Papers by Keyword: Amorphous Silica

Abstract: Scale deposits in geothermal power plants are well-known potential sources of minerals. Extensive research in mineral recovery is crucial due to the considerable variability in scale composition and geochemistry based on location. Geothermal scales from Batangas, Philippines, were used to synthesize size-modified amorphous silica (SiO₂) via sol-gel method. Initial analyses employing x-ray fluorescence spectroscopy (XRF), total dissolved solids (TDS), electrical conductivity (EC), and pH measurements confirmed that the scale is rich in silica and salts at neutral pH. Then, the effect of varying scale concentration, precipitation pH, and aging time on the particle size distribution of recovered amorphous silica were investigated. Dynamic light scattering (DLS) for particle size analysis (PSA) revealed that the sample with 2.5% (w/v) scale precursor in NaOH and precipitated until pH 10 had the lowest average cumulant diameter (1.66 μm). Moreover, the synergy of precipitation pH and aging time was found to significantly affect the polydispersity index and cumulative diameter of precipitated SiO₂ based on 2³ factorial ANOVA at 0.05 significance level. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed that the precipitates were amorphous SiO₂ with spherical morphology. This study proves the viability of utilizing geothermal scales from Batangas, Philippines for the synthesis of amorphous SiO₂ with controlled particle size, which is a potential filler for composite materials.

Abstract: Herein, silica nanoparticles (SiO₂ NPs) were synthesized from a waste product of the zirconium carbide facility (WPZF). Firstly, the WPZF was characterized by using physical and chemical methods like X-ray powder diffraction (XRD), field emission scanning electron microscope (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), and energy dispersive X-ray analysis (EDXA) methods. Then WPZF proceeded via chemical reagents to synthesize SiO₂ NPs by using the sol-gel method. Obtained SiO₂ NPs were characterized by using XRD, SEM, EDXA, and transmission electron microscopy (TEM) methods. The yield of SiO₂ NPs reached up to 96.5% and particles were spherical with a diameter of 20 ± 3 nm. Most importantly observed SiO₂ NPs in this procedure has an amorphous structure.

Abstract: Silica is one of the most important materials used in many industries. The basic factor on which the selection process depends is the structural form, which is dependent on the various physical and chemical properties. One of the common methods in preparing pure silica is that it needs more than one stage to ensure the preparation process completion. The goal of this research is studying the nucleation technique (Bottom-top) for micro-wires and micro-ribbons silica synthesis. The silica nanoand microstructures are prepared using a duality (one step); a combination of alkali chemical etching process {potassium hydroxide (3 wt %) and n-propanol (30 Vol %)} and the ultra-sonication technique. In addition, the used materials in the preparation process are environmentally friendly materials that produce no harmful residues. The powder product is characterized using XRD, FTIR, Raman spectrum and SEM for determining the shape of architectures. The most significant factor of the nucleation mechanism is the sonication time of silica powder production during the dual technique. The product stages are as follows; silica nanoparticles (21-38 nm), nanoclusters silica (46 – 67 nm), micro-wires silica (1.17 – 6.29 μm), and micro-ribbons silica (19.4 – 54.1 μm). It's allowing for use in environmental applications (multiple wastewater purification, multiple uses in air filters, as well as many industrial applications).

Abstract: The article presents a method to obtain silica xerogels with developed specific surface based on nepheline concentrate acid decomposition in C₂H₅OH-H₂SO₄ system. It was found that the use of ethanol instead of water produces stable and steady silica gels. It is proved that the use of ethanol results in almost complete deposition of soda alum and aluminum potassium sulphate out of nepheline decomposition solution without its additional cooling, due to their extremely low solubility in alcohol solution. The morphology, structural and surface properties of synthesized xerogel sample with ~600 m²/g specific surface area (based on the analysis) were investigated; its mixed micro-and mesoporous structure was established. Electron probe microanalysis showed chemical purity of the resulting SiO₂.

Abstract: We chose two glass compositions suitable for the synthesis of foam glass. The influence of additive at the amorphous silica charge in the amount of 20% and 100%, a by-product in the leaching of serpentinite, was studied. By the method of stable temperature drop, the crystallization ability of the welded glass compositions was studied. The surface tension was measured by the sessile drop method.

Abstract: The synthesis of silica particles at the nanoscale through the sol-gel method is of great interest due to their potential use in industrial applications. The Stöber method is the most used method for the silica nanoparticles production using ammonia as a catalyst. This work studied the sol-gel synthesis of amorphous silica nanoparticles described by Stöber, in order to evaluate the influence of the variation of the process parameters (molar ratio water/TEOS = 25 and 55, reagent feed rate = 0.6 mL/min and 18 mL/min, pH = 12 and 9 and reaction time of 0, 5, 30, 60 and 120 minutes) on the particle size distribution and structural functional groups. The particle size distribution was analyzed by dynamic light scattering (DLS) and the structural functional groups was analyzed by infrared spectroscopy through Fourier transform (FTIR). The molar ratio water/TEOS influenced the functional groups presents and the time influenced the particle diameter distribution. It was not possible to identify the influence of the feed rate and pH in the results. The particle diameters found were between 200-500nm. This result may be occurred due to mass diffusion and/or nanoparticles aggregation.

Abstract: The structural, electronic, and optical properties of an amorphous SiO₂ (a-SiO₂) model is investigated by using first-principles calculation. Most research works used beta-cristobalite glass structure as a reference to amorphous silica structure. However, only the electronic properties were been presented without any link towards the optical properties. Here, we demonstrate simultaneous electronic and optical properties, which closely matched to a-SiO₂ properties by generating small sample of amorphous quartz glass. Using the Rietveld refinement, amorphous silica structure was generated and optimized using density functional theory in CASTEP computer code. A thorough analysis of the amorphous quartz structure obtained from different thermal treatment was carried out. The structure of amorphous silica was validated with previous theoretical and experimental works. It is shown that small sample of amorphous silica have similar structural, electronic and optical properties with a larger sample. The calculated optical and electronic properties from the a-SiO₂ glass match closely to previous theoretical and experimental data from others. The a-SiO₂ band gap of 5.853 eV is found to be smaller than the experimental value of ~9 eV. This is due to the underestimation and assumption made in DFT. However, the band gap value is in good agreement with the other theoretical works. Apart from the absorption edge at around 6.5 eV, the refractive index is 1.5 at 0eV. Therefore, this atomic structure can served as a reference model for future research works on amorphous structures.

Abstract: A model of undefected and defected amorphous SiO₂ has been constructed from Rietveld Refinement to investigate the effect of defect structure to its properties. Atomic level study for both structure were carried out using plane-wave pseudo potential by density functional theory. A new electrons trapping energy level appears within the 5.853eV band gap of a-SiO₂ for oxygen-excess defected structure. This defect energy level reduces as more number of excess oxygen atoms was added to the structure of a-SiO₂. A spectral emission at 388nm from SiO₂ glass excited with 350nm (200mW) laser demonstrates the existence of the defective states in the structure in trapping electron at 3.273eV energy level.

Abstract: The frustules of diatoms have excellent elasticity and high strength, but their main composition, amorphous silica, is a kind of typical brittle material. Molecular dynamics simulations of the uniaxial tension were carried out to study the size effect on the mechanical properties of amorphous silica. Stress-strain behavior, the radius of biggest void, radial distribution functions and bond angle distribution were analyzed. Our results show the small model exhibits a better ultimate strength, ductility and toughness than the large model, and the generation and expansion of voids plays an important role in the fracture behavior of the model. For the small model, some of Si-O bonds are stretched, and the average of O-Si-O bond angle decreases from 108o to 95o, which makes the model have a capability to perform larger plastic deformation and lead to a better ductility. However, for the large model, except the change of Si-O-Si bond angle, its structure has no other significant changes. Our results demonstrate that changes of size have significant impact on the mechanical properties and deformation mechanism of intrinsically brittle materials at the nanoscale.

Abstract: This paper presents the synthesis of silica (SiO₂) from rice husk at different firing temperatures. Due to the environmental awareness and to reduce air pollution, agricultural wastes specifically rice husk is used to produce SiO₂. Silica was prepared by washing with clean water without any chemical treatment. The rice husk was fired at 700, 800, 900, 1000, 1100 and 1200°C. In order to determine the effect of firing rice husk at different temperature, X-ray Diffraction (XRD) analyses were conducted. Crystalline silica were obtained at 1100°C and 1200°C firing temperature. At 900°C and 1000°C firing temperature, silica was observed to be in a transitional phase of amorphous into crystalline or it called as semi crystalline. However, at 700°C and 800°C silica remains to be in amorphous phases.