Search results for: silica aerogel

Authors: A. Eštoková, M. Kovalčíková, A. Luptáková, A. Sičáková, M. Ondová

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Concrete durability as an important engineering property of concrete, determining the service life of concrete structures very significantly, can be threatened and even lost due to the interactions of concrete with external environment. Bio-corrosion process caused by presence and activities of microorganisms producing sulphuric acid is a special type of sulphate deterioration of concrete materials. The effects of sulphur-oxidizing bacteria Acidithiobacillus thiooxidans on various concrete samples, based on silica fume and zeolite, were investigated in laboratory during 180 days. A laboratory study was conducted to compare the performance of concrete samples in terms of the concrete deterioration influenced by the leaching of calcium and silicon compounds from the cement matrix. The changes in the elemental concentrations of calcium and silicon in both solid samples and liquid leachates were measured by using X – ray fluorescence method. Experimental studies confirmed the silica fume based concrete samples were found out to have the best performance in terms of both silicon and calcium ions leaching.

Keywords: biocorrosion, concrete, leaching, bacteria

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Authors: Sadao Araki, Daisuke Gondo, Satoshi Imasaka, Hideki Yamamoto

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The separation of organic compounds from aqueous solutions is a key technology for recycling valuable organic compounds and for the treatment of wastewater. The wastewater from chemical plants often contains organic compounds such as ethyl acetate (EA), methylethyl ketone (MEK) and isopropyl alcohol (IPA). In this study, we prepared hydrophobic silica membranes by a sol-gel method. We used phenyltrimethoxysilane (PhTMS), ethyltrimethoxysilan (ETMS), Propyltrimethoxysilane (PrTMS), N-butyltrimethoxysilane (BTMS), N-Hexyltrimethoxysilane (HTMS) as silica sources to introduce each functional groups on the membrane surface. Cetyltrimethyl ammonium bromide (CTAB) was used as a molecular template to create suitable pore that enable the permeation of organic compounds. These membranes with five different functional groups were characterized by SEM, FT-IR, and permporometry. Thicknesses and pore diameters of silica layer for all membrane were about 1.0 μm and about 1 nm, respectively. In other words, functional groups had an insignificant effect on the membrane thicknesses and the formation of the pore by CTAB. We confirmed the effect of functional groups on the flux and separation factor for ethyl acetate (EA), methyl ethyl ketone, acetone and 1-butanol (1-BtOH) /water mixtures. All membranes showed a high flux for ethyl acetate compared with other compounds. In particular, the hydrophobic silica membrane prepared by using BTMS showed 0.75 kg m-2 h-1 of flux for EA. For all membranes, the fluxes of organic compounds showed the large values in the order corresponding to EA > MEK > acetone > 1-BtOH. On the other hand, carbon chain length of functional groups among ETMS, PrTMS, BTMS, PrTMS and HTMS did not have a major effect on the organic flux. Although we confirmed the relationship between organic fluxes and organic molecular diameters or fugacity of organic compounds, these factors had a low correlation with organic fluxes. It is considered that these factors affect the diffusivity. Generally, permeation through membranes is based on the diffusivity and solubility. Therefore, it is deemed that organic fluxes through these hydrophobic membranes are strongly influenced by solubility. We tried to estimate the organic fluxes by Hansen solubility parameter (HSP). HSP, which is based on the cohesion energy per molar volume and is composed of dispersion forces (δd), intermolecular dipole interactions (δp), and hydrogen-bonding interactions (δh), has recently attracted attention as a means for evaluating the resolution and aggregation behavior. Evaluation of solubility for two substances can be represented by using the Ra [(MPa)1/2] value, meaning the distance of HSPs for both of substances. A smaller Ra value means a higher solubility for each substance. On the other hand, it can be estimated that the substances with large Ra value show low solubility. We established the correlation equation, which was based on Ra, of organic flux at low concentrations of organic compounds and at 295-325 K.

Keywords: hydrophobic, membrane, Hansen solubility parameter, functional group

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Authors: Maryam Kiani, Abdul Basit Kiani

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At larger scales, the performance of cementitious materials is impacted by processes occurring at the nanometer scale. These materials boast intricate hierarchical structures with random features that span from the nanometer to millimeter scale. It is fascinating to observe how the nanoscale processes influence the overall behavior and characteristics of these materials. By delving into and manipulating these processes, scientists and engineers can unlock the potential to create more durable and sustainable infrastructure and construction materials. It's like unraveling a hidden tapestry of secrets that hold the key to building stronger and more resilient structures. The present work employs simulations as the computational modeling methodology to predict mechanical properties for carbon/silica based cementitious materials at the molecular/nano scale level. Studies focused on understanding the effect of higher mechanical properties of cementitious materials with carbon silica nanoparticles via Material Studio materials modeling.

Keywords: nanomaterials, SiO₂, carbon black, mechanical properties

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Authors: Diana Rymuszka, Konrad Terpiłowski, Lucyna Hołysz, Elena Goncharuk, Iryna Sulym

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Superhydrophobic surfaces exhibit extremely high water repellency. The commonly accepted basic criterion for such surfaces is a water contact angle larger than 150°, low contact angle hysteresis and low sliding angle. These surfaces are of special interest, because properties such as anti-sticking, anti-contamination and self-cleaning are expected. These properties are attractive for many applications such as anti-sticking of snow for antennas and windows, anti-biofouling paints for boats, waterproof clothing, self-cleaning windshields for automobiles, dust-free coatings or metal refining. The various methods for the preparation of superhydrophobic surfaces since last two decades have been reported, such as phase separation, electrochemical deposition, template method, plasma method, chemical vapor deposition, wet chemical reaction, sol-gel processing, lithography and so on. The aim of the study was to investigate the influence of modified colloidal silica, used as a filler, on the hydrophobicity of the polymer film deposited on the glass support activated with plasma. On prepared surfaces water advancing (ӨA) and receding (ӨR) contact angles were measured and then their total apparent surface free energy was determined using the contact angle hysteresis approach (CAH). The structures of deposited films were observed with the help of an optical microscope. Topographies of selected films were also determined using an optical profilometer. It was found that plasma treatment influence glass surface wetting and energetic properties that is observed in higher adhesion between polymer/filler film and glass support. Using the colloidal silica particles as a filler for the polymer thin film deposited on the glass support, it is possible to produce strongly adhering layers of superhydrophobic properties. The best superhydrophobic properties were obtained for surfaces of the film glass/polimer + modified silica covered in 89 and 100%. The advancing contact angle measured on these surfaces amounts above 150° that leads to under 2 mJ/m2 value of the apparent surface free energy. Such films may have many practical applications, among others, as dust-free coatings or anticorrosion protection.

Keywords: contact angle, plasma, superhydrophobic, surface free energy

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Authors: Chen Yuan, Nick Green, Stuart Blackburn

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The investment casting process offers a great freedom of design combined with the economic advantage of near net shape manufacturing. It is widely used for the production of high value precision cast parts in particularly in the aerospace sector. Various combinations of materials have been used to produce the ceramic moulds, but most investment foundries use a silica based binder system in conjunction with fused silica, zircon, and alumino-silicate refractories as both filler and coarse stucco materials. However, in the context of advancing alloy technologies, silica based systems are struggling to keep pace, especially when net-shape casting titanium alloys. Study has shown that the casting of titanium based alloys presents considerable problems, including the extensive interactions between the metal and refractory, and the majority of metal-mould interaction is due to reduction of silica, present as binder and filler phases, by titanium in the molten state. Cleaner, more refractory systems are being devised to accommodate these changes. Although yttria has excellent chemical inertness to titanium alloy, it is not very practical in a production environment combining high material cost, short slurry life, and poor sintering properties. There needs to be a cost effective solution to these issues. With limited options for using pure oxides, in this work, a silica-free magnesia spinel MgAl₂O₄ was used as a primary coat filler and alumina as a binder material to produce facecoat in the investment casting mould. A comparison system was also studied with a fraction of the rare earth oxide Y₂O₃ adding into the filler to increase the inertness. The stability of the MgAl₂O₄/Al₂O₃ and MgAl₂O₄/Y₂O₃/Al₂O₃ slurries was assessed by tests, including pH, viscosity, zeta-potential and plate weight measurement, and mould properties such as friability were also measured. The interaction between the face coat and titanium alloy was studied by both a flash re-melting technique and a centrifugal investment casting method. The interaction products between metal and mould were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). The depth of the oxygen hardened layer was evaluated by micro hardness measurement. Results reveal that introducing a fraction of Y₂O₃ into magnesia spinel can significantly increase the slurry life and reduce the thickness of hardened layer during centrifugal casting.

Keywords: titanium alloy, mould, MgAl₂O₄, Y₂O₃, interaction, investment casting

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Authors: Fatai O. Oladoyinbo, Felix O. Sanni, Akinwunmi Fatai, Kamoli A. Amusa, Saheed A. Ganiyu, Wasiu B. Ayinde, Tajudeen A. Afolabi, Enock O. Dare

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Silver (Ag) and silica (SiO2) nanoparticles were synthesized using the chemical reduction method from silver nitrate and sodium silicate, respectively. X-ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Uv-Visible spectroscopy, Energy Dispersive X-ray (EDX) spectroscopy and N2 adsorption-desorption techniques were utilized to characterize the composition and structure of the samples. The crystallinity pattern of Ag nanoparticles was indexed as (111), (200), (220) and (311), which allowed reflections from face-centered cubic silver. XRD of SiO2 showed good porosity with a broad-spectrum band at Bragg’s angle 2θ of 22° while that of Ag-SiO2 showed distinct peaks at 2θ values of 39°, 43°, 66° and 79°. The XRD result agreed perfectly with the SEM and HRTEM images which showed Ag-SiO2 isotropic and anisotropic under the varying concentration of reactants. The elemental composition of Ag-SiO2, as displayed by EDX, confirmed Ag enrichment in the Ag-SiO2 heterostructure. The Uv-Visible peak at 421 nm confirmed the Surface Plasmon Resonance absorption peak of silver nanoparticles. N2 adsorption-desorption result showed a broad band of Ag-SiO2 from 3 to 8 nm, which indicated relatively narrow pore size distributions. Humidity sensing measurements performed in a controlled humidity chamber showed very high sensitivity with a sensitivity factor (SF) of 4.63 and high linearity with a steady decrease in resistance to humidity from 880 Ω at 10% RH to 190 Ω at 100% RH, indicating that Ag-SiO2 nanocomposite is a good sensing material with high sensitivity and linearity.

Keywords: silver, silica, nanocomposite, synthesis, heterostructure, core shell

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Authors: Afifa Hafidh, Fathi Touati, Ahmed Hichem Hamzaoui, Sayda Somrani

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The objective of the present study has been to synthesize and to characterize silica hybrid materials using sol-gel technic and to investigate their properties. Silica materials were successfully fabricated using various bi-functional 1,3,4-thiadiazoles and tetraethoxysilane (TEOS) as co-precursors via a facile one-pot sol-gel pathway. TEOS was introduced at room temperature with 1,3,4-thiadiazole 2,5-difunctiunal adducts, in ethanol as solvent and using HCl acid as catalyst. The sol-gel process lead to the formation of monolithic, coloured and transparent gels. TEOS was used as a principal network forming agent. The incorporation of 1,3,4-thiadiazole molecules was realized by attachment of these later onto a silica matrix. This allowed covalent linkage between organic and inorganic phases and lead to the formation of Si-N and Si-S bonds. The prepared hybrid materials were characterized by Fourier transform infrared, NMR ²⁹Si and ¹³C, scanning electron microscopy and nitrogen absorption-desorption measurements. The optic and magnetic properties of hybrids are studied respectively by ultra violet-visible spectroscopy and electron paramagnetic resonance. It was shown in this work, that heterocyclic moieties were successfully attached in the hybrid skeleton. The formation of the Si-network composed of cyclic units (Q3 structures) connected by oxygen bridges (Q4 structures) was proved by ²⁹Si NMR spectroscopy. The Brunauer-Elmet-Teller nitrogen adsorption-desorption method shows that all the prepared xerogels have isotherms type IV and are mesoporous solids. The specific surface area and pore volume of these materials are important. The obtained results show that all materials are paramagnetic semiconductors. The data obtained by Nuclear magnetic resonance ²⁹Si and Fourier transform infrared spectroscopy, show that Si-OH and Si-NH groups existing in silica hybrids can participate in adsorption interactions. The obtained materials containing reactive centers could exhibit adsorption properties of metal ions due to the presence of OH and NH functionality in the mesoporous frame work. Our design of a simple method to prepare hybrid materials may give interest of the development of mesoporous hybrid systems and their use within the domain of environment in the future.

Keywords: hybrid materials, sol-gel process, 1, 3, 4-thiadaizole, TEOS

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Authors: Benedict O. Ayomanor, Cookey Iyen, Ifeoma S. Iyen

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Rice hull (RH) biomass product gives feasible silica for exact temperature and period. The minimal fabrication price turns its best feasible produce to metallurgical grade silicon (MG-Si). In this work, to avoid ecological worries extending from CO₂ release to oil leakage on water and land, or nuclear left-over pollution, all finally add to the immense topics of ecological squalor; high purity silicon > 98.5% emerge set from rice hull ash (RHA) by solid-liquid removal. The RHA derived was purified by nitric and hydrochloric acid solutions. Leached RHA sieved, washed in distilled water, and desiccated at 1010ºC for 4h. Extra cleansing was achieved by carefully mixing the SiO₂ ash through Mg dust at a proportion of 0.9g SiO₂ to 0.9g Mg, galvanised at 1010ºC to formula magnesium silicide. The solid produced was categorised by X-ray fluorescence (XRF), X-ray diffractometer (XRD), and Fourier transformation infrared (FTIR) spectroscopy. Elemental analysis using XRF found the percentage of silicon in the material is approximately 98.6%, main impurities are Mg (0.95%), Ca (0.09%), Fe (0.3%), K (0.25%), and Al (0.40%).

Keywords: siliceous, leached, biomass, solid-liquid extraction

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Authors: Weena Siangphro, Orawon Chailapakul, Kriangsak Songsrirote

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A simple, rapid, sensitive, and economical method based on colorimetry for the determination of paraquat, a widely used herbicide, was developed. Citrate-coated silver nanoparticles (AgNPs) were synthesized as colorimetric probe. The mechanism of the assay is related to aggregation of negatively charged AgNPs induced by positively-charged paraquat resulting from coulombic attraction which causes the color change from deep greenish yellow to pale yellow upon the concentrations of paraquat. Silica gel was exploited as paraquat adsorbent for purification and pre-concentration prior to the direct determination with negatively charged AgNPs without elution step required. The validity of the proposed approach was evaluated by spiking standard paraquat in water and plant samples. Recoveries of paraquat in water samples were 93.6-95.4%, while those in plant samples were 86.6-89.5% by using the optimized extraction procedure. The absorbance of AgNPs at 400 nm was linearly related to the concentration of paraquat over the range of 0.05-50 mg/L with detection limits of 0.05 ppm for water samples, and 0.10 ppm for plant samples.

Keywords: colorimetric assay, paraquat, silica gel, silver nanoparticles

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Authors: M. Shannag, A. Charif, S. Naser, F. Faisal, A. Karim

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Structural lightweight concrete is used primarily to reduce the dead-load weight in concrete members such as floors in high-rise buildings and bridge decks. With given materials, it is generally desired to have the highest possible strength/unit weight ratio with the lowest cost of concrete. The work presented herein is part of an ongoing research project that investigates the properties of concrete mixes containing locally available Scoria lightweight aggregates and mineral admixtures. Properties considered included: workability, unit weight, compressive strength, and splitting tensile strength. Test results indicated that developing structural lightweight concretes (SLWC) using locally available Scoria lightweight aggregates and specific blends of silica fume and fly ash seems to be feasible. The stress-strain diagrams plotted for the structural LWC mixes developed in this investigation were comparable to a typical stress-strain diagram for normal weight concrete with relatively larger strain capacity at failure in case of LWC.

Keywords: lightweight concrete, scoria, stress, strain, silica fume, fly ash

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Authors: Frederick Anlimah, Vinod Gopaldasani, Catherine MacPhail, Brian Davies

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The construction industry, particularly tunnel construction, exposes workers to respirable crystalline silica (RCS), which can cause incurable illnesses such as silicosis and lung cancer. Despite various control measures, exposures remain inadequately controlled. This research aimed to identify the barriers and challenges hindering the implementation of effective controls and the adoption of safe work practices to protect workers from RCS exposure in tunnelling. A mixed-method approach was employed for this research. Tunnel construction workers were observed, surveyed and interviewed to gauge their knowledge and attitudes and understand their challenges in reducing RCS exposure. The preliminary analysis of the data reveals a diverse array of sociotechnical factors interacting to influence RCS exposure. It is noteworthy that participants consistently emphasised the project as the most exemplary one they have been involved in, although there is room for improvement. While there is a commendable level of knowledge about RCS exposure and control in tunnelling, there is a striking lack of perceived satisfaction regarding dust control. Several factors were identified as interacting to prevent the effective management of dust. These include perceived time pressure, absence of on-tool dust controls, low risk perceptions among workers, and inadequate enforcement of controls. Moreover, participants highlighted communication and heat-related challenges as hindrances to the continuous wear of respirators. This research highlights the need for a paradigm shift in tunnel construction to address the barriers associated with RCS exposure reduction. It emphasises the importance of collaboration among various stakeholders, advocating for more effective controls and enforcement strategies and enhanced worker education through knowledge sharing.

Keywords: respirable crystalline silica, dust control, worker practices, exposure prevention, silicosis

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Authors: Kunal Krishna Das, Eddie S. S. Lam

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Preplaced Aggregate Concrete (PAC) is produced by first placing the coarse aggregate into the formwork, followed by injection of grout to fill in the voids in between the coarse aggregates. In this study, tests were carried out to determine the effects of supplementary cementitious materials on the properties of PAC. Cement was partially replaced by ground granulated blast furnace slag (GGBS) and silica fume (SF) at different proportions. Grout properties were determined by the flow cone test and compressive strength test. Grout proportion was optimized statistically. It was applied to form PAC. Hardened properties of PAC, comprising compressive strength, splitting tensile strength, chloride-ion penetration and drying shrinkage, were evaluated. GGBS enhanced the flowability of the grout, whereas SF enhanced the strength of PAC. Both GGBS and SF improved the resistance to chloride-ion penetration with the drawback of increased drying shrinkage. Nevertheless, drying shrinkage was within the range to be classified as low shrinkage concrete.

Keywords: factorial design, ground granulated blast furnace slag, preplaced aggregate concrete, silica fume

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Authors: S. A. Krutovertsev, A. E. Tarasova, L. S. Krutovertseva, O. M. Ivanova

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The aim of the work was to get stable sensitive films with good sensitivity to ethanolamine (C2H7NO) in air. Ethanolamine is used as adsorbent in different processes of gas purification and separation. Besides it has wide industrial application. Chemical sensors of sorption type are widely used for gas analysis. Their behavior is determined by sensor characteristics of sensitive sorption layer. Forming conditions and characteristics of chemical gas sensors based on nanostructured modified silica films activated by different admixtures have been studied. As additives molybdenum containing polyoxometalates of the eighteen series were incorporated in silica films. The method of hydrolythic polycondensation from tetraethyl orthosilicate solutions was used for forming such films in this work. The method’s advantage is a possibility to introduce active additives directly into an initial solution. This method enables to obtain sensitive thin films with high specific surface at room temperature. Particular properties make polyoxometalates attractive as active additives for forming of gas-sensitive films. As catalyst of different redox processes, they can either accelerate the reaction of the matrix with analyzed gas or interact with it, and it results in changes of matrix’s electrical properties Polyoxometalates based films were deposited on the test structures manufactured by microelectronic planar technology with interdigitated electrodes. Modified silica films were deposited by a casting method from solutions based on tetraethyl orthosilicate and polyoxometalates. Polyoxometalates were directly incorporated into initial solutions. Composite nanostructured films were deposited by drop casting method on test structures with a pair of interdigital metal electrodes formed at their surface. The sensor’s active area was 4.0 x 4.0 mm, and electrode gap was egual 0.08 mm. Morphology of the layers surface were studied with Solver-P47 scanning probe microscope (NT-MDT, Russia), the infrared spectra were investigated by a Bruker EQUINOX 55 (Germany). The conditions of film formation varied during the tests. Electrical parameters of the sensors were measured electronically in real-time mode. Films had highly developed surface with value of 450 m2/g and nanoscale pores. Thickness of them was 0,2-0,3 µm. The study shows that the conditions of the environment affect markedly the sensors characteristics, which can be improved by choosing of the right procedure of forming and processing. Addition of polyoxometalate into silica film resulted in stabilization of film mass and changed markedly of electrophysical characteristics. Availability of Mn3P2Mo18O62 into silica film resulted in good sensitivity and selectivity to ethanolamine. Sensitivity maximum was observed at weight content of doping additive in range of 30–50% in matrix. With ethanolamine concentration changing from 0 to 100 ppm films’ conductivity increased by 10-12 times. The increase of sensor’s sensitivity was received owing to complexing reaction of tested substance with cationic part of polyoxometalate. This fact results in intramolecular redox reaction which sharply change electrophysical properties of polyoxometalate. This process is reversible and takes place at room temperature.

Keywords: ethanolamine, gas analysis, polyoxometalate, silica film

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Authors: Binyamien Rasoul

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Portland cement is one of the most widely used construction materials in the world today; however, manufacture of ordinary Portland cement (OPC) emission significant amount of CO2 resulting environmental impact. On the other hand, rice husk ash (RHA), which is produce as by product material is generally considered to be an environmental issue as a waste material. This material (RHA) consists of non-crystalline silicon dioxide with high specific surface area and high pozzolanic reactivity. These RHA properties can demonstrate a significant influence in improving the mechanical and durability properties of mortar and concrete. Furthermore, rice husk ash can provide a cost effective and give concrete more sustainability. In this paper, chemical composition, reactive silica and fineness effect was assessed by examining five different types of RHA. Mortars and concrete specimens were molded with 5% to 50% of ash, replacing the Portland cement, and measured their compressive and tensile strength behavior. Beyond it, another two parameters had been considered: the durability of concrete blended RHA, and effect of temperature on the transformed of amorphous structure to crystalline form. To obtain the rice husk ash properties, these different types were subjected to X-Ray fluorescence to determine the chemical composition, while pozzolanic activity obtained by using X-Ray diffraction test. On the other hand, finesses and specific surface area were obtained by used Malvern Mastersizer 2000 test. The measured parameters properties of fresh mortar and concrete obtained by used flow table and slump test. While, for hardened mortar and concrete the compressive and tensile strength determined pulse the chloride ions penetration for concrete using NT Build 492 (Nord Test) – non-steady state migration test (RMT Test). The obtained test results indicated that RHA can be used as a cement replacement material in concrete with considerable proportion up to 50% percentages without compromising concrete strength. The use of RHA in the concrete as blending materials improved the different characteristics of the concrete product. The paper concludes that to exhibits a good compressive strength of OPC mortar or concrete with increase RHA replacement ratio rice husk ash should be consist of high silica content with high pozzolanic activity. Furthermore, with high amount of carbon content (12%) could be improve the strength of concrete when the silica structure is totally amorphous. As well RHA with high amount of crystalline form (25%) can be used as cement replacement when the silica content over 90%. The workability and strength of concrete increased by used of superplasticizer and it depends on the silica structure and carbon content. This study therefore is an investigation of the effect of partially replacing Ordinary Portland cement (OPC) with Rice hush Ash (RHA) on the mechanical properties and durability of concrete. This paper gives satisfactory results to use RHA in sustainable construction in order to reduce the carbon footprint associated with cement industry.

Keywords: OPC, ordinary Portland cement, RHA rice husk ash, W/B water to binder ratio, CO2, carbon dioxide

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Authors: Ayşin Sev, Meltem Ezel

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Sustainability, being the urgent issue of our time, is closely related with the innovations in technology. Nanotechnology (NT), although not a new science, can be regarded relatively a new science for buildings with brand new materials and applications. This paper tends to give a research review of current and near future applications of nanotechnology (NT) for achieving high-performance and healthy buildings for a sustainable future. In the introduction, the driving forces for the sustainability of construction industry are explained. Then, the term NT is defined, and significance of innovations in NT for a sustainable construction industry is revealed. After presenting the application areas of NT and nanomaterials for buildings with a number of cases, challenges in the adoption of this technology are put forward, and finally the impacts of nanoparticles and nanomaterials on human health and environment are discussed.

Keywords: nanomaterial, self-healing concrete, self cleaning sensor, nanosensor, steel, wood, aerogel, flexible solar panel

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Authors: Damian A. Mooney, Michael T. P. Mc Cann, J. M. Don MacElroy, Olli Antson, Denis P. Dowling

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Atmospheric pressure plasma liquid deposition (APPLD) is a novel technology used for the deposition of thin films via the injection of a reactive liquid precursor into a high-energy discharge plasma at ambient pressure. In this work, APPLD, utilising a TEOS precursor, was employed to produce asymmetric membranes consisting of a thin (100 nm) layer of deposited silica on a microporous silica support in order to assess their suitability for high temperature gas separation applications. He and N₂ gas permeability measurements were made for each of the fabricated membranes and a maximum ideal He/N₂ selectivity of 66 was observed at room temperature. He, N₂ and CO2 gas permeances were also measured at the elevated temperature of 673K and ideal He/N₂ and CO₂/N₂ selectivities of 300 and 7.4, respectively, were observed. The results suggest that this plasma-based deposition technique can be a viable method for the manufacture of membranes for the efficient separation of high temperature, post-combustion gases, including that of CO₂/N₂ where the constituent gases differ in size by fractions of an Ångstrom.

Keywords: asymmetric membrane, CO₂ separation, high temperature, plasma deposition, thin films

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Authors: Ben Yahia Nouha, Sebei Abdelaziz, Boussen Slim, Chaabani Fredj

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The present work aims to determine mineralogical and geochemical characteristics of siliceous rock levels and to clarify the origin through geochemical arguments. This study was performed on the deposit of Tabarka-Babouch, which belongs to the northwestern of Tunisia; they spread out the later Miocene. Investigations were carried out to study mineralogical structure by XRD and chemical analysis by ICP-AES. The X-ray diffraction (XRD) patterns of the powdered natural rocks show that the Babouchite is composed mainly of quartz and clay minerals (smectite, illite, and kaolinite). Siliceous rocks contain quartz as a major silica mineral, which is characterized by two broad reflections at the vicinity of 4.26Å and 3.34 Å, respectively, with a total lack of opal-CT. That confirms that these siliceous rocks are quartz-rich (can reach 90%). Indeed, the amounts of all clay minerals (ACM), constituted essentially by smectite marked by a close association with illite and kaolinite, are relatively high, where their percentages vary from 7 to 46%. Chemical analyses show that the major oxide contents are consistent with mineralogical observations. It reveals that the siliceous rocks of the Babouchite formation are rich in SiO₂. The data of whole-rock chemical analyses indicate that the SiO₂ content is generally in the range 73-91 wt.%; (average: 80.43 wt.%). The concentration of Al₂O₃, which represent the detrital fractions in the studied samples, varies from 3.99 to 10.55 wt. % and Fe₂O₃ from 0.73 to 4.41wt. %. The low levels recorded in CaO (%) show that the carbonate is considered impurities. However, these rocks contain a low amount of some others oxides, such as the following: Na₂O, MgO, K₂O, and TiO₂. The trace elemental distributions also vary with high Sr (up to 84.55 ppm), Cu (5–127 ppm), and Zn (up to 124 ppm), with a relatively lower concentration of Co (2.43-25.54 ppm), Cr (10–61 ppm) and Pb (8-22ppm). The Babouchite siliceous rocks of northwestern of Tunisia have generally high Al/ (Al+Fe+Mn) values (0.63-0.83). The majority of Al/ (Al+Fe+Mn) values are nearly of 0.6, which is the biogenic end-member. Thus, Al/ (Al+Fe+Mn) values revealed the biogenic origin of silica.

Keywords: siliceous rocks, Babouchite formation, XRD, chemical analysis, biogenic silica, Northwestern of Tunisia

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Authors: T. H. N. Nguyen, A. Khodan, M. Amamra, J-V. Vignes, A. Kanaev

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The ultraporous nanofibrous alumina (NOA, Al2O3·nH2O) was synthesized by oxidation of laminated aluminium plates through a liquid mercury-silver layer in a humid atmosphere ~80% at 25°C. The material has an extremely high purity (99%), porosity (90%) and specific area (300 m2/g). The subsequent annealing of raw NOA permits obtaining pure transition phase (γ and θ) nanostructured materials. In this combination, we report on chemical, structural and phase transformations of pure and modified NOA by an impregnation of trimethylethoxysilane (TMES) and tetraethoxysilane (TEOS) during thermal annealing in the temperature range between 20 and 1650°C. The mass density, specific area, average diameter and specific area are analysed. The 3D model of pure NOA monoliths and silica modified NOA is proposed, which successfully describes the evolution of specific area, mass density and phase transformations. Activation energies of the mass transport in two regimes of surface diffusion and bulk sintering were obtained based on this model. We conclude about a common origin of modifications of the NOA morphology, chemical composition and phase transition.

Keywords: nanostructured materials, alumina (Al₂O₃), morphology, phase transitions

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Authors: Anca Dinischiotu, Sorina Nicoleta Voicu

Abstract:

Silica nanoparticles (SiO2-NPs) are widely used in consumer products such as paints, plastics, insulation materials, tires, concrete production, as well as in gene delivery systems and imaging procedures. Environmental human exposure to them occurs during utilization of these products, in a time-dependent manner, the uptake being by topic and inhalation route especially. SiO2-NPs enter cells and induce membrane damage, oxidative stress and inflammatory reactions in a concentration-dependent manner. In this study, MRC-5 cells (human fetal lung fibroblasts) were exposed to amorphous SiO2-NPs at a dose of 62.5 μg/ml for 24, 48 and 72 hours. The size distribution of NPs was a lognormal function, in the range 3-14 nm. A time-dependent decrease of total reduced glutathione concentration by 36%, 50%, and 78% and an increase of NO level by 62%, 32%, respectively 24% compared to control were noticed. An up-regulation of NF-kB expression by 20%, 50% respectively 10% and of Nrf-2 by 139%, 58%, and 16% compared to control after 24, 48 and 72 hours was noticed also. The expression of IL-1β, IL-6, IL-8, and COX-2 was up-regulated in a time-dependent manner. Also, the expression of MMP-2 and MMP-9 were down-regulated after 48 and 72 hours, whereas their activities raised in a time-dependent manner. Exposure of cells to NPs up-regulated the expression of inducible NO synthase, as previously was shown, and probably this is the reason for the increased level of NO, that can react with the thiol groups of reduced glutathione molecules, diminishing its concentration Nrf2 is a transcription factor translocated in nucleus, under oxidative stress, where downstream gene expression activates in order to modulate the adaptive intracellular response against oxidative stress. The cross-talk between Nrf2 and NF-kB activities regulates the inflammatory processes. The activation of NF-kB could activate up-regulation of IL-1β, IL-6, and IL-8. The increase of COX-2 expression could be correlated with IL-1β one. Also, probably in response to the pro-inflammatory cytokines, MMP-2 and MMP-9 were induced and activated. In conclusion, the exposure of MRC-5 cells to SiO2-NPs generated inflammation in a time-dependent manner.

Keywords: inflammation, MRC-5 cells, oxidative stress, silica nanoparticles

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Authors: Fang Li, Jiazhao Wang, Jianmin Ma

Abstract:

The practical application of Li-S batteries is hampered due to poor cycling stability caused by electrolyte-dissolved lithium polysulfides. Dual functionalities such as strong chemical adsorption stability and high conductivity are highly desired for an ideal host material for a sulfur-based cathode. Polypyrrole (PPy), as a conductive polymer, was widely studied as matrixes for sulfur cathode due to its high conductivity and strong chemical interaction with soluble polysulfides. Thus, a novel cathode structure consisting of a free-standing sulfur-polypyrrole cathode and a polypyrrole coated separator was designed for flexible Li-S batteries. The PPy materials show strong interaction with dissoluble polysulfides, which could suppress the shuttle effect and improve the cycling stability. In addition, the synthesized PPy film with a rough surface acts as a current collector, which improves the adhesion of sulfur materials and restrain the volume expansion, enhancing the structural stability during the cycling process. For further enhancing the cycling stability, a PPy coated separator was also applied, which could make polysulfides into the cathode side to alleviate the shuttle effect. Moreover, the PPy layer coated on commercial separator is much lighter than other reported interlayers. A soft-packaged flexible Li-S battery has been designed and fabricated for testing the practical application of the designed cathode and separator, which could power a device consisting of 24 light-emitting diode (LED) lights. Moreover, the soft-packaged flexible battery can still show relatively stable cycling performance after repeated bending, indicating the potential application in flexible batteries. A novel vapor phase deposition method was also applied to prepare uniform polypyrrole layer coated sulfur/graphene aerogel composite. The polypyrrole layer simultaneously acts as host and adsorbent for efficient suppression of polysulfides dissolution through strong chemical interaction. The density functional theory (DFT) calculations reveal that the polypyrrole could trap lithium polysulfides through stronger bonding energy. In addition, the deflation of sulfur/graphene hydrogel during the vapor phase deposition process enhances the contact of sulfur with matrixes, resulting in high sulfur utilization and good rate capability. As a result, the synthesized polypyrrole coated sulfur/graphene aerogel composite delivers a specific discharge capacity of 1167 mAh g⁻¹ and 409.1 mAh g⁻¹ at 0.2 C and 5 C respectively. The capacity can maintain at 698 mAh g⁻¹ at 0.5 C after 500 cycles, showing an ultra-slow decay rate of 0.03% per cycle.

Keywords: polypyrrole, strong chemical interaction, long-term stability, Li-S batteries

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Authors: Jagannath Prasad Tegar, Zeeshan Ahmad

Abstract:

The Ordinary Portland Cement (OPC) is a major constituent of concrete, which is being used extensively since last half century. The production of cement is impacting not only environment alone, but depleting natural materials. During the past 3 decades, the scholars have carried out studies and researches to explore the supplementary cementatious materials such as Ground granulated Blast furnace slag (GGBFS), silica fumes (SF), metakaolin or fly ash (FA). This has contributed towards improved cementatious materials which are being used in construction, but not the way it is supposed to be. The alkali activated slag concrete is another innovation which has constituents of cementatious materials like Ground Granuled Blast Furnace Slag (GGBFS), Fly Ash (FA), Silica Fumes (SF) or Metakaolin. Alkaline activators like Sodium Silicate (Na₂SiO₃) and Sodium Hydroxide (NaOH) is utilized. In view of evaluating properties of alkali activated slag concrete blended with polypropylene shredding and accelerator, research study is being carried out. This research study is proposed to evaluate the effect of polypropylene shredding and accelerating admixture on mechanical properties of alkali-activated slag concrete. The mechanical properties include the compressive strength, splitting tensile strength and workability. The outcomes of this research are matched with the hypothesis and it is found that 27% of cement can be replaced with the ground granulated blast furnace slag (GGBFS) and for split tensile strength 20% replacement is achieved. Overall it is found that 20% of cement can be replaced with ground granulated blast furnace slag. The tests conducted in the laboratory for evaluating properties such as compressive strength test, split tensile strength test, and slump cone test. On the aspect of cost, it is substantially benefitted.

Keywords: ordinary Portland cement, activated slag concrete, ground granule blast furnace slag, fly ash, silica fumes

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Authors: Irfan Turetgen

Abstract:

Closed-circuit cooling towers are cooling units that operate according to the indirect cooling principle. Unlike the open-loop cooling tower, the filler material includes a closed-loop water-operated heat exchanger. The main purpose of this heat exchanger is to prevent the cooled process water from contacting with the external environment. In order to ensure that the hot water is cooled, the water is cooled by the air flow and the circulation water of the tower as it passes through the pipe. They are now more commonly used than open loop cooling towers that provide cooling with plastic filling material. As with all surfaces in contact with water, there is a biofilm formation on the outer surface of the pipe. Although biofilm has been studied very well on plastic surfaces in open loop cooling towers, studies on biofilm layer formed on the heat exchangers of the closed circuit tower have not been found. In the recent study, natural biofilm formation was observed on the heat exchangers of the closed loop tower for 6 months. At the same time, nano-silica coating, which is known to reduce the formation of the biofilm layer, a comparison was made between the two different surfaces in terms of biofilm formation potential. Test surfaces were placed into biofilm reactor along with the untreated control coupons up to 6-months period for biofilm maturation. Natural bacterial communities were monitored to analyze the impact to mimic the real-life conditions. Surfaces were monthly analyzed in situ for their microbial load using epifluorescence microscopy. Wettability is known to play a key role in biofilm formation on surfaces, because characteristics of surface properties affect the bacterial adhesion. Results showed that surface-conditioning with nano-silica significantly reduce (up to 90%) biofilm formation. Easy coating process is a facile and low-cost method to prepare hydrophobic surface without any kinds of expensive compounds or methods.

Keywords: biofilms, cooling towers, fill material, nano silica

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Authors: Majede Modheji, Hamid Emadi, Hossein Vojoudi

Abstract:

An efficient magnetic mesoporous structure was designed and prepared for the facile pre-concentration of As(III) ions. To prepare the sorbent, a core-shell magnetic silica nanoparticle was covered by MCM-41 like structure, and then the surface was modified by guanidine via an amine linker. The prepared adsorbent was investigated as an effective and sensitive material for the adsorption of arsenic ions from the aqueous solution applying a normal batch method. The imperative variables of the adsorption were studied to increase efficiency. The dynamic and static processes were tested that matched a pseudo-second order of kinetic model and the Langmuir isotherm model, respectively. The sorbent reusability was investigated, and it was confirmed that the designed product could be applied at best for six cycles successively without any significant efficiency loss. The synthesized product was tested to determine and pre-concentrate trace amounts of arsenic ions in rice and natural waters as a real sample. A desorption process applying 5 mL of hydrochloric acid (0.5 mol L⁻¹) as an eluent exhibited about 98% recovery of the As(III) ions adsorbed on the GA-MSMP sorbent.

Keywords: arsenic, adsorption, mesoporous, surface modification, MCM-41

Procedia PDF Downloads 122

Authors: Aliyu Usman, Muhaammed Bello Ibrahim, Yusuf D. Amartey, Jibrin M. Kaura

Abstract:

This research is aimed at investigating the effect of using amorphous silica ash (ASA) obtained from rice husk as a partial replacement of ordinary Portland cement (OPC) on the mechanical and microstructure properties of cement paste and mortar. ASA was used in partial replacement of ordinary Portland cement in the following percentages 3 percent, 5 percent, 8 percent and 10 percent. These partial replacements were used to produce Cement-ASA paste and Cement-ASA mortar. ASA was found to contain all the major chemical compounds found in cement with the exception of alumina, which are SiO2 (91.5%), CaO (2.84%), Fe2O3 (1.96%), and loss on ignition (LOI) was found to be 9.18%. It also contains other minor oxides found in cement. Consistency of Cement-ASA paste was found to increase with increase in ASA replacement. Likewise, the setting time and soundness of the Cement-ASA paste also increases with increase in ASA replacements. The test on hardened mortar were destructive in nature which include flexural strength test on prismatic beam (40mm x 40mm x 160mm) at 2, 7, 14 and 28 days curing and compressive strength test on the cube size (40mm x 40mm, by using the auxiliary steel platens) at 2,7,14 and 28 days curing. The Cement-ASA mortar flexural and compressive strengths were found to be increasing with curing time and decreases with cement replacement by ASA. It was observed that 5 percent replacement of cement with ASA attained the highest strength for all the curing ages and all the percentage replacements attained the targeted compressive strength of 6N/mm2 for 28 days. There is an increase in the drying shrinkage of Cement-ASA mortar with curing time, it was also observed that the drying shrinkages for all the curing ages were greater than the control specimen all of which were greater than the code recommendation of less than 0.03%. The scanning electron microscope (SEM) was used to study the Cement-ASA mortar microstructure and to also look for hydration product and morphology.

Keywords: amorphous silica ash, cement mortar, cement paste, scanning electron microscope

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Authors: Reza Eslami-Farsani, Hamed Khosravi, Saba Fayazzadeh

Abstract:

Lightweight and efficient structures have the aim to enhance the efficiency of the components in various industries. Toward this end, composites are one of the most widely used materials because of durability, high strength and modulus, and low weight. One type of the advanced composites is grid-stiffened composite (GSC) structures, which have been extensively considered in aerospace, automotive, and aircraft industries. They are one of the top candidates for replacing some of the traditional components, which are used here. Although there are a good number of published surveys on the design aspects and fabrication of GSC structures, little systematic work has been reported on their material modification to improve their properties, to our knowledge. Matrix modification using nanoparticles is an effective method to enhance the flexural properties of the fibrous composites. In the present study, a silane-coupling agent (3-glycidoxypropyltrimethoxysilane/3-GPTS) was introduced onto the silica (SiO2) nanoparticle surface and its effects on the three-point flexural response of isogrid E-glass/epoxy composites were assessed. Based on the fourier transform infrared spectrometer (FTIR) spectra, it was inferred that the 3-GPTS coupling agent was successfully grafted onto the surface of SiO2 nanoparticles after modification. Flexural test revealed an improvement of 16%, 14%, and 36% in stiffness, maximum load and energy absorption of the isogrid specimen filled with 3 wt.% 3-GPTS/SiO2 compared to the neat one. It would be worth mentioning that in these structures, considerable energy absorption was observed after the primary failure related to the load peak. In addition, 3-GPTMS functionalization had a positive effect on the flexural behavior of the multiscale isogrid composites. In conclusion, this study suggests that the addition of modified silica nanoparticles is a promising method to improve the flexural properties of the grid-stiffened fibrous composite structures.

Keywords: isogrid-stiffened composite panels, silica nanoparticles, surface modification, flexural properties

Procedia PDF Downloads 203

Authors: Ishaq Ahmad, Zhaomin Li, Liu Chengwen, Song Yan Li, Zihan Gu, Li Shaopeng

Abstract:

In order to manage gas mobility in the reservoir, only a small amount of surfactant or polymer is needed because nanoparticles have the potential to improve foam stability. The aim is to enhance foam formation and stability, so it was decided to investigate the foam stability and foam ability of black rice husk ash. Several characterization techniques were used to investigate the properties of black rice husk ash. The best-performing anionic foaming surfactants were combined with black rice husk ash at different concentrations (ppm). Sodium dodecyl benzene sulphonate was used as the anionic surfactant. This study demonstrates the value of black rice husk ash (BRHA), which has a high silica concentration, for foam stability and ability. For the test, black rice husk ash and raw ash were used with SDS (Sodium Dodecyl Sulfate) and SDBS (Sodium dodecyl benzenesulfonate) surfactants under different parameters. Different concentration percentages were utilized to create the foam, and the hydrophobic test and shaking method were applied. The foam scanner was used to observe the behavior of the black rice husk ash foam. The high silica content of black rice husk ash has the potential to improve foam stability, which is favorable and could possibly improve oil recovery.

Keywords: black rice husk ash nanoparticle, surfactant, foam life, foam scanning

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Authors: M. Pacio, H. Juárez, R. Pérez-Cuapio E. Rosendo, T. Díaz, G. García

Abstract:

In this study, zinc oxide (ZnO) quantum dots (QDs) have been prepared by a simple route. The growth parameters for ZnO QDs were systematically studied inside a SiO2 shell; this shell acts as a capping agent and also enhances stability of the nanoparticles in water. ZnO QDs in silica shell could be produced by initially synthesizing a ZnO colloid (containing ZnO nanoparticles in methanol solution) and then was mixed with 3-aminopropylsiloxane used as SiO2 precursor. ZnO QDs were deposited onto silicon substrates (100) orientation by spin-coating technique. ZnO QDs into a SiO2 shell were pre-heated at 300 °C for 10 min after each coating, that procedure was repeated five times. The films were subsequently annealing in air atmosphere at 500 °C for 2 h to remove the trapped fluid inside the amorphous silica cage. ZnO QDs showed hexagonal wurtzite structure and about 5 nm in diameter. The composition of the films at the surface and in the bulk was obtained by Secondary Ion Mass Spectrometry (SIMS), the spectra revealed the presence of Zn- and Si- related clusters associated to the chemical species in the solid matrix. Photoluminescence (PL) spectra under 325 nm of excitation only show a strong UV emission band corresponding to ZnO QDs, such emission is enhanced with annealing. Our results showed that the method is appropriate for the preparation of ZnO QDs films embedded in a SiO2 shell with high UV photoluminescence.

Keywords: ZnO QDs, sol gel, functionalization

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Authors: B. Safi, B. Amrane, M. Saidi

Abstract:

The main purpose of this study is to evaluate the reuse of refractory brick wastes (RBW) as a supplementary cementitious materials (by a total replacement of silica fume) to produce a high performance fiber-reinforced concrete (HPFRC). This work presents an experimental study on the formulation and physico-mechanical characterization of ultra high performance fiber reinforced concretes based on three types of refractory brick wastes. These have been retrieved from the manufacturing unit of float glass MFG (Mediterranean Float Glass) after their use in the oven basin (ie d. they are considered waste unit). Three compositions of concrete (HPFRC) were established based on three types of refractory brick wastes (finely crushed), with the dosage of each type of bricks is kept constant, similar the dosage of silica fume used for the control concrete. While all the other components and the water/binder ratio are maintained constant with the same quantity of the superplasticizer. The performance of HPFRC, were evaluated by determining the essential characteristics of fresh and hardened concrete.

Keywords: refractory bricks, concrete, fiber, fluidity, compressive strength, tensile strength

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Authors: Sefiu A. Bello, Nasirudeen K. Raji, Jeleel A. Adebisi, Sadiq A. Raji

Abstract:

Pure metals are not used in most cases for structural applications because of their limited properties. Presently, high entropy alloys (HEAs) are emerging by mixing comparative proportions of metals with the aim of maximizing the entropy leading to enhancement in structural and mechanical properties. Aluminum Silicon Nickel Iron Vanadium (AlSiNiFeV) alloy was developed using stir cast technique and analysed. Results obtained show that the alloy grade G0 contains 44 percentage by weight (wt%) Al, 32 wt% Si, 9 wt% Ni, 4 wt% Fe, 3 wt% V and 8 wt% for minor elements with tensile strength and elongation of 106 Nmm^-2 and 2.68%, respectively. X-ray diffraction confirmed intermetallic compounds having hexagonal closed packed (HCP), orthorhombic and cubic structures in cubic dendritic matrix. This affirmed transformation from the cubic structures of elemental constituents of the HEAs to the precipitated structures of the intermetallic compounds. A maximum tensile strength of 188 Nmm^-2 with 4% elongation was noticed at 10wt% of silica addition to the G0. An increase in tensile strength with an increment in silica content could be attributed to different phases and crystal geometries characterizing each HEA.

Keywords: HEAs, phases model, aluminium, silicon, tensile strength, model

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Authors: Daniela Istrati, Alina Morosan, Maria Stanca, Bogdan Purcareanu, Adrian Fudulu, Laura Olariu, Alice Buteica, Ion Mindrila, Rodica Cristescu, Dan Eduard Mihaiescu

Abstract:

Our present work is related to the synthesis, characterization and applications of new nanocomposite materials based on silica mesoporous nanocompozites systems. The nanocomposite support was obtained by using a specific step–by–step multilayer structure buildup synthetic route, characterized by XRD (X-Ray Difraction), TEM (Transmission Electron Microscopy), FT-IR (Fourier Transform-Infra Red Spectrometry), BET (Brunauer–Emmett–Teller method) and loaded with Salvia officinalis plant extract obtained by a hydro-alcoholic extraction route. The sustained release of the target compounds was studied by a modified LC method, proving low release profiles, as expected for the high specific surface area support. The obtained results were further correlated with the in vitro / in vivo behavior of the nanocomposite material and recommending the silica mesoporous nanocomposites as good candidates for biomedical applications. Acknowledgements: This study has been funded by the Research Project PN-III-P2-2.1-PTE-2016-0160, 49-PTE / 2016 (PROZECHIMED) and Project Number PN-III-P4-ID-PCE-2016-0884 / 2017.

Keywords: biomedical, mesoporous, nanocomposites, natural products, sustained release

Procedia PDF Downloads 185