Chemical alteration of organic compounds exposed to X-rays from portable micro-focus X-ray fluorescence instruments is a potential concern for many applications (e.g. the analysis of valuable works of art, planetary lander and rover missionsfocused on astrobiology, etc.). We performed a preliminary study ofthe effects of intense and prolonged exposure to X-ray radiation from a micro-focus XRF instrument onthe chemical composition of two organic compounds representative of molecules commonly reported from the terrestrial rock record. Pyrene, a polycyclic aromatic hydrocarbon (PAH), and palmitic acid, a saturated fatty acid, were deposited in glass vials and irradiated for 90 and 24 hours, respectively. Radiation was delivered using a Bruker ARTAX instrument fitted with a polycapillary focusing optic and Rh anode X-ray tube operated at 50 kV/0.6 mA. Controls and samples were compared for chemical alteration by Gas Chromatography/Mass Spectrometry (GC-MS) and Raman spectroscopy,beforeandafter exposure to the X-ray beam. No indication of chemical alteration of the compounds was detected by GC-MS orRaman spectroscopy. A color change that was observed in the vials containing the samples after X-ray irradiation was likely caused by reversible activation of color centers in the borosilicate glass vials.
Micro-X-ray fluorescence (MXRF) was used to locate minute quantities of plutonium in contaminated soil. Because the specimen had previously been prepared for analysis by scanning electron microscopy, it was coated with gold to eliminate electron beam charging. However, this significantly hindered efforts to detect plutonium by MXRF. The gold L peak series present in all spectra increased background counts. Plutonium signal attenuation by the gold coating and severe peak overlap from potassium in the soil prevented detection of trace plutonium using the Pu Mα peak. However, the 14.3 keV Pu Lα peak sensitivity was not optimal due to poor transmission efficiency through the source polycapillary optic, and the instrument silicon drift detector sensitivity quickly declines for peaks with energies above ~10 keV. Instrumental parameters were optimized (eg. using appropriate source filters) in order to detect plutonium. An X-ray beam aperture was initially used to image a majority of the specimen with low spatial resolution. A small region that appeared to contain plutonium was then imaged at high spatial resolution using a polycapillary optic. Small areas containing plutonium were observed on a soil particle, and iron was co-located with the plutonium. Zinc and titanium also appeared to be correlated with themore » plutonium, and these elemental correlations provided useful plutonium chemical state information that helped to better understand its environmental transport properties.« less
During the Genesis mission solar wind was implanted in collector materials for analysis by various instrumental methods. Unfortunately the space craft crash landed upon return to Earth shattering the collectors into small fragments and exposing them to desert soil and spacecraft debris. Thus only small fragments are available for analysis with each having different degrees of contamination present at and embedded within the surface. Cleaning procedures were developed and applied to remove the contamination. To aid in this process bench top total reflection X-ray fluorescence spectrometry (TXRF) was used to characterize a sample surface before and after various cleaning steps. In contrast to TXRF, synchrotron grazing incidence Xray fluorescence spectrometry (GI-XRF) is capable of probing at the surface and below the surface thus providing information about surface deposits as well as implanted material. A number of samples were subjected to both, TXRF and GI-XRF analysis and it was observed that some elements detected by TXRF were present not on top of but below the surface of the collector fragment. This suggested the possibility of using laboratory TXRF to distinguish between surface deposits and ion-implanted subsurface material. The feasibility of this approach was tested with a surface deposited and an ion implanted control sample. In addition a careful TXRF angle scan was also executed with one Genesis flight sample and compared to GI-XRF measurements, confirming the ability of bench top TXRF to distinguish between surface and subsurface material.
In this paper we will introduce the general benefits of X-Ray Fluorescence spectrometry (XRF) for assessing the condition of the outer environment, especially where ambient aerosol particles are causing environmental disturbances. Examples from recent environmental studies are presented, and energy dispersive XRF is concluded to be a powerful, nondestructive yet easily applicable tool to supply detailed elemental information of particles collected in different applications. The further development and future potential of the method for detailed analysis of aerosol particles are discussed.
Using a portable total reflection X-ray fluorescence spectrometer, a sample containing 100 pg each of 3d transition metals, 500 pg of As, and 1 ng each of Sr, Y, and Zr is measured. Although non-monochromatic X-rays from a 5 W X-ray tube (Tube voltage: 25 kV) are used, the trace amounts of these elements are detected. This portable spectrometer is applied to analysis of river water, a leaching solution of a toy, and a lipstick. Several ppb concentrations each of elements in river water are detected. Lead is detected from the leaching solution of the toy. Transition metal elements such as Ti, Mn, and Fe are detected from the lipstick. This portable spectrometer is possible to be applied to an evaluation of environmental pollution and screening for toxic elements in products for daily use.
Load Partitioning in a Duplex Stainless Steel with Surface Strength Gradient and Residual Stresses
Different casting parameters can change the microstructure and residual stresses of castings. The microstructure of Al-Si cast alloys is influenced by the morphology of silicon particles (shape, si ...
Duplex stainless steel SAF 2507 was strain hardened and aged, respectively, which results in a similar increase in the 0.2% proof stress but different property ratio of austenite (γ) to ferrite (α). γ is the harder phase in the deformed specimen but the softer one in the aged condition. X-ray diffraction experiments under in-situ tensile loading with a peak stress close to the 0.2% proof stress were carried out to study the microscopic load sharing and the influence of the relative phase properties. It was observed that under elastic loading, the phase incompatibility caused a slight load transfer from α to γ in the deformed specimen but from γ to α in the aged one. In case of loading of the deformed specimen in the elasto-plastic regime, as both phases yielded under similar applied stress, the phase interaction due to microplasticity was weak and had no obvious influence on the load partitioning. On the other hand, significant load transfer from γ to α accompanied yielding of γ in the aged specimen in the same regime. The specimens were uploaded to the same peak stress after unloading. With elastic loading prevails in the second cycle, γ in the deformed and α in the aged specimen, both having tensile residual stress, take a larger share of the applied load.
The investigations carried out in this study using innovative high strength filler materials with specifically lowered Ms/Mf-temperatures have demonstrated that different transformation temperatures may significantly affect the welding residual stresses. For this kind of filler materials for the first time high energy synchrotron radiation was applied in order to characterise the effect of lowered martensite start temperatures on the welding residual stresses in-situ by means of energy dispersive diffraction. This way likewise the phase transformation temperatures could be determined. Using synchrotron white beam diffraction the phase-specific residual stresses in the martensitic and the austenitic phase were analysed within the same experiment. Low transformation temperature welding material with varying nickel content between 8 % and 12 % was investigated in this study. Butt welds using the high strength base material S690 applying manual metal arc welding were produced in two passes. Residual stress analysis was carried out in longitudinal as well as transverse direction to the weld line. The results clearly indicate that the residual stress distributions show in general a decrease in magnitude caused by phase transformation of the weld metal. Particularly in the transition region from the weld metal to the heat affected zone relatively high compressive residual stresses up to -350 MPa were determined in the martensitic phase. The stress magnitude and distribution in the austenitic phase is strongly influenced by the nickel content and the amount of associated retained austenite.
Residual stresses in a surface layer determine many exploitation characteristics of machined surface. Depending on their kind and the type of applied loading, the influence of residual stresses can be negative or positive. Tensile residual stresses usually exert highly detrimental impact on several functional aspects such as strength, fatigue life, corrosion, wear resistance, etc., whereas compressive residual stresses are considered to have a beneficial effect on these features. The residual stresses found in mechanical parts are mainly generated in the final steps of machining process and are highly dependent on the machining conditions used. The increasing trend in industrial practice to eliminate cutting fluids from machining processes substantially changes machining conditions and influences the relationship between factors causing residual stresses. The main purpose of the presented investigations was to identify the relationship between residual stresses in a surface layer and the method of cooling employed. Using the X-ray diffraction method, residual stresses generated in both the cutting (circumferential) and feed (axial) directions were analysed. On the basis of empirical results the influence of turning with and without the application of emulsion on residual stresses was identified for a broad range of cutting parameters. The results showed that the method of cooling and cutting parameters exert a substantial influence on residual stresses. In the used range of cutting conditions, tensile residual stresses were detected. The elimination of cutting fluid from a turning process of C45 steel increased the magnitude of residual stresses in the surface layer. Residual stresses in the cutting direction turned out to be higher than in the feed direction in most cases of cutting conditions.
This paper examines the application of the incremental slitting technique for residual stress measurement to plastically deformed four-point bent beams and autogenously edge welded steel beams. Initially a study into a number of factors aecting the series expansion approach was conducted. Due to the over-determined nature of the series expansion approach appropriate selection of polynomial series order was necessary to develop the best prediction. The eect of elasto-plastic properties in experimental situations creates local slit tip yielding which could led to errors particularly at shallow depths and in near slit gauges. The specimens used for the plastic four-point bending were manufactured from ferritic steel with dimensions of width 10mm, depth 25mm and length 250mm. These experiments were conducted to create a better understanding of the incremental slitting procedure and its experimental application. The measured stresses were found to be in reasonable agreement with the FE predictions. A set of autogenously welded ferritic beams of width 10mm, depth 50mm and length 180mm were also measured. These beams were edge welded to create a through depth residual stress field. Residual stress measurements for two dierent weld torch speeds were obtained. We show that a suitably chosen set of polynomials and gauge locations produce residual stress measurements with an uncertainty of about 7MPa.
ABSTRACT For a quenched and tempered and subsequently shot peened steel plate of SAE 4140 the residual stress depth distribution was determined non-destructively by means of neutron diffraction at the STRESS-SPEC instrument at the research reactor FRM II, Garching (Germany). In contrast to conventional methods using strain scanning here an alternative approach was chosen. Strain scanning experiments suffer from the fact that for through surface scanning experiments labo-rious corrections have to be applied in order to compensate the geometrical effects of the partly immersed gauge volume. Furthermore the lattice free strain parameters have to be known precisely for stress evaluation. In this project the experiments were carried out according to the well known sin²ψ-method of X-ray stress analysis [1]. The diffraction data were evaluated using the universal plot method [2,3]. For the in-plane residual stress distribution of a shot peened steel the results clearly indicate that the chosen approach is practicable to determine the stress distribution non-destructively up to large depth by simply tilting the sample up to grazing incidence geometry. Within the project it became evident that an appropriate characterization of the neutron beam path is essential for the goodness of the evaluated residual stress data. By using a stress free annealed steel plate an optimal combination of the collimators in the primary and the diffracted beam path and the bending radius of the Si(004)-monochromator were established.
Silicon and diamond monochromators (crystals), often used in the Advanced Photon Source X-ray beamlines, require a good quality surface finish and stress-free installation to ensure optimal performance. The device used to mount the crystal has been shown to be a major contributing source of stress. In this case, an adjustable mounting device is an effective method of reducing stresses and improve the rocking curve to levels much closer to ideal. Analysis by a topography test unit has been used to determine the distribution of stresses and to measure the rocking curve, as well as create CCD images of the crystal. This paper describes the process of measuring these stresses and manipulating the mounting device and crystal to create a substantially improved monochromator.
The development of a novel 2D analysis method for high-energy X-ray diffraction measurements using a synchrotron microbeam is reported. Its application to study in situ the martensitic transformation of small individual austenite (fcc) grains embedded in a complex ferritic/bainitic/martensitic (bcc) multiphase microstructure is also reported.
The value assignment of candidate Standard Reference Material (SRM®) 57b Silicon Metal provided an opportunity to develop an alkali reaction procedure as a precursor to borate fusion for the preparation of test specimens from the metal powder for X-ray fluorescence spectrometry (XRF). Suggested for this purpose by Blanchette in a 2002 Advances in X-ray Analysis article [45, 415–420 (2002)], the alkali reaction uses LiOH∙H2O to convert Si to Li2SiO3. Lithium silicate is fused with lithium borate flux without damage to platinum ware. Once specimens are fused and cast as beads, calibration standards are prepared to closely match the compositions of the specimens, allowing a linear calibration for each analyte. The XRF method yields results that are directly traceable to the mole through NIST SRM spectrometric solutions. The method was validated in two ways. First, the reaction was used on older SRMs for Si metal: SRM 57 and SRM 57a. Second, XRF results for candidate SRM 57b were compared to results obtained using prompt gamma-ray activation analysis (PGAA) and inductively coupled plasma optical emission spectrometry (ICPOES). Bias tests show the XRF results are accurate for the elements Al, S, Ca, Ti, Cr, Mn, Ni, Cu, and Zr. Levels of S, Ca, Cr, and Cu in candidate SRM 57b are near the limits of quantification of the borate fusion method. Iron results may be subject to a low bias. Phosphorus is not quantitatively retained during the alkali reaction and borate fusion. These elements, plus B, which cannot be determined after borate fusion, are listed in manufacturing specifications for Si metal.
The microstructural evolutions of a Mg alloy, ZK60, subjected to plastic deformation through equal-channel-angular processing (ECAP) and uniaxial compression were compared using X-ray diffraction (XRD) for both 2θ-scans and pole-figure measurements to better understand their specific deformation modes. A larger microstrain was observed in the samples deformed by compression at room temperature, as compared to the samples ECAP-ed at 260 0 C. Crystallographic texture changes due to uniaxial compression suggested a twinning deformation contribution. The texture evolution during ECAP was mapped on a partially processed sample, at locations with different shear-strain values. Microstrain relaxation in ECAP-ed samples indicates that the recovery/ recrystallization processes compete with the plastic deformation, which was supported by texture features observed in a late stage of the ECAP deformation.
In the last decade, diamond single crystals have become valuable monochromators for high-heat-load X-ray synchrotron beamlines. However, due to imperfections in the diamond, the rocking curves of diamond crystals are wider (e.g, 30%) than the theoretical values. Proper etching of the diamond can reduce the effects of imperfections. We explore four etching techniques using synthetic diamonds of type Ib and IIa. The diamond surfaces were variously treated by bombarding with ions, treating with a chemical solution, or using an atom-by-atom chemical machining process. Local variations of tilt and lattice parameter can be experimentally separated, and an improvement of the full width at half maximum (FWHM) of the rocking curve has been observed.
X-ray fluorescence spectroscopy is a widely used method for determining the electronic configuration and local structure of dilute species with high sensitivity. In the dilute limit, and for thin films, the X-ray fluorescence signal is directly proportional to the atomic sub-shell absorption coefficient. However, for concentrated samples, the well-documented self-absorption effect often leads to the severe suppression of XANES (X-ray Absorption Near-Edge Structure) and EXAFS (Extended X-ray Absorption Fine-Structure) amplitudes. Thus to recover the real value of the sub-shell absorption coefficient, it is important to apply correction procedures to the measured fluorescence spectra. In this paper, we describe a new straightforward method to correct for self-absorption effects (the difference in the measured fluorescence signal compared to that of the true sub-shell photoabsorption coefficient) in XANES and EXAFS fluorescence measurements. Using a variety of sample and detector configurations, this method is used to extract the sub-shell absorption coefficient on elemental nickel and thick single-crystals of Gd3Ga5O12 and LaAlO3.
