54 research outputs found
Occupation preference values in doped CmIm' multinaries from EXAFS and FTIR correlative analysis
We discuss which x-ray absorption fine structure (EXAFS) data of binary doped CmIm' compound structures can be unfolded to determine elemental bond distances and the deviations from random configurations due to site preference occupations (SOPs). SOP-deviation estimations can be further confirmed by independent Fourier transform infrared (FTIR) data analysis. The limits and restrictions of our model are presented and discussed
Accuracy of a method based on atomic absorption spectrometry to determine inorganic arsenic in food : Outcome of the collaborative trial IMEP-41
Peer reviewedPublisher PD
Accuracy of a method based on atomic absorption spectrometry to determine inorganic arsenic in food: outcome of the collaborative trial IMEP-41
A collaborative trial was conducted to determine the performance characteristics of an analytical method for the quantification of inorganic arsenic (iAs) in food. The method is based on (i) solubilisation of the protein matrix with concentrated hydrochloric acid to denature proteins and allow the release of all arsenic species into solution, and (ii) subsequent extraction of the inorganic arsenic present in the acid medium using chloroform followed by back-extraction to acidic medium. The final detection and quantification is done by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS). The seven test items used in this exercise were reference materials covering a broad range of matrices: mussels, cabbage, seaweed (hijiki), fish protein, rice, wheat, mushrooms, with concentrations ranging from 0.074 to 7.55 mg kg(-1). The relative standard deviation for repeatability (RSDr) ranged from 4.1 to 10.3%, while the relative standard deviation for reproducibility (RSDR) ranged from 6.1 to 22.8%. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Statistical strained-tetrahedron model of local ternary zinc blende crystal structures
The statistical strained-tetrahedron model was developed to overcome two common assumptions
of previous models: 1) rigid undistorted ion sublattice of regular tetrahedra throughout all
five configurations and 2) random ion distribution. These simplifying assumptions restrict the
range of applicability of the models to a narrow subset of ternary alloys for which the constituent
binaries have their lattice constants and standard molar enthalpies of formation (∆fH₀) equal or
quasi-equal. Beyond these limits predictions of such models become unreliable, in particular, when
the ternary exhibits site occupation preferences. The strained-tetrahedron model, free from rigidity
and stochastic limitations, was developed to better describe and understand the local structure
of ternary zinc blende crystals, and interpret experimental EXAFS and far-IR spectra. It considers
five tetrahedron configurations with the shape and size distortions characteristic of ternary zinc
blende alloys, allows nonrandom distributions and, hence, site occupation preferences, conserves
coordination numbers, respects stoichiometry, and assumes that next-neighbor values determine
preferences beyond next-neighbor. The configuration probabilities have three degrees of freedom.
The nineteen inter-ion crystal distances are constrained by tetrahedron structures; to avoid destructive
stresses, we assume that the average tetrahedron volumes of both sublattices relax to
equal values. The number of distance free-parameters ≤ 7. Model estimates, compared to published
EXAFS results, validate the model. Knowing the configuration probabilities, one writes the dielectric
function for far-infrared absorption or reflection spectra. Constraining assumptions restrict
the number of degrees of freedom. Deconvolution of the experimental spectra yields site-occupation-
preference coefficient values and/or specific oscillator strengths. Validation again
confirms the model
The complex stoichiometry of ternary alloys : what lies beyond the canonical Bernoulli distribution?
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High-temperature spectroscopy for nuclear waste applications
Instrumentation has been developed to perform uv-vis-nir absorbance measurements remotely and at elevated temperatures and pressures. Fiber-optic spectroscopy permits the interrogation of radioactive species within a glovebox enclosure at temperatures ranging from ambient to >100{degree}C. Spectral shifts as a function of metal- ligand coordination are used to compute thermodynamic free energies of reaction by matrix regression analysis. Pr{sup 3+} serves as a convenient analog for trivalent actinides without attendant radioactivity hazards, and recent results obtained from 20{degree}--95{degree}C with the Pr-acetate complexation system are presented. Preliminary experimentation on Am(3) hydrolysis is also described. 16 refs., 1 tab
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