Influence of 15 and 80 nano-SiO2 particles addition on mechanical and physical properties of ternary blended concrete incorporating rice husk ash

This study demonstrates the effects of SiO₂ nanoparticles as additives with two different sizes of 15 and 80?nm on compressive strength and porosity of rice husk ash (RHA) blended concrete. Up to 20% of ordinary Portland cement (OPC) was replaced by RHA with average particle size of 5 micron. Also, SiO₂ nanoparticles were added to the above mixture at four different weight percentages of 0.5, 1.0, 1.5 and 2.0 and cured in lime solution. The results indicated that compressive strength of Portland cement–nano SiO₂–rice husk ash (PC–NS–RHA) ternary blended concrete was considerably increased. Moreover, the total amount of porosity decreased to a minimum with respect to the control concrete. This improvement was observed at all the curing ages and replacement levels, but there was a gain in the optimal point with 20% of RHA plus 2% of 80?nm SiO₂ particles at 90 days of curing.     

One-pot fabrication of hollow SiO2 nanowires via an electrospinning technique

Hollow SiO₂ nanowires (NWs) were one-pot fabricated via an electrospinning method. Their morphologies, structures, and chemical compositions were investigated by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In order to fabricate optimum hollow SiO₂ NWs, the relative volume ratio of tetraethyl orthosilicate (TEOS, an alkoxide precursor) to ethanol (solvent) was systematically controlled from 0.02 to 0.36. SEM, HRTEM, XRD, and XPS results indicate that amorphous SiO₂ hollow NWs can be one-pot synthesized by using the volume ratio of 0.18 under a constant voltage of 8.0 kV.     

Water absorption control of ternary blended concrete with nano-SiO2 in presence of rice husk ash

In the current study, the effects of SiO₂ nanoparticles as additive with two different sizes of 15 and 80?nm on water absorption of rice husk ash (RHA) blended concrete have been investigated. Concrete samples were prepared by replacing 10, 15 and 20?wt% of cement with RHA and 0.5, 1.0, 1.5 and 2.0% of cement with SiO₂ nanoparticles followed by curing in lime solution for 7, 28 and 90?days. The results indicated that the resistance to water absorption of Portland cement?Cnano SiO₂?Crice husk ash (PC?CNS?CRHA) ternary blended concrete was considerably improved with respect to the control concrete. This improvement was observed at all curing ages and replacement levels but the optimal point was reached for 20% of RHA incorporating 2% of 80?nm SiO₂ particles at 90?days of curing. Fast formation of C?CS?CH gel in the presence of ultra high active nano-sized SiO₂ and micron level RHA particles together with their high filler effect may result in a continuous cement paste with the lowest weak zones. It has been concluded that the use of novel ternary blended concrete (PC?CNS?CRHA) provides significant reduction in the water absorption of concrete.     

X-ray diffraction analysis of silicon prepared from rice husk ash

Polycrystalline silicon has been prepared by metallothermal reduction of rice husk ash, which contains a considerable amount of amorphous silica. Acid-leached rice husk was burnt at a temperature of 620° C to obtain rice husk ash (RHA). RHA was then reduced with magnesium and major impurities were minimized or removed by an acid leaching process. The end-product was analysed using X-ray diffraction and mass spectrometric techniques. It was found that the powdered silicon obtained from magnesium reduction of RHA had a very low impurity concentration indicating that rice husk, which is an agricultural waste, is a potential source of metallurgical and solar-grade silicon.     

Microstructural development in Al/MgAl2O4 in situ metal matrix composite using value-added silica sources

Abstract

Al/MgAl₂O₄ in situ metal matrix composites have been synthesized using value-added silica sources (microsilica and rice husk ash) containing ～97% SiO₂ in Al-5 wt.% Mg alloy. The thermodynamics and kinetics of MgAl₂O₄ formation are discussed in detail. The MgO and MgAl₂O₄ phases were found to dominate in microsilica (MS) and rice husk ash (RHA) value-added composites, respectively, during the initial stage of holding the composites at 750 °C. A transition phase between MgO and MgAl₂O₄ was detected by the scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS) analysis of the particles extracted from the composite using 25% NaOH solution. This confirms that MgO is gradually transformed to MgAl₂O₄ by the reaction 3SiO_2(s)+2MgO_(s)+4Al_(l)→2MgAl₂O_4(s)+3Si_(l). The stoichiometry of MgAl₂O₄, n, computed by a new methodology is between 0.79 and 1.18. The reaction between the silica sources and the molten metal stopped after 55% of the silica source was consumed. A gradual increase in mean MgAl₂O₄ crystallite size, D, from 24 to 36 nm was observed in the samples held for 10 h.     

Microwave energy-assisted formation of bioactive CaO–MgO–SiO<Subscript>2</Subscript> ternary glass from bio-wastes

Regeneration technique is extensively being sought after as a means of achieving bone repair without adverse immunological response. Silicate-based bioactive glasses containing Mg are gaining increasing attention for their biocompatibility. The current work has been focused on designing a facile and economic route using bio-wastes for synthesizing bioactive glasses in the CaO–MgO–SiO₂ system. Rice husk ash (RHA) obtained from burning rice husk was used as silica source, while Ca was extracted from eggshells for preparing the glass through a modified sol–gel approach. The gel formed was irradiated in microwave before sintering at 950^°C for 3 h. Thereafter, bioactivity test was conducted on the samples in simulated body fluid (SBF) at physiological conditions for a maximum of 14 days. Characterization of samples were performed before and after immersion in SBF to evaluate the composition, morphology and phases present in the glass using energy-dispersive X-ray analysis, scanning electron microscopy and X-ray diffraction. Apatite formation was confirmed using Fourier transform infrared spectroscopy. Results obtained showed the presence of diopside, wollastonite and pseudo-wollastonite as major bioactive phases. Hydroxyapatite formed on the material within 3 days in SBF, indicating good bioactivity.     

Microwave (2.45 GHz)-assisted rapid sintering of SiO2-rich rice husk ash

The as-received SiO₂-rich material, rice husk ash (RHA), was ground to a specific surface area (Blaine) of 4800 cm²/g and then was rapidly sintered by 2.45 GHz microwave energy using a multi-mode system. The sintering temperatures were in a range of 800-1200 °C. The morphology, phase composition, microstructure and reactivity were investigated by SEM, XRD, and hydration heat evolution and strength index. Results show that the sintered ground RHAs (SgRHAs) contain SiO₂-cristolbalite and α-SiO₂ as major phases. The bulk density is up to 0.98 kg/l, and strength index at 28 days of the 800 °C microwave-sintered RHA paste are up by 30% when comparing to the as-received ground RHA (gRHA).     

Optimum production conditions for reactive rice husk ash

Addition of pozzolanic admixtures generally enhances the performance of concrete and in particular the durability. If rice husk ash (RHA) is incinerated in controlled conditions, it can exhibit high pozzolanicity. Significant amount of work has already been reported on the production methodologies of reactive RHA. However, the optimum conditions which will result in highly reactive amorphous ash with minimum production energy have not yet been established. In the present experimental work, RHA samples are produced under various conditions of incineration using laboratory box furnace. Energy consumption has been examined in this study. Reactivity of ash has been established by various techniques, such as X-ray diffraction (XRD), scanning electron microscopic study (SEM), analytical method and conductometric test. RHA-OPC reactivity has also been studied in this work. Based on the experimental investigations on fineness, amorphous silica content, energy consumption and reactivity of ash, the optimum production conditions of reactive RHA have been identified.     

Review Processing, properties and applications of reactive silica from rice husk—an overview

Rice husk is an abundantly available waste material in all rice producing countries. In certain regions, it is sometimes used as a fuel for parboiling paddy in the rice mills. The partially burnt rice husk in turn contributes to more environmental pollution. There have been efforts not only to overcome this but also to find value addition to these wastes using them as secondary source of materials. Rice husk contains nearly 20% silica, which is present in hydrated amorphous form. On thermal treatment, the silica converts to crystobalite, which is a crystalline form of silica. However, under controlled burning conditions, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si₃N₄, elemental Si and Mg₂Si. Due to the high pozzolanic activity, this rice husk silica also finds application in high strength concrete as a substitute for silica fume. Possibility of using this silica as filler in polymers is also studied. The present paper is an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on the processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.     

纳米SiO2与粉煤灰协同改性水泥基材料性能研究

通过调整纳米SiO_2与粉煤灰的比例,研究了两者协同作用对水泥基材料性能的影响。结果表明,纳米SiO_2(NS)和粉煤灰协同作用效果优于NS单一掺加,3%(质量分数,下同)纳米SiO_2和不大于30%的粉煤灰同时掺加可以补偿粉煤灰引起的早期强度降低,且砂浆28d抗压强度不降低。随着NS掺量增加水泥基材料的干燥收缩增大,粉煤灰可以改善纳米SiO_2对干燥收缩的不利影响。随着NS掺量的增加,试件的抗冻性和抗氯离子渗透性能均得到提升,掺加3%NS与30%粉煤灰使水泥基材料达到最佳耐久性能。NS可以缩短水泥水化诱导期,加速水泥水化进程,且使胶凝体系总放热量增加。在水泥粉煤灰体系中掺入NS后,非蒸发水含量在早期明显增多,但在后期增长缓慢。     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Mass Transport Determined Silica Nanowires Growth on Spherical Photonic Crystals with Nanostructure‐Enabled Functionalities

A robust and facile method has been developed to obtain directional growth of silica nanowires (SiO₂NWs) by regulating mass transport of silicon monoxide (SiO) vapor. SiO₂NWs are grown by vapor–liquid–solid (VLS) process on a surface of gold‐covered spherical photonic crystals (SPCs) annealed at high temperature in an inert gas atmosphere in the vicinity of a SiO source. The SPCs are prepared from droplet confined colloidal self‐assembly. SiO₂NW morphology is governed by diffusion‐reaction process of SiO vapor, whereby directional growth of SiO₂NWs toward the low SiO concentration is obtained at locations with a high SiO concentration gradient, while random growth is observed at locations with a low SiO concentration gradient. Growth of NWs parallel to the supporting substrate surface is of great importance for various applications, and this is the first demonstration of surface‐parallel growth by controlling mass transport. This controllable NW morphology enables production of SPCs covered with a large number of NWs, showing multilevel micro‐nano feature and high specific surface area for potential applications in superwetting surfaces, oil/water separation, microreactors, and scaffolds. In addition, the controllable photonic stop band properties of this hybrid structure of SPCs enable the potential applications in photocatalysis, sensing, and light harvesting.     

Synthesis of zeolite T powders by direct dissolution of rice husk ash: an agro-waste material

Rice husk ash (RHA), an agro-waste material, was used for the synthesis of zeolite T powders following a simple and cost-effective process. In this process, silica as silicate was directly extracted from solid RHA particles in the presence of aluminate and other aqueous-based precursor materials. The synthesized powders were characterized by thermogravimetry analysis, differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, N₂ physisorption measurements, and field emission scanning electron microscopy (FESEM). Crystallization of zeolite T powders was noticed at 100 °C/24 h. The vibration bands of the powders at around 580 and 630 cm^?1 indicated the characteristic double six ring of zeolite T. Micropore surface area and micropore volume of zeolite T increased significantly at 100 °C/72 h. FESEM images showed ellipse-shaped morphology of the powders, and their aspect ratio increased with increase in reaction time. A tentative mechanism was proposed for direct extraction of silica as silicate from RHA, and its conversion to zeolite T in the presence of other aqueous-based precursors by a single step process.     

Hybrid nanocomposite of Fe nanoparticles on SiO2 nanowires by sublimation route

A simple route was developed to synthesize the hybrid nanocomposite with Fe nanoparticles (NPs) dispersed on the surface of SiO₂ nanowires (NWs), where SiO₂ NWs with the diameter of 20-40 nm were produced by heating single-crystal silicon wafer, and Fe NPs in the size range of 3-20 nm were generated by heating Fe powders. The nucleation and growth of Fe NPs follows the solid-vapor-solid (S-V-S) mechanism, namely, Fe powders firstly sublime and then Fe atoms deposit on SiO₂ NWs to form Fe NPs.     

Synthesis and characterization of a nanocomposite NiO/SiO2 from a sustainable source of SiO2

ABSTRACT

The search for raw materials obtained from renewable sources is necessary for the sustainable development in the production of engineering materials. In this study, we present the hydrothermal synthesis of biogenic silica extracted from rice husk for the production of NiO/SiO₂ nanocomposite by Pechini method and employed an alternative strategy for the use of tetraethylorthosilicate as precursor agent. The synthesized nanocomposite presents amorphous SiO₂ nanoparticles dispersed in a NiO matrix as observed in the x-ray diffraction patterns and by scanning electron microscopy characterization. The average size of the crystallite measured by XRD was 11?nm. The formation of the aimed composite containing 83% of NiO crystalline phase and 17% of SiO₂ in amorphous phase was confirmed by Infrared and Raman spectroscopic analyses. These results demonstrate that it is possible to develop synthetic routes to produce new materials using several raw materials from sustainable sources and thus reducing environmental impact.     

Catalyst-free synthesis of silicon nanowires by oxidation and reduction process

A new process has been developed to grow silicon (Si) nanowires (NWs), and their growth mechanisms were explored and discussed. In this process, SiNWs were synthesized by simply oxidizing and then reducing Si wafers in a high temperature furnace. The process involves H₂, in an inert atmosphere, reacts with thermally grown SiO₂ on Si at 1100 °C enhancing the growth of SiNWs directly on Si wafers. High-resolution transmission electron microscopy studies show that the NWs consists of a crystalline core of ~25 nm in diameter and an amorphous oxide shell of ~2 nm in thickness, which was also supported by selected area electron diffraction patterns. The NWs synthesized exhibit a high aspect ratio of ~167 and room temperature phonon confinement effect. This simple and economical process to synthesize crystalline SiNWs opens up a new way for large scale applications.     

Assessing the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste

This study assesses the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste. rice husk ash (RHA), palm oil fuel ash (POFA) and river sand (RS) were ground to obtain two finenesses: one was the same size as the cement, and the other was smaller than the cement. Type I Portland cement was replaced by RHA, POFA and RS at 0%, 10%, 20%, 30% and 40% by weight of binder. A water to binder ratio (W/B) of 0.35 was used for all blended cement paste mixes. The percentages of amorphous materials and the compressive strength of the pastes due to the hydration reaction, filler effect and pozzolanic reaction were investigated. The results showed that ground rice husk ash and ground palm oil fuel ash were composed of amorphous silica material. The compressive strength of the pastes due to the hydration reaction decreased with decreasing cement content. The compressive strength of the pastes due to the filler effect increased with increasing cement replacement. The compressive strengths of the pastes due to the pozzolanic reaction were nonlinear and were fit with nonlinear isotherms that increased with increasing fineness of RHA and POFA, cement replacement rate and age of the paste. In addition, the model that was proposed to predict the percentage compressive strength of the blended cement pastes on the basis of the age of the paste and the percentage replacement with biomass ash was in good agreement with the experimental results. The optimum replacement level of rice husk ash and palm oil fuel ash in pastes was 30% by weight of binder; this replacement percentage resulted in good compressive strengths.     

Electrospinning preparation and photoluminescence properties of SrAl2O4:Ce3+ nanowires

One-dimensional monoclinic SrAl₂O₄:Ce³⁺ nanowires (NWs) were prepared by the electrospinning method for the first time. By annealing PVP/SrAl₂O₄:Ce³⁺ composite nanowires (NWs) with different ratio of PVP (M _w ≈ 1300000) to inorganic precursors of the electrospinning solutions, size-controllable NWs were obtained, ranging of 90–180 nm. Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectra, and dynamics were employed to characterize the NWs. The results demonstrate that the positions of excitation and emission bands varied uneven with the ratio of PVP to the inorganic precursors and the NWs diameter, which was attributed to the difference of the crystallinity, porosity, and local micro-structures surrounding Ce³⁺. Two decay time constants were observed for the PL of Ce³⁺, one faster (1–3 ns) and one slower (10–20 ns), which were attributed to the hole-electron capture on the luminescent ions and isolated Ce ions, respectively. It is interesting to observe that for the shorter decay process, a maximum occurred as the concentration of Ce³⁺ varied in the range of 1–10 mol%.     

Synthesis of monodisperse CdS nanowires and their photovoltaic applications

Cadmium sulphide (CdS) nanowires with a monodisperse diameter of 3.6 nm and an aspect ratio of 10–170 were successfully synthesized using a simple and reproducible hot coordinating solvents method. The morphology and optical properties of the CdS nanocrystals were investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM) ultraviolet–visible (UV–Vis) absorption spectroscopy and photoluminescence (PL) spectroscopy. It was found that using a long alkyl chain phosphonic acid-octadecylphosphonic acid (ODPA) causes a low diffusion rate and low reactivity which help to control the morphology of the nanocrystals. The timing of the injection process was also found to have critical effect on the morphology of the nanocrystals. Sharp peaks in both the UV–Vis absorption and PL spectra indicate that the size distribution of the diameter is nearly monodisperse. The photovoltaic properties of photovoltaic devices made with a blend of our nanowires and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) were also investigated. Devices made with the nanowires were found to have double the I_sc observed in devices made with lower aspect ratio CdS nanorods. The possible reason of low photocurrent and high V_oc is maybe due to the presence of ligand in the nanocrystals.     

Utilization of agricultural waste (rice husk) in synthesis of TS-1 zeolite as a support for NiMo nanocatalyst employed in hydrodesulfurization of heavy oil

Agricultural waste, rice husk (RH) was treated to obtain rice husk ash (RHA) and utilized as silica precursor in hydrothermal synthesis of TS-1 zeolite. Results of characterization analyses, XRD, FTIR, FESEM and N₂ adsorption-desorption, confirmed that TS-1 zeolite was properly synthesized from RHA. Synthesis of TS-1 was also carried out with TEOS for comparison of textural properties. Prepared TS-1 zeolite with RHA was used as support for HDS catalyst preparation. Molybdenum active phase and nickel promoter were loaded via three different methods, impregnation, precipitation and solution combustion, to obtain NiMo/TS-1 hydrodesulfurization catalyst. EDX dot-mapping and H₂-TPR analyses indicated on better preparation of NiMo/TS-1 catalyst by solution combustion method, in terms of distribution and amount of successfully loaded metal over the support surface. Hydrodesulfurization (HDS) activity of synthesized samples was examined in hydrodesulfurization of heavy oil feed, carried out in a continuous fixed bed reactor apparatus. Performance test revealed that NiMo/TS-1 catalyst synthesized by solution combustion method eliminated 63.5 % of the feed sulfur content (4000 ppm); a superior hydrodesulfurziation activity, compared to the samples prepared via impregnation and precipitation methods with 40.8 % and 50.2 % sulfur removal, respectively. Amount of sulfur present in the feed and treated product was determined with GC-MS analysis.