Mixture Of MgO Research Articles

Measurement of stress using synchrotron x-rays

Stress analysis in polycrystalline materials reveals that stress can vary considerably amongdifferent subpopulations of grains. Samples of MgO and mixtures of MgO and spinel havebeen studied. After the onset of plastic flow, stronger grains or orientations will supportmore stress than the weaker grains. A grain to grain fabric develops that enables this stresspartitioning. The stress partitioning and the resulting fabric can invalidate staticmeasurements of elastic moduli. However, high temperature flow mechanisms reveal a moreisotropic strength behaviour resulting in a more uniform variation of stress withorientation.

Combined shock-wave synthesis of noble spinel and laves cubic phase

The paper described the shock-wave synthesis of high-pressure high-temperature mineral MgAl2O4 with the parameter a = 8.085(3) A and the Laves phase MgCu2 with a = 7.076(2) A from a mixture of MgO and aluminum powder placed into a copper insert inside a steel conservation ampoule. Spinel MgAl2O4 with a smaller lattice parameter a = 8.0798 A has been formed in an aluminum insert cup.

Preparation of carbon-coated Sn powders and their loading onto graphite flakes for lithium ion secondary battery

Carbon-coated Sn powders were prepared from the powder mixtures of thermoplastic precursor PVA, SnO 2 and MgO. The characterization of composite powders synthesized was carried out by XRD, TG, TEM, SEM and anodic performance measurement. SnO 2 was reduced to metallic Sn by heating with PVA, and its particle size in carbon shell was around 30–100 nm. MgO existence hindered the agglomeration of molten metallic Sn and made the dispersion of metallic Sn as fine particles possible. They showed high anodic performance in lithium ion batteries; high charge capacity as 500 mAh g −1 even after tenth cycle and stable cyclic performance. The spaces left in carbon shell by MgO after its dissolution were supposed to absorb a large volume expansion of Sn metal particle by Li alloying during discharging. When carbon-coated Sn loaded onto graphite flakes, metallic tin contributed to the increase in capacity.

New binary systems Mg– M–O ( M=Y, La, Ce): Synthesis and physico-chemical characterization

New binary oxide Mg– M–O ( M=Y, La, Ce) systems are obtained by co-precipitation and characterized by adsorption methods, X-ray diffraction method (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy of adsorbed probe molecules (CO and CDCl 3). It is shown that Mg–Y–O systems after calcination at 450–750 °C represent the physical mixtures of MgO and Y 2O 3, while the components of Mg–La(Ce)–O systems interact to form La 2MgO x and (Ce,Mg)O 2 solid solutions, respectively. From XPS data, the surface of the binary systems is enriched with lanthanide ions. Addition of ≈5 mol% M 2O 3 to MgO results in an increase in concentrations of strong and weak Lewis acidic sites, the content of the latter being much higher and changing in the series: MgO<Mg–Ce–O<Mg–La–O<Mg–Y–O. At the same time basic sites become stronger in the binary systems but their total content decreases in comparison to that in individual MgO. Mg– M–O samples containing ≈5 mol% M 2O 3 are highly-dispersed and characterized by bimodal porous texture.

Structure, Texture, and Acid-Base Properties of Alkaline Earth Oxides, Rare Earth Oxides, and Binary Oxide Systems

The effect of synthesis conditions on the formation of the phase composition, dispersity, pore structure, and acid-base properties of alkaline earth oxides, rare earth oxides, and the Mg-M-O (M = Y, La, or Ce) and Y(La)-M-O (M = Ca, Sr, or Ba) binary systems was studied. It was found that the nature of the system was responsible for the character of phase transformations: the Mg-M-O samples were a mixture of either MgO with Y2O3 or MgO with a solid solution based on rare earth oxides (LaMg)2O3 or (CeMg)O2); the Y(La)-M-O samples (M = Ca, Sr, or Ba) contained the M2Y2O5, MY2O4, and MLa2O4 compounds, which differ in chemical stability, in addition to La2O3 and Y2O3 phases. According to XPS data, the M/Mg atomic ratios were much higher than the bulk values; this is indicative of an enrichment of the surface of samples in the second component. An increase in the concentration of M2O3 from 5 to 25 mol % resulted in a decrease in the S sp of the Mg-M-O samples from 220 ± 10 to 110 ± 10 m2/g; the S sp of samples calcined at 750°C was lower by a factor of ∼1.5–2. The S sp of the Y(La)-M-O samples was higher than the S sp of individual La2O3 and Y2O3. The samples were characterized by a biporous texture. The concentrations and strength distributions of surface OH groups, Lewis acid sites, and Lewis base sites depend on the nature and concentration of rare earth elements in the binary samples. The activity of the Mg-M-O samples in the oxidative dehydrogenation reaction of propionitrile correlated with the acid-base surface sites. Among the Ru/Y(La)-M-O catalysts for ammonia synthesis, Ru/Y-Ba-O was the most active; this catalyst provided a higher yield of NH3 at 250–300°C, as compared with catalysts prepared with the use of other supports (Sibunit, KVU-1, and C/MgO).

Characterization of in situ mechanically worked PVD Mg–Ti alloys

Mg–Ti alloys with up to 46 wt% Ti in solid solution were produced by physical vapour deposition (PVD) with in situ mechanical working. All the alloys exhibited compositional inhomogeneity, columnar microstructures and typical PVD defects. The thermal stability of the solid solutions decreased with increasing Ti content, with the most stable solid solution breaking up above 566 K. The in situ mechanical working reduced porosity by closing pores and flattened surface asperities. The oxide film on the surface of the Mg–8 wt% Ti alloy was Ti-free. The air formed oxide film on the alloys with a Ti content above 8 wt% was identiffied as a mixture of MgO and TiO2 covered by Mg(OH)2 and hydromagnesite at the outermost surface. Magnesium oxide and titanium oxide were also formed at the columnar boundaries that were not affected by the in situ mechanical working. The oxide chemistry was studied using Auger parameter analysis.

Combustion synthesis of TiB2 ceramics powder from B2O3−TiO2−Mg system in air atmosphere

TiB2 ceramics powder was synthesized from B2O3−TiO2−Mg system. The effects of TiB2 addition as diluent on the combustion synthesis process were investigated. The results of thermodynamic calculation and experiments show that the increase of TiB2 content ranging from 0 to 20wt% can reduce the adiabatic temperature Tad from 3100 K to 2896 K and combustion temperature Tc from 2139 K to 1621 K respectively. The particle size and half width of the particle distribution are also increased with the addition of TiB2 increasing from 0 to 20wt%. The combustion product is a mixture of TiB2, MgO, and other intermediate phases. The leached product contains mainly TiB2, TiO2 and TiN, and its oxygen content is 7.77wt%.

Preconcentration of U(VI) from aqueous solutions after sorption using Sorel’s cement in dynamic mode

Mg(OH)2 was identified as a component of Sorel’s cement being a very strong sorbent for uranium. Sorel’s cement is a mixture of MgO, MgCl2 and water. The optimal conditions for the adsorption of U(VI) was studied by the batch method. A contact time of 2 hours was found to be optimum. Maximum U(VI) uptake was observed in a pH range of 5.5-6.5 with a sorption constant of Kads = 0.9 h-1 at initial concentration of 20 ppm. Polypropylene columns filled with 2 g of Sorel’s cement at a mesh size of 35 were used for the preconcentration of uranium by passing 8 l of water containing 10 ppb U(VI). A flow rate of 0.25 ml/min and a bed height of 5 cm were found to be the optimum for the U(VI) separation. A 5 wt% triphenylphosphine oxide solution in toluene was used as an organic solvent for the separation of uranium from interfering elements such as iron(III) and thorium(IV), prior to spectrophotometric analysis. The determination of U(VI) was accomplished by adding Arsenazo III as a coloring reagent to the solution and using a UV-160A spectrophotometer.

Effective precursor for high yield synthesis of pure BN nanotubes

Large quantities of highly pure BN nanotubes have been synthesized within a wide temperature range through using a mixture of FeO, MgO and boron powder as the precursor. X-ray diffraction pattern indicated highly pure h-BN phase of our sample. The morphology and microstructure were investigated by scanning electron microscopy and transmission electron microscopy. The growth mechanism of BN nanotubes has been clarified to be a catalytic growth.

X-ray characterization and phase transformation kinetics of ball-mill prepared nanocrystalline Mg–Ni-ferrite at elevated temperatures

Nanocrystalline Mg–Ni-ferrite has been synthesized by high-energy ball milling the stoichiometric powder mixture of MgO, NiO and α-Fe 2O 3 and post-annealing the ball-milled powder at 1073 K. A non-stoichiometric and nanocrystalline ferrite phase is noticed to form just after 3 h of milling and the content of it increases with increasing milling time up to 25 h. Post-annealing of 8, 20 and 25 h milled powder at 1073 K for 1 h results in formation of stoichiometric Mg–Ni ferrite phase with range of crystallite size from sub-micron to nanometer. A stoichiometric ferrite phase with sub-micron-sized crystallites, is found to form by sintering the unmilled stoichiometric powder mixture at 1473 K for 3 h. Phase transformation kinetics in ball-milled, post-annealed and sintered samples are characterized by X-ray powder diffraction pattern analysis.

Addition effect of ruthenium on nickel steam reforming catalysts

Several Ni-based catalysts supported on a mixture of MgO, La 2O 3, and Al 2O 3 were prepared. The catalytic performance in the steam reforming of m-cresol was evaluated. In the investigation of the effect of Ru loading added to the Ni-catalyst, it was found that the presence of Ru strongly enhances the catalytic performance of the Ni-based catalyst when increasing Ru loading up to 2 wt%. Effect of Ni loading to the Ru-based catalyst system was also investigated. It was found that the addition of nickel to the Ru-based catalyst up to 15 wt% enhanced significantly the catalytic activity of the catalyst. The lifetime of the Ru–Ni catalysts in the reforming of m-cresol was further tested at 750 °C. In agreement with general observations of the use of Ni monometallic catalyst, deactivation of the catalyst due to the carbon deposition reaction already occurred in the reforming of the oxygenated compound. On the other hand, a reasonable high resistant on the carbon deposition in the reforming of m-cresol was given by the 2 wt% Ru–15 wt% Ni catalyst system. An effort in improving the strength of the catalyst support with this catalyst system was also conducted, and the catalyst showed significant increase in the stability of the reforming of oxygenated aromatic compound.

Enhanced chromium recovery from tanning wastewater

A large volume of tanning wastewater was generated with a Cr 3+ concentration of 3000–6000 mg/L. The prevailing method for Cr 3+ recycle is NaOH precipitation, which is severely limited by the poor sedimentation of the sludge formed. Therefore, bridging cations, Ca 2+ and Mg 2+, and sonication were used to enhance the sedimentation of the precipitate. Microwave irradiation was employed to improve the re-dissolution of Cr-sludge for reuse. All alkalis effectively removed Cr 3+ from the aqueous phase with a removal of higher than 99% and a recovery of ∼60%. The substitution of NaOH with CaO or MgO resulted in much less sludge and shorter sedimentation time. MgO also enhanced the purity and dewatering capability of the sludge. The best alkali was a mixture of CaO and MgO (4:1, by weight) to balance the cost and performance. COD and SS were removed in the process via sweeping by the precipitate with removal percentages of 47.6% and 86.3%, respectively. Two minutes sonication at 0.12 W/cm 3 greatly accelerated the sludge sedimentation, cutting the settling time from 3 h to 1 h. Sonication did not alter the particle size or purity of the sludge. Microwave irradiation of 5 min increased the Cr recovery ratio from 60% to 80%.

Preparation of ZrB2 and HfB2 by Metallothermic Reduction of ZrO2, ZrSiO4, and HfO2

ZrB2 and HfB2 were prepared by metallothermic reduction (MTR) of ZrO2, ZrSiO4, and HfO2 with Mg or Mg and MgO mixtures. We understood that the theory of function-building fine particle preparation was able to be applied to synthesize nano-atomized fine particles of ZrB2. ZrB2 can also be obtained directly from mixture of ZrSiO4, B2O3, and Mg by MTR method. This sample has no borides such as silicon boride except for ZrB2. Therefore, this result shows the possibility to obtain ZrB2 easily from natural source. In addition, HfB2 can also be synthesized by MTR method using HfO2 which was calcined over 750°C.

A new technique for angle-dispersive powder diffraction using an energy-dispersive setup and synchrotron radiation

A new diffraction technique for combined angle- and energy-dispersive structural analysis and refinement (CAESAR), by collecting angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation, is introduced. By step scanning a well calibrated SSD over a limited 2θ range, a series of one-dimensional energy-dispersive data (intensityversusenergy) are obtained as a function of 2θ. The entire intensity (Int) data set consists of several thousand channels covering a range of photon energies,E(up to ∼150 keV), at each of the ∼1000 2θ steps, forming a 2–4 mega-element two-dimensional array, Int(E, 2θ). These intensity data are then regrouped according to photon energies, which are defined in the multichannel SSD as individual channels, yielding a large number of intensityversus2θ (angle-dispersive) data sets, Int(E= const., 2θ), each of which corresponds to a given photon energy or wavelength. The entire data set, selected subsets or composite scans can be used for multiple data set Rietveld refinement. Data collected both on α-Al2O3(a NIST diffraction standard) at ambient conditions and on a mixture of MgO and Au at high pressure were analyzed using the Rietveld technique, with varying schemes of data treatment. Furthermore, it is demonstrated that data within certain energy bands (ΔE/E= ±10%) may be binned together to improve counting statistics in a composite angle-dispersive scan, even when collected with much coarser scan steps of 0.1 or 0.2°. This technique is useful for high-pressure as well as general purpose powder diffraction studies that have limited X-ray access to the sample using synchrotron radiation. Several advantages are discussed.

Characterisation of corrosion products formed on PVD in situ mechanically worked Mg–Ti alloys

Mg–Ti alloys with up to 46 wt.% Ti in solid solution, produced by PVD processing with in situ mechanical working, were subjected to immersion tests in 3 wt.% NaCl solutions. The corrosion resistance of the alloys, assessed with gravimetric tests, was inferior to that of PVD pure Mg. Corrosive attack was favoured at the sites of mechanical working owing to the different microstructure and the higher Mg concentration at these areas. The corrosive attack resulted in exfoliation of the alloys. The corrosion product contained a mixture of MgO, TiO 2 and some Mg(OH) 2 at the outermost surface. Although Ti participation in the corrosion products was enhanced, its beneficial affect was overshadowed by the defective nature of the deposits. The surface chemistry of the alloys was studied using the Auger parameter.

Evidence of different structures in magnesium silicate liquids: coordination changes in forsterite- to enstatite-composition glasses

Combined neutron and X-ray diffraction data show changes in the structure of magnesium silicate glasses, ranging in composition from enstatite (MgSiO 3) to forsterite (Mg 2SiO 4). The most abrupt change occurs in the narrow compositional range 38% SiO 2 to 33% SiO 2 (Mg 2SiO 4). These structural changes reflect a change from a glass characterized by corner shared SiO 4 tetrahedra and an approximately equal mixture of MgO 4 and MgO 5 polyhedra, to one in which the average coordination of magnesium by oxygen is increased from 4.5±0.1 to 5.0±0.1. Both these local environments are very different from that of their crystalline counterparts. Reverse Monte Carlo (RMC) simulation fits to the experimental neutron, and X-ray diffraction data have been performed to extract the partial radial distribution functions for the enstatite and forsterite glasses. The structural changes are interpreted as a change in the underlying configurational landscape and are considered to be a manifestation of similar structural changes in the stable liquid. These configurational changes are associated with a discontinuous change in the rheological properties of these glass-forming liquids close to the forsterite composition and suggest differences in the transport properties of magnesium silicate liquids at high pressure. Preliminary data on compressed magnesium silicate glasses indicates that higher coordinate Mg–O is expected to be more stable with increasing pressure.

Catalytic and non-catalytic growth of amorphous silica nanowires and their photoluminescence properties

A simple method based on the thermal oxidation of Si wafers in presence of a mixture of MgO and graphite powder was developed for large-scale synthesis of very long amorphous silica nanowires. The synthesis was done with and without gold as the catalyst. Almost aligned uniform nanowires with diameters within 60–90 nm and length up to few hundred micrometers were obtained using gold as the catalyst while bicycle chain like nanowires were obtained in absence of the catalyst. The growth sequence of the nanowires was observed through scanning electron microscope. Both forms of the nanowires emitted blue lights at 414 nm (3 eV) under excitation at 250 nm.

Mechanochemical Synthesis of Magnesium Aluminate Spinel Powder at Room Temperature

MgAl2O4 spinel was successfully synthesized using a mechanochemical route that avoided the formation and calcination of its precursors at high temperatures. The method involved a single step in which γ‐Al2O3–MgO, AlO(OH)–MgO, and α‐Al2O3–MgO mixtures were milled at room temperature under air atmosphere. The formation of MgAl2O4 occurred faster with γ‐Al2O3 than with AlO(OH) or α‐Al2O3. After 140 h, the mechanochemical treatment of the γ‐Al2O3–MgO mixture yielded 99% of MgAl2O4.

Thermochemical stability of spinel (MgO·Al 2O 3) under strong reducing conditions

The thermochemical stability of the main refractory oxides and some of their compounds under strong reducing conditions has become increasingly important in recent years. In the present work, the formation, sintering and stability of magnesium–alumina spinel (MgAl 2O 4) under very low oxygen partial pressure were studied using Ellingham diagrams. Reduction processes of spinel at high temperatures 1500–1650 °C were discussed. The experimental treatments were carried out with spinel and equimolar mixtures of MgO and Al 2O 3. The effect of the oxygen partial pressure on stability of spinel was evaluated using different atmospheres: air ( P O 2 = 0.21 atm), CO/CO 2 (80/20), P O 2 < 10 −10 atm), CO ( P O 2 < 10 −15 atm) and C–CO ( P O 2 < 10 −20 atm). Finally, the results were compared with the experimental observations of spinel formation in MgO–C refractories with the addition of aluminium.

Effect of TiO&lt;sub&gt;2&lt;/sub&gt; Additions on the Densification of MgO and MgO-CaO Mixtures

Ti-doped MgO fine powders and MgO-CaO powder mixtures were sintered at temperatures up to 1600°C. TiO 2 was added in the concentration range 0.1 to 2 w%. The promoting effect of TiO 2 is confirmed in all samples having a poor sinterability, i.e. samples with large grain sizes or samples heated at 1.5 w% CaO. The densification of MgO and MgO-CaO mixtures is related to a solid state process wherein cation or anion vacancies diffusion can either be ratedetermining as a function of the sintering stage.