Behavior Of SiO2 Research Articles

Behaviour of SiO2 during a new process applied to nickel concentrate from matte separation at Kola MMC

Kola MMC has built a new nickel site that relies on chlorine leaching of nickel powder followed by electrowinning of nickel with insoluble anodes. After the new site had been commissioned, the operations of the refining facility saw changes, the electric anode furnaces were taken out of service, and a magnetic separation section was commissioned. The latter helps remove unreacted coal, metal oxides and other non-magnetic components from the tube kiln nickel powder thus ensuring its optimized quality. At the same time, once the electric furnaces had been removed from the process, it created the need for strict control over carbon and slag-forming constituent concentration in the nickel powder that goes to the chlorine leaching section. This paper looks at the history of the process behind the production of roasted nickel – the product of fluidized-bed furnaces – and describes the revamping stages witnessed by the Kola MMC site. The paper also analyzes certain features related to the current processing of nickel concentrates – from nickel matte separation to the production of nickel metal powder. The latter is further sent for chlorine leaching and in the presence of chlorine gas it gets dissolved. Then copper, iron, zinc and cobalt are removed from the resultant liquor and the purified sulphate-chloride solution goes in the electrolysis cells where high-purity nickel cathodes are produced. The authors analyzed the compositions of the key components in the studied materials of the nickel processing line. Special attention is given to the behaviour of silicon dioxide as one of the impurities causing most problems in the new process.

In-situ polymerization of silica/polydicyclopentadiene nanocomposites: Improved tribological properties and evaluation of interfacial compatibility

ABSTRACTPolymer materials concluding polydicyclopentadiene (poly-DCPD) are widely used in engineering fields but have low load-carrying capacities which limit its widely application. SiO2/poly-DCPD nanocomposites were prepared by in situ polymerization in this work. polystyrene (PS), chemically modified onto the surface of SiO2 nanoparticles to obtain oil-soluble polystyrene coated silica spheres with core-shell structure (PS@SiO2), was used to improve the interfacial compatibility between SiO2 nanoparticles and poly-DCPD matrix. Field-emission scanning electron microscope (FESEM) was used to observe and evaluate the interfacial structure of SiO2/poly-DCPD nanocomposites. The tribological behaviors of SiO2 /poly-DCPD nanocomposites with different PS@SiO2 loading have been investigated detailly in this work. The results showed that the addition of PS@SiO2 nanospheres could greatly decrease friction coefficient and wear rate of the SiO2/poly-DCPD nanocomposites, especially when the loading of PS@SiO2 nanospheres arrived to 4 wt%. The well interfacial compatibility between the PS shell layer of PS@SiO2 spheres and poly-DCPD matrix should be resposible for the improved tribological properties of SiO2 /poly-DCPD nanocomposites.

Silica /polydicyclopentadiene nanocomposites: Preparation, characterization, and mechanical properties

ABSTRACTSilica/poly-dicyclopentadiene (SiO2/poly-DCPD) nanocomposites with improved mechanical properties were successfully prepared by in-situ ring-opening metathesis polymerization (ROMP) using reaction injecting molding (RIM) technique in this work. To improve the interfacial compatibility between SiO2 nanoparticles and poly-DCPD matrix, polystyrene (PS) was chemically modified onto the surface of SiO2 nanoparticles to obtain oil-soluble polystyrene coated silica spheres with core-shell structure (PS@SiO2). The mechanical behaviors of SiO2 /poly-DCPD nanocomposites with different PS@SiO2 content have been investigated in detail. The improved mechanical properties of SiO2 /poly-DCPD nanocomposites were mainly attributed to the well interfacial compatibility between the PS shell layer of PS@SiO2 spheres and poly-DCPD matrix, which resulted from the swelling of DCPD monomer in PS shell before polymerization.

Electrodeposition of Si in Molten LiF-NaF-KF Mixed with Various Sized SiO2 Particles

Si was electrodeposited potentiostatically on Ag substrates in molten LiF-NaF-KF mixed with various sized SiO2 particles at 873 K for 0.30-45 C cm-2. The electrodeposition mechanism of Si was focused on the addition of various sized SiO2 particles as starting materials: the average particles size of which were ca. 9.1 µm and ca. 0.80 µm. The cyclic voltammograms indicated that the dissolution rate or behavior of SiO2 in molten salt changed with the particles size of SiO2 powders. For using large sized SiO2 particles, growth process of dense c-Si film was observed, although the morphology of electrodeposited Si was rough for using small sized SiO2.

The influence of dopants and complexion transitions on grain boundary fracture in alumina

The fracture of micro-cantilever Al2O3 specimens containing single grain boundaries is quantified via in situ bending experiments performed in the transmission electron microscope. The type of grain boundary complexion plays a dominant role in determining the fracture response, while the dopant chemistry has a secondary effect for the same complexion type. More ‘ordered’ complexions, those containing sub-monolayer adsorbates, are tougher than the undoped material. The behaviors of SiO2 and Y2O3 doped Al2O3 with different complexions are compared and contrasted. In general, grain boundaries exhibiting more ‘disordered’ complexions types, those with multilayer adsorbates, are embrittled relative to undoped Al2O3.

Effect of Ultra-Fine SiO2 and Metakaolin on High Strength Concrete in Aggressive Environment

The behavior of SiO2 and metakaolin in aggressive environment when used separately as a supplementary cementitious material was studied for three different replacement levels: 5%, 10% and 15%. SiO2 and metakaolin were used in two states namely unground and ground (ultra-fine). Ultra-fine state was achieved by subjecting the mineral admixtures to grinding in a planetary ball mill for an optimum period of one hour. The microstructure of the unground and ground mineral admixtures was studied using Scanning Electron Microscope and X-Ray Diffraction. The compressive strength of these systems in normal and aggressive environment was tested after initial curing in water for a month and subsequent curing in acid or base environment for a period of three months to arrive the rate of deterioration. The rate of corrosion in rebars was also determined using Half-cell potential method. The results obtained from the tests were compared with control concrete. From the results it was understood that concrete with 10% ground SiO2 and 5% ground metakaolin provided better resistance to deterioration and corrosion. It also exhibited improved microstructure as well as filler action. Comparing the results of two admixtures, performance of concrete with ground metakaolin found to be better than ground SiO2

Phase Relations in Si-Al-Y-O-C Systems

The present work investigated the phase relations in SiC-Al2O3-Y2O3-SiO2 (Si-Al-Y-O-C) system. As a continuation of our previous works, the purpose of this study is to understand the high temperature reaction behaviors of SiO2 in the system and its effect on the phase relations of the valuable system of SiC-Al2O3-Y2O3. The phase compositions of six solid-state reacted samples with different components of Y2O3:Al2O3:SiC:SiO2 were analyzed by XRD. The phase relations of the systems were determined. The subsolidus phase diagrams of ternary Al2O3-SiC-SiO2 system and the tentative phase diagram of an extended quaternary Y2O3-Al2O3-SiC-SiO2 system were presented latter involving several coexisting regions of four phases. The high temperature reaction behavior of SiO2 in the system and its effect on the phase relations of system were discussed.

Influence of SiO<sub>2</sub> Nanoparticle Codeposition on Homogeneity of Zinc-Nickel Alloy Plating from an Acid Sulphate Bath

Zinc-nickel-SiO2 electrodeposits have been produced from an acid sulphate bath. Thecodeposition behavior of SiO2 and the homogeneity of platings were examined. The presence ofSiO2 nanoparticles in the plating bath appears to change the alloy deposition behavior. Rate ofnickel deposition was considerably decreased with SiO2 nanoparticles in the bath. The homogeneityof platings between zinc and nickel were improved by adding the SiO2 nanoparticles in the bath. Atan early stage of electrodeposition, it seems that the SiO2 nanoparticle acts as a nucleus of theprecipitation. The SiO2 nanoparticle has not uniformly dispersed in a plating film, but distributedonly in the SiO2 rich layer with about 50 nm in thickness formed beneath the surface. In addition,this SiO2 rich layer can improve the anticorrosive performance. Therefore, the zincic use can besuppressed, because film thickness can be more thinned, compared with zinc and zinc-nickel alloyelectroplating.

A model for estimating agglomerate sizes of non-magnetic nanoparticles in magnetic fluidized beds

The behavior of SiO2, TiO2 and ZnO non-magnetic nanoparticles and the effects of processing parameters on agglomerate sizes were investigated systematically in a magnetic fluidized bed (MFB) by adding coarse magnets. A mathematical model is developed based on energy balance among the agglomerate collision energy, magnetic energy, energy generated by turbulent shear and cohesive energy to predict the agglomerate sizes. The results showed that slugging of the bed disappeared and the measured agglomerate sizes decreased, so that the fluidization quality of non-magnetic nanoparticles was significantly improved by adding coarse magnets due to introduction of magnetic field. The average agglomerate sizes predicted by this model are in agreement with the experimental data.

Interfacial Synthesis of SiO<sub>2</sub> Doped by Polyaniline and its Electrorheological Behavior

SiO2 doped by polyaniline for application in electrorheological (ER) fluid was prepared by using a simple one-pot interfacial synthesis method. Scanning electron microscopy (SEM) image shows that the morphologies of SiO2 may be changed from spherical to fibroid structure by changing the molar ratio of tetraethyl orthosilicate(TEOS) and aniline. X-ray diffraction (XRD) proves that polyaniline does not change the crystallinity of SiO2. The ER behaviors of SiO2 doped by polyaniline in silicone oil are investigated with different doping degrees under different shear rate, and the results show that properly doping polyaniline improves electrorheological behavior of SiO2.

Deformation Behavior of SiO<sub>2</sub> Doped Nanocrystalline Monoclinic Zirconia at Low Temperatures

The deformation behavior of SiO2 doped nanocrystalline monoclinic zirconia (MZP) was studied at 1323-1223 K in compression tests. The strain rate of SiO2 doped nanocrystalline MZP was slower than that of high-purity MZP by one order of magnitude. SiO2 doped nanocrystalline MZP exhibited a stress exponent n ≈ 2. The apparent activation energy for the deformation of SiO2 doped nanocrystalline MZP was characterized by a higher value than that observed for high-purity MZP. 1wt% SiO2 doped nanocrystalline MZP was deformed at constant flow stress, while the flow stress of high-purity MZP increased significantly with the strain (strain hardening). While no grain growth was observed after the compressive deformation of 1wt % SiO2 doped nanocrystalline MZP, remarkable grain growth was observed after the deformation of high-purity MZP. The addition of SiO2 into nanocrystalline MZP is effective in limiting grain growth at low temperatures

High-Temperature Behavior of SiO2 at Grain Boundaries in TZP

The chemical reaction between SiO2 and tetragonal zirconia polycrystal (TZP) was directly observed using a TEM in-situ heating technique in order to understand the behavior of SiO2 in TZP at high temperatures. Their dynamic interaction was recorded up to about 1400°C using a CCD camera-video system connected to the TEM. Most of SiO2 phase dissolved into the ZrO2 grains above 1300°C. On the other hand, during cooling from the high temperature to around 400°C, amorphous SiO2 reprecipitated from the surface of ZrO2 grains and formed a thin layer around the ZrO2 grains. This result agrees well with the fact that silicon segregates in the vicinity of grain boundaries in SiO2-doped TZP. In order to confirm the grain boundary segregation at high temperatures, we investigated grain boundaries in quenched specimens by high resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS). It was found that no amorphous phase was present between two adjacent grains in the quenched samples. EDS analysis revealed that silicon segregated at the grain boundaries and that the segregation layer was wider than that in as-sintered specimens. The electron energy loss near edge structure (ELNES) of O K-edge was measured from both grain boundary and grain interior in quenched specimen, and their spectra were interpreted by a first principles molecular-orbital (MO) calculation using the discrete-variational (DV)-Xα method.

Carbon deposition in methane reforming with carbon dioxide

Coke formation in the dry reforming of methane was studied using a thermobalance (TG) and with a catalytic microreactor in the temperature range 800–950 K. Silica-supported and lanthana-supported nickel catalysts were examined. The effects of process variables such as temperature and gas composition (He dilution, CH4/CO2 ratio) on the coke formation rate were determined. The reactivity of H2 on several kinds of carbon was also investigated. The morphology of the coke was studied by scanning electron microscopy (SEM). The induction times for coke formation were significantly affected by temperature and by the CO content in the feed gas. The results of catalytic tests were consistent with the TG measurements. The behaviour of SiO2 and La2O3 supported Ni catalysts agree with a mechanism in which the lanthana support plays an important role in the carbon deposition.

Chemical vapour deposition (CVD) of borophosphosilicate glass films

Chemical vapour deposition (CVD) has become the standard method for the fabrication of microelectronic devices for use in the semiconductor industry. In this investigation, it has been used to grow films of silicon dioxide (SiO2) and borophosphosilicate glass (BPSG) at both atmospheric and low pressures under various conditions. The growth behaviour of SiO2 and BPSG films has been investigated as a function of the O2/SiH4 ratio. Both processes give a similar trend, with the growth rates of BPSG being somewhat higher than SiO2. The variation in the growth rate with O2/SiH4 ratio has been explained in terms of relative transport and kinetic reaction rates. The effects of temperature on the deposition rate have also been studied and the activation energy calculated showed two distinct regions corresponding to mass transport control and kinetic control regimes. Both BPSG and SiO2 have been annealed under various furnacing conditions. It has been shown that the addition of boron and phosphorous results in much lower reflow temperatures and times. This has a significant bearing on the performance characteristics of devices. Initial results from rapid thermal annealing (RTA) work are also presented, and RTA is shown to be a viable annealing process.

Application of TMA and DTA for study of the crystallization behaviour of SiO2 in the thermal transformation of kaolinite

TMA/DTMA with DTA studies on the thermal changes of kaolinite were performed with special emphasis on the crystallization behaviour of amorphous SiO2. The results of four different physical techniques (semiquantitative XRD, DTA, TMA and DTMA) were clearly in good agreement with the fact that the 1420°C exotherm in DTA is due to silica crystallization.

Oxygen isotopes in mantle related and geothermally altered magmatites of the Transhimalayan (Gangdese) ranges

In closed magma systems SiO2 approximately measures differentiation progress and oxygen isotopes can seem to obey Rayleigh fractionation only as a consequence of the behaviour of SiO2. The main role of δ18O is as a sensitive indicator of contamination, either at the start of differentiation (δ18Oinit) or as a proportion of fractionation in AFC. Plots of δ18O vs SiO2-allow to determine initial δ18O values for different sequences for source comparison. For NBS-28=9.60, the δ18O at 48% SiO2-varies between a high 6.4‰ for Kiglapait (Kalamarides 1984), 5.9‰ for Transhimalaya, 5.8‰ for Hachijo-Jima (Matsuhisa 1979), 5.6‰ for Koloula (Chivas et al. 1982) and a low 5.3‰ for the Darran Complex, New Zealand. The Transhimalayan batholiths (Gangdese belt) were emplaced in the ‘Ladakh-Lhasa terrane’, between the present-day Banggong-Nujiang, and Indus-Yarlung Tsangbo suture zones, after its accretion to Eurasia. The gradient of the least contaminated continuous (δ18O vs SiO2-igneous trend line is similar to that of Koloula, and AFC calculations suggest a low secondary assimilation rate of less than 0.05 times the rate of crystallisation. Outliers enriched in 18O are frequent in the Lhasa, and apparently rare in the Ladakh transsect. Low-δ18O (5.0‰−0‰) granitoids and andesites on the Lhasa-Yangbajain axis are the result of present day or recent near-surface geothermal activity; their quartzes still trace the granitoids to the Transhimalaya δ18O trend line, but the distribution of low total rock or feldspar δ18O values could be a guide to more recent heat flow and thermally marked tectonic lineaments. Two ignimbrites from Maqiang show hardly any 18O-contamination by crustal material.