BUNSEKI KAGAKU Abstracts

When the excitation energy is in the vicinity of the absorption-edge of an element, X-ray emission, following the absorption, is called resonant inelastic X-ray scattering (RIXS). RIXS is much more highly sensitive to chemical-states of the element than conventional fluorescent X-rays. Thus, RIXS can be a useful “fingerprint” in material characterization. In this article, the basic aspects of RIXS spectroscopy are surveyed while emphasizing the relationship to X-ray absorption fine structures and fluorescent X-ray spectra. Also, its applications to analytical chemistry are discussed along with several recent examples.

X-ray reflectivity measurements of liquid surfaces were demonstrated using a recently developed liquid interface reflectometer at SPring-8. The reflectometer has two features superior to other surface-horizontal spectrometers currently available at synchrotron facilities around the world : achieving quick measurements and investigating the surface structure for both vertical and horizontal directions simultaneously. We demonstrated X-ray reflectivity measurements of an aqueous ionic liquid, and time-resolved measurements for the adsorption process of a globular protein lysozyme on a water/air interface. X-ray specular and off-specular reflection was also investigated to analyze the out-of-plane and in-plane structures of lysozyme adsorbed at an air/water interface in the presence of a salt.

It is known that zirconium ion exists in an aqueous chloride solution by taking various structures, depending on the concentrations of hydrogen and chloride ions. The structural change of the zirconium species in solution may affect the functional abilities of the solution, such as a crosslink agent for water-soluble polymers, which is one of the industrial applications of a zirconium solution. Therefore, the influence of the component concentrations in the solution on the structure of the zirconium species must be studied to understand the mechanism of its function and to improve it. X-ray absorption fine structure (XAFS) spectroscopy was used to obtain structural information of the zirconium species. Solutions containing zirconium, hydrogen and chloride ions at various concentrations were measured by the transmission method. The EXAFS (Extended XAFS) analysis indicated that the Zr–Zr coordination number, n_Zr–Zr, decreased with increasing the hydrogen chloride concentration, and did not depend on the zirconium concentration. However, if perchloric acid was used to increase the acidity, n_Zr–Zr did not change. The results suggest that halide anion plays an important role for the depolymerization of zirconium species in an acidic solution. For 0.1 and 2.0 M zirconium solutions for which the molar ratio [Cl⁻]/[Zr] was kept at about 2, the n_Zr–Zr values were determined to be 3.7 and 1.9, respectively. However, the same zirconium concentration solutions for which the [Cl⁻]/[Zr] values were around 0.7 showed n_Zr–Zr values of 4.0 and 3.4, respectively. Thus, the value of 0.7 should be selected to obtain a chemically stable solution. The value of [Cl⁻]/[Zr] = 0.7 agrees with that for the most effective crosslink agent solution for polyvinyl alcohol.

To clarify the relationship between the total electron yield (TEY) and the composition ratio in the mixture samples, TEY X-ray absorption spectra (XAS) of some mixture samples were measured using synchrotron radiation. From the TEY-XAS of the sp²/sp³-carbon mixtures (carbon black/diamond) and the boron/carbon mixtures (amorphous boron/carbon black), TEY ratios between the compositions can be obtained as 0.12 for diamond to carbon black and as 0.32 for carbon black to boron. By using the measured TEY ratios, TEY-XAS profiles of the mixture samples can be well reproduced by the synthesized spectra. It is therefore confirmed that composition ratio will be quantitatively analyzed from the TEY-XAS measurements considering the TEY ratios among the compositions.

This paper reports on the distribution of Cd and essential elements in the stems of rice plants, ‘Nipponbare’ and ‘Milyang 23’, measured by synchrotron radiation micro-XRF imaging. X-ray absorption near edge structure (XANES) analysis was applied to estimate the chemical forms of Cd in the roots, stems and leaves, aiming to reveal the mechanisms of Cd transport in rice. The results show that the Cd concentration of ‘Nipponbare’ was found to be higher than that of ‘Milyang 23’ at the root, although there was no significant difference between these two cultivars at the shoot. In addition, the distribution of Cd and the essential elements inside the plant were clearly revealed by micro-XRF imaging. It was found that Cd was also localized to the bundle. The Cd K-edge XANES analysis indicated that Cd was bound to sulfur in the root for both rice plants. Furthermore, the content of Cd combining with S (Cd−S) in the stem of ‘Nipponbare’ became 1.5 times higher after exposing to Cd for a long time, while only a slight change in the stem of ‘Milyang 23’ was found. In contrast with the stem, the leaf of ‘Nipponbare’ contained a lower Cd−S content than that of the control after a long-term exposure, while that of ‘Milyang 23’ became higher. In conclusion, the difference in the chemical form of Cd at the shoots affected the different accumulation behaviors of Cd between ‘Nipponbare’ and ‘Milyang 23’.

The surface modification of poly(butylene terephthalate) by ultraviolet (UV) light irradiation was investigated using near edge X-ray absorption fine structure (NEXAFS) spectroscopy and infrared reflection absorption spectroscopy (IRRAS). The carbon K-edge and oxygen K-edge NEXAFS spectra were drastically changed by UV irradiation. The obtained NEXAFS spectra after UV irradiation were compared with those of some molecules containing carbonyl, carboxylic, ester, and anhydride groups. The spectral features obtained by a UV irradiated PBT surface were analogous to those of pyromellitic dianhydride containing an anhydride group. The IRRAS spectra of PBT surfaces were also changed by UV irradiation. The changes showed the disappearance of an alkyl chain and structural changing of ester bonds by UV irradiation. These results indicated that the alkyl chains and ester bonds in PBT are removed by UV irradiation, and that anhydride groups were formed on a UV irradiated PBT surface.

The formation reaction of autoclaved lightweight concrete (ALC) has been investigated by in situ time-resolved X-ray diffraction (XRD) using high-energy X-rays from a synchrotron radiation source in combination with an autoclave cell and a photon-counting pixel array detector. XRD measurements were conducted in a temperature range of 100 to 190°C under a saturated steam pressure with a time interval of 4.25 min. The effect of adding gypsum to the starting mixture was investigated. It has been revealed that gypsum significantly accelerates tobermorite formation, and that the crystal growth along the c-axis is preferred at the late stage of autoclave. Reaction kinetics of tobermorite formation was discussed on the basis of Avrami-type mechanism.

Gallium is known to exist as a liquid state in the widest temperature region among all elements, since its melting and boiling points are 29.76°C and 2205°C, respectively. So far, there have been a number of interesting work on the physical and chemical properties of its liquid state, because the research can be done at near room temperature. From a view point of applications, it is a highly efficient cooling material, which is a promising alternative to water. On the other hand, the structures of non-equalibrium state, i.e., the freezing and the melting process has not yet been well studied, mainly because of technical limitation in the experiments. For such observations, it is absolutely necessary to collect the X-ray diffraction pattern quickly without moving the sample. Moreover, since the sample usually becomes inhomogeneous, imaging of X-ray diffraction information is crucial. Projection-type X-ray diffraction imaging is a novel technique, which can give real-space image for the X-ray diffraction from an inhomogeneous polycrystalline sample. The present paper reports on some preliminary in situ observation of freezing and melting process of liquid gallium.

Excavated natural fibers (silk, hemp and ramie) found at three tumuli (3C-6C A.D.) in Nara prefecture were investigated by using synchrotron radiation FT-IR microscopy at JASRI (SPring-8), beamline BL43IR. While three tumuli were kept in different long-term preservative environments, comparative studies on excavated fibers were performed for the identification of textile fibers, and for investigating the degraded state of respective fibers. Silk fibers are usually heavily degraded, and hence amide I and amide II peak patterns show different appearances compared with that of modern reference silk fibers. These phenomena are in accordance with the present author’s analysis published separately. In short, the change in the spectral pattern is mainly due to transformation of the second structure components of the amide II peak during long–term preservation in various environments. Besides, the spectra pattern sometimes shows a small variation in the co-presence of metallic objects in tumulus. Plant fibers, such as hemp or ramie, are not severely degraded compared with silk fibers, and they usually show common spectra with plant fibers of a modern reference material. Since the plant fibers are in principle composed of cellulose molecules, exact identifications of materials are rather difficult by only the infrared spectrum. In summary, it was shown that excavated textile fibers sometimes show the small variation in the spectral pattern according to a difference in the preserved environment.

Precious coral is one of the natural resources of which Japan is a major supplier. Since the concentrations of trace elements in the skeletons are less than 1 ppm, it is difficult to determine the behavior of trace elements other than Ca, Mg and Sr using conventional instruments for mapping analysis at a laboratory scale. In this study, the distributions of trace elements in the skeletons of precious corals were analysed with XRF mapping employing synchrotron radiation at a large circular accelerator in SPring-8. Using 37.6 keV X-rays with a beam size of 50 μm (horizontally) × 50 μm (vertically), Ba, I, Mo, Sn, Mn, Zn, Cd and Br, as well as the major element of Ca and Sr, were detected in the skeletons. Two-dimensional maps of the trace element distribution showed that those of Ba, I and Mo concentrations form fine granular structure in the skeletons of precious corals, while Ca and Sr are almost homogeneously distributed. As compared with the element composition in the skeletons of Corallium rubrum from the Mediterranean Sea, Corallium japonicum from Japanese waters, and deep sea corals from Ogasawara and Midway Islands, relatively high contents of Cd and Ba were detected in the deep corals, which suggested that Cd and Ba are incorporated in proportion to the concentrations in the surrounding seawater. These elements are expected to be good marker elements for identifying species and harvest areas.

Composition distributions in high impact polypropylene particles synthesized with Ziegler-Natta catalysts were investigated by using the SPring-8 infrared microscope apparatus. High impact polypropylene is prepared in two stages. At first the homopolymers are produced from propylene, and in the following stage copolymers are synthesized from propylene and ethylene. In most of the second stage, gas phase polymerization processes using heterogeneous Ziegler-Natta catalysts are applied. A particle of the heterogeneous catalyst is the aggregation of the first microparticles. In the polymerization reaction, gaseous monomers contact the microparticles to produce polymers around them, and the growing microparticles result in increasing the size of the second macroparticles. Several kinds of high impact polypropylene particles were cut into cross sections by means of single edge industrial blades. The composition distributions of the samples were measured by using infrared microspectroscopy imaging. It was found that the propylene-ethylene copolymer with high ethylene concentration spots was formed around the surface of the particles. In the case of the particle having voids inside, high ethylene concentration spots were formed not only around the surface but also near the interface of the voids. Mechanism of the formation of high ethylene concentration spots was considered.

The application of synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) was investigated for the forensic discrimination of aluminum foil by comparisons of the elemental components. Small fragments (1 × 1 mm) were taken from 4 kinds of aluminum foils produced by different manufactures and used for measurements of the XRF spectrum at BL37XU of SPring-8. A comparison of the XRF spectra was effective for the discrimination of aluminum foils from different sources, because significant differences were observed in the X-ray peak intensities of Fe, Cu, Zn, Ga, Zr and Sn. These elements, except for Zr and Sn in the aluminum foils and NIST SRM1258 (Aluminium Alloy 6011), were also determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The observed values of Fe, Cu, Zn and Ga in NIST standard samples by ICP-AES showed satisfactorily good agreements with the certified or information values with relative standard deviations from 1.1% for Zn to 6.7% for Ga. The observed values for the aluminum foils by ICP-AES were compared with those by SR-XRF. Correlation coefficients from 0.997 for Cu/Fe to 0.999 for Zn/Fe and Ga/Fe were obtained between the ratio of the elemental concentration by ICP-AES and normalized the X-ray intensity by SR-XRF. This result demonstrates that a comparison of the normalized X-ray intensity is nearly as effective for the discrimination of aluminum foils as quantitative analysis by ICP-AES. Comparisons of the analytical results by SR-XRF allow the discrimination of all aluminum foils using only a 1 mm² fragment with no destruction of the samples.