An economic and environmentally benign approach for the preparation of monolithic silica aerogels

RSC Advances ◽  
2016 ◽  
Vol 6 (96) ◽  
pp. 93374-93383 ◽  
Author(s):  
Yuanyuan Zhang ◽  
Junxia Peng ◽  
Guanqun Du ◽  
Hongxia Zhang ◽  
Yu Fang
Keyword(s):  
Ambient Pressure ◽  
Sol Gel ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Environmentally Benign ◽  
Solvent Exchange ◽  
Monolithic Silica ◽  
One Step ◽  
Thermal Conductivities

One step sol–gel reaction, followed by solvent exchange free ambient pressure drying resulted in various monolithic silica aerogels from super-hydrophobic to hydrophilic with densities as low as 0.026 g cm−3 and thermal conductivities lower than air.

A Novel Route for Preparation of Transparent and Superhydrophobic Silica Aerogels

2009 ◽  
Vol 1234 ◽  
Author(s):  
Guo-you Wu ◽  
Xuan Cheng ◽  
Yu-xi Yu ◽  
Ying Zhang
Keyword(s):  
Surface Modification ◽  
Ambient Pressure ◽  
Sol Gel ◽  
Three Dimensional ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Nanoporous Structure ◽  
Surface Areas ◽  
Superhydrophobic Silica ◽  
Dta Curve

AbstractSilica aerogels were synthesized via sol-gel processing followed by a two-step surface modification and ambient pressure drying, using methyltrimethoxysilane (MTMS) and trimethylchlorosilane (TMCS)/ethanol/n-hexane as surface modification agents. The transparent silica aerogels possessed the porosities, densities and specific surface areas in the range of 87.7–92.3%, 0.27–0.17 g·cm-3 and 852–1005 m2·g-1, respectively. The SEM and HRTEM analysis revealed the three-dimensional nanoporous structure of the silica aerogels. The presence of –CH3 functional groups on the surface of silica particles as indicated by the FTIR spectra was further confirmed by two visible exothermic peaks at 310 and 450–500 °C from the DTA curve. In addition, the silica aerogels were superhydrophobic with the contact angle as high as 160°.

Study on Preparation of Mesoporous Silica Aerogels with Low Density and High Properties via Ambient Pressure Drying

2010 ◽  
Vol 148-149 ◽  
pp. 1491-1496
Author(s):  
Gang Qiang Geng ◽  
Wei Tao Bi ◽  
Yu Zhang ◽  
Deng Ke Sun
Keyword(s):  
Mesoporous Silica ◽  
Ambient Pressure ◽  
Sol Gel ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Ethanol Solution ◽  
Low Density ◽  
Micro Structure ◽  
Gel Time

The SiO2 aerogels of low density was fabricated by ion exchange and sol-gel method on the basis of sodium silicate. The effect of pH, aging，addition of DCCA and annealed temperature on the gel time, aerogel density, porosity and the micro-structure was systemly studied. The results showed that when the pH is 5, aging was 30%Vol .of TEOS/ethanol solution ,the addition of DCCA was 1.5ml, the gel system was annealed at 50 for 84 h, 60 for 72h, the best quality of silica aerogels with low density (0.14g/cm3), higher specific surface(610.643 m2/g) and pore size of 20~40 nm can be obtained.

Effects of Surfactants on the Synthesis of Silica Aerogels Prepared by Ambient Pressure Drying

2012 ◽  
Vol 512-515 ◽  
pp. 1625-1630
Author(s):  
Hua Zheng Sai ◽  
Li Xing ◽  
Jun Hui Xiang ◽  
Fu Shi Zhang ◽  
Li Jie Cui ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Sol Gel ◽  
Drying Shrinkage ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Ammonium Bromide ◽  
High Porosity ◽  
Free Silica ◽  
Sol Gel Process ◽  
Cetyltrimethyl Ammonium

In this research, aerogels were synthesized by a two-step sol-gel process without supercritical conditions. During the process, tetraethoxysilane (TEOS) was used as precursor, and different surfactants, i.e. cetyltrimethyl ammonium bromide (CTAB) and polyethylene glycol–600 (PEG–600), were used as dopants respectively. In order to minimize the drying shrinkage and preserve the high porosity structure, the surface of the gels was modified by trimethylchlorosilane (TMCS) before the ambient pressure drying (APD). The effect of surfactent on the structure of the resulting aerogels was investigated. The aerogels which involved surfactants exhibited resistance to cracking during the APD of the alcogels. The modification by TMCS has been confirmed using Infrared (IR) spectroscopy. The porous structure of aerogels was investigated by Brunauer-Emmett- Teller (BET) instrument, differential scanning calorimeter (DSC) and scanning electron micrograph (SEM). The results indicated that surfactants as dopants could significantly affect the structure and optical property of aerogels and be beneficial for obtaining crack-free silica aerogels via ambient pressure drying process.

scholarly journals The influence of various pH values on the aerogel physical properties by sol-gel technique

2019 ◽  
Vol 17 (41) ◽  
pp. 75-81
Author(s):  
Baha Fakhry Shehab
Keyword(s):  
Physical Properties ◽  
Ph Value ◽  
Ambient Pressure ◽  
Sol Gel ◽  
Silica Aerogels ◽  
Spectroscopic Studies ◽  
Ambient Pressure Drying ◽  
Ph Values ◽  
Bet Method ◽  
The Fourier Transform

Hydrophobic silica aerogels were successfully preparation by an ambient pressure drying method from sodium silicate (Na2SiO3) with different pH values (5, 6, 7, 8, 9 and 10). In this study, acidic HCl (1M), a basic NH4OH (1M) were selected as a catalyst to perform the surface modification in a TMCS (trimethylchlorosilane) solution. The surface chemical modification of the aerogels was assured by the Fourier transform infrared (FTIR) spectroscopic studies. Other physical properties, such as pore volume and pore size and specific surface area were determined by Brunauer-Emmett- Teller (BET) method. The effect of pH values on the bulk density of aerogel. The sol–gel parameter pH value in the sol, have marked effects on the physical properties of the silica aerogels produced by this technique. The density and the hydrophobic tendency of the aerogels were significantly influenced.

Hydrophobic Flexible Silica Aerogels Felts Fabricated by Ambient Pressure Drying

2013 ◽  
Vol 709 ◽  
pp. 32-35
Author(s):  
Xiao Yun Wu ◽  
Yu Xi Yu ◽  
De Qian Guo ◽  
Yong Chen
Keyword(s):  
Aqueous Ammonia ◽  
Ambient Pressure ◽  
Sol Gel ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Ethanol Solution ◽  
Hydrophobic Properties ◽  
Ph Values ◽  
Sol Gel Process ◽  
Hexane Solution

Hydrophobic flexible silica aerogels felts were fabricated successfully by two-steps sol-gel process via ambient pressure drying. First of all, the sol with various pH values was obtained from tetraethylorthosilicate (TEOS) as silicon source, hydrochloric acid/aqueous ammonia ethanol solution as catalysts. Then glass fiber felts was incorporated into the sol to increase the mechanical properties of silica aerogel. After the completion of solvent exchange and surface modification by using trimethylchlorosilane (TMCS)/n-hexane solution, the gel felts were dried under ambient pressure. The samples show excellent hydrophobic properties.

Hydrophobic Silica Aerogels by Ambient Pressure Drying

2015 ◽  
Vol 830-831 ◽  
pp. 476-479
Author(s):  
Srinivasan Nagapriya ◽  
M.R. Ajith ◽  
H. Sreemoolanadhan ◽  
Mariamma Mathew ◽  
S.C. Sharma
Keyword(s):  
Surface Area ◽  
Atmospheric Pressure ◽  
Polar Solvent ◽  
Ambient Pressure ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Sol Gel Process

Silica aerogels have been prepared through sol-gel process by polymerization of TEOS in the presence of NH4F and NH4OH as catalysts. The solvent present in the gel is replaced by ethanol followed by a non-polar solvent such as n-hexane prior to solvent modification step. Gels are made hydrophobic by treating them with HMDZ to prevent rupture during drying, which has been confirmed by FTIR. Gels are then washed and dried carefully in a PID controlled oven at atmospheric pressure. The ageing duration and solvent exchange combinations are optimized to yield crack-free gels prior to drying. Aerogels are characterized for density, specific surface area, pore volume, pore size, thermal stability and contact angle. Hydrophobic, high surface area (570 m2/g), low density (0.07 g/cm3) silica aerogels are synthesized by using optimized mole ratio of precursors and catalysts. Silica aerogel granules (1-3 mm) as well as monoliths (Ф~35 mm) could be produced through ambient pressure drying of gels.

scholarly journals Preparation of Silica Aerogels by Ambient Pressure Drying without Causing Equipment Corrosion

Molecules ◽  
2018 ◽  
Vol 23 (8) ◽  
pp. 1935 ◽  
Author(s):  
Lixiao Zhu ◽  
Yali Wang ◽  
Suping Cui ◽  
Feihua Yang ◽  
Zuoren Nie ◽  
...  
Keyword(s):  
Pore Structure ◽  
Raw Materials ◽  
Ambient Pressure ◽  
Sol Gel ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Molar Ratio ◽  
Insulation Property ◽  
Water Contact ◽  
Thermal Insulation Property

The silica aerogels were prepared via a sol-gel technique and ambient pressure drying by using industrial solid wastes, dislodged sludges, as raw materials. A strategy was put forward to reduce the corrosion of equipment during the drying procedure. The pore structure, hydrophobicity, and thermal insulation property of the obtained samples were investigated in detail. The results show that the corrosion can be effectively avoided by using an equimolar mixture of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS) as silylation agents. At a Si:TMCS:HMDS molar ratio of 1:0.375:0.375, the silica aerogels possess a desirable pore structure with a pore volume of 3.3 ± 0.1 cm3/g and a most probable pore size of 18.5 nm, a high hydrophobicity with a water contact angle of 144.2 ± 1.1°, and a low thermal conductivity of 0.031 ± 0.001 W/(m∙K).

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