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Ferropericlase (Mg, Fe)O is an abundant mineral of Earth's lower mantle and the liquid phase of the material was an important component of the early magma ocean. Using quantum-mechanical, finite-temperature density-functional theory calculations, we compute the electronic component of the electrical and thermal conductivity of (Mg 0.75 , Fe 0.25 )O crystal and liquid over a wide range of planetary conditions: 0–200 GPa, 2000–4000 K for the crystal, and 0–300 GPa, 4000–10,000 K for the liquid. We find that the crystal and liquid are semi-metallic over the entire range studied: the crystal has an electrical conductivity exceeding 10 3 S/m, whereas that of the liquid exceeds 10 4 S/m. Our results on the crystal are in reasonable agreement with experimental measurements of the electrical conductivity of ferropericlase once we account for the dependence of conductivity on iron content. We find that a harzburgite-dominated mantle with ferropericlase in combination with Al-free bridgmanite agrees well with electromagnetic sounding observations, while a pyrolitic mantle with a ferric-iron rich bridgmanite composition yields a lower mantle that is too conductive. The electronic component of thermal conductivity of ferropericlase with X Fe = 0.19 is negligible (<1 W/m/K). The electrical conductivity of the crystal and liquid at conditions of the core-mantle boundary are similar to each other ( 3 × 10 4 S/m). A crystalline or liquid ferropericlase-rich layer of a few km thickness thus accounts for the high conductance that has been proposed to explain anomalies in Earth's nutation. The electrical conductivity of liquid ferropericlase exceeds that of liquid silica by more than an order of magnitude at conditions of a putative basal magma ocean, thus strengthening arguments that the basal magma ocean could have produced an ancient dynamo. [ABSTRACT FROM AUTHOR]

In this work, Algerian kaolinite, a naturally occurring clay mineral, was used as low-cost precursor for the synthesis of cordierite ceramics. The kaolinite was mixed with synthetic magnesia, and the mixture was ball milled and reaction sintered in the temperature range 900–1350 °C for 2 h. Thermogravimetry (TG), differential thermal analysis (DTA), dilatometry, high temperature x-ray powder diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) complementary techniques were used to analyze sintering behavior, characterize phase transformations, and investigate crystallization kinetics. Milling the kaolinite and magnesia mixture for 10 h yielded a homogenous powder, decreased the average particle size, and improved the roundness of particles. Different crystalline phases were present in the samples sintered in the temperature range 900–1150 °C, the cordierite phase started to crystallize at 1200 °C, and the formation of highly dense cordierite (99%) was complete at 1250 °C. The activation energy values for cordierite formation calculated using Kissinger, Boswell, and Ozawa methods were found to be equal to 577, 589, and 573 kJ/mol, respectively. The kinetic parameters n and m had values close to 2. Bulk nucleation with a constant number of nuclei was the dominant mechanism in cordierite crystallization, followed by two-dimensional growth controlled by interface reaction. [ABSTRACT FROM AUTHOR]

• The process of methane dissociation to produce methyl radical (CH 3 •) is studied in this work. • The electron-deficient state can be formed by Li doped, however it will be broken once the oxygen vacancy appears. • The active site with electronic-deficient state is the key to the efficient generation of CH 3 •. • A volcano relationship between the C-H activation energy and the H adsorption free energy exists on the Li doped MgO surfaces. Methyl radical (CH 3 •) is the critical precursor to generate C 2 hydrocarbons in oxidative coupling of methane (OCM) reaction. It is crucial to explore how to efficiently generate CH 3 • and reveal the intrinsic principles behind it. In this study, we select MgO with a relatively simple structure as the research object, and probe the effects of the electronic state of active site on the CH 3 • generation by the density functional theory (DFT) calculation. The results show that the pure MgO with the different crystal surfaces as the benchmark models exhibit poor catalytic performance for CH 3 • generation; while Li doped MgO surface or subsurface that have the electron-deficient of active sites, exhibit excellent catalytic performance for it, which is attributed to that the electron-deficient of active sites are easier to receive electron of H and thereby promote the efficient generation of CH 3 •; pure MgO surface or subsurface with oxygen vacancy as well as Li doped MgO surface or subsurface with oxygen vacancy as the contrast models that have the electron-rich of active sites, exhibit poor catalytic performance. It can be obtained that the active site with electronic-deficient state is the key to the efficient generation of CH 3 •. The study can provide some guidance for designing high efficient OCM catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel method for determination of total inorganic arsenic in water samples, based on magnesium oxide crystals quantitatively preconcentration and graphite furnace atomic absorption spectrometry (GFAAS) detection has been developed. As the MgO crystals could successively act as the adsorbent and matrix modifier, the method presents great potential in practical routine analysis of inorganic arsenic. With optimization of the experimental conditions, 1.5 mg of MgO was added into 4.0 mL water sample and ultrasonic dispersing 15 min for adsorbing the arsenic at first. Then, the mixture was centrifuged 5 min for separating the adsorbents and the water solution; the deposits were collected and dissolved with HNO 3 for arsenic determination. The enrichment factor of 13, limit of detection (LOD) of 0.087 μg L − 1 , relative standard deviation (RSD) of 4.5% ( n = 7, c = 2.0 μg L − 1 ) were achieved under the optimized conditions. The procedure was validated by analysis of certified water sample (GBW08605), which results in good agreement between the certified and the found values. The method was further demonstrated for analysis of lake water, snow water and tap water, and satisfactory spiked recoveries of 98.5% to 103.0% were achieved for these samples. These preliminary results indicated the present method was practical and accurate for analysis of trace-arsenic in natural water samples. [ABSTRACT FROM AUTHOR]

To solve the problem of eutrophication caused by phosphate, a metal-loaded biocarbon composite material is considered to be an effective adsorbent for removing phosphate. In this study, potassium humate was used to prepare modified potassium humate-based carbon material (MPHCM) through magnesium chloride modification and rapid pyrolysis. Studies have shown that MPHCM can effectively remove phosphate from water. At 318 K and with pH=3, the maximum adsorption capacity reached 181.96 mg P g−1, and the adsorption process conformed to the pseudo-first and pseudo-secondary adsorption kinetic models and the Langmuir adsorption model. This adsorption process involved physical and chemical adsorption, which indicated monolayer adsorption. The main adsorption mechanisms for MPHCM were protonation, electrostatic interactions, ligand exchange and inner sphere complex precipitation. Six desorption cycles verified the excellent reproducibility of MPHCM for phosphate removal. Therefore, this study provides a new adsorbent for phosphate removal and expands the application range of potassium humate-based carbon materials. [ABSTRACT FROM AUTHOR]

The kinetic pathway for magnesia-excess magnesium aluminate spinel (MgAl 2 O 4 ) formation is determined from the dilation behaviour of MgO–Al 2 O 3 (34:66 w/w) oxide compacts during reaction sintering under dynamic heating regime at different constant heating rates ( β ). It is calculated from expansion values at different β , analysed through model-free and model-based kinetic methods to arrive at the most suitable and unambiguous kinetic pathway, where spinelisation is best described ( r 2 =0.986) with Avrami model with exponent n =0.65 and activation energy ( E a ) 409 kJ mol −1 . To validate the kinetic model, an isothermal heat treatment of the oxide compact was done and % spinelisation was determined by Rietveld refinement of the XRD data. The results matched the predicted values very closely and validate our kinetic model. This method can be extended to several industrially important thermally activated solid state reactions which require thermal treatment in order to minimise the energy requirement by optimising the heating protocol. [ABSTRACT FROM AUTHOR]

We report on the growth of cuprous oxide on MgO(001) by plasma-assisted molecular beam epitaxy. An increased copper to oxygen ratio enhances the cube-on-cube growth of the Cu 2 O crystallites compared to the Cu 2 O(110)||MgO(100) oriented crystallites. This correlates with the occurrence of a (3√2×√2)R45° surface reconstruction observed during growth. This reconstruction is known to be unstable under oxygen-rich conditions and stabilizes the Cu 2 O(001) surface compared to the Cu 2 O(110) surface for higher copper to oxygen ratios enhancing cube-on-cube growth. High resolution X-ray diffraction analysis of the resulting cube-on-cube Cu 2 O layers indicates partial relaxation by 39.7%. Investigations of the optical absorption and photoluminescence properties of the films reveal excitonic contributions comparable to those of single crystals. [ABSTRACT FROM AUTHOR]

Abstract: Lithium tantalate (LT) is an oxide material whose congruent composition differs from its stoichiometric composition in the Li2O–Ta2O5 binary system. Ionic species in the LT melt are segregated during crystal growth, even at the congruent composition, which leads to crystallization electromotive force (C-EMF) at the solid–liquid. On the other hand, when a compound has a stoichiometric structure at the congruent composition, such segregation does not occur. By employing a new concept of stoichiometry of a material where the activity of any constituent element could be unity, we developed a new lithium tantalate with MgO doping, cs-MgO:LT (Li2O:Ta2O5:MgO=40.8:50.0:9.2), that is stoichiometric and coincident with the congruent composition. Because of this coincidence, cs-MgO:LT does not yield C-EMF and does not show segregation during growth even for ionic species. A bulk crystal was grown from the melt of the cs-MgO:LT composition via the Czochralski (CZ) method, and it showed excellent compositional homogeneity, proved by the constant distribution of the Curie temperature throughout the crystal. [Copyright &y& Elsevier]

Abstract: Ni-MgO catalysts with varying Ni/Mg ratios were prepared by co-precipitation and tested in sorbitol hydrogenolysis. At 473K and 4MPaH2, the best catalyst with Ni/Mg ratio of 3:7 exhibited 67.8% conversion and 80.8% total selectivity of ethylene glycol, 1,2-propylene glycol and glycerol. These catalysts were characterized by XRD, CO2-TPD and H2 chemisorption, revealing that the activity depended strongly on the basicity and Ni surface area. The reaction conditions were optimized, which were relatively mild for this chemoselective conversion. [Copyright &y& Elsevier]

Abstract: Based on the technology of the non-collinear phase-matching about three-wave interaction in uniaxial crystal, the performance of nonlinear crystal MgO:LiNbO3(MgO:LN) including the phase-matching angles, effective nonlinear coefficient and THz-wave gain as well as its absorption coefficients are theoretically discussed under e-ee type phase-matching condition. And an external cavity is developed for terahertz-wave parametric oscillators pumped by picosecond laser (ps-TPOs). For optimizing the ps-TPOs performance, the focusing spot size in MgO:LN crystal, the geometric size of the MgO:LN crystal, the conversion efficiencies, and the stability of the THz-wave generation are designed and calculated. The calculated results provide a comprehensive theoretical basis for the ps-TPOs using difference-frequency generation (DFG) method and optimal performance to generate widely tunable terahertz waves in MgO:LN crystal. [Copyright &y& Elsevier]

Abstract: The effect of calcination temperature and MgO crystallite sizes on the structure and catalytic performance of TiO2 supported nano-MgO catalyst for the transesterification of soybean oil has been studied. The catalyst has been prepared by deposition–precipitation method, characterised by XRD, TEM, XRF, BET and FTIR and tested in a batch autoclave at 225°C. The soybean oil conversion after 15min of the transesterification reaction increased when the calcination temperature was increased from 500 to 600°C and decreased with further increase in calcination temperature. Some glycerolysis activity was also detected on catalysts calcined at 600 and 700°C after 45min of reaction. The soybean oil conversion during the transesterification reaction increased with the decrease in MgO crystallite size for the first 30min. [Copyright &y& Elsevier]

Abstract: The effect of anisotropic strain induced by SrTiO3 (STO) substrate with different orientations on charge ordering (CO) behavior in epitaxial Sm0.5Ca0.5MnO3 (SCMO) films was investigated using cross-sectional transmission electron microscopy at 103K. Incommensurate modulated structure caused by CO transition was observed in the SCMO film grown on a [101]-oriented STO substrate while none were found for SCMO film grown on a [100]-oriented STO substrate. This distinctive orientation-dependent CO transition is correlated with anisotropic strain in the films induced by lattice mismatch, confirming the previous results for growth on different substrates. [Copyright &y& Elsevier]

Abstract: Bi2Sr2CaCu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors. Pyrolysis takes place between 200°C and 450°C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2Sr2CaCu2O8 films were obtained after heat treatment at 840°C in air. The highest Tc of 81K was measured in a 10-layer film. Subsequent post-annealing in Ar and pure O2 did not improve the superconducting properties of the films and resulted in the appearance of Bi2CaCuO5 or Bi2(Sr, Ca)2CuO6 impurities. [Copyright &y& Elsevier]

Abstract: The methodology of characterizing electronic structure in dielectric materials will be presented in detail. Energy distribution of the electrons emitted from dielectric materials by the Auger neutralization of ions is measured and rescaled for Auger self-convolution, which is restructured from the energy distribution of the emitted electrons. The Fourier transform is very effective for obtaining the density of states from the Auger self-convolution. The MgO layer is tested as an example of this new measurement scheme. The density of states in the valence band of the MgO layer is studied by measuring the energy distribution of the emitted electrons for MgO crystal with three different orientations of (111), (100) and (110). The characteristic energy of ɛ 0 corresponding to the peak density of the states in the band is determined, showing that the (111) orientation has a shallow characteristic energy ɛ 0 = 7.4 eV, whereas the (110) orientation has a deep characteristic energy ɛ 0 = 9.6 eV, consistent with the observed coefficient γ of the secondary electron emission for MgO crystal. Electronic structure in new functional nano-films spayed over MgO layer is also characterized. It is therefore demonstrated that secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials. This method simultaneously determines the valence band structure and the coefficient γ of the secondary electron emission, which plays the most important role in the electrical breakdown phenomena. [Copyright &y& Elsevier]

Abstract: The electronic energy levels of six-fold coordinated Ni2+ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni2+ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited 3T2g state fine structure; however, it does not explain why out of four levels arising from the 3T2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn–Teller effect. [Copyright &y& Elsevier]

Abstract: MgO single crystals were implanted with 70keV C/N/O ions at room temperature with respective doses of 2×1016 and 2×1017 ions/cm2. All samples with high-dose implantation showed room temperature hysteresis in magnetization loops. Magnetization and slow positron annihilation measurements confirmed that room temperature ferromagnetism in O-implanted samples was attributed to the presence of Mg vacancies. Furthermore, the introduction of C or N played more effective role in ferromagnetic performance than Mg vacancies. Moreover, the magnetic moment possibly occurred from the localized wave function of unpaired electrons and the exchange interaction formed a long-range magnetic order. [Copyright &y& Elsevier]

Abstract: Single crystals of MgO were synthesized using a simple precipitation method with no templates. The magnesium hydroxide was synthesized at 25°C or 100°C by the precipitation of magnesium nitrate solution, aged at room temperature or 100°C. Precipitation temperature had a great influence on the morphology in the synthesis of magnesium oxide. The N2 physisorption, XRD and electron microscopic (SEM/TEM, HRTEM) analysis associated with the electron diffraction reveal the different morphological structures and pores of MgO synthesized with different synthesis methods. Precipitation at 25°C generated macroporous MgO with plate-like crystals. However, the change of precipitation temperature to 100°C generated mesoporous single crystalline MgO, and the stabilization and growth of MgO(111) planes (with d-spacing of 0.244nm) was observed. The formation of mesopores and single crystallinity of MgO synthesized by the precipitation at 100°C were retained even after calcination at a temperature of 800°C for 5h. [Copyright &y& Elsevier]

Abstract: Although the antibacterial activity of ceramics has been reported in many literatures, there are none that report on the significant relation between the crystallite size and antibacterial activity. The influence of the crystallite size on antibacterial activity of MgO and ZnO powder samples was investigated in the present study. The crystallinity of powder samples was determined by X-ray diffraction measurement. From Williamson–Hall plots calculated from obtained diffraction peaks, it was found that differences in crystallinity were dependent on the crystallite size. Antibacterial activity of the powder samples was examined by the colony count method, using Escherichia coli and Staphylococcus aureus. The powder samples with a small crystallite size showed greater antibacterial activity than those with a large crystallite size. We found that the crystallite size affects the antibacterial activity of MgO and ZnO powder samples. [Copyright &y& Elsevier]

Abstract: Transition metal ions (Mn2+, Cr3+, Fe2+/3+, V2+) as substitutional impurities in cubic crystals play an important role due to their influence on the magneto-optical properties of the virgin crystals. The optical and magnetic properties of commercial MgO(001) single crystals were investigated. The PL spectra of 3d impurity ions (Cr3+ and V2+) show narrow zero phonon lines with decay times in the range of milliseconds and a broad multiphonon sideband decaying in microseconds. The EPR study exhibits hyperfine components corresponding to Mn atoms and to V atoms located in orthorhombic symmetry. The intensity change of the EPR and PL spectra as well as the variation of the decay time with temperature can be explained by electron-spin lattice relaxation due to the Raman process. [Copyright &y& Elsevier]

Abstract: Transesterification of soybean oil with methanol was carried out in the presence of CaO–MgO and KF-modified CaO–MgO catalysts at atmospheric pressure. While the methyl ester yield for the CaO–MgO catalyst with a ratio of 8:2 (CaO:MgO) was 63.6%, it was 97.9% for the KF-modified catalyst at a 2% catalyst to the reactants (methanol/oil mixture) weight ratio, a temperature of 65°C, a methanol–soybean oil ratio of 9:1 and a reaction time of 2.5h. The KF/CaO–MgO catalyst still yielded 86.7% after four successive uses. The catalytic performance of the KF/CaO–MgO catalyst was attributed to the formation of active KCaF3 and K2MgF4 centers. [Copyright &y& Elsevier]

Abstract: Scattering contrast measurements were performed on thin films of amorphous carbon and polycrystalline Au, as well as single-crystal MgO nanocubes. Based on the exponential absorption law, mass-thickness can be obtained within 10% accuracy by measuring the incident and transmitted intensities in the same image. For mass-thickness measurement of a thin amorphous specimen, a small collection semiangle improves the measurement sensitivity, whereas for the measurement of polycrystalline or single-crystal specimens, a large collection semiangle should be used to reduce diffraction-contrast effects. EELS thickness measurements on MgO nanocubes suggest that the Kramers–Kronig sum-rule method (with correction for plural and surface scattering) gives 10% accuracy at medium collection semiangles but overestimates the thickness at small collection semiangles, due to underestimation of the surface-mode scattering. The log-ratio method, with a formula for inelastic mean free path proposed by , provides 10% accuracy at small collection semiangle, while that proposed by is preferable for medium and large collection semiangles. As a result of this work, we provide recommendations of preferred methods and conditions for local-thickness measurement in the TEM. [Copyright &y& Elsevier]

Abstract: A formula is given which, for neutron energies in the range 10−4 < E <10eV, permits calculation of the nuclear capture, thermal diffuse and Bragg scattering cross-sections as a function of magnesium oxide (MgO) temperature and crystal parameters. Computer program has been developed to calculate the total neutron cross-section and transmission through mono-crystalline MgO. The calculated neutron transmission and effective attenuation coefficient values for MgO-single crystal at different temperatures are compared with measured ones. An overall agreement is indicated between the formula fits and experimental data. A feasibility study for the use of MgO-single crystal is discussed in terms of the optimum MgO-single crystal thickness, mosaic spread, temperature and cutting plane for efficient transmission of thermal-reactor neutrons, and also for rejection of the accompanying fast neutrons and gamma rays. Calculation shows that 10cm thick MgO-single crystal cut along its (100) plane, with 0.5° FWHM on mosaic spread and cooled at 77K, is a good thermal neutron filter, with high effect-to-noise ratio. [Copyright &y& Elsevier]

Abstract: A batch production for fabrication of LREBa2Cu3O y (LRE: Sm, Gd, NEG) “LRE-123” pellets are developed in air and Ar-1% O2 using a novel thin film Nd-123 seeds grown on MgO crystals. The SEM and XRD results conformed that the quality and orientation of the seed crystals are excellent. On the other hand, new seeds can withstand temperatures >1100°C, as a result, the cold seeding process was applied even to grow Sm-123 material in Air. The trapped field observed in the best 45mm single-grain puck of Gd-123 was in the range of 1.35T and 0.35T at 77.3K and 87.3K, respectively. The average trapped field at 77.3K in the 24mm diameter NEG-123 samples batch lies between 0.9 and 1T. The maximum trapped field of 1.2T was recorded at the sample surface. Further, the maximum trapped field of 0.23T at 77K was recorded in a sample with 16mm diameter of Sm-123 with 3mol% BaO2 addition. As a result we made more then 130 single grain pucks within a couple of months. Taking advantage of the single grain batch processed material, we constructed self-made chilled levitation disk, which was used on the open day of railway technical research Institute. More then 150 children stood on the levitation disk and revel the experience of levitation. The present results prove that a high-performance good-quality class of LREBa2Cu3O y material can be made by using a novel thin film Nd-123 seeds. [Copyright &y& Elsevier]

Abstract: FePd and CoPd alloy thin films were prepared on MgO single-crystal substrates of (001) B1, (110) B1, and (111) B1 orientations at 600°C by ultra high vacuum rf magnetron sputtering. L10-FePd(001) films with the c-axis perpendicular to the substrate surface are obtained on MgO(001) B1 substrates. FePd epitaxial films consisting of L10(110) and L10(011) crystals are formed on MgO(110) B1 substrates. The c-axis of L10(110) crystal is parallel to the substrate surface, whereas that of L10(011) crystal is 44° canted from perpendicular direction. L10-FePd(111) films with the c-axis 54° canted from the perpendicular direction are formed on MgO(111) B1 substrates. L10 ordering degree of these FePd films varies depending on the substrate orientation. On the other hand, disordered CoPd thin films of (001) A1, (110) A1, and (111) A1 orientations epitaxially grow on MgO substrates of (001) B1, (110) B1, and (111) B1 orientations, respectively. The magnetization properties of L10 ordered FePd and A1 disordered CoPd thin films are influenced by the crystal structure, the ordering degree, and the film orientation. [Copyright &y& Elsevier]

Abstract: Donut-like crystals of Mg–Al layered double hydroxides (LDH) are synthesized using a hydrothermal method with microwave heating. This morphology provides enlargement of the specific surface area of the {h k 0} faces, needed for adsorption application. The growth mechanism for donut-shaped crystals is proposed on the basis of AFM and STEM–EDX images. The nucleation of Mg–Al LDH starts on the amorphous surface of spherical MgO particles, which have a much lower solubility compared to the aluminum trihydroxides at the synthesis pH (∼11). The outgrowing nucleus provides re-entrant corners on both sides. These are preferential sites for the addition of new growth units, allowing lateral growth of the LDH crystal encircling the MgO particles. The dissolving MgO provides the supersaturation needed for growth and once it is depleted, a donut-like structure remains. [Copyright &y& Elsevier]

Abstract: MgO nanobelts were obtained by the decomposition of magnesium nitrate in a direct current arc plasma jet chemical vapor deposition process, with a Mo substrate at 950°C for different durations. The products formed in the first 0.5min were nanobelts, some of which possessed spherical particles on tips of nanobelts, forming “tadpole-like” nanostructures. When the reaction time was extended to 1min, nanobelts become longer although spherical particles were still observed. When the reaction time was 3min, nanobelts became even longer, and no spherical particles were observed. Extending the reaction time to 5min significantly widened the nanobelts, with widths ranging from 10 to 100nm. The MgO nanobelt growth occurred along the 〈100〉 and the 〈111〉 axes. The growth mechanism of the MgO nanobelts was a combination of axial VLS and side VS growth. Nanobelts exhibited strong ultraviolet–blue photoluminescence emission under excitation at 350nm. [Copyright &y& Elsevier]