Search results for: porous silica

Authors: Damandeep Kaur, O.P. Pandey, M.S. Reddy

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In the present research, bio-synthesisation of silica particles has been carried out successfully. For this purpose, agriculture waste rice husk (RH) has been utilized. Among several types of agriculture waste, RH is considered to be cost-effective and easily accessible. In the present investigation, a chemical approach has been followed to extract silica nanoparticles. X-Ray Diffraction (XRD) patterns indicated the amorphous nature of silica at lower temperature range. Silica and other mineral contents have been found using energy dispersive spectroscopy (EDS). Morphological and structural studies have been carried out with the use of Field Emission Scanning Electron Microscopy (FE-SEM) and Fourier Transform Infrared Transmission (FTIR) spectroscopy. Further, extracted silica from RH has been used for preparation of the glasses. The appearance of broad humps in XRD patterns confirmed the amorphous nature of prepared glasses. These glasses exhibited enhanced antibacterial effect against both Gram-positive and Gram-negative bacteria. The as-synthesized glass samples can be further used for physical and structural studies for drug loading applications.

Keywords: rice husk, biosynthesized silica, bioactive glasses, antibacterial studies

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Authors: Amal Maazoun, Abderrazak Mezghani, Ali Ben Moussa

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Aerogel consists of a ramified and inter-connected solid skeleton enclosing a very important number of nano-sized pores filled with air that occupies most of the volume and makes very low density. The thermal conductivity of this material can reach lower values than those of any other material, and it changes with the type of the aerogel and its composition. So, in order to explain the causes of the super-insulation of our material and to determine the factors in which depends on its conductivity we used a numerical simulation. We have developed a numerical code that generates random fractal structure of silica aerogel with pre-defined concentration, properties of the backbone and the gas in the pores as well as the size of the particles. The calculation of the conductivity at any point of domain shows that it is not constant and that it depends on the pore size and the location in the pore. A numerical method based on resolution by inversion of block tridiagonal matrices is used to calculate the equivalent thermal conductivity of the whole fractal structure. The average conductivity calculated for each concentration is in good agreement with those of typical aerogels. And we found that the equivalent thermal conductivity of a silica aerogel depends strongly not only on the porosity but also on the tortuosity of the solid backbone.

Keywords: aerogel, fractal structure, numerical study, porous media, thermal conductivity

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Authors: Abd El-Aziz Said

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In this study, natural silica was used as an active, selective, reusable and eco-friendly catalyst for the liquid phase synthesis of iso-amyl, benzyl and cinnamyl esters. The original and calcined natural silica were characterized by TG-DTA, XRF, XRD, FTIR, SEM, and N2-sorption analysis. The surface acidity of the catalysts was determined using isopropanol dehydration and the strength of available acid sites was measured using chemisorption of pyridine (PY) and dimethyl pyridine (DMPY). The results of acidity specified that the acidic sites are of Brönsted type, while PY-TPD demonstrated that almost of the acidic sites over the surface of natural silica are of weak and intermediate strength. The catalytic activity of natural silica towards esterification of acetic acid with alcohols was extensively studied. The results revealed that natural silica had high catalytic activity with 100% selectivity to all targeted esters. In addition, the yields obtained in batch methods were 83, 81, and 80%, respectively, whereas these yields after simple distillation were improved 97, 99.5, and 90%, respectively.

Keywords: liquid-phase esterification, natural silica, acidity esters, characterization

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Authors: Najme Lari, Shahrokh Ahangarani, Ali Shanaghi

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Sol-gel technology is a promising manufacturing method to produce anti reflective silica thin films for solar energy applications. So to improve the properties of the films, controlling parameter of the sol - gel method is very important. In this study, soaking treatment effect on optical properties of silica anti reflective thin films was investigated. UV-Visible Spectroscopy, Fourier-Transformed Infrared Spectrophotometer and Field Emission Scanning Electron Microscopy was used for the characterization of silica thin films. Results showed that all nanoporous silica layers cause to considerable reduction of light reflections compared with uncoated glasses. With single layer deposition, the amount of reduction depends on the dipping time of coating and has an optimal time. Also, it was found that solar transmittance increased from 91.5% for the bare slide up to 97.5% for the best made sample corresponding to two deposition cycles.

Keywords: sol–gel, silica thin films, anti reflective coatings, optical properties, soaking treatment

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Authors: Mustapha El Mataouy, Abellatif Aaliti, Mouhamed Khaddor

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Erbium actived silica-hafnia planar waveguides have been prepared by sol-gel route. The films were deposited on vitreous silica substrates using dip-coating technique. The parameters of preparation have been chosen to optimize the waveguides for operation in the near infrared (NIR) region, and to increase the luminescence efficiency of the metastable 4I13/2 state of Erbium ions. The waveguides properties were determined by m-lines spectroscopy, loss measurements. Waveguide Raman and luminescence spectroscopy were used to obtain information about the structure of the prepared films and about the dynamical process related to the emission in the C telecom band (1530nm-1565nm) of the Erbium ions. The results are discussed with the aim of comparing the structural and optical properties of Erbium activated silica-hafnia planar waveguides with different molar ratio of Si / Hf.

Keywords: erbium, optical amplifiers, silica-hafnia, sol-gel, waveguide

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Authors: Eva Stefanovska, Estefania Cuenca, Aleksandra Momirov, Monika Fidanchevska, Liberato Ferrara, Emilija Fidanchevski

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Silica is used in construction materials as a part of natural raw materials or as an additive in powder form (micro and nano dimensions). SiO₂ particles in cement act as centers of nucleation, as a filler or as pozzolan material. In this regard, silica improves the microstructure of cementitious composites, increases the mechanical properties, and finally also results into improved durability of the final products. Improved properties of cementitious composites may lead to better structural efficiency, which, together with increased durability, results into increased sustainability signature of structures made with this kind of materials. The aim of the present work was to investigate the influence of silica on the properties of cement. Fly ash (as received and mechanically activated) and synthetized silica (sol-gel method using TEOS as precursor) was used in the investigation as source of silica. Four types of cement mixtures were investigated (reference cement paste, cement paste with addition of 15wt.% as-received fly ash, cement paste with 15 wt.% mechanically activated fly ash and cement paste with 14wt.% mechanically activated fly ash and 1 wt.% silica). The influence of silica on setting time and mechanical properties (2, 7 and 28 days) was followed. As a matter of fact it will be shown that cement paste with composition 85 wt. % cement, 14 wt.% mechanically activated fly ash and 1 wt. % SiO₂ obtained by the sol-gel method was the best performing one, with increased compressive and flexure strength by 9 and 10 % respectively, as compared to the reference mixture. Acknowledgements: 'COST Action CA15202, www.sarcos.eng.cam.ac.uk'

Keywords: cement, fly ash, mechanical properties, silica, sol-gel

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Authors: Gaurav Datta, Sourav Ghosh, Rahul Roy

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The incorporation of silica fume into the normal concrete is a routine one in the present days to produce the tailor made high strength and high performance concrete. The design parameters are increasing with the incorporation of silica fume in conventional concrete and the mix proportioning is becoming complex. The main objective of this paper has been made to investigate the different mechanical properties like compressive strength, permeability, porosity, density, modulus of elasticity, compacting factor, slump of concrete incorporating silica fume. In this present paper 5 (five) mix of concrete incorporating silica fume is cast to perform experiments. These experiments were carried out by replacing cement with different percentages of silica fume at a single constant water-cementitious materials ratio keeping other mix design variables constant. The silica fume was replaced by 0%, 5%, 10%, 15% and 20% for water-cementitious materials (w/cm) ratio for 0.40. For all mixes compressive strengths were determined at 24 hours, 7 and 28 days for 100 mm and 150 mm cubes. Other properties like permeability, porosity, density, modulus of elasticity, compacting factor, and slump were also determined for five mixes of concrete.

Keywords: high performance concrete, high strength concrete, silica fume, strength

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Authors: Aleksander Ostrowski, Hugh J. Byrne, Roland Sanctuary

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Investigation of the polymer interphases is an emerging field nowadays. In many cases interphases determine the functionality of a system. There is a great demand for exploration of fundamental understanding of the interphases and elucidation of their formation, dimensions dependent on various influencing factors, change of functional properties, etc. The epoxy applied on porous glass penetrates its pores with an extent dependent on the pore size, temperature and epoxy components mixing ratio. Developed over the recent time challenging sample preparation procedure allowed to produce very smooth epoxy-porous glass cross-sections. In this study, Raman spectroscopy was used to investigate the epoxy-porous glass interphases. It allowed for chemical differentiation between different regions at the cross-section and determination of the degree of cure of epoxy system in the porous glass.

Keywords: interphases, Raman spectroscopy, epoxy, porous glass

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Authors: Ching Yern Chee

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Various loading of nano silica is added into polyurethane (PU) and then coated on porcelain substrate. The wear and friction properties of the porcelain substrates coated with polyurethane/nano silica nano composite coatings were investigated using the reciprocating wear testing machine. The friction and wear test of polyurethane/nano silica coated porcelain substrate was studied at different sliding speed and applied load. It was found that the optimum composition of nano silica is 3 wt% which gives the lowest friction coefficient and wear rate in all applied load ranges and sliding speeds. For 3 wt% nano silica filled PU coated porcelain substrate, the increment of sliding speed caused higher wear rates but lower frictions coefficient. Besides, the friction coefficient of nano silica filled PU coated porcelain substrate decreased but the wear rate increased with the applied load.

Keywords: porcelain, nanocomposite coating, morphology, friction, wear behavior

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Authors: Hyu Sang Jo, Gyo Woo Lee

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In this study, the mechanical and thermal properties of epoxy composites that are reinforced with micrometer-sized silica particles were investigated by using the specimen experiments. For all specimens used in this study (from the baseline to specimen containing 70 wt% silica filler), the tensile strengths were gradually increased by 8-10%, but the ductility of the specimen was decreased by 34%, compared with those of the baseline samples. Similarly, for the samples containing 70 wt% silica filler, the coefficient of thermal expansion was reduced by 25%, but the thermal conductivity was increased by 100%, compared with those of the baseline samples. The improvement of thermal stability of the silica-reinforced specimen was confirmed to be within the experimented range, and the smaller silica particle was found to be more effective in delaying the thermal expansion of the specimens. When the smaller particle was used as filler, due to the increased specific interface area between filler and matrix, the thermal conductivities of the composite specimens were measured to be slightly lower than those of the specimens reinforced with the larger particle.

Keywords: carbon nanotube filler, epoxy composite, mechanical property, thermal property

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Authors: Saleh H. Abud, Z. Hassan, F. K. Yam

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Characteristics of MSM photodetector based on a porous In0.08Ga0.92N thin film were reported. Nanoporous structures of n-type In0.08Ga0.92N/AlN/Si thin films were synthesized by photoelectrochemical (PEC) etching at a ratio of 1:4 of HF:C2H5OH solution for 15 min. The structural and optical properties of pre- and post-etched thin films were investigated. Field emission scanning electron microscope and atomic force microscope images showed that the pre-etched thin film has a sufficiently smooth surface over a large region and the roughness increased for porous film. Blue shift has been observed in photoluminescence emission peak at 300 K for porous sample. The photoluminescence intensity of the porous film indicated that the optical properties have been enhanced. A high work function metals (Pt and Ni) were deposited as a metal contact on the porous films. The rise and recovery times of the devices were investigated at 390 nm chopped light. Finally, the sensitivity and quantum efficiency were also studied.

Keywords: porous InGaN, photoluminescence, SMS photodetector, atomic force microscopy

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Authors: Siming Wang, Qing Ni, Yu Wu, Ruihai Xu, Hong Ye

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Porous electric heaters, compared to conventional electric heaters, exhibit excellent heating performance due to their large specific surface area. Porous electric heaters employ porous metallic materials or conductive porous ceramics as the heating element. The former attains a low heating power with a fixed current due to the low electrical resistivity of metal. Although the latter can bypass the inherent challenges of porous metallic materials, the fabrication process of the conductive porous ceramics is complicated and high cost. This work proposed a porous ceramic electric heater with dielectric honeycomb ceramic as a substrate and surface conductive coating as a heating element. The conductive coating was prepared by the sol-gel method using silica sol and methyl trimethoxysilane as raw materials and graphite powder as conductive fillers. The conductive mechanism and degradation reason of the conductive coating was studied by electrical resistivity and thermal stability analysis. The heating performance of the proposed heater was experimentally investigated by heating air and deionized water. The results indicate that the electron transfer is achieved by forming the conductive network through the contact of the graphite flakes. With 30 wt% of graphite, the electrical resistivity of the conductive coating can be as low as 0.88 Ω∙cm. The conductive coating exhibits good electrical stability up to 500°C but degrades beyond 600°C due to the formation of many cracks in the coating caused by the weight loss and thermal expansion. The results also show that the working medium has a great influence on the volume power density of the heater. With air under natural convection as the working medium, the volume power density attains 640.85 kW/m3, which can be increased by 5 times when using deionized water as the working medium. The proposed honeycomb ceramic electric heater has the advantages of the simple fabrication method, low cost, and high volume power density, demonstrating great potential in the fluid heating field.

Keywords: conductive coating, honeycomb ceramic electric heater, high specific surface area, high volume power density

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Authors: Nadia Allouache

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The concept of second law is assumed to be important to optimize the energy losses in heat exchangers. The present study is devoted to the numerical prediction of entropy generation due to heat transfer and friction in a double tube heat exchanger partly or fully filled with a porous medium. The goal of this work is to find the optimal conditions that allow minimizing entropy generation. For this purpose, numerical modeling based on the control volume method is used to describe the flow and heat transfer phenomena in the fluid and the porous medium. Effects of the porous layer thickness, its permeability, and the effective thermal conductivity have been investigated. Unexpectedly, the fully porous heat exchanger yields a lower entropy generation than the partly porous case or the fluid case even if the friction increases the entropy generation.

Keywords: heat exchangers, porous medium, second law approach, turbulent flow

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Authors: S. Akridiss, E. El Tabach, K. Chetehouna, N. Gascoin, M. S. Kadiri

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Transpiration cooling combined to regenerative cooling is a technique that could be used to cool the porous walls of the future ramjet combustion chambers; it consists of using fuel that will flow through the pores of the porous material consisting of the chamber walls, as coolant. However, at high temperature, the fuel is pyrolysed and generates solid coke particles inside the porous materials. This phenomenon can lead to a significant decrease of the material permeability and can affect the efficiency of the cooling system. In order to better understand this phenomenon, an experimental laboratory study was undertaken to determine the transport and deposition of particles in a sintered porous material subjected to steady state flow. The test bench composed of a high-pressure autoclave is used to study the transport of different particle size (35

Keywords: experimental study, permeability, porous material, suspended particles

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Authors: Hideo Sawada

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Fluoroalkyl end-capped oligomers [RF-(M)n-RF; RF = fluoroalkyl groups; M = radical polymerizable monomers] can form nanometre size-controlled self-assembled oligomeric aggregates through the aggregations of end-capped fluoroalkyl groups. Fluoroalkyl end-capped oligomeric aggregates can also interact with guest molecules to afford fluorinated aggregate/guest molecule nanocomposites; although the corresponding non-fluorinated oligomers cannot form such molecular aggregates to interact with guest molecules. For example, silica nanoparticles should act as guest molecules in fluorinated oligomeric aggregate cores to give new fluorinated oligomer-coated silica nanoparticles (fluorinated oligomer/silica nanocomposites). In these fluoroalkyl end-capped oligomers/silica nanocomposites, some fluorinated oligomers/silica nanocomposites were found to exhibit no weight loss behavior corresponding to the contents of oligomers in the silica matrices even after calcination at 800 oC. Fluoroalkyl end-capped vinyltrimethoxysilane oligomer-coated silica nanoparticles can be prepared by the sol-gel reaction of the corresponding fluorinated oligomer under alkaline conditions. The modified glass surface treated with this fluorinated oligomeric nanoparticle exhibited a completely super-hydrophobic characteristic. These fluorinated nanoparticles were also applied to the surface modification possessing a super-oleophobic characteristic. Not only fluoroalkyl end-capped oligomers but also low molecular weight fluorinated surfactants such as perfluoro-1,3-propanedisulfonic acid (PFPS) were applied to the preparation of fluorinated surfactants/silica nanocomposites to give no weight loss in proportion to the content of the surfactants in the nanocomposites even after calcination at 800 oC.

Keywords: fluorinated oligomer, silica nanocomposite, nonflammable characteristic, superamphiphobic chracteristic

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Authors: G. E. Gandomkar, E. Bekhradinassab, S. Sabbaghi, M. M. Zerafat

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The reduction of water content in crude oil emulsions reduces pipeline corrosion potential and increases the productivity. Chemical emulsification of crude oil emulsions is one of the methods available to reduce the water content. Presence of demulsifier causes the film layer between the crude oil emulsion and water droplets to become unstable leading to the acceleration of water coalescence. This research has been performed to study the improvement performance of a chemical demulsifier by silica nanoparticles. The silica nano-particles have been synthesized by sol-gel technique and precipitation using poly vinyl alcohol (PVA) and poly ethylene glycol (PEG) as surfactants and then nano-particles are added to the demulsifier. The silica nanoparticles were characterized by Particle Size Analyzer (PSA) and SEM. Upon the addition of nanoparticles, bottle tests have been carried out to separate and measure the water content. The results show that silica nano-particles increase the demulsifier efficiency by about 40%.

Keywords: demulsifier, dehydration, silicon dioxide, nanoparticle

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Authors: Thomas Paris, Vincent Bruyere, Patrick Namy

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A numerical model is developed to simulate gas blowdowns through a thin tube and a filter (porous media), separating a high pressure gas filled reservoir to low pressure ones. Based on a previous work, a one-dimensional approach is developed by using the finite element method to solve the transient compressible flow and to predict the pressure and temperature evolution in space and time. Mass, momentum, and energy conservation equations are solved in a fully coupled way in the reservoirs, the pipes and the porous media. Numerical results, such as pressure and temperature evolutions, are firstly compared with experimental data to validate the model for different configurations. Couplings between porous media and pipe flow are then validated by checking mass balance. The influence of the porous media and the nature of the gas is then studied for different initial high pressure values.

Keywords: compressible flow, fluid mechanics, heat transfer, porous media

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Authors: Muhammad Rizwan Akram, Saim Raza, Hamza Hanif Chauhan

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This paper describes the aim of research to evaluate the performance of ordinary Portland concretes containing cement replacement materials in both binary and ternary system. Blocks of concrete were prepared to have a constant water-binder ratio of 0.30. The test variables included the type and the amount of the supplementary cementious materials (SCMs) such as class of Silica Fume (SF) and ground granulated blast furnace slag (GGBS). Portland cement was replaced with Silica Fume (SF) upto 7.5% and GGBS up to a level of 50%. Then physical properties are assessed from the compressive strength and permeability tests.

Keywords: silica fume, GGBS, compressive strength, permeability

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Authors: Ying Weiyong

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The micro/mesoporous core-shell composites compromising SSZ-13 cores and mesoporous silica shells were synthesized successfully with the soft template of cetytrimethylammonium. The shell thickness could be tuned from 25 nm to 100 nm by varying the TEOS/SSZ-13 ratio. The BET and SEM results show the core-shell composites possessing the tunable surface area (544.7-811.0 m2/g) with plenty of mesopores (2.7 nm). The acidity intensity of the strong acid sites on SSZ-13 was remarkably impaired with the decoration of the mesoporous silica shell, which leads to the suppression of the hydrogen transfer reaction in MTO reaction. The micro/mesoporous core-shell composites exhibit better methanol to olefins reaction performance with a prolonged lifetime and the improvement of light olefins selectivity.

Keywords: core-shell, mesoporous silica, methanol to olefins, SSZ-13

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Authors: S. U. Khan, T. Ayub, N. Shafiq

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The properties of locally produced metakaolin (MK) as cement replacing material and the comparison of reactivity with commercially available micro-silica have been investigated. Compressive strength, splitting tensile strength, and load-deflection behaviour under bending are the properties that have been studied. The amorphous phase of MK with micro-silica was compared through X-ray diffraction (XRD) pattern. Further, interfacial transition zone of concrete with micro-silica and MK was observed through Field Emission Scanning Electron Microscopy (FESEM). Three mixes of concrete were prepared. One of the mix is without cement replacement as control mix, and the remaining two mixes are 10% cement replacement with micro-silica and MK. It has been found that MK, due to its irregular structure and amorphous phase, has high reactivity with portlandite in concrete. The compressive strength at early age is higher with MK as compared to micro-silica. MK concrete showed higher splitting tensile strength and higher load carrying capacity as compared to control and micro-silica concrete at all ages respectively.

Keywords: metakaolin, compressive strength, splitting tensile strength, load deflection, interfacial transition zone

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Authors: Nyiko M. Chauke, James Ramontja, Richard M. Moutloali

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The zeolite ZSM-22 material demonstrated effective hydrophilic character as a nanoadditive filler in the preparation of nanocomposite membranes. In this study, nanorods ZSM-22 zeolite materials were hydrothermally synthesised from a homogenous gel mixture prepared using different silica precursors: colloidal silica, fumed silica, tetraethylorthosilicate (TEOS), and aluminium precursor: aluminium sulphate octadecahydrate (Al₂(SO₄)₃.18H₂O to Si/Al of 60. This was focused on developing a defect-free zeolite framework for effective use in applications such as membrane separation process, adsorption, and catalysis. The obtained ZSM-22 zeolite materials with 60 Si/Al ratio exhibits high crystallinity, hydrophilicity, and needle-like morphologies, suggesting successful synthesis as shown by X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) physicochemical analysis. It was revealed that the use of different nature of silica precursors significantly influenced the properties of the final product and contributed to the development of defect-free zeolite material. As such, the crystalline nanorods of Theta-1 (TON) ZSM-22 obtained from TEOS silica showed high phase purity, defect-free, and narrow particle size distribution. Morphological analysis exhibited that the use of TEOS as silica precursor was effective than its counterparts and produced high crystalline need-like agglomerated particles.

Keywords: silica precursor, hydrothermal synthesis, zeolite material, ZSM-22

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Authors: Mahdi Alsagour, Sam Ramrattan

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This paper was developed to investigate two types of sands from the Kingdom of Saudi Arabia (KSA) for potential use in the global metal casting industry. Four types of sands were selected for study, two of the sand systems investigated are natural sands from the KSA. The third sand sample is a heat processed synthetic sand and the last sample is commercially available US silica sand that is used as a control in the study. The purpose of this study is to define the durability of the four sand systems selected for foundry usage. Additionally, chemical analysis of the sand systems is presented before and after elevated temperature exposure. Results show that Saudi silica sands are durable and can be used in foundry processing.

Keywords: alternative molding media, foundry sand, reclamation, silica sand, specialty sand

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Authors: Alya Harichane, Badreddine Harichane

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The incorporation of polycarboxylate ether superplasticizer (PCE) and silica fume (SF) in high-performance concretes (HPC) leads to the achievement of remarkable rheological and mechanical improvements. In the fresh state, PCEs are adsorbed on cement particles and dispersants, in turn promoting the workability of the concrete. Silica fume enables a very well compacted concrete to be obtained, which is characterized by high mechanical parameters in its hardened state. Some PCEs are incompatible with silica fume, which can result in the loss of slump and in poor rheological behavior. The main objective of the research is the study of the influence of three types of PCEs, which all have a different molecular architecture, on the rheological and mechanical behavior of high-performance concretes containing 10% of SF as a partial replacement of cement. The results show that the carboxylic density of PCE has an influence on its compatibility with SF.

Keywords: polycarboxylate-ether superplasticizer, rheology, compressive strength, high-performance concrete, silica fume

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Authors: Binyamien Ibrahim Rasoul

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Controlled burning of rice husk can produce amorphous rice husk ash (RHA) with high silica content which can significantly enhance the properties of concrete. This study has been undertaken to investigate the relationship between the incineration temperatures and time to produce RHA with ultimate reactivity. The rice husk samples were incinerated in an electrical muffle furnace at 350°C, 400°C, 425°C 450°C, 475°C, and 500°C for 60 and 90 minutes, respectively. The silica structure in the Rice Husk Ash (RHA) was determined using X-Ray diffraction analysis, while chemical properties obtained using X-Ray Fluorescence. The results show that RHA appeared to be the totally amorphous when the husk incineration up to 425°C for 60 and even at 90 minutes. However, with increased temperature to 450°C, 475°C and 500°C, traces of crystalline silica (quartz) were detected. However, cannot be taken into account as it does not affect on the ash structure. In conclusion, the result gives an idea of the temperature and the time required to produce ash from rice husk with totally amorphous form.

Keywords: rice husk ash, silica, compressive strength, tensile strength, X-Ray diffraction, X-R florescence, pozzolanic activity

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Authors: Chang, Ya-Ju, Hsieh, Pei-Hsin, Wu, Jui-Chuang, Chen-Yang, Yui Whei

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A mesoporous silica material was prepared to apply to the lateral-flow immunochromatography for detecting a model biosample. The probe antibody is immobilized on the silica surface as the test line to capture its affinity antigen, which laterally flows through the chromatography strips. The antigen is labeled with nano-gold particles, such that the detection can be visually read out from the test line without instrument aids. The result reveals that the mesoporous material provides a vast area for immobilizing the detection probes. Biosening surfaces corresponding with a positive proportion of detection signals is obtained with the biosample loading.

Keywords: mesoporous silica, immunochromatography, lateral-flow strips, biosensors, nano-gold particles

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Authors: Yongjun Ahn, Sung Gyu Choi, Seung-Yeop Kwak

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Selective removal of free fatty acid (FFA) and chlorophyll in extra virgin olive oil (EVOO) is necessary to enhance the thermal stability in the condition of the deep frying. In this work, we demonstrated improving the thermal stability of EVOO by selective removal of free fatty acid and chlorophyll using (3-Aminopropyl)trimethoxysilane (APTMS) functionalized mesoporous silica with controlled pore size. The adsorption kinetics of free fatty acid and chlorophyll into the mesoporous silica were quantitatively analyzed by Freundlich and Langmuir model. The highest chlorophyll adsorption efficiency was shown in the pore size at 5 nm, suggesting that the interaction between the silica and the chlorophyll could be optimized at this point. The amino-functionalized mesoporous silica showed drastically improved removal efficiency of FFA than the bare silica. Moreover, beneficial compounds like tocopherol and phenolic compounds maintained even after adsorptive removal. Extra virgin olive oil treated by aminopropyl-functionalized silica had a smoke point high enough to be used as commercial frying oil. Based on these results, it is expected to attract the considerable amount of interest toward facile adsorptive refining process of EVOO using pore size controlled and amino-functionalized mesoporous silica.

Keywords: mesoporous silica, extra virgin olive oil, selective adsorption, thermal stability

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Authors: Zahra Neffah, Henda Kahalerras

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A numerical study is made in a parallel-plate porous channel subjected to an oscillating flow and an exothermic chemical reaction on its walls. The flow field in the porous region is modeled by the Darcy–Brinkman–Forchheimer model and the finite volume method is used to solve the governing equations. The effects of the modified Frank-Kamenetskii (FKm) and Damköhler (Dm) numbers, the amplitude of oscillation (A), and the Strouhal number (St) are examined. The main results show an increase of heat and mass transfer rates with A and St, and their decrease with FKm and Dm.

Keywords: chemical reaction, heat and mass transfer, oscillating flow, porous channel

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Authors: D. Srinivasacharya, Nidhi Humnekar

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The goal of this research is to numerically investigate the convection of nanofluid flow in an inclined porous channel. Brownian motion and thermophoresis effects are accounted for by nanofluid. In addition, the flow in the porous region governs Brinkman’s equation. The perturbed state of the generalized eigenvalue problem is obtained using normal mode analysis, and Chebyshev spectral collocation was used to solve this problem. For various values of the governing parameters, the critical wavenumber and critical Rayleigh number are calculated, and preferred modes are identified.

Keywords: Brinkman model, inclined channel, nanofluid, linear stability, porous media

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Authors: Kyuwon Lee, Young-Wook Chang

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Superhydrophobic surfaces have been paid great attentions over the years due to their various applications. In this study, superhydrophobic coatings based on the hybrids of hydrophobically modified silica nanoparticles and waterborne polyolefin were fabricated onto a cotton fabric by spraying a mixture of surface dodecylated silica nanoparticles with aqueous dispersion of polyolefin onto the fabric and a subsequent drying at 80℃. The coated fabrics were characterized using water-contact angle measurement, SEM, and AFM analysis. The coated fabrics exhibit superhydrophobicity with a water contact angle of 155° along with excellent self-cleaning and water/oil separation ability. It was also revealed that such superhydrophobicity was maintained after repeated mechanical abrasion using a sandpaper.

Keywords: superhydrophobic coating, waterborne polyolefin, dodecylated silica nanoparticle, durability

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Authors: Yasser Mahmoudi, Nader Karimi

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The present work examines analytically the effect internal heat generation on temperature fields in a channel partially-filled with a porous under local thermal non-equilibrium condition. The Darcy-Brinkman model is used to represent the fluid transport through the porous material. Two fundamental models (models A and B) represent the thermal boundary conditions at the interface between the porous medium and the clear region. The governing equations of the problem are manipulated, and for each interface model, exact solutions for the solid and fluid temperature fields are developed. These solutions incorporate the porous material thickness, Biot number, fluid to solid thermal conductivity ratio Darcy number, as the non-dimensional energy terms in fluid and solid as parameters. Results show that considering any of the two models and under zero or negative heat generation (heat sink) and for any Darcy number, an increase in the porous thickness increases the amount of heat flux transferred to the porous region. The obtained results are applicable to the analysis of complex porous media incorporating internal heat generation, such as heat transfer enhancement (THE), tumor ablation in biological tissues and porous radiant burners (PRBs).

Keywords: porous media, local thermal non-equilibrium, forced convection, heat transfer, exact solution, internal heat generation

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