Effect of nitrogen on the corrosion-erosion synergism in an austenitic stainless steel

High temperature gas nitrided AISI 304L austenitic stainless steel containing 0.55 wt% N in solid solution, was corrosion, erosion and corrosion-erosion tested in a jet-like device, using slurry composed of 3.5% NaCl and quartz particles. Scanning electron microscopy analysis of the damaged surfaces, mass loss measurements and electrochemical test results were used to understand the effect of nitrogen on the degradation mechanisms. Increasing the nitrogen content improved the corrosion, erosion and corrosion-erosion resistance of the AISI 304L austenitic stainless steel. Smoother wear mark contours observed on the nitrided surfaces indicate a positive effect of nitrogen on the reduction of the corrosion-erosion synergism. (C) 2011 Elsevier Ltd. All rights reserved.

Assessment of the cavitation erosion resistance in high nitrogen austenitic stainless steels: study of the wear mechanisms

Specimens of a UNS S31803 steel were submitted to high temperature gas nitriding and then to vibratory pitting wear tests. Nitrided samples displayed fully austenitic microstructures and 0.9 wt. % nitrogen contents. Prior to pitting tests, sample texture was characterized by electron backscattering diffraction, EBSD. Later on, the samples were tested in a vibratory pit testing equipment using distilled water Pitting tests were periodically interrupted to evaluate mass loss and to characterize the surface wear by SEM observations. At earlier pit erosion, stages intense and highly heterogeneous plastic deformation inside individual grains was observed. Later on, after the incubation period, mass loss by debris detachment was observed. Initial debris micro fracturing was addressed to low cycle fatigue. Damage started at both sites, inside the grains and grain boundaries. The twin boundaries were the most prone to mass-loss incubation. Grains with (101) planes oriented near parallel to the sample surface displayed higher wear resistance than grains with other textures. This was attributed to lower resolved stresses for plastic deformation inside the grains with (101)

Mesoscale plasticity anisotropy at the earliest stages of cavitation-erosion damage of a high nitrogen austenitic stainless steel

A high nitrogen austenitic stainless steel (0.9wt% N) and an ordinary 304 austenitic stainless steel were submitted to cavitation-erosion tests in a vibratory apparatus operating at a frequency of 20 kHz. The high nitrogen stainless steel was obtained by high temperature gas nitriding a 1-mm thick strip of an UNS 31803 duplex stainless steel. The 304 austenitic stainless steel was used for comparison purposes. The specimens were characterized by scanning electron microscopy and Electron Back Scatter Diffraction. The surface of the cavitation damaged specimens was analyzed trying to find out the regions where cavitation damage occurred preferentially. The distribution of sites where cavitation inception occurred was extremely heterogeneous, concentrating basically at (i) slip lines inside some grains and (ii) Sigma-3 coincidence site lattice (CSL) boundaries (twin boundaries). Furthermore, it was observed that the CE damage spread faster inside those grains which were more susceptible to damage incubation. The damage heterogeneity was addressed to plasticity anisotropy. Grains in which the crystallographic orientation leads to high resolved shear stress show intense damage at slip lines. Grain boundaries between grains with large differences in resolved shear stress where also intensely damaged. The relationship between crystallite orientation distributions, plasticity anisotropy and CE damage mechanisms are discussed. (C) 2009 Elsevier B.V. All rights reserved.

High-resolution transmission electron microscopy and electron backscatter diffraction in nanoscaled ferritic and ferritic-martensitic oxide dispersion strengthened-steels

For specific blanket and divertor applications in future fusion power reactors a replacement of presently considered reduced activation ferritic martensitic (RAFM) steels as a structural material by suitable oxide dispersion strengthened ferritic martensitic steels would allow a substantial increase of the operating temperature from similar to 823 to about 923 K. Due to this reason the RAFM-alloy ODS-Eurofer has already been developed and produced with industrial partners. In the He-cooled modular divertor concept, where temperatures above 923 K will arise, an ODS-steel with a purely ferritic matrix is advantageous, because of missing phase transitions. Due to this reason, a special ferritic ODS-steel is being manufactured as well. In this work the microstructures of these two ODS-alloy types, analysed mainly by high resolution TEM are compared, with respect to different manufacturing processes. In addition first results of high resolution EBSD scans together with determined orientation maps of the RAFM steel ODS-Eurofer will also be presented. (C) 2008 Elsevier B.V. All rights reserved.

Electron theoretical investigation of the stability of the B2-TiFe compound

The metastable phase diagram of the BCC-based ordering equilibria in the Ti-Fe system has been calculated using a truncated cluster expansion, through the combination of FP-LAPW and cluster variation method (CVM) in the irregular tetrahedron cluster approximation. The results are compared with phenomenological CVM assessments of the system and suggest that the value for the experimental formation enthalpy of the B2-TiFe compound should be significantly more negative than the currently assessed value. (C) 2008 Elsevier B.V. All rights reserved.

Gas flow analysis in a Kraft recovery boiler

Demands for optimal boiler performance and increased concerns in lowering emission have always been the driving force in the reevaluation and evolution of the Kraft boiler: specifically the air distribution strategies that are directly related to achieving increased residence time of flue gas combustion inside the furnace which in turn lowers atmosphere emission levels and enhances boiler operation. This paper presents the results of a study that analyzes the interaction of the different multilevel air injections have on flue gas flow patterns including various quaternary air supply arrangements. Additionally, this study assesses the performance of the CFD (Computational Fluid Dynamics) model against data available in literature. Simulations were performed considering isothermal and incompressible flows, and did not take into account thermal phenomena or chemical reactions. The numerical solutions generated proved to be coherently related to the data available in literature, and provided proof of the efficiency of tertiary level air injection, as well as revealed that quaternary air injection ports arranged in a symmetrical configuration is most suitable for optimal equipment operation. (C) 2010 Elsevier B.V. All rights reserved.

Structural and morphological studies on SiOxNy thin films

In this work, the structure and morphology of silicon oxynitride films deposited by the PECVD technique were studied. The films were deposited under two different conditions: (a) SiOxNy with chemical compositions varying from SiO2 to Si3N4 via the control of a N2O + N-2 + SiH4 gas mixture, and (b) Si-rich SiOxNy films via the control of a N2O + SiH4 gas mixture. The analyses were performed using X-ray near edge spectroscopy (XANES) at the Si-K edge, transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS). For samples with chemical composition varying from SiO2 to Si3N4, the diffraction patterns obtained by TEM exhibited changes with the chemical composition, in agreement with the XANES results. For silicon-rich silicon oxynitride samples, the formation of a-Si clusters was observed and the possibility of obtaining Si nanocrystals after annealing depending on the composition and temperature was realized. (C) 2007 Elsevier B.V. All rights reserved.

Electron beam induced second-harmonic generation in Er(3+) doped PbO-GeO(2) glasses containing silver nanoparticles

Electron beam induced second harmonic generation (SHG) is studied in Er(3+) doped PbO-GeO(2) glasses containing silver nanoparticles with concentrations that are controlled by the heat-treatment of the samples. The SHG is observed at T = 4.2 K using a p-polarized laser beam at 1064 nm. Enhancement of the SHG is observed in the samples that are submitted to electron beam incidence. The highest value of the nonlinear susceptibility, 2.08 pm/V, is achieved for the sample heat-treated during 72 h and submitted to an electron beam current of 15 nA. The samples that were not exposed to the electron beam present a susceptibility of a parts per thousand 0.5 pm/V.

Photosynthesis and water relations of well-watered orange plants as affected by winter and summer conditions

The aim of this study was to evaluate how the summer and winter conditions affect the photosynthesis and water relations of well-watered orange trees, considering the diurnal changes in leaf gas exchange, chlorophyll (Chl) fluorescence, and leaf water potential (I) of potted-plants growing in a subtropical climate. The diurnal pattern of photosynthesis in young citrus trees was not significantly affected by the environmental changes when compared the summer and winter seasons. However, citrus plants showed higher photosynthetic performance in summer, when plants fixed 2.9 times more CO(2) during the diurnal period than in the winter season. Curiously, the winter conditions were more favorable to photosynthesis of citrus plants, when considering the air temperature (< 29 A degrees C), leaf-to-air vapor pressure difference (< 2.4 kPa) and photon flux density (maximum values near light saturation) during the diurnal period. Therefore, low night temperature was the main environmental element changing the photosynthetic performance and water relations of well-watered plants during winter. Lower whole-plant hydraulic conductance, lower shoot hydration and lower stomatal conductance were noticed during winter when compared to the summer season. In winter, higher ratio between the apparent electron transport rate and leaf CO(2) assimilation was verified in afternoon, indicating reduction in electron use efficiency by photosynthesis. The high radiation loading in the summer season did not impair the citrus photochemistry, being photoprotective mechanisms active. Such mechanisms were related to increases in the heat dissipation of excessive light energy at the PSII level and to other metabolic processes consuming electrons, which impede the citrus photoinhibition under high light conditions.

Localization of Pantoea ananatis inside lesions of maize White Spot Disease using transmission electron microscopy and molecular techniques

The etiological agent of maize white spot (MWS) disease has been a subject of controversy and discussion. Initially the disease was described as Phaeosphaeria leaf spot caused by Phaeosphaeria maydis. Other authors have Suggested the existence of different fungal species causing similar symptoms. Recently, a bacterium, Pantoea ananatis, was described as the causal agent of this disease. The purpose of this Study was to offer additional information on the correct etiology of this disease by providing visual evidence of the presence of the bacterium in the interior of the MWS lesions by using transmission electron microscopy (TEM) and molecular techniques. The TEM allowed Visualization of a large amount of bacteria in the intercellular spaces of lesions collected from both artificially and naturally infected plants. Fungal structures were not visualized in young lesions. Bacterial primers for the 16S rRNA and rpoB genes were used in PCR reactions to amplify DNA extracted from water-soaked (young) and necrotic lesions. The universal fungal oligonucleotide ITS4 was also included to identity the possible presence of fungal structures inside lesions. Positive PCR products from water-soaked lesions, both from naturally and artificially inoculated plants, were produced with bacterial primers, whereas no amplification was observed when ITS4 oligonucleotide was used. On the other hand, DNA amplification with ITS4 primer was observed when DNA was isolated from necrotic (old) lesions. These results reinforced previous report of P. ananatis as the primary pathogen and the hypothesis that fungal species may colonize lesions pre-established by P. ananatis.

Diversity of endophytic yeasts from sweet orange and their localization by scanning electron microscopy

Endophytes are microorganisms that colonize plant tissues internally without causing harm to the host. Despite the increasing number of studies on sweet orange pathogens and endophytes, yeast has not been described as a sweet orange endophyte. In the present study, endophytic yeasts were isolated from sweet orange plants and identified by sequencing of internal transcribed spacer (ITS) rRNA. Plants sampled from four different sites in the state of Sao Paulo, Brazil exhibited different levels of CVC (citrus variegated chlorosis) development. Three citrus endophytic yeasts (CEYs), chosen as representative examples of the isolates observed, were identified as Rhodotorula mucilaginosa, Pichia guilliermondii and Cryptococcus flavescens. These strains were inoculated into axenic Citrus sinensis seedlings. After 45 days, endophytes were reisolated in populations ranging from 10(6) to 10(9) CFU/g of plant tissue, but, in spite of the high concentrations of yeast cells, no disease symptoms were observed. Colonized plant material was examined by scanning electron microscopy (SEM), and yeast cells were found mainly in the stomata and xylem of plants, reinforcing their endophytic nature. P. guilliermondii was isolated primarily from plants colonized by the causal agent of CVC, Xylella fastidiosa. The supernatant from a culture of P. guilliermondii increased the in vitro growth of X. fastidiosa, suggesting that the yeast could assist in the establishment of this pathogen in its host plant and, therefore, contribute to the development of disease symptoms.

Pyrolysis-Gas Chromatography/Mass Spectrometry of Soil Organic Matter Extracted from a Brazilian Mangrove and Spanish Salt Marshes

The soil organic matter (SOM) extracted under different vegetation types from a Brazilian mangrove (Pai Matos Island, Sao Paulo State) and from three Spanish salt marshes (Betanzos Ria and Corrubedo Natural Parks, Galicia, and the Albufera Natural Park, Valencia) was investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The chemical variation was larger in SOM from the Spanish marshes than in the SOM of the Brazilian mangroves, possibly because the marshes included sites with both tidal and nontidal variation, whereas the mangrove forest underwent just tidal variation. Thus, plant-derived organic matter was better preserved under permanently anoxic environments. Moreover, given the low number of studied profiles and sedimentary-vegetation sequences in both areas, depth trends remain unclear. The chemical data also allow distinction between the contributions of woody and nonwoody vegetation inputs. Soil organic matter decomposition was found to cause: (i) a decrease in lignin contents and a relative increase in aliphatics; (ii) an increase in short-chain aliphatics at the expense of longer ones; (iii) a loss of odd-over-even dominance in alkanes and alkenes; and (iv) an increase in microbial products, including proteins, sterols, short-chain fatty acids, and alkanes. Pyrolysis-gas chromatography/mass spectrometry is a useful tool to study the behavior and composition of SOM in wetland environments such as mangroves and salt marshes. Additional profiles need to be studied for each vegetation type, however, to improve the interpretability of the chemical data.

Determination of eight fatty acid ethyl esters in meconium samples by headspace solid-phase microextraction and gas chromatography-mass spectrometry

A number of fatty acid ethyl esters (FAEEs) have recently been detected in meconium samples. Several of these FAEEs have been evaluated as possible biomarkers for in utero ethanol exposure. In the present study, a method was optimized and validated for the simultaneous determination of eight FAEEs (ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate) in meconium samples. FAEEs were extracted by headspace solid-phase microextraction. Analyte detection and quantification were carried out using GC-MS operated in chemical ionization mode. The corresponding D5-ethyl esters were synthesized and used as internal standards. The LOQ and LOD for each analyte were <150 and <100 ng/g, respectively. The method showed good linearity (r(2)>0.98) in the concentration range studied (LOQ -2000 ng/g). The intra- and interday imprecision, given by the RSD of the method, was lower than 15% for all FAEEs studied. The validated method was applied to 63 authentic specimens. FAEEs could be detected in alcohol-exposed newborns ( >600 ng/g cumulative concentration). Interestingly, FAEEs could also be detected in some non-exposed newborns, although the concentrations were much lower than those measured in exposed cases.

Gas Chromatographic Analysis of Dimethyltryptamine and beta-Carboline Alkaloids in Ayahuasca, an Amazonian Psychoactive Plant Beverage

Introduction - Ayahuasca is obtained by infusing the pounded stems of Banisteriopsis caapi in combination with the leaves of Psychotria viridis. P. viridis is rich in the psychedelic indole N,N-dimethyltryptamine, whereas B. caapi contains substantial amounts of beta-carboline alkaloids, mainly harmine, harmaline and tetrahydroharmine, which are monoamine-oxidase inhibitors. Because of differences in composition in ayahuasca preparations, a method to measure their main active constituents is needed. Objective - To develop a gas chromatographic method for the simultaneous determination of dimethyltryptamine and the main beta-carbolines found in ayahuasca preparations. Methodology - The alkaloids were extracted by means of solid phase extraction (C(18)) and detected by gas chromatography with nitrogen/phosphorous detector. Results - The lower limit of quantification (LLOQ) was 0.02 mg/mL for all analytes. The calibration curves were linear over a concentration range of 0.02-4.0 mg/mL (r(2) > 0.99). The method was also precise (RSD < 10%). Conclusion - A simple gas chromatographic method to determine the main alkaloids found in ayahuasca was developed and validated. The method can be useful to estimate administered doses in animals and humans for further pharmacological and toxicological investigations of ayahuasca. Copyright (C) 2009 John Wiley & Sons, Ltd.

Electron beam irradiation of Matricaria chamomilla L. for microbial decontamination

Wild chamomile (Matricaria chamomilla L.) is one of the most popular herbal materials with both internal and external use to cure different health disturbances. As a consequence of its origin, chamomile could carry various microbial contaminants which offer different hazards to the final consumer. Reduction of the microbial load to the in force regulation limits represents an important phase in the technological process of vegetal materials, and the electron beam treatment might be an efficient alternative to the classical methods of hygienic quality assurance. The purpose of the study was to analyze the potential application of the electron beam treatment in order to assure the microbial safety of the wild chamomile. Samples of chamomile dry inflorescences were treated in electron beam (e-beam) of 6 MeV mean energy, at room temperature and ambient pressure. Some loss of the chemical compounds with bioactive role could be noticed, but the number of microorganisms decreased as a function on the absorbed dose. Consequently, the microbial quality of studied vegetal material inflorescences was improved by e-beam. irradiation. (C) 2008 Elsevier B.V. All rights reserved.