MgO Grain Size Research Articles

Formation features of MgO–Y2O3 nanocomposite of complex shape through aqueous slip casting using glycine-nitrate nanopowder

A homogeneous MgO–Y2O3 (50:50 vol%) nanocomposite semispherical green bodies with diameter up to 90 mm and relative green density of 46 % were successfully fabricated by the slip casting using nanopowder, synthesized by the glycine-nitrate method. To advance the rheological properties of MgO–Y2O3 aqueous suspensions, the effect of Dolapix CE64 and NH4PAA as dispersants was examined by viscosity measurements, sedimentation tests. A stable MgO–Y2O3 slurry showing near-Newtonian behavior was prepared with 30 wt% solid loading and 2 wt% of Dolapix CE64. Finally, sinterability of MgO–Y2O3 composite nanopowder was studied by vacuum sintering method for the first time. MgO–Y2O3 nanocomposite of complex shape vacuum-sintered at 1300 °C demonstrate optical transmittance of 45 % at the wavelength of 5.3 μm, and the average grain size of MgO and Y2O3 components of 355 nm and 342 nm, respectively.

Study on the homologous effects on the performance of alkali metal-doping MgO-based adsorbents for CO2 capture

In this article, MgO-based adsorbents with different structure and surface property were prepared by combustion of the colloids containing Mg and alkali metal. At the same time, CO2 adsorption performance tests are conducted to compare the doping effect of alkali metal on MgO adsorbents. As confirmed, the introduction of lithium, sodium, and potassium can reduce the grain size of MgO and enhance the basicity, especially increasing the concentration of oxygen vacancies on MgO surface which exposed more basic adsorption active sites and was more conducive to CO2 adsorption. Among them, the one doped with 0.5 % K which had more electron shell numbers showed larger surface area and smaller crystal size. Most importantly, it provided more number of basic sites along with the improved strength of surface basicity due to the more oxygen vacancies. As a result, the maximum CO2 uptake (1.09 mmol/g) at the adsorption time of 60 min can be obtained which still remained at 0.67 mmol/g after 16 cycles of CO2 adsorption–desorption. With the aid of N2 physical adsorption, inductively coupled plasma-optical emission spectroscopy, powder X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and chemical adsorption, the relationship between CO2 adsorption capacity of MgO-based adsorbent and homologous regularity of alkali metal was disclosed. In other words, by comparing the CO2 adsorption performance of MgO adsorbents prepared by doping different alkali metals, CO2 adsorption capacity increased with the increase of electron shell numbers. Such a configuration is in favor of the electron supply of the p-orbitals and weakens the Mg–O bonds which promoted the formation of oxygen vacancies. The found will provide in-depth understanding for the modification and performance improvement of MgO-based adsorbents.

The Influences of Addition of MgCO<sub>3</sub> on the Properties of the Magnesia Prepared Using Magnesite

Micropowder MgCO3 was added into magnesite as raw materials to prepare magnesia using a two-step calcination method. The sample magnesite was characterized use X-ray diffraction (XRD) and scanning electron microscopy (SEM). Experimental results showed that the sample insulated at 1600° C for 3 hours before and after sintering presented a linear change rate of 15.6 % in the case of without adding micropowder MgCO3, the prepared magnesia had a bulk density of 2.31 g/cm3 and apparent porosity of 32.8 %, while MgO grain size was 3.11 μm. In the case of adding 8 % micropowder MgCO3, the sample magnesite before and after sintering showed a linear change rate of 17.9 %. The bulk density, apparent porosity of prepared magnesia were 2.46 g/cm3 and 28.1 % respectively, while the grain size of MgO was 5.15 mm.

Mesoporous activated carbons synthesized by pyrolysis of waste polyester textiles mixed with Mg-containing compounds and their Cr(VI) adsorption

Magnesium acetate, magnesium oxalate and magnesium oxide were employed to prepare waste polyester textiles-based activated carbons with well-developed mesoporous structures. TG analysis was conducted to explore the pyrolysis process and pore-forming mechanism. N2 adsorption/desorption isotherms, EA, XRD, SEM and FTIR were performed to investigate the influences of different Mg-containing compounds on the physicochemical properties of activated carbons. The results indicated that the samples prepared by two organic magnesium salts exhibited higher specific surface area and porosity than that by magnesium oxide. Diversity in pore structure, morphology and surface groups of the carbons were owing to the differences in grain size of MgO and pyrolysis pathway of Mg-containing compounds. The adsorption isotherm of Cr(VI) for the activated carbons fitted well with Freundlich model, indicating that the adsorption process accorded with the theory of multilayer adsorption. The maximum adsorption capacity of Langmuir model of the sample prepared from magnesium acetate was the highest, and the main adsorption mechanisms were confirmed as electrostatic interaction and reduction reaction.

Study on the Kinetics and Mechanism of Grain Growth during the Thermal Decomposition of Magnesite

The X-ray line broadening technique was used to calculate the grain size of MgO at 1023, 1123, 1223 K respectively either in <TEX>$CO_2$</TEX> or during the thermal decomposition of magnesites in air as well as in vacuum. By referring to the conventional grain growth equation, <TEX>$D^n=kt$</TEX>, the activation energy and pre-exponential factor for the process in air are gained as 125.8 kJ/mol and <TEX>$1.56{\times}10^8\;nm^4/s$</TEX>, respectively. Ranman spectroscopy was employed to study the surface structure of MgO obtained during calcination of magnesite, by which the mechanism of grain growth was analyzed and discussed. It is suggested that a kind of highly reactive MgO is produced during the thermal decomposition of magnesites, which is exactly the reason why the activation energy of the grain growth during the thermal decomposition of magnesite is lower than that of bulk diffusion or surface diffusion.

In situ heat treatment of ultrathin MgO layer for giant magnetoresistance ratio with low resistance area product in CoFeB/MgO/CoFeB magnetic tunnel junctions

In order to promote the grain growth of ultrathin MgO barrier deposited on a CoFeB layer, in situ infrared (IR) heat treatment just after the deposition of MgO barrier was examined. In case that IR heat treatment was not applied, tunneling magnetoresistance (TMR) ratio of CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) was significantly decreased with decreasing resistance area (RA) product to less than 10 Ω μm2. On the other hand, TMR ratio of 206% was achieved at the RA product of 2.1 Ω μm2 when the IR heat treatment was applied. According to the cross sectional transmission electron microscope images for the samples with 0.76-nm-thick (∼4 ML) MgO barrier, the (001) oriented well crystallized structure with smooth interface was observed for the IR heated sample. Moreover, it revealed that the lateral grain size of MgO was significantly enlarged compared to that for the sample without IR heating. The improvement of TMR properties at low RA product region by the heat treatment might be due to the decrease in grain boundaries of MgO layer where the coherent tunneling of Δ1 electrons is not restricted.

Grain-growth kinetics of ferropericlase at high-pressure

Grain-growth kinetics of (Mg 0.85Fe 0.15)O ferropericlase was investigated at pressures of 5 and 10 GPa and temperatures of 1673–1873 K using a Kawai-type multi-anvil apparatus. Presintered ferropericlase aggregate with an average grain size of 4.0 μm was used as starting material of grain-growth annealing experiments. The grain-growth kinetics of ferropericlase is described by G n − G 0 n = k 0 t exp [ − ( E * + P V * ) / R T ] , where G is the average grain size at annealing time t, G 0 the initial average grain size, P the pressure, R the gas constant and T is the absolute temperature, with n = 2.6 ± 0.4, log 10 k 0 = −7.5 ± 1.7 m 2.6/s, E * = 262 ± 30 kJ/mol, V * = 4.7 ± 0.7 cm 3/mol. Compared at same pressure and temperature, grain-growth rate of ferropericlase is similar to olivine and faster than those of wadsleyite and ringwoodite. The present results show that, at the top of the lower mantle ( P = 25 GPa and T = 1773 K) grain size of ferropericlase in single phase system evolves to ∼2 × 10 −2 m after significant geological time (10 My) while a previous study predicts that grain size of MgO in two-phase system is as small as ∼8 × 10 −6 m at same condition.

Sintering and microstructure development in the system MgO–TiO2

The sintering and microstructure development of magnesia containing 0–10 wt% TiO2 at temperatures in the range 1300–1600°C have been investigated. The addition of TiO2 markedly promoted densification at relatively low temperature, and grain growth. Excess TiO2 over the solid solubility limit of TiO2 (0.3 wt%) reacted with magnesia to form inter- and intra-granular magnesium titanate (Mg2TiO4) above 1300°C. The grain size of MgO increased with increasing TiO2 content, and densification was mainly governed by MgO grain growth. © 1998 Kluwer Academic Publishers

Grain size of MgO and polymorphic phases of ZrO2 in zirconia-toughened MgO

Zirconia-toughened MgO was manufactured and examined by scanning and transmission electron microscopes. It was found that ZrO2 particles that are present on the MgO grain boundary limit the grain growth of MgO. The cooling rate has an effect on the ZrO2 phase in zirconia-toughened MgO fired in a cubic ZrO2–MgO field, but it does not have an effect on the ZrO2 phase in specimens fired in a tetragonal ZrO2–MgO field. Tetragonal ZrO2 was retained at room temperature in zirconia-toughened MgO.

Grain Size Effect on Mechanical Strength of MgO-ZrO&lt;sub&gt;2&lt;/sub&gt; Composite Ceramics

Cubic- and tetragonal-ZrO2-MgO composite ceramics were prepared by the pressureless sintering at 1650°C for 4h and 1350°C for 24h respectively, and the effect of grain size and ZrO2 phase on bending strength (at room temperature and 1200°C) was investigated. The bending strength at room temperature of ZrO2-MgO composite ceramics increased with increasing ZrO2 content, because the grain size of MgO decreased with ZrO2 addition. But the effect of ZrO2 phase on the bending strength at room temperature was not recognized. In the case of bending test at 1200°C, when grain size of MgO was below 6μm, specimens deformed plastically before breakage, and the yield stress at 1200°C of c-ZrO2-MgO was larger than that of t-ZrO2-MgO, and fracture stress increased with decreasing the grain size of MgO.