nano-SiO2 Content Research Articles

Strength development of solidified dredged sludge containing humic acid with cement, lime and nano-SiO2

The disposal of dredged sludge (DS) poses an increasingly difficult problem for sediment dredging engineering. This study investigated the strength development of solidifying DS containing humic acid (HA) with cement, lime and nano-SiO2 (NS). A range of unconfined compressive strength (UCS) and pH tests were conducted to explore the roles of cement, NS, HA, lime and curing age on the solidification effect of DS. Furthermore, microstructures and crystalline phases of typical mixes were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The results showed that the addition of NS can significantly improve the strength development of cement-solidified dredged sludge (CDS). The 60-day UCS of CDS with 1.0% NS was more than twice that without NS, concurrently, the addition of NS also reduced the pH of CDS. The HA seriously affected the strength development of CDS, and the influence threshold value of HA content was in the range of 4.5–5.0%. Using lime together with cement for solidifying DS containing HA had advantages over using cement alone, and the optimum mass ratio of lime to cement is 6:9. The optimum NS content of 1.0% was determined to be the most cost-effective for improving the strength development of CDS. The microstructure and mineralogy analysis confirmed that adding NS to CDS can effectively accelerate the hydration reaction and produce more calcium silicate hydrate (CSH), leading to a significant improvement in the strength of CDS.

Properties of soy protein isolate/nano‐silica films and their applications in the preservation of Flammulina velutipes

This work evaluated the properties of soy protein isolate (SPI)/nano-silica (nano-SiO2) films. The particle size distribution of the film solutions and the Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy of films indicated that there were hydrogen bonds and coordinate bonds between the SPI and nano-SiO2. Scanning electron microscopy images indicated that an appropriate increase in the nano-SiO2 content improved the morphology of the films. Finally, the effect of SPI-based nanocomposite films on the preservation of Flammulina velutipes at 4 ± 1°C was investigated. After 10 days of storage, the weight loss and browning degree of F. velutipes in SPI films with 6% nano-SiO2 were significantly lower (p < .05), and the use of SPI/nano-SiO2 films could mitigate the losses of the total soluble solids and soluble protein contents. Therefore, SPI/nano-SiO2 films can prolong the shelf life and optimize the production of F. velutipes. Practical applications Fresh F. velutipes is nutritious and contains essential amino acids, vitamins, minerals, proteins, and fats. However, F. velutipes quickly undergoes browning, aging, and decomposition. Therefore, research in the F. velutipes preservation technology has important practical significance. In food packaging, the application of nanotechnology is gradually replacing traditional food packaging. However, no studies have reported the effects of SPI-based nanocomposite materials on the shelf life of F. velutipes. Therefore, the present study aimed to evaluate the properties of films and applications with F. velutipes.

Effect of nanoparticles on foaming agent and the foamed concrete

Nanoparticles are expected to improve properties of foaming agents and that prefabricated foams, further the performances of foamed concrete. In this study, foaming agents were prepared by introducing a certain content of nano-SiO2 (NS) and graphene (G), respectively. Effect of nanoparticles on foaming agent and that prefabricated foams has been investigated. Stability of prefabricated foams could be improved with the addition of NS, which might be attributed to the increased viscosity and a few changes in surface tension of foaming agents with NS. However, stability of the prefabricated foams would be degraded with the addition of G due to the obvious increase in surface tension of foaming agent with G. Furthermore, prefabricated foams through foaming agents with nanoparticles were used to prepare foamed concrete at dry density level of 500 kg/m3. Foamed concretes with decreased and evenly distributed pore sizes were obtained when foaming agents with NS were used, which is related to the much higher stability of prefabricated foams. Proper content of nanoparticles in foaming agents and the prefabricated foams can improve the mechanical properties of as-prepared foamed concrete. However, improvements for other performance of foamed concrete, such as thermal conductivity, water absorption and shrinkage, were not obvious when foaming agent with nanoparticles were used.

Influence of Nano-SiO2, Nano-CaCO3 and Nano-Al2O3 on Rheological Properties of Cement-Fly Ash Paste.

Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO2 (NS), nano-CaCO3 (NC) and nano-Al2O3 (NA) at different resting times (hydration time of 5 min, 60 min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel–Bulkley (H–B) model, and the influences of these nanomaterials on rheological properties of C–FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C–FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C–FA paste. When the content of NS and NA were 2 wt%, the rheological index of C–FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C–FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m2/g) and NA (120 m2/g) are much larger than that of NC (40 m2/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.

Durability of Steel Fiber-Reinforced Concrete Containing SiO2 Nano-Particles.

An experimental study was conducted to investigate the effect ofnano-SiO2 and steel fiber content on the durability of concrete. Five different dosages of nano-SiO2 particles and five volume dosages of steel fiber were used. The durability of concretes includes permeability resistance, cracking resistance, carbonation resistance, and freezing-thawing resistance, and these were evaluated by the water permeation depth, number of cracks, total cracking area per unit area of the specimens, carbonation depth of the specimens, and the relative dynamic elastic modulus of the specimens after freezing-thawing cycles, respectively. The results indicate that the addition of nano-SiO2 particles significantly improves the durability of concrete when the content of nano-SiO2 is limited within a certain range. With the increase of nano-SiO2 content, the durability of concrete first increases and then decreases. An excessive number of nano-SiO2 particles could have an adverse effect on the durability of the concrete. The addition of the correct amount of steel fibers improves the carbonation resistance of concrete containing nano-particles, but excessive steel fiber reduces the carbonation resistance. Moreover, the addition of steel fibers reduces the permeability resistance of concrete containing nano-particles. The incorporation of steel fiber enhanced the freezing-thawing resistance and cracking resistance of concrete containing nano-particles. With increasing steel fiber content, the freezing-thawing resistance of the concrete containing nano-particles increases, and the cracking resistance of the concrete decreases gradually.

Carbonation resistance of concrete treated with nano-SiO2- modified polymer coatings

This work investigated the effects of nano-SiO2 incorporation on the carbonation resistance of polymer-coated concrete. Three types of organic film-forming coatings, namely, polyurethane, chlo- rinated rubber, and epoxy resin coatings, were modified with 0.4, 1.2, or 2.0 wt.% nano-SiO2 particles. Concrete specimens were then treated with the modified coatings and subjected to accelerated carbona- tion experiments after periodic ultraviolet irradiation. The macro- and microappearances of the coatings after ultraviolet aging were also observed. Results indicated that the carbonation resistance of polymer- coated concrete samples gradually decreased as the polymer coating aged. The incorporation of nano- SiO2 improved the short-term carbonation resistance of coated concrete by increasing coating density and reducing microdefects in the coating film. The presence of nano-SiO2 strengthened the long-term carbonation resistance of coated concrete by shielding and absorbing ultraviolet light and attenuated coating aging. Excessive nano-SiO2 content, however, weakened the carbonation resistance of coated concrete. Thus, a nano-SiO2 dosage of approximately 0.4 wt.% should be applied to develop concrete coatings with the optimal carbonation resistance.

Effect of nano-SiO2 on early hydration of natural hydraulic lime

Abstract Natural hydraulic lime (NHL) containing both hydraulic and air-hardening contents is of an ideal alternative binder for mortars used in interior decoration, cultural relics repair and historic buildings maintenance. In this study, early hydration and hardening properties of NHL2 with nano-SiO2 (NS) were researched. Hydration exothermic rate firstly decreased within 5 h of hydration and then increased after 5 h of hydration with the increase of NS, which could be attributed to the C2S hydration and the additional pozzolanic reaction between Ca(OH)2 and NS. It is noted that the initial hydration of C2S would be restrained by the increase content of NS in NHL2 due to the delayed exothermic peak occurring time within 5 h of hydration. A decreased porosity of hardened NHL pastes with the increase of NS at each curing age were observed, which might be also caused by the pozzolanic reaction between Ca(OH)2 and NS. Meanwhile, an increased capacity for the pores about 50 nm and decreased capacity for the pores about 1 μm with the increase of NS were also observed. In addition, mechanical level of NHL could be improved from NHL2 to NHL3.5 when more than 2% NS were added.

Effects of pozzolanic and non-pozzolanic nanomaterials on cement-based materials

Although it has been verified that nanomaterials can improve the properties of cement-based materials, the research on the characteristics and mechanism of different types of nanomaterials is still inadequate. Two typical types of nanomaterials, nano-SiO2 (pozzolanic material) and nano-TiO2 (non-pozzolanic material), are utilized in this paper to investigate the combined effects of reactivity, size, and content on the efficiency of nanomaterials in cement-based materials. The experimental results indicate that the size and content effect of nano-SiO2 is obvious. Small size and large content of nano-SiO2 can significantly improve the compressive strength of cement paste. However, the size effect of nano-TiO2 is much weaker than that of nano-SiO2, and the content effect of nano-TiO2 is only obvious at the early age. For the late age compressive strength, the small content of nano-TiO2 shows a similar obviously improving effect as the big content of nano-TiO2. The pore structure analysis shows that both nano-SiO2 and nano-TiO2 can reduce the total porosity of cement paste, but nano-TiO2 is more effective than nano-SiO2 at reducing the harmful pores. Therefore, the small content of nano-TiO2 is more effective to enhance the impermeability of cement-based materials. The results of this paper show that nano-SiO2 and nano-TiO2 have different effects and they should be selected based on the properties requirement of cement-based materials.

Facile fabrication of ultraviolet light cured fluorinated polymer layer for smart superhydrophobic surface with excellent durability and flame retardancy

Functional superhydrophobic coatings have raised wide concern due to their promising application in superhydrophobic paints, packaging materials, building materials etc, which call for the requirements of mechanical stability and flame retardancy. Herein, a series of UV cured superhydrophobic PVDT coatings with mechanical stability and flame retardancy were prepared using an all-in-one suspension containing trimethylolpropane triacrylate (TMPTA), vinyltriethoxysilane (VTES), 1H, 1H, 2H, 2H-Perfluorododecanethiol (PFDT), 9,10-Dihydro-9-Oxa-10-Phosphaphenanthrene-10-Oxide (DOPO), nano-SiO2 particles, and 2-Hydroxy-2-methylpropiophenone (HMPP). The reaction mechanism, surface morphology, phase composition of the PVDT coatings were investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The PVDT coatings exhibited excellent low adhesion against water droplets, superhydrophobicity and self-cleaning property when the content of nano-SiO2 reached to 40 wt%. Good mechanical and chemical stability of PVDT coatings was confirmed by abrasion test, tape adhesion test and corrosive media treatment. Further, the combustion experiments indicated that the PVDT coatings exhibited excellent flame retardancy and significant ignition delay. All these results demonstrated that the prepared PVDT coatings tended to achieve wide application in waterproof and fireproof materials.

Dielectric Properties of Epoxy Resin Impregnated Nano-SiO₂ Modified Insulating Paper.

Epoxy resin-impregnated insulation paper (RIP) composites are used as the inner insulation of dry condenser bushing in the ultra-high voltage direct current (UHVDC) power transmission system. To improve the dielectric properties of RIP, nano-SiO2 is added to the insulation paper at concentrations of 0–4wt % before impregnation with pure epoxy resin. X-ray diffraction (XRD), scanning electron microscopy observations as well as the typical dielectric properties of relative permittivity, DC volume conductivity, DC breakdown strength, and thermally stimulated depolarization current (TSDC), were obtained. The effects of trap parameters on the breakdown field strength and volume conductivity were investigated. The DC breakdown electric field strength of the sample increased as the trap level increased. The maximum DC breakdown strength of nano-SiO2-modified RIP was increased by 10.6% the nano-SiO2 content of 2 wt %. The relative permittivity and DC volume conductivity were first decreased and then increased with increasing nano-SiO2 content. These changes occurred near the interfaces between nano-SiO2 and RIP. The increased DC breakdown strength was mainly attributed to the increased trap level.

Smart Cement Compressive Piezoresistive, Stress-Strain, and Strength Behavior with Nanosilica Modification

Abstract In this study, smart cement with a water-to-cement ratio of 0.38 was modified with up to 1 % silica nanoparticles (NanoSiO2) to evaluate the effect not only on the sensing properties but also on the compressive stress-strain relationship and strength. The oil well cement (class H) and cement modified with NanoSiO2 were characterized using X-ray diffraction analysis and thermal gravimetric analysis. The smart cement was prepared by adding 0.1 % of the conductive filler based on the percolation theory concept to make the cement piezoresistive yet remain a nonconductive material. Testing evaluated the smart cement behavior with and without NanoSiO2 to verify the sensitivity of electrical resistivity changes with time and compressive loading. The addition of 0.5 and 1 % NanoSiO2 increased the initial electrical resistivity of the smart cement by 17 and 35 %, respectively. In one day, the maximum change in the electrical resistivity (RI24hr) for the smart cement without NanoSiO2 was 364 %. The RI24hr for the smart cement with NanoSiO2 decreased with the amount of NanoSiO2. The addition of 1 % NanoSiO2 increased the compressive strength of the smart cement by 14 and 42 % after 1 and 28 days of curing, respectively. The nonlinear Vipulanandan p-q curing model was used to predict the changes in electrical resistivity with curing time. The piezoresistivity of smart cement with NanoSiO2 was over 500 times higher than the regular cement, depending on the curing time and NanoSiO2 content. The Vipulanandan p-q stress strain and stress change in resistivity models also predicted the experimental results very well. For smart cement modified with NanoSiO2, the resistivity change at peak stress was over 1,250 times higher than the change in the compressive strain. A linear correlation was obtained between the RI24hr and the compressive strength of the modified smart cement based on the curing time.

Experimental study on ASR performance of concrete with nano-particles

ABSTRACT Alkali-silica reaction (ASR) is a serious durability problem, resulting in significant maintenance and reconstruction cost of concrete infrastructure all over the world, so more and more attention has been attracted to it. This paper tends to discuss whether nano-SiO2 and nano-Fe2O3 can mitigate the concrete deterioration caused by ASR. The test results show that the concretes with nano-particles have lower expansion and higher sonic velocity. Therefore, it is an available method for concrete to mix with nano-particles to mitigate ASR and the optimum content of nano-SiO2 and nano-Fe2O3 in concrete is 2.0% and 1.0%, respectively. The mitigating mechanism is revealed through the effect of mixing water on the porosity.

Role of nano-SiO2 on the performance of microporous foamed polystyrene polymer

Microporous foamed polymers are widely used in numerous fields hence, research on these materials has great practical significance. In this work, the effects of nano-SiO2 on the micromorphology of polystyrene (PS) microporous foamed materials were systematically studied by varying nano-SiO2 content and foaming temperature. Relative to PS, the results show that addition of nano-SiO2 significantly affects the foaming of PS materials. The use of nano-SiO2 as a nucleating agent reduces the size and increases the density of the cells in the PS matrix. Moreover, the addition of nano-SiO2 reduced the viscoelasticity and resistance in the foaming process, whereas the expansion ratio improved. A foamed material with minimum standard deviation of the cell diameter was obtained using PS with 3% nano-SiO2 content. The addition of nano-SiO2 led to an increase in the foaming temperature of the foaming material with the maximum expansion ratio as well as the one having the maximum cell diameter. Further, this addition also led to flattening of the expansion ratio curve in the region of the maximum expansion ratio.

Preparation and properties of super hydrophobic films from siloxane-modified two-component waterborne polyurethane and hydrophobic nano SiO2

Nanocomposite films with super hydrophobic surface were prepared by building rough micro/nano structure on the surface of siloxane-modified two-component waterborne polyurethane (2K-WPU) with hydrophobic nano SiO2. Firstly, nano SiO2 prepared by StÖber method with tetraethoxysilane (TEOS) as precursor was modified with trimethylethoxysilane (TMES), in order to cover a layer of hydrophobic methyl groups on the surface of nano SiO2. Then, a series of nanocomposite films with different water contact angles were obtained by adding different contents of TMES modified SiO2 into the siloxane-modified 2K-WPU. The effects of the content of nano SiO2 on the morphology and hydrophobicity of film surface were investigated. The results showed that the surface structures of the nanocomposite films became rougher and the water contact angle of nanocomposite films was increased obviously with the increase of the content of hydrophobic nano SiO2. Super hydrophobic nanocomposite film with water contact angle over 150° was successfully fabricated by using polysiloxane as low surface energy material and hydrophobic nano SiO2 as micro/nano rough structure builder on the polymer surface. Moreover, incorporating nano SiO2 into the 2K-WPU matrix could increase the glass transition temperature and thermal stability of the nanocomposite films.

Study on the grindability of nano-vitrified bond CBN grinding wheel for nickel-based alloy

This paper aims to study the effect of nano-vitrified bond grinding wheels on the grinding ability of nickel-based alloys and explores the effect of different content of nano-materials on the performance of grinding wheels. The nano-vitrified bond grinding wheel is manufactured by adding nano-materials into the conventional vitrified bond. When the content of nano-SiO2 is 10% and the content of nano-Al2O3 is 5%, the refractoriness, fluidity, and bending strength of the bond are superior to those of the conventional vitrified bond grinding wheel. Through the grinding experiment of high-temperature nickel-based alloy GH4169, it proved that the grinding force of nano-vitrified bond grinding wheel and the grinding temperature are lower than the conventional vitrified bond grinding wheel, and the grinding surface quality is better than the conventional vitrified abrasive. Obviously, nano-vitrified bond CBN grinding wheel is more suitable for the grinding of high-temperature alloy.

TIPS behavior for IPP/nano-SiO2 blend membrane formation and its contribution to membrane morphology and performance

Abstract In the present work, the TIPS behavior of isotactic polypropylene (iPP)/di-n-butyl phthalate (DBP)/dioctyl phthalate (DOP)/nano-SiO2 system and the competition relation between liquid–liquid phase separation and polymer crystallization are successfully adjusted by adding nano-SiO2. The liquid–liquid phase separation temperature of the system increases with increasing nano-SiO2 content. Besides, iPP crystallization temperature is also changed after adding nano-SiO2. IPP/nano-SiO2 blend hollow fiber microporous membrane is prepared via TIPS method. SEM photos show that the membrane exhibits mixed morphology combining cellular structure relating to liquid–liquid phase separation and branch structure originating from polymer crystallization. The relative weight of cellular structure first decreases and then increases with the increase of nano-SiO2 content. Furthermore, porosity, connectivity among pores and pure water flux of the membrane first increase and then decrease with increasing nano-SiO2 content. However, mechanical performance of the membrane is improved at all times with increasing nano-SiO2 content.

Study on the effects Nano‐SiO2 and spent catalyst ratios on characteristics of metakaolin‐based geopolymers

This study focused on nano‐SiO2 (NS) addition levels (0.5%–2%) and spent catalyst replacement levels (0%–20%) in the geopolymerization reaction and subsequent network formation of metakaolin‐based geopolymers (MKGP), which affect the mechanical properties and microstructure of the geopolymers. The geopolymers had high flexural strength (72.9 MPa), high bulk density (1.37 g/cm3), and low porosity (41.4%) when 0.5% NS was constantly added and the spent catalyst replacement level was 5%. The geopolymer weight loss was due to the structural water evaporation occurring at temperatures ranging from 350°C to 550°C. Therefore, weight loss was slightly higher than 0.5% NS MKGP without spent catalyst (1.25%) at the spent catalyst replacement level of 5% (1.44%). Regarding the chemical shifts in 29Si MAS NMR spectra, when the geopolymer contained 0.5% NS, the peak center of Q4 (2Al, −97 ppm) shifted to an even higher magnetic of Q4 (3Al, −90 ppm). The NS surface, which was in an active and high free‐energy state, reacted with the geopolymerization system, forming chemical interfacial bonding with the binder phase. The MKGP with 0.5% NS content and 5% spent catalyst replacement yielded more favorable mechanical characteristics and microstructure, according to the flexural strength, TG/DTA, and NMR analyses. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 220–227, 2019

Influences of surface modification of nano-silica by silane coupling agents on the thermal and frictional properties of cyanate ester resin

Abstract The surface of nano-silicon dioxide (nano-SiO2) particles was modified by small molecular coupling agent KH-560 and macromolecular coupling agent SEA-171, respectively, to change the surface activity and structure. The modified nano-SiO2 was then used for reinforcing cyanate ester resin (CE). Influences of the content of nano-SiO2 and the interfacial structure over the thermal and frictional properties of nano-SiO2/CE composites were investigated. The mechanism of the surface modification of silicon dioxide by KH-560 and SEA-171 was discussed. The experimental results show that the addition of coupling agents increased the interfacial bonding between nano-SiO2 particles and the CE resin so that the heat resistance and friction properties of the composites were improved. After surface treatment of nano-SiO2 by SEA-171, the thermal decomposition temperature of the 3.0 wt% nano-SiO2/CE composites increased nearly by 75 °C and the frictional coefficient was reduced by 25% compared with that of the pure CE, and the wear resistance increased by 77%.

Development and Characterization of a Novel Ecofriendly Biodegradable Whey Protein Concentrate Film with nano-SiO2

Abstract Nowadays, researchers have attracted to substitute petroleum-based materials by biopolymers due to limitation of petroleum resources and environmental concerns. Nano-fillers were used to reduce some drawbacks of biopolymers as packaging materials. Nanocomposite films composed of 5 % (wt% dry base) whey protein concentrate (WPC), 30 % glycerol, (1 %, 3 %, and 5 %) nano-SiO2 (NS). The films were prepared by solution casting method. Tensile strength of WPC/NS nanocomposites increased around 50 % compared to WPC by increasing NS content up to 3 %. While elongation at break (EB) decreased around 20 % compared to WPC, simultaneously. But at high NS content (5 %), EB decreased to 17.93 %. Sensibility of WPC/NS nanocomposites film to water and water vapor permeability was decreased with increasing NS content up to 3 %. NS content was an effective factor on the color properties of the films. SEM micrographs revealed uniform distribution of NS into polymer matrix at low NS content. Consequently, crystallinity and thermal properties of the film were improved by adding NS content as compared to WPC film. It seems NS can improve some drawbacks of WPC such as mechanical weakness, hydrophilic properties as a packaging material and allowing the development of biodegradable bionanocomposite.

Effect of nano-SiO2 on physical and electrical properties of PPC cement using complex impedance spectroscopy

The aim of this study was to investigate the effect of nano-SiO2 incorporated in cement blended with 30% class F fly ash on consistency, setting times, compressive strength, chloride penetration, complex impedance spectra and conductivity at 10 kHz. The composite cement was composed of nano-SiO2 in 0, 1, 2 and 3% by weight of cement. The consistency was found to be increasing with the increase in nano-SiO2 content whereas retarding effect was observed for setting time. The compressive strength of cement mortar cube sample was found to be less than the control samples. Depth of chloride penetration was also found decreasing with the increasing dosage of nano-SiO2. Complex impedance spectra are found in semicircle shape in later hours due to the formation of hydration products. Conductivity of all samples found to be decreasing because of the dissolution of ions and formation of hydration products. A good correlation between conductivity and setting time was observed with the help of complex impedance spectroscopy.