Particle-size growth

Garzon FH, Davey JR, Bomp R. 2006. Fuel cell catalyst particle size growth characterized by X-ray scattering methods. ECS Transactions 1(8) 153. 

Sarkar, A., Seth, D., Dozier, A. K., Neathery, J. K., Hamdeh, H. H., and Davis, B. H. 2007. Fischer-Tropsch synthesis Morphology, phase transformation and particle size growth of nano-scale particles. Catalysis Letters 117 1-17. 

One of the newest particle sizing techniques is light scattering. This technique is used to measure particle size distribution, colloid behavior, particle size growth, aerosol research, clean room monitoring, and pollution monitoring. 

The particle size for which the rate of particle-size growth will be a maximum must satisfy the condition... 

In the preparation and stablization of small, supported-catalyst particles, the consideration of surface mobility is essential. If the active component is in a high state of dispersion, conditions under which high mobility is attained must be avoided, since these conditions lead to particle size growth. On the other hand, a poorly dispersed component may be partially redispersed by treatment in a more highly mobile state. In supported catalyst systems, the interaction between the dispersed species (the active component) and the support is always of important concern, and a measure of the mobility of the active component is an indirect measure of this important interaction. 

The particle size distribution of an ultraLne material may increase spontaneously if measures are not taken to stabilize the particles. Particle size growth can occur via agglomeration or crystal growth. This particle size increase will result in a decrease of the available surface area, and hence a decrease of the dissolution rate, potentially lowering drug bioavailability. 

Of the parameters of Eq. (2), only C(oo), the solubility of the PFC in the aqueous phase, varies significantly among PFCs, resulting in a dramatic effect on particle size growth over time (Fig. 3). 

Fig. 7 Particle size growth measurement in real time at-line. (From RefJ l)...

Crystal growth of an industrially manufactured salicylic acid (9) powder (60 jt/m stated particle size) was demonstrated. A microscopic examination about eight months after its preparation showed a maximum particle size of 200-500 fjm. About one year later, examination showed further crystal growth, particle size now was 500-800 pm. A further examination after eight months showed no further particle size growth. Particle size growth of salicylic acid occurred even in the dry powder state and not only in ointments. 

Operated properly, F-T catalysts in slurry reactors undergo only modest deactivation. The modest deactivation seen in these runs may be due to sintering or conversion of aetive carbons or carbides to less active forms, but further TEM and XRD will be needed to verify particle size growth and possible phase changes. Catalysts that are known to deactivate more quickly (1% Cu/Fe reacted at 270°C, Fig. 5, or Fe reacted at 215°C in Fig. 3) have carbides which react with H2 at higher temperatures than catalysts that are known to deactivate more slowly (1% Cu/Fe reacted at 215°C, Fig. 5 and Fig. 3)... 

Physical form and particle size growth (Oswald Ripening) may... 

As with the prior discussion on VOC oxidation catalysts, deposits on the catalyst with commercial use are expected. These deposits are removable with a cleaning treatment by analogy to the VOC oxidation catalysts. In addition, thermal sintering behavior occurs in this service, by analogy to VOC oxidation behavior. However, with chlorinated hydrocarbons, it has been observed that exposure of the catalyst to halogenocarbons causes an accelerated rate of growth of metal particle size, and hence deactivation. The suppon on which the metal is dispersed also affects this particle size growth rate. 

Thus (ph2so4/ h2so4) — 1 0017, and in this case the Kelvin effect is negligible the increase in water vapor pressure due to the droplet curvature is only 0.166% above that of a flat surface. The particle size growth factor at 90% relative humidity is 2.12. Thus the 1 pm diameter drop at 50% RH will grow to become a drop of (2.12/1.48) (1) = 1.43 pm at 90% RH. 

Particle Size Growth Factor without Kelvin Effect, Dp / Dp0... 

Neglecting ion-ion recombination, the particle size growth in the sequence of ion-molecular reactions (8-129)-(8-132) can be described based on (8-137) by the following equation ... 

Fig. 2. The effect of particle size growth with time...

Table n. Experimental Conditions for Monitoring Colloid Particle Size Growth and Surface Charge with Photon Cwrelation Spectroscopy and... 

The equation (9) supposes (at /=const) % increase in a number technical carbon-nanoshungite-microshungite as 196-1069-3434 relative units, i.e. diffusion intensification at diffusible particles size growth. At the same time diffusivity D for these particles can be described by the well-known Einstein s relationship [11] ... 

In order to achieve ORR activity target of fourfold increase over the state-of-the-art Pt/C catalyst, one could either increase the Pt dispersion or increase the area-specific activity of the catalysts. It was shown that there are several pathways to the requirement. Some electrocatalysts prepared via these approaches have shown promising initial ORR activities, but none of them have yet been demonstrated to retain high activity throughout life. Loss of Pt surface area due to particle-size growth and partial loss of the less-noble metal from alloy catalysts are common phenomena. 

Jumaa and Muller investigated colloidal emulsions with different oils and non-ionic surfactants and found a strong dependence of the stability upon autoclaving on the oil. Furthermore for emulsions stabilized with surfactants with a low clouding point (70-76°C) an increase in the particle size was observed whereas emulsions of castor oil or mixed oil (castor oil/medium chain triglycerides, castor/soybean oil) stabilized with poloxamer 188 (cloud point > 100°C) could be autoclaved without distinct particle size growth. ... 

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