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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Cystathionine gamma lyase-H2S contributes to osteoclastogenesis during bone remodeling induced by mechanical loading

Highlights: • This study investigated the role of H{sub 2}S and osteoclastogenesis in bone remodeling induced by mechanical loading in mice. • CSE-H{sub 2}S was a dominant H{sub 2}S generating system in osteoclasts, while CBS did not generate H{sub 2}S. • In CSE-deficient mice, osteoclastogenesis and tooth movement were inhibited, which could be rescued by a H{sub 2}S donor. Hydrogen sulfide (H{sub 2}S), a gaseous signaling molecule produced by cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), influences bone remodeling in many ways. Osteoclasts play an important role in bone remodeling during tooth movement induced by mechanical loading, which increases the rate of tooth movement. Recently, we found that osteoclasts could produce H{sub 2}S. However, whether H{sub 2}S modulates bone remodeling by affecting osteoclasts remains unclear. In this study, we found that CSE-H{sub 2}S was a dominant H{sub 2}S generating system in osteoclasts, while CBS did not generate H{sub 2}S. A significant increase in CSE mRNA expression and H{sub 2}S production was observed in periodontal ligament (PDL) tissues of wild-type (WT) mice after 3 days of mechanical loading. CSE gene knockout led to a significant reduction in the number of maxillary osteoclasts and in the amount of tooth movement. The number of RANKL-induced TRAP-positive osteoclasts and the mRNA expression of osteoclast markers were downregulated after 6 days of incubation in monocytes extracted from CSE{sup −/−} mice. The expression of IL-1, IL-6 and TNF-α, which can stimulate osteoclastogenesis in periodontal tissue and serum samples, was lower in CSE{sup −/−} mice after mechanical loading. Application of the H{sub 2}S donor GYY4137 increased the number of RANKL-induced osteoclasts, the number of osteoclasts in periodontal tissues and tooth movement distance in CSE{sup −/−} mice. The results suggested that endogenous H{sub 2}S and CSE play vital roles in the osteoclastogenesis and alveolar bone resorption induced by mechanical loading.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

The shear fracture toughness, K IIc , of graphite

In this study, the critical shear stress intensity factor, K IIc , here-in referred to as the shear fracture toughness, K IIc (MPa m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce the specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of K IIc from large specimens for PCEA and NBG-18 are 2.26 MPa m with an SD of 0.37 MPa m and 2.20 MPa m with an SD of 0.53 MPa m, respectively. The value of K IIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of K IIc / K Ic ≈ 1.6. .

36 MATERIALS SCIENCE↗
DOE OSTI2018

Five kHz thermometry in turbulent spray flames using chirped-probe-pulse femtosecond CARS, part II: Structure of reaction zones

Temperature was measured in turbulent spray flames of ethanol and acetone stabilized on the piloted Sydney Needle Spray Burner (SYNSBURN TM ) using single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman spectroscopy (CPP-fs-CARS) with a repetition rate of 5 kHz. The burner features air-blast atomization of liquid injected from a needle that can be translated by a length Lr within a co-flowing air stream so that piloted spray flames ranging from dilute to dense can be studied. Part I of these investigations has reported on the CPP-fs-CARS technique and extensive details of data processing methodology. Part II is concerned with the structure of the reaction zones at different spray loadings and for different departures from blow-off. While not performed simultaneously, measurements of the size distribution of liquid fragments are also reported and discussed in conjunction with the measured temperature. Measured probability density functions of temperature show that for flames with the same liquid loading but different recess lengths, Lr, the near-field spray structure that forms upstream of x/D = 10 affects flame structure and stability further downstream. As the spray exiting the burner becomes denser, with a higher proportion of ligaments and ‘irregular’ shaped objects, the entrainment of hot pilot gases into the spray envelope is affected, hence changing the rates of vaporization and subsequent combustion. The reported results will also form a useful platform for validating sub-models of atomization and combustion in turbulent, dilute to dense spray flames.

42 ENGINEERING↗
DOE OSTI2020

Molecular scale insight of pore morphology relation with mechanical properties of amorphous silica using ReaxFF

Porous materials are typically heterogeneous and they contain large variations of micro-/nano-pore structures, causing complicated behaviors. In continuum models, most mechanical properties of porous materials are estimated based on porosity, while the variations of micro/nano structures are ignored. That could be problematic as the microscopic heterogeneity may affect the mechanical response of porous materials. Thus, understanding micro/nano heterogeneity impact has been the focus in many scientific and engineering subjects. In the present study, we investigated the effect of nanopore structure (including pore shape and orientation) as well as porosity on mechanical properties of amorphous silica (a-SiO 2 ). The pore sizes in our simulations are comparable to the corresponding ones observed in a-SiO 2 based materials. We found that the existing of nanopores strongly influences Young’s modulus (E) and critical energy release rate (G IC ). These properties decrease with increasing porosity. Importantly, the impact of nanopores was characterized by structural parameters of porous materials. In addition to dependency on porosity, Young’s modulus also was found to vary as a function of potential energy per atom, which highly depends on nanopore shape. Furthermore, critical energy release rate was found to increase with increasing ligament length (also known as pore wall thickness). Finally, the results highlighted the importance of nanopore structures, which must be taken into account when studying fracture mechanisms in porous materials. Based on our findings, it was proposed that mechanical properties of porous materials can be controlled by nano-engineering pore structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Flow visualisation in real-size optical injectors of conventional, additised, and renewable gasoline blends

Research on renewable and alternative fuels is crucial for improving the energy and environmental efficiency of modern gasoline internal combustion engines. To highlight the influence of fuel rheological and thermodynamic properties on phase change and atomisation processes, three types of gasoline blends were tested. More specifically, the campaign comprised a reference gasoline, an ethanol/gasoline blend (10% v/v) representative of renewable fuels, and an additised gasoline sample treated with viscoelasticity-inducing agents. High-speed imaging of the transient two-phase flow field arising in the internal geometry and the near-nozzle spray region of gasoline injectors was performed employing Diffuse Backlight Illumination. The metallic body of a commercial injector was modified to fit transparent tips realising two nozzle layouts, namely a two-hole real size model resembling the Engine Combustion Network spray G injector and an enraged replica with an offset hole. Experiments were conducted at realistic operating conditions comprising an injection pressure of 100 bar and ambient pressures in the range of 0.1–6.0 bar to cover the entire range of chamber pressures prevailing in Gasoline Direct Injection engines. The action of viscoelastic additives was verified to have a suppressive effect on in-nozzle cavitation (6% reduction in cavitation extent) , while also enhancing spray atomisation at flash-boing conditions, in a manner resembling the more volatile gasoline/ethanol blends. Finally, persisting liquid ligaments were found to form after the end of injection for the additised sample, owing to the surfactant nature of the additives.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Nanomechanical investigation of the interplay between pore morphology and crack orientation of amorphous silica

Porous amorphous silica (a-SiO 2 ) is of both fundamental and practical interests, as they exhibit a large specific surface area and tunable porous network. However, the brittle nature of a-SiO 2 and the presence of pre-existing cracks at both micro- and nano-scales lead to complex mechanical behavior. Here, we systematically investigate the effects of pre-existing crack and its orientation on the mechanical properties of a-SiO 2 with varying pore shapes using reactive molecular dynamics simulations. We demonstrate that pore shape will primarily influence the Young’s modulus (E) and critical energy release rate (G IC ). We further investigate the impact of pore shape and crack orientation by local characterization of the structural parameters. By defining the high stress and inter-mediate regions, the overall mechanical properties are found to be greatly influenced by the pore shape which can be reflected through the spatial distribution of von Mises stress. Overall, G IC is found to increase with the increase of ligament length (also known as pore wall thickness). Meanwhile, the effect of the pre-existing crack on the crack propagation process is confirmed by analyzing the density distribution evolution. These results highlight the interplay between pore morphology and crack orientation in controlling the fracture behaviors in brittle porous materials.

42 ENGINEERING↗
DOE OSTI2020

X-Ray Fluorescence Microscopy: A Method of Measuring Ion Concentrations in the Ear

This technical note describes synchrotron x-ray fluorescence microscopy (XFM) as a method for measuring the concentrations of various elements in cross-sections of the ear at extremely high resolution. This method could be of great importance for addressing many open questions in hearing research. XFM uses synchrotron radiation to evoke emissions from many biologically relevant elements in the tissue. The intensity and wavelength of the emitted radiation provide a fingerprint of the tissue composition that can be used to measure the concentration of the elements in the sampled location. Here, we focus on energies that target biologically-relevant elements of the periodic table between magnesium and zinc. Since a highly focused x-ray beam is used, the spot size is well below 1 mu m and the samples can be scanned at a nanometer lateral resolution. This study shows that measurement of the concentrations of different elements is possible in a mid-modiolar cross-section of a mouse cochlea. Images are presented that indicate potassium and chloride "hot spots" in the spiral ligament and the spiral limbus, providing experimental evidence for the potassium recycling pathway and showing the cochlear structures involved. Scans of a section obtained from the incus, one of the middle ear ossicles, in a developing mouse have shown that zinc is not uniformly distributed This supports the hypothesis that zinc plays a special role in the process of ossification. Although limited by sophisticated sample preparation and sectioning, the method provides ample exciting opportunities, to understand the role of genetics and epigenetics on hearing mechanisms in ontogeny and phylogeny.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Mitigating cutting-induced plasticity in the contour method, Part 2: Numerical analysis

Cutting-induced plasticity can have a significant effect on the measurement accuracy of the contour method. The present study examines the benefit of a double-embedded cutting configuration that relies on self-restraint of the specimen, relative to conventional edge-crack cutting configurations. A series of finite element analyses are used to simulate the planar sectioning performed during double-embedded and conventional edge-crack contour cutting configurations. The results of numerical analyses are first compared to measured results to validate the cutting simulations. The simulations are then used to compare the efficacy of different cutting configurations by predicting the deviation of the residual stress profile from an original (pre-cutting) reference stress field, and the extent of cutting-induced plasticity. Comparisons reveal that while the double-embedded cutting configuration produces the most accurate residual stress measurements, the highest levels of plastic flow are generated in this process. As a result, this cutting-induced plastic deformation is, however, largely confined to small ligaments formed as a consequence of the sample sectioning process, and as such it does not significantly affect the back-calculated residual stress field.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Phase stability, swelling, microstructure and strength of Ti 3 SiC 2 -TiC ceramics after low dose neutron irradiation

In this study, M n+1 AX n (MAX) phase Ti 3 SiC 2 materials were neutron irradiated at ~400, ~630, and 700 °C to a fluence of ~2 × 10 25 n/m 2 (E > 0.1 MeV). After irradiation at ~400 °C, anisotropic c-axis dilation of ~1.5% was observed. Room temperature strength was reduced from 445 ± 29 MPa to 315 ± 33 MPa and the fracture surfaces showed flat facets and transgranular cracks instead of typical kink-band deformation and bridging ligaments. XRD phase analysis indicated an increase of 10–15 wt% TiC. After irradiation at ~700 °C there were no lattice parameter changes, ~5 wt% decomposition to TiC occurred, and strength was 391 ± 71 MPa and 378 ± 31 MPa. The fracture surfaces indicated kink-band based deformation but with lesser extent of delamination than as-received samples. Finally, Ti 3 SiC 2 appears to be radiation tolerant at ~400 °C, and increasingly radiation resistant at ~630–700 °C, but a higher temperature may be necessary for full recovery.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A linked-scale coupled model of mass erosion and redistribution in plasma-exposed micro-foam surfaces

Surface evolution due to exposure to harsh environments is of importance in many scientific and technological applications. In plasma-exposed materials, the surface receives charged particles from the plasma, leading to a series of processes that drive the system far from equilibrium and may lead to the severe deterioration of the surface properties. Although surface morphological changes are driven by atomic collisions taking place over picoseconds and nanometers, these processes result in mass loss and redistribution of matter over much larger length and time scales. This necessitates a multi-scale approach capable of capturing the range of processes linking primary atomic collision events with engineering-level surface geometry changes. In this paper, we develop a computational model to simulate the morphological evolution and effective erosion rate of micro-architected tungsten foams during low-energy plasma ion bombardment. Furthermore, the model acts on several length scales, with the energy and angular dependence of the sputtering yield of flat tungsten surfaces determined using the SRIM code based on the binary collision approximation. This information is introduced into a low-fluence, short-term Monte Carlo raytracing model, and further into a high-fluence, long-term particle transport model. In the latter, material particles representing billions of atoms are described in a digitized 3-D representation of the foam structure from X-ray tomography data, and are sputtered off and redeposited using the atomistic information. We show that the redeposition of sputtered atoms leads to partial self-healing in the bottom layers with a sharp reduction in the sputtering coefficient of low density foams, roughly 25% of the solid W value. This is in qualitative agreement with recent experiments on low porosity W structures. At high fluence, the foam structure degrades considerably as there are fewer ligaments available to recapture sputtered atoms and, consequently, the sputtering rate increases again.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Intense cyclic heating effects on thermo-fracture and thermal shock of solid tungsten and open-cell tungsten foam

Here we investigate here the effects of transient (cyclic) arc-jet plasma and laser heating on fracture behavior of W-foam and solid tungsten. The two key parameters that control the foam thermomechanical response are its density and mean cell size expressed in Pores Per Inch (PPI). Tungsten foam samples were fabricated with Chemical Vapor Deposition (CVD) with variety of PPI and relative density. These were tested under two types of qualitatively different conditions: (1) high-enthalpy arc-jet, and (2) high-power cyclic laser heating. None of the foam samples showed macroscopic through-thickness cracks. However, distributed micro-cracks were observed on ligaments and their triple junctions. Under the same loading conditions, W-foam and solid tungsten showed similar crack network pattern and characteristic length-scale. However, Crack Opening Displacement (COD) was twice as large in solid W as compared to W-foam. Foam samples that have been previously exposed to a low-pressure helium plasma showed significant changes in their surface forming nano-texture fuzz which was removed by subsequent testing in the arc-jet. Extensive fracture and re-crystallization were observed in the thin solid W disk that was fully-constrained from expansion. Thicker and fully-constrained solid W disks did not display recrystallization, grain growth, and extensive cracking. However, thicker disks that were free to expand showed some recrystallization and extensive through-thickness cracks due to less effective cooling and thus higher temperatures. Laser beam testing showed no visible damage formation at 0.19 GW/m 2 and 0.38 GW/m 2 for both low-density (23%) and high-density (43%) foams at low pulses (100-1000). Micro-cracks were observed after 10,000 pulses at 0.19 GW/m 2 in both foams, and in low-density foam after 100,000 at 0.38 GW/m 2 . The nature of thermomechanical damage in W-foam exposed to extreme power (GW/m 2 ) short-duration laser pulses was found to be qualitatively similar to that of high power (MW/m 2 ) long-duration arc-jet.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Facile synthesis and microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere and multi-shelled NiO hollow sphere

We reported the preparation of C@Ni–NiO core–shell hybrid solid spheres or multi-shelled NiO hollow spheres by combining a facile hydrothermal route with a calcination process in H{sub 2} or air atmosphere, respectively. The synthesized C@Ni–NiO core–shell solid spheres with diameters of approximately 2–6 μm were in fact built from dense NiO nanoparticles coated by random two-dimensional metal Ni nanosheets without any visible pores. The multi-shelled NiO hollow spheres were built from particle-like ligaments and there are a lot of pores with size of several nanometers on the surface. Combined Raman spectra with X-ray photoelectron spectra (XPS), it suggested that the defects in the samples play a limited role in the dielectric loss. Compared with the other samples, the permeability of the samples calcined in H{sub 2} and air was increased slightly and the natural resonance frequency shifted to higher frequency (7, 11 and 14 GHz, respectively), leading to an enhancement of microwave absorption property. For the sample calcined in H{sub 2}, an optimal reflection loss less than − 10 was obtained at 7 GHz with a matching thickness of 5.0 mm. Our study demonstrated the potential application of C@Ni–NiO core–shell hybrid solid sphere or multi-shelled NiO hollow sphere as a more efficient electromagnetic (EM) wave absorber. - Highlights: • C@Ni–NiO core–shell hybrid solid sphere was synthesized by a facile method. • Multi-shelled NiO hollow sphere was synthesized by a facile method. • It suggested that the defects in the samples play a limited role in dielectric loss. • The permeability of the samples calcined in H{sub 2} and air was increased. • Microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere was investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultrafine grained structure and improved mechanical properties of low temperature friction stir spot welded 6061-T6 Al alloys

Highlights: • Friction stir spot welding of Al alloy was successfully done at low rotation speed. • The highest welding temperature was lower than 200 °C. • The average grain size of less than 500 nm was formed in the stir zone. • No hardness reduction of the HAZ region could be detected. • Shear tensile tests of the welds revealed a maximum shear load of about 5400 N. - Abstract: In this study, 1 mm thick 6061-T6 aluminum alloy plates were subjected to friction stir spot welding (FSSW) at a very low rotation speed of 30, 40 and 50 rpm, aiming to prevent the hardness reduction in the heat affected zone (HAZ) of this precipitate hardening Al joints. Two kinds of rotating tools, namely, one with a 1 mm long probe and the other one with a flat shoulder without a probe, were used and the corresponding force applied to the rotating tools was ranged from 4 to 8 tons. Under this special welding condition, the highest welding temperature was measured lower than 200 °C. As a result, no hardness reduction of the HAZ region could be detected and an ultrafine grain structure with a high density of dislocations was formed in the stir zone. The average grain size obtained in the stir zone was less than 500 nm for all the welds, which was much smaller than that in conventional FSSW processed 6061-T6 Al joints. In addition, no hook-like bonding ligaments were formed in the joints due to the very different material flows and the shear tensile tests showed that the spot welds prepared by the low speed FSSW can reach a maximum shear load of about 5400 N, much higher than those prepared by the conventional FSSW technique.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure characterization by X-ray tomography and EBSD of porous FeCr produced by liquid metal dealloying

Highlights: • FeCr-Ni precursors were dealloyed in a Mg bath to give FeCr-Mg bicontinuous structure. • FeCr-Mg bicontinuous structure was immersed in HNO{sub 3} solution to get porous FeCr. • (FeCr){sub x}-Ni{sub 1−x} precursors are fully FCC phase while porous FeCr are fully BCC phase. • Composition & dealloying parameters are key parameters for controlling microstructure - Abstract: Liquid metal dealloying is a promising technique to get nanoporous materials which are attractive for their excellent functional properties. From a (FeCr){sub x}-Ni{sub 1−x} precursor, it is possible to get porous FeCr with this technique. While immersing precursors in a molten Mg bath, Ni atoms selectively migrate into the Mg bath. After cooling down to room temperature, the resulting microstructure is a bi-continuous structure of FeCr and Mg (with Ni in solid solution). A final etching step removes the Mg solid-state solution phase. Precursors with different compositions were dealloyed and imaged in 3D. From X-ray tomography images, porous FeCr characteristics as solid fraction, phase size, specific surface were extracted. EBSD maps were acquired on samples before and after dealloying. We will show that precursor composition is a key parameter to control pores and grains size while dealloying parameters (time and temperature) are key parameters to control ligaments size and in fine specific surface. By controlling precursor composition and dealloying parameters it is now possible to get dealloyed nanoporous metals with desired grain and porous microstructure by liquid metal dealloying.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Design of bicontinuous metallic nanocomposites for high-strength and plasticity

We demonstrate design of Cu/Mo nanocomposite thin films with bicontinuous intertwined morphologies for high strength and plastic deformability. Through co-sputtering Cu and Mo at different temperatures, nanocomposites with lateral and random concentration modulations (LCMs and RCMs) were fabricated. Ligament size and coherency of the Cu/Mo interfaces was also controlled via the deposition conditions. It was discovered that nanocomposites with LCM structure and coherent interfaces have high strength but limited deformability. Enhanced deformability was achieved when the interface was altered to semi-coherent, although plasticity was localized in kink bands. The RCM structure design with semi-coherent interfaces showed an excellent combination of high flow strength and plastic deformability due to suppression of shear and kink bands.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Facile one-pot synthesis and characterization of nickel supported on hierarchically porous carbon

Highlights: • Novel, inexpensive, one-pot, synthesis method for Ni on hierarchically porous carbon. • Disappearance of surfactant mesopores seen with incorporation of nickel. • Distribution of Ni nanoparticles on the hierarchically porous carbon support was studied by SEM. • Nickel nanoparticles were dispersed on macropore walls and not within carbon. - Abstract: Described is a novel, facile route for the synthesis of nickel supported on hierarchically porous carbon (Ni/HPC) using a one-pot co-gelation sol–gel method. Ni/HPC with varying nickel loadings (0.5, 1, 2.5 and 5 wt% Ni) were synthesized and the materials characterized by nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) and Raman spectroscopies. The results show a three-dimensional network of disordered carbon with fine nickel nanoparticles of sizes ranging from 8 nm to 13 nm at 0.5 wt% Ni loading which gradually increased with increase in the Ni loading. The carbon structure was retained at the macropore level, but not at the mesoscale where the ordered mesopores were lost on nickel addition. The nickel nanoparticles were observed to grow on the surface of the ligaments. This may make them particularly suitable for low pressure Ni-catalyzed organic transformations e.g., hydrogenations, C–C coupling, C-heteroatom coupling, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Fracture resistance of hierarchical Cu–Mo nanocomposite thin films

We report the fracture behavior of high-temperature co-sputtered Cu/Mo nanocomposite thin films was investigated through in situ 3-point bend testing of pre-notched microbeams in SEM. The as-synthesized nanocomposites present hierarchical nano/microstructures composed of a matrix of phase-separated Cu–Mo with nanoscale ligaments dispersed with sub-micron scale Cu-rich islands containing Mo nano-precipitates. Results show a significant crack growth resistance in the hierarchical nanocomposite, several times higher than that measured in Cu/Mo nanoscale multilayers. Based on electron microscopy characterization, three mechanisms of crack growth resistance in the hierarchical structures are proposed: crack bridging by the Cu-rich layer, crack deflection via shear along the Cu/Mo interface, and multiple cracking. This work demonstrates an approach to increase toughness in high strength nanocomposites through interface micro-structure design.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Production of fine calcium powders by centrifugal atomization with rotating quench bath

Recently, a novel Al/Ca composite was produced by severe plastic deformation of Al powders and Ca granules for possible use as a high-voltage power transmission conductor. Since the strength of such composites is inversely proportional to the Ca filament size, fine Ca powders (less than ~250 μm) are needed to achieve the desired high strength for the powder metallurgy production of an Al-matrix composite reinforced by nano-scale Ca filaments. However, fine Ca powders are not commercially available. Therefore, we have developed a method to produce fine Ca powders via centrifugal atomization to supply Ca powder for prototype development of Al/Ca composite conductor. A secondary goal of the project was to demonstrate that Ca powder can be safely prepared, stored, and handled and could potentially be scaled for commercial production. Our results showed that centrifugal atomization can yield as much as 83 vol. % Ca powder particles smaller than 250 μm. The mean particle size sometimes matches, sometimes deviates substantially from the predictions of the Champagne & Anger equation likely due to unexpected secondary atomization. The particle size distribution is typical for a ligament-disintegration atomization mode. Scanning electron micrographs showed that the morphology of these Ca powders varied with powder size. Spark testing and auto-ignition tests indicated that the atomized powders were difficult to ignite, providing confidence that this material can be handled safely in air.

36 MATERIALS SCIENCE↗