Mixture Of MgO Research Articles

Effect of inclusions on microstructure and toughness of deposited metals of self-shielded flux cored wires

The effect of inclusions on the microstructure and toughness of the deposited metals of self-shielded flux cored wires was investigated by optical microscopy, electron microscopy and mechanical testing. The deposited metals of three different wires showed different levels of low temperature impact toughness at −40°C mainly because of differences in the properties of inclusions. The inclusions formed in the deposited metals as a result of deoxidation caused by the addition of extra Al–Mg alloy and ferromanganese to the flux. The inclusions, spherical in shape, were mixtures of Al2O3 and MgO. Inclusions predominantly Al2O3 and 0.3–0.8μm in diameter were effective for nucleation of acicular ferrite. However, inclusions predominantly MgO were promoted by increasing Mg in the flux and were more effective than Al2O3 inclusions of the same size. These findings suggest that the control of inclusions can be an effective way to improve the impact toughness of the deposited metal.

Growth Behavior of Initial Product Layer Formed on Mg Alloy Surface Induced by Polyaniline

The quality of the interfacial protective layer induced by polyaniline (PANI) has been claimed to play a crucial role for the enhanced corrosion protection of Mg alloy, but its growth behavior is not well understood. Here some composition, structure and growth kinetics of the protective layer formed at the PANI-emeraldine base (EB) coating/AZ91D Mg alloy interface were investigated to explore the growth mechanism. Upon immersion in 0.5 M NaCl solution, the growing interface layer under EB coating exhibited a fast passivation rate and an increased corrosion resistance, which was largely influenced by ion concentration. XPS depth profiles showed that the EB-induced layer was a mixture of MgO and Mg(OH)2, in which no significant bi-layer structure existed and MgO was dominant throughout the bulk film. These observations suggest that the interaction between EB and Mg can promote the faster growth of a stable MgO-rich layer mixed with Mg(OH)2 probably by solid reaction. Meanwhile less hydration of MgO and dissolution-precipitation reaction occur, thus leading to less Mg(OH)2 in the outer layer.

ChemInform Abstract: Reinvestigation and Characterization of the Magnesium Borate Fluoride Mg5(BO3)F.

AbstractThe title compound is prepared by a two‐step process starting with heating a mixture of MgO, H3BO3, and Na2CO3 (Pt crucible, 1.

ChemInform Abstract: Synthesis, Crystal Structure, and Characterization of a Congruent Melting Compound Magnesium Strontium Diborate MgSrB2O5.

AbstractThe title compound is prepared by solid state reaction of a stoichiometric mixture of MgO, Sr(NO3)2, and H3BO3 (Pt crucible, 1.

Effect of mechanical alloying on the phase evolution, microstructure and bio-corrosion properties of a Mg/HA/TiO2/MgO nanocomposite

In this study, a magnesium-matrix nanocomposite comprising bioactive ceramics of Mg-substituted hydroxyapatite (HA), farringtonite (Mg3(PO4)2), perovskite (CaTiO3), geikielite (MgTiO3) and brucite (Mg(OH)2) was synthesised through mechanical alloying and annealing of a Mg–HA–TiO2–MgO mixture by mechanically induced self-propagating reactions. The phase evolution and microstructure were analysed using X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The results indicated that after 16h of milling, the powder mixture exhibited a homogenous distribution of fine agglomerates composed of spherical particles with an average size of 83nm. The crystallinity and thermal stability of the HA phase decreased with increasing milling time because of the substitution of Mg atoms in the HA structure. The mean crystallite size of the product phases was approximately 75nm after 8h of mechanical alloying, and these values increased slightly to 82 and 88nm after 1h of annealing at 500 and 630°C, respectively. The bio-corrosion properties of the nanocomposites were investigated using electrochemical tests and immersion tests after different milling times and subsequent annealing. The electrochemical tests revealed that the corrosion potential (Ecorr) of the as-blended samples shifted towards a nobler direction from −1565 to −1457mVSCE by increasing the amount of HA from 12.5wt% to 25wt%. After 16h of milling, the corrosion resistance of the milled samples comprising 12.5wt% and 25wt% HA increased to 4.63 and 4.97kΩcm2, respectively. The milled samples annealed at 630°C exhibited lower corrosion rates compared with those annealed at 500°C. The present study suggests that the high-energy ball milling of the Mg–HA–TiO2–MgO mixture accompanied with post annealing is a promising option for controlling the rapid corrosion rate.

Hybrid Electrolyte Membranes Based on Sulfonated Poly (arylene ether sulfone ketone) Multiblock Copolymer for PEMFC Operating at Elevated Temperatue under Low Humidity

Polymer electrolyte membrane fuel cells (PEMFCs) operated under low relative humidity (RH) have been received great attention due to simplifying thermal management and reducing the cost of the system. However, the state-of-the-art electrolyte membrane (Nafion), has several problems, such as high production cost, environmental incompatibility, and insufficient thermomechanical properties above 80 oC.[1] To overcome these problems, aromatic hydrocarbon polymers are considered promising alternatives, such as sulfonated poly arylene ether sulfone ketone (SPESK) multiblock membranes have been reported.[2]Nevertheless, SPESK membrane exhibits poor performance under low relative humidity (RH).We have developed high proton conducting membranes based on modifying non-fluorinated aromatic ionomers using hygroscopic metal oxide and inorganic proton conductors. We have synthesized novel composite membrane using porous hygroscopic titanium dioxide nanotubes (TNTs) incorporated SPESK membrane. TNTs with average diameter of 90 nm were incorporated into SPESK solution so as to provide the proton migration pathway in SPESK membrane. Compared to pristine SPESK, SPESK-TNT delivered 2.4 times higher maximum power density at 80 oC under 30 % RH. The higher PEMFC performance under low RH was due to the hygroscopic property of TiO2which can retain water and due to the tubular morphology which facilitates the proton transport channel through membrane.We also fabricated inorganic proton cluster modified graphene oxide SPESK composite membrane. The deposition of phosphotungstic acid (PW) on the modified graphene oxide sheet with positively charged functional group was carried out through an electrostatic interaction between PW and the modified graphene sheets to make heterogeneous system. The modified graphene oxide (mGO) was synthesized through a simple condensation reaction. A mixture of mGO and PW aqueous dispersion was stirred to fabricate PW-mGO. The physico-chemical characterization of inorganic cluster and the modified graphene oxide was confirmed by UV-visible, IR and cyclic voltammetry studies and these results revealed that that an alteration of the electronic structure of deposited cluster as a result of strong hybridization between the graphene oxide and PW [3].These SPESK composite membranes exhibited much higher proton conductivity at relatively low humidity than the pristine SPESK, and the composite membrane showed higher maximum power density PEMFC operated under 18 % RH than that of pristine membrane. The synthesis of composite aromatic membranes, conductivity and fuel cell performance at elevated temperature under low relative humidity will be discussed in this presentation.

Impacts of Mg and Al Substitution on Na2/3Ni1/3Mn2/3O2 As Positive Electrode Materials for Na-Ion Batteries

IntroductionRecently, layered Na x MeO2 (Me = metal element(s), x = ~1) compounds have been extensively explored as positive electrode materials for Na-ion batteries. From a viewpoint of materials abundance, Na-ion batteries are promising candidates as next generation energy storage devices. Average operating potential of Na x MeO2 is usually lower than that of Li x MeO2, resulting in lower energy density in Na-ion cells even though P2-type layered materials are considered to be potential candidates for high capacity positive electrode materials. Among the P2-type layered materials, Na2/3[Ni1/3Mn2/3]O2 performs at a relatively high operating voltage and delivers specific capacity of 150 mAh g−1 in the voltage range of 2.0–4.5 V in Na cells without compensation of initially deficient sodium in the structure.1 However, the reversible capacity of Na2/3[Ni1/3Mn2/3]O2 electrode is known to rapidly fade during cycles in the wide voltage range, probably due to a drastic lattice shrinkage of the fully charged state and electrolyte decomposition. In this study, we significantly improve the capacity retention of Na2/3Ni1/3Mn2/3O2 electrode by partial substitution of Mg and Al for the transition metals.ExperimentalNa2/3[Ni1/3 − x Mn2/3 − y Me x +y ]O2 (x = y = 1/36 for Me = Al, and x = 1/18, y = 0 for Me = Mg) was prepared by the calcination of stoichiometric mixtures of Mn2O3, Ni(OH)2, Na2CO3, Al(OH)3, and MgO with 5% excess sodium.2 The mixtures were pelletized and heated at 900 °C for 24 h in air and then quenched to room temperature. Crystal structures and morphology of the samples were examined by using powder X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM). Electrochemical properties were tested using a coin-type cell. Positive electrodes consisted of the active material, acetylene black, and polyvinylidenefluoride (PVdF) with a gravimetric ratio of 80:10:10. Metallic sodium was used as a counter electrode. The electrolyte used was 1.0 mol dm-3 NaPF6 / PC.Results and discussionIn XRD patterns of synthesized samples, all diffraction lines can be assigned into the P2-type layered structure with space group P63/mmc without any crystalline impurities. Hexagonal platelet morphology for all the samples is found from SEM images. These particles have a diameter from 2 to 4 μm. Single phase P2-type layered samples modified with the Mg and Al substitution with similar particle morphology were successfully synthesized. The cycle stability of the sample electrodes operated at room temperature is shown in Fig. 1. The Mg and Al substitution effectively improves capacity retention. The substituted sample electrodes exhibit excellent cycle capability for 20 cycles. The capacity retention of the Al and Mg substituted samples is approximately 94 and 92%, respectively, after 20 cycles. Moreover, the Mg and Al substitution enhances rate capability. Although, at 2 C rate (about 260 mA g-1), Na2/3[Ni1/3Mn2/3]O2 delivers only 37% specific capacity of that at C / 20, the Al and Mg substituted samples show 78 and 77% of specific capacity of that at C / 20 rate. Influence of the Al and Mg substitution on electrochemical properties and structural changes induced by sodium extraction will be further discussed.

Size-Controlled Pd Nanoparticles in 2-Butyne-1,4-diol Hydrogenation: Support Effect and Kinetics Study

Structured catalyst has been developed for C–C triple bond three-phase hydrogenation. The sintered metal fiber (SMF) coated by different oxides served as support for monodispersed Pd nanoparticles (6.4 ± 0.5 nm). The effect of acid–base properties and reducibility of metal oxide coating on catalytic performance in the liquid phase (T = 303–348 K; P = 1–20 bar) hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol (B2) has been studied. The oxides MgO, ZnO, Ga2O3, Al2O3, ZrO2, SnO2, and SiO2 and the mixtures of MgO + ZnO + Al2O3, MgO + Al2O3, and ZnO + Al2O3 were tested. The catalyst activity was higher up to 10-fold for Pd0 on acidic supports, like SiO2, but demonstrated lower selectivity to B2 as compared to the basic oxides. The highest yield (∼99%) of the target B2 and stability over four consecutive runs were attained over the 0.2% Pd0/ZnO/SMF catalyst. The high selectivity to B2 was attributed to the formation of an active phase containing intermetallic PdZn alloy as confirmed by XPS. The reaction ...

Simultaneously rapid synthesis and consolidation of nanostructured Mg0.3Al1.4Ti1.3O5 by high-frequency induction heating

A one-step synthesis and consolidation of nanostructured Mg0.3Al1.4Ti1.3O5 was achieved by high-frequency induction heating, using the stoichometric mixture of MgO, Al2O3 and TiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10 h. From the milled powder mixture, a highly dense nanostructured Mg0.3Al1.4Ti1.3O5 compound could be obtained within one minute, under the simultaneous application of 80 MPa pressure and an induced current. The advantage of this process is that it allows an instant densification to the near theoretical density, while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg0.3Al1.4Ti1.3O5 compound were evaluated.

Porous Metal Oxide Nanotubes Modified Proton Exchange Membranes for Fuel Cells Operating at Elevated Temperature and Low Humidity

Polymer electrolyte membrane fuel cells (PEMFC) have been widely accepted as one of the most promising power sources for automobile application due to high energy conversion efficiency and environmental compatibility. However, the current PEMFC technology, utilizes perfluorosulfonic acid (PFSA) polymer membranes, e.g., Nafion, as electrolyte, is limited owing to expensive components and poor performance at elevated temperature (100 – 200 °C). PEMFC operated at elevated temperature results in enhancing the performance due to improving electrode kinetic and reduction of adsorption poisoned species such as CO [1]. The deterioration of PEMFC performance at elevated temperature is mainly attributed to the loss of proton conductivity of the Nafion membrane which results in drastic increase in the ohmic over potential [2]. Proton conductivity of Nafion membrane is strongly influenced by the water content and the conductivity is maximum when the membrane is fully hydrated. Operating PEFC at elevated temperature leads to membrane dehydration which dramatically reduces the proton conductivity in order of magnitude. Thus, it is highly desirable to enhance proton conductivity Nafion membrane at elevated temperature in order to achieve high PEFC performance. Porous metal oxides nanotubes (TiO2, ZrO2, and CeO2) with diameter in a range of 30 – 180 nm were synthesized by calcining electrospun metal ions embedded polyacrylonitrile nanofiber, which was prepared using a conventional single spinneret electrospinning technique, at 600 oC under an air atmosphere. Compared to a commercial membrane (Nafion®212) operated at 80, 100, and 110 oC, the Nafion-TiO2 membrane delivered improved power density at 0.6 V. The performance of composite membranes was evaluated by making MEA and subsequently the composite membranes were investigated the H2/O2 fuel cell at 100 oC under 100 %RH and at 80 oC under 18 %RH. Fig. 1B illustrates the polarization and power density plots obtained at 100 oC under 100 %RH. It was found that the power density at 0.6 V obtained from Nafion-TiO2 composite membrane operated at 100 oC was 730 mW/cm2, which is 1.6 times higher than commercial membrane (NRE-212) and recast Nafion membrane. On the other hand, the Nafion-TiO2 composite membrane delivered maximum power density of 640 mW cm-2, which is 3 times higher than that of the performance obtained from NRE-212 and recast Nafion membranes (Fig. 1C). The higher PEMFC performance at 100 oC and low RH was due to the hygroscopic property of TiO2 which can retain water at 100 oC and due to the tubular morphology which facilitates the proton transport channel through membrane. We also fabricated inorganic proton cluster modified graphene oxide Nafion composite membrane. The deposition of phosphotungstic acid (PW) on the modified graphene oxide sheet with positively charged amine was carried out through an electrostatic interaction between PW and the modified graphene sheets to make heterogeneous system. The modified graphene oxide (mGO) was synthesized through a condensation reaction. A mixture of mGO and PW aqueous dispersion was stirred to fabricate PW-mGO. The interaction between inorganic cluster and the modified graphene oxide was confirmed by UV-visible, IR and cyclic voltammetry studies and these results revealed that that an alteration of the electronic structure of deposited cluster as a result of strong hybridization between the graphene oxide and PW [3]. The NRE-212/PW-mGO composite membrane exhibited much higher proton conductivity at relatively low humidity than the Nafion-212 (NRE-212), and the composite membrane showed 4-fold higher maximum power density PEMFC operated under 18 % RH than that of pristine Nafion-212 membrane. The synthesis of composite perfluorosulfonic acid membrane, conductivity and fuel cell performance at elevated temperature under low relative humidity will be discussed in this presentation. References E. Chalkova, M. B. Pague, M. V. Fedkin, D. J. Wesolowski, S. N. Lvov, J. Electrochem. Soc. 2005, 152, A1035.K. A. Mauritz and R. B. Moore, Chem. Rev. 104 (2004) 4535.Y. Kim, and S. Shanmugam, ACS Appl. Mat. Int., (2013) DOI:10.1021/am4043245.

Preparation of γ-AlON Transparent Ceramics by Pressureless Sintering

In this paper, AlON powders were prepared by carbothermal reduction and nitridation method. By adding a mixture of Y2O3, La2O3 and MgO as sintering agent, transparent AlON ceramics with high strength were fabricated by pressureless sintering at 1950°C for 8h under nitrogen atmosphere. The obtained ceramic had a relative density of 99.9% and average grain size of 150μm. The transmittance of the 2mm thick ceramics was 82.4% at 1100nm and flexural strength was 300 MPa.

Silicothermic self-reducing MoO3 briquettes for direct alloying of Mo in molten steel

The use of molybdenum trioxide (MoO3), which is cheap and relatively abundant MoO3 has been evaluated as a potential alternative to expensive FeMo as a steel alloying method. Pure MoO3 volatilises very significantly above its melting point (1068 K) and results in a poor alloy yield when added to steel. The volatilisation of MoO3 in FeSi–MoO3, MoO3–CaO and MoO3–MgO mixtures have been investigated by TG-DTA. Self-reducing experiments of industrial MoO3 mixed with FeSi, CaO and CaF2 have been performed in an electric resistance furnace. The results show that the volatilisation of industrial MoO3 can be effectively inhibited when adding CaO and FeSi and addition of CaF2 helps form a low melting point slag and results in good separation of metal and slag, The Mo quickly dissolves in the molten steel with 95% recovery.

ChemInform Abstract: Effect of Local Structure Distortion on Superconductivity in Mg‐ and F‐Codoped LaOBiS2.

AbstractPolycrystalline samples of La1‐xMgxO1‐2xF2xBiS2 (x = 0.1—0.35) are prepared by solid state reactions of stoichiometric mixtures of La2O3, La2S3, Bi2S3, BiF3, MgF2, LaF3, MgO, S, and Bi (evacuated quartz tube, 1073 K, 10 h).

Advantages of combined sintering compared to conventional sintering of mechanically activated magnesium titanate

In this article, the advantages of combined sintering in comparison with the conventional one, of mechanically activated magnesium titanate ceramic were investigated. The stoichiometric mixtures of MgO and TiO2 were mechano-chemically activated for 0, 10, 40, 80 and 160 minutes by ball milling and then isostatically pressed (CIP) to form green bodies. Conventional sintering was realized by heating up to 1400 oC and hold for 30 minutes in air atmosphere. Resulting ceramic samples with closed porosity were post-sintered by pressure assisted technique Hot Isostatic Pressing (HIP) at 1280 oC/3h in argon atmosphere with a pressure of 200 MPa. The best results were observed in the case of samples post-sintered by HIP, when single-phase MgTiO3 samples with relative density of 96% were prepared.

Products of hydratation in fine grained mixtures MgO – SiO2

The aim of this study was to evaluate the influence of time of ageing on phase evolution of paste from MgO-SiO2-H2O phase system. The paste was composed of fine grained sintered magnesia and microsilica in 1:2 molar ratio and water, with water to solid ratio equal 0,5. After preparation the paste was ageing during specified time up to 180 days in temperature 20° C. Phase composition of mixture of MgO and SiO2 with water was studied by XRD, DTA-TGA. The analysis revealed that product of reaction in mixture of MgO, SiO2 and water was a probably poorly crystalline magnesium silicate.

Microwave synthesis and sintering of Mg4Nb2O9 nanoceramics

Mg4Nb2O9 nanopowders were prepared from MgO and Nb2O5 mixtures by using a high energy ball milling method, combined with subsequent annealing at low temperatures by microwave heating. After milling for 20 h, pure phase Mg4Nb2O9 nanopowders with an average grain size of 127 nm were obtained at 850, 130 °C lower than that required by a conventional solid state reaction process. Mg4Nb2O9 ceramics sintered at a low temperature of 1,300 °C using microwave heating showed almost full density and excellent microwave dielectric properties (er = 12.9, Q × f = 174,200 GHz and τf = −68).

Preparation of MgO/B2O3 coatings by plasma spraying on SUS304 surface and effects of heat-resistant

This study mainly deals with the preparation of MgO/B2O3 coatings by plasma spraying on the SUS304 surface and the effects of heat-resistant. The power materials of low thermal conductivity were selected to control the heat divergent performance of high temperature parts. The reticular micro-structure between the cover thermal layer and the substrate was prepared by using the plasma spraying method. The powder mixture of MgO and B2O3 were selected as spraying materials and the SUS304 was used as the substrate material. The MgO/B2O3 coating was prepared on the surface of the SUS304 to provide better cover thermal performance. The properties of the microstructures and the morphologies were studied by Optical Microscope, Scanning Electron Microscope, Electron Probe Microanalyzer, and X-ray Diffraction. The results showed that the cover thermal performance has been improved.

산업부산물을 첨가한 MgO 기반 모르타르의 기초물성 및 수화특성에 관한 연구

Hydration and physical characteristics of chemically-bonded phosphate ceramic (CBPC) binder based on dead-burned Mg-O with six different blends are investigated for efficient repair construction material by retarding set phase with H3BO3. The test specimen of the blender with silica fume shows higher compressive strength after 75 days. The CBPC with silica fume results in higher modulus of rupture that others. The test specimens of CBPC eludes lower calcium ion than that of OPC (Ordinay Portland Cement). The X-ray diffraction pattern shows that hydration results in the formation of magnesium hydroxide, M-S-H gel and MgCO3 for the specimen with silica fumes. Combination with calcium for MgO is not desirable due to no formation of chemical bond between two components. Based on the experimental program, the mixture of MgO and silica fume shows efficient performance in strength and durability.

Simultaneous synthesis and rapid consolidation of a nanocrystalline Mg0.6Al0.8Ti1.6O5 by high-frequency induction heating and its mechanical properties

A single-step synthesis and consolidation of nanostructured Mg0.6Al0.8Ti1.6O5 was achieved by high-frequency induction heating using the stoichometric mixture of MgO, Al2O3 and TiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10h. From the milled powder mixture, a highly dense nanostructured Mg0.6Al0.8Ti1.6O5 compound could be obtained within one minute under the simultaneous application of 80MPa pressure and an induced current. The advantage of this process is that it allows an instant densification to the near theoretical density while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg0.6Al0.8Ti1.6O5 were evaluated.

ChemInform Abstract: Synthesis, Characterization, and Chemical Vapor Transport of Solid Solutions in the MgMoO4—NiMoO4 System.

AbstractPowder samples of solid solutions in the MgMoO4—NiMoO4 system are prepared from stoichiometric mixtures of MgO, MoO3, and NiO (quartz crucible, 1173 K, 60 h).