Sample thickness and quantitative concentration measurements in Br K‐edge XANES spectroscopy of organic materials

While XANES spectroscopy is an established tool for quantitative information on chemical structure and speciation, elemental concentrations are generally quantified by other methods. The edge step in XANES spectra represents the absolute amount of the measured element in the sample, but matrix effects and sample thickness complicate the extraction of accurate concentrations from XANES measurements, particularly at hard X‐ray energies where the X‐ray beam penetrates deeply into the sample. The present study demonstrates a method of quantifying concentration with a detection limit approaching 1 mg kg^?1 using information routinely collected in the course of a hard X‐ray XANES experiment. The XANES normalization procedure unambiguously separates the signal of the absorber from any source of background. The effects of sample thickness on edge steps at the bromine K‐edge were assessed and an empirical correction factor for use with samples of variable mass developed.     

同步辐射软X射线近边吸收谱方法研究长期施肥对黑土有机氮官能团的影响

有机态氮是土壤氮素的主要存在形式,在农田生态系统氮循环中占有重要地位。了解土壤有机氮官能团组成,可为制定合理的农田管理措施提供科学依据。同步辐射软X射线近边吸收谱(N K-edge XANES)技术,是原位测定土壤有机氮官能团组成最有效的方法,但利用该技术对长期施肥条件下土壤有机氮官能团组成的研究尚未见报道。本试验利用N K-edge XANES方法,研究了长期(18年)不同施肥措施[即休闲(Fallow)、不施肥(CK)、施氮磷钾化肥(NPK)、有机肥配施化肥(NPKM)、1.5倍量的有机肥配施化肥(1.5NPKM)和玉米秸秆配施化肥(NPKS)]对黑土全土及粘粒中有机氮官能团的影响。结果表明：各处理均在401.2～401.6和402.7～403.1 eV范围内出现特征吸收峰,分别归属为酰胺/胺和吡咯类化合物,粘粒中特征吸收峰通常较全土更为明显。半定量分析结果指出,全土和粘粒均以酰胺/胺的相对比例最高,是有机氮官能团的主要存在形态;与休闲处理相比,对照处理中酰胺/胺的相对比例较低,而吡咯类氮的相对比例较高;有机无机配施条件下,酰胺/胺的相对比例随有机肥量的增加而下降,而吡咯类氮的相对比例则呈相反的变化趋势;全土中以NPKS处理的酰胺/胺相对比例最高,而粘粒中则以休闲处理的腈类/芳香氮相对比例最高。利用N K-edge XANES方法原位测定不同施肥措施下土壤有机氮官能团组成的变化是可行的。     

Effect of Li2O Addition on the Preparation of (Y2‐yLiy)Ti2O7‐y

A new series of (Y_2‐yLi_y)Ti₂O_7‐y having an ordered pyrochlore phase was prepared by a solid state reaction method with a solid solution range of 0.05 ≥ y ≥ 0.10. Unit cell parameters obtained by the Rietveld refinement method shows that the a‐axis decreases linearly with increasing the amount of Li ion addition, indicating the successful incorporation of the Li ion into unit cell. The average x‐fractional coordinate of the O(1) site depends on the ionic radius ratio of r(A³+)/r(Ti⁴⁺) in the A₂Ti₂O₇ with a pyrochlore phase. The Ti K‐edge XANES spectra of the (Y_2‐yLi_y)Ti₂O_7‐y show that the valence of the Ti ions is slightly less than 4 so that Ti is in the mixed valence state. Average particle size increases with increasing the amount of extra Li ion addition, which acts as a flux to lower the melting point of the materials.     

Chlorination and characterization of natural rubber and its adhesion to nitrile rubber

Chlorinated natural rubber (CNR) vulcanized sheets were prepared by immersing the NR sheets in sodium hypochlorite solution for various chlorination times ranging from 0 to 30 min. The degree of chlorination as indicated by X-ray Absorption Near-Edge Spectroscopy (XANES) implied that the chlorine content increases with the chlorination time from 0 to 10 min then levels off. Atomic Force Microscopy (AFM) showed an evolution of the surface roughness and stiffness. These two properties increased gradually with chlorination time. The bond strength between CNR and nitrile rubber (NBR) also increased gradually. The data showed cohesive failure beginning at 1 min and extending throughout the 30 min of the study. The maximum peel strength was found at 1 min of chlorination time and decreased afterwards. The decrease in peel strength was caused by the increase in surface stiffness of NR that acted as weak boundary layer. The surface stiffness governed the peel strength between NR and NBR.     

The tribological behaviours of dithiocarbamate‐triazine derivatives as additives in mineral oil

Ashless and non‐phosphorus hydroxyl‐containing dithiocarbamate‐triazine compounds,2,4,6‐tri[N,N‐di‐i‐octyldithiocarmate‐(2′‐hydroxyl)‐propionylthio]‐1,3,5‐s‐triazine (LDION) were prepared and their tribological behaviour as additives in mineral oil were evaluated using a four‐ball tester. Thermal degradation tests were conducted to identify their thermal stabilities using a thermo‐gravimetric analyser. The worn surfaces were investigated by X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near edge structure (XANES) spectroscopy. The results indicate that the additive LDION possesses high thermal stabilities and good load‐carrying capacities. Moreover, it has good anti‐wear property at all test concentration and under all test loads. The results of XPS and XANES analyses illustrate that the prepared compounds as additives in mineral oil forms a protective film containing oxidised compounds and organic nitrogen‐containing compounds and inorganic sulfate on the metal surface during sliding process. Copyright © 2008 John Wiley & Sons, Ltd.     

Early commissioning results for spectroscopic X‐ray Nano‐Imaging Beamline BL 7C sXNI at PLS‐II

For spectral imaging of chemical distributions using X‐ray absorption near‐edge structure (XANES) spectra, a modified double‐crystal monochromator, a focusing plane mirrors system and a newly developed fluorescence‐type X‐ray beam‐position monitoring and feedback system have been implemented. This major hardware upgrade provides a sufficiently stable X‐ray source during energy scanning of more than hundreds of eV for acquisition of reliable XANES spectra in two‐dimensional and three‐dimensional images. In recent pilot studies discussed in this paper, heavy‐metal uptake by plant roots in vivo and iron's phase distribution in the lithium–iron–phosphate cathode of a lithium‐ion battery have been imaged. Also, the spatial resolution of computed tomography has been improved from 70 nm to 55 nm by means of run‐out correction and application of a reconstruction algorithm.     

X-ray absorption spectroscopy of ultramarine pigments: A new analytical method for the polysulfide radical anion S3 chromophore

Blue and mauve ultramarine artists' pigments and their heat-treated products have been investigated by sulfur K-edge X-ray absorption. X-ray absorption near-edge structure spectra are dominated by features of reduced sulfur and sulfate species. There is also a pre-peak at about 2468.0 eV which reflects the presence of the unpaired electron on the polysulfide radical anion (S₃⁻). Pre-peak intensity is directly proportional to the depth of blue coloration, and provides a new, independent method for estimating the proportion of ultramarine cage sites occupied by the blue chromophore. The occupancy of the polysulfide radical anion S₃⁻ is estimated to be 33% in an intense ultramarine blue pigment, 22% in a dark blue ultramarine pigment, and 1% in deep royal blue lazurite from Afghanistan. The more efficient development of color in lazurite is attributed to extensive annealing of the mineral structure in the natural environment.     

Speciation of copper and zinc in size-fractionated atmospheric particulate matter using total reflection mode X-ray absorption near-edge structure spectrometry

The health effects of aerosol depend on the size distribution and the chemical composition of the particles. Heavy metals of anthropogenic origin are bound to the fine aerosol fraction (PM_2.5). The composition and speciation of aerosol particles can be variable in time, due to the time-dependence of anthropogenic sources as well as meteorological conditions. Synchrotron-radiation total reflection X-ray fluorescence (SR-TXRF) provides very high sensitivity for characterization of atmospheric particulate matter. X-ray absorption near-edge structure (XANES) spectrometry in conjunction with TXRF detection can deliver speciation information on heavy metals in aerosol particles collected directly on the reflector surface. The suitability of TXRF-XANES for copper and zinc speciation in size-fractionated atmospheric particulate matter from a short sampling period is presented. For high size resolution analysis, atmospheric aerosol particles were collected at different urban and rural locations using a 7-stage May cascade impactor having adapted for sampling on Si wafers. The thin stripe geometry formed by the particulate matter deposited on the May-impactor plates is ideally suited to SR-TXRF. Capabilities of the combination of the May-impactor sampling and TXRF-XANES measurements at HASYLAB Beamline L to Cu and Zn speciation in size-fractionated atmospheric particulate matter are demonstrated. Information on Cu and Zn speciation could be performed for elemental concentrations as low as 140 pg/m³. The Cu and Zn speciation in the different size fraction was found to be very distinctive for samples of different origin. Zn and Cu chemical state typical for soils was detected only in the largest particles studied (2–4 μm fraction). The fine particles, however, contained the metals of interest in the sulfate and nitrate forms.