Electron Microprobe Microanalysis Research Articles

Integrated textural and geochemical analysis of igneous zircon by atom probe tomography

Mechanisms relating to growth and/or compositional modification of zircon occur at the atomic scale. For felsic igneous systems, processes responsible for growth patterns in zircon have previously remained elusive as the volume of material needed to analyze these compositional features using traditional in-situ methods is considerably larger than the typical sub-micron scale distribution of trace elements. To illuminate some of these driving forces, we characterize and quantify minor and trace element concentrations in igneous zircon grains by combining methods of cathodoluminescence (CL) imaging, electron microprobe microanalysis (EMPA) elemental maps for Hf, Y, Yb and U or Th, and atom probe tomography (APT). We focus on igneous zircon from the Chon Aike Silicic Large Igneous Province (Patagonia) that provide novel insights into (1) dissolution and re-crystallization during crustal anatexis, (2) crystallization to produce oscillatory zonation patterns that are typical of igneous zircons, and (3) the incorporation of trace element impurities (e.g., P, Be, and Al) at the nanoscale. Significantly, these APT volumes provide nanoscale sampling of boundaries between oscillatory growth zones in an igneous zircon to reveal compositional zoning of Y and, to a lesser extent P, which appear as high-angle, planar features. These concentration boundaries measured on the order of 10 to 12 nm are difficult to reconcile with proposed mechanisms for generating fine-scaled oscillations. Lastly, we fit diffusional profiles to measured Y concentrations to provide an estimate on the maximum timescales of zircon growth prior to eruption, as a function of the temperature at which diffusion occurred. When combined with known pressure-temperature-time paths for the magmatic system considered, these extremely short diffusion profiles that are resolvable by APT provide a powerful method to constrain timescales of crystal growth.

Electrochemical reactions driving Mn-enrichment in Fe[sbnd]Mn supergene ores: A mineralogical perspective

Iron and manganese oxides embody a geochemical system of great environmental, biological, and economical relevance. Chemical equilibria and the stability of FeMn phases under surface or near-surface conditions can influence the fate of contaminants in the environment, impact biological metabolic processes, or Fe and Mn phase distribution in weathered ores. In the present work, we focus on the textural, mineralogical, and chemical study of FeMn ores from the weathered zone of a vein-hosted deposit outcropping in the Iberian Pyrite Belt, SW Portugal, by means of micro-Raman spectroscopy coupled with electron microprobe microanalysis. The aims of our investigation are i) identifying the several Fe and Mn phases occurring in differently enriched ores samples, ii) relating their chemical composition with possible mineralization mechanisms, and iii) defining the mineral paragenetic pathway related to the observed textural features. Our approach enabled both the identification of the coexisting Fe and Mn phases, and unravelling paragenetic pathways leading to supergene enrichment mineralizations. Collected evidence demonstrates that changes in Eh/pH can lead to goethite dissolution under reductive conditions, promoting the release of Fe2+ into solution, whose electrochemical interaction with Mn4+ results in the formation of several types of Mn oxides, and secondary goethite. Our data shows a clear relationship between the type of Mn oxide crystallized and the ratio of aqueous Mn3+/Mn4+, alongside other prevalent cations, incorporated into tunnel or interlayer structural sites, which may be also desorbed/solubilized from primary goethite.

Geochemistry of apatite in Late Permian coals, Bowen Basin, Australia

Apatite may be a common accessory mineral in coal seams, but interpretation of its origins can vary from syndepositional mineral detritus, early precipitation during diagenesis, and post coalification precipitation and replacement from hydrothermal or other fluids. It is hypothesised that paragenesis is reflected in the modes of occurrence in different stratigraphic units of the Late Permian in the Bowen Basin. From samples analysed in this study, apatite in the youngest unit, the Rangal Coal Measures, most commonly occurs as pore-apatites (i.e. apatites infilling preserved plant cell cavities of fusinite and semifusinite macerals and commonly associated with kaolinite) and less commonly as fracture-apatites (i.e. apatites infilling micro-fractures) and detrital-apatites intermixed with the organic coal layers (Detrital-B). In the tuffaceous Fort Cooper Coal Measures and equivalents, apatite occurs more commonly as detrital-apatites intermixed with the lithic layers (Detrital-A) (Detrital. Within the basal unit, the Moranbah Coal Measures and its equivalents, the mode is commonly encrusting-apatites (i.e. small apatite crystallites encrusting silicate minerals). Almost all apatites in the coal samples tested by electron microprobe microanalysis (EPMA), regardless of stratigraphic location and mode, are fluorapatite. Although there are some locality-driven enrichments, the minor and trace-element chemistry vary more so by mode of occurrence. For comparison, apatites from dykes intersecting the coal measures and from tuffs were also added to the study. These had lower fluorine (F) but measurable chlorine (Cl) contents and are enriched in light rare earth elements (LREE), similar to the Durango apatite that is of magmatic origins. Most of the detrital-A apatites are also enriched in LREE similar to the tuff-apatites, but with variable enrichment in the rare earth and yttrium elements. Detrital-B apatites have minimal Cl but also show the magmatic LREE trend. The pore- and fracture-apatites exhibited two trends. In the samples from tuffaceous coals (e.g., Fort Cooper Coal Measures), the pore- and fracture apatites tended to follow the magmatic LREE trend. In the Rangal Coal Measures, the pore- and fracture-apatites have elevated F contents, minimal Cl contents and depleted LREE contents (or Middle REE enrichment). Depletion of LREE could occur through leaching in an acidic environment, which is suggested by the abundance of kaolinite. Apatite precipitates under more neutral conditions although pore-apatites are commonly considered “early” and fracture-apatites “late” or post coalification. Their geochemical similarity suggests they have similar fluid origins and/or timing, with geothermal fluids moving through the porosity afforded by the structured inertinite group macerals and fractures. Verification of that geothermal source still requires further work and a technique that can analyse the isotopic composition—e.g., carbon (13C/12C), oxygen (18O/16O) and strontium (87Sr/86Sr)—of micron-sized crystals in situ.

Characteristics and mechanisms of Pb(II) sorption onto Fe-rich waste water treatment residue (WTR): A potential sustainable Pb immobilisation technology for soils

Pb contamination of soils is a global problem. This paper discusses the ability of an Fe-rich waste, water treatment residual (WTR), to adsorb Pb(II). This was investigated using batch sorption experiments, X-ray diffraction, electron microprobe microanalysis, PHREEQC modeling and Extended X-ray Absorption Fine Structure (EXAFS) analysis. The WTR is composed of approximately 23 wt. % natural organic matter (NOM), 70 wt. % ferrihydrite and <10 wt. % silicate material. Pb(II) sorption to WTR was dependent on initial Pb(II) load, particle size, time and pH, but not on ionic strength. EXAFS analysis at the Pb LIII-edge confirmed that Pb(II) sorbed to WTR by co-existing bidentate edge-sharing and monodentate or corner-sharing complexes, with 2 O at ∼2.31–2.34 Å, 1 Fe at ∼3.32–3.34 Å, 2 Fe at ∼3.97–3.99 Å and 1 Pb at ∼3.82–3.85 Å. Linear combination showed that the Pb(II)-sorbed spectra were best fit with a ∼0.9 ± 0.1 and 0.1 ± 0.1 contribution from Pb(II)-sorbed ferrihydrite and Pb(II)-sorbed humic acid end members, respectively. Overall, we show that Pb(II) sorbs via strong inner-sphere complexation of Pb(II) to the ferrihydrite component of the WTR, which itself is stable over a wide pH range. Therefore, we suggest that Fe-rich WTR wastes could be used as effective adsorbents in Pb(II)-contaminated soils to help ensure sustainable terrestrial ecosystems.

Mg/Ca and Sr/Ca as novel geochemical proxies for understanding sediment transport processes within coral reefs

Sediment transport is a key driver of reef zonation and biodiversity, where an understanding of sediment dynamics gives insights into past reef processes and allows the prediction of geomorphic responses to changing environmental conditions. However, modal conditions within the back-reef seldom promote sediment transport, hence direct observation is inherently difficult. Large benthic foraminifera (LBF) have previously been employed as ‘tracers’ to infer sediment transport pathways on coral reefs, as their habitat is largely restricted to the algal flat and post-mortem, their calcium carbonate test is susceptible to sediment transport forces into the back-reef. Foraminiferal test abundance and post-depositional test alteration have been used as proxies for sediment transport, although the resolution of these measures becomes limited by low test abundance and the lack of variation within test alteration. Here we propose the novel use of elemental ratios as a proxy for sediment transport. Two species, Baculogypsina sphaerulata and Calcarina capricornia, were analysed using a taphonomic index within One Tree and Lady Musgrave reefs, Great Barrier Reef (Australia). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) was used to determine Mg/Ca and Sr/Ca and these ratios were compared with taphonomic data. Decreases in test Mg/Ca accompany increases in Sr/Ca in specimens from algal-flat to lagoonal samples in both species, mirroring trends indicated by taphonomic values, therefore indicating a relationship with test alteration. To delineate mechanisms driving changes in elemental ratios, back-scattered electron (BSE) images, elemental mapping and in situ quantitative spot analyses by electron microprobe microanalysis (EPMA) using wavelength dispersive X-ray spectrometers (WDS) were performed on un-altered algal flat and heavily abraded tests for both species. EPMA analyses reveal heterogeneity in Mg/Ca between spines and the test wall, implying the loss of appendages results in a decrease in Mg/Ca. BSE imaging and WDS elemental mapping provided evidence for cementation, facilitated by microbial-boring as the primary cause of increasing Sr/Ca. These novel proxies hold advantages over taphonomic measures and further provide a rapid method to infer sediment transport pathways within back-reef environments.

Graphite‐bearing mineral assemblages in the mantle beneath Central Aldan superterrane of North Asian craton: combined confocal micro‐Raman and electron microprobe characterization

Mantle‐derived lherzolitic and harzburgitic Cr‐pyropes from lamprophyres of the Chompolo field (Central Aldan superterrane, North Asian Craton) were studied using micro‐Raman spectroscopy and electron microprobe microanalysis. These garnets enclose graphite coexisting with forsterite, diopside, Ba‐Cl‐phlogopite, tschermakite, rutile, magnesiochromite, Mg‐ilmenite, apatite, chalcopyrite, dolomite, magnesite and lindsleyite inclusions. The PT conditions of residence of graphite‐bearing assemblage in the mantle were estimated, using a combination of mineral thermometers and barometers, to be as high as 2.87–3.55 GPa and 710–770 °C. Generally, graphite within inclusions is well ordered; D1 and D2 disordered bands in its spectra are restricted to inclusion edges. The residual pressure up to 2.1 GPa was inferred for graphite assuming pressure dependence of the G‐band upshift (1580 cm−1 at ambient conditions vs 1588.6 cm−1 at 2.1 GPa). Disordered graphite most likely appears due to the stress‐induced distortion of the fully ordered graphite crystal structure. The distortion results from difference in the thermoelastic properties of graphite inclusions and their garnet hosts exposed to decompression during ascent to the surface with lamprophyre magma. The mineralogy of inclusions in the studied garnets strongly suggests an episode(s) of metasomatism by carbon‐rich agent(s) (COH‐fluid or carbonatitic melt) in the lithospheric mantle of the Central Aldan superterrane, which was coeval with the formation of graphite inclusions and the host pyropes. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Depletion of Manganese in the Surface Layers of Fe-Mn-Si Shape Memory Alloys by Annealing

X-ray diffraction (XRD) and electron microprobe microanalysis (EPMA) were used for characterizing the structure and composition of surface layers formed on austenitic Fe-Mn-Si shape memory alloys under vacuum. The XRD results demonstrated that during annealing, face centered cubic austenite is transformed to hexagonal close packed martensite on the alloy surface. The EMPA results revealed that manganese in the surface layer was depleted during annealing. Further, this analysis determined that the thickness of the surface layer of the alloy annealed at 1173 K for 1 h was approximately 20 μm and that value is consistent with the depth detected by XRD. The compositional changes of the surface layers such as manganese depletion by annealing were discussed based on the ternary Fe-Mn-Si phase diagram. Although the formation of body centered cubic ferrite is detrimental to shape memory alloys, the amount of manganese was also observed to change during processing and strongly influence the stability of the shape memory alloys.

Growth and characterization of Ga doped ZnSnAs2 thin films on InP substrates

AbstractWe have grown Ga doped ZnSnAs2 thin films on InP substrates using all‐solid source MBE technique. Using the optimum substrate temperature of 340 ºC and Zn:Sn:As4 beam equivalent pressure ratio (BEPR) of 24:1:52, samples were prepared with different Ga concentration achieved by changing the Ga flux. Compositional analysis was performed using electron microprobe microanalysis (EMPA). We found that Ga concentration on the cation sites is 20.9% and 8.7%. XRD patterns of Ga doped samples showed only assignable to ZnSnAs2:Ga and InP substrate. The lattice constant decreases linearly from 0.5862 to 0.5829 nm with decreasing Ga concentration. The observed concentration dependence indicates that the lattice constant of the thin films can be controlled by Ga doping concentration. Hall coefficient and resistivity of Ga 8.7% doped sample can be well explained by the impurity band model. We were able to resolve the experimentally obtained carrier concentration pexp and mobility μexp into valence band carrier concentration pv with mobility μv and acceptor band carrier concentration pa with mobility μa. The computed apparent values papp and μapp are in good agreement with pexp and μexp, respectively. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Minor Elements in Layered Sphalerite as a Record of Fluid Origin, Mixing, and Crystallization in the Navan Zn-Pb Ore Deposit, Ireland

Research Article| September 01, 2014 Minor Elements in Layered Sphalerite as a Record of Fluid Origin, Mixing, and Crystallization in the Navan Zn-Pb Ore Deposit, Ireland* D. Gagnevin; D. Gagnevin 1Tullow Oil plc, Number 1, Central Park, Leopardstown, Dublin 18, Ireland Search for other works by this author on: GSW Google Scholar J. F. Menuge; J. F. Menuge † 2UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland †Corresponding author: e-mail, j.f.menuge@ucd.ie Search for other works by this author on: GSW Google Scholar A. Kronz; A. Kronz 3Geowissenschaftliches Zentrum, Georg-August-Universität, D-37077 Göttingen, Germany Search for other works by this author on: GSW Google Scholar C. Barrie; C. Barrie 4Isoprime Ltd, Isoprime House, Earl Road, Cheadle Hulme, Cheadle SK8 6PT, United Kingdom Search for other works by this author on: GSW Google Scholar A. J. Boyce A. J. Boyce 5Scottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 0QF, United Kingdom Search for other works by this author on: GSW Google Scholar Author and Article Information D. Gagnevin 1Tullow Oil plc, Number 1, Central Park, Leopardstown, Dublin 18, Ireland J. F. Menuge † 2UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland A. Kronz 3Geowissenschaftliches Zentrum, Georg-August-Universität, D-37077 Göttingen, Germany C. Barrie 4Isoprime Ltd, Isoprime House, Earl Road, Cheadle Hulme, Cheadle SK8 6PT, United Kingdom A. J. Boyce 5Scottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 0QF, United Kingdom †Corresponding author: e-mail, j.f.menuge@ucd.ie Publisher: Society of Economic Geologists Received: 20 Mar 2013 Accepted: 31 Oct 2013 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (6): 1513–1528. https://doi.org/10.2113/econgeo.109.6.1513 Article history Received: 20 Mar 2013 Accepted: 31 Oct 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. Gagnevin, J. F. Menuge, A. Kronz, C. Barrie, A. J. Boyce; Minor Elements in Layered Sphalerite as a Record of Fluid Origin, Mixing, and Crystallization in the Navan Zn-Pb Ore Deposit, Ireland. Economic Geology 2014;; 109 (6): 1513–1528. doi: https://doi.org/10.2113/econgeo.109.6.1513 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract This study tests the utility of the minor to trace element composition of sphalerite to discriminate between possible sources of ore-forming fluids, and to constrain processes involved in ore genesis of the world-class Irish-type Navan Zn-Pb orebody, Ireland. Detailed petrography and electron microprobe microanalyses were performed on layered sphalerite previously analyzed for Zn, Fe, and S isotope compositions. Layered sphalerite displays a wide range of chemical composition at both sample and crystal scales. The color, style, and scale of layering show variations with chemical composition, but none of these correlations are consistent between samples. However, there are strong intersample correlations between chemical and S-Fe-Zn isotope compositions at the millimeter scale. Sphalerite precipitated from deep, hydrothermal fluids with 34S-enriched sulfide is enriched in Cd, Sb, Cu, and Ag, whereas Fe and As are enriched in sphalerite precipitated from shallow, bacteriogenic brines with isotopically light S. Significant chemical variations also occur at the micrometer scale in sphalerite regardless of its genetic affinity. These variations are interpreted as being due to variations in temperature, pH, and sulfur activity following the arrival at the site of deposition of pulses of hydrothermal fluids at specific stages of sphalerite growth. Therefore the chemistry of sphalerite, coupled with its texture, appears to be a powerful tool to elucidate fluid typing and ore genesis. The results support the hypothesis that layered sphalerite forms by rapid crystallization due to mixing of two fluids of contrasting physicochemical properties, a process required for the formation of Irish-type and some other hydrothermal deposits including, most notably, Mississippi Valley-type (MVT) deposits. The existence of layered sphalerite, coupled with its texture and chemical composition, may therefore provide useful insight for the mineral exploration industry in Ireland and elsewhere. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Textural Evolution of Plagioclase Feldspar across a Shear Zone: Implications for Deformation Mechanism and Rock Strength

Caledonian amphibolite-facies shear zones developed in granulitefacies anorthosites and anorthositic gabbros of the Bergen Arcs, western Norway, allow a detailed study of the relationships between fluid-infiltration, mineral reactions, the evolution of microstructure and deformation mechanisms. A sequence of rocks from the relatively pristine granulites into a shear zone has been studied by optical microscopy, electron microprobe microanalysis (EMPA), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), focusing on the progressive development of microstructure in the plagioclase feldspars, leading up to their deformation in the shear zone. At the outcrop scale, fluid infiltration into the granulites is marked by a distinct colour change in the plagioclase from lilac^brown to white. This is associated with the breakdown of the intermediate composition plagioclase (� An50) in the granulite to a complex intergrowth of Na-rich and Ca-rich domains. EBSD analysis shows that this intergrowth retains the crystallographic orientation of the parent feldspar, but that the Ca-rich domains contain low-angle grain boundaries. Within the shear zone, this complex intergrowth coarsens by grain boundary migration, annihilating these grain boundaries but retaining the Na-rich and Ca-rich zoning pattern. Analysis of nearestneighbour misorientations of feldspar grains in the shear zone demonstrates that local crystallographic preferred orientation (CPO) is inherited from the parent granulite grain orientations. Random pair misorientation angle distributions show that there is no CPO in the shear zone as a whole, nor is there significant shape preferred orientation (SPO) in single grains. These observations are interpreted in terms of fluid-induced weakening and deformation by dissolution^ precipitation (pressure solution) creep.

Combining trace elements micro-analysis in deposited dredged sediments: EPMA and μ-XRF analysis

Since deposited dredged sediments are rich in metallic contaminants, they present a risk for environment. This work aims to study dredged sediments chemical composition, identify metal-carrier minerals and understand their mobility. Combining chemical and spectroscopic techniques at multi-scale for an integrative approach of trace elements (zinc, lead, iron) behaviour is therefore necessary. The global mineralogy and the chemistry of the sediment were determined by X-ray diffraction and fluorescence (XRF), respectively. Zn and Pb enriched fractions were separated using a sequential chemical extraction procedure and measured by inductively coupled plasma atomic emission and mass spectroscopy. Microanalyses using scanning electron microscopy (SEM), electron microprobe microanalysis (EPMA), combined with synchrotron radiation X-ray fluorescence (μ-XRF) were carried out to characterize mineralogical phases and identify Zn and Pb carrier minerals. Iron oxyhydroxides and iron sulphides were consistently identify as Zn and Pb carriers. The assumption that carbonate fraction was the major Zn carried phase, as demonstrated by chemical extraction results, was not verified by EPMA or μ-XRF.

Caracterização dos argilominerais usados em matéria-prima cerâmica, da formação Rio do Rasto, Bacia do Paraná, no município de Turvo, SC

No sudeste de Santa Catarina existem inúmeras minas de exploração de argilas destinadas à indústria cerâmica da região. Para o conhecimento desta matéria prima foi realizada a caracterização em detalhe de uma frente de lavra em atividade. A exploração é realizada em terrenos sedimentares da Formação Rio do Rasto (Permiano Superior) na Bacia do Paraná que afloram como morros testemunho. Foram coletadas quatorze amostras representativas dos níveis desta mina composta de argilitos com intercalação de siltitos de pequena espessura. As amostras foram analisadas por difratometria de raios X pelo método do pó na rocha total e na fração &lt; 4 µm. A composição química foi determinada por fluorescência de raios X. Foram realizadas observações ao microscópio eletrônico de varredura (elétrons secundários) de fragmentos das amostras e microanálises por microssonda eletrônica de lâminas delgadas. Os resultados mostraram uma grande variação vertical da mineralogia, tendo sido identificados três níveis diferentes. Até 2,00 m há predomínio de esmectita. Entre 2,00 m e 5,50 m a esmectita é o principal argilomineral, mas com quantidade significativa de ilita/mica, e acima de 5,50 m há grande aumento do feldspato potássico e mica detrítica. Estudos de detalhe por difratometria de raios X (determinação do parâmetro b) e microanálises WDS por microssonda eletrônica permitiram identificar como montmorilonita a espécie argilomineral do grupo das esmectitas.

Enrichment and depletion of alloying elements in surface layers of iron base alloys annealed under different conditions

Abstract X-ray photoelectron spectroscopy (XPS), electron microprobe microanalysis (EPMA), and secondary ion mass spectrometry (SIMS) have been used for analyzing the chemical composition in surface layers of iron-base alloys. Samples analyzed in this study were a ferritic Fe–Mn alloy annealed under low partial pressure of oxygen and an austenitic Fe–Mn–Si–Cr alloy annealed under vacuum. The XPS results showed that manganese was enriched and oxidized while iron was metallic in the surface layer of the Fe–Mn alloy annealed under a low partial pressure of oxygen. The EPMA results showed that manganese was depleted while chromium was enriched in the surface layer of the Fe–Mn–Si–Cr alloy annealed under vacuum. The SIMS depth profiles coupled with the EPMA results indicated that the enrichment of chromium in the surface layer improves the oxidation resistance of the alloy. The enrichment and depletion of manganese in the surface layer is discussed on the basis of the thermodynamic properties of the iron–manganese system.

On the Contact of Liquid Nickel with Tungsten Carbide or Boron Carbide

Metal matrix composites (MMCs), consisting of a ceramic reinforcing phase combined with a tough metal matrix can be applied to steel substrates as wear coatings. The processing behaviour of two nickel matrix MMC's is investigated: Ni-WC and Ni-B4C. Experiments were designed and carried out where WC or B4C was added to molten nickel. The temperature range was from 1773 to 1973 K, with times of contact between ceramic and nickel ranging from less than one minute to over 30 minutes. The nominal addition of WC ranged from a molar ratio (Ni:ceramic) of 4.2 to 167.0 while B4C additions varied from about 1 to 94. The melt was sampled following the addition of the ceramic. Analysis techniques included chemical analysis, optical microscopy, electron microprobe microanalysis and X-ray diffraction. In the Ni-WC system, a portion of WC reacted resulting in tungsten dissolution into the nickel. Reactions in the Ni-B4C system produced nickel borides, principally Ni3B in the form of a eutectic with nickel and primary nickel dendrites. No B4C was detected in any of the samples utilizing the aforementioned test methods.

Early Viridian Pigment Composition CHARACTERIZATION OF A (HYDRATED) CHROMIUM OXIDE BORATE PIGMENT

Pigment analyses on more than 90 paintings dating from between 1885 and 1943 (A. Jawlensky, W. Kandinsky, F. Hodler and C. Amiet) have revealed that the majority of samples with chromium oxide hydrate green contain a spectroscopically conspicuous by-product. With the aim of tracking down the origin of this component, the so-called Guignet green, a variation of viridian produced by calcination, was systematically synthesized under varying conditions. The resulting products were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, energy dispersive spectrometry, electron microprobe microanalysis with wavelength dispersive spectrometry, X-ray diffraction, thermogravimetric analysis, secondary electron and backscattered electron imaging by scanning electron microscopy, polarized light microscopy and colorimetry. The composition of pigment products varies with the calcination conditions. Higher temperatures and/or longer calcination times lead to an insoluble borate matrix incorporating chromium oxide particles. The result is an amorphous chromium oxide borate Cr2O3·(xH2O)–Cr3BO6 polymorph with low water content. Interpreting chromium oxide hydrate green samples within this context, it turns out that calcination conditions in the past were highly variable, leaving behind considerable amounts of borates in the final product. Current data covering more than 60 paintings by Jawlensky suggest that the use of a specific production batch can be resolved in time. Identification of borates in chromium oxide hydrate green samples from paintings may thus provide information about the origin of the paint product used.

Sol–gel synthesis and spectrometric structural evaluation of strontium substituted hydroxyapatite

Investigations of the electronic structures of substituted strontium apatites were carried out by using X-ray photo electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction technique (XRD) has been used to determine the structural parameters. Electron microprobe microanalysis technique was used to estimate the elemental concentrations in each substituted apatite material. The present work aims at studying the changes in the electronic structure of Sr 5(PO 4) 3OH (Sr-HAP) upon isomorphic substitution by F and Cl at the OH site of apatite and Sr by Na at trans Sr-HAP. The ion exchange between Na + in sodium alginate and aqueous Ca 2+ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na 4P 2O 7 and aqueous Sr 2+ afforded strontium hydroxyapatite at the specific ratio. The structure of calcium and strontium phosphates prepared from the sol–gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na 4P 2O 7 and the corresponding divalent cations. The findings have ensured that substitution of Sr-HAP by Na enhances the binding energy of O and Sr core levels. It was also noticed that the same substitution decreases the binding energy of P 2s-level. These observations point out to a decrease in the electron density at P and an increase in the electron density at O in Sr atoms.

Thermal reaction of SiC films with tungsten and tungsten–rhenium alloys

Solid-state reactions between SiC films and W–xRe (x = 0, 5 and 25 at%) substrates on thermal annealing between 1673 K and 1873 K for various durations have been investigated. SiC coatings were deposited on metallic wires by hot filament chemical vapour deposition (HFCVD) from a gas mixture of tetramethylsilane (TMS) and hydrogen at 1373 K under normal pressure. The interface zones were characterized using scanning electron and optical microscopies, X-ray diffraction and electron microprobe microanalysis. All analyses reveal that SiC reacts with substrates. Various metal silicides and carbides were formed in layered reaction and the presence of these phases was confirmed by electron probe microanalysis. The effects of rhenium on the reactivity were established by the determination of growth kinetics deducted from the thicknesses of reaction zones as a function of annealing time. It has been found that an increase in the diffusion kinetics and activation energy with the quantity of rhenium in the tungsten wire.

A complex multi-chamber magmatic system beneath a late Cenozoic volcanic field: evidence from CSDs and thermobarometry of clinopyroxene from a single nephelinite flow (Djbel Saghro, Morocco)

Abstract We used quantitative textural measurement, electron microprobe microanalysis and thermobarometry on clinopyroxene from a Cenozoic pyroxene-nephelinite flow located along the northern boundary of the West African craton to decipher magma differentiation processes in underlying magma chambers. The crystal size distributions of clinopyroxene phenocrysts show straight but also curved and kinked patterns and the clinopyroxene show large compositional variations in a single flow (Mg-number 48–88). These observations are strong evidence for magma mixing between a nephelinite magma and a more differentiated phonolitic melt at depth. Detailed thermobarometry on these clinopyroxene shows that at least three magma chambers are present below Saghro and that they are emplaced at the main physical interface within the lithosphere: (1) at the crust–mantle boundary, where the mantle-derived nephelinite has been mixed with a pre-existing phonolitic magma chamber; (2) at the lower–upper crust boundary; (3) close to the surface in a sub-volcanic magma chamber. Some high-pressure phenocrysts (up to 14 kbar) have also probably crystallized within the upper lithospheric mantle. The high clinopyroxene proportion in samples from the base of the flow is thought to reflect crystal settling during cooling of the nephelinite flow at the surface.

Characterization of in situ synthesized TiC particle reinforced Fe-based composite coatings produced by multi-pass overlapping GTAW melting process

In this paper, in situ synthesized TiC particles reinforced Fe-based surface composite coatings by multi-pass overlapping gas tungsten arc welding (GTAW) melting process employing a proper amount of graphite and ferrotitanium (FeTi) on AISI 1020 steel substrate was produced. The microstructure and wear properties of the composite coatings were investigated by means of an electron microprobe microanalysis (EPMA), X-ray diffractometer and wear tester. The results showed that the multi-pass overlapping GTAW melting surface composite coatings can be obtained under suitable welding parameters, and no crack and porosity are found in the tracks. The X-ray and EPMA results confirm that TiC particles can be formed via reaction of FeTi and graphite during multi-pass overlapping GTAW melting process. TiC particles present cubic and dendrite shape in the non-overlapping zone. It is found that there occurred TiC particles coarsening at the overlap regions, which can lead to detrimental effects on the hardness and wear performance. Composite coatings give a high hardness and excellent wear resistance; and the wear friction coefficient of the coating is less than that of the 1020 steel. As a result, multi-pass overlapping GTAW melting process can be used effectively for producing surface composite coatings with a pre-placed powder to improve wear resistance of the AISI 1020 steel.

Uranium Sequestration by Aluminum Phosphate Minerals in Unsaturated Soils

AbstractA mineralogical and geochemical study of soils developed from the unmined Coles Hill uranium deposit (Virginia) was undertaken to determine how phosphorous influences the speciation of uranium in an oxidizing soil/saprolite system typical of the eastern US. This paper presents mineralogical and geochemical results that identify and quantify the processes by which uranium has been sequestered in these soils. It was found that uranium is not leached from the saturated soil zone (saprolites) overlying the deposit due to the formation of a sparingly soluble uranyl phosphate mineral of the meta-autunite group. The concentration of uranium in the saprolites is approximately 1000 mg uranium per kg of saprolite. It was also found that a significant amount of uranium was retained in the unsaturated soil zone overlying uranium-rich saprolites. The uranium concentration in the unsaturated soils is approximately 200 mg uranium per kg of soil (20 times higher than uranium concentrations in similar soils adjacent to the deposit). Mineralogical evidence indicates that uranium in this zone is sequestered by a barium-strontium-calcium aluminum phosphate mineral of the crandallite group (gorceixite). This mineral is intimately inter-grown with iron and manganese oxides that also contain uranium. The amount of uranium associated with both the aluminum phosphates (as much as 1.4 weight percent) has been measured by electron microprobe microanalyses and the geochemical conditions under which these minerals formed has been studied using thermodynamic reaction path modeling. The geochemical data and modeling results suggests the meta-autunite group minerals present in the saprolites overlying the deposit are unstable in the unsaturated zone soils overlying the deposit due to a decrease in soil pH (down to a pH of 4.5) at depths less than 5 meters below the surface. Mineralogical observations suggest that, once exposed to the unsaturated environment, the meta-autunite group minerals react to form U(VI)-bearing aluminum phosphates.