder with well-defined mesopores (~ 3 nm in diameter) decreased to 0.40 kcps/wt.%, from 0.99 kcps/wt.% for the non-porous silica nanopowder. The use of the Si fluorescence signal along with the scattered radiation of the X-ray tube lines expands the applicability of conventional XRF spectrometers to the quantitative determination of water content in silica powder.     

Evaluation of the interelemental effect in X-ray fluorescence analysis by the total addition method

Summary An algorithm for quantifying interelemental effects in X-ray fluorescence techniques is developed. By applying an addition process, the ratio between the mass absorption coefficients of the analyte and the unknown sample ( _i ^* / _s ^* ) is calculated to correct the fluorescence intensity of the element to be determined and linearize the I-c calibration plot. This coefficient can be calculated graphically and numerically. The method is applied to the determination of tin in lead alloys with good results over wide concentration ranges.Notation used Q Constant of proportionality in Eq. (4) X-ray fluorescence intensity of the I _i ^o standard - I _i ^s unknown sample - I _i ^ns dilute unknown sample - I _i ^ms unknown sample after addition of i analyte Corrected fluorescence intensity of the I _i ^cs unknown sample - I _i ^msc unknown sample after addition of i analyte Relationship of fluorescence intensity between R_i sample and standard - R _i dilute sample and standard Factor of f_m addition - f_x addition equivalent to the mass fraction of the i analyte in the unknown sample Mass absorption coefficient of _i ^* analyte - _s ^* unknown sample - _ms ^* unknown sample after addition Mass fraction of c _i ^s analyte - c _i ^ms unknown sample after addition     

The structure of octachloropentafulvalene

The structure of octachloropentafulvalene has been redetermined by a 3-dimensional X-ray crystallographic analysis. The space group is monoclinic, C2/c, and cell parameters are a = 14·998, b= 7·9110, c= 11·8068 Å, β= 103·38°. The X-ray intensity data were measured on a computer-controlled diffractometer using Mo radiation. The least-squares structure refinement used anisotropic temperature factors for C and Cl and gave a final R of 0·036. Corrections were applied for absorption, Cl dispersion and secondary isotropic extinction. The central CC is twisted by 37° as a result of Cl?Cl repulsions from one C₅Cl₄ half to the other. The central CC length, 1·365 Å, is only slightly larger than the standard 1·34 Å ethylenic value. The bond distance increase can be explained in terms of a decrease in π-bond character accompanying the CC twist. Carbon-carbon distances in the 5-ring have typical values for the cyclopentadienylidene moiety; there is no evidence for single-double bond delocalization.     

Analysis of painted steel by a hand-held X-ray fluorescence spectrometer

Steel with a paint layer was analyzed with a hand-held X-ray fluorescence spectrometer. When the 0.5 mm thick paint layer was composed mainly of light elements, alloying elements in steel such as Fe, Cr, Ni, W, and Mo were easily detected. 0.2% Mo in steel was detectable even if the paint contained Ti or Fe as a main element. The signal intensity of each element in steel decreased exponentially when the paint thickness increased, and the degree of decrease depended on the X-ray energy. Therefore the peak intensity for non-painted steel could be calculated from the paint thickness. The paint thickness was estimated from the intensity ratio Fe Kβ/Kα or W Lβ/Lα. When a paint of Ti (0.07–0.49 mm thick) was used, the peak intensities of the Fe Kα, Cr Kα, Ni Kα, and Mo Kα lines for non-painted steel were estimated by using the intensity ratio Fe Kβ/Kα, with errors of less than 30%. The content of each element in steel is estimated when the fluorescent X-rays are detectable by analysis of painted steel without removing the paint layer. On-site screening of painted steel can be performed on the basis of the alloy composition estimated by analysis with a hand-held XRF spectrometer.     

Standardless energy-dispersive X-ray fluorescence analysis using primary radiation monochromatized with LiF(200) crystal

Energy-dispersive X-ray fluorescence spectrometer (EDXRF) with primary radiation monochromatized by LiF(200) crystal was developed. In the constructed spectrometer, the radiation from the Ag target X-ray tube operated at 50 kV and 40 mA excites the secondary target (Cu, Se, Zr or Mo). The characteristic radiation (Cu K_α, Se K_α, Zr K_α or Mo K_α) of the target is monochromatized with LiF(200) crystal and excites elements in the analyzed sample. The X-ray spectra are collected by thermoelectrically cooled Si-PIN detector with resolution of 145 eV at 5.9 keV. The pinhole collimator placed in front of the X-ray detector allows reducing size of the analyzed area. Quantitative analysis is performed using standardless fundamental parameters (FP) method. Because sample is excited using highly monochromatized radiation, the calculations are much simpler and analysis error resulting from uncertainty of X-ray tube spectral distribution is completely eliminated. Moreover, EDXRF system allows obtaining very low background and appropriate secondary target can be selected for the best excitation of the determined elements and to avoid overlapping of the analyte peaks with characteristic radiation originating from the secondary target. The FP calculations were verified using several certified reference materials of stainless steel. The spectrometer was used for nondestructive analysis of mono- and polycrystals of selenide spinels of general formula M_xN_yCr_zSe₄ (where M, N are Cu²⁺, Zn²⁺, Cd²⁺, Mn²⁺, Ge²⁺, Ni²⁺, V³⁺, Sb³⁺, Ga³⁺). The results from EDXRF were compared with those obtained by means of the wavelength-dispersive X-ray fluorescence spectrometry (WDXRF).     

Thermal decomposition of novel rare-earth selenites

TG and DTA have been carried out on new anhydrous rare-earth selenites R₂Se_aO_3+2a (a=3.5,4) in order to establish their stability. Decomposition occurs in three steps attributed to successive losses of SeO₂. The first process gives rise to other new group of selenites of composition R₂Se₃O₉, which crystallize in two different forms depending on the rare-earth element. The second process leads to isomorphous compounds R₂SeO₅. The final product of thermal degradation is R₂O₃. All products were characterized by chemical analysis and X-ray powder diffraction methods.     

Conductance of nano-tube junctions and its scaling law

The conductance is calculated by Landauer’s formula with a simple tight binding model for junctions connecting two different metallic carbon nanotubes. These junctions are formed by a pair of disclinations, a 5-membered ring and a 7-membered ring, without dangling bonds. Conductances of about eight hundred kinds of junctions are obtained. The conductance is determined only by the ratio i/R where i is the distance between the two disclinations and R is the circumference of the thinner tube. When i/R ? 1, the conductance is found to be almost proportional to (i/R)^-3. Even when the Fermi energy is shifted by doping, an extended scaling law holds, so far as the channel number is kept two.     

A calculated background correction method for XRF

A special type of glass discs—prepared of sodium tetraborate with varying concentrations of only one element—are used for the calibration of XRF spectrometers. The same glass discs are used for the determination of background influence coefficients F_i,j which makes it possible to calculate the background signal in the unknown samples concerning the analyte (i) when only the characteristic radiation from the interfering elements (j) are measured together with the i-signal on a blank disc of pure sodium tetraborate. The determination of strontium is used as an example.     

Structure and molecular interactions in {ethanol + (propan-1-ol/propan-2-ol)} mixtures at 303.15 K

In view of industrial importance of binary {ethyl alcohol + (propan-1-ol/propan-2-ol)} mixtures, the densities (ρ) and refractive indices (n _D ) of these alkanols mixtures were measured for different compositions at 303.15 K. Molar volumes (V _m) and excess molar volumes (V ^E) of these binary mixtures were calculated from experimental density data of pure solvents and solvents mixtures. The measured refractive index and density data was used to calculate specific refractions (R _D ), molar refractions (R _M) and apparent molar refractions (R _{φ, i} ) of binary mixtures. From mole fraction dependence of apparent molar refractions, the limiting apparent molar refractions (R _{φ, i} ^○ ) of propan-1-ol and propan-2-ol have been determined. The graphical values of R _{φ, i} ^○ for propan-1-ol and propan-2-ol were found to be 9.5664 and 7.405 cm³ mol^?1 respectively. Structural changes, geometrical fittings and molecular interactions in binary mixtures of these alkanols have been discussed.     

The site preference and doping effect on mechanical properties of Ni3Al-based γ′ phase in superalloys by combing first-principles calculations and thermodynamic model

The fundamental aspects of site preference of alloying elements on sublattice of the strengthen γ′ phase with L1₂ structure have not been well understood, which hinders the optimized design of advanced Ni-based high-temperature alloys. In this contribution, the temperature- and composition-dependent site occupying preferences of the binary, ternary, and quaternary of Ni₃Al-based γ′ phase alloyed with M_i where M_i represents the additional transitional metals Co, Cr, Cu, Fe, Mn, Mo, Re, Ta, Ti, V, or W atoms (arranged in alphabetical order) chosen frequently, were studied using a two-sublattice thermodynamic model (Ni, Al, M_i)_1a(Ni, Al, M_i)_3c. The site occupying fractions (SOFs) were calculated based on a thermodynamic database established in this work, where the thermodynamic data of the end-members involved were obtained using first-principles calculations and phonon spectrum calculations. The calculated SOFs results show that there is an obvious site preference for stoichiometry binary Ni₃Al, and its site configuration changes from (Al)_1a(Ni)_3c at room temperature to (Al_0.9984Ni_0.0015)_1a (Al₀Ni_0.9994)_3c at 1273 K. For the γ′ phase with the composition 78Ni-26Al-4M_i (atom ratio and x_Ni/x_Al = 3:1), Mo atoms always preferred to occupy the 1a sublattice (Al site), Co, Mn, and Ti atoms always prefer the 3c sublattice (Ni site) in the whole temperature range, while the site preference of Cr, Cu, Fe, Re, Ta, V, or W atom is affected by temperature. For example, when the heat treatment temperature is lower than 700 K, Cr, Cu, Fe, Ta, V, and W atoms occupy the 1a and 3c sublattice randomly, and Re atoms prefer to 3c sublattice, while when the heat treatment temperature is higher than 1273 K, Cr, Cu, and W atoms prefer 3c sublattice, Fe and Ta atoms prefer to 1a sublattice, while all Re atoms occupy the 3c sublattice exclusively, and all V atoms occupy the 1a sublattice exclusively, respectively. Likewise, the site preference of the quaternary system with selective compositions 78Ni-26Al-2 M₁-2 M₂ was also predicted. Based on calculated SOFs results, the mechanical and thermodynamic properties were studied at the ground state. It has been revealed that Cr, Re, and V doping can improve the microhardness of Ni₃Al alloys; in particular, the effect of Cr is extraordinary; and all elements, except Mn, Mo, and Ti, would enhance the bulk modulus of Ni₃Al-based γ′ phase, in which Mn have the greatest influence on reducing the bulk and shear modulus, respectively. Furthermore, all the B/G ratios of the computed Ni₃Al-based γ′ phase are >1.75, showing inherent ductility. Only Cr doping significantly enhances the Debye temperature of the Ni₃Al-based γ′ phase.     

Molecular ordering in some liquid aromatic hydrocarbons

This study presents a comparison of the structures and molecular correlations for the linear aromatic hydrocarbons: benzene, naphthalene, and anthracene in the liquid phase, performed for the first time by the method of X-ray diffraction. Also for the first time the X-ray diffraction results obtained for anthracene at 513?K have been reported. Monochromatic radiation CuK_α was used to determine the scattered radiation intensity between S _min?=?4π?sin?Θ_min/λ?=?0.417?Å^?1 and S _max?=?4π?sin?Θ_max/λ?=?7.06?Å^?1. The mean angular distributions of X-ray scattered intensity were measured and the differential radial distribution functions of electron density (DRDFs) were calculated. The mean distances between the neighbouring molecules and the mean coordination numbers were found. The most probable models of local ordering of these molecules were suggested. Correlations have been found between the number of benzene rings in the molecules studied and their physical properties.     

Chemical-effect variation of Kβ/Kα X-ray intensity ratios in 3d elements

Chemical effects on Kβ/Kα X-ray intensity ratios for some Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn compounds are studied experimentally. The X-ray spectra were measured by using a Si (Li) solid state detector with high resolution. The vacancies were produced by heavily filtered ²⁴¹Am gamma rays. It is found that the Kβ/Kα X-ray intensity ratios measured with compounds deviated up to 43% from the corresponding values of the pure elements. The values for pure elements are compared with the other experimental and with theoretical values.     

Asymmetric nitrogen

The¹H NMR spectra ofO-derivatives of 1-hydroxy-2,2-bis(trifluoromethyl)aziridine containing such substituents as EtO₂CCH₂, (R/S)-RO₂CCH(Me) (R=Me, Prⁱ, or Bu^t), (R/S)-H₂NC(O)CH(Me), and (R)-H₂NC(O)CH(Me) were analyzed. Both of the diastereomerically pure amides of the latter type were isolated. The validity of the¹H NMR criteria, which were suggested for the determination of absolute configurations of diastereomers ofN-alkoxyaziridines, was confirmed by X-ray diffraction study of the (R,R)-amide.     

A theoretical study on the strength of multiple metal-metal bonds in binuclear complexes and transition-metal dimers by a non-local density functional method

The strength of multiple metal-metal bonds in the metal dimers M₂ (M = Cr, Mo or W) and binuclear complexes M₂(OH)₆ (M = Cr, Mo or W), M₂Cl₄(PH₃)₄ M = V, Cr, Mn, Nb, Mo, Tc, Ta, W or Re) has been studied by a non-local density functional theory. The method employed here provides metal-metal bond energies [D(M-M)] in good accord with experiments for Cr₂ and Mo₂, and predicts that W₂ of the three dimers M₂ (M = Cr, Mo or W) has the strongest metal-metal bond with D(W-W) = 426 kJ mol⁻¹ and R(W-W) = 2.03 Å. Among the binuclear complexes studied here we find the 3d elements to form relatively weak metal-metal bonds (40–100 kJ mol⁻¹), compared to the 4d and 5d elements with bonding energies ranging from 250 to 450 kJ mol⁻¹. The metal-metal bond for a homologous series is calculated to be up to 100 kJ mol⁻¹ stronger for the 5d complex, than for the 4d complex. An energy decomposition of D(M-M) revealed that the σ-bond is somewhat stronger than each of the π-bonds, and one order of magnitude stronger than the δ-bond. For the same transition metal we find D(M-M) to be larger for M₂(PH₃)₄Cl₄ (M = Cr, Mo or W) than for M₂(OH)₆ (M = Cr, Mo or W), and attribute this to a stronger π-interaction in the former series. While many of the findings here are in agreement with previous HFS studies, the order of stability D(3d-3d) « D(4d-4d) < D(5d-5d) differs from the order D(3d-3d) « D(5d-5d) < D(4d-4d) obtained by the HFS method, and the present method provides in general more modest values for D(M-M) than the HFS scheme.     

In situ Ru K-edge X-ray absorption spectroscopy of a high-area ruthenium dioxide electrode in a Nafion-based supercapacitor environment

Changes in the state of charge of a high-area RuO_x electrode in an operating RuO_x|Nafion|IrO_x supercapacitor were monitored in situ by time-resolved, transmission Ru K-edge X-ray absorption spectroscopy (XAS). Linear and reversible variations in the intensity of the transmitted X-ray beam as a function of time were found by fixing the energy of the incident X-ray beam, E_i, at judiciously selected values within the Ru K-edge X-ray near edge structure (XANES), while the supercapacitor was charged and discharged at constant current. The sign of the slope of these temporal signals was found to vary, depending on the value of E_i. This behavior could be rationalized based on the spectral differences between the Ru K-edge XANES of RuO_x in the fully oxidized and fully reduced states, recorded in situ from films of the material electrodeposited on a gold substrate in the fluorescence mode.This paper is dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday for his outstanding contributions to electrochemistry     

Diastereoselective synthesis of 3-tert-butyl-3,4-dihydropyrazolo[5,1-c][1,2,4]triazine-3,4-diyl dicarboxylates

The reactions of 3-tert-butyl-7-R¹-8-R²-pyrazolo[5,1-c][1,2,4]triazines (R¹ = H, Br; R² = Me, n-Bu) with N-bromosuccinimide in the presence of R³CO₂H (R³ = Me, t-Bu, Ph) afforded novel diastereomerically pure 3-tert-butyl-7-R¹-8-R²-3,4-dihydropyrazolo[5,1-c][1,2,4]triazine-3,4-diyl dicarboxylates. The structures of the isolated products were established on the basis of IR, ¹H, ¹³C, 2D NOESY NMR, high resolution mass spectrometry and X-ray single-crystal analysis. The steric and mechanistic origins of the observed regio- and stereoselectivity were also discussed.     

Steric influences on sulphur inversion barriers in group 6a tetracarbonyl complexes of dithioethers

The complexes cis-[M(CO)₄(RSCH₂CH₂SR)] (M = Cr, Mo, W, R =^t Bu; M = W, R = Me, Et, ⁱPr, ^tBu) and cis-[M(CO)₄(cis-RSCHCHSR)] (M = Cr, Mo, W; R = Me, ^tBu) have been synthesised, and sulphur inversion studied using variable temperature ¹H and ¹³C {¹H} NMR techniques. For complexes of the saturated ligands, signals due to both DL and meso invertomers were observed at −90°C, with the relative populations of these invertomers being dependent on the steric bulk of the alkyl groups attached to sulphur. Sulphur inversion barriers, which have been calculated via total bandshape analysis of the variable temperature NMR spectra of these complexes, show a marked dependence on the steric requirements of the dithioether ligand. For the complexes of the unsaturated ligands, only the meso-invertomers were observed at limiting low temperatures (ca. −90°C), and sulphur inversion barriers were therefore not able to be calculated in these cases.     

Some considerations about equations correlating valence and length of a chemical bond

It is confirmed that the Zachariasen equation is more accurate than the Brown-Shannon equation. Moreover, it is shown that, given the value of the parameter R₁ relative to the MoO bond in MoO₆ octahedra, the calculated valence of molybdenum in Mo(V)O₆ octahedra remains very close to 5 v.u. by varying the other bond parameter B in a wide range. For other oxidation states of molybdenum in MoO₆ octahedra, the difference between the calculated valence and the formal oxidation state shows different types of dependence on B. These behaviours could explain some errors in valence data of the literature. The parameters for the MoO bond in MoO₆ octahedra are recalculated as R₁=1.8788 Å and B=0.3046 Å for all molybdenum oxidation states from +3 to +6.