Increase Of MgO Concentration Research Articles

Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li2O–MgO–Al2O3–SiO2 glass-ceramic for the application of joining Si3N4 ceramics. We investigated the influence of the MgO/Al2O3 composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi2O6 and Mg2SiO4 were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg2SiO4. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10−6/°C, which was very close to that of Si3N4 ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si3N4 ceramic surface was 32° and the interface was well bonded.

Study of the Effect of Doping ZrO2 Ceramics with MgO to Increase the Resistance to Polymorphic Transformations under the Action of Irradiation.

The purpose of this study is to assess the effect of doping ZrO2 ceramics with MgO on radiation swelling and polymorphic transformations, as a result of irradiation with heavy ions. Interest in these types of materials is due to the great prospects for their use as structural materials for new-generation reactors. The study established the dependences of the phase composition formation and changes in the structural parameters following a change in the concentration of MgO. It has been established that the main mechanism for changing the structural properties of ceramics is the displacement of the cubic c-ZrO2 phase by the Zr0.9Mg0.1O2 substitution phase, which leads to an increase in the stability of ceramic properties to irradiation. It has been determined that an increase in MgO concentration leads to the formation of an impurity phase Zr0.9Mg0.1O2 due to the type of substitution, resulting in changes to the structural parameters of ceramics. During studies of changes in the strength properties of irradiated ceramics, it was found that the formation of a phase in the Zr0.9Mg0.1O2 structure leads to an increase in the resistance to cracking and embrittlement of the surface layers of ceramics.

Remote sensing and petrological observations on the 2012–2013 fissure eruption at Tolbachik volcano, Kamchatka: Implications for reconstruction of the eruption chronology

Abstract We present a reconstruction of the chronological sequence of events that took place during the first days of the 2012–2013 Tolbachik fissure eruption using petrological data and remote sensing methods. We were forced to use this approach because bad weather conditions did not allow direct observations during the first two days of the eruption. We interpreted infrared images from the scanning radiometer VIIRS Suomi NPP and correlated the output with the results of the geochemical study, including comparison of the ash, deposited at the period from 27 to 29 November, with the samples of lava and bombs erupted from the Menyailov and Naboko vents. We argue that the compositional change observed in the eruption products (the decrease of SiO 2 concentration and K 2 O/MgO ratio, increase of MgO concentration and Mg#) started approximately 24 h after the eruption began. At this time the center of activity moved to the southern part of the fissure, where the Naboko group of vents was formed; therefore, this timeframe also characterizes the timing of the Naboko vent opening. The Naboko group of vents remained active until the end of eruption in September 2013.

Synthesis and optical properties of MgO-doped ZnO microtubes using microwave heating

The Zn1−xMgxO (x=0%, 2% and 5%) microtubes have been successfully synthesized via a microwave heating method. The as synthesized microtubes were carefully investigated. Field emission scanning electron microscope (FE-SEM) showed that all the microtubes exhibit an exact hexagonal hollow structure with smooth surfaces and straight characteristics throughout their whole lengths. UV–Vis measurement indicates that the absorption peak for ZnO microtube was shifted from 378.88nm (3.27eV) to 369.91nm (3.35eV) for Zn0.95Mg0.05O microtube. Room temperature photoluminescence (PL) spectra showed that the intensity of UV emission peak decreased with increase of MgO concentration and the visible emission band showed a blue shift from 538.06812nm for ZnO microtube to 529.54114nm for Zn0.95Mg0.05O microtube. Energy-dispersive spectrometer (EDS) analysis revealed the presence of Zn and O as the only elementary components with the absence of MgO as a doping material.

Effects of melt composition on Fe3+/Fe2+ in silicate melts: a step to model ferric/ferrous ratio in multicomponent systems

The effect of Al 2 O 3 , MgO and total iron on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts in the temperature range 1400- 1550 °C at 1 atm total pressure. The experiments were done mostly in air and partially in pure CO 2 . It is demonstrated that an increase in Al2O3 concentration in a basaltic melt results in a moderate decrease of Fe 3+ /Fe 2+ ratio. In con- trast, the increase in Al2O3 in more silicic melts results in a much more pronounced decrease of Fe 3+ /Fe 2+ ratio. The increase of MgO concentration in a basaltic melt results in a moderate increase of Fe 3+ /Fe 2+ ratio but has a negligi- ble effects in more silicic melts. The different behavior of Al 2 O 3 and MgO in basaltic and more silicic melts indicates that at constant T-fO2 conditions, the effects of melt com- position on ferric/ferrous ratio cannot be predicted accu- rately as a function of ΣdiXi where di are fixed empirical coefficients and X i are mole fractions of the main oxide component in silicate melts. We suggest an alternative approach which accounts for the interaction of cations in complex silicate melts. Based on the data obtained in this study, an equation predicting the ferric/ferrous ratio of ultramafic to silicic melts at air conditions with changing SiO 2 , TiO 2 , Al 2 O 3 , total iron, MgO and P 2 O 5 is proposed.

Physical, Optical, and Spectroscopic Studies on MgO-BaO-B2O3 Glasses

The mixed alkaline effect in double alkaline borate glasses MgO-BaO-B2O3 containing small proportions of copper oxide (CuO) has been studied. The glass samples are characterized by optical absorption, electron paramagnetic resonance (EPR), and Fourier transform infrared spectroscopy (FTIR). A red shift in optical absorption peaks with increasing MgO (decreasing BaO) concentration has been observed. The values of “g” tensor and hyperfine “A” tensor have shown inflections with glass composition. The number of spins (N) and paramagnetic susceptibility (χ) also exhibited mixed alkaline effect. The broadening of glass network with increase in MgO concentration is found from the FTIR spectra. Interestingly both density and molar volume have shown decreasing trend with glass composition. The optical band gaps exhibited a nonlinear compositional dependence. As expected, the glass samples possessed higher values of optical basicity (Λ), molar electronic polarizability (αm), and Urbach energy (ΔE).

The effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 manganite

Abstract The effect of MgO doping on the structural, magnetic, and magnetotransport properties of La0.8Sr0.2MnO3 (LSMO)/x MgO has been investigated. All samples were prepared by a solid-state reaction method. Alternating current susceptibility measurements for LSMO/x MgO samples show that the Curie transition temperature (T c) and magnetization decrease with the increase of MgO concentration. The rate of the decrease of T c at higher doping level is very fast. Also, samples with low doping level (x ≤ 2) show insulator-metal transition, but the transition temperature decreases and resistivity increases with the amount of MgO. It is observed that there is no insulator-metal transition at higher MgO doping level (x ≥ 3). Also, the results show that the value of low-field magnetoresistance decreases with the increase of MgO doping level. It seems that due to the higher sintering temperature and almost the same ionic radii of Mg2+ and Mn3+, Mg2+ mostly replaced Mn3+ and weakened the double-exchange interaction, and consequently, T c and magnetoresistance decrease and resistivity increases with MgO doping.

Low-frequency Raman spectra and structural correlations in metal oxide glasses

Raman and FT-IR studies are reported for the (1 − x)TeO 2 xMgO system where 0.05 < x < 0.40. The destruction of the three-dimensional TeO 4 chain network with increase in MgO concentration is followed by comparing the intensities of the TeO 3 and TeO 4 stretching-mode bands in the 700 cm −1 spectral region. Examination of the same systems after recrystallization yields spectra in which the basic contour often resembles the band envelope of the initial glasses. The decomposition of the Boson peak and its shoulder leads to the suggestion that the strongest feature in the band mass can always be assigned to the long-range descriptive element but the broad shoulder seems to be related to modes associated with more medium-range external interactions within the polyhedron latticework.

Iron diffusion and electrical conductivity in magnesio-wüstite solid solutions (Mg, Fe)O

Diffusion of 59Fe and electrical conductivity in magnesio-wüstite solid solution (Mg x Fe 1− x )O with x = 0.26 and 0.5 have been measured as a function of temperature and oxygen partial pressure. For both solid solutions, the results show that at 1100°C the diffusivity D of 59Fe is directly proportional to p o2 1 6 , whereas the electrical conductivity σ is directly proportional to p o2 1 3.4 . At a given temperature and oxygen partial pressure, the value of D decreases with an increase in MgO concentration in the solid solution. The results are discussed in terms of the coexistence of variously ionized cation vacancies and their change in concentration with MgO additions.