Presence Of MgO Research Articles

Low core loss and high DC bias performance of FeSiAl soft magnetic composites cores with hybrid insulating layers of MgO/SiO2

Soft magnetic composites (SMCs) play an indispensable role in electromagnetic conversion, transmission, and storage. However, in order to achieve miniaturization, energy conservation, and meet the application requirements of premagnetisation in direct-current (DC) components, SMCs are required to have low core loss and high DC bias performance. In this work, FeSiAl SMCs with hybrid insulating layers of MgO/SiO2 have been successfully prepared by the decomposition of magnesium acetate tetrahydrate and silicone resin. The presence of MgO and SiO2 insulating layers can effectively compensate for each other's coating defects, thereby forming complete insulating layers on the surface of FeSiAl powders to reduce the core loss. Finally, the FeSiAl@MgO/SiO2 SMC gets remarkable comprehensive magnetic properties with a low core loss (Pcv) of 163.7 mW/cm3 at 50 mT/100 kHz, a high DC bias performance of 53.7 % at 100 Oe, and an effective permeability (μe) of 46, which is promising for high-frequency and high-power applications.

HIGHLY EFFICIENT ONION PEEL ASH CATALYST FOR DEGRADATION OF METHYLENE BLUE

Methylene blue is a dye commonly used by the textile industry. However, its presence in textile effluent poses significant risks to human health and water resources. Various environmental technologies have been developed to remove this refractory pollutant from contaminated effluent. However, those techniques have limitations, such as high operational costs and use of unsustainable resources. In this study, the efficacy of an ash catalyst derived from household waste, namely onion peel waste, for degrading methylene blue was evaluated. Inductively coupled plasma-optical emission spectroscopy analysis revealed the presence of magnesium oxide, MgO, (528.00 ± 40.00 ppb) as one of the primary elements in onion peel ash, crucial for methylene blue degradation. Additionally, Fourier-transform infrared spectroscopy analysis identified an absorption band at around 871 cm-1, indicating the presence of MgO in the onion peel ash. The findings revealed that onion peel ash degraded methylene blue with an 84% (0.00616 min−1) degradation rate under sunlight and a 95% (0.00578 min−1) degradation rate under UV-lamp exposure. This research suggests that onion peel ash holds promise for effectively degrading methylene blue in textile effluents, offering a sustainable solution for addressing environmental concerns associated with textile dye pollution.

Production of renewable fuels by the photocatalytic reduction of CO2 using magnesium doped natural ilmenite

The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h−1 gcat−1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h−1 gcat−1.

Steam reforming of butanol-ethanol mixture for H2 production over Ru catalysts

The present work investigates the steam reforming of butanol – ethanol mixtures for H2 production over Ru-based catalysts. Α 5 wt% Ru/Al2O3 and a 5 wt% Ru/MgO-Al2O3 catalysts were synthesized via the wet impregnation method and physicochemically characterized with various techniques. Catalytic activity tests were carried out using a ButOH/EtOH/H2O mixture between 550 and 700 °C. The ButOH and EtOH conversion as well as H2 selectivity were found to be equal to ca. 100 % for all tested catalysts at 700 °C. The superior performance of Ru/Al2O3 compared to its Ru/MgO-Al2O3 counterpart was mainly attributed to the higher Ru metal dispersion achieved in the former case. The presence of MgO appears to suppress the H2 selectivity in favor of hydrocarbon reaction intermediates production. The higher activity and H2 selectivity of the Ru/Al2O3 is accompanied by remarkable stability after 45 h of exposure to the reaction mixture at 700 °C. Our work suggests that Ru-based catalysts may outperform Pt-based ones in technically challenging steam reforming processes involving alcohol mixtures toward H2 production.

Partial Oxidation of Bio-methane over Nickel Supported on MgO–ZrO2 Solid Solutions

Syngas can be produced from biomethane via Partial Oxidation of Methane (POM), being an attractive route since it is ecofriendly and sustainable. In this work, catalysts of Ni supported on MgO–ZrO2 solid solutions, prepared by a one-step polymerization method, were characterized by HRTEM/EDX, XRD, XPS, H2-TPR, and in situ XRD. All catalysts, including Ni/ZrO2 and Ni/MgO as reference, were tested for POM (CH4:O2 molar ratio 2, 750 ºC, 1 atm). NiO/MgO/ZrO2 contained two solid-solutions, MgO–ZrO2 and NiO-MgO, as revealed by XRD and XPS. Ni (30 wt%) supported on MgO–ZrO2 solid solution exhibited high methane conversion and hydrogen selectivity. However, depending on the MgO amount (0, 4, 20, 40, 100 molar percent) major differences in NiO reducibility, growth of Ni0 crystallite size during H2 reduction and POM, and in carbon deposition rates were observed. Interestingly, catalysts with lower MgO content achieved the highest CH4 conversion (~ 95%), high selectivity to H2 (1.7) and CO (0.8), and low carbon deposition rates (0.024 g carbon.gcat−1 h−1) with Ni4MgZr (4 mol% MgO) turning out to be the best catalyst. In situ XRD during POM indicated metallic Ni nanoparticles (average crystallite size of 31 nm), supported by MgO–ZrO2 solid solution, with small amounts of NiO–MgO being present as well. The presence of MgO also influenced the morphology of the carbon deposits, leading to filaments instead of amorphous carbon. A combustion-reforming mechanism is suggested and using a MgO–ZrO2 solid solution support strongly improves catalytic performance, which is attributed to effective O2, CO2 and H2O activation at the Ni/MgO–ZrO2 interface.

Microstructure and properties of Sn58Bi/Ni solder joint modified by Mg particles

In this paper, various mass fractions (0, 0.1, 0.2, 0.4, 0.6, 0.8 wt%) of Mg particles were added to the Sn58Bi solder to achieve the purpose of modification, through which the Ni substrate was connected successfully through bonding at 250 °C for 2 min. Meanwhile, the microstructure, interfacial IMC, and properties of the joint were focused on. The experimental results indicated that the appropriate addition of Mg particles is able to decrease the melting point of the solder quite slightly and significantly improve the wettability of the solder on the Ni substrate. When the content of Mg is less than 0.4 wt%, the presence of MgO on the surface does not affect the normal use of solder. Likewise, Mg particles are capable of refining the microstructure of the solder and reducing the thickness of the interfacial Ni3Sn4 IMC layer and the grain size. Accordingly, the mechanical property of the joint is markedly enhanced by 53.48%, whose fracture is mainly characterized by brittle fracture, and the Mg2Sn phase plays the central role of strengthening. In a word, it is the Sn58Bi-0.4Mg/Ni solder joint that processes the best combination performance.

Improving remineralization and manganese-removal of soft waters using a mixed CaCO3/MgO contactor

The aim of this study was to investigate the role of MgO on the long-term operation of a mixed media contactor. Specifically, the simultaneous removal of aqueous manganese and the remineralization of soft waters using pure calcite are limited by a remineralization breakthrough after 600 h of operation in the presence of high Mn concentrations (5 mg Mn/L). The introduction of as little as 5 % (m/m) MgO was able to improve the Mn removal kinetic, while maintaining remineralization objectives over 720 h of operation. After treating elevated concentrations of Mn, both media exhibited a Mn-coated layer which contributed to limiting the mass transfer from the media core to the liquid phase. X-ray photoelectron spectroscopy (XPS) identified this superficial layer as 10 % Mn oxides (MnOx) on MgO media compared to 1.4 % MnOx on calcite, suggesting the MgO acts as the preferred reaction surface during Mn removal. Therefore, it is postulated that in the presence of MgO, Mn removal is impacted by high pH conditions (pH = 10.5) which introduces a significant precipitation mechanism as Mn2+ is oxidized. For all the examined conditions, the formation of this coating improved Mn removal due to the autocatalytic nature of the adsorption/oxidation of dissolved manganese by MnOx. MgO is therefore thought to contribute to a complex sorption-coprecipitation process in the operation of a mixed media contactor.

Effect of MgO on electrochemical properties of silicon-based anode composite material

A silicon (Si)/magnesia (MgO)/graphite composite (denoted as SMG@C) was synthesized by high-energy ball milling (HEBM) via the reduction of silica (SiO) by magnesium (Mg) and subsequent addition of graphite, followed by pitch pyrolysis for carbon coating. The particles of MgO in the SMG@C were removed by hydrogen chloride (HCl) leaching to form the Si/graphite composite (denoted as SG@C). The microstructural characteristics of the two composite materials were analyzed by X-ray diffraction and transmission electron microscopy and their electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and capacity cycling tests. Results indicated that the a homogeneous mixture of nanoscale Si and MgO was fabricated by HEBM, and some of the Si and MgO formed a specific crystallographically coherent interface which was determined as Si(220)//MgO(200). The values of Warburg coefficient for SMG@C and SG@C were determined to be 1.84 Ω/S1/2 and 203.42 Ω/S1/2, respectively. When the SMG@C anode composite material was cycled for 440 cycles at a current density of 200 mA/g, its reversible capacity retention rate was 87.8%, showing excellent long-cycle performance compared to the SG@C. The presence of MgO in the anode composite material greatly improved the electrochemical properties.

Insights into the influence of oxide inclusions on corrosion performance of additive manufactured magnesium alloys

The corrosion performance of binder jet additive samples is compared with cast samples through potentiodynamic polarization in Na2SO4 solution. Higher zinc levels in the magnesium matrix and the presence of MgO within the microstructure of the binder jet printed alloy contribute to increases in the anodic and cathodic kinetics, respectively. It is proposed that electron inhomogeneity at the Mg/MgO interface in the binder jet printed alloy is the source of the catalytic activity of the hydrogen evolution reaction. The removal of MgO inclusions suppressed the cathodic reaction relative to the large increase in kinetics seen in similarly treated cast samples.

What are the catalytically active species for aqueous-phase isomerization of D-glucose into D-fructose in the presence of alkaline earth metal (hydr)oxides?

The isomerization of D-glucose into D-fructose presents a key transformation in the concept of cellulose valorization. Herein, we considered the isomerization of D-glucose into D-fructose and the reverse reaction in the presence of MgO, CaO, SrO, and Ba(OH)2 as catalysts. Our results suggest homogeneous catalysis by hydroxide ions OH– released by partial dissolution of the materials. MgO (pKsp 9.8) steadily generates OH– during reaction, whereas more soluble CaO (pKsp 5.3), SrO (pKsp 3.2), and Ba(OH)2 (pKsp 3.6) induce alkalinity directly upon immersion into the reaction solution. Very similar conversion-selectivity plots were obtained during isomerization in presence of the different metal (hydro)oxides indicating the common catalytically active species OH–. The applicability of filtration tests and contact tests to estimate the contributions of homogeneous and heterogeneous catalysis is comprehensively evaluated. For isomerization catalyzed by bases, deceptive results of these tests owing to in situ generation of hydroxide ions can be obtained.

Synthesis and characterization of MgO nanoparticle via microwave and sol-gel methods

This investigation aims to study the characterization of MgO nanoparticles prepared using two different routes via microwave method and sol-gel route. The characteristics of the fabricated of MgO nanoparticles were examined by FESEM, XRD, FTIR and BET. The results of XRD for microwave method and sol-gel route revealed peaks indicating the uniform crystalline. The images of FESEM of MgO nanoparticles by microwave method evinced an irregular shape, but the MgO nanoparticles synthesized by sol-gel route were found crystallites, nano spherical shape. The results of this work manifested that the MgO nanoparticles prepared via sol-gel route had smaller grain size as (≈ 50 nm) compared to the microwave method (≈ 72 nm). The specific surface area of the MgO nanoparticles using sol-gel route was more than with microwave route. FTIR examination reveals that the presence of Mg-O in the sample.

Enhancement of Biodiesel Production from Chicken Fat Using MgO and MgO@Na2O Nanocatalysts

AbstractBiodiesel was produced from chicken fat in the presence of MgO and MgO@Na2O nanocatalysts via transesterification. The characteristics of MgO and MgO@Na2O were examined using various analyses, including BET specific surface areas, energy‐dispersive X‐ray spectroscopy/mapping scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and transmission electron microscopy. The maximum yields of biodiesel production using MgO and MgO@Na2O nano‐catalysts were 95.17 and 95.22 %, respectively, which are significant biodiesel yields. 1H NMR analysis was used to determine the molecular structure of the chicken fat oil and the produced biodiesel. Furthermore, the reusability of the catalysts was examined for up to six steps, showing that both catalysts can be used for up to four steps in biodiesel production.

Photocatalytic hydrogen production using FeTiO3 concentrates modified by high energy ball milling and the presence of Mg precursors

Ilmenite (FeTiO3) concentrates were modified by high energy ball milling (HEBM) at different times (1, 2, and 3 h) and in the presence of MgO or metallic Mg at different contents (0.5, 1.0, and 3.0 wt%), with the aim of obtaining a low-cost and highly available photocatalyst with enhanced performance towards H2 production. FeTiO3 concentrates were obtained from ilmenite-rich black sand by gravimetric concentration followed by wet electromagnetic and dry magnetic separation. HEBM was performed to insert Mg into FeTiO3 structure and to simultaneously reduce the particle size. The insertion of Mg intended to shift the conduction band of the materials to more negative potentials, in spite of the band-gap widening. XRD patterns of the milled samples showed a decrease in the intensity of ilmenite peaks without any displacement, indicating slight amorphization without significant changes in the crystalline structure. However, the increase in the intensity of hematite peaks suggests substitutional doping according to the proposed solid-state reactions. Although thermodynamic analyses showed that doping with metallic Mg should be more favorable, doping with MgO appears to be kinetically favored due to the physical characteristics of the precursor, as it was revealed by XRD, XPS, Raman spectroscopy, SEM–EDS, and UV–Vis DRS results. Deconvolution of high-resolution XPS spectra corresponding to Mg1s exhibited the presence of an additional component peak for the sample milled with metallic Mg, in comparison to that with MgO. This result evidenced the formation of a new phase, suggesting that part of the metallic Mg was not inserted into FeTiO3, as it was confirmed by Raman spectroscopy. UV–Vis DRS analyses showed an increase in the band-gap of the samples milled in the presence of Mg precursors (from 2.51 to 2.55–2.59 eV) which were attributed to slight modifications of the conduction band due to the insertion of Mg. The performance towards hydrogen production under UV irradiation was improved from 240.5 µmol g−1 h−1 (unmilled sample) to 255.3 µmol g−1 h−1 (2 h milled in the absence of Mg precursor), 296.0 µmol g−1 h−1 (2 h milled with 1.0 wt% MgO), and 265.2 µmol g−1 h−1 (2 h milled with 1.0 wt% metallic Mg). This improvement was attributed mainly to the insertion of Mg, and the consequent modification of the band structure, rather than the modification in the surface area.

Microstructure and properties of fly ash/cement-based pastes activated with MgO and CaO under hydrothermal conditions

Lime-activated fly ash cementitious materials are widely used as masonry cement and autoclaved building materials. This study investigated the effects of MgO on the microstructure and properties of the fly ash/cement-based pastes under hydrothermal conditions. The activator (i.e., CaO + MgO) was fixed at 17 wt%, and CaO was replaced with MgO at 0–30 wt%. The properties assessed were compressive strength, linear expansion, fluidity, porosity and pore size distribution. The microstructure was investigated by means of XRD, TG-DSC and SEM. Experimental results show that the compressive strength depended on the autoclave temperature, time and MgO content. Overall, as the MgO/(MgO + CaO) ratio was less than about 20, 15 and 12% at 140, 180 and 210 °C, respectively, MgO contributed to improve the compressive strength. In addition, appropriately extending the autoclave time or raising the autoclave temperature was in favor of strength development. The lower MgO content had a little influence on the expansion, but once the MgO/(MgO + CaO) ratio exceeded 20%, the expansion remarkably increased. Microstructural analyses demonstrated that MgO promoted the formation and crystallization of tobermorite likely through a solid phase or liquid-solid reaction mechanism. Besides, the micro-morphology of tobermorite tended to be slender in the presence of MgO.

Microstructural evolution of Mg-Al-Re alloy reinforced with alumina fibers

Abstract Few studies were reported on the phases’ relationships of AE44 (Mg-4.0Al-4.1RE-0.3Mn, wt.%) and its composites. In this work, AE44 alloy and Saffil (δ-Al2O3)/AE44 Metal matrix composite (MMC) were both prepared by slow shot high pressure die casting (SS-HPDC) technology and their phase constitutions were all studied in detail using experimental techniques combined with CALPHAD (Calculation of Phase Diagram) modeling. The results revealed that the alloy consists of the α-Mg matrix, Al11RE3 intermetallic phase, and one trace phase Al3RE, while the composite contains five major phases: α-Mg, δ-Al2O3, Al3RE, MgO and Mg2Si, and two trace phases of Al2RE and Al11RE3, respectively. Al11RE3 is partly derived from Al2RE, while Al3RE is a product of the peritectoid reaction between the two precipitates. The presence of MgO and Mg2Si is due to the interfacial reaction between the SiO2 binder in the fiber preforms and the molten magnesium during infiltration. The use of SiO2 binder in the preform manufacturing was limited/minimized to reduce the MgO formation in the MMC casting process, which can be detrimental to the fatigue performance of the MMC materials.

Synergistic decarbonization and desulfurization of blast furnace gas via a novel magnesium-molybdenum looping process

In this work, a novel system for synergistic decarbonization and desulfurization of blast furnace gas (BFG) was proposed via a magnesium-molybdenum looping process (MMLP): MgO ↔ MgCO3 and MoO3 ↔ MoS2. The system is comprised of a desulfurization/decarbonization reactor (DDR) and a carbon–sulfur carrier regeneration reactor (CRR). The simulation was conducted for feasibility verification and parameter optimization with applied ASPEN Plus software. Four carbon–sulfur carriers, MgO-MoO3, MgO-Fe2O3, MgO-MnO2, and MgO-SnO2, were preliminary investigated for screening. Results indicate that MgO-MoO3 performs superior capability of synergistic decarbonization and desulfurization. Both water–gas shift and COS/CS2 hydrolysis can be promoted in the presence of MgO via the CO2 absorption and the sorption-enhanced organic sulfur hydrolysis. The effects of MgO/C and 2MoO3/S mole ratios, temperature, pressure, O2 flow rate, and H2O flow rate were intensively discussed. Excessive temperature (>240 °C) in DDR leads to a decrease in carbon removal efficiency. A suitable amount of H2O is beneficial for CO2 capture, organic sulfur hydrolysis, and water gas shift reaction while excessive H2O decreases the organic sulfur hydrolysis efficiency and increases the system energy consumption. Carbon removal efficiency (CRE) of 99.70%, sulfur removal efficiency (SRE) of 100.00%, and H2 yield at 0.276 kmol/h (BFG flow rate = 1 kmol/h) can be obtained under the typical conditions of MgO/C = 2MoO3/S = 1.1, temperature = 240 °C, pressure = 1 atm and H2O/(CO + COS + CS2) = 1.2, providing theoretical guidance for the synergistic removal of sulfides and COx of BFG.

Hydrogen production via steam reforming of coke oven gas enhanced by steel slag-derived CaO

Steel slag, a waste from steelmaking plant, has been proven to be good candidate resources for low-cost calcium-based CO2 sorbent derivation. In this work, a cheap and sintering-resistance CaO-based sorbent (CaO (SS)) was prepared from low cost waste steel slag and was applied to enhance catalytic steam reforming of coke oven gas for production of high-purity hydrogen. This steel slag-derived CaO possessed a high and stable CO2 capture capacity of about 0.48 g CO2/g sorbent after 35 adsorption/desorption cycles, which was mainly ascribed to the mesoporous structure and the presence of MgO and Fe2O3. Product gas containing 95.8 vol% H2 and 1.4 vol% CO, with a CH4 conversion of 91.3% was achieved at 600 °C by steam reforming of COG enhanced by CaO (SS). Although high temperature was beneficial for methane conversion, CH4 conversion was remarkably increased at lower operation temperatures with the promotion effects from CaO (SS), and CO selectivity has been also greatly decreased. Reducing WHSV could increase methane conversion and reduce CO selectivity due to longer reactants residence time. Reducing C/A could increase methane conversion and hydrogen recovery factor, and also decrease CO selectivity. When being mixed with catalyst during SE-SRCOG, CaO (SS) with a uniform size distribution favored methane conversion due to the high utilization efficiency of catalyst. Promising stability of CaO (SS) in cyclic reforming/calcination tests was evidenced with a hydrogen recovery factor >2.1 and CH4 conversion of 82.5% at 600 °C after 10 cycles using CaO (SS) as sorbent.

Reverse leaching of magnesium from ferronickel slag using alkali solvent NaOH

A research based on magnesium extraction of ferronickel slag waste processed by reverse leaching using sodium hydroxide (NaOH) solutions has been carried out. The ferronickel slag has the main compositions of magnesium silicate and iron silicate. The early procedure of the research was the preparation of ferronickel slag grinding using a ball mill until it gets a size of –200 mesh. Secondly, the calcination of ferronickel slags to remove crystal water and increase the size of the porosity so that it would facilitate the leaching process. The next procedure was reverse leaching using sodium hydroxide (NaOH) to dissolve silica. By dissolving the silica, it was expected that the contents of elements such as magnesium and iron would increase in the residue. The variations in this ferronickel slag leaching research were leaching time, solvent concentration and leaching temperature. The reverse leaching of ferronickel slag was carried out with a time variation of 15 to 240 minutes, the temperature of 30 °C, 70 °C, and 100 °C and NaOH concentrations are 9 M, 10 M, and 11 M. The XRD (X-ray diffraction) analysis, (XRF X-ray fluorescence) analysis, SEM (Scanning Electron Microscope) analysis, and ICP-OES (Inductively Coupled Plasma) analysis were used to observe the initial characteristics of the ferronickel slag and the results after the leaching process. The characterization result towards ferronickel slag samples by XRD analysis shows that the compositions of the dominant compounds are forsterite (Mg 2 SiO 4 ), enstatite (MgSiO 3 ) and fayalite (Fe 2 SiO 4 ). Moreover, the result is also supported by XRF analysis and SEM mapping analysis. The quantitative analysis of XRF shows that ferronickel slag contains 45.69 % of SiO 2 , 29.32 % of MgO and 16.5 % of Fe 2 O 3 . The results of the SEM mapping analysis show that Mg, Si, Fe and O bond together that indicates the presence of magnesium silicate and iron silicate. The highest percentage of magnesium extraction is 73.10 % under experimental temperature conditions of 100 °C for 240 minutes, 10 M of solvent concentration and 300 rpm of stirring speed. Increasing percentage of magnesium extraction is caused by the dissolution of silica in the leaching process. The dissolution of silica is proved by the existence of magnesium hydroxide and iron(II) hydroxide in the residue that is shown by the XRD analysis. It resulted in the MgO content in the residue increase significantly to 42.8 % as shown by the XRF analysis. Moreover, the SEM mapping analysis shows that Mg and O bond together that indicated the presence of MgO. It also can be determined that MgO is dominant

Sensitivity of the properties and performance of Co catalyst to the nature of support for CO2 reforming of CH4

The structural phases, spinel inversion degree, metal reduction, and performance of Al-Ox and Mg-Al-Ox supported monometallic Co and Ni catalysts, prepared by co-precipitation method, were studied for dry reforming reaction. Catalysts were characterized using ICP-MS, N2-physisorption, XRD, 27Al NMR, CO2-TPD, Ni/Co K-edge XANES and TPO. Incorporation of MgO increased the pore size, while BET surface area was decreased. XRD showed a single spinel phase of NiAl2O4 and CoAl2O4, and the introduction of MgO created an additional phase (MgO-solid) and increased the degree of spinel inversion in both supported Ni and Co monometallic catalysts. These changes promoted better metal dispersion, increased basicity and easy reduction of the active metal. Increased performance was also noticed in the Mg-Al-Ox supported catalysts, with higher resistance to carbon deposition due to the above-mentioned properties related to the structural changes in the catalyst system with the presence of MgO. Slightly better performance was observed for the Co-Mg-Al-Ox catalyst compared to Ni-Mg-Al-Ox catalyst, due to its stronger basicity per site owing to better interaction between Co and MgO.

Formation of Mo5Si3/Mo3Si-MgAl2O4 Composites via Self-Propagating High-Temperature Synthesis.

In situ formation of intermetallic/ceramic composites composed of molybdenum silicides (Mo5Si3 and Mo3Si) and magnesium aluminate spinel (MgAl2O4) was conducted by combustion synthesis with reducing stages in the mode of self-propagating high-temperature synthesis (SHS). The SHS process combined intermetallic combustion between Mo and Si with metallothermic reduction of MoO3 by Al in the presence of MgO. Experimental evidence showed that combustion velocity and temperature decreased with increasing molar content of Mo5Si3 and Mo3Si, and therefore, the flammability limit determined for the reaction at Mo5Si3 or Mo3Si/MgAl2O4 = 2.0. Based upon combustion wave kinetics, the activation energies, Ea = 68.8 and 63.8 kJ/mol, were deduced for the solid-state SHS reactions producing Mo5Si3– and Mo3Si–MgAl2O4 composites, respectively. Phase conversion was almost complete after combustion, with the exception of trivial unreacted Mo existing in both composites and a minor amount of Mo3Si in the Mo5Si3–MgAl2O4 composite. Both composites display a dense morphology formed by connecting MgAl2O4 crystals, within which micro-sized molybdenum silicide grains were embedded. For equimolar Mo5Si3– and Mo3Si–MgAl2O4 composites, the hardness and fracture toughness are 14.6 GPa and 6.28 MPa m1/2, and 13.9 GPa and 5.98 MPa m1/2, respectively.