Thermal. Acoustical and Structural Properties of Silica Aerogels

1986 ◽  
Vol 73 ◽  
Author(s):  
J. Fricke ◽  
G. Reichenauer
Keyword(s):  
Optical Properties ◽  
Structural Properties ◽  
Silica Aerogels ◽  
Low Density ◽  
Density Structure ◽  
Secondary Particles ◽  
Window Systems ◽  
Fractal Properties ◽  
Primary Particles ◽  
Highly Porous

ABSTRACTSilica aerogels either in monolithic or in granular form provide excellent thermal insulation and thus may be used as superinsulating spacer in all kinds of window systems. Highly porous aerogels also are exciting acoustic materials with sound velocities in the order of 100 m/s and acoustic impedances between 104 and 105 kg/(m2·s). Silica aerogels produced from TMOS seem to consist of massive primary particles (ø ≅ 1 nm, ρ ≅ 2000 kg/m3) which form secondary particles (ø ≅ 5 to 6 nm, ρ ≅800 kg/in 3) displaying fractal properties (D≅ 2). The further buildup creates the highly porous low-density structure which is responsible for the special thermal, acoustical and optical properties of aerogels. Above about 100 nm, transparent aerogels should be homogeneous.

Partially Hydrolyzed Alkoxysilanes as Precursors for Silica Aerogels

1988 ◽  
Vol 121 ◽  
Author(s):  
T. M. Tillotson ◽  
L. W. Hrubesh ◽  
I. M. Thomas
Keyword(s):  
Sol Gel ◽  
Silica Aerogels ◽  
Low Density ◽  
Density Range ◽  
Moist Air ◽  
Wide Range ◽  
Sol Gel Process ◽  
Hydrolysis Of ◽  
Highly Porous ◽  
Controlled Hydrolysis

ABSTRACTThe classical sol-gel process for synthesizing SiO2 aerogels involves the hydrolysis/condensation of tetraethyoxysilane (TEOS) and/or teramethyoxysilane (TMOS) to produce a gel which can then be super-critically extracted to a low density, highly porous aerogel glass. Controlled hydrolysis of TEOS and TMOS leads to partially hydrolyzed compounds that can be subsequently water processed to form silica aerogels in the density range from .020 to .500 gms/cc. The partially hydrolyzed compounds are stable when sealed from moist air and can be stored for future use.We discuss the controlled conditions used to obtain these compounds and present data that characterize their structure. We detail the procedures for preparing the wide range of aerogel densities. We also report on their use as an adhesive.

Structural properties of low-density liquid alkali metals

Pramana ◽  
2005 ◽  
Vol 65 (6) ◽  
pp. 1085-1096 ◽  
Author(s):  
A. Akande ◽  
G. A. Adebayo ◽  
O. Akinlade
Keyword(s):  
Structural Properties ◽  
Alkali Metals ◽  
Low Density ◽  
Liquid Alkali Metals

NMR studies of superfluid in low density silica aerogels

2003 ◽  
Vol 329-333 ◽  
pp. 292-295
Author(s):  
J.E. Baumgardner ◽  
L.V. Polukhina ◽  
Y. Lee ◽  
J.F. Poco ◽  
L.W. Hrubesh ◽  
...  
Keyword(s):  
Silica Aerogels ◽  
Low Density ◽  
Nmr Studies

Effect of UV Treatment on Optical Properties of Low-Density Polyethylene Films Doped with Eu(TTA)3phen Complex

2014 ◽  
Vol 895 ◽  
pp. 155-161
Author(s):  
M.I. Khairuldin ◽  
N.M.A. Aziz ◽  
N.M. Nashaain ◽  
S. Wedianti ◽  
I. Farehah ◽  
...  
Keyword(s):  
Optical Properties ◽  
Emission Spectra ◽  
Low Density Polyethylene ◽  
Rare Earth Complex ◽  
Low Density ◽  
Uv Treatment ◽  
Uv Spectrum ◽  
Light Manipulation ◽  
Emission Transition ◽  
Ft Ir

Low-Density Polyethylene (LDPE) films doped with Eu (TTA)3phen complex (TTA=2-thenoyltrifluoroacetone, phen=1,10-phenanthroline) were fabricated by hot-blowing technique for thickness of 100 μm. The films were doped with 0.1 % of Eu (TTA)3phen to the total weight of LDPE and exposed to UV irradiation from deuterium lamp for 5, 10, 20, 40 and 60 hours to investigate the effect of its optical properties. The films were characterized by Spectrofluorometer, UV/VIS Spectrophotometer and FT-IR Spectrometer to measure their emission spectra, lifetimes, transmission transparency and chemical bonding. Photoluminescence of the room-temperature Eu (TTA)3phen doped films consist of typical Eu3+emission transition lines with hypersensitive5D07F2emission band at 610 nm. After 20 hours UV treatment, the peak intensity dropped by 90 % and shortened the luminescent lifetimes from 0.654 ms to 0.305 ms. Longer UV treatment also has accelerated degradation in doped LDPE films shown by significant reducing in absorption peak of FTIR at 3395, 3186 and 1645 cm-1. The results would provide a mechanism to improve the lifetime of the LDPE by utilizing the light-manipulation property of Eu (TTA)3phen complex to absorb UV spectrum and covert into red emission.Keywords: LDPE, rare-earth complex, photoluminescence

scholarly journals Productionof poly(L-CO-D,L LacticAcid) porous fibers by electrospinning

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Nayara Maysa da Silva Carvalho ◽  
Bárbara E. Ciocca ◽  
Rubens Maciel Filho ◽  
Marcele Fonseca Passos ◽  
Maria Regina Wolf Maciel ◽  
...  
Keyword(s):  
Pore Formation ◽  
Scientific Community ◽  
Low Dielectric Constant ◽  
Porous Scaffolds ◽  
Low Density ◽  
Fiber Morphology ◽  
Low Dielectric ◽  
Mean Diameter ◽  
Porous Fibers ◽  
Highly Porous

The production of porous scaffolds has been widely investigated by the scientific community due to its suitability for tissue engineering. Among techniques that allow the fabrication of porous materials, electrospinning is appealing for being robust and versatile. This research investigated the pore formation in poly (L-co-D,L lactic acid) fibers obtained by conventional electrospinning and the influence of chloroform as a single solvent on fiber morphology. Random and highly porous fibers with a mean diameter of 2.373 ± 0.564 µm were collected. Chloroform affects the fiber morphology, mainly for its fast evaporation and low density of charges. The solvent on the surface evaporates quickly, and the low stretch of the jet does not help the polymer to reorganize over the length of the fiber, forming pores. In conclusion, the low dielectric constant and boiling point of chloroform induce pores formation along the PLDLA fibers.  

Structural and optical properties of low-density and In-rich InAs∕GaAs quantum dots

2007 ◽  
Vol 101 (2) ◽  
pp. 024918 ◽  
Author(s):  
B. Alloing ◽  
C. Zinoni ◽  
L. H. Li ◽  
A. Fiore ◽  
G. Patriarche
Keyword(s):  
Quantum Dots ◽  
Optical Properties ◽  
Low Density ◽  
Structural And Optical Properties

Surface Chemical Effects on the Optical Properties of Thin Nanocrystalline Diamond Films

1996 ◽  
Vol 423 ◽  
Author(s):  
A. V. Khomich ◽  
V. I. Polyakov ◽  
P. I. Perov ◽  
V. P. Varnin ◽  
I. G. Teremetskaya ◽  
...  
Keyword(s):  
Optical Properties ◽  
Optical Transmission ◽  
Diamond Films ◽  
Nanocrystalline Diamond ◽  
Surface Chemical ◽  
Chemical Effects ◽  
Nanocrystalline Diamond Films ◽  
Hot Filament Cvd ◽  
Hot Filament ◽  
Highly Porous

AbstractThe effect of annealing in air on internal structure and optical properties of hot filament CVD nanocrystalline diamond films was investigated. Oxidation of the films lead to selective removal of intercrystallite layers with formation of highly porous structure with characteristic dimensions of several nanometers. Dramatic changes in optical transmission and Raman spectra were also observed. The origin of the two Raman spectrum maxima at 1140 and 500 cm−1 is discussed. Hydrogen absorption and desorption processes in porous diamond were studied.

scholarly journals Computer Simulation of Fracture in Aerogels

2006 ◽  
Vol 978 ◽  
Author(s):  
Brian Good
Keyword(s):  
Computer Simulation ◽  
Amorphous Silica ◽  
Fracture Behavior ◽  
Pair Potential ◽  
Silica Aerogels ◽  
Potential Range ◽  
Fractal Structures ◽  
Molecular Statics ◽  
Secondary Particles ◽  
Order Of Magnitude

AbstractAerogels are of interest to the aerospace community primarily for their thermal properties, notably their low thermal conductivities. While the gels are typically fragile, recent advances in the application of conformal polymer layers to these gels has made them potentially useful as lightweight structural materials as well. In this work, we investigate the strength and fracture behavior of silica aerogels using a molecular statics-based computer simulation technique. The gels' structure is simulated via a Diffusion Limited Cluster Aggregation (DLCA) algorithm, which produces fractal structures representing experimentally observed aggregates of so-called secondary particles, themselves composed of amorphous silica primary particles an order of magnitude smaller. We have performed multi-length-scale simulations of fracture in silica aerogels, in which the interaction between two secondary particles is assumed to be described by a Morse pair potential parameterized such that the potential range is much smaller than the secondary particle size. These Morse parameters are obtained by atomistic simulation of models of the experimentally-observed amorphous silica “bridges,” with the fracture behavior of these bridges modeled via molecular statics using a Morse/Coulomb potential for silica. We consider the energetics of the fracture, and compare qualitative features of low-and high-density gel fracture.

Sign in / Sign up

Export Citation Format

Share Document