In the past, several researchers have added X-Ray Fluorescence (XRF) to SEMs, using the standard Energy-Dispersive Spectrometers (EDS) already in place [1]-[2]. Most used the electron beam to create fluorescing x rays with a thin transmission target placed between the beam and the sample. The main problem with this approach was the low incident x-ray flux onto the sample, especially if the analysis area is restricted. The advantages of XRF (e.g., improved sensitivities and peak-to-background ratios) were then lost because of the low count rates achieved. We solved this problem by attaching a separate x-ray source onto the SEM, with flux outputs orders of magnitude higher than those produced by SEM beams in transmission targets. By restricting the sample analysis area with apertures or active focusing optics, one can still achieve count rates in these small areas that are typical of standalone XRF spectrometers, with all the advantages of the XRF technique [3].
Resources
Publications
Integrated XRF in the SEM
B.J. Cross* and K.C. Witherspoon
Keywords: SEM-XRF, electron microscopy
Combined Electron and X-Ray Induced Microbeam XRF in the SEM
Brian J. Cross & Kenny C. Witherspoon
Energy-Dispersive X-Ray Spectroscopy (ED-XRS or EDS) is a powerful and easy-to-use technique for the elemental analysis of a wide variety of materials. Most commonly, this technique is called X-Ray Fluorescence (XRF), which classically uses x-ray photon sources to excite the sample. A Scanning Electron Microscope (SEM), of course, uses electrons as the excitation source for microbeam x-ray spectroscopy together with sample imaging using characteristic x rays and/or secondary electrons. These two XRS techniques are used independently, although often the same sample is analysed by both, to provide complementary information.
Keywords: SEM-XRF, electron microscopy
Advancements in Integrated Micro-XRF in the SEM
K.C. Witherspoon, B.J. Cross, R.D. Lamb and P.-O. Sjoman
Over the last few years, small x-ray tubes have been modified for mounting on Scanning Electron Microscopes. There have been two main types: (a) low-power miniature tubes mounted re-entrantly within the SEM [1], and (b) higher-power tubes with integrated x-ray optics to produce smaller beam spots at the sample with intensities still high enough for routine analytical work [1, 2]. This addition allows samples to be analyzed both by X-Ray Fluorescence (XRF), and by the electron beam (SEM-EDS), as illustrated with the two spectra in FIG. 1.
Keywords: SEM-XRF, electron microscopy
Combined Quantitative Analysis Using both Micro-XRF and EDS Analysis Inside the Scanning Electron Microscope
Kenny C. Witherspoon, Rich Lamb, Per Sjimon, and Mandi D. Hellested
In 2014 [1], the first commercial Micro-focus x-rays tubes were added to the Scanning Electron Microscope (SEM) providing x-ray fluorescence (XRF). These x-ray tubes excite a sample and produce characteristic x-rays in the same manner as Energy Dispersive Spectroscopy (EDS). The characteristics x-rays are then collected by an unmodified EDS detector. The addition of XRF compliments standard EDS analysis primarily due to the absence of the background continuum created by the decelerated electrons generated by the electron beam (Bremsstrahlung). The electron beam is more suited for lighter elements, below 2.0keV. While XRF analysis typically detects ppm level trace elements above 2.0keV, hence offering an increased level of analytical capability over standard EDS systems.
Keywords: SEM-XRF, electron microscopy
Micro X-Ray Fluorescence in Food Forensics & Food Safety
Var L. St. Jeor & Carrie A. Lendon
For this study, Energy Dispersive Micro X-ray Fluorescence (µXRF) is applied in a practical sense to real problems existing within the food industry. It is also compared to electron-based Energy Dispersive Spectroscopy (EDS). Both systems are generally considered non-destructive methods for determining elemental composition; however µXRF demonstrates specific advantages for elements heavier than phosphorus, or above ~2KeV in the energy spectrum. Elements such as iron, nickel and copper, can be detected in smaller concentrations by µXRF than EDS. Although the X-ray probe is fixed, two-dimensional elemental dot maps can be collected by robotically scanning the SEM stage using available software. Since µXRF employs small probe sizes (focal points are usually 10-50µm), and X-ray probes are not usually optically visible, a simple method for aligning and “aiming” of that probe is presented so that very small, specific regions, or very small particles can be analyzed. When combined with SEM, µXRF becomes a very powerful tool.
Keywords: SEM-XRF, electron microscopy
Investigations of high-temperature corrosion of Cr-Ni cast steel
R. Zapała; B. Kalandyk
Austenitic cast steels of Cr25-Ni32-Nb grade have found wide application in chemical and petrochemical industries. This study discusses the problem of the kinetics of oxidation of these materials in the atmosphere of laboratory air at temperatures of 930 and 1000 °C. Considering the operating conditions of castings (centrifugally cast reformer tubes), the results of the oxidation test of specimens taken from the zone of columnar crystals and equiaxial grains were presented.
Keywords: SEM/EDS, electron microscopy, microanalysis, SEM-XRF, austenitic steel
Comparing the Detection of Iron-Based Pottery Pigment on a Carbon-Coated Sherd by SEM-EDS and by Micro-XRF-SEM
Michael W. Pendleton, Dorothy K. Washburn, E. Ann Ellis, and Bonnie B. Pendleton
The same sherd was analyzed using a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) and a micro X-ray fluorescence tube attached to a scanning electron microscope (Micro-XRF-SEM) to compare the effectiveness of elemental detection of iron-based pigment. To enhance SEM-EDS mapping, the sherd was carbon coated. The carbon coating was not required to produce Micro-XRF-SEM maps but was applied to maintain an unbiased comparison between the systems. The Micro-XRF-SEM analysis was capable of lower limits of detection than that of the SEM-EDS system, and therefore the Micro-XRF-SEM system could produce elemental maps of elements not easily detected by SEM-EDS mapping systems. Because SEM-EDS and Micro-XRF-SEM have been used for imaging and chemical analysis of biological samples, this comparison of the detection systems should be useful to biologists, especially those involved in bone or tooth (hard tissue) analysis.
Keywords: SEM/EDS, SEM-XRF, electron microscopy, pottery pigment, archeology
Characteristics of centrifugally cast GX25CrNiSi18-9 steel
R. Zapała, B. Kalandyk and A. Rakowska
The paper presents the results of microstructural examinations of the industrial heat-resistant centrifugally cast GX25CrNiSi18-9 steel characterised by increased content of Cu. The study included changes in the microstructure of base cast steel respective of the steel held at a temperature of 900 and 950°C for 48 hours. Based on the results obtained, an increase in microhardness of the examined cast steel matrix with increasing temperature was stated, which was probably caused by fine precipitates enriched in Cr, Mo, and C forming inside the matrix grains.The layer of scale formed on the tested cast steel oxidised in the atmosphere of air at 900 and 950°C was characterised by an increased tendency to degradation with increasing temperature of the conducted tests.
Keywords: SEM/EDS, electron microscopy, microanalysis, SEM-XRF, steel
Advancements in Integrated Micro-XRF in the SEM
K.C. Witherspoon • B.J. Cross • R.D. Lamb • P.-O. Sjoman
Electronic components are everywhere in our modern world. It is imperative that these components are reliable, as they control extremely important systems from every day items, to electronically controlled military equipment as well as a variety of aerospace equipment. To assure this reliability components must go through a battery of tests. XRF analysis is an irreplaceable tool for the semiconductor industry to not only guarantee but to also certify their products. Electrical or photonic circuits are one of these components that are the foundation for so many other products. These circuits begin their lives on silicon wafers. As the wafers and associated circuits and boards become more specialized they require different types of testing.
Keywords: SEM-XRF, electron microscopy, XRF, SEM
Securing timelines in the ancient Mediterranean using multiproxy annual tree-ring data
Charlotte Pearson, Matthew Salzera , Lukas Wackerd, Peter Brewera , Adam Sookdeod, and Peter Kuniholma
Calendar-dated tree-ring sequences offer an unparalleled resource for high-resolution paleoenvironmental reconstruction. Where such records exist for a few limited geographic regions over the last 8,000 to 12,000 years, they have proved invaluable for creating precise and accurate timelines for past human and environmental interactions. To expand such records across new geographic territory or extend data for certain regions further backward in time, new applications must be developed to secure “floating” (not yet absolutely dated) tree-ring sequences, which cannot be assigned single-calendar year dates by standard dendrochronological techniques. This study develops two approaches to this problem for a critical floating tree-ring chronology from the East Mediterranean Bronze–Iron Age. The chronology is more closely fixed in time using annually resolved patterns of 14C, modulated by cosmic radiation, between 1700 and 1480 BC. This placement is then tested using an anticorrelation between calendardated tree-ring growth responses to climatically effective volcanism in North American bristlecone pine and the Mediterranean trees. Examination of the newly dated Mediterranean tree-ring sequence between 1630 and 1500 BC using X-ray fluorescence revealed an unusual calcium anomaly around 1560 BC. While requiring further replication and analysis, this anomaly merits exploration as a potential marker for the eruption of Thera.
Keywords: hyperspectral imaging, micro XRF, tree-ring, tree ring sequences, Laboratory of Tree-Ring Research
Distribution and chemical form of selenium in Neptunia amplexicaulis from Central Queensland, Australia
Guillaume Echevarriaf, Antony van der Ent, et al.
Selenium (Se), a trace element essential for human and animal biological processes, is deficient in many agricultural soils. Some extremely rare plants can naturally accumulate extraordinarily high concentrations of Se. The native legume Neptunia amplexicaulis, endemic to a small area near Richmond and Hughenden in Central Queensland, Australia, is one of the strongest Se hyperaccumulators known on Earth, with foliar concentrations in excess of 4000 μg Se g−1 previously recorded. Here, we report on the Se distribution at a whole plant level using laboratory micro X-ray Fluorescence Microscopy (μXRF) and scanning electron microscopy (SEM-EDS), as well as on chemical forms of Se in various tissues using liquid chromatography-mass spectrometry (LC-MS) and synchrotron X-ray absorption spectroscopy (XAS). The results show that Se occurs in the forms of methyl-selenocysteine and seleno-methionine in the foliar tissues, with up to 13 600 μg Se g−1 total in young leaves. Selenium was found to accumulate primarily in the young leaves, flowers, pods and taproot, with lower concentrations present in the fine-roots and stem and the lowest present in the oldest leaves. Trichomes were not found to accumulate Se. We postulate that Se is (re)distributed in this plant via the phloem from older leaves to newer leaves, using the taproot as the main storage organ. High concentrations of Se in the nodes (pulvini) indicate this structure may play an important a role in Se (re)distribution. The overall pattern of Se distribution was similar in a non-Se tolerant closely related species (Neptunia gracilis), although the prevailing Se concentrations were substantially lower than in N. amplexicaulis.
Keywords: hyperspectral imaging, micro XRF, phytometallomics, plants, botany
Time-resolved laboratory micro-X-ray fluorescence reveals silicon distribution in relation to manganese toxicity in soybean and sunflower
Antony van der Ent, Lachlan W Casey, F Pax C Blamey and Peter M Kopittke
Synchrotron- and laboratory-based micro-X-ray fluorescence (µ-XRF) is a powerful technique to quantify the distribution of elements in physically large intact samples, including live plants, at room temperature and atmospheric pressure. However, analysis of light elements with atomic number (Z) less than that of phosphorus is challenging due to the need for a vacuum, which of course is not compatible with live plant material, or the availability of a helium environment.
A new laboratory µ-XRF instrument was used to examine the effects of silicon (Si) on the manganese (Mn) status of soybean (Glycine max) and sunflower (Helianthus annuus) grown at elevated Mn in solution. The use of a helium environment allowed for highly sensitive detection of both Si and Mn to determine their distribution.
The µ-XRF analysis revealed that when Si was added to the nutrient solution, the Si also accumulated in the base of the trichomes, being co-located with the Mn and reducing the darkening of the trichomes. The addition of Si did not reduce the concentrations of Mn in accumulations despite seeming to reduce its adverse effects.
The ability to gain information on the dynamics of the metallome or ionome within living plants or excised hydrated tissues can offer valuable insights into their ecophysiology, and laboratory µ-XRF is likely to become available to more plant scientists for use in their research.
Keywords: hyperspectral imaging, micro XRF, phytometallomics, plants, botany
Distribution of aluminium in hydrated leaves of tea (Camellia sinensis) using synchrotron- and laboratory-based X-ray fluorescence microscopy
Antony van der Ent, Peter M. Kopittke, David J. Paterson, Lachlan W. Casey and Philip Nti Nkrumah
Aluminium (Al) is highly toxic to plant growth, with soluble concentrations being elevated in the ∼40% of arable soils worldwide that are acidic. Determining the distribution of Al in plant tissues is important for understanding the mechanisms by which it is toxic and how some plants tolerate high concentrations. Synchrotron- and laboratory-based X-ray fluorescence microscopy (XFM) is a powerful technique to quantitatively analyse the distribution of elements, including in hydrated and living plants. However, analysis of light elements (Z < phosphorus) is extremely challenging due to signal losses in air, and the unsuitability of vacuum environments for (fresh) hydrated plant tissues. This study uses XFM in a helium environment to avoid Al signal loss to reveal the distribution of Al in hydrated plant tissues of Tea (Camellia sinensis). The results show that Al occurs in localised areas across the foliar surface, whereas in cross-sections Al is almost exclusively concentrated in the apoplastic space above and in between adaxial epidermal cells. This distribution of Al is related to the Al tolerance of this species, and accumulation of phytotoxic elements in the apoplastic space, away from sensitive processes such as photosynthesis in the palisade mesophyll cells, is a common tolerance mechanism reported in many different plant species. This study develops an XFM method on both synchrotron and laboratory sources that overcomes the drawbacks of existing analytical techniques, permitting measurement of light elements down to Al in (fresh) hydrated plant tissues.
Keywords: hyperspectral imaging, micro XRF, phytometallomics, plants, botany
Bridging the Gap: MXRF Technique Rapidly Maps Centerline Segregation
Joydeep Sengupta, Jackie Leung and Kenny Witherspoon
Advanced high-strength steel (AHSS) and ultrahigh-strength steel (UHSS) slabs produced from ArcelorMittal casters worldwide have high alloy contents — manganese up to 5%, silicon up to 2% and aluminum up to 2% — for achieving desired mechanical properties for automotive customers. These specialty steel grade groups include dual-phase (DP) and transformation-induced plasticity (TRIP) steel grades. High-strength, low-alloy (HSLA) steel grades slated for the line pipe industry also have high manganese content (up to 1%) and relatively higher sulfur (>50 ppm) and phosphorus (>100 ppm) contents compared to other steel grades. During continuous casting of these specialty steel grades, alloying elements often segregate along the centerline of slabs (Fig. 1). If a continuous channel of solute-enriched liquid is formed near the final solidification point due to sub-optimal casting conditions, a centerline with segregated elements remains frozen inside the slab. In the absence of adequate strand containment, strand bulging often encourages movement of liquid within this solute-enriched continuous channel and aggravates the problem of centerline segregation. Casting parameters such as super-heat, spray cooling practice and casting speed determine the severity and extent of centerline segregation in these slabs. Fig. 2 shows the range of centerline segregation severity typically found in AHSS slabs. In addition to the centerline segregation defect, internal midway cracks may also appear if excessively large bulging strains are created at the continuous caster near the solidifying front. Equipment maintenance-related parameters, such as caster roll misalignment, roll wear, and plugged and/or leaky spray nozzles also have a detrimental effect on internal quality of slabs. Review of published literature indicates that slab centerline segregation can lead to the formation of martensitic banded structure in hot- and cold-rolled sheet products, which may have some impact on their final mechanical properties. The detrimental impact of severe continuous martensitic banding on mechanical properties of DP steel sheets has been reported. Hence, to protect the interest of the customers, minimization and control of centerline segregation is very important to all steelmakers that produce AHSS slabs.
Keywords: micro-XRF, microEDXRF, centerline segregation, steel, continuously cast
A preliminary survey of nickel, manganese and zinc (hyper)accumulation in the flora of Papua New Guinea from herbarium X-ray fluorescence scanning
Do, C., Abubakari, F., Remigio, A.C. et al.
The flora of Papua New Guinea is amongst the richest in the world with an estimated 25,000 plant species. The extreme levels of biodiversity, climatic ranges and soil types suggest a high possibility of metal hyperaccumulator plants existing in Papua New Guinea. However, no hyperaccumulator plants have been reported from this region yet. The use of handheld X-ray fluorescence instruments is a non-destructive and effective method for the systematic quantitative assessment of hyperaccumulation in vast numbers of herbarium specimens. X-ray fluorescence scanning was undertaken at the Queensland Herbarium (Australia) on all Papua New Guinea specimens from seven major families (Celastraceae, Cunoniaceae, Phyllanthaceae, Proteaceae, Rubiaceae, Salicaceae and Violaceae), covering 3164 plant specimens. This preliminary survey revealed the existence of ten zinc hyperaccumulator species (> 3000 µg g−1 Zn), eight manganese accumulator species (> 5000 µg g−1 Mn) and one nickel hyperaccumulator species (> 1000 µg g−1 Ni). These results highlight the potential for discovery of numerous new metal hyperaccumulator plants from the flora of Papua New Guinea if larger-scale systematic screening efforts were undertaken.
Keywords: (hyper)accumulation, micro XRF, plants, botany
Silica nanoparticles aid in structural leaf coloration in the Malaysian tropical rainforest understorey herb Mapania caudata
Greg Strout, Scott D. Russell, Drew P. Pulsifer, Sema Erten, Akhlesh Lakhtakia and David W. Lee
Background and AimsBlue-green iridescence in the tropical rainforest understorey sedge Mapania caudata creates structural coloration in its leaves through a novel photonic mechanism. Known structures in plants producing iridescent blues consist of altered cellulose layering within cell walls and in special bodies, and thylakoid membranes in specialized plastids. This study was undertaken in order to determine the origin of leaf iridescence in this plant with particular attention to nano-scale components contributing to this coloration. Methods Adaxial walls of leaf epidermal cells were characterized using high-pressure-frozen freeze-substituted specimens, which retain their native dimensions during observations using transmission and scanning microscopy, accompanied by energy-dispersive X-ray spectroscopy to identify the role of biogenic silica in wall-based iridescence. Biogenic silica was experimentally removed using aqueous Na2CO3 and optical properties were compared using spectral reflectance. Key Results and Conclusions Blue iridescence is produced in the adaxial epidermal cell wall, which contains helicoid lamellae. The blue iridescence from cell surfaces is left-circularly polarized. The position of the silica granules is entrained by the helicoid microfibrillar layers, and granules accumulate at a uniform position within the helicoids, contributing to the structure that produces the blue iridescence, as part of the unit cell responsible for 2° Bragg scatter. Removal of silica from the walls eliminated the blue colour. Addition of silica nanoparticles on existing cellulosic lamellae is a novel mechanism for adding structural colour in organisms.
Keywords: SEM/EDS, cell wall, circular polarization, Cyperaceae, epidermis, helicoids, iridescence, leaf, Mapania, nanoparticle, photonics, silica
Mechanism of Pinhole Formation in Membrane Electrode Assemblies for PEM Fuel Sells
Vesna Stanic and Mark Hoberecht
The pinhole formation mechanism was studied with a variety of MEAs using ex-situ and in-situ methods. The ex-situ tests included the MEA aging in oxygen and MEA heat of ignition. In-situ durability tests were performed in fuel cells at different operating conditions with hydrogen and oxygen. After the in-situ failure, MEAs were analyzed with an Olympus BX 60 optical microscope and Cambridge 120 scanning electron microscope. MEA chemical analysis was performed with an IXRF EDS microanalysis system. The MEA failure analyses showed that pinholes and tears were the MEA failure modes. The pinholes appeared in MEA areas where the membrane thickness was drastically reduced. Their location coincided with the stress concentration points, indicating that membrane creep was responsible for their formation. Some of the pinholes detected had contaminant particles precipitated within the membrane. This mechanism of pinhole formation was correlated to the polymer blistering.
Keywords: SEM/EDS, electron microscopy, microanalysis
Combined Electron Excitation and X-Ray Excitation for Spectrometry in the SEM
Kenny C. Witherspoon, Brian J. Cross, and Mandi D. Hellested
Energy-dispersive X-ray spectrometry (EDS) is an analytical technique used to determine elemental composition. It is a powerful, easy-to-use, non-destructive technique that can be employed for a wide variety of materials. In this technique the electron beam of the scanning electron microscope (SEM) impinges on the sample and excites atomic electrons causing the production of characteristic X rays. These characteristic X rays have energies specific to elements in the sample. The EDS detector collects these X rays as a signal and produces a spectrum. Samples also can be excited by X rays. Collimated and focused X rays from an X-ray source produce characteristic X rays that can be detected by the same EDS detector. When X rays are used as the source of excitation, the method is then called X-ray fluorescence (XRF) or micro-XRF.
Keywords: SEM/EDS, electron microscopy, microanalysis, SEM-XRF
A Test of Diagenetic Ordering in Siliceous Lithofacies, Montery Formation, Southwestern Casmalia Hills: Santa Maria Basin, Ca
Idu Opral C. Ijeoma and Richard J. Behl
A detailed analysis of a well-exposed section through the Sisquoc and Monterey formations test the results of previous silica diagenesis studies by Isaacs (1981), Pisciotto (1981), and Murata and Nakata (1974). From these studies, a key understanding was that for each compositional range, there would be a regular progression of opal-A → opal-CT→ progressive ordering of opal-CT d101 spacing → quartz. This progression should apply to any stratigraphic succession for strata of a particular compositional range, and opal-CT d101 could be used as a geothermometer and indicator of maximum burial depth. Surprisingly, these classic studies analyzed only limited numbers of samples in single successions, so we decided to test if the same trends are evident in a very dense data set in one stratigraphic sequence, 230 outcrop and road-cut samples were collected from a 700-meter thick sections and analyzed for composition, silica phase, and d101-spacing using combined EDS/XRF and XRD. The field area has a down-section stratigraphic trend from opal-A to opal-CT to interbedded opal-CT and quartz-phase rocks. Samples ranging from siliceous mudstone to cherty porcelanite were plotted in narrow, 10 percent compositional brackets on a carbonate-, apatite-, organic matter-free basis. The data displayed a wide range of opal-C d101 spacing for all depths and compositional ranges, and do not show a simple trend of decreased d101-spacing with depth as would be predicted by previous, well-cited studies. A literature search to understand the discrepancy in the results found several publications that also found opal-CT d101- spacing decreasing only subtly with depth and with wide degree of scatter. It is little appreciated that Isaacs’ well-known silica diagenesis diagram that shows the differences in d101-spacing with composition was not constructed from a stratigraphic succession, but from relationships at multiple locations with different burial depths and temperatures — working geologists have inferred that this trend is applicable to single stratigraphic sections. Our new results do not necessarily refute the conceptual model of increased ordering (decreasing d101) with burial depth and temperature, but strongly suggest that other spatially important variables besides burial depth/temperature and composition are critical. Consequently, use of opal-CT d101-spacing should be used as a geothermometer only with great caution.
Keywords: EDS/XRF, siliceous lithofacies
Detecting iron-based pigments on ruthenium-coated ancestral Pueblo pottery using variable pressure scanning electron microscopy
M.W.Pendleton, D.K.Washburn, E.A.Ellis and B.B.Pendleton
Ancestral Puebloan black-on-white ceramics of the American Southwest can be classified as containing pigments within their painted designs containing high levels of organic-based elements such as potassium, or mineral-based elements such as iron, or a mixture of these elements. The identification of pigment elements of the pottery of a site is fundamental in determining the site’s cultural and temporal context. This paper will concentrate only on the analysis of mineral based pigment which was shown by previous researchers to exhibit greater concentrations of iron than organic based pigment. Although the visual discrimination of these pigments can be difficult if the pigment is a mixture of both pigment types or if the pigment is worn, this paper will describe a sherd sample previously shown to contain only mineral pigment. For the present study, a Tescan variable pressure scanning electron microscope, a JEOL 6400 scanning electron microscope, and a Hitachi S-3400N scanning electron microscope were used with the same sherd. This sherd was coated with ruthenium to reduce charging without the visual color change associated with sputtered metal coatings. A reduction in microscope chamber vacuum also greatly reduced charging of unpainted areas. An energy dispersive spectrometry detector produced a map of the iron present in the sherd. Areas of iron in the sherd were identified using a backscatter electron detector. Iron as well as other elements present in the paint pigment was also detected using micro-X-ray fluorescence on the same sherd.
Keywords: EDS/XRF, archeological pottery, pigments, iron, electron microscopy
Hematite spherules in basaltic tephra altered under aqueous, acid-sulfate conditions on Mauna Kea volcano, Hawaii: Possible clues for the occurrence of hematite-rich spherules in the Burns formation at Meridiani Planum, Mars
R.V. Morris ,*, D.W. Ming , T.G. Graff , R.E. Arvidson , J.F. Bell III , S.W. Squyres , S.A. Mertzman , J.E. Gruener , D.C. Golden f , L. Le and G.A. Robinson
Iron-rich spherules (> 90% Fe2O3 from electron microprobe analyses) ∼10–100 μm in diameter are found within sulfate-rich rocks formed by aqueous, acid-sulfate alteration of basaltic tephra on Mauna Kea volcano, Hawaii. Although some spherules are nearly pure Fe, most have two concentric compositional zones, with the core having a higher Fe / Al ratio than the rim. Oxide totals less than 100% (93–99%) suggest structural H2O and/or OH− 1. The transmission Mössbauer spectrum of a spherule-rich separate is dominated by a hematite (α-Fe2O3) sextet whose peaks are skewed toward zero velocity. Skewing is consistent with Al3+ for Fe3+ substitution and structural H2O and/or OH− 1. The grey color of the spherules implies specular hematite. Whole-rock powder X-ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra. Whether spherule formation proceeded directly from basaltic material in one event (dissolution of basaltic material and precipitation of hematite spherules) or whether spherule formation required more than one event (formation of Fe-bearing sulfate rock and subsequent hydrolysis to hematite) is not currently constrained. By analogy, a formation pathway for the hematite spherules in sulfate-rich outcrops at Meridiani Planum on Mars (the Burns formation) is aqueous alteration of basaltic precursor material under acid-sulfate conditions. Although hydrothermal conditions are present on Mauna Kea, such conditions may not be required for spherule formation on Mars if the time interval for hydrolysis at lower temperatures is sufficiently long.
Keywords: concretions, hematite, Mars, Mars Exporation Rover, Meridiani Planum, Spherule, sulfate, SEM/EDS
High-Temperature Superconducting Fiber
Daniel Homa, Yongxuan Liang and Gary Pickrell
In this study, we demonstrated superconductivity in a fiber with an yttrium barium copper oxide core and fused silica cladding. The fibers were fabricated via a modified melt-draw technique and post-process annealing treatment in excess oxygen. The fibers maintained overall diameters ranging from 100–900 microns and core diameters of 50–700 microns. Superconductivity of this fiber design was validated via the traditional four-point probe test method in a bath of liquid nitrogen at temperatures on the order of 93 K. The high-temperature superconducting fiber provides a glimpse of its cross cutting potential in fields of electromagnetism, healthcare, optics, and energy and lends credence to the promise for superconductivity.
Keywords: SEM/EDS, superconductor, fiber, analysis
Novel Synthesis of Kanamycin Conjugated Gold Nanoparticles with Potent Antibacterial Activity
Jason N. Payne, Hitesh K. Waghwani, Michael G. Connor, William Hamilton, Sarah Tockstein, Harsh Moolani, Fenil Chavda, Vivek Badwaik, Matthew B. Lawrenz and Rajalingam Dakshinamurthy
With a sharp increase in the cases of multi-drug resistant (MDR) bacteria all over the world, there is a huge demand to develop a new generation of antibiotic agents to fight them. As an alternative to the traditional drug discovery route, we have designed an effective antibacterial agent by modifying an existing commercial antibiotic, kanamycin, conjugated on the surface of gold nanoparticles (AuNPs). In this study, we report a single-step synthesis of kanamycin-capped AuNPs (Kan-AuNPs) utilizing the combined reducing and capping properties of kanamycin. While Kan-AuNPs have increased toxicity to a primate cell line (Vero 76), antibacterial assays showed dose-dependent broad spectrum activity of Kan-AuNPs against both Gram-positive and Gram-negative bacteria, including Kanamycin resistant bacteria. Further, a significant reduction in the minimum inhibitory concentration (MIC) of Kan-AuNPs was observed when compared to free kanamycin against all the bacterial strains tested. Mechanistic studies using transmission electron microscopy and fluorescence microscopy indicated that at least part of Kan-AuNPs increased efficacy may be through disrupting the bacterial envelope, resulting in the leakage of cytoplasmic content and the death of bacterial cells. Results of this study provide critical information about a novel method for the development of antibiotic capped AuNPs as potent next-generation antibacterial agents.
Keywords: SEM/EDS, antibacterial activity, antibiotic resistance, characterization, gold nanoparticles, kanamycin
Macroscopic X-Ray Fluorescence Capability for Large-Scale Elemental Mapping
Heather M. Volz, George J. Havrilla, Robert M. Aikin, Jr. and Velma M. Montoya
Compositional information at moderate resolution over many centimeters will be powerful in materials research, not only to validate casting models but also to understand large-scale phenomena during solidification. These elemental differences across a part have a huge impact on materials properties so that identifying variations will help industry immensely with process optimization and quality control. Therefore, a nondestructive method of obtaining spatially resolved elemental compositions over large areas would be very useful. To this end, we have developed an enhanced macro-x-ray fluorescence (XRF) capability in conjunction with IXRF Systems (Austin, Texas) to accommodate samples larger than those that typically fit into an XRF instrument chamber. Our system can accommodate samples up to 70 cm x 70 cm x 25 cm, which is unique in that most systems are trending toward smaller micro- and nano-XRF. This system uses a rhodium tube having a maximum power of 35 kV and 100 JlA; the detector is a liquid-nitrogen cooled, lithium-drifted silicon detector, and the smallest spot size is approximately 400 micrometers. Reference standard specimens will enable quantitative elemental mapping and analysis. Challenges to modifying the equipment are described. Nonuniformities in the INCONEL 718 system will be shown and discussed. As another example, segregation of niobium and molybdenum in depleted uranium (DU) castings has been known to occur based on wet chemical analysis [inductively coupled-plasma mass spectrometry (ICPMS)], but this destructive and time-consuming measurement is not practical for routine inspection of ingots. The U-Nb system is complicated because of overlap of the Nb K-alpha line with the U L-beta. Preliminary quantitative results are included on the distribution ofNb across slices from DU castings with different cooling rates. We foresee this macro-XRF elemental mapping capability becoming a valuable asset to the materials industry.
Keywords: spatially resolved elemental analysis, XRF, EDXRF, mapping,
Study of the possibility of using IXRF technique to detect the elements present in dust using Monte Carlo N particles
R. Dehghan , A. Negarestani and M. R. Rezaie
Detecting heavy metals present in soil and dust as a major factor of environmental pollution has got a particular importance. An experimental (laboratory) method based on energy-dispersive X-ray fluorescence (EDXRF) technique was utilized so far to detect the elements. In this research, the Monte Carlo method based on the EDXRF technique was used to detect the elements. MCNPX2.7 code is based on Monte Carlo calculations and is able to trace 32 particles including photons within the range of X-rays and γ-rays. In this paper, the outcomes of multi-source EDXRF simulation technique were compared with the experimental results. The comparison shows that multi-source EDXRF technique (IXRF) is able to detect the percentage of elements present in soil and dust with a high compatibility.
Keywords: multi-source XRF, heavy metals, soil, dust, elemental analysis
