Machine learning and molecular dynamics simulations aided insights into condensate ring formation in laser spot welding.

Condensate ring formation can be used as a benchmark in welding processes to assess the efficiency and quality of the weld. Condensate formation is critical as the resulting condensate settles into the powder thereby altering the quality of unconsolidated powder. This study investigates the intricate relationship between alloy composition, vapor pressure, and condensate ring thickness as seen in a two-dimensional micrograph.

Impact of environmental oxygen on nanoparticle formation and agglomeration in aluminum laser ablation plumes.

The role of ambient oxygen gas (O2) on molecular and nanoparticle formation and agglomeration was studied in laser ablation plumes. As a lab-scale surrogate to a high explosion detonation event, nanosecond laser ablation of an aluminum alloy (AA6061) target was performed in atmospheric pressure conditions. Optical emission spectroscopy and two mass spectrometry techniques were used to monitor the early to late stages of plasma generation to track the evolution of atoms, molecules, clusters, nanoparticles, and agglomerates.

Evaluating Stage Motion for Automated Electron Microscopy.

Precise control is an essential and elusive quality of emerging self-driving transmission electron microscopes (TEMs). It is widely understood these instruments must be capable of performing rapid, high-volume, and arbitrary movements for practical self-driving operation. However, stage movements are difficult to automate at scale, owing to mechanical instability, hysteresis, and thermal drift.

One dimensional wormhole corrosion in metals.

Corrosion is a ubiquitous failure mode of materials. Often, the progression of localized corrosion is accompanied by the evolution of porosity in materials previously reported to be either three-dimensional or two-dimensional. However, using new tools and analysis techniques, we have realized that a more localized form of corrosion, which we call 1D wormhole corrosion, has previously been miscategorized in some situations.

Metallic technetium sequestration in nickel core/shell microstructure during Fe(OH) transformation with Ni doping.

This study investigates the impacts of Ni doping on technetium-99 (Tc) sequestration in aqueous solutions through transformation of Fe(OH)(s) to iron spinel (magnetite) under alkaline conditions. Extensive solid characterization was performed for the mineral phases produced, as well as the Tc/Ni speciation and distribution within these phases. X-ray diffraction results show that iron spinel was the dominant mineral product without detectable Ni incorporation.

Iodine Capture with Mechanically Robust Heat-Treated Ag-Al-Si-O Xerogel Sorbents.

Various radionuclides are released as gases during reprocessing of used nuclear fuel or during nuclear accidents including iodine-129 (I) and iodine-131 (I). These isotopes are of particular concern to the environment and human health as they are environmentally mobile and can cause thyroid cancer. In this work, silver-loaded heat-treated aluminosilicate xerogels (Ag-HTX) were evaluated as sorbents for iodine [I] capture.

Towards data-driven next-generation transmission electron microscopy.

Electron microscopy touches on nearly every aspect of modern life, underpinning materials development for quantum computing, energy and medicine. We discuss the open, highly integrated and data-driven microscopy architecture needed to realize transformative discoveries in the coming decade.

An Atomic-Scale Understanding of UO Surface Evolution during Anoxic Dissolution.

Our present understanding of surface dissolution of nuclear fuels such as uranium dioxide (UO) is limited by the use of nonlocal characterization techniques. Here we discuss the use of state-of-the-art scanning transmission electron microscopy (STEM) to reveal atomic-scale changes occurring to a UO thin film subjected to anoxic dissolution in deionized water. No amorphization of the UO film surface during dissolution is observed, and dissolution occurs preferentially at surface reactive sites that present as surface pits which increase in size as the dissolution proceeds.

Gaseous Iodine Sorbents: A Comparison between Ag-Loaded Aerogel and Xerogel Scaffolds.

Silver-exchanged aluminosilicate aerogels and xerogels were investigated as gaseous iodine [I] sorbents. The structures, morphologies, compositions, and porosities of aerogels (as-made and heat-treated at 350 °C) and xerogels are compared by using powder X-ray diffraction (PXRD), scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and specific surface area (SSA) as well as pore size analyses. The as-made aerogels, xerogels, and heat-treated aerogels were ion exchanged with Ag in AgNO solutions of deionized water and methanol (5:1 by volume), and PXRD patterns showed the presence of nanocrystalline Ag after the Ag exchange.

Evaluation of Getter Metals in Na-Al-Si-O Aerogels and Xerogels for the Capture of Iodine Gas.

In this paper, sodium aluminosilicate aerogels and xerogels were evaluated as scaffolds for a variety of different getters including Ag, Cs, Cu, Fe, K, Li, Rb, Sb, Sn, and Sn for the capture of gaseous iodine coming from nuclear facilities. The exchange capacities varied widely from a near complete exchange in the case of Ag to much lower exchange levels for some of the Sn compounds [i.e.

Crystal structure and chemistry of tricadmium digermanium tetra-arsenide, CdGeAs.

A cadmium germanium arsenide compound, CdGeAs, was synthesized using a double-containment fused quartz ampoule method within a rocking furnace and a melt-quench technique. The crystal structure was determined from single-crystal X-ray diffraction (SC-XRD), scanning and transmission electron microscopies ( SEM, STEM, and TEM), and selected area diffraction (SAD) and confirmed with electron backscatter diffraction (EBSD). The chemistry was verified with electron energy loss spectroscopy (EELS).

Silver-Loaded Aluminosilicate Aerogels As Iodine Sorbents.

In this paper, aluminosilicate aerogels were used as scaffolds for silver nanoparticles to capture I(g). The starting materials for these scaffolds included Na-Al-Si-O and Al-Si-O aerogels, both synthesized from metal alkoxides. The Ag particles were added by soaking the aerogels in aqueous AgNO solutions followed by drying and Ag reduction under H/Ar to form Ag crystallites within the aerogel matrix.

Anomalous water expulsion from carbon-based rods at high humidity.

Three water adsorption-desorption mechanisms are common in inorganic materials: chemisorption, which can lead to the modification of the first coordination sphere; simple adsorption, which is reversible; and condensation, which is irreversible. Regardless of the sorption mechanism, all known materials exhibit an isotherm in which the quantity of water adsorbed increases with an increase in relative humidity. Here, we show that carbon-based rods can adsorb water at low humidity and spontaneously expel about half of the adsorbed water when the relative humidity exceeds a 50-80% threshold.

In situ atomic scale visualization of surface kinetics driven dynamics of oxide growth on a Ni-Cr surface.

We report the in situ atomic-scale visualization of the dynamic three-dimensional growth of NiO during the initial oxidation of Ni-10at%Cr using environmental transmission electron microscopy. A step-by-step adatom growth mechanism in 3D is observed and a change in the surface planes of growing oxide islands can be induced by local surface kinetic variations.

Adsorption Kinetics in Nanoscale Porous Coordination Polymers.

Nanoscale porous coordination polymers were synthesized using simple wet chemical method. The effect of various polymer surfactants on colloidal stability and shape selectivity was investigated. Our results suggest that the nanoparticles exhibited significantly improved adsorption kinetics compared to bulk crystals due to decreased diffusion path lengths and preferred crystal plane interaction.

Direct in Situ TEM Observation of Modification of Oxidation by the Injected Vacancies for Ni-4Al Alloy Using a Microfabricated Nanopost.

Vacancy injection and selective oxidation of one species in bimetallic alloy at high temperature is a well-known phenomenon. However, detailed understanding of the behavior of the injected vacancies and consequently their effect on oxidation remains elusive. The current research examines the oxidation of high-purity Ni doped with 4.

Catalyst composition and impurity-dependent kinetics of nanowire heteroepitaxy.

The mechanisms and kinetics of axial Ge-Si nanowire heteroepitaxial growth based on the tailoring of the Au catalyst composition via Ga alloying are studied by environmental transmission electron microscopy combined with systematic ex situ CVD calibrations. The morphology of the Ge-Si heterojunction, in particular, the extent of a local, asymmetric increase in nanowire diameter, is found to depend on the Ga composition of the catalyst, on the TMGa precursor exposure temperature, and on the presence of dopants. To rationalize the findings, a general nucleation-based model for nanowire heteroepitaxy is established which is anticipated to be relevant to a wide range of material systems and device-enabling heterostructures.

Chalcogen-based aerogels as sorbents for radionuclide remediation.

The efficient capture of radionuclides with long half-lives such as technetium-99 ((99)Tc), uranium-238 ((238)U), and iodine-129 ((129)I) is pivotal to prevent their transport into groundwater and/or release into the atmosphere. While different sorbents have been considered for capturing each of them, in the current work, nanostructured chalcogen-based aerogels called chalcogels are shown to be very effective at capturing ionic forms of (99)Tc and (238)U, as well as nonradioactive gaseous iodine (i.e.

Interface stoichiometry and structure in anodic niobium pentoxide.

High-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS) were performed on electrochemically anodized niobium and niobium oxide. Sintered anodes of Nb and NbO powders were anodized in 0.1 wt% H3PO4 at 10, 20, and 65 V to form surface Nb2O5 layers with an average anodization constant of 3.

Complementary control by additives of the kinetics of amorphous CaCO3 mineralization at an organic interface: in-situ synchrotron x-ray observations.

The kinetics of biomimetic mineralization at a fatty acid monolayer interface have been measured in situ by synchrotron x-ray reflectivity. The formation of biologically relevant amorphous calcium carbonate films is affected by soluble macromolecules, supersaturation rate of change, and Mg cations. We find that these solution conditions influence mineral film formation in a complementary fashion.

A new paradigm for biomineral formation: mineralization via an amorphous liquid-phase precursor.

Biologically mineralized tissues are well recognized for their unusual crystal morphologies and hierarchically organized composite structures. The soluble acidic macromolecules associated with biominerals are thought to play an important role in modulating the mineral morphology. Our in vitro studies, which use acidic polypeptide additives to modify crystal growth of calcium-based minerals, have demonstrated a crystallization mechanism that proceeds via a liquid-phase mineral precursor.