MgO Nanopowders Research Articles

Low temperature synthesis of highly pure cordierite materials by spark plasma sintering nano-oxide powders

The development of cordierite ceramics, using traditional materials and conventional methods, remains a key challenge because of the high and narrow sintering temperature range. In this work, single-phase cordierite ceramics were produced by spark plasma sintering nano-oxide powders, at low temperatures. A starting mixture of Al2O3, SiO2, and MgO nano-powders with the composition of stoichiometric cordierite was first sonicated, then, sintered in the temperature range 900–1200 °C. The raw powders, sonicated powder mixture, phase transformations, and fracture surface of sintered specimens were characterized by using an x-ray diffractometer and a field emission scanning electron microscope (FE-SEM). The hardness and fracture toughness were measured using the indentation technique. The influence of testing conditions, process parameters, characterization technique, and calculation method on hardness and fracture toughness was investigated. The FE-SEM images, x-ray maps, and EDS results revealed the homogeneity and stoichiometry of the sonicated powder and sintered samples. Highly pure α-cordierite was formed at 1150 °C. Samples that were sintered at 1150 and 1200 °C had bulk density of 2.58 g/cm3 (relative density of 100%), and maintained low average grain sizes of 28.68 and 34.95 nm, respectively. With the decrease in the temperature from 1200 to 1150 °C, the hardness of cordierite was slightly increased from 8.25 ± 0.158 to 8.46 ± 0.188 GPa, the fracture toughness was marginally improved from 2.2 ± 0.158 to 2.25 ± 0.238 MPa mm1/2, and the critical strain energy release rate was raised from 32.46 to 33.95 J/m2.

MgO nanopowders catalyzed synthesis of pyrano[4,3‐d]thiazolo[3,2‐a]pyrimidine derivatives

A cubic phase of pure MgO nanopowders was prepared in an aqueous solution containing freshly squeezed orange juice with pulp and characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDS), and Fourier transform infrared (FT‐IR) spectroscopic techniques. The catalytic potential of MgO nanopowders was evaluated in preparation of pyrano[4,3‐d]thiazolo[3,2‐a]pyrimidine and chromeno[4,3‐d]thiazolo[3,2‐a]pyrimidines derivatives using the three simple methods including thermal, ultrasonic irradiation, and high‐speed ball milling (HSBM) technique under solvent‐free conditions. All products were successfully formed in high yields.

In Situ Spinel Formation in a Smart Nano-Structured Matrix for No-Cement Refractory Castables.

The hydration of an equimolar mixture of MgO and Al2O3 nano-powders has been proven to be an effective way to synthesize Mg6Al2CO3(OH)16∙4H2O as a component of a nano-structured matrix and magnesia-alumina spinel precursor for high-performance cement-free corundum-spinel refractory castables. (Mg3)–OH–brucite sites (417 °C) formed initially within the magnesia–alumina hydrating blended paste were replaced with (Mg2Al)–OH and (Mg3)–OH hydrotalcite sites, which were dehydroxylated at 420 °C and 322 °C, respectively. This reorganization was connected with the incorporation of anions and water molecules in the interlayer spacing of hydrotalcite, which was dehydrated at 234 °C. Hence, the thermal decomposition of a nano-structured matrix system containing mainly Mg6Al2CO3(OH)16∙4H2O consists of a complex sequence of dehydration, dehydroxylation and decarbonization, and this finally leads to the formation of inverse spinel MgAl2O4 and periclase MgO through many intermediate stages containing the mixed tetrahedral-octahedral Al phase and MgO-like structure. Hence, the hydraulic bond that primarily existed was replaced by a ceramic bond at a relatively low temperature, i.e., 700 °C, where a spinel was formed. Important changes in oxygen coordination polyhedra around Al3+ in the dehydrated-dehydroxylated hydrotalcite occurred between 600 and 1100 °C.

IR-transparent MgO-Y2O3 ceramics by self-propagating high-temperature synthesis and spark plasma sintering

A glycine–nitrate self-propagating high temperature synthesis (SHS) was developed to produce composite Y2O3–MgO nanopowders. Based on the thermodynamic calculations a 0.25YMg2(NO3)7-0.75NH2CH2COOH precursor composition was selected to prepare low agglomerated uniform composite yttria-magnesia powder. Near full dense composite ceramics were fabricated based on the prepared powders by the spark plasma sintering method. IR-transmittance and hardness of the Y2O3–MgO ceramics were studied in correlation with sintering conditions. The best transmittance of 80.9%@5 μm and Hv = 10.2 GPa were measured for the sample obtained at 1150 °C.

Synthesis of highly-infrared transparent Y2O3–MgO nanocomposites by colloidal technique and SPS

Infrared (IR) transparent Y2O3–MgO nanocomposites with a volume ratio of 50:50 were synthesized by combining colloidal and spark-plasma-sintering (SPS) techniques. In order to attain well-dispersed and homogeneous starting Y2O3–MgO nanopowder mixture, the effects of the pH value and the amount of polyetherimide (PEI) dispersant on the suspension stability were studied. Rheological measurement reveals that highly-dispersed and stable suspension was obtained at 7 wt% of PEI dispersant under pH = 10.6. The obtained nanopowders with particle size of 20–30 nm were densified using SPS at several sintering temperatures. The sintered composites show fine grains, narrow grain size distribution and uniform microstructure. The nanocomposite sintered at 1250 °C showed the maximum IR transmittance of 84% at a wavelength range of 2.5–6 μm. The Vickers hardness of the nanocomposite was about 11.9 ± 0.3 GPa, which is significantly higher than those of single phase MgO or Y2O3. Successful fabrication of the high-performance Y2O3–MgO nanocomposite indicates that i) the colloidal technique is an effect method to obtain highly dispersed and homogeneous nanopowders and ii) the SPS technique is a powerful tool to fabricate fine-grained dense transparent ceramics, which are suitable for fabricating IR transparent Y2O3–MgO composite ceramics from commercial starting powders.

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.

Study on a novel antibacterial light-cured resin composite containing nano-MgO

A new type of photocurable resin composite containing nano-MgO was synthesized in order to reduce the occurrence of secondary caries. Different mass ratios (0 %, 1 %, 2 %, 4 %, 8 %) of nano-MgO were added into resin composites. The antibacterial properties of nano-MgO powder and modified resin composites against Streptococcus mutans (S. mutans) were detected by antibacterial ring test and film contact test, respectively. Compressive strength (CS) and wear resistance were determined by a universal testing machine and an abrasion test machine. The results indicated that antibacterial activity and wear resistance of resin composites containing nano-MgO were superior to the control group (p < 0.05). The antibacterial rate reached as high as 99.4 % when the mass ratio of nano-MgO was 8 %. However, the CS values tended to decline as the content of nano-MgO increase. Hence, the addition of nano-MgO showed excellent antibacterial property to resin composites and enhanced wear resistance, but was detrimental to their mechanical properties.

Properties of NaCu3Ti3NbO12 based-ceramics doped with nanopowders

In this work, the properties of NaCu3Ti3NbO12 based ceramics preparing by mixed oxide method were studied. The starting materials including Na2CO3, CuO, TiO2 and Nb2O5 were mixed by ball milling for 24 hours with stoichiometry, calcined at 950 °C for 24 hours and were doped with (0–2.0 vol%) MgO, Al2O3 and ZrO2 nanopowders. Then, the mixed powder was pressed into a disc shape. The green bodies were sintered at 975–1025 °C for 10 hours. Phase formation was investigated by XRD and microstructure by SEM. The body-centered cubic perovskite-related structure of space group Im-3 and small amount of second phase were detected. The normal grain growth is observed and shown rectangular grain shape. Density of the sintered samples was measured by Archimedes’s method using distilled water as the fluid medium. The highest density of NCTNO and NCTNO/Al2O3 ceramics were found at 1025 °C sintered temperature and 1000 °C for NCTNO/MgO and NCTNO/ZrO2 samples. Dielectric constant of the samples was examined using an LCR meter and the mechanical properties of samples were investigated by Vickers microhardness tester. The addition of nanopowders can be improved the mechanical property and 1.0 vol%ZrO2 doping sample showed the highest the dielectric constant.

Influence of sintering temperature on structural and optical properties of Y2O3–MgO composite SPS ceramics

The paper studies infrared-transparent 50:50 vol% Y2O3–MgO fine-grained composite ceramics produced via glycine-nitrate process and spark plasma sintering (SPS). Effect of SPS temperature (T = 1100, 1200, 1250 and 1300 °С) on consolidation processes of Y2O3–MgO nanopowders and on ceramics properties has been investigated. Morphology, structural-phase state, density, Vickers microhardness and infrared transmittance of Y2O3–MgO nanocomposites have been studied. Transmittance has been found to increase with the SPS temperature reaching 71%@6000 nm wavelength at T = 1300 °C. Maximal Vickers hardness of 10.9 GPa has been achieved at T = 1200 °C. The correlation between processing conditions of ceramics and indicated characteristics was investigated.

Aqueous Media Synthesis of Pyrano[3,2-c]chromen Derivatives Using Magnesium Oxide Nanoparticles as a Recyclable Catalyst

Here, the synthesis of MgO nanopowders via a simple precipitation method is defined. The morphology, phase identification, particle size distribution and specific surface area of the sample was investigated by FE-SEM, TEM, XRD, DLS, and BET techniques. The structural parameters were determined through XRD pattern. The sample crystallized in a pure cubic phase with the average crystallite size of 55 nm. The micro-strain (ε) and dislocation density (δ) of the sample were also calculated to be 0.1153 and 3.306 × 10−4, respectively. The catalyst has a specific surface area and of 26.7 m2g−1. The catalytic activity of MgO nanopowders was studied in the three-component condensation of aldehydes, 4-hydroxycoumarin, and malononitrile in aqueous media. A range of aromatic aldehydes undergoes the reaction to produce a series of pyrano[3,2-c]chromen derivatives in good yields.

Water dissociation on the low-coordinated sites of MgO nanopowders

Abstract

Anomalies of the Thermodynamic Parameters of the Heterogeneous Li2CO3–Na2CO3–K2CO3–MgO Nanopowder System

The thermodynamic parameters of the heterogeneous Li2CO3–Na2CO3–K2CO3–MgO nanopowder system are detemined by differential scanning calorimetry (DSC). The melting temperature and the reduced enthalpy of melting of the salt phase are found to decrease anomalously as the magnesium oxide content in the composite material increases.

Microstructure and Mechanical Properties of Fe/MgO Micro-Nano Composite for Electrotechnical Applications

AbstractThe composite based on the microns iron size powder and MgO nanopowder was prepared using pressing followed by conventional and microwave sintering. Microstructure of the composite was investigated to evaluate the changes induced by different sintering technology. Young’s modulus, flexural strength and hardness of composites were analyzed to investigate the mechanical properties in dependence on MgO content, as well as in dependence on the sintering method. Microstructure and mechanical properties as well as functional magnetic properties of prepared composites are discussed in the paper. The main benefit of microwave heating found within process time shortening was confirmed in the case of the microwave sintered Fe/MgO composite.

In situ Raman Spectroscopic Investigation of Solvation in the Disperse System Li2CO3–Na2CO3–K2CO3-melt–MgO-nanopowder

Interparticle interactions in the high-temperature disperse system Li2CO3–Na2CO3–K2CO3-melt–MgO-nanopowder were studied using Raman spectroscopy to provide the in situ information required to optimize the carbonate-fuel-cell operating environment. Addition of MgO nanopowder to the carbonate melt changed the system vibrational spectrum because of solvation of solid particles by salt-melt ions.

Effects of Y2O3 additive percentage on MgO ceramic by Co-Precipitation and SPS methods

MgO nanopowders were synthesized through the co-precipitation method with different Y2O3 percentages (0, 2.5, 5, and 10 wt %). The nanocomposite powder was characterized by thermal gravimetric-differential thermal analysis (TG-DTG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and field-emission scanning electron microscope (FESEM) analysis. Y2O3 can have positive effect on synthesis and sintering of MgOY2O3 ceramic likewise particles size and densification process. Crystallite size decreased with increasing amount of Y2O3 additive, and it was 32.6 nm for MgO-10%, and the average particle size by FESEM image was 52.2 nm for this sample. Lattice parameter increased (from 4.2188 to 4.2243 A0) by increasing the additive percentage from 0 to 5%, but it decreased (4.2195 A0) in 10% additive. Nanopowder was sintered by the SPS technique at 1400°C. MgO-2.5% sample had the highest relative density (99.1%) and transmittance (15%), with an average grain size of 0.41 μm. MgO-5% sample, however, had the highest hardness (10.57 GPa), thanks to the finer average grain size (0.25 μm).

Fabrication of Gd2O3‐MgO nanocomposite optical ceramics with varied crystallographic modifications of Gd2O3 constituent

AbstractThe fabrication of Gd2O3‐MgO nanocomposite optical ceramics via hot‐pressing using sol‐gel derived cubic‐Gd2O3 and MgO nanopowders was investigated. The precursor powder calcined at 600°C had an average particle size of 12 nm. The effects of hot‐pressing temperature on constituent phases, microstructure, mid‐infrared transmittance, and microhardness were studied. The crystallographic modifications of Gd2O3 phase varied with the increase in sintering temperature from 1250 to 1350°C. The monoclinic‐Gd2O3 phase was retained for the composite sintered at 1350°C and the sample had an average grain size of 90 nm, excellent transmission (80.4%‐84.8%) over 3‐6 μm wavelength range, and enhanced hardness value of 14.1 GPa.

Photocatalytic Studies of MgO Nano Powder; Synthesized by Green Mediated Route

MgO nano powders were synthesized by a bio mediated route. The obtained products were characterized by powder X-ray diffraction (PXRD), diffuse reflectance spectroscopy (DRS) Scanning electron microscope (SEM), Transmissionelectron Microscope (TEM) and Fourier transform infrared spectroscopy (FTIR). PXRD patterns show hexagonal single cubic phase MgO matched with JCPDS Card No 78-0430. The crystallite size obtained from TEM was found to be ∼ 15-20 SEM result reveals porous nature of the obtained nano-powder. The optical energy gap is 3.20eV which demonstrates that there is a movement to the higher wavelengths of the absorption edge with reduction of the energy gap when using green fuel for synthesis. The photocatalytic studies relatively high activity for degradation of Malachite Green (MG) and Rhodamine-B (Rh-B) under sunlight irradiation compared to UV light. The good structure and excellent performance of ZnO nano-composites, suggest its promising application in dye decolarization

Spectroscopic, thermal, and electrical properties of MgO/ polyvinyl pyrrolidone/ polyvinyl alcohol nanocomposites

In this study, we aimed to control the optical and electrical properties of polyvinyl alcohol (PVA) in order to broaden its industrial and technological applications, which we achieved by blending PVA with polyvinyl pyrrolidone (PVP) and adding sol–gel prepared MgO nanopowder. The blended film and nanocomposite films were prepared using the solution casting technique. X-ray diffraction analyses showed that the crystallite size was ∼18.4 nm for MgO and the highest degree of crystallinity (XC) in the films was about 24.34% at 1.0 wt% MgO. High resolution transmission electron microscopy determined the nanoribbon morphology of MgO. Scanning electron microscopy (SEM) indicated the uniform distribution of the MgO nanoribbons on the surfaces of the PVA/PVP films. SEM and Fourier transform infrared spectroscopy also confirmed the interaction between the blend and MgO fillers. The effects of the additives on the glass transition (Tg) and melting (Tm) temperatures were evaluated by differential thermal analysis and differential scanning calorimetry. The appearance of one melting point confirmed the miscibility of the two polymers. According to ultraviolet–visible–near infrared spectroscopy measurements, the optical properties and optical constants of PVA could be adjusted by the addition of PVP and MgO, where the optical band gap (Eg) determined for PVA increased with the PVP content, whereas it decreased to 4.8 eV as the MgO content increased. The DC conductivity (σdc) of the films increased whereas the activation energy (Ea) decreased after the addition of MgO, possibly because the nanoribbon shape fixed the preferred conducting pathways. In addition, MgO could break the H-bond in OH groups of the blends to allow the free movement of the molecular chains.

Diverse Nano Dimension of SDS, PEG and CTAB Roofed MgO Nano Powder Synthesized by Co-precipitation Method

The SDS, PEG and CTAB roofed MgO nano powders were synthesized by co-precipitation method. The sintered nano powders was shown Fm-3m space group with cubic phase obtained by the XRD pattern. The lattice strain was calculated to be used Williamson-Hall equations (W-H). The formation of Mg-O bond and hydroxyl radicals on the surface were confirmed by the FTIR analyses. The TEM revealed that the morphology of sintered nano powders has three different dimensions (0D, 1D, 2D) with average crystallites size was about ̴ 20-80 nm and length usually 200-500 nm. The UV-DRS spectra show that the ionic surfactants roofed MgO leads to band gap shrinkage. The evaluated optical band gap energy is Eg= 4.10eV, 3.41eV and 3.12eV for SDS, PEG and CTAB-MgO nano powder respectively. Also extending light absorption towards the visible region due to decrease in crystallite size of surfactants roofed MgO nano powders utilizing for photocatalytic purpose and opto electronic devices.

Exo-Electron Emission From MgO Nanopowders on MgO Thin Film of Alternating Current Plasma Display Panels—Part I. Mechanism of Exo-Electron Emission

Exo-electron emission from MgO nanopowders sprayed on MgO thin film of alternating current plasma display panels was measured experimentally. Effects of several key parameters including panel temperature on the emission currents were measured and compared with a thermostimulated exo-electron emission model with three energy levels proposed in this paper. The results indicate that the exo-electron emission phenomenon is controlled by a thermal excitation of trapped electrons at shallow levels, ~0.2 ~ 0.3 eV below the conduction band edge. The MgO nanopowders increases the emission current significantly over the MgO thin film, possibly due to a higher concentration of recombination centers at deeper energy levels.