Small Amount Of SiO2 Research Articles

GAM-7: an organic-inorganic hybrid layered aluminophosphate crystal formed by zeolite transformation.

The interzeolite conversion (IZC) of metallo- and aluminophosphate zeolites was demonstrated using a non-cyclic secondary amine, diisopropylamine, as the organic structure-directing agent (OSDA). The IZC of AlPO4-5 with AFI topology could successfully produce an unknown highly crystalline phase, named GAM-7. In metallo-aluminophosphates (metal-AlPOs), SAPO-5 with a small amount of SiO2 was also interconverted to a single crystal GAM-7, designated as [Si]GAM-7. However, in other metal-AlPOs, the corresponding GAM-7 crystals were formed as either an intermediate or a mixture of plural crystals. Additionally, it was found that GAM-7 could also be obtained by hydrothermal synthesis (HTS), but not synthesized from a silico-aluminophosphate hydrogel, indicating that [Si]GAM-7 can be prepared by only the IZC technique. The obtained GAM-7 crystal was well-characterized to elucidate the framework structure, and this revealed that GAM-7 was a new organic-inorganic hybrid layered aluminophosphate having a terminal POH group in the corrugated layered sheets, and the OSDA molecule between the layers was robustly interacting with an acidic POH site by a hydrogen bond. Furthermore, we have performed the tracking of pH values during the transformation from AlPO4-5 into GAM-7 and have argued a reasonable consideration for the IZC process.

Preparation, mechanical and ablation properties of a C/C-TaB2-SiC composite

A C/C-TaB2-SiC composite was successfully prepared by high-solid-loading slurry impregnation combined with polymer infiltration and pyrolysis. The composite had a density of 3.46 g/cm3 and consisted of pyrolyzed carbon, carbon fibers, TaB2 particles, and precursor-derived SiC with their mass fractions of 7.8%, 13.0%, 58.6%, and 20.6%, respectively. The C/C-TaB2-SiC composite possessed a flexural strength of 248.2 ± 16.8 MPa and a fracture toughness of 13.7 ± 1.6 MPa·m1/2, and demonstrated a non-brittle fracture behavior. After exposure to oxyacetylene flame with a heat flux of 4.18 MW/m2 for 120 s, the ablation temperature of the sample surface reached a maximum of 2263°C, and the mass and line ablation rates were 2.24 mg/s and 12.92 μm/s, respectively. The ablation resistance mainly comes from the hindrance of oxygen diffusion by the oxide layer composed of tantalum oxide and a small amount of SiO2. The raw/processed data required to reproduce these findings cannot be shared at this time due to the fact that the authors do not have permission to share data.

Study on Growth Mechanism and Characteristics of Zirconium Alloy Micro-Arc Oxidation Film

Ceramic coatings on R60705 zirconium alloy were prepared on the surface by the micro-arc oxidation (MAO) technique in electrolytes containing Na2SiO3, NaOH, and Na2EDTA. The growth behavior of the MAO ceramic coatings at different stages, including growth rate, microstructure, and phase composition, was investigated using the method of direct observation of the boundary area. The results showed that the growth of the MAO coatings on R60705 zirconium alloy occurred in both inward and outward directions. At an oxidation time of 5 min, the thickness of the oxidation layer increased fastest, reaching 103.43 μm, with a growth rate of 0.345 μm/s. After 5 min, the growth rate decreased and tended to level off around 15 min, with a thickness and growth rate of 162.7 μm and 0.181 μm/s, respectively. The total thickness of the coatings continuously increased throughout the process, with the outward growth thickness always higher than the inward growth thickness. The composition of the zirconium alloy micro-arc oxidation coatings mainly consisted of monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2), and a small amount of SiO2. The main elements in the coatings were Zr, O, and Si. The corrosion resistance of the zirconium alloy micro-arc oxidation coatings increased first and then decreased with increasing oxidation time, with a corrosion current density of 8.876 × 10−9 A·cm−2 at 15 min, indicating the best corrosion resistance.

Effect of SiO2-doped on microstructural evolution and hydrogen storage performances of AB2 type alloy

The influence of impurities (such as Si, O) on the properties of hydrogen storage alloys in industrial processes received extensive attention, yet the role of Si and O coexisting on the hydrogen absorption and desorption properties of AB2-type hydrogen storage alloys remains to be clarified. We investigated the doping of SiO2 on the microstructure and hydrogen storage properties of Ti-Mn based AB2-type hydrogen storage alloy. When a small amount of SiO2 (<1.0 wt%) was added, the hydrogen storage properties of the alloy did not change much and still maintained excellent cyclic stability, and the only difference was the plateau pressure of the alloys doped with SiO2 decreased. However, when excessive SiO2 (∼2.0 wt%) was added, the hydrogen storage plateau slope of the alloy increased sharply, and the hydrogen storage capacity decreased. It is ascribed that the formation of ZrO2 phase and the doping of Si with the SiO2 content increase, resulting in the lattice constant of the alloy increasing and the plateau pressure decreasing. These findings hold promising reference prospects for practical production.

Mechanisms of SiO oxidation: Implications for dust formation

Reactions of SiO molecules have been postulated to initiate efficient formation of silicate dust particles in outflows around dying (AGB) stars. Both OH radicals and H2O molecules can be present in these environments and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation and clustering reactions of SiO, Si2O2 and Si2O3 have been calculated using master equation calculations based on density functional theory calculations. The calculations show that the reactions involving OH are fast. Reactions involving H2O are not efficient routes to oxidation but may under the right conditions lead to hydroxylated species. The reaction of Si2O2 with H2O, which has been suggested as efficient producing Si2O3, is therefore not as efficient as previously thought. If H2O molecules dissociate to form OH radicals, oxidation of SiO and dust formation could be accelerated. Kinetics simulations of oxygen-rich circumstellar environments using our proposed reaction scheme suggest that under typical conditions only small amounts of SiO2 and Si2O2 are formed and that most of the silicon remains as molecular SiO.

Thermophysical properties of molten (Fe2O3)0.95-(SiO2)0.05 measured by aerodynamic levitation

In order to establish an evaluation method/numerical simulation for nuclear reactor safety under severe accidental conditions, it is necessary to obtain the physical properties of the relevant molten materials at very high temperatures. In particular, the reaction/interaction between the melt of stainless-steel oxide originating from the nuclear reactor component and the composition of structural concrete is an important phenomenon in terms of understanding of the progress of severe accidents in nuclear power plants and the planning/installation of equipment/devices as countermeasures. The installation of a core catcher is one possible countermeasure to safely terminate a severe accident. For this to work a sacrificial material is placed in the core catcher to increase the fluidity of the molten material. Iron oxide (Fe2O3) is considered a promising candidate. In this study, thermophysical properties such as the density and the viscosity of a (Fe2O3)0.95-(SiO2)0.05 mixture were obtained using the aerodynamic levitation method. The chosen composition is representative for the Molten-Core-Concrete-Interaction at early stages of a severe accident event. Although partial Fe2O3 changes to Fe3O4 during the experiment, this composition change would occur under the actual severe accident conditions. The physical property values of the (Fe2O3)0.95-(SiO2)0.05 mixture were almost the same as those of Fe2O3 obtained in an earlier study. Therefore, it can be concluded that the fluidity of Fe2O3 is not significantly affected in the early stages of a severe accident whereby small amounts of SiO2 (approximately 5 mol. %) are dissolved into Fe2O3.

High efficient and clean utilization of coal for the carbothermic reduction of silica

In order to alleviate the problems of large amount of reducing agent, low output and high energy consumption in the production process of industrial silicon, TGA, SEM, XRD, Raman spectroscopy and other methods were used to study the properties of carbonaceous materials prepared from distiller’s grains (DG) and soft coal (SC) in the ratio of 20:80 and 50:50, and their effects on the reaction behavior of silica reduction process. The results showed that sorghum distillers’ grains (S-DG) had a strengthening effect when mixed with SC at a 20% mixing ratio, and Tmax and activation energy are reduced. Corn distillers’ grains (C-DG) inhibit the graphitization of SC to a greater extent and produce amorphous carbon structures. Through the silica carbothermal reduction experiment, it was found that there are a large number of SiC diffraction peaks in the S-DG and a small amount of SiO2, but there is basically no SiO2 in the C-DG. This shows that in the process of carbothermic reduction, silica first reacts in large quantities to form SiC, so the reduction effect of C-DG on silica is better.

Optimization of response surface methodology (RSM) for defluorination of spent carbon cathode (SCC) in fire-roasting aluminum electrolysis

• Response surface methodology can effectively remove fluoride from SCC. • Determine the optimal treatment process in a conventional muffle furnace. • When the roasting temperature is 1499 °C, the treatment time is 3.33 h, and the average particle size is 10 mm, the fluorine removal rate reaches 88%. Spent carbon cathode (SCC) is a typical toxic and hazardous solid waste generated in aluminum electrolysis. The harmless treatment of SCC is extremely important for the aluminum electrolysis industry. Herein, the response surface methodology was used to investigate the best process for removing fluoride from the SCC of aluminum electrolysis using the roasting method. A Box–Behnken design (BBD) was used to investigate the effects of three independent variables, namely, particle size, roasting temperature, and treatment time, on the fluorine removal rate of the SCC. Seventeen groups of experiments were conducted according to these three factors. Statistical analysis system software and a second-order polynomial model were used to analyze the data and predict the response. The results showed that the particle size, roasting temperature, and treatment time significantly influenced fluoride removal in the SCC. Under optimum process conditions, the system predicted a fluoride removal rate of 87% for the SCC. Validation experiments were conducted on the fluoride removal rate of the SCC under optimum process conditions. The results showed that the actual value reached 88%. The X-ray diffraction analysis before and after calcination showed that a small amount of SiO 2 was converted into SiC through a carbon thermal reduction reaction after calcination. This paper provides a theoretical basis for the best process of roasting SCC to remove fluoride. It also has a certain guiding significance for other solid waste treatments.

Pore structure and thermal oxidation curing behavior of porous polymer derived ceramics with superhigh porosity fabricated by freeze casting

Porous ceramics with porosity up to 92.5 % have been successfully fabricated by freeze casting of polycarbosilane (PCS) solution. The effect of PCS concentration and thermal oxidation curing on the pore structure and compressive properties was investigated. Curing mechanism and thermodynamics were illuminated through analyzing the molecular structure, curing activation energy, and curing degree. Porous ceramics, mainly composed of SiC and a small amount of SiO2, have dendritic pore structure which well replicates the solidification morphology of camphene solvent. Results of FT-IR and Gaussian computation of PCS electron density show that Si–H and Si–CH3 bonds play a dominant role in thermal oxidation curing reaction. Both curing degree and ceramic yield increase with the increase in curing temperature and time. The curing degree of Si–H bond is close to 52 % and the corresponding ceramic yield is about 83 % when the porous PCS was cured at 200 °C for 90 min. Both polymer concentration and curing time have influences on the compressive strength of porous ceramics.

Synergistic inhibition effect and mechanism of polycation and polyanion on colloidal silica

The silica inhibition of Reverse osmosis (RO) membrane can be treated by adding scale inhibitor. The polycation adipic acid/amine-terminated polyethers D230/diethylenetriamine copolymer (AA/AT/DE) was found to be an effective silica scale inhibitor. The drawback of this scale inhibitor is that small amounts of SiO2 -AA/AT/DE white insoluble floc appear in the solution during the inhibition process. In this study, polyepoxysuccinic acid (PESA) was added to solve this problem. The scale inhibition efficiency of different combinations was tested by static screening tests. The content of silicon dioxide was determined by silicomolybdate spectrophotometric method. In a certain dose range (< 50 ppm), the introduction of PESA can improve the inhibition performance of AA/AT/DE, while, it will have a negative impact when the concentration of PESA was increased to 50 ppm. Based on zeta potential and atomic force microscopy (AFM) topographical analyses, the effect of polycation on the formation of silica particles and the mechanism of the synergistic effect of AA/AT/DE and PESA were placed attention on.

Properties and Structure of Low-Cement Concrete According to its Compositional Parameters

Abstract Refractory concretes with the usual cement content (about 20%) present, besides their well-known advantages, several important disadvantages which make such concretes unfit for certain applications. The relatively high CaO content in concretes, the presence of even small amounts of SiO2 and Fe2O3 in cement reduce in the first place the concretes refractoriness; if their relatively high porosity is also taken into account, the concretes behavior is further damaged in regard to the structural and thermal-chemical stability. especially at their high operating temperatures. This work is an attempt to correct the shortcomings shown by reducing the cement dosage and using appropriate admixtures in the technological process of concrete making.

Study on the corrosion resistance of cordierite-mullite and SiC refractories to Li-ion ternary cathode materials

The corrosion reactions of Li-ion ternary cathode material on cordierite-mullite and SiC refractories were studied at 780 °C for 20 h. The XRD and SEM technologies were used to study the corrosion process. The results showed that the interaction between Li2O and cordierite-mullite material produced a large number of reactants, which led to the failure of cordierite-mullite refractories. For SiC refractories, a small amount of SiO2 were formed by the SiC oxidation reaction, then the SiO2 reacted with Li2O to form lithium silicate compound. Moreover, Li2O tended to diffuse into the interior of SiC refractory slabs through pores, which avoided the formation of a large amount of reaction products and gave good corrosion resistance to the material without damaging its structure. It has been found that the corrosion resistance of the two materials can be effectively improved by the alumina sol impregnation method.

Processing thin, dense, transparent Ce:Y3Al5O12 films from flame made nanopowders for white light applications

Flame made metal oxide nanopowders enable processing of dense, transparent thin (< 50 μm) films of Ce3+ doped Y3Al5O12 for white light applications. The addition of very small amounts of SiO2 (0.14 wt. %) and the use of a final 95:5 N2:H2 atmosphere sintering step permits nearly complete removal of pores from films originally sintered in O2. Furthermore, the introduction of this final step allows reduction in processing temperatures needed to effect Ce4+ reduction to Ce3+ by several hundred degrees below typical temperatures of >1600 °C. At 20–50 μm, the reported films are also much thinner than previously reported for the same materials normally produced by solid state reactions of micron size powders. Spectrofluorometric measurements of the dense transparent films exhibit excitation spectra centered around 450 nm and broad emission spectra in the 470–750 nm range with two peaks centered at 537 and 570 nm, confirming their applicability as a phosphor for white light emitting diodes.

The Influences of Sio2 on the Sintering Behavior and the Properties of Na+- Β/Β"-Al2O3 Solid Electrolyte

SiO2-doped Na+-β/β″-Al2O3 was synthesized via a solid-state reaction, and the relationship between the SiO2 content and properties of Na+-β/β″-Al2O3 was investigated. Respective specimens were doped with 0 – 5 wt.% SiO2 as a liquid phase sintering promotor and sintered. The specimens were characterized by XRD, SEM, densimeter and impedance analyzer. In the sintered samples, the phase fraction of β″-Al2O3 decreased as the SiO2 content increased, whereas the relative sintered density was enhanced with the inclusion of less than 0.7 wt.% SiO2. The relative sintered density of Na+- β/β″-Al2O3 sintered specimen with 0.7 wt.% SiO2 doping reached 99.2 % of the theoretical density and the sintered density decreased when the amount of SiO2 was larger than 1 wt.% result from excessive liquid-phase formation during sintering. Similarly, the ionic conductivity of SiO2-doped Na+-β/β″-Al2O3 was enhanced by doping with a small amount of SiO2, whereas the addition of more than 1 wt.% SiO2 negatively affected the ionic conductivity of Na+-β/β″-Al2O3 due to a decrease in the sintered density and unfavorable phase relationship. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.14246

More superior pyroelectric performance of synthesized dravite by high-pressure solid-state method

It’s of great significance to explore the synthesis of tourmaline with simple chemical composition to study the mechanism of its pyroelectric properties due to the presence of crystal defects and isomorphous substitution in natural tourmaline. In the present work, dravite is firstly synthesized by high pressure solid-state method at 5-6 GPa and 550-650 °C. X-ray powder diffraction and electron microprobe analysis data indicate that the synthesized sample is the compound of the dravite with the formula of NaMg3Al6Si6B3O27(OH)4 and a small amount of SiO2. Compared with the natural dravite, the pyroelectric coefficient of the synthesized dravite is improved by an order of magnitude due to the great increase of the intrinsic dipole moment in synthesized dravite. The temperature dependent infrared spectra shows that the dipole moment of each ionic group in the synthesized dravite increases with temperature, leading to the raise of the pyroelectric coefficient with the increment of temperature. And in all ionic groups, [SiO4] tetrahedron and [BO3] triangle are the most important ionic groups that caused the pyroelectricity of tourmaline.

Relevant changes in the properties of Co(Ni)Mo/Al2O3HDS catalysts modified by small amounts of SiO2

Abstract

Effect of Al-B2O3-TiO2 Exothermic System on Performances of Fly Ash Glass/Ceramic Composite Coating

Glass/ceramic composite coatings were prepared on 40Cr steel matrix by thermo-chemical reaction with fly ash and a small amount of SiO2, Al2O3, MgO, and albite as main raw materials. On this basis, adding 10% Al-TiO2-B2O3 exothermic system, the morphology, phase, thermal shock resistance, and corrosion resistance of the coating were tested, and the influence of exothermic system on the structure and properties of the composite coating was studied. The experimental results show that the addition of exothermic system can promote the formation of NaB15, TiB2, Na2B4O7, Ca2Al2SiO7, and other new phases by thermo-chemical reaction; when compared to the composite coating without addition of exothermic system, combined with a good interface, higher compactness, and lower porosity. The highest micro hardness can be reached 725HV0.1. The number of thermal shock from 700 °C to room temperature can reach more than 50 times; acid, salt, oil immersion corrosion test, composite coating with exothermic system relative to the matrix increased by 27.40 times, 3.97 times, and 1.88 times, respectively. The overall performance is better than that of the composite coating without exothermic system.

The crystal morphology and mechanical properties based on poly(l-lactic acid)/silica nanocomposites

Nano silica (SiO2) was introduced into Poly(L-lactic acid) (PLLA) matrix to prepare PLLA/SiO2 nanocomposites, and the crystal morphology, crystallization behavior and mechanical performance were investigated. The XRD experimental data indicated that nano SiO2 could improve the crystallization of PLLA, and PLLA/SiO2 nanocomposites exhibited sharp diffraction peak after isothermal crystallization. In addition, through the POM analysis, PLLA/SiO2 sample had the typical spherulite structure, and the size of the spherulite became larger with the increase of crystallization temperature. The tensile testing showed that a small amount of SiO2 could improve and retain the mechanical performance of PLLA

Large-sized La$lt;inf$gt;2$lt;/inf$gt;O$lt;inf$gt;3$lt;/inf$gt;-TiO$lt;inf$gt;2$lt;/inf$gt;-SiO$lt;inf$gt;2$lt;/inf$gt; Amorphous Oxide Fabricated by Hot Press Sintering

La2O3-TiO2 amorphous oxide has prospective applications because of its remarkable optical properties. However, due to its poor glass-forming abilities, it is difficult to prepare this material in a traditional way. The containerless solidification method can overcome this shortcoming, but the formed material size is generally restricted to be less than 10 mm. In order to obtain large-sized La2O3-TiO2 amorphous oxide, a small amount of SiO2 was added to the La2O3-TiO2 oxide system to form the amorphous oxide powders by aerodynamic levitation furnace. Subsequently, the high-density La2O3-TiO2-SiO2 materials were fabricated by vacuum hot press sintering. Compositions and microstructure properties were systematically studied by XRD and SEM. The results showed that SiO2 could improve the glass-forming ability of La2O3-TiO2. The raw powders made by aerodynamic levitation furnace were completely non-crystal, while the sintered samples had weak crystallization, which affected fully densification of sintered samples. There was a small amount of porosity in the high-density product made by vacuum hot press sintering. In addition, sintering densification mechanism of the La2O3-TiO2-SiO2 amorphous powders was analyzed. Finally, the optical property of hot pressed La2O3-TiO2-SiO2 material was investigated. It is found that La2O3-TiO2-SiO2 material still kepts high refractive index of above 2.2 in the visible light region. Small amount addition of SiO2 species improves the glass-forming abilities, yet decreases the refractive index slightly.

The structural studies of aluminosilicate gels and thin films synthesized by the sol-gel method using different Al2O3 and SiO2 precursors

AbstractAluminosilicate materials were obtained by sol-gel method, using different Al2O3 and SiO2 precursors in order to prepare sols based on water and organic solvents. As SiO2 precursors, Aerosil 200TM and tetraethoxysilane TEOS: Si(OC2H5)4 were applied, while DisperalTM and aluminium secondary butoxide ATSB: Al(OC4H9)3 were used for Al2O3 ones. Bulk samples were obtained by heating gels at 500 °C, 850 °C and at 1150 °C in air, while thin films were synthesized on carbon, steel and alundum (representing porous ceramics) substrates by the dip coating method. Thin films were annealed in air (steel and alundum) and in argon (carbon) at different temperatures, depending on the substrate type. The samples were synthesized as gels and coatings of the composition corresponding the that of 3Al2O3·2SiO2 mullite because of the specific valuable properties of this material. The structure of the annealed bulk samples and coatings was studied by FT-IR spectroscopy and XRD method (in standard and GID configurations). Additionally, the electron microscopy (SEM) together with EDS microanalysis were applied to describe the morphology and the chemical composition of thin films. The analysis of FT-IR spectra and X-ray diffraction patterns of bulk samples revealed the presence of γ-Al2O3 and δ-Al2O3 phases, together with the small amount of SiO2 in the particulate samples. This observation was confirmed by the bands due to vibrations of Al–O bonds occurring in γ-Al2O3 and δ-Al2O3 structures, in the range of 400 to 900 cm−1. The same phases (γ-Al2O3 and δ-Al2O) were observed in the deposited coatings, but the presence of particulate ones strongly depended on the type of Al2O3 and SiO2 precursor and on the heat treatment temperature. All thin films contained considerable amounts of amorphous phase.