Particle size sensitivity, ethylene

This structure sensitivity of the respective population between the various states of adsorbed oxygen could explain why it has long been found that ethylene oxidation is structure-sensitive, with higher selectivity, up to 60-70%, for nonpromoted catalysts with sizes of about 40-50 nm [68,69]. A similar result has been recently reported for model Ag/a-A Os catalysts of very narrow size distribution (Table 1) [70]. The particle-size sensitivity has been attributed to a change of the equilibrium Ag crystal shape with cluster size (geometric effect) [71]. This leads to a change in the relative concentration of facets and edges at the metal... 

Except for support effects, structure sensitivity has usually appeared in one of two aspects, variation of rate with svirface crystal face or with particle size. In ICC 1 Gwathmey reported in one of the first experiments with single crystal faces that different faces machined fi om Ni single crystal spheres catalyzed the hydrogenation of ethylene at different rates (ICC 1 paper 5). 

The kinetics of ethylene hydrogenation on small Pt crystallites has been studied by a number of researchers. The reaction rate is invariant with the size of the metal nanoparticle, and a structure-sensitive reaction according to the classification proposed by Boudart [39]. Hydrogenation of ethylene is directly proportional to the exposed surface area and is utilized as an additional characterization of Cl and NE catalysts. Ethylene hydrogenation reaction rates and kinetic parameters for the Cl catalyst series are summarized in Table 3. The turnover rate is 0.7 s for all particle sizes these rates are lower in some cases than those measured on other types of supported Pt catalysts [40]. The lower activity per surface... 

The mechanical properties of rapidly polymerizing acrylic dispersions, in simulated bioconditions, were directly related to microstructural characteristics. The volume fraction of matrix, the crosslinker volume in the matrix, the particle size distribution of the dispersed phase, and polymeric additives in the matrix or dispersed phase were important microstructural factors. The mechanical properties were most sensitive to volume fraction of crosslinker. Ten percent (vol) of ethylene dimethacrylate produced a significant improvement in flexural strength and impact resistance. Qualitative dynamic impact studies provided some insight into the fracture mechanics of the system. A time scale for the elastic, plastic, and failure phenomena in Izod impact specimens was qualitatively established. The time scale and rate sensitivity of the phenomena were correlated with the fracture surface topography and fracture geometry in impact and flexural samples. 

Aqueous suspensions are prepared in much the same manner, except that before bringing the batch to final volume with additional sterile water, the solid that is to be suspended is previously rendered sterile by heat, by exposure to ethylene oxide, or ionizing radiation (y or electrons), or by dissolution in an appropriate solvent, sterile filtration, and aseptic crystallization. The sterile solid is then added to the batch, either directly or by first dispersing the solid in a small portion of the batch. After adequate dispersion, the batch is brought to final volume with sterile water (329). Because the eye is sensitive to particles larger than 25 pm in diameter, proper raw material specifications for particle size of any dispersed solids must be established and verified on each lot of raw material and final product. The control of particle size of the final suspended material is very important, not only for comfort of the product but also for improving physical stability and resuspendability of the suspension throughout the shelf life and the in-use life by patients. 

Properties Yel.-orange fine powd. 3 avg. particle size char, odor sol. with decomp, in alkaline sol ns. si. sol. in water insol. in benzene, ethylene dichloride sp.gr. 1.66 decomp. pt. 190-220 C gas yield 220 cc/g STP gas 65% N, 24% CO, 5% CO2,5% NH3 Toxicology LD50 (oral, rat) 6.8 g/kg, (dermal, rabbit) > 2 g4rg si. eye irritant repeated min. inh. may cause respiratory sensitization and asthma decomp, gases may cause irritation to eyes, lungs, mucous membranes... 

Temperature-sensitive micron-sized monodispersed composite polymer particles were prepared by seeded copolymerisation of dimethylaminoethyl methacrylate and ethylene glycol dimethacrylate with 1.77 micrometresized monodispersed PS seed particles. The change in surface properties at temperatures above and below 35C was examined by DSC, trypsin activity and the adsorption/ desorption behaviours of low molecular weight cationic emulsifier as well as biomolecules. From the results, it is concluded that the micron sized monodispersed PS/ poly(dimethylaminoethyl methacrylate-co-ethylene glycol dimethacrylate) composite particles can be expected to be a temperature-sensitive carrier for biomolecules. Potential in chromatographic applications is suggested. 20 refs. 

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