Glassy particles

Glassy Particles Deformable Into Ellipsoidal Shapes... 

Figure 14-5 shows a photograph of a good powder produced in a small (1 m ) laboratory spray dryer. We see that it consists of spherical glassy particles, of which the largest have a diameter of about 50 pm. Many of the particles are hollow - we come back to that in a moment. The flow properties of spherical particles are expected to be good if ... 

Coal generally contains a mineral fraction that amounts to 5-20 wt.%. During combustion, most of the minerals are transformed into dust-sized, glassy particles and, along with some unaltered mineral grains and unburned carbon, are emitted from the smoke stacks. These particles contribute to the smog problem, are eye- and respiratory irritants, and act as substrates for the deposition of sulfuric and nitric acid. 

An additional entry phenomenon can be brought forward at high 4>p, that is, entry of a z-mer into a glassy particle, is impeded because of slow diffusion through the interface. The hindered z-mer then desorbs... 

The idea of gradual addition of monomer to polymerizing micro emulsions is not new and has been attempted for methylmethacrylate [31] and styrene [32-34] to make more efficient use of the surfactant. For example, Gan et al. have performed styrene microemulsion polymerizations where monomer was added gradually either dropwise or using a hollow-fiber membrane [32,35]. They observed relatively large ( 40 nm) and uniform particle sizes with no indications of continuous particle nucleation. However, this result is more likely due to a combination of fast monomer addition relative to the polymerization rate and depletion of the redox initiator system employed rather than to the growth of glassy particles. 

Photograph 10-27 Polished thin section of fly ash, >75 pm, showing black opaque carbon particles, glassy particles (some with a variety of included phases and colors), and quartz (arrow). (S A6895)... 

The vehicle format we have used to produce aquasomes is the complex particulate multicomponent system. In general, complex particulate delivery systems are assemblies of simple polymers, complex lipid mixtures or ceramic materials that tend to measure individually between 30 and 500 nm in diameter. Being solid or glassy particles dispersed in an aqueous environment, they exhibit the physical properties of colloids their mechanism of action is controlled by their surface chemistry. They may deliver agents through a combination of specific targeting, molecular shielding, and slow release processes. 

The second possibility for slower evaporation is diffusion limitations within the particle itself, or possibly slow annealing of a particle to its equilibrium morphology (as in Ostwald s ripeiung). In this case the surface composition would not reflect the average composition of the particle. Glassy particles typify this possibility. The timescale for diffusive mixing of a constituent in a spherical particle is Tm = 3,600 D) [87], where D in cm s is the diffusion constant of that... 

When more hydrophobic monomers are used, the hydro-phobicity of the CCT reagents can be altered and when tetraphenylcobaloxime boron fluoride (COPhBF) is used, it is found to reside predominantly in the organic phase. The best results are often achieved under monomer-flooded conditions that keep the glass transition temperature (Tg) of the monomer-filled particles below the reactor temperature. CCT does actually reduce the rate of polymerization such that the monomer can be fed at a rate that maintains the instantaneous conversion low enough for the particle to be swollen with monomer, allowing diffusion of the catalysts between the aqueous and monomer phases. If the amount of the catalyst is reduced and the rate increases, this can lead to viscous, glassy particles that prevent catalyst mobility, which is observed as a... 

This evidence in general tends to confirm the view of Miyauchi and Aomine that in fine clay fractions of volcanic ash soils, hydrous alumina and silica are cross-linked essentially as allophane A, and although as in the case of the Kaharoa sample, small amounts of cristobalite and amorphous silica may persist in finer clay fractions, these may, in young soils, be due partly to low-density vesicular glassy particles larger than 0.2 / m. 

Figure 12. Electron micrographs of some allophanic clays separated from New Zealand soils, (a) Clay dispersed in sodium carbonate at pH 9 from Kaharoa soil (b) clay dispersed in sodium carbonate at pH 9 from Egmont Ash soil (c) fibrous clay dispersed with acid from Egmont Ash soil (d) coarse glassy particles in clay dispersed with alkali from Egmont Ash soil.

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