Increase Of SiO Research Articles

Simulation and Optimization of Surface Acoustic Wave Devices With High Electromechanical Coupling Factor and Zero Temperature Coupling Coefficient by Pattern Piezoelectric Layer

Recently, a more popular patterned surface acoustic wave (SAW) device with better performance was proposed. This structure has a large electromechanical coupling factor. To make surface acoustic wave devices easy to be applied to integrated circuit technology, a multilayer structure based on patterned Al/ZnO/Si is designed by using finite element method (FEM). Firstly, dependence of ZnO piezoelectric material on electromechanical coupling factor is studied systematically. The results show that Al/ZnO/Si structure excites Rayleigh mode and Sezawa mode with high electromechanical coupling factor. The patterning of piezoelectric materials could be achieved by etching. The electromechanical coupling factor of Rayleigh mode is as high as 7.98%, and the electromechanical coupling factor of Sezawa mode is up to 9.68%. As we all know, temperature will affect the characteristics of SAW devices. Therefore, the temperature characteristics based on this structure are systematically studied. To achieve zero temperature coupling coefficient, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is used as an intercalation layer for temperature compensation. The structure of Rayleigh mode and Sezawa mode with the thinner SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is easier to achieve zero temperature coupling coefficient than that of conventional structure. Meanwhile, the electromechanical coupling factor of Sezawa mode based on patterned Al/ZnO/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si structure does not change significantly with the increase of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness, with the maximum value of 10.78%, and the minimum value of 10.62%, which is 1.1% larger than that of structure without SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Interfacial reactions between magnesia refractory and electric arc furnace (EAF) slag with use of direct reduced iron (DRI) as raw material

Interfacial reactions between the electric arc furnace (EAF) slag, i.e., CaO–SiO 2 –FeO–MgO–Al 2 O 3 –MnO system, and the magnesia refractory as a function of direct reduced iron (DRI) addition (0, 10, 20, 30 wt%) were investigated at 1550 °C under an Ar atmosphere. MgO solubility increases with increasing DRI content by decreasing basicity (i.e., CaO/SiO 2 ratio), which is due to an increase in SiO 2 supplied from DRI. The measured MgO content was always lower than the theoretical MgO saturation level irrespective of DRI content because the magnesiowüstite (MW) intermediate layer, which formed at the slag/refractory interface, retarded the direct dissolution of the refractory by acting as a self-protective layer. The thickness of the MW intermediate layer and dissolution depth were proportional to DRI content. However, the penetrativity decreased with increasing DRI content by decreasing the fluidity of the slag. Several kinetic parameters were estimated, including the dissolution rate constant of the MW intermediate layer, the dissolution rate of the MgO refractory, and the rate constant of MW growth. Dissolution of MgO refractory is controlled by the dissolution of the MW intermediate layer. Increasing the growth rate is very important for protecting refractory after the formation of a MW intermediate layer. In addition, we provided a schematic diagram of the slag/refractory interfacial reaction phenomena that compares situations of low and high DRI content. The results of the present study show that it is necessary to control DRI content to minimize refractory degradation during the EAF process. If a large amount of DRI must be used in the EAF process, then MgO content in the slag should be at the saturation limit at first, which accelerates growth of the MW intermediate layer.

Numerical simulation of thermal and dielectric properties for SiO&lt;sub&gt;2&lt;/sub&gt;/polytetrafluoroethylene dielectric composite

Coefficient of thermal expansion (CTE) and dielectric constant for the SiO&lt;sub&gt;2&lt;/sub&gt;/polytetrafluoroethylene (SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE) dielectric composite are mainly influenced by their filling content, and how to accurately predict the effect is still a great challenge untill now. In this work, the CTE and dielectric constant of SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE dielectric composite are systematically investigated by numerical simulation. The results show that with the increase of SiO&lt;sub&gt;2&lt;/sub&gt; content, CTE of SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE dielectric composite decreases, and the dielectric constant increases, which are in good agreement with the data reported in the literature (Han K K, Zhou J, Li Q Z, Shen J, Qi Y Y, Yao X P, Chen W &lt;ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1007/s10854-020-03449-w"&gt;2020 &lt;i&gt;J. Mater. Sci. Mater. Electron.&lt;/i&gt; &lt;b&gt;31&lt;/b&gt; 9196&lt;/ext-link&gt;). The 30% (volume fraction) solid SiO&lt;sub&gt;2&lt;/sub&gt; sphere (SSS)/PTFE dielectric composite is the smallest CTE of 7.5×10&lt;sup&gt;–5&lt;/sup&gt; K&lt;sup&gt;–1&lt;/sup&gt;, while 10% (volume fraction) hollow solid sphere (HSS)/PTFE possesses the smallest dielectric constant of 2.06. The CTE of SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE dielectric composite may decrease when the SiO&lt;sub&gt;2&lt;/sub&gt; distribution is dense at the bottom. The large aspect ratio of SiO&lt;sub&gt;2&lt;/sub&gt; filler may reduce CTE&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; of SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE dielectric composite. The molding parameters have little effect on the thermal expansion coefficient of the solid SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE composite dielectric material. This work provides a clear insight into the controlling of CTE and dielectric constant of SiO&lt;sub&gt;2&lt;/sub&gt;/PTFE dielectric composite by adjusting its microstructure.

Effect of HF and NaOH etching on the composition and structure of SiOC ceramics

Porous SiOC ceramics were prepared with tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) as sol−gel precursors, and followed by etching with HF and NaOH solution. The microstructure evolution and chemical etching as a function of pyrolysis temperature were investigated. The amorphous carbon increases as rising the temperature from 800 o C to 1200 o C, and the graphitic carbon increases with further etching by HF and NaOH. However, the effect of pyrolysis temperature on the structure of C is more significant. The hydroxylation reaction and phase separation of SiOC ceramics results in the increase of SiO 4 unit, which reacts with HF and NaOH to form micro- and mesopores. The existence of mesopore after HF etching provides more specific surface area and pore volume. However, NaOH etching produces more micropores, and the contribution of micropores to specific surface area and pore volume is higher than that of mesopores. Although HF and NaOH etching increase the specific surface area of SiOC ceramics, the etching effect of NaOH is superior to that of HF etching, and the carbon-enriched SiOC ceramics are obtained after NaOH etching.

Effect of SiO2 Films with Different Thickness Deposited on Copper Electrode Surface for Insulation Properties of Propylene Carbonate

In this work, 100, 200, and 400 nm SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films are deposited on the electrode surface by magnetron sputtering, and the effect of film thickness on the insulation performance of propylene carbonate is studied. We use the Weibull distribution to calculate the breakdown voltage of propylene carbonate under different conditions. Space charge distribution of the liquid is measured based on the Kerr effect. Test results show that the breakdown voltage of propylene carbonate increases from 8.4 to 18.7% with increasing film thickness compared with the case where the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film is not deposited. Bipolar injection mode of space charge is not affected by the increase of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film thickness, but the amount of space charge injection is significantly reduced. The thicker the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film deposited on the electrode surface, the higher the ratio of increasing the breakdown voltage of propylene carbonate, but the smaller the magnitude of the increase.

Synthesis of ZSM-5 with the silica source from industrial hexafluorosilicic acid as transalkylation catalyst

Abstract A new effective process to improve the utilization of industrial fluorosilicic acid of phosphate fertilizer by-product has been investigated to comprehensive application of the silicon and fluorine source. Two-step ammoniation was applied to recover high-quality silica. The recovered silica can be used to hydrothermal synthesize ZSM-5 zeolite without impurity phase contamination, which was confirmed by XRD, TG, SEM, BET and EDS characteristic techniques. It was found that with the increase of SiO 2 /Al 2 O 3 ratio and the extension of reaction time, the crystal type transform from the orthorhombic to the monoclinic phase. The impurity fluorine content of the recovered SiO 2 from H 2 SiF 6 has great influence on the hydrothermal process for ZSM-5 crystal structure formation. Moreover, the increase of fluorine ions content in the hydrothermal process can control the crystal morphology and size of synthesized ZSM-5. Catalytic properties of synthesized HZSM-5 with different SiO 2 /Al 2 O 3 ratio in transalkylation of toluene and 1,2,4-trimethylbenzene show good and stable catalytic performance. The ZSM-5 synthesized with recovered silica source exhibits similar catalyst life as the performance of small particle size HZSM-5, because the ZSM-5 synthesized with the silica source from industrial hexafluorosilicic acid prefers a thin disk crystal along the b axis direction, which shortens the diffusion distance of generated products.

Reaction bonded silicon nitride foams: The influence of iron disilicide on microstructure and mechanical strength

In this study open-cell reaction bonded silicon nitride (RBSN) foams with high and controlled level of porosity have been produced based on the wet processing of Si-PMMA suspensions in the presence of iron disilicide (FeSi2) as an additive. The investigation focuses on the effect of FeSi2 on the mechanical strength, nitriding mechanisms, and microstructure of the RBSN foam. The nitriding reactions and the foam microstructures and properties were investigated under various nitriding conditions and for different FeSi2 contents.It was observed that 1wt% FeSi2 significantly increases the strength of the RBSN foams regardless of the nitriding temperature and atmosphere. The nitriding conditions have a strong influence on RBSN foam strength. The maximum strength was achieved under a N2 atmosphere at 1390°C with a foam porosity of 71vol%. The high porosity level of the foam significantly affects the nitriding mechanisms and consequently the foam microstructure, compared to “dense” RBSN ceramics. FeSi2 promotes the formation of both α- and β-Si3N4 phases depending on its concentration and its addition also increases the whisker content of the foam microstructure due to an increase in SiO and Si vapor formation.

Effect of SiO2/B2O3 Replacements on the Structure, Physicochemical and Electrical Properties of Bi2O3-Containing Glasses

The effect of increasing SiO 2 at the expense of B 2 O 3 on the internal structure of xSiO 2-(40-x) B 2 O 3-60Bi 2 O 3 glass matrix (where x=0, 10, 20, 30 and 40 mole %) was investigated. The glass structure was indicated that Bi 3+ cations are incorporated in the glass structure as pyramidal [BiO 3] and [BiO 6] octahedral units and boron ions are incorporated in BO 3 and BO 4 units. The presence of distorted [BiO 6] octahedral units in the glass network was observed and the degree of distortion was found to be decreased on progressive substitution of B 2 O 3 by SiO 2. The results revealed that increase of SiO 2/B 2 O 3 replacements, led to increase the density, microhardness and chemical durability of the studied glasses. However, the molar volume was decreased. The increase of SiO 2/B 2 O 3 replacements generally decreased the AC conductivity. That decrease may be due to the decrease in distortion of [BiO 6] octahedral units in glass network on progressive substitution of B 2 O 3 by SiO 2. Dielectric constants of the samples are complex, which may be an indication of the distortion (number of free charges or broken bonds) in the network of the glass. The obtained experimental data were argued to the internal structure of glass network and the change of the structure of the samples from pyramidal to octahedral and the presence of boron ions in BO 3 and BO 4 units.

Effect of composition on sinter-crystallization and properties of low temperature co-fired α-cordierite glass–ceramics

Abstract This article investigates effect of composition, including SiO 2 and impurity defined to contain K 2 O, Na 2 O, Fe 2 O 3 , etc., from K-feldspar, on sinter-crystallization and properties of the low temperature co-fired α-cordierite glass–ceramics. Increasing impurity content from 5.72 wt% to 9.16 wt% leads to enhanced crystallinity, formation of leucite and more pores but the crystallinity and porosity decreased with a further increase to 10.8 wt%. The main impurity K 2 O is critical for formation of α-cordierite and leucite. Only α-cordierite was precipitated from the glasses with different SiO 2 contents but an increase of SiO 2 content slightly improves their densification. The impurity and SiO 2 contents greatly affect the properties of glass–ceramics. Notably, some glass–ceramics from K-feldspar show high densification at low temperature, low dielectric constant (6–8), low loss (about 0.005), appropriate linear CTEs (4.32–5.87 × 10 −6 K −1 ) and flexural strength (above 100 MPa), all of which meet the requirements of LTCC substrates.

Enhanced Middle-Infrared Light Transmission Through Au/SiOxNy/Au Aperture Arrays

The enhanced middle-infrared light transmission through Au/SiO(x)N(y)/Au aperture arrays by changing the refractive index and the thickness of a dielectric layer was studied experimentally. The results indicated that the transmission spectra was highly dependent on the refractive index and the thickness of SiO(x)N(y). We found that the transmission peaks redshifted regularly along with the refractive index from 1.6 to 1.8, owing to the role of surface plasmon polaritons (SPP) coupling in the Au/SiO(x)N(y)/Au cascaded metallic structure. Simultaneously, a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO2.1N0.3/Au cascaded metallic structure with small refractive index (1.6) than in Au/SiO0.6N1/Au cascaded metallic structure with large refractive index (1.8). When the thickness of SiO(x)N(y) changes from 0.2 to 0.4 microm, the shape of transmission spectra exhibits a large change. It was found that a higher transmission efficiency and narrower transmission peak was obtained in Au/SiO(x)N(y)/Au cascaded metallic structure with a thin dielectric film (0.2 microm), with the increase of SiO(x)N(y) film's thickness, the transmission peak gradually widened and disappeared finally. This effect is useful in applications of biochemical sensing and tunable integrated plasmonic devices in the middle-infrared region.

Determination of the optical constants of HfO 2–SiO 2 composite thin films through reverse fitting of transmission spectra

Composite thin films of HfO 2:SiO 2 with wide range of relative composition from 100:0 (pure HfO 2) to 10:90 have been deposited on fused silica substrates by co-evaporation technique and the optical properties of the films have been studied by measuring the transmission spectra of the samples by spectrophotometer. Different important optical parameters viz., band gap, refractive index and absorption coefficients of the samples have been obtained by fitting the measured optical spectra with theoretically generated spectra and the variation of the optical constants as a function of SiO 2 content in the films have been obtained. Two different dispersion models viz., the single effective oscillator model and the Tauc–Lorentz model have been used to generate the theoretical spectra in the above fitting procedure. X-ray reflectivity (XRR) measurement technique has been used to find the densities of the films in order to explain the observed variation in optical properties of the films with increase in SiO 2 content.

Cretaceous-Paleogene transition at the Paraíba Basin, Northeastern, Brazil: Carbon-isotope and mercury subsurface stratigraphies

Abstract The Paraiba Basin in northeastern Brazil contains a complete carbonate sequence that recorded the Cretaceous–Paleogene transition, and is composed of the Itamaraca, Gramame and Maria Farinha formations. In this study, the behavior of C and O isotopes, major and trace element chemistry have been examined in core drill carbonate samples from three drill holes (Poty Quarry, Olinda and Itamaraca). The deposition of carbonates in this basin was initiated during a marine transgression with temperature and bioproductivity increase in the Early Maastrichtian. δ 18 O values for this interval vary from −3‰ to −5‰ VPDB, and δ 13 C, from −1.2‰ to 0.1‰, reaching a maximum in the Late Maastrichtian, with values around +2‰. Early Danian carbonates have recorded a small positive δ 13 C excursion(+2‰), followed by values around +1‰ right after the Cretaceous–Paleogene transition with increase of SiO 2 and Al 2 O 3 associated to terrigenous contribution. Upsection, carbonates recorded a period of marine regression, bioproductivity falls as recorded by the δ 13 C curve (+1‰) and carbonate sediments with higher Mg/Ca ratios were possibly deposited in a shallow-marine environment. Carbon and oxygen isotope pathways in carbonates of the Paraiba Basin from the drill holes at Poty Quarry, Olinda and Itamaraca localities are similar to each other and to that observed in the El Kef type section, Tunisia, and in the Yacoraite Basin, in Argentina. In the Poty drill hole, remarkable negative spikes may have resulted from multiple meteorite impacts that predated the Cretaceous–Paleogene transition. Mercury stratigraphy in the same drill hole displays a prominent positive anomaly in the K-T transition and suggests that important volcanism witnessed the transition scenario.

The eruptive history of Morne Jacob volcano (Martinique Island, French West Indies): Geochronology, geomorphology and geochemistry of the earliest volcanism in the recent Lesser Antilles arc

Martinique is the Lesser Antilles Island where the most complete volcanic history of the arc can be found from the Oligocene to the present time. In this study, we focused on the construction of Morne Jacob shield volcano in Martinique, which is the largest volcano of the Lesser Antilles. We have dated twenty representative samples from the Morne Jacob, by K–Ar based on the Cassignol–Gillot technique, used geochemical data and obtained morphological constraints that have helped us to reconstruct better the volcanic history of this shield volcano. Our results and the lack of reliable ages on other Plio-Pleistocene islands show that the Morne Jacob is the oldest volcano of the aerial recent arc that has been dated so far. It has a longer history than previously inferred, with different stages ranging between 5.2 and 1.5 Ma. A large basaltic to andesitic shield volcano was first built between 5.2 and 4.0 Ma (J1) with tholeiitic lavas characterized by an increase of SiO 2 content through time. After 800 kyr of repose, calc–alkaline andesites erupted over the first shield from 3.2 to 2.2 Ma (J2a). The accumulation of lavas over a hyaloclastitic basement provoked spreading and northeast creeping of the northern flank of the volcano. The mass movement induced regressive erosion, particularly at the centre of the edifice. Then, between 2.1 and 1.5 Ma (J2b), calc–alkaline lavas, which show a decrease of the SiO 2 content through time, erupted at the central vent and from peripheral fissures, over the previous shield and down to the Caribbean coast. Eruptive volumes were reconstructed, permitting estimates of minimum output rates for the volcano's history. Minimum volume erupted during the first stage is 112 ± 20 km 3 and 33 ± 25 km 3 during the whole second stage, yielding rates of about 0.107 km 3/kyr and 0.019 km 3/kyr, respectively. Considering the entire history of Morne Jacob shield volcano, between 5.14 ± 0.07 and 1.54 ± 0.03 Ma, we obtain a total volume of 145 ± 32 km 3 above the sea level, and a time-averaged construction rate of 0.040 ± 0.008 km 3/kyr. With comparison between the reconstructed paleotopographies and the DEM of present topography, we have calculated an eroded volume of 18 km 3 over the outcropping 210 km 2 that have occurred during the last 1.5 Myr. Finally, our set of twenty K–Ar ages, obtained on groundmass separates, allow us to revise the eruptive chronology of Morne Jacob volcano and to date the earliest subaerial volcanic activity so far identified for the recent Lesser Antilles arc.

Influence of Ru/Ru–SiO 2 underlayers on the microstructure and magnetic properties of CoPt–SiO 2 perpendicular recording media

SiO 2 was doped into Ru underlayer to reduce the grain size of CoPt–SiO 2 perpendicular media. The effects of SiO 2 volume fraction and sputtering deposition pressure of Ru–SiO 2 underlayer on the microstructure and magnetic properties of CoPt–SiO 2 media were studied. Increasing SiO 2 volume fraction in Ru–SiO 2 layer decreased the grain sizes of Ru and CoPt. Adding 5% SiO 2 to Ru–SiO 2 layer increased the coercivity and enhanced the exchange decoupling and thermal stability of CoPt–SiO 2 layer. A further increase in SiO 2 volume fraction caused the deterioration of magnetic properties of CoPt–SiO 2 layer. Deposition of Ru–SiO 2 layer at 1.3 Pa resulted in a smaller activation volume and higher thermal stability of the CoPt–SiO 2 media than that deposited at 0.4 Pa.

Synthesis and characterization of spray pyrolyzed nanocrystalline CeO 2–SiO 2 thin films as passive counter electrodes

Nanocrystalline CeO 2–SiO 2 thin films were spray pyrolyzed onto fluorine-doped tin oxide (FTO) coated glass substrates using a blend of equimolar concentrations of cerium nitrate hexahydrate and trimethoxymethylsilane in methanol with appropriate volumetric proportions. CeO 2–SiO 2 films were polycrystalline with cubic fluorite crystal structure and transforms to amorphous with increasing SiO 2 content. The room temperature electrical resistivity of the film varied from 1.05×10 10 to 1.13×10 6 Ω cm with the increase in SiO 2 concentration (0–6 vol% SiO 2). In all cases the resistivity follows an Arrhenius behavior with negative temperature dependence in the range of 298–553 K with a thermal activation energy of 0.84±0.04 eV. Films were transparent ( T∼80%), showing a decrease of the band gap energy ( E g) from 3.45 eV for pristine CeO 2 to 3.02–3.12 eV for CeO 2–SiO 2 films. The ion storage capacity (ISC) and electrochemical stability of the films was affected by different morphological features of the film obtained with different CeO 2–SiO 2 compositions. A CeO 2–SiO 2 film prepared with 3 vol% Si having a thickness of 580 nm showed the highest porosity and the high ISC of 28 mC cm −2 with an electrochemical stability of 3500 cycles in 0.5 M LiClO 4+PC electrolyte. The optically passive behavior of such CeO 2–SiO 2 film is confirmed by its negligible transmission modulation upon Li + ion insertion/extraction, irrespective of the extent of Li + ion intercalation.

Organic–inorganic crosslinked and hybrid membranes derived from sulfonated poly(arylene ether sulfone)/silica via sol–gel process

A series of covalently crosslinkable organic–inorganic hybrid membranes have been prepared from sulfonated poly(arylene ether sulfone) (SPAES) with pendant propenyl moiety and various amounts of vinyl substituted silica via sol–gel process which are then thermally crosslinked in the presence of benzoyl peroxide (BPO) initiator. The obtained membranes are characterized in terms of oxidative stability, thermal property, ion exchange capacity (IEC), water uptake, swelling ratio in methanol aqueous solution, proton conductivity, and methanol permeability coefficient. The results indicate that the oxidative stability and thermal stability of the hybrid membranes are improved. Moreover, introduction of silica reduces the water uptake and methanol swelling of membranes. The swelling ratio of membranes in 2 mol L −1 methanol aqueous solution at 80 °C slowly decreases from 26 to 19% with the increase of SiO 2 content from 0 to 12 wt.%. Furthermore, with the increase in silica content, the methanol permeability coefficient of the hybrid membranes decreases at first and then increases. When the silica content reaches 8 wt.%, the methanol permeability coefficient is at the minimum of 6.02 × 10 −7 cm 2 s −1, a 2.64-fold decrease compared with that of the pristine SPAES membrane. Moreover, the proton conductivity is found to be at about 95% of that of pristine polymer at that silica content.

Influence of SiO 2 on the structure and optical properties of lithium bismuth silicate glasses

Bismuth silicate glasses containing lithium oxide with composition 20Li 2O·(80 − x)Bi 2O 3· xSiO 2 (5 ⩽ x ⩽ 70 mol%) have been prepared by melt-quench technique. Density ( D), molar volume ( V M) and glass transition temperature ( T g) for all the glass samples have been measured. FTIR spectroscopy has been employed to investigate the structure of these glasses in order to obtain information about the competitive role of Bi 2O 3 and SiO 2 in the formation of glass network. The increase of SiO 2 content in the glass matrix results in increasing the Si–O–Si bond angle and hence the ionicity of Si–O bond increases with decrease in Bi 2O 3/SiO 2 ratio. The optical transmittance spectra of all the glasses have been recorded in the wavelength range 200–3300 nm. The values of optical band gap ( E g) have been determined from the cutoff wavelength of these glasses. The average electronic polarizability of oxide ion ( α o 2 - ) and the optical basicity ( Λ th) have been estimated from the calculated values of the E g and were found to be dependent directly on Bi 2O 3/SiO 2 ratio. The variation in different physical parameters such as D, V M and T g and optical parameters; viz., E g, α o 2 - , Λ th with Bi 2O 3/SiO 2 ratio have been analyzed and discussed in terms of change in the glass structure.

The nature of erupting kimberlite melts

The compositions of kimberlite magma and associated melts during eruption and hypabyssal intrusion are elusive due to contamination by xenolithic material and strong alteration, notably by serpentinisation. Textures and mineralogical attributes of kimberlite dykes and sills indicate that some groundmass minerals, including igneous calcite, are replaced in the process of serpentinisation. Large volume changes during serpentinisation occur in chemically open systems, producing an increase in SiO 2 and MgO and decrease in CaO and CO 2 in bulk rock chemistry. Reconstructed compositions of kimberlite melt components, taking into account alteration, are shifted towards compositions transitional to carbonatite, indicating overestimation of SiO 2 and MgO contents in previous published estimates of kimberlite melt compositions. Further evidence that these compositions are problematic come from experimental investigations of three putative kimberlite melt compositions. Experiments at 100 and 200 MPa at temperatures of 1100 °C to 1275 °C with excess CO 2, H 2O and CO 2–H 2O mixtures show that previously proposed compositions cannot be pure melts under eruptive conditions. Their SiO 2 and MgO-rich characteristics lead to high liquidus temperatures (> 1350 °C) inconsistent with estimated kimberlite magma temperatures (< 1200 °C). The experimental residual melts are depleted in MgO and have high CaO and SiO 2 contents, characteristics that are not consistent with kimberlite groundmass mineralogy that indicate significantly lower SiO 2 in the natural systems. Serpentinisation, causing changes in the relative proportions of CaO, MgO and SiO 2, can explain these results. Recognising the effects of serpentinisation, combined with petrographic observations, suggest that kimberlite melts have low SiO 2, SiO 2/MgO < 1 and evolve by crystallization towards increasingly silica-poor carbonate-rich residual melts during eruption of intrusion.

Melting Characteristics and Wettability of Binding Phase in Sinter

The melting characteristics and wettability of the binding phase in high basicity sinter were studied. By changing n CaO: n Fe 2O 3 (molar ratio of CaO to Fe 2O 3) as well as the percentage of MgO, SiO 2, and A1 2O 3, the melting characteristics and wettability of the binding phase were discussed. The results indicated that the characteristic melting temperature was the lowest and wettability was the best at n CaO: n Fe 2O 3 = 1:1 (without addition); the addition of MgO increased the characteristic melting temperature and contact angles; when the percentage of SiO 2 or AI 2O 3 was 3%, the characteristic melting temperature was the lowest, whereas the contact angles increased with an increase in SiO 2 and A1 2O 3 contents.

Preparation and characterization of core–shell structured Co/SiO 2 nanosphere

The Co/SiO 2 nanospheres have been prepared by the improved sol–gel method combined with hydrogen reduction. The size, the phase and the shape of the particles varied with the molar ratio of SiO 2, reduction temperature and drying temperature. The initial temperature of the phase transformation from hcp-Co to fcc-Co in core–shell structured Co/SiO 2 nanospheres is lower than that in the bulk case due to the lower surface energy of nanoscale particles. Result of the thermogravimetric analysis (TGA) indicates that the thermal stability of Co/SiO 2 nanoparticles is much better than that of pure Co particles. The value of saturation magnetization decreases with the increase of SiO 2 content due to the presence of the nonmagnetic silica coating.