Section Of Mg Research Articles

Re-assessment of the Mg–Zn–Ce system focusing on the phase equilibria in Mg-rich corner

The Mg–Zn–Ce alloys exhibit good creep resistance and strength at elevated temperature due to the formation of intermetallic compounds. However, the ternary compounds and phase equilibria in the Mg-rich corner are still controversial which restrains the development of Mg–Zn–Ce alloys. The present work experimentally investigated the phase equilibria in Mg-rich corner of the Mg–Zn–Ce system at 350 and 465 °C and thermodynamically assessed the Mg–Zn–Ce system. The existence of ternary compounds τ1 and τ3 were confirmed by a combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystal structure of τ1 was resolved as space group of Cmc21 with a = 0.9852(2)–1.0137(2) nm, b = 1.1361(3)–1.1635(3) nm and c = 0.9651(2)–0.9989(2) nm by Rietveld refinement of the XRD pattern. Three invariant reactions, L→τ3+CeMg3+CeMg12, L+CeMg12→α-Mg+τ1 and L+τ1→τ2+α-Mg, were revealed by differential scanning calorimeter (DSC) measurement and microstructure characterization. Then, a set of self-consistent thermodynamic parameters was thereafter constructed by assessing the phase equilibria, solid solubilities of CeMg12, τ1, CeMg3 and τ3, as well as the formation enthalpies of binary and ternary compounds calculated by density functional theory. The comparison of calculated phase diagram with experimental results and the literature were discussed. The calculated isothermal section of Mg–Zn–Ce system at 465 °C agreed with our experimental data. The two three-phase equilibria, τ1+α-Mg+CeMg12 and CeMg3+τ3+CeMg12, were confirmed in the Mg-rich corner. This thermodynamic database can be used for the further alloys design of Mg–Zn–Ce system.

Phase equilibria in water–salt systems from sodium, magnesium, and calcium nitrates and deicing properties of nitrate compositions

Phase equilibria have been studied in the sections of Mg(NO3)2–NaNO3–H2O and Ca(NO3)2–NaNO3–H2O systems at the ratio of salt components from 3: 1 to 1: 3 at temperatures of 0 to–35°C. A series of nitrate compositions has been determined, which are promising as deicing agents. Their theoretical (under equilibrium conditions) fusion ability with respect to ice at–5 to–10°C has been calculated. The corrosion activity of the composition of calcium and magnesium nitrates (1: 1) with respect to cement concrete (in collaboration with the test laboratory of OOO RSTs Opytnoe) has been measured. It has been found that the reagent meets criteria according to the action on cement concrete and can be used in aerodromes. This composition has been chosen as original for the development of a solid granular deicing agent on its basis for aerodromes.

Enhanced one-photon double ionization of atoms and molecules in an environment of different species.

The correlated nature of electronic states in atoms and molecules is manifested in the simultaneous emission of two electrons after absorption of a single photon close to the respective threshold. Numerous observations in atoms and small molecules demonstrate that the double ionization efficiency close to threshold is rather small. In this Letter we show that this efficiency can be dramatically enhanced in the environment. To be specific, we concentrate on the case where the species in question has one or several He atoms as neighbors. The enhancement is achieved by an indirect process, where a He atom of the environment absorbs a photon and the resulting He(+) cation is neutralized fast by a process known as electron transfer mediated decay, producing thereby doubly ionized species. The enhancement of the double ionization is demonstrated in detail for the example of the Mg · He cluster. We show that the double ionization cross section of Mg becomes 3 orders of magnitude larger than the respective cross section of the isolated Mg atom. The impact of more neighbors is discussed and the extension to other species and environments is addressed.

Isothermal section of Mg–Nd–Gd ternary system at 723 K

An isothermal section of the Mg–Nd–Gd ternary system at 723 K was established by diffusion triple technique and electron probe microanalysis (EPMA). Mg3Gd and Mg3Nd form a continuous solid solution (Gd, Nd)3Mg, and a continuous solid solution (Gd, Nd)Mg is also formed between MgGd and MgNd. Mg7Gd, Mg5Gd, Mg2Gd, Mg41Nd5, (Gd, Nd)3Mg and (Gd, Nd)Mg are found in the ternary system. In these intermetallic phases, Mg7Gd has been reported to be a metastable phase in previous literatures. The solubilities of Mg, Gd and Nd in all the phases were detected. Furthermore, four three-phase equilibria, α(Mg)+Mg7Gd+ Mg41Nd5, Mg7Gd+Mg5Gd+Mg41Nd5, Mg5Gd+Mg41Nd5+(Gd, Nd)3Mg and (Gd, Nd)3Mg+(Gd, Nd)Mg+Mg2Gd, were identified in the isothermal section.

Fitting Equation of K-Shell Cross Section of Mg and Fe Atoms

Fitting Equation of K-Shell Cross Section of Mg and Fe Atoms

Electron impact double ionization of Mg+ ions

Theoretical studies of electron impact double ionisation cross sections of Mg+ ions have been performed in the binary encounter approximation (BEA). Direct double ionisation has been investigated in the modified double binary encounter model. Ionization cross sections of different shells have been also calculated in order to analyse the contributions to double ionisation from ionisation-autoionization. The effect of the Coulombic field of the target ion on the incident electron has been considered in the present work. Accurate expression of σ ΔE (cross-section for energy transfer ΔE) and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. The theoretical results show satisfactory agreement with the experimental observations.

Isothermal section of Mg–Zn–Zr ternary system at 345 ° C

Isothermal section of Mg–Zn–Zr ternary system at 345 ∘C has been determined by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy assisted with energy dispersive X-ray spectroscopy using a series of Mg–Zn–Zr alloys. The results show that there exist three intermetallic compounds ZnZr, Zn 2Zr 3, (Mg,Zn) 2Zr, and a liquid phase in equilibrium with the α -Mg phase. The presence of two other three-phase regions in equilibrium, Liquid+MgZn+(Mg,Zn) 2Zr and MgZn+Mg 2Zn 3+(Mg,Zr)Zn 2, has also been confirmed. The addition of Zn can significantly increase the solubility of Zr and vice-versa in the α -Mg matrix.

Calculation of (e, 2e) triple differential cross sections of Mg in coplanar geometry

We report the results of triple differential cross section of coplanar (e, 2e) processes on Mg (3s) atom in modified distorted wave Born approximation (DWBA). The standard DWBA formalism has been modified by including the correlation-polarization potential (which is function of electron density) and post collision interaction. We compare our computed results with the available experimental data and observe that the inclusion of polarization potential in the standard DWBA is able to improve the agreement with experimental results.

Double photoionization of Be and Mg atoms using theR-matrix-with-pseudostates method

The $R$-matrix-with-pseudostates (RMPS) method is used to obtain total cross sections for double photoionization of Be and Mg atoms from their ground singlet and metastable triplet terms. Time-dependent close-coupling (TDCC) calculations are also carried out for the total and energy differential double photoionization cross sections of Mg from its ground term. The RMPS total ground-term cross sections for Be and Mg are in good agreement with results from TDCC and convergent close-coupling calculations at lower energies but are above them at higher energies. They are also in good agreement with the results of synchrotron measurements. The total cross sections for double photoionization from the triplet metastable terms of Be and Mg are found to be two to three times smaller than those from their singlet ground terms.

Relative single- and double-photoionization cross sections of Mg around the2p→nlresonances

Using highly monochromatized synchrotron light and the ion time-of-flight method to detect singly and doubly charged magnesium ions, we have measured relative single- and double-photoionization cross sections of Mg from $55\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}58\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, which includes the region of the $2p\ensuremath{\rightarrow}nl$ inner-shell excitations. The resonances were analyzed using Fano profiles and the resonance positions are compared to previously published data. The quantum defect theory is applied to the resonance energies revealing that the published Mg $2{p}_{1∕2}$ and $2{p}_{3∕2}$ thresholds need to be revised. In addition, we have determined the double-to-single photoionization ratio in the $55\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}71\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ region.

(e,2e)triple differential cross section of Mg in coplanar symmetric geometry

Spin-averaged static exchange potential and modified semiclassical exchange potential have been used in the distorted-wave Born approximation to calculate the triple differential cross section of Mg $(3{s}^{2})$ in the coplanar symmetric geometry. The calculations have been carried out at impact energies ranging from $(R=)$ 1.78 to 8.84 times the first ionization potential for Mg. The effect of post-collision interactions has been included by making use of the Gamow factor introduced by Whelan et al. [Phys. Rev. A 50, 4394 (1994)]. Present results have been compared with recent experiments of Murray [Phys. Rev. A 72, 062711 (2005)] and are found to be in excellent agreement with the same except for the lowest impact energy (that is, for $R=1.78$ times above the first ionization potential).

Electron-impact ionization of Mg+ near the 2p inner-shell edge

Electrons above about 50 eV can ionize Mg+ by the ejection of a 2p electron. New R-matrix calculations are reported on these L-shell processes in the electron-impact ionization cross section of Mg+. Our background cross section agrees well with previous calculations and with the structure obtained in recent measurements. Resonances arising from interference of inner-shell and outer-shell channels are quantified, and we discuss in detail the 2p53s2nl series.

A simple apparatus for determining column density and absolute photoabsorption cross sections

This article presents a simple measuring apparatus that is capable of measuring column density and absolute photoabsorption cross sections. The apparatus includes a simple high-temperature heatpipe furnace, an MKS Instruments Baratron, a hydrogen discharge lamp, and an optical detecting system. The heatpipe furnace provides an absorbing medium with a steady total pressure in a closed system so that the column density can be obtained using the ideal gas relation. The apparatus is designed for a working temperature range below 1000 K and a pressure range up to 10 Torr. Encountered experimental difficulties and their found solutions will be discussed in detail. In this work, the absolute photoabsorption cross section of Mg is measured near the 3s threshold using this apparatus. The absolute photoabsorption cross section result at the 3s threshold, which is 2.1±0.3 Mb, is in good agreement with hook method data (2.36 Mb).

Stopping power obtained from complex backscattering spectra: the isotopes of magnesium

The simple electronic structure of alkali and earth-alkali metals — tightly bound core electrons and almost free plasma electrons — makes these elements favorites of stopping theory. However, measurements of stopping cross sections ϵ will be afflicted with the high reactivity of these materials: targets generally have to be produced on massive backings in situ under UHV conditions and have to be measured in backscattering geometry. In that way, ϵ of Li, Rb Ca, and Sr has been determined before. The measurement of Mg suffers from the fact, that due to the three isotopes of Mg each backscattering spectrum is composed of three individual spectra. We have developed a computer code to determine by a least squares fit the widths of spectra of up to three components. From this we deduce absolute stopping cross sections of Mg for protons (from 15 to 600 keV) and helium ions (from 50 to 740 keV). Deviations from standard stopping power tables of more than 30% are found.

Auger and X-ray photoelectron diffraction in MgO(001)

A new method for preparing the MgO(001) surface is introduced. Al Kα-excited, angular distributions of MgKL 2,3L 2,3 Auger, Mg 1s, and O 1s core-level photoemission intensities were measured. We show that high-kinetic-energy MgKL 2,3L 2,3 Auger and O 1s photoelectron diffraction patterns are strongly dependent upon the atomic numbers of atoms neighboring the emitter. The physical cause for this result is the inherent differences in the elastic scattering cross sections of Mg and O. In addition, we show that low-kinetic-energy Mg 1s photoelectron diffraction patterns are sensitive to input atomic charges and radii, in contrast to the behavior observed for their high-energy counterparts.

The Use of Equivalent Potential Vorticity to Diagnose Regions of Conditional Symmetric Instability

Abstract Conditional symmetric instability (CSI) is an important property of the atmosphere when diagnosing and predicting mesoscale bands of moderate to heavy precipitation within winter cyclones. Within regions of CSI, slantwise convection can increase snow totals over narrow regions. Typically, CSI is evaluated in a cross-sectional plane chosen normal to the middle-tropospheric thermal wind using Mg, the absolute geostrophic momentum, and θ e, the equivalent potential temperature. Regions where Mg, surfaces slope less than θe, surfaces are subject to CSI. We describe an objective measure of CSI, called the equivalent potential vorticity (EPV), that makes evaluating CSI quick and effective. Cross sections of Mg, versus θe, and EPV are compared for two cases to demonstrate the effectiveness of using EPV cross sections to diagnose CSI. The distinction between slantwise convection and upright convection is also demonstrated by these case studies.

Quantum defect orbital calculations on the alkaline-earth elements: oscillator strengths and photoionization cross sections

The quantum defect orbital (QDO) formalism is applied to the computation of oscillator strengths of Mg, Ca, Sr, and Ba and photoionization cross sections of Mg and Ca. For [Formula: see text] transitions, QDO oscillator strengths reproduce fairly well the experimental values both in magnitude and trend. Photoionization cross sections for ns2 → nsεp transitions agree well with experimental results where no autoionization resonances are present. The results of both sets of calculations are at least comparable in quality to those of other more complex procedures.

Extending a model-based efficiency calibration of a Si(Li) detector below the Si K-edge

The full-energy peak efficiency of a well-collimated Si(Li) detector was measured using calibrated radioactive sources for energies between 3.3 and 105 keV; below the Si K-edge (1.84 keV), the efficiency was determined from thick-target analysis of K ionization cross sections of Mg, Al, and Si measured for 80–180 keV protons. A previously introduced model function was fitted to the efficiency data in the two energy regions. Using the known thickness of the dead-silicon layer for our detector, excellent agreement with the accepted value of the Si K-edge jump are obtained from the fits.

Total Neutron Cross Sections of Magnesium, Aluminum, Silicon, Zirconium, Niobium and Molybdenum in Energy Range from 0.001 to 0.3 eV

Total neutron cross sections of Mg, Al, Si, Zr, Nb and Mo at room temperature have been measured in the energy range of 0.001–0.3 eV using a chopper and TOF facility of the Musashi Institute of Technology Research Reactor. The experiments were performed for solid and powdered samples. For these samples inelastic and elastic scattering cross sections were respectively calculated with the THRUSH code assuming Debye-type frequency spectrum and with the UNCLE-TOM code using crystal structure and lattice constants of each sample. For solid samples the measured cross sections agreed well with the calculations below the Bragg cut-off energies. For the powdered samples there were good agreements above the Bragg cut-off, and the measurements were larger than the calculations below the Bragg cut-off. The experimental cross section, adopting the results of powdered and solid samples for energy ranges above and below the Bragg cut-off respectively, agreed well with the calculation which was performed for the samples in perfect polycrystalline state.

Total neutron cross sections of magnesium, aluminum, silicon, zirconium, niobium and molybdenum in energy range from 0.001 to 0.3 eV.

Total neutron cross sections of Mg, Al, Si, Zr, Nb and Mo at room temperature have been measured in the energy range of 0.001-0.3 eV using a chopper and TOF facility of the Musashi Institute of Technology Research Reactor. The experiments were performed for solid and powdered samples. For these samples inelastic and elastic scattering cross sections were respectively calculated with the THRUSH code assuming Debye-type frequency spectrum and with the UNCLE-TOM code using crystal structure and lattice constants of each sample.For solid samples the measured cross sections agreed well with the calculations below the Bragg cut-off energies. For the powdered samples there were good agreements above the Bragg cut-off, and the measurements were larger than the calculations below the Bragg cut-off.The experimental cross section, adopting the results of powdered and solid samples for energy ranges above and below the Bragg cut-off respectively, agreed well with the calcula-tion which was performed for the samples in perfect polycrystalline state.