Alumina Aerogel Research Articles

Facile one-step precursor-to-aerogel synthesis of silica-doped alumina aerogels with high specific surface area at elevated temperatures

Silica-doped alumina aerogels offer the potential alternative to the applications as thermal insulators, catalysis, or catalytic support at elevated temperatures. However, the production process of silica-doped alumina aerogels was complicated and time-consuming. We developed a one-step precursor-to-aerogel method of silica-doped alumina aerogels with high specific surface area and thermal stability. Compared to conventional methods, the developed method reduced time and solvent waste of alumina-based aerogels production. Here, we investigated the alumina aerogels doped with silica to stabilize γ-phase at higher temperatures. XRD, FTIR, TEM, TG-DSC, and BET analysis results showed that silica stabilized the γ-Al2O3 at 1200 °C. The stabilization mechanism analysis showed that silica addition could significantly hinder the contact among alumina particles and the formation of necks in the sintering process, thereby retarding the transition of γ–θ phase and maintaining the high specific surface area at elevated temperatures. Silica and alumina particles formed mullite at 1200 °C, which could suppress α-phase transformation. In addition, silica-doped alumina aerogels exhibited the high specific surface area of 311 m2/g at 1000 °C and 146 m2/g at 1200 °C when the silica content was in the range of 10.6–13.1 wt%.

Study on flame retarded flexible polyurethane foam/alumina aerogel composites with improved fire safety

In this article, a novel strategy has been proposed for the preparation of polyurethane/alumina aerogel (FPU/Alag) composites with homogeneous dispersion of alumina aerogel. The FPU/Alag composites have been prepared via immersing FPU foams into alumina sols followed by a freeze-drying method. Fire safety performance of the FPU composites with various Alag compositions in terms of thermal properties and flammability performance were evaluated. The composites demonstrated an earlier thermal degradation but higher thermal stability with increasing temperature and greater char yields than pure FPU. Total heat and smoke release, and rate of smoke emission of the FPU/Alag composites were found to be greatly reduced in comparison with those of FPU. Morphology and thermal conductivity (κ) properties of FPU/Alag composites and their corresponding residual char were investigated. The κ values of the composites were measured to be higher than that of FPU due to the accumulation of alumina flakes on the cell-walls of FPU. In contrast, the κ values of the char were lower than that of the calcinated alumina aerogel (C-Alag) counterpart, due to the formation of side by side, partially-opened compartments isolated by alumina flakes. Nitrogen adsorption analysis showed that C-Alag had a specific surface area of 211.5m2/g and mesoporous volume of 0.28cm3/g. The remarkable improvement in fire safety of FPU foams with the addition of Alag could be attributed to the combined effects of thermal-insulating, retention and adsorption of C-Alag that was in-situ formed inside FPU matrix during the combustion process.

Fabrication and characterization of the monolithic hydrophobic alumina aerogels

The monolithic hydrophobic mesoporous alumina aerogels were successfully synthesized by acid–base sol–gel polymerization of aluminium chloride hexahydrate (AlCl3·6H2O) in deionized water/alcohol solution (v/v = 3:7). To minimize shrinkage during drying, alumina hydrogels were aged in tetraethylorthosilicate (TEOS)/acetonitrile solution, and modified using trimethylchlorosilane (TMCS)/acetonitrile solution. Properties of the final product were examined by contact angle measurement, FTIR, FESEM, TEM and BET analyses. Surface modification was confirmed by FTIR spectroscopy. It was found that hydrophobic property of the alumina aerogels was affected by the contents of TMCS. When the molar ratio of TMCS to AlCl3·6H2O is 0.35, hydrophobic alumina aerogels shows lower bulk density (0.453 g/cm3) and higher surface area (495 m2/g) than those of unmodified alumina aerogels (0.933 g/cm3, 413 m2/g).

Analysis of insulation performance of multilayer thermal insulation doped with phase change material

The transient heat transfer characteristics of a new kind of combined multilayer thermal insulation material (MTIM) were numerically investigated in this paper. This new kind of multilayer thermal insulation is composed by silica aerogel and alumina aerogel doping with erythritol and stearic acid phase change materials. Finite Volume method combined with Enthalpy method as well as the Discrete Ordinate method is used to consider the combined conduction and radiation heat transfer with phase change problems. Based on the constructed numerical model, the transient heat transfer characteristics of the MTIM with two kinds of different arrangements were calculated and analyzed in detail. The results indicated that: (1) putting the PCMs at the bottom of the MTIM fails to enhance the thermal insulation performance of the MTIM; (2) in contrast, putting the PCMs at the middle of the MTIM can enhance the thermal insulation performance of the MTIM successfully; (3) there is an optimum doping content of the PCMs that can lead to the lowest of the temperature of the MTIM which makes the thermal insulation performance of the MTIM to be the best.

Alumina Particles Are Snowballing with Propylene Oxide–Synthesis of Alumina Aerogels with Free Adjustable Particle and Pore Sizes

AbstractAbstract: Porous materials have widely application like adsorption, separation, catalysis, thermal insulation, etc., but how to prepare a kind of porous material with the specific particle and pore sizes according to the actual needs is always a tough problem. Although many studies have been involved in the regulation of the particle and channel sizes, until now the report clearly accessed to continuously adjustable particle and pore sizes is still very little. Here we demonstrate a simple method to prepare alumina aerogels with the required particle and pore size, which do not need to use any other complex structural directing materials, and can be easily achieved only by changing the amount of propylene oxide. This method realizes the controllable synthesis in real sense, which is helpful to promote the practical application of alumina aerogels, and also has a promising application in controllable synthesis of other porous materials.

Production of high-energy-density fuels by catalytic β-pinene dimerization: Effects of the catalyst surface acidity and pore width on selective dimer production

High carbon number hydrocarbon fuels were produced by catalytic β-pinene dimerization. These fuels can be used as high-energy-density fuels, including diesel and jet fuels. To suppress the production of oligomers composed of more than two pinene units, which are undesirable in liquid fuels because of their high boiling temperatures and viscosities, the pore width of the silica–alumina aerogel catalysts was modified and their surfaces were treated chemically. The chemical treatment of the catalyst surface improved the selectivity of fuel-grade dimer production and suppressed oligomer formation. The reaction pathways for dimer production from pinenes were also studied. It was found that Brønsted acids are responsible for pinene condensation, although earlier works reported that Lewis acids are responsible for condensate formation.

How to Tune the Alumina Aerogels Structure by the Variation of a Supercritical Solvent. Evolution of the Structure During Heat Treatment

Alumina aerogels are obtained by supercritical drying (SCD) in four solvents of different chemical natures. The phase transformations, the morphological changes, and the thermal stability during heat treatment in the range 20–1200 °C are investigated. The as-prepared samples obtained by SCD in MeOH are identified as crystalline aluminum hydroxide methoxide, and those obtained by SCD in i-PrOH consist of alumina with small size of crystallite grains. In contrast to alcohol-dried samples, the initial ether-dried aerogels are amorphous (as determined by X-ray diffraction). Calcination of the samples causes their crystallization and recrystallization. After heat treatment at 1200 °C, all samples consisted only of the α-alumina phase. TEM study demonstrated that the nature of the solvent used for SCD significantly affects the morphology of the aerogels. Low-temperature nitrogen adsorption investigation of the aerogel samples confirms the influence of the nature of supercritical fluid (SCF) on the structure of ...

Scattering and absorption coefficients of silica-doped alumina aerogels.

Alumina-based aerogels are especially useful in many applications due to their excellent stability at high temperatures. This study experimentally analyzed the radiative properties of silica-doped alumina aerogels through spectral directional-hemispherical measurements for wavelengths of 0.38-25 μm. The silica-doped alumina aerogel samples were prepared with a 1.4∶1 molar ratio of silica to alumina. A two-flux model was used to describe the radiation propagation in a 1D scattering absorbing sample to derive expressions for the normal-hemispherical transmittances and reflectances based on the transport approximation. The normal-hemispherical transmittances and reflectances were measured at various spectral wavelengths and sample thicknesses using the integrating sphere method. The spectral absorption and transport scattering coefficients of silica-doped alumina aerogels were then determined from the measured normal-hemispherical data. The absorption and transport scattering coefficients of silica-doped alumina aerogels are (0.1 cm-1, 36 cm-1) and (0.1 cm-1, 112 cm-1) for wavelengths of 0.38-8.0 μm. The spectral transport scattering coefficient varies in the opposite direction from the spectral absorption coefficient for various wavelengths. The radiative properties for silica and alumina aerogels were quite different for the absorption coefficient for wavelengths of 2.5-8.0 μm and for the transport scattering coefficient for wavelengths of 0.38-2.5 and 3.5-6.0 μm. The measured radiative properties were used to predict the spectral normal-hemispherical reflectance and transmittance of the silica-doped alumina aerogels for various sample thicknesses and wavelengths. The predicted values do not change for the sample thicknesses greater than a critical value. The analysis provides valuable reference data for alumina aerogels for high-temperature applications.

Rapid preparation process, structure and thermal stability of lanthanum doped alumina aerogels with a high specific surface area

In this study, we developed a new and rapid preparation method of alumina aerogels based on the sol–gel method and supercritical drying technique and prepared alumina aerogels with high specific surface area.

Performance and mass transfer of aqueous fluoride removal by a magnetic alumina aerogel

A novel magnetic alumina aerogel was evaluated for F− removal from water. It is an effective and easily prepared adsorbent with moderate cost that operates in a magnetic separation-enhanced sequencing batch mode which fully benefits from the fast kinetics of fine powders.

Synthesis of Monolithic Fe2O3-Al2O3Composite Aerogels via Organic Solvent Sublimation Drying

Monolithic Fe2O3-Al2O3composite aerogels have been prepared successfully via organic solvent sublimation drying method. The results show that a new phase forms when the right amount of ferric oxide is added to the alumina aerogel. From the TEM pictures we can see a shuttle-type structure with the length of about 15 nm forms, which leads to the high surface areas of composited aerogel.

Hydrogen production by tri-reforming of methane over nickel–alumina aerogel catalyst

A mesoporous nickel–alumina aerogel catalyst (NAA) was prepared by an epoxide-initiated gelation method and a subsequent supercritical carbon dioxide drying method. For comparison, a mesoporous nickel–alumina xerogel catalyst (NAX) was also prepared by an epoxide-initiated gelation method without supercritical carbon dioxide drying. Both catalysts were applied to the hydrogen production by tri-reforming of methane. The effect of preparation method on the physicochemical properties and catalytic activities of the catalysts was investigated. Although both catalysts exhibited a well-developed mesoporous structure, NAA catalyst retained higher surface area and larger pore volume than NAX catalyst. It was also revealed that NAA catalyst retained higher nickel dispersion and larger methane adsorption capacity than NAX catalyst. In the hydrogen production by tri-reforming of methane, both catalysts exhibited a stable catalytic performance. However, NAA catalyst showed higher hydrogen yield and higher CH4 conversion than NAX catalyst. High nickel dispersion and strong affinity with methane of NAA catalyst was responsible for its high catalytic performance.

XRD characterization of structural evolution and morphology properties of silica-doped alumina aerogels

XRD characterization of structural evolution and morphology properties of silica-doped alumina aerogels

Production of renewable p-xylene from 2,5-dimethylfuran via Diels–Alder cycloaddition and dehydrative aromatization reactions over silica−alumina aerogel catalysts

We report the selective conversion of biomass-derived 2,5-dimethylfuran (DMF) to p-xylene (~70% selectivity) through Diels–Alder cycloaddition and subsequent dehydration with silica−alumina aerogel (SAA) catalysts. The high activity of SAA can be attributed to its high surface area, large mesoporous volume, and high acid site concentrations. The conversion of DMF and the yield of p-xylene were strongly dependent on the silica alumina ratio of SAA. A higher aluminum content in SAA led to a progressive increase in the concentration of Brønsted acid sites and a corresponding increase in the p-xylene production rate. The effect of solvent on the production of p-xylene was examined, and it was found that the p-xylene production rate increases significantly in polar aprotic solvents (i.e. 1,4-dioxane).

Epoxide-assisted alumina aerogels by rapid supercritical extraction

Aerogels offer a potential alternative to noble metals that could reduce both the cost and environmental impact associated with catalytic converter production. The environmental impact of the production of aerogel catalysts could be further reduced by using a rapid supercritical extraction (RSCE) technique, which reduces the time and solvent waste associated with aerogel preparation. Alumina aerogels, which have shown activity in catalyzing exhaust processing reactions, were prepared using an epoxide-assisted gelation technique with RSCE processing in a contained mold in a hydraulic hot press. Samples were characterized by FTIR, XRD, SEM, EDX, nitrogen adsorption porosimetry and pycnometry. Solvent characterization by GC–MS headspace analysis shows that excess propylene oxide and chloropropanol products of an irreversible epoxide ring-opening reaction are present in the alumina gel following gelation, but can be removed via solvent exchange. Alumina aerogels with surface areas as high as 790m2/g and bulk densities as low as 0.05g/mL were prepared. Preliminary characterization of these aerogels, utilizing a catalytic test bed and a simulated emission gas blend, demonstrates that they have moderate ability for removal of hydrocarbons, carbon monoxide and nitrogen oxide.

Influence of Ethyl Acetoacetate on the Structure and Thermal Stability of Alumina Aerogel

Alumina aerogels were prepared from aluminum sect-butoxide via sol-gel process and supercritical drying. The influence of Ethyl acetoacetate (Etac) on the aerogel properties, microstructure, and thermal stability was systematically studied. At the same time, reaction mechanism was also investigated. The results show that, without and with Etac addition, the alumina aerogels are consisted of crystalline boehmite and amorphous network, respectively. When nEtac/nAl molar ratio is 0.01~0.15:1, Al2O3 aerogels have larger surface area (71~98 m2/g) than pure alumina aerogel (61m2/g) after heated at 1200°C, a proper ratio of Etac is helpful to increases the gelation time and stability of alumina sol, and is useful to improve the thermal stability of Al2O3 aerogels.

Facile synthesis of strong alumina–cellulose aerogels by a freeze-drying method

The strong alumina–cellulose aerogels (ACAs) were firstly prepared via sol–gel process and freeze-drying method. The hydrosoluble hydroxy ethyl cellulose (HEC) was chosen as reinforcement phase to enhance the skeletal strength of alumina aerogels. Fourier transform infrared (FT-IR) spectra, thermo gravimetric (TG) analysis and scanning electron microscopy (SEM) were used to investigate the microstructure and the connection of chemical groups. The compressive measurement result shows that ACAs possess high mechanical property and can realize partial elastic recovery.

Synthesis of high strength monolithic alumina aerogels at ambient pressure

Mechanically strong monolithic alumina aerogels were obtained via ambient pressure drying by incorporating attapulgite (ATP) and alumina sol.

Synthesis of monolithic aerogel-like alumina via the accumulation of mesoporous hollow microspheres

Monolithic aerogel-like alumina was synthesized via the accumulation of mesoporous hollow microspheres through an epoxide-driven sol–gel method. The addition of propylene oxide to the solution controls the gelation process, while the aging time and H2O/ethanol molar ratio in the initial component determine the morphology of the gel. The bulk density of the as-prepared sample was 0.133g/cm3, and the BET surface area was 505.6m2/g, which were very close to the values for the common alumina aerogel synthesized through the supercritical drying method. The microstructural evolution of the aerogel-like material as a function of aging time was carefully studied by SEM and TEM. The transition from solid particles to urchin-like mesoporous hollow microspheres can be explained as a self-templating process according to the Ostwald ripening mechanism. In addition, the samples were heat treated to 800°C, 1000°C and 1200°C for 2h. With an increase of the heat treatment temperature, the crystalline phases of the aerogel-like alumina varied from γ-phase alumina to θ-phase alumina. The microstructures as well as the physical properties, such as the thermal conductivity and elastic modulus, of samples heat-treated at different temperatures were also measured and revealed that the samples exhibited excellent stability against high temperature.

Trimethylethoxysilane-modified super heat-resistant alumina aerogels for high-temperature thermal insulation and adsorption applications

Download options Please wait... Article information DOI https://doi.org/10.1039/C4RA08832H Article type Paper Submitted 18 Aug 2014 Accepted 06 Oct 2014 First published 06 Oct 2014 Download Citation RSC Adv., 2014,4, 54864-54871 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Trimethylethoxysilane-modified super heat-resistant alumina aerogels for high-temperature thermal insulation and adsorption applications W. Wang, Z. Zhang, G. Zu, J. Shen, L. Zou, Y. Lian, B. Liu and F. Zhang, RSC Adv., 2014, 4, 54864 DOI: 10.1039/C4RA08832H To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Wenqin Wang Zhihua Zhang Guoqing Zu Jun Shen Liping Zou Ya Lian Bin Liu Fan Zhang