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Cristobalite is a low-pressure, high-temperature SiO2 polymorph that occurs as a metastable phase in many geologic settings, including as crystals deposited from vapor within the pores of volcanic rocks. Such vapor-phase cristobalite (VPC) has been inferred to result from silica redistribution by acidic volcanic gases but a precise mechanism for its formation has not been established. We address this by investigating the composition and structure of VPC deposited on plagioclase substrates within a rhyolite lava flow, at the micrometer to nanometer scale. The VPC contains impurities of the form [AlO4/Na+]0-coupled substitution of Al3+ charge-balanced by interstitial Na+-which are typical of cristobalite. However, new electron probe microanalysis (EPMA) element maps show individual crystals to have impurity concentrations that systematically decline from crystal cores-to-rims, and atom probe tomography reveals localized segregation of impurities to dislocations. Impurity concentrations are inversely correlated with degrees of crystallinity [observed by electron backscatter diffraction (EBSD), hyperspectral cathodoluminescence, laser Raman, and transmission electron microscopy (TEM)], such that crystal cores are poorly crystalline and rims are highly ordered tetragonal α-cristobalite. The VPC-plagioclase interfaces show evidence that dissolution-reprecipitation reactions between acidic gases and plagioclase crystals yield precursory amorphous SiO2 coatings that are suitable substrates for initial deposition of impure cristobalite. Successive layers of cubic β-cristobalite are deposited with impurity concentrations that decline as Al-bearing gases rapidly become unstable in the vapor cooling within pores. Final cooling to ambient temperature causes a displacive transformation from β→α cristobalite, but with locally expanded unit cells where impurities are abundant. We interpret this mechanism of VPC deposition to be a natural proxy for dopant-modulated Chemical Vapor Deposition, where halogen-rich acidic gases uptake silica, react with plagioclase surfaces to form suitable substrates and then deposit SiO2 as impure cristobalite. Our results have implications for volcanic hazards, as it has been established that the toxicity of crystalline silica is positively correlated with its purity. Furthermore, we note that VPC commonly goes unreported, but has been observed in silicic lavas of virtually all compositions and eruptive settings. We therefore suggest that despite being metastable at Earth's surface, cristobalite may be the most widely occurring SiO2 polymorph in extrusive volcanic rocks and a useful indicator of gas-solid reaction having occurred in cooling magma bodies.

The current study presents an original chemical, elemental and mineralogical characterization of new quartz mineral deposits situated in Ios island, Cyclades, Aegean sea, Greece, via X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) trace-element analysis. Actually, the mineral Quartz (crystalline SiO2) is found in nature in varying quality and is explored and traded for use in different applications of significant importance depending on the quartz purity. The results of the thorough chemical and mineralogical analysis indicate that quartz originating from the location examined in this research is almost free from other microcrystalline phases, and therefore it can be characterized as highly pure α-quartz. Thus, it can be used in the industry of ultra-high purity quartz production for specific applications, as long as the deposits are exploitable. In this framework, a preliminary estimation of the economic benefits from a potential exploration versus the environmental aspects of mining, taking into account sustainability issues in the region, is provided highlighting the local social needs

The study was conducted to determine the mineral composition and relative distribution of light and heavy sand minerals and the effect of weathering processes on their presence and distribution within the horizons of some soils from the Middle Euphrates regions. Four sites were selected from the Middle Euphrates regions, including the Tuwairij area in Karbala Governorate, the College of Agriculture at the University of Kufa in Najaf Governorate, the College of Agriculture at the University of Al-Qadisiyah in Diwaniyah Governorate, and the Nile District in Babylon Governorate. The results showed clear differences in the proportions of light and heavy minerals between the governorates, reflecting the variation in the geological and environmental characteristics of these regions. The study found that the proportions of heavy minerals were much lower than light minerals in the sand section and for all study soils, reflecting the influence of various factors such as weathering, transportation and sedimentation. Quartz (SiO2) was dominant in all soil samples, and two types of single-crystalline and polycrystalline quartz were identified in soil samples. Feldspar came in second place after quartz in the mineral composition of sand, and orthoclase and microcline were identified in soil samples, with heterogeneous distribution appearing in all soil horizons. The results also showed the relative variation between potassium and plagioclase feldspar between different regions, which reflected the influence of the local geological environment. The proportions of polycrystalline quartz were lower than single-crystalline quartz. The light minerals identified in the study samples included a group of minerals, and according to their dominance, they included (carbonate rocks, flint, clay rocks, evaporites, in addition to igneous and metamorphic rocks, clay-covered particles, and other minerals). (The results also showed through studying the weathering index of light minerals (Wrl) and despite the presence of variation and heterogeneity in its values, they were low, which indicated that these soils were not exposed to severe weathering, and therefore are considered to be of recent formation.

In this work, we investigate the electrical properties of a metal–insulator–semiconductor (MIS) heterojunction based on porous silicon dioxide (Ag/pSiO2/Si). The porous silicon (PS) films were elaborated by electrochemical anodization under specific experimental conditions to obtain a porosity of about 55%. Porous silicon (PS) was oxidized by IR-RTP at different oxidation temperatures (Tox) ranging from 200 to 950 °C under an oxygen atmosphere. The morphology of the samples was analyzed using a scanning electron microscope (SEM). Ag/Al and Ag contacts were screen printed on the back and front sides of the heterojunction, respectively. Both the series and shunt resistances were derived from dark current–voltage (I–V) characteristics related to the various Ag/pSiO2/Si heterojunctions. In this context, the reflectance was also measured at different oxidation temperatures to investigate its correlation with the series resistance (Rs) and shunt resistance (Rsh). The optimum electrical performance was obtained for an oxidation temperature close to 400 °C. Depending on the pSiO2 thickness, two conduction mechanisms were highlighted within the devices. For a Tox below 200 °C, as well as for the non-oxidized devices, the conduction mechanism is governed by the tunneling current through the pSiO2 film. However, when the Tox increases and exceeds 200 °C, the pSiO2 thickness increases, leading to the switching of the conduction mechanism to a thermionic instead of a tunneling effect mechanism.

As major waste materials in the rice milling industry, rice husks (RHs) have potential industrial applications. In this work, acid solutions were used to extract high-value-added polysaccharide components (hemicellulose and cellulose) from RHs to obtain sugar residues (SRs) for comprehensive utilization. The SRs were converted into C/SiO 2 composites after carbonization and ball-milling. The C/SiO 2 composites with crystalline cellulose content in the precursor possessed desirable electrochemical properties when tested as an anode material for lithium-ion batteries (LIBs), including cycle performance, initial Coulombic efficiency (ICE) and electrical impedance. Meanwhile, a high reversible specific capacity of 553 mAh g −1 was maintained after 100 cycles at a current density of 0.1 A g −1 . This method can be used to turn biomass into a potentially valuable anode material with desirable electrochemical properties for LIBs.

Biosilica obtained from frustules of diatoms have very delicate nanostructures similar to many micro- and nanofluidic devices. In the present investigation, a cheaper and ecofriendly metal-oxide-semiconductor (MOS) tool has been fabricated exploiting frustules of the diatom Halamphora subturgida. The structural, optical, and chemical characterizations of the cleaned frustules of cultured diatom were investigated through various techniques. Electron microscopic images revealed intricate morphology of the nanostructured silica with very minute pores making the frustules very hard but light material. UV-Vis spectroscopy showed maximum absorbance at 223 nm. The absorption maximum for photoluminescence was centered at 462 nm and that of cathodoluminescence was at 439.9 nm and 466.6 nm. Bulk of extracted silicon dioxide (SiO2) nano-powder from diatom frustules was used as a source material for preparing a high-quality crystalline film on P-type silicon (p-Si) by vapor-liquid-solid (VLS) method. The crystalline quality of the film was tested by X-ray diffraction (XRD) and the crystalline size obtained was 62 ± 2.4 nm. From scanning electron microscopic (SEM) investigation, the growth of a continuous film from diatom biosilica on p-Si substrate was revealed. The thickness of the as-grown SiO2 film was 22.2 ± 1.6 nm, obtained from spectroscopic ellipsometry (SE) study. The performances of fabricated Al/SiO2/Si metal-oxide-semiconductor capacitor were tested by measuring leakage current (~ 43 ± 8 × 10−11 A μm−2 at +2 V), capacitance-voltage, constant current (0.1 μA), and voltage stress (at − 2 V) for reliable gate dielectrics applications in MOS devices. Overall, the process was cost-effective and provides an alternative technique to design high-quality diatom-derived “Bio-SiO2 films” on p-Si substrate.

This article reports the results synthesis of crystalline (Fe3O4@c-SiO2) and amorphous (Fe3O4@a-SiO2) nanoparticles from natural resources (iron sand and silica sand). The synthesis of Fe3O4 and SiO2 nanoparticles used co-precipitation and hydrothermal-coprecipitation methods with polyethylene glycol (PEG) 4000 as a template. The XRD data analysis presented that the amorphous SiO2 particles were successfully produced using hydrothermal and co-precipitation methods. The XRD data analysis also presented that the crystalline phases were formed in quartz and tridymite phases after calcination process of the amorphous phase. SEM images exhibited that the amorphous phase had different particle size and morphology from the crystalline phase. FTIR spectra presented some absorption peaks of new functional groups indicating the existence of Si-O-Si (silanol), Fe-O, C-N, and Fe-O-Si as new functional groups.

Microcrystalline cellulose/nano-SiO 2 composite films have been successfully prepared from solutions in ionic liquid 1-allyl-3-methylimidazolium chloride by a facile and economic method. The microstructure and properties were investigated by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, water contact angle, thermal gravimetric analyses, and tensile testing. The results revealed that the well-dispersed nanoparticles exhibit strong interfacial interactions with cellulose matrix. The thermal stability and tensile strength of the cellulose nanocomposite films were significantly improved over those of pure regenerated cellulose film. Furthermore, the cellulose nanocomposite films exhibited better hydrophobicity and a lower degree of swelling than pure cellulose. This method is believed to have potential application in the field of fabricating cellulose-based nanocomposite film with high performance, thus enlarging the scope of commercial application of cellulose-based materials.

In this work we show the influence of material preparation technology on the thermoluminescent properties of single crystalline films (SCFs) of Ce3+-doped Lu2SiO5 (LSO) and Y2SiO5 (YSO) orthosilicates. LSO:Ce and YSO:Ce SCFs were grown by the liquid phase epitaxy method from two different melt-solutions based on PbO-B2O3 and Bi2O3 fluxes. Absorption, cathodoluminescence, and thermoluminescent properties of LSO:Ce and YSO:Ce SCFs grown from the two previously mentioned types of fluxes were compared, and results of spectrally resolved thermoluminescence measurements and thermoluminescent glow curves of SCFs recorded in different spectral ranges were presented. We have found that the observed differences in thermoluminescent properties of the SCFs under study can be caused by the domination of Ce4+ and Pb2+ emission centers in LSO:Ce and YSO:Ce SCFs grown using PbO-B2O3 flux, and Ce3+ and Bi3+ emission centers in the SCFs grown from Bi2O3 flux.

In this paper, we investigated the microstructure and electrical properties of Bi 2 SiO 5 (BSO) doped SrBi 2 Ta 2 O 9 (SBT) films deposited by chemical solution deposition. X-ray diffraction observation indicated that the crystalline structures of all the BSO-doped SBT films are nearly the same as those of a pure SBT film. Through BSO doping, the 2Pr and 2Ec values of SBT films were changed from 15.3  μ C/cm 2 and 138 kV/cm of pure SBT to 1.45  μ C/cm 2 and 74 kV/cm of 10 wt.% BSO-doped SBT. The dielectric constant at 1 MHz for SBT varied from 199 of pure SBT to 96 of 10 wt.% BSO-doped SBT. The doped SBT films exhibited higher leakage current than that of non-doped SBT films. Nevertheless, all the doped SBT films still had small dielectric loss and low leakage current. Our present work will provide useful insights into the BSO doping effects to the SBT films, and it will be helpful for the material design in the future nonvolatile ferroelectric memories.