Carmen M. Andrei

The Microstructure of Unirradiated and Neutron Irradiated Inconel X750

Inconel X750 is a high temperature, age-hardenable superalloy that has excellent corrosion properties and good mechanical strength and ductility, making it suitable for use in nuclear reactors [1]. These physical properties can change during reactor operation as neutrons cause displacement damage by knocking atoms out of their lattice sites, producing dislocation loops, tangles, voids and precipitates [1, 2]. As a first step to understand the effect of neutron irradiation, unirradiated and irradiated X750 were characterized by X-ray diffraction (XRD), light and electron (SEM, TEM) microscopy. X750 was solution treated for < 15 minutes, cold-worked and then age-hardened at a temperature of 700 to 750 C for 16 h. Analyses of the material indicated major chemical constituents (in wt.%) as follows: Ni, 74.0; Cr, 15.0; Fe, 7.30; Ti, 2.50; Al, 0.68; Nb, 0.99; Mn, 0.15; C, 0.067.

From Nanoparticles to Process: An Aberration-Corrected TEM Study of Fischer-Tropsch Catalysts at Various Steps of the Process

χThe nanostructure of Fischer-Tropsch (FT) Fe carbides are investigated using aberration-corrected high-resolution transmission electron microscopy (TEM). The plasma-generated Fe carbides are analyzed just after synthesis, following reduction via a H2 treatment step and once used as FT catalyst and deactivated. The as-produced nanoparticles (NPs) are seen to be abundantly covered with graphitic and amorphous carbon. Using the extended information limit from the spherical aberration-corrected TEM, the NPs could be indexed as a mixture of NPs in the θ-Fe3C and χ–Fe5C2 phases. The reduction treatment exposed the NPs by removing most of the carbonaceous speSubscript textcies while retaining the χ–Fe5C2. Fe-carbides NPs submitted to conditions typical to FT synthesis develop a Fe3O4 shell which eventually consumes the NPs up to a point where 3-4 nm residual carbide is left at the center of the particle. Subscript textVarious mechanisms explaining the formation of such a microstructure are discussed.

Gentle reduction of SBA-15 silica to its silicon replica with retention of morphology

We report the transformation of mesoporous silica to its silicon replica with maintenance of structural regularity. The method employs mild displacement reactions with Mg intermetallics as the source of Mg vapor at low partial pressure. The mild conditions aid in high fidelity replication of the nanoporous framework of the starting silica.

Biomineralization of Hydroxyapatite Revealed by in situ Electron Microscopy

Hydroxyapatite (HA) is the principal mineral component of human bones and teeth. Within these mineralized tissues, HA distributes itself in a highly organized arrangement in a fibrous collagen matrix. Although many bone mineralization mechanism theories have been put forward based on in vitro models, many questions such as the formation of an amorphous calcium phosphate (ACP) intermediary, and the functions of non-collagenous proteins (NCPs) on crystals nucleation and subsequent growth, still remain due to the lack of real-time experimental evidence [1]. Liquid-phase transmission electron microscopy (LP-TEM), with the ability to record biomineralization process in situ with nanoscaled spatial resolution and sufficient temporal resolution, is a promising technique to unveil bone mineralization mechanisms. The formation of intermediate amorphous phases has been noted in situ for simpler mineralized systems, such as calcium carbonate [2]. However, understanding the mechanisms of more complex HA mineralization is critical for both pathological biomineralization research and biomimetic material synthesis related to humans.

In-situ Transmission Electron Microscopy to Probe the Electrochemical Deposition of Nanostructured Materials

Nanomaterials and nanostructured materials have been used extensively in biosensing platforms, and their morphology strongly influences the detection limit and dynamic range of these sensing systems [1]. This makes it very important to precisely tune the biosensing substrate at the biomolecular scale or the nanoscale. To develop nanostructures with desired morphology, a detailed understanding of the growth mechanism is very essential. Considerable effort has been devoted to investigate the mechanisms involved in electrochemical deposition, but controversy regarding the growth modes still remains due to the lack of direct experimental proof of the nucleation and growth kinetics [2]. Real-time observation of the growth process through high resolution in-situ microscopy allows direct and precise study of the structural evolution; however, some difficulties in real-time imaging in liquid environments remain [3].