Structure of Silica Xerogels Synthesized with Organoalkoxysilane Co-reactants Hints at Multiple Phase Separation

2006 ◽  
Vol 110 (15) ◽  
pp. 7757-7765 ◽  
Author(s):  
Cédric J. Gommes ◽  
Monika Basiura ◽  
Bart Goderis ◽  
Jean-Paul Pirard ◽  
Silvia Blacher
Keyword(s):  
Phase Separation ◽  
Silica Xerogels ◽  
Multiple Phase

scholarly journals Inhomogeneities in acid-catalyzed titania–silica and zirconia–silica xerogels as revealed by small-angle x-ray scattering

2000 ◽  
Vol 15 (9) ◽  
pp. 1998-2005 ◽  
Author(s):  
G. Mountjoy ◽  
J. S. Rigden ◽  
R. Anderson ◽  
G. W. Wallidge ◽  
R. J. Newport ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Phase Separation ◽  
Metal Oxide ◽  
Small Angle ◽  
Silica Xerogels ◽  
Silica Network ◽  
X Ray ◽  
X Ray Scattering ◽  
Acid Catalyzed ◽  
Ray Scattering

The small-angle x-ray scattering (SAXS) technique was used to investigate inhomogeneities on the scale of 10 to 600 Å in acid-catalyzed titania–silica and zirconia–silica xerogels. SAXS of (TiO2)x(SiO2)1−x and (ZrO2)x(SiO2)1−x xerogels with x < 0.1, in which there was no phase separation, showed the presence of two types of inhomogeneity. For Q < 0.05 Å−1 there was a clear departure from Porod scattering which showed that xerogel powder particle surfaces were rough. For 0.1 < Q < 0.4 Å−1 there was a plateau feature corresponding to micropores within the silica-based network, and this feature changes with heat treatment. SAXS of xerogels with x > 0.3 showed the presence of phase-separated regions of metal oxide, which were initially amorphous and crystallized at higher temperatures. A (TiO2)0.18(SiO2)0.82 xerogel that was not initially phase separated became phase separated after heat treatment at 750 °C due to reduced solubility of Ti in the silica network.

Bulk standards for low-temperature biological x-ray microanalysis

1984 ◽  
Vol 42 ◽  
pp. 282-283
Author(s):  
P. Echlin ◽  
M. McKoon ◽  
E.S. Taylor ◽  
C.E. Thomas ◽  
K.L. Maloney ◽  
...  
Keyword(s):  
Phase Separation ◽  
Low Temperature ◽  
Analytical Method ◽  
Salt Solutions ◽  
Absolute Concentration ◽  
Cooling Process ◽  
X Ray ◽  
The Absolute ◽  
Analytical Procedures ◽  
Electrical Conductors

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

Phase separation in sol gel-derived ceramic films of silica-zirconia, alumina-zirconia, and titania-zirconia system

1994 ◽  
Vol 52 ◽  
pp. 646-647
Author(s):  
J. Tong ◽  
L. Eyring
Keyword(s):  
Fracture Toughness ◽  
Phase Separation ◽  
Sol Gel ◽  
Great Influence ◽  
High Strength ◽  
Chemical Durability ◽  
Separation Method ◽  
Toughening Mechanism ◽  
Ceramic Films ◽  
Zirconia Toughened Alumina

There is increasing interest in composites containing zirconia because of their high strength, fracture toughness, and its great influence on the chemical durability in glass. For the zirconia-silica system, monolithic glasses, fibers and coatings have been obtained. There is currently a great interest in designing zirconia-toughened alumina including exploration of the processing methods and the toughening mechanism.The possibility of forming nanocrystal composites by a phase separation method has been investigated in three systems: zirconia-alumina, zirconia-silica and zirconia-titania using HREM. The morphological observations initially suggest that the formation of nanocrystal composites by a phase separation method is possible in the zirconia-alumina and zirconia-silica systems, but impossible in the zirconia-titania system. The separation-produced grain size in silica-zirconia system is around 5 nm and is more uniform than that in the alumina-zirconia system in which the sizes of the small polyhedron grains are around 10 nm. In the titania-zirconia system, there is no obvious separation as was observed in die alumina-zirconia and silica-zirconia system.

Multiple phase transitions investigated by high-speed TEM

1990 ◽  
Vol 48 (4) ◽  
pp. 550-551
Author(s):  
Oleg Bostanjoglo ◽  
Peter Thomsen-Schmidt
Keyword(s):  
Phase Transitions ◽  
High Speed ◽  
Short Exposure ◽  
Semiconductor Film ◽  
Time Resolved ◽  
Short Exposure Time ◽  
Multiple Phase ◽  
Model Substance ◽  
History Of ◽  
Electron Image

Thin GexTe1-x (x = 0.15-0.8) were studied as a model substance of a composite semiconductor film, in addition being of interest for optical storage material. Two complementary modes of time-resolved TEM were used to trace the phase transitions, induced by an attached Q-switched (50 ns FWHM) and frequency doubled (532 nm) Nd:YAG laser. The laser radiation was focused onto the specimen within the TEM to a 20 μm spot (FWHM). Discrete intermediate states were visualized by short-exposure time doubleframe imaging /1,2/. The full history of a transformation was gained by tracking the electron image intensity with photomultiplier and storage oscilloscopes (space/time resolution 100 nm/3 ns) /3/. In order to avoid radiation damage by the probing electron beam to detector and specimen, the beam is pulsed in this continuous mode of time-resolved TEM,too.Short events ( <2 μs) are followed by illuminating with an extended single electron pulse (fig. 1c)

Phase separation in fluid additive hard sphere mixtures?

1998 ◽  
Vol 95 (2) ◽  
pp. 131-135 ◽  
Author(s):  
DOUGLAS HENDERSON DEZSO BODA KWONG-YU CHAN
Keyword(s):  
Phase Separation ◽  
Hard Sphere

Thermal and vibrational properties of silica xerogels

1998 ◽  
Vol 77 (2) ◽  
pp. 333-340 ◽  
Author(s):  
A. Fontana, F. Rossi, G. Carini, G. D'
Keyword(s):  
Vibrational Properties ◽  
Silica Xerogels
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