Silica aerogels have been widely used as thermal insulators, but their fragility has hindered the potential applications. In this work, a novel way of improving aerogel skeletal structure was ...proposed where composites were reinforced by three functional layers of glass fiber (GF)/ carbon fiber (CF). Heat insulation performance of fiber-reinforced aerogel composites was also investigated in a simulated solar radiation system. Composites composed of three layers of fiber were prepared by a sol-gel process under ambient pressure drying. The results showed that, as three layers were all GF blankets, the composite heat conductivity increased with increasing glass fiber content. Flexural strength increased initially and reached a maximum at 20% glass fiber content before decreasing. To find a balance between promoting heat insulation performance and strengthening the composite structure, two layers of 5% glass fiber blankets were used as structure strengthening layers and one carding 5% carbon fiber as the heat insulation layer were recommended. Under these conditions, the composite showed extremely low thermal conductivity (0.031 W/m K), almost comparable to that of pure aerogel (0.036 W/m K) while maintaining high flexural strength (2.846 MPa), superior than previous studies. Composites with other ratios of glass/carbon fibers with sandwiched alignments also demonstrated better flexural strength and lower thermal conductivity than GF aerogel composites. This work provided an alternative way to prepare robust and sustainable heat insulation aerogel composites for practical uses.
Highlights
Heat insulation performance of silica aerogels composited with different ratios of glass fiber and carbon fiber was investigated.
The flexural strength increased with increased glass fiber loading, and reached its highest value when glass fiber content was 20%.
5% carbon fiber inserted between the two 5% glass fiber layers was found the most ideal condition in terms of flexural strength (2.846 MPa) and thermal conductivity (0.031 W/m K).
This paper presents the production of a 3D cotton-wool-like structured inorganic fibrous material for bone regeneration electrospun from a sol–gel precursor solution. The fibrous material possesses ...interconnected nano to macro pores, large surface area and high porosity. The cotton-wool-like structured material is moldable which means it could easily be packed into complex bone defects. Display omitted
Inorganic sol–gel solutions were electrospun to produce the first bioactive three-dimensional (3-D) scaffolds for bone tissue regeneration with a structure like cotton-wool (or cotton candy). This flexible 3-D fibrous structure is ideal for packing into complex defects. It also has large inter-fiber spaces to promote vascularization, penetration of cells and transport of nutrients throughout the scaffold. The 3-D fibrous structure was obtained by electrospinning, where the applied electric field and the instabilities exert tremendous force on the spinning jet, which is required to be viscoelastic to prevent jet break up. Previously, polymer binding agents were used with inorganic solutions to produce electrospun composite two-dimensional fibermats, requiring calcination to remove the polymer. This study presents novel reaction and processing conditions for producing a viscoelastic inorganic sol–gel solution that results in fibers by the entanglement of the intermolecularly overlapped nanosilica species in the solution, eliminating the need for a binder. Three-dimensional cotton-wool-like structures were only produced when solutions containing calcium nitrate were used, suggesting that the charge of the Ca2+ ions had a significant effect. The resulting bioactive silica fibers had a narrow diameter range of 0.5–2μm and were nanoporous. A hydroxycarbonate apatite layer was formed on the fibers within the first 12h of soaking in simulated body fluid. MC3T3-E1 preosteoblast cells cultured on the fibers showed no adverse cytotoxic effect and they were observed to attach to and spread in the material.
ZnO nanoparticles were synthesized at different pH values by the sol–gel method and centrifuged at 3000
rpm for 30
min. The ZnO powders agglomerate when synthesized in acidic and neutral conditions ...(pH 6 and 7). Fine powders were obtained when the pH of the sols was increased to 9. The maximum crystallite size (25.36
nm) of the ZnO powder was obtained at pH 9. The particles sizes of the ZnO synthesized between pH 6 and 11 were in the range of 36.65–49.98
nm. Ultraviolet–visible analysis (UV–vis) also demonstrated that ZnO synthesized from pH 8 to 11 has good optical properties with band gap energy (
E
g
) between 3.14 and 3.25
eV.
Hollow carbon fibers (HCF) with ultra‐large diameter have been synthesized and the versatility to convert them into the corresponding carbon‐based composites has been demonstrated. The hollow carbon ...fibers were fabricated by thermal controlled carbonization of electrospun polyacrylonitrile fibers. For the existence of inorganic silica shell during pyrolysis, heat release will be blocked at the boundary, driving the polyacrylonitrile precursor fiber to form hollow structure. The diameter of the as‐prepared hollow carbon fibers can exceed 150 nm. Sol‐gel‐derived Fe3O4 nanoparticles can grow on the outer‐surface and the inner‐surface of hollow carbon fibers. The microwave absorption performance of ternary HCF@Fe3O4@PPy composite is testified and the values of reflection loss exceeding −10 dB can be obtained in the frequency of 3.3‐11.3 GHz. The large diameter of hollow carbon fibers can have inner and outer interfaces in the corresponding composites, which make them great potential for a variety of applications in future.
Hollow carbon fibers with ultra‐large diameter and the versatility to construct composites with inner and outer interfaces.
Soil samples were collected at alluvial sites of the Litavka River, Czech Republic, in 2005 and 2006. Higher heavy metal levels in soils (Cd, Pb, Zn, Cu) are due to the composition of the parent ...rock, emissions from lead processing industry and the leak of toxic material from the steel works sludge ponds in the 1970s and 1980s. The samples were collected from six sites located at different distances from the contamination source (the former sludge ponds) and chemical and biological properties were determined. The ratio of the microbial biomass C to oxidisable C concentration dropped down significantly on more heavily contaminated sites. Basal respiration activity did not correlate with the level of heavy metals in soil. Nevertheless, it tended to decrease with increasing intensity of soil contamination. Respiration activities significantly correlated with the total C, oxidisable C and the total N concentrations. Dehydrogenases and arylsulphatase activities decreased with increasing contamination. Urease activity showed a relationship with the N concentration in soil. Dehydrogenases, arylsulfatase and urease activities significantly correlated with the microbial biomass C.
Monolithic cordierite with a cocontinuous macroporous structure has been successfully prepared by the sol–gel process accompanied by phase separation in the presence of poly(acrylamide) (PAAm). ...Propylene oxide (PO) acts as an acid scavenger to mediate the gelation of MgO–Al2O3–SiO2 ternary system, while PAAm works as a phase-separation inducer as well as a network former. The dried gel and that heat-treated at 800°C are amorphous, and the sapphirine begins to precipitate at 900°C, then transforming to orthorhombic β-cordierite at 1100°C. After heat-treated at and above 1200°C, the resultant β-cordierite further transforms to stable hexagonal α-cordierite. Heat-treatment changes the macroporous structure of cordierite monoliths such as macropore size and its distribution. The macroporous cordierite monolith after heat-treated at 1200°C is found to possess a total porosity of 54%, interconnected macropores and dense solid skeletons.
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•Nanostructured Ga-doped ZnO were synthesized by the sol–gel method.•The effects of Ga doping level on the structural, morphological and sensing properties of ZnO were ...investigated.•Ga doping promotes the enhancement of CO sensing allowing to detect CO at sub-ppm concentrations in air.
The microstructural and functional characterization of pure and Ga (1–5at.%)-doped ZnO nanoparticles synthetized by sol–gel method is reported. All the samples, characterized by XRD and TEM, showed the nanocrystalline ZnO wurtzite structure. However, depending on the Ga content, the morphological, microstructural and electrical properties of doped samples changed markedly with respect to the undoped ZnO. The effect of gallium dopant on sensing properties of thick films of ZnO nanoparticles, deposited on alumina substrates provided with Pt interdigited electrodes for the application as CO resistive sensors, have been investigated. Sensors based on Ga-doped ZnO exhibited a higher response (R0/R=9, to 50ppm of CO at the operating temperature of 250°C) and lower response/recovery time (8 and 35s, respectively) than the pure ZnO sample, allowing to detect CO at sub-ppm concentrations in air.
Magnesium nanoferrites are gaining a lot of scientific attention because of its magnificent dielectric characteristics such as large dielectric constant with minute dielectric losses, which make it ...suitable for potential applications such as high frequency, microwave devices, switching devices, power, magnetic storage devices, and many more. A series of manganese- and silver-substituted magnesium nanoferrites with the chemical composition Mg
1−
y
Mn
y
Ag
x
Fe
2−
x
O
4
(0.1 ≤
y
≤ 0.4, 0.0 ≤
x
≤ 0.3) were synthesized via sol–gel auto-combustion technique for reporting the electrical and dielectric study of synthesized specimens. In the present investigation, the dc resistivity (
ρ
) of prepared nanoferrites goes on decreasing as a function of Ag
+
and Mn
2+
concentrations extensively indicate its semi-conductor behavior. From the dielectric measurements, dielectric constant (∈′) increases with the increase in frequency, whereas the dielectric loss tangent (tan
δ
) shows an inverse behavior with the increasing frequency, respectively. In relation with the dielectric investigations, AC conductivity (
σ
ac
) shows similar behavior to that of dielectric constant. Therefore, such materials of high dielectric constant with minute dielectric losses make it suitable for the power application.
Highlights
Silver and manganese-doped magnesium nanoferrites were synthesized via sol–gel auto-combustion technique.
Indicating semi-conductor behavior of synthesized samples.
Dielectric constant (∈′) increases with very low dielectric losses (tan δ) which make it suitable for the power application.
► Nano-TiO
2 films were fabricated on AZ31 alloys as protective layers by sol–gel method. ► The inhibition effects were evaluated. ► The formation of defect structures on the films was analyzed and ...related with the degradation of coated alloys.
A nano TiO
2 film was coated on AZ31 alloy substrate by sol–gel method. The TiO
2 film was characterized by X-ray diffractometry (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TG), field emission scanning electron microscopy (FE-SEM) and energy dispersion spectroscopy (EDS). The degradation of the nano-TiO
2 coated alloy was evaluated by immersion test and electrochemical measurement. An attempt was made to relate corrosion of coated alloys with the annealing treatment and resultant structural evolution.
In the present study, Ag-doped nickel oxide nanoparticles (NiO-NPs) were synthesized through a sol–gel method using of
Cydonia oblonga
plant extract as a new green stabilizing agent and employed ...Ni(NO
3
)
2
·6H
2
O and AgNO
3
as nickel and silver sources, respectively. The synthesized Ag-doped NiO-NPs have been calcinated at 400 °C. Formation of Ag-doped NiO-NPs was confirmed by the means of XRD, FESEM/EDAX, FTIR, TGA/DTG, UV–Vis spectrophotometry, and VSM techniques, and effect of silver diluent doping on the photocatalytic properties of NiO-NPs was investigated. The XRD results have indicated that the size of Ag-doped NiO-NPs has increased as the Ag concentration had been raised. The obtained particle size in optimized conditions (Ag-doped 3%) has been reported to be about 9.24 nm. In the following, the photocatalytic activity of Ag-doped NiO-NPs has investigated the degradation of Rhodamine B (RhB) dye, and according to the obtained results, about 75% of RhB degraded under UV-light after 200 min. The cytotoxicity effect of Ag-doped NiO-NPs on PC12 cell lines has been investigated by MTT assay, and the results showed that Ag-doped NiO-NPs inhibited cancer cells (IC
50
̴ 35 µg/ml).
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