Silica particles density

Pt cuboctahedra and octahedra were also deposited on the silica substrate in an identical manner. These 2D model catalysts have the attributes of tunable particle density and the deposition of the different particles changes the relative ratio of exposed [100] and [11 1] surfaces. 

StOber silica particles also show a low density of the powder as precipitated. All reported literature values are at or below a density of 2.0 g cm-3, and van Helden et al. (14,15) reported values of as low as 1.61 g cm-3. These results are in accordance with the previously discussed microporosity and TEM substructure in the particles. 

Only at calcination temperatures above 800°C does the density increase to the literature value of amorphous silica of 2.2 to 2.25 g cm-1. The exact microstructure within the Stober silica particles depends very much on the specific precipitation conditions, which are discussed in more detail in section 2.1.4. 

Microporous silica particles with a density of 2.2 g/mL and a diameter of 10 pm have a measured surface area of 300 m2/g. Calculate the surface area of the spherical silica as if it were simply solid particles. What does this calculation tell you about the shape or porosity of the particles ... 

The porous volume Vp (textural volume) was estimated by the volume adsorbed at the end of the pore filling (end of the step) and the silica specific volume Vs was taken at 1/2.2 where 2.2 is the density of amorphous silica. This calculation confirmed that for pressure higher than 0.8 kbar, the particle density strongly increased from 0.89 without compression to 1.15 at 4.7 kbar. The... 

For sub-micron silica particles with grafted PDMS (up to 22 K), a different result was obtained (Yates and Johnston, 1999). The particles were unstable and flocculated well above the UCSD of the PDMS-C02 binary system. These results may suggest that it is necessary to raise the density to the UCSD for PDMS at infinite molecular weight (theta density). Another possibility is that the parameters used in the theory and simulation are not applicable to PDMS, since the polymer-polymer interactions are far stronger than the polymer-C02 interaction, unlike the case for PFOA. 

As in carbon-black-filled EPDM and NR rubbers, the physical network in silica-filled PDMS has a bimodal structure [61]. A loosely bound PDMS fraction has a high density of adsorption junctions and topological constraints. Extractable or free rubber does virtually not interact with the silica particles. It was found that the density of adsorption junctions and the strength of the adsorption interaction, which depends largely on the temperature and the type of silica surface, largely determine the modulus of elasticity and ultimate stress-strain properties of filled silicon rubbers [113]. 

The authors proposed a mechanism that accounts for the reduction in flammability properties, which depends on physical processes in the condensed phase rather than chemical reactions. Three factors are critical in determining the silica behavior during the combustion process the density and surface area of the additive, the melt viscosity of the polymer. The interplay between these factors can determine whether the silica will accumulate near the surface or sink through the polymer melt. Fumed silica and silica gel provide examples for the first case where the silica particles accumulated on the surface and formed an insulating layer that provide protection to the underlying polymer. This is in contrast to the other case where the fused silica particles sank through the polymer melt. 

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