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At least 1,621 records · Page 90

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DOE OSTI2019

Surface Structure and Corrosion Behavior of Mg{sub 68−x}Zn{sub 28+x}Ca{sub 4}(x = 0.4) Bulk Metallic Glasses after Immersion in Ringer’s Solution

The main aim of the present study was to determine the impact of Zn on the surface structure and corrosion behavior of Mg-based metallic glasses after immersion in Ringer’s solution. The corrosion rate expressed by the volume of released hydrogen in the form of a function of immersion time in Ringer’s solution at 37 °C was presented. The surface structure and corrosion products, which were formed during the immersion tests, were examined by means of scanning electron microscopy and the following spectroscopic methods: x-ray photoelectron spectroscopy, x-ray diffractometry, secondary ion mass spectrometry and energy-dispersive x-ray spectroscopy. As a result of the investigations of the surface structure, oxides (MgO, CaO, ZnO), hydroxides (Mg(OH){sub 2}, Ca(OH){sub 2}) and carbonates (CaCO{sub 3}) were identified. The analysis of the research results allowed the determination of a probable course and corrosion mechanism of the above-mentioned metallic glasses during immersion in Ringer’s solution.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Stress Corrosion Cracking of AZ91 + xCe Alloy Using Proof Ring Test in ASTM D1384 and NaCl-K{sub 2}CrO{sub 4} Solutions

The effect of cerium addition on AZ91 magnesium alloy and its influence on stress corrosion cracking (SCC) were studied using constant load proof ring testing NaCl-K{sub 2}CrO{sub 4} and ASTM D1384 solutions at 70 and 80% of yield stress, respectively. The investigation revealed that the optimum grain refinement of desired phases occurred with 0.5% addition of cerium. The addition levels of cerium above 1.5 wt.% to AZ91 alloy resulted in premature failures due to poor SCC resistance in both solutions (K{sub 2}CrO{sub 4} and ASTM D1384 solutions). The microstructural studies of the experimental alloys were characterized by using optical and scanning electron microscopy. The elemental compositions of cerium-added AZ91 magnesium alloys were studied by energy-dispersive spectroscopy. The results indicate that the mode of SCC failure was found to be transgranular in nature along with secondary cracks containing cleavages which resulted from the hydrogen embrittlement and anodic dissolution phenomena. The AZ91 alloy with 0.5 wt.% cerium exhibits better mechanical properties and high stress corrosion resistance.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Comparative Corrosion Behavior of Five Different Microstructures of Rebar Steels in Simulated Concrete Pore Solution with and Without Chloride Addition

The present work discusses the effect of five different microstructures, coarse, fine and very fine ferrite–pearlite, martensite and tempered martensite, made by furnace cooling, air cooling, forced air-cooling, water quenching and tempering, respectively, of a rebar steel on its corrosion performance in freely aerated with and without chloride-contaminated simulated concrete pore solution using the dynamic polarization and electrochemical impedance spectroscopy. The corrosion performance of the steels with five different microstructures relates to the polarization resistance, protective ability of rusts and the extent of the galvanic attack. The corrosion rate of the steels has been found to be comparable in the simulated concrete pore (SCP) solution. However, in chloride-containing SCP solution, corrosion rate has been found to increase in the following sequence: forced air-cooled–air-cooled–quenched–furnace-cooled–tempered steels.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Transferring Ions from Solution to the Gas Phase: The Two Basic Principles

The efficient formation of gaseous ions is the crucial step in all successful mass spectrometric experiments. The invention of electrospray ionization (ESI) has strongly facilitated this step by transferring preformed ions directly from solution to the gas phase – thereby circumventing the need to first convert analytes to the gas phase and then ionize them – and therefore ESI has become an extremely useful and widely applied MS technique. The invention of sonic spray ionization (SSI) has also allowed for the transfer of ions from solution into the gas phase, but without the assistance of a voltage or heating. Numerous ionization techniques, using similar principles to those applied in either ESI or SSI, have subsequently been developed. Although experimental conditions used in such techniques vary markedly, herein we argue that they are all based on either one of two basic principles by which ions can be transferred from solution to the gas phase, that is: via (1) neutralizing the counter ion, or (2) separating the ions. We have selected 35 such techniques and categorized them accordingly. This article thereby aims to establish the basic principles by which gaseous ions can be obtained from solvated ions. We further propose that any new ionization technique used to transfer solvated ions to the gas phase will similarly fall into one of these two mechanistic categories. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Continuous solutions to a class of first-order fuzzy differential equations with discontinuous coefficients

In this paper, we study the continuity of solution functions to a class of fuzzy differential equations (FDEs) in the form y{sup ′}(t)=((φ(t))/((t−α){sup p}))⊙y(t)+ψ(t), where the coefficient function ((φ(t))/((t−α){sup p})) is a discontinuous function at the point t=α and α is an inner point of the interval under study. At first, the continuity of solutions for the crisp case of the problem is investigated and those results are extended to the fuzzy case of the problem from the view point of strongly generalized differentiability (G-differentiability). Next, we obtain explicit formulas of solutions and the conditions of their existence for a special class of these problems. Finally, the results are illustrated by solving some examples.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2022

Bifurcation Analysis Reveals Solution Structures of Phase Field Models

The phase field method is playing an increasingly important role in understanding and predicting morphological evolution in materials and biological systems. Here, in this study, we develop a new analytical approach based on the bifurcation analysis to explore the mathematical solution structure of phase field models. Revealing such solution structures not only is of great mathematical interest but also may provide guidance to experimentally or computationally uncover new morphological evolution phenomena in materials undergoing electronic and structural phase transitions. To elucidate the idea, we apply this analytical approach to three representative phase field equations: the Allen-Cahn equation, the Cahn-Hilliard equation, and the Allen-Cahn-Ohta-Kawasaki system. The solution structures of these three phase field equations are also verified numerically by the homotopy continuation method.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2016

Atmospheric-pressure solution-cathode glow discharge: A versatile ion source for atomic and molecular mass spectrometry

We report an atmospheric-pressure solution-cathode glow discharge (SCGD) has been evaluated as an ion source for atomic, molecular, and ambient desorption/ionization mass spectrometry. The SCGD consists of a direct-current plasma, supported in the ambient air in the absence of gas flows, and sustained upon the surface of a flowing liquid cathode. Analytes introduced in the flowing liquid, as an ambient gas, or as a solid held near the plasma are vaporized and ionized by interactions within or near the discharge. Introduction of acidic solutions containing metal salts produced bare elemental ions as well as H 2 O, OH - and NO 3 - adducts. Detection limits for these elemental species ranged from 0.1 to 4 ppb, working curves spanned more than 4 orders of linear dynamic range, and precision varied between 5 and 16% relative standard deviation. Small organic molecules were also efficiently ionized from solution, and both the intact molecular ion and fragments were observed in the resulting SCGD mass spectra. Fragmentation of molecular species was found to be tunable; high discharge currents led to harder ionization, while low discharge currents produced stronger molecular-ion signals. Ambient gases and solids, desorbed by the plasma from a glass probe, were also readily ionized by the SCGD. Indeed, strong analyte signals were obtained from solid samples placed at least 2 cm from the plasma. These findings indicate that the SCGD might be useful also for ambient desorption/ionization mass spectrometry. In conclusion, combined with earlier results that showed the SCGD is useful for ionization of labile biomolecules, the results here indicate that the SCGD is a highly versatile ion source capable of providing both elemental and molecular mass-spectral information.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2015

Quantitative experimental determination of the solid solution hardening potential of rhenium, tungsten and molybdenum in single-crystal nickel-based superalloys

Here, the solid-solution hardening potential of the refractory elements rhenium, tungsten and molybdenum in the matrix of single-crystal nickel-based superalloys was experimentally quantified. Single-phase alloys with the composition of the nickel solid-solution matrix of superalloys were cast as single crystals, and tested in creep at 980 °C and 30–75 MPa. The use of single-phase single-crystalline material ensures very clean data because no grain boundary or particle strengthening effects interfere with the solid-solution hardening. This makes it possible to quantify the amount of rhenium, tungsten and molybdenum necessary to reduce the creep rate by a factor of 10. Rhenium is more than two times more effective for matrix strengthening than either tungsten or molybdenum. The existence of rhenium clusters as a possible reason for the strong strengthening effect is excluded as a result of atom probe tomography measurements. If the partitioning coefficient of rhenium, tungsten and molybdenum between the γ matrix and the γ' precipitates is taken into account, the effectiveness of the alloying elements in two-phase superalloys can be calculated and the rhenium effect can be explained.

36 MATERIALS SCIENCE↗

DOE OSTI2024

The many faces of θ' -Al 2 Cu precipitates: Energetics of pristine and solute segregated Al/ θ' semi-coherent interfaces

θ'-Al 2 Cu precipitates in Al-Cu alloys have various distorted octagon shapes, which can be explained by the competition between {100} and {110} type semi-coherent interfaces with the Al matrix. While most prior studies on the semi-coherent Al/θ' interfaces have focused on the {100} orientation, little is known about the {110} interface. We have investigated the energetics of pristine and solute-segregated {110} semi-coherent Al/θ' interfaces with advanced characterization and first-principles studies. We report interfacial, strain, and solute segregation energetics of the {110} Al/θ' semi-coherent interface for 39 elements and compared them with previously reported values of the {100} interface. We discuss the atomic features and atomic local structures to identify similarities and differences between the two types of Al/θ' semi-coherent interfaces. Here, the isotropy in pristine Al/θ' semi-coherent interfacial energy and the anisotropy resulting from solute segregation provide insight into the formation of different types of θ' precipitate “faces” reported in the literature.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Grain boundary solute segregation across the 5D space of crystallographic character

Solute segregation in materials with grain boundaries (GBs) has emerged as a popular method to thermodynamically stabilize nanocrystalline structures. However, the impact of varied GB crystallographic character on solute segregation has never been thoroughly examined. Here, this work examines Co solute segregation in a dataset of 7272 Al bicrystal GBs that span the 5D space of GB crystallographic character. Considerable attention is paid to verification of the calculations in the diverse and large set of GBs. In addition, the results of this work are favorably validated against similar bicrystal and polycrystal simulations. As with other work, we show that Co atoms exhibit strong segregation to sites in Al GBs and that segregation correlates strongly with GB energy and GB excess volume. Segregation varies smoothly in the 5D crystallographic space but has a complex landscape without an obvious functional form.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Exact solutions of the Klein–Gordon equation in the Kerr–Newman background and Hawking radiation

This work considers the influence of the gravitational field produced by a charged and rotating black hole (Kerr–Newman spacetime) on a charged massive scalar field. We obtain exact solutions of both angular and radial parts of the Klein–Gordon equation in this spacetime, which are given in terms of the confluent Heun functions. From the radial solution, we obtain the exact wave solutions near the exterior horizon of the black hole, and discuss the Hawking radiation of charged massive scalar particles. - Highlights: • The covariant Klein–Gordon equation for a charged massive scalar field in the Kerr–Newman black hole is solved. • Both angular and radial parts are transformed to a Heun-type equation. • The resulting Hawking radiation spectrum of scalar particles has a thermal character.