ZrC–ZrO2 composite ceramic microspheres were prepared by internal gelation combined with carbothermic reduction using fructose as a chelating agent and carbon source. Fructose in the precursor solution formed complex with zirconium ions, which was conducive to the refining of the microstructure of the sintered composite. ZrC–ZrO2 composite with ZrC content as high as 60?wt% could be prepared.
In this paper, fructose was used as a chelating agent and an organic carbon source to prepare ZrCO microspheres by internal gelation and carbothermic reduction. The fructose in the precursor solution could form complex with zirconium ions, which was conducive to the refining of the microstructure of the sintered composite. ZrC–ZrO2 composite with crystal size of ZrO2 and ZrC in nanometer range and ZrC content as high as 60?wt% could be successfully prepared.
Fiber needle felt–silica aerogel composite was successfully prepared by via sol–gel process based on water glass. The thermal conductivity show V-type variation tendency with the increase of water to Si. Thermogravimetric analysis-differential scanning calorimetry analysis revealed that the thermal stability was up to approximately 390.58?°C. It has been found that the fire hazard of the composites decreased with the increased ratio of water to Si according to the cone calorimeter test, which can be characterized by peak heat release rate, fire performance index, and fire growth rate index. The fiber needle felt/aerogels present greatly improved compressive and flexural strength (elastic modulus: 0.1–0.97?MPa; flexural modulus: 0.33–0.66?MPa) while keeping inherent properties of pure silica aerogel: low bulk density (0.166?g/cm3), low thermal conductivity of 0.0236?W/m·K, and high specific surface area (1091.62?m2/g). As a result, the as-prepared composite shows a great potential to be applied in the thermal insulation field.
YAG:Ce and YAG:Eu sols were synthesized by a polymeric sol-gel route. The crystallization temperature of YAG was determined by X-ray diffraction as a function of the calcination temperature, revealing that YAG starts to crystallize directly from the amorphous phase at 800?°C. The effects of the thermal treatment and the dopant amount on the photoluminescent properties were studied, observing the highest emission after calcination at 1000?°C for 1?h in both cases and with a concentration of 1 and 3?mol% of Ce and Eu, respectively. Core-shell materials were prepared by dipping YAG:Ce or YAG:Eu sintered pellets into the synthesized sols and then, these materials were calcined at 1000?°C for 1?h. An effective energy transfer from Ce to Eu was observed in the sample YAG:Eu (core)–YAG:Ce (shell) when blue light (λ?=?465?nm) is used as excitation source. This wavelength excites the Ce but not the Eu; however, in the photoluminescence emission spectrum, the bands associated to both ions can be clearly detected, confirming that the core-shell strategy is a good method for the preparation of warmer white LEDs.
In this study, the effective TiO2/Ag composite antibacterial aerogel powder is prepared by facile sol–gel method and ethanol supercritical technology. The surface morphology, structural properties, and chemical components are monitored by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and energy disperse?spectroscopy (EDS). Meanwhile, absorbance spectra and specific surface area of TiO2/Ag composite aerogel are characterized by UV-Vis spectra and Brunauer–Emmett–Teller. The TiO2/Ag composite aerogel with Ti/Ag molar ratios of 10:1, 30:1, 50:1 are measured for its antibacterial property by using Escherichia coliform (E.coli) and Staphylococcus aureus (S. aureus). The results show that the size of TiO2 and Ag nanoparticles are 40?nm and 25?nm, respectively. Simultaneously, the obtained composite aerogel with a porous structure possessed a surface area of 148?m2/g, an average pore size 11.5?nm, and a pore volume 0.39?cm3/g. With the increase of Ag content, the antibacterial properties of composite aerogel are greatly improved compared with pure TiO2 aerogel. When Ag/Ti molar ratios was 1:10, the highest antibacterial rate can up to 99%, and the inhibition bands of E. coli and S. aureus are 23?mm and 19?mm, respectively.
Trimethylethoxysilane (TMES) has been recognized as a good co-precursor to increase the degree of hydrophobicity during the synthesis of a silica aerogel because of its methyl groups. Therefore, some physical properties of silica aerogels, including the contact angle and porosity, were investigated using TMES as a co-precursor at different molar ratios with the main precursor such as tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). In contrast to TMES, most silylating agents such as hexamethyldisilazane (HMDZ) and trimethylchlorosilane (TMCS) have been used for surface modification because of their ability to enhance the hydrophobicity of the aerogel surface. This work examines the silylation effect, which includes increasing hydrophobicity by TMES to determine the possibility of using it as an alternative silylating agent during ambient pressure drying in the synthesis of sodium silicate-based silica aerogel. In addition, the physical properties of sodium silicate-based silica aerogels with silylation under different TMES/TMCS volume ratio are investigated. The physical properties of sodium silicate-based aerogels can be changed by the TMES/TMCS volume ratio during the surface modification step. Aerogels with a high specific surface area (458?m2/g), pore volume (3.215?cm3/g), porosity (92.7%), and contact angle (131.8°) can be obtained TMES/TMCS volume ratio of 40/60.
The mesoporous silica samples with different concentrations of phosphonic acid groups on the surface were obtained by direct template synthesis. The block-copolymer Pluronic P123 was used as a template, and sodium meta-silicate with diethylphosphatoethyltriethoxysilane as precursors. According to the SAXS diffractograms, mesoporous silica samples have a p6mm hexagonal symmetry. In addition, we used sol–gel method to synthesize xerogel with the same groups for comparison. All samples possess high values of specific surface area 615–730?m2/g and sorption pore volume. FTIR and potentiometric titration methods were used to investigate the surface layer of these samples. Sorption properties of the samples with phosphonic acid groups were studied in respect to a row of metal cations, among which we focused on lead(II), cadmium(II), and dysprosium(III) cations.
In this study, stearic acid/silica phase change composites were prepared by the sol-gel method using stearic acid as phase change materials (PCMs). The effects of mass fraction of stearic acid were comprehensively investigated. The structures and thermal properties of the obtained composites were characterized by various methods, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), leakage tests, and thermogravimetry analysis (TG). The results indicated that composite containing 76% stearic acid had the best thermal properties and low mass leakage, making 76% stearic acid as the maximum content that silica matrix could protect in the composites. The latter was further confirmed by morphological analyses of the silica matrix. Silica matrix exhibited spherical particle clusters, following big–small–big–small size pattern as stearic acid rose. The composite with 76% stearic acid was at the key point of change in particle size. These findings look promising for future to prepare silica-based phase change composites with good thermal properties easily.
In this study, a specific technique was used to quickly, easily, and single step, synthesize core-shell magnetite-silica nanoparticles by controlling the reaction conditions using the proper surfactant. In the first step, the magnetite nanoparticles were prepared by co-precipitation method and silica shell was immediately formed by the sol-gel process. Synthesis was performed at 80?°C with stirring at 12,000?rpm in an alkaline medium. The structural and morphological characteristics of core-shell nanoparticles were examined by XRD, TEM, SEM, and BET analyses. In addition, vibrating sample magnetometer (VSM) was used to evaluate the magnetic characteristics. XRD analysis confirmed the existence of both magnetite and silica phases in the final structure. TEM images showed the presence of nanocomposite particles with core-shell structure of 25?nm diameter. The mean core and shell size were estimated to be about 20 and 2.5?nm, respectively. A study of the magnetic characteristics showed super-paramagnetic behavior with 60?emu/g saturation magnetization (Ms). Due to the high ratio of core size to shell thickness, the magnetic saturation for the synthetized core-shell nanoparticles in this research was significant. In comparison to other multi-step synthesis techniques, the results obtained from this research confirmed the formation of magnetite-silica core-shell structures with the desired magnetic behavior in a quick and single-step process.
Powders of Sm0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.
Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using conventional and microwave ignition routes. The effects of starting solution acidity on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy and diffuse reflectance spectrometry techniques. The chelated species in dried gels were predicted by theoretical calculations and confirmed by Fourier transform infrared spectroscopy. The combustion reaction rate increased with the increase of pH values. Single phase and well-crystalline ZnO powders were achieved by both of ignition methods regardless of pH values. The hexagonal particles (200–80?nm) formed by microwave ignition were larger than the spherical particles (60–40?nm) in conventional heating. Conventionally combusted ZnO powders exhibited higher photocatalytic activity under ultraviolet irradiation, due to their narrower band gap and smaller particle size.
C/C0 vs. irradiation time for photodegradation of MB dye under ultraviolet light irradiation by the as-combusted ZnO powders (filled symbols present conventional combusted powders and open symbols are for the microwave combusted powders)
Measuring humidity in dynamic situation needs very high sensitive and fast response sensors. For this purpose, a new high sensitive humidity sensor based on ZnO/ITO (ZITO) composite nanostructure were designed on alumina substrate by sol–gel technique. Step by step monitoring of fabricated substrate after annealing at 400?°C was performed using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and UV–Vis techniques. An oscilloscope and digital ohmmeter were applied to determine time-varying voltage and resistance signal of the fabricated sensors, respectively, while exposed to various humidity level. Sensitivity, response, recovery time, deposited layers thicknesses, composition ratio of ZnO:ITO and annealing temperature parameters were considered to achieve optimum conditions. The optimum conditions for maximum sensitivity were obtained as 1:1(ITO:ZnO) ratio, 400?°C annealing temperature, and three times layer by layer coating. Fabricated sensor has excellent response and recovery time (1.0 and 9?s) and long life time at room temperature (25?±?1?°C) for monitoring human breath and dynamic situation.
The influence of the water content in the initial composition on the size of silica particles produced using the Stöber process is well known. We have shown that there are three morphological regimes defined by compositional boundaries. At low water levels (below stoichiometric ratio of water:tetraethoxysilane), very high surface area and aggregated structures are formed; at high water content (>40?wt%) similar structures are also seen. Between these two boundary conditions, discrete particles are formed whose size are dictated by the water content. Within the compositional regime that enables the classical Stöber silica, the structural evolution shows a more rapid attainment of final particle size than the rate of formation of silica supporting the monomer addition hypothesis. The clearer understanding of the role of the initial composition on the output of this synthesis method will be of considerable use for the establishment of reliable reproducible silica production for future industrial adoption.
Dual-network aerogels (HPSA) with improved mechanical property and thermal insulation were prepared by vacuum impregnation of HNTs/PVA aerogels (the first network aerogel, HPA) in tetraethoxysilane (TEOS). Scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and N2 adsorption–desorption analysis were used to study micromorphology and microstructure of HPSA, while compression tests and thermal conductivity tests were used to investigate related properties. The results showed that the dual-network frame was successfully constructed, this enabled HPSA to display enhanced compressive properties with increased HNTs content. The addition of silica sol improved the mesoporous characteristics including specific surface area and pore volume and also reduced the thermal conductivities. The first network made it possible for HPSA to possess good mechanical property, while SiO2 aerogel allowed HPSA greater thermal insulation. The obtained aerogel samples exhibited a high compressive strength (i.e., 1.36?MPa) and a low thermal conductivity (i.e., 0.022?W/(m?K)). HNTs/SiO2 dual-network aerogels with improved strength and thermal insulation could show great potential in a wide variety of applications.
Superhydrophilic surfaces without the need of other stimuli are usually realized by constructing a rough morphology. However, constructing rough surfaces usually require specialized equipment or complicated processing. Besides, rough surfaces can cause undesirable scattering, which strongly limits the use in optical devices. In this article, we prepared superhydrophilic TiO2 films with ultra-smooth surfaces using simple sol-gel dip-coating method. The hydrophilicity of the TiO2 films varied with different post-heat treatments. The films heat-treated at 400?°C exhibited a durable superhydrophilicity and anti-fogging property. This superhydrophilicity was attributed to the decrease of surface hydrophobic alkoxy groups and the formation of point defects, i.e., Ti3+ and oxygen vacancies, which are favourable for dissociative water adsorption. The amount of surface organic groups was influenced by autophobicity effects, further hydrolysis and decomposition of residual alkoxy groups. Additionally, the wettability behaviours of the films were also explained from the perspective of the surface energy. These results can benefit the design and manufacture of anti-fogging and self-cleaning superhydrophilic TiO2 films.
In this work, sol–gel-based non-stick ceramic coating formulations were prepared and coated onto aluminum panels in order to investigate their surface properties. The effect of the addition of optimal amount of fluorine-containing silane compound (FAS) on the surface and adhesion properties were also investigated. The morphology, structure, and elemental chemical composition of the coatings were characterized by scanning electron microscopy, atomic force microscopy (AFM), energy dispersion spectrum (SEM/EDAX), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), respectively. Moreover, several properties of the coatings such as cross-cut adhesion, hardness, gloss, and contact angle (CA) were determined. When fluorine was introduced, the pencil hardness was increased to 6H. Fluorinated non-stick ceramic coatings were found to have good adhesion on the aluminum substrates.
Mixed-metal compounds, especially for the sulfides, have been investigated as a very attractive type of electroactive materials for supercapacitors. In this work, we demonstrate nickel?manganese (Ni?Mn) sulfides are very attractive for supercapacitors with promising electrochemical performance. The Ni?Mn sulfides with different Ni to Mn ratios have been synthesized via a facile one-pot hydrothermal method, which show a similar structure of interconnected particles and are very porous in microstructure. And then, the Ni?Mn sulfides are investigated by three-electrode measurements and demonstrate strong synergy between Ni and Mn. The Ni?Mn sulfide with a Ni to Mn ratio of 2:1 demonstrates superior performance of 1068?F?g?1 at 1?A?g?1. Lastly, The Ni?Mn sulfide with a Ni to Mn ratio of 2:1 are used as positive electrode for two-electrode test, and the asymmetric supercapacitor shows both high energy and power densities combined with excellent cycling stability. Our work demonstrates that the Ni?Mn sulfides are also very electrochemical active for supercapacitors and their performance can be tuned by changing the Ni to Mn ratio.
For the first time, sintered alumina with high transparency in mid infrared region, composed of submicron grains, has been fabricated using sol–gel processing. Commercially available boehmite powder was used to prepare the stable sol. The sol was mixed with appropriate amount of sintering aids and alumina seeds. The sol was further gelled, dried, and heat treated at 1000?°C for producing alumina powder. The powder was further shaped into pellets by compaction and sintered at temperatures between 1200 and 1400?°C in air. Sintered samples were further pressed hot isostatically to produce sintered submicron transparent alumina. The synthesized powder was characterized for its morphology and phase. The sintered and hot isostatically pressed samples were characterized for their physical, mechanical, and optical properties. The present method produced transparent alumina with transparency upto 87% in mid-wave infrared region. These transparency values were at par with the transparency of single crystal sapphire in the mid-wave infrared region and the hardness values were even superior than sapphire.
Novel La-doped Bi2WO6 composites were successfully prepared via a facile solvothermal method and well characterized by X-ray diffraction, Brunner?Emmet?Teller measurements, scanning electron microscopy, transmission electron microscopy/high-resolution, energy dispersive spectrometry, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy. The photocatalytic activity of modified catalysts was evaluated by degrading tetracycline hydrochloride under visible light (450?W Xe lamp irradiation). It was found 5%La-Bi2WO6 had the highest light-absorption ability, great morphology, and microstructures. The La dopant enlarged surface area and increased crystal defects, which may enhance the optical absorption activity and inhibit the recombination of the photo-generated charge carrier, respectively. After 150?min illumination, the photocatalysts that 5%La-Bi2WO6 and pure Bi2WO6 exhibited the best and worst photocatalytic performance, respectively (96.25% vs. 88.92%).
Since the late 1960s, ceric hydrogen phosphates have attracted the attention of scientists due to remarkable ion exchange, sorption, proton-conduction and catalytic properties. In this work, through the application of various solvents, we, for the first time, have obtained monolithic aerogels based on ceric hydrogen phosphates with high porosity (~99%) and extremely low density (~10?μg/cm3). The composition and structure of aerogels were thoroughly studied with XRD, TEM, SEM, XPS, low temperature nitrogen adsorption methods, TGA/DSC, Fourier-transform infrared spectroscopy (FTIR) and small-angle neutron scattering (SANS). The aerogels were found to belong to the fibrous macroporous aerogels family.
The behaviour of alginate gel film in response to the tensile load is analysed in this paper. The bubbles of 0.5?mm diameter were embedded in the film by the fluidic method prior to gelation, thus providing uniform voidage over the entire film. Further, the intrinsic porosity of the gel matrix around the voids was varied by removing water through either evaporation under vacuum, or employing lyophilisation. The Poisson’s ratio and the modulus of elasticity were estimated from direct measurements. The viscoelasticity of the gel matrix was characterized from stress-relaxation measurement. The transient response to tensile loading and the evolution of stress contours were studied through numerical simulation in ANSYS. The ultimate strength was studied for the gel films with embedded voids of different sizes. The numerical simulations were validated by experimental measurements.
