共查询到20条相似文献,搜索用时 31 毫秒
1.
P. R. Aravind P. Shajesh P. Mukundan K. G. K. Warrier 《Journal of Sol-Gel Science and Technology》2009,52(3):328-334
Ambient pressure drying has been carried out for the synthesis of silica–titania aerogel monoliths. The prepared aerogels
show densities in the range 0.34–0.38 g/cm3. The surface area and pore volume of these mixed oxide aerogels are comparable to those of the supercritically dried ones.
The surface area for 5wt% titania aerogel has been found to be as high as 685 m2/g with a pore volume of 2.34 cm3/g and the 10wt% titania aerogel has a surface area of 620 m2/g with a pore volume of 2.36 cm3/g. Some gels were also made hydrophobic by a surface treatment with methyltrimethoxysilane and trimethylchlorosilane. The
surface modified aerogels possess high surface areas in the range of 540–640 m2/g, and are thermally stable in terms of retaining hydrophobicity up to a temperature of 520 °C. The pore size distribution
of the aerogels clearly indicates the preservation of the aerogel structure. High Resolution Transmission Electron microscopy
has been employed to characterise the aerogels and Fourier Transform infrared spectroscopy to study the effect of titania
addition to silica and the surface modification. X-ray diffraction patterns were recorded to verify the molecular homogeneity
of the aerogel. 相似文献
2.
Interest in improving the optical transmission of sodium silicate-based aerogels by ambient pressure drying led to the synthesis of aerogels using a two-step sol–gel process. To produce optically transparent silica aerogel granules, NH4F (1 M) and HCl (4 M) were used as hydrolyzing and condensation catalysts, respectively. The silica aerogels were characterized by their bulk density, porosity (%), contact angle and thermal conductivity. Optical transmission of as synthesized aerogels was studied by comparing the photos of aerogel granules. Scanning electron microscopic study showed the presence of fractal structures in these aerogels. The degree of transparency in two step sol–gel process-based aerogels is higher than the conventional single step aerogels. The N2 adsorption–desorption analysis depicts that the two step sol–gel based aerogels have large surface areas. Optically transparent silica aerogels with a low density of ∼0.125 g/cc, low thermal conductivity of ∼0.128 W/mK and higher Brunauer, Emmett, and Teller surface area of ∼425 m2/g were obtained by using NH4F (1 M), HCl (4 M), and a molar ratio of Na2SiO3::H2O::trimethylchlorosilane of 1::146.67::9.46. The aerogels retained their hydrophobicity up to 500 °C. 相似文献
3.
Uzma K. H. Bangi A. Parvathy Rao H. Hirashima A. Venkateswara Rao 《Journal of Sol-Gel Science and Technology》2009,50(1):87-97
Experimental results on the physico-chemical properties of ambiently dried sodium silicate based aerogels catalyzed with various
acids are reported. The aerogels were prepared by hydrolysis and polycondensation of sodium silicate followed by subsequent
washings, surface chemical modification and ambient pressure drying using 10 various acid catalysts consisting of strong and
weak acids. The strength and concentration of acids have the major effect on the gelation of sol and hence the physico-chemical
properties of the silica aerogels. Strong acids such as HCl, HNO3 and H2SO4 resulted in shrunk (70–95%) aerogels whereas weak acids such as citric and tartaric acids resulted in less shrunk (34–50%)
aerogels. The physical properties of silica aerogels were studied by measuring bulk density, volume shrinkage (%), porosity
(%), pore volume, thermal conductivity, contact angle with water, Transmission Electron Microscopy (TEM), Atomic Absorption
Spectroscopy (AAS), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric-Differential Thermal (TG-DT) analyses
and N2 adsorption–desorption BET surface analyzer. The best quality silica aerogels in terms of low density (0.086 g/cm3), low volume shrinkage (34%), high porosity (95%), low thermal conductivity (0.09 W/m K) and hydrophobic (148°) were obtained
for molar ratio of Na2SiO3:H2O:citric acid:TMCS at 1:146.67:0.72:9.46 with 20 min gelation time. The resulting aerogels exhibited the thermal stability
up to around 420 °C. 相似文献
4.
The experimental results by using various exchanging solvents in the preparation of two step (acid and base) processed ambient
pressure dried hydrophobic silica aerogels, are reported. Silica alcogels were prepared by hydrolysis with oxalic acid and
condensation with NH4OH of ethanol diluted tetraethylorthosilicate (TEOS) precursor and hexamethyldisilazane(HMDZ) methylating agent. The exchanging
solvents used were: hexane, cyclohexane, heptane, benzene, toluene and xylene. The physical properties such as % of volume
shrinkage, density, pore volume, % of porosity, thermal conductivity, % of optical transmission, surface area, pore size distribution
and contact angle (θ) of the silica aerogels with water, were measured as a function of EtOH/TEOS molar ratios (R) for all the exchanging solvents. It was found that the physical and hydrophobic properties of the silica aerogels strongly
depend on the nature of the solvent and R. Heptane solvent resulted in highly transparent (≈90% optical transmission at 700 nm for 1 cm thick sample), low density
(≈0.060 g/cm3), low thermal conductive (≈0.070 W/m·K), high % of porosity (97%), high surface area (750 m2/g), uniform porosity and hydrophobic (θ ≈ 160°) aerogels compared to other solvents. On the otherhand, xylene resulted in aerogels with higher hydrophobicity (θ ≈ 172°) among other solvents. 相似文献
5.
Ann M. Anderson Mary K. Carroll Emily C. Green Jason T. Melville Michael S. Bono 《Journal of Sol-Gel Science and Technology》2010,53(2):199-207
Hydrophobic silica aerogels have been prepared using the rapid supercritical extraction (RSCE) technique. The RSCE technique
is a one-step methanol supercritical extraction method for producing aerogel monoliths in 3 to 8 h. Standard aerogels were
prepared from a tetramethoxysilane (TMOS) recipe with a molar ratio of TMOS:MeOH:H2O:NH4OH of 1.0:12.0:4.0:7.4 × 10−3. Hydrophobic aerogels were prepared using the same recipe except the TMOS was replaced with a mixture of TMOS and one of
the following organosilane co-precursors: methytrimethoxysilane (MTMS), ethyltrimethoxysilane (ETMS), or propyltrimeth-oxysilane
(PTMS). Results show that, by increasing the amount of catalyst and increasing gelation time, monolithic aerogels can be prepared
out of volume mixtures including up to 75% MTMS, 50% ETMS or 50% PTMS in 7.5–15 h. As the amount of co-precursor is increased
the aerogels become more hydrophobic (sessile tests with water droplets yield contact angles up to 155°) and less transparent
(transmission through a 12.2-mm thick sample decreases from 83 to 50% at 800 nm). The skeletal and bulk density decrease and
the surface area increases (550–760 m2/g) when TMOS is substituted with increasing amounts of MTMS. The amount of co-precursor does not affect the thermal conductivity.
SEM imaging shows significant differences in the nanostructure for the most hydrophobic surfaces. 相似文献
6.
Lightweight polydicyclopentadiene (pDCPD) based aerogels were developed via a simple sol-gel processing and supercritical
drying method. The uniform pDCPD wet gels were first prepared at room temperature and atmospheric pressure through ring opening
metathesis polymerization (ROMP) incorporating homogeneous ruthenium catalyst complexes (Grubbs catalyst). Gelation kinetics
were significantly affected by both catalyst content and target density (i.e., solid content), while gel solvents also played
important role in determining the appearance and uniformity of wet gel and aerogel products. A supercritical carbon dioxide
(CO2) drying method was used to extract solvent from wet pDCPD gels to afford nanoporous aerogel solid. A variety of pDCPD based
aerogels were synthesized by varying target density, catalyst content, and solvent and were compared with their xerogel analogs
(obtained by ambient pressure solvent removal) for linear shrinkage and thermal conductivity value (1 atm air, 38 °C mean
temperature). Target density played a key role in determining porosity and thermal conductivity of the resultant pDCPD aerogel.
Differential scanning calorimetery (DSC) demonstrated that the materials as produced were not fully-crosslinked. The pDCPD
based aerogel monoliths demonstrated high porosities, low thermal conductivity values, and inherent hydrophobicity. These
aerogel materials are very promising candidates for many thermal and acoustic insulation applications including cryogenic
insulation.
相似文献
George L. GouldEmail: |
7.
Baomin Wang Hainan Ma Kai Song 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(7):1196-1201
The silica aerogels were successfully fabricated under ambient pressure from diatomite. The influence of different dilution ratios of diatomite filtrate on physical properties of aerogels were studied. The microstructure, surface functional groups, thermal stability, morphology and mechanical properties of silica aerogels based on diatomite were investigated by BET adsorption, FT-IR, DTA-TG, FESEM, TEM, and nanoindentation methods. The results indicate that the filtrate diluted with distilled water in a proportion of 1: 2 could give silica aerogels in the largest size with highest transparency. The obtained aerogels with density of 0.122–0.203 g/m3 and specific surface area of 655.5–790.7 m2/g are crack free amorphous solids and exhibited a sponge-like structure. Moreover, the peak pore size resided at 9 nm. The initial aerogels were hydrophobic, when being heat-treated around 400°C, the aerogels were transformed into hydrophilic ones. The obtained aerogel has good mechanical properties. 相似文献
8.
Je Kyun Lee George L. Gould Wendell Rhine 《Journal of Sol-Gel Science and Technology》2009,49(2):209-220
Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and
supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure
by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity
of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and
equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO2) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity
values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature
to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity
values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property
and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated
with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications
and as a thermal insulation component of spacesuits. 相似文献
9.
Pradip B. Sarawade Jong-Kil Kim Askwar Hilonga Hee Taik Kim 《Solid State Sciences》2010,12(5):911-918
We report a method to synthesize low-density transparent mesoporous silica aerogel beads by ambient pressure drying (APD). The beads were prepared by acid–base sol–gel polymerization of sodium silicate in aqueous ammonia solution via the ball dropping method (BDM). To minimize shrinkage during drying, wet silica beads were initially prepared; their surfaces were then modified using trimethylchlorosilane (TMCS) via simultaneous solvent exchange and surface modification. The effects of the volume percentage (%V) of TMCS on the physical and textural properties of the beads were investigated. The specific surface area and cumulative pore volume of the silica aerogel beads increased with an increase in the %V of TMCS. Silica aerogel beads with low packing bed density (0.081 g/cm3), high surface area (917 m2/g), and large cumulative pore volume (2.8 cm3/g) was obtained when 10%V TMCS was used. Properties of the final product were examined by FE-SEM, TEM, BET, and TG–DT analyses. Surface chemical modifications were confirmed by FTIR spectroscopy. The hydrophobic silica aerogel beads were thermally stable up to 411 °C. We discuss our results and compare our findings for modified versus unmodified silica beads. 相似文献
10.
A. Parvathy Rao A. Venkateswara Rao Uzma K. H. Bangi 《Journal of Sol-Gel Science and Technology》2008,47(1):85-94
The experimental results on the preparation of low thermal conductivity and transparent ambient pressure dried silica aerogels
with the sodium silicate solution, TMCS silylating agent with methanol, isopropyl alcohol, hexane and xylene solvents, are
reported. This study is focussed on the effect of preparation conditions such as varying the number of preparation steps,
pH of the hydrosol and hydrogel ageing temperature, for the production of the low thermal conductive silica aerogels and the
results are analysed. Density, thermal conductivity, % of optical transmission and contact angle of the aerogels were measured.
The Fourier Transform Infrared Spectroscopy (FTIR) studies revealed the presence of Si–C and C–H along with the Si–O–Si and
OH bonds and their intensities strongly depend on the processing steps, pH of the hydrosol and gel ageing temperature. The
UV–Visible spectra indicated the % of optical transmission of the aerogels decreased with increasing the number of processing
steps, increase in the pH of the hydrosol from 3 to 8 and decreased for ageing temperature up to 50 °C. Further increase in
temperature >50 °C, the % of optical transmission of the aerogels increased. The TGA-DTA data showed the thermal stability
of the aerogels with respect to hydrophobicity is 325 °C. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy
(SEM) analyses revealed the nanostructure of the aerogels. The porosity of the aerogels was studied using the pore size distribution.
Silica aerogels with low density (0.051 g/cc), low thermal conductivity (0.049 W/m K), optical transmission (65%), high hydrophobicity
(159°) and resistance to humid atmosphere >1 year was obtained in the present studies. 相似文献
11.
S. Gutzov N. Danchova S. I. Karakashev M. Khristov J. Ivanova J. Ulbikas 《Journal of Sol-Gel Science and Technology》2014,70(3):511-516
This work focuses on the dependence preparation conditions—structure—physical properties of hydrophobic silica aerogels, all of them prepared under subcritical drying conditions (70 °C and 0.4 atm.), thus aiming at potential application as case insulation filling in heat pumps. The so prepared, millimeter scaled nano-porous hydrophobic silica aerogel granules were analyzed with standard electron microscope and atomic force microscopy, IR spectroscopy, UV/Vis spectroscopy, differential scanning calorimetry and thermal conductivity measurements. The physical properties of the aerogels were compared with commercial aerogel granules. A method for contact angle measurement of micro-droplets situated on the silica granules was proposed to quantify the level of their hydrophobicity. 相似文献
12.
Simerjeet K. Gill Preston Brown Mobolaji Tayo Ogundiya Louisa J. Hope-Weeks 《Journal of Sol-Gel Science and Technology》2010,53(3):635-640
Nickel (II) oxide aerogels with an amorphous alumina support were synthesized by the expoxide addition method. The monoliths
were obtained by adding propylene oxide to an alcoholic solution of hydrated metal nitrate salts. The wet gels were dried
by supercritical extraction to produce porous monolithic aerogels. The as-synthesized aerogels were amorphous containing aluminum
and nickel hydroxides. Annealing of the as-synthesized aerogels at 400 °C yields crystalline nickel oxide materials which
retain the high surface areas (>160 m2/g) and porosities of the original aerogels. The resultant aerogel materials were characterized using powder X-ray diffraction,
thermo-gravimetric analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis,
and nitrogen adsorption/desorption analysis. 相似文献
13.
Michael S. BonoJr. Ann M. Anderson Mary K. Carroll 《Journal of Sol-Gel Science and Technology》2010,53(2):216-226
Alumina aerogels with surface areas from 460 to 840 m2/g and bulk densities from 0.025 to 0.079 g/cm3 were successfully fabricated using variations of an aluminum isopropoxide-based recipe developed by Armor and Carlson and
the rapid supercritical extraction (RSCE) process developed at Union College. By utilizing the Union College RSCE method,
it is possible to convert an alumina aerogel precursor mixture into aerogel monoliths in as little as 7.5 h. This process
is safer than methanol extraction in an autoclave and faster and simpler than liquid CO2 solvent exchange and extraction. By increasing the concentration of aqueous HNO3 used in the precursor mixture, we were able to fabricate aerogels with significantly increased surface area, decreased bulk
density, and altered microstructure. We attribute the observed variation in these aerogel properties at a given HNO3 concentration to environmental factors such as humidity. The ability to more easily fabricate alumina aerogels with desirable
properties will assist in making them a viable option for catalytic and other applications. 相似文献
14.
Sung-Woo Hwang Hae-Hyun Jung Sang-Hoon Hyun Young-Soo Ahn 《Journal of Sol-Gel Science and Technology》2007,41(2):139-146
Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been
developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution
(4–10 wt% SiO2). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface
modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore
water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific
surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm3, and ∼675 m2/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%. 相似文献
15.
In the present paper, we report the synthesis of tetrapropoxysilane (TPOS)-based silica aerogels with high surface area and large pore volume. The silica aerogels were prepared by a two-step sol-gel process followed by surface modification via a simple ambient pressure drying approach. In order to minimize drying shrinkage and obtain hydrophobic aerogels, the surface of the alcogels was modified using trichloromethylsilane as a silylating agent. The effect of the sol-gel compositional parameters on the polymerization of aerogels prepared by TPOS, one of the precursors belonging to the Si(OR)4 family, was reported for the first time. The oxalic acid and NH4OH concentrations were adjusted to achieve good-quality aerogels with high surface area, low density, and high transparency. Controlling the hydrolysis and condensation reactions of the TPOS precursor turned out to be the most important factor to determine the pore characteristics of the aerogel. Highly transparent aerogels with high specific surface area (938 m2/g) and low density (0.047 g/cm3) could be obtained using an optimized TPOS/MeOH molar ratio with appropriate concentrations of oxalic acid and NH4OH. 相似文献
16.
Ha-Yoon Nah Vinayak G. Parale Kyu-Yeon Lee Haryeong Choi Taehee Kim Chang-Hyun Lim Ji-Yeon Seo Yang Seo Ku Jae-Woo Park Hyung-Ho Park 《Journal of Sol-Gel Science and Technology》2018,87(2):319-330
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. 相似文献
17.
Uzma K. H. Bangi M. S. Kavale Seungsu Baek Hyung-Ho Park 《Journal of Sol-Gel Science and Technology》2012,62(2):201-207
The successful incorporation of multiwalled carbon nanotubes (MWCNTs) into silica aerogels prepared by sol–gel method is reported
herein. Pure silica aerogels prepared using sodium silicate precursor by ambient pressure drying are so fragile that they
cannot be used easily. MWCNTs were used as reinforcements to improve the mechanical properties of silica aerogels. Results
show that inserting small amounts of MWCNTs in the gels causes enhanced dimensional stability of silica aerogels. The silica
aerogels were prepared by doping MWCNTs in silica matrix before gelation. The influence of MWCNTs on some microstructural
aspects of silica matrix has been studied using nitrogen adsorption–desorption isotherms. From SEM study it is confirmed that
the silica particles get capped on the surface of MWCNTs suggesting an enhanced toughness. Further, FTIR, Raman, EDAX, thermal
conductivity and hydrophobicity studies of these doped aerogels were carried out. By addition of MWCNTs, silica aerogels were
formed with 706 m2/g BET and 1,200 m2/g Langmuir surface areas and 149o contact angle. Low density (0.052 g/cc) and low thermal conductivity (0.067 W/m K) MWCNTs doped silica aerogels were obtained
for the molar ratio of Na2SiO3::H2O::MWCNTs::citric acid::TMCS at 1::146.67::2.5 × 10−3::0.54::9.46 respectively with improved mechanical strength. 相似文献
18.
The effect of heat-treatment on the physico-chemical properties of silica aerogel prepared by sub-critical drying technique 总被引:3,自引:0,他引:3
K. Balkis Ameen K. Rajasekar T. Rajasekharan M. V. Rajasekharan 《Journal of Sol-Gel Science and Technology》2008,45(1):9-15
Synthesis of transparent and crack-free monoliths of silica aerogel by sub-critical drying technique is reported in the present
article. Silane ageing with 50% tetraethylorthosilicate:ethanol followed by solvent exchange using ethanol was adopted. The
effect of heat-treatment on the textural and physical characteristics of silica aerogel was evaluated. The chosen composition
resulted in a high surface area silica aerogel of 1,000 m2 g−1 and a pore volume of 1.4 cm3 g−1 at room temperature. The aerogel heat-treated at 900 °C possessed a surface area of 450 m2 g−1 with a pore volume of 0.4 cm3 g−1. The decrease in surface area and pore volume was associated with the sintering process. The present technique seems advantageous
in preserving the high surface area of the material at high temperatures. The XRD studies showed that the amorphous nature
of aerogel matrix was retained till 1,400 °C, beyond which it crystallized to phase pure crystoballite. 相似文献
19.
Jyoti L. Gurav A. Venkateswara Rao Digambar Y. Nadargi 《Journal of Sol-Gel Science and Technology》2009,50(3):275-280
The experimental results on the study of thermal conductivity and effect of humidity on HMDZ modified TEOS based aerogels
dried at ambient pressure, are reported. Silica sol was prepared by keeping the MeOH/TEOS molar ratio, Acidic water (Oxalic
acid) and basic water (NH4OH) concentrations constant at 16.5, 0.001 and 1 M, respectively throughout the experiments and the HMDZ/TEOS molar ratio
(h) was varied from 0.34 to 2.1. Finally, the surface modified wet gels were dried at an ambient pressure. The thermal conductivity
of the aerogel samples was measured. Further, the humidity study was carried out in 80% humid surrounding at 30 °C temperature
over 80 days. The best quality aerogels in terms of low bulk density, thermal conductivity and durability (no moisture absorption)
with an only 2% of weight gain were obtained for TEOS: MeOH: Acidic H2O: Basic H2O: HMDZ molar ratio at 1:16.5:0.81:0.50:0.681, respectively. The thermal stability and hydrophobicity of the aerogel have
been confirmed with Thermo gravimetric and Differential Thermal (TG–DT) analyses and Fourier Transform Infrared Spectroscopy
(FTIR), respectively. Microstructural studies were carried out by Scanning Electron microscopy (SEM). 相似文献
20.
Room Temperature Synthesis of Noble Metal Clusters in the Mesopores of Mechanically Strong Silica-Polymer Aerogel Composites 总被引:1,自引:0,他引:1
Bertino M.F. Hund J.F. Zhang G. Sotiriou-Leventis C. Tokuhiro A.T. Leventis N. 《Journal of Sol-Gel Science and Technology》2004,30(1):43-48
Clusters of Ag and Au have been formed in the bulk of mechanically strong silica-polymer aerogel composite monoliths. For that purpose, base-catalyzed silica hydrogels were washed with a 50% w/w acetone/diisocyanate (di-ISO) solution, and cured at 55°C for 3 days. Unreacted di-ISO solution was washed off with acetone, and the gels were washed with a acetone solutions of Ag+ or AuCl–
4 (3 × 10–4 mol · L–1), containing also 0.2 mol · L–1 of 2-propanol as radical scavenger. Metal clusters were formed upon radiolytic reduction ( rays, 48–72 h, 7–7.5 kGy) of the precursor ions. After irradiation, the hydrogels were washed with acetone, and dried in supercritical CO2. The resulting aerogel monoliths had a density of 0.56 g·cm–3, a surface area of about 160 m2 · g–1, and an average pore diameter of about 200 nm. Transmission electron microscopy showed that the metal clusters are free of contamination, with a cubic face centered structure, and a narrow size distribution, centered around 10 nm. The elastic module, measured with a three-point flexural bending method, was in the 60–70 MPa range, and the load at rupture between 16 and 19 kg. Thermogravimetric analysis showed that the composites were stable up to about 300°C. These results are in excellent agreement with results obtained previously for as-grown, di-ISO cross-linked silica aerogels, and show that addition of metal clusters and gamma irradiation to a dose corresponding to a permanence of several years in low earth orbit at high inclination did not affect the chemical identity, the mechanical strength, the porosity and the bulk density of the composite aerogel monoliths. 相似文献