Silica Content Research Articles

Knowledge, attitudes and practices regarding respirable silica exposure and personal protective equipment use among brick kiln workers in Nepal

ObjectivesBrick kiln workers in Nepal are a neglected population who are exposed to high respirable silica concentrations, and few use interventions to reduce exposure. We aimed to characterise the prevalence...

Towards an understanding of the correlation between the physicochemical and thermal properties of ground rice husks and particle size

The comminution of rice husk has been commonly used to convert it into biogenic silica, bio-oil, biogas, and bioenergy. The composition and structure of biomass are anisotropic, e.g., the surface of the rice husk has a higher silica content than the bulk. It is possible to expect that the physicochemical properties of grinding and sieving rice husks will be distinct due to the difference between the mechanical properties of inorganic and organic matter. A sample of rice husk was ground in a pin mill and sieved. The anisotropic distribution of the inorganic matter was measured on the cross-section of rice husk by SEM-EDX. The chemical composition and textural properties of the rice husk ash were determined by X-ray fluorescence and nitrogen adsorption of each granulometric fraction. Thermochemical, proximate, and ultimate properties of non-calcined grinding rice husks were measured through thermal analysis. Pin, hammer, and knife mills were used to process the rice husks and to determine the effect of the mill type on the comminution operation. Silica is anisotropically distributed in the rice husk but mainly concentrates on the surface. So, The granulometric fractions have very different physicochemical and thermal properties; those with smaller diameters have a higher inorganic matter content; specifically, the pan fraction presents twice the ash content as the non-grinded rice husk. Interestingly, through multivariate analysis, it is possible to classify the fractions into homogeneous groups according to their physicochemical properties for use in technological applications such as pellet fabrication.

Electric recycling of Portland cement at scale

Cement production causes 7.5% of global anthropogenic CO2 emissions, arising from limestone decarbonation and fossil-fuel combustion1–3. Current decarbonation strategies include substituting Portland clinker with supplementary materials, but these mainly arise in emitting processes, developing alternative binders but none yet promises scale, or adopting carbon capture and storage that still releases some emissions4–8. However, used cement is potentially an abundant, decarbonated feedstock. Here we show that recovered cement paste can be reclinkered if used as a partial substitute for the lime–dolomite flux used in steel recycling nowadays. The resulting slag can meet existing specifications for Portland clinker and can be blended effectively with calcined clay and limestone. The process is sensitive to the silica content of the recovered cement paste, and silica and alumina that may come from the scrap, but this can be adjusted easily. We show that the proposed process may be economically competitive, and if powered by emissions-free electricity, can lead to zero emissions cement while also reducing the emissions of steel recycling by reducing lime flux requirements. The global supply of scrap steel for recycling may treble by 2050, and it is likely that more slag can be made per unit of steel recycled. With material efficiency in construction9,10, future global cement requirements could be met by this route.

Edaphological Description of the Type Habitat of Coptis' Teeta Wall. - an Endangered Species of Medicinal Importance in Arunachal Pradesh

The edaphic conditions of the habitat of Coptis tetla Wall. have been discussed. The soils, where this species grows either under cultivation or in wild are moderately acidic to highly acidic, poor in surface porosity, very rich in silica content and possess insufficient amount of inorganic binding agents. However, the soils in cultivated fields are satisfactory in organic carbon status, water-holding ability and cation exchange capacity but inadequate presence of liming material and temperate climate adversely effect their energy materials. The 3oils at Malenja where this species is growing wild have textural limitation and anthropogenic interference. In the end the paper is concluded with suggestions. Results depict that the reasons for rarity and depletion of this species are not only anthropogenic but also environmental.

Improving the mechanical and abrasion properties of silica-reinforced styrene-butadiene rubber composites by optimizing the concentrations of compatibilizers

Silica (chemical formula SiO2) is a promising, more environmentally friendly alternative to carbon black (CB) used in the rubber industry as a filler. Although silica is already used in rubber products, it is not used as extensively as CB because the polar surface of silica cannot interact well with the apolar polymer molecules of the most frequently used rubbers. To solve this problem, experts have tried different grafting methods and several coupling agents for a stronger silica-elastomer connection. In this article, we used bis[3-(triethoxysilyl)propyl] tetrasulfide (TESPT) and polyethylene glycol (PEG) combined to improve the connection between the surface of silica and the apolar styrene-butadiene rubber (SBR) matrix. We examined mechanical and structural properties and found that adding 3 phr PEG and 4.5 phr TESPT to SBR is optimal for 60 phr silica content. This ratio of additives resulted in a 48% improvement in tensile strength. The positive effect of the coupling agents shows up in abrasion mass loss and tear strength as well.

Zeolite Synthesis Based Silica from Saccharum officinarum L. with Black Stem Using the Hydrothermal Method

Saccharum officinarum L. has a high amount of silica content, which can be used as the main component of zeolite synthesis. Silica was isolated from Saccharum officinarum L. bagasse with NaOH and HCl. This research aims to synthesize zeolite using silica from Saccharum officinarum L. with black stem and alumina from aluminium foil. The Saccharum officinarum L. used in this research was sourced from Lombok Island, West Nusa Tenggara Province, Indonesia. Silica was sourced from Saccharum officinarum L. using the sol-gel method. The silica from the isolation of dregs ash obtained 20 g of silica with a high percentage (yield) of 50%. This study found that 5.29 g of aluminium foil produced 14.29 g of alumina with the addition of 22.50 g of Na2CO3. The zeolite obtained was 3.88 g with a SiO2:Al2O3 ratio of 5:3. From this study, the percent (%) of obtained zeolite was 48.5% from the weight of the silica and alumina produced. The zeolite results synthesized from Saccharum officinarum L. ash were characterized using FTIR. Based on the FTIR results, absorption was found at wave numbers (cm-1) 960, 729, and 668. The zeolite obtained was pure white and had a FTIR spectrum similar to that of Zeolite X from previous research. It can be predicted that the zeolite obtained from this research has been formed. This research is expected to be useful in increasing the effectiveness of the silica extraction process from Saccharum officinarum L. with black stem. Further analysis using XRD and SEM is needed to determine the characteristics of the zeolite produced.

Novel treatment method of coal bottom ash for strain-hardening alkali-activated composite

This study explored the viability of using coal bottom ash (CBA), treated as a silicate source for preparing activators, as a filler in strain-hardening alkali-activated composites. The silica content provided by CBA was approximately 30% of that provided by silica fume, and its surface morphology exhibited a rough texture after treatment. The incorporation of CBA led to an improved compressive strength, and the subsequent substitution of treated CBA up to 100% resulted in a 10% increase in the compressive strength. Furthermore, incorporating the treated CBA enhanced the bond strength and pullout energy by up to 70% and 75%, respectively, compared with those of plain composites. The treated CBA also improved the tensile performance, as the replacement rate increased. At a substitution rate of 100%, the tensile strength, strain capacity, and strain energy density increased by 168.64%, 118.3%, and 479.41%, respectively, compared with those of plain composites. Thus, utilizing CBA as an alkaline activator is a promising solution to environmental challenges in the field of construction materials.

Optimizing Synergistic Silica–Zinc Oxide Coating for Enhanced Flammability Resistance in Cotton Protective Clothing

This study reports process optimization studies of silica and zinc oxide-based flame-retardant (FR) coatings on cotton fabric for protective clothing and enhanced flammability properties. The experiments were designed by central composite design (CCD) using response surface methodology (RSM) to assess the synergistic protective effects of silica and zinc oxide FR coating. These prepared sols were coated on cotton fabrics by a simple dip dry cure process. The resulting FR-finished fabrics were characterized by SEM, mechanical properties, flame retardancy, and air permeability. SEM results confirmed the homogenous spreading of particles on cotton fabrics. From TGA results, it was noticed that the incorporation of silica and ZnO in the prepared nano-sols results in improved thermal stability of the FR-finished fabrics. These sol–gel-treated FR cotton fabrics showed excellent comfort properties, which shows their suitability for fire-retardant protective clothing. RSM analysis proved that the predicted values are in good agreement with the experimental values since R2 values for time to ignite, flame spread time, and air permeability were greater than 0.90. The optimized concentration of silica and ZnO in FR-finished fabrics was found to be 0.302% and 0.353%, respectively, which was further confirmed by confirmatory experiments. The optimization analysis successfully optimized the process for synergistic coating of silica and zinc oxide nanoparticles for enhanced flammability properties of FR cotton fabric for protective clothing.

Scalable Jet‐Based Fabrication of PEI‐Hydrogel Particles for CO2 Capture

The capture, regeneration, and conversion of CO2 from ambient air and flue gas streams are critical aspects of mitigating global warming. Solid sorbents for CO2 absorption are very promising as they have high mass transfer areas without energy input and reduce emissions and minimize corrosion as compared to liquid sorbents. However, precisely tunable solid CO2 sorbents are difficult to produce. Here, we demonstrate the high‐throughput production of hydrogel‐based CO2‐absorbing particles via liquid jetting. By wrapping a liquid jet consisting of an aqueous solution of cross‐linkable branched polyethylenimine (PEI) with a layer of suspension containing hydrophobic silica nanoparticles, monodisperse droplets with a silica nanoparticle coating layer was formed in the air. A stable Pickering emulsion containing PEI droplets was obtained after these ejected droplets were collected in a heated oil bath. The droplets turn into mm‐sized particles after thermal curing in the bath. The diameter, PEI content, and silica content of the particles were systematically varied, and their CO2 absorption was measured as a function of time. Steam regeneration of the particles enabled cyclic testing, revealing a CO2 absorption capacity of 6.5 ± 0.5 mol kg−1 solid PEI in pure CO2 environments and 0.7 ± 0.3 mol kg−1 solid PEI for direct air capture. Several thousands of particles were produced per second at a rate of around 0.5 kg per hour, with a single nozzle. This process can be further scaled by parallelization. The complete toolbox for the design, fabrication, testing, and regeneration of functional hydrogel particles provides a powerful route toward novel solid sorbents for regenerative CO2 capture.

Self-healing glassy hybrids based on imidazole-functionalized silica nanoparticles with zinc complexes using dynamic and reversible cross-linking

Self-healing glass materials can potentially overcome the inherent limitations of glass, such as brittleness and difficulties in repairing broken sections while maintaining its critical properties. This paper reports a structural design and synthetic strategy for preparing glassy self-healing hybrids with high silica contents. The developed hybrids exhibited excellent self-healing properties based on dynamic and reversible crosslinking owing to the high density of zinc/imidazole units on the silica surface. First, core–shell silica nanoparticles with small multifunctional imidazole/butyl units (diameter: approximately10 nm) and good processability (homogeneous colloidal dispersions in common organic solvents) were synthesized. Afterwards, imidazole-functionalized silica nanoparticles were fabricated using Zn species to obtain self-healing hybrids with high silica contents (>60 wt%). These nanoparticles served as multifunctional and reversible crosslinking sites that dissipated energy, resulting in excellent mechanical, thermal, and healing characteristics. The obtained zinc/imidazole-based silica hybrids remain solid with high storage elasticity in the temperature range of 25–160 °C and high thermal stability corresponding to a 5 wt% weight loss above 280 °C, which were critical for self-healing glass applications. They also exhibited a moderate Young’s modulus of 330 MPa and a self-healing recovery efficiency of 87%. The findings of this study provide new insights into the roles of reversible interactions (metal/ligand exchange reactions) at particle–particle interfaces and high surface functionalities that serve as non-covalent crosslinking points. The prepared hybrids with high silica contents remain solid over a wide temperature range, which can open new avenues for self-healing glass materials.

Effect of silica fume type on rheology and compressive strength of geopolymer mortar

Silica fume (SF) is widely used in the developing of high-performance geopolymer systems. Previous studies have shown that using different types of SF may have different influences on the performance of geopolymers. What are the key factors (affecting the properties of geopolymers) still need to be clarified? This paper investigated the effects of three types of silica fume (SF1− SF3) with various silica contents (98.0%, 94.7% and 53.1%) and particle sizes (D50: 3.3 μm, 3.1 μm and 11.8 μm) on the rheology and compressive strength of alkali-activated calcium alumina cement (CAC)/fly ash mortar. The incorporation of SF can significantly increase the plastic viscosity. The increase in plastic viscosity was due to the ball-bearing action of the spherical SF particles, which reduced the friction between the particles under shearing. Replacing 20% of the fly ash with SF1 and SF2 improved the compressive strength of geopolymer mortars while the incorporation of SF3 decreased the compressive strength at the same replacement ratio. Inductively coupled plasma (ICP) spectrometry results indicated that the amorphous silica in the SFs was dissolved in an alkali solution. Activators with high concentrations of monomer and dimmer silicon groups may promote the reaction between precursors and activators. The formation of additional aluminosilicate gels reduced the amount of large capillary pores (500 nm to 1000 nm), leading to improved strength. The incorporation of coarse SF3 introduced extra voids in the mixture, as suggested by calculations of packing density, leading to reduced strength.

Enhancing biogas production through photocatalytic pretreatment of rice straw co-digested with cow dung and food waste using a novel g-C3N4/SiO2/bentonite catalyst

This study investigates the application of a novel composite photocatalyst, g-C3N4/SiO2/ Bentonite, for rice straw pretreatment, aiming to enhance biogas production in anaerobic digestion. The photocatalytic pretreatment disrupts rice straw's lignin and hemicellulose structures, reducing silica content for improved microbial degradation. Five 2 L anaerobic digesters were employed with rice straw as the substrate and co-digestion materials, including cow dung and food waste. Rice straw treated with the g-C3N4/7.5% SiO2/5% Bentonite catalyst exhibited a remarkable 37% increase in methane yield compared to untreated rice straw. This photocatalytic process led to a 31% increase in cellulose content and a 30% reduction in lignin after 6 hours of pretreatment. Simultaneously, silica content in the rice straw decreased to 6.4% after 6 hours, resulting in a 48% increase in the carbon proportion. These findings underscore the potential of integrated photocatalysts for significantly enhancing biogas production efficiency through the pretreatment of lignocellulosic biomass.

Reproduction toxicity study with the synthetic amorphous silica SYLOID® AL-1 FP, HDK® N20, LUDOX® P T-40 F and SYLOID® MX 107 in the earthworm species Eisenia fetida

Ecotoxicology studies were performed in the earthworm Eisenia fetida with four different synthetic amorphous silica (SAS) (SYLOID® AL-1 FP, SYLOID® MX 107, LUDOX® P T-40 F, and HDK® N20) mixed into artificial soil to determine a NOEC/LOEC for effects on reproduction (56 days after application), mortality and biomass development (28 days after application) using a standardized artificial soil with 10% peat. The LC50 for test-item effects on adult mortality, and an EC10 and EC50 for reproduction were also determined. Furthermore, earthworms underwent histopathology evaluation, and the amount of silica in different organs from these organisms was evaluated using EDX (Energy Dispersive X-ray Spectroscopy). Histopathology revealed no findings in any organ of the earthworms, except for desiccated dissepiments in evaluated decedents at extremely high SAS doses. To measure SAS uptake into the organs, a fully quantitative method for silica was established and validated using standards containing known concentrations of silica to ensure the accuracy of the analyses undertaken. Results from EDX analysis demonstrated the negligible presence of silicon within the brain ganglia and gonads of adult earthworms comparable to controls. Therefore, any deposition of the test items within these two organs was excluded. In contrast, traces of silicon higher than in controls were found in the intestinal lumina of the earthworms due to ingestion of SAS with soil and feed, but not in other organs.

Organic/metallic component analysis of lignocellulosic biomass: A thermochemical-perspective-based study on rice and bamboo waste

Thermochemical treatment is significantly impacted by the physiochemical properties of lignocellulosic biomass. Traditional characterization methods lack granularity, requiring advanced analytical techniques for comprehensive biomass characterization. This study analyzed elemental composition and their distribution in untreated rice husk, rice straw, and bamboo chips at micron and sub-micron scales. Results reveal significant variations in composition and spatial distribution of metallic components among agro-residues. Thermogravimetric analysis shows divergent decomposition patterns, while spectroscopic analysis indicates structural complexities and distinct silica content. Surface mapping illustrates prevalent silica and alkali metals on rice husk and rice straw. Atomic force microscopy depicts distinctive surface morphologies, with rice straw exhibiting heightened roughness due to silica bodies. Inductively coupled plasma-mass-spectrometry identified the abundance of alkali and alkaline earth metals in rice waste. Time-of-flight secondary ion mass spectrometry elucidates elemental spatial localization, affirming heterogeneous distribution across rice waste and homogenous distribution across bamboo waste. This study bridges the gap between biomass composition and optimized thermochemical conversion outcomes.

Insulating refractories based on rice husk ashes functionalized by flame-sprayed alumina coatings for steel ingot casting

This study investigates a new insulating refractory material based on rice husk ashes (RHA) for its application in the steel ingot casting process. The excellent insulating properties of this material may improve heat- and energy balance during ingot casting. A flame-sprayed alumina coating is applied to provide chemical inertness of the substrate material against the steel melt. The refractoriness, oxidation resistance, phase evolution and thermal expansion of four different grades of RHA materials and phase evolution and thermal expansion of flame-sprayed alumina coatings are studied. The refractoriness of the RHA materials increased with increasing silica content, showing sufficient refractoriness up to 1600°C for SiO2>94wt%. Immersion tests with composite materials made from RHA substrate and a flame-sprayed alumina coating were successfully performed in a steel casting simulator. No deformation of the substrate material nor spalling of the flame-sprayed alumina coating was observed despite an immersion without preheating.

Nonclassical crystallization of goethite nanorods in limpet teeth by self-assembly of silica-rich nanoparticles reveals structure–mechanical property relations

The intricate organization of goethite nanorods within a silica-rich matrix makes limpet teeth the strongest known natural material. However, the mineralization pathway of goethite in organisms under ambient conditions remains elusive. Here, by investigating the multi-level structure of limpet teeth at different growth stages, it is revealed that the growth of goethite crystals proceeds by the attachment of amorphous nanoparticles, a nonclassical crystallization pathway widely observed during the formation of calcium-based biominerals. Importantly, these nanoparticles contain a high amount of silica, which is gradually expelled during the growth of goethite. Moreover, in mature teeth of limpet, the content of silica correlates with the size of goethite crystals, where smaller goethite crystals are densely packed in the leading part with higher content of silica. Correspondingly, the leading part exhibits higher hardness and elastic modulus. Thus, this study not only reveals the nonclassical crystallization pathway of goethite nanorods in limpet teeth, but also highlights the critical roles of silica in controlling the hierarchical structure and the mechanical properties of limpet teeth, thus providing inspirations for fabricating biomimetic materials with excellent properties.

Effect of the Photoreduction Process on the Self-Cleaning and Antibacterial Activity of Au-Doped TiO2 Colloids on Cotton Fabric.

This study aims at understanding the effect of the photoreduction process during the synthesis of gold (Au)-doped TiO2 colloids on the conferred functionalities on cotton fabrics. TiO2/Au and TiO2/Au/SiO2 colloids were synthesized through the sol-gel method with and without undergoing the photoreduction step based on different molar ratios of Au:Ti (0.001 and 0.01) and TiO2/SiO2 (1:1 and 1:2.3). The colloids were applied to cotton fabrics, and the obtained photocatalytic self-cleaning, wet photocatalytic activity, UV protection, and antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria were investigated. The obtained results demonstrated that the photoreduction of Au weakened the self-cleaning effect and reduced the photocatalytic activity of coated fabrics. Also, an excess amount of Au deteriorated the photocatalytic activity under both UV and visible light. The most efficient self-cleaning effect was obtained on fabrics coated with a ternary TiO2/Au/SiO2 colloid containing ionic Au, where it decomposed coffee and red-wine stains after 3 h of illumination. Adding silica (SiO2) made the fabrics superhydrophilic and led to greater methylene blue (MB) dye adsorption, a faster dye degradation pace, and more efficient stain removal. Moreover, the photoreduction process affected the size of Au nanoparticles (NPs), weakened the antibacterial activity of fabrics against both types of tested bacteria, and modestly increased the UV protection. In general, the photoactivity of Au-doped colloids was influenced by the synthesis method, the ionic and metallic states of the Au dopant, the concentration of the Au dopant, and the presence and concentration of silica.

Compositional Remote Sensing and Hyperspectral Laboratory Analyses of Sinters in Hydrothermal Fields in Chile, With Relevance to Astrobiological Targets on Mars

AbstractSiliceous hot spring deposits, or sinters, deposit from hot spring discharge at Earth's surface and are sites of exceptional preservation of biosignatures. Their macro‐ and micro‐textures are regarded as important evidence of past microbial activities in hydrothermal environments. However, biology mimics do occur, and bona fide microbial textures could be destroyed by subsequent diagenesis or other post‐depositional processes. Thus, it is paramount to narrow the search for prospective Martian silica‐rich deposits that may contain biosignatures from both orbital and rover‐based perspectives. This study investigates hydrothermal deposits in Chile, which are analogs of high‐silica deposits discovered in the Gusev crater on Mars, through remote sensing and laboratory analysis. Results indicate that compositional remote sensing based on multispectral data with a high spatial resolution of <4 m/pixel reflects various concentrations of silica, which assisted in identifying the direction of discharged hydrothermal flows from the vent to the apron. Micro‐infrared mapping of sinters from similar hydrothermal fields linked spectral features to specific textures revealed by scanning electron microscope and chemical compositions confirmed by electron microprobe analysis, indicating that sinters with no shift in their emissivity minimum in the thermal infrared range were more likely to preserve cellular structures. An instrument for collecting multispectral data with higher spatial resolution could aid in characterizing the geologic settings of potential hot springs on Mars. Locating emissivity minima in the infrared regions of silica that do not shift to a lower position would suggest the potential for well‐preserved microbial structures in Martian sinters, if life ever did exist there.

Pengaruh Abu Bonggol Jagung Sebagai Substitusi Semen Terhadap Kuat Tekan Beton Alir

Abstract The use of flow concrete is the main choice in construction because of its high workability that facilitates compaction. In this study, utilizing corn cob ash as a partial substitution material for cement because the content of corn cob ash makes the waste potentially used as a concrete mixing material. One of the most important silica content in concrete is silica (SiO2). Corn cob ash has a fairly high silica content of 59%. Silica plays an important role in concrete because it can increase the compressive strength of concrete. This study aims to determine the effect of corn cob ash with variations of 0%, 4%, 5%, 7%, 9% on the compressive strength of flow concrete with a proportion of superplasticizer 1.5% at the age of 7, 21, and 28 days. From the results of the study, it can be concluded that the maximum compressive strength of concrete is in the CCA mixture of 7% at the age of 28 days of concrete, which is 35.22 MPa. The compressive strength of concrete with a mixture of 0% to 7% CCA continues to increase in each life of concrete. Based on the results of this study, corn cob ash as a partial substitution of cement can affect the compressive strength value of concrete. Keywords—Flow Concrete, Corn Cob Ash, Compressive Strength of Concrete

Investigation of the Effect of Silica and Phosphorus Content on the Performance of Active Matrix as Component of Cracking Catalyst

Fluid catalytic cracking (FCC) is a technique that converts heavy-fraction feed into fuel. The FCC catalyst components consist of a composite material made of zeolite, filler, binder, and an active matrix. The active matrix is used as a pre-cracker for the heavy-fraction feed. This study examined the impact of the Si/Al ratio and the addition of phosphorus on the physical properties and activity of the active matrix. The synthesis technique refers to US patent 6723297 B2. The utilized variants consisted of SiO2 ranging from 50 to 80 weight percent and a phosphorous addition ranging from 1 to 2 weight percent. The physical characteristics of the active matrix were assessed using nitrogen physisorption and NH3-Temperature programmed adsorption/desorption techniques. A chemical activity test was conducted using the micro activity test (MAT) method, with vacuum gas oil (VGO) as the feedstock. This test was done in accordance with the ASTM D 5154 – 03 standard. The results indicated that the silica composition in the active matrix is directly related to the average pore diameter but inversely related to the specific surface area. Additionally, the inclusion of phosphorus had a similar impact. The silica-alumina-phosphorous variant containing 75%-wt of SiO2 exhibited the most superior active matrix activity, achieving the maximum acquisition of light cycle oil (LCO) at 33%-wt.