SEARCH · Search NASA
Results for “nucleate”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Modeling of aqueous species interaction energies prior to nucleation in cement-based gel systems
Arguably the most ubiquitous construction material in modern civilization, concrete is enabling the development of megacities around the globe together with increasing living standards in developing nations. However, the exact formation mechanisms of the strength-giving calcium-rich gels remain a topic of debate. Using density functional modeling, we simulate the fundamental solution-based building blocks of cement hydrates (calcium ions and silicate and aluminate monomers) and their propensity to form pair-wise complexes with bonding environments characteristic of those found in calcium-silicate-hydrate, calcium-alumino-silicate-hydrate and sodium-containing calcium-alumino-silicate-hydrate gels, as assessed from Gibbs free energies of chemical reactions. By accurately simulating the high pH pore solution chemistry in Portland cements and related systems, along with discrete solvation of the species, we hypothesize potential early age formation routes of the gels and discuss limitations and future work associated with this approach.
Crack nucleation and growth during dynamic indentation of chemically-strengthened glass
Dynamic point impact loading is a primary cause of fracture of glass screens on mobile devices. An improved understanding of crack initiation and evolution under high-speed indentation could contribute to the development of materials with better performance, but experimental observations are challenging due to the short timescales and limited depth-of-field of optical microscopy. To address this need, we have observed fracture of a chemically-strengthened glass during dynamic indentation using in situ x-ray phase-contrast imaging (XPCI). Median cracks initiate below the surface of the glass, at a depth approximately corresponding to the depth at which the surface residual compressive stress diminishes to zero. These cracks initially propagate at ~10ms –1 , rapidly accelerating to > 100ms –1 . We also observe some evidence for rate-dependent behavior, in that indentation at the lowest rates studied here (below about ~0.15ms –1 ) fails to initiate cracks regardless of the depth of the indentation (up to 18μm), while indentation at higher rates produces median cracks that either arrest or cause complete fracture, depending on the depth of indentation.
A framework for nucleation in electrochemical systems and the effect of surface energy on dendrite growth
Not provided.
Local micro-mechanical stress conditions leading to pore nucleation during dynamic loading
Not Available
Stress-induced transition from vacancy annihilation to void nucleation near microcracks
Not Available
Influence of sub-zero temperature on nucleation and growth of copper nanoparticles in electrochemical reactions
Not Available
Unseeded, spontaneous nucleation of spherulitic magnesium calcite
Most of the sedimentary carbonates deposited in the marine environments are composed of calcium carbonate minerals with varying amounts of incorporated Mg 2+ . However, understanding how interactions of impurities with carbonate and their incorporation affect sediments behavior remains a challenge. Here, a new insight is obtained by monitoring solution composition, morphology, and electrokinetic potential of carbonate particles formed in a spontaneous unseeded batch precipitation experiment using electrochemical and scanning electron microscopy methods. The solid composition and growth rate are extracted from changes in the bulk composition and fitted to chemical affinity rate law, revealing that the precipitation pathway consists of second-order dissolution and first-order precipitation. The molecular dynamics simulations show that the lattice strain induced by randomly substituting Ca 2+ by Mg 2+ stabilizes spherical nanoparticles and reduces their surface area and volume. Combining kinetics and thermodynamics insight, we conclude that variation in the carbonate bulk and interfacial energies, along with the solution supersaturation, lead to the dissolution-precipitation transformation pathway from Mg-rich to Mg-poor carbonate phase that preserves spherulitic morphology. Furthermore, our findings are relevant for long-standing questions of how impurities influence diagenesis of carbonate sediments and spherulitic carbonate particles' origin.
Crystallography and elastic anisotropy in fatigue crack nucleation at nickel alloy twin boundaries
Not provided.
Helium bubble nucleation and growth in alloy HT9 through the use of in situ TEM: Sequential he-implantation and heavy-ion irradiation versus dual-beam irradiation
The formation of He bubbles in Ferritic/Martensitic steel HT9 is investigated through the use of in situ Transmission Electron Microscopy coupled with He implantation and heavy ion irradiation. Of particular interest is the effect of increasing He appm/dpa ratio on the formation and growth of the bubbles, as well as the effect of the sequential order of ion irradiation i.e. He-pre-implantation followed by heavy-ion irradiation versus true dual-beam irradiation. Finally, the role of He is discussed.
Implementation and Validation of the Hydride Nucleation-Growth-Dissolution (HNGD) model in BISON
Not Available
Predicting the hydride rim by improving the solubility limits in the Hydride Nucleation-Growth-Dissolution (HNGD) model
Not Available
Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing
Not Available
Barrierless melt nucleation at solid-solid interface in energetic nitramine octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine
Not Available
Nucleate boiling simulation using interface tracking method
Not Available