Use Of XANES Research Articles

Use of XANES and XPS to investigate the effects of ethanol contamination on anti-wear ZDDP tribofilms

This work uses synchrotron radiation XANES and XPS measurements to investigate the structure of ZDDP tribofilms formed from lubricants contaminated with anhydrous and hydrated ethanol (5%wt). The tribofilms were formed at 40 °C from PAO8 lubricant containing only ZDDP additive onto carbon steel specimens using sliding tests, cylinder-on-flat configuration (line contact) under boundary lubrication. Ethanol increased friction as well as surface damage, detected by an increase in relative porous area. Angle-resolved measurements (15°, 45°, 90°) helped detecting differences along the thickness of the tribofilm. The amount of long-chain phosphates apparently reduced with ethanol, leading to reduced wear performance. The sulphides in the tribofilms were richer in Fe in the presence of ethanol, also indicative of more severe wear.

Full-Field Calcium K-Edge X-ray Absorption Near-Edge Structure Spectroscopy on Cortical Bone at the Micron-Scale: Polarization Effects Reveal Mineral Orientation.

Here, we show results on X-ray absorption near edge structure spectroscopy in both transmission and X-ray fluorescence full-field mode (FF-XANES) at the calcium K-edge on human bone tissue in healthy and diseased conditions and for different tissue maturation stages. We observe that the dominating spectral differences originating from different tissue regions, which are well pronounced in the white line and postedge structures are associated with polarization effects. These polarization effects dominate the spectral variance and must be well understood and modeled before analyzing the very subtle spectral variations related to the bone tissue variations itself. However, these modulations in the fine structure of the spectra can potentially be of high interest to quantify orientations of the apatite crystals in highly structured tissue matrices such as bone. Due to the extremely short wavelengths of X-rays, FF-XANES overcomes the limited spatial resolution of other optical and spectroscopic techniques exploiting visible light. Since the field of view in FF-XANES is rather large the acquisition times for analyzing the same region are short compared to, for example, X-ray diffraction techniques. Our results on the angular absorption dependence were verified by both site-matched polarized Raman spectroscopy, which has been shown to be sensitive to the orientation of bone building blocks and by mathematical simulations of the angular absorbance dependence. As an outlook we further demonstrate the polarization based assessment of calcium-containing crystal orientation and specification of calcium in a beta-tricalcium phosphate (β-Ca3(PO4)2 scaffold implanted into ovine bone. Regarding the use of XANES to assess chemical properties of Ca in human bone tissue our data suggest that neither the anatomical site (tibia vs jaw) nor pathology (healthy vs necrotic jaw bone tissue) affected the averaged spectral shape of the XANES spectra.

Speciation of antimony and arsenic in the soils and plants in an old antimony mine

The speciation changes of antimony (Sb) in soil–plant system are largely unknown as compared with those of arsenic (As). In this study, indigenous plants and associated soils were sampled at the Xikuangshan Sb mine (XKS), China. The Sb in the soils (441–1472mg/kg) were far greater than As (32–354mg/kg), and the Sb and As availabilities in the soils, were 5.5% and 3.9% in average, respectively. HPLC-ICP-MS revealed the presence of four species of Sb in the soils and plants, including SbIII, SbV, TMSb and UnkSb (unknown). The use of XANES revealed that the UnkSb consisted of inorganic Sb in the form of SbV. Inorganic Sb were prevalent in the soil and plant samples at the eight sites, whereas TMSb was observed in only a few of the rhizosphere soils, and, in plants at a few of the sites, primarily in the leaves and to a lesser extent in the stems. Arsenic was detected in the soils primarily as inorganic forms, while, DMA was detected in high proportions in all of the plant tissues at all of the sites. The methylation of Sb was far less than that of As in the indigenous plants at XKS. The results suggest that As and Sb differ in transformation characteristics in the soil–plant system in XKS.

XANES analysis of catalytic systems under reaction conditions

ABSTRACT The article gives an overview of the XANES technique contribution to the analysis of multicomponent catalysts. The theoretical basis of the technique, the interpretation of the energy position and intensity of XANES features, and the numerical methods developed to interpret XANES data on catalytic systems are described and discussed in the first part. In the second part, the most recent XANES studies of catalytic samples are reviewed, giving particular attention to the solid state chemistry information extracted under real, in-situ conditions. This concerns structural and redox properties of the systems during preparation stages, activation treatments like reduction, oxychlorination, or sulfidation, and reaction conditions. Additional effort was made to describe the use of XANES to gain insight on electronic properties of catalysts. The influence of all these redox, geometrical and electronic properties on catalytic behavior, particularly as a function of particle size and active metal-support interaction, has also been examined on the light of XANES data.

The Use of XANES, STM, and XPS to Identify the Precipitation Products Formed during the Reaction of U, Cr, and Se with Zerovalent Iron

Shallow groundwaters in the western U.S. often contain elevated levels of trace oxyanions such as selenate, chromate, and uranyl. A potential remediation method is to react the water with zero-valent iron. Both in-situ permeable reactive barrier walls and pump-n-treat technologies are being used for to treat these contaminated waters (Wilson, 1995). In this reaction, the iron serves as both an electron source and as a catalyst. The objectives of this research were to determine the factors that affect the rate of reaction and the types of secondary products formed, including the iron hydroxide mineralogy and the fate of the trace elements. Variables that we studied included pH, ionic strength, 02, competitive ions and forms of iron.

Studies on the Structure of Cationic Dimer of Molybdenum(VI) in Acidic Solution by XANES and EXAFS

Abstract Structure of the cationic dimer of molybdenum(VI) species in acidic solution was investigated by the use of XANES and EXAFS. It was found that each Mo atom in the dimer has two terminal oxygens and Mo–O–Mo bond angle is ca. 125°.

Ligand binding processes in hemoglobin. Chemical reactivity of iron studied by XANES spectroscopy

K-absorption edge of coordinated ions exhibits a fine structure (through the use of XANES, or x-ray absorption near edge structures) that reflects the electronic repartition and the chemical reactivity of these ions. Comparative analysis of iron K-absorption-edge shape for hemoglobin derivatives with different ligand affinity suggests strongly that in hemoglobin, iron-forms with high and low affinity are highly improbable.

Elastic scattering of slow electrons by atomic oxygen

The speciation changes of antimony (Sb) in soil–plant system are largely unknown as compared with those of arsenic (As). In this study, indigenous plants and associated soils were sampled at the Xikuangshan Sb mine (XKS), China. The Sb in the soils (441–1472 mg/kg) were far greater than As (32–354 mg/kg), and the Sb and As availabilities in the soils, were 5.5% and 3.9% in average, respectively. HPLC-ICP-MS revealed the presence of four species of Sb in the soils and plants, including SbIII, SbV, TMSb and UnkSb (unknown). The use of XANES revealed that the UnkSb consisted of inorganic Sb in the form of SbV. Inorganic Sb were prevalent in the soil and plant samples at the eight sites, whereas TMSb was observed in only a few of the rhizosphere soils, and, in plants at a few of the sites, primarily in the leaves and to a lesser extent in the stems. Arsenic was detected in the soils primarily as inorganic forms, while, DMA was detected in high proportions in all of the plant tissues at all of the sites. The methylation of Sb was far less than that of As in the indigenous plants at XKS. The results suggest that As and Sb differ in transformation characteristics in the soil–plant system in XKS.