Papers by Keyword: Aerogels

Abstract: In this work, the Cu-alginate/graphene aerogels were prepared by using alginate, graphene and copper chloride as precursors by a freeze-drying process. Finally, N-doped carbon aerogels supported by Cu nanoparticles (NPs) (Cu/N-CAs) were obtained through annealing in the NH₃ atmosphere. The morphology, microstructures, specific surface area, and pore size distribution were studied by SEM, XRD, and BET analysis. The results showed that a significant amount of Cu NPs were uniformly disseminated on the aerogels’ surface, and the catalysts’ specific surface area reached 141 m²/g. Electrochemical tests revealed good catalytic capabilities for the oxygen reduction reaction (ORR) of the as-obtained Cu/N-CAs. Compared to the commercial 20%Pt/C, the Cu/N-CAs exhibited comparable catalytic performance, superior catalytic stability and methanol resistance. The transfer of 3.94 electrons indicated that the Cu/N-CAs were undergoing a four-electron (4e^-) ORR process.

Abstract: In this paper, tetraethyl orthosilicate and anhydrous ethanol were used as raw materials, and hexane was used for solvent replacement of the gel. Surface modification of three methyl silane (TMCS) was carried out, and SiO₂ aerogels were prepared by sol-gel process and atmospheric drying process. The effect of TMCS and the calcination temperature on the properties of the SiO₂ gel were studied. The physicochemical properties of aerogels were characterized by field emission electron microscopy (FESEM), energy dispersive spectrometry (EDS), X ray diffraction (XRD), infrared analysis (FT-IR) and specific surface area (BET). The results show that the material is composed of round nanoparticles with a diameter of less than 20 nm. EDX analysis shows that the material is composed of Si and O elements. The XRD spectrum shows no obvious characteristic diffraction peak when SiO₂ aerogels calcinated at 500 °C and 900 °C, which indicates that the phase group of the material is disordered amorphous SiO₂; when calcinated at 1100 °C, it occure SiO₂ crystal. After 10 hours of modification with 20% TMCS/hexane solution, the SiO₂ aerogels had a larger specific area. The BET of the modified aerogel is about 930 m²/g.

Abstract: The aim of this work was to develop methods for the synthesis of organic aerogels based on epoxy resins and to investigate their properties. Aerogels based on DGEBA-epoxy resin were obtained by CO₂-supercritical drying of gel samples prepared from acetone solutions of epoxy resin with different amount of catalyst and solvents. As a result, aerogels of different density were obtained; the dependence of density on the solvent content in the samples was revealed. The aerogels were characterized by infrared spectroscopy to define the degree of conversion of the epoxy groups, by SEM to confirm nanoscale morphology of aerogels, as well as by the BET method to determine the specific surface area of the samples and its dependence on the catalyst content and curing conditions.

Abstract: The article presents a method to obtain silica xerogels with developed specific surface based on nepheline concentrate acid decomposition in C₂H₅OH-H₂SO₄ system. It was found that the use of ethanol instead of water produces stable and steady silica gels. It is proved that the use of ethanol results in almost complete deposition of soda alum and aluminum potassium sulphate out of nepheline decomposition solution without its additional cooling, due to their extremely low solubility in alcohol solution. The morphology, structural and surface properties of synthesized xerogel sample with ~600 m²/g specific surface area (based on the analysis) were investigated; its mixed micro-and mesoporous structure was established. Electron probe microanalysis showed chemical purity of the resulting SiO₂.

Abstract: In the present paper, water glass was used to synthesize silica aerogels and calcium magnesium silica aerogels. The present research was aimed to investigate the effect of gel aging time (1 and 24 hours) on the physical and surface properties of aerogels. Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, Fourier Transform Infrared spectroscopy and scanning electron microscopy techniques were used to characterize aerogels. Successful formation of nanopores (2.8-4.4 nm) was approved by N₂ adsorption/desorption isotherms. The aerogels contained porous network structure with different surface areas (388.9-729.9 m² g^-1). Aging for longer times led to an ability to decrease the density of the aerogels. The bulk density was higher in silica aerogels than in calcium magnesium silica aerogels. The well-tailored network matrix with high BET surface area (729.9 m² g^-1) and low density (0.116 g cm^-3) was achieved via 24 hours gel aging of calcium magnesium silica aerogel.

Abstract: This paper will provide a review of the current research on the material characterisation and mechanical behaviour of polymer enhanced silica aerogels. Aerogels have been in existence for many years; however, the engineering applications of aerogels have been limited due to their poor mechanical behaviour. Recently a new type of polymer enhanced silica aerogel, a nanostructured form of silica has been developed. The new material is having a low density, very low thermal conductivity, excellent acoustic insulation and high mechanical which makes it ideal for energy efficient building material. This paper will discuss the start-of-the-art development of this material and issues to apply the material in energy efficient buildings.

Abstract: Mesoporous silica aerogels with a high surface area and narrow pore size distribution were prepared from tetraethylorthosilicate (TEOS) precursor at ambient pressure by using a water miscible ionic liquid (IL) [Hmim]Br as a template. The aerogels were characterized by scanning electron microscopy (SEM) and N2 gas adsorption-desorption isotherms (BET and BJH analyses), and the effect of the IL on gel structure was also studied. The results showed that IL plays an important role in regulating the nanostructure of the aerogels, in particular, pore sizes and their distribution. By increasing the IL/Si molar ratio from 4 to 7, the specific surface area of the resultant aerogel increased from 822.38 to 992.43 m2/g, while the pore volume decreased from 1.568 to 1.031 cm3/g. More importantly, the pore size distribution became narrower with minimum average pore radius centralized at 20 nm as the IL/Si molar ratio of 7. Compared with other IL templating methods previously reported, notable attributes of this method include gelation at a much wider range of the IL/Si molar ratios (up to 7) and the formation of homogeneous porous structure whose size can be up to meso-scale (2 nm - 50 nm).

Abstract: Nanocomposite aerogel is proposed as a host matrix for the synthesis of glass ceramics. The large porosity is used as a sponge to incorporate chemical species getting a two phases material. We describe the steps of the synthesis of glass ceramics for nuclear waste containment, from nanocomposite aerogels loaded with actinides surrogates (Ce and Nd). The glass synthesis is obtained without melting, by a control of several solid phase transformations: sintering, viscous flow, crystallization and foaming. Thanks to their high resistance to thermal shock and water corrosion, these glass ceramics are certainly good candidates as actinides containment materials.

Abstract: Silica aerogels have been studied with the objective of understanding the mechanical behavior of these extremely porous (pore volume higher than 85%) glassy materials. Elastic and plastic behaviors are investigated using Hg porosimetry. Because of the peculiar structure of these materials, Hg liquid cannot enter their porous network and consequently induces an isostatic pressure. Due to the high compliance of the solid network, under isostatic pressure aerogels display an irreversible shrinkage caused by plastic deformation. The magnitude of the plastic shrinkage and the increase of the associated mechanical properties depend on the different parameters (porosity, elastic properties and structural features). The structural features are followed by X Rays scattering. The irreversible compaction can be explained by siloxane bond formation between clusters constituting the porous materials, retaining the strained structure. The pore collapse mechanism is favored by the large pores structure and loose cluster structure (low fractal dimension). This densification process could offer a new way to synthesize porous glasses at room temperature.

Abstract: Fractal and aggregate structures of porous materials were studied by a variety of the structure characterization techniques (TEM, small angle X-ray scattering, nitrogen sorption). Scattering data (SAXS, USAXS) for porous materials measured with laboratory equipment and synchrotron technique were interpreted in terms of Guinier, Emmerling, Freltoft, modified Freltoft theories, and simple power law expressions. The evaluation of scattering measurements resulted in fractal dimensions, sizes of the elementary units, the fractal domains or the aggregates. TEM images confirmed the sizes of the elementary building units, while the pore size distributions could be obtained by nitrogen adsorption. The specific surface area was calculated with respect to the possibility of multilayer formation during nitrogen absorption.