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Precipitation behavior of alloy 33 upon isothermally aging at 700 °C and at 900 °C was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray energy dispersive spectroscopy (XEDS). The name, alloy 33, reflects the quasi-equal atomic content of the base elements Fe, Ni and Cr close to 33%, with the addition of Mo and N. The most remarkable features of the microstructural evolution resulting from the aging heat treatments are described as follows: aging at 700 °C leads to homogeneous and heterogeneous grain boundary precipitation, where the discontinuous mode is dominant at this temperature. Conversely, the opposite behavior was observed when the alloy is aged at 900 °C: predominantly homogeneous precipitation together with grain boundary precipitation, however with rare evidence for discontinuous precipitation (DP), even after longer aging times. In the present study, the topology and content of the DP colonies generated by the combined effect of grain boundary migration diffusion and precipitation under isothermal aging at 700 °C were particularly investigated. A variety of morphological features were observed: mainly (1) classical-type microstructure with straight and parallel lamellar precipitates with regular interlamellar spacing and (2) another microstructure with irregular and complex DP colonies. According to our analytical electron microscopy observations, the latter shows that there are more than one precipitate phase within the same colony, which is new to the current theory and experimental evidence on this subject. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of nanosized particles with antibacterial properties is of great interest in the development of new pharmaceutical products. Silver nanoparticles (Ag NPs) are known to have inhibitory and bactericidal effects. In this article we present the synthesis of Ag NPs prepared by chemical reduction from aqueous solutions of silver nitrate, containing a mixture of hydrazine hydrate and sodium citrate as reductants and sodium dodecyl sulfate as a stabilizer. The results of the characterization of the Ag NPs show agglomerates of grains with a narrow size distribution (from 40 to 60 nm), whereas the radii of the individual particles are between 10 and 20 nm. Finally, the antibacterial activity was measured by the Kirby-Bauer method. The results showed reasonable bactericidal activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The standard dilution micromethod, determining the minimum inhibitory concentration leading to inhibition of bacterial growth, is still under way. Preliminary results have been obtained. From the Clinical Editor: In this paper the synthesis of Ag NPs via chemical reduction from aqueous solutions is discussed. Reasonable bactericidal activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus was demonstrated. [Copyright &y& Elsevier]

Quantitative analyses produce important information concerning the microstructural characteristics of materials, which are reflected in the main properties of the materials. The secondary and backscattered electron modes represent the two main techniques most used in scanning electron microscopy, to produce images and, consequently, realize a quantitative analysis. However, each technique has its advantages and problems. The present work proposed evaluate what is the best SEM technique to quantify secondary phases in a cladding of Inconel 686, which can be extended to the other classes of nickel based alloys rich in Mo. It was performed a quantitative analysis of several images to characterize the microstructure of Inconel 686 weld cladding. The images were obtained using three modes: secondary electron (SE), Z contrast backscattered electron (BSE) and topographic backscattered electron (BSE). The segmentation and quantify of secondary phases was performed by SVRNA software. The statistical results revealed differences between the techniques. The secondary electron mode included several artefacts that reduced the precision of the quantification study. The BSE modes are shown to be the best techniques for quantification. [ABSTRACT FROM AUTHOR]