MgO Crystallites Research Articles

Fabrication of low conductivity and high strength MgO-MgAl2O4 aggregates with sub-micron pore structure

Lightweight MgO-MgAl2O4 refractory aggregates were fabricated by using fine MgO and spherical Al(OH)3 powders as starting materials. The evolutions of microstructure and pores and their effects on the properties of the specimens were investigated. During heating process, MgO crystallites diffused into the formed Al2O3 pseudomorph, producing sub-micron intra-particle pores in both MgAl2O4 cores and MgO matrix. Besides, larger inter-particle pores between the MgAl2O4 cores and MgO matrix were occurred, attributing to the Kirkendall effect resulting from in-situ spinalization. As MgO content increased from 50 wt% to 80 wt%, due to reduction of the number of the porous MgAl2O4 cores, the inter-particle pores caused by Kirkendall effect decreased sharply in both number and size, while no obvious changes occurred in the intra-particle pores as the porous MgO matrix amount increased simultaneously. The decrease of large inter-particle pores caused obvious improvement in strength but slight increase in thermal conductivity. With a further increase of MgO to 90 wt%, as the number of the porous MgAl2O4 cores reduced further and the MgO matrix densification improved obviously, intra-particle pores and thermal insulation performance reduced significantly. The specimen with 80 wt% MgO showed the best performance, with a median pore diameter of 0.26 μm, apparent porosity of 36.0 %, flexural strength of 23.9 MPa, and thermal conductivity of 2.1 W/(m·K) at 500 °C.

Influence of on-off pulsed current pattern on processes during spark plasma sintering of MgB2 superconductor

High density samples (92–94.5 %) of MgB2 were prepared by Spark Plasma Sintering (SPS). The on-off pulsed current patterns of SPS processing were 8–4, 12–2, 24–2, 99–1. Patterns with more on pulses favor formation of a higher amount of the secondary MgB4 phase through the decomposition of MgB2. They also promote enhancement of larger MgO crystallites without a strong increase in the amount of this phase. Densification rate and pressure in the SPS chamber show a similar behavior, but their amplitude varies and the temperatures defining different stages present some shifts. As-revealed differences induced by pulsed patterns impact superconducting properties in a complex manner. An attempt to assess correlations between the pattern and different superconducting parameters is presented.

Deciphering the structural dynamics in molten salt-promoted MgO-based CO2 sorbents and their role in the CO2 uptake.

The development of effective CO2 sorbents is vital to achieving net-zero CO2 emission targets. MgO promoted with molten salts is an emerging class of CO2 sorbents. However, the structural features that govern their performance remain elusive. Using in situ time-resolved powder x-ray diffraction, we follow the structural dynamics of a model NaNO3-promoted, MgO-based CO2 sorbent. During the first few cycles of CO2 capture and release, the sorbent deactivates owing to an increase in the sizes of the MgO crystallites, reducing in turn the abundance of available nucleation points, i.e., MgO surface defects, for MgCO3 growth. After the third cycle, the sorbent shows a continuous reactivation, which is linked to the in situ formation of Na2Mg(CO3)2 crystallites that act effectively as seeds for MgCO3 nucleation and growth. Na2Mg(CO3)2 forms due to the partial decomposition of NaNO3 during regeneration at T ≥ 450°C followed by carbonation in CO2.

Tuning material properties of amorphous zinc oxynitride thin films by magnesium addition

The amorphous n-type multi-cation and multi-anion compound zinc magnesium oxynitride was fabricated by reactive long-throw magnetron co-sputtering from a metallic zinc and a metallic magnesium target. We achieved magnesium cation compositions in the thin films between 1 at. % and 7.5 at. % by varying the magnesium target power (variable-power approach) and compared this approach to a continuous composition spread. Both approaches lead to a reduction in Zn2+, an addition of Mg2+ cations, and a correlated increase in the oxygen content. Both these methods have the same effect on the optoelectrical properties: The increased magnesium content leads to a systematic decrease in the free charge carrier concentration regime from 1019 cm−3 to 1015 cm−3, a decrease in Hall mobility from 54 cm2 V−1 s−1 to 9 cm2 V−1 s−1, and a spectral shift of the absorption edge from 1.3 eV to 1.7 eV. The amorphous phase of zinc magnesium oxynitride is maintained until MgO crystallites form at a magnesium content ≥3 at. %. The electrical properties of the zinc magnesium oxynitride thin films show excellent long-term stability for at least 12 months.

Formation Mechanism of In Situ Intergranular CaZrO3 Phases in Sintered Magnesia Refractories

Sintered magnesia refractories combined by in situ intergranular CaZrO3 phases were synthesized using natural MgO-containing natural minerals with CaO and SiO2 impurities and nano-sized ZrO2 additive. A homogenous distribution of intergranular CaZrO3, independent from the intergranular CaO-MgO-SiO2 phases, was formed in situ within the sintered magnesia aggregates by introducing 0.75 wt pct nano-sized ZrO2 into the magnesite. The formation mechanism of the in situ intergranular CaZrO3 phases was determined. The nano-sized ZrO2 was introduced and uniformly distributed at grain boundaries of the magnesia due to the micron-nano-sized particles composite system and wetting grinding process. Then the CaO in impurities were prior to SiO2 to react with the ZrO2 for generating CaZrO3 at the grain boundaries by increasing sintering temperature. Nevertheless, the nano-sized ZrO2 particles were encapsulated in the MgO crystallites with similar particle size decomposed from brucite and prevented from reacting with CaO impurities in magnesite. The mixing homogeneity of magnesite particles and ZrO2 particles and the direct contact between ZrO2 and CaO impurities in magnesite has a crucial effect on the formation of intergranular CaZrO3 phases. Furthermore, the intergranular CaZrO3 phases could enhance the bonding of magnesia grains and have great potential for improving the service performance of magnesia.

Microstructure, optical and photocatalytic properties of MgO nanoparticles

The present work is focused on the synthesize of MgO nanoparticles using combustion method. The magnesium nitrate is used as a precursor with urea as a fuel. The precursor material is dissolved in 50 ml DI water along with the fuel and the solution is heated at 80 °C for 2 h. Then, the solution is transferred to crucible and kept it in the temperature of 500 °C. The as-synthesized MgO nanopowders are analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), photoluminescence (PL) and photocatalytic studies. The XRD results of MgO nanoparticles indicated the cubic structure with the crystallite size of 27 nm. The FESEM studies indicated the formation of MgO crystallites in spherical shape. In addition, MgO nanoparticles are porous and agglomerated. PL spectrum of MgO materials exhibit emission peaks, which indicates the occurrence of band to band transition with the bandgap of 2.9 eV. The photocatalytic degradation of methylene blue dye is evaluated using the as-prepared MgO nanoparticles under UV light. The photocatalytic studies indicate the 75% degradation efficiency of the catalyst after 120 min irradiation. Hence, the MgO Nanoparticles (NPs) can be used for the treatment of effluents from the dye industries.

Physical properties of the organic polymeric blend (PVA/PAM) modified with MgO nanofillers

Magnesium oxide/polyvinyl alcohol/polyacrylamide (MgO/PVA/PAM) nanocomposite films were prepared via a solution chemical method. The effect of PVA and MgO nanoparticles (NPs) loading on the physical properties of PAM is discussed. X-ray diffraction reveals that the average MgO crystallite size of the NPs is ∼25 nm, while adding PVA increases the crystallinity of PAM. FTIR spectra confirm the interaction between blend chains and MgO NPs. Differential scanning calorimetry thermograms illustrate the miscibility between the PVA and the PAM. The melting temperature, the glass transition, as well as the equilibrium swelling ratio, depend on the films' composition. PAM showed a transmittance of 87%, that increased to 90% after PVA addition, but decreased to 74% after MgO loading. Meaningful changes are observed in the extinction coefficient and indirect/direct band gap of PAM due to PVA blending and MgO addition. The influence of MgO NPs on the dielectric constant ( ɛ′) of the blend film is reported. The maximum value of AC conductivity of the blend is 4.77 × 10−3 Sm−1, which increased to 8.07 × 10−3 Sm−1 by increasing the MgO loading to 5.0 wt.%. The conduction mechanism changed from the correlated barrier hopping, in the blend, to the large Polaron tunneling with MgO loading. The observed improvements in optical properties and AC conductivity encourage the use of these nanocomposite films in the semiconductors industry.

Microstructural evolution of a forged 2XXX series aluminum powder metallurgy alloy

The microstructural response to hot upset forging was studied for a commercially relevant 2000-series aluminum powder metallurgy alloy. Sufficiently large specimens were produced such that the tensile property development was recorded for true compressive forging strains 0 mm/mm to 1.55 mm/mm. Full theoretical density values were obtained and up to a four-fold improvement in tensile ductility was observed. The tensile strength of a sintered-T6 component was measured at 357 MPa, while forging to 1.40 mm/mm increased that to 418 MPa. Microstructural reinforcement was found to be predominantly S-phase precipitates. Prior particle boundaries (PPB) of an unforged specimen were found to be continuously decorated with MgO and Mg2Sn crystallites. Such boundaries in hot forged specimen were discretized into clusters, producing regions of PPB devoid of oxides or other secondary phases. Improvements to mechanical properties were largely attributed to this effect.

Green synthesis and characterization of hexagonal shaped MgO nanoparticles using insulin plant (Costus pictus D. Don) leave extract and its antimicrobial as well as anticancer activity

Green synthesis is an ecofriendly novel technology and attractive research area for the production of metal oxide nanoparticles in bio-medical and chemical applications. The green perspective includes solvents, reductants or stabilizing agents obtained from a natural resource as they are non-toxic and ecofriendly. In this study, a sustainable green synthetic strategy to synthesize magnesium oxide nanoparticles by employing Costus pictus D. Don plant leaf extract as a reducing agent. The successful formation of magnesium oxide nanoparticles was confirmed by comprehensive characterization techniques. The presence of biomolecules and metal oxides were confirmed by Fourier transform Infrared (FT-IR) spectral data analysis. The X-ray diffraction (XRD) revealed the formation of pure cubic MgO crystalline nanoparticles. The surface morphology of MgO particles observed by Scanning electron microscope (SEM) showed the hexagonal-shaped MgO crystallites. The average size of biosynthesized MgO nanoparticles was measured to be around 50 nm by Transmission Electron Microscopy (TEM). The mechanism for the formation of MgO nanoparticles was suggested in this study. The biosynthesized magnesium oxide particles showed good antimicrobial and exhibited maximum inhibition rate for MgO nanoparticles at 200 µg showing efficient anticancer activity.

Magnesiothermic reduction of silica glass substrate—Chemical states of silicon in the generated layers

We applied magnesiothermic reduction to silica glass substrates at various conditions including solid state or solid-Mg liquid reaction, and solid-Mg vapor reaction. Magnesium silicide with highly oriented to the 〈110〉 direction against the substrate surface was obtained in the solid state reaction at temperatures from 600 °C to 700 °C using Mg grains while Si crystallites were obtained in the reaction with Mg film deposited on the glass substrate at 560 °C. On the other hand, in the reduction with Mg vapor at 575 °C, brown and amorphous layer was formed on the surface of the silica glass substrate. The layer was transparent in the visible and near-infrared regions, and showed an interference pattern in the transmission spectra, indicating the homogeneity of the layer. The thickness and refractive index were estimated as 770 nm and 1.94, respectively. As the reaction with Mg vapor proceeded further, Mg2Si and MgO crystallites were formed. Oxidation states and their depth profiles of silicon atoms in the layers were investigated by X-ray photoelectron spectroscopy. The silicon atoms in the brown and amorphous layer existed in intermediate oxidation states, −2 and +3. The reaction proceeding, the formal charge of the silicon atoms varied to −4 corresponding to Mg2Si and +2.

Synthetic Architecture of MgO/C Nanocomposite from Hierarchical-Structured Coordination Polymer toward Enhanced CO2 Capture.

Highly efficient, durable, and earth-abundant solid sorbents are of paramount importance for practical carbon capture, storage, and utilization. Here, we report a novel and facile two-step strategy to synthesize a group of hierarchically structured porous MgO/C nanocomposites using flowerlike Mg-containing coordination polymer as a precursor. The new nanocomposites exhibit superb CO2 capture performance with sorption capacity up to 30.9 wt % (at 27 °C, 1 bar CO2), fast sorption kinetics, and long cycling life. Importantly, the achieved capacity is >14 times higher than that of commercial MgO, and favorably exceeds the highest value recorded to date for MgO-based sorbents under similar operating conditions. On the basis of the morphological and textural property analysis, together with CO2 sorption mechanism study using CO2-TPD and DRIFT techniques, the outstanding performance in CO2 uptake originates from unique features of this type of sorbent materials, which include hierarchical architecture, porous building blocks of nanosheets, high specific surface area (ca. 300 m2/g), evenly dispersed MgO nanocrystallites (ca. 3 nm) providing abundant active sites, and the in situ generated carbon matrix that acts as a stabilizer to prevent the growth and agglomeration of MgO crystallites. The nanocomposite system developed in this work shows good potential for future low-cost CO2 abatement and utilization.

Lattice Expansion in Metal Oxide Nanoparticles: MgO, Co3O4, & Fe3O4

Uniform sets of mono‐crystalline nanoparticles ranging from 6 nm to over 100 nm were prepared for the MgO, Co3O4, and Fe3O4 oxide systems. The nanoparticles were characterized by transmission electron microscopy (TEM) and x‐ray diffraction (XRD). A careful analysis shows increased lattice parameter for smaller nanoparticles of each oxide system: 0.47% expansion from bulk for 7 nm MgO crystallites, 0.15% expansion from bulk for 9 nm Co3O4 crystallites, and 0.13% expansion from bulk for 6 nm Fe3O4 crystallites. The compressive surface stresses and expansion energies against hydrostatic pressure for each oxide system were calculated, respectively, to be 4.13 N/m and 1.8 meV/formula unit for MgO, 3.09 N/m and 0.87 meV/formula unit for Co3O4, and 1.26 N/m and 0.67 meV/formula unit for Fe3O4. The fundamental understanding of oxide nanoparticle mechanics as presented here will facilitate integration of these materials into technological applications in a rationally designed manner.

Cubic-Shaped Al-Doping MgO Powders Used in PDPs

In order to improve the secondary electron emission coefficient of MgO, we propose to dope Al into MgO. The precursor was obtained by hydrothermal method in the condition of different reaction temperature, different filling volume and different reaction time by using urea, Mg (CH3COO)2and AlCl3. The Al-doping MgO crystallites powders were obtained by calcining the precursor. The crystal phase and morphology of the products were characterized by XRD and SEM. The results showed that the Al-doping MgO powders were cubic-shaped crystallites. The discharge characteristics of Al-doping MgO powders were tested in a chamber as when the panel was sealed in Ne and 7% Xe at 450 torr. As expected, the discharge voltage of the panel is lower with the Al-doping MgO protective layer than without that.

Sol–gel synthesis and optical behavior of Mg–Ce–O nano-crystallites

The Mg–Ce–O powder are shown to contain periclase-type MgO and/or fluoride-type cerium oxide (CeO2) depending upon the composition (x) defined by Ce/(Ce + Mg) atomic ratio. Lattice contraction of pariclase phase of MgO (average crystallite size ~8.8 nm) at Ce content of ‘x’ = 0.20 in comparison to pure MgO (crystallite size ~9.5 nm) has been realized due to oxygen vacancy formation. The optical band gap values of CeO2 varies (3.0–3.2 eV) due to oxygen vacancy formation in CeO2 phase, crystallite size and/or Ce3+/Ce4+ ratio. Further, the addition of Ce has shown to reduce the physisorption and chemisorption of water significantly as reflected by (1) suppression of related absorption peaks and (2) absence of magnesium hydroxide, Mg(OH)2, bands in Fourier transform infrared spectra.

Effect of calcination temperature and MgO crystallite size on MgO/TiO2 catalyst system for soybean oil transesterification

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 15 min 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 45 min of reaction. The soybean oil conversion during the transesterification reaction increased with the decrease in MgO crystallite size for the first 30 min.

A Facile Microwave-Assisted Solution Combustion Synthesis of Highly Stable Magnesium Oxide for Multicomponent Mannich Reaction

A green and robust solid base MgO has been synthesized by a rapid microwave-assisted solution combustion synthesis method and evaluated for multicomponent Mannich reaction under solvent-free conditions at ambient temperature in the liquid phase. The synthesized catalyst was characterized by various techniques to ascertain its phase composition and thermal stability. Catalyst characterization studies revealed that magnesium oxide synthesized by microwaveassisted solution combustion synthesis method offers stable nanosized MgO crystallites. Good to excellent yields of β-amino carbonyl compounds were achieved with aromatic aldehydes bearing an electron withdrawing group.

Sol-Gel Synthesis of Highly Stable Nano Sized MgO from Magnesium Oxalate Dihydrate

A sol-gel method was used to synthesize a highly stable form of MgO from magnesium oxalate dihydrate. The sol-gel products were characterized using simultaneous thermogravimetric analysis (STA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV-Visible light spectroscopy (UV-Vis). From the XRD analysis, all the MgO samples showed a single face-centered cubic phase. FESEM micrographs showed a crystallite size ranging from 10 nm to 59 nm. The size of the MgO crystallites increased with increasing temperatures. The crystallite size of the MgO is still relatively small, that is, below 100 nm even when the precursor was calcined at a higher temperature of 950 °C and a longer time of 36 h. Such results indicated that the growth of the crystallites is slow for this route of synthesis. The morphologies of the MgO samples are varied from the all spherical of the lower temperature to the more cubic shape with less agglomeration of the higher calcined samples. The band gap energy of the MgO samples also increased with temperature.

Effect of Calcination Temperature and MgO Crystallite Size on MgO/TiO2 Catalyst System for Soybean Transesterification

Effect of Calcination Temperature and MgO Crystallite Size on MgO/TiO2 Catalyst System for Soybean Transesterification

Effect of Li on the catalytic activity of MgO for the synthesis of flavanone

We have investigated the effects of Li on the structure, surface basicity and catalytic activity of MgO for the synthesis of flavanone. Introduction of low amounts of Li (i.e., ≤0.1 wt.%) was found to promote the rate of the Claisen–Schmidt condensation reaction, which is the first step in this process. However, at Li loadings above 0.1 wt.% a detrimental effect was observed, due to a concomitant decrease in surface area and increase in MgO crystallite size. A strong correlation was observed between surface-normalized basicity and catalytic activity. The increase in activity at higher levels of surface basicity can be attributed to the increased ability of Li–O − pairs to abstract a proton from the 2′-hydroxyacetophenone reactant, thus facilitating the adsorption and subsequent surface reactions of this molecule.

Promoting Effect of Ce on the Oxidative Coupling of Methane Catalysts

The promoting effect of ceria was studied on the oxidative coupling of methane reaction with Li/Ce/MgO and Na/Ce/MgO. Catalytic tests were conducted with unpromoted Li/MgO and Na/MgO catalysts and showed that samples doped with ceria affected the OCM reaction. In situ XRD results showed growth of MgO and CeO2 crystallites on the Na/Ce/MgO, decreasing the activity and selectivity. The Li/Ce/MgO catalyst presented small and stable crystallites which increased markedly the activity, selectivity and stability. In addition, Diffusion Reflectance Spectroscopy (DRS) results of calcined samples revealed the charge transfer from cerium to oxygen ions, as well as oxygen transfer into the lattice. Different sites may influence the selectivity in C2 and C2 yield. The Li/Ce/MgO catalyst presented higher methane conversion and C2 selectivity than the Na/Ce/MgO catalyst, probably due to different types of involved active site promoted by ceria during the reaction. The promoting effect of ceria was studied on the oxidative coupling of methane reaction with Li/Ce/MgO and Na/Ce/MgO. Catalytic tests were conducted with unpromoted Li/MgO and Na/MgO catalysts and showed that samples doped with ceria affected the OCM reaction.