Surface phenomena during

Surface Phenomena During Pyrolysis The Effects of Treatments with Various Inorganic Gases... 

MAREK AND Albright Surface Phenomena During Pyrolysis... 

Ozone degradation is a surface phenomenon and hence a physical anti-ozonant must form a protective barrier. A chemical anti-ozonant can be added during polymer fabrication, but again it must diffuse to the surface. It must also provide a defence over the lifetime of the article. 

Asymmetric induction during the reduction of 4-(48) was observed when a surface-modified carbon cathode was used.70 Optical yields were low but the effect of the chiral amino acid bound to the carbon surface was proved to be a true surface phenomenon. Induction of chirality by homogeneous rather than surface-bound agents has also been studied.71 All the isomeric acetylpyridines (48) were reduced in the presence of three different chiral alkaloids. Both carbinol products 2- and 4-(49) were shown to possess induced chirality, but the 3-carbinol (49) had none under any of the conditions tried. More rapid protonation of the intermediate was proposed to account for the lack of induced chirality. Optimization of optical yields was done.72 The pinacols (50) formed along with 49 were found to have no induced chirality. Optical yields have been as high as 50%.73 The role of electroabsorption was found to be important in the reduction of 2-(48).74 Product distributions were noted as a function of surfactant present in the electrolyte, carbinol 49 being favored... 

The very striking phenomenon of surface migration during condensation is presumably due to the molecules striking the surface with considerable kinetic energy, so that they take some time to settle down into thermal equilibrium with the underlying solid, the oscillations of the atoms when... 

The production of the passive state is attributed to a disturbance of this equilibrium. During anodic polarisation of iron the more reactive or a ions dissolve with greater rapidity than equilibrium can be established, with the result that an excess of noble, inert, or passive jB ions collects on the surface of the metal, tending to render it passive. This explains why passivity is purely a surface phenomenon. Hydrogen ions, like halogens, are assumed to catalytically accelerate the conversion of a into / ions until equilibrium is re-established. 

The change of surface profile during chemical-mechanical planarization (CMP) is monitored continuously in this study. The influences fiom pattern dependency and substrate effects are discussed. Step height reduction rate is a function of pattern density and down force. The rate decreases with time until planarization is achieved. As the polish approaches the patterns underneath, the interaction between substrate effects and pattern dependency results in the resurgence of step height. The implication of this newly found phenomenon is discussed. 

In this study, we examined evolution of surface profiles during CMP, and the pattern dependency and substrate effects associated with it. Step height reduction rate decreases with polish time or remaining step height, and is also a function of pattern density. After planarization has been achieved, the film is thinned down continuously and step height reappears as the polish approaches the interface between the blanket oxide and the nitride patterns underneath. This phenomenon may result from the interaction between substrate effects and pattern dependency and it may be the origin of dishing effects. 

The concentration polarization model, which is based on the stagnant fihn theory, was developed to describe the back-diffusion phenomenon during filtration of macromolecules. In this model, the rejection of particles gives rise to a thin fouling layer on the membrane surface, overlaid by a concentration polarization layer in which particles diffuse away from the membrane surface, where solute concentration is high, to the bulk phase, where the solute concentration is low [158]. At steady state, convection of particles toward the membrane surface is balanced by diffusion away from the membrane. Thus, integrating the onedimensional convective-diffusion equation across the concentration polarization layer gives... 

The surface may influence the catalytic activity of the electrode and the adsorption of the substrate. Sometimes in the reduction of certain nitro compounds at a tin electrode, for example, the surface changes during the electrolysis as if some of the metal has been dissolved and reduced again [118]. Such a phenomenon is also observed during the reduction of n-nitrobenzenesulfonic acid in a fluidized bed electrode [119]. The role of stannous salts (Chapter 29) added to the catholyte in certain reductions has a bearing on this problem. 

Monitoring by the STM technique of the lead deposition either in a bulk deposition process (BDP) or in a UPD process was an important early example of STM application to monitor electrochemical processes in real time. Christoph et al. studied bulk Pb deposition on a Ag(lOO) substrate. During the potential-controlled Pb phase deposition, they observed irreversible changes of the Ag(lOO) surface morphology by the Pb deposit. Furthermore, they reported a recrystallization phenomenon during repetitive Pb depo-sition/dissolution processes. Additionally, they determined the... 

Hydrophobic Silicas. Because foaming is a surface phenomenon, any antifoam used must concentrate at the surface (or gas—liquid interface). Hydrophobic silicas, which are silicas that have been treated with a compound that causes them to float on the top of water, have been used to fulfill this function for almost 30 years. U.S. Patent 3 408 306 (5) discloses the use of a hydrophobic silica dispersed in a hydrocarbon oil. Hydrophobic silica for this composition, which is still in use today, is made either by continuous ( dry roast ) or batch process. In either process, precipitated silicas rather than silica gels or fumed silicas are typically used to make antifoams. During a continuous process, silicone oils, usually poly(dimethylsiloxane), are sprayed onto a bed of hydrophilic silica. The bed is heated to temperatures ranging up to 300 °C, and reaction times are up to 20 h. At these temperatures and reaction times, bond formation between the silica particle and silicone oil may occur in addition to simple coating of the particle. 

Vink has produced evidence in total conflict with previous experience which is suggested to show that the photo-oxidation of polypropylene is a bulk reaction rather than a surface phenomenon. ESCA studies, however, have shown that the photo-oxidation of polypropylene is clearly a surface phenomenon.In a recent study by Kollmann and Wood the photo-oxidation of polypropylene was found to be dependent upon the intensity of the light source. Thus, for unstabilized polymer the rate was proportional to I , whereas for stabilized polymer the rate was proportional to 1O 8-0.9 Thej-e appears to be some conflict in the literature as to whether chemical changes during the photo-oxidation of polyolefins correlate with the changes in mechanical properties.This has always been a difficult... 

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