Textural properties of ambient pressure dried water-glass based silica aerogel beads: One day synthesis

A crack-free silica aerogel monolith is a nanostructured material with so many surprising properties such as high specific surface area, high porosity, low dielectric constant, low density and outstanding heat insulation properties that were fabricated from a cheap water glass derived silicic acid solution.In this research , the OH surfaces of the wet gel were modified using a HMDZ/n-hexane or TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at different temperature under ambient pressure.The properties of hydrophobic silica aerogels synthesized by this new route were investigated by scanning electron microscopy (SEM), differential temperature analysis (DTA) and Fourier-transform infrared spectroscopy (FT-IR).The results showed that 20 wt% HMDZ as surface modifier and 75 °C as drying temperature resulted an acceptable hydrophobic silica aerogel with the density of 0.15 gr/cm³ and specific surface area of about 520 m²/gr.

Download Full-text

Carbon Fiber—Silica Aerogel Composite with Enhanced Structural and Mechanical Properties Based on Water Glass and Ambient Pressure Drying

Nanomaterials ◽

10.3390/nano11020258 ◽

2021 ◽

Vol 11 (2) ◽

pp. 258

Author(s):

Agnieszka Ślosarczyk

Keyword(s):

Carbon Fiber ◽

Carbon Fibers ◽

Silica Aerogel ◽

Water Glass ◽

Structural Parameters ◽

Ambient Pressure ◽

Ambient Pressure Drying ◽

Physical Parameters ◽

Synthesis Time ◽

Aerogel Composite

The article presents the synthesis of silica aerogel from a much cheaper precursor of water glass that was reinforced with short pitch carbon fiber by way of ambient pressure drying. Before being added to the silica gel, the carbon fibers were surface modified to increase adhesion at the interfacial border. We were able to obtain stable structures of the composite with the amount of fibers above 10% by volume. The presence of fibers in the silica matrix resulted in lower synthesis time of the composite, improved adhesion of fibers to the aerogel nanostructure, and increased mechanical and structural parameters. An additional effect of the presence of fibers in excess of 10% by volume was a new function of the nanocomposite—the ability to conduct electric current. The most optimal parameters of the composite, however, were obtained for silica aerogel reinforced with 10 vol.% of carbon fibers. This material indicated relatively low density and good physical parameters. The paper also analyzes the results on the synthesis of fiber-reinforced silica aerogels that have appeared in recent years and compares these to the results gained in presented work.

Download Full-text

Thermal Gelation for Synthesis of Surface-Modified Silica Aerogel Powders

Gels ◽

10.3390/gels7040242 ◽

2021 ◽

Vol 7 (4) ◽

pp. 242

Author(s):

Kyoung-Jin Lee ◽

Jae Min Lee ◽

Ki Sun Nam ◽

Haejin Hwang

Keyword(s):

Silica Aerogel ◽

Water Glass ◽

Ambient Pressure ◽

Porous Silica ◽

Ambient Pressure Drying ◽

Bet Surface Area ◽

Water Contact ◽

Thermal Gelation ◽

Granule Surface ◽

Surface Modified

A spherical silica aerogel powder with hydrophobic surfaces displaying a water contact angle of 147° was synthesized from a water glass-in-hexane emulsion through ambient pressure drying. Water glass droplets containing acetic acid and ethyl alcohol were stabilized in n-hexane with a surfactant. Gelation was performed by heating the droplets, followed by solvent exchange and surface modification using a hexamethyldisilazane (HMDS)/n-hexane solution. The pH of the silicic acid solution was crucial in obtaining a highly porous silica aerogel powder with a spherical morphology. The thermal conductivity, tapped density, pore volume, and BET surface area of the silica aerogel powder were 22.4 mW·m−1K−1, 0.07 g·cm−3, 4.64 cm3·g−1, and 989 m2·g−1, respectively. Fourier transform infrared (FT–IR) spectroscopy analysis showed that the silica granule surface was modified by Si-CH3 groups, producing a hydrophobic aerogel.

Download Full-text

Environmental microscopy of capillary stress-induced strain behavior in ambient-pressure aerogels

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100166713 ◽

1996 ◽

Vol 54 ◽

pp. 850-851

Author(s):

Sudeep M. Rao ◽

Joshua Samuel ◽

Sai S. Prakash ◽

C. Jeffrey Brinker

Keyword(s):

Silica Aerogel ◽

Ambient Pressure ◽

Drying Shrinkage ◽

Pore Filling ◽

Silica Network ◽

Strain Behavior ◽

Partially Saturated ◽

Capillary Stress ◽

Wetting Liquid ◽

Aerogel Films

Ambient pressure silica aerogel thin films have recently been prepared by exploiting reversible drying shrinkage caused by derivatization of the internal gel surface. Aerogels have porosities of upto 99.9% and due to the small size of the pores (few nanometers), large capillary stresses are produced in gels that are partially saturated with a wetting liquid. As a result of these capillary stresses, the flexible silica network undergoes strain which has been observed using environmental microscopy. This technique allows variation of the equilibrium vapor pressure and temperature, and a simultaneous monitoring of the deformation of the unconstrained film thickness. We have observed >600% deformation during the pore-filling and pore-emptying cycles. In this presentation, we discuss the unique stress-strain behavior of these films.Ref.: Sai S. Prakash, C. Jeffrey Brinker, Alan J. Hurd & Sudeep M. Rao, "Silica aerogel films prepared at ambient pressure by using surface derivatization to induce reversible drying shrinkage", Nature. Vol. 374, 30 March, 1995, 439-443.

Download Full-text